JPH0433396B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a detection device for identifying a detected object interposed between a light-emitting element and a light-receiving element that are arranged facing each other, and is used, for example, in a copying machine to detect the size of a copy document. The present invention relates to a photoelectric object detection device. [Prior Art] A photoelectric object detection device includes a plurality of pairs of corresponding light emitting elements and light receiving elements, and the incident light on the light receiving element is blocked or attenuated by an object interposed in the optical path of both elements. By detecting changes in the object, the presence of an object and further the size of the object can be identified. For example, this type of conventional photoelectric object detection device built into a copying machine uses multiple light-emitting devices and light-receiving devices to form an optical path corresponding to each size of the copy document at the position where it is set. has been done. Then, a change in the output of the light receiving element that occurs when a copy document of a certain size is set in the copying machine is detected. That is, the output signals obtained by photoelectric conversion from a plurality of light receiving elements are amplified and voltage-compared by the output signal processing means such as an amplifier and a comparator provided independently for each light receiving element. It was used to detect the size of the original. However, in the conventional structure described above, since each light receiving element has an independent output signal processing means, the circuit configuration becomes complicated and a large number of parts are required. This has the drawback of complicating assembly work and increasing costs. By the way, Utility Model Application Publication No. 51-16951 discloses an amplifying means for amplifying an output signal using a feedback signal,
A device is disclosed that has a comparison means for comparing the output voltage outputted from the amplification means with a comparison level, and a level adjuster made of a variable resistor that can arbitrarily change the comparison level of the comparison means. . Further, Japanese Utility Model Publication No. 55-44219 discloses an apparatus having time division means for time division of signal processing. As a result, when the devices disclosed in the above-mentioned Utility Model Publication No. 51-16951 and Utility Model Publication No. 55-44219 are combined, the time division means is connected to the amplification means, comparison means, and level adjuster. By amplifying the output signal obtained from each photodetector using individual time-divided feedback signals, the amplified output voltage and the comparison modified according to the time-divided output signal are Since it is possible to adopt a circuit configuration that can compare the levels, it is possible to process multiple output signals with one amplification means and comparison means, which simplifies the circuit configuration of the photoelectric object detection device. becomes possible. However, in the above-mentioned photoelectric object detection device, the comparison level of the comparison means is changed according to the time-divided output voltage, so a number of level adjusters corresponding to each output voltage is required, or a number of level adjusters corresponding to each output voltage are required. A level adjuster with a circuit configuration that outputs a comparison level corresponding to the voltage is required, and this level adjuster makes it insufficient to simplify the circuit configuration of the photoelectric object detection device. In addition, in this photoelectric object detection device, since the output voltage and the comparison level have a one-to-one correspondence, individual variations in the output signal obtained from the light-receiving element can be compensated for by the individual feedback signals of the amplification means and the level adjuster. Adjustments must be made using individual comparison levels, which increases the number of adjustments and requires time and effort. [Object of the Invention] The present invention has been made in consideration of the above-mentioned conventional problems.It is an object of the present invention to simplify assembly work and reduce costs by simplifying the circuit configuration and reducing the number of parts. It is an object of the present invention to provide a photoelectric object detection device that can be easily adjusted. [Structure of the Invention] A photoelectric object detection device of the present invention is a photoelectric object detection device that detects an object interposed in an optical path formed between a light emitting element and a light receiving element. The device includes a control means for time-divisionally driving the light-receiving element at a synchronized timing, an amplification means for amplifying the output of the light-receiving element, and a voltage comparison means for comparing the output voltage of the amplification means with a comparison level. The amplifying means has a feedback resistor switching circuit that switches a feedback resistor corresponding to each light receiving element in synchronization with the driving of each light receiving element,
The voltage comparison means has a first comparison level used for adjusting the output voltage, and a second comparison level used for actual use of the output voltage set to a level lower than the first comparison level. The feature is that two comparison levels are set. [Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. A copying machine equipped with a photoelectric object detection device has a second
As shown in the drawings and FIG. 3, five light emitting diodes 1a to 1e, which are light emitting elements such as infrared light emitting diodes, and five photodiodes 2a to 2e, which are light receiving elements, are provided. The light emitting diodes 1a to 1e are connected to an inner frame plate 4 having a slit 4a provided below a glass plate 3 serving as a document table.
while the photodiodes 2a to 2e
is fixed to the support plate 5. A visible light cut filter 7 is provided on the upper surface near the end of the glass plate 3 above the photodiodes 2a to 2e via an intervening plate 6 having a slit 6a.
