JPH0666525A - Measuring apparatus for thickness using laser range finder - Google Patents

Abstract

PURPOSE:To reduce an error in measurement due to vibration by emitting pulsed lasers from light sources of two sets of laser range finders simultaneously and by sensing lights reflected from the opposite surface and rear of an object of measurement in the same time section of the same time. CONSTITUTION:Based on the same pulse signal from a pulse generating circuit 11, pulsed lasers of the same time width are applied onto the opposite surface and rear (the rear and the surface at the same position) of an object (steel plate) 9 of measurement at the same timing from laser generators 2A and 2B disposed on the upper and lower sides of the object 9. In response to a start pulse from the circuit 11, image sensors 5A and 5B read out sensed light signals of pixels in the sensors in the sequence of arrangement and give them to signal processing circuits 6A and 6B. In response to readout start signals from the sensors 5A and 5B, the circuits 6A and 6B detect imaged positions of laser reflected lights and calculate distances La and Lb. Using the distances La and Lb and a distance Lo between two range finders 1A and 1B set beforehand, an arithmetic unit 13 calculates the plate thickness (t) of the object 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the thickness of a steel plate or the like using two laser rangefinders.

[0002]

Laser range finder 2 based on the principle of triangulation
A thickness gauge has been put into practical use, which measures the thickness by sandwiching a measurement object on a table. This thickness gauge is non-contact, has a high-speed response, and can reduce the laser spot diameter, so it can measure the thickness of a comparatively small range of the object to be measured compared to conventional thickness gauges using radiation. Therefore, it is possible to measure the thickness of a steel sheet or the like flowing through the line at high speed accurately and with high density.

Further, as a laser range finder based on the principle of triangulation using this thickness meter, one using an image sensor in which a charge-coupled image pickup device (CCD) or the like is one-dimensionally arranged in a light receiver is comparatively used. Recently, it has been widely used because it can ensure the accuracy even for the measuring object at a long distance. Therefore, the measurement principle of a thickness meter using such a laser rangefinder will be described with reference to FIG. As shown in FIG. 3, in the upper laser rangefinder 1A, first, laser light 7A is emitted from the laser generator 2A toward the measurement target 9. At this time, an irradiation spot 8A is generated on the measurement surface 9A of the measuring object 9 by the laser light 7A. Then, the reflected light from this irradiation spot is received by the light receiver 3A. In the light receiver 3A, the reflected light is condensed by a condenser lens 4A composed of a convex lens and focused on the image sensor 5A. In the image sensor 5A, when the read start pulse is input, the electric charge accumulated by receiving the reflected light until then is sequentially discharged to the signal processing circuit 6A from one end a ₁ to the other end a ₂ and newly reflected. Light is received and begins to accumulate. Therefore,
As shown in FIG. 4, in the signal processing circuit 6A, a signal of the received light intensity is obtained in time series with the read start pulse as a reference, and the number Ta of pixels from the read start end of the one-dimensional image sensor to the image forming position is calculated. By counting
The image forming position Da on the image sensor 5A is obtained. That is, the light receiving signals of the pixels (minimum unit photoelectric conversion elements) arranged one-dimensionally in the one-dimensional image sensor are sequentially read in the order of arrangement to count the pulses (shift pulses), grasp the read position, and detect the light receiving intensity. It is assumed that the laser reflected light is imaged at the peak position Da. Since the shift pulse has a constant cycle, the count value (Da) also represents the elapsed time after the read start pulse is generated.

The light receiver 3A is fixed in advance to a predetermined position with respect to the laser generator 2A, and the laser light 7
Since the visual field direction of the light receiver 3A is also determined with respect to the irradiation direction of A, the distance La between the imaging position Da and the irradiation spot on the measurement surface 9A is La according to the principle of triangulation. = F (Da), and the distance La can be calculated by obtaining Da. Similarly, in the lower laser rangefinder 1B, the image forming position Db of the laser reflected light on the one-dimensional image sensor is obtained.
The distance Lb can be calculated. Two laser rangefinders 1A and 1B are arranged so as to face each other with the measurement object 9 sandwiched therebetween and the optical axes thereof are arranged on the same straight line.
If the distance is L0, the thickness t of the measured object can be calculated from the following equation (1).
Is obtained.

