JPH01245110A - Optical scanning type displacement sensor - Google Patents

Abstract

PURPOSE:To curtail the memory capacity by providing a linearity correcting means for calculating a second distance measuring signal being proportional to a displacement of a distance to an object to be detected in accordance with a first distance measuring signal. CONSTITUTION:A light beam P from a projecting means 1 is scanned on the surface of an object to be detected 2 by a deflecting means 7. Subsequently, a reflected light beam R from the object 2 is condensed by an optical system 3 for a light receiving. Next, in a position detecting means 4 provided on the condensing surface of the optical system 3, a pair of position signals IA, IB opposed to each other corresponding to a position of a condensing spot S for moving in the condensing surface in accordance with a distance to the object 2 are outputted. Also, in an arithmetic means, the first distance measuring signal L0 being proportional to a position variation of the spot S is calculated, based on the output of the means 4. Subsequently, in a linearity correcting means, by setting a displacement DELTAl of a distance to the object 2 as a variable, a value of an inverse function of a function L0 (DELTAl) for calculating the signal L0 is calculated from the signal L0, the signal L0 is multiplied by a signal which has added a constant value to this inverse function, and the second distance measuring signal L being proportional to the displacement DELTAl to the object 2 is calculated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a visual sensor for robots that perform welding, deburring, etc., or a displacement sensor for FA used as a sensor for detecting product defects and measuring dimensions. It is related to
In particular, the present invention relates to an optical scanning displacement sensor that measures the two-dimensional shape of the surface of a detected object using an optical triangulation method.

[Conventional technology] In recent years, factory FA (factory automation)
In order to meet these demands, there is a need for displacement sensors that can position objects and recognize the presence or absence of objects using information about the distance to the object. Displacement sensors that perform distance detection in a non-contact manner include those that optically measure the distance to an object to be detected, and those that use a triangulation method have been put into practical use because of their relatively simple configuration.

Generally, as shown in FIG. 2, this type of displacement sensor irradiates a detected object 2 with a light beam emitted from a light projecting means 1 equipped with a semiconductor laser, a light emitting diode, etc., and receives the diffusely reflected light. The light is focused by the light receiving optical system 3, and the light spot S formed on the light collecting surface of the light receiving optical system 3 is focused by the PSD.
The position detecting means 4 is configured to receive the light.

The position detection means 4 is an element capable of obtaining an electric signal corresponding to the position of the focused spot S, and based on this electric signal, the distance to the detected object 2 is calculated by a triangulation method. That is, as shown in FIG. 1, when the position of the detected object 2 changes from A to B to C and the distance between the light projecting means 1 and the detected object 2 changes, the light receiving surface of the position detecting means 4 changes. Since the position of the condensed spot S to be formed moves from a to b to c on the paper surface, by using a one-dimensional position detection means 4 that can detect the position on the paper surface, it is possible to detect the distance to the detected object 2. It is capable of detecting distance.

On the other hand, as shown in FIG. 3, it is conceivable to provide the light projection means 1 with a deflection means 7 such as a scanning mirror so as to scan the light beam on the surface of the object to be detected 2. The light projecting means 1 is
As shown in FIG. 4, an oscillation circuit 10 that generates a clock pulse that sets the timing of light emission, and a light emitting element 1 for light emission.
2 and a light projection optical system 13 consisting of a convex lens, the light emitted from the light projection light emitting element 12 is formed into a light beam by the light projection optical system 13, and the light is projected. It has become. This light beam is scanned over the object to be detected 2 in the X-axis direction by a deflection means 7 such as a scanning mirror. The reflected light diffusely reflected on the surface of the object to be detected 2 is collected by the light receiving optical system 3. The position detection means 4 disposed on the light condensing surface outputs device signals IA, I, which is composed of a zero position detection means 4 that outputs contradictory position signals IA, I8 corresponding to the position of the condensed spot S. A distance measurement signal in the Z-axis direction is obtained by processing B in the calculation means 5 as shown in FIG. can be obtained. On the other hand, a scanning angle signal Xm is obtained from the scanning mirror drive circuit 17. The two-dimensional shape on the scanning line on the surface of the object to be detected 2 can be detected using the ranging signal L0 and the scanning angle signal Xm.

