JPH09100032A - Sheet detection apparatus and image forming apparatus - Google Patents

Abstract

(57) Abstract: The present invention reduces the number of signal lines of a sheet detection device to improve the assembling property of the device, and at the same time, achieves cost reduction and cost performance when a sheet cassette is set as an option. It is an object of the present invention to provide an improved sheet detection device and an image forming apparatus including the same. SOLUTION: Sheet size detection switches 13a, 13b,
The digital signal from 13c is converted into an analog voltage by the D / A converter 23 to output an analog voltage, and an output voltage setting circuit corresponding to the digital signal from the sheet presence sensor 14
24 is configured to output a fixed voltage and superimpose the fixed voltage on the analog voltage from the D / A converter 23 and output the analog voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet detection device for detecting the size of a sheet stored in a sheet cassette and the presence / absence of the sheet, and an image forming apparatus having the same.

[0002]

2. Description of the Related Art A conventional sheet detecting device for detecting the size of a sheet accommodated in a sheet cassette and the presence or absence of the sheet will be described with reference to FIGS. Reference numeral 100 denotes a sheet cassette configured to be attachable to and detachable from the image forming apparatus main body 101 in the direction of arrow a in FIG. 11, and the apparatus main body 101 detects the size of the recording sheet P accommodated in the sheet cassette 100. A sheet size detection switch 102 is provided. Further, a sheet presence / absence sensor 103 is provided in the apparatus main body 101 corresponding to the upper portion of the recording sheet P accommodated in the sheet cassette 100.

The image forming apparatus main body 101 is a sheet cassette.
Whether 100 is installed or sheet cassette 10
The size of the recording sheet P loaded in 0 is detected by the sheet size detection switch 102.

That is, specifically, mechanical projections 100a, 100b, 100c are provided on the sheet cassette 100 corresponding to the size of the recording sheet P loaded in the sheet cassette 100, and the projections are the sheet size detection switch 102. The 3-bit switches 102a, 102b, 102c are turned ON / OFF, and the size of the recording sheet P and the sheet cassette 10 are determined by the codes.
Recognize the wearing state of 0.

When a print execution instruction is issued from the host computer (not shown) to the image forming apparatus main body 101, the image forming apparatus main body 101 determines whether or not the sheet cassette 100 is mounted, or the recording sheet of a desired size. Whether or not P is loaded in the sheet cassette 100 is determined by a sheet size detection switch 102 and a sheet presence sensor.
Judging from the detection signal of 103, if a suitable recording sheet P is loaded in the sheet cassette 100, the feeding operation and the image forming operation are started.

Here, the sheet cassette 100 is the apparatus main body 10
If the recording sheet P is not attached to item 1 or the size of the recording sheet P does not fit, the fact is notified to the host computer.

FIG. 12 is a block diagram of the control system. 104
Is a control unit including a CPU (Central Information Processing Unit), and the control unit 104 is connected to the 3-bit sheet size detection switches 102a, 102b, 102c and the sheet presence / absence sensor 103.

The mechanical protrusions 100a, 100b, 100c provided on the sheet cassette 100 turn on / off the 3-bit sheet size detection switches 102a, 102b, 102c.
Then, the CPU of the control unit 104 recognizes the size code of the recording sheet P loaded in the sheet cassette 100.

For example, when loading the A4 size recording sheet P into the sheet cassette 100, the user uses the A4 size dedicated sheet cassette 100. At this time, the protrusions 100a, 100b, 100c provided on the sheet cassette 100 cause the sheet size detection switch 102, for example, the switch 102a to be turned on.
N, the switch 102b is turned off, the switch 102c is turned off, and when the recording sheet P is a letter size, for example, the switch 102a is turned on, the switch 102b is turned on, and the switch 102c is turned off. To be done.

In this way, when the dedicated sheet cassette 100 corresponding to the size of the recording sheet P is prepared,
The switches 102a, 102b, 10 are arranged so that the code corresponding to the size of the recording sheet P loaded in the sheet cassette 100 is obtained.
Sheet cassettes with protrusions 100a, 100b, 100c for pushing 2c
It is equipped with 100.

Further, in a form in which one sheet cassette 100 can load various kinds of recording sheets P, the projections 100a, 100b, 100c of the sheet cassette 100 are changed by the user setting the sheet size setting dial. The desired switches 102a, 102b, 102c are turned on / off.

[0012]

However, in the above-mentioned prior art, the sheet size detection switches 102a and 102a are used.
In order to transmit the 3-bit information of b and 102c as a digital signal to the CPU of the control unit 104, it is necessary to connect the signal lines for three digital signals with one sheet cassette 100. In the mode in which the sheet cassettes 100 are connected and used, each time the number of the sheet cassettes 100 increases, three signal lines for the sheet size detection switch 102 and one signal line for the sheet presence sensor 103 must be added. Therefore, there is a problem that the arrangement of these signal lines becomes complicated, the assemblability of the device is deteriorated, and the cost is increased.

