JP4771813B2 - Fixing device temperature control device - Google Patents

Description

  The present invention relates to a temperature control apparatus used in an image forming apparatus such as a copying machine. More specifically, the present invention relates to a heater ignition phase or arc extinction phase or a predetermined time based on a detected temperature so that a fixing temperature becomes a target temperature. The present invention relates to a temperature control device for a fixing device that includes PID control means that variably controls any one of the number of lighting waves as a control target value and thermally fixes a toner image formed on a recording material.

  Conventionally, in image forming apparatuses such as copying machines, printers, facsimiles, etc., transfer materials, photosensitive paper, electrostatic recording paper, printing by appropriate image forming process equipment such as electrophotographic system, electrostatic recording system, magnetic recording system, etc. An image is formed and supported on a recording material such as paper in accordance with target image information by a transfer method or a direct method.

  In the image forming apparatus employing the transfer method, a fixing device adjusted to a predetermined target temperature is used to thermally fix the unfixed toner image formed and supported on the recording material onto the recording material surface. It is pressed against the recording material.

  The fixing device is provided with a heater that heats the fixing device in a cylindrical shape, and energization to the heater is controlled based on a temperature detected by temperature detecting means for detecting the temperature of the fixing device. Thus, the temperature is controlled so as to be a predetermined target temperature.

  In the temperature control, PID (Proportional Integral Differential) control is performed by PID control means that variably controls either the ignition phase or extinction phase of the alternating current output to the heater or the number of lighting waves per predetermined time as a control target value. Has been.

  The PID control has an advantage that flicker can be suppressed since a rapid change in current consumption can be suppressed with simple control.

JP 2004-212905 A

  In the PID control, as shown in FIG. 9, for example, if the responsiveness of the temperature control is improved by setting the heat capacity of the fixing device itself small, the time until the fixing device reaches the target temperature is Although it becomes shorter, there is a feature that overshoot and undershoot with respect to the target temperature become large until it stabilizes at the target temperature thereafter. For this reason, when the recording material is pressed against the fixing device, the recording material absorbs heat from the fixing device, so that the temperature of the fixing device, which has been stabilized at the target temperature, is increased. When the temperature decreases, the temperature of the fixing device quickly reaches the target temperature again during the press contact with the recording material by the fixing device, but then reaches the target temperature until it stabilizes at the target temperature. On the other hand, overshoot and undershoot occur, and as a result, a fixing failure such as hot offset or cold offset may occur in the toner image fixed on the recording material pressed by the fixing device. It was a problem.

  On the other hand, by setting the heat capacity of the fixing device itself to be large so that the influence of the amount of heat absorbed by the recording material from the fixing device on the temperature of the fixing device is reduced, When the temperature of the fixing device is lowered due to some influence, a large amount of heat is required for the fixing device to reach the target temperature, and as a result, the responsiveness of temperature control is lowered. It was.

  In view of the above-described conventional drawbacks, the present invention provides a temperature control device for a fixing device that controls the temperature of the fixing device so as to obtain a good image while suppressing the flicker and ensuring the responsiveness of the temperature control. Is to provide

In order to achieve the above-mentioned object, the first characteristic configuration of the temperature control device for the fixing device according to the present invention is to detect the fixing temperature so as to be a target temperature as described in claim 1 of the claims. PID control means for variably controlling either the ignition phase or extinction phase of the heater or the number of lighting waves per predetermined time based on the temperature as a control target value, and thermally fixing the toner image formed on the recording material A temperature control device for a fixing device, wherein the PID control unit calculates a duty ratio, which is an energization time ratio with respect to a predetermined period, as the control target value, and corresponds to each duty ratio corresponding to the calculated duty ratio configured as an output signal pattern selected from the output signal pattern imparted to control the heater, non-transportable in the startup device, the control target value, the recording material by the fixing device Set the first duty ratio fixing temperature is held can preset the target temperature when, after the start of image forming operation, immediately before the recording material reaches the fixing device, the control target value, fixing Forcibly change at least once to the second duty ratio that generates a larger amount of heat than the first duty ratio that can be maintained at the target temperature. The control object value setting means for setting is provided.

