JPH06130855A - Image printing device - Google Patents

Abstract

PURPOSE:To attain low cost and high reliability without lowering the temperature control accuracy of a fixing device. CONSTITUTION:Two temperature fuses 102a and 102b are provided closely to a fixing roller 103 and a backup roller 104, respectively. By connecting two heaters 100a and 100b and the temperature fuses 102a and 102b in series, feed is stopped by opening either temperature fuse in the case that an AC power control element 110a is ruptured in a short circuit mode. Namely, safety is improved in terms of the winding of paper to a roller, and the faulty assembling of the temperature fuse or the defect of parts. Since a feed amount is controlled by one AC power control element by connecting two heaters in series, the parts constituting a circuit are decreased, the cost is made low and the reliability is improved, then a failure that exessive feed is performed to either heater because of the disconnection of the other heater is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image printing apparatus such as an electrophotographic printer such as a laser printer or an electrophotographic copying machine, and more particularly to a fixing apparatus for fixing a toner image adhered to a sheet onto the sheet. Regarding optimal protection control.

[0002]

2. Description of the Related Art An image printing apparatus, such as a copying machine or a laser printer, which uses electrophotography, passes through a sheet while rotating in contact with each other in order to fix the toner image adhered to the sheet. A fixing device using two fixing rollers is provided. In the fixing device in the monochrome image printing device, the heater is arranged only in one of the two fixing rollers (normally the side in contact with the toner image). Heaters are arranged on both fixing rollers of the book. The reason for arranging the heaters on the two fixing rollers in the color image printing apparatus is to prevent the occurrence of offset (a phenomenon in which toner that should adhere to the paper adheres to the fixing rollers).

In a fixing device in which a heating heater is arranged on each of two fixing rollers, the temperature of each heating heater is controlled independently, and a control device provided with a protection circuit for preventing abnormal heating is installed. However, the economic problem of an expensive control device occurs.

FIG. 2 is a perspective view showing a schematic structure of a conventional fixing device. The fixing device includes a fixing roller 103 having a first heater 100a incorporated therein, a backup roller having a second heater incorporated therein and arranged in pressure contact with the fixing roller 103, and the fixing roller 103.
A first temperature detecting element 101a arranged in close proximity to
A second temperature detecting element 101b and an abnormal heating preventing temperature fuse 102b, which are arranged close to the backup roller 104, are provided.

FIG. 3 shows a control circuit in the conventional fixing device. The first heater 100a is an AC power control element 1
The second heater 100b is connected to the power supply 10 with the AC power control element 110b and the temperature fuse 102b interposed in series. Then, the temperature control processing circuit (not shown) includes the temperature detection elements 101a,
Each heater 100 according to the detection signal obtained from 101b.
The AC power control elements 110a and 110b are controlled so as to independently change the energization amount to a and 100b.

The fixing device having such a structure has no problem in temperature control accuracy, but has the following problems. (1) The cost is high because there are many components of the control circuit. (2) The reliability is low due to the large number of components of the control circuit. In particular, regarding the item (2), since the temperature fuse 102b is arranged only on the backup roller 104 side, when the paper is wrapped around the backup roller 104, the temperature fuse 102b accurately responds to the temperature of the backup roller 104. However, there is a problem in ensuring safety.

[0007]

As described above, the fixing device in the conventional image printing apparatus for printing a color image, in particular, faces the fixing roller in order to secure image quality (countermeasures for offset of color toner). Since the heater is also arranged on the backup roller side to be arranged, the potential for PL accidents such as smoking and ignition is increasing.
However, if this is to be guaranteed by the control circuit, there are problems that the number of circuit components increases, the cost increases, and the reliability decreases.

An object of the present invention is to realize low cost and high reliability without lowering the temperature control accuracy of the fixing device. The cause of abnormal heating mode in the fixing device is
(1) Destruction of heater on / off AC power control element in short-circuit mode, (2) heater disconnection, (3) heater temperature control circuit component failure (short-circuit / open), (4) paper inside fixing device In other words, etc., it is necessary to inexpensively construct a control device that does not cause a PL accident in any case.