In addition, the slits 4a and 6 of the inner frame board 4 and the interlayer board 6
In this device, the light emitting diodes 1a to 1e are duplex driven and 2 to 3 of them emit light at the same time, so the light emitting diodes 1a to 1e
Depending on the light directionality of the light, there is a risk that the light may be received by a photodiode other than the corresponding photodiode, and this is provided to prevent this. Further, in order to cover the glass plate 3 from above during copying, a reflecting plate 8 is provided on the lower surface of a document cover 8a which is provided at the end of the copying machine so as to be openable and closable. With the above structure, light emitted from the light emitting diodes 1a to 1e passes through the slit 4a formed in the inner frame plate 4, the glass plate 3, the reflection plate 8, the visible light cut filter 7, and the slit 6a of the interlayer plate 6. , and are configured to be incident on the corresponding photodiodes 2a to 2e. Furthermore, corresponding light emitting diode 1
Optical paths 9a to 9b formed by a to 1e and photodiodes 2a to 2e are B5, A4, B4,
Copy originals 10 of each size of A3 are placed on the glass plate 3 above.
It is configured to be shut off by placing it in a predetermined position. That is, the optical path 9e is blocked by the B5 copy original 10, and the A4 copy original 1
0, the optical paths 9d and 9e are connected to the B4 copy original 10.
Therefore, the optical paths 9c, 9d, and 9e are blocked by the A3 copy original 10, and the optical paths 9b, 9c, 9d, and 9e are blocked, respectively. The circuit configuration of this device including the above-mentioned light emitting diodes 1a to 1e and photodiodes 2a to 2e is as shown in FIG. The photodiodes 2a to 2e are connected to corresponding connection points 11 of a microcomputer 11 serving as a control means.
a to 11e at the cathode, and the anode is connected in common and grounded via a load resistor 12. Two diodes 13 and 14 connected in parallel in opposite directions are connected to this resistor 12. The non-grounded side of the resistor 12 is connected through a DC-blocking capacitor 15 to an input terminal of an amplifier 17 which is grounded through a resistor 16. Further, the connection points 11a to 11e are open-drain output terminals, thereby forming a first switching circuit.
The anodes of diodes 18a to 18e for backflow prevention are connected to the connection points 11a to 11e, respectively, and the cathodes of analog switches 19a to 19e, which serve as a second switching circuit, are connected to respective gate terminals. Note that a pull-down resistor is omitted from this gate terminal. analog switch 1
One terminal of 9a to 19e is commonly connected and connected to the grounded input terminal of the amplifier 17 via a resistor 20, and the other terminal is connected to the input terminal of the amplifier 17 via semi-fixed variable resistors 21a to 21e. It is connected to the output side of 17. These variable resistors 2
1a to 21e and analog switches 19a to 19
A feedback circuit is constructed by e. Amplifier 17
The output side of is connected to the input terminal of a comparator 24 via a capacitor 22 and a resistor 23, and the connection point between the capacitor 22 and the resistor 23 is grounded via a resistor 55. Comparator 24
A resistor 25 is interposed between the output side and the input terminal, and a resistor 2 connected in series is connected to the input terminal.
+Vcc is supplied through 6, 27, 28, and 29. The above-mentioned resistors 25 and 26 are resistors for providing hysteresis. The connection point between the resistors 26 and 27 is grounded via a resistor 30 and a capacitor 31, and the connection point between the resistors 28 and 29 is grounded via a Zener diode 32. Further, a switch 33 is connected in parallel to the resistor 28. The output side of the comparator 24 is connected to the base of a transistor 35 via a resistor 34. The base of this transistor 35 is directly grounded through a resistor 36, the emitter is directly grounded, and +Vcc is supplied through a resistor 37 to its collector. Furthermore, the collector is connected to the input terminal 38 of the microcomputer 11. The microcomputer 11 is also provided with a monitor output terminal 39, data output terminals 40, 41, 42 for sending outputs _O0 , _O1 , _O2 , and output terminals 43, 44. Output terminal 4
3 is connected via a capacitor 45 and a resistor 46 to the base of a transistor 47 for driving a light emitting diode, and this base is grounded via a resistor 48. Similarly, the output terminal 44 is connected to a resistor 52 of a transistor 51 for driving a light emitting diode via a capacitor 49 and a resistor 50.
