Energization control device and image forming apparatus

Abstract

To correctly control turn-on and turn-off of a heater even if the cycle of AC voltage is disturbed.SOLUTION: An energization control device 81 comprises: triacs 86, 87 that turn on and off energization to a fixing heater 31 that generates heat upon energization at a zero-cross point of AC voltage; a triac driving circuit 82 that drives the triacs 86, 87 to cause the triacs 86, 87 to turn on the energization at the zero-cross point of the AC voltage; an AC half wave detection unit 83 that detects if the AC voltage is positive or negative; and a printing control unit 103 that identifies a positive period during which the AC voltage is positive and a negative period during which the AC voltage is negative from a result of the detection, and causes the triac driving circuit 82 to drive the triacs 86, 87 at a first timing included in the positive period or a second timing included in the negative period.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to an energization control device and an image forming apparatus. [Background technology]

[0002] In an image forming apparatus utilizing an electrophotographic process, a toner image, which is a developer image transferred onto a medium, is heated by a heater serving as a heat source, thereby fixing the toner image onto the medium. Conventionally, image forming apparatuses perform phase control by detecting zero-cross points of an AC (Alternating Current) voltage using a zero-cross circuit and controlling the on / off of a heater based on the detected zero-cross points. (See, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-1016 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when controlling the on / off of the heater in accordance with the cycle of the AC voltage (for example, a 10 ms cycle), if the cycle of the AC voltage is disrupted, the on / off control of the heater will not be performed correctly.

[0005] Therefore, an object of one or more aspects of the present disclosure is to correctly control the on and off of a heater even if the cycle of the AC voltage is disrupted. [Means for solving the problem]

[0006] A current control device according to one embodiment of the present disclosure includes a switch that turns current to a heater that generates heat when current is passed through it on and off at zero-crossing points of an AC voltage, a drive unit that drives the switch to cause the switch to turn on the current at the zero-crossing points of the AC voltage, a detection unit that detects whether the AC voltage is positive or negative, and a control unit that identifies, from a result of the detection, a positive period when the AC voltage is positive and a negative period when the AC voltage is negative, and causes the drive unit to drive the switch at a first timing included in the positive period or a second timing included in the negative period. Effect of the Invention

[0007] According to one or more aspects of the present disclosure, even if the cycle of the AC voltage is disrupted, it becomes possible to correctly control turning a heater on and off. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating a configuration of a main part of an image forming apparatus according to an embodiment; [Diagram 2] FIG. 2 is a block diagram illustrating a schematic configuration of a control system of the image forming apparatus. [Diagram 3] 3A and 3B are schematic diagrams illustrating the internal configuration of a fixing unit. [Figure 4] 1 is a circuit diagram of a current control device 81 that controls current supply to a planar fixing heater of a fixing unit. [Diagram 5] 6 is a flowchart showing an operation for determining a temperature control period and a temperature control timing of the fixing unit. [Figure 6] 10 is a flowchart showing an operation of monitoring a state of an AC half-wave signal. [Figure 7] FIG. 2 is a schematic diagram showing an AC half-wave signal when the AC voltage is standard. [Figure 8] FIG. 2 is a schematic diagram showing an AC half-wave signal when the AC voltage is slightly biased toward the negative side. [Figure 9]4 is a time chart showing an AC half-wave signal, a time stamp, and a state of the AC half-wave signal. [Figure 10] FIG. 11 is a schematic diagram illustrating an example of change point information. [Figure 11] 11A and 11B are schematic diagrams showing calculation results of a temperature control period and a temperature control timing. [Figure 12] 6 is a flowchart showing an operation of a print control unit to perform temperature control. [Figure 13] 11 is a time chart showing an AC voltage, on / off of a first heater-on signal, and a heater current actually output to a main heater. [Figure 14] 1A and 1B are block diagrams illustrating an example of a hardware configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1 is a schematic diagram of a main part of an image forming apparatus 11 according to an embodiment of the present invention.

[0010] The image forming apparatus 11 is, for example, an electrophotographic color printer. Image forming device 11 has four independent image forming sections, image drum units (hereinafter referred to as ID units) 12K, 12Y, 12M, and 12C, which are arranged in a detachable manner in order from the upstream side of the transport direction along the direction of arrow A, which is the transport direction of recording medium 40. The ID units 12K, 12Y, 12M, and 12C each form a toner image as a developer image.

[0011] ID unit 12K forms a black (K) image, ID unit 12Y forms a yellow (Y) image, ID unit 12M forms a magenta (M) image, and ID unit 12C forms a cyan (C) image.

