JP2690403B2 - Electrophotographic printing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an electrophotographic printing device that develops, transfers, and prints.

[0002]

2. Description of the Related Art In a general electrophotographic printing apparatus, the surface of a photoconductor made of a photoconductive material is uniformly charged and the photoconductor surface is selectively irradiated with light corresponding to input image information. Is exposed to form an electrostatic latent image, and toner adhering to the surface of the photoconductor is supplied to the electrostatic latent image to develop and visualize the electrostatic latent image. On the other hand, the paper is charged, and the toner image visualized by the electrostatic attraction is transferred from the surface of the photoconductor to the paper. Then, after the transfer, the paper is subjected to a fixing process for fixing the toner image on the paper by heat and pressure and then discharged, and the photoconductor removes the toner remaining on its surface against the electrostatic attraction and the unnecessary charge. To remove static electricity.

By the way, EEH (edge emitter array hea)
The d) type electrophotographic printing apparatus is composed of end face light emitting elements arranged in a line, has a line head disposed adjacent to the photoconductor, and selectively drives these light emitting elements to form the photoconductor. Is exposed line by line. As the edge light emitting element, for example, a light emitting diode, a semiconductor laser, or an EL (electroluminescence) element is used. The light emitting diode and the semiconductor laser have output characteristics that depend on the ambient temperature, and are controlled according to changes in the ambient temperature so as to keep the output constant during the printing operation.
On the other hand, the EL element has an output characteristic that is almost independent of its ambient temperature and is not subject to the control that a light emitting diode or a semiconductor laser receives.

[0004]

However, in the conventional electrophotographic printing apparatus, the print quality may deteriorate even if the output of the light emitting element is kept constant. This occurs because the static elimination effect changes depending on the ambient temperature of the photoconductor. For example, when the ambient temperature of the photoconductor is low, unnecessary charges are not completely removed from the photoconductor, which increases the potential of the photoconductor during charging and reduces the sensitivity of the photoconductor. This decrease in the sensitivity of the photoconductor thins the line elements of the electrostatic latent image drawn on the surface of the photoconductor, and makes printed characters and drawings unclear.

Therefore, the present invention is intended to provide an electrophotographic printing apparatus capable of maintaining good print quality even when the ambient temperature of the photoconductor changes.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a photoconductor, a charging means for charging the surface of the photoconductor, and an exposure for selectively exposing the charged surface of the photoconductor to form an electrostatic latent image. Means, a developing means for supplying a developer adhering to the surface of the photoconductor to develop the electrostatic latent image formed by the exposing means, and a transfer means for charging the paper and transferring the developed image to the paper. , A charge removing means for removing unnecessary electric charges remaining on the surface of the photoconductor after image transfer so that the surface of the photoconductor can be recharged, a temperature detecting means for measuring the ambient temperature of the photoconductor, and the temperature detecting means. It detects which temperature range of a plurality of continuous temperature ranges the measured temperature belongs to, controls the exposure unit so that the exposure amount decreases as the detected temperature range increases, and the measured temperature within the detected temperature range. Is high It is provided with a control means for controlling the developing means so as to reduce the developer supply.

[0007]

In the apparatus of the present invention having such a structure, the ambient temperature of the photosensitive member is measured by the temperature detecting means, and the temperature range to which this temperature belongs is detected by the control means. The control unit controls the exposure unit so that the exposure amount is reduced as the detected temperature range is higher, and the developing unit is controlled so that the developer supply amount is reduced as the measured temperature is higher within the detected temperature range. That is, the exposure amount of the photoconductor is controlled when the sensitivity of the photoconductor changes with the change of the ambient temperature. However, this control can roughly compensate the sensitivity change of the photoconductor, but cannot sufficiently compensate the sensitivity change. Therefore, the supply amount of the developer is reduced within the detection temperature range as the measurement temperature is higher, and this compensates for the change in the sensitivity of the photoconductor which cannot be compensated by the adjustment of the exposure amount.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the internal structure of the electrophotographic printing apparatus. Reference numeral 1 denotes a cabinet whose upper portion can be opened by rotation. The cabinet 1 is provided with a photosensitive drum 2 which is arranged substantially in the center and rotates clockwise, and a drive motor 3 which drives the photosensitive drum 2 and various mechanisms.

