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The robotic spine has a lot of potential for snake-like, quadruped, and humanoid robots, as it can improve their mobility, flexibility, and overall function. A common approach to developing an articulated spine uses geared motors to imitate vertebrae. Instead of using geared motors that rotate 360 degree, a bioinspired gearless electromechanical actuator was proposed and developed as an alternative, specifically for humanoid spine applications. The actuator trades off angular flexibility for torque, while the geared motor trades off speed for torque. This article compares the proposed actuator and conventional geared motors regarding torque, acceleration, and copper loss for a vertebra's angular flexibility. When its angular flexibility is lower than 14∘, the proposed actuator achieves higher torque capability without gears than with conventional motors. Lower angular flexibility, which means smaller airgaps, allows the proposed actuator to produce a much stronger torque for the same input power. The actuator's nonlinear electrical and mechanical dynamics models are developed and used for position control of a six-module distributed spine. In addition, two different position-control architectures are developed: an outer loop proportional-integral (PI) position controller with an inner loop PI current controller and an outer loop PI position controller with an inner loop PI torque controller. 

Control of an articulated spine is important for humanoids' dynamic and balanced motion. Although there have been many spinal structures for humanoids, their actuation is still limited due to the usage of geared motors for joints. This paper introduces position control of a distributed electromechanical spine in a vertical plane. The spine dynamics model is approximated as an open chain. Gravitational and spring torques are compensated for the control. Moreover, torque-to-current conversion for the actuator is developed. Experimental results show the implemented control of the electromechanical spine for undulatory motions.