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A hybrid actuation approach for human-friendly robot design
Abstract
Safety is a critical characteristic for robots designed to operate in human environments. This paper presents the concept of hybrid actuation for the development of human- friendly robotic systems. The new design employs inherently safe pneumatic artificial muscles augmented with small electrical actuators, human-bone-inspired robotic links, and newly designed distributed compact pressure regulators. The modularization and integration of the robot components enable low complexity in the design and assembly. The hybrid actuation concept has been validated on a two-degree-of-freedom prototype arm. The experimental results show the significant improvement that can be achieved with hybrid actuation over an actuation system with pneumatic artificial muscles alone. Using the manipulator safety index (MSI), the paper discusses the safety of the new prototype and shows the robot arm safety characteristics to be comparable to those of a human arm.
... The internal mechanical compliance not only decouples the inertia of the motors from the load, thereby ensuring safety as an intrinsic feature especially during any kind of human-robot interaction, but can also be used to store energy, especially during tasks in which the kinetic energy can be absorbed during impacts and released when needed. Various methods have been applied to get passive (intrinsic) compliance, including the use of the series elastic actuators (SEA) [12], cable-driven joints [13], pneumatic [14] and hydraulic [15] actuation, etc. The trade-off between the control performance and safety leads the current research to focus and develop joints with variable compliance [16] to be able to cover safe interaction with low stiffness and better control performance with high stiffness. ...
... Consequently, the model becomes as shown in Fig. 5c and the first differential equation is derived see (14). ...
... Substitute (11) into (14) T in N 2 ...
Variable Stiffness Actuators (VSA) have been proposed as an alternative actuation system for manipulators that are utilized for safe physical Human-Robot Interaction (pHRI). However, in the incidents of collision, the need of a fast response in stiffness tuning would rise to ensure safety. In this paper, we present a novel Discrete Variable Stiffness Actuator (DVSA) to be used in a compliant robotic manipulator for safe physical Human-Robot Interaction (pHRI). The novelty of this actuator lies in its design topology which allows the stiffness level to change swiftly among predefined levels without the need of complex stiffness tuning mechanism. Through this topology, three springs in parallel are connected serially between the motor and the link via gear train. The stiffness of the actuator is altered by adding/subtracting the number of involved springs, which can be realized through engagement/disengagement electromagnetic clutches on two of these spring’s shafts. The working principle, and the detailed design of the actuator are illustrated. Moreover, the stiffness model and the dynamic model are presented and discussed thoroughly. In order to validate these mathematical models and achieve optimal control, system identification for the dynamic parameters was performed experimentally on the physical model. Furthermore, the system’s ability of tracking desired trajectory was achieved through the implementation of different control techniques including PID (Proportional-Integral-Derivative), LQR (Linear Quadratic Regulator) and pole placement. The results show the high potential of utilizing the actuator in compliant manipulators. Moreover, DVSA is also characterized for safety in pHRI through Head-Injury Criterion (HIC). Finally, an application of DVSA in human augmentation task (Weight Bearing Task) is presented.
... They include active methods that monitor the environment and robot states using machine vision and/or sensor fusion and try to avoid risky situations; and passive methods that try to develop inherently safe robots that are not able to cause high damage in case of system failure or unpredicted situations. Using hybrid pneumatic-electric actuators (HPEA) in robots has been proposed as a solution to increase inherent safety without sacrificing precision [2] [3]. ...
... Since the introduction of the HPEA idea in 1987 [4], different designs have been proposed to develop this type of actuator. They include a combination of a DC motor and a rotary pneumatic motor in parallel [5], pneumatic muscle actuators (PMA) with a DC motor [2][6] [7], and pneumatic cylinders with a DC motor [8] [9]. Recently the same concept has been used to develop a hybrid hydraulic-electric actuator for off-road vehicles [10]. ...
... The pneumatic force is the result of the difference in the forces at the two sides of the piston as indicated in (2). In this equation, ...
... These approaches include active methods that monitor the environment and robot states using machine vision and/or sensor fusion and try to avoid risky situations; and passive methods that try to develop inherently safe robots that are not able to cause high damage in cases of system failure or unpredicted situations. Using hybrid pneumatic-electric actuators (HPEA) to drive the robot's joints has been proposed as a solution to increase inherent safety without sacrificing precision [2,3]. ...
... Since the introduction of the HPEA idea in 1987 [4], different designs have been proposed to develop this type of actuator. They include a combination of a DC motor and a rotary pneumatic motor in parallel [5], pneumatic muscle actuators (PMA) with a DC motor [2,[6][7][8], pneumatic cylinders with a DC motor [9,10], and a pneumatic cylinder integrated within a linear motor [11,12]. ...
... The motion controller structure for HPEAs and other redundant actuators incorporates three levels [13]: (1) The high-level motion controller that uses a control method to determine the virtual high-level inputs (force or torque), (2) The input allocation level that distributes the virtual inputs between the actuators using predefined algorithms, and (3) The internal controller within each actuator that defines the low level inputs (like command signals to the valves of rudder motors) that can provide the virtual input with enough accuracy. With optimization-based motion controllers, it is possible to merge the motion control and input allocation problems and address them in a single control law. ...
Hybrid pneumatic-electric actuators (HPEAs) are redundant actuators that combine the large force, low bandwidth characteristics of pneumatic actuators with the large bandwidth, small force characteristics of electric actuators. It has been shown that HPEAs can provide both accurate position control and high inherent safety, due to their low mechanical impedance, making them a suitable choice for driving the joints of assistive, collaborative, and service robots. If these characteristics are mathematically modeled, input allocation techniques can improve the HPEA's performance by distributing the required input (force or torque) between the redundant actuators in accordance with each actuator's advantages and limitations. In this paper, after developing a model for a HPEA-driven system, three novel model-predictive control (MPC) approaches are designed that solve the position tracking and input allocation problem using convex optimization. MPC is utilized since the input allocation can be embedded within the motion controller design as a single optimization problem. A fourth approach based on conventional linear controllers is included as a comparison benchmark. The first MPC approach uses a model that includes the dynamics of the payload and pneumatics; and performs the motion control using a single loop. The latter methods simplify the MPC law by separating the position and pressure controllers. Although the linear controller was the most computationally efficient, it was inferior to the MPC-based controllers in position tracking and force allocation performance. The third MPC-based controller design demonstrated the best position tracking with RMSE of 46%, 20%, and 55% smaller than the other three approaches. It also demonstrated sufficient speed for real-time operation.
... The HPEA prototypes described in [14], [16], and [18] included one or two pneumatic muscle actuators (PMAs) connected by cable(s) to an output pulley, along with a DC motor connected to the output pulley by a gearbox. In [14] a 0.0305 m radius pulley was used with a gearbox with a 28:1 reduction ratio. ...
... The HPEA prototypes described in [14], [16], and [18] included one or two pneumatic muscle actuators (PMAs) connected by cable(s) to an output pulley, along with a DC motor connected to the output pulley by a gearbox. In [14] a 0.0305 m radius pulley was used with a gearbox with a 28:1 reduction ratio. The PMA pressure was controlled using a proportional valve and a simple PID controller. ...
... Third, the power generated by the pneumatic actuator is transmitted with a pair of rack gears that are meshed with a single pinion coupled to the output shaft. This approach allows the extension and retraction forces from the pneumatic actuator to be used, rather than only the retraction forces, as is the case with a belt-pulley or cable-pulley transmission [14], [16], [18]. This however comes with the tradeoff that it is less compact than those previous designs. ...
