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Design of a Serial-Parallel Hybrid Leg for a Humanoid Robot
... A hybrid serial-parallel leg presents yet another approach to a robot's kinematic structure. In this configuration, five out of the six actuators (for a robot model having three actuators for each leg) are placed in the hip, utilizing a combination of serial and parallel mechanisms [27]. A five-bar linkage pantograph mechanism in the serial mechanism with two actuators generates two DoFs of motion for hip and knee flexion/extension, facilitating the placement of actuators near the hip joint. ...
... A five-bar linkage pantograph mechanism in the serial mechanism with two actuators generates two DoFs of motion for hip and knee flexion/extension, facilitating the placement of actuators near the hip joint. This approach can reduces robotic leg inertia and may simplify robot control, particularly during walking on flat ground [27]. However, this mechanical structure does not support human-like movements due to its non-anthropomorphic design. ...
While the concept of humanoid robots stems from the goal of replicating human movement, these systems have yet to match the elegance and efficiency of human locomotion. A key reason for this gap is that current humanoid robots differ from humans in their kinematics, dynamics, and actuator properties. This work seeks to close that gap by designing an optimized humanoid robot with characteristics closely resembling those of an average human. For this purpose, we built a detailed framework for the in-depth electromechanical modeling of actuator components. This model was used in the comprehensive optimization of the robot’s actuator system, which was designed as a multi-objective scheme based on the objectives introduced in our previous work. This process helped both in achieving efficient and high-performance actuators and in streamlining the design of the structural parts to have mass and inertia distributions similar to those of humans. The proposed design process was utilized in the design of our humanoid robot, Mithra. Initial test showed that Mithra achieved its design goals in terms of human-like kinematics and dynamics characteristics, together with sufficient actuator strength for tasks such as stair navigation, squatting, and running.
... Han et al. proposed a humanoid leg design with a four-bar linkage mechanism in the knee and ankle to place all the actuators at the hip [22]. Gim et al. presented a humanoid leg design that combined serial and parallel linkage mechanisms [23]. Asai et al. developed a high-speed table tennis robot using a parallel robot with linkage mechanisms [12]. ...
In human-robot interaction (HRI) research, ball games pose significant challenges that demand robotic solutions that are both cost-effective and user-friendly for non-experts. Air hockey, characterized by safe, non-direct-contact play and a simplified state-action space, emerges as an ideal platform for such research. Despite the availability of various air hockey robots, their high cost and complexity have limited widespread use among researchers requiring robotics expertise. Addressing this gap, we introduce a low-cost, accessible air hockey robot designed to facilitate HRI studies. Featuring a lightweight five-bar linkage mechanism powered by low-cost servomotors for position control, this robot combines efficiency with ease of use. The complete robot's cost is estimated at $346.8, with the arm weighing a mere 19 grams. The robot precisely returns the puck by intermittently adjusting its target joint positions, achieving a play with an average return error of 42.6 mm. These characteristics affirm the robot's potential as a valuable tool for advancing HRI research.
... Since hybrid robots could have multiple kinematic chains with possibly (redundant) actuated joints, they help model the motions of the human body [29]. Examples of hybrid robots are humanoid, multi-legged, multi-armed, exoskeletons, and industrial robotic mechanisms with miscellaneous applications [39][40][41][42][43][44]. Serial-parallel robots are an intriguing use of combined open and closed kinematic chains. ...
Conventional virtual decomposition control (VDC) is a Newton–Euler formulation-based distributed adaptive control algorithm dealing with complex robotic systems. However, the VDC has the following characteristics. Firstly, the algorithm should be implemented recursively, assuming a known force/moment transformation matrix. Secondly, the local stability of each subsystem can be proved using the virtual power flow concept, which ensures the entire system’s stability. Therefore, this paper proposes a fully decentralized control algorithm as an alternative to the conventional VDC. The key idea is to design an estimator for the coupling interconnection term. In addition, this work avoids using the concept of virtual power flow as a constraint (condition) for proving the virtual stability of the individual subsystem. Adaptive approximation control is used as a basis for control architecture. Besides, the proposed controller is applicable to mixed open/closed-chain mechanisms. For a closed-chain mechanism subsystem, the problem is formulated as the minimization of the actuator torques with equality constraints (in the case of over-actuation). A direct solution is obtained for an open-chain subsystem. We present symbolic calculations for some robots with a kinematic loop to clarify the proposed modeling procedure. Simulations are performed for a 6-link biped robot with two kinematic chain configurations to investigate the proposed algorithm’s effectiveness. In addition, a comparative analysis is performed to prove the validity of the results.