The calculation means 5 shown in FIG. 4 includes light receiving circuits 21a and 21b which amplify the device signals (contradictory current signals IA and Ie) constituted by the position detection means 4 and convert them into voltage signals vA and v day, respectively. , level detection circuits 22a and 22b that check the output levels of the light receiving circuits 21a and 21b based on the output of the oscillation circuit 10 (determine the level in synchronization with the clock pulse), and outputs of the level detection circuits 22a and 22b ( A subtraction circuit 23 that performs subtraction of the position signal IA, I (hereinafter referred to as IA, I because it corresponds 1:1 to the level of the day) and a level detection circuit 22a.
, 22b, and a first signal (IA
Is) and a second signal (IA+IB) output from the adder circuit 24.
A Is)/(IA+Ia)) is output.

The distance measurement signal L0 described above has the following relationship with respect to the displacement distance Δl. As shown in FIG. 2, the distance p from the displacement measuring device to the detected object 2 is 1-1c+Δ1 (where 1c is the reference distance when the focused spot S is focused on the center point of the position detecting means 4). , and Δl is the displacement distance from the distance 1c), and the distance from the light receiving optical system 3 to the position detection means 4 is
F is the distance from the center point of the position detecting means 4 of the focused spot S of the reflected light R from the detected object 2 to Δ.
2. If the intersection angle of the optical axes of the light projecting means 1 and the light receiving optical system 3 is θ, then (fc/cosθ+Δ(cosθ)Δz=(Δ
t'sinθ)F, °, Δz=(tanθ)FΔ1/
(lc/eos2θ+Δ1) Here, if we set a=(tanθ)F and b=t'c/cos2θ, then Δz=aΔ1/(b+Δ1)...
・■, and the relationship between the movement distance Δ2 of the focused spot S and the displacement distance Δl of the detected object 2 is non-linear.

Here, the device signal IA constituted by the position detection means 4
, 1. If the effective length of the position detecting means 4 is 2 fp, the relationship between and the moving distance ΔZ is as follows: <I A I e)/(I A+ I e)=Δz
/1p - ■. As is clear from equations (1) and (2), the distance measurement signal L0 output from the calculation means 5 is the displacement distance Δ! However, it does not have a linear relationship with the displacement distance Δl. Therefore, in order to make the measurement accuracy of the displacement distance Δl the same regardless of distance changes (displacement magnitude), A linearity correction circuit 6 is provided,
It was necessary to make corrections so that a linear distance measurement signal could be obtained.

Next, as shown in FIG. 3, deflection means 7 such as a scanning mirror
Let us consider the movement of the condensed spot S on the light receiving surface of the position detecting means 4 when the light beam is scanned by the following. When the object to be detected 2 is a flat plate perpendicular to two axes, the condensed spot S draws a trajectory S' as shown in Fig. 4. In Fig. 4, the 2° axis corresponds to the X axis of the light beam. This is the axis in which the focused spot S moves in response to changes in the distance of the detected object 2 when the object is not being scanned in the same direction, and the X° axis is an axis perpendicular to the Z° axis on the focusing surface. It is. The locus S° of the focused spot S when scanning the light beam should be parallel to the X' axis on the position detection means 4 under ideal conditions, but in reality Due to the inclusion of various errors such as the twisting of the detection means 4 and the optical axis and the twisting of the projected beam, the shape is tilted with respect to the X' axis as shown in FIG. When the detected object 2 moves in the two-axis direction, this trajectory S' does not move parallel to the two-axis direction while maintaining a constant inclination, but due to the above-mentioned error, the detected object 2 moves in the two-axis direction. In other words, by scanning the light beam in the X-axis direction, the distance measurement signal L
There is an error in 0, and this error is a function of both X and 2. Therefore, as shown in FIG. 4, it is necessary to input the scanning angle signal Xl11 to the linearity correction circuit 6 to correct the error in the X-axis direction.

In addition, there are factors that cause linearity errors in the position detecting means 4 itself.Normally, the linearity error of the position detecting means 4 is caused by moving the focused spot S on the Z′ axis on the position detecting means 4 by Z°. When the distance measurement signal L0 is moved by Δ2 in the axial direction, the deviation from the straight line of the distance measurement signal L0 is evaluated. An example of this linearity error characteristic is shown by the solid line in FIG.

The linearity error characteristic when the movement axis of the focused spot S is shifted by × in the ×° axis direction on the position detection means 4 is as follows.
As shown by the broken line in FIG.
If the zero position detection means 4 has ideal characteristics, which is different from the characteristic when the focused spot S moves on the axis, the linearity error should be zero, but in reality, the resistance in the position detection means 4 The resistance value distribution of the layer is not uniform, and this appears as an error in the ranging signal L0. Since this non-uniform resistance value distribution also exists in the X'-axis direction of the position detection means 4, if the movement axis of the focused spot S differs, the linearity error characteristic will also change.

