Applications of Stretch Reflex for the Upper Limb of Musculoskeletal Humanoids: Protective Behavior, Postural Stability, and Active Induction

TL;DR

The paper addresses embedding a stretch reflex in the upper limb of a musculoskeletal humanoid to achieve protective behavior, postural stability, and active manipulation. It implements a trigger-and-release reflex on the Musashi robot with simple thresholds and timing parameters, and validates four experiments across protective, stabilizing, and active lifting tasks. Key findings show that the reflex prevents joint-limit penetration, reduces posture deviation after impacts, and can enable higher peak yet lower final muscle loads during heavy lifting when combined with joint-angle feedback. This work demonstrates the feasibility and utility of translating human reflexes to biomimetic robotics, with potential for automatic parameter adaptation and integration with additional reflex pathways.

Abstract

The musculoskeletal humanoid has various biomimetic benefits, and it is important that we can embed and evaluate human reflexes in the actual robot. Although stretch reflex has been implemented in lower limbs of musculoskeletal humanoids, we apply it to the upper limb to discover its useful applications. We consider the implementation of stretch reflex in the actual robot, its active/passive applications, and the change in behavior according to the difference of parameters.

Figures (12)

• Figure 1: The basic musculoskeletal structure.
• Figure 2: The flow chart of the implemented stretch reflex.
• Figure 3: The classification of applications of stretch reflex.
• Figure 4: Muscle arrangement of the musculoskeletal humanoid Musashi used in our experiments.
• Figure 5: The experiment of the protective behavior of stretch reflex when adding sudden impact to the elbow joint.