JPH054754A - Sheet detecting device - Google Patents

Abstract

PURPOSE:To prolong the life of a light emitting and a light receiving elements by driving these elements on the basis of a light emitting control signal and a light receiving control signal stored in a storage means to detect the existence of a sheet. CONSTITUTION:A light emitting element 40 and a light receiving element 42 are driven on the basis of a light emitting control signal and a light receiving control signal stored in a storage means 49 to detect the existence of a sheet. The light emitting control signal and light receiving control signal after the light receiving output of the light receiving element 42 being controlled into an allowed range are compared with the limit control signals thereof, and when at least one of the light emitting control signal and light receiving control signal deviates from the limit control signal, an alarm is emitted. The sensitivity of the light emitting element 40 and light receiving element 42 is thereby adjusted automatically within the allowed range, and the life of the elements 40, 42 can be prolonged to the maximum for use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet detecting apparatus suitable for being applied to a sheet conveying apparatus for conveying an original or a sheet in a copying machine, an image reader or the like.

[0002]

2. Description of the Related Art In an apparatus for transferring and recording an original image on a sheet such as a copying machine, the topmost or the bottommost one of a plurality of sheets placed on a paper feed tray is taken out one by one, and the sheet is skewed. It is necessary to feed the image to the image transfer position without it. Further, in the automatic document feeder, which sequentially feeds the originals placed on the original tray onto the platen of the copying machine, the originals are picked up one by one on the tray and copied without skewing. Must be fed on the platen of the machine.

Therefore, in such a sheet feeding apparatus for taking out sheets (hereinafter, including originals) one by one and feeding them, the front end or the rear end of the sheet has been fed to a predetermined position or discharged. A large number of optical sheet detection devices that detect the fact that the sheet has been cut are provided at necessary portions.

This sheet detecting device comprises a light emitting element and a light receiving element. The light receiving element receives reflected light or transmitted light emitted from the light emitting element to irradiate the sheet. It is typically configured to detect.

However, in such a sheet detecting apparatus, since the light receiving element and the light emitting element have different initial sensitivities, a voltage (light emission control signal) applied to the light emitting element is usually used.
Alternatively, the output control voltage (light reception control signal) of the light receiving element is manually adjusted by a variable resistor or the like so that the output voltage (light reception output) of the light receiving element falls within an allowable range.

[0006]

However, even if the initial sensitivity of the light emitting element or the light receiving element is manually adjusted, the sensitivity may gradually change due to aging, or the light emitting surface or the light receiving surface may be contaminated by paper dust or the like, or Changes rapidly,
The presence or absence of the sheet cannot be detected accurately. For this reason, conventionally, it has been necessary for a maintenance staff to regularly perform a sensitivity check, and the work and management for that purpose have been extremely troublesome. Further, there is a problem that the sensitivity is increased more than necessary, and as a result the life of the device is shortened.

An object of the present invention is to provide a sheet detecting apparatus which can automatically adjust the sensitivities of a light emitting element and a light receiving element within an allowable range and further extend the life of these elements to the maximum extent. Is to provide.

[0008]

In order to achieve the above object, the present invention comprises a light emitting element and a light receiving element, and the reflected light or the transmitted light of the light emitted from the light emitting element and applied to the sheet is received by the light receiving element. In a sheet detection device that receives light and detects the presence or absence of a sheet based on the amount of received light, at least one of the light emission control signal of the light emitting element and the light reception control signal of the light receiving element is allowed to be received by the light receiving element at a predetermined time. Sensitivity control means for varying the light reception output of the light receiving element within a permissible range and storage means for storing at least the variable side signal of the light reception control signal after controlling the light reception output of the light receiving element within an allowable range. To detect the presence or absence of a sheet by driving the light emitting element and the light receiving element based on the light emission control signal and the light receiving control signal stored in the storage means. It was.

Further, there is provided comparison means for comparing the light emission control signal and the light reception control signal after controlling the light reception output of the light receiving element within an allowable range, and the light emission control signal and the light reception control signal. A warning is issued when at least one of the two deviates from the limit control signal.

[0010]

In the above structure, at a predetermined time such as when the power is turned on, either the light emission control signal of the light emitting element or the light reception control signal of the light receiving element is automatically controlled so that the light receiving output of the light receiving element falls within the allowable range. Since the adjustment is performed, the sensitivity adjustment work by the maintenance personnel becomes unnecessary until the life of the element is almost exhausted. Therefore, the maintenance work interval is significantly lengthened, and the work cost therefor is reduced. Further, the device can be used until just before it must be replaced, and the life of the device can be substantially extended.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed description will be given below based on an embodiment in which the present invention is applied to an automatic double-sided document feeder.

