JP3927306B2 - Displacement measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a displacement measuring apparatus that measures a displacement amount of an object to be measured in a non-contact manner, and more particularly, to a displacement measuring apparatus that can cope with a large variation in the amount of received light and can improve measurement accuracy.
[0002]
[Prior art]
The displacement measuring apparatus can irradiate the measurement object with measurement light and measure the displacement amount of the measurement surface of the measurement object based on the light receiving state of the light receiving element. This displacement measuring device irradiates the measurement surface of the object to be measured on the principle of triangulation, for example, and the displacement of the measurement surface of the object to be measured based on the light receiving position of the reflected light detected on the light receiving surface of the position sensor. Measure the amount.
[0003]
In such a displacement measuring apparatus, the amplification factor (gain) of the processing circuit is set in a plurality of stages so that the received light amount (level) is suitable for the detection process in the light receiving element that receives the reflected light and the subsequent processing circuit. Continuously variable setting is possible.
Recently, the processing circuit is provided with an AGC function, and when the amount of received light is large, the gain is lowered to prevent signal saturation in the processing circuit, while when the amount of received light is small, the gain is reduced to reduce the noise component. The process to raise is made.
It should be noted that this gain is such that the received light amount is as high as possible because the received light amount is not saturated and is not affected by noise in either case of manual or automatic variable using the AGC function. It is desired to set.
[0004]
[Problems to be solved by the invention]
The optimum gain according to the displacement state of the measurement surface of the object to be measured is a configuration that must be selected manually, and the measurement surface state of the object to be measured will change even if measurement is started with the gain once set. When the amount of received light increases, the signal may be saturated. At this time, there is a problem that the amount of displacement cannot be measured accurately.
[0005]
Even when the AGC function that automatically changes the gain of the processing circuit according to the change in the amount of received light is used, if the amount of received light changes greatly in a short time (for example, the frequency of change in the amount of received light approaches the modulation frequency). In other words, the received signal is saturated and the measurement cannot be performed.
The above state occurs when the scattering state of the measurement surface of the object to be measured changes greatly. For example, when the object to be measured rotates to measure the displacement amount of the measurement surface, the object to be measured rotates at a high speed. In some cases, the problem of being unable to measure has occurred.
[0006]
The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a displacement measuring apparatus that can accurately measure the amount of displacement without being affected by fluctuations in the amount of light received during measurement of the object to be measured. It is said.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a displacement measuring apparatus according to the present invention radiates measurement light from a light source onto a measurement surface of an object to be measured and receives the reflected light by a light receiving element. In a non-contact type displacement measuring device that measures the amount of displacement,
A pair of amplifiers 10 and 10 for amplifying and outputting a received light amount signal of the light receiving element with a fixed gain during measurement of the object to be measured ;
A pair of multipliers 31 for multiplying a received light amount signal amplified by the pair of amplifiers by a predetermined coefficient α; an adding means 32 for obtaining a sum of a pair of received light amount signals from the pair of multipliers; A subtracting unit 33 for obtaining a difference between a pair of received light amount signals from the multiplier, a threshold setting unit 35 for setting a threshold value indicating a predetermined received light amount, and a level of the received light amount signal during measurement of the object to be measured. Input level variable means 36 for setting the coefficient calculated by dividing the threshold value by the output of the adding means corresponding to each time the threshold value set in the threshold setting means is exceeded, and the adding means And a displacement amount calculating means 34 for calculating and outputting a displacement amount of the object to be measured based on the output of the subtracting means ,
It is characterized by comprising.
[0008]
The invention according to claim 2 is the displacement measuring apparatus according to claim 1,
A light source driving circuit 5 capable of stepwise changing the projection power of the measurement light applied to the object to be measured;
The gain of the pair of amplifiers 10 and 10 is variably controlled stepwise based on the level of the received light amount signal input to the arithmetic means, and the received light amount signal level is predetermined during measurement of the object to be measured. A gain selecting means 12 for controlling the gain of the pair of amplifiers to be decreased step by step from the highest gain in the initial gain state corresponding to each time the threshold value is exceeded;
The projection power of the light source driving circuit is variably controlled stepwise based on the level of the received light amount signal input to the arithmetic means, and the received light amount signal level is set to a predetermined level during measurement of the object to be measured. And a projection power selection means 20 for performing control to lower the projection power of the light source driving circuit one step at a time from the current stage corresponding to each time the threshold is exceeded,
The gain selection unit 12 performs variable gain control of the pair of amplifiers, the light projection power selection unit 20 performs light projection power control of the light source driving circuit, and the input level variable unit 36 inputs the pair of multipliers 31. is the level variable amount of received light signals, any one to switch freely in, or both, characterized in that it is performed at the same time.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing a first embodiment of the displacement measuring apparatus of the present invention.
