JP2009057145A - Recording medium detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording medium detector capable of preventing any erroneous detection caused by the effect of external light or the like, and correctly discriminating presence/absence of any recording medium without requiring any complicated constitution or control. <P>SOLUTION: The recording medium detector comprises a reflection type photosensor having a light emission unit and a light reception unit for detecting the light output from the light emission unit, and a recording medium discrimination unit for discriminating the presence/absence of any recording medium of a storage unit based on the output of the reflection type photosensor arranged in the storage unit. The recording medium discrimination unit is constituted for discriminating the presence/absence of the recording medium based on the output change of the light reception unit before and after the drive timing of the light emission unit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reflective photosensor having a light emitting portion and a light receiving portion for detecting output light from the light emitting portion, and a recording medium of the accommodating portion based on the output of the reflective photosensor disposed in the accommodating portion. The present invention relates to a recording medium detection apparatus including a recording medium determination unit that determines the presence or absence of a recording medium.

  A reflection type photosensor provided with a light emitting unit and a light receiving unit for detecting output light from the light emitting unit is used as a sensor for determining the presence or absence of a recording medium, for example, a document or recording paper.

  The reflective photosensor for such use is arranged at a position facing the recording medium, and when the recording medium is at the detection position of the reflective photosensor, the output light from the light emitting unit is reflected by the recording medium and reflected light is reflected. Is detected by the light receiving unit. The output from the light receiving unit that detects the reflected light is input to a recording medium determining unit that determines the presence or absence of the recording medium. Since the output of the light receiving unit changes depending on the detected light intensity or the like, the recording medium determining unit can determine whether there is a recording medium at the detection position of the reflective photosensor based on the change in the output of the light receiving unit. it can.

  For example, the reflective photosensor is disposed in an ADF (Auto Document Feeder) or a paper feed tray of the image forming apparatus, and the reflective photosensor is detected based on an output from the reflective photosensor. The presence / absence of the recording medium at the position is determined by the recording medium determination unit. By determining the presence or absence of the recording medium at the detection position of the reflection type photosensor, it is possible to detect whether or not the recording medium is set at a predetermined position on the ADF or the paper feed tray, or the size of the recording medium.

  However, when there is no recording medium at the detection position of the reflective photosensor, the output of the light receiving unit changes depending on light other than output light from the light emitting unit, such as extraneous light such as room light. For this reason, there is a risk of erroneous detection that the recording medium is at the detection position. Therefore, various techniques have been proposed to prevent the erroneous detection.

  Patent Document 1 is equipped with an automatic document feeder that automatically conveys a document to a reading position, reads an image of the document that is conveyed to the reading position by the automatic document feeder, and records the read image on a recording sheet. The image forming apparatus includes a pair of a light emitting unit and a light receiving unit, and has a plurality of optical sensors installed at arbitrary positions, and the light irradiated from the light emitting unit to the document or the recording paper is received by the light receiving unit. And detecting at least one of the transport position and size of the document or the transport position of the recording paper by detecting the presence or absence of the document or the recording paper. An image forming apparatus has been proposed in which the light receiving pattern of the light receiving unit is compared with each other and the presence or absence of a document or recording paper is determined based on the comparison result.

  Japanese Patent Application Laid-Open No. 2004-259561 discloses that a light-emitting unit is turned on in a document transport device including a reflective optical sensor in which a light-emitting unit and a light-receiving unit are arranged at positions facing a document on a document placing unit exposed to external light. Means for preventing erroneous detection by sampling the output of the light receiving unit with a drive pulse for controlling turning off, and means for comparing the output waveform of the light receiving unit with the sampling waveform when the light emitting unit is not driven And a control means for automatically recognizing in advance that an erroneous detection of the presence of a document is detected when both waveforms are equivalent to each other. Has been proposed.

