JPH065166B2 - Optical displacement measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention has a structure in which light reflected by an object to be detected of a light beam projected from a light projecting means to a detection area is arranged at a side of the light projecting means with a predetermined distance. The present invention relates to a triangulation type optical displacement measuring device which receives light by a light receiving means and measures a displacement of a distance to a detected object in a detection area based on an output of the light receiving means.

(Background Art) Conventionally, this type of triangulation type optical displacement measuring device is
As shown in FIGS. 2 and 3, the light projecting means 1 for projecting the light beam P onto the object X to be detected includes an oscillating circuit 10 for generating a clock pulse for setting a light projecting timing. Drive circuit 11 for driving the light emitting element 12 for projecting light
And a convex lens to form a light projecting optical system 13, so that light emitted from the light projecting light emitting element 12 is shaped into a light beam P by the projecting optical system 13 and projected onto a detection area. It has become. Predetermined distance from this light projecting means 1
_The light receiving optical system 3 which is arranged laterally with ₀ and collects the reflected light R of the light beam P by the detected object X is formed by a convex lens. Positions at which a pair of contradictory position signals I _A and I _B corresponding to the position of the focused spot S (moving in the M direction corresponding to the distance) are provided on the focusing surface of the light receiving optical system 3 are output. The detection means 4 is formed of, for example, a one-dimensional position detection element (hereinafter referred to as PSD4), and the position signals I _A and I _B are contradictory current signals. PSD4
The calculation means 5 for calculating the displacement of the distance to the detected object X on the basis of the output of the voltage signal V _A , amplifies the position signals (reciprocal current signals I _A , I _B ) output from the PSD 4, respectively. light receiving circuit 21a for converting the V _B, 21b, the light receiving circuit 21a, 21b
Output level of the level detection circuits 22a and 22b for checking (determining the level in synchronization with the clock pulse) based on the output of the oscillation circuit 10, and the output of the level detection circuits 22a and 22b (of the position signals I _A and I _B ). The level corresponds to 1: 1 and is therefore referred to as I _A , I _B in the following).
And a first signal output from the adder circuit 24 that adds the outputs I _A and I _B of the level detection circuits 22a and 22b, and the subtraction circuit 23.
(I _A -I _B) and the second signal output from the addition circuit 24 (I _A
+ I _B ), and a division circuit 25 for calculating a ratio with the distance measurement signal L ₀ (= (I _A -I _B ) / (I _A + I _B )).
Is output. The above-mentioned PSD4
Instead of this, it is needless to say that the output of each photodiode may be used as the position signals I _A and I _B by using two photodiodes connected in the M direction (moving direction of the focused spot S).

The distance measurement signal L ₀ has the following relationship with the displacement distance Δ. That is, the distance from the displacement measuring device to the detected object X is = _c + Δ (however,
c is the distance when the focused spot S is focused on the central point of the PSD 4 which is the position detecting means, Δ is the displacement distance from the distance c), and the distance from the light receiving optical system 3 to the PSD 4 is F, If the moving distance of the condensed spot S of the reflected light R from the detected object X from the center of the PSD 4 is Δx, and the crossing angle between the optical axes of the light projecting means 1 and the light receiving optical system 3 is θ, then (c / cosθ + Δcosθ) Δx = ( Δsinθ) F ∴Δx = (tanθ) FΔ / (c / cos 2 θ + Δ) where, a = (tanθ) F, putting a ^{b = c / cos 2 θ,} Δx = aΔ / ( b + Δ) (1), and the relationship between the moving distance Δx and the displacement distance Δ is non-linear.

Here, the position signal I _A outputted from the PSD 4, the relationship between the moving distance Δx between I _B, if the effective length of PSD 4 and _{2 p, (I A -I B} ) / (I A + I B) = Δx / _p (2) Therefore, as is clear from the equations (1) and (2), the distance measurement signal L ₀ output from the computing means 5 is a signal including information on the displacement distance Δ, but has a linear relationship with the displacement distance Δ. It's not. Therefore, in order to make the measurement accuracy of the displacement distance Δ the same even when the distance changes (the magnitude of displacement), the linearity correction circuit 6 is provided,
It was necessary to perform correction so that a linear distance measurement signal L was obtained.

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. Since it is necessary to set the optimum correction value individually according to the variation of parts, the cost is significantly increased and it has not been mass-produced.

