Virtual Grasping: Closed-Loop Force Control Using Electrotactile Feedback

Figure 3

Control signals and prosthesis state variables recorded during a representative trial. In the hand closing phase, the joystick controls the hand aperture and after contacting the object, it controls the grasping force. Initially the subject increased the force faster to bring the signal in the vicinity of the target window. Afterwards, the subject becomes more careful, slowing down the force increase and performing fine corrections. To achieve stable control, a dead zone for the joystick signal was adopted.