Image forming device

Abstract

Provided is an image forming apparatus that can realize more appropriate drive control while also taking into consideration load fluctuations due to environmental temperature, reducing power consumption and preventing temperature increases in the clutch. [Solution] Printer 1 includes clutches 121-123 that switch between a drive transmission state and a drive disconnection state in response to power supplied from a power source, a temperature sensor 140 that detects the ambient temperature, and a CPU 101 that controls the amount of power supplied to clutches 121-123 by setting the duty ratio of a pulse width modulation signal. CPU 101 sets the duty ratio of the pulse width modulation signal to a first duty ratio until a first time has elapsed since clutches 121-123 were placed in the drive transmission state, and after the first time has elapsed, sets the duty ratio of the pulse width modulation signal to a second duty ratio that is smaller than the first duty ratio, in accordance with the temperature detected by temperature sensor 140.

Description

[Technical Field]

[0001] The present application relates to an image forming apparatus equipped with a clutch. [Background technology]

[0002] Patent Document 1 describes an image forming apparatus that can reduce power consumption by effectively supplying power to a clutch that drives and controls a driven object whose load changes over time. In this image forming apparatus, when the clutch is in a drive connection state, the duty ratio of the pulse width modulation signal of the energizing current is controlled in accordance with the load fluctuation, allowing for flexible response to expected load fluctuations. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-37736 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although the load on the clutch driven object also varies depending on the ambient temperature, the image forming apparatus described in Patent Document 1 does not control the clutch in consideration of the ambient temperature.

[0005] The present application aims to provide an image forming apparatus that can achieve more appropriate drive control while also taking into account load fluctuations due to ambient temperature, reducing power consumption and preventing the clutch from overheating. [Means for solving the problem]

[0006] In order to achieve the above object, the image forming apparatus described in the embodiment includes a clutch that switches between a drive transmission state and a drive disconnection state by power supply from a power source, a temperature sensor that detects the ambient temperature, and a control unit that controls the amount of power supplied to the clutch by setting the duty ratio of a pulse width modulation signal, wherein the control unit sets the duty ratio of the pulse width modulation signal to a first duty ratio until a first time has elapsed since the clutch is placed in the drive transmission state, and after the first time has elapsed, sets the duty ratio of the pulse width modulation signal to a second duty ratio that is smaller than the first duty ratio, depending on the temperature detected by the temperature sensor. [Effects of the Invention]

[0007] According to the image forming device described in the embodiment, the duty ratio of the pulse width modulation signal can be set to an appropriate second duty ratio that is smaller than the first duty ratio in accordance with the load of the driven object that fluctuates depending on the ambient temperature of the image forming device, thereby reducing the power consumption of the entire image forming device and preventing the clutch from heating up. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a color laser printer according to an embodiment. [Figure 2] FIG. 3 is an explanatory diagram of the loads of the first motor and the second motor. [Figure 3] FIG. 2 is a block diagram illustrating the electrical configuration of the printer. [Figure 4] 6 is a flowchart showing a procedure for a first electromagnetic clutch control process. [Figure 5] 10 is a flowchart showing a procedure for a duty ratio determination process. [Figure 6] 10 is a flowchart showing a procedure for a duty ratio change process. [Figure 7] 10 is a flowchart showing the procedure of a modified example of the duty ratio changing process. [Figure 8] 10 is a flowchart showing a procedure for a second electromagnetic clutch control process. [Figure 9] 10 is a flowchart showing the procedure of a modified example of the duty ratio change process in the second electromagnetic clutch control process. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present application will be described in detail with reference to the drawings.

[0010] FIG. 1 shows a cross-sectional view of the schematic configuration of a color laser printer (hereinafter simply referred to as printer) 1 according to one embodiment. Printer 1 is a so-called tandem laser printer that uses four colors of toner. Printer 1 is an example of an image forming device. For ease of explanation, the up-down direction and front-rear direction of printer 1 are defined as shown by the arrows in FIG. 1. Furthermore, the left-right direction is defined as the direction from the front of printer 1 facing the left-hand side of a user facing printer 1, and the right-hand side is defined as the direction from the front of printer 1 facing the left-hand side.

[0011] As shown in FIG. 1, the printer 1 includes a main body housing 2, a conveying unit 10, and a print engine 20. The main body housing 2 is generally box-shaped. The conveying unit 10, the print engine 20, and the like are housed inside the main body housing 2. An ejection tray 5 is formed on the top surface of the main body housing 2. The printer 1 ejects sheets S on which images have been formed in a stacked state onto the ejection tray 5. A front cover 2a is provided on the front surface of the main body housing 2. The front cover 2a is a cover that opens and closes an opening 2b formed on the front surface of the main body housing 2. The front cover 2a can rotate forward, for example, around a rotation shaft 2c provided at the bottom end, and can rotate from a position where the opening 2b shown in FIG. 1 is closed to a position where the opening 2b is opened (opened).

