JP3227212B2 - Optical displacement measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement measuring device for measuring a distance to an object in a non-contact manner by using a triangulation method.

[0002]

2. Description of the Related Art Conventionally, a displacement measuring device for optically measuring a distance based on a triangulation method has been provided for use as a visual sensor of a robot in the field of factory automation (FA) and the like. This type of displacement measuring device has the advantage that the distance to the object can be measured without contact since the distance is measured optically. FIG.
As shown in FIG. 1, a sensor head 10 for detecting information on the distance to an object, and a sensor head 10 for calculating a distance to the object based on information obtained by the sensor head 10 and performing various determinations according to the distance to the object It is provided separately from the controller 20 and is connected via a connection line. With such a configuration in which the sensor head 10 and the controller 20 are separated from each other, the size of the sensor head 10 is reduced, and it is easy to incorporate the sensor head 10 into a robot or the like.

A sensor head 10 irradiates an object with a light beam to form a light spot, which is a point-like light pattern, on the surface of the object. Light receiving means 2 for detecting light reflected on the surface of the object
And The light receiving means 2 converts the incident light into a light receiving optical system 13.
(See FIG. 9) by converging through the PSD
A light receiving spot as an image of a light projecting spot is formed on the light receiving surface of the position detecting element 14, and a pair of position signals I ₁ and I ₂ corresponding to the position of the light receiving spot are output. That is, the position detection element 14 is a pair of position signals I, which are current signals whose magnitude ratio is determined according to the position of the light receiving spot.
₁ and I ₂ , and the two position signals I ₁ and I ₂
If the position of the light receiving spot is detected based on the relationship, the distance to the object can be obtained based on the triangulation method. The sum of the two position signals I ₁ and I ₂ corresponds to the amount of received light detected by the position detection element 14.

[0004] This will be described more specifically. Light emitting means 1
A light beam is formed by providing a light emitting element 11 composed of a laser diode. The light emitting element 11 is driven by a laser diode driving circuit 12, and the laser diode driving circuit 12 includes an original oscillator 2 provided in a controller 20.
The output of the modulator 22 that performs pulse modulation (pulse amplitude modulation) of the clock signal generated from 1 is input as a control signal. The modulator 22 changes the amplitude of the output of the modulator 22 so that the energy supplied to the light emitting element 11 changes according to the signal level of the DC signal output from the integrator 23 described later.

On the other hand, a pair of position signals I ₁ and I ₂ output from the position detecting element 14 are supplied to amplifiers 15a and 1a, respectively.
5b, the position signals I ₁ and I ₂ are converted from current signals to voltage signals V ₁ and V ₂ , amplified and output to the controller 20. The controller 20
There are provided signal processing units 24a and 24b to which voltage signals V ₁ and V ₂ corresponding to the position signals I ₁ and I ₂ are inputted. The signal processing units 24a and 24b amplify the voltage signals V ₁ and V ₂ , remove noise components below a predetermined frequency, and detect the voltage signals V ₁ and V ₂ in synchronization with the clock signal from the original oscillator 21. I do. The amplification factors of the voltage signals V ₁ and V _{2 in} the signal processing units 24a and 24b can be adjusted from outside.

The output signals V ₁₁ and V ₁₂ from the signal processing units 24 a and 24 b are proportional to the voltage signals V ₁ and V ₂ , and both outputs are subtracted by a subtractor 25 as subtraction means to obtain a subtraction value (V
₁₁ −V ₁₂ ) is obtained, and is added by the adder 26 to obtain an added value (V ₁₁ + V ₁₂ ). Subtractor 2
The output of 5 is a sample-and-hold circuit which is a sample-and-hold means for holding the output value of the subtractor 25 when the amount of light received by the position detecting element 14 is insufficient or excessive, when the amount of light is normal. DC operation unit 27 through 30
Is input to The DC calculation unit 27 removes components having a frequency equal to or higher than a predetermined frequency, and also includes a slope (proportional constant) described later,
An offset value of the measurement distance is externally set, the linearity is corrected, the measurement value is corrected, and the corrected subtraction value is used as a displacement output. Specifically, the slope is adjusted by adjusting the attenuation rate with respect to the input level, and the offset value is adjusted by adjusting the level to be added to the input level.

