JPH0449048B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a photoelectric position detection device, and in particular,
An illumination system suitable for non-contact measurement of thickness, displacement, etc. of a remote object using a triangulation method, which irradiates a light beam onto an object to be measured, and which emits light reflected from the light beam from the object to be measured. an objective lens that collects and forms an image; a photoelectric sensor having a one-dimensional light receiving surface for generating a detection signal corresponding to the light amount distribution of the formed image; and a light amount on the one-dimensional light receiving surface from the detection signal. The present invention relates to an improvement in a photoelectric position detection device that includes a processing circuit that generates a barycenter signal corresponding to the barycenter position of a distribution, and determines the position or displacement of a measurement object from a change in the barycenter signal.

[Conventional technology]

With the automation of production and the introduction of robots in industry, there is a rapid demand for in-process measurement, higher speed, and higher accuracy. There is also a growing need for a position detection device that can measure the thickness, displacement, etc. of a remote object in a non-contact manner. As shown in FIG. 7, a promising example of such a non-contact position detection device is a photoelectronic device that detects the position or displacement by triangulation by irradiating the object 10 with a light beam such as a laser beam 14. type position detection devices are known. The position detection device shown in FIG. 7 includes an illumination system 12 that irradiates a laser beam 14 onto an object to be measured 10, and an objective lens 16 that collects reflected light of the laser beam from the object to be measured 10 and forms an image on an imaging plane. , a semiconductor position detector (PSD) 18 as a photoelectric sensor having a one-dimensional light receiving surface for generating detection signals b, c corresponding to the light intensity distribution of the formed image, and the detection signals b, c. and a processing circuit 20 for generating a center of gravity signal d corresponding to the center of gravity position O' or A' of the light intensity distribution on the one-dimensional light receiving surface. When the measurement object 10 is relatively displaced in the X direction, the irradiation point of the laser beam 14 changes from point O to point A.
The center of gravity of the imaging position by the objective lens 16 also moves from point O' to point A', and the center of gravity signal d changes accordingly. Therefore, by recording the center of gravity signal d while relatively displacing the measurement object 10 in the X direction, the shape of the measurement object 10 can be measured. Further, even when there is no relative displacement in the X direction, if the measurement object 10 is displaced in the Z direction, the amount of displacement or the position in the Z direction can be similarly determined from the center of gravity signal d.

[Problems to be solved by the invention]

However, in such a photoelectric position detection device, a type of noise signal is superimposed on the center of gravity signal d due to surface properties such as surface roughness of the measurement surface of the measurement object 10, which deteriorates detection accuracy. There was a problem. That is, as shown in FIG. 8, the measurement surface 10S of the measurement object 10 has microscopically irregular irregularities, and the light intensity distribution on the imaging surface is also irregular accordingly. It's summery. Therefore, measurement object 1
0 in the X direction, the Z of the measurement object 10
Even when the displacement in the direction can be ignored as an average, the light intensity distribution changes as m or n, and a kind of noise signal is mixed into the center of gravity signal d, so an unnecessary displacement signal is output and the measurement accuracy is reduced. It gets worse. To solve this problem, the diameter of the laser beam 14 is
Although it is conceivable to increase the value, there are problems such as a decrease in the resolution in the X direction and distortion of the image on the imaging plane.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and provides a photoelectric position detection device that is not easily affected by the surface roughness of the measurement surface of the object to be measured, and that allows easy vibration of the vibrating mirror. The purpose is to provide

[Means to solve the problem]

The present invention provides an illumination system that irradiates a light beam onto an object to be measured, an objective lens that collects reflected light of the light beam from the object to form an image, and a detection system that corresponds to the light intensity distribution of the formed image. to generate a signal,
It includes a photoelectric sensor having a one-dimensional light-receiving surface, and a processing circuit that generates a center-of-gravity signal corresponding to the position of the center of gravity of the light amount distribution on the one-dimensional light-receiving surface from the detection signal,
In the photoelectric position detection device that determines the position or displacement of the object to be measured from a change in the center of gravity signal, the illumination system includes a vibrating mirror that changes the direction of the light beam, and a sinusoidal drive signal that rotates the signal mirror back and forth. a vibrating exciter that causes the light beam to slightly vibrate on the object to be measured; The above object is achieved by providing an integrating circuit that integrates the center of gravity signal and generating a signal indicating the position or displacement of the object to be measured based on the integrated signal of the integrating circuit.