[0012] The ID units 12K, 12Y, 12M, and 12C have the same configuration, and differ only in the color of the toner they contain. For this reason, the internal structure of the black (K) ID unit 12K will be described here as an example. In addition, in Figure 1 and Figure 2 described later, the capital letters K, Y, M, and C represent the toner colors, but in the following, when there is no need to particularly distinguish the toner colors, the capital letters K, Y, M, and C will be omitted.

[0013] The ID unit 12K includes a photoconductor drum 13K, a charging roller 14K, a developing roller 16K, and a toner supply roller 18K.

[0014] The photoconductor drum 13K is an image carrier that carries an image. The charging roller 14K is a charging portion that uniformly charges the surface of the photoconductor drum 13K.

[0015] The developing roller 16K is a developing unit that adheres black toner to the electrostatic latent image formed on the surface of the photosensitive drum 13K to form a toner image. A developing blade 19K is pressed against the developing roller 16K. The developing blade 19K thins the black toner supplied from the toner supply roller 18K on the developing roller 16K. The developing roller 16K is a member that carries toner on its surface for developing the electrostatic latent image, and is disposed so as to contact the surface of the photosensitive drum 13K. The developing roller 16K has, for example, a metal shaft and a semiconductive urethane rubber layer covering the outer periphery thereof. The developing roller 16K is configured to rotate in the opposite direction to the photosensitive drum 13 at a predetermined peripheral speed.

[0016] The toner supply roller 18K is a developer supplying section that is pressed against the developing roller 16K and supplies toner to the developing roller 16K. The toner supply roller 18K supplies black toner contained in a toner cartridge 20K that is detachably attached to the ID unit 12K to the developing roller 16K, and frictionally charges the toner.

[0017] The cleaning blade 27K, which is in pressure contact with the surface of the photoconductor drum 13K, scrapes off residual toner that remains on the photoconductor drum 13K after transfer. The cleaning blade 27K is made of, for example, a flexible rubber material or a plastic material.

[0018] An exposure head 15K is disposed above the photoconductor drum 13K so as to face the photoconductor drum 13K. Similarly, exposure heads 15C, 15M, and 15Y are disposed on the other photoconductor drums 13Y, 13M, and 13C, respectively.

[0019] The exposure head 15 selectively exposes the photoconductor drum 13 to light in accordance with image data of a corresponding color, forming an electrostatic latent image on the surface thereof. The exposure head 15 includes, for example, a plurality of light sources that emit irradiation light, and a lens array that focuses the irradiation light on the surface of the photosensitive drum 13. Examples of these light sources include light-emitting diodes (LEDs) and laser elements. The exposure head 15 is held, for example, by an upper cover (not shown), and moves away from the ID unit 12 as the upper cover rotates in the opening direction.

[0020] Below each of the photoconductor drums 13 of the four ID units 12, a transfer unit 21 that transfers a toner image onto a medium is disposed. The transfer unit 21 includes transfer rollers 17K, 17Y, 17M, and 17C, a transfer belt driving roller 21a, a transfer belt driven roller 21b, and a transfer belt . Residual toner adhering to the transfer belt 26 is scraped off by a belt cleaning blade 34 and collected in a belt cleaner container 35 .

[0021] The transfer rollers 17 are arranged in pressure contact with the corresponding photosensitive drums 13 via the transfer belt 26, and in the nip portion formed by the pressure contact, the recording medium 40 transported by the transfer belt 26 is charged to the polarity opposite to that of the toner, thereby transferring the toner image formed on the corresponding photosensitive drum 13 onto the recording medium 40.

[0022] Below the transfer unit 21 of the image forming apparatus 11, a paper feed tray 24 serving as a medium storage unit for storing a recording medium 40 to be supplied to the transfer belt 26 is provided. The hopping roller 43 picks up one sheet of recording medium 40 from the paper feed tray 24 . The pair of registration rollers 44 and 45 transport the sheet of recording medium 40 picked up by the hopping roller 43 .

[0023] A paper detection sensor 49 disposed after the pair of registration rollers 45 detects the passage of the paper by contact or non-contact. The detection signal of the paper detection sensor 49 becomes the reference for the light emission timing of the exposure head 15 and the timing for applying a high voltage to the transfer roller 17.

[0024] Furthermore, on the discharge side of the recording medium 40 by the transfer belt 26, a fixing device 28 is provided as a fixing section. The fixing device 28 has a fixing belt 29 equipped with a fixing heater 31 as a heater serving as a heat source therein, a backup roller 30 that is biased against the fixing belt 29 by a compression spring (not shown), and a non-contact temperature sensor 32. The fixing device 28 fixes the toner image transferred to the recording medium 40 by applying heat and pressure. In other words, the fixing device 28 fixes the toner image to the recording medium 40 using the fixing heater 31 that generates heat when energized.

