JPS63108217A - Optical displacement measuring instrument - Google Patents

Abstract

PURPOSE:To facilitate adjusting operation for a correction constant for correcting the linearity of a distance measurement signal by forming an arithmetic means that the distance measurement signal is obtained by multiplying the sum of the correction constant and another proper constant by the rate of 1st and the 2nd signals. CONSTITUTION:The arithmetic means 5 is so formed as to obtain the distance measurement signal L corresponding to the displacement of distance l to a body X to be detected by multiplying the rate (IA-IB)/(AA+kIB) of a 1st signal (IA-IB) obtained by calculating the difference between a couple of position signals IA and IB and a 2nd signal (IA+kIB) obtained by multiplying one position signal IB by the correction coefficient (k) and adding those position signals. Here, C is a constant. Then, a linearity correcting means 6 is formed of a variable resistor VR which gives the position signal IB a (k)-fold gain. Consequently, the linearity adjustment is completed by making an adjustment once by using the correcting constant (k) and the adjustment time is shortened greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention is directed to a light beam projected onto a detection area from a light projecting means, which is reflected by an object to be detected. The present invention relates to a triangulation type optical displacement measuring device that receives light with a light receiving means and measures displacement of distance to a detected object within a detection area based on the output of the light receiving means.

(Background technology) Conventionally, this type of triangulation type optical displacement measuring device
As shown in FIGS. 2 and 3, the light projecting means 1 that projects the light beam P onto the detected object X includes an oscillation circuit 10 that generates a clock pulse that sets the light projection timing; Drive circuit 11 that drives the light emitting element 12 for projecting light
and a light projection optical system 13 consisting of a convex lens, and the light emitted from the light emitting element 12 is shaped into a light beam P by the light projection optical system 13 and projected onto the detection area. It has become. A light beam P generated by the object to be detected X is disposed laterally at a predetermined distance from the light projecting means
The light receiving optical system 3 that collects the reflected light R is formed of a convex lens. A pair of contradictory position signals I An I arranged on the light-condensing surface of the light-receiving optical system 3 and corresponding to the position of the condensing spot S (moving in the direction M in accordance with the distance l)
The position detecting means 4 that outputs the signal B is formed of, for example, a one-dimensional position detecting element (hereinafter referred to as PSD 4), and the position signals I A and I are contradictory current signals. The calculation means 5 which calculates the displacement of the distance l to the detected object
light receiving circuits 21m and 21b which amplify and convert n) into voltage signals vA and v, respectively, and a light receiving circuit 21m.

Level detection circuits 22a and 22b that check the output level of 21b based on the output of the oscillation circuit 10 (determine the level in synchronization with a clock pulse), and the level detection circuit 22
The output of m, 22b (corresponds 1:1 to the level of the position signals IA, IB, so in the following, IA, 1
．． a subtraction circuit 23 that performs subtraction of the outputs IA and I of the level detection circuits 22a and 22b; , and a division circuit 25 that calculates the ratio of the second signal (IA+IB) output from the addition circuit 24, and the distance measurement signal L from the division circuit 25.
11 (=(IA IB)/(IA+IB)) is output. In addition, instead of the PSD 4 described above, it is also possible to use two photodiodes arranged in series in the direction M (direction of movement of the focal spot S) and use the outputs of each photodiode as position signals IA and IB. Needless to say.

Here, this distance measurement signal L0 is the displacement distance Δ! The relationship is as follows. In other words, the distance #l from the displacement measuring device to the detected object X! l is 1=Ic+Δ1 (where lc is PSD4 where the condensed spot S is the position detection means)
is the distance when the light is focused on the center point of , and Δl is the distance 1
c), and from the light receiving optical system 3 to the PSD 4
F is the distance to F, the moving distance of the condensing spot S of the reflected light R from the detected object Then, <lc/cosθ+Δ1cosθ)Δ=(Δ1si
nθ)F,, Δx= (tanθ)FΔl/ (ic/
cos2θ+Δl) Here, if we set a=(tanθ)F and b=lc/cos”θ, then Δx=aΔ1/(b+Δ1)
,, -(1), and the relationship between the moving distance ΔX and the displacement distance Δl is non-linear.

Here, the device signal consisting of PSD4 ■^.

The relationship between IB and moving distance X is (I A I B) / (I An I
s)=Δx/19−(2). Therefore, as is clear from equations (1) and (2), the distance measurement signal output from the calculation means 5. is the displacement distance Δl
Although the signal includes information on the displacement distance Δl, 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 even if there is a distance change (displacement size), it is necessary to provide a linearity correction circuit 6 and perform correction so that a linear distance measurement signal is obtained. there were.

