Computational Synthesis of Wearable Robot Mechanisms: Application to Hip-Joint Mechanisms

TL;DR

This paper introduces an autonomous computational method for designing wearable robot mechanisms, specifically hip-joint mechanisms, using gradient-based optimization to efficiently explore complex design spaces and validate functionality through simulations and prototypes.

Contribution

The paper presents a novel gradient-based optimization approach for synthesizing wearable robot mechanisms, enabling arbitrary topology generation and eliminating exhaustive search methods.

Findings

Successfully designed non-series-type hip joint mechanisms

Validated multi-moment assistance capability through biomechanical simulations

Fabricated prototypes confirming wearability and functionality

Abstract

Since wearable linkage mechanisms could control the moment transmission from actuator(s) to wearers, they can help ensure that even low-cost wearable systems provide advanced functionality tailored to users' needs. For example, if a hip mechanism transforms an input torque into a spatially-varying moment, a wearer can get effective assistance both in the sagittal and frontal planes during walking, even with an affordable single-actuator system. However, due to the combinatorial nature of the linkage mechanism design space, the topologies of such nonlinear-moment-generating mechanisms are challenging to determine, even with significant computational resources and numerical data. Furthermore, on-premise production development and interactive design are nearly impossible in conventional synthesis approaches. Here, we propose an innovative autonomous computational approach for synthesizing such wearable robot mechanisms, eliminating the need for exhaustive searches or numerous data sets. Our method transforms the synthesis problem into a gradient-based optimization problem with sophisticated objective and constraint functions while ensuring the desired degree of freedom, range of motion, and force transmission characteristics. To generate arbitrary mechanism topologies and dimensions, we employed a unified ground model. By applying the proposed method for the design of hip joint mechanisms, the topologies and dimensions of non-series-type hip joint mechanisms were obtained. Biomechanical simulations validated its multi-moment assistance capability, and its wearability was verified via prototype fabrication. The proposed design strategy can open a new way to design various wearable robot mechanisms, such as shoulders, knees, and ankles.