Abstract
We propose a novel virtual torque sensor for commercial low-cost radio-controlled (RC) servo motors. The virtual torque sensor has played an important role for conventional robots. It has been used for torque-required control applications such as human–robot interaction and under-actuated robots. However, most virtual torque sensors are based on the inversion of actuators or robot dynamics with the assumption that entire dynamics are known. This is not applicable to the RC servo motors that have unknown control structures. As RC servo motors enable researchers and hobbyists to create lightweight but high performance robots in an easy and cost-effective manner, the development of a virtual torque sensor for these motors is necessary. In this study, we propose a design method of a virtual torque sensor for RC servo motors. First, the virtual sensor is derived mathematically based on internal dynamic models with parametric constraints and compared to the conventional model. Second, a dedicated system identification method is developed for the proposed virtual sensor to implement the sensor in actual experiments. Finally, we compare experimental results with the measurements obtained by an actual sensor.
Highlights
Radio-controlled (RC) servo motors are compact actuators that are originally equipped with a sensor, a torque transmission system, and a built-in controller. These motors have been adopted by numerous researchers and hobbyists to realize lightweight but high performance robots using a simple interface in a cost-effective manner
We investigated a virtual torque sensor for commercial RC servo motors under an unknown control structure
Based on the internal dynamic models of RC servo motors, the controllers were substituted by closed-loop systems under a specially designed condition
Summary
Radio-controlled (RC) servo motors are compact actuators that are originally equipped with a sensor (potentiometer), a torque transmission system (gearbox), and a built-in controller (embedded board). To the best knowledge of authors, there are various products in the market for the RC servo motors having no internal torque information In this respect, the development of virtual torque sensor which is applicable to most kinds of RC servo motors provides greater flexibility for choosing actuators according to one’s budget and desired dimensions of the motors in purchase stage, and for reusing conventional robots to the torque-required applications. The framework of a virtual torque sensor was implemented and validated for industrial robots [16,17], rehabilitation robots [18], and series elastic actuators in [19] All these approaches assume that control structures are configurable or known by end users, which is not applicable to low-cost commercial RC servo motors with unknown control structures. We propose a design method of a virtual torque sensor for commercial RC servo motors under an unknown control structure.
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