JPH0682251A - Object detector - Google Patents

Abstract

PURPOSE:To set a distance used as a reference for detection of an object easily at high accuracy, in an object detector using a PSD. CONSTITUTION:The output of a PSD 33 is integrated by integration circuits 38 and 39 in synchronizm with the timing of projection through I/V conversion circuits 34 and 35. When the output of the integration circuit 38 reaches a threshold V0, the output signal VCOM of a comparator circuit 44 moves to a low level and, hence, the output of the integration circuit 39 is digitized with an A/D conversion circuit 45 to be transferred to a control means 20 as distance data. While an operating section 46 is operated, a distance data outputted from the A/D conversion circuit 45 is written into a memory 47. Otherwise, the control means 20 transfers the distance data to a comparator 48. The comparator 48 compares the current distance data transferred from the control means 20 with the distance data as reference value of a distance stored in the memory 47 to output a signal representing whether an object exists or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object detecting device for detecting whether or not an object exists in a predetermined detection area,
Especially as a position detecting element, a semiconductor position detecting element (Position
Sensitive Detectors) (hereinafter referred to as PSD).

[0002]

2. Description of the Related Art Conventionally, an object detecting device using a PSD as a position detecting element is known. The schematic structure is shown in FIG.
Will be described with reference to. The object detection device includes a light projecting unit 1, a light receiving unit 2, and a signal processing unit 3. The light projecting unit 1 projects a light emitting element 4 such as a light emitting diode (LED), a pulse lighting circuit 5 for pulse-lighting the light emitting element 4, and pulse light emitted by the light emitting element 4 to a predetermined detection area. The lens 6 is provided as an optical unit for

The light receiving portion 2 is a PSD 7 as a position detecting element.
And a lens 8 which is an optical means for focusing and forming the reflected light from the detection area direction on the light receiving surface of the PSD 7. Here, the light receiving section 2 is arranged in a triangulation manner with respect to the light projecting section 1 and the detection area.

When the detected object 18 does not exist in the detection area, the pulsed light projected from the light projecting section 1 is reflected by the background 19 such as a wall surface or a floor surface as shown by a solid line in the figure, The reflected light is imaged by the lens 8 at the position P ₁ on the light receiving surface of the PSD 7. The PSD 7 outputs two currents I ₁ and I ₂ according to the image formation position of the reflected light on the light receiving surface, which are processed in the signal processing unit 3 as follows.

First, these two output currents I ₁ and I ₂ are converted into current / voltage conversion circuits (hereinafter referred to as I / V conversion circuits).
Are converted into voltages V ₁ and V ₂ by 9 and 12, respectively,
It is input to the amplifiers 10 and 13 having the amplification factor α. At this time, as can be seen from the image forming position on the light receiving surface of PSD 7 in the figure, I ₁
> I ₂ , and therefore V ₁ > V ₂ , the amplifier 1
The outputs αV ₁ and αV ₂ of 0 and 13 have a relationship of αV ₁ > αV ₂ .

Here, the AGC circuit 11 monitors so that αV ₁ is not saturated, and controls the amplification factor α of the two amplifiers 10 and 13 within a practical range. Output alpha] V ₁ of amplifier 10, 13, alpha] V ₂ is inputted predetermined arithmetic processing in the arithmetic circuit 14, for example _{(αV 1 -αV 2) / (} αV 1 + αV 2) = (V 1 -V 2) / (V ₁ + V ₂ ) (1) or V ₁ / (V ₁ + V ₂ ) (2) etc. are calculated, and a signal indicating the distance to the detected object (hereinafter referred to as a distance signal) is generated. . This distance signal is input to the comparison means 15 and compared with the preset reference value by the comparison reference setting means 16.

The output circuit 17 performs a predetermined process according to the output of the comparison means 15. For example, when the output of the comparison means 15 indicates the existence of the detected object, the detected object exists. Output a signal.