Around the photosensitive drum 2, a charging unit 4,
The exposure unit 5, the developing unit 6, the transfer unit 7, the cleaning device 9, and the charge eliminating device 10 are arranged to perform a printing operation by an electrophotographic process.

The photosensitive drum 2 has a photosensitive member surface made of a photoconductive material. The charging unit 4 uniformly charges the surface of the photoconductor of the photosensitive drum 2, and the exposure unit 5
Selectively forms an electrostatic latent image on the surface of the photoconductor by selectively exposing it to light corresponding to the input image information, and the developing device 6 corresponds to the electrostatic latent image and develops the surface of the photoconductor. The electrostatic latent image is developed by supplying the toner attached to the sheet, the transfer unit 7 charges the sheet and transfers the toner image from the surface of the photoconductor to the sheet by the electrostatic attraction, and the cleaning device 9 transfers the sheet. The toner remaining on the surface of the photoconductor is removed against the post-electrostatic attraction, and the static eliminator 10 removes unnecessary charges from the surface of the photoconductor after transfer so that the surface of the charged body can be charged again. .

This electrophotographic printing apparatus further includes a charge eliminating section 8, a paper cassette 11, a pickup roller 12, a fixing device 13, paper ejection rollers 14A and 14B, a fan motor 15, a DC power supply device 16, an open detection switch 17, and a temperature sensor. 18 are provided.

The sheets are stacked and stored in the sheet cassette 11, picked up one by one by the pickup roller 12 at a predetermined timing, and supplied to the transfer unit 7 through a conveyance path PH. .

The discharging unit 8 is arranged adjacent to the transfer unit 7 located below the photosensitive drum 2, and discharges the sheet charged by the transfer unit 7 after the transfer.

The sheet is then supplied to the fixing device 13 for fixing the toner image on the sheet by heat and pressure, and is further discharged onto the upper surface of the cabinet 1 by the discharge rollers 14A and 14B. .

The discharge rollers 14A and 14B and the pickup roller 12 are operated by the driving force of the drive motor 3. The fan motor 15 releases the heat inside the cabinet 1 to the outside, and the opening detection switch 17 detects that the upper part of the cabinet 1 is opened. The temperature sensor 18 is provided adjacent to the photosensitive drum 2 and detects the ambient temperature of the photosensitive surface thereof.

FIG. 2 shows a circuit configuration. A microprocessor 21 for processing various data necessary for controlling print operations, a ROM (read only memory) 22 for storing a control program for the microprocessor 21, and an external host. A RAM (ramdom access memory) 23 for temporarily storing input / output data of the microprocessor 21 including image information and various commands sent from the computer;
An I / O port 24 is provided for connecting to. The microprocessor 21 includes a ROM 22, a RAM 23, an I
It is connected to the / O port 24 via a bus line 25.

At the I / O port 24, a motor drive circuit 26, an exposure unit 5, a high voltage power supply circuit 27, a toner sensor circuit 30, an operation panel 31, a paper sensor 32, a temperature measuring section 33, a fan motor 15, The interface 34 and the DIP switch 35 are connected.

The motor drive circuit 26 drives and controls the drive motor 3, and the high-voltage power supply circuit 27 supplies a high voltage to the charging section 4, the developing unit 6 and the transfer section 7. The toner sensor circuit 30 takes in output signals from the toner empty sensor 28 and the toner full sensor 29 provided in the developing device 6, and the operation panel 31 is operated to input information necessary for controlling the printing operation. It has become so.

The paper sensor 32 detects the position of the paper being conveyed, and the temperature measuring unit 33 is provided with the temperature sensor 18. The open detection switch 17 is inserted into the power supply line for supplying 24 V of power from the DC power supply device 16 to the exposure unit 5, the motor drive circuit 26, the high voltage power supply circuit 27 and the fan motor 15, and when the upper part of the cabinet 1 is opened. It is designed to shut off this power supply. The toner supply amount in the developing device 6 can be adjusted according to the bias voltage applied to the developing device 6 from the high-voltage power supply circuit 27, and the bias voltage is I
It is controlled by the microprocessor 21 via the / O port 24.