Actuators used in robot arms need to be powerful, precise and safe. We present the design, implementation and control of a novel rotary hybrid pneumatic-electric actuator (HPEA) for use in robot arms, and collaborative robots in particular (also known as “cobots”). This HPEA is capable of producing torque 3.5 times larger than existing HPEA designs, while maintaining low mechanical impedance (due to low values of friction and inertia) and inherent safety. The HPEA prototype has 450 times less inertia and 15 times less static friction in comparison to a conventional robot actuator with similar maximum continuous output torque. The HPEA combines the large slow torque generated by four pneumatic cylinders, connected to the output shaft via rack and pinion gears, with the small fast torque generated by a small DC motor directly connected to the output shaft. The direct connection of the motor avoids the higher cost and lower precision caused by a gearbox or harmonic drive. The control system consists of an outer position control loop and two inner pressure control loops. High precision position tracking control is achieved due to the combination of a model-based pressure controller, model-based position controller, adaptive friction compensator and offline payload estimator. Experiments were performed with the actuator prototype rotating a link and payload in the vertical plane. Averaged over five tests, a root-mean-square error of 0.024° and a steady-state error (SSE) of 0.0045° were achieved for a fast multi-cycloidal trajectory. This SSE is almost ten times smaller than the best value reported for previous HPEAs. An offline payload estimation algorithm is used to improve the control system’s robustness. Finally, the superior safety of the HPEA is shown by modeling and simulating a constrained head-robot impact, and comparing the result with similar electric and pneumatic actuators.
... Compared with the pneumatic motor operating alone (under SMC), the hybrid actuator reduced the settling time from 1.2 s to 0.5 s for the step input, and the maximum tracking error from 20° (10%) to less than 10° (5%) for the sinusoidal input. In [14] the HPEA prototype included two pneumatic muscle actuators (PMAs) connected by cables to an output pulley with a 0.0305 m radius. A DC motor was connected to the output pulley by a 28:1 gearbox. ...
... Third, the pneumatic power is transmitted using a pair of rack gears meshing with a pinion gear attached to the output shaft. This design allows both the pneumatic extension and retraction forces to be used, rather than only the retraction forces as is the case when a belt-pulley or cablepulley transmission is used [14]; although it is less compact than those prior designs. The rack gears are placed above and below the pinion resulting in reduced loading on the output shaft and its support bearings compared with the single rack design utilized in [15] [16]. ...
... The rack gears are placed above and below the pinion resulting in reduced loading on the output shaft and its support bearings compared with the single rack design utilized in [15] [16]. Fourth, low friction pneumatic cylinders are employed rather than a rotary pneumatic motor [13] or PMAs [14]. Rotary pneumatic motors suffer from large friction torques due to their seals, while PMAs suffer from friction induced hysteresis and a displacement dependent output force [17]. ...
Robot arms require actuators that are powerful, precise and safe. In this paper we present the design and implementation of a novel rotary hybrid pneumatic-electric actuator (HPEA) for use in robot arms, particularly those intended for collaborative applications. It produces 3.5 times higher torque than prior HPEAs while maintaining the low mechanical impedance and inherent safety of the HPEA approach. Its low mechanical impedance results from its low friction and inertia. It has 450 times less inertia and 15 times less static friction than an industrial robot actuator with similar maximum continuous output torque. The design features four pneumatic cylinders connected in parallel with a small DC motor. The DC motor is directly connected to the output shaft. After the mechatronic design and system model are described, the control system design consisting of an outer position control loop and inner pressure control loop is presented. Experiments were performed with the actuator prototype rotating a link and payload with a rotational inertia equivalent to a linear actuator moving a 573 kg mass. Averaged over five tests, a root-mean-square error of 0.038° was achieved for upwards vertical moves. The steady-state error (SSE) was only 0.0045°, even when the arm was under maximum gravity load, primarily due to the adaptive friction compensator employed in the outer control loop. This SSE is almost ten times smaller than the best value reported for previous HPEAs.
... After identifying that safety of a manipulator is influenced mainly by the e↵ective inertia of the robot, this index is used to compare e↵ective inertia and hence safety of di↵erent manipulators under a constant impact velocity and interface sti↵ness. This metric was used to validate safety of a manipulator after design modifications in [168,169]. [137] developed and investigated three danger indexes whose results were interpreted based on HIC. The work investigated force, distance and acceleration related danger indexes on a model to give quantitative measure of severity and likelihood of injury. ...
... The most widely used performance metric in mechanical design of robotic manipulators is the payloadto-weight ratio which is defined as the ratio of maximum payload that the robot can manipulate to its standalone weight. Mechanical designs in domestic robot manipulators are aimed at achieving a higher payload-to-weight ratio while being able to perform tasks defined in their use case [76,168]. ...
... It should also be noted that, VIA design also incorporates damping of the compliant joints to avoid unnecessary vibrations during operation. [168] One of the earliest generation of manipulators designed for human interaction is the DLR lightweight robot with moderate joint compliance and suitable sensing and control capability [76]. See Figure 2.3(a). ...
... Esto requiere aplicar medidas específicas como, por ejemplo, contar con una tensión de alimentación igual o inferior a 12V, incorporar mecanismos de parada de emergencia y de desconexión frente a un posible fallo de alimentación, limitar físicamente los rangos articulares, o reducir la rigidez de las transmisiones y la impedancia del dispositivo. En esta línea, se optó por investigar y desarrollar un nuevo tipo de actuador híbrido basado en el concepto de los macro-mini actuadores distribuidos (DM 2 ) (Shin et al., 2008). Este dispositivo combinaría la acción a reacción a través de unos ligeros propulsores de agua con la rápida respuesta de un motor eléctrico convencional. ...
... Para dimensionar el motor eléctrico se ha seguido la línea de lo propuesto en (Shin et al., 2008), de manera que se establece un par máximo no superior al 20 % del par debido al peso propio (1, 51N · m). El actuador eléctrico escogido para este prototipo es un motor sin escobillas Maxon EC Flat 60, capaz de proporcionar hasta 0, 298N · m sin necesidad de añadir un reductor, por lo que presenta una inercia de 8, 35 · 10 −5 kg · m 2 . ...
Muchos trastornos motores pueden provocar discapacidades crónicas limitando la calidad de vida de quienes las padecen. La robótica de rehabilitación ha demostrado ser eficaz como complemento a la terapia convencional, aunque muchos de los individuos que sufren estas enfermedades a menudo son excluidos de este tipo de terapias. El proyecto SPLASH pretende investigar un nuevo paradigma de rehabilitación que combine la rehabilitación robótica y la terapia acuática, lo que ha llevado al desarrollo de actuadores híbridos acuáticos. El proyecto NOHA profundiza en el estudio de estos sistemas para elaborar una prueba de concepto. En este artículo se resume el proceso de diseño de un actuador híbrido acuático, particularizando su aplicación en un dispositivo robótico de miembro superior. En primer lugar, se plantean las ecuaciones que modelizan el comportamiento del sistema. A continuación, se establecen los requisitos de diseñoo, se presenta un diseño conceptual y se seleccionan los componentes a utilizar. Por último, se proponen líneas de trabajo futuro en el desarrollo de este dispositivo.
... However, interaction with humans warrants additional safety measures, including compliant manipulation. This requirement is problematic for many conventional actuators, which typically use high stiffness to achieve high performance, thereby increasing inertia and leading to large impact forces upon collision [1]. ...
... Similar applications have dominated the field over the years, with PAM-powered devices for orthotics and rehabilitation [4][5][6] and biologically-inspired humanoid robotic devices [7,8]. Looking to other applications, these actuators are particularly desirable in portable robotic systems intended for interaction with humans [1], such as those envisioned for nursing assistance and in casualty extraction. Similar designs with bi-directional capabilities [9] may permit an even greater range of applications. ...
Lightweight, compliant actuators are particularly desirable in robotic systems intended for interaction with humans. Pneumatic artificial muscles (PAMs) exhibit these characteristics and are capable of higher specific work than comparably-sized hydraulic actuators and electric motors. The objective of this work is to develop a control algorithm that can smoothly and accurately track the desired motions of a manipulator actuated by pneumatic artificial muscles. The manipulator is intended for lifting humans in nursing assistance or casualty extraction scenarios; hence, the control strategy must be capable of responding to large variations in payload over a large range of motion. The present work first investigates the feasibility of two output feedback controllers (proportional-integral-derivative and fuzzy logic), but due to the limitations of pure output feedback control, a model-based feedforward controller is developed and combined with output feedback to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the physical parameters of the pneumatic muscles and the manipulator dynamics. Simulations were performed in order to validate the control algorithms, guide controller design and predict optimal gains. Using real-time interface software and hardware, the controllers were implemented and experimentally tested on the manipulator, demonstrating the improved capability.