[0012] The conveying unit 10 includes a supply tray 11 for receiving sheets S, a pickup roller 12, a separation pad 13, a pressure plate 14, and various rollers including a registration roller 15. The sheets S are, for example, standard-sized sheets such as A4 size, but are not limited to paper media such as plain paper or cardboard, and may also be other recording media such as transparencies. The supply tray 11 is detachably attached to the bottom of the main body housing 2. The pressure plate 14 is provided within the supply tray 11. A displacement mechanism (not shown) is provided below the pressure plate 14. Prior to image formation, the displacement mechanism displaces the pressure plate 14 to an inclined position so that the front side is higher. As a result, the sheets S received in the supply tray 11 are pulled toward the pickup roller 12 by the pressure plate 14, separated one by one by the pickup roller 12 and the separation pad 13, and the leading edges of the sheets S are aligned by the registration roller 15 before being conveyed to the print engine 20 by other rollers. The sheet S conveyed from the supply tray 11 is conveyed along the conveying path R by the print engine 20, the discharge rollers 65, etc., and is discharged onto the discharge tray 5.

[0013] The print engine 20 is located approximately in the center of the main body housing 2 and includes developer cartridges 30Y, 30M, 30C, and 30K, an exposure unit 40, a transfer unit 50, and a fixing unit 60. The developer cartridges 30Y, 30M, 30C, and 30K contain yellow, magenta, cyan, and black toner, respectively. The four developer cartridges 30Y to 30K are arranged in this order from the front to the rear of the printer 1. The developer cartridges 30Y to 30K can be removed and replaced by opening the front cover 2a and removing them through an opening 2b in the main body housing 2.

[0014] The developing cartridge 30K includes a photosensitive drum 31, a charger 32, and a toner cartridge 33K. The other developing cartridges 30C, 30M, and 30Y have different toner colors, but are otherwise configured similarly to the developing cartridge 30K. For this reason, the following description will mainly focus on the developing cartridge 30K, and descriptions of the other developing cartridges 30C, 30M, and 30Y will be omitted as appropriate.

[0015] The charger 32 is, for example, a scorotron charger including a charging wire 32a and a grid portion 32b. The charger 32 uniformly and positively charges the surface of the photosensitive drum 31 prior to forming an electrostatic latent image on the surface of the photosensitive drum 31 during image formation. The device that charges the photosensitive drum 31 is not limited to a scorotron charger, but may be another device such as a roller-type charging roller. Furthermore, the polarity with which the photosensitive drum 31 is charged is not limited to positive charging, but may also be negative charging.

[0016] The toner cartridge 33K includes a toner storage chamber 33a, an agitator 33e, a supply roller 33b, a developing roller 33f, and a layer thickness regulating blade 33d. The toner storage chamber 33a contains black toner. The agitator 33e agitates the toner stored in the toner storage chamber 33a. The supply roller 33b is provided in the toner storage chamber 33a and rotates by receiving a driving force from a first motor 111 (see FIG. 2) provided in the main body housing 2. The supply roller 33b supplies the toner supplied from the toner storage chamber 33a to the developing roller 33f. The photosensitive drum 31 rotates, for example, clockwise in FIG. 1. The developing roller 33f is provided diagonally below and behind the supply roller 33b and is in contact with the supply roller 33b. The developing roller 33f is located downstream of the charger 32 in the rotational direction of the photosensitive drum 31. The developing roller 33f also rotates by receiving a driving force from the first motor 111. A positive voltage is applied to the roller shaft of the developing roller 33f. The toner supplied to the developing roller 33f is carried on the developing roller 33f as the developing roller 33f rotates. The layer thickness regulating blade 33d is provided so as to press against the developing roller 33f from above, and regulates the thickness of the toner adhering to the outer surface of the developing roller 33f to a constant value. The toner cartridges 33C, 33M, and 33Y of the other colors (cyan, magenta, and yellow) shown in FIG. 1 have the same configuration as the toner cartridge 33K.

[0017] The exposure unit 40 is provided at the top inside the main body housing 2 and includes a laser light source, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). A laser beam emitted from the laser light source is deflected by the polygon mirror, etc., and emitted from the exposure unit 40. The exposure unit 40 exposes the surface of the photosensitive drum 31 by emitting a light beam, indicated by a dashed line in FIG. 1, to the surface of the photosensitive drum 31. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 31. The toner carried on the development roller 33f moves to the electrostatic latent image on the photosensitive drum 31 due to the potential difference between the development roller 33f and the electrostatic latent image formed on the photosensitive drum 31, forming a toner image.