Patent Document 3 discloses a reflection type optical sensor including a document table on which a document is placed and conveyed, a light emitting unit that irradiates light on the document placed on the document table, and a light receiving unit that receives reflected light from the document. Stored in the storage means for storing the reference base value set in advance, the detection means for detecting the reflected light value of the reflective optical sensor after the document is placed, and the storage means By comparing a reference base value with the reflected light value, the presence / absence of a document is determined, and a determination unit that outputs a signal for driving the document table according to the determination of the presence of the document, and the document is transferred to the document table by the determination unit. There has been proposed a document conveying apparatus including base value update means for updating a reference base value of the storage means to a new reference base value when it is determined that the document is not placed.
JP-A-11-116102 JP 2000-292990 A JP 2003-140272 A

  However, in the image forming apparatus described in Patent Document 1, erroneous detection occurs when external light having the same pattern as the light emission pattern of the light emitting unit is incident on the light receiving unit. In addition, in order to prevent the erroneous detection, there is a problem that a plurality of light emission patterns are provided and the light emission pattern must be changed when it matches the pattern of the external light, and the control and configuration of the light emitting unit becomes complicated. was there.

  In the document conveying apparatus described in Patent Document 2, since the external light pattern is sampled when the document is “None”, the external light pattern cannot be sampled if the document is set since the power is turned on. There was a risk of erroneous detection. Further, when the document is “None”, a complicated control is required, such as sampling an external light pattern and storing the pattern.

  In the document conveying device described in Patent Document 3, if the reference base value and the reflected light value match, an erroneous detection occurs. In addition, since the reference base value is updated when the document is not placed, if the document has been set since the power is turned on, the reference base value cannot be updated and erroneous detection may occur. Furthermore, complicated control is required, for example, when a reference base value must be acquired and stored when the document is not placed.

  In view of the above-described problems, an object of the present invention is a recording that can accurately determine the presence or absence of a recording medium by preventing erroneous detection due to the influence of external light or the like without requiring a complicated configuration or control. The object is to provide a medium detection device.

  In order to achieve the above-mentioned object, the first characteristic configuration of the recording medium detection device according to the present invention is to detect a light emitting unit and output light from the light emitting unit as described in claim 1 of the claims. Recording medium detection apparatus comprising: a reflection type photosensor provided with a light receiving unit configured to detect and a recording medium determination unit that determines the presence or absence of a recording medium in the storage unit based on an output of the reflection type photosensor disposed in the storage unit The recording medium determining unit determines whether or not the recording medium is present based on an output change of the light receiving unit before and after driving timing of the light emitting unit.

  When the recording medium is set in the housing portion, the recording is performed at the detection position of the reflective photosensor when the reflective photosensor is disposed in the housing portion so that the recording medium is at the detection position of the reflective photosensor. If there is a medium, extraneous light is blocked by the recording medium before the driving timing of the light emitting unit, and there is no output light from the light emitting unit, so the output from the light receiving unit is the value when there is no incident light. However, after the drive timing of the light emitting unit, the extraneous light is shielded by the recording medium, and the output light from the light emitting unit is reflected by the recording medium and detected by the light receiving unit. The value corresponds to the output light. That is, when there is a recording medium at the detection position of the reflective photosensor, the output change of the light receiving unit is relatively large before and after the driving timing of the light emitting unit.

  On the other hand, when there is no recording medium at the detection position of the reflective photosensor, the output from the light receiving unit is a value corresponding to the external light, either before or after driving the light emitting unit. That is, when there is no recording medium at the detection position of the reflective photosensor, there is no change in the output of the light receiving unit before or after the drive timing of the light emitting unit, or the output is relatively small.

  When the light emitting unit is driven at the timing when the recording medium is set at the detection position of the reflective photosensor, there is no recording medium at the detection position of the reflective photosensor before the driving timing of the light emitting unit. Is a value corresponding to extraneous light, and after the drive timing of the light emitting unit, there is a recording medium at the detection position of the reflective photosensor, and extraneous light is shielded by the recording medium. The value corresponds to the output light from the reflected light emitting unit. That is, the output change of the light receiving unit is relatively large before and after the drive timing of the light emitting unit.

