JPH02239274A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a requested temperature at least within a set time by setting an objective temperature gradient so that a temperature at which feeding starts is obtained within the set time after the point of time that temperature rise is detected, and controlling a temperature so that a surface temperature is not lower than the objective temperature gradient. CONSTITUTION:A means 19 stores surface temperature data detected by a temperature detecting means 22 at set time intervals after the start of temperature control; a temperature gradient calculating means 27 calculates a temperature gradient related to arbitrary time elapsing after the start of temperature control; an image forming device is provided with the means 22 and the temperature gradient calculating means 27. The temperature gradient calculating means 27 calculates a temperature gradient between the surface temperature data detected at the time of setting and the objective temperature at the prescribed time after the setting, as reference temperature gradient data; a heater control means 20 controls a temperature so that a temperature gradient, which is calculated from a surface temperature data detected after the calculation of the reference temperature gradient data, follows the reference temperature gradient data. Thus, a requested target temperature can be obtained at least within a prescribed time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus having a fixing device that makes it possible to prevent fixing defects.

[Prior Art] In conventional electrophotographic apparatuses, the feeding operation of the recording material was usually started when the surface temperature of the heating roller of the fixing device was lower than the fixing temperature.

The conventional method will be explained using FIG. 5 of the accompanying drawings. Fifth
The figure shows temperature changes on the surface of the heating roller, where To is the standby temperature when no print signal is received, T2 is the temperature at the time of starting paper feeding, and T is the fixing temperature.

In such a device, the time T. When a print signal is received at the point in time, T is reached up to that point. The heater whose temperature was adjusted at 'C' is now T. 'c temperature adjustment (T+>To
), as a result, the surface temperature of the heating roller gradually increases. Thereafter, when the surface knitting of the heating roller reaches T2°C, feeding is started (T2<TI).

Here, 1+-11 is set shorter than the time it takes for the recording material to reach the fixing device after being fed, and by the time the recording material reaches the fixing device, the surface temperature of the heating roller has reached the fixing temperature T1.
It is configured to reach ℃.

[Problems to be Solved by the Invention] However, in the conventional apparatus described above, when the recording material is fed at a temperature T2 and at the same time the heating roller and the pressure roller start rotating while being in pressure contact, the heat of the heating roller and the pressure increase. Since the toner is taken away by the roller, it may be transported to the recording material or the fixing device before the surface temperature of the heating roller reaches Tr°C, resulting in poor fixing. Moreover, the amount of heat absorbed by the pressure roller varies depending on the ambient temperature, making it difficult to predict and difficult to deal with.

The present invention solves the above problems and achieves the optimum temperature T. ″
An object of the present invention is to provide an image forming apparatus having a fixing device that maintains C and does not cause fixing defects.

[A Thousand Steps to Solve the Problem] The above purpose is to provide a rotatable heating roller that has a heater inside, a pressure roller that is rotatable in pressure contact with the heating roller, and a heater that controls the heater. An image forming apparatus comprising a control means and a temperature detection means for detecting a surface temperature of the heating roller, and capable of starting temperature control at any time to raise the surface temperature of the heating roller from a standby temperature, from the start of the temperature control. It has means for storing surface temperature data detected by the temperature detecting means at set time intervals, and temperature gradient calculating means for calculating a temperature gradient with respect to time at an arbitrary elapsed time from the start of the temperature control, The temperature gradient calculating means calculates the temperature gradient between the detected surface temperature data at the time of setting and the target temperature at a predetermined time after the setting time as reference temperature gradient data, and the heater control means This is achieved by setting the temperature control so that it follows the temperature gradient calculated from the surface temperature data detected after calculating the temperature gradient data or the reference temperature gradient data. [Function] As described above, the present invention rotates the heating roller and the pressure roller at the same time as the print command in order to take into account the heat taken by the pressure roller, and calculates the temperature gradient after an arbitrary time. Detects the degree to which the temperature rises at the end of the temperature rise, sets a target temperature gradient so that the feeding start temperature is reached within a set time from that point, and performs temperature control so that the surface temperature does not fall below the target temperature gradient. As a result, the desired temperature can be obtained at least within the set time.

[Embodiment] A first embodiment of the present invention will be described with reference to FIGS. 1 to 3 of the accompanying drawings.