[Effect]

The present invention provides a triangulation-type photoelectric position detection device as described above, in which the illumination system includes a vibrating mirror that changes the direction of the light beam and an exciter that rotates the vibrating mirror back and forth. Since minute vibrations are made on the object to be measured, the influence of the roughness of the measurement surface of the object to be measured can be reduced. Further, the processing circuit is provided with an integrating circuit that integrates the center of gravity signal only when the exciter is in the neutral position in synchronization with the reciprocating rotation of the exciter, and the integrated signal of the integrating circuit is used to integrate the center of gravity signal. Since the signal indicates the position or displacement of the object, the center of gravity signal in the region where the reciprocating rotation of the vibrating mirror is unstable is removed, making it possible to detect the position or displacement with high accuracy. Furthermore, the vibrating mirror,
Since the mirror is rotated back and forth using a sinusoidal drive signal, the drive signal can be generated easily and inexpensively, and the vibrating mirror can be easily vibrated.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. In this embodiment, as shown in FIG.
An illumination system 30 consisting of a laser diode 32, a collimator lens 34, a vibrating mirror 36, an exciter 38, and an illumination lens 40 for irradiating a laser beam 14 as a light beam onto the object 1 to be measured.
an objective lens 16 similar to the conventional one that collects the reflected light of the laser beam 14 from zero and forms an image; As a photoelectric sensor
It is configured to include a PSD 18 and a processing circuit 42 that generates a barycenter signal d corresponding to the barycenter position of the light amount distribution from the detection signals b and c. In the figure, 44 is a frame. In the illumination system 30, a laser diode 3
2 is provided near the focal point of the collimator lens 34, and the vibrating mirror 36 is provided near the focal point of the illumination lens 40. Therefore, when the vibrating mirror 36 is vibrated (reciprocated) in the θ direction by the vibrator 38, the laser beam 14 is slightly vibrated in the x direction parallel to the surface of the object 10 to be measured. In this case, the laser beam 14 is transmitted through the illumination lens 4
Although the laser beam 14 is focused near the focal point on the opposite side from the oscillating mirror 36 of 0, the diameter of the laser beam 14 that enters the illumination lens 40 is not so large.
A wide area before and after the focus becomes the measurement range in the Z direction. The vibrator 38 includes, for example, a magnetic frame 38A and a permanent magnet 38B, as shown in FIG.
A galvanometer-type vibrator can be used, which is configured to include a coil 38C and a rotating shaft 38D including an iron piece, and a vibrating mirror 36 is fixed to the rotating shaft 38D. In this galvanometer type exciter, an excitation signal a is applied to the coil 38C.
When a sinusoidal alternating current is applied as
D rotates back and forth in the θ direction. Further, as shown in FIG. 3, the vibrator 38 is configured to include a coil 38E and a U-shaped diaphragm 38F made of iron, and a oscillating mirror 36 is fixed to the U-shaped diaphragm 38F. A natural vibration type exciter can also be used. Even in this natural vibration type exciter, when a sinusoidal alternating current is passed through the coil 38E as the excitation signal a, the U-shaped diaphragm 38
Since F vibrates at its natural frequency, the vibrating mirror 36 rotates back and forth in the θ direction. The vibrators shown in FIGS. 2 and 3 both have known configurations, but the vibrator 38 may have other configurations, as long as it can reciprocate in the θ direction. . As shown in detail in FIG. 4, the processing circuit 42 receives the detection signals b,
A current-voltage converter 42A that converts c into a voltage, a subtracter 42B and an adder 42C that calculate the difference and sum of the outputs of the current-voltage converter 42A, respectively, and a subtracter 42B and an adder 42C that respectively calculate the difference and sum of the outputs of the current-voltage converter 42A, and from these outputs correspond to the center of gravity position of the light amount distribution. and a divider 42D that generates a center of gravity signal d. The center of gravity signal d is expressed by the following equation using a coefficient k, and is made to correspond to an accurate center of gravity position even if the amount of light decreases as a whole. d=k(b-c)/(b+c)...(1) This center of gravity signal d is integrated by the integrating circuit 42F while the analog switch 42E is off, and becomes an integral signal e. When switch 42G is turned off, the signal is held in sample/hold (S/H) circuit 42H. The signal held in the S/H circuit 42H is taken into a microprocessor (CPU) 42J via an analog/digital (A/D) converter 42I, and after being subjected to processing such as averaging, it is converted into a digital signal. /Analog (D/A)