On the other hand, the output of the adder 26 is
And a difference from the reference value output from the reference value generation unit 28 is obtained. The output value from the adder 26 is subtracted from the reference value, and the difference is averaged by the integrator 23 and input to the modulator 22. Therefore, the light emitting element 11
The light output from is controlled in a feedback manner in accordance with the amount of light received by the position detecting element 14. When the feedback system is operating stably, the amount of light emitted from the light emitting element 11 is adjusted so that the output of the adder 26 matches the reference value set by the reference value generator 28, and the amount of light received by the position detection element 14 is It is kept almost constant. Therefore, the addition value (V ₁₁ + V ₁₂ ) output from the adder 26 is constant in an ideal system ignoring the dynamic range and the response performance of the circuit, and the subtraction value (V ₁₁ −V) output from the subtracter 25. V ₁₂₎
It is proportional to _{(V 11 -V 12) / (} V 11 + V 12). As described above, the adder 26, the reference value generator 28, the error amplifier 29, the integrator 23, and the modulator 22 constitute a light amount control unit that performs feedback control so as to keep the received light amount constant. The integrator 23 is configured to invert and integrate the output of the error amplifier 29.

Next, the principle of distance measurement in the above configuration will be described. As shown in FIG. 9, when the light receiving spot is formed at the center of the light receiving surface of the position detecting element 14, the distance from the center of the light receiving optical system 13 to the object 3 in the optical axis direction of the light projecting means 1 is represented by r. Assume that the distance to the object 3 has increased by Δr. At this time, the position of the light receiving spot moves to the left in FIG. 9 by Δx. Assuming that the effective length of the light receiving surface of the position detecting element 14 is 2L, the position signals I ₁ and I ₂ have the following relationship.

I ₁ / I ₂ = (L−Δx) / (L + Δx) When the equation is modified, the following equation is obtained. (I ₁ −I ₂ ) / (I ₁ + I ₂ ) = Δx / L Since the effective length 2L of the light receiving surface of the position detecting element 14 is constant, the amplifiers 15a and 15 corresponding to the position signals I ₁ and I ₂ are provided.
Based on the output of b, (I ₁ −I ₂ ) / (I ₁ + I ₂ )
If the value corresponding to is obtained, the position of the light receiving spot can be known. That is, (V ₁₁ −V ₁₂ ) / (V
₁₁ + V ₁₂ ), the displacement Δx of the light receiving spot at the position detecting element 14 can be obtained. Here, as described above, the output of the subtractor 25 is (V ₁₁ −V ₁₂ ),
Since (V ₁₁ + V ₁₂ ) is maintained at a constant value by the feedback control, an output proportional to the left side of the equation is obtained from the subtractor 25 without dividing the output of the subtractor 25. Become. Therefore, by setting a proportional constant (slope) to the output of the subtractor 25 in the DC calculation unit 27, the displacement Δx of the light receiving spot can be obtained.

The distance between the center of the light receiving optical system 13 and the position detecting element 14 is represented by f, and a straight line connecting the point at the distance r on the optical axis of the light projecting means 1 and the center of the position detecting element 14 is projected. Assuming that the angle between the optical means 1 and the optical axis is θ, the following relationship is obtained. (R / cos θ + Δr / cos θ): f / cos θ = (Δr / sin θ): Δx∴Δr = r · Δx / ｛(f / sin θ) −Δx｝ = b · Δx / (a−Δx) Where a = f / sin θ and b = r. That is,
According to the equation, the displacement distance Δr can be determined by determining Δx, and it can be seen that the displaced distance Δr can be determined based on the equation and the equation. However, the DC operation unit 27 performs the operation corresponding to the expression to obtain the displacement Δx, and the operation of the distance Δr by the expression is performed at a later stage than the DC operation unit 27.