As shown in the figure, the displacement measuring apparatus is roughly composed of 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 are provided to irradiate the measuring object W with measuring light such as laser light, and the reflected light from the measuring object W is received by a light receiving element (for example, It is detected by the position sensor 6 and moves on the light receiving element 6 according to the distance between the sensor head and the object W to be measured.
A signal corresponding to the position and light intensity of the image of the light spot on the light receiving element 6 is obtained, amplified by the amplifier 7 at a predetermined amplification factor, and output to the processing means 2.
[0018]
The processing means 2 is provided with an amplifier 10 at the input stage, amplifies the received light amount signal with a predetermined amplification factor, and outputs it to the arithmetic means 11.
The amplifier 10 has a variable amplification factor (gain) and can change the gain stepwise. At the highest gain, the amplification factor is 100%, and the gain is increased in each stage (for example, 100%, 90%, 80%, 70%,... Etc.).
[0019]
The calculating means 11 calculates the displacement amount of the measurement surface of the workpiece W based on the received light amount signal after gain adjustment, and outputs this displacement amount to the outside. The calculation result including the displacement amount may be stored and stored in a storage means (not shown). In addition, a threshold for determining the input light reception amount (level) is set in the calculation means 11, and a level over signal is output when the level of the light reception amount signal exceeds the threshold.
This threshold value 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 calculation means 11.
[0020]
This gain is controlled to be switched by the gain selection means 12. The gain selection unit 12 functions when the measurement mode is set to a semi-automatic mode, which will be described later. Each time a level over signal is input from the calculation unit 11, the gain (amplification factor) of the amplifier 10 is currently set. Switching control is performed to lower the level by one step.
Further, when the semi-automatic mode is reset by a reset function (not shown), the amplifier 10 is operated at the highest gain when measuring a new workpiece W, and each time the level over signal is input, the amplifier 10 is step by step. Decrease the gain.
Further, when a level over occurs, the received light amount signal may be multiplied by a predetermined coefficient α to lower the level (details will be described later in the third embodiment).
[0021]
The mode selection unit 14 selects and sets either a manual setting mode for manually setting the gain of the amplifier 10 or a semi-automatic mode for causing the gain selection unit 12 to function. The mode selection unit 14 is selected and set by an operator's switch operation or the like. .
[0022]
FIG. 2 is a diagram showing a setting screen at the start of measurement. As shown in the figure, the processing means 2 is provided with a CRT or liquid crystal display (not shown), and a screen for various settings necessary for measuring the workpiece W is displayed on the display screen.
Among them, 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” and “manual” modes are displayed for the gain of the amplifier 10, and one of them is designated. Can be selected. This selection is performed 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.
The “semi-automatic” mode may be selected depending on whether the signal level input to the “semi-automatic” mode selection pin of the connector provided in the apparatus is high or low.
[0023]
The computing means 11, the gain selecting means 12, and the mode selecting means 14 can be configured by hardware such as a CPU, ROM, RAM, and a semi-automatic mode control processing program stored in the ROM.
[0024]
Next, the operation content of the semi-automatic mode configured as described above will be described. FIG. 3 is a flowchart showing the gain adjustment operation of the processing means 2 in the semi-automatic mode, and FIG. 4 is a timing chart showing signals of each part of the processing means 2.
The processing means 2 resets the gain at the start of measurement of the object to be measured (SP1-YES). When newly measuring the amount of displacement of the workpiece W, the gain of the amplifier 10 is reset (SP1-YES) by specifying 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 gain 100%) (SP2).
[0025]
Next, measurement of the displacement amount of the workpiece W is started. When the sensor head 1 irradiates the measurement object W with the measurement light, the light receiving element 6 receives the reflected light and receives a received light amount signal at a level corresponding to the distance from the measurement object W (FIG. 4A). )) Is output to the processing means 2.
Then, the calculation means 11 of the processing means 2 amplifies the received light amount signal in the gain initial state by the amplifier 10 and calculates and outputs the displacement amount based on the received light amount signal, but is measured at time A in FIG. When the amount of light received from the measurement surface that irradiates the measurement light to the object W greatly fluctuates and the level of the light reception amount signal exceeds a predetermined threshold (SP3-YES), FIG. As shown, a level over signal is output to the gain selecting means 12 to lower the gain of the amplifier 10 by one step from the current stage (SP4).
On the other hand, when the level of the received light amount signal remains smaller than a predetermined threshold value (SP3-NO), the comparison processing in SP3 is continuously executed via SP1 during the measurement period of the workpiece W. To do.
