JPS62222265A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a photosensitive drum from being overheated by controlling a heating means based on the temperature of the drum. CONSTITUTION:When a power supply is applied, a control part 7 turns a signal (f) to an 'H' level and outputs a signal (f) as 'H' level. If the temperature of the photosensitive drum is low, the resistance of a thermistor is high, so that the value of a signal (a) becomes higher than a reference value (b) and the outputs of a comparator 4 and an AND circuit 8 are turned to 'H' levels. Thereby, a transistor (Tr) 2 is turned on and electric power is supplied to a heater 1. When the temperature of the drum is increased, the resistance of the thermistor is reduced and the signal (a) becomes less than the reference value (b), so that the output of the circuit 8 is turned to the 'L' level. Thereby, the Tr 2 is turned off and power supply to the heater 1 is interrupted. When the temperature of the drum is dropped due to the interruption of power supply and the resistance of the thermistor 3 is increased, the signal (a) is raised and the output of the comparator 4 is turned to the 'H' level again. Thereby, the Tr 2 is turned on and power is supplied to the heater. Repeat of said operation makes it possible to hold the temperature of the drum at an almost constant value near the temperature corresponding to the reference value (b).

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an image forming apparatus equipped with a heating means for heating an image carrier.

(Prior art) As shown in Figure 3, photoreceptor drums used in electronic copying machines generally have the characteristic that as the temperature decreases, the surface potential increases in both dark and bright areas. A blurring phenomenon occurred, leading to a decline in image quality.

Therefore, in conventional electronic copying machines, there are methods to prevent this by detecting the temperature of the photoreceptor drum and changing the exposure amount and developing bias accordingly, or by heating the photoreceptor drum with a heater etc. By keeping the temperature constant, the temperature dependence of the photoreceptor drum was eliminated.

In the case of the latter method, the temperature of the photoreceptor drum is detected using a heat-sensitive element such as a thermistor, and the amount of power supplied to the heater is controlled in accordance with the result.

However, if the thermistor is disconnected or you forget to plug in the connector, power will continue to be supplied to the heater, leaving the photoreceptor drum in a high temperature state, resulting in deterioration of the photosensitive characteristics. .

(Problems to be Solved by the Invention) Conventional image forming apparatuses have a problem in that overheating of the heating means for heating the image carrier is not prevented.

The present invention has been made in response to such circumstances, and an object of the present invention is to provide an image forming apparatus in which overheating of the heating means is prevented.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides an image carrier on which an electrostatic latent image is formed, and a heating device for heating the image carrier. a temperature detection means for detecting the temperature on or near the surface of the image carrier; a time detection means for detecting the elapsed time since the heating means was turned on; and a temperature detection means for detecting the temperature detected by the temperature detection means. If it is outside the setting range and the time detected by the time detection means is outside the setting range, the heating means is turned off.
It is necessary to have a control means for setting the F state.

(Function) Therefore, if the temperature detected by the temperature detection means is outside the predetermined range even after a predetermined period of time has passed after the heating means is turned on, the control means determines that the temperature detection means is malfunctioning. Turn off the heating means.

(Example) The present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a heater control system according to an embodiment of the present invention.

This heater control system includes a heater 1 for heating the photoreceptor drum, a transistor 2 for changing the power supplied to the heater 1 to 0N10FF, a thermistor 3 for detecting the temperature of the photoreceptor drum, and a thermistor 1 for heating the photoreceptor drum. signal a from 3
A comparator 4 that compares the signal a from the thermistor 3 with another reference value C that is higher than the reference value A, and a power supply A timer 6 that is started by a signal @d (reset signal) input at the time of turning on and changes the output signal e after a predetermined time (approximately 6 minutes), a control section 7 consisting of a microcomputer,
It is composed of an ND circuit 8.

In this embodiment, as shown in FIG. 2, a charger 10, a developer 11, a transfer device 12, a peeler 13, and a cleaner 14 are arranged around the photoreceptor drum 9, and a roughly pipe-shaped heater 1 is arranged around the photoreceptor drum 9. is mounted inside the photoreceptor drum 9, and the cleaner 14
A thermistor 3 for detecting the surface temperature of the photoreceptor drum 9 is provided at the front of the photoreceptor drum 9 .

Next, the operation of this heater control system will be explained.