When the feedback system is operating stably, the output value of the adder 26 (V ₁₁ + V ₁₂ )
Since is substantially constant, the output value of the subtracter 25 as described above (V ₁₁ -V _{12) is, (V 11 -V 12) /} (V 11 + V 12)
However, if the reflectivity of the object is high and the amount of received light is excessive and the circuit is saturated, or if the reflectivity of the object is low and the amount of received light is insufficient to obtain a sufficient amount of emitted light, the addition is performed. Since the output value of the heater 26 is not maintained at a constant value,
Displacement cannot be measured correctly. Therefore, when the amount of received light becomes excessive or the amount of emitted light becomes insufficient,
It is necessary to hold the measured value at that time and, in some cases, notify the outside that an abnormality has occurred.

In order to achieve this object, a sample-and-hold circuit 30 is provided, and the point of transition from the normal state to the abnormal state is detected based on the output of the integrator 23. . That is, the output of the integrator 23 is input to the sample-and-hold comparator 31 so that the output value of the integrator 23 falls within the allowable range between the upper and lower thresholds set by the two threshold generators 32a and 32b. In this case, the sample / hold circuit 30 is not operated, and if it is out of the allowable range, a hold signal is generated through the logic circuit 33, so that the sample / hold circuit 30 holds the output value of the subtracter 25. ing. Sample / hold comparator 31, threshold value generators 32a, 3
2b, the logic circuit 33 constitutes a hold signal generating means. As shown in FIG. 6, the sample-and-hold comparator 31 includes two comparators CP ₁ and CP _2.
And the comparators CP ₁ and CP ₂ have an integrator 23
Output is input by smoothing by a resistor R ₅ and capacitor C _5. Threshold value generator 32a, 32b are resistors R ₁ ~
R ₄ . Further, the NAND circuit NA, which is the logic circuit 33, outputs the negation of the logical product of the output values of the comparators CP ₁ and CP ₂ . Sample and hold circuit 30
Comprises a voltage follower composed of operational amplifier OP outputs a terminal voltage of the capacitor C ₆ is charged via the analog switch AS ₁ ~AS _3, resistor R _6.

Therefore, if the output value of the integrator 23 is within the allowable range set by the threshold value generators 32a and 32b, the outputs of the comparators CP ₁ and CP ₂ are both at H level, and the output of the NAND circuit NA is at L level. When the level is kept outside the permissible range, one of the outputs of the comparators CP ₁ and CP ₂ goes low, and the output of the NAND circuit NA goes high. As a result, when the output value of the integrator 23 is out of the permissible range, the L-level control signal obtained by inverting the output of the NAND circuit NA by the NOT circuit NT is output to the analog switch AS ₁ connected to the output terminal of the subtractor 25. , AS ₂ is turned off. Further, the output of the NAND circuit NA, the analog switches AS ₃ which is inserted into the output of the voltage follower is turned on. That is, the value of immediately before the out of tolerance are retained in the capacitor C _6, is that this value is used as the output value.

In the above configuration, the reflectance of the object (FIG. 7A)
7C), the output V of the integrator 23 according to FIG.
b changes. That is, if the reflectance is high, the adder 26
Is closer to the reference value generated from the reference value generator 28, the output Vb of the integrator 23 decreases, and if the reflectance is low, the output Vb of the integrator 23 increases. Therefore,
The output Vc of the modulator 22 changes as shown in FIG.
Assuming that the upper and lower thresholds H ₁ and H ₂ are set in the threshold generators 32a and 32b as shown in FIG. 7C, the output Vb of the integrator 23 becomes the two thresholds H ₁ and H _2. Is within the allowable range, the NAND circuit NA as shown in FIG.
Is at H level, and the sample and hold circuit 3
The 0 analog switches AS ₁ and AS ₂ are turned on, and the output value of the subtractor 25 is output as it is. On the other hand, when the output Vb of the integrator 23 is out of the allowable range, the NAND circuit N
The output of A goes low to generate a hold signal, and the sample / hold circuit 30 holds the output value of the subtractor 25.