  According to the above-described configuration, the control target value is set by the fixing device after the image forming operation on the recording material is started and immediately before the recording material reaches the fixing device. The fixing temperature during conveyance is forcibly changed to a predetermined duty ratio that can be maintained at the target temperature, and is larger than the duty ratio that is a value calculated by the PID control means immediately before the recording material is not conveyed by the fixing device. Since a large amount of power is supplied to the heater based on the duty ratio, sufficient fixing performance is ensured without causing a sudden temperature drop even immediately after the recording material is conveyed to the fixing device. become.

  That is, when the fixing device presses the recording material, the recording material absorbs heat from the fixing device, so that the amount of heat released from the fixing device increases and the fixing temperature rapidly decreases. However, since the increase in the amount of heat released from the fixing device can be compensated immediately before the recording material absorbs heat from the fixing device, the fixing generated by the fixing device press-contacting the recording material. The temperature change of the vessel can be suppressed.

In the second characteristic configuration, as described in claim 2, in addition to the first characteristic configuration described above, the second duty ratio is set corresponding to the thickness, size, and material of the recording material. Is the point that is the value to be.

  It is possible to appropriately control the temperature of the fixing device in order to ensure sufficient fixing performance corresponding to the thickness, size and material of the recording material.

In the third feature configuration, as described in claim 3, in addition to the first or second feature configuration described above, the control target value setting means is configured such that the recording material is a fixing device during the image forming operation. When a certain time elapses after passing, the control target value is forcibly changed to the second duty ratio .

  When the fixing device releases the pressure contact of the recording material, the recording material no longer absorbs heat from the fixing device, so the amount of heat released from the fixing device is reduced, and the amount of heat given excessively is accumulated in the fixing device. The With the above-described configuration, in order to suppress the amount of heat given to the fixing device after the recording material no longer absorbs the amount of heat from the fixing device, the fixing device is configured to suppress the amount of heat given to the fixing device. It is possible to suppress a change in the temperature of the fixing device which is generated by releasing the pressure contact of the recording material.

  In the fourth feature configuration, as described in claim 4, in addition to the third feature configuration described above, the image forming operation on a plurality of recording materials is continuously performed for a certain period of time. The fixing unit is set to be longer than the passing time of the recording material, and switching of the control target value too frequently can be avoided.

  In the fifth feature configuration, in addition to any one of the first to fourth feature configurations described above, the control target value is included in a predetermined cycle of the AC wave of the power supply voltage. It is in the point which is the lighting half-wave number with respect to the total half-wave number.

  As described above, according to the present invention, the temperature control device for a fixing device that controls the temperature of the fixing device so as to obtain a good image while suppressing the flicker and ensuring the responsiveness of the temperature control. Can now be provided.

  Hereinafter, an embodiment in which a temperature control device for a fixing device according to the present invention is applied to a digital copying machine as an image forming apparatus will be described. As shown in FIG. 2, the digital copying machine includes an image reading unit 1 that reads image data of a document, and an image that generates output image data by performing predetermined processing on the document image data read by the image reading unit 1. A processing unit 2, an image output unit 3 that forms and outputs an image on the recording material 10 based on output image data from the image processing unit 2, and a mode setting that sets operation modes of various jobs by the digital copying machine A key, a print switch for activating a set job, and the like are arranged, and an operation unit 4 including a touch panel type liquid crystal display unit on which setting information by the mode setting key is displayed is configured.

  The image reading unit 1 is fed by a document tray 12 on which a document is placed, a document feeding unit (not shown) that feeds a document placed on the document tray 12, and a document feeding unit. A CCD linear sensor (not shown) for reading the image of the original is provided.

