A Computational Approach for Internal Tendon Routing Channels in a Tendon-Driven Continuum Joint

Tendon-driven continuum soft robots are currently applied in research and are given a promising perspective for future applications. For the routing of the tendons from the actuator to the point where the loading is demanded, two routing possibilities exist in the literature: internal routing of the tendons with the help of structurally embedded Bowden sheaths and external tendon routing where the tendon is not in contact with the soft structure. The application of the latter is a clear disadvantage for applications due to the high risk of interference with the tendon, for example, causing the tendon to break. The first option on the other hand introduces high friction forces into the tendon transmission and affects the elastic characteristic of the continuum and therefore the desired workspace of the system. This article overcomes the aforementioned problems by integrating tendon routings within tendon channels eroded from the continuum structure by a model-based design method. The channels within the continuum structure are computed a priori such that the tendons do not interact with the continuum while moving through its workspace. Overall, a new model-based method for tendon channel design is introduced and a corresponding manufacturing process is established. A continuum joint module prototype is designed to enable roll-pitch-yaw motions with a large accessible workspace. The capabilities of the system are measured in experiments using an external camera for the range of motion. Moreover, walking experiments on the ANYmal robot from ETHZ are presented.