First, when the power is turned on, the timer 6 is activated by inputting a reset signal d, and the control section 7 outputs an output signal f as a torque signal.

At this time, if the photoreceptor drum 9 is in a low temperature state, the resistance of the narmistor 3 is high, so the value of the signal a is higher than the reference value S, and the output of the comparator 4 becomes torbel. The output of the AND circuit 8 also becomes l-level, and the transistor 2 turns on.
state, and power is supplied to the heater 1.

As the temperature of the photoreceptor drum 9 increases due to the heater 1, the resistance of the nermistor 3 decreases, and the value of the signal a usually becomes smaller than the value of 1 (value C) within 6 minutes.

As a result, when the output of the comparator 5 becomes the torque level, the control unit 7 detects that the predetermined time has elapsed by the signal @e from the timer 6, but in this case, the output signal Mf is maintained at the torque level.

Further, as the temperature of the photosensitive drum 9 changes, the resistance of the thermistor 3 decreases, and the value of the signal @a becomes smaller than the reference value. Then, the output of comparator 4 changes to trubel,
The output of the AND circuit 8 also becomes a torque signal. As a result, the transistor 2 is turned off, and power to the heater 1 is cut off.

Next, as the temperature of the photoreceptor drum 9 decreases and the resistance of the thermistor 3 increases, the value of signal @a increases, and the output of the comparator 4 becomes a torque level again, and the transistor 2 is turned on and sent to the heater 1. Power is supplied.

We decided to repeat the above operation, and the photoreceptor drum 9
i% (maintains approximately constant around the temperature corresponding to the value).

In this embodiment, the temperature corresponding to the reference value C is 35°C, and the temperature corresponding to the reference value C is 20'C. This is because, as shown in FIG. 3, the characteristics of the photoreceptor are most stable around 35°C.

On the other hand, if the thermistor 3 is disconnected or a connector or the like is forgotten, power is supplied to the heater 1, and even if the temperature of the photosensitive drum 9 rises, the value of the signal a remains at the reference value C. remains higher. In other words, the output of the comparator 5 is maintained at the torque level.

On the other hand, the control section 7 detects from the signal e that a predetermined time has elapsed after the power is turned on, and changes the output signal f@L level if the output of the comparator 5 is a torque level.

Then, the output of the AND circuit 8 becomes a torque signal, the transistor 2 is turned off, and the supply of power to the heater 1 is stopped.

By doing so, even if the thermistor 3 has an abnormality such as a disconnection, overheating by the heater 1 can be prevented, and the photosensitive drum can be protected.

Further, when the control section 7 of this embodiment detects an abnormality in the thermistor 3 as described above, it displays the abnormality, for example, makes a service call, and disables the copying operation.

This eliminates the need to make unnecessary copies, and allows quick inspection and repair of abnormalities.

Note that in this embodiment, the resistance value of the thermistor 3 is a certain value J
Although only the case where ζ is smaller than a certain value is considered to be an abnormality, abnormality when the value is smaller than a certain value, such as a short circuit, can be detected in the same way.

Further, as the temperature detection means, it is also possible to use a heat sensitive element other than a thermistor, such as a thermocouple.

[Effects of the Invention] As explained above, according to the present invention, since the control means for detecting an abnormality in the temperature detection means and controlling the heating means is provided, overheating of the image carrier by the heating means is prevented. The image carrier can be protected.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a heater control system in an embodiment of the present invention, Fig. 2 is a sectional view of the peripheral part of a photoreceptor drum in the same embodiment, and Fig. 3 shows the temperature characteristics of the surface potential of the photoreceptor. It is a graph. 1... Heater 2... Transistor 3... Thermistor 5... Comparator 6... ..... Timer 7 ..... Control section 8 ..... AND circuit 9 ..... Photosensitive drum Applicant Toshiba Corporation Agent Patent Attorney Sa Suyama - Figure 1 Figure 2

Claims (1)

[Claims] an image carrier on which an electrostatic latent image is formed, a heating means for heating the image carrier, a temperature detection means for detecting the temperature on or near the surface of the image carrier, and the heating means is turned on. If the temperature detected by the time detection means and the temperature detection means is outside the set range, and the time detected by the time detection means is outside the set range, An image forming apparatus comprising: a control means for turning off a heating means.