Static Force and Position Feedforward Control of an Antagonistic McKibben Joint Based on Experimentally Identified Inverse Maps
Year: 2026
Type: preprint
Abstract: Pneumatic artificial muscles (PAMs) combine high force-to-mass ratio and intrinsic compliance, but their nonlinear and hysteretic force–pressure–contraction behavior complicates control. This study investigates a static feedforward strategy for a one-degree-of-freedom joint actuated by two custom McKibben muscles in an agonist–antagonist arrangement. Each actuator was experimentally characterized under isometric conditions over contraction ratios from 0% to 35% and pressure up to 2.75 bar. The resulting static surfaces were inverted to determine the two pressure commands maps required for a prescribed joint angle, co-contraction force, and signed tangential output-force demand. A preliminary MATLAB/Simulink model was used to verify the feasibility of the two-map command concept before hardware implementation. Validation was then performed on a dedicated sprocket-chain test bench. Static positioning tests at co-contraction levels from 150 to 400 N produced mean absolute angular errors from 2.0° to 10.7°, depending on the operating region. Output-force tests were conducted at 0–50° in both clockwise and counter-clockwise directions; across 223 command points, the median absolute percentage error was 15.3%, with markedly better accuracy in favorable configurations. The maximum tested output-force command was 1250 N at 50°, where the measured antagonistic force difference reached 1138 N. The results show that experimentally identified inverse maps can provide low-complexity static force–position commands, provided that the configuration-dependent operating envelope is explicitly considered.
Source: Preprints.org
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221552575
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