JP6424571B2 - Fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device of a thermal type in an electrophotographic image forming apparatus, and an image forming apparatus such as a copying machine, a printer, or a facsimile equipped with the fixing device.

  A fixing device used in an electrophotographic image forming apparatus has a fixing roller or the like configured by opposed rollers, a belt, or a combination thereof. For example, in a fixing device using a belt fixing method, a fixing belt (endless belt) including a heating roller having a heater and a fixing roller, and a pressure roller in contact with the fixing belt are the fixing rotating body. Heat and pressure are applied to the toner-transferred recording medium that has reached the fixing device by the fixing rotary member, and the toner image is fixed.

  In the fixing device of the belt fixing type, the heat capacity of the fixing belt is reduced because the fixing belt is directly heated by the heating roller. There is a problem that temperature ripple of the fixing belt becomes large when ON / OFF control that is general in the pressure belt system is used for temperature control of the fixing belt.

  For this reason, while using ON / OFF control, phase control, etc., the accuracy of temperature control is improved by changing electric power according to the difference of target temperature and detection temperature. For example, Patent Document 1 discloses a technique for temporarily providing a period in which switching of alternating current supplied to a heating body is not performed in order to suppress harmonic current in heating control of a heater.

  However, these methods have the following three problems.

  The first is the generation of harmonics. When an alternating voltage is applied to a non-linear circuit incorporating a switching element, harmonic current is generated. Since phase control is turned on / off at a high voltage, harmonic distortion tends to be large. On the other hand, since ON / OFF control performs zero cross control which is turned on / off when the power supply voltage is near 0 V, harmonic distortion can be reduced.

  The second is the occurrence of flicker (flickering phenomenon). As described above, in the configuration in which the fixing belt is directly heated, the heat capacity is small, so temperature control is performed in a short cycle. Therefore, the power fluctuates more frequently than the conventional pressure belt method. When the image forming apparatus uses a commercial power supply, voltage fluctuations occur in the commercial power supply line, causing flickers that adversely affect other devices.

  In particular, voltage flicker with high line impedance is larger in on / off control than in phase control. In phase control, the current fluctuation period is 100 Hz or more, and the human eyes do not see flicker. On the other hand, in the ON / OFF control, for example, when 10 half waves are grouped and the first half half waves are turned on and the second half half waves are turned off and power is controlled in 10 steps, the current fluctuation period becomes 10 Hz and flickering occurs It becomes easy to recognize with eyes. Further, as the electric power of the heater increases, the current fluctuation at the time of turning ON / OFF becomes large, so the flicker is further deteriorated.

  The third is the variation in the life of the heater. The lifetime of the heater is determined by the strength of the output of the heater and the lighting time. In the case where the fixing device includes a plurality of heaters, when the heater used for each state transition of image formation is fixed and lighted, the intensity of the output and the lighting time vary for each heater. As a result, the lifetime of the heater also varies.

  If the plurality of heaters are uniformly turned on / off to suppress this variation, the heating will be performed with wattage more than necessary, which causes a new problem such as an increase in overshoot from the target temperature.

  In order to solve these problems, according to Patent Document 2, heating amounts of three heating sources are calculated by PID based on temperatures detected by the three temperature detection units, and the calculated results are corrected to obtain each heating source. A technology for controlling the Further, in Patent Document 3, soft start software that uses phase control to control the heater, gradually increases the energization time to the heater when the heater starts lighting, and gradually reduces the energization time to the heater when the heater is turned off. A stop type technology is disclosed.

  The techniques disclosed in these patent documents can be expected to reduce both harmonics and flicker. However, the problem of reducing the variation in the lifetime of the plurality of heaters has not been solved.

  Therefore, the present invention aims to provide a fixing device having a plurality of heating means, which reduces the occurrence of both harmonics and flicker and suppresses the variation of the life of the plurality of heating means.

    A pressure member that forms a fixing nip portion between the fixing member, the fixing member, a plurality of heating units that heat the fixing member, and a temperature detection unit that detects a surface temperature of the fixing member; And a temperature control means for controlling energization of the heating means based on the surface temperature, wherein the fixing means performs fixing through a recording medium carrying a toner image in the fixing nip portion, the temperature control means comprising The PID control is used for at least one of the heating means, and the ON / OFF control is used for the remaining heating means, and the value calculated by multiplying the duty calculated by the PID control by the number (N) of the plurality of heating means is SUM_DUTY. , Where T is the maximum lighting duty of ON / OFF control, and (1) if SUM_DUTY <T, SUM_DUTY is a heating means using the PID control (2) In the case of T ≦ SUM_DUTY, use ON / OFF control for each of n heating means determined by n ≦ SUM_DUTY / T and n ≦ N−1 (where n is a natural number) The maximum lighting duty (T) is distributed, and the remaining duty is distributed to the heating means using the PID control, and the temperature control means controls the duty per control cycle for each of the plurality of heating means. A fixing device characterized by calculating an accumulated count value which is a sum of fixed periods multiplied by a period, and switching the heating means having the largest accumulated count value among the plurality of heating means to PID control, Resolved.

  In the fixing device of the present invention, at least one of the plurality of heating units is subjected to PID control, and the rest is turned on / off at the maximum lighting duty using the ON / OFF control. As a result, since the number of ON / OFF control of ON / OFF control can be reduced, both harmonics and flicker can be improved.

  In addition, since the cumulative count value is calculated for each of the plurality of heating units, and the heating unit having the largest accumulated count value among the plurality of heating units is switched to PID control, the plurality of heating units can be used equally, and the plurality of heating units can be used. It is possible to suppress the variation in the life of the means.

FIG. 1 is a schematic view showing a cross section of a full color multifunction peripheral that is an embodiment of an image forming apparatus. FIG. 2 is a schematic view of a fixing device mounted on the image forming apparatus. It is a block diagram of a temperature control means. It is a flowchart which shows the switching procedure of the control method of a heater. It is a block diagram which shows the modification of a temperature control means. It is a flowchart which shows the procedure which changes the distribution destination of largest lighting duty (T). It is a flowchart (the 2) which shows the procedure which changes the distribution destination of largest lighting duty (T). It is a flowchart which shows the change procedure of the control method of a heater.