  Conversely, when the light emitting unit is driven at the timing when the recording medium is removed from the detection position of the reflective photosensor, the recording medium is located at the detection position of the reflective photosensor before the driving timing of the light emitting unit. Since the light is shielded by the recording medium and there is no output light from the light emitting unit, the output of the light receiving unit is the value when there is no incident light, and is recorded at the detection position of the reflective photosensor after the driving timing of the light emitting unit. Since there is no medium and the output light of the light emitting unit is not reflected, the output of the light receiving unit has a value corresponding to the external light. That is, the output of the light receiving unit before the driving timing of the light emitting unit is a value when there is no incident light, and the output change of the light receiving unit is relatively large before and after the driving timing of the light emitting unit.

  That is, the recording medium determining unit detects the output of the light emitting unit before and after the driving timing of the light emitting unit, and whether there is a recording medium in the accommodating unit based on whether the output change is equal to or greater than a predetermined value set in advance. Can be determined. That is, the recording medium determining unit determines that the storage unit has a recording medium if the output change is equal to or greater than a predetermined value, and determines that there is no recording medium in the receiving unit if the output change is smaller than the predetermined value.

  According to the above configuration, the recording medium determination unit is based on whether the output change of the light receiving unit detected before and after the driving timing of the light emitting unit is equal to or greater than a predetermined value without providing a complicated hardware configuration. Can accurately determine the presence or absence of a recording medium by eliminating the influence of external light or the like.

  As described in the second aspect, the second characteristic configuration is that, in addition to the first characteristic configuration described above, the recording medium determining unit intermittently drives the light emitting unit at a predetermined timing.

  According to the above-described configuration, even if the intensity of the extraneous light may fluctuate greatly in a short time, the light emitting unit is intermittently driven at every predetermined timing. In addition, the output change of the light receiving unit can be acquired, and the presence or absence of the recording medium can be accurately determined based on the plurality of output changes. Further, when it is necessary to always determine the presence / absence of a recording medium, the recording medium determination unit can accurately determine the presence / absence of a recording medium by setting the predetermined timing interval short.

  As described above, according to the present invention, a recording medium capable of accurately determining the presence or absence of a recording medium by preventing erroneous detection due to the influence of external light or the like without requiring a complicated configuration or control. A detection device can be provided.

  A copier as an example of an image forming apparatus provided with the recording medium detection device of the present invention will be described below.

  As shown in FIG. 2, the copying machine 100 includes an operation unit 110 on which operation keys for inputting a liquid crystal screen, print conditions, and the like are arranged, and a document that sequentially feeds documents placed on a document feeding table 28. A paper feed unit 200, an image reading unit 120 that photoelectrically converts an original image to read it as digital image data, an image processing unit 130 that converts digital image data into output image data, and a toner image based on the output image data Then, a functional block such as an image forming unit 140 that transfers to a sheet conveyed from the sheet storage unit 400, a fixing unit 141 that melts and fixes the toner image on the sheet, and a predetermined image by controlling these functional blocks. A control unit 300 or the like that executes the formation process is provided.

  The operation unit 110 detects pressing of an operation key or the like by the user and outputs a copy condition or the like to the control unit 300, and displays an operation screen, a warning screen, or the like on the liquid crystal screen based on control from the control unit 300.

  The image reading unit 120 includes a light source that illuminates the document, and a CCD that photoelectrically converts reflected light from the document that enters through a plurality of mirrors and lenses to read the document image as digital image data.

  The image processing unit 130 includes an ASIC for image processing and the like, performs gadging correction on the digital image data read by the image reading unit 120 and image processing based on the copy condition input by the operation unit 110 to output image data. Convert.