[0018] The transfer unit 50 is disposed at a position above the conveying unit 10 and below the developing cartridge 30C. The transfer unit 50 conveys the sheet S supplied by the conveying unit 10 toward the discharge tray 5. The transfer unit 50 includes a drive roller 51, a driven roller 52, a conveying belt 53, and a plurality of (four in this embodiment) transfer rollers 54. The conveying belt 53 is, for example, an endless belt formed in a loop, and is stretched between the drive roller 51 located below the rear end side of the developing cartridge 30C and the driven roller 52 located below the front end side of the developing cartridge 30K.

[0019] Each of the multiple transfer rollers 54 is disposed at a position facing each photosensitive drum 31 in the vertical direction, with a sheet conveying surface 53A, which is the outer peripheral surface of the conveying belt 53, sandwiched therebetween, and is in contact with the conveying belt 53 from the back side of the sheet conveying surface 53A. A negative transfer voltage is applied to each of the multiple transfer rollers 54 in accordance with the conveyance timing of the sheet S, thereby transferring the toner image carried on the surface of the photosensitive drum 31 onto the sheet S being conveyed along the sheet conveying surface 53A.

[0020] The fixing unit 60 is provided downstream in the conveying direction from the position of the transfer unit 50. The fixing unit 60 includes a heating roller 61 that heats the sheet S, and a pressure roller 62 that sandwiches the sheet S between the heating roller 61. The print engine 20 conveys the sheet S, on which the toner image has been transferred, to the fixing unit 60. The fixing unit 60 thermally fixes the toner image transferred to the sheet S to the sheet S by conveying the sheet S between the heating roller 61 and the pressure roller 62. The sheet S on which the image has been printed is discharged onto the discharge tray 5 by discharge rollers 65.

[0021] Although the fixing unit 60 has been described as including the heating roller 61 and the pressure roller 62, the invention is not limited to this. For example, the fixing unit may have a heater, a nip plate that receives radiant heat from the heater, a heating belt that rotates around the nip plate, and a pressure roller.

[0022] The fixing unit may have a substrate on which a heat generating pattern is formed, a belt that rotates around the substrate, and a pressure roller, and the substrate and the belt are in contact with each other.The fixing unit may also have a heating roller, a heater, and a pressure belt.

[0023] Furthermore, the printer 1 is equipped with a developing roller moving mechanism 133 (see FIG. 2) that switches the state of the developing roller 33f between a pressure-contact state in which the developing roller 33f is in pressure contact with the photosensitive drum 31 and a separated state in which the developing roller 33f is separated from the photosensitive drum 31. This developing roller moving mechanism 133 separates the developing roller 33f from the photosensitive drum 31 when an image is not being formed on the sheet S, and can bring the developing roller 33f into pressure contact with the photosensitive drum 31 when an image is being formed on the sheet S, thereby extending the life of the photosensitive drum 31. Note that a known developing roller moving mechanism 133 may be used, and therefore illustration and description of its configuration will be omitted.

[0024] The printer 1 also includes a temperature sensor 140 (see FIG. 3) for detecting the temperature around the printer 1. The temperature sensor 140 may be, for example, a thermistor.

[0025] FIG. 2 shows an example of a load connected to the first motor 111 and an example of a load connected to the second motor 112. As shown in FIG. 2, the first motor 111 is connected to the photosensitive drums 31 for the respective colors Y, M, C, and K and the drive roller 51 for driving the conveyor belt 53 via a predetermined drive mechanism (not shown). The first motor 111 is also connected to the developing rollers 33f for the respective colors Y, M, and K except for black (K) via a YMC switching mechanism 131 made up of a pendulum gear. The driving force of the first motor 111 is further transmitted to the developing roller 33f for black (K) via a first electromagnetic clutch 121. When color printing is performed on the sheet S, the driving force of the first motor 111 is transmitted to the developing rollers 33f for the respective colors Y, M, and K except for black (K) by the YMC switching mechanism 131. On the other hand, when monochrome printing is performed on the sheet S, the driving force of the first motor 111 is not transmitted to the developing rollers 33f for the respective colors Y, M, and K except for black (K) by the YMC switching mechanism 131. In contrast, whether color printing or monochrome printing is performed on the sheet S, the first electromagnetic clutch 121 is turned on during printing, and the driving force of the first motor 111 is transmitted to the developing roller 33f for black (K) via the first electromagnetic clutch 121.

[0026] The second motor 112 is connected to the discharge roller 65 and the developing roller moving mechanism 133 via a predetermined drive mechanism (not shown), and is also connected to the heating roller 61 of the fixing unit 60 via a planetary gear 132. The driving force of the second motor 112 is transmitted to the registration roller 15 via a second electromagnetic clutch 122, and to the pickup roller 12 via a third electromagnetic clutch 123.