T = L0-La-Lb (1) By the way, a continuous wave laser (for example, He-Ne laser) is used for the laser generator in such a laser rangefinder, and the upper laser distance is used. FIG. 5 shows the oscillation timings of the laser generators 2A and 2B and the readout timings of the image sensors 5A and 5B of the total 1A and the lower laser rangefinder 1B. Simultaneously with the start of the measurement, laser light 7A, 7B is continuously emitted toward the object 9 to be measured, and the upper and lower image sensors 5A,
5B is read out intermittently at the same time, and the laser rangefinders 1A, 1B to the measurement object surface 9A,
The distances La and Lb to 9B are obtained, and the thickness t of the measuring object 9 is obtained. Therefore, the charges discharged from the respective elements of the image sensors 5A and 5B to the signal processing circuits 6A and 6B are reflected within a time period from immediately after being discharged from the same element at the previous read timing to being discharged at the current timing. It is the charge that is received and accumulated.
However, depending on the thickness and position of the measurement object 9, the laser light irradiation spots 8A, 8 on the measurement object surfaces 9A, 9B.
The image forming position lengths Da and Db of the elements of the image sensors 5A and 5B that receive B and the times Ta and Tb accompanying them are different. Therefore, if the received light intensity waveforms of the upper laser rangefinder 1A and the lower laser rangefinder 1B as shown in FIG. 5 are obtained, the distance value obtained from the time Da corresponding to the upper laser rangefinder 1A and the lower laser rangefinder 1A are obtained. With the distance value obtained from the time Db corresponding to the distance meter 1B,
The time when the reflected light is received is different from Tu and Td.

As described above, when the reception timing or the reception time of the reflected light differs between the upper and lower laser rangefinders, there is no problem as long as the object to be measured is in a stationary state. In the case of measuring, the steel plate thickness is obtained by measuring the distance to the surface that is partially different in the steel plate moving direction with the upper laser range finder and the lower laser range finder. Cannot be measured. In most cases, the steel plate is conveyed while vibrating up and down. In that case, the vibration component that is canceled in principle cannot be canceled completely because the measurement timing is different, which causes a large error. It will be. As a result, when the vibration of the steel sheet is substantially absent, the variation in the thickness measurement value is small as shown in FIG. 7A, but when the vibration of the steel sheet is large, the thickness measurement value becomes smaller as shown in FIG. Fluctuation increases and measurement error increases.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to reduce the measurement error due to the vibration of the object to be measured.

[0008]

According to the present invention, the laser light source (2A / 2B), the image sensor (5A / 5B), the laser light source (2A / 2B) emits an object ( Optical system (4A, 4A for imaging the laser reflected from 9) on the image sensor (5A / 5B)
B), and the laser image forming position (Da / Db) on the image sensor (5A / 5B) is detected, and the laser light source (2A) is detected from the position (Da / Db) based on the principle of triangulation. / 2B) to the object (9)
(La / Lb) has a distance calculating means (6A / 6B) to calculate, the light projection optical axis (7A / 7B) of the laser light source (2A / 2B) is placed on a straight line (9) Two sets of laser rangefinders (1A
/ 1B); and the thickness of the object (9) from each distance (La / Lb) to the object (9) calculated by these laser rangefinders (1A / 1B)
In a thickness measuring device using a laser rangefinder, which comprises a thickness calculating means (13) for calculating (t), each laser rangefinder (1
(A / 1B) laser light source (2A / 2B) pulse laser modulator (12A / 12B) for pulsing each laser light source (2A / 2B) to emit a pulsed laser, and the pulse modulation Laser (2A / 2B) of each laser rangefinder (1A / 1B) to simultaneously emit a pulsed laser of the same time width (Tu = Td) to the instrument (12A / 12B). A radiation instruction pulse (laser oscillation pulse) is given to the image sensor (5A / 5B), which is a signal (readout star) for instructing reading of a light reception signal outside the section of the pulsed laser radiation.
And a timing control means (11) for giving a pulse).

Symbols in parentheses indicate corresponding elements or corresponding matters in the embodiments shown in the drawings and described later.

[0010]

Operation: By controlling the timing control means (11) through the pulse modulator (12A / 12B), two sets of laser rangefinders (1A /
(1B) laser light source (2A / 2B), same time width (Tu = Td)
It emits a pulsed laser. As a result, the image sensor (5A / 5B) of the laser range finder (1A / 1B) receives the reflected light of the same time section (Tu = Td) at the same time on the front and back sides of the object (9). The signal of the level corresponding to the light intensity is maintained.

However, the timing control means (11) is a signal for instructing the image sensor (5A / 5B) to read the light reception signal outside the section (Tu = Td) where the laser reflected light is being received. Therefore, the image sensor (5A / 5B) outputs a signal corresponding to the light intensity in the section (Tu = Td) to the section where the laser reflected light is not received.

From the above, the signal output from the image sensor (5A / 5B) indicates the reflected light level in the same time section (Tu = Td) at the same time on the opposite surface of the object (9), The front and back surfaces have no positional deviation, and there is no difference in the accumulation time of the laser reflected light signal. Therefore, there is no need to measure the distances to different surfaces, and even if the steel plate vibrates up and down, the vibration component does not appear in the output of the image sensor (5A / 5B).

[0013]

FIG. 1 shows an embodiment of the present invention. The two laser rangefinders 1A and 1B are fixed to the C frame 10, and the distance L ₀ between them is fixed. The laser generators 2A and 2B are semiconductor lasers, and the pulse modulators 12A and 12B pulse-energize the laser generators A and 2B in response to the laser oscillation pulse generated by the pulse generation circuit 11. Therefore, the pulse laser is projected on the steel plate 9.

