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Development of an Intelligent Joint Actuator Prototype for Climbing and Walking Robots
Abstract
In this paper, a new joint actuator is introduced which builds the basis for the newly developed SpaceClimber robot by the German Research Center for Artificial Intelligence. Based on in-house developed joint actuators for ambulating robots, this complete new design combines performance, stability, and space-related components. The newly developed on-board electronics enables the possibility of a biologically inspired functionality like decentralized autonomous joint control. In this paper, we explain the design and the control architecture of the actuator. We describe the selected components and present the fully functional prototype. The results of the first performance experiments are presented.
... @BULLET The overall look-and-feel of the robot shall be anthropomorphic and aesthetical. @BULLET The development of the arm drives shall be an improvement of existing components developed at our center for previous robotics systems (Spaceclimber [8]) while, at the same time, ensuring compatibility with them. @BULLET The working height of the arms and the center of gravity of the upper limbs shall be adjustable with regard to the mobile base. ...
... The arm joints and the horizontal axes of the mobile platform use brushless DC motors from Robodrive. A similar control approach to the one previously described has been used for these motors, which has already been successfully integrated in the SpaceClimber robot [8][9]. In this case, the in-house developed motor electronics consists of a stack of three circular PCBs. ...
This paper presents the design of the robot AILA, a mobile dual-arm robot system developed as a research platform for investigating aspects of the currently booming multidisciplinary area of mobile manipulation. The robot integrates and allows in a single platform to perform research in most of the areas involved in autonomous robotics: navigation, mobile and dual-arm manipulation planning, active compliance and force control strategies, object recognition, scene representation, and semantic perception. AILA has 32 degrees of freedom, including 7-DOF arms, 4-DOF torso, 2-DOF head, and a mobile base equipped with six wheels, each of them with two degrees of freedom. The primary design goal was to achieve a lightweight arm construction with a payload-to-weight ratio greater than one. Besides, an adjustable body should sustain the dual-arm system providing an extended workspace. In addition, mobility is provided by means of a wheel-based mobile base. As a result, AILA's arms can lift 8kg and weigh 5.5kg, thus achieving a payload-to-weight ratio of 1.45. The paper will provide an overview of the design, especially in the mechatronics area, as well as of its realization, the sensors incorporated in the system, and its control software.
... Background DFKI X-Joint: The overall design and the integrated approach of the DFKI-X joint, as described in [1] is based on the iStruct joint, initially developed for the Charlie robot [7], and is the further advancement of the SpaceClimber joint, developed in 2007 [8]. Until today a wide variety of modular robotic joints has been developed for terrestrial and underwater robotic applications at DFKI RIC, spanning a range of nominal torque from 2.5 Nm up to 1000 Nm. ...
Within this paper we present the electro-mechanical development and testing of a highly integrated robotic joint. We are giving insight in the design of mechanical and electrical components and their evaluation with respect to a LEO mission. Furthermore, the model philosophy is described to adapt a joint, originally developed for terrestrial robots, to space qualification. The result is a novel and compact motor unit with integrated control electronics for space applications.
... The DFKI-X design is based on the iStruct joint, which was initially developed for the Charlie robot [2]. Its design is the advancement of the SpaceClimber joint which was developed in 2007 [13]. A comparison of these two motor modules is given in Fig. 3(a). ...
Within this paper we present the electro-mechanical and control software development of a highly integrated robotic joint. We are giving insight in the selection of mechanical and electrical components and their evaluation with respect to a LEO mission. Apart from laboratory tests and initial radiation tests, further environmental tests are plannedto qualify the system in the near future. The result is a novel and compact motor unit with integrated control electronics for space applications.
... Suppose a system of robot joint actuators and different kinds of sensor nodes connected on each joint. Figure 1 shows a common network topology of such a system, usually found in robotics applications [3]. It consists of joint actuators for example of a walking robot leg, connected in a network chain topology. ...