First Embodiment
Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

  FIG. 1 is a schematic view showing a cross section of a full-color multifunction peripheral as an embodiment of the image forming apparatus. The image forming apparatus 200 has an image forming unit 200A at the center of the main body, a sheet feeding unit 200B below the image forming unit 200A, and an image reading unit (not shown) above the image forming unit 200A.

  At the center of the image forming unit 200 A, photosensitive members 205 Y, 205 M, 205 C, and 205 K, which are image carriers, are juxtaposed along the transfer surface of the intermediate transfer belt 213. The photosensitive members 205Y, 205M, 205C, and 205K are respectively constituted by drums rotatable in the same direction (counterclockwise), and are toners of complementary colors (yellow (Y), magenta (M), cyan) (C), carrying a black (K) image. Note that, since these photosensitive members have the same configuration except for the difference in developer (toner) color, in the following description, the suffixes of Y, C, M and K in the reference numerals are appropriately omitted and described.

  Around the photosensitive member 205, a charging device 202, a developing device 203, a cleaning device, and the like are disposed. Further, the primary transfer device 204 is disposed with the intermediate transfer belt 213 interposed therebetween. Furthermore, two light writing devices 201 are provided above the respective photosensitive members 205 to form an image in the process of rotating the respective photosensitive members 205. The developing device 203 contains color toners corresponding to the respective subscripts.

  The intermediate transfer belt 213 is wound around a driving roller and a driven roller, and is movable in the direction of arrow A in the drawing. Therefore, it can move in the same direction as the photosensitive member 205 at the position facing the photosensitive member 205. Further, a secondary transfer roller 215 is provided at a position facing the roller 214 which is one of the driven rollers, with the intermediate transfer belt 213 interposed therebetween.

  Next to the secondary transfer roller 215, a fixing device 206 is provided. The fixing device 206 fixes the toner image carried on the recording medium to the recording medium by applying heat and pressure.

  A paper feed tray 220 is provided in the paper feed unit 200B, and the paper P as a recording medium is stacked on the paper feed tray 220. The sheet P is taken out by the pick roll 221 and conveyed onto the conveyance path 217 by the conveyance roll 222. Then, the sheet is conveyed toward the registration roller 223 and the secondary transfer roller 215 in the direction of the arrow R1 in the drawing.

  A control board 225 is provided in the image forming unit 200A, and a main control unit 226 in the control board 225 controls an operation at the time of image formation. Further, a power supply base 227 for supplying power to the entire apparatus is provided in the sheet feeding unit 200B. A voltage detection circuit 228 in the voltage board 227 detects an operating voltage of the image forming apparatus 200.

  In the image forming apparatus 200 configured as described above, an operation at the time of image formation will be described. First, the sheet P is taken out by the pick roll 221 and conveyed by the conveyance roll 222 and the registration roller 223 in the direction toward the secondary transfer roller 215 on the conveyance path 217.

  Next, while the sheet P is transported, the surface of the photosensitive member 205Y is uniformly charged by the charging device 202Y, and an electrostatic latent image is formed on the photosensitive member 205Y based on image information from an image reading unit (not shown). It is formed.

  Next, the electrostatic latent image is visualized as a toner image by the developing device 203Y containing yellow toner, and the toner image is transferred onto the intermediate transfer belt 213 by the primary transfer device 204Y to which a predetermined bias is applied. Be done. The same image formation is performed with the other photosensitive members 205M, 205C, and 205K only with different toner colors, and toner images of the respective colors are sequentially transferred and superimposed on the intermediate transfer belt 213 by electrostatic force.

  Subsequently, the toner image primarily transferred from the photosensitive member 205 onto the intermediate transfer belt 213 is transferred onto the sheet P conveyed by the roller 214 and the secondary transfer roller 215.

  Next, the sheet P on which the toner image has been transferred is conveyed to the fixing device 206. When the sheet P passes through the fixing device 206, heat and pressure are applied to fix the toner image as a permanent image. Then, the sheet P discharged from the fixing device 206 is delivered to the stacker 216 along the discharge path.

  The above description is an image forming operation for forming a full color image on the sheet P. However, any one of the image forming means may be used to form a single color image, or an image of two or three colors. It can also be formed.

  FIG. 2 is a schematic view of a fixing device mounted on the image forming apparatus. As shown in FIG. 2, the fixing device 206 includes a fixing roller 207, a heating roller 208, a fixing belt 209 which is a fixing member, and a pressure roller 210 which is a pressure member. In addition, the fixing device 206 includes first to third heaters 231, 232 and 233, which are heating means, and a heater 240. Furthermore, the fixing device 206 includes a temperature detection sensor 245 which is a temperature detection means, a temperature control means 250 for controlling energization to the first to third heaters 231, 232 and 233, and the like.

  A fixing belt 209, which is a fixing member, is stretched over the fixing roller 207 and the heating roller 208 with a constant tension. The fixing belt 209 is an endless belt, and its cross section has a two-layer structure in which an elastic layer such as a silicon rubber layer (300 to 500 μm) is formed on a base material such as nickel, stainless steel or polyimide.

  The pressure roller 210 is positioned below the fixing belt 209 and is rotatably pressed against the fixing belt 209. A fixing nip portion is formed by the pressure roller 210 and the fixing belt 209. The pressure roller 210 also has a heater 240 as a heating unit.

  The fixing roller 207 has a structure in which silicon rubber is formed on a metal core metal. The heating roller 208 is a hollow roller made of aluminum or iron, and internally has first to third heaters 231, 232, and 233 as heating means.

  The first to third heaters 231, 232, and 233 control the power supplied from a power supply unit (not shown) by the temperature control unit 250, and each heat the entire surface of the fixing belt 209. The heater 240 is controlled to be turned on / off by a device (not shown), and heats the entire surface of the pressure roller 210.

  A temperature detection sensor 245 is disposed to face the center of the heating roller 208 and detects the surface temperature of the fixing belt 209. For example, a thermistor or the like is used as the temperature detection sensor 245. A plurality of temperature detection sensors may be disposed to detect temperatures at a plurality of locations of the fixing belt 209.

  The temperature control unit 250 is configured by a computer including a CPU, a ROM, a RAM, an I / O, and the like. The temperature control unit 250 controls energization of the first to third heaters 231, 232, and 233 so that the fixing temperature of the fixing belt 209 becomes the target temperature based on the temperature detected by the temperature detection sensor 245.