... However, interaction with humans warrants additional safety measures, including compliant manipulation. This requirement is problematic for many conventional actuators, which typically use high stiffness to achieve high performance, thereby increasing inertia and leading to large impact forces upon collision [1]. ...
... Similar applications have dominated the field over the years, with PAM-powered devices for orthotics and rehabilitation [4][5][6] and biologically-inspired humanoid robotic devices [7,8]. Looking to other applications, these actuators are particularly desirable in portable robotic systems intended for interaction with humans [1], such as those envisioned for nursing assistance and in casualty extraction. Similar designs with bi-directional capabilities [9] may permit an even greater range of applications. ...
Pneumatic artificial muscles are lightweight, compliant actuators capable of high force to weight ratios, which are ideal characteristics for actuators in robotic systems, especially those that interact with humans. However, smooth and precise control of these actuators is difficult because of nonlinearities in the dynamic response. The purpose of this paper is to evaluate two output feedback control strategies, proportional-integral-derivative (PID) and fuzzy control, on a two degree-of-freedom proof-of-concept heavy-lift robotic manipulator that is driven by pneumatic artificial muscles. A mathematical model that integrates the manipulator, control valves, and controller was developed, and model simulations were conducted. Simulations were found to validate the feedback control strategies and gains were optimized to enhance performance. The two controllers were then implemented experimentally, and comparisons of simulation data to experimental tests indicated that the model was able to predict the manipulator behavior well. Finally, the controllers were refined through an experimental gain tuning procedure. Results from the two strategies were compared in terms of accuracy and smoothness. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
... Various methods have been applied to make robots to be compliant, ranging from active control approaches [1,2] to hardware implementation including using the series elastic actuators (SEA) [3,4,5,6], cable driven joints [7], pneumatic [8] and hydraulic [9] actuations. Extensive researches on compliant manipulators have been carried out. ...
... As the manipulator is assumed to be operated around the impact configuration q 0 (q 10 , q 20 ), the dynamic model of equation (14) can be linearized based on equation (8) and (10) by replacing q 1 and q 2 with q 10 +Δq 1 and q 20 +Δq 2 as following: ...
This paper presents a study on setting the joint stiffness for compliant robots in order to protect the actuators when the arm comes up against impact. System dynamic equations of compliant manipulators integrated with impact model are linearized to identify the maximum joint torques in the impact. Based on this, different directions of end-effector velocity and impact normal in different configurations in the robot workspace are calculated based on a given magnitude of end-effector velocity. By tuning the stiffness for each compliant joint to ensure the joint torque does not exceed the maximum value of the actuator, candidate stiffness values are obtained to make the compliant actuators safe in all cases when the robot end-effector moves with a velocity within the fixed magnitude value used in the calculation. The theory and procedure are firstly laid and demonstrated in a 1-DOF planar manipulator, then the work is applied to a 2-DOF compliant manipulator and the candidate stiffness is obtained based on the method.
... Zinn et al. [11] introduced a macro-mini approach, using small on-joint motors for high-frequency tasks and cable pulley with spring element for low-frequency tasks. Shin et al. [12] adopted a similar concept with pneumatic actuators to reduce mechanical complexity compared to cabledriven elastic actuation. While these combinations enhance robotic performance, they introduce mechanical complexity and control challenges. ...
Research on human-friendly robots focuses on safety through software and hardware. Hardware-based safety offers a significant advantage over software-based safety if an accurate hardware model is integrated into the solution. Design of elastic and off-joint actuation has established safety by hardware, where the inherent qualities of elastic and lightweight nature make the robot safe for interaction. Combining series elastic actuators with cable/belt pulley-based remote transmission offers inherently safe hardware design, albeit with increased design and modeling complexity. This paper introduces remote and elastic actuation as a single-element solution for robot arm design using a flexible shaft. The test-bench approach studies the remote and elastic effects of a flexible shaft-based transmission for a robot. A set of nine flexible shafts, differing in length and diameter, are used for benchmarking as 3-D surface empirical maps to facilitate their optimal selection for robot design. An example 3 Degree Of Freedom (DOF) robot arm using a flexible shaft as a remote and elastic actuator is designed and modeled. A low-level control based on a flexible shaft is proposed, backed by the experimental results.
... However, the placement of two or more actuators at different positions may cause large joints and links when implementing conventional actuators with transmission elements such as cables, gears, and belts [7], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [27], [28], [29], [31]. In addition, when robots dedicated to interacting with humans are designed using the hybrid actuation approach, transmission mechanisms have to be covered for assured safety. ...
The response of robot actuators to various dynamic interactions during contact tasks is not trivial because there exists a tradeoff between actuator-thrust force density and back-drivability. Although hybrid actuation approaches are promising, complex transmission mechanisms are necessary to synthesize forces from heterogeneous actuators. This study presents a novel concept of a fusion hybrid linear actuator to address the fundamental problems in conventional hybrid actuation approaches. The concept embodies an integrated structure of an air cylinder and a linear motor and shares the moving spaces of the piston and moving part of the linear motor inside the compact housing of the actuator. Herein, the design strategy requirements and its structural optimization processes are discussed. A kinetic friction model of a pneumatic cylinder that considers a piston structure is proposed to improve the force characteristics during dynamic interaction. Furthermore, a quantitative benchmark test is developed to maintain the contact force constant against a load actuator, to evaluate the disturbance resistance under a wide range of target contact force conditions. The concept and performance were validated by experiments comparing the proposed hybrid actuation condition with conventional pneumatic actuation conditions.
... In a separate study, Shin et. al. [3] utilized a hybrid actuation approach for the control of a humanfriendly robot. In the design, merging of pneumatic and electrical actuators was successfully carried out. ...
The purpose of this project is to develop a Pneumatic Muscle Actuator (PMA) system for a robotic hand that can accurately imitate the motion and function of a human muscle. The project consists of several different areas of design which include: a mechanical component, an electrical component, a programming component, a pneumatic component, and a control systems component. The mechanical components are designed to be simple, and they consist of a mechanical hand and a testing station or panel. The mechanical hand structure was designed to have a total of three, independently operated limbs, each of which contained a Single Degree of Freedom (SDOF). The electrical system consists of an Arduino Mega 2560 micro-controller, six linear potentiometers and a power supply. The micro-controller is used to produce three Pulse Width Modulation (PWM) output signals which are varied in accordance with the analogue inputs of the potentiometers. The programming component for the project involves the programming of the micro-controller. The pneumatic component of the project consisted of three PMA's, three rapid switching valves and an air purifier. The PWM outputs from the micro-controller are then used to control the rapid switching valves which in turn will control three PMA's. Controlling the pressure and positioning of the PMA's proved to be problematic and thus several control systems will be considered. Index Terms-pneumatic, muscle actuator system, robotic hand.
... A solution proposed in literature [15] to increase the dynamic range of a robotic device is the micromacro approach, where a reduced motor (macro) is coupled to the output in parallel with a direct-drive motor (micro). The solution has been explored for grounded haptic devices in the shape of robotic manipulators arranged for haptic rendering [18] and [24]. In other haptic devices presented in literature, it is implemented in a series configuration where the "micro" actuator is placed at the end-effector of a desktop or grounded haptic device [14,16,20] to enhance its output bandwidth. ...
Wearable haptic devices are used to render sense of touch in different virtual reality, simulated or teleoperated environments. Design of these devices has to comply with dimensional constraints imposed by ergonomics and usability, introducing compromises between size of the actuators and features of the rendered haptic stimuli, such as peak forces and bandwidth. We propose a new design approach for wearable haptic devices resembling the micro-macro actuation concept: it is based on two distinct actuators with different mechanical reduction, coupled by an elastic element. We show this better matches the output range of the actuators to features of the signals used in typical haptic rendering. We investigated the approach through an analytical model, a numerical model, and physical experiments conducted after design and development of a working prototype. The theoretical and simulated models allow to better understand dynamic interaction of the system parts, and to define design guidelines for the development of the real device. The adopted design solutions were implemented and evaluated in the prototype of a highly wearable fingertip device. Final experimental results show how the implementation of the proposed method is capable of an effective haptic rendering, that better matches the desired frequency response.