Further, when the sheet cassette 100 is set as an option, there are many unused connectors or pins when the sheet cassette 100 is connected to the minimum, so that cost performance (cost efficiency) is improved. There is a problem of being bad.

The present invention solves the above-mentioned problems, and
The purpose is to reduce the number of signal lines of the sheet detection device to improve the assembly property of the device, reduce the cost, and further improve the cost performance when the sheet cassette is set as an option. An object of the present invention is to provide a detection device and an image forming apparatus equipped with the detection device.

[0015]

A typical structure according to the present invention for achieving the above object is a sheet cassette for accommodating sheets, and a sheet size for detecting the size of a sheet accommodated in the sheet cassette. A detection unit; a sheet presence / absence detection unit for detecting the presence / absence of a sheet accommodated in the sheet cassette; and a digital / analog signal converting the digital signal output by the sheet size detection unit
The analog conversion unit and the analog signal output from the digital / analog conversion unit are added to the analog signal corresponding to the digital signal output by the sheet presence / absence detection unit, and the analog signal output is stored in the sheet cassette. The sheet detection device is configured to recognize the size of the sheet to be formed and / or the presence or absence of the sheet.

According to the above construction, the digital signal output from the sheet size detecting means is converted into an analog signal by the digital / analog converting means, and the analog signal corresponding to the digital signal output from the sheet presence detecting means is added. By outputting the analog signal as an analog signal, it is possible to reduce the number of signal lines, which was required in the digital signal transmission.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A sheet detecting apparatus according to the present invention and an image forming apparatus equipped with the same will be described in detail as an example when applied to an electrophotographic image forming apparatus. FIG. 1 is a sectional explanatory view showing an overall configuration of an image forming apparatus equipped with a sheet detecting apparatus according to the present invention, and FIG. 2 is a first image forming apparatus equipped with the sheet detecting apparatus according to the present invention.
FIG. 3 is a block diagram showing the configuration of the control system of the embodiment, FIG.
FIG. 4 is a circuit diagram showing the configuration of the sheet detection device of the embodiment, and FIG. 4 shows the analog voltage value output from the D / A converter corresponding to the digital signal code output from the sheet size detection means in the first embodiment. FIG.

First, the overall construction of an image forming apparatus equipped with a sheet detecting apparatus according to the present invention will be described with reference to FIGS. In FIG. 1, the image forming apparatus main body 1 is provided with a sheet cassette 2 which is detachably attached to the apparatus main body 1 in the direction of arrow a in FIG.

The recording sheet P made of paper, synthetic resin or the like contained in the sheet cassette 2 is fed out by a feeding roller 3 constituting a sheet feeding means and then conveyed by a conveying roller 4. The image is detected by the registration sensor 5, the image recording timing is adjusted, and the image is sent to the image forming unit 6 serving as an image forming unit.

In the image forming section 6, after the outer peripheral surface of the electrophotographic photosensitive drum 7 is uniformly charged, laser light corresponding to image information is irradiated to form a latent image, and toner is attached thereto. After the transfer roller 8 transfers the toner image onto the recording sheet P, the fixing unit 9 is heated and pressed by the fixing roller having a built-in heater to fix the toner image onto the recording sheet P. The passed recording sheet P is detected by a discharge sensor 10, and then discharged through a discharge path 11 onto a discharge tray 12 provided on the upper portion of the apparatus main body 1,
Be loaded.

A sheet size detection switch 13 is provided in the apparatus main body 1 and serves as a sheet size detection means for detecting size information of the recording sheets P accommodated in the sheet cassette 2. The sheet size detection switch 13 turns on / off the 3 bits of the switches 13a, 13b, 13c, and recognizes the size of the recording sheet P and the mounting state of the sheet cassette 2 with respect to the apparatus main body 1 by identifying these codes.

The sheet size detection switch 13 is provided on the sheet cassette 2 and engages with the mechanical projections 2a, 2b, 2c whose positions are set according to the size of the recording sheet P, so that the respective switches 13a, 13b and 13c are turned on / off.

When the sheet cassette 2 is detached from the apparatus main body 1, all the switches 13a, 13b, 13c are turned off (see code 8 in FIG. 4).
The sheet size detection switch 13 is adapted to detect that the sheet cassette 2 is detached from the apparatus main body 1.

For example, when loading the A4 size recording sheet P into the sheet cassette 2, the user uses the A4 size dedicated sheet cassette 2. At this time, among the sheet size detection switches 13, the switch 13a is turned on by the projections 2a, 2b, 2c provided on the sheet cassette 2 and the switch 13 is turned on.
b is turned off and the switch 13c is turned off (see code 1 in FIG. 4). If the recording sheet P is letter size, the switch 13a is turned on and the switch 13b is turned on.
Is turned on and the switch 13c is turned off (see code 4 in FIG. 4).

Reference numeral 14 is a sheet presence / absence detecting means provided on the apparatus main body 1 and arranged as a sheet presence / absence detecting means arranged facing the recording sheet P so as to engage with the recording sheet P accommodated in the sheet cassette 2. Sensor, the sheet presence sensor
The drive knob 14a of 14 engages / disengages the recording sheet P housed in the sheet cassette 2 to detect the sheet presence / absence sensor.
14 is turned on and off.

