Fig. 2.

Block diagrams. a System architecture. b Admittance controller with inner velocity control loop running at 5.36 kHz on the motor drive (ESCON). The Teensy computes the reference angular velocity ${\dot{\theta }}_{\mathit{\text{ref}}}$ according to the measured force F_ref applied by the user on the handle and transmits it to the motor drive. The motor drive records the angular velocity ${\dot{\theta }}_{\mathit{\text{meas}}}$ of the motor shaft, combines it with the reference angular velocity ${\dot{\theta }}_{\mathit{\text{ref}}}$ reflected at the motor shaft and computes the current command for the motor thanks to an integrated PI (proportional-integral) controller. R is the reduction ratio of the gear stage (i.e. 475:1)