[0015]

However, in actual systems, there are variations in optical specifications and electronic circuit specifications.
The following problems occur. For example, as shown in FIG. 7E, even when the output Va of the error amplifier 29 is stable and the feedback control is being performed stably, as shown in FIG. output Vb is sometimes hold signal exceeds the threshold value H ₁ of the higher reflectance occurs, despite the margin is left in the dynamic range of the device, may not be fully utilized. Conversely, as shown in FIG.
Despite the feedback control is not performed stably output Va of 9 becomes unstable, the output Vb of the integrator 23 as shown in FIG. 8 (c) does not exceed the threshold value H _1, FIG. 8 (d) In some cases, a hold signal is not generated as shown in FIG. In such a situation, there will be errors in the measurements,
Thereafter, even if the output value of the subtractor 25 is held by the sample and hold circuit 30, the output value in an unstable state is held, which is inconvenient.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and to reliably detect an unstable state of a feedback system and hold a measured value without delay, thereby suppressing the occurrence of an error in the measured value. An object of the present invention is to provide an improved optical displacement measuring device.

[0017]

According to the first aspect of the present invention, in order to achieve the above object, a light projecting means for irradiating a surface of an object with a light spot, which is a point-like light pattern, The reflected light on the object surface of the irradiated light is converged by passing through a light receiving optical system, and a pair of position signals are output which determine an output level ratio corresponding to the position of the light receiving spot formed as an image of the projected spot. Light receiving means, subtracting means for calculating a difference between output levels of the respective position signals, an error amplifier for obtaining a difference between the amount of light received by the light receiving means and a predetermined reference value, and an integrator for averaging the output of the error amplifier. A light quantity control means for feedback-controlling a light emission quantity of the light emitting means based on an output value of the integrator, and an output of a subtraction means at the time when a hold signal is inputted from the outside; Keep value That the sample-and-hold means and, if a state in which the reflectivity of the object exceeds the dynamic range of the system is detected by comparing the output with a predetermined threshold of the error amplifier hold signal generating means for generating a hold signal
And the comparing means for comparing the output of the error amplifier with the threshold value.
This is provided with a hysteresis providing means for providing a steeresis .

According to the second aspect of the present invention, the light projecting means includes a light emitting element composed of a laser diode, and the amount of emitted light is controlled by a pulse-modulated control signal based on the output value of the integrator.

[0019]

According to the configuration of the first aspect, the output value of the error amplifier provided in the preceding stage of the integrator is compared with the allowable range to determine whether or not the hold signal needs to be generated. It is possible to reliably detect an unstable state of the system as compared to the output after the delay, and if the feedback system becomes unstable, a hold signal can be generated without delay. Nodea which can hold a little error value for the output value of the subtraction means to the sample-hold means is, further hysteresis imparted hand
The stage provides the comparison means for comparing the output of the error amplifier with the threshold value.
The hold signal oscillates because the
And the hold signal can be held stably.
You can.

The structure of claim 2 is a desirable embodiment.

[0021]

In this embodiment, as shown in FIGS. 1 and 2, the basic configuration is the same as the conventional configuration shown in FIGS. 5 and 6.
The difference is that the necessity of generation of the hold signal can be determined on the basis of the output. That is, a stability determination unit that compares the output value of the error amplifier 29 with a predetermined threshold value that determines the lower limit and generates a hold signal through the logic circuit 33 if the output value of the error amplifier 29 is outside the allowable range that determines the upper limit. 34. Further, the sample-and-hold comparator 31 sets one comparator CP so that the output value is set to the L level only when the output value of the integrator 23 becomes larger than the threshold value generated from the threshold value generation unit 32. It consists of only _two . That is, the integrator 23
Only the saturation of the amount of emitted light is detected based on the output value of. In FIG. 2, although the two comparators are shown, only the comparator CP ₂ is utilized, the remaining comparator not involved in the operation. Other configurations denoted by the same reference numerals as the conventional configuration are the same as the conventional configuration.