In the image forming apparatus main body 1, when a print instruction is issued from a host computer (not shown), whether or not the sheet cassette 2 is mounted, or whether or not a recording sheet P of a desired size is loaded in the sheet cassette 2. Whether or not it is detected by the sheet size detection switch 13 and the sheet presence / absence sensor 14, and if the desired recording sheet P is loaded, the feeding operation and the image forming operation of the recording sheet P are performed.

If the sheet cassette 2 is not installed or the recording sheet P is not suitable, the host computer is notified of that fact.

In FIG. 2, reference numeral 15 is a control unit including a CPU (central information processing unit) provided in the host computer. The control unit 15 includes a laser drive unit 16 for outputting laser light and the laser drive unit. A scanner motor drive unit 17 for rotating a polygon mirror for irradiating the laser beam output by the unit 16 on the outer peripheral surface of the photosensitive drum 7 while scanning is connected.

Further, the control section 15 includes a photosensitive drum 7
And applying a bias voltage to the transfer roller 8 to charge it,
A high voltage controller 18 for controlling development and transfer, and a heater driver for controlling the fixing unit to a constant temperature.
19, a main roller driving unit 20 for driving the feeding roller 3, the conveying roller 4, the photosensitive drum 7, and the fixing roller of the fixing unit 9, and a solenoid driving unit 21 used for driving the feeding roller 3. The registration sensor 5 and the discharge sensor 10 are connected to each other.

Furthermore, the output signal (analog voltage Vout) of the output terminal 22 shown in the circuit diagram of the sheet detecting apparatus of the first embodiment shown in FIG. 3 and described later, which is a feature of the present invention.
Is transmitted to the control unit 15.

Next, the first embodiment of the sheet detecting apparatus, which is a feature of the present invention, will be described in detail with reference to the circuit diagram of FIG. Referring to FIG. 3, in the present embodiment, the D / A converter 23 that serves as a digital / analog conversion unit for the 3-bit digital signal output from the sheet size detection switch 13 is used.
The analog voltage output from the D / A converter 23 is a predetermined analog voltage corresponding to the digital signal output from the sheet presence sensor 14 by the output voltage setting circuit 24. The analog voltage Vout added to is output from the output terminal 22 and transmitted to the CPU of the control unit 15.

The sheet size detection switch 13 has its one end grounded and its other end connected to the bias voltage Vcc through pull-up resistors 25a, 25b and 25c, respectively, and is normally held in the OFF state. 13c in parallel D /
The A converter 23 is connected to input terminals D2, D1 and D0, respectively.

Further, the D / A converter 23 has a reference voltage Vref.
Is connected, and as a result, ON / OF as a digital signal output from the sheet size detection switch 13
The F signal is converted into an analog voltage as an analog signal and the analog voltage output to the output terminal 26 is maintained at a predetermined voltage value.

Here, for example, only the switch 13a is turned on.
Then, when the switches 13b and 13c are OFF (code 1 in FIG. 4)
Output), the output voltage of the output terminal 26 of the D / A converter 23 is
{Vref / 2} V, that is, {4Vref / 8} V ... (1), only the switch 13b is ON, and the switches 13a and 13c
D is OFF (see code 2 in Figure 4), D / A converter 23
The output voltage of the output terminal 26 is {Vref / 4} V, that is,
{2Vref / 8} V ... (2).

When only the switch 13c is ON and the switches 13a and 13b are OFF (see code 3 in FIG. 4), D
The output voltage of the output terminal 26 of the / A converter 23 is {Vref /
8} V ... (3), and switches 13a and 13b
Is on and switch 13c is off (code 4 in Figure 4
(See the above), from the output voltage (1) + output voltage (2),
The output voltage of the output terminal 26 of the A converter 23 is {6Vref / 8}.
V.

When the switch 13a and the switch 13c are ON and the switch 13b is OFF (see code 5 in FIG. 4), the output voltage (1) + output voltage (3) causes
The output voltage of the output terminal 26 of the converter 23 is {5Vref / 8} V.
Then, when the switch 13b and the switch 13c are ON and the switch 13a is OFF (see code 6 in FIG. 4), the output terminal of the D / A converter 23 is obtained from the output voltage (2) + the output voltage (3). The output voltage of 26 is {3Vref / 8} V.

When all the switches 13a, 13b and 13c are ON (see code 7 in FIG. 4), the output voltage (1) + output voltage (2) + output voltage
From (3), the output voltage of the output terminal 26 of the D / A converter 23 becomes {7Vref / 8} V, and when all the switches 13a, 13b and 13c are OFF (see code 8 in FIG. 4). , The output voltage of the output terminal 26 of the D / A converter 23 becomes {0} V. At this time, the sheet cassette 2
Is a state of being detached from the apparatus main body 1.

