FA-88199 / Inverse kinematics solvers / Member archive

Redundant arm forward kinematics uses relative angles as absolute · case 04

The task error is computed from the wrong tip position.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [lengths(3), q(3 deg), target, qc(3 deg), k]: planar 3R arm, position task only. One step dq = J+ e + (I - J+ J) z, J+ = J^T (J J^T)^-1, e = target - fk(q), z = k*(qc-q) in radians. Return the updated q in degrees rounded to 4, or "singular" when |det(J J^T)|<1e-12.

Why this case matters

Inverse kinematics code turns task-space goals into joint commands; a wrong branch, sign, limit or update order sends a real arm to the wrong pose.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
task only	`[9.3316, 57.6188, 75.1212]`	`[-9.6761, 48.859, 73.9791]`	Failed

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