FIG. 3 shows the structure of the exposure unit 5 in detail. The exposure unit 5 includes an exposure control circuit 51,
An EEH (edge emitter array head) 52, a block driver 53, and a common driver 54 are included. The exposure control circuit 51 controls the block driver 53 and the common driver 54, and the block driver 53 and the common driver 54 cooperate to drive the EEH 52. The EEH 52 is arranged close to the photosensitive drum 2.

As shown in FIG. 4, the EEH 52 is an EL (electroluminescence) element 7 arrayed in a line for exposing the surface of the photosensitive body of the photosensitive drum 2 line by line.
1 and a block electrode CH and a common electrode CM that are provided to selectively cause the EL elements 71 to emit light.

Each of the EL elements 71 emits light when a common signal and a block signal as shown in FIG. 5 are supplied. The common signal is an AC voltage pulse having a maximum value of + 260V and a minimum value of 232V, and the block signal is a DC voltage pulse having an amplitude of 0 to + 28V. These E
The output of the L element, that is, the exposure amount on the surface of the photosensitive drum can be changed by increasing or decreasing the number of AC voltage pulses of the common signal supplied together with the block signal.

The exposure control circuit 51 converts each line of image information and exposure amount designation data supplied from the microprocessor 21 into exposure control data for exposure by the EEH 52. . The block driver 53 sequentially supplies the block signal to the block electrode CH every time the exposure control data is supplied, and the common driver 54 supplies the block signal to the block electrode CH of the EL element whose block signal is specified according to the exposure control data. Common electrodes CM of these EL elements while being supplied
The common signal is sequentially supplied to. This exposure control data includes pulse number designation data corresponding to the exposure amount designation data, and this data is any one of 2 to 4 AC voltage pulse numbers of the common signal supplied from the common driver 54 to the common electrode CM. To decide. Said E
The output of the L element 71 has two AC voltage pulses and three
0.2mW and 0.25m for 4 pieces and 4 pieces, respectively
W, set to 0.3 mW.

FIG. 6 shows the structure of the temperature measuring unit 33. In this temperature measuring unit 33, a series circuit of a resistor 61 and a zener diode 62 is connected to the DC power supply circuit 16 at 5V.
Of the operational amplifier 64, the non-inverting input terminal (+) of the operational amplifier 64 is connected to the connection point of the resistor 61 and the Zener diode 62 via the resistor 63, and the temperature sensor 18 is connected. Via the resistor 66, the inverting input terminal (-) of the operational amplifier 64 is connected to the output terminal of the operational amplifier 64 via the resistor 66, and
Grounded. The temperature sensor 18 is composed of, for example, a thermistor whose internal resistance changes according to a temperature change.

The output terminal of the operational amplifier 64 is connected to the input terminal VIN of the A / D converter 67, and the output terminal OUT and the clock terminal CLK of the A / D converter 67 are connected to the I / O port 24. ing. That is, the operational amplifier 64 amplifies the non-inverting input voltage determined according to the resistance value of the temperature sensor 18, and the A / D converter 67 causes the operational amplifier 6 to operate.
The output voltage of 4 is A / D converted in the clock cycle. This A
The output signal of the / D converter 67 is supplied to the microprocessor 21 via the I / O port 24.

Next, the printing operation of this electrophotographic printing apparatus will be described.

When the printing operation is started, the photosensitive drum 2 rotates, and the charging unit 4, the exposure unit 5, the developing unit 6, the transfer unit 7, the cleaning device 9, and the charge eliminating device 10 sequentially perform the processing. When the charging unit 4 uniformly charges the surface of the photosensitive drum, the charged surface is scanned and selectively exposed by the light emitted from the EEH 52 of the exposure unit 5 corresponding to the input image information. By this exposure, when an electrostatic latent image is formed on the surface of the photosensitive drum, the developing device 6 supplies toner to the surface of the photosensitive drum. The toner adheres to the surface of the photosensitive drum corresponding to the electrostatic latent image, and visualizes the electrostatic latent image as a toner image.