  The temperature control of the fixing belt 209 detects the surface temperature of the fixing belt 209 by the temperature detection sensor 245, and according to the difference from the target temperature, the ratio of the energization time to the heater per unit time (hereinafter referred to as control cycle) Hereinafter, a method of changing the duty) is generally used. For this reason, a method is employed in which power is varied according to the difference between the target temperature and the detected temperature while using ON / OFF control or phase control.

  However, although ON / OFF control can suppress the generation of harmonics, fluctuation of power in a short cycle causes flicker. On the other hand, phase control is effective to suppress flicker, but since phase control is turned on / off at a high voltage, generation of harmonics becomes a problem. As described above, it has been difficult to properly control the temperature of the fixing belt 209 while suppressing the generation of harmonics and flickers.

  Therefore, in the present embodiment, PID control is used for at least one of the first to third heaters 231, 232, and 233, and ON / OFF control is used for the remaining heaters. Then, after calculating the duty necessary to heat the fixing belt 209, the duty is preferentially distributed to the heater using ON / OFF control, and the remaining is distributed to the heater using PID control. That is, the control method used for the plurality of heaters is changed based on the calculated duty value. Thus, the temperature control of the fixing belt 209 is properly performed while suppressing the generation of harmonics and flickers.

  The ON / OFF control in this embodiment is control for turning on the heater when the detected temperature is lower than a predetermined target temperature and turning off the heater when the detected temperature is higher.

  FIG. 3 is a block diagram of temperature control means according to the present embodiment. As shown in FIG. 3, the temperature control unit 250 includes a feedback unit 255, a main control unit 260, and first to third heater control units 271, 272, and 273.

The feedback unit 255 obtains a difference value (= T _ref −T _cur ) from the target value (T _ref ) of the fixing temperature of the fixing belt 209 and the current temperature (T _cur ) of the fixing belt 209 detected by the temperature detection sensor 245. calculate. Then, the calculated difference value is sent to the main control unit 260.

  The main control unit 260 calculates the duty using the sent difference value and any one of the first to third heater control units 271, 272, 273 and the PID control parameter. Since the first to third heaters 231, 232, and 233 heat the entire surface of the fixing belt 209, the first to third heaters can be regarded as one heater. Therefore, the duty calculated by any one of the first to third heater control units 271, 272, and 273 is multiplied by three to calculate the total duty (SUM_DUTY).

  Then, based on the calculated total duty (SUM_DUTY), the main control unit 260 determines the control method of the first to third heaters 231, 232, and 233, and the duty to be distributed to the respective heaters.

  There are two control methods, and either "PID control" or "ON / OFF control" is used. In "ON / OFF control", the maximum lighting duty (T) is distributed, or the duty is not distributed. In the "PID control", the remaining duty distributed to the "ON / OFF control" is distributed. The distribution method of the total duty (SUM_DUTY) will be described later.

  The main control unit 260 sends the determined control method and the distributed duty to the first to third heater control units 271, 272, 273.

  The first to third heater control units 271, 272, 273 receive information on the control method and the duty to be distributed. Then, energization of the first to third heaters 231, 232 and 233 is controlled at a predetermined duty using a predetermined control method, and the fixing belt 209 is heated.

  Subsequently, the operation of the temperature control means 250 will be described. As an example, the control method of the first heater 231 is PID control, and the maximum lighting duty (T) of the ON / OFF control is 100%.

First, the temperature control means 250 calculates a difference (= T _ref −T _cur ) from the target value (T _ref ) of the fixing temperature of the fixing belt 209 and the current temperature (T _cur ) of the fixing temperature detected by the temperature detection sensor 245. Calculate). Next, the temperature control means 250 calculates the duty (DUTY1) of the first heater 231 using the calculated difference value and the parameter of the PID control of the first heater control unit 271.

  Next, the temperature control means 250 calculates the total duty (SUM_DUTY). The total duty (SUM_DUTY) is a value (SUM_DUTY = 3 × DUTY1) obtained by multiplying the duty (DUTY1) of the first heater 231 by three.

  From the total duty (SUM_DUTY), the duty distributed to the first to third heater control units 271, 272, 273 is determined as follows.

(1) When the total duty (SUM_DUTY) is smaller than the maximum lighting duty (T) of the ON / OFF control (SUM_DUTY <T) The total duty (SUM_DUTY) is distributed only to the first heater control unit 271 using PID control. . In addition, the second and third heaters 232 and 233 are not energized (no light).

(2) When the total duty (SUM_DUTY) is equal to or greater than the maximum lighting duty (T) of the ON / OFF control (T ≦ SUM_DUTY)
Assuming that n is a natural number, the control method of n heaters determined by n ≦ SUM_DUTY / T and n ≦ 2 is ON / OFF control, and the maximum lighting duty (T) is distributed.
The remaining duty (SUM_DUTY−n × T) is distributed to the first heater control unit 271 using PID control.

  As a specific example, the case where the duty (DUTY1) of the first heater 231 is 30% (case 1), 80% (case 2), and 40% (case 3) will be described.

  Case 1 assumes that the image forming apparatus 200 is on standby. When the duty (DUTY1) of the first heater 231 is 30%, the total duty (SUM_DUTY) is 90% (= 30% × 3). Since the total duty (SUM_DUTY) is smaller than the maximum lighting duty (T = 100%) of the ON / OFF control, 90% of the duty is distributed to the first heater control unit 271 using PID control, and the second and third The heaters 232 and 233 are not energized (no light).

  In this case, since the number of heaters to be lit by PID control is one, generation of harmonics is small.

  Case 2 assumes that the image forming apparatus 200 starts up (when the power is turned on). When the duty (DUTY1) of the first heater 231 is 80%, the total duty (SUM_DUTY) is 240% (= 80% × 3). This is because the total duty (SUM_DUTY) is larger than the maximum lighting duty T (100%) of the on / off control. Therefore, the duty of 100% is distributed to the second and third heater control units 272 and 273 using ON / OFF control, and the remaining 40% of the duty is distributed to the first heater control unit 271 using PID control.

  In this case, since the second and third heaters 232 and 233 are turned on / off at the maximum lighting duty (T = 100%) and turned on, the number of times of ON / OFF is reduced, and the occurrence of flicker can be suppressed. Further, the temperature ripple which causes a problem in the ON / OFF control can be suppressed by the first heater 231 using the PID control.

