JPH10267648A - Optical displacement gauge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical displacement gauge the light receiving quantity of which can be controlled to a prescribed level in a short time and from which stable measured results can be obtained. SOLUTION: A duty cycle control loop constituted of an LPF/amplifier circuit 21, a peak hold circuit 22, a microcomputer 23, and an A/D converter 24 controls the duty cycle of laser diode driving pulse signals LD so that the peak voltage of light receiving signals LS1 may become equal to a reference voltage. An AGC loop composed of the LPF/amplifier circuit 21, an AGC amplifier 26, a peak hold circuit 27, a subtractor 28, an error integrating circuit 29, and a reference voltage generating circuit 30 controls the gain of the AGC amplifier 26 so that the peak voltage of the output signal LS2 of the amplifier 26 may become equal to the reference voltage. A digital processing circuit 32 composed of an A/D converter 31, a digital processing circuit 32, and the microcomputer 23 detects the peak position in a received light quantity distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical displacement meter for measuring a displacement of an object.

[0002]

2. Description of the Related Art An optical displacement meter to which triangulation is applied is used to measure an amount of movement of an object, dimensions of the object, and the like. FIG. 9 is a block diagram showing a configuration of a main part of a conventional optical displacement meter.

In FIG. 9, a drive circuit 101 drives a laser diode 102 based on a light output control signal Va. The laser light emitted from the laser diode 102 is applied to the measurement object 100 through the light projecting lens 103. The diffuse reflection component of the reflected light from the measurement object 100 passes through the light receiving lens 104 and the light position detecting element (PS
D) Received by 105.

When the object 100 is displaced in the direction indicated by the arrow X, the position of the light spot on the light receiving surface of the light position detecting element 105 moves. Two output signals corresponding to the position of the light spot on the light receiving surface are output from the light position detecting element 105, and the output signals are respectively converted into currents by current-voltage conversion circuits (IV conversion circuits) 106a and 106b. The voltage is converted. One output signal of the light position detecting element 105 has a current value proportional to the distance from one end of the light receiving surface to the light spot, and the other output signal is proportional to the distance from the other end of the light receiving surface to the light spot. It has a current value. Therefore, the displacement of the measuring object 100 can be detected based on the current values of these two output signals.

In such an optical displacement meter, the intensity of the reflected light varies depending on the material and surface condition of the object 100 to be measured, so that the amount of light received by the light position detecting element 105 becomes a certain level. It is necessary to adjust the light output of the laser diode 102.

FIG. 10 is a block diagram showing an example of a conventional control circuit for controlling the amount of light received by the light position detecting element 105. The control circuit of FIG.
6a, 106b, an adder 112, a subtractor 113, an error integrating circuit 114, a reference voltage generating circuit 115, and an optical output adjusting circuit 111.

[0007] The current-voltage conversion circuits 106a and 106b
The current signal of the light position detecting element 105 is converted into a voltage signal. The adder 112 adds the respective voltage signals on the FAR side and the NEAR side to output the amount of light received by the light position detecting element 105 as the amount of received light voltage VL. The reference voltage generation circuit 115 generates a predetermined reference voltage Vr. The subtracter 113 outputs a difference between the received light voltage VL obtained by the adder 112 and the reference voltage Vr generated by the reference voltage generating circuit 115 as an error signal VE. The error integration circuit 114 integrates the error signal VE output from the subtractor 113 and converts the integrated error signal to a control voltage VC.
To the optical output adjustment circuit 111.

As a result, the light output adjusting circuit 1 causes the received light voltage VL outputted from the adder 112 to be equal to the reference voltage Vr generated by the reference voltage generating circuit 115.
Eleven voltages are controlled. Therefore, by controlling the voltage of the light output control signal Va given from the light output adjustment circuit 111 to the drive circuit 101 in FIG. 9, the amount of light received by the light position detection element 105 can be controlled to a constant level.

