When a spoon-feeding arm meets a moving mouth, what sets the force on the lips: the sensor, the approach speed or a force cap?

What it found

A stdlib planar point-mass twin of a feeding arm and a swaying mouth, with 200 paired trials per row. With a 0.05 s forward lead the push on a blocked tip is 20 N·s/m × speed, so peak lip force tracks approach speed (1.0 N at 0.05 m/s, 4.0 N at 0.20). A camera lowers the share of trials that touch the lips (0.40 against 0.72 at 30 mm sway) without lowering the peak, and its advantage fades with latency (touch share 0.07 at no delay, 0.71 at 0.4 s). A 1 N force cap trims the worst peak but not the share of comfortable feeds. Stylised: all constants are assumed, the peak-force result is largely an identity of the chosen controller, and no human model or Assistive Gym was used.

A figure from its own output

Paper, code and results

• README and method
• Experiments and results
• Code
• Tests

More in Open-source purpose-built robots

• Does a spoon-feeding arm need more than two joints? Tip mass, lip force and servo cost of 2 to 6 joint armsDoes a spoon-feeding arm need more than two joints? From 2 to 6 joints the tip mass moves only 0.63 to 0.50 kg and lip force not clearly at all, while servo cost triples (stylised; extends osrobot-assist).
• Does the stylised feeding-arm lip-force result survive real contact physics? osrobot-assist re-run in MuJoCoDoes the stylised feeding-arm lip-force result survive MuJoCo contact physics? The steady push matches KP × LEAD × speed, but the impact peak is 1.84 × higher and the share fed at most 2 N falls from 1.00 to 0.45 at 0.10 m/s (stylised; extends osrobot-assist).
• Is the peak force of a feeding arm on the lips set by the lips' stiffness, the arm's force loop, or its approach lead?Is the peak force of a feeding arm on the lips set by lip stiffness, the force loop or the approach lead? Lip stiffness moves the mean peak from 0.32 to 2.02 N at 0.20 m/s (stylised; extends osrobot-assist).
• If the person being fed judges the spoon better as it nears the mouth, how much of a camera's value does a blind feeding arm get back?If the person being fed judges the spoon better as it nears the mouth, how much of a camera's value does a blind arm get back? A misjudgement shrinking to zero at the lips lifts the blind arm's safe share at 40 mm from 0.47 to 0.84 and restores every feed; stylised, extends osrobot-leannoise.
• If the person being fed misjudges the spoon, or sees it late, can a blind feeding arm still do without a camera?If the person being fed misjudges the spoon or sees it late, can a blind feeding arm still do without a camera? A 20 mm misjudgement drops the blind arm's safe share from 1.00 to 0.60 (camera arm 0.78); stylised, extends osrobot-lean.
• If the person being fed leans toward the spoon, can a blind feeding arm do without a camera?If the person being fed leans toward the spoon, can a blind feeding arm do without a camera? At 30 mm sway and 0.20 m/s the blind arm's safe share rises from 0.21 to 1.00 as the lean reaches 100 mm/s (stylised; extends osrobot-assist).

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.