JPH0540527Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a fixing device for an image forming apparatus such as an electronic copying machine, and more particularly, to control of energization of a fixing heater.

(Background of the invention) An electronic copying machine exposes a charged photoreceptor (hereinafter explained using a photoreceptor drum as an example) to light according to document information to form an electrostatic latent image, which is then converted into a visible image using toner. This device transfers and fixes this visible toner image onto transfer paper. In recent years, this type of electronic copying machine has been used in all fields of industry.

FIG. 4 is a diagram showing an example of the configuration of this type of electronic copying machine. When the operator presses a copy button (not shown), the device shown begins the copying process. That is, after the remaining toner on the drum 1 is removed by a blade in the cleaning section 2 of the photosensitive drum 1 rotating in the direction of the arrow, the surface of the photosensitive drum 1 is charged with an electric charge by the charging electrode 3.

Next, the charge erasing section 4 erases the charges on the unnecessary portions of the photosensitive drum 1 . Thereafter, the charged area of the photosensitive drum 1 is exposed to light reflected by the original 6, and an electrostatic latent image of the original image is formed on the drum surface. That is, the original 6 is irradiated with light from the exposure unit 5, which is movable in the direction of the arrow shown in the figure, and the reflected light containing the original information reaches the photosensitive drum 1 via the mirrors _M1 to _M3 and the lens system L. Then, the drum surface is exposed to light to form an electrostatic latent image on the drum surface. This electrostatic latent image is converted into a visible image by adsorption of toner in the developing section 7. Thereafter, the toner visible image on the drum surface is transferred to transfer paper (copy paper) by a transfer section 8.
The transfer paper after the transfer is separated from the photosensitive drum 1 and sent to the fixing roller 10 by the conveyance mechanism 9. Then, the transfer paper is heated by the fixing roller 10, the toner is fused to the transfer paper, and the copying process is completed.

A portion (encircled by broken lines) consisting of the exposure section 5 and mirrors M ₁ , M ₂ , and M ₃ constitutes an optical unit 20, and is moved in the direction of the arrow in the figure by a moving mechanism (not shown). It is now possible to move. Here, the first mirror _M1 and the exposure section 5 are connected to the second and third mirrors in order to keep the optical path length constant.
It is designed to move at twice the speed of M ₂ and M ₃ . Here, since the light source 21 in the exposure device 5 is composed of, for example, a bar-shaped fluorescent light perpendicular to the paper surface,
The optical unit 20 can scan the entire surface of the original 6.

Incidentally, a fixing heater for heating the fixing roller 10 is provided inside the fixing roller 10, and is supplied with power from a power supply device (not shown). If the temperature of the fixing roller 10 is not constant, the degree of fixing of the copied image will vary depending on the transfer paper, resulting in an uneven image, which is undesirable. Therefore, the temperature of the fixing roller is controlled to a predetermined value. As a method of controlling this temperature,
There is an on/off control. FIG. 5 is a diagram showing the operation mode of the on/off control, in which the vertical axis represents the temperature T detected by the temperature detection sensor attached to the fixing roller, and the horizontal axis represents the time t. Also, Ts1 and Ts3 are the energization stop temperatures in idling mode and copy mode, which will be described later, respectively, and Ts2 and Ts4 are energization start temperatures in idling mode and copy mode, respectively, and Ts1-Ts
2, Ts3-Ts4 are the hysteresis widths of the idling mode and copy mode, respectively. Hysteresis width Δ ₁ = Ts1−Ts2 in both modes,
Δ ₂ =Ts3−Ts4 are chosen to be equal in the conventional device.

Next, the on/off control shown in FIG. 5 will be explained. At time _t0 , the fixing heater is turned on. As a result, the detected temperature gradually increases as shown in the figure. Then, at time t ₁ , the detected temperature is the energization stop temperature.
When Ts1 is exceeded, power to the fixing heater is turned off. Even when the power is turned off, the detected temperature will rise for a while due to the heat capacity, but after that, the detected temperature will start to decrease. When the detected temperature falls below the energization start temperature Ts2 at time _t2 , the energization to the fixing heater is turned on again. The same operation is repeated below. time
At t ₃ , the copy button is pressed to start the copy process, and the energization stop temperature Ts1 and the energization start temperature are
Ts2 is also the setting value Ts3, Ts in the Copu process
Changed to 4. Energization stop temperature from the above time t ₀
The period from time t ₁ to time t 1 when Ts1 is reached is the warming-up mode, and from time t ₁ to the start of the copy process.
The period up to t ₃ is the idling mode, and the period after time t ₃ is the copy mode.

(Problem to be solved by the invention) In such on/off control, by setting a large hysteresis width, the on/off period of electricity supply to the fusing heater becomes longer, and the frequency of intermittent on/off is reduced. This is useful for extending the life of the heater, but if you enter copy mode with a large hysteresis width when idling, the hysteresis width will be too wide and the energization stop temperature in copy mode will drop.
Around Ts3, the temperature is too high and the toner re-adheres to the fixing roller (this phenomenon is called hot offset), causing problems such as smudging of images and deterioration of the durability of the fixing roller.

The present invention was developed in view of these points, and its purpose is to extend the life of the fixing heater, prevent deterioration of the fixing roller, and realize a fixing device for an image forming apparatus that can obtain high-quality images. It's about doing.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, provides a fixing device of an image forming apparatus that fixes a toner image formed on a transfer paper using a fixing roller heated by a fixing heater. a temperature detection sensor that outputs a signal related to the surface temperature of the fixing roller; and a temperature point at which energization of the fixing heater is turned off in accordance with the detection signal of the temperature detection sensor from a temperature point at which it is turned on. The present invention is characterized in that the hysteresis width in the idling mode is made wider than the hysteresis width in the copy mode.