[0025] The non-contact temperature sensor 32 is a non-contact temperature sensor that receives infrared rays radiated from the surface of the fixing belt 29 and converts them into temperature. The temperature detection position of the non-contact temperature sensor 32 is disposed on the inlet side of the recording medium 40 in the circumferential direction and in the center in the longitudinal direction.

[0026] On the discharge side of the fixing unit 28, there are provided a discharge detection sensor 50, a paper guide section 42, a pair of transport rollers 46 arranged along the paper guide section 42, a pair of discharge rollers 47, and a paper stacker section 48. The discharge detection sensor 50 is also a sensor that detects the presence or absence of the recording medium 40, and the detection signal of the discharge detection sensor 50 serves as a criterion for determining whether or not a series of image forming processes for the recording medium 40 has been completed.

[0027] FIG. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 11. As shown in FIG. The host interface unit 100 receives print data, which is image formation data described in PDL (Page Description Language) or the like, sent from a higher-level device such as a personal computer (PC), and provides the print data to a command / image processing unit 101.

[0028] A command / image processing unit 101 converts print data sent from a host interface unit 100 into bitmap data.

[0029] The exposure head interface unit 102 outputs the bitmap data converted by the command / image processing unit 101 to the exposure heads 15K, 15Y, 15M, and 15C under the control of the print control unit 103.

[0030] The print control unit 103 is composed of a control circuit network including a CPU, ROM, RAM, I / O ports, and timers, and is a control unit that performs overall control of the mechanism and applied voltage by analyzing information signals from each sensor and each part, performing calculations and condition judgments, and outputting operation instruction signals to each part. The print control unit 103 is also responsible for calculating the gradient of increase in the temperature detected by the non-contact temperature sensor 32 (described later), and for storing and comparing the results of the calculation.

[0031] The print control unit 103 controls the ID units 12K, 12Y, 12M, and 12C and the transfer unit 21. In addition, the print control unit 103 controls the hopping roller 43 and the pair of registration rollers 44 and 45 .

[0032] Furthermore, the print control unit 103 controls the temperature of the fixing heater 31 of the fixing unit . For example, the print control unit 103 receives temperature information from a non-contact temperature sensor 32 arranged close to the fixing unit 28, and controls the heat generation of the fixing heater 31 so that the detected temperature of the fixing unit 28 approaches a target temperature according to printing conditions such as paper size or paper thickness. The temperature control of the fixing heater 31 will be described in detail later.

[0033] The conveying motor 111 drives and rotates the hopping roller 43, the registration roller pairs 44 and 45, the conveying roller pair 46, and the discharge roller pair 47, and the ID motor 112 drives and rotates each of the rotating bodies of the ID units 12K, 12Y, 12M, and 12C.

[0034] The high voltage generating unit 104 applies high voltage as a bias to the charging roller 14, the developing roller 16, and the toner supply roller 18 in the ID unit 12, as well as to the transfer roller 17, in accordance with the control from the print control unit 103. The print control unit 103 appropriately controls the magnitude of these high voltages.

[0035] The belt motor 113 drives and rotates the transfer belt drive roller 21a, and the fuser motor 114 drives and rotates the backup roller 30 of the fuser 28. Each motor is driven in response to an instruction signal from the print control unit 103.

[0036] 3A and 3B are schematic diagrams illustrating the internal configuration of the fixing unit 28. FIG. FIG. 3A is a front view of the internal configuration of the fixing unit 28 as viewed from the paper feed side that receives the recording medium 40, and FIG. 3B is a right side view of the internal configuration of the fixing unit 28. In FIG. 3A, fixing belt 29 is shown in a see-through view in order to clearly show the inside thereof.

[0037] As shown in FIG. 3A, fixing belt 29 formed in an endless cylindrical shape and backup roller 30 are brought into contact with each other by a biasing means (not shown), and a nip portion is formed at the contact portion.

[0038] In order to obtain an appropriate rigidity, the fixing belt 29 is here constructed of a member having multiple layers. For example, the fixing belt 29 has a multi-layer structure in which a resin such as PI (polyimide) or an elastic metal such as SUS having appropriate rigidity and flexibility is used as the base material on the inner circumference side, and an elastic layer such as silicone rubber and a surface layer made of a fluororesin coating represented by PTFE (polytetrafluoroethylene) or PFA (perfluoroalkoxyalkane) or a tube made of these are layered on top of it.