... Such a solution has been explored in grounded haptic devices in a series configuration, i.e. a very compact "micro" actuator is placed at the end-effector of a desktop or grounded haptic device [9,11,15] to enhance its dynamic response. Concept of parallel micro-macro configuration via elastic parallel transmission was proposed in [10] and then developed for robotic arm manipulators in [13] and [17]. To the knowledge of authors, micro-macro solutions have never been applied to a fully wearable and compact fingertip haptic display. ...
Design of wearable fingertip haptic devices is often a compromise between conflicting features: lightness and compactness, against rich and neat haptic feedback. On one side direct drive actuators (i.e. voice coils) provide a clean haptic feedback with high dynamics, with limited maximum output forces. On the other side mechanical transmissions with reduction can increase output force of micro sized motors, at the cost of slower and often noisy output signals. In this work we present a compact fingertip haptic device based on a parallel elastic mechanism: it merges the output of two differently designed actuators in a single, wide bandwidth haptic feedback. Each actuator is designed with a different role: one for rendering fast, high frequency force components, the other for rendering constant to low frequency components. In the work we present design and implementation of the device, followed by experimental characterization of its performance in terms of frequency response and rendering capabilities.
... Actuator technology has been an enabling factor in the form design of robotic systems [1], which is recently moving from classical focus in robustness, precision and efficiency towards collaborative, physically safe and wearable applications [2]. Recent development in soft robotics [3] addresses this emerging need for physical human-robot interaction (pHRI) in robot designs [4], and special attention has been paid to bio-inspired designs to generate robotic motion and force [5]. ...
Classical rigid-bodied robotic systems are presented with proven success in theoretical development and industrial applications, are recently challenged by the emergence of soft robotics due to a growing need in physical human-robot interactions (pHRI), such as wearable devices, medical robots, personal robots, etc. In this paper, we present the design and fabrication of a robust, hybrid bending actuator build from both rigid and soft components inspired by crustaceans, where its bending radius and axis can be mechanically programmed through the selective activation of the rigid exterior joints, actuated by the soft actuators inside. The hybrid actuator was experimentally measured in terms of bending and force tests to demonstrate the utility of this design. Finally, a case study was presented to demonstrate its capacity to adapt to specific objects geometry, anticipating its potential application in situations where compliance is the priority.
... Actuator technology has been an enabling factor in the form design of robotic systems [1], which is recently moving from classical focus in robustness, precision and efficiency towards collaborative, physically safe and wearable applications [2]. Recent development in soft robotics [3] addresses this emerging need for physical human-robot interaction (pHRI) in robot designs [4], and special attention has been paid to bio-inspired designs to generate robotic motion and force [5]. ...
Soft actuators have drawn significant attention from researchers with an inherently compliant design to address the safety issues in physical human-robot interactions. However, they are also vulnerable and pose new challenges in the design, fabrication, and analysis due to their inherent material softness. In this paper, a novel hybrid actuator design is presented with bio-inspirations from the lobster, or crustaceans in a broader perspective. We enclose a soft chamber with rectangular cross-section using a series of articulated rigid shells to produce bending under pneumatic input. By mimicking the shell pattern of lobsters' abdomen, foldable rigid shells are designed to provide the soft actuator with full protection throughout the motion range. The articulation of the rigid shells predefines the actuator's bending motions. As a result, the proposed design enables one to analyze this hybrid actuator with simplified quasi-static models and rigid-body kinematics, which are further validated by mechanical tests. This paper demonstrates that the proposed hybrid actuator design is capable of bridging the major design drawbacks of the entirely rigid and soft robots while preserving their engineering merits in performance.
... Actuator technology has been an enabling factor in the form design of robotic systems [1], which is recently moving from classical focus in robustness, precision and efficiency towards collaborative, physically safe and wearable applications [2]. Recent development in soft robotics [3] addresses this emerging need for physical human-robot interaction (pHRI) in robot designs [4], and special attention has been paid to bio-inspired designs to generate robotic motion and force [5]. ...
Classical rigid-bodied robotic systems are presented with proven success in theoretical development and industrial applications, are recently challenged by the emergence of soft robotics due to a growing need in physical human-robot interactions (pHRI), such as wearable devices, medical robots, personal robots, etc. In this paper, we present the design and fabrication of a robust, hybrid bending actuator build from both rigid and soft components inspired by crustaceans, where its bending radius and axis can be mechanically programmed through the selective activation of the rigid exterior joints, actuated by the soft actuators inside. The hybrid actuator was experimentally measured in terms of bending and force tests to demonstrate the utility of this design. Finally, a case study was presented to demonstrate its capacity to adapt to specific objects geometry, anticipating its potential application in situations where compliance is the priority.
... Actuator technology has been an enabling factor in the form design of robotic systems [1], which is recently moving from classical focus in robustness, precision and efficiency towards collaborative, physically safe and wearable applications [2]. Recent development in soft robotics [3] addresses this emerging need for physical human-robot interaction (pHRI) in robot designs [4], and special attention has been paid to bio-inspired designs to generate robotic motion and force [5]. ...
Soft actuators have drawn significant attentions from researchers with an inherently compliant design to address the safety issues in physical human-robot interactions. However, they are also vulnerable and pose new challenges in the design, fabrication, and analysis due to their inherent material softness. In this paper, a novel hybrid actuator design is presented with bio-inspirations from the lobster, or crustaceans in a broader perspective. We enclose a soft chamber with rectangular cross-section using a series of articulated rigid shells to produce bending under pneumatic input. By mimicking the shell pattern of lobsters’ abdomen, foldable rigid shells are designed to provide the soft actuator with full protection throughout the motion range. The articulation of the rigid shells predefines the actuator’s bending motions. As a result, the proposed design enables one to analyze this hybrid actuator with simplified quasi-static models and rigid-body kinematics, which are further validated by mechanical tests. This paper demonstrates that the proposed hybrid actuator design is capable of bridging the major design drawbacks of the entirely rigid and soft robots while preserving their engineering merits in performance.
... Stephen M Cain et al. in [58], studied locomotor adaptation to powered ankle-foot orthoses using two different orthosis control methods. Dongjun Shin et al. in [59], proposed the concept of hybrid actuation for human friendly robot systems by using distributed macro-Mini control approach [60]. The hybrid actuation controller employ modified bang-bang controller to adjust the flow direction of pressure regulator. ...
Robot hands have attracted increasing research interest in recent years due to their high demand in industry and wide scope in number of applications. Almost all researches done on the robot hands were aimed at improving mechanical design, clever grasping at different angles, lifting and sensing of different objects. In this chapter, we presented the detail classification of control systems and reviewed the related work that has been done in the past. In particular, our focus was on control algorithms implemented on pneumatic systems using PID controller, Bang–bang controller and Backstepping controller. These controllers were tested on our uniquely designed ambidextrous robotic hand structure and results were compared to find the best controller to drive such devices. The five finger ambidextrous robot hand offers total of of freedom (DOFs) and it can bend its fingers in both ways left and right offering full ambidextrous functionality by using only 18 pneumatic artificial muscles (PAMs).
... -The payload of a tendon-driven robot depends on the tensile strength of the tendons and the maximum force that can be generated by the electrical drives. -Pneumatically actuated manipulators are inherently compliant and suitable to share the working environment with humans [21,30]. ...
The application of soft robots can result in significant improvements within a number of areas where traditional robots are currently deployed. However, a challenging task when creating soft robots is to exert effective forces. This paper proposes to combine pneumatic and tendon-driven actuation mechanisms in an entirely soft outer sleeve realising a hybrid actuation principle, to realise a new type of robotic manipulator that can collapse entirely, extend along its main axis, bend along its main axis and vary its stiffness. The created robot arm is inherently flexible manufactured from sections that consist of an internal stretchable, air-tight balloon and an outer, non-stretchable sleeve preventing extension beyond a maximum volume. Tendons connected to the distal ends of the robot sections run along the outer sleeve allowing each section to bend in one direction when pulled. The results from our study show the capabilities of such a robot and the main advantages of the proposed technique compared to traditional, single-actuation type robot manipulators.