Conventionally, a linearity correction circuit 6 as shown in FIG. 7 has been used as means for correcting the various linearity errors as described above. Ranging signal.

and the scanning angle signal Xl11 are each sent to the A/D converter 61.
．． The signal is converted into a digital signal at 62 and input to the CPU 63. The CPU 63 reads out correction value data from the memory 64 according to the input ranging signal L0 and scanning angle signal Xm. The memory 64 stores correction value data for linearity correction of the ranging signal L0 and a scanning angle signal Xs.
The correction value data for correcting the linearity error in the X-axis direction is the distance measurement signal. and scanning angle signal Xm are stored in advance in a matrix format corresponding to the respective values. The CPU 63 corrects the input data using the correction value data read from the memory 64 and sends the corrected data to the D/A converter 65 . The D/A converter 65 converts the digital signal output from the CPU 63 into an analog signal.
Output as a distance measurement signal after linearity correction.

[Problems to be Solved by the Invention] However, in the case of the conventional example described above, in order to increase the resolution, it is necessary to increase the storage capacity of the memory 64. For example, in order to obtain a resolution of 1/4000 of full scale in the two-axis direction and a resolution of 1/1000 of full scale in the x-axis direction, 4.000,000 correction value data must be stored in the memory 64. must be, also,
Since it is necessary to set the optimal correction value individually according to the variation in parts, it is necessary to create a number of correction value data for each device according to its resolution during adjustment, which increases the adjustment cost significantly. This made it unsuitable for mass production because it took time to adjust.

The present invention has been made in view of these points, and its purpose is to reduce the storage capacity of correction value data for linearity correction and to facilitate adjustment work. An object of the present invention is to provide an optical scanning displacement sensor.

[Means for Solving the Problems] In order to solve the above problems, the optical scanning displacement sensor according to the present invention applies a light beam to the surface of the detected object 2, as shown in FIGS. 1 to 4. A light projecting means 1 for projecting light P, a deflecting means 7 for scanning the light beam P on the surface of the detected object 2, and a light receiving optical system for condensing the reflected light R of the light beam P by the detected object 2. 3, and a pair of contradictory position signals I A corresponding to the position of a condensing spot S, which is disposed on the condensing surface of the light receiving optical system 3 and moves within the condensing plane according to the distance to the detected object 2. , 1. a calculation means 5 that calculates a first distance measurement signal L0 proportional to a change in the position of the focused spot S based on the output of the position detection means 4; and a calculation means 5 that calculates the distance to the detected object 2. The displacement Δl of the first
The function to calculate the ranging signal L0 is the inverse function Δ of (Δ1)
1 (Lo) as the first ranging signal. A signal obtained by adding a constant value to the value of this inverse function Δ1 (Lo) is multiplied by the first ranging signal L0 to obtain a second signal proportional to the displacement Δl of the distance to the detected object 2. The linearity correction means 6 calculates the distance measurement signal.

[Effect] The principle of the present invention will be explained below using mathematical formulas.

From the 0.0 formula, the distance measurement signal is obtained. can be expressed as . In other words, the ranging signal L0 is the function L0(
Δ1), this ■formula is Δ! Solving for □−L
0 p and Δl is a function of Lo. This function ΔN(L,
) is an inverse function of the function L0 (Δ1) shown by equation (2).

Furthermore, by adding a constant S to this Δ1(Lo), α(L
A correction value of o)=Δ1(L,)+b...■ is determined. This correction value α(Lo) can be theoretically determined from the value of the ranging signal L0. Multiplying the formula ■ by the formula ■ gives L=L,,・α(Lo) =−・Δl...■ p As shown in the formula 0, the distance measurement signal L0 is linearized and becomes a measurement proportional to Δl. A distance signal can be obtained.

In other words, the calculations of formula 0 and formula (2) are performed from the distance measurement signal L0 to obtain the correction value α (Lo), which is then used as the distance measurement signal.

Linearization is performed by multiplying by .

If there are no variations in the parts of each device and the constants a and b are as designed, complete linearization can be achieved with just this.

Next, a linearization method when there are component variations or assembly errors will be described. First, consider the linearity error in the Z-axis direction.

■From the formula, component variations and assembly errors are constant a.

It can be seen that this is related to b. Therefore, if the constants in the state of variation are a' and b', the equation (2) becomes as follows.

