Drum roll: increasing bandwidth through passive impedance modulation

Abstract

People can accomplish many high bandwidth tasks despite the slow response of the neuromuscular system. Reaction times are well over 100 ms, but skilled drummers can play a drum roll at over 30 Hz. Drummers take advantage of a passive dynamic interaction: they let the drumstick bounce against the drum head at least twice on each hand stroke. Because the bounce occurs too quickly for neuromuscular response, the control parameters that govern the interaction must be predetermined. In this paper, we present evidence that drummers vary the stiffness of their hands to control the bounce frequency. The drum roll is thus an example of the explicit use of impedance modulation to increase effective bandwidth in a manipulation task. To confirm this explanation, we have constructed a simple robot joint that performs a drum roll in much the same manner as a human drummer. It has slow pneumatic actuators which can modulate passive joint stiffness as well as position or torque. Our experiments show that drum roll frequency can be controlled by varying the robot's passive stiffness, as surmised for human drummers.