  The image forming unit 140 includes a photosensitive member, a charging device that uniformly charges the surface of the photosensitive member, and an exposure device that scans a laser beam based on output image data to expose the surface of the photosensitive member to form an electrostatic latent image. And a developing device that visualizes the formed electrostatic latent image as a toner image, a static elimination lamp that neutralizes charges on the surface of the photoreceptor, and the like.

  The fixing unit 141 includes a fixing roller in which a fixing heater is incorporated, and a pressure roller pressed against the fixing roller. In the fixing unit 141, the sheet on which the toner image is transferred passes between the fixing roller and the pressure roller, so that the toner image is melted and fixed on the sheet.

  As shown in FIGS. 3A and 3B, the document feeder 200 includes a document feeder 28 and a sheet feeding mechanism 26 that sequentially feeds the documents placed on the document feeder 28. And a document discharge table 29 on which the document fed by the paper feed mechanism 26 is discharged.

  A document guide 22 for regulating the placed document in the width direction, a document size sensor 23 for detecting the document size, and whether or not a document is placed on the document feed table 28 is placed on the document feed table 28. A document placement sensor 21 for detecting the above is disposed. The document placement sensor 21 is arranged in front of the document feed table 28 in the feeding direction and in the center in the width direction so that it can detect whether or not a document is placed regardless of the document size. . The document size sensor 23 is arranged behind the document feeding table 28 in the sheet feeding direction and in the center in the width direction, and a document of a large size such as A3 is placed on the document loading table 28 which is a housing portion of the present invention. It is detected whether or not.

  As shown in FIG. 4, the document guide 22 has a rack 22a in the lower part, and the document guide 22 converts the document placed on the document feed table 28 in the document width direction by the cooperation of the rack 22a and the pinion 22b. Regulate in the center. A plurality of document width sensors 22d are arranged in the document width direction below the document guide 22. The document width sensor 22 d is configured by a transmissive photosensor including a light emitting unit and a light receiving unit that detects output light from the light emitting unit, and the output of each transmissive photosensor 22 d is input to the control unit 300.

  When the document guide 22 moves so as to sandwich the document placed on the document placement table 28, the light receiving portion from the light emitting portion of one document width sensor 22d is projected by the projection 22c of the one document guide 22 according to the movement. The output light of the original document width sensor 22d in which the output light is shielded is changed. In the present embodiment, the document width sensor 22d is configured to output a positive voltage when the output light is blocked.

  As shown in FIG. 5A, the document placement sensor 21 and the document size sensor 23 include a light emitting unit 21a (23a) and a light receiving unit 21b (23b) that detects output light from the light emitting unit 21a (23a). It is composed of a reflective photosensor.

  As shown in FIG. 5B, the light emitting unit 21a (23a) includes a light emitting diode constituting a photocoupler, and the light receiving unit 21b (23b) includes a photodiode constituting a photocoupler. The output Vo of the light receiving unit 21b (23b) is amplified by the amplifier 21c (23c), level-inverted by the inverter, and input to the control unit 300.

  A DC voltage Vdc is applied to the anode of the light emitting diode constituting the light emitting portion 21a of the document placement sensor 21, and the cathode is grounded. Therefore, the light emitting unit 21a constantly outputs light during application of the DC voltage Vdc.

  A DC voltage Vdc is applied to the anode of the light emitting diode constituting the light emitting portion 23a of the document size sensor 23, and the cathode is connected to the collector of the transistor Q23d. The base of the transistor Q23d is connected to the output port of the controller 300, and the emitter is grounded. Therefore, when a high level drive signal is output from the control unit 300, the transistor Q23d becomes conductive, the light emitting unit 23a drives to output light, and when a low level drive signal is output, the transistor Q23d The light emitting unit 21a stops and the output light stops.