... Many researchers have studied the kinematics of the hybrid robots, including their position and velocity analysis. For example, these issues were considered by Tanev [7] for two serially connected tripod mechanisms; Moosavian et al. [8] for a planar robot with a serial PUMA-type robotic arm attached to its output link; Zheng et al. [9] for two tripods, designed such that the smaller one is inside the larger one; Nazari et al. [10] for a tripod with cylindrical and revolute joints and a serial robotic arm mounted on the tripod moving plate; Kucuk and Gungor [11] for a Stewart platform placed on a SCARA-type robot; Zhang et al. [12] for a 5-DOF Exechon robot, which consists of a tripod and a 2-DOF serial wrist mechanism; Xu et al. [13] for a polishing machine based on a translational Delta-like robot with linear drives and a separate serial module with three rotational DOFs; Gim et al. [14] for a humanoid robotic leg composed of two planar closed loops, each followed by a link with passive joints and connected to each other and the moving plate through an actuated revolute joint; Milutinović et al. [15] for a Tricept robot based on a tripod with translational DOFs equipped with a 2-DOF wrist; My and Hoan [16] for a serial robotic arm with two intermediate parallel loops. ...
This article presents the velocity and singularity analysis for a five-degree-of-freedom (5-DOF) parallel-serial manipulator. The hybrid structure of the manipulator combines a tripod-like parallel part and a serial part, represented as two carriages moving in perpendicular directions. This manipulator provides its end-effector with a 3T2R motion pattern, which includes three independent translations and two independent rotations. First, the study briefly discusses the manipulator design and the results of the position analysis. These results form the basis for the subsequent velocity and singularity analysis, performed by screw theory. The screw coordinates of the unit twists are written for each manipulator joint, and then through the reciprocal screw approach, the actuation and constraint wrenches of the manipulator are obtained by simple inspection. Based on these twists and wrenches, the paper forms the velocity equation and shows an example of the inverse velocity analysis for a given end-effector trajectory. The same example is solved by numerical differentiation to verify the proposed approach. Next, the paper investigates singular configurations by analyzing the wrench system of the manipulator and presents several conditions for serial and parallel singularities. Each condition has both a symbolic representation, given by an equation for screw coordinates of certain wrenches, and a visual representation, which shows the manipulator in a singular configuration.
... Apart from joint-specic solutions, few researchers took a dierent approach to the kinematic structure. Gim et al. [35] designed a hybrid serial-parallel leg, where ve of the six leg actuators are located in the hip. This greatly reduces the leg inertia and in turn the required joint velocities and torques, which are also more uniform. ...
Purpose of Review
As new technological advancements are made, humanoid robots that utilise them are being designed and manufactured. For optimal design choices, a broad overview with insight on the advantages and disadvantages of available technologies is necessary. This article intends to provide an analysis on the established approaches and contrast them with emerging ones.
Recent Findings
A clear shift in the recent design features of humanoid robots is developing, which is supported by literature. As humanoid robots are meant to leave laboratories and traverse the world, compliance and more efficient locomotion are necessary. The limitations of highly rigid actuation are being tackled by different research groups in unique ways. Some focus on modifying the kinematic structure, while others change the actuation scheme. With new manufacturing capabilities, previously impossible designs are becoming feasible.
Summary
A comprehensive review on the technologies crucial for bipedal humanoid robots was performed. Different mechanical concepts have been discussed, along with the advancements in actuation, sensing, and manufacturing. The paper is supplemented with a list of the recently developed platforms along with a selection of their specifications.
