Accepted Manuscripts

Technical Brief  
Peter L Wang, Ulrich Rhem and J. Michael McCarthy
J. Mechanisms Robotics   doi: 10.1115/1.4040027
This paper applies kinematic synthesis theory to obtain the dimensions of a constrained spatial serial chain for a valve mechanism that cleans and closes a soil conditioning port in a tunnel boring machine. The goal is a smooth movement that rotates a cylindrical array of studs into position and then translates it forward to clean and close the port. The movement of the valve is defined by six positions of the RPR (revolute-prismatic-revolute) serial chain. These six positions are used to compute the dimensions of the two SS (spherical spherical) dyads that constrain the RPR chain to obtain a one degree-of-freedom spatial mechanism. An example design of this valve mechanism is provided in detail.
TOPICS: Design, Valves, Chain, Dimensions, Boring machines, Degrees of freedom, Kinematics, Soil, Tunnels
Xin-Jun Liu, Gang Han, Fugui Xie, Qizhi Meng and Sai Zhang
J. Mechanisms Robotics   doi: 10.1115/1.4040028
Driving system parameters optimization, especially the optimal selection of specifications of motor and gearbox, is very important for improving high-speed parallel robots’ performance. A very challenging issue is parallel robots’ performance evaluation that should be able to illustrate robots’ performance accurately and guide driving system parameters optimization effectively. However, this issue is complicated by parallel robots’ anisotropic translational and rotational dynamic performance, and the multi-parameters of motors and gearboxes. In this paper, by separating the influence of translational and rotational degrees of freedom (DOFs) on robots’ performance, a new dynamic performance index is proposed to reflect the driving torque in instantaneous acceleration. Then the influence of driving system’s multi-parameters on robots’ driving torque in instantaneous acceleration and cycle time in continuous motion is investigated. Based on the investigation, an inertia matching index is further derived which is more suitable for minimizing the driving torque of parallel robots with translational and rotational DOFs. A comprehensive parameterized performance atlas is finally established. Based on this atlas, the performance of a high-speed parallel robot developed in this paper can be clearly evaluated and the optimal combination of motors and gearboxes can be quickly selected to ensure low driving torque and high pick-and-place frequency.
TOPICS: Robots, Optimization, Torque, Motors, Anisotropy, Degrees of freedom, Mechanical drives, Cycles, Performance evaluation, Inertia (Mechanics)
Technical Brief  
Chih-Hsing Liu, Chen-Hua Chiu, Ta-Lun Chen, Tzu-Yang Pai, Mao-Cheng Hsu and Yang Chen
J. Mechanisms Robotics   doi: 10.1115/1.4039972
This study presents a topology optimization method to synthesize an innovative compliant finger for grasping objects with size and shape variations. The design domain of the compliant finger is a trapezoidal area with one input and two output ports. The topology optimized finger design is prototyped by 3D printing using flexible filament, and be used in the developed gripper module which consists of one actuator and two identical compliant fingers. Both fingers are actuated by one displacement input, and can grip objects through elastic deformation. The gripper module is mounted on an industrial robot to pick and place a variety of objects to demonstrate the effectiveness of the proposed design. The results show the developed compliant finger can be used to handle vulnerable objects without causing damage to the surface of grasped items. The proposed compliant finger is a monolithic and low-cost design which can be used to resolve the challenge issue for robotic automation of irregular and vulnerable objects.
TOPICS: Engineering prototypes, Grasping, Optimization, Shapes, Topology, Additive manufacturing, Design, Grippers, Damage, Robotics, Displacement, Actuators, Deformation, Robots, Gates (Closures)
Technical Brief  
Sung Yul Shin, Ashish Deshpande and James Sulzer
J. Mechanisms Robotics   doi: 10.1115/1.4039973
The cost of therapy is one of the most significant barriers to recovery after neurological injury. Robotic gait trainers move the legs through repetitive, natural motions imitating gait. Recent meta-analyses conclude that such training improves walking function in neurologically impaired individuals. While robotic gait trainers promise to reduce the physical burden on therapists and allow greater patient throughput, they are prohibitively costly. Our novel approach is to design a new underactuated robotic trainer that maintains the key advantages of the expensive trainers but with a simplified design to reduce cost. Our primary design challenge is translating the motion of a single actuator to an array of natural gait trajectories. We address this with an eight-link Jansen mechanism that matches a generalized gait trajectory. We then optimize the mechanism to match different trajectories through link length adjustment based on nine different gait patterns obtained from gait database of 113 healthy individuals. To physically validate the range in gait patterns produced by the simulation, we tested kinematic accuracy on a motorized wooden proof-of-concept of the gait trainer. The simulation and experimental results suggested that an adjustment of two links can reasonably fit a wide range of gait patterns under typical within-subject variance. We conclude that this design could provide the basis for a low-cost, patient-based electromechanical gait trainer for neurorecovery.
TOPICS: Design, Wounds, Nervous system, Robotics, Simulation, Trajectories (Physics), Actuators, Databases, Patient treatment, Kinematics
Nathan M. Cahill, Thomas Sugar, Yi Ren and Kyle Schroeder
J. Mechanisms Robotics   doi: 10.1115/1.4039772
Comparatively slow growth in energy density of both power storage and generation technologies has placed added emphasis on the need for energy efficient designs in legged robots. This paper explores the potential of parallel springs in robot limb design. We start by adding what we call the Exhaustive Parallel Compliance Matrix (EPCM) to the design. The EPCM is a set of parallel springs which includes a parallel spring for each joint and a multi-joint parallel spring for all possible combinations of the robot's joints. Then we carefully formulate and compare two performance metrics which improve various aspects of the system performance. Each performance metric is analyzed and compared, their strengths and weaknesses being rigorously presented. The performance benefits associated with this approach are dramatic. Implementing the spring matrix reduces the sum of square power exerted by the actuators by up to 47 percent, the peak power requirement by almost 40 percent, the sum of squared current by 55 percent, and the peak current by 55 percent. These results were generated using a planar robot limb and a gait trajectory borrowed from biology. We use a fully dynamic model of the robotic system including inertial effects. We also test the design robustness using a perturbation study which shows that the parallel springs are effective even in the presence of trajectory perturbation.
TOPICS: Design, Robotics, Stiffness, Springs, Robots, Trajectories (Physics), Actuators, Energy storage, Density, Robustness, Dynamic models, Biology
Technical Brief  
Jacob Rice and Joseph M. Schimmels
J. Mechanisms Robotics   doi: 10.1115/1.4039591
Passive compliance control is an approach for controlling the contact forces between a robotic manipulator and a stiff environment. If the manipulator is redundant, the elastic behavior of the robot end-effector can be controlled by adjusting the manipulator configuration and the intrinsic joint stiffness. Serial manipulators with real-time adjustable joint stiffness are capable of time-varying elastic behavior of the end-effector in task space, a beneficial quality for constrained manipulation tasks such as opening doors, turning cranks, assembling parts, etc. The challenge in passive compliance control is finding suitable joint commands for producing the desired time-varying end-effector position and compliance (task manipulation plan). This problem is addressed here by extending the redundant inverse kinematics problem to include compliance. This paper presents an effective method for simultaneously attaining the desired end-effector position and end-effector elastic behavior by tracking a desired variation in both the position and compliance. The method also compensates for joint deflection due to known external loads, e.g. gravity.
TOPICS: Manipulators, End effectors, Elasticity, Stiffness, Kinematics, Gravity (Force), Doors, Robots, Stress, Deflection

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