  The image output unit 3 includes an image forming unit 6 that forms a toner image on the photoconductor 60 based on the output image data, a conveyance unit 7 that conveys a recording material 10 onto which the formed toner image is transferred, The recording material 10 is heated and melted by heat-melting the toner image on the recording material 10 by pressure-conveying the recording material 10 with a pressure roller 8b and a fixing roller 8a as a fixing device heated to a predetermined temperature. A fixing unit 8 for fixing the material 10 is provided. A heater for heating the fixing roller 8a is installed inside the fixing roller 8a, and a thermistor element for detecting the temperature of the fixing roller 8a is installed on a predetermined surface portion of the fixing roller 8a. Has been.

  The image forming unit 6 is arranged in order around the photoconductor 60, the periphery of the photoconductor 60, and exposes the charged photoconductor 60 to uniformly corona charge the surface and forms an electrostatic latent image. A print head 62, a developing unit 63 that electrostatically attaches toner to the formed electrostatic latent image to make it visible, a transfer unit that transfers the toner image to the recording material 10, and a toner that remains after transfer A cleaning unit 64 to be removed and a static elimination lamp 65 that lowers the residual potential on the surface of the photosensitive member to be uniform are provided. The developing unit 63 has four colors of cyan, magenta, yellow, and black so that a color image can be generated. Color development blocks are arranged.

  The transport unit 7 transports the recording materials 10 one by one from a general paper feed cassette 11a in which recording materials 10 of different sizes are accommodated or a manual feed cassette 11b in which recording materials 10 of arbitrarily different sizes are installed. A feeding / conveying section 7a, a feeding / recording material 10 conveyed to a transfer section, a recording / conveying material 10 onto which a toner image has been transferred, conveyed toward a fixing section 8, and a fixing section. A first paper discharge portion 7c that discharges the recording material 10 that has passed 8 to the paper discharge tray 9 face-up, a second paper discharge portion 7d that discharges the face-down method, and the second paper discharge portion 7d. A third paper discharge unit 7e that transports the image to the image reading unit 1 and a re-transport unit 7f for double-sided printing are provided, and a transport roller is provided for each.

  As shown in FIG. 3, the control unit of the digital copying machine described above includes an image reading control unit 1 </ b> A that controls a document reading operation by the image reading unit 1, the image processing unit 2, and the image output unit 3. The image output control unit 3A to be controlled, the operation control unit 4A to control the input / output signals of the operation unit 4, and the timing of each of the control blocks 1A, 2, 3A and 4A described above are controlled to execute a copying operation or the like. The control block 1A, 2, 3A, 4A, 5 is provided with a CPU and a ROM in which an operation program by the CPU is stored.

  The image reading control unit 1A drives the document feeding unit 101 to feed the document placed on the document tray 12, and outputs an analog signal corresponding to the document image read by the CCD linear sensor 102 to the A / A. The image data obtained by converting into digital data by the D conversion means 103 is subjected to shading correction and γ correction by the input image processing means 104 provided with a predetermined conversion table.

  The image processing unit 2 includes an image processing unit 201 that generates output image data by performing spatial filter processing, halftone processing, enlargement / reduction processing, and the like on the image data output from the input image processing unit 104; Data conversion means 202 that converts output image data from 201 into a drive signal for the print head 62 and the like are provided, and the converted drive signal is output to the drive circuit of the print head 62.

  In the above-described digital copying machine, an original is placed on the original tray 12, and the operation switch 4 is appropriately pressed to set mode setting keys such as the number of copies, the size of the recording material, and the copy magnification, and then the print switch is pressed. Thus, the copying operation is started. That is, the system control unit 5 outputs a document image reading command to the image reading control unit 1A, outputs an output image generation command based on the read image data to the image processing unit 2, and outputs an image output control unit. An image output command is output to 3A. The image output control unit 3A drives the transport unit 7 to transport the recording material 10 from the general paper feed cassette 11a or the manual feed cassette 11b, and then outputs an image data output command to the image output control unit 3A at a predetermined timing. Then, the print head 62 is driven. When a toner image is formed on the photoreceptor 60 exposed by the print head 62, the toner image is transferred to the recording material 10, fixed by the fixing unit 8, and then discharged outside the apparatus.