  When a document is placed on the document feeder 28 and the document is at the detection positions of the document placement sensor 21 and the document size sensor 23, the output light from the light emitting unit 21a (23a) being driven is reflected by the document, The output from the light receiving unit 21b (23b) that has detected the reflected light changes. In the present embodiment, the light receiving unit 21b (23b) is configured to output a positive voltage when light is detected. Therefore, when a document is placed at the detection position, the light output from the light emitting unit 21a (23a). And the light receiving unit 21b (23b) outputs a high positive voltage when the detected light intensity is high and a low positive voltage when it is weak.

  As shown in FIG. 6, the control unit 300 includes a CPU 30, a ROM 31 that stores a control program, a RAM 32 that is used as a work area of the CPU 30, an input port 33 that receives sensor output and the like, an actuator and a motor. An output port 34 that outputs a drive signal to a drive circuit and the like, and an interface circuit 35 and the like with each functional block are configured. The input port 33 includes an AD converter, and is configured to AD-convert at least outputs from the document placement sensor 21 and the document size sensor 23 to the CPU 30 by the AD converter.

  When the image forming apparatus is powered on, the CPU 30 initializes the RAM 32, the input port 33, the output port 34, and the like, and then calls and executes a control program stored in the ROM 31. The control unit 300 performs a predetermined image forming process by performing overall control of each functional block based on a copy condition from the user via the operation unit 110 in cooperation with the CPU 30 that executes the control program. Configured to do. As one of the image forming processes, the control unit 300 detects the presence or absence of a document placed on the document feeding unit 200 and the document size.

  As shown in FIG. 7A, when a document is placed on the document feed table 28, the document placement sensor 21 outputs a positive voltage, and the controller 300 receives the input document placement sensor 21. When the output exceeds the threshold voltage Vth1, it is determined that the document is placed on the document feeder 200. When the document is placed on the document placement table 28, the control unit 300 causes the pressing force between the pickup roller 25 of the paper feed mechanism 26 to fall within a predetermined range in accordance with the load amount of the placed document. To move in, the tray motor (not shown) is driven to move the document table 28 up and down.

  Further, when the document guide 22 is moved by the user placing the document so as to sandwich the document, a positive voltage is output from one document width sensor 22d in which output light is blocked in accordance with the movement, and the control is performed. The unit 300 determines the document width sensor 22d that has output the positive voltage, and detects the width-direction size of the placed document.

  As shown in FIG. 7A, when the control unit 300 determines that the document is placed on the document feed table 28 based on the output from the document placement sensor 21, it is at a high level for a predetermined time T0. A drive signal is output to drive the light emitting unit 23a of the document size sensor 23. After the driving timing of the light emitting unit 23a, the control unit 300 detects whether the placed document is a large size such as A3 based on the output from the light receiving unit 23b.

  That is, after the drive timing of the light emitting unit 23a, if the output Vo from the light receiving unit 23b is a voltage higher than the threshold voltage Vth2, the control unit 300 determines that there is a document at the detection position of the document size sensor 23, If it is detected that a document of a large size is placed on the document feeder 28 and the output Vo from the light receiving unit 23b is lower than the threshold voltage Vth2, the controller 300 determines that there is no document at the detection position. A determination is made and it is detected that a document of a small size is placed on the document feeder 28.

  As described above, the control unit 300 determines whether or not a document is placed on the document feed table 28 based on the output from the document placement sensor 21, and based on the output from the document width sensor 22d. The size in the width direction of the document placed on the sheet feed table 28 is detected, and whether the document placed on the document feed table 28 is large or small is detected based on the output from the document size sensor 23.

  However, when a small-size document is placed on the document feeder 28, the document size sensor 23 receives external light such as room light in the room where the copier 100 is installed in addition to the output light of the light emitting unit 23a. As shown in FIG. 7B, when the output Vo from the light receiving unit 23b that has detected the extraneous light is equal to or higher than the threshold voltage Vth2, as shown in FIG. If the original is placed, it will be erroneously detected.

