The authors developed a new type of rotary acceleration sensor. It has the capability to sense an angular acceleration independently to the rotational speed and has an unlimited rotation range. The authors believe that this sensor can be used in robust motor control, vibration control, and any other application where a reliable acceleration signal is needed. The sensor's structure and basic performance are presented in this paper. Experimental results are shown using two prototypes: one for a motor shaft and one for a robot joint. The sensitivity and accuracy of the prototypes appeared to be sufficient for these applications. >