This article gives an overview about a new network communication protocol suitable for the requirements of sensor-and actuar networks , especially in the context of robotics and sensorial materials. This protocol consists of two different routing and node addressing strategies requiring different amount of computing power united in one protocol structure and header, providing both a software and hardware implementation of the protocol stack using ASIC/FPGA technology. This protocol can satisfy requirements in short-and long distance networks using relative delta-and absolute addressing strategies..
... Besides the ankle joint motors, the lower leg is equipped with an actuator on top, which serves simultaneously as interface between lower leg and thigh and as knee joint. The actuator is based on the BLDC motors developed within the Space-Climber project [HKBK09]. Each leg of Charlie is equipped with four of these actuators. ...
With increasing mechanization of our daily lives, the expectations and demands in robotic systems increase in the general public and in scientists alike. In recent events such as the Deepwater Horizon''-accident or the nuclear disaster at Fukushima, mobile robotic systems were used, e.g., to support local task forces by gaining visual material to allow an analysis of the situation. Especially the Fukushima example shows that the robotic systems not only have to face a variety of different tasks during operation but also have to deal with different demands regarding the robot's mobility characteristics. To be able to cope with future requirements, it seems necessary to develop kinematically complex systems that feature several different operating modes. That is where this thesis comes in: A robotic system is developed, whose morphology is oriented on chimpanzees and which has the possibility due to its electro-mechanical structure and the degrees of freedom in its arms and legs to walk with different gaits in different postures. For the proposed robot, the chimpanzee was chosen as a model, since these animals show a multitude of different gaits in nature. A quadrupedal gait like crawl allows the robot to traverse safely and stable over rough terrain. A change into the humanoid, bipedal posture enables the robot to move in man-made environments. The structures, which are necessary to ensure an effective and stable locomotion in these two poses, e.g., the feet, are presented in more detail within the thesis. This includes the biological model and an abstraction to allow a technical implementation. In addition, biological spines are analyzed and the development of an active, artificial spine for the robotic system is described. These additional degrees of freedom can increase the robot's locomotion and manipulation capabilities and even allow to show movements, which are not possible without a spine. Unfortunately, the benefits of using an artificial spine in robotic systems are nowadays still neglected, due to the increased complexity of system design and control. To be able to control such a kinematically complex system, a multitude of sensors is installed within the robot's structures. By placing evaluation electronics close by, a local and decentralized preprocessing is realized. Due to this preprocessing is it possible to realize behaviors on the lowest level of robot control: in this thesis it is exemplarily demonstrated by a local controller in the robot's lower leg. In addition to the development and evaluation of robot's structures, the functionality of the overall system is analyzed in different environments. This includes the presentation of detailed data to show the advantages and disadvantages of the local controller. The robot can change its posture independently from a quadrupedal into a bipedal stance and the other way around without external assistance. Once the robot stands upright, it is to investigate to what extent the quadrupedal walking pattern and control structures (like the local controller) have to be modified to contribute to the bipedal walking as well.
... Each part of the exoskeleton contains a network of decentralized joint controllers containing a Spartan-6 FPGA [19,20]. Each joint works as an independent processing unit and is responsible for the first-level " Technische Unterstützungssysteme, die die Menschen wirklich wollen" signal acquisition and conditioning (e.g., Hall sensors, position encoders) and implements a cascaded control algorithm to allow a direct control and actuation of the attached BLDC-or servo motors. ...
In this paper, the concept of the innovative exoskeleton for stroke rehabilitation of the Recupera-Reha project is presented. By applying innovative electromechanical solutions, advanced control approaches, and by using biosignal data, the system will be well-fitted. Furthermore, it will behave transparently to the user and will support different training modalities. The therapy situation will be supported and exercises in the field of everyday practice in the private or professional environment will be enabled. As an autonomous treatment system, it will give assistance as much as needed and will enable the patient to make therapies across sector borders (rehab-outpatient-work) for the first time.
... The design of the Type III (120Nm) and Type IV (300Nm) is currently being finished. All actuators are based on previous modular actuators designed at DFKI (see example reference in [6]). They combine Robodrive brushless DC motors with Harmonic Drive gears. ...