... hip flexion-extension, knee, ankle, torso and wrist [42] (see Fig. 2 d). Disney Research in 2018 also reported a design of a bipedal robot [43] which has hybrid legs [44] optimized for achieving a fast walking behavior. ...
Parallel mechanisms are used increasingly often as modular subsystem units in various robots and man-machine interfaces for their superior stiffness, payload-to-weight ratio and dynamic properties. This leads to series-parallel hybrid robotic systems which utilize closed loop linkages and parallel kinematic machines as an abstraction of a certain kinematic joint. This paper presents a survey of recently developed series-parallel hybrid robots in various application domains such as legged robotics, humanoids, exoskeletons and industrial automation. In particular, we focus on modular and distributive aspects of such systems with an intention to bring the current design paradigm into focus, which simplifies the robot development process by promoting the effective reuse of hardware and software components and overcomes the shortcomings of traditional serial robots like poor payload capacity and stiffness.
One of the most fascinating applications of walking robots is in the film industry, for creating special effects and animatronics. For this reason, the Walt Disney Company is investing efforts to develop bipedal walking robots. A serial-parallel hybrid leg for a humanoid robot was designed by Disney’s team, consisting of a pair of twin hybrid chains whose main body is a 5-bar linkage. This paper analyzes the wrench capability of a planar version simplification of this serial-parallel hybrid leg, aiming to determine the leg’s posture that provides the highest supporting and impulse forces during the robot’s gait. The wrench capability is calculated through Davies’ method. This paper demonstrates that the robot applies higher impulse forces when stepping forward or provides higher resistance forces when landing on the ground if the legs are brought closer to the actuators.
In this paper, a 6 degrees of freedom (DOFs) generalized parallel manipulator is presented which can be used as a humanoid leg. Based on the Number Synthesis and Graph Synthesis method, all the possible contracted graphs of the 6-DOFs leg are provided. Then, a novel method named as Node Response Method (NRM) is presented to identify the isomorphism of contracted graphs. In order to obtain the optimal manipulator, the Lie group is used to analyze all limbs. Furthermore, a terrain adaptive index named as Global Maximum Stride Distance Ratio (GMSDR) is established, which is used to assess the performance of a biped robot in different terrains. The DOF of proposed manipulator is verified by translating into a two-layer and two-loop (TL-TL) topological structure. Afterwards, the kinematics and the Jacobian matrix of the manipulator are calculated. Moreover, the performance indexes of the manipulator are analyzed. In order to obtain an optimal kinematics performance, the structural parameters are optimized using genetic algorithm. Finally, two basic gaits are proposed for a biped robot which consists of two manipulators and a simulation is carried out.
A Two-step Division-Merge (TDM) based inverse kinematics (IK) mechanism is proposed for robots with multiple degrees of freedom (multi-DOFs) in unstructured environments. For any robot with n-DOFs (n>6), a division point is selected first to divide it into a lower part subsystem from its base to the division point, together with an upper part one from the point to its end-effector. Once a collision-free configuration is found for the upper part subsystem to match with the target, the lower part subsystem is then planned to merge with the upper part subsystem at the division point. Specifically, the division point is selected such that the lower part subsystem has 6-DOFs, while the upper part subsystem has (n-6)-DOFs. Furthermore, a Reverse & Random Rotation (RRR) algorithm is also proposed to solve the IK of the upper part subsystem in unstructured environments, while the IK of the lower part subsystem is solved analytically. The proposed TDM based mechanism is verified via experiments using a lab-customized humanoid apple harvesting robot with 11- and 13-DOFs, respectively. Under the various scenarios with different target and obstacle configurations, errors in position coordinates and orientation angles between the target pose and those of the end-effector obtained with forward kinematics (FK) are calculated. Results show that the errors in position and orientation are less than 0.005 mm and 0.007°, respectively, and the average computational time is less than 2 s for the IK solution of the entire robot. Such results indicate that the proposed mechanism is reliable and capable of reducing the complexity of IK for multi-DOFs humanoid robots. With the proposed algorithm, the apple harvesting success rate of a lab-customized 11-DOFs robot reaches 89.2%, which can be further increased up to 93.3% with error compensation, while the average time starting from the robot action to the end-effector reaching the target pose of the apple is around 12.3 s.
