Pre-Shaped Open Loop Drive of Electrothermal Micromirror by Continuous and Pulse Width Modulated Waveforms

Open loop drive is simple but it often leads to large nonlinearity. Closed loop drive can compensate nonlinearity but it increases system complexity and cost. This paper reports open loop drive methods that minimize nonlinearity by using special input waveforms. A procedure for open loop control of electrothermal micro-electro-mechanical systems is established and demonstrated by using a thermal bimorph based 1-D electrothermal micromirror. Constant linear velocity scan profile is achieved over 90% of the full scan range. Constant angular velocity scan of an electrothermal micromirror is achieved by continuous wave actuation over a ±4.5° range. A pulse width modulated (PWM) waveform that is equivalent to the continuous waveform is derived and experimentally verified. PWM based open loop control can significantly reduce hardware cost and size in case of micromirror array actuation.