[0008]

By the way, the distance from the light projecting portion 1 and the light receiving portion 2 to the background 19 changes depending on the mounting position of the object detecting device, and therefore the reference value in the comparing means 15 also. It needs to be changed according to the distance to the background 19. This is because the reference value of the comparison means 15 needs to be a distance signal obtained when no object to be detected exists in the detection area, that is, a distance signal corresponding to the distance to the background 19.

Therefore, in the conventional object detecting device, the comparison reference setting means 16 including a variable resistor or the like is used.
It is usually possible to change the reference value by means of this, but this reference value is set every time the object detection device is attached, and moreover, it has to be done manually, which is very troublesome. Besides, it is not only troublesome, but it causes a malfunction if the setting is wrong.

Further, the AGC circuit 11 of the signal processing unit 3 is provided for stabilizing the signal,
There is a limit to the controllable signal level range, and PSD7
Since the noise component is also amplified when the output from the device is very small, improvement of the S / N ratio cannot be expected.

On the other hand, instead of providing the AGC circuit, the amount of light emitted from the light emitting element 4 is controlled by the amplifier 10 or the amplifier 1.
It is also proposed to stabilize the signal by changing it according to the output signal level of 3.
Since the circuit configuration is complicated and the current that can be supplied to the LED is limited, it is very difficult to dramatically improve the S / N ratio.

Further, when the arithmetic operation is performed by the arithmetic circuit 14 by the equation (1), the arithmetic characteristic at the image forming position (x) on the light receiving surface of the PSD is as shown in the graph of FIG. , The PSD is symmetrical with respect to the center x ₀ of the light-receiving surface, only half of the light-receiving surface of the PSD can be used, and reflected light is imaged on the other side due to an assembly error or the like. In some cases, it could cause malfunction.

Therefore, in order to prevent such malfunction, the center of the light-receiving lens 8 and the center of the light-receiving surface of the PSD 7 must be aligned with high accuracy, and the assembly is very troublesome.

Further, when the calculation of the above formula (2) is performed, the calculation characteristic is as shown in FIG. 7, and since it is possible to use the entire light receiving surface of the PSD, the lens as described above is used. (1) although it does not require the optical axis adjustment of PSD and
Since the slope of the characteristic curve is gentler than the characteristic obtained as a result of the equation, there is a problem that the resolution of object detection is lowered.

Furthermore, an addition circuit and a division circuit are required to perform the operation of the equation (2), and a subtraction circuit is additionally required to perform the operation of the equation (1). There is a problem that the configuration is complicated and the cost is high.

The present invention is intended to solve the above problems, and it is possible to easily and highly accurately set a reference value supplied to a comparing means, that is, a level corresponding to a distance serving as a reference for object detection. It is an object of the present invention to provide an object detection device which is not only capable of being saturated, but also which can significantly improve the S / N ratio as compared with the prior art.

It is another object of the present invention to provide an object detection device having a simple circuit structure and high resolution with respect to distance.

[0018]

In order to achieve the above object, an object detecting device of the present invention comprises a light projecting section for projecting a light projecting beam toward a predetermined detection area and a position detecting element. A semiconductor position detecting element and a condensing optical system arranged in front of the semiconductor position detecting element, and the light projecting section and the detection area are arranged in a triangulation manner and projected from the light projecting section. In an object detection device including a light receiving unit that receives reflected light from a beam detection area and a signal processing unit that processes an output signal of the semiconductor position detection element, an optical axis of the focusing optical system is the semiconductor position detection unit. The signal processing means is shifted from the center position of the light receiving surface of the element in any of the longitudinal directions of the light receiving surface. The power on the side where the axis is displaced First current to convert the output into a voltage /
The voltage converting means, the second current / voltage converting means for converting the current output on the other side of the semiconductor position detecting element into a voltage, and the output voltages of the first and second current / voltage converting circuits, respectively. First and second integrating means for integrating in synchronization with the light projecting timing of the light projecting section, and an output voltage of the first integrating means when the output voltage of the second integrating means reaches a predetermined threshold value. A / D conversion means for A / D conversion, memory means for storing the output value of the A / D conversion means as a reference value for object detection, and output value of the A / D conversion means for the memory means When it is judged that an object exists by comparing the output value of the A / D conversion means with the reference value written in the memory means, the object exists. Ratio to output a signal to that effect Means, A of the A / D conversion means
Reset means for resetting the first and second integrating means after the / D conversion operation is completed.