... This issue was raised about two decades ago (see for instance [1]), which led to several concepts that aim at developing inherently safe robots for physical human-robot interactions [2]. Examples of such concepts are series elastic actuators (SEA) [3], distributed macro-mini actuation (DM2) [4], S2R [5], variable impedance actuation (VIA) [6], mechanical joint clutches [7] and series clutch actuators [8]. Innovative commercial robots developed based on some of these advances can be considered to be human friendly (e.g. ...
When a robot manipulator is designed to interact with a human being, performance is often compromised due to safety constraints. The interaction becomes thus less responsive and less intuitive, making the use of such robots difficult to implement in an industrial context. This letter revisits the concept of macro-mini manipulator to improve the interaction bandwidth, by introducing a novel low impedance mini mechanism specifically designed for physical human-robot cooperation. This mini structure, consisting of passive joints, combined with a macro robot is experimentally compared with a nonredundant fully actuated manipulator. The experiments demonstrate that the resulting effective impedance is greatly reduced with the addition of the passive mechanism. Therefore, such an architecture has the potential to provide passive contacts and safer interactions while providing large payload capability, extensive range of motion, and end-effector agility and responsiveness.
... -The payload of a tendon-driven robot depends on the tensile strength of the tendons and the maximum force that can be generated by the applied electrical drives. -Pneumatically actuated manipulators are inherently compliant and suitable to share the working environment with humans [5,26]. ...
The application of soft robots can result in significant improvements within a number of areas where traditional robots are currently deployed. However, a challenging task when creating soft robots is to exert effective forces. This paper proposes to combine pneumatic and tendon-driven actuation mechanisms in an entirely soft outer sleeve realising a hybrid actuation principle, to realise a new type of robotic manipulator that can collapse entirely, extend along its main axis, bend along its main axis and vary its stiffness. The created robot arm is inherently flexible manufactured from sections that consist of an internal stretchable, airtight balloon and an outer, non-stretchable sleeve preventing extension beyond a maximum volume. Tendons connected to the distal ends of the robot sections run along the outer sleeve allowing each section to bend in one direction when pulled. The results from our study show the capabilities of such a robot and the main advantages of the proposed technique compared to traditional, single-actuation type robot manipulators.
... BramVanderborght et al. in (Ham, Verrelst, Daerden, & Lefeber, 2003), (Verrelst, Vanderborght, Vermeulen, Ham, Naudet, & Lefeber, 2005(Vanderborght, Bram, Ham, Verrelst, Damme, & Lefeber, 2008) and (Vanderborght B. , Verrelst, Ham, Vermeulen, & Lefeber, DynamicControl of a Bipedal Walking Robot actuated with Pneumatic ArtificialMuscles, 2005) controlled a bipedal robot actuated by pleated pneumatic artificial muscles using bangbang pressure controller. Stephen MCain et al. in (Cain, Gordon, & Ferris., 2007), studied locomotor adaptation to powered ankle-foot orthoses using two different orthosis 978-1-4673-7606, Sardellitti, & Khatib, 2008), proposed the concept of hybrid actuation for human friendly robot systems by using distributed macro-Mini control approach (Zinn, Khatib, Roth, & Salisbury., 2002). The hybrid actuation controller employ modified bang-bang controller to adjust the flow direction of pressure regulator. ...
Production of robotic hands have significantly increased in recent years due to their high demand in industry and wide scope in number of applications such as tele-operation, mobile robotics, industrial robots, biomedical robotics etc. Following this trend, there have been many researches done on the control of such robotic hands. Since human like clever manipulating, grasping, lifting and sense of different objects are desirable for researchers and crucial in determining the overall performance of any robotic hand, researchers have proposed different methods of controlling such devices. In this paper, we discussed the control methods applied on systems actuated by pneumatic muscles. We tested three different controllers and verified the results on our uniquely designed ambidextrous robotic hand structure. Performances of all three control methods namely proportional–integral-derivative control (PID), Bang-bang control and Back stepping control has been compared and best controller is proposed. For the very first time, we have validated the possibility of controlling multi finger ambidextrous robot hand by using Back stepping Control. The five finger ambidextrous robot hand offers total of 13 degrees of freedom (DOFs) and it can bend its fingers in both ways left side and right side offering full ambidextrous functionality by using only 18 pneumatic artificial muscles (PAMs). Pneumatic systems are being widely used in many domestic, industrial and robotic applications due to its advantages such as structural flexibility, simplicity, reliability, safety and elasticity.
... Combining two types of actuation principles leads often to enhanced manipulation capabilities compared when only a single actuation principle is employed [2], including the improved control of the robot's configuration, stiffness and compliance. An example of a hybrid robot concept can be found in [26] where pneumatic artificial muscles are integrated with small electrical motors. In [27], extrinsically and intrinsically actuation mechanisms were fused. ...
This paper explores a new hybrid actuation principle combining pneumatic and tendon-driven actuators for a soft robotic manipulator. The fusion of these two actuation principles leads to an overall antagonistic actuation mechanism whereby pneumatic actuation opposes tendon actuation - a mechanism commonly found in animals where muscles can oppose each other to vary joint stiffness. We are taking especially inspiration from the octopus who belongs to the class of Cephalopoda; the octopus uses its longitudinal and transversal muscles in its arms to achieve varied motion patterns; activating both sets of muscles, the octopus can control the arm stiffness over a wide range. Our approach mimics this behavior and achieves comparable motion patterns, including bending, elongation and stiffening. The proposed method combines the advantages of tendon-driven and pneumatic actuated systems and goes beyond what current soft, flexible robots can achieve: because the new robot structure is effectively an inflatable, sleeve, it can be pumped up to its fully inflated volume and, also, completely deflated and shrunk. Since, in the deflated state, it comprises just its outer 'skin' and tendons, the robot can be compressed to a very small size, many times smaller when compared to its fully-inflated state. In this paper, we describe the mechanical structure of the soft manipulator. Proof-of-concept experiments focus on the robot's ability to bend, to morph from completely shrunk to entirely inflated as well as to vary its stiffness.
... Various methods have been applied to make robots to be compliant, ranging from active control approaches [1,2] to hardware implementation including using the series elastic actuators (SEA) [3][4][5][6][7], cable driven joints [8], pneumatic [9] and hydraulic [10] actuations. Extensive researches on compliant manipulators have been carried out. ...
... In [24]- [26], force and position control has been combined to create a hybrid control architecture. Another hybrid robot concept is the one described in [27]; the authors created a system where pneumatic actuators are combined with an electromechanical actuation mechanism. Also, the work by Immegal [12] aims at bringing together extrinsically and intrinsically actuation principles. ...
This paper proposes a soft, inflatable manipulator that is antagonistically actuated by tendons and pneumatics. The combination of the two actuation mechanisms in this antagonistic robot structure is inspired by the octopus which uses its longitudinal and transversal muscles to steer, elongate, shrink and also stiffen its continuum arms. By 'activating' its antagonistic muscle groups at the same time, the octopus can achieve multiple motion patterns as well as stiffen their arms. Being organized in a similar fashion, our robot manipulator uses, on the one hand, pneumatic actuation and, on the other hand, tendon-based actuation - one opposing the other, achieving an overall antagonistic actuation framework. Controlling the pressure inside the robot while at the same time controlling the tendons' displacements, the robot can be moved into a wide range of configurations while simultaneously controlling the arm's stiffness. This paper builds on earlier work by the authors: Here, we present a new conic-shaped manipulator structure and the control architecture. Using a constant curvature model, we have derived an approach suitable for controlling the robot manipulator. The manipulator's reachable workspace is analyzed and proof-of-concept experiments were conducted to show the robot's stiffness control and motion abilities.