[0039] As shown in FIG. 3B, the backup roller 30 is rotated in the direction of the arrow C by the fixing device motor 114 (see FIG. 2), and the fixing belt 29 rotates in conjunction with the backup roller 30.

[0040] A planar fixing heater 31 is disposed inside the nip portion of the fixing belt 29. In order to reduce temperature unevenness in the longitudinal direction of the fixing heater 31, a metal heat diffusion member with high thermal conductivity may be disposed between the fixing heater 31 and the fixing belt 29. A sliding grease (not shown) is applied to the surface of the fixing heater 31 to improve sliding with the fixing belt 29.

[0041] The planar fixing heater 31 is a planar heating element extending in the width direction (hereinafter sometimes referred to as the longitudinal direction) of the fixing belt 29. The fixing heater 31 is configured by laminating an electrical insulating layer, a resistance heating element, electrodes, and a protective layer in this order on a stainless steel or ceramic substrate, and can generate heat by supplying power to the resistance heating element. The protective layer side of the planar fixing heater 31 transfers heat to the fixing belt 29 directly or via a heat diffusion member.

[0042] The planar fixing heater 31 has a heat generating portion divided into three in the longitudinal direction, and includes a main heater 60 located in the center, and a left side heater 61L and a right side heater 61R adjacently disposed on both the left and right sides of the main heater 60. These three divided heaters are formed symmetrically with respect to the center of the main heater 60 in the longitudinal direction, and the left side heater 61L and the right side heater 61R are electrically connected in parallel as described below, and are simultaneously energized to generate heat at the same time.

[0043] The widths of the main heater 60 and the left and right side heaters 61L, 61R are determined arbitrarily based on design requirements, user requests, etc. Here, the width of the main heater 60 corresponds to the width size (210 mm) of A4 paper in portrait orientation. When printing A4 paper in portrait orientation, only the main heater 60 is driven. For paper widths ranging from A4 portrait to A4 landscape (297 mm = maximum width printable by the image forming device 11), the heat generation amounts of the left and right side heaters 61R, 61L are adjusted according to the paper width.

[0044] A main heater rear thermistor 70, a left side heater rear thermistor 71L, and a right side heater rear thermistor 71R are disposed on the rear surfaces of the main heater 60, the left side heater 61L, and the right side heater 61R, respectively, on the substrate side of the main heater 60, the left side heater 61L, and the right side heater 61R, respectively, to detect their temperatures. Each of these thermistors provides the print control unit 103 with information on the temperature detected by each of them.

[0045] The main heater back thermistor 70 and the left and right side heater back thermistors 71 are used to protect against runaway overheating of the corresponding main heater 60 and left and right side heaters 61L, 61R, respectively, and against overheating of non-paper passing areas due to incorrect paper settings by the user. In addition, a non-contact temperature sensor 32 is installed on the outside of the fixing belt 29, at the center position in the longitudinal direction, to detect the temperature of the surface of the fixing belt 29. The non-contact temperature sensor 32 is a sensor that detects temperature without contact, and a thermopile, for example, can be used.

[0046] The backup roller 30 is composed of a surface layer of PTFE or PFA, a silicone rubber layer, and a core metal that serves as the shaft. Of these, the silicone rubber layer is often made of sponge-type rubber that has poor thermal conductivity in order to avoid an extension of the warm-up time of the fixing unit 28 due to heat conduction to the backup roller 30.

[0047] As shown in Fig. 3(B), the fixing device 28 configured as described above conveys the recording medium 40 sent from the transfer unit 21 (Fig. 1) in a nip portion in the direction of the arrow A. During this conveyance, the toner image transferred onto the recording medium 40 and adhering thereto by weak electrostatic force is melted by heat and then fixed to the recording medium 40 by application of pressure.

[0048] FIG. 4 is a circuit diagram of a current control device 81 that controls current supply to the planar fixing heater 31 of the fixing device . As shown in FIG. 4, the energization control device 81 includes a print control unit 103, triacs 86 and 87 as switches, a triac driving circuit 82 as a driving unit, and an AC half-wave detection unit 83 as a detection unit.

[0049] As shown in FIG. 4, temperature information detected by the main heater rear thermistor 70, the left side heater rear thermistor 71L, the right side heater rear thermistor 71R and the non-contact temperature sensor 32 is provided to the print control unit 103.