[0009]

However, FIG.
Since the voltage of the light output adjusting circuit 111 is controlled by analog control in the control circuit of FIG.
Overshoot and ringing occur in L, and it takes time for the level of the received light voltage VL to reach a predetermined level. As a result, it takes time for the amount of light received by the light position detecting element 105 to stabilize to a certain level.

Further, in the control circuit of FIG. 10, since the control range of the light output adjustment circuit 111 is limited, it is difficult to secure a wide dynamic range.

Further, the distribution of the amount of light received by the light position detecting element 105 includes noise components such as stray light. Note that the stray light is reflected light from portions other than the target portion. FIG. 11 is a diagram illustrating an example of the distribution of the amount of received light by the light position detection element 105. The light reception amount distribution in FIG. 11 includes a light reception amount peak PK2 due to noise components such as stray light, in addition to a light reception amount peak PK1 due to reflected light from the measurement object 100.
In this case, the light position detection element 105 outputs an output signal corresponding to the barycenter position P1 of all the received light amount distribution including the peak PK2 of the received light amount due to the noise component. Therefore, it is difficult to accurately determine the center of gravity position P0 of the peak PK1 of the amount of light received by the reflected light from the measurement object 100. Thus, there is a problem that the measurement result becomes unstable due to the influence of noise components such as stray light.

An object of the present invention is to provide an optical displacement meter which can control the amount of received light to a predetermined level in a short time and can obtain a stable measurement result.

Another object of the present invention is to provide an optical displacement meter capable of controlling a received light amount to a predetermined level in a short time, obtaining a stable measurement result, and having a wide dynamic range. It is.

[0014]

Means for Solving the Problems and Effects of the Invention An optical displacement meter according to a first aspect of the present invention is an optical displacement meter for measuring a displacement of an object, and a light emitting element for irradiating the object with light. A linear image sensor that receives reflected light from an object and outputs the received light signal as a light receiving signal, a conversion unit that converts the light receiving signal output from the linear image sensor into digital data, and a digital data obtained by the conversion unit. And control means for controlling the light emitting element so that the level of the light receiving signal from the linear image sensor becomes a predetermined level.

Here, the linear image sensor means not only a CCD type image sensor which sequentially outputs charges accumulated in each light receiving section to a shift register and then sequentially outputs the charges, but also sequentially charges accumulated in each light receiving section. It also includes an image sensor of the type that transfers and outputs.

In the optical displacement meter according to the present invention, the reflected light from the object is received by the linear image sensor and output as a light receiving signal. Then, the light receiving signal is converted into digital data, and the light emitting element is controlled based on the digital data so that the level of the light receiving signal from the linear image sensor becomes a predetermined level.

As described above, since the light emitting element is controlled based on the digital data, no problem of overshoot or ringing occurs, and the level of the light receiving signal is controlled in a short time in synchronization with the transfer cycle in the linear image sensor. Is done. Also, since the received light signal output from the linear image sensor represents the received light amount distribution, it is possible to accurately measure the center of gravity of the peak of the received light amount due to reflected light based on digital data corresponding to the received light amount distribution. It becomes possible.

An optical displacement meter according to a second aspect of the present invention is the optical displacement meter according to the first aspect, wherein the control means comprises:
The lighting time of the light emitting element is controlled based on digital data obtained by the conversion means.

In this case, the level of the amount of light received by the linear image sensor can be controlled by controlling the lighting time of the light emitting element. In particular, since the level of the amount of light received by the linear image sensor is proportional to the lighting time of the light emitting element, the level of the amount of light received can be easily controlled.

An optical displacement meter according to a third aspect of the present invention is the optical displacement meter according to the first aspect, wherein the control means comprises:
The light output of the light emitting element is controlled based on digital data obtained by the conversion means.

In this case, the level of the amount of light received by the linear image sensor can be controlled by controlling the light output of the light emitting element.

An optical displacement meter according to a fourth aspect of the present invention is the optical displacement meter according to the first aspect, wherein the control means comprises:
The lighting time and light output of the light emitting element are controlled based on digital data obtained by the conversion means.