[0019]

In the present invention, the memory means and the timing means are provided. The memory means stores a value used as a reference value for object detection in the comparison means, and the timing means gives a timing for writing the reference value to the memory means.
Therefore, when the memory means receives the write timing from the timing means, it writes the digital value output from the A / D conversion means at that time. This is the standard value. As a result, the distance signal corresponding to the distance to the background, which is the determination reference for object detection, can be directly set as the reference value in the comparison means, so that not only can object detection be performed with high accuracy, but the setting, Changes can be made easily.

Further, in the present invention, the optical axis of the condensing optical system arranged on the front surface of the PSD is displaced from the center position of the light receiving surface of the PSD in any of its longitudinal directions.
This deviation amount is not required to be accurate enough to require position adjustment with the condensing optical system, so that the labor of position adjustment at the time of assembly can be saved.

Further, in the present invention, the distance signal is the second signal.
Since the output voltage of the first integrating means is obtained by A / D conversion when the output voltage of the integrating means reaches a predetermined threshold value, the resolution of the distance can be greatly improved as compared with the conventional case. In addition, since a circuit for performing the conventional calculation is not required, the cost can be reduced.

Furthermore, in the present invention, an AGC circuit is not provided,
Since the two output currents of the PSD are each converted into a voltage and then integrated by synchronizing with the light projecting timing of the light projecting unit, there is provided an integrating means, even if the light reflected from the background is very weak. S / N ratio is n ^1/2 by integrating twice
It can be doubled and the signal saturation can be prevented.

[0023]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an embodiment of an object detecting device according to the present invention, in which 20 is a control unit, 21 is a light projecting unit, and 2 is a light emitting unit.
2 is a drive circuit, 23 is a light emitting diode (hereinafter referred to as LED) that emits infrared rays, 24 is a lens, 31 is a light receiving portion, 32 is a lens, 33 is PSD, 34 and 35 are I / V.
Conversion circuits, 36 and 37 are switches, 38 and 39 are integration circuits, 40 and 41 are reset switches, 44 is a comparison circuit,
45 is an A / D conversion circuit, 46 is an operation unit, 47 is a memory,
Reference numeral 48 is a comparator, 49 is an output circuit, 51 and 52 are high-pass filters (hereinafter referred to as HPF), and 53 is a reference voltage generation circuit.

In FIG. 1, the control means 20 centrally manages the operation of each part of the object detecting apparatus, and is composed of a microprocessor and its peripheral circuits. The details of the operation will be described later. Projector 21
Is provided with an LED 23, a drive circuit 22 for driving the LED 23, and a lens 24 for projecting pulsed light emitted from the LED 23 in the direction of a predetermined detection area. The drive circuit 22 is composed of, for example, a constant current circuit as shown in the drawing, and the drive signal D output from the control means 20.
It is designed to operate only when R is at a predetermined level, for example, a high level as shown in FIG. 2A.

The light receiving section 31 includes a PSD 33 and a lens 32 as a condensing optical system for forming an image of reflected light from the detection area direction on the light receiving surface of the PSD 33. The optical axis of the lens 32 is the PSD 33. It is arranged so as to be offset from the center position of the light receiving surface by the offset amount D _{OF in} the longitudinal direction of the light receiving surface.

The output currents I ₁ and I ₂ of the PSD 33 are converted into voltages by the I / V conversion circuits 34 and 35, and are input to the HPFs 51 and 52. HPF 51, 52
Is provided to remove a noise component due to ambient light.

The switches 36 and 37 are closed in synchronization with the light emission of the LED 23. That is, the switches 36 and 37 are closed only when the drive signal DR is at high level.