The performance measurements for the parallel manipulator can be divided into kinematic and dynamic indexes. The kinematic estimations have been well explored and contributed in the parallel structure selection, singularity avoidance and dimension synthesis. The dynamic performance assessments will also have significant contributions for parallel robots. In this research, the complete inverse dynamic model is formulated via the Lagrangian approach and verified by the simulation results. Two novel dynamic indices are proposed to explore the coupled inertia features among different kinematic limbs. The multiple dynamic indices are analyzed and compared on two translational parallel mechanisms with similar joint configurations. A feasible controller is provided to track the desired trajectory of the mobile platform.
Robots with kinematic loops are known to have superior mechanical performance. However, due to these loops, their modeling and control is challenging, and prevents a more widespread use. In this paper, we describe a versatile Inverse Kinematics (IK) for the retargeting of expressive motions onto mechanical systems with loops. We support the precise control of the position and orientation of several end-effectors, and the Center of Mass (CoM) of slowly walking robots. Our formulation safeguards against a disassembly when IK targets are moved outside the workspace of the robot, and we introduce a regularizer that smoothly circumvents kinematic singularities where velocities go to infinity. With several validation examples and three physical robots, we demonstrate the versatility and efficacy of our IK on overactuated systems with loops, and for the retargeting of an expressive motion onto a bipedal robot.
ATRIAS 1.0 is a spring-legged, monopod robot designed and built as a prototype towards a human-scale 3D biped. The monopod has to meet certain requirements concerning locomotion dynamics and energy efficiency to meet the goal of a biped that can autonomously walk and run efficiently and robustly outdoors, untethered over realistic (non-ideal) terrain. The design of ATRIAS 1.0 includes adequate control authority for robust locomotion as well as incorporating the idea of passive dynamics for high energy economy. Towards this effort, the passive dynamics of ATRIAS 1.0 are designed to match the key features of the Spring Loaded Inverted Pendulum model: a massless leg, mass centered at the hip joint, and a series spring between the ground and the mass at the hip joint. In this paper the authors discuss the key features of this unique robot design.
Purpose
– The purpose of this paper is to describe a calibration method developed to improve the accuracy of a six degrees-of-freedom medical robot. The proposed calibration approach aims to enhance the robot’s accuracy in a specific target workspace. A comparison of five observability indices is also done to choose the most appropriate calibration robot configurations.
Design/methodology/approach
– The calibration method is based on the forward kinematic approach, which uses a nonlinear optimization model. The used experimental data are 84 end-effector positions, which are measured using a laser tracker. The calibration configurations are chosen through an observability analysis, while the validation after calibration is carried out in 336 positions within the target workspace.
Findings
– Simulations allowed finding the most appropriate observability index for choosing the optimal calibration configurations. They also showed the ability of our calibration model to identify most of the considered robot’s parameters, despite measurement errors. Experimental tests confirmed the simulation findings and showed that the robot’s mean position error is reduced from 3.992 mm before calibration to 0.387 mm after, and the maximum error is reduced from 5.957 to 0.851 mm.
Originality/value
– This paper presents a calibration method which makes it possible to accurately identify the kinematic errors for a novel medical robot. In addition, this paper presents a comparison between the five observability indices proposed in the literature. The proposed method might be applied to any industrial or medical robot similar to the robot studied in this paper.
