A Study on Generation of Passive Softness at Load-end by the Soft-Actuation with Stepping Motor

负载端的柔软性被期望在机器人和/或机械手上引入柔和和安全的运动。本研究提出了一种所谓的“软驱动”步进电机的驱动方案，并进行了实验验证。(1)软驱动步进电机具有固有的被动柔软性，因为它们除了轴轴承外没有机械接触。当通过步进电机的电流适当降低时，可以降低失步阈值以产生被动柔和。例如，实验证明，在软驱动状态下，机械臂可以平稳地接住自由落体的物体。(2)步进电机的力矩参考控制在软驱动状态下，只要适当调节力矩角度，就可以实现步进电机的力矩参考控制。实验给出了具有良好线性度的力矩特性。在该方案中，步进电机的动作可以表示为运动方程中的力矩，这意味着许多众所周知的运动控制方法可以应用于步进电机驱动的机器人系统。(3)软驱动串联连杆机器人的实验结果1。在力矩参考状态下实现了合理的位置/速度可控性。成功地完成了一次无高度信息的物体拾取和堆放任务。运用摸索策略演示了障碍物的躲避运动。提出了一种无直接力和/或柔顺控制的销孔实验，该方法一般不容易同时实现运动的可控性和柔软性，但所提出的方案可以成功地提供可接受的位置/速度可控性和抵抗机械手负载端碰撞或约束的被动柔度。

Softness at load ends has been expected to introduce soft and safe motion on robots and/or manipulators. In this study, a driving scheme of stepping motor, so called "soft actuation", was proposed and examined experimentally.(1) Soft actuationStepping motors have inherent passive softness against external force, since they have no mechanical contact except for shaft bearings. When the current through the stepping motor is appropriately lowered, the threshold for miss-stepping can be decreased to generate passive softness. For example, it was demonstrated experimentally that a robot arm driven under the soft actuation regime can smoothly catch a free falling object.(2) Torque reference control of stepping motorUnder the soft actuation regime, the torque reference control of stepping motor is available, if the torque angle is regulated appropriately. The torque characteristics which show acceptable linearity were presented experimentally. In this scheme, the action of stepping motor can expressed as the torque in the equation of motion, and it means that lots of well known motion control methods can be applied on the robotic systems driven with stepping motors.(3) Experimental results obtained from serial link manipulators driven with soft actuation1. Reasonable position/velocity controllability under torque reference regime was achieved.2. An object picking and piling task without height information was performed successfully.3. An evading motion of obstacle was demonstrated with groping strategy.4. A peg-in-hole experiment without direct force and/or compliance control was presented.It is generally not easy to achieve controllability and softness in motion simultaneously, but the proposed scheme can successfully provide both acceptable position/velocity controllability and passive softness against collision or restriction of load ends of robotic manipulators.