[0050] One electrode of each of the heaters 60, 61L, 61R constituting the planar fixing heater 31 is connected to one terminal of a commercial power source 85 via a relay 84, and is also connected to an input terminal of an AC half-wave detector 83.

[0051] The AC half-wave detector 83 detects whether the AC voltage is positive or negative. For example, the AC half-wave detector 83 monitors the AC voltage from the commercial power source 85, and provides the print controller 103 with an AC half-wave signal that indicates High when the AC voltage is positive and Low when the AC voltage is negative.

[0052] The other terminal of the main heater 60 is connected to one terminal of a triac 86 , and the other terminals of the left and right side heaters 61 L, 61 R are connected to one terminal of a triac 87 .

[0053] The other terminals of the two triacs 86 and 87 are both connected to the other terminal of the commercial power supply 85 and are also connected to an input terminal of the AC half-wave detector 83 . The gate terminal of the triac 86 and the gate terminal of the triac 87 are connected to the triac drive circuit 82 .

[0054] The triacs 86 and 87 are switches that, when driven by the triac drive circuit 82, turn on the power supply to the fixing heater 31 and turn on and off the power supply to the fixing heater 31 at the zero crossing points of the AC voltage.

[0055] The triac driving circuit 82 drives the triacs 86 and 87 to turn on the power supply to the fixing heater 31 at the zero cross point of the AC voltage. The triac driving circuit 82 is configured to insulate between the primary and secondary using a phototriac, and changes the time for which current is passed through the triacs 86, 87 according to the pulse width (DUTY value) of a first heater-on signal 93 and a second heater-on signal 94 input from the print control unit 103. This allows the print control unit 103 to control the heating of the fixing heater 31.

[0056] The print control unit 103 identifies a positive period in which the AC voltage is positive and a negative period in which the AC voltage is negative based on the detection result from the AC half-wave detection unit 83. Then, the print control unit 103 outputs at least one of a first heater-on signal 93 and a second heater-on signal 94 to the triac drive circuit 82 to drive the triacs 86 and 87 at a first timing included in the positive period or a second timing included in the negative period.

[0057] Here, the print control unit 103, based on the result of detection by the AC half-wave detection unit 83, identifies the positive period and the negative period by averaging the periods when the AC voltage is positive and the periods when the AC voltage is negative, respectively.

[0058] The print control unit 103 sets a timing closer to the middle of the positive period than the start and end of the positive period as the first timing, and sets a timing closer to the middle of the negative period than the start and end of the negative period as the second timing. Here, the print control unit 103 sets the middle of the positive period as the first timing, and the middle of the negative period as the second timing.

[0059] A printing operation in the image forming apparatus 11 configured as above will now be briefly described. First, the image forming apparatus 11 receives print data written in a PDL or the like from an external device (not shown) via a host interface unit 100 .

[0060] The input data is converted into bitmap data by the command / image processing unit 101. The converted bitmap data is provided to the print control unit 103.

[0061] Thereafter, the print control unit 103 starts the fixing control. Specifically, the print control unit 103 rotates the fixing belt 29 and the backup roller 30, and at the same time, energizes the fixing heater 31 to warm up the fixing heater 31 to a temperature at which printing is possible.

[0062] After the warm-up, the print control unit 103 performs temperature control so as to maintain a temperature at which printing is possible. For example, the print control unit 103 controls the power supply to the fixing heater 31 so as to maintain the temperature detected by the non-contact temperature sensor 32 at 150° C.

[0063] When the fixing unit 28 is warmed up, the recording medium 40 in the paper feed tray 24 is fed by the hopping roller 43, sent to the registration roller pairs 44 and 45, where the skew is corrected, and then sent to the transfer belt 26. The recording medium 40 is transported sequentially to the ID units 12K, 12Y, 12M, and 12C as the transfer belt 26 travels. A paper detection sensor 49 is disposed after the pair of registration rollers 45 , and detects the passage of the recording medium 40 in a contact or non-contact manner, and outputs a detection signal to the print control unit 103 .

[0064] Meanwhile, in the ID unit 12, the surface of the photoconductor drum 13 is charged by the charging roller 14 and then exposed by the corresponding exposure head 15, and an electrostatic latent image is formed on the surface by this exposure. At this time, the exposure heads 15K, 15Y, 15M, and 15C are each turned on in accordance with the converted bitmap data.

[0065] A thin layer of toner on the developing roller 16 is electrostatically attached to the portion where the electrostatic latent image is formed, forming a toner image of the corresponding color. The toner image formed on the photoconductor drum 13 is transferred to the recording medium 40 by the corresponding transfer roller 17, and a color toner image is formed on the recording medium 40. After transfer, the toner remaining on the photoconductor drum 13 is removed by a cleaning blade 27.