In this case, the level of the amount of light received by the linear image sensor can be controlled by controlling the lighting time and light output of the light emitting element.

An optical displacement meter according to a fifth aspect of the present invention is the optical displacement meter according to the first aspect, wherein the control means comprises:
The lighting time of the light emitting element and the light output for the predetermined time are controlled based on the digital data obtained by the conversion means.

If the lighting time or light output is not longer than a predetermined value, a light receiving signal cannot be obtained. Therefore, by controlling the light emitting element for a predetermined lighting time and a predetermined light output, the level of the amount of light received by the linear image sensor is controlled. Can be controlled.

An optical displacement meter according to a sixth aspect of the present invention comprises
In the configuration of the optical displacement meter according to any one of the fifth inventions, an amplifying unit having a variable gain and amplifying a light receiving signal from the linear image sensor; a reference voltage generating unit generating a predetermined reference voltage; And a gain control means for controlling the gain of the amplification means so that the voltage of the output signal of the amplification means becomes equal to the reference voltage generated by the reference voltage generation means.

In the optical displacement meter according to the present invention, the light emitting element is controlled so that the level of the light reception signal from the linear image sensor becomes a predetermined level, and the amplification for amplifying the light reception signal from the linear image sensor is performed. The gain of the amplifying means is controlled so that the output signal of the means is equal to a predetermined reference voltage.

As described above, since the light receiving signal from the linear image sensor is amplified in addition to the control of the light emitting element, it is possible to secure a wide dynamic range.

[0029]

FIG. 1 is a block diagram showing the configuration of an optical displacement meter according to an embodiment of the present invention.

The optical displacement meter shown in FIG. 1 comprises a head 1 and a main body 2. The head unit 1 includes a laser diode 11, a driving circuit 12, a CCD one-dimensional image sensor (hereinafter, referred to as a CCD sensor) 13, a CCD control circuit 1,
4, amplifying circuit 15, light projecting lens 16, and light receiving lens 1
7 inclusive.

On the other hand, the main body 2 includes an LPF (low-pass filter) / amplifier circuit 21, a peak hold circuit 22, a microcomputer 23, and a D / A converter (digital / digital
Analog converter) 25. Microcomputer 2
3 is an A / D converter (analog / digital converter) 24
Built-in. The main unit 2 includes an AGC (automatic gain control) amplifier 26, a peak hold circuit 27, a subtractor 2
8, including an error integrating circuit 29 and a reference voltage generating circuit 30. Further, main unit 2 includes a clock generation circuit 33 and a power supply circuit 34.

The microcomputer 23 generates a laser diode drive pulse signal LD for controlling the lighting time of the laser diode 11. The drive circuit 12 drives the laser diode 11 in response to the laser diode drive pulse signal LD. The drive circuit 12 supplies a current to the laser diode 11 during an active period (for example, a high level period) of the laser diode drive pulse signal LD, for example. Therefore, the laser diode drive pulse signal L
The lighting time of the laser diode 11 is controlled according to the pulse width of D.

The light emitted from the laser diode 11 is applied to the measuring object 100 through the light projecting lens 16. The diffuse reflection component of the reflected light from the measurement object 100 is received by the CCD sensor 13 through the light receiving lens 17. The output signal of the CCD sensor 13 is amplified by the amplifier circuit 15, and the amplified output signal is supplied to the LPF / amplifier circuit 21 as the light receiving signal LS0. The CCD control circuit 14 controls the operation of the CCD sensor 13 in synchronization with the clock signal CK generated by the clock generation circuit 33.

In the main unit 2, the LPF / amplifier circuit 2
1, peak hold circuit 22, microcomputer 2
3 and A / D converter 24 form a duty cycle control loop. This duty cycle control loop performs feedback control of the duty cycle of the laser diode drive pulse signal LD so that the peak voltage of the light receiving signal LS0 becomes a predetermined level.