The stability judging section 34 includes a resistor R ₇ having one end connected to the output end of the error amplifier 23 and the other end connected to a capacitor C ₇ . The anodes of the diodes D ₁ and D ₂ are connected to the connection point between the capacitor C ₇ and the resistor R ₇ , the cathode of the diode D ₁ is connected to the power supply, and the cathode of the diode D ₂ is connected to the capacitor C ₈ and the resistor R 7. One end of the parallel circuit with ₈ is connected.

By the way, as shown in FIG. 3A, when the reflectivity of the object is standard and the feedback system is stable, as shown in FIG. 3B, the output Vc of the modulator 22 is output. The value is relatively small. At this time, as shown in FIG. 3C, the output Va of the error amplifier 23 fluctuates around the ground level (0 V) including a slight ripple component. Therefore, in a stable state, the potential at the connection point between the capacitor C ₇ and the resistor R ₇ is kept at almost 0V. In this state, the diode D ₂ is because it is off, as shown in FIG. 3 (d), are almost 0V also the terminal voltage Vd of the capacitor C _8.

On the other hand, if an object having a high reflectance is present, the amount of received light increases, and as shown in FIG.
An attempt is made to reduce the amount of emitted light based on the output of No. 3. At this time, if the system is stable, the output of the error amplifier 29 is
The ripple component is increased near the ground level as shown in FIG. Here, if a voltage that applies a forward bias to the diode D ₂ is output from the error amplifier 29,
The capacitor C ₈ is charged by applying the voltage divided by the resistor R ₇ and the resistor R ₈ . This charging time constant is determined by the parallel capacitance of the capacitors C ₇ and C ₈ and the relationship between the charging time by the resistor R ₇ and the discharging time by the resistor R ₈ . That is, while the system ripple component is small in the output of the error amplifier 29 are stable, as shown in FIG. 3 (d), it is possible to maintain the terminal voltage Vd of the capacitor C ₈ to a low state.

The terminal voltage of the capacitor C ₈ is determined by the resistances R ₉ , R
The threshold H ₃ which is determined by the _10, is compared by the comparator CP _3, the output of the comparator means serving the comparator CP ₃ and the terminal voltage of the capacitor C ₈ is also higher than the threshold value H ₃ becomes L level. The comparator CP ₃ is resistor R in order to impart a hysteresis between the input terminal and the output terminal
₁₁ is inserted, and when the output becomes L level, the threshold value H ₃
Is to be reduced. Here, the resistance R ₁₁
Constitutes a hysteresis providing means. The output of the comparator CP ₃ is inputted to the NAND circuit NA ₁ is a logic circuit 33. NAND circuit NA ₁ is a of outputting a negative logical product of the output value of the comparator CP ₂ and the comparator CP _3, when at least one of the outputs of the comparators CP _2, CP ₃ is L level, the output The hold signal is generated at H level.

According to the above configuration, the feedback system operates stably even when the amount of received light increases due to the reflected light from the object having a high reflectivity, and the modulator 22 as shown in FIG.
While it can be dealt with by reducing the amplitude of the output Vc of
3 because there is a relatively small ripple component of the output Va of the error amplifier 29 as shown in (c), without exceeding the threshold H ₃ terminal voltage Vd of the capacitor C ₈ as shown in FIG. 3 (d), the 3 No hold signal is generated as in (e).

