JPH11237208A - Measuring device for displacement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure quantity of displacement without influence by fluctuation of received light quantity when a measured object is measured. SOLUTION: Measurement light from a light source 4 of a sensor-head 1 irradiates a measured side of a measured object W, and its reflected light is received by a photodetector 6. Thereby, quantity of displacement of the measured side is measured. The detection signal of the photodetector 6 is amplified by an amplifier 10 to output to a calculation means 11. The calculation means 11 calculates the quantity of the displacement of the measured object W based upon the detection signal amplified to output. A gain selection means 12 performs control that lowers the gain of the amplifier 10 a stage to prevent the saturation of the detection signal when the level of the detection signal input by the calculation means 11 exceeds a predetermined threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device for measuring a displacement of an object to be measured in a non-contact manner, and more particularly to a displacement measuring device capable of coping with a large fluctuation of a received light amount and improving the measurement accuracy. .

[0002]

2. Description of the Related Art A displacement measuring device irradiates a measuring object with measuring light and can measure a displacement amount of a measuring surface of the measuring object based on a light receiving state of a light receiving element. This displacement measuring device
For example, the measuring surface of the object is irradiated with the measuring light based on the principle of triangulation, and the displacement of the measuring surface of the object is measured based on the light receiving position of the reflected light detected on the light receiving surface of the position sensor.

In such a displacement measuring device, a plurality of amplification factors (gains) of a processing circuit are provided so that a light receiving element for receiving reflected light and a light receiving amount (level) suitable for detection processing in a subsequent processing circuit are obtained. It can be variably set stepwise or continuously. Recently, an AGC function is provided in a processing circuit, and when the amount of received light is large, the gain is reduced to prevent signal saturation in the processing circuit, while when the amount of received light is small, the gain is reduced so as to reduce noise components. Is raised. It should be noted that the gain is set to a gain that can obtain the highest possible amount of received light because the amount of received light does not saturate and is not affected by noise regardless of whether the gain is manually or automatically changed using the AGC function. It is desired to set.

[0004]

The optimum gain in accordance with the displacement state of the measurement surface of the object to be measured must be manually selected. Even if the measurement is started with the gain once set, the optimum gain is not affected. When the amount of received light increases due to a change in the state of the measurement surface of the measurement object, the signal may be saturated. At the time of this saturation, there has been a problem that the displacement amount cannot be measured accurately.

[0005] Further, even when the AGC function for automatically changing the gain of the processing circuit according to the change in the received light amount is used, when the received light amount changes greatly in a short time (for example, the frequency of the change in the received light amount is modulated). (When the frequency approaches), there is a problem that the signal cannot be measured because the received signal is saturated and cannot be measured. The above-described state occurs when the scattering state of the measurement surface of the measurement object greatly changes. For example, when the measurement object is rotated and the displacement amount of the measurement surface is measured, the measurement object rotates at a high speed. In such a case, there was a problem that the measurement could not be performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a displacement measuring apparatus capable of accurately measuring a displacement amount without being affected by fluctuations in a received light amount when measuring an object to be measured. It is intended to be.

[0007]

In order to achieve the above object, a displacement measuring device according to the present invention has the following features.
In a non-contact type displacement measuring device that irradiates measurement light of a light source to a measurement surface of an object to be measured and receives reflected light thereof with a light receiving element to measure a displacement amount of the measurement surface, based on a light reception amount signal of the light receiving element Calculating means for calculating and outputting the displacement amount of the device under test, and detecting the level of the light receiving amount signal input to the calculating device and setting the level of the light receiving amount signal to a predetermined threshold during the measurement of the device under test. Means for performing control for lowering the level of a signal used for calculating the amount of displacement each time the value exceeds the threshold.

According to a second aspect of the present invention, there is provided a non-contact type displacement measuring device which irradiates a measuring surface of an object to be measured with a measuring light of a light source and receives a reflected light thereof by a light receiving element to measure a displacement of the measuring surface. In the measuring device, an amplifier that amplifies and outputs a light-receiving amount signal of the light-receiving element and has a variable gain (10), and a calculation that calculates and outputs a displacement amount of the object to be measured based on the light-receiving amount signal amplified by the amplifier. Means (11) for variably controlling the gain of the amplifier based on the level of the received light signal input to the arithmetic means, wherein the level of the received light signal is set to a predetermined threshold during the measurement of the device under test. And a gain selecting means (12) for performing control to reduce the gain of the amplifier in response to every time the gain is exceeded.