! p(b'+Δl) Now, let β be the correction value of constant S, and let γ be the correction value of constant a, and define each as the following equation.

β=b'-b γ=a/a'...■Here, multiplying both sides of the formula by α, β, and γ as follows, L = L O(α(L,)+β)・γ=-Δ!
. . ■p As shown in equation 0, the distance measurement signal L0 is linearized. In other words, the equations 0 and 0 are calculated from the distance measurement signal L0 to obtain a theoretical correction value α (Lo), and this correction value α (Lo) is added to a correction value determined by variations in individual devices. By adding β and γ and performing calculations such as equation 0, the linearity error in the Z-axis direction is corrected.

Next, consider the linearity error in the X-axis direction.

FIG. 5 shows the locus S' of the condensed spot S on the light receiving surface of the position detection means 4. When the light beam is scanned in this way, the distance measurement when the condensed spot S passes on two axes is The value is linearized by performing the operation of the 0 expression. Now, when the focused spot S on the 2° axis of the position detecting means 4 passes through the center of the position detecting means 4, Z is when the focused spot S moves by X in the X' axis direction.

Let the deviation in the axial direction be Ac(x), and 0 at x'=x
If the values of the constants a and b in the formula are TI and b, then the formula 0 becomes as follows.

1. '-L, +Ac(x) ip(b"+Δl) Here, the correction value of constant S is β(x), the correction value of constant a is γ(x), and β(x) = b" -b γ (x)=a/a” ...■.Here, α(L
o), β(x), r(x), A c(x), L = (L o' Ac(x)Hα(L
o)+β(X)+7(X)lp (b''+Δ!)a' = -Δl...@p As shown in equation 0, the distance measurement signal L0° is linearized.In other words, the distance measurement signal L0° is linearized. From the distance signal Lo' and the scanning angle signal Xm at that time, the distance measurement signal Lo''Lo'-A
Find c(x) and use this distance measurement signal. A theoretical correction value α(Lo) is obtained from the above, and a correction value β(×) determined by variations in individual devices is added to this correction value α(Lo).

By adding γ(x) and performing calculations such as equation 0, linearization in the Z-axis direction including the X-axis direction is performed.

[Example] Examples will be described below. The hardware configuration of the linearity correction circuit 6 in this embodiment is almost the same as that of the conventional example shown in FIG. 7, but as described above, the processing algorithm is different and the way the memory 64 is used is completely different. In other words, in the embodiment, as shown in FIG.
Only fp, b, β(x), γ(x), and Ac(x) are stored in the memory 64. Among these, a/1p and b are constants calculated based on design values, and β( ×), γ
(x) and Ac(x) are correction constants specific to each individual device. By performing calculations using these constants and following the flow shown in FIG. 1, a linearized distance measurement signal can be obtained.

These constants stored in memory 64 are independent of the resolution of the ranging signal. In other words, no matter how high the resolution is, the number of constants required for correction does not change.Therefore, there is no need to have millions of correction value data depending on the resolution as in the conventional example. , correction value β
(X), γ(x), Ac(x) are scanning angle signals Xll1
Therefore, the number of constants corresponding to the resolution of the scanning angle signal x11 is required.
Since the error caused by scanning in the axial direction is not so large, it is possible to compress the memory space by setting a constant for each appropriate section of the scanning angle signal Xm, taking into account errors in design and assembly. For example, 1/1000 of the scanning angle signal Xm
If the scanning angle signal X+n is divided into 100 sections and 100 correction constants are stored in each section, then
Memory space can be significantly compressed.

Furthermore, correction values β(x), γ(x), A
The adjustment work for c(x) can also be greatly reduced. As shown in Fig. 9, the displacement on the far side is Δ with respect to the reference pressure MIC.
IF, when the displacement on the short distance side is Δ1N, Δ1. =
When the detected object 2 is placed at a position where ΔIN...■ is established, that is, at a position equidistant from near and far, the magnitude of the distance measurement signal, LN, is equal as shown in the following equation when linearized correctly. Become.

l LFI = l LNI Here, since L p > O and L N < O, the above equation can be expressed as follows.

LF=-LN . . . By making use of this property, the adjustment work can be easily performed. Each of the distance measurement signals L p and L N is calculated as follows using the formula 0, L F = (LOF" - A c (x) l (αF
β(x))γ(x)L++=(LoN'-Ac(x)H
It can be expressed as ah+β(x)l r(x)...■. Substitute formula 0 into formula 0, eliminate γ(x),
Find β(×).