  Case 3 assumes that the image forming apparatus 200 is in the process of passing paper. When the duty (DUTY1) of the first heater 231 is 40%, the total duty (SUM_DUTY) is 120% (= 40% × 3). This is because the total duty (SUM_DUTY) is larger than the maximum lighting duty (T = 100%) of the on / off control. Therefore, the duty of 100% is distributed to the second heater control unit 272 using ON / OFF control, and the remaining 20% of the duty is distributed to the first heater control unit 271 using PID control. Then, the third heater 233 is not energized (no light). Note that the duty of 100% may be distributed to the third heater control unit 273 and the second heater 232 may not be energized (no light).

  In this case, since the number of heaters to be lit can be limited, the generation of harmonics and flicker can be suppressed. In addition, since the first heater control unit 271 using PID control can finely turn on / off, it is possible to improve the followability to the target fixing temperature.

The above contents are shown in Table 1.

  As described above, the temperature control unit 250 provided in the fixing device 206 of the present embodiment switches and uses two types of “PID control” or “ON / OFF control” to control a plurality of heaters. Then, the calculated total duty (SUM_DUTY) is distributed prior to ON / OFF control, and the remaining is distributed to PID control. Thus, the heater using the ON / OFF control can be turned on at the maximum lighting duty (T), so the number of times of ON / OFF can be reduced, and the occurrence of flicker can be suppressed.

  Further, since the temperature control means 250 can perform precise temperature control by PID control, it is possible to suppress temperature ripples which become a problem in ON / OFF control, and to improve the followability of the target fixing temperature. Furthermore, since the number of heaters to be used is limited when distributing the total duty (SUM_DUTY), the generation of harmonics and flickers can be suppressed.

  Then, the method to suppress the dispersion | variation in the lifetime of several heater is demonstrated. The life of the heater is determined by the duty of the heater and the lighting time. Normally, the ON / OFF control that lights up at the maximum lighting duty has a larger output and a longer lighting time than PID control. Therefore, it is desirable to switch ON / OFF control and PID control according to the duty and lighting time of the heater in order to suppress the variation in the life of the plurality of heaters.

  Therefore, the temperature control unit 250 of the present embodiment switches the control method of the plurality of heaters under prescribed conditions. Specifically, first, for each heater, a sum (hereinafter, referred to as an accumulated count value) of a value obtained by multiplying the duty for each control cycle by the control cycle is calculated. Then, the heater using PID control is determined based on the cumulative count value of each heater and the number of heaters.

Table 2 shows an example of cumulative count values of the first to third heaters.

  As shown in Table 2, the control cycle of the first to third heater control units 271, 272, 273 is 100 (msec), and the accumulated count value up to 1500 (msec) is obtained. The duty of the first heater control unit 271 using the ON / OFF control is always 100%. Further, the duty of the second heater control unit 272 using PID control is changed for each control cycle. The duty of the non-lighting third heater control unit 273 is always 0%. The cumulative count value after the elapsed time 1500 (msec) is 150000 for the first heater control unit 271, 87500 for the second heater control unit 272, and 0 for the third heater control unit 273.

  A large cumulative count value indicates that the heater has a high output for a long time, so it is desirable that heaters using PID control should be preferentially selected from among a plurality of heaters with a large cumulative count value. .

  For example, Table 3 shows the results when the duty (DUTY2) of the second heater control unit 272 is 90% and the total duty (SUM_DUTY) is 270%.

  As shown in Table 3, the first heater control unit 271 is newly switched to PID control, and ON / OFF control is used for the second and third heater control units 272 and 273.

  Also, for example, when the total duty (SUM_DUTY) is 90%, the number of heaters using PID control may be one or plural. That is, the number of heaters using PID control may be determined based on the number of heaters along with the accumulated count value.

  FIG. 4 is a flowchart showing a switching procedure of the control method of the heater. First, in step S1, the temperature control unit 250 receives a start-up execution signal from the main body control unit 226 that controls the overall operation of the image forming apparatus 200. Next, in step S2, the temperature control unit 250 selects a heater having a large cumulative count value among the plurality of heaters. Next, in step S3, PID control is used for the selected heater. Then, the process proceeds to step S4, and the temperature control unit 250 starts temperature control of the fixing member.

  In step S1, the signal received by the temperature control means 250 is not limited to the start-up execution signal. The control method of the heater may be selected in response to signals at the time of state transition such as before paper passing, after paper passing, and waiting.

  As described above, the temperature control unit 250 of the present embodiment calculates the cumulative count value, and uses PID control to control the heater with the largest cumulative count value. The intensity of the outputs of the plurality of heaters and the lighting time can be accurately grasped by the accumulated count value, and the control of the heaters can be switched appropriately. Therefore, the plurality of heaters can be used evenly, and variations in the lifetime of the heaters can be suppressed.

(Modification)
FIG. 5 is a block diagram showing a modification of the temperature control means. In FIG. 5, the same components as those in FIG. 3 are denoted by the same reference numerals, and the detailed description thereof is omitted. As shown in FIG. 5, the temperature control means 250a may set the number of heaters to N (N is a natural number). Indicates the change point at that time.
As an example, the control method of the first heater 231 is PID control, and the maximum lighting duty (T) of the ON / OFF control is 100%.

  In the main control unit 260a, the total duty is calculated as SUM_DUTY = N × DUTY1. From the total duty (SUM_DUTY), the duty distributed to the first to n-th heater control units 271, 272, ..., 27n is determined as follows.

(1) When the total duty (SUM_DUTY) is smaller than the maximum lighting duty (T) of ON / OFF control (SUM_DUTY <T)
The total duty (SUM_DUTY) is distributed only to the first heater control unit 271. Also, the second to nth heaters 232,..., 23n are not energized (no light).

(2) When the total duty (SUM_DUTY) is equal to or greater than the maximum lighting duty (T) of the ON / OFF control (T ≦ SUM_DUTY)
Assuming that n is a natural number, a control method of n heaters determined by n ≦ SUM_DUTY / T and n ≦ N−1 is ON / OFF control, and the maximum lighting duty (T) is distributed.
The remaining heater control method is PID control, and the remaining duty (SUM_DUTY-N × T) is distributed.
Note that at least one heater using PID control is used.