Since the reset switch 40 of the integrating circuit 38 and the reset switch 41 of the integrating circuit 39 are normally opened, the signals input via the switches 36 and 37 are sequentially integrated. The output voltage V ₁ of the integration circuit 38 is input to the comparison circuit 44 and compared with a predetermined reference voltage V ₀ .

The comparison circuit 44 compares V ₁ with the reference voltage V _0, and when V ₁ <V ₀ , it is at a high level, V ₁ ≧ V
_When it is ₀ , a low level is output, but the comparison circuit 44 is composed of a comparator circuit or the like having hysteresis in order to stabilize the operation. In the comparator circuit having no hysteresis, the threshold value V _TH1 when falling from the high level to the low level and the threshold value V _TH2 when rising from the low level to the high level are the same value, and the following problems occur. That is, the output voltage V of the integrating circuit 38
₁ shows that the S / N ratio is improved by the effect of signal integration, but the noise component is not at all present, and therefore the output voltage V ₁ may fluctuate due to noise or other factors. Threshold V _{TH1 as} shown in 3A
When it occurs in the vicinity of (= V _{TH 2} ), the output V _COM of the comparison circuit 44 frequently repeats the low level and the high level as shown in FIG. 3B, and a stable output cannot be obtained.

On the other hand, in the comparison circuit having hysteresis, since V _TH1 > V _TH2 is set, even if the output voltage V ₁ of the integrating circuit 44 fluctuates to some extent as shown in FIG. 3C. , V ₁ does not fall below V _TH2 , the state is maintained once it becomes low level as shown in FIG. 3D, so that a stable output can be obtained. In the comparison circuit 44 shown in FIG. 1, the difference between V _TH1 and V _TH2, that is, the width of hysteresis is V _C × R ₁ /
It is given by (R ₁ + R ₂ ), but in reality, about 0.1 V is sufficient.

As described above, the signal based on the reflected light from the background or the detected object is sequentially integrated in synchronism with the projection timing, so that the S / N ratio is higher than that in the case of using the conventional AGC circuit. Can be significantly improved. For example, when there is an object with a small reflectance in the distance, the reflected light becomes very weak, but the signal based on the reflected light is integrated every time the light is projected, so the integrating circuit 3
An output signal having a good S / N ratio can be obtained from Nos. 8 and 39.

The output signal V _COM of the comparison circuit 44 is transferred to the control means 20. Then, the control means 20 outputs the signal V _COM.
Is monitored, and when the signal V _COM becomes low level as shown in FIGS. 2B and 2C, the A / D conversion circuit 45 is set at a predetermined timing.
Outputs a signal AD instructing to start the A / D conversion operation to
After that, when the A / D conversion operation is completed, as shown in FIG. 2D, the reset switch 40 of the integrating circuit 38 and the integrating circuit 3 are
Signal RE for closing the reset switch 41 of 9
Output S. The integrating circuits 38 and 39 hold the n-th integrated value until the (n + 1) -th integration operation is performed, and therefore also have a sample / hold function. After finishing and (n
When the signal V _COM becomes low level before the +1) th integration operation is started and the signal AD is output from the control means 20, the A / D conversion circuit 45 outputs the stable output voltage V ₂ from the integration circuit 39. Can be taken in and A / D converted.

The reset switches 40 and 41 of the integrating circuits 38 and 39 are closed at the rising edge of the signal RES,
This resets the integrating circuits 38 and 39. Therefore, at this time, the output signal V _COM of the comparison circuit 44 is as shown in FIG.
As shown in B, it becomes high level.

The timing at which the control means 20 outputs the signal RES can be set as appropriate. For example, A
Since the time required for the A / D conversion circuit 45 to take in the voltage applied to the input terminal V _IN after the A / D conversion start is instructed is determined by the A / D conversion circuit used, the signal AD is output. Alternatively, the signal RES may be output after the time has elapsed, and the control means 20 outputs the signal RES when it detects that the output data is transferred from the A / D conversion circuit 45. You can also do so.