... Various methods have been applied to make robots to be compliant, ranging from active control approaches [1,2] to hardware implementation including using the series elastic actuators (SEA) [3][4][5][6][7], cable driven joints [8], pneumatic [9] and hydraulic [10] actuations. Extensive researches on compliant manipulators have been carried out. ...
This paper proposes a method of stiffness design for a spatial Three Degrees of Freedom (3DOF) serial compliant manipulator with the objective of protecting the compliant joint actuators when the manipulator comes up against impact. System dynamic equations of serial compliant manipulators integrated with an impact model are linearized to identify the maximum joint torques in the impact. Based on this, a general procedure is given in which maximum joint torques are calculated with different directions of end-effector velocity and impact normal in the manipulator workspace based on a given magnitude of end-effector velocity. By tuning the stiffness for each compliant joint to ensure the maximum joint torque does not exceed the maximum value of the actuator, candidate stiffness values are obtained to make the compliant actuators safe in all cases. The theory and procedure are then applied to the spatial 3DOF serial compliant manipulator of which the impact configuration is decomposed into a 2DOF planar serial manipulator and a 1DOF manipulator with a 2DOF link based on the linearized impact-dynamic model. Candidate stiffness of the 3DOF serial compliant manipulator is obtained by combining analysis of the 2DOF and 1DOF manipulators. The method introduced in this paper can be used for both planar and spatial compliant serial manipulators. [DOI: 10.1115/1.4007492]
... For instance, force reflecting master arms or haptic interfaces are used in many robotics medical devices Zarrad et al. (2007). Other possible applications are walking robots Verrelst et al. (2005), soft grippers, cooperative robots Shin et al. (2008) and smooth grinding. These applications need some actuators which fulfill specific requirements: they should be able to generate long duration static force and provide a high force output per unit weight Richer and Hurmuzlu (September 2000). ...
Is it possible to synthesize an easy-to-implement predictive force controller for electropneumatic cylinders?
In this paper, this problem is treated in details. As an electropneumatic cylinder is a highly nonlinear actuator, our strategy is based on the precise nonlinear modeling of the actuator and the application of a feedback linearization strategy. This enables to have an equivalent linearized model and therefore, to find an explicit solution of the predictive optimization problem. The obtained controller is then an easy-to-implement one and the number of control parameters is very reduced: the weighting coefficient and the prediction horizon. Experimental results prove the availability of this control approach and good performances in terms of capacity of tracking long duration static forces of high amplitudes.
... The patent discusses a control algorithm in qualitative terms only. The hybrid actuator designs proposed in [13] and [14] are the most relevant designs found in the literature. In [13] they connected a 3 DC motor in parallel with a rotary pneumatic motor using a pair of gears. ...
The design, modeling and position control of a novel hybrid pneumatic–electric actuator for applications in robotics and automation is presented. The design incorporates a pneumatic cylinder and DC motor connected in parallel. By avoiding the need for a high ratio transmission, the design greatly reduces the mechanical impedance that can make collisions with conventionally actuated robot arms dangerous. A novel discrete-valued model-predictive control (DVMPC) algorithm is proposed for controlling the position of the pneumatic cylinder with inexpensive on/off solenoid valves. A variant of inverse dynamics control is proposed for the DC motor. A prototype was built for validating the actuator design and control algorithms. It is used to rotate a single-link robot arm. The actuator inertia and static friction torque values for the prototype were only 0.6% and 4%, respectively, of the values found for a comparable actuator from an industrial robot. Simulation results for position control of pneumatic actuators with different valve speeds and friction coefficients show that the DVMPC algorithm outperforms a sliding mode control algorithm in terms of position error and expected valve life. Experimental results are presented for vertical rotary cycloidal trajectories. Even with the poor quantization caused by the on/off valves, the pneumatic cylinder controlled by the proposed DVMPC algorithm achieved a 0.7% root mean square error (RMSE) and a 0.25% steady-state error (SSE). With the addition of the DC motor to form the hybrid actuator, the RMSE and SSE were reduced to 0.12% and 0.04%, respectively. By incorporating a novel estimation algorithm, the system was made robust to an unknown payload.
Underwater minirobots have attracted significant interest due to their value in complex application scenarios. Typical underwater minirobots are driven mainly by a soft or rigid actuator. However, soft actuation is currently facing challenges, including inadequate motional control accuracy and the lack of a continuous and steady driving force, while conventional rigid actuation has limited actuation efficiency, environmental adaptability, and motional flexibility, which severely limits the accomplishment of complicated underwater tasks. In this study, we developed underwater minirobots actuated by a hybrid driving method (HDM) that combines combustion-based actuators and propeller thrusters to achieve accurate, fast, and flexible underwater locomotion performance. Underwater experiments were conducted to investigate the kinematic performance of the minirobots with respect to the motion modes of rising, drifting, and hovering. Numerical models were used to investigate the kinematic characteristics of the minirobots, and theoretical models developed to unveil the mechanical principle that governs the driving process. Satisfactory agreement was obtained from comarisons of the experimental, numerical, and theoretical results. Finally, the HDM was compared with selected hybrid driving technologies in terms of acceleration and response time. The comparison showed that the minirobots based on HDM were generally superior in transient actuation ability and reliability.
We develop methods to compute dynamics and control for articulated body systems that are actuated by linear contractile elements. We motivate the conditions under which our mathematical formulation is suitable for modeling muscle actuated robots as well as the human musculoskeletal system. In detail, we: (i) specify the conditions under which sets of piecewise linear contractile muscle fibers (actuators) can model the action of muscle volumes, (ii) use the muscle Jacobian to obtain an expression for predicting how muscle forces produce forces and accelerations at operational points on articulated bodies (muscle-to-task ‘forward’ maps), (iii) use the muscle Jacobian to obtain an expression for predicting the muscle forces required to produce specified forces at operational points on articulated bodies (task-to-muscle ‘inverse’ maps), and (iv) present an interative algorithm for resolving task-to-muscle maps with a proof of convergence and empirical results to show fast (–100 iterations) convergence for detailed human musculoskeletal models with hundreds of muscles and tens of degrees of freedom.
This study experimentally investigates that tracking control performance of an unscented-Kalman-filter-based position control system for a McKibben pneumatic artificial muscle (PAM), using only a pressure sensor. Because nonlinearities in the PAM cause a mismatch in the PAM's length and inner pressure, achieving acceptable tracking performance using position control based on pressure measurement is challenging. This study employs the UKF to estimate the PAM's length using a measured inner pressure, and demonstrates the tracking performance of a UKF-based proportional-integral-derivative control system, comparing it with a position-feedback control system. This demonstration concludes that the UKF-based position control system using only a pressure sensor is practical.
This paper considers position control of a practical McKibben pneumatic artificial muscle without measuring a PAM length. Unscented Kalman filter is employed to estimate the length based on pressure measurement. Comparing with some PID control systems, the effectiveness that UKF can be used as a distance sensor for the PAM position control is illustrated.
A significant challenge in the development of human-safe robots is how to optimize performance while maintaining high safety standards. One promising solution is a hybrid actuation concept which combines low-frequency and high-frequency actuators. However, actuator sizing of the hybrid actuation is a difficult proposition, since motor torque capacity significantly affects robot control performance and safety. Deriving an analytical model of the hybrid actuation, we propose a design methodology to determine an optimal actuator size, which provides a combination of high control bandwidth and low impedance. Our simulation and experimental results validated the proposed methodology showing that the obtained actuator parameters from the methodology improved control bandwidth while keeping effective inertia minimum.
Human-centered robotics draws growing interest in utilizing pneumatic artificial muscles (PAMs) for robots to cooperate with humans. In order to address the limited control performance which prevents PAMs from being more widely used, a hybrid actuation scheme has been proposed to combine PAMs and a low inertia DC motor, and presented significantly improved control performance without loss of robot safety.While the DC motor provides high precision and reliability, the small motor has, however, difficulties in dealing with the large stored energies of the PAMs, especially in the events of PAMs failure and large initial load changes. In order to further ensure robot safety, we developed a new hybrid actuation scheme with PAMs (macro) and a particle brake (mini), which provides high torque-toweight ratio and inherent stability.We then conducted comparative studies between hybrid actuations with (1) a DC motor and (2) a brake in terms of robot safety and performance. Experimental comparisons show that the hybrid actuation with PAMs and a brake provides higher energy efficiency for control bandwidths under 2 Hz, and is capable of effectively reducing large impacts due to the brake’s high torque capacity and passive energy dissipation. These comparative studies provide insight that the hybrid actuation with PAMs and a brake can be a competitive solution for the applications that require high efficiency, but accept a relatively low control performance, for example, a waist joint.