[0009]

SUMMARY OF THE INVENTION The present invention includes a fixing roller and a backup roller, each of which has a built-in heater and which rotates while facing each other to pass and fix a sheet on which a toner image is attached, and a fixing roller and a backup roller. A temperature detection element for detecting the temperature, a control circuit for controlling the amount of power supply to the heater in accordance with a detection signal obtained from the temperature detection element, and a circuit for supplying power to the heater by opening the roller when the temperature of the roller excessively rises. In an image printing apparatus having a fixing device having a temperature fuse for shutting off, a two series of temperature fuses are provided close to the fixing roller and the backup roller respectively, and one series circuit is formed by connecting each heater in series. , An AC power control element interposed between the series circuit and a power source, and the temperature detection element provided to detect the temperature of one of the rollers. A temperature control processing circuit for controlling the AC power control device in accordance with the obtained detection signal, characterized in that the provided.

[0010]

By providing two temperature fuses in the vicinity of the fixing roller and the backup roller and connecting two heaters and the temperature fuse in series, it is possible to prevent the AC power control element from being broken in the short circuit mode. The thermal fuse opens to shut off the power supply. That is, the safety is improved against winding of the paper around the roller, defective incorporation of the thermal fuse, or defective components.

Further, since two heaters are connected in series and the amount of power supply is controlled by one AC power control element, the number of circuit components is reduced and the reliability is improved at a low cost. The inconvenience of excessive power supply to the heater is eliminated.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 8 shows a cross-section of a main part of the color laser printer 200 connected to the information processing apparatus 300. The printing unit of the color laser printer 200 uniformly charges the surface of the photoconductor 211 and a belt-shaped photoconductor 211 that is wound around a rotating wheel so as to rotate at a constant speed in the arrow direction. A charger 212 and a scanning exposure device 21 for exposing a uniformly charged surface of a photoreceptor to form an electrostatic latent image on the surface.
3 and four developing devices 214, 215, 216 and 217 for developing an electrostatic latent image to form a toner image (each developing device has a built-in sensor (not shown) for detecting the presence or absence of a developer. A cleaner 219 for removing the toner remaining on the surface of the photoconductor after the transfer of the toner image and an erase lamp 218 for removing the electric charge remaining on the surface of the photoconductor are provided.

The scanning exposure device 213 collects the laser light output from the semiconductor laser 213a in accordance with the video data with a condenser lens 213b to form a parallel laser beam, and a polygon mirror 213d rotated at a constant speed by a mirror motor 213c. The laser beam is reflected by the laser beam to be repeatedly deflected, and the deflected beam is applied to the surface of the photoconductor through the projection lens 213e and the folding mirror 213f to form a beam spot, and the beam spot is scanned to scan the photoconductor. This is a structure for exposing the surface.

As shown in FIG. 9, the scanning exposure apparatus 213 includes a beam detector 213g for detecting the timing when the beam spot passes the deflection scanning start reference position in each deflection scanning.
The signal obtained from 3g is amplified by the amplifier 213h and output as the deflection scanning start reference detection signal BDT1.

The developing device 214 uses a yellow toner as a developer, the developing device 215 uses a magenta toner as a developer, and the developing device 216 uses a cyan toner as a developer. The developing device and developing device 217 are developing devices that use black toner as a developer, and the developing function is imparted to or deleted from each developing device by controlling the bias voltage. The control of the bias voltage is performed by a designation signal from the information processing device 300 so that the developing device corresponding to the designated color of the video data used to form the electrostatic latent image effectively functions.

The transfer drum 221 is used for superimposing a plurality of toner images formed on the surface of the photoconductor to complete one color toner image and transferring the color toner image to a sheet. The transfer drum 221 is driven so as to rotate in the arrow direction at a speed synchronized with the surface of the photoconductor while being in contact with the surface of the photoconductor, and the photoconductor is placed inside the transfer drum in a region in contact with the surface of the photoconductor. A transfer device 222 for transferring the toner image on the body surface to the transfer drum surface is installed. Further, in order to remove the toner remaining on the surface of the transfer drum 221, a cleaner 223 capable of controlling contact and separation is provided on the surface.