connected to a grounded base. The emitter of the transistor 47 is grounded, and the collector is connected via a resistor 53 to the cathode of the light emitting diode 1a of the light emitting diodes 1a, 1c, and 1e connected in series in the same direction. On the other hand, a light emitting diode 1 connected in series in the same direction is connected to the collector of the transistor 51 via a resistor 54.
b, 1d are connected to the cathode of the light emitting diode 1b. In addition, light emitting diodes 1e and 1d
Both anodes are connected to a 24V power supply. In the above configuration, when this device is driven,
As shown in FIG. 4A, the connection point 11a of the microcomputer
~11e, a signal with a voltage of +5V is sent out in a time-division manner sequentially from the connection point 11a. Note that the broken line indicates high impedance. As a result, the corresponding photodiodes 2a to 2e receive a reverse bias and are driven in a time-division manner. In the photodiodes 2a to 2e, the cathode side thereof is opened by the first switching circuit during the off period, so that no photocurrent flows. On the other hand, output signals synchronized with the outputs of the connection points 11a to 11e are sent from the output terminals 43 and 44. As a result, the transistor 47,
51 is driven, and these transistors 4
The light emitting diodes 1a to 1e are driven by the light emitting diodes 1a to 1e, and the light emitting outputs shown in a and b in FIG. 4B are obtained from the light emitting diodes 1a to 1e. Therefore,
When there is no light shielding object such as a copy original 10 in the optical paths 9a to 9e, the photodiode 2 shown in FIG.
Output voltages from a to 2e are available across load resistor 12. The output voltage is input to the amplifier 17 and amplified by an amplification factor determined by the resistor 20 and variable resistors 21a to 21e. by the way,
Light emitting diodes 1a to 1e, photodiode 2
a to 2e, and the glass plate 3 and visible light cut filter 7 interposed in the optical paths 9a to 9e between them.
etc., each has variations in operation or optical function. Therefore, when the amplification factor of the amplifier 17 is constant, the same level of output may not be obtained from the amplifier 17 depending on the presence or absence of the copy document 10. At this time, the output levels can be made equal by adjusting the variable resistors 21a to 21e that constitute the feedback circuit. The analog switches 19a to 19e of the feedback circuit are as follows:
It is turned on and off in response to the output from the connection points 11a to 11e of the microcomputer 11 sent through the diodes 18a to 18e, and is turned on only when there is an output, and turned off during other non-selected periods. Also,
The diodes 18a to 18e prevent photocurrent from flowing through the photodiodes 2a to 2e during the non-selection period. Here, if an A3 copy original 10 is set on the glass plate 3, the optical paths 9b to 9e
will be blocked. As a result, the incident light to the photodiodes 2b to 2e is completely blocked, or only a small amount of light is transmitted through the copy original 10. On the other hand, the light projected from the light emitting diode 1a is incident on the photodiode 2a at a normal intensity. Then, the photodiode 2a is activated by the first switching circuit constituted by the microcomputer 11, and the connection point 11 is activated.
When a reverse bias of +5V is applied from the photodiode 2a, a photocurrent obtained by photoelectric conversion from the photodiode 2a flows through the load resistor 12, and an output voltage is generated across the load resistor 12. Further, the analog switch 19a is turned on by inputting the output of the connection point 11a to the gate terminal through the diode 18a. As a result, the variable resistor 21 is connected to the amplifier 17.
The amplification factor determined by a and the resistor 20 is set, and the output voltage across the load resistor 12 is amplified by this amplification factor. The output voltage of the amplifier 17 is compared with a comparison level of a comparator 24 at the next stage.
The above output voltage is naturally higher than this comparison level, and an L level output is obtained from the comparator 24, but if it is lower, an H level output is obtained. By the way, the comparison level of the comparator 24 is the first comparison level Vref 1 and the second comparison level
It is configured so that it can be set in two stages: Vref 2. That is, when the switch 33 is turned on, the resistor 28 is shot, and the first comparison level Vref 1, which is a high level, is set. In this state,
When the optical paths 9a to 9e are not blocked at all,
The variable resistors 21a to 21e are adjusted so that the critical point at which the output of the comparator 24 is inverted from the H level to the L level is at a level close to the critical point. If the optical paths 9a to 9b are cut off at this time, all outputs of the comparator 24 naturally become H level. Then, when the switch 33 is turned off, the lower second comparison level is set.