[0066] The recording medium 40 on which the color toner image has been formed is sent to the fixing device 28. The toner image is fixed to the recording medium 40 by heat and pressure in the fixing device 28, and a color image is formed. The recording medium 40 on which the color image has been formed is transported along the paper guide section 42 by a pair of transport rollers 46, and is discharged to the paper stacker section 48 by a pair of discharge rollers 47.

[0067] In this manner, a color image is formed on the recording medium 40. Residual toner adhering to the transfer belt 26 is collected in a belt cleaner container 35 by a belt cleaning blade 34.

[0068] FIG. 5 is a flowchart showing an operation for determining the temperature control period and the temperature control timing of the fixing unit . The print control unit 103 checks whether the relay 84 for ensuring safety can be turned off (S10). The process of step S10 is performed when the power is turned on, when returning from sleep, when the cover is closed, or the like.

[0069] Next, the print control unit 103 starts detecting the period of the AC half-wave signal (S11). Here, the print control unit 103 starts recording the AC half-wave signal change points. For example, the print control unit 103 turns on an AC half-wave signal change point recording flag to start recording the change points in the AC half-wave signal monitoring process described later.

[0070] Next, the print control unit 103 judges whether or not to end detection of the period of the AC half-wave signal (S12). For example, the print control unit 103 monitors the AC half-wave signal change point record flag, and judges to end detection of the period of the AC half-wave signal when the AC half-wave signal change point record flag is turned off. If it is judged to end detection of the period of the AC half-wave signal (YES in S12), the process proceeds to step S13.

[0071] In step S13, the print control unit 103 calculates the temperature control period and the temperature control timing from the period detected between steps S11 and S12. Details of the process here will be described later.

[0072] FIG. 6 is a flowchart showing the operation of monitoring the state of an AC half-wave signal. This operation is executed every 1 ms (millisecond) measured by a timer included in the print control unit 103.

[0073] First, the print control unit 103 identifies the state of the AC half-wave signal based on the AC half-wave signal from the AC half-wave detection unit 83, and updates the time stamp, which is time information from the change point (S20). The state identified here is whether the AC half-wave signal is High or Low. Also, the time stamp is incremented by 1 ms for each operation.

[0074] Next, the print control unit 103 compares the state of the AC half-wave signal determined in step S20 with the state of the AC half-wave signal determined previously, and determines whether the state of the AC half-wave signal has changed from the state determined previously (S21). Here, the print control unit 103 stores the state of the AC half-wave signal determined previously, for example, in a buffer (not shown). If the state of the AC half-wave signal has changed from the state determined previously (YES in S21), the process proceeds to step S22, and if the state of the AC half-wave signal has not changed from the state determined previously (NO in S21), the process proceeds to step S27.

[0075] In step S22, the print control unit 103 determines whether or not the period of the AC half-wave signal is being detected. For example, if the AC half-wave signal change point recording flag indicates ON, the print control unit 103 determines that the period of the AC half-wave signal is being detected, and if the AC half-wave signal change point recording flag indicates OFF, the print control unit 103 determines that the period of the AC half-wave signal is not being detected. If the period of the AC half-wave signal is being detected (YES in S22), the process proceeds to step S23, and if the period of the AC half-wave signal is not being detected (NO in S22), the process proceeds to step S26.

[0076] In step S23, the print control unit 103 records information indicating the change point of the AC half-wave signal in the change point information (S23). The information indicating the change point is, for example, a timestamp indicating the elapsed time from the start of detection of the period of the AC half-wave signal, and information indicating at least the state after the change.

[0077] Next, the print control unit 103 judges whether the number of transition points indicated by the transition point information has reached a predetermined number (S24). If the number of transition points indicated by the transition point information has reached the predetermined number (YES in S24), the process proceeds to step S25, and if the number of transition points indicated by the transition point information has not reached the predetermined number (NO in S24), the process proceeds to step S26. Here, the predetermined number is 10, but is not limited to this number.

[0078] In step S25, the print control unit 103 ends the detection operation of the period of the AC half-wave signal. Here, the print control unit 103 turns off the AC half-wave signal change point recording flag. Then, the process proceeds to step S26.

[0079] In step S26, the print control unit 103 clears the timestamp by initializing it. Here, the print control unit 103 sets the timestamp to 0. Then, the process proceeds to step S27.

[0080] In step S27, the print control unit 103 saves the state acquired in step S20 by storing it in a buffer as the previously specified state.