The cassette 231 accommodates the sheet 232, and the sheet feeding roller 233 extracts the sheet 232 and supplies it to the registration roller 234. The registration roller 234 suppresses the leading edge of the paper 232 sent by the paper feed roller 233 to stop the progress of the paper 232, and adjusts the paper preparation and paper feed timing.

The transfer device 241 applies a transfer charge to the back surface of the paper 232 in the area where the paper 232 conveyed from the registration rollers 234 contacts the transfer drum 221, and transfers the toner image on the surface of the transfer drum to the paper 232. To do.

The fixing device 251 has a structure in which the sheet 232 having the toner image transferred thereon is passed between a heating roller and a pressure roller to fuse (fix) the toner image to the sheet 232.

The paper discharge roller 261 discharges the paper 232 having the toner image fixed thereon to the outside of the machine.

The control device 270 is the upper information processing device 30.
0 is connected to the information processing device to exchange control information and print data (video data) with the laser printer 20.
The internal control means is controlled to execute printing control.

FIG. 5 is a schematic perspective view of the fixing device according to the present invention, and FIG. 6 is a vertical sectional side view. The paper 232 passes between two rollers of the fixing device and is discharged to the outside of the apparatus. The toner image side roller 103 is a fixing roller, and the fixing roller 103 is a fixing roller.
The roller 104, which is arranged in pressure contact with the roller 104, is called a backup roller. Each roller is set and heated by heaters 100a and 100b arranged inside, and in order to ensure the safety of the product from abnormal heating due to a failure, the temperature fuses 102a and 102b are brought close to each roller. It is arranged. Temperature detection is performed by a temperature detection element 101a arranged close to the fixing roller 103 for temperature control, and ON / OFF control of the heaters 100a and 100b is performed according to the detection signal to keep the temperature at a set temperature. . These are fixing device covers 105
a, 105b.

A control circuit for controlling the fixing device having such a structure is shown in FIG. The power supply circuit of the heater is the AC power supply 10
Two heaters 100a, 100b connected in series via relay contacts 112a, 112b connected in series to the
And two thermal fuses 10 connected in series with the heater
2a, 102b and AC power control element 110a. The ON / OFF means in the power supply circuit includes relay contacts 112a and 112 for cutting off power supply to the heaters 100a and 100b when abnormal heating occurs, and heaters 100a and 100b for heating and keeping the rollers 103 and 104 at a set temperature. AC power control element 110a for controlling ON / OFF of power supply
There are two systems.

On / off control by the AC power control element 110a will be described. The detection signal voltage corresponding to the resistance ratio between the temperature detecting element 101a arranged close to the fixing roller 103 and the voltage dividing resistor 122 is the comparator 115a,
It is input to one input terminal of 115b. The comparison reference voltage Va is input to the other input terminal of the comparator 115a, and the comparison reference voltage Vb is input to the other input terminal of the comparator 115b. The comparison reference voltage Va is
It corresponds to the set temperature Ta of the temperature characteristic curve of the fixing roller 103 shown in FIG. 4, and the comparison reference voltage Vb corresponds to the abnormal heating detection temperature Tb.

When the surface temperature of the fixing roller 103 is lower than the set value, the output signal HON of the comparator 115a becomes "H" level, and the AC power control element 110a is controlled to be turned on via the ignition circuit 116. Heater 1
00a and 100b are heated by power supply. Also, the fixing roller 1
When the surface temperature of 03 is higher than the set value, the output signal HON of the comparator 115a becomes "L" level, and the AC power control element 110a is controlled to be turned off via the ignition circuit 116 to the heaters 100a and 100b. Stop power supply. In this way, the heaters 100a, 10
0b is repeatedly turned on / off to heat the surface temperature of the fixing roller 103 to a set temperature as shown in FIG.
Control to keep warm.