The LPF / amplifier circuit 21, AGC amplifier 26, peak hold circuit 27, subtracter 28, error integrating circuit 29, and reference voltage generating circuit 30 constitute an AGC (automatic gain control) loop. This AGC loop has A
The gain (gain) of the AGC amplifier 26 so that the peak voltage of the output signal LS2 of the GC amplifier 26 becomes a predetermined level.
Feedback control.

Further, the A / D converter 31, digital processing circuit 32 and microcomputer 23 constitute a digital processing unit. This digital processing unit converts the output signal LS2 of the AGC amplifier 26 into digital data, and determines the peak position of the light-receiving amount distribution by the CCD sensor 13 based on the obtained digital data that is equal to or greater than a certain threshold. To detect.

The data of the peak position detected by the digital processing section is output to the D / A converter 25 as a displacement measurement result. The D / A converter 25 converts the data at the peak position into an analog signal and outputs it as a measurement result.

In this embodiment, the laser diode 11 corresponds to a light emitting element, the CCD sensor 13 corresponds to a linear image sensor, the peak hold circuit 22 and the A / D converter 24 correspond to conversion means, and the microcomputer 2
3 corresponds to a control means. Further, the AGC amplifier 26 corresponds to an amplifying means, the reference voltage generating circuit 30 corresponds to a reference voltage generating means, and the peak hold circuit 27, the subtracter 28 and the error integrating circuit 29 constitute a gain control means.

FIG. 2 is a diagram for explaining the operation of the duty cycle control loop in the optical displacement meter of FIG.

The LPF / amplifier circuit 21 removes the high-frequency component of the received light signal LS0 supplied from the amplifier circuit 15 of the head unit 1, amplifies the received light signal LS0, and outputs the amplified light signal LS1. Peak hold circuit 22
Holds the peak voltage of the light receiving signal LS1 and outputs it as the peak hold voltage Vp1. The A / D converter 24 is
The peak hold circuit 22 converts the peak hold voltage Vp1 and the predetermined reference voltage Vr provided from the peak hold circuit 22 into digital data.

The microcomputer 23 compares the digital data of the peak hold voltage Vp1 with the digital data of the reference voltage Vr, and controls the duty cycle of the laser diode drive pulse signal LD so that the peak hold voltage Vp1 becomes equal to the reference voltage Vr. I do. here,
The duty cycle of the laser diode drive pulse signal LD is a value obtained by dividing the pulse width Tw of the laser diode drive pulse signal LD by the period T.

FIG. 3 is a flowchart showing the processing of the microcomputer 23 in the duty cycle control loop of FIG.

The microcomputer 23 first turns on the laser diode 11 for a time t1 (step S1). Here, the time t1 corresponds to the pulse width Tw of the laser diode drive pulse signal LD.

Next, the microcomputer 23 performs analog / digital conversion of the peak hold voltage Vp1 supplied from the peak hold circuit 22 (step S).
2).

Then, the lighting time t of the laser diode 11 is calculated by the following equation so that the peak hold voltage Vp1 becomes equal to the reference voltage Vr (step S3).

T = (Vr / Vp1) · t1 (1) Next, the calculated lighting time t is set as the next lighting time t1 of the laser diode 11 (step S4). That is,
The pulse width Tw of the laser diode drive pulse signal LD is adjusted to the next lighting time t1.

FIG. 4 shows a laser diode drive pulse signal L.
FIG. 4 is a signal waveform diagram showing a relationship between D and a light receiving signal LS1.
As shown in FIGS. 4A and 4B, when the pulse width Tw of the laser diode drive pulse signal LD becomes half,
The peak voltage (peak height) H of the light receiving signal LS1 is also halved. Thus, the pulse width Tw of the laser diode drive pulse signal LD and the peak voltage H of the light receiving signal LS1 are obtained.
Is in a proportional relationship. Therefore, when the peak voltage H of the light receiving signal LS1 is set to the target value, the pulse width Tw of the laser diode drive pulse signal LD is obtained by a simple proportional calculation as shown in the above equation (1). As a result, the peak voltage H of the light receiving signal LS1 can be easily and accurately controlled.