FIG. 1 is a sectional view showing an embodiment of a double-sided document automatic feeding apparatus to which the present invention is applied. The feeding unit 3 for feeding, the feeding unit 4 for feeding the fed originals one by one to a predetermined position of the platen P, the document after the image processing is discharged, or the front and back sides are reversed and the platen P is again fed. It is composed of a reversal discharge section 5 which leads to a predetermined position, and a discharge tray 6 on which discharged documents are placed.

The paper feed section 3 comprises a pickup roller 7, a document pressing member 35, an empty sensor 8, a separation roller 9, a separation pad 36 and a registration sensor 10, and a motor M1 as a power source for the pickup roller 7 and the separation roller 9. The pickup roller 7 picks up the originals placed on the paper feed tray 2 from the bottom several sheets at a time, and the separation roller 9 and the separation pad 36 separate only the lowermost originals, so that a large loop margin is provided. Is sent to the open space 11. Here, the outer guide plate 12
The document whose direction has been changed along the path passes through the linear guide portion 13 and reaches the nip point between the registration roller 14 and the pinch roller 15 of the conveying portion 4.

The conveying unit 4 stretches the registration roller 14 and the pinch roller 15, the wide conveying belt 16, the driving roller 17 and the driven roller 18 for rotating the conveying belt 16 and the conveying belt 16 on the upper surface of the platen P. A plurality of pinch rollers 19 are provided, and the document fed to the entrance of the registration roller 14 rotates while the registration roller 14 and the pinch roller 15 are pressed against each other. Is conveyed in the direction of the platen P, and is conveyed onto the platen P by the conveyance belt 16 which starts rotating simultaneously with the registration rollers 14.

At this time, since the optical registration sensor 10 is turned on until the trailing edge of the document is sent out from the position of the registration sensor 10, the control unit described later starts from the timing of starting the rotation of the registration roller 14 and the drive roller 17. The number of pulses applied to the motor M2, which is the power source of the drive roller 17 and the registration roller 14, until the timing when the registration sensor 10 is turned off by the passage of the trailing edge of the document (specifically, the pulse from the encoder attached to the motor M2). Number), and the document size is classified into a standard size by the count value.

When copying only one side, the motor M2 is stopped when a pulse corresponding to the distance L0 from the position of the registration sensor 10 to the predetermined position A on the platen P is applied to the motor M2. As a result, the document is set at the predetermined position A on the platen P.

The registration roller 14 is the conveyor belt 1.
6 and a drive motor M2, a registration clutch G is interposed between the registration roller 14 and the conveyance belt 16 while the conveyance belt 16 is rotating.
The rotation of is not stopped.

Next, the reversing and discharging section 5 includes a reversing roller 20, driven rollers 21a and 21b which are pressed against the reversing roller 20, a switching claw 22 which reversely feeds the document in the direction of the conveying belt 16 with the front and back sides thereof reversed, and a paper ejection sensor. 23, a sensor 24 for determining a stop timing at the time of reverse feeding, a paper discharge roller 25, and a motor M3 as a power source of the reversing roller 20,
The original conveyed by the conveying belt 16 in the discharge direction upon completion of image processing on one side of the original is conveyed by the reverse roller 20 in the discharge direction. At this time, the switching claw 22
Is shown in the figure, the sheet is discharged onto the sheet discharge tray 6 by the sheet discharge roller 25. However, the switching claw 22
Is switched to the reverse feeding side, the guide belt 16 is guided toward the driven roller 18, and the platen P is again set at a predetermined position by the reverse rotation of the conveyor belt 16.

On the other hand, at the time of double-sided copying, in order to arrange the discharge order of the originals, the originals are passed once over the platen P and the reverse discharge unit 5 reverses the front and back sides of the originals. Set to to copy one side. After that, the front and back sides of the document are reversed by the reversing and discharging section 5 and set again at the predetermined position A, and the remaining one side is copied. After that, the switching claw 22 of the reversing and discharging section 5 is switched to the state shown in the drawing, and the discharge tray is discharged. Discharge to 6.

