Angle control of a loosely coupled mechanism in 3D space using length sensors

We describe here a mechanism for controlling angles of a human-like joint using length sensors in threedimensional (3D) space. This joint mechanism, which is called a loosely coupled mechanism, includes a viscoelastic object and soft actuators in place of the cartilage and muscles of a human arm. To confirm motion of the link using one length sensor, we constructed a prototype of the mechanism in two-dimensional (2D) space. Based on this prototype, we constructed a 3D loosely coupled mechanism with length sensors, and we were able to control two projecting angles of the 3D prototype. In addition, we propose an appropriate method of measurement to reduce errors in measurement due to the length sensors. Using this method, we found that, for each projecting plane, the errors were less than 1.0 deg in our 3D prototype.