Further, an analog linearity correction circuit 6 that is approximated by a polygonal line function has been proposed. Linearity correction circuit 6 shown in FIG. 3 (b) is an operational amplifier OP, a diode D ₁ to D _3, volume VR ₁ to VR ₆ and the resistor R _1, R
_The linearity correction is performed by approximating the distance measurement signal L ₀ with four broken lines, and the number of broken points is three, and the six volumes VR _{1 to} VR ₆ can be adjusted. You will need it. By the way, in such a conventional example, in order to reduce the correction error due to the 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. Configuration becomes complicated,
There is a problem that the adjustment work becomes troublesome and the cost becomes high.

Therefore, conventionally, the linearity correction is performed by forming the calculation means 5 so that the distance measurement signal L becomes L = (I _A −I _B ) − (I _A + kI _B ), and changing the correction constant k. Is proposed. In this case, the distance measurement signal L is And in the above equation Substituting The condition for this equation to be linear is So if you solve this, become. Therefore, if k is adjusted to this value, the correction error of linearity correction can theoretically be set to zero. In this case, the number of adjustment points in the linearity correction is one, which simplifies the configuration and simplifies the adjustment work, facilitates mass production, and reduces the cost.

However, in this conventional example, when the correction constant k is adjusted, the distance measurement signal L is linear with respect to the displacement distance Δ while actually moving the detected object X.
It is necessary to adjust k. Specifically, as shown in FIG. 4, the linearity error (deviation from the straight line of the distance measurement signal L) when the detected object X is moved by ± Δ ₁ from the reference distance is adjusted to zero. However, since the value of the distance measurement signal L at each point continuously changes depending on the value of the correction constant k, the adjustment is first performed by setting the correction constant k, and then ± from the reference distance. The distance measuring signal L when the detected object X is moved by Δ ₁ is measured, the correction constant k is reset thereafter, and the distance measuring signal L when the detected object X is moved is measured. Since it is necessary to repeat a series of adjustment work to be performed many times, it is difficult to shorten the adjustment time.

(Object of the Invention) The present invention has been made in view of the above points,
It is an object of the present invention to provide an optical displacement measuring device capable of easily adjusting the correction constant for linearity correction.

(Disclosure of the Invention) Configuration In an optical displacement measuring apparatus according to the present invention, a light projecting means for projecting a light beam to a detection area, and an object to be detected which is arranged at a side of the light projecting means with a predetermined distance. At the position of the receiving optical system that collects the reflected light of the light beam by the, and the focusing spot that moves on the focusing surface that is arranged on the focusing surface of the receiving optical system and moves according to the distance to the detected object. Position detecting means for outputting a corresponding pair of opposite position signals, a first signal for adding / subtracting the pair of position signals output from the position detecting means, and a first signal for adding / subtracting one position signal or a pair of position signals. And a calculation means for calculating a ratio with the signal of 2 to obtain a ranging signal corresponding to the displacement of the distance to the detected object,
The calculation means is provided with a linearity correction means for correcting the linearity of the distance measurement signal with respect to the displacement distance by multiplying one position signal included in the first or second signal by an appropriate correction constant. In the displacement measuring device, an arithmetic means is formed so as to obtain a distance measuring signal by multiplying the sum of the correction constant and another appropriate constant by the ratio of the first signal and the second signal. In addition, the adjustment work of the correction constant for correcting the linearity of the distance measurement signal can be easily performed.

Embodiment 1 FIG. 1 shows an embodiment of the present invention. In an optical displacement measuring device similar to that shown in FIG.
_A first signal (I _A -I _B ) obtained by subtracting I _A and I _B , and a pair of position signals
Of the I _A and I _B , one of the position signals I _B is multiplied by a correction constant k and the pair of position signals is added to produce a second signal (I _A + kI
_B ) and the ratio (I _A -I _B ) / (I _A + kI _B ) multiplied by (k + C) to calculate the measurement corresponding to the displacement Δ of the distance to the detected object X. The calculation means 5 is formed so as to obtain the distance signal L. Here, C is a constant. In this embodiment, in order to obtain the ratio of the first signal (I _A -I _B ) and the second signal (I _A + kI _B ), the division circuit 25 as in the conventional example is not used. so,
The ratio is calculated by the light amount feedback. That is, the output signal I from the level detection circuits 22a and 22b
_A and I _B are input to the correction addition differential circuit 16 and one of the signals I _B
Is multiplied by the correction constant k and added to the other signal I _A to create the second signal (I _A + kI _B ), and the total amount of received light is (I _A + kI _B ) / (k + C) Thus, the light emission amount of the light emitting element 12 is feedback-controlled. The output of the correction addition differential circuit 16 is transmitted through the integration circuit 15 and the modulation circuit 14 to the light emitting element 12 for projection.
Is input to the drive circuit 11. 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 that sets the light emission timing. Correction addition differential circuit 16, as shown in Fig. 1 (b), an operational amplifier OP, resistors Rf, consists Rs and volume VR, the linearity in volume VR to provide a gain of k times the position signal I _B Correction means 6 is formed. Since the other configurations and operations are the same as those of the conventional example of FIG. 3, duplicated description will be omitted.