This paper discusses the actuator-level control of Valkyrie, a new humanoid robot designed by NASA's Johnson Space Center in collaboration with several external partners. Several topics pertaining to Valkyrie's series elastic actuators are presented including control architecture, controller design, and implementation in hardware. A decentralized approach is taken in controlling Valkyrie's many series elastic degrees of freedom. By conceptually decoupling actuator dynamics from robot limb dynamics, the problem of controlling a highly complex system is simplified and the controller development process is streamlined compared to other approaches. This hierarchical control abstraction is realized by leveraging disturbance observers in the robot's joint-level torque controllers. A novel analysis technique is applied to understand the ability of a disturbance observer to attenuate the effects of unmodeled dynamics. The performance of this control approach is demonstrated in two ways. First, torque tracking performance of a single Valkyrie actuator is characterized in terms of controllable torque resolution, tracking error, bandwidth, and power consumption. Second, tests are performed on Valkyrie's arm, a serial chain of actuators, to demonstrate the robot's ability to accurately track torques with the presented decentralized control approach.
This paper gives an overview of the development of a novel biped walking machine for a humanoid robot, Roboray. This lower-limb robot is designed as an experimental system for studying biped locomotion based on force and torque controlled joints. The robot has 13 actuated DOF and torque sensors are integrated at all the joints except the waist joint. We designed a new tendon type joint modules as a pitch joint drive module, which is highly back-drivable and elastic. We also built a decentralized control system using the small controller boards named Smart Driver. The forward walking experiment with this lower limbs was conducted to test the mechanical structure and control system.
The incorporation of passive compliance in robotic systems could improve their performance during interactions and impacts, for energy storage and efficiency, and for general safety for both the robots and humans. This paper presents the recently developed COMpliant huMANoid COMAN. COMAN is actuated by passive compliance actuators based on the series elastic actuation principle (SEA). The design and implementation of the overall body of the robot is discussed including the realization of the different body segments and the tuning of the joint distributed passive elasticity. This joint stiffness tuning is a critical parameter in the performance of compliant systems. A novel systematic method to optimally tune the joint elasticity of multi-dof SEA robots based on resonance analysis and energy storage maximization criteria forms one of the key contributions of this work. The paper will show this method being applied to the selection of the passive elasticity of COMAN legs. The first completed robot prototype is presented accompanied by experimental walking trials to demonstrate its operation.
This paper presents a computational technique for creating whole-body motions of human and animal characters without reference motion. Our work enables animators to generate a natural motion by dragging a link to an arbitrary position with any number of links pinned in the global frame, as well as other constraints such as desired joint angles and joint motion ranges. The method leads to an intuitive pin-and-drag interface where the user can generate whole-body motions by simply switching on or off or strengthening or weakening the constraints. This work is based on a new interactive inverse kinematics technique that allows more flexible attachment of pins and various types of constraints. Editing or retargeting captured motion requires only a small modification to the original method, although it can also create natural motions from scratch. We demonstrate the usefulness and advantage of our method with a number of example motion clips.
This paper discusses the dynamics computation of structure-varying
kinematic chains which imply mechanical link systems whose structure may
change from open kinematic chain to closed one and vice versa. The
proposed algorithm can handle and compute the dynamics and motions of
any rigid link systems in a seamless manner without switching among
algorithms. The computation is developed on the foundation of the
dynamics computation algorithms established in robotics, which is
superior in efficiency due to explicit use of the generalized
coordinates to those used in the general-purpose motion analysis
softwares. Although the structure-varying kinematic chains are commonly
found in computing human and animal motions, the computation of their
dynamics has not been discussed in literature. The developed computation
will provide a general algorithm for the computation of motion and
control of humanoid robots and computer graphics human figures
This paper summarizes how Team KAIST prepared for the DARPA Robotics Challenge (DRC) Finals, especially in terms of the robot system and control strategy. To imitate the Fukushima nuclear disaster situation, the DRC performed eight tasks and degraded communication conditions. This competition demanded various robotic technologies, such as manipulation, mobility, telemetry, autonomy, and localization. Their systematic integration and the overall system robustness were also important issues in completing the challenge. In this sense, this paper presents a hardware and software system for the DRC-HUBO+, a humanoid robot that was used for the DRC; it also presents control methods, such as inverse kinematics, compliance control, a walking algorithm, and a vision algorithm, all of which were implemented to accomplish the tasks. The strategies and operations for each task are briefly explained with vision algorithms. This paper summarizes what we learned from the DRC before the conclusion. In the competition, 25 international teams participated with their various robot platforms. We competed in this challenge using the DRC-HUBO+ and won first place in the competition.