  As described above, even if the number of heaters is N, two controls of "PID control" or "ON / OFF control" can be switched and used. Further, the cumulative count value may be calculated for N heaters, and PID control may be used to control the heater having a large cumulative count value. As a result, even if the number of heaters is N, the same effect as in the previous embodiment can be obtained.

Second Embodiment
When the glass tube of the heater is heated above the heat resistant temperature (T _h ), its life is drastically reduced. For example, when thick paper or the like is passed, the required power is increased, and the heater which is turned on using the ON / OFF control is turned on for a long time at the maximum lighting duty (T). Therefore, the temperature of the glass tube becomes higher than the heater that is turned on using PID control, and the life of the glass tube is reduced.

Therefore, in the present embodiment, in the fixing device described in the first embodiment, the time during which the plurality of heaters using the ON / OFF control are lighted at the maximum lighting duty (T) is counted. And when it lights on more than continuous lighting time (U), a distribution place of maximum lighting duty (T) is changed to a plurality of heaters using ON / OFF control. This prevents the temperature of the glass tube of the heater from reaching the heat resistant temperature (T _h ) and improves the life of the heater.

  The fixing device according to the present embodiment is the same as the fixing device according to the first embodiment (see FIG. 2), and can be mounted on the image forming apparatus according to the first embodiment (see FIG. 1). Further, the block diagram of the temperature control unit according to the present embodiment is the same as the block diagram (see FIG. 3) of the temperature control unit according to the first embodiment.

  Hereinafter, the procedure of changing the distribution destinations of the maximum lighting duty (T) for a plurality of heaters using ON / OFF control will be described in detail.

  FIG. 6 is a flowchart showing a procedure of changing the distribution destination of the maximum lighting duty (T).

  First, in step S1, the temperature control means 250 determines whether or not there is a heater whose duty is the maximum lighting duty (T) among the plurality of heaters using the ON / OFF control. If there is such a heater (in the case of YES), the process proceeds to step S2, and if not (in the case of NO), the process returns to step S1.

  In step S2, the temperature control unit 250 counts the elapsed time of the heater lit at the maximum lighting duty (T), and determines whether the value is equal to or longer than the continuous lighting time (U). If U or more has elapsed (in the case of YES), the process proceeds to step S3, and if it has not elapsed (in the case of NO), the process returns to step 2.

  In step S3, the temperature control means 250 selects the heater with the smallest total of the lighting count value during the latest continuous lighting time (U) among the plurality of heaters using the ON / OFF control. Here, the lighting count value is a value obtained by multiplying the duty for each elapsed time by the count cycle.

  Subsequently, the process proceeds to step S4, and the temperature control means 250 distributes the maximum lighting duty (T) to the heater with the smallest sum of the lighting count values. At the same time, the duty is not distributed (turned off) to the heaters that are lit for the continuous lighting time (U) or more at the maximum lighting duty (T). Then, the process ends.

  Table 4 shows an example of the duty and the lighting count value for each elapsed time of the first to third heaters.

  Here, the maximum lighting duty is T = 100%, the continuous lighting time is U = 15.0 (s), and the count cycle is 1000 (ms).

  As shown in Table 4, ON / OFF control is used for the second and third heater control units 272 and 273. While the elapsed time is between 1.0 s and 15.0 s, the second heater control unit 272 lights up at the maximum lighting duty (T = 100%), while the third heater control unit 273 has a duty of 0% (lights out) It is.

  In addition, the second heater control unit 272 has elapsed for the continuous lighting time (U = 15.0s) or more, and the third heater control unit 273 has the total of the lighting count values of 0 in the latest continuous lighting time (U). is there. Therefore, the duty of 100% is distributed to the third heater control unit 273, and the duty is not distributed to the second heater control unit 272.

As described above, the fixing device according to the present embodiment counts the time during which the lighting is performed with the maximum lighting duty (T) of the plurality of heaters using the ON / OFF control. And when it lights on more than continuous lighting time (U), a distribution place of maximum lighting duty (T) is changed to a plurality of heaters using ON / OFF control. As a result, the temperature of the glass tube of the heater can be prevented from reaching the heat resistant temperature (T _h ), and the lifetime of the heater can be improved.

(Modification)
Among the plurality of heaters using the ON / OFF control, the plurality of heaters may be turned on at the maximum lighting duty (T). The case will be described.

  FIG. 7 is a flowchart (part 2) showing the procedure for changing the distribution destination of the maximum lighting duty (T).

  In the flowchart of FIG. 7, steps S1 and S2 are the same as steps S1 and S2 of the flowchart of FIG.

  In step S3, the temperature control means 250 orders the heaters in ascending order of the total of the lighting count value in the latest continuous lighting time U among the plurality of heaters using the ON / OFF control.

  Next, the process proceeds to step S4, and the temperature control means 250 distributes the maximum lighting duty (T) in order from the heater having the smallest total of the lighting count values, as ordered. At the same time, the duty is not distributed (turned off) to the heaters that are lit for the continuous lighting time (U) or more at the maximum lighting duty (T). Then, the process ends.

  As a result, even when there are a plurality of heaters that light up at the maximum lighting duty (T) among the plurality of heaters using the ON / OFF control, it is possible to determine the distribution destination of the maximum lighting duty (T).

As described above, if the distribution destinations of the maximum lighting duty (T) are changed with respect to the plurality of heaters in which the ON / OFF control is used, the temperature of the glass tube of the heater reaches the heat resistant temperature (T _h ) You can prevent. However, when the amount of heat required to fix the toner image is small, such as thin paper or monochrome printing, the temperature of the glass tube of the heater is unlikely to reach the heat resistant temperature (T _h ). Therefore, it is determined whether the distribution destination of the maximum lighting duty (T) is to be changed, based on the division of the sheet thickness and / or the image pattern fixed to the sheet.

  Table 5 shows the relationship between the paper thickness division and the first changeover switch.

  In Table 5, the paper thickness division is the division of the paper to be printed into five stages according to the size of the basis weight. When the first changeover switch is ON, the distribution destination of the maximum lighting duty (T) is changed, and when the first changeover switch is OFF, the distribution destination of the maximum lighting duty (T) is not changed.