In FIG. 1, 1 is a photosensitive drum whose surface is endlessly movable. The surface of the photosensitive drum l is connected to a charger 2 disposed above.
Exposure is performed by a laser beam 7 irradiated from a laser light emitting means 6 which is uniformly charged and includes a laser light emitting element 3, a scanner mirror 4, a scanner motor 5, etc., and an electrostatic latent image is formed on the surface. The electrostatic latent image is developed by a developing device 8 disposed opposite the photosensitive tram 1, and a toner image is formed on the surface. The toner image is transferred by a transfer charger 12 onto a recording material conveyed by a recording material feeding means including a paper feed cassette 9, a paper feed roller 10, and a registration roller 1l. The transferred recording material is conveyed to a fixing device 13 and heated by a heating roller 14.
The pressure roller 15 performs fixing, and the paper discharge roller 16 discharges the paper onto a paper discharge tray 17 .

In the apparatus of this embodiment, the fixing device 13 is connected to a control device shown in FIG. 2 which controls the temperature of the fixing section.

In Figure 2, l9 is a microprocessing unit (
A central processing unit (hereinafter referred to as MPU), a random access memory which is a readable/writable storage means, and a blockram memory in which a blockram is written;
It has a data memory in which data is written. The MPU 19 is connected to a signal transmission means 21 such as a ν-ray so as to control the heater 2o in the heating roller l4, and is connected to a thermistor 22 which is a temperature detection means provided outside the recording material passage area and an A/D It is connected via a signal conversion means 23 such as a converter. Further, the signal conversion means 23 is also connected to a comparator 24, and the comparator 24
is connected to the MPU 19, and compares the data from the signal conversion means 23 with the set value from the MPU 19, and reads the result to the MPLI 19. Also,
The heating roller I4 and the pressure roller 15 are connected via a buffer 25 so that their rotation can be controlled.

Also, whether data is read from the signal converting means 23 at set time intervals, or whether the set time is
The time is measured by a time counter 26 connected to. When the above-mentioned time counting counter 26 receives the reset signal mentioned above from the MP 119, the internal count value becomes "0", and each time a pulse signal is sent from the MPU 19, the internal count value is incremented by 1. . Therefore, the time interval can be measured by sending a reset signal after reading the previous data, sending pulse signals at regular intervals to the time counter 26, and reading the internal value of the time counter 26 with the MPU 19. Note that the pulse signals sent to the time counting counter at fixed intervals are always sent at an interval of 1 pulse/lmsec completely asynchronously with the fixing operation, etc., and if you want to refer to the internal value, count after sending the reset signal. Just do it like this. Furthermore, the above time counter 2
6 is also connected to a temperature gradient calculator 27 connected to the MPUI 9 as a temperature gradient calculation means, and the temperature gradient calculator 27 calculates the temperature gradient based on the count value of the time counter 26 and the data from the signal conversion means 23. It calculates the temperature gradient and sends the data to the liver υl9.

Further, this control device is connected to the main control section 28, and starts processing upon receiving a print command signal from the control section 28.

A method for controlling the surface temperature of the heating roller 14 based on the temperature gradient in the apparatus of this embodiment as described above will be explained with reference to FIG.

First, when there is a print command from the main control unit 28,
The heating roller 14 and pressure roller 15 are rotated to reach the standby temperature T. Temperature adjustment is started from to paper feed temperature T2 (Fig. 3 1).
00→l01). Then, the temperature at this time is detected and stored (FIG. 3 102), and the time counter 26 is reset in order to input the temperature data again after a set time.
Time measurement is started (FIG. 3, 103). After that, reading and comparison are repeated until the set value and the count value become equal. (Fig. 3 104→105). Next, when the set time is reached, the temperature data is input again (Fig. 3, 106), and the temperature gradient is calculated using the previously input data (Fig. 3, 1).
07). To explain the process up to this point using P in FIG. 4, it is time t when the roller starts rotating. Then, the second temperature data was input at time t3. Therefore, the temperature gradient is obtained by dividing the temperature change T3-To by the time t:+-to.

Next, the feeding start temperature T
Calculate the target temperature gradient so that it is 2.

That is, (T2 Ts)/(tz-b) becomes the target temperature gradient. Thereafter, the temperature is adjusted so that the temperature gradient does not fall below the target value until the feeding temperature T2 is reached (FIG. 3, 1-8→i09→110→103).