The temperature control accuracy (shown in FIG. 11) obtained by turning on / off the power supply to the two heaters 100a and 100b by one temperature detecting element 101a is the same as that of each heater which has been conventionally used. Even if compared with the control accuracy (shown in FIG. 10) obtained by individually controlling, there is no great difference.

Next, on / off control by the AC relay contacts 112a and 112b will be described. The signal HERR, which is the comparison result of the detection signal voltage obtained from the temperature detection element 101a and the comparison reference voltage Vb, means that it is below the abnormal temperature Tb of FIG. At the level, it means that the temperature is equal to or higher than the abnormal temperature Tb. When the AC power control element 110a fails in the short circuit mode, the heater 100a,
Since the continuous power supply to 100b is performed, the surface temperature of the fixing roller 103 rises as shown by the curve b in FIG. 4, and finally, the phenomenon of reaching the abnormal temperature Tb occurs. At this time, since the output signal HERR of the comparator 115b becomes "L" level, the output of the AND element 114 is inverted from "H" level to "L" level, and the AC relay coil 112c.
The drive transistor 113 for controlling the heaters is turned off, and the heaters 100a, 10
The power supply to 0b is cut off.

Next, the control processing by the CPU 120 will be described with reference to FIG. When the power is turned on, the CPU
120 is an output signal HER in the comparator 115b
It is checked whether the level of R is "H" or "L". Since the output signal HERR is normally at "H" level, the CPU1
20 outputs the “H” level to the HCTL signal, and passes through the AND element 114 and the transistor 113 to the relay coil 11
2c is energized to turn on the relay contacts 112a and 112b. When it becomes the "L" level, the process at the time of abnormality is performed (processes 500 to 502).

Next, the output signal HO of the comparator 115a
N (“H” or “L”) is read and stored in the memory 121, and the energization time management value “ts” is set in the CPU internal register. “Ts” is the heater on time t in FIG.
The time is sufficiently longer than the on time and the heater off time toff, and is a time such that the fixing device is not damaged even if the heater is continuously heated for "ts" time (process 503-.
505).

After the delay time "td", the energization time management value "ts-1" (decrement processing) is executed, and thereafter,
The HON signal is read and its value is compared with the contents previously (previously) stored in the memory 121. If it is different from the previously stored content, that content is newly stored in the memory 121, and the above-described processings 504 to 509 are repeated. If it is the same as the previous data, it is checked whether "ts-1" = 0.
If "ts-1>0", the processes 506 to 510 are performed again. When the elapsed time becomes “ts” = 0, the process at the time of abnormality is performed.

When it is determined that there is an abnormality, the CPU 120 outputs the "L" level to the HCTL signal, and the AND element 11
4, the relay coil 112c is deenergized through the transistor 113 to turn off the relay contacts 112a and 112b, and the power supply to the heaters 100a and 100b is cut off. afterwards,
Each actuator 123 is turned off and an abnormality is reported to the host (processes 510 to 513).

However, these protection operations are guaranteed only when the temperature detecting element 101a is normal and when the CPU 120 is normally operating, and therefore it is necessary to install a temperature fuse in terms of safety standards.

In the present invention, the temperature fuses 110a and 110b, which are respectively arranged close to the fixing roller 103 and the backup roller 104, are connected in series and inserted in the power supply circuit to improve safety.

The temperature fuses 102a and 102b are in a state where the AC power control element 110a fails in the short circuit mode, the temperature detection element 101a fails, and the energization time management control by the CPU 120 becomes uncontrollable due to the runaway of the CPU 120. It works when overlapping. In such an uncontrollable state, the heaters 100a and 100b are in the continuous power supply mode, and the fixing roller 103 and the backup roller 104 are abnormally heated. Therefore, the curve c in FIG.
As described above, when the roller surface temperature reaches the fuse fusing temperature Tf, either of the temperature fuses 102a and 102b is blown and the power supply is cut off to ensure the safety of the apparatus.

Moreover, the temperature fuses 102a, 102b
Are arranged on the rollers 103 and 104 respectively,
And since it is connected in series, one of the temperature fuse
Even if the 102a (102b) is defective, the other thermal fuse 102b (102a) operates, so that the safety of the device can be ensured with high reliability.
If the two temperature fuses 102a and 102b are in a normal state, even when the paper is wound around one roller, the temperature fuse of the other roller operates to ensure the safety of the apparatus.