Upon receiving the signal AD from the control means 20, the A / D conversion circuit 45 outputs the value of V _IN / (V _{REF (+) -} V _{REF (-)} ) (3) as a digital value. However, in FIG.
_Since the terminal of _{REF (-)} is grounded, the value of V _IN / V _{REF (+)} = V ₂ / V _{REF (+)} (4) is digitized. However, in the configuration shown in FIG. 1, the relationship of V _{REF (+)} / V ₀ = V _{REF (+)} / V ₁ (5) holds, and if the value of this equation (5) is K, then K
> 1, and the equation (4) becomes V ₂ / V _{REF (+)} = V ₂ / K × V ₁ = (1 / K) × V ₂ / V ₁ (6) Therefore, the output of the A / D conversion circuit 45 is the digitized value of the equation (6). It is obvious that the output of this A / D conversion circuit indicates the distance to the background or object in the detection area. (Hereinafter, this is referred to as distance data). It is also apparent that the outputs of the A / D conversion circuit 45 are the same when they are at the same distance, although the number of times of integration differs depending on the difference in reflectance of the object.

Further, the output characteristic of the A / D conversion circuit 45 is as shown in FIG. 4, and it can be seen that the resolution is improved at a long distance as compared with the conventional case. That is, the value obtained by dividing the output current I ₂ from the PSD 33 by I ₁ is given by I ₂ / I ₁ = (L-2x) / (L + 2x) (7). Note that L is the length of the light receiving surface of the PSD 33, and the origin of the horizontal axis x in FIG. 4 is the center position of the light receiving surface of the PSD 33. The output currents I ₁ and I ₂ from the PSD 33 are converted into voltage values proportional to the current values by the I / V conversion circuits 34 and 35, respectively, so that I ₂ / I ₁ =
It can be V ₂ / V ₁ . Here, in the configuration of FIG. 1, assuming that an image is formed at a position where the optical axis of the lens 32 and the light receiving surface of the PSD 33 intersect, that is, the image forming position when infrared rays are incident from the point at infinity is indicated by P in FIG. Since the optical axis of the lens 32 and the center of the light receiving surface of the PSD 33 are displaced by the offset amount D _OF , V ₂ > V ₁ , and therefore V _{2 with} respect to the image forming position x on the light receiving surface of the PSD 33. The characteristics of the operation of / V ₁ are as shown in FIG.
Therefore, the image formation point of the reflected light reflected from the finite position becomes P as the detected object approaches the object detection device.
It was found that the lens 32 and the PSD 33 should be arranged so as to move to the left in FIG. 4 through the center on the light receiving surface of the SD 33, which can improve the resolution at a long distance. it can. The amount of displacement Δx of the light imaging position x from the point P is f, the focal length of the light receiving lens 32, and the base line length, that is, the lens 24 of the light projecting unit 21 and the light receiving unit 31.
It is possible to obtain Δx = f × S / L, where S is the distance between the centers of the lenses 32 and L is the distance to the object. From this equation, it can be seen that Δx increases as the object approaches, and the resolution improves at a short distance. That is, it can be said that the output characteristic and the optical characteristic of the A / D conversion circuit have a complementary relationship.

The control means 20 writes the distance data from the A / D conversion circuit 45 into the memory 47 immediately after the operation section 46 composed of a switch such as a push button switch is operated. When the operation unit 46 is not operated, the distance data is transferred to the comparator 48. That is, the operation unit 46 gives the write timing of the memory 47.

The comparator 48 compares the distance data transferred from the A / D conversion circuit 45 with the distance data as the reference value written in the memory 47 and outputs a signal indicating the presence or absence of an object. The operation is the same as that of the comparison means 15 of the conventional object detection device shown in FIG. 5 except that the data to be handled is a binarized digital value.
The output circuit 49 is also similar to the output circuit 17 shown in FIG.

Therefore, by operating the operation unit 46 after installing this object detection device, it is possible to write the distance data as a reference of the distance for object detection in the memory 47. Then, when it is necessary to change the distance reference, such as when the detection area is changed after the distance reference is once set, the operation unit 46 is operated again to store a new distance reference in the memory 47. You can write to.

