Fig. 6: Force estimation with kinetic analysis of sensory information from rotational triboelectric bidirectional (RTBD) sensor.

a (i) Schematics and (ii) the generated signals from the rotational triboelectric bidirectional shoulder (RTBD-S) sensor and the rotational triboelectric bidirectional elbow (RTBD-E) sensor during the punch, the channels of BF, BB, SF, SB, EF, EB, WF, WB, FF, and FB represent the forward (clockwise) and the backward (counterclockwise) rotations of the rotational triboelectric bidirectional back (RTBD-B) sensor, the rotational triboelectric bidirectional shoulder (RTBD-S) sensor, the rotational triboelectric bidirectional elbow (RTBD-E) sensor, the rotational triboelectric bidirectional wrist (RTBD-W) sensor, and the linear triboelectric bidirectional finger (LTBD-F) sensor. L1 and L2 represent the length of the upper arm and the forearm, α, β, and γ represent the angles between the upper arm and the centerline, the forearm and the centerline, as well as the forearm and the upper arm. b (i) Schematics and (ii) measured data for the relationship between three angles and the position of the fist. c Comparison between the measured position and the position calculated by the sensory information. d The estimated instantaneous linear velocity of the fist against the varied angle of α for the given rotation speeds of 10, 50, 100 and 200 revolutions per minute (RPM). e The estimated punching force exerted on the target against the changing velocity of the fist and the variation of the duration for stopping, the mass of the participant’s arm is ~5.5 kg. f The estimated punching force exerted on the target against the varied angle of α for a specific rotation speed, the actual effective motion range of the fist is shaded. g Demonstration of punching force estimation through the data of the rotation sensing from the RTBD sensors in virtual space, (i) process of determining the level of the virtual punch based on the rotation sensing information, (ii) light punch and heavy punch demonstrations. Photo credit: Minglu Zhu, National University of Singapore.