Hereinafter, the principle of linearity correction in this embodiment will be described. When the correction addition differential circuit 16 as shown in FIG. 1 (b) is used, the distance measurement signal L is obtained as follows. First, as a conditional expression, Now, if Rf = Rs and Rf / VR = k, Therefore, the conventional distance calculation formula is multiplied by (k + 2). Now, when the partial differential coefficient with respect to the change of VR of the distance measurement signal L is calculated, Therefore, it can be seen that when m = 1, 2, the distance measurement signal L does not change even if the set value of the volume VR is changed. This is shown graphically in FIG. Displacement distance Δ from the reference distance _c of the distance to the detected object X on the horizontal axis
, The vertical axis represents the linearity error of the distance measurement value. When the correction constant k is an optimum value, the linearity error is completely eliminated and becomes a straight line. When the correction constant k is smaller than that, the linearity error is convex upward, and when it is larger than the linearity error, the linearity error is convex downward. Then, as previously obtained, there are two points (in the case of I _A = I _B and I _A = 2I _B ) where the distance measurement signal L does not change at all with respect to the change of the correction constant k. By using this characteristic, the linearity can be easily adjusted (correction constant k can be adjusted).

An example of the adjusting method will be described with reference to FIG. The detected object X is moved to obtain the distance measurement signal value L ₁ at the point ₁ of I _A = 2I _B. The value of this point α does not change even if the correction constant k is adjusted. That is, the straight line connecting the origin and the point α is the straight line after the linearity correction.
Therefore, the signal value L ₂ at the point β at the distance ₂ is calculated from this straight line so that the value of the distance measurement signal L when the detected object X is installed at the distance ₂ becomes the signal value L ₂ at the point β. , The correction constant k is adjusted. By doing so, it is not necessary to perform the repetitive adjustment work that has been performed conventionally, and the linearity adjustment is completed by only adjusting the correction constant k once, thereby enabling a significant reduction in the adjustment time. You can

Embodiment 2 As another embodiment, the distance measurement signal L is The linearity correction is performed by changing the correction constant k by forming the calculation means 5 so that the volume VR in the correction addition differential circuit 16 shown in FIG. position signal I _B the insertion position of
It suffices to change from the side to the position signal I _A side, and the operation is the same as in the first embodiment.

Third Embodiment As still another embodiment, the ranging signal L is The linearity correction is performed by changing the correction constant k by forming the calculating means 5 so that the position signal I _A is not changed and the subtraction circuit 23 in the first embodiment is omitted. You can output it.

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

And Substituting Therefore, if the value of k is adjusted so that the term of Δ in the denominator of the above equation becomes 0, Therefore, the linearity correction will be performed.

Fourth Embodiment As still another embodiment, the distance measurement signal L is It is needless to say that there is the one in which the calculating means 5 is formed so that the linearity correction is performed by changing the correction constant k, and the operation is the same as that of the third embodiment.

Embodiment 5 As still another embodiment, the distance measurement signal L is There is a device in which the linearity correction is performed by changing the correction constant k by forming the calculating means 5 so that the subtraction circuit 23 in the first embodiment is omitted and the position signal I _B is output as it is. The operation is similar to that of the third embodiment.

Sixth Embodiment As still another embodiment, the distance measurement signal L is There is one in which the arithmetic means 5 is formed so as to perform the linearity correction by changing the correction constant k, and the operation is the same as that of the third embodiment.

Embodiment 7 As still another embodiment, the distance measurement signal L is The linearity correction is performed by changing the correction constant k by forming the calculating means 5 so that the first signal (using the addition circuit instead of the subtraction circuit 23 in the first embodiment) I _A + I _B ), and the light amount feedback is applied so that the total amount of received light is (I _A −kI _B ) / (k + C).

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

And Substituting Therefore, if the value of k is adjusted so that the term of Δ in the denominator of the above equation becomes 0, the linearity correction can be performed.