The transfer section 7 charges the paper supplied from the paper feed cassette 11 and transfers the toner image from the surface of the photosensitive drum to the paper by the electrostatic attraction. After the transfer, the cleaning device 9 removes the toner remaining on the surface of the photosensitive drum against the electrostatic attraction, and the charge removing device 10 removes unnecessary charges from the surface of the photosensitive drum. After the charge is removed, the photosensitive drum 2 is ready to be charged again.

After the transfer of the sheet, the sheet is subjected to the static elimination and fixing processing by the static elimination section 8 and the fixing device 13, and the discharge rollers 14A and 14A.
It is discharged to the outside by 4B.

In such operation, E of EEH52
The L output and the bias voltage of the developing device 6 are measured by the temperature sensor 18 in order to maintain the diameter of the dots constituting the image to be printed at the standard 85 μm at the printing density of 300 dots / inch. Adjusted based on ambient temperature.

In FIG. 7, the alternate long and short dash line represents the potential of the surface of the photosensitive drum charged from the uncharged state, and the dotted line represents the potential of the surface of the photosensitive drum that has been discharged after transfer. The charge removal efficiency on the surface of the photosensitive drum deteriorates due to the decrease in the ambient temperature of the photosensitive drum 2, which raises the potential after charge removal and lowers the sensitivity. If the printing operation is continued in this state, an unclear image will be printed on the paper.

Therefore, the microprocessor 21 reads the ambient temperature measured by the temperature sensor 18 prior to the charging of the surface of the photosensitive drum in each printing operation, and the measured temperature ranges from 0 ° C. to less than 12 ° C. in the first temperature range, 1
Second temperature range from 2 ° C to less than 22 ° C, 22 ° C to 35 ° C
Which of the third temperature ranges below ° C it belongs to is detected. If it does not belong to any range, it will be an error.

The microprocessor 21 has the first measured temperature.
The first exposure amount designation data is supplied to the exposure control circuit 51 when it belongs to the temperature range, the second exposure amount designation data when it belongs to the second temperature range, and the third exposure amount designation data when it belongs to the third temperature range. The exposure control circuit 51 responds to the first exposure amount designation data, the second exposure amount designation data, and the third exposure amount designation data, respectively, from the common driver 54 to E.
The number of AC voltage pulses supplied to the EH52 as a common signal is set to four, three, and two, and the EL output of the EEH52 is set to 0.3 mW according to the number of AC voltage pulses as shown in FIG. Set to 0.25 mW and 0.2 mW. That is, the EL output of the EEH52 is adjusted so as to be reduced as the temperature range to which the measured temperature belongs increases.
As shown by the solid line in FIG. 7, 0.3 mW is set in the first temperature range of 0 ° C. or higher and lower than 12 ° C.
It is set to 0.25 mW in the second temperature range of less than 0 ° C and 0.2 mW in the third temperature range of 22 ° C or more and less than 35 ° C.

In the EL element of this embodiment, when the peripheral temperature of the surface of the photosensitive drum is 17 ° C., dots are printed with a diameter of 85 μm. If the output of the EL element is always constant, the dot diameter increases as the ambient temperature rises and decreases as the ambient temperature lowers, as shown in FIG. When the ambient temperature rises to 35 ° C, the dot diameter becomes 237 dots /
It is 107 μm, which corresponds to a print density of inch. When the ambient temperature drops to 0 ° C, the dot diameter becomes 400
This is 63 μm, which corresponds to a print density of dots / inch. However, the EL output is 0.3 mW as described above,
Since it is adjusted to either 0.25 mW or 0.2 mW, the change in dot diameter is limited to the range centered on 85 μm as shown in FIG.

Further, the microprocessor 21 adjusts the bias voltage applied from the high voltage power supply circuit 27 to the developing device 6 as shown in FIG. 12, and decreases the toner supply amount as the measured temperature is higher in each temperature range. This is EL
The dot diameter change, which cannot be compensated by the stepwise adjustment of the output, is further finely adjusted to maintain the dot diameter at approximately 85 μm as shown in FIG.

As described above, even if the sensitivity of the photoconductor 2 changes with a change in the ambient temperature, it can be reliably compensated by both the adjustment of the exposure amount and the adjustment of the toner supply amount, and the deterioration of the print quality can be surely performed. Can be prevented. In other words, photoconductor 2
Even if the ambient temperature changes, the good print quality can always be maintained.