On the other hand, when the amount of received light becomes excessive and the operation of the feedback system becomes unstable, and the amplitude of the output Vc of the modulator 22 becomes unstable as shown in FIG.
Increases the ripple component of the output Va of the error amplifier 29 as shown in (c), the terminal voltage Vd of the capacitor C ₈ as shown in FIG. 4 (d) will be exceeding the threshold value H _3, FIG. 4 (e)
A hold signal is generated as shown in FIG. Moreover, it is to hold the hold signal stably with the threshold H ₃ drops exceeds the threshold H ₃ once. Further, since the hold signal can be generated without passing through the integrator 23, the response time until the detection of the excessive amount of received light is shortened.

[0028]

As described above, according to the present invention, the sample and hold means for holding the output value of the subtraction means at the time when the hold signal is input from the outside, and the state where the reflectance of the object exceeds the dynamic range of the system. A hold signal generating means for generating a hold signal when detected by comparing the output of the error amplifier with a predetermined threshold value, so that the output value of the error amplifier provided before the integrator is within a permissible range. The magnitude comparison is performed to determine the necessity of the generation of the hold signal, and it is possible to reliably detect the unstable state of the system as compared with the output after averaging by the integrator. When the system becomes unstable, a hold signal can be generated without delay, and a sample error with a small error with respect to the output value of the subtraction means at the time when the unstable state occurs is obtained. It has the advantage that it can be held in a de means. In addition, the hysteresis provision
The comparison means for comparing the output of the amplifier with the threshold value has a hysteresis.
The hold signal oscillates
And the hold signal can be held stably
There are advantages.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an embodiment.

FIG. 2 is a circuit diagram of a main part showing an embodiment.

FIG. 3 is an operation explanatory diagram of the embodiment.

FIG. 4 is a diagram illustrating the operation of the embodiment.

FIG. 5 is a block circuit diagram showing a conventional example.

FIG. 6 is a circuit diagram of a main part showing a conventional example.

FIG. 7 is an operation explanatory diagram of a conventional example.

FIG. 8 is an operation explanatory diagram of a conventional example.

FIG. 9 is an explanatory view showing the operation principle of the optical displacement measuring device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light projecting means 2 light receiving means 11 light emitting element 13 light receiving optical system 14 position detecting element 22 modulator 23 integrator 25 subtractor 26 adder 28 reference value generator 29 error amplifier 30 sample and hold circuit 31 sample and hold comparator 32 threshold generator 33 logic circuit 34 stability determiner

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-226607 (JP, A) JP-A-2-262004 (JP, A) JP-A-59-60426 (JP, A) JP-A-60-260 88306 (JP, A) JP-A-61-10711 (JP, A) JP-A-62-81520 (JP, A) JP-A-63-108217 (JP, A) JP-A-63-243709 (JP, A) JP-A-6-42958 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 3/06 G01B 11/00

Claims (2)

(57) [Claims] 1. A light projecting means for irradiating a light projecting spot, which is a point-like light pattern, onto a surface of an object, and a light reflected from the object surface of light emitted from the light projecting means being converged by passing through a light receiving optical system. Light-receiving means for outputting a pair of position signals whose output level ratio is determined in accordance with the position of the light-receiving spot formed as an image of the projected spot; subtraction means for calculating the difference between the output levels of each position signal; An error amplifier for obtaining the difference between the amount of light received by the light receiving means and a predetermined reference value and an integrator for averaging the output of the error amplifier are provided, and the amount of received light is kept substantially constant based on the output value of the integrator. As described above, the light amount control means for performing feedback control of the light emission amount of the light projecting means, the sample and hold means for holding the output value of the subtraction means at the time when the hold signal is inputted from the outside, and the dynamic reflectivity of the system. And a hold signal generating means for generating a hold signal when the conditions beyond Nji detected by comparing the output with a predetermined threshold of the error amplifier, the error increase
Hysteresis is applied to the comparison means that compares the output of the breadth with the threshold.
An optical displacement measuring device comprising: a hysteresis imparting means for imparting a hysteresis . 2. The light emitting device according to claim 1, wherein the light projecting means includes a light emitting element comprising a laser diode, and a light emission amount is controlled by a control signal pulse-modulated based on an output value of the integrator. Optical displacement measuring device.