  Hereinafter, the temperature control of the fixing roller 8a as a fixing device for thermally fixing the toner image formed on the recording material 10 will be described in detail. The temperature control of the fixing roller 8a is executed by the image output control unit 3A as the temperature control device 3A of the fixing device.

  As shown in FIG. 1, the functional block configuration for controlling the temperature of the fixing roller 8a is based on the temperature detected by the thermistor element 57 so that the temperature of the fixing roller 8a becomes a target temperature. PID control means 51 for variably controlling the number of lighting waves per predetermined time of the alternating current output to the control target value, and forcing the control target value at least once after the start of the image forming operation on the recording material 10 The control target value setting means 52 for changing and setting automatically is provided.

  The PID control means 51 monitors the alternating current output from the alternating current power supply 53 to the heater 56 by a zero cross detector 54 that detects a zero cross point Pz of the alternating current as shown in FIG. Then, a predetermined cycle in the AC current, for example, 10 cycles (20 cycles when converted to an AC half-wave) is defined as one duty, and a predetermined AC half-wave is output for each one duty, whereby the AC current is output. Is configured to perform ON / OFF control of the switching element 55 such as a triac so that a predetermined duty ratio Rd is obtained.

  More specifically, the duty ratio Rd is, as shown in [Equation 1], the number Nc of AC half waves selectively output by the PID control means 51 in the total number Na of AC half waves at the one duty. As shown in FIG. 5, the AC half wave selectively output by the PID control means 51 is predetermined as the output signal pattern for each duty ratio Rd.

The predetermined duty ratio Rd _n controlled by the PID control means 51, on the basis of the temperature detected by the thermistor element 57 is derived in accordance with expression (2).

Here, in the equation, Rd _n-1 is the previous duty ratio, ΔMV _n is the current duty change difference, T is the target temperature, T _n is the current detected temperature, T _n-1 is the previous detected temperature, and T _{n. -2} is the previous detected temperature, En is the current deviation, En _-1 is the previous deviation, En _-2 is the previous deviation, Kp is the proportional constant of the PID calculation, Ki is the integration constant of the PID calculation, and Kd is It is a differential constant of PID calculation.

  That is, the PID control means 51 derives a predetermined duty ratio Rd to be controlled this time according to [Equation 2] based on the detected temperature of the thermistor element 57, and an output signal pattern corresponding to the derived duty ratio and Thus, the switching element 55 is ON / OFF controlled. For example, when the duty ratio is 50%, AC half waves W1, W3, W5, W7, W9, W11, W13, W15, W17, W19 are output as shown in FIG. ON), AC half waves W2, W4, W6, W8, W10, W12, W14, W16, W18, W20 are not output (OFF).

Note that the PID control means 51, details when entered the predetermined initial value from the control object value setting means 52 will be described later, once was the input to the current duty ratio Rd _n in the expression (2) Substituting the initial value, the derivation of the duty ratio according to the following [Equation 2] is continued.

  Hereinafter, the specific operation of the PID control means 51 will be described with reference to the flowchart of FIG. When the digital copying machine is activated, the PID control means 51 starts temperature detection of the fixing roller 8a by the thermistor element 57 (SA1).

Further, when the initial value from the control object value setting means 52 is input (SA2), the current of the while substituting the input initial value to the duty ratio Rd _n in expression (2) (SA3), thereafter The derivation of the duty ratio according to [Equation 2] is repeated at predetermined time intervals, for example, every 200 ms (SA4).

The PID control means 51, each deriving the current duty ratio Rd _n, selects the output signal patterns corresponding to the duty ratio as the derived (SA5), the switching element in accordance with the selected output pattern ON / OFF control is executed (SA6).

  When a predetermined initial value is input from the control target value setting means 52 (SA7), the process returns to step SA3.