According to a third aspect of the present invention, in the amplifier (10), the gain can be changed in a plurality of stages, and the gain selecting means (12) controls the light receiving during the measurement of the device under test. It may be configured to perform control to reduce the gain of the amplifier to a corresponding stage based on the level of the amount signal.

According to a fourth aspect of the present invention, in the amplifier (10), the gain can be changed in a plurality of stages, and the gain selecting means (12) controls the light receiving during the measurement of the device under test. A configuration may be adopted in which control is performed to decrease the gain of the amplifier one step at a time, each time the level of the amount signal exceeds a predetermined threshold.

According to a fifth aspect of the present invention, there is provided a non-contact type displacement measuring device for irradiating a measuring surface of an object to be measured with a measuring light of a light source, receiving a reflected light thereof by a light receiving element and measuring a displacement amount of the measuring surface. And a light source drive circuit (5) capable of changing the projection power of the measurement light applied to the object to be measured, and calculating and outputting a displacement amount of the object to be measured based on a light reception amount signal detected by the light receiving element. Calculating means (11) for variably controlling the light emission power of the light source drive circuit based on the level of the received light amount signal input to the calculating means; And a projection power selection means (20) for performing control to reduce the projection power of the light source drive circuit each time the level exceeds a predetermined threshold value.

According to a sixth aspect of the present invention, in the light source driving circuit (5), the light projecting power can be changed in a plurality of stages, and the light projecting power selecting means (20) is provided in the light source driving circuit (5). During the measurement, the control may be performed to reduce the light projection power of the light source drive circuit to a corresponding stage based on the level of the received light amount signal.

According to a seventh aspect of the present invention, in the light source driving circuit (5), the light projection power can be changed in a plurality of stages, and the light projection power selecting means (20) is provided with the object to be measured. The control may be performed such that the light emission power of the light source drive circuit is decreased by one step each time the level of the received light amount signal exceeds a predetermined threshold during the measurement of the above.

According to an eighth aspect of the present invention, there is provided a non-contact type displacement measuring device for irradiating a measuring surface of an object to be measured with a measuring light of a light source and receiving a reflected light thereof by a light receiving element to measure a displacement amount of the measuring surface. A calculating means (11) for calculating and outputting a displacement amount of the object to be measured based on a light receiving amount signal of the light receiving element; and detecting a level of the light receiving amount signal inputted to the calculating means to detect a level of the object to be measured. Input level varying means (36) for performing control to lower the level of the received light amount signal input to the arithmetic means in response to every time the level of the received light amount signal exceeds a predetermined threshold during the measurement. It is characterized by.

According to a ninth aspect of the present invention, the variable gain control of the amplifier (10) by the gain selecting means (12) according to the second aspect and the light projection power selecting means according to the fifth aspect. (20) light projection power control of the light source driving circuit (5) by the light source driving circuit (5); and input light level change of the received light amount signal input to the calculating means (11) by the input level changing means (36). It is also possible to switch to any one of them, or to execute them simultaneously.

The operation of the configuration according to the fourth aspect will be described. The detection output from the light receiving element that receives the reflected light from the object to be measured is amplified by the amplifier 10, and the displacement amount is calculated and output by the calculating means 11. The gain selection means 12 performs control to decrease the gain of the amplifier one by one in response to every time the level of the received light amount signal input to the calculation means 11 exceeds a predetermined threshold. Further, in the configuration in which the light projection power selecting means 20 is provided, the light source driving circuit 5 of the light source 4 corresponds to every time the level of the received light amount signal inputted to the arithmetic means 11 exceeds a predetermined threshold value.
Control for lowering the light projection power of each of the steps one by one. In any of the configurations, even when the position of the measurement surface fluctuates greatly and the level of the received light amount signal greatly changes during the measurement of the workpiece W, the displacement amount is accurately calculated without saturating the input to the calculation means 11. be able to.