This paper presents a humanoid robot HRP-2Kai, which is the improvement version of HRP-2 towards disaster response tasks. HRP-2 stands for a humanoid robotics platform-2, which was developed in phase two of the Japanese national project HRP (Humanoid Robotics Project, from 1998FY to 2002FY), while Kai means improvement in Japanese. In a year of the ninth year from releasing HRP-2, the Great East Japan Earthquake shook Japan on March 11, 2011. Since we reflected on that we were not able to deploy our robots for emergency response at that time, we started a study of the disaster response humanoid robots by improving HRP-2. Improvements are presented with its basic specification in this paper.
This paper presents the design principles for highly efficient legged robots, the implementation of the principles in the design of the MIT Cheetah, and the analysis of the high-speed trotting experimental results. The design principles were derived by analyzing three major energy-loss mechanisms in locomotion: heat losses from the actuators, friction losses in transmission, and the interaction losses caused by the interface between the system and the environment. Four design principles that minimize these losses are discussed: employment of high torque-density motors, energy regenerative electronic system, low loss transmission, and a low leg inertia. These principles were implemented in the design of the MIT Cheetah; the major design features are large gap diameter motors, regenerative electric motor drivers, single-stage low gear transmission, dual coaxial motors with composite legs, and the differential actuated spine. The experimental results of fast trotting are presented; the 33-kg robot runs at 22 km/h (6 m/s). The total power consumption from the battery pack was 973 W and resulted in a total cost of transport of 0.5, which rivals running animals' at the same scale. 76% of the total energy consumption is attributed to heat loss from the motor, and the remaining 24% is used in mechanical work, which is dissipated as interaction loss as well as friction losses at the joint and transmission.
This paper describes the technical approach, hardware design, and software algorithms that have been used by Team THOR in the DARPA Robotics Challenge (DRC) Trials 2013 competition. To overcome big hurdles such as a short development time and limited budget, we focused on forming modular components—in both hardware and software—to allow for efficient and cost-effective parallel development. The hardware of THOR-OP (Tactical Hazardous Operations Robot–Open Platform) consists of standardized, advanced actuators and structural components. These aspects allowed for efficient maintenance, quick reconfiguration, and most importantly, a relatively low build cost. We also pursued modularity in the software, which consisted of a hybrid locomotion engine, a hierarchical arm controller, and a platform-independent remote operator interface. These modules yielded multiple control options with different levels of autonomy to suit various situations. The flexible software architecture allowed rapid development, quick migration to hardware changes, and multiple parallel control options. These systems were validated at the DRC Trials, where THOR-OP performed well against other robots and successfully acquired finalist status.
This paper describes the means of tuning-up method of the walking parameters to go up and down stairs for a biped robot with leg mechanisms using Stewart platforms. It has been confirmed that the stroke range of use could be reduced by tuning up the waist yaw trajectory and preset ZMP trajectories for motion pattern generation. By using the developed method, a walking experiment involving movement up and down a stair with the rise of 250 mm and certain walking experiments ascending and descending stairs carrying a human were successfully completed. Through these experiments, the effectiveness of the proposed method was confirmed.
This paper describes the mechanism of biped locomotor, WL-16 (Waseda Leg No. 16), its compliance control method and experiments carrying a human. This robot is developed based on WL-15's basic design using new gimbals' mechanisms with small backlash and new linear actuators dealing with a heavy payload and a wide movable range. Walking experiments carrying a human are successfully completed and the effectiveness of WL-16's mechanism and control method are confirmed.
Comparison of the Characteristics Between Serial and Parallel Robots
- Z Pandilov
- V Dukovski
Realization of Dynamic Human-Carrying Walking by a Biped Locomotor
- Y Sugahara