Thereafter, when the feeding temperature T2 is reached, a signal to start feeding is sent to the main control unit 28, and paper feeding is started. Then, the time set shorter than the time required for the recording material to reach the heating roller, that is, 1 in P in FIG. Set the target gradient value (T, -72)/(L-tz) again so that the fixing temperature T+ is reached at time -12) (FIG. 3, 112). Repeat the temperature adjustment again until the temperature reaches 2 (Fig. 3, 113 → 109 → 1ro 3). Thus, when the recording material reaches the roller, the predetermined fixing temperature T,
Since this is maintained, poor fixing will not occur.

Next, a second embodiment of the present invention will be explained using Q in FIG. In the first embodiment, the heater 20 was controlled so as to reach the target temperature within a predetermined time, but in this embodiment, the temperature gradient calculated at the beginning is maintained, the time required to reach the target temperature is determined, and the heater 20 is adjusted according to that time. This is used to control feeding. In this example, the temperature gradient (TR
The heater 2 is controlled so as to maintain I'-To)/(t.-t.), and the time t11 at which the fixing temperature becomes T is calculated from this reference temperature gradient data, and the recording material is moved to the roller. Calculate the time t2° so that the time t11-t2' is shorter than the time to reach t2', calculate the temperature 721 at the time t2' again from the temperature gradient data that serves as the reference above, and supply the temperature T2°. Set as the sending start temperature.

In this way, if you start feeding when the temperature T2 is reached while maintaining the temperature gradient, the fixing temperature T will be maintained by the time the recording material reaches the roller, and fixing failure will not occur. do not have.

[Effects of the Invention] As explained above, according to the present invention, by using the temperature gradient, the difference between the target temperature and the actual temperature at any time after starting temperature control can be corrected, and the difference between the target temperature and the actual temperature can be corrected within at least a predetermined time. The temperature can be controlled to reach the desired target temperature, so even if situations that are difficult to predict in advance, such as a drop in surface temperature due to contact with the pressure roller or changes in the ambient temperature of the heating roller, the temperature remains constant. It is possible to maintain the fixity of

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of the first embodiment of the device of the present invention, FIG. 2 is a schematic configuration diagram of the control device of the first embodiment, FIG. 3 is a flowchart of control of the first embodiment of the device, and FIG. The figure shows temperature changes due to temperature control in the first and second embodiments, and the $5 figure shows temperature changes due to temperature control by a conventional device. l4... Heating roller l5... Pressure roller 20... - Heater

Claims (2)

[Claims] (1) a rotatable heating roller that has a heater inside; a pressure roller that is rotatable in pressure contact with the heating roller;
An image forming apparatus comprising a heater control means for controlling the heater and a temperature detection means for detecting the surface temperature of the heating roller, and capable of starting temperature control at any time to raise the surface temperature of the heating roller from a standby temperature, Means for storing surface temperature data detected by the temperature detection means at set time intervals from the start of the temperature control, and temperature gradient calculation means for calculating a temperature gradient with respect to time at an arbitrary elapsed time from the start of the temperature control. The temperature gradient calculation means calculates the temperature gradient between the detected surface temperature data at the time of setting and the target temperature at a predetermined time after the time of setting as reference temperature gradient data, and Image forming characterized in that the control means is set to perform temperature control such that the temperature gradient calculated from the surface temperature data detected after calculation of the reference temperature gradient data follows the reference temperature gradient data. Device. (2) a rotatable heating roller that has a heater inside; a pressure roller that is rotatable in pressure contact with the heating roller;
A heater control means for controlling the heater, a temperature detection means for detecting the surface temperature of the heating roller, and a recording material feeding means for feeding the recording material to the two rollers, the surface temperature of the heating roller being In an image forming apparatus capable of starting temperature control to raise the temperature from a standby temperature and feeding of the recording material at any time, means for storing surface temperature data detected by the temperature detection means at set time intervals from the start of the temperature control; , temperature gradient calculation means for calculating reference temperature gradient data from surface temperature data at an arbitrary elapsed time from the start of the temperature control; arrival time calculation means for calculating the time until reaching the temperature gradient from the reference temperature gradient data, and the recording material feeding means is arranged such that the recording material reaches the heating roller after the elapse of the arrival time. An image forming apparatus characterized in that the image forming apparatus is configured to control a feeding start timing.