In this paper, we propose an optimal control framework for pneumatic actuators. In particular, we consider using Pneumatic Artificial Muscle (PAM) as a part of Pneumatic-Electric (PE) hybrid actuation system. An optimal control framework can be useful for PE hybrid system to properly distribute desired torque outputs to the actuators that have different characteristics. In the optimal control framework, the standard choice to represent control cost is squared force or torque outputs. However, since the control input for PAM is pressure rather than the force or the torque, we should explicitly consider the pressure of PAM as the control cost in an objective function of the optimal control method. We show that we are able to use pressure input as the control cost for PAM by explicitly considering the model which represents a relationship between the pressure input and the force output of PAM. We demonstrate that one-DOF robot with the PE hybrid actuation system can generate pressure-optimized ball throwing movements by using the optimal control method.
Humans use their hands for a large variety of tasks during daily life. In this chapter, a discussion of human hand use is presented, including classification schemes for grasping and manipulation behaviors. First, a simple classification of the Activities of Daily Living (ADLs) is presented, providing some structure to a terminology that is typically used in an ad hoc manner. Next, an overview of work related to classifications and taxonomies of static grasp types is presented, followed by a study investigating the frequency of use of various grasp types by a housekeeper and machinist. Finally, a taxonomy classifying hand-based manipulation is presented, providing a hand-centric and motion-centric categorization of hand use. These descriptions and classifications of hand use should prove useful to researchers interested in robotic manipulation, prosthetics, rehabilitation, and biomechanics.
This thesis presents a novel safety architecture that enables combination of conventional safety procedures with reversibility-based safety assessment as a backup for unpredicted situations. Within this architecture the thesis presents two approaches to assess safety using the principle of reversibility – “Don’t Do Things You Can’t Undo”.
The research is motivated by the fact that robots are entering our life and safety is now one of the most important aspects of their usage. Robots’ autonomy increases rapidly and it is just a matter of time before robots will be making decisions on their own. The goal of this study is to develop a framework to en- able future robots to behave safely in a wide variety of situations by combining extrinsic and intrinsic safety procedures.
Safety in robotics is usually viewed in the context of mechanical safety of robot’s body and manipulators as well as their conventional control using situation-specific routines. Alternatively, safety is viewed in the context of ethics, legal rights and as a responsibility of robots’ designer. The research on autonomous robot actions, based on intrinsic motivations and abstract principles, is not concerned about safety of resulting behaviors.
In the approach described in this thesis, robot designer supplies safety rules for known situations, while the reversibility-based safety assessment is applied to truly autonomous decisions – when no situation-specific logic is applicable. This way the proposed safety architecture can be integrated into a conventional robot control system, serving as a backup for unpredicted situations. In such situations only reversible actions are intrinsically safe and irreversible actions must be sup- pressed to make the robot behave safely.
This thesis proposes two approaches to assess safety within the proposed hybrid safety architecture. The world-model-free approach is using distance measures between the states to find relevant data and to measure action reversibility. The world-model-based approach proposes to assess action reversibility through calculation of the predicted cost of undoing the action; robot actions in the environment are simulated internally to calculate the cost of returning back to the initial state.
The experiments conducted in simulated environments with two different robots demonstrate that the robot, governed by the world-model-free reversibility assessment, exhibits a safe behavior of obstacle avoidance. The simulated experiments with actions of different types and lengths demonstrate that the world- model-free approach can also be used to identify the pairs of actions that undo each other. In the experiments conducted in simulated and real environments with a movable obstacle, the world-model-based approach to assess action reversibility permits the robot, governed by the hybrid safety architecture, to increase area coverage using reversible object manipulation.
This study presents a passively variable threshold torque Spring-Clutch (PVSC). When human beings and robots work together as in the service robot example, physical safety of the former should be guaranteed. A passive mechanism is usually preferred because of its high reliability and fast response to collision. The PVSC comprises the Spring-Clutch mechanism (in that a spring and cam are utilized for generating threshold torque), and an adjuster (an additional cam and lever mechanism to adjust the threshold torque). It functions as a rigid joint between the input and output. However, when the applied torque exceeds the threshold value, the PVSC joint is fully released and becomes freely rotatable to guarantee safety during contact. The threshold torque is passively adjusted according to the gravitational torque and, therefore, a constant releasing torque is maintained for all joint rotation angles. The threshold torque of the PVSC increases (or decreases) in response to the variation in the deflection of the spring (achieved by using the adjuster) according to the rotation angle (or gravitational torque). Experiments were performed and the PVSC was implemented in the second joint of the SS-Arm IV.
This paper presents a back-drivable two-fingered four-degree of freedom hand that can generate a large grasping force of 120 N and perform a high speed motion of larger than 750 °/s. All fingers are 98 mm in length and the weight of the hand is 1.2 kg. The hand can generate a large grasp force with a new force-magnification mechanism. The force-magnification mechanisms installed in our previous hands need a non-backdrivable element so that their high-speed drive mechanisms cannot be back-driven when the force-magnification mechanisms are activated, which results in low compliance. The new force-magnification mechanism in this paper uses a rack and pinion gear connection mechanism to establish the drive connection with the high-speed drive mechanism only when it is activated. Therefore, the high-speed drive mechanism can be back driven keeping high compliance. However, when the tooth crests of the rack hits that of the pinion gear, the connection mechanism is jammed. Therefore, a rack gear tilting mechanism is also proposed.
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This presents a coupled driven variable transmission unit that can vary its gear ratio 1/60 and 1/300. Conventional variable transmission units such as V-belt and roller CVTs are not appropriate for robot joints because they cut off power transmission while varying gear ratios or are simply too large. Variable transmission units that use two motors are also developed for robot fingers. However, one of the motors in the units does not contribute output, which is a dead weight during operation. The proposed variable transmission unit uses two motors for output based on coupled drive of them. The rotation directions of the two motors determine the gear ratio and the rotation direction of the output shaft. This paper describes installation of the developed variable transmission unit using worm gears. Experimental results validate the variable transmission unit, which is effective especially for power saving.
This paper presents the design and stiffness modeling of a new 3 DOF soft finger mechanism using a spring as a backbone. The mechanism consists of a spring and 3 cylinders, which behave like joints. To control each joint, wires of different length are penetrated into the cylinders which have small holes in their cross-sectional areas, and each joint can be controlled by pulling each wire. Also, the stiffness modeling is conducted to measure the softness of the finger mechanism as well as to estimate the actuator size. First, the forward kinematics is solved by using the geometry of mechanism, and length of wires and Jacobian are obtained. In order to evaluate the efficiency of the proposed mechanism, the position control, the flexibility and safety, and the stiffness model are verified through experimental work.
Pneumatic artificial muscles (PAMs) are actuators known for their light weight, high specific force, and natural compliance. Employed in antagonistic schemes, these actuators closely mimic biological muscle pairs, which has led to their use in humanoid and other bio-inspired robotics applications. Such systems require precise actuator modeling and control in order to achieve high performance. In the present study, refinements are introduced to an existing model of pneumatic artificial muscle force-contraction behavior. The force balance modeling approach is modified to include the effects of non-constant bladder thickness and up to a fourth-order polynomial stress-strain relationship is adopted in order to more accurately capture nonlinear PAM force behavior in both contraction and extension. Moreover, the polynomial coefficients of the stress-strain relationship are constrained to vary linearly with pressure, improving the ability to predict behavior at untested pressure levels while preserving model accuracy at tested pressure levels. Additionally, a detailed geometric model is applied to improve force predictions, particularly during PAM extension. By modeling bladder end effects as sections of an elliptic toroid, PAM force predictions as a function of strain are improved. These modeling improvements combine to enable enhanced model-based control in PAM actuator applications.