[0017]

FIG. 1 is a block diagram showing a first embodiment of a displacement measuring device according to the present invention. As shown in the drawing, the displacement measuring device is generally constituted by a sensor head 1 and a processing means 2. Inside the sensor head 1, a light source (LD) 4
And a light source driving circuit 5 for irradiating the object W with measurement light such as a laser beam, and the reflected light from the object W is detected by a light receiving element (for example, a position sensor) 6 so that the sensor head and the object It moves on the light receiving element 6 according to the distance from the measurement object W. A signal corresponding to the position of the image of the light spot on the light receiving element 6 and the light intensity is obtained, amplified by the amplifier 7 at a predetermined amplification rate, and output to the processing means 2.

The processing means 2 is provided with an amplifier 10 at an input stage. The processing means 2 amplifies an input received light amount signal at a predetermined amplification factor and outputs the amplified signal to a computing means 11. The amplifier 10 has a configuration in which the amplification factor (gain) can be varied, and the gain can be changed stepwise. At the highest gain, the amplification factor is 100%, and the gain is increased at each stage (for example, 100%, 90%, 80%, 70%) by a resistance circuit having a different resistance value for each stage.
%,... (Omitted),..., 50%).

The calculating means 11 calculates the amount of displacement of the measurement surface of the workpiece W based on the received light amount signal after the gain adjustment, and outputs the amount of displacement and the like to the outside. Further, the calculation result including the displacement amount may be stored in a storage unit (not shown) or the like. In addition, a threshold for determining the input light receiving amount (level) is set in the calculating means 11, and a level over signal is output when the level of the light receiving amount signal exceeds the threshold. This threshold is set to a level (saturation level> threshold) immediately before the level of the received light amount signal output from the amplifier 10 is saturated at the input level of the arithmetic unit 11.

The gain is controlled to be switched by the gain selecting means 12. The gain selection means 12 functions when the measurement mode is set to a semi-automatic mode to be described later. Each time a level over signal is input from the calculation means 11, the gain (amplification rate) of the amplifier 10 is set to the present value. The switching control for lowering by one stage from the stage is performed. When the semi-automatic mode is reset by a reset function (not shown), the amplifier 10 is operated at the highest gain when a new DUT is measured, and each time a level over signal is input, the amplifier 10 is switched one stage at a time. Decrease the gain of Further, when a level over occurs, the received light amount signal may be multiplied by a predetermined coefficient α to lower the level (the details will be described later in a third embodiment).

The mode selection means 14 includes a manual setting mode for manually setting the gain of the amplifier 10 and the gain selection means 1.
In this case, any one of the semi-automatic modes for making the second function function is selected and set by an operator's switch operation or the like.

FIG. 2 is a diagram showing a setting screen at the start of measurement. As shown in the figure, the processing unit 2 is provided with a display unit (not shown) of a CRT or a liquid crystal, and displays various setting screens necessary for measuring the object W on the display screen. The setting screen of the mode selection means 14 is displayed on the screen shown in FIG. 2, and the selection items of the "semi-automatic" or "manual" mode for the gain of the amplifier 10 are displayed, and one of them is designated. You can choose. This selection is made using a keyboard, a touch switch, or a mouse provided in the processing means 2. The gain is reset by designating and selecting the "semi-automatic" item displayed on the screen.
Note that the “semi-automatic” mode may be selected based on whether the signal level input to the “semi-automatic” mode selection pin of the connector provided in the apparatus is High or Low.

The calculating means 11, the gain selecting means 12,
The mode selection means 14 can be configured by hardware such as a CPU, a ROM, and a RAM, and a control processing program in a semi-automatic mode stored in a ROM or the like.

Next, the operation of the semi-automatic mode with the above configuration will be described. FIG. 3 is a flowchart showing the gain adjustment operation of the processing means 2 in the semi-automatic mode,
5 is a timing chart showing signals of respective units of the processing unit 2. The processing means 2 resets the gain at the start of the measurement of the device under test (SP1-YES). When a new displacement amount of the object W is measured, the gain of the amplifier 10 is reset (SP1-YES) by designating and selecting the item "semi-automatic" on the setting screen shown in FIG. The gain is set to the initial state (for example, the maximum amplification factor is 100%) (SP2).