It is set to Vref 2, and Vref 1>Vref 2.
In this way, by setting the comparison level of the comparator 24 and actually using it at the comparison level Vref 2, it is possible to prevent the photodiodes 2a to 2e from deteriorating due to deterioration of the light emitting diodes 1a to 1e or dirt on the glass plate 3 in the optical path. Even if the output voltage is lowered, it will operate without any abnormality up to the level of Vref 2. Of course, Vref 2 is set higher than the output voltage due to noise and ambient light. Due to the function of the comparator 24 described above, the optical path 9
It is determined whether there is a copy document 10 in a to 9e, and the output is taken into the microcomputer 11 from the input terminal 38 via the transistor 35. By storing the data in the microcomputer 11 in accordance with the switching timing in the first switching circuit, the photodiodes 2a to 2e are
It is determined which one is selected when the optical output is on, and the data O ₀ , O ₁ , O ₂ is output as 3-bit output from the data output terminals 40 , 41 , 42 as shown in the first
It is output in the format shown in the table.

〔Effect of the invention〕

As described above, the photoelectric object detection device of the present invention includes a control means for time-divisionally driving a plurality of pairs of light emitting elements and light receiving elements at synchronized timing, and an amplifying means for amplifying the output of the light receiving elements. , voltage comparison means for comparing the output voltage of the amplification means with a comparison level, and the amplification means has a feedback resistance switching circuit for switching a feedback resistor corresponding to each light receiving element in synchronization with driving of each light receiving element. The voltage comparison means has a first comparison level that is used for adjusting the output voltage, and a first comparison level that is used for actual use of the output voltage that is set to a lower level than the first comparison level. This is a configuration in which two comparison levels are set, including the second comparison level. As a result, only one amplification means and one voltage comparison means are required, and two comparison levels are required.
The circuit configuration is extremely simplified. As a result, the number of parts can be significantly reduced and costs can be reduced, and the assembly work can be simplified by reducing the number of parts to be attached. Furthermore, variations in individual output voltages can be adjusted by the feedback resistance switching circuit of the amplification means, and variations common to the whole can be adjusted by the first comparison level of the comparison means, so the number of adjustments is reduced and the output voltage is reduced. This has the effect that voltage adjustment work is easy.

[Brief explanation of drawings]

1 to 5 show an embodiment of the present invention, in which FIG. 1 is a circuit diagram of a photoelectric object detection device, FIG. 2 is an explanatory diagram showing the upper part of a copying machine, and FIG. An explanatory diagram showing the arrangement relationship of a light emitting diode, a photodiode, and a copy document. Figure 4 A, B, and C show the output at each connection point of the microcomputer, the output of each light emitting diode, and the load resistance shown in Figure 1, respectively. Time chart showing the output voltage at both ends, No. 5
Figures a, b, c, and d are time charts showing the output of the output terminal 43, the output of the output terminal 44, the monitor output, and the data outputs _O0 to _O2, respectively. 1a to 1e are light emitting diodes, 2a to 2e are photodiodes, 11 is a microcomputer, 12 is a load resistor, 17 is an amplifier, 19a to 19e are analog switches, 21a to 21e are variable resistors, and 24 is a comparator.

Claims (1)

[Claims] 1. In a photoelectric object detection device that detects an object intervening in an optical path formed between a light emitting element and a light receiving element, a plurality of pairs of light emitting elements and light receiving elements are arranged at synchronized timing. a control means for driving in a time-division manner; an amplification means for amplifying the output of the light receiving element;
voltage comparison means for comparing the output voltage of the amplification means with a comparison level; the amplification means has a feedback resistor switching circuit that switches a feedback resistor corresponding to each light receiving element in synchronization with driving each light receiving element; The voltage comparison means has a first comparison level used for adjusting the output voltage, and a first comparison level used for actual use of the output voltage set to a level lower than the first comparison level. A photoelectric object detection device characterized in that two comparison levels are set.