... Most of the processing elements are placed in the system in direct neighbourhood of actuation units. Since the introduction of custom PCBs for BLDC motor control in the robots developed at the DFKI RIC [5], the motor actuation and control is realized locally. The technological advancement allowed us to move from Xilinx Spartan 3 FPGAs having roughly 17,000 logic elements to Spartan 6 modules containing 44,000 logic cells while staying roughly in the same form factor. ...
This paper presents the multi-legged robot MANTIS which is developed within the project LIMES at the DFKI RIC and the University of Bremen. In particular, we describe the mechanical design, the sensor setup, electronics, and computing hardware. Furthermore we give a short introduction to the software framework for simulation-based motion behavior generation and optimization for such kinematically complex robots as well as to the online locomotion control and evaluation approach for context-based utilization and adaptation of these behaviors. Finally, applied methodologies and experiments allowing to assess and reduce the difference between observed and simulated behavior of the robot and its subsystems are presented.
... • Joint design based on and compatible to [5]. ...
This chapter presents the design of the robotic platform AILA, a mobile dual-arm robot system developed as a research platform for investigating aspects of the currently booming multidisciplinary area of mobile manipulation. The robot integrates and allows in a single platform performance of research in most of the areas involved in autonomous robotics: navigation, mobile and dual-arm manipulation planning, active compliance and force control strategies, object recognition, scene representation, and semantic perception. AILA has 32 degrees of freedom (DOF), including 7-DOF arms, a 4-DOF torso, a 2-DOF head, and a mobile base equipped with 6 wheels, each of them with 2 degrees of freedom. Additionally, the left hand of the robot was equipped with a RFID reader in order to receive the information coming from the DPM. This chapter provides an overview of the design, the variety of sensors incorporated in the system, and its required control software.
... The manipulation device is one of the integral components to solving the given contest tasks. The developed manipulator consist of six actuators with BLDC 2 motors from RoboDrive and Harmonic Drive transmissions with a reduction ratio 1:100 [2]. In order to adapt to development time all six actuators are identical. ...
This paper describes the development and test of a mobile manipulation platform intended for a terrestrial robotic competition. While current space missions are planned to minimize complex manipulation tasks, plans for future space missions go beyond these restrictions. Infrastructure deployment, human-robot cooperative mis-sions and complex sample collection require increasingly complex manipulation capabilities. To meet this need the Spacebot Cup consists of several complex manipulation tasks in unstructured terrain. These requirements were the main design driver for the presented system. The pre-sented rover consists of a 3-Boogie-Chasis designed to in-crease the maximum stepping size, flexible rubber wheels to increase the maximal climbing inclination on loose sur-faces and a small six degree of freedom manipulator to handle objects within the competition. The iterative sim-ulation and experiment process used to develop the flexi-ble rubber wheels is presented. Furthermore experiments are presented which allow a performance comparison be-tween flexible and rigid wheels on loose surfaces.
... The encoder signals are read in at the system frequency of 18.4MHz. The construction of the actuator is similar to that in Hilljegerdes et al. (2009). ...
Chattering is a very undesired phenomenon in technical systems. There can be many causes for it. In this paper, at first simulation results are shown that insufficient setpoint updating can also lead to chattering in form of intersample ripple. The difference between setpoint updating rate and the control frequency can be traced back to the multi-layered software architecture of an overall system. As a solution, a joint space interpolator is suggested, which is a novel construction mainly combining a trajectory interpolator with a jitter buffer in joint space. On the one hand it provides supplementary setpoints to the controller and on the other hand it ensures very strict real-time performance of the closed-loop system. At last, experiment results are shown to support the proposed method. This scheme is implemented for, but not limited to, actuators utilizing geared brushless DC (BLDC) motors with FPGA-based controllers. The simulations and experiments have focus on robotic motion control in joint space.
... The actuator modules furthermore provide electronics containing power electronics, electronics for sensor data acquisition as well as an FPGA for implementation of control algorithms, logging capabilities and communication with other actuators and the central processing unit. The power consumption of the joints is 30 W, 18 W and 13 W while exerting 23 Nm, 16 Nm and 12 Nm at 3 rpm respectively [18]. ...