[0081] Next, a method for calculating the temperature control period and the temperature control timing in step S13 of FIG. 5 will be described. FIG. 7 is a schematic diagram showing an AC half-wave signal when the AC voltage is standard. The AC half-wave signal is High when the AC voltage is positive and Low when the AC voltage is negative. When the AC voltage is in a standard state, the duty ratio of the AC half-wave signal is approximately 1:1.

[0082] FIG. 8 is a schematic diagram showing an AC half-wave signal when the AC voltage is slightly negative. When the AC voltage is slightly biased toward the negative side, the AC voltage remains negative for a longer period of time, so the duty ratio of the AC half-wave signal is greater on the negative side than on the positive side.

[0083] Next, with reference to FIGS. 9 and 10, a description will be given of change point information obtained by monitoring the state of the AC half-wave signal, as described with reference to FIG. 6, in the state shown in FIG.

[0084] FIG. 9 is a time chart showing an AC half-wave signal, a time stamp, and a state of the AC half-wave signal. The print control unit 103 identifies the change point at the timing indicated by the upward arrow in Fig. 9. Here, the change point is identified every 1 ms.

[0085] When the state of the AC half-wave signal changes from the previously specified state, the print control unit 103 records the change point of the AC half-wave signal in the change point information. For example, as shown in FIG. 9, if the state of the AC half-wave signal is Low at timestamp 11 ms and the state of the AC half-wave signal becomes High at timestamp 12 ms, the print control unit 103 records the timestamp 12 ms and the information of the change pattern L→H in the change point information as information indicating the change point. Similarly, information on the timestamp 8 ms and the change pattern H→L, and information on the timestamp 12 ms and the change pattern L→H are recorded in the change point information.

[0086] FIG. 10 is a schematic diagram showing an example of the change point information. The change-point information shown in FIG. 10 is obtained by detecting change-points ten times and recording information indicating the change-points.

[0087] FIG. 11 is a schematic diagram showing the calculation results of the temperature control period and the temperature control timing calculated in step S13 of FIG. 5 based on the change point information shown in FIG. 10, the time stamp corresponding to the change pattern L→H indicates the period when the AC half-wave signal is low and the AC voltage is negative, whereas the time stamp corresponding to the change pattern H→L indicates the period when the AC half-wave signal is high and the AC voltage is positive.

[0088] As a result, the print control unit 103 calculates the average periods of the negative and positive AC voltage periods, and sets each calculated average period as the temperature control period. If the calculated average value includes a decimal value, the first decimal place is rounded off to the nearest whole number to set the average period as a positive integer. In FIG. 11, an average period in which the phase is positive is a positive period, and an average period in which the phase is negative is a negative period.

[0089] Then, the print control unit 103 determines any timing during which the AC voltage is in the negative period as the temperature control timing during the negative AC voltage period (second timing), and any timing during which the AC voltage is in the positive AC voltage period as the temperature control timing during which the AC voltage is in the positive AC voltage period (first timing). However, because the positive and negative periods of the AC voltage fluctuate due to disturbances in the waveform of the AC voltage, and because the change point is identified by a timestamp every 1 ms, if the state of the AC half-wave signal changes just before or just after the timestamp, the error becomes large, so it is preferable that the temperature control timing is closer to the middle of the temperature control period than the start or end of the temperature control period. Here, the print control unit 103 sets the temperature control timing to half of each of the positive and negative temperature control periods, in other words, the timing obtained by shifting each of the positive and negative temperature control periods by half a period. Note that if the value obtained by halving each of the positive and negative temperature control periods includes a decimal point, the print control unit 103 sets the temperature control timing to a positive integer by rounding down the decimal point.

[0090] For example, as shown in FIG. 11, in a temperature control period when the AC voltage is positive, the temperature control timing (first timing) is 4 ms after the change point where the AC voltage changes to positive, and in a temperature control period when the AC voltage is negative, the temperature control timing (second timing) is 6 ms after the change point where the AC voltage changes to negative.

[0091] FIG. 12 is a flowchart showing the operation of the print control unit 103 in performing temperature control. The flow shown in FIG. 12 is a flow that is executed when controlling the temperature of the fixing heater 31. The flow shown in FIG. 12 also uses the timestamps described in FIG.

[0092] The print control unit 103 determines whether or not a change point of the AC half-wave signal has been detected based on the AC half-wave signal from the AC half-wave detection unit 83 (S30). The determination here is the same as the determination in step S21 of the flow shown in Fig. 6. If a change point of the AC half-wave signal has been detected (YES in S30), the process proceeds to step S31.