FIG. 2 is a block diagram showing the arrangement of a control unit for controlling the document conveyance. The control unit is specifically configured by the microcomputer 30. The microcomputer 30 includes an empty sensor 8,
In addition to inputting output signals of the registration sensor 10, the paper discharge sensor 23, and the sensor 24 for detecting the stop timing, outputs from encoders (not shown) attached to the motors M1, M2, and M3. The clock pulses φ1, φ2, and φ3 are input.

The output signal is sent to the motor M1 for rotating and driving the separation roller 9 and the like of the sheet feeding section 1, the motor M2 for rotating the conveyor belt 16, and the motor M3 for rotating the reversing roller 20. Applied pulse PM1-PM
3, an ON signal RCL to the registration clutch G for transmitting the rotation of the motor M2 to the registration roller 14,
A drive signal SD or the like is output to a solenoid (not shown) for switching the switching claw 25.

In such a double-sided document feeder, the registration sensor 10, the paper discharge sensor 23, and the sensor 24 for detecting the paper discharge timing are composed of optical sensors. Among these, the registration sensor 10 is a transmissive type, the paper discharge sensor 23,
The sensor 24 for detecting the discharge timing is composed of a reflection type sensor. Then, the sensitivity is automatically adjusted by using the microcomputer 30.

FIG. 3 is a circuit diagram showing an example of a structure for automatically adjusting the sensitivity of the reflection type paper discharge sensor 23, so that the light emitted from the light emitting element 40 is directed toward the document conveying path. If there is no document, the background plate 41 on the rear side of the document transport passage is illuminated. The background plate 41 is formed of a member having a reflecting surface whose reflectance is lower than that of the original, and the light reflected by the background plate 41 is incident on the light receiving element 42. In the light receiving element 40, the power supply voltage Vcc is applied to the anode, the cathode is grounded through the transistor 43 and the resistor 44, and the initial sensitivity setting voltage V0 is input to the inverting input of the operational amplifier 45 to set the initial sensitivity setting voltage V0. A corresponding voltage is applied to emit light with a light emission brightness corresponding to V0.

On the other hand, the light-receiving element 42 has its emitter grounded through the load resistor 46 and outputs an output voltage Vin corresponding to the amount of light received from the background plate 41.

The initial setting voltage V0 input to the inverting input of the operational amplifier 45 is output from the DA converter 47, and the output voltage Vin of the light receiving element 42 is input to the AD converter 48. The DA converter 47 converts the voltage information output from the CPU 30 into a corresponding voltage value and inputs it to the operational amplifier 45. On the other hand, the AD converter 48 converts the output voltage Vin of the light receiving element 42 into corresponding voltage information and inputs it to the CPU 30.

At the end of product assembly, the CPU 30 inputs preset voltage information for initial sensitivity setting to the DA converter 47 so that the output voltage information of the AD converter 48 falls within the initial sensitivity allowable range. If the set voltage V0 is changed little by little and falls within the allowable range of the initial sensitivity, the nonvolatile memory 4 in which the voltage information input to the DA converter 47 at this time can be electrically written.
It is stored in No. 9 and used to detect the presence or absence of the sheet thereafter.

The configuration of FIG. 3 is for adjusting the amount of emitted light. However, as shown in FIG. 4, a constant voltage is applied to the light emitting element 40 and the emitter load resistor 46 of the light receiving element 42 is applied. Connect the field effect transistor 50 in series,
A configuration of a light receiving voltage adjusting method may be used in which the resistance value between the source and the drain of the field effect transistor 50 is controlled by the gate control voltage V0 so that the output voltage Vin of the light receiving element 42 falls within the allowable range of the initial sensitivity.

Further, as shown in FIG. 5, the configurations of FIGS. 3 and 4 are combined to apply the voltage to the light emitting element 40 and the light receiving element 4.
Both of the two output voltages may be controlled by using the operational amplifier 45 and the field effect transistor 50.
In FIG. 5, the initial sensitivity setting voltage input to the operational amplifier 45 is V01, and the field effect transistor 50 is
The control voltage input to V2 is shown as V02.

In each case, the sensitivities of the light emitting element and the light receiving element are adjusted by the voltage information, but the voltage and the current can be treated equivalently if the resistance in the circuit is constant. Even if it is adjusted by, the completely equivalent effect can be obtained.