As shown in FIG. 3, sampling is performed when the laser diode 11 is turned on for the first time, and the light receiving signal LS1 is output when the laser diode 11 is turned on for the second time.
Can be set to the target value. in this case,
Since control is performed based on digital data, unlike in the case of analog control, a change in the level of the light receiving signal LS1 does not cause overshoot or ringing. Therefore, it is possible to control the amount of received light with high responsiveness, accurately, and easily.

FIG. 5 shows AGC in the optical displacement meter of FIG.
FIG. 9 is a diagram for explaining an operation of a loop.

As described above, the LPF / amplifier circuit 21
Light receiving signal LS given from amplifying circuit 15 of head unit 1
0 high-frequency components are removed and the received light signal LS0 is removed.
And outputs it as a light receiving signal LS1. The AGC amplifier 26 amplifies the light receiving signal LS1. The peak hold circuit 27 holds the peak voltage of the output signal LS2 of the AGC amplifier 26 and outputs it as a peak hold voltage Vp2. On the other hand, the reference voltage generation circuit 30 outputs a predetermined reference voltage V
generate r.

The subtracter 28 outputs the difference between the reference voltage Vr and the peak hold voltage Vp2 as an error signal Ve.
The error integration circuit 29 integrates the error signal Ve and supplies the integrated error signal to the AGC amplifier 26 as a control voltage Vc. Thereby, the gain of AGC amplifier 26 is controlled based on control voltage Vc such that the peak voltage of output signal LS2 of AGC amplifier 26 becomes equal to reference voltage Vr.

FIG. 6 shows a laser diode drive pulse signal L
FIG. 3D is a signal waveform diagram showing D, a light receiving signal LS1, and an output signal LS2 of the AGC amplifier 26.

As shown in FIG. 6, when the peak voltage of the light receiving signal LS1 does not reach the reference voltage Vr even when the duty cycle of the laser diode driving pulse signal LD is set to 100%, the AGC amplifier 26 of the AGC loop is turned on. Amplifies the light receiving signal LS1, and the peak voltage of the output signal LS2 of the AGC amplifier 26 becomes the reference voltage Vr.

The dynamic range of the duty cycle control loop of FIG. 2 is determined by one cycle in the CCD sensor 13 and the minimum pulse width. For example, CCD sensor 1
When the period of No. 3 is 512 μs and the minimum pulse width is 3.2 μs, the dynamic range becomes 160 times. However, when measuring from a measurement object 100 having a high reflectance such as a metal to a measurement object 100 having a low reflectance such as black rubber, a dynamic range of about 1000 times is required. In the optical displacement meter of this embodiment, the AGC of FIG.
By amplifying the light receiving signal LS1 by, for example, about 10 times by the loop, it is possible to secure a dynamic range of 1000 times or more.

In the optical displacement meter of this embodiment, FIG.
Independent of the duty cycle control loop of FIG.
Since the C loop is configured, control of the duty ratio of the duty cycle control loop and control of the gain of the AGC amplifier 26 in the AGC loop are simple and easy, and stable measurement is possible.

FIG. 7 is a diagram for explaining the operation of the digital processing unit in the optical displacement meter of FIG.

The A / D converter 31 converts the output signal LS2 of the AGC amplifier 26 in the AGC loop from analog to digital, and outputs digital data D0. The digital processing circuit 32 extracts data having a value larger than a predetermined threshold value Th from the digital data D0, and outputs the data as digital data D1. Specifically, the digital processing circuit 32 calculates the threshold value Th from the digital data D0.
Is subtracted, and only data larger than 0 is set as digital data D1. The microcomputer 23 uses the digital data D1 extracted by the digital processing circuit 32 to calculate the position of the center of gravity of the received light amount distribution.

FIG. 8 is a waveform diagram showing an example of digital data D0 obtained by the A / D converter 31 and digital data D1 obtained by the digital processing circuit 32.

As shown in FIG. 8, the digital data D0 includes the peak PR of the received light amount due to the reflected light from the measurement object 100 and the peak P of the received light amount due to noise components such as stray light.
N. By extracting only digital data having a value greater than the threshold value Th from the digital data D0, the digital data D1 contains the object 1 to be measured.
Only the peak PR of the amount of light received by the reflected light from 00 is included.

