AbstractRemote center-of-motion (RCM) mechanisms provide a way for surgical instruments to pass through a remote center (e.g., skin incision) under geometrical constraints, facilitating safer operations in minimally invasive surgery (MIS). One rotation and one translation (1R1T, pitch and insertion) are the basic requirements for RCM mechanisms. To make the structure simpler and control easier, a novel concept of 1R1T RCM mechanisms with partially decoupled motions, inspired by the double-parallelogram 1R RCM mechanisms, is proposed in this article, by investigating and proving its motion combination principle based on the screw theory. New evolution procedures based on the configuration evolution method have been derived to design 1R1T RCM mechanisms based on two approaches of inserting the T-motion in an original 1R RCM mechanism, resulting in two types of 1R1T RCM mechanisms with partially decoupled motions and base-locating actuators. The kinematic models of one typical proposed mechanism (including the forward and inverse kinematics) and its Jacobian matrix are derived. The performance analysis is presented, including RCM validation, velocity, singularity, and workspace analysis. Then, the dimensional optimization based on the discrete solution method is derived. Finally, a prototype of the proposed mechanism is presented with preliminary experiments performed to verify the feasibility of the synthesized RCM mechanisms. The results show that the RCM mechanism performs the 1R1T partially decoupled motion, and it can be used as the basic element of an active manipulator of an MIS robot.

AbstractIn this paper, we propose a novel passive parallel continuum ankle exoskeleton that can provide assistive torque during ankle plantar flexion. Due to the flexible branches arranged in compliance with ankle motion and shape, the compact design can also offer some vertical support. The proposed parallel mechanism consists of two types of branches. The first type is a pre-bent flexible rod, mainly used to apply assistive force/torque during ankle plantar flexion. The second type of branch consists of a bounded sphere joint, flexible rod, and bounded sphere joint (BFB), which is mainly used for support. We formulate the kinetostatic model of the BFB branch as a series of parallelizable unconstrained optimization problems to ensure efficient solvability. After that, we derive the kinetostatic model of the proposed mechanism. After calibration, the wrench error of the kinetostatic model is 9.07%. Simulation analysis based on the calibrated model shows that the designed mechanism has high supporting stiffness and low rotational stiffness. The assistive torque caused by the nonlinear rotational stiffness in the sagittal plane is similar to that of passive clutch-like mechanisms. These properties can still be maintained when the joint center changes within a small range. Besides, a walking experiment was conducted, and the results show that the proposed design can reduce gastrocnemius activity.

AbstractThis article reports the design, modeling, and experiments of a novel retinal surgery robot based on spatial variable remote center-of-motion (RCM) mechanism. The general design criteria for parallel mechanisms are proposed, and the planar five-bar mechanisms are evaluated and selected. The planar-spatial evolution process, including the parallel connection of the planar mechanism and the equivalent substitution of joints, is adopted to develop a spatial variable RCM mechanism and then the robot. The mobility and singularity of the robot are analyzed, and the forward/inverse kinematics and workspace are modeled. Dimension optimization is conducted based on a comprehensive performance indicator that characterizes the motion range of linear actuators and the global dexterity performance index of robot. The prototyped robot is fabricated and assembled, and the kinematic calibration is performed. The position error of end-effector is within 34 μm, and both the position error and deviation of the RCM point are within 23 μm. The robot is demonstrated to reach the desired position and execute the RCM motion with high precision simultaneously.

AbstractWe developed a small jumping mechanism inspired by planthopper. The planthopper jump is characterized by two functions of the hind legs; the leg synchronization using physical contact of the trochanter head and the power amplification using a torque reversal latch. The proposed jump mechanism adopts the unique leg synchronization strategy of the planthopper, and the nymphal and adult models of the hind legs are designed. However, the power amplification is modified to incorporate two torque reversal structures in a single-motion axis. The mechanisms were fabricated by 3D printer with polylactic acid (PLA) material and equipped with extension springs. They weighed 26 g and performed 260 cm vertical jump within one rotation in the frontal plane. The jump height is over 40 times greater than the body length. The experimental findings indicate that the precise synchronization of the rapid leg movement is an effective approach for the design of a jumping mechanism.

AbstractThis paper presents an approach to passively realize any specified object spatial compliance using the grasp of a robotic hand. The kinematically anthropomorphic hands considered have multiple 4-joint fingers making hard point contact with the held object, and the joints of each finger have selectable passive elastic behavior. It is shown that the space of passively realizable compliances is restricted by the kinematic structure of the anthropomorphic hand. To achieve an arbitrary compliant behavior, fingers must be able to adjust their orientation. Synthesis procedures for grasps having 3, 4, and 5 or more fingers are developed. These procedures identify the finger configurations and the individual finger joint compliances needed to passively achieve any specified spatial object compliance matrix in the 20-dimensional subspace of grasp-realizable behaviors.