FIG. 6 shows that in the structure shown in FIG. 3, the light emitting element 40 is caused to emit light at an amount of emitted light corresponding to the initial setting voltage V0 when the product is assembled, and the amount of light reflected from the background plate 41 and received by the light receiving element 42 is within the allowable range. To see if it fits in
9 is a flowchart showing an operation procedure for adjusting the initial setting voltage V0 so that it is within an allowable range.
After the initial setting voltage V0 is output from the A converter 47, the output voltage Vin of the AD converter 48 and the reference voltage V
R is compared (S1, S2). As a result, when Vin is larger than “VR + v” (where v is a permissible difference voltage), the light emitting element 40 has too large a light emitting capacity to emit too much light, or the light receiving element 42 has too high sensitivity. This means that the initial setting voltage V0 output from the DA converter 47 is lowered by the stepping voltage e, and the lowered voltage is set as a new initial setting voltage V0 again to the operational amplifier 4 again.
5, and the light emitting element 40 is caused to emit light at the new initial setting voltage V0 (S3, S4). As a result, Vin is "VR
+ V ”, then Vin <VR
-V, and if Vin> VR-v, it means that the output of the light receiving element 42 is within the range between VR.

On the contrary, if Vin <VR-v, it means that the amount of emitted light is too small.
The initial setting voltage V0 output from the above is increased by the stepping voltage e, and the increased voltage is input to the operational amplifier 45 again as a new initial setting voltage V0, and the new initial setting voltage V0 is output.
The light emitting element 40 is caused to emit light (S5, S6). As a result, Vin is larger than "VR-v" and "VR +
smaller than “v” and the output voltage of the light receiving element 42 is “VR ±
Since it has fallen within the allowable range of “v”, the initial setting voltage information input to the DA converter 47 at this time is stored in the memory 49 (S7).

As a result, the background plate 4 on which no document exists
The adjustment of the sensitivity when only 1 is completed. In the actual sheet detection, the presence or absence of the sheet is detected by using the initial setting voltage information stored in the memory 49 in the initial sensitivity setting operation. That is, since the actual document has a higher reflectance than the background plate 41, the output voltage of the light receiving element 42 becomes higher than VR, and the presence or absence of the document can be detected by this.

However, as described above, the sensitivities of the light emitting element 40 and the light receiving element 42 change with time, or the light emitting surface and the like are clogged with paper dust, so that the sensitivities change.

Therefore, it is necessary to readjust the sensitivity at a predetermined time. The timing of readjustment is, for example, when the power is turned on, after a predetermined number of sheets have passed, or after a certain period of time has passed, after an arbitrary period of time has passed by the maintenance personnel.

7 to 8 are flow charts showing an operation procedure for adjusting the sensitivity each time the power is turned on.
The initial setting voltage information stored in the memory 49 is read and input to the DA converter 47, and the light emitting element 40 is read.
Is emitted with the amount of emitted light corresponding to the initial setting voltage V0 (S10, S11). Then, in this light emitting state, the output voltage Vin of the light receiving element 42 is compared with the paperless threshold voltage VTH (however, VTH> VR), and if Vin ≧ VTH, it is detected that there is paper, even if there is no paper. Therefore, for some reason, it is recognized that the document exists in front of the background plate 41, the jam processing is performed, and the paper jam is removed by the maintenance personnel (S12, S13, S14).

However, if Vin≤VTH, the output voltage Vin of the AD converter 48 is compared with the reference voltage VR (S15). As a result, when Vin is larger than “VR + v” (where v is a tolerance voltage), the light emitting element 4
0 means that the sensitivity ability is too large and the amount of emitted light is too large, or that the sensitivity of the light receiving element 40 is too high.
Initial setting voltage V0 output from the DA converter 47
Is reduced by the stepping voltage e (S17), and the reduced voltage is input to the operational amplifier 45 again as a new initial setting voltage V0, and the light emitting element 40 is caused to emit light at the new initial setting voltage V0. As a result, if Vin becomes smaller than “VR + v”, then it is compared whether Vin <VR−v (S1
8) If Vin> VR-v, it means that the output of the light receiving element 42 is within the range between VR.

On the other hand, if Vin <VR-v, it means that the amount of emitted light is too small.
The initial setting voltage V0 output from the circuit is increased by the increment voltage e (S19), and the increased voltage is input to the operational amplifier 45 again as a new initial setting voltage V0, and the light emitting element 40 is driven with the new initial setting voltage V0. Make it glow. As a result, V
If in becomes larger than "VR-v", the limit voltage VHL indicating the maximum limit voltage of V0 is compared with the currently set initial setting voltage V0 (S21, S22), and V0
If> VHL, it is impossible to further increase the light emission amount of the light emitting element 40, so an alarm signal is output and a maintenance worker is instructed to inspect for paper dust clogging (S23). If the alarm signal is generated due to paper dust clogging, the sensitivity is adjusted again by turning on the power after removing the paper dust. Note that VHL is a value limited by the allowable current value of the light emitting element 40 and the like.

