Proposes decoupled humanoid arm design

A humanoid arm works best when its joints do not fight each other. A February 12 paper proposes a tendon-driven arm that builds that separation into the mechanism itself. (mdpi.com) In a typical cable- or tendon-driven arm, moving one joint can tug on cables that affect another joint. The new design, called the fully decoupled tendon-driven humanoid arm, aims to stop that coupling at the hardware level instead of correcting for it later in control software. (mdpi.com) The paper was authored by Diwei Huang, Hao Li, Xiao Jiang, Jiahao Shen, Hong Luo, Chongkun Xia and Xueqian Wang, with affiliations including Sun Yat-sen University and Tsinghua University’s Shenzhen International Graduate School. It was published in *Biomimetics* on February 12, 2026. (mdpi.com) The basic idea comes from the human upper limb, where tendons pull in opposing pairs and joints carry some passive stiffness even before motors or muscles actively react. The authors say their arm uses antagonistic actuation and joint regulation to reproduce part of that behavior mechanically. (mdpi.com) That matters because humanoid arms are moving out of fenced industrial cells and into spaces shared with people. In those settings, lower inertia, built-in compliance and simpler control can be as important as raw strength. (mdpi.com) The team built a prototype and reported a mean positioning error of 0.40 millimeters. They also reported a maximum end-effector velocity of 3.62 meters per second in whole-arm motion tests. (mdpi.com) The paper says the arm’s passive joint stiffness is in the same order of magnitude as values reported for the human upper limb. That is the part meant to make the machine behave less like a rigid industrial linkage and more like a limb that yields under load. (mdpi.com) The authors also modeled the arm at both the joint level and the whole-arm level to account for rolling constraints introduced by the mechanism. In plain terms, they had to show that the cable routing and joint geometry still produce predictable motion across the arm’s workspace. (mdpi.com) The design arrives as other researchers are also chasing fully decoupled cable-driven arms, but often for different goals such as base-mounted motors, radiation resistance or underwater use. One recent example, D3-Arm, reported a 776 millimeter moving section, 1.6 kilogram arm weight, 1.29 millimeter average positioning error and 2.0 kilogram payload capacity. (arxiv.org) The distinction in this paper is the attempt to combine decoupling with human-like antagonistic tendons and passive stiffness in a humanoid format. The authors frame it as a mechanical route toward manipulation in human-interactive environments, where the arm itself absorbs part of the control problem. (mdpi.com)