JPS6217163B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a proximity sensor for detecting the movement and distance of a non-diffuse reflective object in a short range,
In particular, the present invention relates to a proximity sensor that can be effectively used for positioning, shape measurement, collision prevention detectors, etc. for materials handling in production systems. Various types of proximity sensors have been proposed in the past, including electromagnetic sensors, pneumatic sensors, and optical sensors. However, electromagnetic sensors have the drawback that the objects for which distance detection is limited to electromagnetic induction objects, and the detection range is limited to several millimeters, while pneumatic sensors require large devices and The drawback is that the detectable range is extremely narrow. Also,
Optical sensors combine a pair of light-emitting elements and light-receiving elements with a lens system to detect distance, etc.
This method has the drawbacks that the device is complicated, the detection operation is complicated, and short distances cannot be detected. Furthermore, such optical sensors are usually used for objects that reflect diffusely, and have the disadvantage that they cannot measure objects that do not reflect diffusely, such as metal surfaces or mirror surfaces. SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a proximity sensor with a simple configuration that does not have the above-mentioned drawbacks. This invention will be explained below. Figure 1 shows the basic principle of this invention, and 1 and 2 are light emitting diodes (e.g. GaAs-LED) that emit highly diffused and uniformly spread light.
and is driven by two repetitive signals, each 90° out of phase. A phototransistor 4 as a light-receiving element with strong directivity is provided in the middle of the mounting plate 3 where these light emitting diodes 1 and 2 are attached, and in front of the phototransistor 4 there is a target whose distance x is to be detected. There is object 5. Here, of the light emitted from the light emitting diodes 1 and 2, only the light that is diffusely reflected by the surface P of the target object 5 is received by the phototransistor 4. Considering only the frequency components, it is sufficient to consider that the brightness of the light emitting diodes 1 and 2 changes periodically with a sine wave and a cosine wave. Therefore, the brightness G ₁ and G ₂ of light emitting diodes 1 and 2 are given by A and B as constants. The contributions L ₁ and L ₂ by the light emitting diodes 1 and 2 at point P on the surface of the target object 5 are expressed as follows, assuming that the reflectance of the target object 5 is C. becomes. Also, It is Therefore, the above equation (2) becomes as shown below. Here, the brightness L _P at point P is expressed as L _P =L ₁ +L ₂ (6), so by substituting equation (5) into this, we end up with the following equation. however It is. As is clear from these equations (7) to (9), the phase is a function of only the distance x (A, B, a, and b are each constant), and the reflectance C of the surface of the target object 5
unaffected by Therefore, if the brightness L _P at point P is detected by the phototransistor 4 and the phase difference between the two lights is determined, the distance x can be measured conversely from this. Note that the brightness L at point S of the phototransistor 4 that receives light
_S is proportional to the brightness L _P at point P, and if its proportionality constant is K, then Therefore, it does not affect the phase of equation (7) above. Here, a specific example of a measurement circuit is shown in FIG. 2 and explained.
The output of is input to the light emitting diode 1, and
The signal is input to the light emitting diode 2 via the phase shifter 11. In the phase shifter 11, the phase is advanced (or delayed) by 90 degrees, and the light emitting diodes 1 and 2 are driven to emit light using rectangular wave repetition signals corresponding to sine and cosine, respectively. Figure 3A shows P by light emitting diode 1.
This shows an example of the brightness of a point, and FIG. 3B shows an example of the brightness of a point P by the light emitting diode 2.
As shown in Figure C, they are synthesized into a step-like shape. Such stepwise brightness is photoelectrically detected by a phototransistor 4, amplified by an amplifier 12, and then harmonics and subharmonics are removed by a bandpass filter 13 to become a sine wave, which is converted into a sine wave by an automatic gain circuit (AGC) 14. The signal maintained at a predetermined level is input to the phase difference detection circuit 20. The phase difference detection circuit 20 includes an oscillator 10
A reference rectangular wave from is inputted, and a phase shift with respect to this reference rectangular wave is detected. Specifically, the sine wave output of the automatic gain circuit 14 is converted into a rectangular wave with a threshold of 0 level by a rectangular wave conversion circuit (for example, a comparator) 21, and this rectangular wave signal is multiplied by the reference rectangular wave from the oscillator 10. A circuit 22 performs multiplication and obtains a phase difference from the product signal.
