Measurable-range extension of range-finding speedometer using self-mixing laser diode

We propose a new range-finding speedometer in order to extend a measurable range. The speedometer employing a self-mixing laser diode (SM-LD) is FM-modulated with a trapezoidal pulse current superimposed on a DC current so as to increase the peak power under a condition of maintaining the mean power within a safety level. Owing to a laser diode with a higher peak output power of 20 mW, the measurable range by the new sensor is greatly extended from 10 cm through more than 200 cm. The measurement accuracy for range and for velocity of ±4 mm/s through ±30 mm/s was about 1%, and 2%, respectively. The new sensor can be applied to a robot visual sensor for sensing an approximate shape of parts or work placed near an assembler robot