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Laser Doppler Velocity Sensor
Introduction
Features
Specifications
Theory/Applications
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Diagrams
Output Connector pin number and function Chart
External Dimentions
Example for Speed Deviation Detection
Optical Sensor Installation Method Diagram
Measuring with a High Reflectivity Object Diagram
Movie
Theory
OTHER LASER DOPPLER VELOCITY SENSOR
LASER DOPPLER VELOCITY SENSOR VIDEO

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INTRODUCTION

High-Precision, Compact, Low Cost, Next Generation of Non Contact Laser Doppler Velocimeters

Canon laser Doppler velocimeters, equipped with diffraction gratings, take advantage of an optical system (diffraction laser light Doppler method) that will not dependent on the laser wavelength. Therefore, the measurement precision is unaffected by fluctuations in the semiconductor laser wavelength due to changes intemperature. Not only are these sensors environmental stability they can be used for a wide variety of applications; since we use an E/O frequency shifter, they are capable of taking measurement from a still as well as a running state.



FEATURES

  • Since the unit is of non-contact type, measurement can be taken even with velocity irregularities, and it does not place any extra load on the object whose velocity is being measured.
  • By Canon’s original diffraction laser-light Doppler system, the sensor unit is ultra-compact with high precision.
  • The E/O frequency shifter enables the unit to measure velocities varying from -200 to 2,000mm/sec (LV-20Z).


THEORY

The laser light emitted by a semiconductor laser is positioned so that it is a linearly polarized beam with respect to the z-axis. Then, a collimator lens makes it into a parallel light beam. The grating array direction of this parallel light beam is the direction of the y-axis, and the diffraction grating with a grating pitch d divides the beam into two light beams by a diffraction angle of q. Here, the equation d sin θ = λ holds. These two light beams pass through a first lens and are then irradiated into an E/O frequency shifter consisting of electro-optical crystals. After that, they are diffracted by a second lens before irradiated to the object moving at a velocity of V, which is being measured. The incidence angle of the two irradiated light beams is θ. The first and second lenses form an afocal optical system with a magnification of m, and the aberration is corrected so that sin θ / sin θ = m. The two light beams that are now modified to have a frequency difference fR by the E/O frequency shifter are then irradiated to the object to be measured, and the diffused beams coming back from the object proceed through the second lens and a condensing lens, eventually reaching the photo diode. The beat signal (i.e., the Doppler frequency) of these light

beams containing the speed information obtained here is F=2V/md+fR, independent of the laser frequency; in addition, it is possible to measure the velocity from an object that is originally in a still state. By signal-processing this Doppler frequency, the unit displays the velocity and sends the F/V output and pulse output.

APPLICATION EXAMPLES

OA Equipment ·Detection of the speed of copying paper & speed irregularities ·Detection of rotation irregularities of photo-conductor drums ·Detection of the displacement of printer paper

AV Equipment ·Detection of speed irregularities of magnetic tapes ·Detection of rotation irregularities of magnetic heads

for Office Automation machine
Rotation/motion speed detection and speed deviation detection of;
- Paper feeding
- Sensitivity drum
- Belt and gear

for Audio Visual machine
Rotation/motion speed detection and speed deviation detection of;
- Recording tape
- Rotary head

for Factory equipment
Rotation/motion speed detection and speed deviation detection of;
- Machine tools
- Printing machine
for Producing spot
Conveyer speed detection or length measurement of;
- Steel sheet
- Processed goods (paper, film, cable, etc)

SENSOR INSTALLATION METHOD

1. The measuring accuracy according to the installation is not influenced by the angle a shown in following figure.
2. The angle β causes an error of 1-cos β.
3. The deviation angle between the bottom surface and the movement direction causes an error of 1-cos γ.
4. When the bottom surface and the positioning holes are used as reference
5. Install positioning pins as shown in the figure in the mounting surface set up parallel to the speed direction. After positioning
with the positioning holes in the bottom surface of the body, fix the body with screws.”
6. Pay attention to the angle β and γ, use the bottom surface and the positioning holes as reference for installation.


SPECIFICATIONS

LV-20Z
LV-50Z
Optical sensor
S-100Z
Signal Processing unit
P-20Z
P-50Z
Measurement Range
- 200 to 2000 mm / sec.
- 50 to 5000 mm / sec.
Maximum Resolution
2.5 µm / pulse
5 µm / pulse
Focal Length
40 mm
Depth of focus
± 5 mm
Laser spot size 2.4 x 0.1 mm (at focal point)
Velocity fluctuation response frequency 0 to 300 Hz
Effective object surface
Reflectance 20 % or more, flat scattered
Output Signal 1 : F/ V analog output
- 4 to + 5 V (at RANGE 4 )
- 0.6 to + 7.5 V (at RANGE 4 )
Accuracy less than ± 1 % of full scale
2 : A,B phase balanced output 2.5, 5, 10, 20, 40, 80, 160, 320 µm
5, 10, 20, 40, 80, 160, 320, 640 µm
Phase difference 90 ± 30 deg
3 : Doppler pulse output 120 to 1000 kHz
180 to 2200 kHz
Measurement Certainty <100 mm / sec : ± 0.2 mm / sec, > 100 mm / sec : ± 0.2 %
4 : Optical shift frequency output 200 kHz, CMOS level
5 : UP/DOWN pulse output pulse per Δd moving to positive/negative direction
6 : Measurement error output Indicate high level when error
Velocity display
5 digit (mm / sec, m / min. selectable)
Light source
Semiconductor laser ( 680 nm)
Voltage
100 ~ 240 V
External dimensions Optical sensor
33 x 98 x 39 mm
Main unit
235 x 290 x 115 mm
Ambient conditions
Operating Temperature
0 to 45 ºC
Storage Temperature - 30 to 60 ºC
Humidity 80 % RH or less (no condensation)


 
 
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