As shown in FIG. 2, the laser oscillation pulse generated by the pulse generation circuit 11 is a high-level H pulse signal during Tu = Td, and the same pulse signal is pulse modulators 12A and 12B. Is given to the laser generator 2
A and 2B simultaneously project laser pulses having the same time width on the steel plate 9. That is, both the upper and lower laser generators 2A, 2B
At the same timing, a pulsed laser having the same time width is applied to the opposite front and back surfaces (front and back at the same position) of the steel sheet 9.

The pulse generation circuit 11 operates in the low level section (without laser generation) of the laser oscillation pulse, and at the timing when the reading of the light receiving signals of the image sensors 5A and 5B is completed within the low level section. A read start pulse is applied to the image sensors 5A and 5B. Image sensor 5
In response to the start pulse, A and 5B read the light receiving signals of each pixel (minimum unit photoelectric conversion element) in the sensor in the order of arrangement and give them to the signal processing circuits 6A and 6B. A laser pulse is not generated during this reading, but a laser pulse is generated after the reading is completed.

The signal processing circuits 6A and 6B detect the peak positions (Da: FIG. 4) of the light receiving signals of the image sensors 5A and 5B in response to the read start signals, that is, the image sensors 5A and 5B. The imaging positions Da and Db of the laser reflected light on 5B are detected, the distances La and Lb are calculated from them, and the data indicating these distances La and Lb are updated and stored in the output latch.

The arithmetic unit 13 is responsive to the arithmetic start pulse generated by the pulse generating circuit 11 to generate a signal processing circuit 6A,
The data La and Lb of the output latch 6B are read, the plate thickness t of the steel plate 9 is calculated using the preset data indicating L ₀ , and this is updated and stored in the output latch. The arithmetic start pulse is generated at a timing slightly after the time when the signal processing circuits 6A and 6B finish calculating the distances La and Lb. Due to the above-mentioned generation of the pulse by the pulse generation circuit 11, the laser projection and the reading of the light receiving signal of the image sensor become the timings shown in FIG.

[0018]

[Effect] In order to confirm the effect of the present invention, the results of applying a vibration having an amplitude of about 5 mm to a thick plate having a thickness of about 5.15 mm are shown in FIG. 6 (Example of the present invention) and FIG. )
Shown in. In the embodiment of the present invention, the cycle of the read start pulse of the image sensor is 2 msec, the time required for the read is about 1 msec, and the time width of the pulse laser (Tu = Td in FIG. 2).
Is about 0.4 msec. In the conventional method (Fig. 7), when there is vibration, the thickness measurement values vary considerably, whereas
In the embodiment of the present invention shown in FIG. 6, the measured value is almost the same as the case without vibration even if there is vibration, and it can be seen that the error due to the influence of vibration is very small.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing generation timings of various signals of the measuring apparatus shown in FIG.

3 is an enlarged block diagram showing a portion of a laser range finder of the measuring apparatus shown in FIG.

FIG. 4 is a time chart showing a light receiving signal output from the image sensor 5A shown in FIG.

FIG. 5 is a time chart showing generation timings of various signals of a conventional measuring apparatus.

FIG. 6 is a graph showing plate thickness measurement values by a conventional measuring device.

FIG. 7 is a graph showing plate thickness measurement values by the measuring apparatus of the present invention shown in FIG.

[Explanation of symbols]

1A, 1B: Laser distance meter 2A, 2B: Laser generator 3A, 3B: Light receiver 4A, 4B: Condensing lens 5A, 5B: Image sensor 6A, 6B: Signal processing circuit 7A, 7B: Laser light 8A, 8B: Laser light irradiation spot 9: measurement target 9A, 9B: measurement surface of measurement target 10: C frame 11: pulse generation circuit 12A, 12B: pulse modulator 13: calculator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Otsuka 1 Kimitsu, Kimitsu-shi Kimitsu Works, Nippon Steel Co., Ltd. Industrial stock company

Claims (1)

[Claims] 1. A laser light source, an image sensor, an optical system for forming an image of the laser emitted from the laser light source and reflected from an object on the image sensor, and the image sensor. It has a distance calculation means for detecting the laser image formation position on the upper side and calculating the distance from the laser light source to the object based on the principle of triangulation from the position. 2 placed on a straight line and facing each other with the object in between
A thickness using a laser rangefinder, which includes a set of laser rangefinders; and a thickness calculation means for calculating the thickness of the target from each distance to the target calculated by these laser rangefinders. In the measuring device, a pulse modulator for energizing each laser light source so as to emit a pulsed laser from the laser light source of each laser rangefinder, and the pulse modulator to the laser light source of each laser rangefinder At the same time, a laser emission instruction pulse for emitting a pulsed laser having the same time width is given, and a signal for instructing the image sensor to read out a light reception signal outside the section of the pulsed laser emission. And a timing control means for providing a thickness measurement device using a laser range finder.