Next, the measurement of the displacement of the workpiece W is started. When the sensor head 1 irradiates the measuring object W with the measuring light, the light receiving element 6 receives the reflected light and receives a light receiving amount signal of a level corresponding to the distance from the measuring object W (FIG. 4).
(See (a)) to the processing means 2. Then, the calculating means 11 of the processing means 2 amplifies the received light amount signal in the initial gain state by the amplifier 10 and calculates and outputs the displacement amount based on the received light amount signal. When the amount of light received from the measurement surface that is irradiating the object W with the measurement light greatly fluctuates and the level of the amount of received light signal exceeds a predetermined threshold (SP3-YES), FIG. As shown, a level over signal is output to the gain selection means 12 to lower the gain of the amplifier 10 by one stage from the current stage (SP
4). On the other hand, when the level of the light reception amount signal remains smaller than the predetermined threshold value (SP3-NO), the comparison process in SP3 is continuously performed via SP1 during the measurement period of the device under test W. I do.

As a result, when the level of the received light amount signal exceeds a predetermined threshold at the time A, the gain of the amplifier 10 is reduced by one stage from the current stage, as shown in FIG. The level of the received light amount signal becomes a level that can be processed (below a threshold) by the calculating means 11. Thereafter, the gain of the amplifier 10 is reduced by this one stage. However, when the level of the received light amount signal exceeds the threshold value again at a later time,
By outputting the level over signal, the amplifier 10 is set to a gain one stage lower (two stages lower than the initial stage).

As described above, the processing means 2 sets the highest gain in the initial state of the gain, and the gain of the amplifier 10 is increased by 1 every time the received light amount signal greatly changes during the measurement of the device under test W and exceeds the threshold value. Since the step can be lowered, the arithmetic means 11 can always perform the arithmetic processing accurately. This is because the control is such that the light reception amount is not saturated and the light reception amount is as high as possible without being affected by noise. By the way, since the threshold value is set to the level immediately before reaching the saturation level, the fluctuation of the level of the received light amount signal input to the calculating means 11 does not affect the calculation processing of the displacement amount.

In the above embodiment, the configuration in which the gain selecting means 12 variably controls the gain of the amplifier 10 in the processing means 2 has been described. In addition, the configuration in which the gain of the pre-amplifier 7 in the sensor head 1 is variably controlled. The configuration may be such that the gains of the amplifiers 7 and 10 are both variably controlled.

Next, FIG. 5 is a block diagram showing a second embodiment of the displacement measuring device of the present invention. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the above-described embodiment, the configuration in which the gain of the amplifier 10 that amplifies the output of the light receiving element 6 is changed, but in the present embodiment, the light source 4 of the sensor head 1 is changed.
Variably controls the projection power of the measurement light. Amplifier 1
The gain of 0 is fixed.

In the above configuration, the calculating means 11 outputs a level over signal to the light emitting power selecting means 20 when the level of the received light quantity signal exceeds a predetermined threshold value, The selection means 20 controls the light source drive circuit 5 to lower the projection power by one stage from the current stage. As described above, even in the configuration in which the light projection power selecting means 20 is provided in place of the above-described gain selecting means 12 and the control for gradually lowering the light projection power of the light source 4 is performed, the first
As in the embodiment, the calculation means 11 can always perform a stable calculation process of the displacement amount without the light receiving level being saturated.

Next, in addition to the variable control of the gain and the projection power described in the above embodiment, a configuration in which a threshold value is set for the output of the amplifier 10 and the level of the received light amount signal input to the calculating means 11 is variably controlled. It may be. FIG. 6 illustrates this third
FIG. 3 is a block diagram illustrating an internal configuration of a calculation unit 11 according to the embodiment. In the figure, the gain of the amplifier 10 is fixed. The amplified received light amount signal output from the amplifier 10 is subjected to A / D conversion by the A / D converter 30,
Multiplier 31 multiplies by coefficient α. Thereafter, the sum of the pair of received light amount signals is obtained by the adding means 32, and the subtracting means 33
The difference is obtained by At the output of the adding means 32, a signal corresponding to the amount of received light is obtained, and at the output of the subtracting means 33, a corresponding signal corresponding to the amount of received light and the position of the light spot is obtained. The displacement calculating means 34 calculates the displacement of the workpiece W based on these outputs.