  Therefore, in order to prevent such erroneous detection, as shown in FIGS. 1A and 1B, the control unit 300 controls the document feed table 28 based on the output from the document placement sensor 21. If it is determined that the document is placed, first, the output Vo from the light receiving unit 23b is acquired and stored. Next, the control unit 300 outputs a high level drive signal for a predetermined time T0 to drive the light emitting unit 23a, and obtains the output Vo from the light receiving unit 23b again.

  The control unit 300 determines the presence / absence of a recording medium at the detection position of the document size sensor 23 based on the output change of the light receiving unit 23b acquired before and after the driving timing of the light emitting unit 23a, and is placed on the document feeding table 28. Detect the size of the original. That is, if the output change is smaller than the predetermined value, the control unit 300 determines that there is no document at the detection position of the document size sensor 23 and detects that the document placed on the document feed table 28 is a small size. If the output change is equal to or greater than a predetermined value, it is determined that there is a document at the detection position of the document size sensor 23, and the document placed on the document feeder 28 is detected to be a large size.

  That is, the control unit 300 is a recording medium determination unit according to the present invention. The recording medium detection device according to the present invention includes the document size sensor 23 arranged on the document feeding table 28 serving as a storage unit according to the present invention and the control unit 300. Is configured.

  The operation of determining whether or not the document placed on the document feed table 28 by the control unit 300 is a large size will be described with reference to the flowchart shown in FIG.

  When the control unit 300 determines that the document is placed on the document feeding table 28 based on the output from the document placement sensor 21 (S1), the control unit 300 acquires the output Vo1 of the light receiving unit 23b of the document size sensor 23, and then The drive signal is output to drive the light emitting unit 23a, and the output Vo2 of the light receiving unit 23b of the document size sensor 23 is acquired again (S2, S3, S4).

  When the output Vo2 of the light receiving unit 23b acquired after the driving timing of the light emitting unit 23a is smaller than the threshold voltage Vth2, the control unit 300 determines that there is no document at the detection position of the document size sensor 23, and the document feeding table 28. It is detected that the document placed on is a small size (S5, S9, S10).

  When the output signal of the light receiving unit 23b acquired after the drive timing of the light emitting unit 23a is equal to or higher than the threshold voltage Vth2, the control unit 300 derives the absolute value of the difference between the output Vo2 and the output Vo1, and the absolute value is a predetermined value. If it is below, it is determined that there is no document at the detection position of the document size sensor 23, and it is detected that the document placed on the document feeder 28 is a small size (S5, S6, S9, S10). If the absolute value is larger than the predetermined value, it is determined that there is a document at the detection position of the document size sensor 23, and the document placed on the document feed table 28 is detected as having a large size (S5, S6, S7, S8).

  Another embodiment will be described below.

  In the above-described embodiment, the reflection type photosensor of the present invention is described as the document size sensor 23. However, the document placement sensor 21 may also be the reflection type photosensor of the present invention. In this case, even when the document placement sensor 21 is arranged at a position where extraneous light other than the output light from the light emitting portion 21a enters the light receiving portion 21b of the document placement sensor 21, the control unit 300 Based on the output from the light receiving portion 21b of the document placement sensor 21, it is possible to accurately detect whether or not a document is placed on the document feed base 28.

  Specifically, similarly to the light emitting unit 23a of the document size sensor 23, the light emitting unit 21a of the document placement sensor 21 is configured to be driven by a drive signal from the control unit 300, and the control unit 300 is configured to emit light. The controller 300 outputs a driving signal for the light emitting unit 21a at a short time interval, and intermittently drives the light emitting unit 21a at a predetermined timing of the short time interval, whereby the control unit 300 places the document before and after the driving timing of the light emitting unit 21a at every predetermined timing. Based on the output change of the light receiving unit 21 b of the sensor 21, it is determined whether or not there is a document at the detection position of the document placement sensor 21, and whether or not the document is placed on the document feeder 28 is detected. it can.