Therefore, the 3-bit switches 13a, 13b,
An analog voltage as an analog signal output to the output terminal 26 of the D / A converter 23 by a combination of digital signals (ON / OFF) input from 13c to the input terminals D2, D1, D0 of the D / A converter 23 Is 0V to {7Vref /
It is divided into 8 in the range of 8} V.

Therefore, 0V is set as a code in a state where the sheet cassette 2 is detached from the apparatus main body 1, and {Vref / 8}
V, {2Vref / 8} V, {3Vref / 8} V, {4V
ref / 8} V, {5Vref / 8} V, {6Vref / 8}
V and {7Vref / 8} V are made to correspond to the size codes of the seven kinds of recording sheets P used respectively.

A buffer 27 provided in the output voltage setting circuit 24 is connected to the output terminal 26 of the D / A converter 23,
Further downstream, the output terminal is connected to the cathode terminal of a diode 28 whose anode terminal is connected to the output side of the buffer 27.
22 is connected, and the output terminal 22 is connected to the control unit 15.

D / A converter by the action of the buffer 27
The voltage output from the output terminal 26 of 23 is maintained as an accurate analog voltage signal without being affected by ambient noise,
It is transmitted from the output terminal 22 to the control unit 15. Further, the diode 28 has an electromotive force V applied to a pull-down resistor 33 which will be described in detail later.
It has a function of preventing the current from flowing backward to the buffer 27 when r occurs and protecting the buffer 27.

In the sheet presence / absence sensor 14, the cathode terminal of the photodiode and the emitter terminal of the phototransistor of the photointerrupter 29 composed of an optical relay are grounded, and the anode terminal of the photodiode is biased via the current limiting resistor 30. The collector terminal of the phototransistor is connected to the bias voltage Vcc via the pull-up resistor 31.

As shown in FIG. 1 and described above, when the drive knob 14a of the sheet presence / absence sensor 14 is engaged with the recording sheet P accommodated in the sheet cassette 2, the drive knob 14a is rotated and the drive knob 14a is rotated. A sensor cutoff portion provided on the other end side of 14a withdraws from the optical path between the photodiode and the phototransistor of the photointerrupter 29, and the light from the photodiode is transmitted to the phototransistor to turn on the phototransistor. It becomes a state.

The recording sheet P in the sheet cassette 2
When the drive knob 14a disappears, the drive knob 14a rotates to move the drive knob 14a.
A sensor cutoff portion provided on the other end side of a cuts off the optical path between the photodiode and the phototransistor of the photointerrupter 29 to turn off the phototransistor.

To the collector terminal of the phototransistor of the photointerrupter 29, the base terminal of the transistor 32 provided in the output voltage setting circuit 24 is connected,
The collector terminal of the transistor 32 is connected to the bias voltage Vcc, and the emitter terminal is connected to the cathode terminal of the diode 28. The cathode terminal of the diode 28 is connected to the ground via the pull-down resistor 33.

With the above structure, when the recording sheet P is accommodated in the sheet cassette 2 and the phototransistor of the photointerrupter 29 is turned on, the base of the transistor 32 is grounded, the transistor 32 is turned off, and the output terminal 22 is connected to the output terminal 22. The output voltage becomes an analog voltage output from the output terminal 26 of the D / A converter 23 via the buffer 27 and the diode 28.

The recording sheet P in the sheet cassette 2
When the phototransistor 29 of the photointerrupter 29 is turned off, the drive voltage is applied to the base of the transistor 32, the transistor 32 is turned on, and the bias current is supplied to the pulldown resistor 33 and the pulldown resistor 33.
An electromotive force Vr is generated at both ends of.

At this time, by setting the resistance value of the pull-down resistor 33 to an appropriate value, the value of the electromotive force Vr is larger than the maximum voltage {7Vref / 8} V output from the D / A converter 23. Is set to a value, which
At this time, the voltage output to the output terminal 22 is Vr (> {7
Vref / 8}) V, which is a fixed voltage that does not depend on the output voltage from the D / A converter 23.

That is, when the recording sheet P is in the sheet cassette 2, the sheet size detecting switches 13a, 13b, 13
An analog voltage value corresponding to the digital signal information detected by c, that is, 0V, {Vref / 8} V, {2Vref / 8}
V, {3Vref / 8} V, {4Vref / 8} V, {5V
ref / 8} V, {6Vref / 8} V, {7Vref / 8}
V is transmitted to the control unit 15, and when the recording sheet P is not in the sheet cassette 2, a fixed voltage Vr (> {7Vref / 8}
V) is transmitted to the control unit 15.

Analog voltage V output from the output terminal 22
out is input to an A / D conversion port that converts an analog signal included in the CPU of the control unit 15 into a digital signal, is converted into a digital signal again, and instructs the control operation of the control unit 15.

With the above configuration, the control unit
By detecting the analog voltage Vout output from the output terminal 22, the CPU 15 recognizes the size of the recording sheet P detected by the sheet size detection switch 13 only when the recording sheet P is present, and the recording sheet P is detected. When there is no recording sheet P, it can be recognized regardless of the detection state of the sheet size detection switch 13.

