Measurement and Analysis of Gait Pattern during Stair Walk for Improvement of Robotic Locomotion Rehabilitation System

Background. Robotic locomotion rehabilitation systems have been used for gait training in patients who have had a stroke. Most commercialized systems allow patients to perform simple exercises such as balancing or level walking, but an additional function such as stair-walk training is required to provide a wide range of recovery cycle rehabilitation. In this study, we analyzed stair-gait patterns and applied the result to a robotic rehabilitation system that can provide a vertical motion of footplates. Methods. To obtain applicable data for the robotic system with vertically movable footplates, stair-walk action was measured using an optical marker-based motion capture system. The spatial position data of joints during stair walking was obtained from six healthy adults who participated in the experiment. The measured marker data were converted into joint kinematic data by using an algorithm that included resampling and normalization. The spatial position data are represented as angular trajectories and the relative displacement of each joint on the anatomical sagittal plane and movements of hip joints on the anatomical transverse plane. Results. The average range of motion (ROM) of each joint was estimated as (−6.75°,48.69°) at the hip, 8.20°,93.78° at the knee, and −17.78°,11.75° at the ankle during ascent and as 6.41°,31.67° at the hip, 7.38°,91.93° at the knee, and −24.89°,24.18° at the ankle during descent. Additionally, we attempted to create a more natural stair-gait pattern by analyzing the movement of the hip on the anatomical transverse plane. The hip movements were estimated to within ±1.57 cm and ±2.00 cm for hip translation and to within ±2.52° and ±2.70° for hip rotation during stair ascent and stair descent, respectively. Conclusions. Based on the results, standard patterns of stair ascent and stair descent were derived and applied to a lower-limb rehabilitation robot with vertically movable footplates. The relative trajectory from the experiment ascertained that the function of stair walking in the robotic system properly worked within a normal ROM.

Dynamic Output Controllers for Exponential Stabilization of Periodic Orbits for Multidomain Hybrid Models of Robotic Locomotion

The primary goal of this paper is to develop an analytical framework to systematically design dynamic output feedback controllers that exponentially stabilize multidomain periodic orbits for hybrid dynamical models of robotic locomotion. We present a class of parameterized dynamic output feedback controllers such that (1) a multidomain periodic orbit is induced for the closed-loop system and (2) the orbit is invariant under the change of the controller parameters. The properties of the Poincaré map are investigated to show that the Jacobian linearization of the Poincaré map around the fixed point takes a triangular form. This demonstrates the nonlinear separation principle for hybrid periodic orbits. We then employ an iterative algorithm based on a sequence of optimization problems involving bilinear matrix inequalities to tune the controller parameters. A set of sufficient conditions for the convergence of the algorithm to stabilizing parameters is presented. Full-state stability and stability modulo yaw under dynamic output feedback control are addressed. The power of the analytical approach is ultimately demonstrated through designing a nonlinear dynamic output feedback controller for walking of a three-dimensional (3D) humanoid robot with 18 state variables and 325 controller parameters.

De-electroadhesion of Flexible and Lightweight Materials: An Experimental Study

Electroadhesion (EA) is an emerging prehension method with wide application in robotics, including object handling, component assembly, and robotic locomotion. A major challenge with EA is the development of novel solutions for speeding up the release process, where residual charges inhibit release. In this work, a comprehensive study on the effects of EA base substrate and object material types on de-electroadhesion time is presented. Experimental results show that the de-electroadhesion speed is highly dependent on the base substrate and object material type. There is a strong inverse correlation between dielectric constant and de-electroadhesion rate, while a higher molecular weight demonstrates slower dielectric relaxation and hence release time. These findings will enable the design of cost-effective EA-based robotic end effectors with rapid release capabilities. EA grippers with quicker de-adhesion abilities could significantly improve the overall throughput of assembly lines where material pick-and-place tasks are involved. In addition, more efficient and faster locomotion speeds could be achieved for crawling or climbing robots where EA is employed as their active adhesion and de-adhesion feet.