Conventionally, a digital correction circuit using a correction value memory has been proposed as the linearity correction circuit 6, but in order to improve the resolution, it is necessary to increase the storage capacity of the correction value memory. However, since it is necessary to individually set the optimum correction value depending on the variation in parts, the cost is significantly high and mass production has not been possible.

Furthermore, an analog linearity correction circuit 6 has been proposed that approximates the linearity by the number of lines. The linearity correction circuit 6 shown in FIG. 3(b) is formed by an operational amplifier OP, diodes D, ~D1, volumes VR, ~VR, and resistors R+, R2, and converts the distance measurement signal L0 into four polygonal lines. It performs linearity correction by approximation, and there are three breaking points, and six volumes VR,
~VR, adjustment is required. By the way, in such a conventional example, in order to reduce the correction error due to polygonal line approximation, it is sufficient to increase the number of polygonal lines, but when the number of polygonal lines is increased, the number of adjustment points increases significantly. This poses a problem in that the configuration becomes complicated, and the adjustment work becomes troublesome, increasing costs.

Therefore, conventionally, the distance measurement signal is L=(I A - I n)
It has been proposed to perform linearity correction by forming the calculating means 5 and changing the correction constant k so that /(IA+klB). In this case, the distance measurement signal is , and the condition for this equation to be linear is , so solving this gives . Therefore, if k is adjusted to this value, linearity correction This means that the correction error can theoretically be reduced to zero. In this case, there is only one adjustment location for linearity correction, which simplifies the configuration, and also simplifies adjustment work, facilitating mass production and reducing costs.

However, in this conventional example, when adjusting the correction constant k, while actually moving the detected object X, so that the distance measurement signal becomes linear with respect to the displacement distance Δl,
It is necessary to adjust k.

Specifically, as shown in Fig. 4, the adjustment should be made so that the linearity error (deviation from the straight line of the distance measurement signal) becomes zero when the detected object X is moved by ±Δ11 from the reference distance. However, the value of the distance measurement signal at each point changes continuously depending on the value of the correction constant, so when making adjustments, first set the correction constant, then adjust ±Δl from the reference distance. Measure the distance measurement signal when the detected object X is moved by , then reset the correction constant, and measure the distance measurement signal when the detected object X is moved. It was necessary to repeat a series of adjustment operations many times, making it difficult to shorten the adjustment time.

(Object of the invention) The present invention has been made in view of the above points, and
The purpose is to provide an optical displacement measuring device that allows easy adjustment of correction constants for linearity correction.

(Disclosure of the Invention) The optical displacement measuring device according to the present invention includes a light projecting means for projecting a light beam onto a detection area, and a light projecting means disposed at a predetermined distance on the side of the light projecting means. A light-receiving optical system that focuses the reflected light of the light beam from the sensing object, and a light-receiving optical system that is arranged on the focusing surface of the light-receiving optical system and moves within the focusing surface according to the distance to the sensing object. A position detecting means that outputs a pair of contradictory position signals corresponding to the position, a first signal obtained by adding and subtracting the pair of position signals output from the position detecting means, and one position signal or a pair of position signals. and a calculation means for calculating the ratio of the detected object to the second signal to obtain a ranging signal corresponding to the displacement of the distance to the detected object,
The calculation means includes an optical system that corrects the linearity of the ranging signal with respect to the displacement distance by multiplying one of the position signals included in the first or second signal by an appropriate correction constant. In the equation displacement measuring device, a calculation means is formed to obtain a distance measurement signal by multiplying the ratio of the first signal and the second signal by the sum of the correction constant and another appropriate constant. This makes it possible to easily adjust the correction constant for correcting the linearity of the ranging signal.

111- FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows an optical displacement measuring device similar to the conventional example.

A first signal (IAIR) obtained by subtracting the pair of position signals I A, I and one position signal 1. of the pair of position signals I/'w I. is multiplied by the correction constant k and the second signal (IA+kIB) is obtained by adding these pair of position signals.
) to the ratio (■＾−IB)/(I＾+k1.), (k
The calculating means 5 is configured to calculate the distance measurement signal Δl corresponding to the displacement Δl of the distance l to the detected object X by calculating the value multiplied by +C). Here, C is a constant 0 In this embodiment, the first signal (IA l1l) and the second signal
In order to find the ratio with the signal (I^+k1.), the ratio is found by light amount feedback without using the division circuit 25 as in the conventional example. That is, the output signal I A+ from the level detection circuits 22i and 22b
IB is input to the correction addition differential circuit 16, and one signal I
, is multiplied by the correction constant k and added to the other signal IA, and the second
A signal (IA + kla) is created, and the total amount of received light is (I A
The amount of light emitted from the light emitting element 12 for projecting light is feedback-controlled so that +kI a)/(k+C). The output of the correction addition differential circuit 16 is sent to the integration circuit 15 and the modulation circuit 1.
4 to the drive circuit 11 of the light emitting element 12 for projecting light. The modulation circuit 14 chops the output of the integration circuit 15 and transmits it to the drive circuit 11 in synchronization with the oscillation output of the oscillation circuit 10 that generates a clock pulse for setting the light projection timing. As shown in FIG. 1(b), the correction addition differential circuit 16 includes an operational amplifier OP, a resistor Rf,
It consists of Rs and volume VR, and the position signal 1. The linearity correction means 6 is formed of a volume VR that has twice the gain. Note that the other configurations and operations are the same as those of the conventional example shown in FIG. 3, and therefore redundant explanations will be omitted.