Therefore, in this embodiment, the sheet presence / absence information from the sheet presence / absence sensor 14 is used as the sheet size detection switch.
By adding it to the sheet size information by 13, the necessary sheet size information is transmitted to the CPU of the control unit 15 only when there is a sheet, and when there is no sheet, only the sheet absence information is transmitted, so that the minimum necessary Information transmission can be realized.

The digital signal from the sheet size detection switch 13 is converted into an analog signal, and the sheet presence sensor 14
By adding an analog signal corresponding to the digital signal from the
It is possible to reduce the number of signal lines transmitted to U to improve the assembling property of the apparatus and to reduce the cost.

Further, the cost performance can be improved when the sheet cassette is set as an option.

Next, a second embodiment of the image forming apparatus equipped with the sheet detecting device according to the present invention will be described with reference to FIGS. FIG. 5 is a circuit diagram showing the configuration of the sheet detection device of the second embodiment, and FIG. 6 is a D / A corresponding to the digital signal codes output from the sheet size detection means and the sheet presence / absence detection means in the second embodiment. It is a figure which shows the analog voltage value output from a converter. In addition, the first
The same components as those in the embodiment are designated by the same reference numerals and the description thereof will be omitted.

5, in this embodiment, the circuit configurations of the sheet size detection switch 13 and the sheet presence / absence sensor 14 are the same as those in the first embodiment. The output digital signal is converted into an analog signal by the D / A converter 40 serving as a digital / analog conversion means, and an analog voltage is output from the output terminal 41, and the output terminal is output via the buffer 27.
The analog voltage Vout is output from 22 and CP of the control unit 15
It is transmitted to U.

Sheet size detection switches 13a, 13b, 13
One ends of the c connected to the bias voltage Vcc through the pull-up resistors 25a, 25b, 25c are connected to the input terminals D2, D1, D0 of the D / A converter 40, respectively. The collector terminal connected to the bias voltage Vcc through the pull-up resistor 31 of the phototransistor of the photointerrupter 29 is connected to the input terminal D3 of the D / A converter 40.

When the phototransistor of the photointerrupter 29 is in the ON state, the collector terminal of the phototransistor is grounded and the OFF signal is input to the input terminal D3 of the D / A converter 40. In the OFF state, the ON signal is input to the input terminal D3 of the D / A converter 40 by the voltage applied to the collector terminal of the phototransistor connected to the bias voltage Vcc via the pull-up resistor 31.

In the present embodiment, the 3-bit switch 13
4 bits obtained by adding 1 bit of the sheet presence / absence sensor 14 to a, 13b, 13c to input terminals D0, D1, of the D / A converter 40
Digital signals (ON / OF) input to D2 and D3 respectively
The combination of F) is configured to output an analog voltage as an analog signal to the output terminal 41 of the D / A converter 40.

In the D / A converter 40, the same as above,
The reference voltage Vref is connected, whereby the ON / OFF signal as a digital signal output from the sheet size detection switch 13 and the sheet presence / absence sensor 14 is converted into an analog voltage and output to the output terminal 41. Is maintained at a predetermined voltage value.

Here, for example, there is a recording sheet P in the sheet cassette 2, that is, the sheet presence detection sensor 14
Is turned on, the phototransistor of the photo interrupter 29 is turned on, and the signal input to D3 is turned off. When only the switch 13a of the sheet size detection switch 13 is turned on and the switches 13b and 13c are turned off (see FIG. 6). Code 10), the output voltage of the output terminal 41 of the D / A converter 40 is {Vref / 2} V, that is, {8Vref / 16} V.
(1), and only switch 13b is ON, switch 13
D / A when a and 13c are OFF (see code 11 in Fig. 6)
The output voltage of the output terminal 41 of the converter 40 is {Vref / 4}.
V, that is, {4Vref / 16} V ... (2).

When only the switch 13c is ON and the switches 13a and 13b are OFF (see code 12 in FIG. 6), D
The output voltage of the output terminal 41 of the / A converter 40 is {Vref /
8} V, that is, {2Vref / 16} V ... (3), the switches 13a and 13b are ON, and the switch 13c
Is off (see code 13 in Figure 6), the output voltage
(1) + output voltage (2), output terminal 41 of D / A converter 40
Output voltage is {3Vref / 4} V, that is, {12Vref
/16}V...(4).

When the switch 13a and the switch 13c are ON and the switch 13b is OFF (see code 14 in FIG. 6), the output voltage (1) + output voltage (3) causes
The output voltage of the output terminal 41 of the converter 40 is {5Vref / 8}
V, that is, {10Vref / 16} V ... (5), and when the switch 13b and the switch 13c are ON and the switch 13a is OFF (see code 15 in FIG. 6), the output voltage is
(2) Output terminal 41 of D / A converter 40 from + output voltage (3)
Output voltage is {3Vref / 8} V, that is, {6Vref / 8
16} V ... (6).