It is outputted to the outside as a displacement signal f via the converter 42K. The on/off control circuit for the analog switches 42E and 42G includes an oscillator 42L, a window comparator 42M, and an inverter 42N. The oscillator 42L generates a sinusoidal alternating current signal for the excitation signal a to the vibrator 38, and part of it is input to the window comparator 42M whose reference signals are Vref ⁺ and Vref ^- . This window comparator 42M outputs a signal h which is at a high level when the excitation signal a is at an intermediate level between the reference signals Vref ⁺ and Vref ^- , and is at a low level in other cases. The effects of the embodiment will be explained below. FIG. 5 shows the center of gravity signal d obtained in this example. First, in the state shown in FIG.
As shown in section T ₁ in the figure, it changes sinusoidally with an average value d ₁ , but noise due to the influence of surface roughness etc. is superimposed. Next, when the measurement object 10 is displaced in the X direction and crosses a step, the center of gravity signal d repeats a sinusoidal vibration with an average value d ₂ that is changed by Δd from T ₁ as shown in section T ₂ shown in FIG. . Therefore, it is sufficient to find the average value d ₁ or the like, but using a simple low-pass filter may cause an error. That is, as is clear from the enlarged view of the center of gravity signal d shown in FIG.
Experiments have revealed that in the concave portion (region R), the signal excluding the noise component deviates from the ideal sine wave (dashed line). That is, regions Q and R are the first
This includes the region where the vibrating mirror 36 shown in the figure is displaced the most from the neutral point of reciprocating rotation, and the excitation signal a reaches its maximum value in these regions Q and R, as shown in FIG. 6A. Or the minimum. Therefore, since the operation of the vibrating mirror 36 becomes unstable near the turning point of vibration, it is considered that the center of gravity signal d also becomes unstable. Therefore, in the present invention, as in the embodiment, the reference signal
A window comparator 42M having Vref ⁺ and Vref ^- is used. The output h of this window comparator 42M is as shown in FIG. 6B, and by integrating the center of gravity signal d only when the output h is at a high level, the center of gravity signal d is in a neutral region that can be approximated by a sine wave. I am trying to extract only the signal at that time. Further, this portion is a region where the sine wave can be approximated by a straight line, and it can be considered that substantially only the portion where the center of gravity signal d can be directly approximated is extracted and integrated. Specifically, the area P ₁ in FIG. 6C is integrated,
_P2 , and as seen from the vibrator 38, the center of gravity signal d is integrated only within the range where the vibrator 38 is in the neutral region P, as shown in FIG. 6A. As shown in Fig. 6D, the maximum value of the integral signal e is e ₂ →e ₁
→e ₂ ..., but this value is the S/H circuit 42
The data is taken into the CPU 42J via H. The CPU 42J calculates the average of the maximum values e ₂ and e ₁ . It is conceivable to multiply by a pre-stored coefficient. In any case, these values are averaged and removed by the influence of surface roughness, etc., and correspond to the average value d ₁ or z ₁ in Fig. 5, and the displacement signal f
It is output externally as . Here, since the deviation of the center of gravity signal d in Fig. 6C from the ideal sine wave is not always constant and may change from time to time,
With conventional devices that do not extract and process the regions P ₁ and P ₂ , it is possible to correct the error with a constant error during normal times, but there is a risk that a large error may occur at times. In this embodiment, since the excitation signal a immediately generates the signal h that determines the timing of integration, the signal h can be obtained relatively easily. Note that the method of generating the signal that determines the timing of integration is not limited to this, and for example, a signal obtained by feeding back the movement of the vibrator 38 may be input to the window comparator 42M instead of the excitation signal a. Therefore, it is also possible to obtain more accurate timing. This is particularly effective when the vibrator is of a natural vibration type. Further, in this embodiment, since the illumination lens 40 was added to the illumination system 30, the laser beam 1
4 can be vibrated in parallel on the object to be measured 10, making it possible to perform highly accurate measurements. Note that it is also possible to omit the illumination lens 40. In this case, the laser beam will be vibrated in a fan shape, but if the amount of vibration is small, the error will be negligible. In the above embodiment, the PSD 18 was used as the photoelectric sensor, but the type of photoelectric sensor is not limited to this, and a two-split photodiode or the like can also be used.