This paper describes three projects that are con-
cerned with the exploration of the interior of steep craters,
with special focus on exploring lunar craters with heteroge-
neous robotic teams. Within the project LUNARES (Lunar
Exploration System), a terrestrial demonstrator for a lunar
sample return mission has been created. The task of fetching
a soil sample from within a permanently shadowed lunar
crater had to be accomplished by a heterogeneous team of
robots consisting of a wheeled rover and a legged scout. By
means of different locomotion principles, the unique skills
of these systems have been combined in order to increase
the overall performance in the team. The follow-up project
RIMRES (Reconfigurable Integrated Multi-Robot Exploration
System) develops a rover and a six legged scout in a co-
design process. The key idea remains: Robots with different
locomotion capabilities cooperate as a team, in order to explore
permanently shaded craters at the lunar poles. The third
project, SpaceClimber, focusses on developing a six-legged free-
climbing robot for crater environments. The SpaceClimber
robot is likely to be used as antetype for the scout system
in RIMRES. For more detailed information on the projects,
references are provided.
... The first four joints of each leg are built identically. In previous work, the basis for these leg joints was laid out in [23]. The developed joint has the dimensions 65 mm x 90 mm (L) at a weight of 430 g. ...
Today’s and future space missions (will) have
to deal with increasing requirements regarding autonomy
and flexibility in the locomotor system. To cope with these
requirements, a higher bandwidth for sensor information
is needed. In this paper, a robotic system is presented that
is equipped with artificial feet and a spine incorporating
increased sensing capabilities for walking robots. In the
proposed quadrupedal robotic system, the front and
rear parts are connected via an actuated spinal structure
with six degrees of freedom. In order to increase the
robustness of the system’s locomotion in terms of traction
and stability, a foot-like structure equipped with various
sensors has been developed. In terms of distributed local
control, both structures are as self-contained as possible
with regard to sensing, sensor preprocessing, control and
communication. This allows the robot to respond rapidly
to occurring events with only minor latency.
... In general, an optimization of every aspect of a manipulator arm is desirable including the variation of the DOF number, their alignment, the link lengths, the cross-sectional area parameters, or the drive train. In our case, a drive train optimization is not needed because motors and gearboxes are chosen based on former experiences [6] which have to be adapted to the required torques. ...
The planetary exploration rover Sherpa is equipped with a manipulator arm used for handling payload items as well as for improving its locomotive abilities. Due to the high weight of Sherpa of approx. 200kg and the maximum weight of a payload item of 5 kg, both applications need high torques. In addition, a dextrous operating space is needed which has to allow ground contact and the placement of payload items on pre-defined positions on the rover itself. In this paper we describe an optimization method which evolves a manipulator arm morphology that requires minimal torques to accomplish these to some extent conflictive applications. Covariance Matrix Adaptation Evolution Strategy in parallel processing is used to optimize the link lengths of the manipulator arm. A real-time simulation is used to model the rover, all constraints, and to evaluate each morphology by analyzing the required torques for accomplishing pre-defined tasks. The paper presents the simulation results and the final manipulator arm morphology.
... The core electronic component which undertakes tasks like direct motor control, current, speed and position control, real time logging of sensor data, and communication between other actuators and the central processing unit is built up by a Xilinx Spartan 3 FPGA which can be easily replaced by space-qualified FPGA modules. Further details about the components and system architecture of the SpaceClimber actuator can be found in [16]. ...
In this paper, we present the SpaceClimber integration study, a six-legged, bio-inspired, energy-efficient, and adaptable free-climbing robot for mobility in steep gradients. The long-term vision is to provide a system for the purpose of extraterrestrial surface exploration missions paying special attention to mobility in lunar craters in order to retrieve or analyze scientific samples from the interior of these craters. We present an envisaged mission for SpaceClimber and give a description of the system¿s morphology and the design steps. Apart from hardware design, parts of the control software as well as the utilization of evolutionary algorithms for both morphology design and locomotion control are presented.
