Control Strategies for Gait Tele-Rehabilitation System Based on Parallel Robotics

Among end-effector robots for lower limb rehabilitation, systems based on Stewart–Gough platforms enable independent movement of each foot in six degrees of freedom. Nevertheless, control strategies described in recent literature have not been able to fully explore the potential of such a mechatronic system. In this work, we propose two novel approaches for controlling a gait simulator based on Stewart–Gough platforms. The first strategy provides the therapist direct control of each platform using movement data measured by wearable sensors. The following scheme is designed to improve the level of engagement of the patient by enabling a limited degree of control based on trunk inclination. Both strategies are designed to facilitate future studies in tele-rehabilitation settings. Experimental results have illustrated the feasibility of both control interfaces, either in terms of system performance or user subjective evaluation. Technical capacity to deploy in tele-rehabilitation was also verified in this work.

Kinematics analysis of a new parallel robotics

A new type of parallel robot ROBO_003 is presented. Its mechanisms, kinematics, and virtual prototype technology are introduced. The research of degrees of freedom (DOF) is based on screw theory, a set of screw is separated as a branch, which named as constrain screw. The type of three DOF gained by counting constrain screw, the moving platform’s frame, and base platform’s frame is set, respectively, a complete kinematic research including closed-form solutions for direct kinematic problem. The 3-D model of ROBO_003 is established using SOLIDWORKS; position and orientation of motion platform can be gained using ADMAS, which is a type of virtual prototype technology. The resultant shows that the structure of ROBO_003 is reasonable, three DOF of motion platform can be operated in a reasonable range, the solutions to the direct kinematics are right, and robot ROBO_003 can be used in many industrial fields. The research of this article provides a basis for the practical application of parallel robotics ROBO_003.

Sampling-based motion planning with reachable volumes for high-degree-of-freedom manipulators

Motion planning for constrained systems is a version of the motion planning problem in which the motion of a robot is limited by constraints. For example, one can require that a humanoid robot such as a PR2 remain upright by constraining its torso to be above its base or require that an object such as a bucket of water remain upright by constraining the vertices of the object to be parallel to the robot’s base. Grasping can be modeled by requiring that the end effectors of the robot be located at specified handle positions. Constraints might require that the robot remain in contact with a surface, or that certain joints of the robot remain in contact with each other (e.g., closed chains). Such problems are particularly difficult because the constraints form a manifold in C-space, and planning must be restricted to this manifold. High-degree-of-freedom motion planning and motion planning for constrained systems has applications in parallel robotics, grasping and manipulation, computational biology and molecular simulations, and animation. We introduce a new concept, reachable volumes, that are a geometric representation of the regions the joints and end effectors of a robot can reach, and use it to define a new planning space called RV-space where all points automatically satisfy a problem’s constraints. Visualizations of reachable volumes can enable operators to see the regions of workspace that different parts of the robot can reach. Samples and paths generated in RV-space naturally conform to constraints, making planning for constrained systems no more difficult than planning for unconstrained systems. Consequently, constrained motion planning problems that were previously difficult or unsolvable become manageable and in many cases trivial. We introduce tools and techniques to extend the state-of-the-art sampling-based motion planning algorithms to RV-space. We define a reachable volumes sampler, a reachable volumes local planner, and a reachable volumes distance metric. We showcase the effectiveness of RV-space by applying these tools to motion planning problems for robots with constraints on the end effectors and/or internal joints of the robot. We show that RV-based planners are more efficient than existing methods, particularly for higher-dimensional problems, solving problems with 1000 or more degrees of freedom for multi-loop and tree-like linkages.

Design of a Stewart-Gough Platform for Engineering Material Characterization

Stewart-Gough platforms have been used as the basis for multiaxial test machines in multiple applications. Their stiffness coupled with the ability to simultaneously create a combined loading (tensile/bending/twisting) of any design enables them to excite material parameters in any conceivable coupling. For engineered materials, whose properties are often nonlinear and nonisotropic, such loadings are necessary to understand the as-built material parameters inherent within these designed systems. However, the design of a Stewart-Gough is nontrivial as the presence of singular configurations is poorly understood. In the proximity of these singular configurations, precision control of the loading applied by the system is difficult to control due to large gradients in the forces generated. This work uses a combination of simulation and surrogate modeling to establish a “map” of the singular configurations of the Stewart-Gough platform. As a result, a “home” location where the system provides a zero loading upon a specimen is found so as to maximize distance from a singular configuration, and a greater understanding of the nature of singularities in parallel robotics structures is obtained.

PRIGo: a new multi-axis goniometer for macromolecular crystallography

The Parallel Robotics Inspired Goniometer (PRIGo) is a novel compact and high-precision goniometer providing an alternative to (mini-)kappa, traditional three-circle goniometers and Eulerian cradles used for sample reorientation in macromolecular crystallography. Based on a combination of serial and parallel kinematics, PRIGo emulates an arc. It is mounted on an air-bearing stage for rotation around ω and consists of four linear positioners working synchronously to achievex, y, ztranslations and χ rotation (0–90°), followed by a φ stage (0–360°) for rotation around the sample holder axis. Owing to the use of piezo linear positioners and active correction, PRIGo features spheres of confusion of <1 µm, <7 µm and <10 µm for ω, χ and φ, respectively, and is therefore very well suited for micro-crystallography. PRIGo enables optimal strategies for both native and experimental phasing crystallographic data collection. Herein, PRIGo hardware and software, its calibration, as well as applications in macromolecular crystallography are described.

Analyses of Error and Precision of 6-DOF Platform

A particular subset of 6-DOF parallel mechanisms is known as Stewart platforms (or hexapod). Stewart platform characteristic analyzed in this paper is the effect of small errors within its elements (strut lengths, joint placement) which can be caused by manufacturing tolerances or setting up errors or other even unknown sources to end effector. The biggest kinematics problem is parallel robotics which is the forward kinematics. On the basis of forward kinematic of 6-DOF platform, the algorithm model was built by Newton iteration, several computer programs were written in the MATLAB and Visual C++ programming language. The model is effective and real-time approved by forwards kinematics, inverse kinematics iteration and practical experiment. Analyzing the resource of error, get some related spectra map, top plat position and posture error corresponding every error resource respectively. By researching and comparing the error spectra map, some general results is concluded.

The Application of Parallel Robotics to Investigate the Effect of Lumbar Bracing on Trunk Muscle Activity

Lumbar bracing is prescribed frequently for disability caused by low back pain; however, investigations into this practice demonstrate a range of patient outcomes. This inconsistency may arise from the practice of employing voluntary, single-axis trunk movements when investigating braces. Alternatively, this study employed a parallel robot to create a standardised, multi-axis testing environment. Surface electromyographic (sEMG) data were collected from the trunk of 24 asymptomatic participants, who were seated on the robot, tilted to 15°, then circumducted while attempting to maintain an upright posture. Multiple trials were performed for three randomised conditions: non-braced, soft-material brace and stiff-material brace. As expected, the sEMG activity was significantly reduced in the majority of muscle responses (201/240). Unexpectedly, a paradoxical increase in the sEMG activity was observed in 39/240 responses. While lumbar bracing reduces the sEMG activity on average, these data suggest the existence of an infrequent paradoxical response that may provide a possible explanation for the discordant results observed in previous bracing investigations.