Automatic measurement of velocity and length of moving plate using self-mixing laser diode

We proposed and demonstrated to automatically measure both a velocity and a length of a moving plate employing a novel laser speckle velocimeter using a self-mixing laser diode (SM-LD). We derived empirical equations including velocity or length of the moving plate such as white paper and plastic. After determining a pair of constants f _s(0) and β in advanced calibration, we can automatically obtain velocity or length from measured speckle signal frequency and/or the number of speckle pulses counted during the measuring time. An investigated range of velocity and length was 100 mm/s to 950 mm/s, and 10 mm to 100 mm, respectively. Measurement accuracy of the velocity and the length was about 1% and a few percent, respectively