When all the switches 13a, 13b and 13c are ON (see code 16 in FIG. 6), the output voltage (1) + output voltage (2) + output voltage
From (3), the output voltage of the output terminal 41 of the D / A converter 40 is {7Vref / 8} V, that is, {14Vref / 16} V ...
(7), and when all the switches 13a, 13b, and 13c are OFF (see code 17 in FIG. 6)
Is the output voltage of the output terminal 41 of the D / A converter 40 is {0} V
… (8). At this time, the sheet cassette 2 is detached from the apparatus main body 1.

Further, the recording sheet P is stored in the sheet cassette 2.
State, that is, the sheet presence / absence detection sensor 14 is turned off, and the phototransistor of the photo interrupter 29 is turned on.
In the FF state, the input to D3 is turned ON, and the analog output voltage of the output terminal 41 of the D / A converter 40 in this state is
Each of the output voltages (1) to (8) is configured to have a value obtained by adding {1Vref / 16} V (code 18 in FIG. 6).
~ See Code 25).

Therefore, the 4-bit switches 13a, 13b,
Digital signals (O) input to the D0, D1, D2, and D3 of the D / A converter 41 from the 13c and the sheet presence sensor 14
The analog voltage as the analog signal output to the output terminal 41 of the D / A converter 40 by the combination (N / OFF) is divided into 16 in the range of 0V to {15Vref / 16} V.

Therefore, the analog voltage output from the output terminal 41 of the D / A converter 40 to the output terminal 22 via the buffer 27 is 0V and {1Vref / 16} V (code in FIG. 6).
17 and code 25) are the code with the sheet and the code without the sheet when the sheet cassette 2 is detached from the apparatus main body 1, respectively, and are {8Vref / 16} V and {9Vref / 16} V (code 10 and FIG. 6). Code 18
), {4Vref / 16} V and {5Vref / 1
6} V (see code 11 and code 19 in FIG. 6), {2V
ref / 16} V and {3Vref / 16} V (see code 12 and code 20 in FIG. 6), {12Vref / 16} V
And {13Vref / 16} V (see code 13 and code 21 in FIG. 6), {10Vref / 16} V and {11
Vref / 16} V (see code 14 and code 22 in FIG. 6), {6Vref / 16} V and {7Vref / 16}
V (see code 15 and code 23 in FIG. 6), {14Vre
f / 16} V and {15Vref / 16} V (see code 16 and code 24 in FIG. 6) are used as the code with sheet and the code without sheet corresponding to the size codes of the seven types of recording sheets P, respectively.

The other structure is the same as that of the first embodiment, and the same effect can be obtained. Further, the present embodiment has an advantage that the sheet size information can be recognized without depending on the presence / absence state of the recording sheet P by the above configuration.

In the above embodiment, the sheet cassette 2
When there is no recording sheet P inside, that is, when the sheet presence detection sensor 14 is OFF, the analog output voltage of the output terminal 41 of the D / A converter 40 is the output voltage of the code 10 to the code 17.
Although the values obtained by adding {1Vref / 16} V to (1) to (8) are used, the analog voltages having other numerical values may be added or subtracted to form each code.

Next, a third embodiment of the image forming apparatus equipped with the sheet detecting apparatus according to the present invention will be described with reference to FIGS. FIG. 7 is a block diagram showing the configuration of the control system of the third embodiment, and FIG. 8 is a circuit block diagram showing the configuration of the sheet detection device of the third embodiment. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, a plurality of sheet cassettes 2
And a plurality of sheet detection devices shown in the first embodiment corresponding to each sheet cassette 2 are provided. That is, as shown in FIG. 8, the sheet size detection switches 13A and 13A corresponding to the first and second sheet cassettes 2A and 2B are configured in the same manner as in the first embodiment.
B, and sheet presence / absence sensors 14A, 14B, and D / A
Converters 23A, 23B and output voltage setting circuits 24A, 24B
Are provided and are connected in the same manner as in the above-described first embodiment, and the respective output terminals 22A and 22B are respectively connected to the CPU of the control unit 15 as shown in FIG.

As described above, the signal lines connected to the CPU of the control unit 15 corresponding to the number of the plurality of sheet cassettes 2 are wired by the number of the sheet cassettes 2. That is, in the present embodiment,
Although two sheet cassettes 2 have been described, when a plurality of other sheet cassettes 2 are used as necessary, the sheet size detection switch 13 and the sheet presence / absence sensor 14, corresponding to the number, are used. A plurality of D / A converters 23 and a plurality of output voltage setting circuits 24 are provided respectively, and a plurality of signal lines corresponding to the number of a plurality of sheet cassettes 2 are provided in parallel with the CPU of the control unit 15 from the respective output terminals 22. Connected.

Then, the analog voltage Vout A, which is an analog signal output from the respective output terminals 22A, 22B,
B is input to an A / D conversion port that converts an analog signal included in the CPU of the control unit 15 into a digital signal, is converted into a digital signal again, and instructs the control operation of the control unit 15.