(Lop″-Ac(x)■αF+β(X))-(L o
N' -A c(x)■αN+β(X))...[Phase] In other words, using β(x) as found by the [Phase] formula, 0
By calculating the formula, the ranging signal L01 is linearized. In addition, the correct distance measurement signal at distance Δb is converted to LFT.
Then, the tilt correction value γ(×) is the scanning angle signal Xl1
1, it can be determined by ...O. By correcting the tilt using γ(x) thus obtained, a linearized ranging signal can be obtained.

Therefore, during adjustment, the origin is determined by placing a flat plate perpendicular to the optical axis at the reference distance 1c, and the correction value Ac(x) when the light beam is scanned is first determined, and from there, the equidistant distance on both far and near sides ΔlF = ΔlN The distance measurement signal for each scanning angle signal Xm when the flat plate is translated in parallel. p',
The correction value β(x) may be obtained from L ON' using the [phase] equation, and then the correction value γ(x) may be obtained using the 0 equation.

In this way, the correction values β(X) and γ(×) specific to each device are
and Ac(x), the target object 2 is moved twice and the data L, N', L for the scanning angle signal Xff1 are calculated.
All you need to do is take ap' and Ac(x) and then use the O formula to calculate β(x) and γ(x), which eliminates the need to collect millions of pieces of data in the conventional example. Compared to other methods, it is possible to reduce adjustment time and costs.

[Effects of the Invention] As described above, the present invention calculates, from the first ranging signal, the value of the inverse function of the interval for calculating the first ranging signal using the displacement of the distance to the detected object as a variable. , the signal obtained by adding a constant value to the value of this inverse function is multiplied by the first ranging signal to calculate the second ranging signal that is proportional to the displacement of the distance to the detected object. , to perform linearity correction, the first
All you need to do is memorize the constant value for calculating the theoretical correction value from the distance measurement signal.
Since it is not necessary to store a huge number of correction values corresponding to 1, there is an effect that the memory capacity can be significantly reduced.

In addition, a first correction value to be added to the first ranging signal, a second correction value to be multiplied by the inverse function, and a third correction value to be added to the constant value are determined for each scanning angle of the deflection means. Once set, variations in individual devices can be corrected with only a small number of correction values, and the first to third correction values can be calculated by performing simple measurements, making it possible to correct variations in individual devices using only a small number of correction values. Since it is not necessary to obtain all the correction value data corresponding to the resolution of 1=1 at the time of adjustment, it is possible to significantly reduce the adjustment cost.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the processing flow of the linearity correction means used in the present invention, FIG. 2 is a schematic configuration diagram of a conventional distance measuring optical system, FIG. 3 is a perspective view showing the overall configuration of the conventional example, and FIG. 4
The figure is a block circuit diagram of the signal processing circuit used in the conventional example, Figure 5 is an explanatory diagram of the same operation as above, Figure 6 is a diagram showing linearity error characteristics as above, and Figure 7 is a block circuit of the linearity correction circuit used in the above. FIG. 8 is an explanatory diagram showing the stored contents of the memory used in the present invention, and FIG. 9 is an explanatory diagram of the operation of the present invention. 1 is a light projecting means, 2 is an object to be detected, 3 is a light receiving optical system, 4
5 is a position detection means, 5 is a calculation means, 6 is a linearity correction circuit, and 7 is a deflection means.

Claims (2)

[Claims] (1) Light projecting means for projecting a light beam onto the surface of the detected object, deflection means for scanning the light beam on the surface of the detected object, and light receiving means for condensing the light reflected from the light beam by the detected object. outputs a pair of contradictory position signals corresponding to the positions of the light-condensing spots that are arranged on the light-converging surfaces of the light-receiving optical system and the light-receiving optical system and move within the light-converging plane according to the distance to the object to be detected. a position detection means; a calculation means for calculating a first distance measurement signal proportional to a change in the position of the focused spot based on the output of the position detection means; The value of the inverse function of the function that calculates the distance signal is calculated from the first ranging signal, and the signal obtained by adding a constant value to the value of this inverse function is multiplied by the first ranging signal to determine the detected object. An optical scanning displacement sensor comprising: linearity correction means for calculating a second distance measurement signal proportional to the displacement of the distance to the object. (2) A first correction value to be added to the first ranging signal, a second correction value to be multiplied by the inverse function, and a third correction value to be added to the constant value for each scanning angle of the deflection means. The optical scanning displacement sensor according to claim 1, wherein the optical scanning displacement sensor is set as follows.