The phase difference signal obtained in this way is sent to the display device 30, where the phase difference is converted into a distance and the distance is displayed, and the distance signal is separately processed as required. Next, as shown in FIG. 4, consider the case where light perpendicular to the surface S ₁ illuminates the surface S ₂ forming an angle θ with the surface S ₁ . Here, if l ₁ and l ₂ are the power of light per unit area of surfaces S ₁ and S ₂ , the total power passing through surfaces S ₁ and S ₂ is equal, so l ₂ = l ₁・cosθ... …(11) holds true. In addition, the light source Q and the light receiving part S in the case of the above-mentioned detector are simplified as shown in Fig. 5, and applying the above discussion, the light per unit area at point P on the plane k perpendicular to . power l ₁ becomes. However, the power of light source Q is assumed to be Gq. Also, the power of light per unit area on surface i l ₂
is l ₂ = l ₁・cos (δ−θ ₁ ) (13), and since it is assumed that the reflection on each surface is diffuse reflection, the reflectance is C and the power in the PS direction is l ₃ . Then, l ₃ =C/cosδ·l ₂ (14) holds true. Therefore, from equations (12) to (14) above, It can be seen that the influence of the inclination of the surface appears in the coefficient cos (δ-θ ₁ )/cos δ (16). Note that this argument holds regardless of the sign of δ and the relationship between the magnitudes of θ and δ. From this premise, as shown in Figure 6, 1
Phototransistor 41 as two light receiving elements
(position S), and positions Q-Q', R- on a straight line that are symmetrical and equidistant from this phototransistor 41.
A system can be considered consisting of light emitting diodes 42, 43 and 44, 45 arranged in R'.
Further, the light emitting diodes 42 and 43 are driven by a sine wave, and the light emitting diodes 44 and 45 are driven by a cosine wave. Here, the output of the phototransistor 41 is the sum of the light reflected from the two sets of light emitting diodes 42-44 and 43-45, which are light emitting sources, on the inclined surface i. Therefore, S at point P due to the set of light sources 42-44
The power M ₁ of the reflected light in the direction is calculated as follows using the above equation (15). Similarly, the power M ₂ of the light reflected in the S direction at point P by the other light source sets 43 to 45 is expressed by the following equation (18). M ₂ =C/cosδ・{cos(δ+θ ₁ )・sinωt/a ² +x ² +cos(δ+θ ₂ )・cosωt/b ² +x ²
}...(18) Here, since the total power M in the PS direction at point P is expressed as the sum of equations (17) and (18), it is as follows. however It is. Here, the effects when the surface of the target object is tilted are as shown in the characteristics marked with ● in Figure 7.
It can be seen that there is no effect at all up to about 20°. In addition,
Characteristic A in FIG. 7 shows the theoretical value for the device shown in FIG. 1, and the circle mark shows an example of the measured value. Thus, by using the above-described device, it is possible to accurately measure the distance x from the position S of the light receiving device to the surface P of the target object, regardless of the inclination of the target surface. In this way, when one set of light sources is used, distance data containing information approximately proportional to the slope of the surface can be obtained, and by using two sets of light sources, it is possible to obtain distance data that is not affected by the slope of the surface. The distance to the target surface can be measured. Furthermore, since the difference between these two distance data is proportional to the inclination of the surface, the inclination of the surface can be measured by switching between the two sets of light sources (for example, Japanese Patent Application No. 50176-1982). . In the above case, the surface of the target object reflects diffusely and the phototransistor has strong directivity, but if the surface of the target object has non-diffuse reflection, that is, a mirror surface, and the phototransistor is non-directional. The optical system shown in FIG. 8 can be considered in correspondence with FIG. 1. In the figure, ML is a mirror surface, and the light from the light emitting diodes R and Q is considered to be incident on the mirror surface at a reflection angle equal to the incident angle, and non-directionally incident on the phototransistor S from a wide direction. Now, if we consider a general case where the mirror surface has an inclination δ, the result will be as shown in FIG. In the figure, ML is a mirror surface, and light emitting diodes 42 to 4
5 and phototransistor 41 are sensor image plane SL
The light of each emitted light is equivalently emitted on the sensor image plane SL and transferred to the phototransistor 4.
1. Here, mirror ML
_Letting ^{the slope} _of ^{_ _ _ _} (b+2xsin2δ) ……(22) ₁ ² =2x ² (1+cos2δ)+a(a+2xsin2δ) ……(23) ₁ ² =2x ² (1+cos2δ)+a(a−2xsin2δ) ……(24) ′ ₁ ² = 2x ² (1+cos2δ)+b(b-2xsin2δ) (25) Therefore, the power M of light at a point P on the mirror surface ML at a distance x is given by the following equation. however It is. Here, the above formula (27) is specifically tanφ={2x ² (1+cos2δ)+b ² /2x ² (1+cos2δ)+a ² } ×{4x ⁴ (1+cos2δ) ² +4x ² a ² (1+cos2δ)・cos2δ+a ⁴ /4x ⁴ (1+cos2
δ) ² +4x ² b ² (1+cos2δ)・cos2δ+b ⁴ }......(28) When δ=0°, that is, the slope is 0°, tanφ=4x ² +a ² /4x ² +b ² ...... (29) becomes. However, the units of a and b are, for example, cm. Then, for the slope δ = 0°, 30°, the distance x
= 1, 2, 3 (cm), distance a = 1cm, b = 3cm
When calculating tanφ in the case of , the result is as shown in Table 1 below.