The principle of linearity correction in this embodiment will be explained below. When using the correction addition differential circuit 16 as shown in FIG. 1(b), the distance measurement signal is determined as follows. First, as a conditional expression, if Rf = Rs, Rf / V R = k, then L-IA-I day = (m 1) I B Therefore, the conventional distance measurement formula is multiplied by (k + 2). It takes shape. Now, if we calculate the partial differential coefficient of this distance measurement signal with respect to the change in VR, it becomes as follows.It can be seen that when s=1.2, the distance measurement signal does not change even if the set value of the volume VR is changed. FIG. 5 shows this in a graph. The horizontal axis shows the displacement distance Δl of the distance to the detected object X from the reference distance lc.
The vertical axis represents the linearity error of the measured distance value. When the correction constant k is a certain optimum value, there is no linearity error and the line becomes a straight line, but when it is smaller than that, the linearity error is convex upward, and when it is larger than that, the linearity error is convex downward. As previously determined, there are two points where the distance measurement signal does not change at all in response to a change in the correction constant (when IA=I day and when IA=2rB). Utilizing this characteristic, it is possible to easily adjust the linearity M (adjustment M to the correction constant).

An example of the adjustment method will be explained using FIG. 6.

Move the detected object X to point l of IA=21B,
Find the ranging signal value at . The value of this point α does not change even if the correction constant k is adjusted, that is, the value of the origin and point α
The straight line connecting them becomes the straight line after linearity correction. Therefore, point β at a distance of 12 from this straight line
The correction constant k is calculated so that the value of the distance measurement signal when the detected object X is placed at a distance of 12 becomes the signal value L2 at point β. If you do this,
It is no longer necessary to perform the repetitive adjustment work that was conventionally performed, and the linearity adjustment can be completed by adjusting the correction constant only once, thereby making it possible to significantly shorten the adjustment time.

As another example, the calculation means 5 is formed so that the distance measurement signal becomes Δ, and the linearity correction is performed by changing the correction constant k. In this case, as shown in FIG. The insertion position of the volume VR in the correction addition differential circuit 16 shown in (b) is indicated by the position signal I.
6 side to the position signal IA side, and the operation is the same as in the first embodiment.

Furthermore, as another embodiment, there is one in which the calculation means 5 is formed so that the distance measurement signal is as follows, and the linearity correction is performed by changing the correction constant k. The subtraction circuit 23 in Example 1 may be omitted and the position signal IA may be output as is.

The principle of linearity correction in this embodiment is as follows.

Therefore, if we adjust the value of k so that the term Δl in the denominator of the above equation becomes 0, we get =AΔz+B (A and B are constants), and linearity correction will be performed. .

As another embodiment, the calculation means 5 is formed so that the distance measurement signal becomes Δ, and the linearity correction is performed by changing the correction constant k, which is similar to the third embodiment described above. Needless to say, the operation will be as follows.

As another embodiment, the calculating means 5 is formed so that the distance measurement signal becomes , and the linearity correction is performed by changing the correction constant k. The subtraction circuit 23 may be omitted and the position signal IB may be output as is, resulting in the same operation as in the third embodiment.

夾1''J- As yet another embodiment, there is one in which the calculation means 5 is formed so that the distance measurement signal becomes RI, and the linearity correction is performed by changing the correction constant k. The operation is similar to 3.

As another embodiment, the calculation means 5 is formed so that the distance measurement signal becomes RI, and the linearity correction is performed by changing the correction constant k. By using an adder circuit instead of the subtractor circuit 23,
The signal (rA+Is) is created, and the total amount of received light is (
This can be achieved by applying light amount feedback so that IA kIa)/(k+c).

The principle of linearity correction in this embodiment is as follows.

