Bio-inspired backlash reduction of a low-cost robotic joint using closed-loop-commutated stepper motors

The majority of current robotic joints are primarily actuated by rotational mechanisms. These electrical drives have substantially different features than the features found in human muscular systems. This paper presents a cost-effective solution to the backlash a phenomenon known to cause positioning errors and other undesirable dynamic effects in drives. These errors are particularly pronounced when relatively major changes appear in the preload conditions of the motor such as in the case of a robotic leg or arm with a high degree of freedom. Current solutions require an accurate time-varying model of the drives that is not available in the majority of practical cases. Therefore, a digitally-controlled mechanical solution is proposed in this paper that is inspired by the human flexor-extensor mechanism. The idea is to construct an antagonistic actuator pair that is analogous to the flexor and extensor muscles. In order to obtain good control performance even in the low speed range, permanent magnet stepper motors were chosen as actuators that are commutated in a digital closed-loop fashion. The operation of the controlled structure has been verified in a real experimental environment where measurements showed good results and good match with previous simulations.