(Function) The fixing heater is controlled on and off in the idling mode with a wide hysteresis width, and in the copy mode it is controlled on and off with a narrower hysteresis width than in the idling mode.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of the present invention together with peripheral configurations. In this figure, the same parts as in FIG. 4 are designated by the same numbers. In the figure, 30 is a temperature detection sensor that outputs a signal related to the surface temperature of the fixing roller 10, and 31 is a fixing heater 3 that outputs a signal related to the surface temperature of the fixing roller 10.
This is an energization control circuit that controls energization to 2.

FIG. 2 is an explanatory diagram of the temperature control width of the energization control circuit 31 in the present invention. In the figure, as in FIG. 5, Ts1 is the temperature at which power supply to the fixing heater 32 starts in idling mode, Ts2 is the temperature at which power supply to the fixing heater 32 is stopped in idling mode, Ts3 is the power supply start temperature in copy mode, and Ts4 is in copy mode. is the energization stop temperature at . In this invention, the hysteresis width Δ ₁ = Ts
It is set so that the relationship Δ ₁ >Δ ₂ holds between 1−Ts2 and Δ ₂ =Ts3−Ts4.

If the idling mode control is now performed with a hysteresis width _Δ1 and the mode is shifted to the copy mode, the hysteresis width _Δ2 in the copy mode will be narrower than the hysteresis width _Δ1 in the idling mode. This is because Ts3 is set to a value close to Ts4, and since the temperature required for fixing is regulated by Ts4, no fixing failure occurs. or,
Since Ts3 is low, no hot offset occurs.

The temperature in normal idling mode is lower than the temperature in copy mode. Therefore, when changing from idling mode to copy mode, if it is heated all at once to the copy mode energization stop temperature Ts3,
The actual temperature of the fixing roller 10 is determined by the temperature detection sensor 3.
Due to the delay due to the thermal time constant of 0, the energization stop temperature Ts
3, resulting in the above-mentioned inconvenience. Therefore, at the first time when the copy mode is entered, the power supply to the fixing heater 32 is turned off at the copy mode power supply start temperature Ts4.

FIG. 3 is a flowchart showing the flow of temperature control in the present invention, where a indicates the idling mode and b indicates the copy mode.

In the idling mode, first, the temperature detected by the temperature detection sensor 30 and the energization start temperature are compared with Ts2 (step). And the detected temperature <
In the case of Ts2, energization to the fixing heater 32 is started (power ON) (step), but if the detected temperature > Ts2, the detected temperature and the energization stop temperature Ts1
Let's move on to the step of comparing. Then, if the detected temperature > Ts1, the energization is stopped (power OFF)
(step), and if the detected temperature is < Ts1, the state remains as it is.

In the copy mode, the first time the mode is changed from the idling mode to the copy mode, the fixing heater 32 is first energized (step). and,
The detected temperature and the energization start temperature Ts4 are compared (step), and if the detected temperature>Ts4 is detected, the energization is stopped (step). After that, normal copy mode operation resumes. In other words, by comparing the detected temperature with the energization start temperature Ts4 (step), the detected temperature <
If Ts4, energize (step), and if detected temperature > Ts4, detect temperature and energization stop temperature.
Moving on to the step of comparing with Ts3. and,
If the detected temperature is > Ts3, the current supply is stopped (step); if the detected temperature is < Ts3, the current state is maintained.

With this configuration, the hysteresis width Δ ₁ in idling mode is controlled to be wider than the hysteresis width Δ ₂ in copy mode, so the cycle of on-off control in idling mode is the same as that of on-off control in copy mode. Since Ts3 becomes longer than the cycle and becomes lower, overheating of the fixing heater in the copy mode is prevented.

(Effects of the invention) As explained in detail above, according to the invention,
The hysteresis width can be made different between the idling mode and the copy mode, the life of the fixing heater can be extended, the deterioration of the fixing roller can be prevented, and a fixing device for an image forming apparatus that can obtain high-quality images can be realized.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the present invention together with the peripheral configuration, Fig. 2 is an explanatory diagram of the hysteresis width of the energization control circuit in the present invention, and Fig. 3 is a flowchart showing the flow of temperature control in the present invention. FIG. 4 is a diagram showing an example of the configuration of an electronic copying machine, and FIG. 5 is a diagram showing an on/off control mode. 1...Photosensitive drum, 2...Cleaning section, 3
...Charging section, 4... Charge erasing section, 5... Exposure section,
6... Original document, 8... Transfer unit, 9... Conveyance mechanism, 1
0... Fixing roller, 20... Optical unit, 21
...Light source, 30...Temperature detection sensor, 31...Electricity control circuit, 32...Fusing heater.

Claims (1)

[Claims for Utility Model Registration] (1) A fixing device of an image forming apparatus that fixes a toner image formed on transfer paper using a fixing roller heated by a fixing heater, A temperature detection sensor that outputs a related signal, and a temperature detection sensor that controls energization to the fixing heater in accordance with the detection signal of the temperature detection sensor so that a temperature point at which the temperature shifts to OFF is set higher than a temperature point at which the temperature shifts to ON. It has an energization control circuit that
A fixing device for an image forming apparatus, characterized in that a hysteresis width in an idling mode is wider than a hysteresis width in a copy mode. (2) Utility model registration claim 1, characterized in that the energization control circuit is a circuit that stops energization for the first time when shifting from idling mode to copy mode, and stops energization at the temperature at which energization starts in copy mode. A fixing device for an image forming apparatus as described in 2.