The other structure is the same as that of the first embodiment, and the same effect can be obtained. In the present embodiment, the above configuration is advantageous because the number of signal lines can be reduced when a plurality of sheet cassettes 2 are mounted on the apparatus body 1 and used.

Next, a fourth embodiment of the image forming apparatus equipped with the sheet detecting apparatus according to the present invention will be described with reference to FIGS. 9 and 10. FIG. 9 is a block diagram showing the configuration of the control system of the fourth embodiment, and FIG. 10 is a circuit diagram showing the configuration of the sheet detection device of the fourth embodiment. The same components as those in the first and third embodiments are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, the output terminals 22A, 22 are passed through the output voltage setting circuits 24A, 24B in the third embodiment.
Analog voltage V as an analog signal output from B
Out A and B are selected by a selector circuit 50 as a selection means and transmitted to the CPU of the control unit 15.

As shown in FIG. 10, the output voltage setting circuit 24
A selector circuit 50 is provided at the output terminals 22A and 22B passing through A and 24B.
The input terminals of the buffers 51 and 52 provided in the above are respectively connected. The output side terminals of both the buffers 51 and 52 are connected to the output terminal 53, and when selected by a select signal which will be described later, either one of the output signals output to the output terminals 22A and 22B. Only the output signal of is output to the output terminal 53 via the buffers 51 and 52.

Between the buffer 51 and the buffer 52,
An inverter 54 for inverting an input signal and an output signal is connected, and the input side of the inverter 54 is a buffer 52,
The output side is connected to the buffer 51, respectively. Further, a select signal input terminal 55 for inputting a select signal transmitted from the CPU of the controller 15 is connected to the input side of the inverter 54.

When the select signal input from the CPU of the control unit 15 to the select signal input terminal 55 of the selector circuit 50 is "HIGH", the buffer 52 is "HIGH".
Signal is input to operate the buffer 52, and the output signal from the output terminal 22B that has passed through the output voltage setting circuit 24B is output to the output terminal 53 via the buffer 52.
Is transmitted to

At this time, since "HIGH" of the select signal is inverted to "LOW" by the inverter 54 and input to the buffer 51, the buffer 51 does not operate and the output terminal passing through the output voltage setting circuit 24A. The output signal from 22A is blocked by the buffer 51 and does not reach the output terminal 53.

In addition, the CPU of the control unit 15 selects the selector circuit.
When the select signal input to the select signal input terminal 55 of 50 is “LOW”, the inverter 54 inverts the “LOW” of the select signal to “HIGH” and buffers it.
The buffer 51 is operated by being input to the buffer 51, and the output signal from the output terminal 22A passing through the output voltage setting circuit 24A is output to the buffer 51.
It is output to the output terminal 53 via the and is transmitted to the CPU of the control unit 15.

At this time, the "LOW" signal is input to the buffer 52, the buffer 52 does not operate, and the output signal from the output terminal 22B via the output voltage setting circuit 24B is cut off by the buffer 52. , Output terminal 53 is not reached.

Therefore, the select signal "HIGH".
Corresponding to the second sheet cassette 2B and the select signal "LOW" corresponding to the sheet cassette 2A, the analog signals output from the output terminals 22A and 22B via the output voltage setting circuits 24A and 24B. Can be selectively transmitted to the CPU of the control unit 15.

Other structures are the same as those of the first and third embodiments, and similar effects can be obtained. In the present embodiment, as described above, the CPU of the controller 15 operates the select signal for selecting the sheet cassette 2 to be used, whereby the sheet information of the sheet cassette 2 connected to the controller 15 can be selected. .

Therefore, even when two sheet cassettes 2 are used, the number of signal lines of the sheet detecting device can be set to the same number as when one sheet cassette 2 is used, and the number of signal lines can be reduced. You can do it. Furthermore, the control unit
Since 15 A / D conversion ports included in the CPU can be realized by one port, there is an advantage that the load on the CPU can be reduced.

The sheet size detection switch 13 and the sheet presence / absence detection sensor 14 shown in FIGS.
Sheet size code, sheet presence code and output terminal 2
Various combinations of analog voltage values in 6 and 41 are conceivable, and it is not necessary to limit them.

In each of the above embodiments, the recording sheet P
The case where the dedicated sheet cassette 2 corresponding to the size is prepared has been described. However, as another configuration, one sheet cassette 2 can be loaded with various kinds of recording sheets P, and the user can set the sheet size. By setting the dial for the sheet, the projections 2a, 2b,
2c changes to turn on the desired switches 13a, 13b, 13c
The same can be applied even when configured to turn on / off.

[0088]

Since the sheet detecting device and the image forming apparatus having the same according to the present invention have the above-described configuration and operation, the number of control signal lines connected to the CPU of the control unit is small, and the CPU of the CPU is small. Since the control load can be reduced, the assembling property of the apparatus can be improved and the cost can be reduced especially in the configuration in which a plurality of sheet cassettes are connected.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing the overall configuration of an image forming apparatus including a sheet detection device according to the present invention.

FIG. 2 is a block diagram showing the configuration of the control system of the first embodiment of the image forming apparatus including the sheet detection device according to the present invention.

