A speed regulating scheme for air-turbine dental handpieces

Air-turbine dental handpieces (ATDH) are used in most of dental practices as the main cutting tool. However, the speed of these handpieces is reduced while cutting a tooth; because no speed controller has been provided for them. This speed-reduction decreases the cutting efficiency of air-turbine handpieces. A review of literature indicated no study concerned with designing a speed controller for ATDH. Thus, in this paper, a control scheme is proposed for regulating the speed including `measurement', `actuation', and `controller-design' stages. An accelerometer was employed to capture vibrations of the handpiece; and the frequency associated with the first peak in the spectrum was indicated to represent the speed. An on/off solenoid valve with pulse-width modulation (PWM) technique was employed to regulate the speed through controlling the input pressure to the handpiece. Changing the duty-cycle of the PWM pulses could vary the speed. A process model from the applied duty-cycle to the measured speed was obtained. This process model includes a linear dynamic and a nonlinear static part. Then, a proportional-integral- (PI) controller was selected, and the gains were tuned. The practicality and efficiency of the proposed control scheme with the PI controller was confirmed by experimental results.