Control of and experimentation on an active dual-mode twisted string actuation mechanism

In this paper, we present the control of and experimentation on an active dual-mode twisted string actuation mechanism for automatic transmission. This mechanism has a two-stage transmission ratio and is implemented by changing the twisted radius of the string in each mode (force mode or speed mode). Control algorithms for implementing different transmission ratios are proposed and experimentally verified. Moreover, this mechanism was able to change its compliance characteristics depending on the mode and it was also experimentally confirmed by impulse testing. Since this is a compact and simple transmission mechanism, it can be simply applied to small robotic system and provide a wide operating range and variable compliance.