Prototyping and Experimental Investigation of Digital Hydraulically Driven Knee Exoskeleton

Abstract

Digital hydraulic drives are known for their superior efficiency, power density, and robustness. Such advantages make them an attractive alternative (to electric drives) for actuation of exoskeleton devices. This work presents development of a prototype for such a digital hydraulically driven knee exoskeleton and its experimental testing. The device uses two miniature hydraulic cylinders and a novel mechanism to translate the linear motion to rotary motion. The device is controlled via a passive control method in the stance phase and a simplified model predictive control method in the swing phase. In this work, the design of the exoskeleton device is optimized with respect to compactness and weight. Next, the features of the design are further refined to ensure that the device is able to support the operational loads. This design is then realized into a prototype with a mixture of inhouse manufactured parts and procured components. Finally, via experimental tests, the performance of the design and the control strategy are investigated. Certain drawbacks related to valve size and overall weight are observed in the prototype, which will be addressed in future studies.

Digital Hydraulic Technology: Applications, Challenges, and Future Direction

“…Recently, Rituraj et al made significant advancements in the field of hydraulically driven knee exoskeletons by developing and testing a prototype with a parallel digital hydraulic drive system [41]. The design of this innovative exoskeleton is illustrated in Figure 8, showcasing its two primary components: the thigh and shank sections, which can be easily attached to the corresponding human limb parts.…”

Optimizing Exoskeleton Design with Evolutionary Computation: An Intensive Survey

“…• Hunt et al [55] retrieved the optimal actuator location, maximizing its stiffness volume both for (i) translation and (ii) rotation of their shoulder exoskeleton for assistive use; • Deboer et al [62] retrieved the optimal link lengths, spring stiffness values, angles, and displacements that minimize (i) the peak power and (ii) the total length of the two actuators of their leg exoskeleton for assistive use; • Paez et al [63] retrieved the optimal link lengths and joint locations that minimize (i) the moment load at the joint, (ii) the difference between the natural human posture and that observed while wearing the exoskeleton to promote a natural torso motion, and (iii) the torque deviation to match a linear profile while independently maximizing the torque output of their knee exoskeleton for assistive use; and • Rituraj et al [68] retrieved the optimal link lengths and angles that minimize (i) the maximum distance between the actuators and (ii) the load on the device of their assistive/rehabilitative knee exoskeleton for rehabilitation and assistive use.…”

“…Even so, we found that most of the studies reviewed in this survey specifically mentioned the name NSGA-II, showing that the authors have sufficient knowledge about EA rather than simply relying on a black-box method. There are a few exceptions to this observation: Hunt et al [55] only reported that the MATLAB Optimization Toolbox was used, without mentioning NSGA-II, whereas Rituraj et al [68] stated that they used NSGA-II in the MATLAB environment, although it is not clear if they used the toolbox or recreated the algorithm from scratch. Lastly, Paez et al [63] reported that NSGA-II allowed them to mutate over the possible populations of solutions through a definition of the objectives, which clearly refers to the ability to select the appropriate design parameters out of a pool of trade-off solutions rather than specifying fixed preferences among objectives and obtaining only one solution (e.g., WBGA).…”

Design, Modelling, and Analysis of a Capacitive Reservoir Based PWM Digital Circuit of Electro-Hydraulic Proportional Valve

“…Zagar et al proposed a piezo-electric valve actuator used for hydraulic exoskeleton drives [3]. Based on the digital hydraulic drive technology, Rituraj et al developed a knee exoskeleton device driven by two hydraulic cylinders [4]. He et al retrofitted an electro-hydraulic proportional system to drive an excavator's arm [5].…”