FIG. 3 is a circuit diagram showing a configuration of a sheet detection device according to the first embodiment.

FIG. 4 is a diagram showing an analog voltage value output from a D / A converter corresponding to a digital signal code output from a sheet size detecting unit in the first embodiment.

FIG. 5 is a circuit diagram showing a configuration of a sheet detection device according to a second embodiment.

FIG. 6 is a diagram showing an analog voltage value output from a D / A converter corresponding to a digital signal code output from a sheet size detecting unit and a sheet presence / absence detecting unit in the second embodiment.

FIG. 7 is a block diagram showing a configuration of a control system of a third embodiment.

FIG. 8 is a circuit block diagram showing a configuration of a sheet detection device according to a third embodiment.

FIG. 9 is a block diagram showing a configuration of a control system of a fourth embodiment.

FIG. 10 is a circuit diagram showing a configuration of a sheet detection device according to a fourth embodiment.

FIG. 11 is a diagram illustrating a conventional example.

FIG. 12 is a diagram illustrating a conventional example.

[Explanation of symbols]

1 ... Image forming apparatus main body, 2, 2A, 2B ... Sheet cassette, 2a, 2b, 2c ... Protrusion, 3 ... Feed roller, 4 ... Conveying roller, 5 ... Registration sensor, 6 ... Image forming section, 7 ...
Photoconductor drum, 8 ... Transfer roller, 9 ... Fixing section, 10 ... Ejection sensor, 11 ... Ejection path, 12 ... Ejection tray, 13, 13A, 13
B, 13a, 13b, 13c ... Sheet size detection switch, 1
4, 14A, 14B, ... Sheet presence / absence sensor, 14a ... Drive knob, 15 ... Control section, 16 ... Laser drive section, 17 ... Scanner motor drive section, 18 ... High voltage control section, 19 ... Heater drive section, 20 ... Main motor Drive unit, 21 ... Solenoid drive unit, 22, 22A,
22B ... Output terminal, 23, 23A, 23B ... D / A converter, 24,
24A, 24B ... Output voltage setting circuit, 25a, 25b, 25c ... Pull-up resistor, 26 ... Output terminal, 27 ... Buffer, 28 ... Diode, 29 ... Photo interrupter, 30 ... Current limiting resistor,
31 ... Pull-up resistance, 32 ... Transistor, 33 ... Pull-down resistance, 40 ... D / A converter, 41 ... Output terminal, 50 ... Selector circuit, 51, 52 ... Buffer, 53 ... Output terminal, 54 ... Inverter, 55 ... Select signal input terminal

Claims (6)

[Claims] 1. A sheet cassette for accommodating sheets, a sheet size detecting means for detecting a size of a sheet accommodated in the sheet cassette, and a sheet presence / absence detection for detecting the presence / absence of a sheet accommodated in the sheet cassette. Means, digital / analog conversion means for converting the digital signal output by the sheet size detection means into an analog signal, and a digital signal output by the sheet presence / absence detection means in addition to the analog signal output from the digital / analog conversion means The sheet detection device is characterized in that the size and / or the presence / absence of a sheet accommodated in the sheet cassette are recognized by an analog signal output by adding an analog signal corresponding to. 2. A sheet cassette for accommodating sheets, a sheet size detecting means for detecting a size of a sheet accommodated in the sheet cassette, and a sheet presence / absence detection for detecting the presence / absence of a sheet accommodated in the sheet cassette. Means, and a digital / analog conversion means for converting a digital signal output by the sheet size detection means and the sheet presence / absence detection means into an analog signal, wherein the sheet presence / absence is included in the digital signal output by the sheet size detection means. The digital signal output from the detection means is added, and the size and / or the presence / absence of the sheet accommodated in the sheet cassette are recognized based on the analog signal output from the digital / analog conversion means. Characteristic sheet detection device. 3. An analog voltage corresponding to the digital signal output by the sheet presence / absence detection means is superimposed on the analog voltage output from the digital / analog conversion means based on the digital signal output by the sheet size detection means. The sheet detecting apparatus according to claim 1, wherein the sheet detecting apparatus is configured to output the sheet. 4. The analog voltage output from the digital / analog conversion means based on the digital signal output from the sheet size detection means when the sheet presence / absence detection means detects that there is no sheet in the sheet cassette. The sheet detecting apparatus according to claim 3, wherein the sheet is forcibly set to a predetermined fixed voltage. 5. The sheet detecting device according to claim 1 or 2, comprising a plurality of sheet detecting devices corresponding to each of a plurality of sheet cassettes detachably attached to the apparatus body, and selecting means. The sheet detecting apparatus is configured so that one analog signal is selected from the plurality of analog signals output from the plurality of digital / analog converting means. 6. A sheet feeding device that feeds a sheet stored in the sheet cassette of the sheet detection device according to claim 1, and a sheet feeding device that feeds the sheet. An image forming apparatus comprising: an image forming unit that forms an image on a sheet according to image information.