  The control target value setting unit 52 sets an initial value of the duty ratio as a control target value, and forcibly changes the duty ratio at least once after the start of an image forming operation on the recording material 10. Configured to set.

  More specifically, the control target value setting means 52 keeps the fixing roller 8a at a target temperature in a state where the recording material 10 is not pressed and conveyed to the fixing roller 8a under a predetermined environmental condition. A first ideal duty ratio that can be maintained, and a second ideal duty ratio that can keep the fixing roller 8a at a target temperature in a state where the recording material 10 is pressed and conveyed to the fixing roller 8a. Are stored in advance. In other words, the control target value setting means 52 has an ideal duty ratio that can compensate for the amount of heat equivalent to the amount of heat released from the fixing roller 8a under a predetermined environmental condition. The recording material 10 is stored under different conditions depending on whether the recording material 10 is not being pressed and conveyed. The second ideal duty ratio is stored as a duty ratio that increases the amount of heat generated by the heater as compared with the first ideal duty ratio.

  Then, the control target value setting means 52 determines that the recording material 10 is switched from the state where the recording material 10 is not pressed and conveyed to the fixing roller 8a to the state where the recording material 10 is pressed and conveyed to the fixing roller 8a. When this is done, the second ideal duty ratio is output to the PID control means 51 as the initial value, and from the state where the recording material 10 is pressed and conveyed to the fixing roller 8a, it is transferred to the fixing roller 8a. When it is determined that the recording material 10 is switched to a state where the recording material 10 is not being pressed and conveyed, the first ideal duty ratio is output to the PID control means 51 as the initial value.

  The first and second ideal duty ratios are preferably stored corresponding to the thickness, size, material, and the like of the recording material 10, respectively.

  Hereinafter, a specific operation of the control target value setting means 52 will be described based on the flowchart of FIG. When the digital copying machine is activated, the control target value setting means 52 outputs the first ideal duty ratio as the initial value to the PID control means 51 (SB1, SB2).

  For example, when the control target value setting unit 52 detects the recording material 10 conveyed to the fixing roller 8a by a recording material detection unit that detects the recording material 10 immediately before the fixing roller 8a (SB3), the fixing roller It is determined that the state in which the recording material 10 is not pressed and conveyed to 8a is switched to the state in which the recording material 10 is pressed and conveyed to the fixing roller 8a, and the second ideal duty ratio is set as the initial value. The recording material 10 is output to the PID control means 51 at the timing when it is detected (SB4, SB5)). In other words, the control target value setting means 52 sets the control target value to the first level when the recording material 10 is on standby or when the recording material 10 is not passing immediately before the recording material 10 reaches the fixing roller 8a as a fixing device. The control target value is switched from the control target value to the second control target value at which the calorific value is higher.

  Further, when the recording material 10 has not passed through the detection position of the recording material 10 detected by the recording material detection means and the recording material 10 is no longer detected (SB6), the fixing roller 8a receives the It is determined that the recording material 10 is switched from a state where the recording material 10 is pressed and conveyed to a state where the recording material 10 is not pressed and conveyed to the fixing roller 8a, and the first ideal duty ratio is set as the initial value. After the recording material 10 is no longer detected, it is output to the PID control means 51 after a certain time Tth has passed (SB7, SB8). That is, the control target value setting means 52 determines the third control target value when the recording material 10 passes after the recording material 10 passes through the fixing roller 8a as a fixing device during the image forming operation. It switches to the 4th control object value whose calorific value becomes lower than it.

  Note that the control target value setting unit 52 is more specifically configured by the recording material detection unit when a plurality of the recording materials 10 passes the fixing roller 8a continuously at a predetermined time interval. After the recording material 10 has finished passing through the detection position of the recording material 10, the recording material detection means again after the fixed time Tth has elapsed after the recording material 10 is no longer detected. Thus, when another recording material 10 is detected, the output of the initial value to the PID control means 51 is reserved.

