In the TestBed, we designed and developed a high-resolution, compact system delivering electrotactile stimulation to the finger for the closed-loop control of a variable stiffness robot gripper. The feedback conveys information about both gripper aperture and commanded stiffness by modulating the location and frequency of stimulation, respectively. The explicit information about the position and stiffness of a compliant actuator was envisioned to provide better force control without the need to measure and feed back the contact forces between the gripper and the object.

TestBed provides accurate positioning of the gripper without any visual cues. Moreover, stiffness feedback prevents dangerous and harmful grasps, allowing the operator to evaluate the commanded stiffness directly and adjust it proactively. This TestBed underlines stiffness as a primary determinant of safe and effective grasping in robots and demonstrates that even minimal cutaneous feedback can support informed modulation of grasp behavior.