... The arm joints and the horizontal axes of the mobile platform use brushless DC motors from Robodrive. A similar control approach to the one previously described has been used for these motors, which has already been successfully integrated in the Space-Climber robot [48] [6]. In this case, the in-house developed motor electronics consists of a stack of three circular PCBs. ...
In classical industrial robotics, robots are concealed within structured and well-known environments performing highly-repetitive tasks. In contrast, current robotic applications require more direct interaction with humans, cooperating with them to achieve a common task and entering home scenarios. Above all, robots are leaving the world of certainty to work in dynamically-changing and unstructured environments that might be partially or completely unknown to them. In such environments, controlling the interaction forces that appear when a robot contacts a certain environment (be the environment an object or a person) is of utmost importance. Common sense suggests the need to leave the stiff industrial robots and move towards compliant and adaptive robot manipulators that resemble the properties of their biological counterpart, the human arm. This thesis focuses on creating a higher level of intelligence for active compliance control methods applied to robot manipulators. This work thus proposes an architecture for compliance regulation named Predictive Context-Based Adaptive Compliance (PCAC) which is composed of three main components operating around a 'classical' impedance controller. Inspired by biological systems, the highest-level component is a Bayesian-based context predictor that allows the robot to pre-regulate the arm compliance based on predictions about the context the robot is placed in. The robot can use the information obtained while contacting the environment to update its context predictions and, in case it is necessary, to correct in real time for wrongly predicted contexts. Thus, the predictions are used both for anticipating actions to be taken 'before' proceeding with a task as well as for applying real-time corrective measures 'during' the execution of a in order to ensure a successful performance. Additionally, this thesis investigates a second component to identify the current environment among a set of known environments. This in turn allows the robot to select the proper compliance controller. The third component of the architecture presents the use of neuroevolutionary techniques for selecting the optimal parameters of the interaction controller once a certain environment has been identified.
Driven by advances in miniaturized electronics, many robotic systems today consist of modular hardware components. This leads to numerous computing units that are distributed within such systems. In order to make better use of such hardware structures from a computational point of view, the implementation of classical control approaches should be reconsidered. Following this idea, a method for distributed computation of motion dynamics of robotic systems using Field Programmable Gate Arrays is discussed. In this approach, local low-level actuator controllers are regarded as interconnected nodes, which are aware of their actuated degree of freedom and the resulting motion of the attached rigid body link element. A modified recursive Newton–Euler algorithm is computed by these nodes, where each node only exchanges data with the neighboring nodes. In the computations, a linear dependency on the dynamic parameters is kept in order to simplify the direct use of dynamic parameters estimated from experimental data. Implementation details and experimental results using a robotic manipulator arm are presented. The experiments show that the method allows compliant motion control. Payloads and external forces acting on a link are considered in the distributed computation of the model by informing the node controlling the respective link of the additional forces.
In this article, we present SpaceClimber,1 a six-legged, bio-inspired, energy-efficient and adaptable free-climbing robot for mobility on steep gradients. The long-term stool is to provide a system for extraterrestrial surface exploration missions, paying special attention to mobility in lunar craters to retrieve or analyze scientific samples from the interior of these craters. We present an envisaged mission for SpaceClimber and summarize the deriving system requirements. The robot's morphology determination procedure is depicted, considering the predefined demands and utilizing a simulation environment in combination with evolutionary optimization strategies, followed by a detailed description of the system's hardware design. The theoretical concept for the control of such machines with an extensive sensory–motor configuration is explained, as well as the implemented locomotion control approach and attempts to optimize the behavior of the robot using machine learning techniques. In addition, the experimental plant that was built for testing and evaluating the performance of the developed system in an environment as realistic as possible is introduced, followed by a description of the experiments performed. Concluding, we summarize the results and experiences and give an outlook on further developments. © 2012 Wiley Periodicals, Inc. (Web page: http://wwww.dfki.de/robotik.)