[0036]

According to the present invention, the AC power control element is provided by providing two temperature fuses in the vicinity of the fixing roller and the backup roller in the fixing device and connecting the two heaters and the temperature fuses in series. When is broken in the short circuit mode, one of the temperature fuses is opened and power supply is stopped, so that safety is improved against winding of the paper around the roller, improper incorporation of the temperature fuse, or defective parts.

Further, since two heaters are connected in series and the amount of power supply is controlled by one AC power control element, the number of circuit components is reduced and the reliability is improved at a low price. The inconvenience of excessive power supply to the heater is eliminated.

[Brief description of drawings]

FIG. 1 is a control circuit diagram of a fixing device in a color laser printer according to the present invention.

FIG. 2 is a schematic perspective view of a conventional fixing device.

FIG. 3 is a control circuit diagram of a conventional fixing device.

FIG. 4 is a temperature characteristic curve diagram in the fixing device of the color laser printer according to the present invention.

FIG. 5 is a schematic perspective view of a fixing device of a color laser printer according to the present invention.

FIG. 6 is a vertical sectional side view of the fixing device of the color laser printer according to the present invention.

FIG. 7 is a temperature control processing flowchart in the fixing device of the color laser printer according to the present invention.

FIG. 8 is a vertical sectional side view of the color laser printer according to the present invention.

FIG. 9 is a perspective view of an external appearance of a main part of an optical system of a color laser printer according to the present invention.

FIG. 10 is a roller surface temperature characteristic curve diagram during temperature control in a conventional fixing device.

FIG. 11 is a roller surface temperature characteristic curve diagram during temperature control in the fixing device of the color laser printer according to the present invention.

[Explanation of symbols]

100a, 100b ... Heater, 101b ... Temperature detecting element, 102a, 102b ... Thermal fuse, 103 ... Fixing roller, 104 ... Backup roller, 110a ... AC power control element, 112a, 112b ... Relay contact, 11
2c ... Relay coil, 115a, 115b ... Comparator, 116 ... Firing control circuit, 120 ... CPU, 200 ... Color laser printer, 300 ... Information processing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ken Kato, 1-1 1-1 Higashitaga-cho, Hitachi, Hitachi, Ibaraki, Ltd. Information & Video Media Division, Hitachi, Ltd. (72) Michio Sumiyoshi, Higashi-taga, Hitachi, Ibaraki 1-1, 1-1, Information & Video Media Division, Hitachi, Ltd. (72) Sakae Kamata 1-1-1, Higashitaga-cho, Hitachi, Hitachi, Ibaraki Prefectural Information & Media Division, Hitachi, Ltd. (72) Inventor Hiroyuki Tadokoro 1-1-1 Higashi-Taga-cho, Hitachi-shi, Ibaraki Prefectural Information & Video Media Division, Hitachi, Ltd.

Claims (2)

[Claims] 1. A fixing roller and a backup roller, each of which has a heater built therein and rotates while being in contact with each other while passing a sheet having a toner image attached thereon to fix the sheet, and a temperature detecting element for detecting the temperature of the roller. A control circuit for controlling the amount of electric power supplied to the heater according to a detection signal obtained from the temperature detecting element, and a temperature fuse for opening the circuit when the temperature of the roller excessively rises to cut off the electric power supply to the heater. In an image printing apparatus having a fixing device, two temperature fuses are provided near the fixing roller and the backup roller, respectively, and one series circuit is formed by connecting each heater in series, and between the series circuit and a power source. According to a detection signal obtained from the AC power control element interposed between the roller and the temperature detection element provided to detect the temperature of one of the rollers. Image printing apparatus characterized in that a, a temperature control processing circuit for controlling the AC power control device. 2. The image printing apparatus according to claim 1, wherein the temperature control processing circuit opens a power supply circuit relay when a detection signal obtained from the temperature detection element exceeds a predetermined safety set value.