M. Sumi

Compact and high-precision range finder with wide dynamic range and its application

Described is a new range finder using a self-mixing laser diode (SM-LD). The range finder has a high accuracy of +or-0.15% and a wide dynamic range of 0.2-1 m using only one sensor head. Compared to ultrasonic range finders, the light beam of this laser range finder can be focused and scanned. The feasibility study shows a possible application of the range finder to a visual sensor of a robot. The proposed range finder has been successfully applied as an infrared (IR) active type range finder of a single-lens reflex camera. >

Compact and versatile self-mixing type semiconductor laser Doppler velocimeters with direction-discrimination circuit

A compact vector-velocimeter is described which uses a self-mixing type laser Doppler velocimeter (SM-LDV). It electrically identifies features of the sawtooth-like Doppler beat signal waveform to determine the direction of target motion within a velocity range of 23 mm/s-23 m/s. The range of velocity measured is 0.2 mm/s-34 m/s. The measured vector velocity of a reciprocally moving target as well as a rotating target agrees well with the theoretical value. >

Correlation-based speckle velocimeter with self-mixing interference in a semiconductor laser diode

We propose a novel self-mixing laser diode speckle velocimeter based on autocorrelation. The self-mixing laser diode launches and receives reflected light from a moving surface that has a random reflection profile. Some portion of the scattered light backcouples into the laser cavity and causes random intensity variations in the form of speckle signals. These speckle signals obtained from a self-mixing laser diode are processed by use of autocorrelation. The linear relation between the velocity and the reciprocal of the correlation time of the speckle intensity fluctuations allows us to determine the velocity easily if proper calibration is performed. The range of the investigated velocity is 20-450 mm/s. For an aluminum target that moves at a velocity of 350 mm/s, the measurement error is less than 2%.

Simultaneous measurement of velocity and length of moving surfaces by a speckle velocimeter with two self-mixing laser diodes

A novel laser speckle velocimeter with two self-mixing laser diodes (SM-LDs) for velocity and length measurements of moving surfaces is reported. The mean frequency of the speckle signal obtained in the measurement system depends on the surface path illuminated by the SM-LD. This behavior of the speckle signal in the SM-LDs is exploited to detect the front and the end edges of a target surface by sampling continuously the number of intensity changes in a speckle signal waveform. Once the edges are determined, the velocity and the length of the surface are calculated easily. The error for length and velocity measurements of a target with a homogeneous rough plane surface of 60-mm length, moving at a velocity of 200 mm/s, can be as low as 2.1% and 1.75%, respectively.

Acquisition of 3-D image of still or moving objects utilizing laser diode range-finding speedometer

Described is acquisition of a 3-D image of some still or moving objects utilizing the laser diode range-finding speedometer. The laser beam is scanned in x and y directions by two plane mirrors. Measurement errors of both the contour and the depth of a still 10 cm/spl times/10 cm white paper positioned at 30 cm were 1.2 mm or 0.4%, and its measuring time was 30 seconds to survey 11/spl times/11 points. An image of the same square paper moving at 2 mm/s was obtained in 12 seconds surveying 7/spl times/7 points with depth error 1.8 mm or 0.6% and contour error 15 mm or 5%. A 3-D image of a standstill or moving white spherical ball is also obtained.<<ETX>>

New range-finding speedometer using a self-mixing laser diode modulated by triangular wave pulse current

A new laser diode range-finding speedometer is proposed, which is modulated by a triangular pulse current superimposed on a dc current instead of a continuous triangular wave employed in the previous sensor. Since a target velocity is directly obtained from a pure Doppler beat frequency measured during the non-modulation period, the new sensor is free from the difficulties due to the critical velocity encountered in the previous sensor. Measurement of a target velocity, 4 mm/s-30 mm/s has been successfully done without the influence of the critical velocity when the target is moving at distances 30 cm-60 cm from the laser diode (LD). The measurement accuracy was 0.5%-1.5% for range and within 2% for velocity. The new sensor will expand the measurable range of velocity in many applications.<<ETX>>

Velocity measurement by a self-mixing laser diode using speckle correlation

We propose a new self-mixing laser diode (SM-LD) speckle velocimeter based on autocorrelation. SM-LD launches and receives reflected light from a moving surface which has a random reflection profile. The speckle signals obtained from SM-LD are processed using autocorrelation. The linear relation between the velocity and the correlation length of the speckle intensity fluctuations allows the determination of the velocity of the target easily. The range of the investigated velocity is 20 mm/s to 450 mm/s.

New digital vibrometer with high accuracy using self-mixing type LDV

We propose a new compact digital vibrometer using a self-mixing laser Doppler velocimeter (SM-LDV) with a new measurement circuit. The Doppler beat signal obtained from a self-mixing laser diode (SM-LD) has a sawtooth-like waveform, in which every sawtooth corresponds to a displacement of a half light wavelength. The new measurement circuit can always, discriminate precisely a positive or a negative displacement by comparing a rise time with a fall time of a sawtooth employing a magnitude comparator. The measurement accuracy for the vibrational displacement is greatly increased within 0.5 percent even for a degraded sawtooth. We can obtain a vibrational displacement waveform as well as its frequency spectrum by FFT. Since the new digital vibrometer with high accuracy can be made compact and inexpensive, it is useful for vibration analysis of many kinds of vibrating bodies.

Detection of mesa spots and indents on slowly moving object surface by laser-light beam scanning

Measuring time of mesa spots and indents on a slowly moving (less than 8 mm/s) is greatly reduced to 3.5 seconds (for 121 points) by utilizing a 3D range image measuring system. In the system, a laser light beam from a range-finding speedometer is mechanically scanned to illuminate a successive point on the object surface. The minimum detectable size of a square mesa or a square indent which is moving 2 times the minimum scanning length (MSL=7.6 mm), and the minimum detectable depth of those was 6 mm-7 mm.

New digital displacement measuring circuit for aperiodic vibration using self-mixing type LDV

It has been confirmed by the novel method that the vibrational displacement of a loudspeaker can be measured easily by a laser Doppler velocimeter (LDV) using a self-mixing semiconductor laser diode. The number of waves in the Doppler beat signal which is counted up or down from the output of the new counter circuit is stored in a computer. Then the digital displacement information of the aperiodic vibration of the loudspeaker surface also is obtained as the actual surface motion. In this measurement the speaker vibration driven by an audio signal also can be measured. This method will be applied to various vibrational measurements for its simplicity.<<ETX>>