Thus, the microcomputer 23
Is the peak PR of the amount of light received by the reflected light from the measuring object 100 using the digital data D1 containing no noise component.
Can be calculated. Therefore,
The measurement result is stabilized, the number of data used for calculation is significantly reduced, and the calculation time is shortened.

In the above embodiment, the CCD sensor 13
The lighting time of the laser diode 11 is controlled by controlling the duty cycle of the laser diode drive signal LD in order to make the level of the amount of light received by the laser diode a predetermined level. May be controlled to control the light output of the laser diode 11. Alternatively, both the lighting time of the laser diode 11 and the light output may be controlled in order to set the level of the amount of light received by the CCD sensor 13 to a predetermined level.

Although the laser diode 11 is used as the light emitting element in the above embodiment, another light emitting element such as a light emitting diode may be used as the light emitting element. Furthermore, in the above embodiment, the CCD one-dimensional image sensor 13 is used as the linear image sensor, but a CCD two-dimensional image sensor may be used as the linear image sensor.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical displacement meter according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining an operation of a duty cycle control loop in the optical displacement meter of FIG.

FIG. 3 is a flowchart showing processing of a microcomputer in a duty cycle control loop of FIG. 2;

FIG. 4 is a signal waveform diagram showing a relationship between a laser diode drive pulse signal and a light receiving signal.

5 is a diagram for explaining an operation of an AGC loop in the optical displacement meter of FIG.

FIG. 6 is a signal waveform diagram showing a laser diode driving pulse signal, a light receiving signal, and an output signal of an AGC amplifier.

FIG. 7 is a diagram for explaining an operation of a digital processing unit in the optical displacement meter of FIG.

FIG. 8 is a waveform diagram showing an example of digital data obtained by an A / D converter and digital data obtained by a digital processing circuit.

FIG. 9 is a block diagram showing a configuration of a main part of a conventional optical displacement meter.

10 is a block diagram showing an example of a control circuit for controlling the amount of light received by a light position detecting element in the optical displacement meter of FIG.

FIG. 11 is a diagram illustrating an example of a light reception amount distribution in a light position detection element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Head part 2 Main body part 11 Laser diode 12 Drive circuit 13 CCD one-dimensional image sensor 21 LPF / amplifier circuit 22, 27 Peak hold circuit 23 Microcomputer 24, 31 A / D converter 26 AGC amplifier 28 Subtractor 29 Error integration circuit 30 Reference voltage generation circuit 32 Digital processing circuit 33 Clock generation circuit 100 Measurement object

Claims (6)

[Claims] 1. An optical displacement meter for measuring a displacement of an object, comprising: a light emitting element for irradiating the object with light; and a linear image receiving light reflected from the object and outputting the light as a light receiving signal. A conversion unit for converting a light reception signal output from the linear image sensor into digital data; and a level of the light reception signal from the linear image sensor based on the digital data obtained by the conversion unit. Control means for controlling the laser diode so that 2. The optical displacement meter according to claim 1, wherein said control means controls a lighting time of said light emitting element based on digital data obtained by said conversion means. 3. The optical displacement meter according to claim 1, wherein said control means controls an optical output of said light emitting element based on digital data obtained by said conversion means. 4. The optical displacement meter according to claim 1, wherein said control means controls a lighting time and a light output of said light emitting element based on digital data obtained by said conversion means. 5. The optical device according to claim 1, wherein the control unit controls a lighting time of the light emitting element for a predetermined time or more and a light output for a predetermined time or more based on the digital data obtained by the conversion means. Type displacement meter. 6. An amplifying means having a variable gain and amplifying a light receiving signal from the linear image sensor; a reference voltage generating means for generating a reference voltage; 6. The optical displacement meter according to claim 1, further comprising gain control means for controlling a gain of said amplification means so as to be equal to said reference voltage generated by said means.