In the threshold setting means 35, a threshold indicating a predetermined amount of received light is set. Input level variable means 36
Is based on the output of the adding means 32 (the level of the amount of received light) and the threshold value set by the threshold value setting means 35.
(Sum output) to calculate a coefficient α. This coefficient α is
The value is set in the multiplier 31. Thus, the level of the received light amount signal output from the amplifier 10 is adjusted and output by the coefficient α set by the multiplier 31. Also in the above configuration, when the level of the received light amount signal is higher than the threshold value in the threshold value comparison process of SP3 based on the flowchart of FIG.
Α set to 1 is set to 1 or less to vary the level of the received light amount signal. The stage when the amount of received light signal varies is a stage corresponding to the value of the coefficient α. As the value of the coefficient α is finely calculated, it can be varied continuously rather than stepwise.

The variable gain of the amplifier 10 described in the first embodiment, the variable projection power of the light source 4 described in the second embodiment, and the variable level of the received light signal in the third embodiment are used. It goes without saying that a configuration in which control is performed by switching between the two or a combination of control is possible. In each of the above embodiments, when the level of the received light amount signal exceeds the threshold, the gain selection unit 12 or the projection power selection unit 20 outputs the level over signal shown in FIG. The light source 4 is configured to vary the gain and the projection power by the input of the single pulse. However, the present invention is not limited to this. For example, the gain of the amplifier 10 or the projection power of the light source driving circuit 5 is directly changed to a predetermined stage. And outputs a control signal to the amplifier 1 based on the control signal.
A configuration in which the gain of 0 and the projection power of the light source 4 are changed may be adopted.

When the object to be measured W rotates at high speed, the level of the received light amount signal fluctuates greatly in a short time. According to the above configuration, the gain or the projected power is reduced by one step only when the level exceeds. Since the lowering control is performed, the displacement amount can always be obtained stably. The present invention is not limited to such a high-speed rotation, and it goes without saying that the same effect can be obtained by using the object to be measured W in which the amount of light received from the measurement surface changes greatly.

[0035]

According to the displacement measuring apparatus of the present invention, the level of the received light signal input to the calculating means for calculating and outputting the displacement of the object is detected, and the level of the received light is measured during the measurement of the object. Each time the level of the amount signal exceeds a predetermined threshold value, a means for performing control for lowering the level of the signal used for calculating the displacement amount is provided. Even if the scattering state changes greatly and the level of the received light amount signal changes greatly, the input to the calculating means does not saturate, and the calculation of the displacement amount can be executed stably.
Also, the same effect can be obtained by a configuration in which the gain selecting means performs control to lower the gain of the amplifier based on the level of the received light amount signal input to the calculating means. The same effect can be obtained even when the light emitting power selecting means controls the light emitting power of the light source driving circuit to lower the light emitting power based on the level of the received light amount signal input to the arithmetic means. As described above, by controlling the gain, the projection power, or the level of the received light amount signal, the signal level can be obtained as high as possible without saturating the level of the received light amount signal and without being affected by noise. The displacement amount can be accurately obtained. In particular, when the measurement surface of the object to be measured moves at high speed, for example, when the measurement surface rotates at high speed, even if the level of the received light amount signal fluctuates greatly in a short time, it can cope with this, and the calculation of the displacement amount is continued. Then, it can be performed in a stable state. By the way, the gain control, the light projection power control, and the level control of the signal used for the calculation of the displacement can be switched to any one, or the same effect can be obtained even if both are executed simultaneously. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a displacement measuring device according to the present invention.

FIG. 2 is a diagram showing a setting screen at the start of measurement.

FIG. 3 is a flowchart illustrating a gain adjustment operation of a processing unit in a semi-automatic mode.

FIG. 4 is a timing chart showing signals of respective parts of the processing means.

FIG. 5 is a block diagram showing a second embodiment of the displacement measuring device of the present invention.