However, if V0 <VHL, that is, if the limit voltage is not reached, the process returns to step S15 again. As a result, the output voltage Vin of the light receiving element 42 becomes VR.
If it falls within the allowable range of ± v, the initial setting voltage information input to the DA converter 47 at this time is stored in the memory 4
9 (S20).

By the way, the light emitting element 40 or the light receiving element 4
When the sensitivity of No. 2 is further deteriorated due to aging, the output voltage Vin of the light receiving element 42 may not fall within the allowable range of VR ± v even if the paper dust is removed and the limit voltage VHL is exceeded. .

In order to deal with such a case, the limit voltage VHL is set to VHL0, VHL1, VHL each time the paper dust is cleaned.
2 ... and so on until the final limit voltage V
If it does not fall within the allowable range even if it is raised to the HLL, it is instructed to replace the element.

FIGS. 9 to 11 show the procedure therefor. Every time the paper dust is cleaned, the maintenance staff is made to input that the paper dust was cleaned (S38) and stored in the memory 49. The paper dust cleaning count NC is updated (S39). Then, after cleaning the paper dust, the power is turned on again to start the operation of FIG. 7, and when step S19 of FIG. 7 is reached, the process proceeds to step S30 of FIG. , And then the limit voltage VHLn (n = 1, 2, 3 ...) Corresponding to the number of times of cleaning paper dust is selected (S).
31). As shown in FIG. 10, the limit voltage VHLn corresponds to the voltage V0 set in the initial sensitivity setting mode by the coefficient a,
It is calculated by multiplying b, c ... And stored in the memory 49 in advance.

The limit voltage VHLn selected at this time is
(N = 1, 2, 3 ...) and the set voltage V currently output
0 is compared (S32, S33), and if VHLn <V0, the process returns to step S15 of FIG. 7 to perform the subsequent processing. However, if VHLn> V0, VHLn is compared with the final limit voltage VHLL (S34), and if VHLn ≧ VHLL, further improvement in sensitivity cannot be expected, so the device itself should be replaced. An alarm is output (S37). However, if VHLn ≧ VHLL is not satisfied, the limit voltage can be further increased, and therefore a paper dust cleaning alarm is output (S36).

In this way, by gradually increasing the sensitivity of the light emitting element 40 and the light receiving element 42 until just before the end of their life, the sensitivity is not raised too much, and the light emitting element 40 and the light receiving element 42 are completely deteriorated. It becomes possible to accurately detect the presence or absence of the sheet until after. As a result, the life of the element itself can be improved and maintenance management can be extremely simplified.

By the way, when the light emission amount of the light emitting element 40 or the sensitivity of the light receiving element 42 is lowered due to the attachment of paper dust or the like, and the light emission amount of the light emitting element 40 is increased to compensate for it, the paper attached for some reason When the powder is removed, the background plate 41
The output voltage Vin of the light receiving element due to the reflected light from may exceed the paperless threshold VTH. In such a case, a serious malfunction occurs in which the paper-free state is erroneously detected as "paper present".

Therefore, with respect to the initial setting voltage V0 for controlling the light emission amount of the light emitting element 40, the light receiving element output voltage Vin due to the reflected light from the background plate 41 is VT in the state without paper dust stain.
Set VLMT that gives an amount of light emission that does not exceed H, and set V0>
When VLMT occurs, an alarm requesting maintenance work such as paper dust removal is output. After cleaning the paper dust, the maintenance personnel perform the initial setting again and reset the VLMT. In this way, the VLMT is set for each cleaning of the paper dust, and the final limit voltage V
When the HLL is reached, the device replacement is instructed.

12 and 13 show a procedure therefor. When the power is turned on and the process reaches step S19 in FIG. 7, the process proceeds to step S50 in FIG. 12 to set V0 and VLM.
Compare with T. If V0 <VLMT, the process returns to step S15 in FIG. 7 to perform the subsequent processing. However, V0> VL
If MT, compare the final limit voltage VHLL and V0,
If V0 <VHLL (S52, 53), the sensitivity can be recovered by cleaning the paper dust, so an alarm for instructing the paper dust is output (S54). If V0>, the limit of the element has been reached, so an alarm instructing replacement of the element itself is output (S54).