[0026]
As a result, when the level of the received light amount signal exceeds a predetermined threshold value at time A, the gain of the amplifier 10 is lowered by one step from the current stage. Therefore, as shown in FIG. Is a level that can be processed by the computing means 11 (below the threshold value). Thereafter, the gain of the amplifier 10 is lowered by one stage. When the level of the received light amount signal exceeds the threshold value at a later time, a level over signal is output and the amplifier 10 is further lowered by one stage. The gain is set to 2 steps below the initial state.
[0027]
In this way, the processing means 2 sets the highest gain in the initial gain state, and the gain of the amplifier 10 is decreased by one step each time the received light amount signal greatly fluctuates during measurement of the workpiece W and exceeds the threshold value. Due to the configuration, the calculation means 11 can always perform accurate calculation processing. This is because the received light amount is not saturated and the control can obtain the highest received light amount without being affected by noise. By the way, since the threshold value is set to a level immediately before reaching the saturation level, fluctuations in the level of the received light amount signal input to the calculating means 11 do not affect the calculation processing of the displacement amount.
[0028]
In the above-described embodiment, the configuration in which the gain selection unit 12 variably controls the gain of the amplifier 10 in the processing unit 2 has been described. However, the gain selection unit 12 may be configured to variably control the gain of the front-stage amplifier 7 in the sensor head 1. Further, the gains of these amplifiers 7 and 10 may be variably controlled.
[0029]
Next, FIG. 5 is a block diagram showing a second embodiment of the displacement measuring apparatus of the present invention. In the embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the 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 has been described. However, in the present embodiment, the light projection power of the measurement light from the light source 4 of the sensor head 1 is variably controlled. The gain of the amplifier 10 is fixed.
[0030]
In the above configuration, the calculation means 11 outputs a level over signal to the light projection power selection means 20 when the level of the received light amount signal exceeds a predetermined threshold value, and the light projection power selection means 20. Controls the light source drive circuit 5 to lower the light projection power by one step from the current level.
As described above, in the configuration in which the light projection power selection unit 20 is provided instead of the gain selection unit 12 and the light projection power of the light source 4 is controlled to be lowered stepwise, the light reception level is the same as in the first embodiment. Thus, the calculation means 11 can always perform stable calculation processing of the displacement amount without saturating.
[0031]
Next, not only the variable control of the gain and the light projection power described in the above embodiment, but also a configuration in which a threshold value is set for the output of the amplifier 10 to variably control the level of the received light amount signal input to the calculation means 11. .
FIG. 6 is a block diagram showing the internal configuration of the computing means 11 in the third embodiment.
In the figure, the gain of the amplifier 10 is fixed. The amplified received light amount signal output from the amplifier 10 is A / D converted by the A / D converter 30 and then multiplied by the coefficient α by the multiplier 31. Thereafter, the sum of the pair of received light amount signals is obtained by the adding means 32 and the difference is obtained by the subtracting means 33. A signal corresponding to the amount of received light is obtained at the output of the adding means 32, and a signal corresponding to the amount of received light and the position of the light spot is obtained at the output of the subtracting means 33. The displacement amount calculating means 34 obtains the displacement amount of the workpiece W based on these outputs.
[0032]
The threshold value setting means 35 is set with a threshold value indicating a predetermined amount of received light. The input level varying means 36 calculates (threshold / sum output) based on the output (level of received light amount) of the adding means 32 and the threshold set in the threshold setting means 35 to calculate the coefficient α. This coefficient α is set in the multiplier 31.
As a result, 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 received light amount signal level is higher than the threshold value in the threshold value comparison process of SP3 based on the flowchart shown in FIG. 3, α set in the multiplier 31 is set to 1 or less, and the received light amount signal Change the level.
The step of changing the received light amount signal corresponds to the value of the coefficient α, and can be continuously changed instead of stepwise as the value of the coefficient α is finely calculated.
[0033]
By the way, it is switched to any one of the variable gain of the amplifier 10 described in the first embodiment, the variable projection light power of the light source 4 described in the second embodiment, and the variable level of the received light amount signal in the third embodiment. Needless to say, it can be configured to be controlled in combination or controlled in combination.
Further, in each of the above embodiments, the gain selection unit 12 or the light projection power selection unit 20 outputs the level over signal shown in FIG. 4B as a single pulse when the level of the received light amount signal exceeds the threshold value and outputs the amplifier 10. The light source 4 is configured to change the gain and the light projection power by the input of this single pulse. However, the present invention is not limited to this. For example, the gain of the amplifier 10 or the light projection power of the light source driving circuit 5 is directly changed to a predetermined stage. The control signal may be output, and the gain of the amplifier 10 and the light projection power of the light source 4 may be changed based on the control signal.
[0034]
When the workpiece W rotates at a high speed, the level of the received light amount signal fluctuates greatly in a short time. However, according to the above configuration, the gain or the projection power is controlled to be lowered by one step only when the level is over. As a result, the amount of displacement can always be obtained stably. Needless to say, the present invention is not limited to such high-speed rotation but can be used for the workpiece W in which the amount of light received from the measurement surface changes greatly.