Such an object detecting device can be used for various purposes. For example, the case where it is used as a sensor for detecting the presence or absence of a vehicle in each parking space of a parking lot will be described below. .

Since the height of the ceiling varies depending on the parking lot, it takes a lot of time if the distance, which is the reference value for object detection, is manually set by a variable resistor or the like as in the prior art. According to the above configuration, it is possible to easily write the distance data to the floor, which is the background, as the reference value in the memory 47 simply by operating the operation unit 46 after installing the object detection device on the ceiling. When there is a vehicle in the parking space, a signal indicating the presence of the vehicle can be output. On the contrary, when the operating unit 46 is operated to write the reference value in the memory 47 when the vehicle is present, when the vehicle exits, a signal indicating that fact can be output.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. For example, the control means, the comparison means, the memory, and the A / D conversion circuit can be configured by a microcomputer IC or the like in one package. In that case, the number of parts can be reduced and the cost can be reduced. .

Further, in the above-mentioned embodiment, the operator manually operates the operation unit, but if the distance data, which is the reference for object detection, is automatically written in the memory when the power is turned on, a large number of objects can be detected at one time. A reference value can be set for the device. Further, it is possible to store two reference values having different values in the memory and detect only an object having a size within a desired range or outside the desired range.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing timing of signals used in the configuration of FIG.

FIG. 3 is a diagram for explaining hysteresis of a comparison circuit 44.

FIG. 4 is a diagram for explaining the effect of the present invention.

FIG. 5 is a diagram showing a conventional configuration example of an object detection device using a PSD.

FIG. 6 is a diagram for explaining a problem of a conventional object detection device.

FIG. 7 is a diagram for explaining a problem of a conventional object detection device.

[Explanation of symbols]

20 ... Control means, 21 ... Projector, 22 ... Drive circuit, 23
... LED, 24 ... Lens, 31 ... Light receiving part, 32 ... Lens, 33 ... PSD, 34, 35 ... I / V conversion circuit, 3
6, 37 ... Switch, 38, 39 ... Integrating circuit, 40, 4
1 ... Reset switch, 44 ... Comparison circuit, 45 ... A / D
Conversion circuit, 46 ... operation unit, 47 ... memory, 48 ... comparator, 49 ... output circuit, 51, 52 ... high-pass filter,
53 ... Reference voltage generating circuit.

Claims (1)

[Claims] 1. A light emitting section for emitting a light emitting beam toward a predetermined detection area, a semiconductor position detecting element as a position detecting element, and a condensing optical system arranged in front of the semiconductor position detecting element. A light receiving unit that is arranged triangularly with respect to the light projecting unit and the detection area to receive the reflected light from the detection area of the projection beam projected from the light projecting unit; and the semiconductor position detection element. In an object detection device including a signal processing unit that processes an output signal, an optical axis of the condensing optical system is shifted from a central position of a light receiving surface of the semiconductor position detecting element in any direction of a longitudinal direction of the light receiving surface. The signal processing means converts a current output of the two current outputs of the semiconductor position detecting element on the side where the optical axis of the condensing optical system is displaced into a voltage, which is a first current / voltage. Converting means and the semiconductor position Second current / voltage conversion means for converting the current output on the other side of the output element into a voltage, and output voltages of the first and second current / voltage conversion circuits respectively for the light projecting timing of the light projecting section. First and second integrating means for integrating in synchronization, and A for A / D converting the output voltage of the first integrating means when the output voltage of the second integrating means reaches a predetermined threshold value.
/ D conversion means, memory means for storing the output value of the A / D conversion means as a reference value for object detection, and timing for writing the output value of the A / D conversion means in the memory means When it is determined that an object exists by comparing the output value of the A / D conversion means with the timing means and the reference value written in the memory means, a signal indicating that the object exists is output. An object detection device comprising: a comparison unit; and a reset unit that resets the first and second integration units after the A / D conversion operation of the A / D conversion unit is completed.