Department of Advanced Robotics
Istituto Italiano di Tecnologia (IIT)
Title: Design Optimization of an Actuation System Applied to Wearable Robots
One of the critical aspects in the design of an assistive wearable robot is the comfort of the system, being the weight one of the most important factors. At the same time, the weight constrain is an important limitation for the power and autonomy of the system. The way to comply with all these requirements is to increase the energy efficiency of the actuation system. Several strategies have been used in previous research, mostly based on energy harvesting, compliant elements for mechanical energy accumulation (springs or elastic cords), ratchets and clutches. However, the design of the optimal actuator arrangement is highly dependent on the task, which increases significantly the complexity of the design process. Most of the previous work try to optimize the mechanism parameters starting from a predefined arrangement, which can be based on engineering or biological aspects.
We present an optimization method able to find the best actuator arrangement starting from a set of passive and quasi-passive components (i.e. spring, damper, clutch, etc). The result of this optimization is a set of possible actuator arrangements (including components and their relative configuration) and their corresponding optimal parameters. Using passive or quasi-passive components, the interaction between the wearable device and the user is more natural since the exoskeleton is using only internal energy. Furthermore, the control strategies can be simplified requiring fewer computational efforts.
This method is applied to the design of a lower limb soft exoskeleton, optimized for the assistance of a post-stroke patient during a walking task. This analysis includes ankle, knee and hip joint movements in the sagittal plane. The optimized mechanism is able to reduce the energy requirements by 20-65%, depending of the joint. The proposed mechanism is currently under development within the XoSoft EU project, a modular soft lower-limb exoskeleton to assist people with mobility impairments. The second example of application of this method is done for a lightweight quasi-passive trunk assistive device for industrial and logistics applications. In this preliminary design, we analyze lifting, carrying and lowering tasks with different levels of weight (between 5 and 15 Kg).