Therefore, linearity correction can be performed by adjusting the value of k so that the term Δl in the denominator of the above equation becomes 0.

Still another embodiment is one in which the calculation means 5 is formed so that the distance measurement signal becomes RI, and the linearity correction is performed by changing the correction constant k, and the operation is as described above. This is the same as in Example 7.

Further, as shown in FIG. 7, the arithmetic expression shown in the first embodiment holds true even when distance measurement calculation is performed using the division circuit 25. In the circuit of FIG. 7, the correction subtraction circuit 26 receives the signals IA, 1. output from the level detection circuits 22a and 22b. , the numerator of the ranging signal (I A
r a)(k+C), and the correction addition circuit 27
calculates the denominator (IA+kIs) of the ranging signal,
The distance measurement signal is obtained by executing division by the division circuit 25.

X1j1'' and 2'' - Similarly, each of the calculation formulas shown in Examples 2 to 8 above holds true even when distance measurement calculations are performed using the division circuit 25, as explained in Example 9 above. do. These cases are referred to as Examples 10 to 16.

Furthermore, in the first embodiment, the level detection circuit 22a,
We assumed that the light receiving gain up to 22b is the same for both channels A and B, but even if a gain difference J is provided in order to change the reference distance at which the distance measurement signal output is zero in the circuit. , the effects of the present invention can be obtained. An example of this is shown in FIG. 8. In this example, there is a gain difference J between the signal IA obtained from the level detection circuit 22a and the signal J obtained from the level detection circuit 22b. , the reference distance at which the distance measurement signal becomes zero is PS
It shifts not to the center point of D4 but to the point where IA=JIB holds true. It goes without saying that the same thing holds true when any one of the arithmetic expressions shown in Examples 2 to 8 above is used.

C) Effects of the Invention) As described above, the present invention collects the reflected light from the object to be detected of the light beam projected from the light projecting means to the detection area using a light receiving device disposed at a predetermined distance to the side of the light projecting means. A first signal obtained by adding and subtracting a pair of position signals received by the optical system and output from a position detecting means disposed on the condensing surface of the light receiving optical system, and one position signal or a pair of position signals. and a calculation means for calculating a ratio of the added and subtracted second signal to obtain a distance measurement signal corresponding to a displacement of the distance to the detected object,
In an optical displacement measuring device provided with a linearity correction means for correcting the linearity of the ranging signal with respect to the displacement distance by multiplying one of the position signals included in the first or second signal by an appropriate correction constant, the correction Although the calculation means is formed to obtain a ranging signal by multiplying the sum of a constant and another appropriate constant by the ratio of the first signal and the second signal, linearity correction is not performed. This has the effect of making it easier to adjust the correction constants.

[Brief explanation of the drawing]

FIG. 1(a) is a block circuit diagram of an embodiment of the present invention, FIG. 1(b) is a specific circuit diagram of the main part of the same, and FIG. 2(a) is a diagram showing a schematic configuration of the main part of a conventional example. Figure 3 (b) is a sectional view of the main parts of the above, Figure 3 (a) is a block circuit diagram of the main parts of the same, Figure (b) is a circuit diagram of the main parts of the same, and Figure 4 is an explanatory diagram of the operation of the same. , FIG. 5 and FIG. 6 are explanatory diagrams of the operation of the present invention, FIG. 7 is a main block circuit diagram of another embodiment of the present invention, and FIG. 8 is a block circuit diagram of still another embodiment of the present invention. It is. 1 is a light projecting means, 3 is a light receiving optical system, 4 is a position detection means,
5 is a calculation means, and 6 is a linearity correction means.

Claims (1)

[Claims] (1) A light projecting means for projecting a light beam onto a detection area, a light receiving optical system disposed at a predetermined distance to the side of the light projecting means and condensing light reflected from the light beam by an object to be detected, a position detecting means that outputs a pair of contradictory position signals corresponding to the position of a condensing spot that is disposed on a condensing surface of the optical system and moves within the condensing plane according to the distance to the detected object; The distance to the detected object is determined by calculating the ratio between the first signal obtained by adding and subtracting the pair of position signals output from the detection means and the second signal obtained by adding and subtracting one position signal or the pair of position signals. a calculation means for obtaining a distance measurement signal corresponding to the displacement; the calculation means calculates the distance measurement signal for the displacement distance by multiplying one of the position signals included in the first or second signal by an appropriate correction constant; In an optical displacement measuring device provided with a linearity correction means for correcting the linearity of a signal, the sum of the correction constant and another appropriate constant is added to the ratio of the first signal and the second signal. 1. An optical displacement measuring device, characterized in that a calculation means is formed to obtain a distance measurement signal by multiplying the signals.