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Robot-assisted technology has been increasingly employed in the therapy of post stroke patients to deliver high-quality treatment and alleviate therapists’ burden. This paper introduces a novel parallel end traction apparatus (PETA) to supplement equipment selection. Considering the appearance and performance of the PETA, two types of special five-bar linkage mechanisms are selected as the potential configurations of the actuation execution unit because of their compact arrangement and parallel structure. Kinematic analysis of each mechanism, i.e., position solutions and Jacobian matrix, is carried out. Subsequently, a comparative study between the two mechanisms is conducted. In the established source of nondimensional parameter synthesis, the singularity, maximum continuous workspace, and performance variation trends are analyzed. Based on the evaluation results, the final scheme with determined configuration and corresponding near-optimized non-dimensional parameters is obtained. Then, a prototype is constructed. By adding a lockable translational degree of freedom in the vertical direction, the PETA can provide 2D planar exercise and 3D spatial exercise. Finally, a control system is developed for passive exercise mode based on the derived inverse position solution, and preliminary experiments are performed to verify the applicability of the PETA.

This study presents a novel four-degrees-of-freedom parallel gripper with potential application to industrial automation. The gripper adopts a parallel grasping mode on objects and can independently complete in-plane horizontal and vertical motions and in-hand twisting motion. Kinematic and dynamic models of the gripper–object system are developed. The controllable internal force acting on the object is calculated to obtain the minimum driving force/torque. An energy-based manipulability index is developed on the basis of the derived solutions. The numerical simulation includes a comparison between the MATLAB model and the ADAMS model to verify the motion forms of the parallel gripper and the rationality of analytical modeling studies. Manipulability performance is evaluated along the transportation path of the object. Results indicate that the gripper can achieve horizontal transmission to supplement the workspace of a robotic arm, and it exhibits relatively better performance in in-hand manipulation and in-plane vertical transmission.

SUMMARYAgainst 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.

The Ortho-SUV frame (OSF) is a hexapod external fixator widely applied in orthopedics deformity correction. The possibility of collision between OSF's struts and the soft tissue is an essential but overlooked issue. To avoid the issue, a novel collision detection algorithm is established based on a cone-cylinder model of the tibial limb-strut interaction for detecting the closeness of the tibial limb and external fixator. The algorithm is constructed using the vector analysis based on the model of the minimum distance between the truncated cone generatrix and the cylinder axis. The motion simulation is performed on the overall alignment through the Solidworks-motion module to verify the feasibility of the algorithm. Subsequently, the installation parameter deviations of the bone-fixator system are described to investigate the influence of orientation and position deviation on the closeness of the tibial limb and external fixator through the numerical method. The investigation results show that the orientation deviation γ (around the z-axis), the position deviation τ1 and τ2 (along the x and y-axes, respectively) have greater sensitivity to closeness and the influence of multiple deviations on the closeness has the property of superposition. The proposed algorithm can assist clinicians to strictly design and appraise frame configurations prior to their application to avoid the collision between the external fixator and the limbs during the correction. It has great application significance in the development of computer-aided correction software. This article is protected by copyright. All rights reserved.

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.

Foot and ankle deformity remains a common presenting complaint in orthopedic surgery. External fixator is a key medical device to assist gradual correction. Its configuration selection has a significant influence on correction results. Among two external fixators currently used in clinic, conventional Ilizarov external fixator (IEF) has high use difficulty and low accuracy, whereas the single configuration of later hexapod external fixator (HEF) leads to inadequate adaptation to diverse deformity types in foot and ankle. To solve the above problems, this paper presents a novel parallel distraction apparatus (PDA). First, corrective degree-of-freedom (c-DOF) is defined to determine expected posture transformation of external fixator required by corrective manipulation. By summarizing and classifying c-DOF, predominant foot and ankle deformities with fewer correction requirements are divided into six types. Subsequently, six lower-mobility parallel mechanisms are introduced as the configurations of external fixators via the c-DOF based configuration synthesis approach. After performing reconfigurable structural design, PDA can respectively form six types of parallel external fixators for six deformity types. Finally, clinical case simulations are provided to verify the application potential and advantages of PDA.

Repetitive and intensive physiotherapy is indispensable to patients with ankle disabilities. Increasingly robot-assisted technology has been employed in the treatment to reduce the burden of the therapists and the related costs of the patients. This paper proposes a configuration of a wearable parallel mechanism to supplement the equipment selection for ankle rehabilitation. The kinematic analysis, i.e., the inverse position solution and Jacobian matrices, is elaborated. Several performance indices, including the reachable workspace index, motion isotropy index, force transfer index, and maximum torque index, are developed based on the derived kinematic solution. Moreover, according to the proposed kinematic configuration and wearable design concept, the mechanical structure that contains a basic machine-drive system and a multi-model position/force data collection system is designed in detail. Finally, the results of the performance evaluation indicate that the wearable parallel robot possesses sufficient motion isotropy, high force transfer performance, and large maximum torque performance within a large workspace that can cover all possible range of motion of human ankle complex, and is suitable for ankle rehabilitation.

As a basic osteotomy technique, U osteotomy can be applied for certain complex foot and ankle deformities. Gradual correction cases using Ilizarov apparatus and Taylor Spatial Frame have been reported. This paper proposes a novel parallel distraction apparatus for U osteotomy (PDA-Uos) to supplement the correction equipment for surgeon. Designed with an adjustable structure, the PDA-Uos can adopt different assembly shapes (joint connection points). However, the influence of the change in assembly shape on interference-free workspace and self-structural performance of the external fixator have received little attention. To address this issue and enhance the selection of the most suitable assembly shape for patient, an algorithm to obtain the interference-free workspace of different assembly shapes is proposed based on the inverse position solution of the PDA-Uos. Additionally, correction ability indices are defined according to the requirements of accurately controlled motion and high structural stiffness of the external fixator along the correction path. The results of simulation cases indicate that the interference-free workspace and the correction ability vary according to the assembly shape and thus the proposed method can be used to select an assembly shape with sufficient workspace and the best correction ability before performing correction for a given patient. Graphical abstract.

The ankle rehabilitation robot is essential equipment for patients with foot drop and talipes valgus to make up deficiencies of the manual rehabilitation training and reduce the workload of rehabilitation physicians. A parallel ankle rehabilitation robot (PARR) was developed which had three rotational degrees of freedom around a virtual stationary center for the ankle joint. The center of the ankle should be coincided with the virtual stationary center during the rehabilitation process. Meanwhile, a complete information acquisition system was constructed to improve the human-machine interactivity among the robot, patients, and physicians. The physiological motion space (PMS) of ankle joint in the autonomous and boundary elliptical movements was obtained with the help of the RRR branch and absolute encoders. The natural extreme postures of the ankle complex are the superposition of the three typical movements at the boundary motions. Based on the kinematic model of PARR, the theoretical workspace (TWS) of the parallel mechanism was acquired using the limit boundary searching method and could encircle PMS completely. However, the effective workspace (EWS) was smaller than TWS due to the physical structure, volume, and interference of mechanical elements. In addition, EWS has more clinical significance for the ankle rehabilitation. The PARR prototype satisfies all single-axis rehabilitations of the ankle and can cover most compound motions of the ankle. The goodness of fit of PMS can reach 93.5%. Hence, the developed PARR can be applied to the ankle rehabilitation widely.