Further, VLMT is set after the process of setting the sensitivity (FIG. 6) at the initial stage or after cleaning the paper dust, and as shown in FIG. 13, the coefficient a preset to V0 set by the initial sensitivity setting is set. It is calculated by multiplication (S56). This coefficient a is the paperless threshold voltage VTH and the paperless reference voltage V
It is set to a value smaller than the ratio VTH / VR with R. The set VLMT is stored in the EEPROM, and thereafter, the value is not updated until the sensitivity is set after the next paper dust cleaning (S57).

[0048]

As described above, in the present invention, the light emitting element and the light receiving element are provided, and the reflected light or the transmitted light of the light emitted from the light emitting element and applied to the sheet is received by the light receiving element.
In a sheet detection device that detects the presence or absence of a sheet by the amount of received light, at least one of the light emission control signal of the light emitting element and the light reception control signal of the light receiving element is set within a permissible range of the light receiving output of the light receiving element at a predetermined time. A sensitivity control means for varying so that the light emission control signal after controlling the light reception output of the light receiving element within an allowable range and a storage means for storing at least a variable side signal of the light reception control signal, The presence or absence of the sheet is detected by driving the light emitting element and the light receiving element based on the light emission control signal and the light receiving control signal stored in the storage means.

Further, there is provided comparison means for comparing the light emission control signal and the light reception control signal after controlling the light reception output of the light receiving element within an allowable range, and the light emission control signal and the light reception control signal. A warning is issued when at least one of the two deviates from the limit control signal.

Therefore, the sensitivities of the light emitting element and the light receiving element can be automatically adjusted within an allowable range, and the life of these elements can be extended to the maximum and used. Further, the maintenance work interval is significantly lengthened, and the work cost therefor is reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a document feeder to which the present invention is applied.

FIG. 2 is a configuration diagram of a control unit.

FIG. 3 is a circuit diagram showing a first embodiment of the sheet detecting device of the present invention.

FIG. 4 is a circuit diagram showing a second embodiment of the sheet detecting device of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the sheet detecting device of the present invention.

FIG. 6 is a flowchart showing an initial sensitivity adjustment procedure of the embodiment of FIG.

FIG. 7 is a flowchart showing a sensitivity adjustment procedure performed when the power is turned on in the embodiment of FIG.

8 is a flowchart showing a latter part of the flowchart of FIG.

FIG. 9 is a flowchart showing a procedure for issuing a warning when the sensitivity adjustment reaches a limit.

FIG. 10 is a flowchart showing a procedure for inputting that paper dust has been cleaned.

FIG. 11 is a flowchart showing a procedure for setting a limit voltage according to the number of times of cleaning paper dust.

FIG. 12 is a flowchart showing another example of a procedure for issuing a warning when the sensitivity adjustment reaches a limit.

FIG. 13 is a flowchart showing a procedure for calculating a limit voltage used in FIG.

[Explanation of symbols]

1 Automatic document feeder 10 Registration sensor 23 Paper ejection sensor 30 microcomputer 40 light emitting element 41 background plate 42 Light receiving element 45 operational amplifier 47 DA converter 48 AD converter 49 Non-volatile memory 50 field effect transistor

Claims (2)

[Claims] 1. A sheet detection device comprising a light emitting element and a light receiving element, wherein the light receiving element receives reflected light or transmitted light emitted from the light emitting element to irradiate a sheet, and the presence or absence of the sheet is detected by the amount of the received light. In the device, sensitivity control means for varying at least one of the light emission control signal of the light emitting element and the light reception control signal of the light receiving element so that the light receiving output of the light receiving element falls within an allowable range at a predetermined time, and the light receiving means. Storage means for storing the light emission control signal after controlling the light reception output of the element within an allowable range and a signal on at least a variable side of the light reception control signal are provided, and the light emission control signal and the storage means stored in the storage means. A sheet detecting apparatus, characterized in that the presence or absence of a sheet is detected by driving the light emitting element and the light receiving element based on a light receiving control signal. 2. The light emission control signal and the light reception control signal are provided with a comparison means for comparing the light emission control signal and the light reception control signal after controlling the light reception output of the light receiving element within an allowable range, and the light emission control signal and the light reception control signal. 2. The sheet detecting device according to claim 1, wherein a warning is issued when at least one of the two deviates from the limit control signal.