The sheets of paper thickness divisions 1 and 2 are thin paper, and the amount of heat required for fixing is small. Since the glass tube of the heater is unlikely to be heated beyond the heat resistance temperature (T _h ), the first changeover switch is turned off. On the other hand, the paper having three to five paper thickness divisions is thick paper, and the amount of heat required for fixing is large. Since there is a high possibility that the glass tube of the heater is heated beyond the heat resistant temperature (T _h ), the first changeover switch is turned on.

  The divisions of these sheet thicknesses are sent from the main body control unit 226 in the image forming apparatus 200 to the temperature control means 250. The temperature control means 250 determines whether or not the distribution destination of the maximum lighting duty (T) is to be changed by the first changeover switch determined by the division of the sheet thickness.

  Table 6 shows the relationship between the image pattern and the second changeover switch.

  In Table 6, there are two image patterns fixed to the paper: monochrome mode and full color mode. Further, the ON / OFF of the second changeover switch works the same as the ON / OFF of the changeover switch 1.

  When the image pattern is in the monochrome mode, the amount of heat required to fix the toner image is small, so the second switch is turned off. On the other hand, in the case of the full color mode, since the amount of heat required for fixing the toner image is large, the second changeover switch is turned on.

  The mode of the image pattern is sent from the body control unit 226 in the image forming apparatus 200 to the temperature control unit 250. The temperature control means 250 determines whether or not the distribution destination of the maximum lighting duty (T) is to be changed by the second changeover switch determined by the image pattern.

  Note that it is also possible to determine whether or not to change the distribution destination by using both the paper thickness division and the image pattern. For example, if at least one of the first changeover switch and the second changeover switch is ON, the distribution destination may be changed.

  As a result, the temperature control means 250 does not change the distribution destination depending on the paper thickness division and / or the image pattern, so the load such as the calculation process of the lighting count can be reduced.

  By the way, it is desirable that the temperature control means 250 is provided with a storage device such as a flash memory, and can store control log data such as the operation time of each heater and the number of times PID control or ON / OFF control is applied. If the data of the storage device is read, the plurality of heater operating states can be grasped, and the maintainability of the product can be improved.

Third Embodiment
Also in the present embodiment, it is an object of the present invention to prevent the temperature of the glass tube of the heater from reaching the heat resistant temperature (T _h ) and to improve the lifetime of the heater. Specifically, the control method of the plurality of heaters is changed according to the cumulative number of sheets from the start of sheet passing. In addition, a heater control pattern set in advance is used to change the control method.

  The fixing device according to the present embodiment is the same as the fixing device according to the first embodiment (see FIG. 2), and can be mounted on the image forming apparatus according to the first embodiment (see FIG. 1). Further, the block diagram of the temperature control unit according to the present embodiment is the same as the block diagram (see FIG. 3) of the temperature control unit according to the first embodiment.

  First, the heater control pattern will be described. The heater control pattern is a table of combinations of a plurality of heater control methods set in advance. A table of this combination is stored in the ROM of the temperature control means 250. The temperature control means 250 reads this table and changes the control method of the plurality of heaters.

  Table 7 shows heater control patterns when there are three heaters.

  As shown in Table 7, there are three heater control patterns. For example, in the heater control pattern (No. 1), the first heater control unit 271 uses PID control, and the second and third heater control units 272 and 273 use ON / OFF control. In addition, the maximum lighting duty (T) is preferentially distributed to the heaters described as (excellent) in the ON / OFF control. That is, when only one heater is turned on by ON / OFF control, the maximum lighting duty (T) is distributed to the second heater control unit 272. The same applies to the heater control patterns (No. 2) and (No. 3).

  The temperature control means 250 reads the heater control pattern in the order of (No. 1) → (No. 2) → (No. 3) → (No. 1) ... and changes the control method of each heater. The timing of switching is determined by the cumulative number of sheets from the start of sheet passing. Details of the switching timing will be described later.

  There are two points to be noted in setting the heater control pattern. The first one is that ON / OFF control and preferential distribution of the maximum lighting duty (T) are not continuous for each heater. The second is that PID control does not continue for each heater.

  The first reason is that when the maximum lighting duty (T) is distributed in the ON / OFF control, the temperature of the glass tube of the heater is greatly increased. Therefore, the heater to which the maximum lighting duty (T) is distributed by the ON / OFF control does not preferentially distribute the maximum lighting duty (T) even if the next control method is PID control or ON / OFF control. Or any of the above. Thereby, the temperature of the glass tube of a heater can be reduced.

  The second reason is to refrain from continuous use of PID control which repeats on / off more frequently than on / off control.

  In Table 7, the second heater control unit 272 uses ON / OFF control in the heater control pattern (No. 1), and the maximum lighting duty (T) is preferentially distributed. In 2), PID control is used. And in heater control pattern (No. 3), ON / OFF control is used so that PID control may not continue.

  FIG. 8 is a flowchart showing the procedure of changing the control method of the heater.

  Here, a heater control pattern shown in Table 7 is used as the heater control pattern. And control of the 1st-3rd heater control parts 271, 272, and 273 makes a heater control pattern (No. 1). That is, PID control is used for the first heater control unit 271, and ON / OFF control is used for the second and third heater control units 272 and 273. Further, it is assumed that the maximum lighting duty (T) is distributed to the second heater control unit 272, but the duty is not distributed to the third heater control unit 273.

  First, in step S1, the temperature control unit 250 receives an instruction to start sheet passing from the main body control unit 226 in the image forming apparatus 200, and counts the cumulative number of sheets (L) for each sheet passing.

Next, the process proceeds to step S2, and the temperature control means 250 determines whether or not the cumulative sheet number (L) from the start of sheet passing is _{equal to} or more than the threshold number (L _TH ). If it is greater than the threshold number (L _TH ) (if YES), the process proceeds to step S3, and if it is not greater than the threshold number (L _TH ) (if NO), the process returns to step S1.

The threshold number of sheets (L _TH ) is determined by the configuration of the fixing device, but in the present embodiment, the number is set to 200 in A4Y conversion as an example. The threshold number (L _TH ) is stored in the ROM of the temperature control unit 250.