Embodiment 8 In still another embodiment, the distance measurement signal L is The linearity correction is performed by changing the correction constant k by forming the calculation means 5 so that the operation is the same as in the seventh embodiment.

Ninth Embodiment Further, as shown in FIG. 7, the arithmetic expression shown in the first embodiment holds true even when the distance measurement calculation using the division circuit 25 is performed. In the circuit of FIG. 7, the correction subtraction circuit 26 has a signal I output from the level detection circuits 22a and 22b.
The numerator (I _A -I _B ) (k + C) of the distance measurement signal L is calculated from _A and I _B , and the correction addition circuit 27 calculates the denominator (I _A + kI _B ) of the distance measurement signal L. Therefore, the distance measuring signal L is obtained by executing the division by the division circuit 25.

Similarly to the tenth to sixteenth embodiments, each of the arithmetic expressions shown in the above second to eighth embodiments holds as it is even when the distance measurement calculation using the division circuit 25 is performed as described in the ninth embodiment. Each of these cases is referred to as Examples 10-16.

Seventeenth Embodiment Further, in the first embodiment, the level detection circuits 22a and 22b are
It is assumed that the light receiving gains up to are the same for both A and B channels, but even if a gain difference J is given in order to change the reference distance at which the distance measurement signal output becomes zero in a circuit manner, The effect of the present invention can be obtained. An example thereof is shown in FIG. In this embodiment, the level detection circuit 22
a signal I _A obtained from a, the gain difference J exists between the signal JI _B obtained from the level detecting circuit 22b, reference distance ranging signal L becomes zero, rather than the center point of the PSD 4, It shifts to the point where I _A = JI _B holds. Needless to say, the same holds true when any one of the arithmetic expressions shown in Examples 2 to 8 is used.

(Effects of the Invention) As described above, the present invention is for receiving the reflected light of the light beam projected from the light projecting means to the detection area by the object to be detected, which is arranged 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 the position detecting means arranged on the condensing surface of the light receiving optical system, and one position signal or a pair of position signals. And a calculation unit that calculates a ratio with the second signal obtained by addition and subtraction to obtain a distance measurement signal corresponding to the displacement of the distance to the detected object,
In the optical displacement measuring device provided with linearity correction means for correcting the linearity of the distance measurement signal with respect to the displacement distance by multiplying one position signal included in the first or second signal by an appropriate correction constant, Since the arithmetic means is formed so as to obtain the distance measurement signal by multiplying the ratio of the first signal and the second signal by adding the constant and another appropriate constant, the linearity correction Therefore, there is an effect that the adjustment work of the correction constant can be easily performed.

[Brief description of drawings]

FIG. 1 (a) is a block circuit diagram of one embodiment of the present invention.
(b) is a specific circuit diagram of a main part of the above, FIG. 2 (a) is a diagram showing a schematic configuration of a main part of a conventional example, (b) is a sectional view of the main part of the same, and FIG.
FIG. 4A is a block circuit diagram of an essential part of the same, FIG. 4B is a circuit diagram of an essential part of the same, FIG. 4 is an operation explanatory diagram of the same, FIG. 5 and FIG.
FIG. 7 is a diagram for explaining the operation of the present invention, FIG. 7 is a block circuit diagram of a main part of another embodiment of the present invention, and FIG. 8 is a block circuit diagram of yet another embodiment of the present invention. 1 is a light projecting means, 3 is a light receiving optical system, 4 is a position detecting means,
Reference numeral 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 to a detection area, and a light receiving optical system arranged at a side of the light projecting means with a predetermined distance to collect reflected light of the light beam by an object to be detected. Position detecting means disposed on the light collecting surface of the light receiving optical system and outputting a pair of contradictory position signals corresponding to the positions of the light collecting spots that move within the light collecting surface according to the distance to the object to be detected. , A ratio of a first signal obtained by adding / subtracting the pair of position signals output from the position detecting means to a second signal obtained by adding / subtracting one position signal or a pair of position signals is calculated, and And a calculating means for obtaining a distance-measuring signal corresponding to the displacement of the distance. The calculating means multiplies one of the position signals included in the first or second signal by an appropriate correction constant to obtain the displacement distance. Correct the linearity of the ranging signal In an optical displacement measuring device provided with linearity correction means, a distance measurement signal is obtained by multiplying a ratio of the first signal and the second signal by a value obtained by adding the correction constant and an appropriate other constant. An optical displacement measuring device characterized in that arithmetic means is formed so as to obtain.