Moreover, since it is possible to obtain a substantially uniform dot diameter by only adjusting the EL output in three steps, it is not necessary to adjust the EL output steplessly, and the adjustment control is simple.

The present invention is not limited to the above-described embodiments, but various modifications can be made without departing from the gist of the invention. In the embodiment, the output of the EL element is adjusted by changing the number of AC voltage pulses supplied to the common electrode as a common signal, but this adjustment is performed by, for example, the DC voltage supplied to the block electrode. It can also be done by changing the voltage level of the pulse.
Further, the photosensitive drum of the above-described embodiment can be changed to a different type of photosensitive member.

[0040]

As described in detail above, according to the present invention, it is possible to provide an electrophotographic printing apparatus capable of maintaining good print quality even when the ambient temperature of the photoconductor changes.

[Brief description of the drawings]

FIG. 1 is an internal structure diagram showing an embodiment of the present invention.

FIG. 2 is a circuit block diagram in the embodiment.

FIG. 3 is a diagram showing a detailed configuration of an exposure unit in the embodiment.

FIG. 4 is a diagram showing a detailed structure of a light emitting head in the embodiment.

FIG. 5 is a diagram showing a waveform of a voltage applied to an EL element in the example.

FIG. 6 is a diagram showing in detail a configuration of a temperature measuring unit in the embodiment.

FIG. 7 is a graph showing the relationship between the peripheral temperature of the photosensitive drum, the drum surface potential, and the output of the EL element in the example.

FIG. 8 is a graph showing the relationship between the number of AC voltage pulses generated from the common driver and the output of the EL element in the example.

FIG. 9 is a graph showing the relationship between the dot diameter printed by the EL element and the ambient temperature on the surface of the photosensitive drum when the EL element output is constant in the example.

FIG. 10 is a graph showing the relationship between the dot diameter printed by the EL element and the ambient temperature on the surface of the photosensitive drum when the EL element output is adjusted in the example.

FIG. 11 is a graph showing the relationship between the dot diameter printed by the EL element and the ambient temperature on the surface of the photosensitive drum when both the toner supply amount and the EL element output are adjusted in the example.

FIG. 12 is a graph showing the relationship between the bias voltage supplied to the developing device for determining the toner supply amount and the ambient temperature on the surface of the photosensitive drum in the embodiment.

[Explanation of symbols]

2 ... Photosensitive drum, 4 ... Charging part, 5 ... Exposure unit, 6
... developing device, 7 ... transfer unit, 10 ... static eliminator, 18 ... temperature sensor, 21 ... microprocessor, 51 ... exposure control circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 15/043 15/08 115 (56) References JP-A-60-86560 (JP, A) Special features Kaihei 1-1121870 (JP, A) JP 1-167780 (JP, A) JP 1-207767 (JP, A) JP 1-235963 (JP, A) JP 64-7064 ( JP, A) JP 63-58462 (JP, A) JP 61-190348 (JP, A) JP 61-126575 (JP, A) JP 60-146256 (JP, A) Flat 1-149651 (JP, U)

Claims (2)

(57) [Claims] 1. A photoconductor, a charging means for charging the surface of the photoconductor, an exposing means for selectively exposing the charged surface of the photoconductor to form an electrostatic latent image, and the exposing means. Developing means for supplying a developer that adheres to the surface of the photoconductor to develop the formed electrostatic latent image, transfer means for charging the paper and transferring the developed image to the paper, and surface of the photoconductor after the image transfer. A charge removing unit that removes unnecessary charges remaining on the surface of the photoconductor to recharge the surface of the photoconductor, a temperature detection unit that measures the ambient temperature of the photoconductor, and a plurality of temperatures measured by the temperature detection unit. Of the continuous temperature ranges, the exposure means is controlled to reduce the exposure amount as the detected temperature range is higher, and the higher the measured temperature within the detected temperature range is, the higher the developer is. Supply An electrophotographic printing apparatus, characterized in that control means for controlling the developing means is provided so as to reduce the amount of toner. 2. The exposure means comprises an array of electroluminescent elements, the electric signal applied to the array is a pulse signal, and the output level is adjusted by changing the number of the pulse signals. The electronic print photographic device described.