  Next, in step 3, the temperature control means 250 reads the heater control pattern (No. 2) and changes the control method of each heater. That is, the first heater control unit 271 is changed to ON / OFF control, the second heater control unit 272 is changed to PID control, and the third heater control unit 273 is maintained to ON / OFF control. However, the duty is not distributed to the first heater control unit 271, and the maximum lighting duty (T) is distributed to the third heater control unit 273.

  The temperature of the glass tube of the second heater 232 is lowered by changing the second heater control unit 272 in which the ON / OFF control is used and the maximum lighting duty (T) is distributed to PID control.

  Next, the process proceeds to step 4 and the temperature control unit 250 changes the heater control pattern to the next control pattern (heater control pattern (No. 3)).

  Then, the process goes to step 5, the temperature control means 250 resets the accumulated sheet number (L) to zero, and the process ends.

As described above, the fixing device according to the present embodiment switches the heater control pattern when the accumulated sheet number (L) from the start of sheet passing is equal to or more than the threshold number (L _TH ). In addition, since the heater control pattern is set so that the maximum lighting duty (T) is not continuously distributed to each heater by ON / OFF control, if the heater control pattern is changed, the glass of the heater is The temperature of the tube decreases. As a result, the temperature of the glass tube of the heater can be prevented from reaching the heat resistant temperature (T _h ), and the lifetime of the heater can be improved.

  Table 8 shows heater control patterns when there are four heaters.

  As shown in Table 8, there are four heater control patterns. For example, in the heater control pattern (No. 1), the first heater control unit uses PID control, and the second to fourth heater control units use on / off control. In addition, the maximum lighting duty (T) is distributed preferentially to the second and fourth heaters that are written (excellent) in the ON / OFF control. The same applies to the heater control patterns (No. 2), (No. 3) and (No. 4).

  The temperature control means 250 reads the heater control pattern in the order of (No. 1) → (No. 2) → (No. 3) → (No. 4) → (No. 1). change.

  As described above, even if the number of heaters is four, (1) the maximum lighting duty (T) is not continuously distributed to each heater by the ON / OFF control, and (2) each heater is In contrast, the heater control pattern may be set so that PID control does not continue. This is the same even if the number of heaters is five or more.

With such a heater control pattern, even if the heater has the maximum lighting duty (T) distributed by ON / OFF control, if the heater control pattern is switched, the temperature of the glass tube of the heater tends to decrease, and the glass It is possible to prevent the temperature of the tube from reaching the heat resistant temperature (T _h ).

As described above, when the cumulative sheet number (L) from the start of sheet passing is equal to or more than the threshold number (L _TH ), the control method is changed for a plurality of heaters. However, in order for the temperature of the glass tube of the heater to have a sufficient safety margin with respect to the heat resistant temperature (T _h ), the temperature of the fixing member, the length in the sheet conveyance direction, the basis weight of the sheet, and / or the operating voltage It is desirable to correct the accumulated sheet number (L) by These are described below.

(Temperature of fixing member)
As can be seen from FIG. 3 described above, the current temperature (T _cur ) of the fixing member (fixing belt 209) is detected by the temperature detection sensor 245. Further, the target temperature (T _ref ) of the fixing member is generated by the temperature control means 250.

Here, when the current temperature (T _cur ) of the fixing member becomes larger than the target temperature (T _ref ), the temperature of the glass tube of the heater also rises. Therefore, the current temperature _{(T cur)} and the target temperature of the fixing member _{(T ref),} the temperature control means 250 multiplies the correction value to the accumulated paper feeding sheets from the sheet passing the start (L). Table 9 shows correction values for the current temperature of the fixing member.

As shown in Table 9, when the current temperature (T _cur ) of the fixing member at the start of sheet _feeding is equal to or lower than the target temperature (T _ref ), the temperature of the glass tube of the heater is lower than the heat resistant temperature (T _h ). Therefore, the correction value is set to 1.0 (not corrected). On the other hand, when the current temperature (T _cur ) of the fixing member at the start of sheet passing is higher than the target temperature (T _ref ), the temperature of the glass tube of the heater is close to the heat resistant temperature (T _h ). Therefore, the accumulated sheet number (L) is multiplied by 1.2 which is a correction value. By multiplying the correction value, the control method of the heater is changed at an early timing, so that the temperature of the glass tube of the heater can have a sufficient safety margin with respect to the heat resistant temperature (T _h ).

(Length in the paper conveyance direction)
As the length of the sheet in the transport direction increases, the contribution to the temperature rise of the glass tube per sheet increases. Therefore, the temperature control means 250 multiplies the accumulated sheet count (L) from the start of sheet feeding by the correction value according to the length in the sheet conveyance direction. Table 10 shows correction values for the sheet conveyance direction length.

  As shown in Table 10, the length in the sheet conveyance direction is determined by the sheet size. Here, a correction value for the accumulated number of sheets (L) from the start of sheet passing when the sheet (A4Y) is passed is set to 1.0, and this is used as a reference. For example, for a sheet (A3T) whose length in the transport direction is 2.0 times that of the sheet (A4Y), the correction value is set to 2.0. On the other hand, for a sheet (A6T) whose correction length is shorter than that of the sheet (A4Y), the correction value is set to 0.7. Also in the case of correcting by the length in the sheet conveyance direction, the same effect as the correction by the temperature of the fixing member is obtained.

(Paper basis weight)
As the basis weight of the sheet increases, the contribution to the temperature rise of the glass tube per sheet increases. Therefore, the temperature control means 250 multiplies the accumulated sheet count (L) from the start of sheet passing by the correction value according to the basis weight of the sheet. Table 11 shows correction values for paper basis weight.

  As shown in Table 11, a correction value for the cumulative number of sheets (L) from the start of sheet feeding when the sheet thickness E (basis weight: 163.1 to 220.0 gsm) is passed is set to 1.0. Based on For example, for a sheet whose basis weight is smaller than the sheet thickness E, such as a sheet thickness G (basis weight: 256.1 to 300.0 gsm), the correction value is set to 1.2. On the other hand, for a sheet whose basis weight is smaller than the sheet thickness E, such as the sheet thickness A (basis weight: 52.3 to 63.0 gsm), the correction value is set to 0.6. In the case of correcting by the basis weight of the sheet, the same effect as the correction by the temperature of the fixing member can be obtained.

