As the population ages, increasingly more individuals experience ankle disabilities caused by stroke and cerebral palsy. Studies on parallel robots for ankle rehabilitation have been conducted under this circumstance. This paper presents a novel parallel ankle rehabilitation robot with the key features of a simple configuration and actuator nonredundancy. The mechanical design is determined, and a prototype is built. Additionally, inverse position solution is addressed to calculate the workspace of the parallel robot. Jacobian matrices mapping the velocity and force from the active joint space to the task space are derived, and kinetostatic performance indices, namely, motion isotropy, force transfer ratio, and force isotropic radius are defined. Moreover, the inverse dynamic model is presented using the Newton–Euler formulation. Dynamic evaluation index, i.e., dynamic uniformity, is proposed according to the derived Jacobian matrix and inertia matrix. Based on the workspace analysis, the parallel robot demonstrates a sufficient workspace for ankle rehabilitation compared with measured range of motion of human ankle joint complex. The results of the kinetostatic and dynamic performance analysis indicate that the parallel robot possesses good motion isotropy, high force transfer ratio, large force isotropic radius, and relatively uniform dynamic dexterity within most of the workspace, especially in the central part. A numerical example is presented to simulate the rehabilitation process and verify the correctness of the inverse dynamic model. The simplicity and the performance of the proposed robot indicate that it has the potential to be widely used for ankle rehabilitation.

Summary: In order to make the end of the three-axis platform follow the control command and achieve stable control of the end attitude, an improved orientation vector spherical linear interpolation (SLERP) method is proposed for the requirements, which specifically handles the position of the gimbal lock, so that the platform can move smoothly around the gimbal lock position. A three-axis platform with a camera at the end is set up for the validity of the proposed algorithm. At first, an adaptive speed measurement method based on incremental encoder is introduced, which can automatically adapt to high and low speed, and estimate the ultra-low speed to realize the speed measurement of large dynamic range, and this is used for the motion control of the three-axis platform. Then, the SLERP method for the quaternion interpolation on the starting and ending attitudes represented in quaternion is introduced in detail, and it is continuously improved in response to its existing problems for the platform. Finally, an orientation vector SLERP method is proposed, which uses viscosity factor and rejection factor to adjust the algorithm near the platform’s gimbal lock position. A tracking experiment was designed using the red ball as the following target detected by the designed target tracking algorithm using the camera, which verified the effectiveness of the attitude tracking control based on the proposed improved orientation vector SLERP.

Wrist impairments caused by stroke or long-term immobilization should be given more attention than the rehabilitation of proximal limb segments. In addition, the physiological effect of wrist exoskeletons on the training lacks sufficient research. According to the design requirements, a novel parallel wrist rehabilitation robot (PWRR) with two electric linear actuators and a passive prismatic joint was developed to achieve the training of the flexion/extension (F/E) and radial/ulnar deviation (R/U). The constraint forces caused by the axis misalignment were significantly reduced under the passive and active training by 0.75 ± 0.22 N and 2.50 ± 0.72 N, respectively. The total work of the active training increased with the velocity, whereas it was much smaller and had no obvious linear relationship with the velocity for the passive training. The sequence and degree of muscular activation of targeted muscles were measured and analyzed at three velocities to reveal the effects of the training mode and velocity on the physiological effects. PWRR could achieve the isometric training of wrist muscles at any angle of F/E and R/U validated by the comparative experiments of this device and weights. At each interactive force, the median frequency (MNF) of the EMG power spectrum and the average rectified value (ARV) of its amplitude decreased with increasing training time. The MNF slope increased with interactive thresholds, where the maximum slope was (−29.5±2.42) ×10 ⁻³ %/s at 15 N. Conversely, the ARV slope gradually decreased with the thresholds, where the maximum slope was (−61.0±8.55) ×100 ⁻³ %/s at 5 N.

SUMMARY: Against the backdrop of accelerated ageing around the globe, an increasing number of individuals suffer from hip motion disability and gait disorders. In this paper, the performance analysis of a novel parallel assistive mechanism with 2 DOF for hip adduction/abduction (AB/AD) and flexion/extension (FL/EX) assistance is completed and evaluated, particularly the velocity and force transfer features. The analysis shows that the assistive mechanism has advantages of fine motion assistive isotropy, high force transfer ratio and large force isotropic radius, which indicates that the parallel assistive mechanism is suitable for hip AB/AD and FL/EX assistance.

Based on the anti-parallelogram mechanism, an approximate cylindrical rolling joint is proposed to develop a novel cable-driven snake-arm robot with multiple degrees of freedom (DOF). Furthermore, the kinematics of the cable-driven snake-arm robot are established, and the mapping between actuator space and joint space is simplified by bending decoupling motion in the multiple segments. The workspace and bending configurations of the robot are obtained. The static model is established by the principle of minimum potential energy. Furthermore, the simplified cable constraints in the static model are proposed through Taylor expansion, which facilitates the equilibrium conformation analysis of the robot under different external forces. The cable-driven snake-arm robot prototype is developed to verify the feasibility of the robot design and the availability of the static model through the experiments of the free bending motion and the external load on the robot.