In this paper, a realistic simulation of extraterrestrial legged robot in trade-off between accuracy and simulation time is presented which provides an enough accuracy to simulate the dynamical properties and locomotions of the legged robot as well as simplified models in a possible timing rate for the realtime simulation. To simplify the complex joint actuator model, an abstract joint actuator model is defined and its parameters are identified. To connect the abstract model to the whole robot kinematic model in a possible timing rate for the real-time simulation, a bi-directional power coupling is proposed. To verify the accuracy of the robot simulation with the abstract model and the power coupling, real experiments are performed and compared with the simulation results. In the proposed realistic simulation, an approach for force measurement for impedance control to improve the locomotion behavior of the legged robot with contact dynamics is developed.
The advanced simulation technology with the rapid growth of computing power leads many new approaches towards design of robot systems. In the typical top-down design of a robot system, the design of the lower phase would be limited by the design from the higher phase. Moreover, it is difficult to well-design the higher phase in predicting problems of the lower phase. Such problems can be effectively improved in the simulation-based system design. All design phases can be done simultaneously with the suitable simulation environment where the hardware and software properties can be flexibly selected and changed. In this paper, a simulation-based design approach of an extraterrestrial six-legged robot (named SpaceClimber) is presented. The highlevel system properties such as fitness functions, energy-efficient morphology and intelligent locomotions are designed in the realtime simulation. The low-level system properties such as joint motor, robot kinematics and dynamical control properties are designed in the precise simulation based on ADAMS/VIEW and MATLAB/SIMULINK.
This article gives a design overview of the new hardware synthesis tool ConPro used for development of application-specific digital logic systems providing a high-level approach with imperative programming features filling the gap be-tween hardware and software level. It is an experimental platform for studying different hybrid scheduling strategies, too. The ConPro development tool and programming lan-guage guides the user from an algorithmic programmer soft-ware view to RTL hardware architecture. Concurrency is explicitly modelled with communicating processes and in-terprocess communication primitives known from traditional and well-known parallel software development using leight weight processes (threads), like semaphores or mutexes. The process modell provides only a single control path resulting in strict sequential instruction scheduling. Concurrency in-side processes is limited to the data path. Beneath explic-itly modelled concurrency, automatic exploitation of inher-ent concurrency is provided by the synthesis compiler using a multi-pass hybrid scheduler.
We present six and an eight-legged walking robots, which are controlled with the same biomimetic ambulation control approach. The goal is to develop walking robots for outdoor environments. The control of these robots is based on models of two biological control primitives: Central Pattern Generators and Reflexes. The Central Pattern Generator Model is controlled from a higher central control level by means of Basic Motion Patterns (BMPs) and posture control primitives (PCPs). With this approach omnidirectional walking and a smooth and fast crossing between different motion patterns is possible. Additionally the posture and the speed of the robot can be changed while walking. The robots were successfully tested in rough, sandy and rocky terrain.
The paper presents the performance enhanced humanoid robot LOLA which is currently being manufactured. The goal of the project is the realization of a fast, human-like walking motion. The robot is characterized by its lightweight construction, a modular, multi-sensory joint design with brushless motors and an electronics architecture using decentralized joint controllers. The fusion of motor, gear and sensors into a highly integrated, mechatronic joint module has several advantages for the whole system, including high power density, good dynamic performance and reliability. Additional degrees of freedom are introduced in elbow, waist and toes. Linear actuators are employed for the knee joints for a better mass distribution in the legs
A third generation of torque-controlled light weight robots has been developed in DLR's robotics and mechatronics lab which is based on all the experiences that have been had with the first two generations. It aims at reaching the limits of what seems achievable with present day technologies not only with respect to light-weight, but also with respect to minimal power consumption and losses. One of the main gaps we tried to close in version III was the development of a new, robot-dedicated high energy motor designed with the best available techniques of concurrent engineering, and the renewed efforts to save weight in the links by using ultralight carbon fibres.
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Scarabaeus "A Walking Robot Applicable to Sample Return Missions
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