[0035]
【The invention's effect】
According to the displacement measuring apparatus of the present invention, the threshold value is calculated by dividing the threshold value by the output of the adding means every time the level of the received light amount signal exceeds the threshold value set in the threshold value setting means during measurement of the object to be measured . Since the coefficient is set in a pair of multipliers and the level of the received light amount signal output from the amplifier is adjusted by the coefficient set in the pair of multipliers, when the received light amount signal level is higher than the threshold value, The coefficient set for the pair of multipliers is set to 1 or less, and the level of the received light amount signal can be varied. Thus, even when the scattering state of the measurement surface changes greatly during measurement of the object to be measured and the level of the received light amount signal fluctuates greatly, the input to the calculation means is not saturated and the calculation of the displacement is stably performed. it is possible. Their to, variable time steps the amount of received light signal becomes a phase corresponding to the value of the coefficient, in accordance with finely calculate the value of the coefficient, it becomes possible to continuously variable rather than gradual.
Further, the level control of the signal used for calculating the displacement amount and the highest level in the initial gain state corresponding to every time the level of the received light amount signal input to the calculation means during measurement of the object to be measured exceeds a predetermined threshold value. The gain control for decreasing the gain of the amplifier for which the gain is set step by step, and the light projection power selection means based on the level of the received light amount signal input to the calculation means, If the projection power control, which is lowered by one step from the stage, can be switched to any one or both at the same time, the level of the received light amount signal will not be saturated, and as much as possible without being affected by noise Since a high signal level can be obtained, 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 in a short time, this can be dealt with, and the displacement amount calculation continues. It will be possible to remain in a stable state.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of a displacement measuring apparatus of the present invention.
FIG. 2 is a diagram showing a setting screen at the start of measurement.
FIG. 3 is a flowchart showing a gain adjustment operation of a processing unit in a semi-automatic mode.
FIG. 4 is a timing chart showing signals at various parts of the processing means.
FIG. 5 is a block diagram showing a second embodiment of the displacement measuring apparatus of the present invention.
FIG. 6 is a block diagram showing an internal configuration of a calculation unit in the 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 ... Calculation means, 12 ... Gain selection means, 14 ... Mode selection means, 20 ... Projection power selection means, 36 ... Input level variable means.

Claims (2)

In a non-contact type displacement measuring device that irradiates the measurement surface of the object to be measured with the measurement light of the light source and receives the reflected light by the light receiving element to measure the displacement amount of the measurement surface.
A pair of amplifiers (10, 10) for amplifying and outputting the received light amount signal of the light receiving element with a fixed gain during measurement of the measured object;
A pair of multipliers (31) for multiplying the received light amount signals amplified by the pair of amplifiers by a predetermined coefficient (α), and addition means (32) for calculating the sum of the pair of received light amount signals from the pair of multipliers ), A subtracting means (33) for obtaining a difference between a pair of received light amount signals from the pair of multipliers, a threshold value setting means (35) for setting a threshold value indicating a predetermined received light amount, and the measurement object A coefficient calculated by dividing the threshold value by the output of the adding means is set in the pair of multipliers corresponding to each time the level of the received light amount signal exceeds the threshold value set in the threshold setting means during measurement. A calculation means (11) including an input level variable means (36), and a displacement amount calculation means (34) for calculating and outputting a displacement amount of the device under test based on outputs of the addition means and the subtraction means;
A displacement measuring apparatus comprising: The displacement measuring device according to claim 1,
A light source drive circuit (5) capable of stepwise changing the light projection power of the measurement light applied to the object to be measured;
The gain of the pair of amplifiers (10, 10) is variably controlled stepwise based on the level of the received light amount signal input to the arithmetic means, and the level of the received light amount signal during the measurement of the object to be measured. A gain selection means (12) for performing a control to lower the gain of the pair of amplifiers one step at a time from the highest gain in the initial gain state corresponding to each time when exceeds a predetermined threshold;
The projection power of the light source driving circuit is variably controlled stepwise based on the level of the received light amount signal input to the arithmetic means, and the received light amount signal level is set to a predetermined level during measurement of the object to be measured. And a projection power selection means (20) for performing control to lower the projection power of the light source driving circuit by one step from the current level in response to each time the threshold is exceeded,
Before the gain variable control of the pair of amplification device according Kige in selection means (12), a light projecting power control before the light source driving circuits by Kito light power selection means (20), the entering force level varying means The displacement measuring device is characterized in that it can be switched to any one of the variable level of the received light amount signal input to the pair of multipliers (31 ) according to (36), or both can be performed simultaneously.

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