A hybrid robot is proposed in this paper, which is used for the automatic assembly of a blowout preventer to prevent the oil blowout. The hybrid robot has three components, which are waist component, parallel mechanism component and wrist component. And the parallel mechanism component is mainly in charge of the transport of the blowout preventer with high speed by actuating the end-effector. The parallel mechanism component is actually a parallelogram structure with special configuration of linkages' length. The parallelogram structure can enhance the load capacity and rigidity of the robot. And it also can enlarge the motion displacement of the end-effector. In order to establish the kinematic model of the hybrid robot by Denabit-Hartenberg (D-H) law, an equivalent mechanism with serial structure is proposed to replace the parallel mechanism based on the analysis of the law of motion of the parallel mechanism. The formulations of the joints' angles of the equivalent mechanism have been presented in this paper. And meanwhile the relationship between the drive capability of the parallel mechanism and the length of the linkage has been demonstrated, which is helpful for the designing and workspace analysis of the robot. The correctness of these analyses has been verified by the simulation of the workspace.
Describes the McKibben muscle and its major properties. Outlines the analogy between this artificial muscle and the skeletal muscle. Describes the actuator composed of two McKibben muscles set into antagonism based on the model of the biceps-triceps system, and explains its natural compliance in analogy with our joint litheness. Reports some control experiments developed on a two d.o.f. robot actuated by McKibben muscles which emphasize the ability of these robot-arms to move in contact with their environment as well as moving loads of high ratio to the robot's own weight. Also outlines control difficulties and accuracy limitations and discusses applications.
In recent years, many successful robotic manipulator designs have been introduced. However, there remains the challenge of designing a manipulator that possesses the inherent safety characteristics necessary for human-centered robotics. In this paper, we present a new actuation approach that has the requisite characteristics for inherent safety while maintaining the performance expected of modern designs. By drastically reducing the effective impedance of the manipulator while maintaining high frequency torque capability, we show that the competing design requirements of performance and safety can be successfully integrated into a single manipulation system.
This paper presents a new actuator system consisting of a micro- actuator and a macro-actuator coupled in parallel via a compliant transmission. The system is called the parallel-coupled micro-macro actuator, or PaCMMA.
In this system, the micro-actuator is capable of high-bandwidth force control owing to its low mass and direct-drive connection to the output shaft. The compliant transmission of the macro-actuator reduces the impedance (stiffness) at the output shaft, and increases the dynamic range of force. Performance improvement over single- actuator systems was expected in force control, impedance control, force distortion, and transient impact force reduction.
Several theoretical performance limits are derived from the sat uration limits of the system. A control law is presented. A prototype test bed was built and an experimental comparison was performed between this actuator concept and two single-actuator systems.
A set of quantitative measures is proposed and the actuator system is evaluated against them with the following results: force bandwidth of 56 Hz, torque dynamic range of 800: 1, peak torque of 1,040 mNm, and minimum torque of 1.3 mNm. Peak impactforce, fonce distortion, and back-driven impedance of the PaCMMA system are shown to be better than either of the single-actuator configurations considered.
To date, the most widely recognized advantage of the layered manufacturing methodology is the relative ease of automatically planning and executing the fabrication of complex geometric shapes. But building shapes using selective material-additive processes has a second, far-reaching advantage—the creation of heterogeneous structures composed of multimaterial regions and with prefabricated devices embedded into the structure. The capability to fabricate heterogeneous structures is important because it enables the realization of new, complex designs. Shape deposition manufacturing, a layered manufacturing process described in this paper, addresses how to build multimaterial, embedded structures such as advanced tooling and embedded electronic devices.
Human-centered robotics involves the close interaction between robotic systems and human beings, including direct human-manipulator contact. In such applications, we must consider the requirements of safety in addition to traditional performance metrics. While there has been significant progress in manipulator and actuator design, there has yet to be a successful manipulator design that possesses the characteristics of both safety and performance. To address this need, a new actuation method, referred to as Distributed Macro-Mini actuation (DM2), has been developed. Recognizing that manipulator torque requirements, as a function of frequency, fall-off sharply at higher frequencies, the DM2 approach partitions the actuation into separate macro- and mini-actuators that provide the low- and high-frequency torques, respectively. Locating the actuators at arm locations where they are most effective, referred to as distributed actuation, is an essential feature of this new approach. Large, macro actuators provide the low-frequency torque required to compensate gravity and provide acceleration torques. Locating the macro actuators at the base of a manipulator reduces the size and weight of the manipulator substantially. The use of a compliant element between the macro actuator and drive-train decouples the reflected inertia of the macro actuator from the manipulator, further reducing the effective inertia. To recover high-frequency torque capability, the mini actuators are collocated at the joints, providing the high mechanical bandwidth necessary for high performance tasks. Because the required high-frequency torque magnitude is small, the mini motors can be kept small enough so that they contribute only a minor increase in manipulator size and weight. Using a two-axis testbed, the DM2 approach was evaluated for impact behavior, position tracking performance, force tracking performance, and haptic performance. Experimental results demonstrated that by drastically reducing the effective inertia of the manipulator, while maintaining high-frequency torque capability, the competing design requirements of performance and safety can be successfully integrated into a single manipulation system. Finally, an extension to multi-degree-of-freedom manipulator control is presented in the form of a six-degree-of-freedom robot composed of a torso with two three-degree-of-freedom manipulators arranged in an anthropomorphic configuration. A description of the design and fully-assembled hardware is included.
Recently, on the base of distributed macro-mini actuation approach (DM2), a new robotic manipulator with hybrid actuation, air muscles-DC motor, has been developed. Among existing actuators, the hybrid actuation employs air muscles because they represent an advantageous tradeoff of performance and safety, due to their power/weight ratio and inherent compliance. The air muscles, however, are limited in bandwidth and their behavior is highly nonlinear. In order to overcome these limitations, the paper presents a torque control strategy based on a pair of differentially connected force-controlled air muscles. This controller was implemented and evaluated on a single joint testbed, first by itself and then as macro component into the Macro-Mini control strategy.
It is traditional to make the interface between an actuator and its load as stiff as possible. Despite this tradition, reducing interface stiffness offers a number of advantages, including greater shock tolerance, lower reflected inertia, more accurate and stable force control, less inadvertent damage to the environment, and the capacity for energy storage. As a trade-off, reducing interface stiffness also lowers zero motion force bandwidth. In this paper, the authors propose that for natural tasks, zero motion force bandwidth isn't everything, and incorporating series elasticity as a purposeful element within the actuator is a good idea. The authors use the term elasticity instead of compliance to indicate the presence of a passive mechanical spring in the actuator. After a discussion of the trade-offs inherent in series elastic actuators, the authors present a control system for their use under general force or impedance control. The authors conclude with test results from a revolute series-elastic actuator meant for the arms of the MIT humanoid robot Cog and for a small planetary rover
Consideration of dynamics is critical in the analysis, design, and control of robot systems. This article presents an extensive study of the dynamic properties of several important classes of robotic structures and proposes a number of general dynamic strategies for their coordination and control. This work is a synthesis of both previous and new results developed within the task-oriented operational space formulation. Here we introduce a unifying framework for the analysis and control of robotic systems beginning with an analysis of inertial properties based on two models that independently describe the mass and inertial characteristics associated with linear and angular motions. To visualize these properties, we propose a new geometric representation, termed the belted ellipsoid, that displays the magnitudes of the mass/inertial properties directly rather than their square roots. Our study of serial macro/mini structures is based on two models of redundant mechanisms. The first is a ...
Human friendly robot control system design and exper-imental validation
- P Thaulad
P. Thaulad, " Human friendly robot control system design and exper-imental validation ", Degree of Engineer Thesis, Stanford University, Stanford, CA, 2005.
Occupational Biomechan-ics
- D Chaffin
- G Andersson
- B Martin
D. Chaffin, G. Andersson, B. Martin, " Occupational Biomechan-ics ",Fourth Edition, Wiley, pp.47-49, 2006