  Further, the control target value setting means 52 determines that the predetermined time Tth is a time during which the recording material 10 passes through the fixing roller 8a when the image forming operation on the plurality of recording materials 10 is continuously performed. It is good also as a structure set large.

  That is, the digital copying machine controls the amount of heat for supplementing the amount of heat released from the fixing roller 8a before the temperature of the fixing roller 8a suddenly changes due to the change in the amount of released heat. By adjusting the duty ratio as the target value, control is performed so that the temperature of the fixing roller 8a does not change rapidly.

  Hereinafter, another embodiment will be described. In the above-described embodiment, the PID control unit 51 variably controls the lighting wave number per predetermined time of the alternating current output to the heater 56 as a control target value. However, the PID control unit 51 It is good also as a structure which carries out variable control by making the ignition phase or extinction phase of the alternating current output to the said heater 56 into a control object value.

  Specifically, as shown in FIGS. 8A and 8B, each AC half-wave in the AC current is set to one duty, and a predetermined phase is output for each duty, whereby the AC The PID control means 51 controls the switching element 55 so that the current has a predetermined duty ratio, that is, the ratio of the ignition phase occupying the AC half wave or the ratio of the arc extinction phase occupying the AC half wave. It is good also as a structure which performs ON / OFF control.

  Note that the above-described embodiment is merely an example of the present invention, and it is needless to say that the specific configuration and the like of each block can be changed and designed as appropriate within the scope of the effects of the present invention.

Explanatory drawing of a functional block configuration for performing temperature control of the fixing roller Illustration of digital copier Illustration of circuit configuration of digital copier (A) Zero cross point in alternating current, 1 duty, and explanatory diagram of alternating half wave, (b) is an example of alternating current selected and output at a predetermined duty ratio Illustration of the relationship between duty ratio and output signal pattern Flow chart for explaining the operation of the PID control means Flow chart for explaining the operation of the control target value setting means Example of alternating current selectively output at a predetermined duty ratio in another embodiment Explanatory diagram of temperature change of fixing unit

5: System control unit 8: Fixing unit 8a: Fixing roller 10: Recording material 51: PID control unit 52: Control target value setting unit 53: AC power supply 54: Zero cross detector 55: Switching element 56: Heater 57: Thermistor element

Claims (5)

PID control means for variably controlling either the ignition phase or extinction phase of the heater or the number of lighting waves per predetermined time based on the detected temperature so that the fixing temperature becomes the target temperature, and a recording material A temperature control device for a fixing device that thermally fixes a toner image formed thereon,
The PID control means calculates a duty ratio, which is a ratio of energization time with respect to a predetermined cycle, as the control target value, and an output signal selected from an output signal pattern associated with each duty ratio corresponding to the calculated duty ratio Configured to control the heater in a pattern,
When the apparatus is started, the control target value is set to a preset first duty ratio that can maintain the fixing temperature when the recording material is not conveyed by the fixing device at the target temperature,
After the start of the image forming operation, immediately before the recording material reaches the fixing device, the control target value is set to a preset first value that can hold the fixing temperature during conveyance of the recording material by the fixing device at the target temperature . A temperature control device for a fixing device, comprising control target value setting means for forcibly changing and setting at least once a second duty ratio in which a calorific value is larger than one duty ratio . 2. The temperature control apparatus for a fixing device according to claim 1, wherein the second duty ratio is a value set corresponding to the thickness, size, and material of the recording material. The control target value setting means forcibly changes and sets the control target value to the second duty ratio when a predetermined time elapses after the recording material passes through the fixing device during an image forming operation. The temperature control apparatus according to 1 or 2.   The fixing device temperature according to claim 3, wherein the predetermined time is set longer than a passing time of the recording material in the fixing device when image forming operations on a plurality of recording materials are continuously performed. Control device.   5. The temperature control device for a fixing device according to claim 1, wherein the control target value is a lighting half-wave number with respect to a full half-wave number included in a predetermined cycle of an AC wave of a power supply voltage.