[Table] As is clear from Table 1, the influence of the slope δ is considerable. However, when the slope δ is small, that is, when δ<15°, φ≈f(x, a, b), and the influence of the slope δ is small, so the distance x (cm) can be determined from the phase φ. For example, if it is known that the sensor plane and the object plane are parallel, the distance x can be measured with the inclination δ=0°. In this case, the above equation (29) may be used. Furthermore, if the light emitting diodes 44 and 45 are driven in a tilt mode in which sinωt and cosωt are used, φ″=tan ⁻¹ {xcosδ−bsinδ/xcosδ
+b sin δ} (30) is obtained, and if the slope δ is known, the distance x can be found. This characteristic is shown in FIG. Here, if the phototransistor 41 is given directivity to cause diffuse reflection on the surface of the target object,
The relationship between the distance x and the phase φ is as shown in FIG. 10, but if the target object has non-diffuse reflection characteristics, it becomes difficult for reflected light to enter the phototransistor. When the phototransistor is made omnidirectional, even if the surface of the target object has non-diffuse reflection characteristics, the relationship between the distance x and the phase φ is as shown in (29) above.
Based on the formula, the characteristics are as shown in FIG. Similarly, the relationship between the slope δ and the phase φ is as shown in FIG. 11. On the other hand, the detection of the phase φ, distance x, and slope δ according to the present invention can be configured by a circuit as shown in FIG. Reference signal S1 and detection signal S2
is input to the phase detector 40, and the detected phase φ
is input to the display 42 and also to the converter 41, and the phase φ-distance x is converted as described above. Therefore, if the phototransistor 41 is made non-directional in the configuration shown in FIG. 6, even if the surface of the target object has non-diffuse reflection like a mirror surface, it will be able to reflect over a nearly twice as wide range as the conventional sensor. It becomes possible to detect. As described above, according to the present invention, even if the surface of the target object is a non-diffuse reflective surface such as a metal surface or a mirror surface, it is possible to reliably measure the phase shift from the reference signal if the inclination is known. From this, the distance, movement, etc. of the target object can be determined. In addition, the device is small, lightweight, and inexpensive, and has the advantage of easy signal processing, and can be applied not only to robot hands but also to three-dimensional information detectors for object recognition. Note that although a light-emitting diode is used as the light-emitting element and a phototransistor as the light-receiving element in the above description, it is also possible to use other elements, and the repetitive signal for driving the light-emitting element may be a triangular wave, a sine wave, or a rectangular wave. Waves etc. are also possible. Further, in the above description, the light receiving element is attached to the same mounting surface as the light emitting element, but it is also possible to configure the light receiving element to be attached directly to the moving body (the surface of the target object).

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic principle of this invention, Fig. 2 is a block diagram showing an example of its measurement circuit, Figs. 3 A to C are diagrams showing the phase relationship between light emission and light reception, and Fig. 4
5 and 5 are diagrams for explaining the influence of the inclination of the detection surface, FIG. 6 is a diagram showing the measurement system that is the basis of this invention, and FIG. 7 is a diagram illustrating the influence of the inclination of the target surface. Figures 8 and 9 are diagrams for explaining the present invention, Figure 10 is a characteristic diagram showing the distance-phase relationship, Figure 11 is a characteristic diagram showing the phase-inclination relationship, and Figure 12 is a characteristic diagram showing the relationship between phase and inclination. FIG. 2 is a block diagram showing a distance and inclination detection system for phase difference. DESCRIPTION OF SYMBOLS 1, 2... Light emitting diode, 3... Mounting plate, 4... Phototransistor, 5... Target object, 10... Oscillator, 11... Phase shifter, 12... Amplifier, 13... Bandpass filter, 14... Automatic gain circuit, 20... Phase difference detection circuit, 21... Rectangular wave conversion circuit, 22... Multiplication circuit, 30... Display device, 41... Phototransistor, 42-45... Light emitting diode.

Claims (1)

[Claims] 1 Consisting of one non-directional light receiving device disposed facing the surface of a target object for non-diffuse reflection, and four light emitting elements arranged symmetrically on a straight line from this light receiving device, the light receiving device A first light emitting device and a second light emitting device, each pair of which emit light using repetitive signals that are 90° out of phase with each other, emit light from each pair of light emitting elements symmetrical to each other.
and a conversion means for converting a phase difference into a distance value, the irradiated light from the first and second light emitting devices is non-diffusely reflected on the surface of the target object,
The phase difference between the power of the light non-directionally input to the light receiving device and the repetitive signal is determined, and when the tilt of the target object is known, the phase difference is calculated using the conversion means. A proximity sensor, characterized in that the distance between the light receiving device and the target object can be detected according to the distance between the light receiving device and the target object.