Estimator locates contact on tendon-driven continuum robots from tendon data alone

Haitham El-Hussieny has shown in an arXiv paper that contact along a tendon-driven continuum robot cannot in general be located from tendon measurements, because the mapping from contact forces to measurements has a null space of at least seven dimensions. When the shape of the obstacle is known, however, the contact force becomes identifiable, and the paper presents a constrained moving horizon estimator that runs in real time as one quadratic program per sample.

In finite-element simulations of a robot with two sections pushing and sliding along a wall, the new estimator was within 0.9 mm on the contact point and 0.22 N on the force, compared with 65 mm and 0.72 N for a well-tuned Kalman filter with state projection, and it stayed better in all 40 trials with random model errors.