[0093] In step S31, the print control unit 103 compares the timestamp with the temperature control period corresponding to the previously identified state of the AC half-wave signal, and determines whether the difference between them is within ±1 ms. If the difference between them is within ±1 ms (YES in S31), it can be determined that the change point is accurate, and the process proceeds to step S32, but if the difference between them exceeds ±1 ms (NO in S31), it can be determined that a change point has been erroneously detected due to noise or the like, and the process returns to step S30.

[0094] In step S32, the print control unit 103 determines whether the timestamp after being cleared in step S26 of Fig. 6 is the temperature control timing corresponding to the current state of the AC half-wave signal. If the timestamp is the temperature control timing (Yes in S32), the process proceeds to step S33.

[0095] In step S33, at least one of the first heater-on signal 93 and the second heater-on signal 94, which are temperature control signals for controlling the temperature of the fixing heater 31, is output to the triac drive circuit 82. Specifically, the print control unit 103 performs a PID calculation based on the difference between the temperature detected by the non-contact temperature sensor 32 and the target temperature determined from the printing conditions for each temperature control period (100 ms) to determine the duty value of the heater control signal. Then, the print control unit 103 selects a pattern of the determined duty value from a heater-on pattern table stored in advance, and outputs at least one of the first heater-on signal 93 and the second heater-on signal 94 corresponding to that pattern.

[0096] FIG. 13 is a time chart showing the AC voltage, the on / off state of the first heater-on signal 93, and the heater current actually output to the main heater 60. In FIG. As shown in FIG. 13, the output timing (timing of change) of the first heater-on signal 93 is the timing when the temperature control timing corresponding to the current state of the AC half-wave signal has elapsed after the change point of the AC half-wave signal is detected.

[0097] This allows the heater to be turned on or off more precisely since the timing for turning the heater on or off is away from the zero crossing of the AC voltage.

[0098] A part or all of the print control unit 103 and AC half-wave detection unit 83 described above can be configured, for example, as shown in Fig. 14(A), by a memory 1 and a processor 2 such as a CPU (Central Processing Unit) that executes a program stored in the memory 1. Such a program may be provided through a network, or may be provided by being recorded on a recording medium. That is, such a program may be provided, for example, as a program product.

[0099] In addition, part or all of the print control unit 103 and the AC half-wave detection unit 83 can also be configured as a processing circuit 3 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), for example, as shown in FIG. 14(B). As described above, the print control unit 103 and the AC half-wave detection unit 83 can be realized by a processing circuit network.

[0100] In the embodiment described above, the image forming apparatus 11 is a color printer. However, the image forming apparatus 11 may be a copier, facsimile, or multifunction machine that uses similar heater control. [Explanation of symbols]

[0101] 11 image forming apparatus, 12 ID unit, 15 exposure head, 21 transfer section, 28 fixing unit, 81 current control device, 82 triac drive circuit, 83 AC half-wave detection section, 86 triac, 87 triac, 103 print control section.

Claims

1. a switch that turns on and off the power supply to the heater that generates heat when powered on at a zero cross point of the AC voltage; a drive unit that drives the switch to turn on the energization at a zero cross point of the AC voltage; A detection unit that detects whether the AC voltage is positive or negative; a control unit that specifies a positive period during which the AC voltage is positive and a negative period during which the AC voltage is negative from a result of the detection, and causes the drive unit to drive the switch at a first timing included in the positive period or a second timing included in the negative period. A current control device comprising:

2. The control unit determines the positive period and the negative period by averaging the periods in which the AC voltage is positive and the periods in which the AC voltage is negative based on the result of the detection. The energization control device according to claim 1 .

3. The control unit determines a timing closer to a middle of the positive period than a start and an end of the positive period as the first timing, and determines a timing closer to a middle of the negative period than a start and an end of the negative period as the second timing. The energization control device according to claim 1 .

4. The control unit determines a timing closer to a middle of the positive period than a start and an end of the positive period as the first timing, and determines a timing closer to a middle of the negative period than a start and an end of the negative period as the second timing. The energization control device according to claim 2 .

5. The control unit sets a middle point of the positive period as the first timing and a middle point of the negative period as the second timing. The energization control device according to claim 1 .

6. The control unit sets a middle point of the positive period as the first timing and a middle point of the negative period as the second timing. The energization control device according to claim 2 .

7. The energization control device according to any one of claims 1 to 6, an image forming unit for forming a developer image; a transfer section for transferring the developer image onto a medium; a fixing unit that fixes the developer image to the medium by using the heater. An image forming apparatus comprising:

Images