JP2002296960A - Fixing device for electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the temperature of a heat roll surface from being outside the range of appropriate temperature. SOLUTION: In the device, the on/off changeover of a heater is carried out when an absolute value of the temperature gradient in printing is greater in comparison to the absolute value of an average value of the temperature gradient of the heat roll surface temperature at a non-printing time immediately after starting of the machine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic apparatus.

[0002]

2. Description of the Related Art A conventional fixing device of an electrophotographic apparatus will be described with reference to FIG. During continuous printing, the printing paper 2 onto which the toner 1 has been transferred from the photoconductor is preheated by the preheater (preheating plate) 3 from the back surface of the printing paper 2. A heat roll (heating roller) 4 constantly rotating in the direction A, and the heat roll 4
The toner 1 is fixed on the printing paper 2 by heating and pressing with a backup roll (pressure roller) 5 rotating in the direction B by contact with the printing paper 2. Here, the heat roll 4
Are heated by four heaters 6 of different lengths mounted inside. Further, three non-contact type temperature sensors 7 are arranged in the longitudinal direction of the roll with a constant gap from the surface of the heat roll 4, and each of the non-contact type temperature sensors 7 is independent of the heat roll 4. Surface temperature is constantly measured. From the signal data from the non-contact type temperature sensor 7, the heater 6 is turned on when the surface temperature of the heat roll 4 is lower than the lower limit Ta ° C, and when the surface temperature is higher than the upper limit Tb ° C, the heater is turned on. 6 is OF
F, the surface temperature of the heat roll 4 becomes (Tc ± Td)
℃ is controlled.

[0003]

In a fixing device of a conventional electrophotographic apparatus, when a relatively gentle temperature gradient occurs during continuous printing or the like, the surface temperature of the heat roll 4 is set to (Tc).
Although it is possible to control stably in the range of ± Td) ° C., as described above, conventionally, only the temperature data of the lower limit value Ta ° C. and the upper limit value Tb ° C. of the surface temperature of the heat roll 4 are set as slice levels. Since the ON / OFF of the heater has been switched, for example, when the temperature suddenly drops at the start of printing and rises at the time of recovery, especially when the printed paper is thick or the water content is high,
Temperature fluctuation exceeding (Tc ± Td) ° C. occurred temporarily. The former is a cause of print quality failure resulting in insufficient fixing strength of a printed portion, and the latter is a cause of reliability reduction resulting in shortening of the life of the heat roll.

[0004] An object of the present invention is to provide a fixing device for ensuring stable print quality and component reliability, irrespective of the specifications of printing paper and printing conditions, as described above. .

[0005]

The above object is achieved by monitoring temperature gradient data obtained from a non-contact temperature sensor of a heat roll.

[0006]

FIG. 2 shows a specific embodiment of the present invention.
This will be described with reference to FIG. The basic configuration of the fixing device is the same as that of the conventional example shown in FIG.

FIG. 2 shows the surface temperature of the heat roll from the start of the machine to the start and stop of printing, obtained from one non-contact type temperature sensor 7, using two types of paper having different thicknesses. 3 shows a conceptual graph plotting the change over time. The solid line shows the data for thick paper, and the broken line shows the data for thin paper.
The printing status of each part in the drawing is shown below. Part A: During non-printing Part B: Immediately after starting printing Part C: Immediately after a rapid temperature recovery D Part: During continuous printing In the figure, the surface temperature of the heat roll is always kept within the range of (Tc + Td) ° C and (Tc-Td) ° C. Under control, Ta ° C. is a lower limit value for turning on the heater 6, and Tb ° C. is an upper limit value for turning off the heater 6. Explaining the change over time of the heat roll surface temperature, the machine starts to operate, and Tc
The heat roll surface temperature is controlled so as to be stable around ℃ (part A). Immediately after printing is started, a sharp temperature drop occurs (part B), but the magnitude of the temperature drop varies depending on the thickness of the paper to be printed and the difference in water content. For example, as shown in the drawing, the larger the sheet thickness, the greater the temperature drop. In this case, if the temperature temporarily drops to (Tc−Td) ° C. or less, the fixing strength of the printing unit may be insufficient. Further, when the temperature is rapidly recovered, the reverse tendency occurs, and the gradient of the temperature rise in the thin paper becomes large, and the temperature temporarily exceeds (Tc + Td) ° C. (part C). During continuous printing, the temperature is relatively stably controlled within the range of (Tc ± Td) ° C. (D section).

[0008] The surface temperature of the heat roll is always (Tc ± Td) ° C. regardless of the specifications of printing paper and printing conditions.
In order to maintain the temperature within the range, the following temperature control was invented. This will be described with reference to FIGS.

FIG. 3 shows the details of the portion A. Surface temperature sampling time during non-printing immediately after machine startup:
Absolute value of the temperature difference at h: | ΔTe |
Tave. | Is stored.

FIG. 4 shows the details of the portion B. After the start of printing, the absolute value of the temperature difference at the sampling time: h: | ΔT
When f | is the following condition, the heater 6 is turned on even if the lower limit value Ta ° C. is not reached. However, if the following conditions are not satisfied, when the temperature reaches the lower limit Ta.degree.
Turn ON. | ΔTave. | <| ΔTf | (∴ Tf <Ta) On the contrary, when the temperature of the portion C is rising, the sampling time is:
If the absolute value of the temperature difference at h: | ΔTg | satisfies the following conditions, the heater 6 is turned off even if the temperature does not reach the upper limit Tb ° C. However, if the following conditions are not satisfied, the heater 6 is turned on when the temperature reaches the upper limit Tb ° C. | ΔTave. | <| ΔTg | (∴ Tb <Tg)

[0011]

According to the present invention, a rapid decrease and an increase in the surface temperature of the heat roll can be detected quickly, so that control in an appropriate temperature range is possible. Therefore,
It is possible to prevent the fixing strength of the printing portion from becoming insufficient or the life of the component from being shortened, which is caused by a temperature drop outside the appropriate temperature range during printing or a temperature rise.

[Brief description of the drawings]

FIG. 1 is a side view of a fixing device of an electrophotographic apparatus.

FIG. 2 is an explanatory diagram showing a heat roll surface temperature obtained from a non-contact type temperature sensor.

FIG. 3 is a detailed explanatory diagram of a heat roll surface temperature.

FIG. 4 is a detailed explanatory diagram of a heat roll surface temperature.

[Explanation of symbols]

Reference numeral 1 denotes toner, 2 denotes printing paper, 3 denotes a pre-heater, 4 denotes a heat roll, 5 denotes a backup roll, 6 denotes a heater, and 7 denotes a non-contact type temperature sensor.

Claims (2)

[Claims] 1. A preheating plate provided on a downstream side in a sheet conveying direction for transferring a toner image formed on a photoreceptor onto a long continuous sheet and preheating from a back surface of the sheet, and a plurality of rotating pre-heating plates. A heating roller having a built-in heater, a plurality of non-contact type temperature sensors arranged in a longitudinal direction for detecting the surface temperature of the heating roller, and a pressure roller rotating by contact with the heating roller. In a fixing device of an electrophotographic apparatus in which a toner image is fixed on paper by pressure, a temperature gradient per unit time is monitored from temperature data obtained from the non-contact type temperature sensor during printing, and a heater of the heating roller is heated. A fixing device for an electrophotographic apparatus, characterized by controlling a temperature. 2. The heater temperature of the heating roller is controlled by comparing a temperature gradient per unit time during non-printing with a temperature gradient per unit time during printing. A fixing device for the electrophotographic apparatus according to the above.