FIG. 6 is a block diagram showing an internal configuration of a calculation unit according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sensor head, 2 ... Processing means, 4 ... Light source, 5 ... Light source drive circuit, 6 ... Light receiving element, 7 ... Amplifier, 10 ... Amplifier
11 arithmetic operation means, 12 gain selection means, 14 mode selection means, 20 light projection power selection means, 36 input level variable means.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinji Hamano 5--10-27 Minamiazabu, Minato-ku, Tokyo Anritsu Corporation

Claims (9)

[Claims] 1. A non-contact type displacement measuring device which irradiates a measuring surface of an object to be measured with a measuring light of a light source and receives a reflected light thereof by a light receiving element to measure a displacement amount of the measuring surface. Calculating means for calculating and outputting the displacement of the object based on the received light signal; detecting the level of the received light signal input to the calculating means to detect the level of the received light signal during the measurement of the measured object A means for performing control for lowering the level of a signal used for calculating a displacement amount in response to every time a value exceeds a predetermined threshold value. 2. A non-contact type displacement measuring device which irradiates a measuring surface of an object with measuring light of a light source and receives a reflected light thereof by a light receiving element to measure a displacement amount of the measuring surface. An amplifier for amplifying and outputting the received light amount signal and having a variable gain; (10) calculating means for calculating and outputting a displacement amount of the device under test based on the received light amount signal amplified by the amplifier; and The gain of the amplifier is variably controlled based on the level of the received light amount signal input to the means, and each time the level of the received light amount signal exceeds a predetermined threshold during the measurement of the device under test, A displacement measuring device, comprising: a gain selecting means (12) for performing control to lower the gain of the amplifier. 3. The amplifier (10) has a variable gain in a plurality of stages, and the gain selecting means (12) is configured to adjust the gain of the amplifier based on the level of the received light amount signal during measurement of the device under test. 3. The displacement measuring device according to claim 2, wherein control is performed to reduce the gain of the second stage to a corresponding stage. 4. The amplifier (10) has a variable gain in a plurality of stages, and the gain selecting means (12) adjusts the level of the received light amount signal to a predetermined threshold during the measurement of the device under test. 3. The displacement measuring apparatus according to claim 2, wherein control is performed to decrease the gain of the amplifier one step at a time in response to each of the steps. 5. A non-contact type displacement measuring device which irradiates a measuring surface of a measuring object with measuring light of a light source and receives a reflected light thereof by a light receiving element to measure a displacement amount of the measuring surface. A light source drive circuit (5) capable of changing the light projection power of the measurement light applied to the light source; and a calculating means (11) for calculating and outputting a displacement amount of the object to be measured based on a received light amount signal detected by the light receiving element. The light emitting power of the light source driving circuit is variably controlled based on the level of the received light amount signal input to the arithmetic means, and the level of the received light amount signal is set to a predetermined threshold during the measurement of the device under test. A projecting power selecting means (2) for controlling the projecting power of the light source driving circuit to decrease in response to every time it exceeds
0), and a displacement measuring device. 6. The light source drive circuit (5) is capable of changing the light projection power in a plurality of stages, and the light projection power selection means (20) is configured to control the light reception amount signal during the measurement of the device under test. 6. The displacement measuring apparatus according to claim 5, wherein control is performed to lower the projection power of the light source driving circuit to a corresponding stage based on the level of the light source driving circuit. 7. The light source drive circuit (5) has a variable light projection power in a plurality of stages, and the light projection power selection means (20) controls the light reception signal during measurement of the device under test. 6. The displacement measuring apparatus according to claim 5, wherein control is performed to lower the projection power of the light source drive circuit by one step each time the level exceeds a predetermined threshold. 8. A non-contact type displacement measuring device which irradiates a measuring surface of an object to be measured with measuring light of a light source and receives a reflected light thereof by a light receiving element to measure a displacement amount of the measuring surface. Calculating means for calculating and outputting a displacement amount of the object based on the received light signal; detecting a level of the received light signal input to the calculating means to detect the level of the received light during measurement of the measured object; Displacement measuring means (36) for performing control to lower the level of the received light amount signal input to the calculating means in response to each time the signal level exceeds a predetermined threshold value. apparatus. 9. The variable gain control of the amplifier (10) by the gain selecting means (12) according to claim 2, and the light projection power selecting means (20) according to claim 5.
And a variable level of a received light amount signal input to the calculating means (11) by the input level varying means (36) according to claim 8. Displacement measuring device characterized in that it can be switched to one or both are executed simultaneously.