(Operating voltage)
The power (W) for operating the image forming apparatus 200 is supplied by the voltage board 227. As the power (W) increases, the contribution to the temperature rise of the glass tube increases. Therefore, the temperature control unit 250 multiplies the accumulated sheet count (L) from the start of sheet feeding by the correction value by the operating voltage of the image forming apparatus 200 detected by the voltage detecting circuit 228. Table 12 shows correction values for the detected voltage.

  As shown in Table 12, when the voltage (V) at the start of sheet feeding is smaller than 95% of the standard voltage, the power (W) used to fix one sheet of paper decreases, and thus the glass tube The temperature is hard to rise. Therefore, the correction value is set to 0.9. On the other hand, if the voltage (V) at the start of paper passing is greater than 105% of the standard voltage, the power (W) used to fix one sheet of paper increases, so the temperature of the glass tube tends to rise . Therefore, the correction value is set to 1.1. If the voltage (V) at the start of sheet feeding is 95% or more of the standard voltage and 105% or less of the standard voltage, the correction value is set to 1.0 and no correction is made. Also in the case of correcting with the operating voltage, the same effect as the correction by the temperature of the fixing member can be obtained.

  The correction values shown in Tables 9 to 12 may be changed as appropriate depending on the configuration of the fixing device and / or the image forming apparatus.

  By the way, the printing operation of the image forming apparatus may be interrupted due to a user's instruction, paper jamming, or the like. When the toner adhesion amount adjustment is performed when it is interrupted during the sheet passing to the fixing device, the duty distributed to each heater decreases from the sheet passing time, and the temperature of the glass tube also decreases. Therefore, when the interruption operation is performed during sheet passing, the temperature control means 250 changes the control method regardless of the number of sheets passing.

In addition, when the cumulative sheet number (L) from the start of sheet passage becomes equal to or more than the threshold number (L _TH ), or when the interruption operation is inserted during the sheet passage, the temperature control means 250 starts the sheet passage. Reset the cumulative sheet count (L) of. Thereby, it is possible to continuously change the control method based on the cumulative number of sheets (L) from the start of sheet passing.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. For example, the fixing device or the image forming apparatus may be provided with all the technical features described in the first to third embodiments.

200 image forming apparatus 200A image forming unit 200B sheet feeding unit 201 light writing device 202 charging device 203 developing device 204 primary transfer device 205 primary transfer device 205 fixing device 207 fixing roller 208 heating roller 209 fixing belt 210 pressure roller 213 intermediate transfer belt 214 roller 215 secondary transfer roller 216 stacker 217 conveyance path 220 paper feed tray 221 pick roll 222 conveyance roll 223 registration roller 225 control base 226 main body control section 227 power supply base 228 voltage detection circuit 231 first heater 232 second heater 233 second 3 heater 23 n n heater 240 heater 245 temperature detection sensor 250, 250 a temperature control means 255 feedback unit 260, 260 a main control unit 271 first heater Control unit 272 the second heater control unit 273 third heater control unit 27n n-th heater controller

Patent No. 5424066 specification Patent No. 4685514 specification Patent No. 538 1000 specification

Claims (13)

A pressure member that forms a fixing nip portion between the fixing member, the fixing member, a plurality of heating units that heat the fixing member, and a temperature detection unit that detects a surface temperature of the fixing member; A temperature control unit for controlling energization of the heating unit on the basis of the surface temperature, and performing fixing through a recording medium carrying a toner image in the fixing nip portion;
The temperature control means uses PID control for at least one of the plurality of heating means, and uses ON / OFF control for the remaining heating means.
A value obtained by multiplying the duty calculated by the PID control by the number (N) of the plurality of heating units is set as SUM_DUTY, and the maximum lighting duty of the ON / OFF control is set as T.
(1) If SUM_DUTY <T, distribute SUM_DUTY only to the heating means using the PID control,
(2) In the case of T ≦ SUM_DUTY, the maximum lighting duty (T using ON / OFF control for each of n heating means determined by n ≦ SUM_DUTY / T and n ≦ N−1 (where n is a natural number)) And distributing the remaining duty to the heating means using the PID control,
Furthermore, the temperature control means calculates, for each of the plurality of heating means, an accumulated count value which is the sum of a fixed period of a value obtained by multiplying the duty of each control cycle by the control cycle. A fixing device characterized in that the heating means having the largest accumulated count value is switched to PID control.   There are a plurality of heating means using the ON / OFF control, and among the plurality of heating means using the ON / OFF control, the heating means which is continuously lit at the maximum lighting duty (T) and for the continuous lighting time (U) or more The fixing device according to claim 1, wherein the temperature control unit changes a distribution destination of the maximum lighting duty (T) with respect to the plurality of heating units using the ON / OFF control.   Among the plurality of heating means using the ON / OFF control, heating is the smallest in total of lighting count values which is a value obtained by multiplying the duty for each elapsed time by the count cycle among the most recent continuous lighting time (U) The fixing device according to claim 2, wherein the maximum lighting duty (T) is distributed to the means.   The fixing device according to claim 2, wherein the temperature control unit determines whether to change the distribution destination of the maximum lighting duty (T) based on the basis weight of the recording medium.   The temperature control means determines whether or not to change the distribution destination of the maximum lighting duty (T) based on the image pattern fixed on the recording medium. The fixing device described in.   The fixing device according to any one of claims 1 to 5, wherein the temperature control unit includes a storage device, and stores control log data of the plurality of heating units in the storage device. The temperature control means changes the control method for the plurality of heating means, where L ≧ L _th where L is the cumulative number of sheets from the start of paper passing and L _th is the threshold number of sheets. The fixing device according to any one of claims 1 to 6, wherein   The fixing device according to claim 7, wherein the temperature control unit corrects the accumulated number of sheets in accordance with a current temperature and a target temperature of the fixing member at the start of sheet passing.   The fixing device according to claim 7, wherein the temperature control unit corrects the accumulated sheet number according to a basis weight of the recording medium.   An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.   A fixing device according to any one of claims 7 to 9, and a voltage detection circuit for detecting an operating voltage, wherein the temperature control means corrects the accumulated number of sheets by the operating voltage. Image forming device.   12. The image forming apparatus according to claim 11, wherein the temperature control unit changes control methods for the plurality of heating units by interrupting operation. 13. The image forming apparatus according to claim 11, wherein the temperature control unit resets the accumulated sheet number when L ≧ L _th or in an interruption operation.

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