【Effect of the invention】

As explained above, according to the present invention, it is difficult to be affected by the surface roughness of the measurement surface of the object to be measured,
Moreover, it becomes possible to perform highly accurate measurements. Furthermore, it has excellent effects such as easy vibration of the vibrating mirror.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the overall configuration of an embodiment of a photoelectric position detection device according to the present invention, and FIG. 2 is a cross-sectional view showing the structure of an example of the vibrator used in the embodiment. FIG. 3 is a front view showing the structure of another example of the vibrator, FIG. 4 is a block diagram showing the structure of the processing circuit used in the above embodiment, and FIG. 5 is a front view showing the structure of another example of the vibrator. FIG. 6 is a diagram showing an example of the change state of the center of gravity signal d in the example, FIG. 6 is a diagram showing an example of the signal waveform of each part in the example, and FIG. 7 is the configuration of an example of a conventional photoelectric position detection device. FIG. 8 is an enlarged sectional view for explaining problems caused by surface roughness of the prior art. 10...Measurement object, 14...Laser beam,
16... Objective lens, 18... PSD (photoelectric sensor), b, c... Detection signal, O', A'... Center of gravity position, 30... Illumination system, 32... Laser diode, 36... Vibrating mirror , 38... vibrator, a...
...Excitation signal, 40...Illumination lens, 42...Processing circuit, d...Centroid signal, 42E, 42G...Analog switch, 42F...Integrator circuit, e...Integral signal, f...Displacement signal, 42L ...oscillator, 42
M...window comparator, 42N...inverter, _P1 , _P2 ...integral region, p...neutral region.

Claims (1)

[Claims] 1. An illumination system that irradiates a measurement target with a light beam;
an objective lens that collects reflected light of the light beam from the object to be measured and forms an image; a photoelectric sensor that has a one-dimensional light-receiving surface for generating a detection signal corresponding to the light intensity distribution of the formed image; and a processing circuit that generates a center of gravity signal corresponding to the center of gravity position of the light intensity distribution on the one-dimensional light receiving surface from the detection signal, and determines the position or displacement of the object to be measured from a change in the center of gravity signal. In the illumination system, the illumination system includes a vibrating mirror that changes the direction of the light beam, and an exciter that rotates the vibrating mirror back and forth in response to a sine wave drive signal, so that the light beam is minutely directed onto the object to be measured. At the same time as vibrating, the processing circuit is provided with an integrating circuit that integrates the center of gravity signal only when the vibrating mirror is in a neutral region in synchronization with the reciprocating rotation of the vibrator, and based on the integral signal of the integrating circuit. A photoelectric position detection device that generates a signal indicating the position or displacement of an object to be measured.