  In addition, when the document placement sensor 21 is disposed on the document feeder 28 as the reflection type photosensor of the present invention, the control unit 300 controls the light receiving unit 21b before and after the driving timing of the light emitting unit 21a of the document placement sensor 21. In addition to determining whether or not a document has been placed on the document feeding table 28 based on the output change, it is also possible to determine whether or not the document has been removed from the document feeding table 28 based on the output change. it can.

  In the above-described embodiment, the control unit 300 determines that the document is placed on the document feeding table 28 based on the output change from the document placement sensor 21, and then outputs the light from the light receiving unit 23 b of the document size sensor 23. The light emitting unit 23a is driven at the subsequent timing. However, when there is a possibility that the intensity of the external light may fluctuate greatly in a short time, the control unit 300 places the document on the document feeding table 28. After being placed, the driving signal may be output several times at a predetermined timing to drive the light emitting unit 23a intermittently.

  In this case, the output change of the light receiving unit 23b before and after the drive timing of the light emitting unit 23a is acquired at each predetermined timing, and the opposed size of the document size sensor 23 is determined based on the output change that approximates the average value or the change amount of the output change. By configuring the control unit 300 so as to determine whether or not there is a document at the position to be performed, it is possible to more accurately determine the presence or absence of the document.

  In the above-described embodiment, the storage unit in which the reflective photosensor of the present invention is disposed is the document feed table 28, but the storage unit is not limited to the document feed table 28. For example, as with the document feeder 28, even a manual feed tray that has a high possibility of extraneous light, such as room light, entering a reflective photosensor arranged to detect the presence or absence of paper and the paper size. Good.

  In addition, even in a paper feed cassette as a paper storage unit that is unlikely to receive extraneous light such as room light, for example, a reflective photosensor arranged to detect the presence of paper and the paper size In addition, when there is a possibility that light from a static elimination lamp or the like constituting the image forming unit 140 may enter, the paper feeding cassette may be the housing unit.

  In the above embodiment, the copying machine 100 provided with the recording medium detection device of the present invention has been described. However, the recording medium detection device according to the present invention can be applied to any image forming apparatus other than the copying machine. Needless to say.

  Each of the above-described embodiments is merely an example of the present invention, and the scope of the present invention is not limited by the description. The specific configuration of each part is appropriately selected within the scope of the effects of the present invention. It goes without saying that changes can be designed.

(A) is a timing chart for explaining the document presence / absence detection operation by the document size sensor, and (b) is a timing chart for explaining the document presence / absence detection operation by the document size sensor. Illustration of copier (A) is an explanatory diagram of a document feeder, and (b) is an explanatory diagram of a document feeder. Illustration of the document guide (A) is explanatory drawing of a document placement sensor and a document size sensor, (b) is a circuit diagram of a document placement sensor and a document size sensor. Configuration diagram of control unit (A) is a timing chart for explaining the document presence / absence detection operation by the document size sensor according to the prior art, and (b) is a timing chart for explaining the document presence / absence detection operation by the document size sensor according to the prior art. Flowchart explaining original size detection by control unit

Explanation of symbols

21: Document placement sensor 22: Document guide 22d: Document width sensor 23: Reflection type photo sensor (document size sensor)
23a: Light emitting part (light emitting diode)
23b: Light receiving part (photodiode)
28: Storage unit (document feeder)
200: Document feeder 300: Recording medium discrimination unit (control unit)

Claims (2)

A reflection type photosensor provided with a light emitting unit and a light receiving unit for detecting output light from the light emitting unit, and the presence or absence of a recording medium in the storage unit based on the output of the reflection type photosensor disposed in the storage unit A recording medium detection device comprising a recording medium determination unit for
The recording medium detection device, wherein the recording medium determination unit determines the presence or absence of the recording medium based on a change in output of the light receiving unit before and after driving timing of the light emitting unit.   The recording medium detection device according to claim 1, wherein the recording medium determination unit intermittently drives the light emitting unit at a predetermined timing.

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