[0027] Fig. 3 shows a schematic diagram of the electrical configuration of the printer 1. As shown in Fig. 3, the printer 1 includes a CPU 101, a user IF 102, a memory 103, a print engine 20, first and second motors 111 and 112, first to third electromagnetic clutches 121 to 123, and a temperature sensor 140, which are electrically connected to one another via a bus 105. "IF" is an abbreviation for Interface. The first to third electromagnetic clutches 121 to 123 are examples of clutches, and the CPU 101 is an example of a control unit.

[0028] The CPU 101 executes various processes in accordance with the control program 103A read from the memory 103 and based on user operations. Note that the printer 1 may be provided with a single piece of hardware as the CPU 101, or may be provided with multiple pieces of hardware corresponding to the respective functions. The memory 103 stores various programs and various data, including the control program 103A and setting information 103B. The control program 103A is a program that causes the printer 1 to perform various operations. Details of each program and data will be described later with reference to FIGS. 4 to 9. The memory 103 is also used as a work area when various processes are executed. A buffer provided in the CPU 101 is also an example of a memory. The setting information 103B includes information stored in a volatile memory such as a RAM and information stored in a non-volatile memory such as an NVRAM.

[0029] Note that an example of memory 103 is not limited to a ROM, RAM, NVRAM, HDD, etc. built into printer 1, but may also be a storage medium that is readable and writable by CPU 101. For example, an external memory such as a USB memory or HDD connected to printer 1 via a communication IF (not shown), or a memory or HDD provided in a device connected to printer 1 via a communication IF are also examples of memory 103.

[0030] The user IF 102 is an interface that exists between the CPU 101 and a user who operates the printer 1, and includes, for example, a touch panel and physical operation keys.

[0031] The temperature sensor 140 is installed on the outer surface or inner surface of the main body housing 2, and outputs a signal corresponding to the ambient temperature of the printer 1. The CPU 101 acquires the signal output from the temperature sensor 140 via the bus 105.

[0032] The drive control of each of the first and second motors 111 and 112 is performed by, for example, a motor driver (not shown) in response to instructions from the CPU 101 regarding the start of drive and drive force.

[0033] The transmittable drive torques of the first to third electromagnetic clutches 121-123 increase as the amount of power supplied to each of the electromagnetic clutches 121-123 increases after the electromagnetic clutches 121-123 are turned on (transmitted state), and decrease as the amount of power supplied to each of the electromagnetic clutches 121-123 decreases. The CPU 101 increases or decreases the on-time by pulse-width modulation control of the predetermined voltages applied to each of the electromagnetic clutches 121-123, thereby increasing or decreasing the amount of power supplied to each of the electromagnetic clutches 121-123. Specifically, the CPU 101 increases or decreases the amount of power applied to each of the electromagnetic clutches 121-123 by increasing the duty ratio of the on-time of the pulse-width modulation signal used for the pulse-width modulation control, and decreases the amount of power applied to each of the electromagnetic clutches 121-123 by decreasing the duty ratio. The method for setting the duty ratio will be described later.

[0034] The printer 1 configured as above, and in particular the control processing executed by the CPU 101, will be described with reference to FIGS.

[0035] 4 shows the procedure of the first electromagnetic clutch control process executed by CPU 101. The first electromagnetic clutch control process is started, for example, when CPU 101 acquires a print job. Note that in the following explanation of each process, steps will be represented as "S."

[0036] 4, the CPU 101 initializes a counter N for counting the number of printed pages to "0" (S10). The counter N may be configured as a software counter that uses a predetermined area on the memory 103 as a counter, for example.

[0037] Next, the CPU 101 sets the duty ratio DR of the pulse width modulation signal to an initial value of "100%" (S11). Then, the CPU 101 starts driving the first motor 111 and the second motor 112 (S12) and turns on (connected) the first electromagnetic clutch 121 (S13). At this time, since the duty ratio DR is set to the maximum value of "100%," which is the initial value, the drive torque transmitted by the first electromagnetic clutch 121 is maximum. This initial value of "100%" of the duty ratio DR is an example of a first duty ratio. It goes without saying that the initial value of the duty ratio DR is not limited to "100%".

[0038] Next, CPU 101 waits until the developing roller moving mechanism 133 has completed switching from a separated state in which developing roller 33f is separated from photosensitive drum 31 to a pressed state (S14: NO). Then, when the switching from the separated state to the pressed state is completed (S14: YES), CPU 101 initializes the value of TIMER to "0" (S15). TIMER is a timer for measuring the elapsed time since the developing roller 33f has been pressed against the photosensitive drum 31. TIMER may be configured as a software timer that uses, for example, a predetermined area on memory 103 as the timer.

[0039] Next, CPU 101 waits until the value of TIMER exceeds time T1 (S16: NO). Here, time T1 is the time assumed by the developer of printer 1 as the time that elapses from when development roller 33f is pressed against photosensitive drum 31 until the relative speed between the peripheral speed of development roller 33f and the peripheral speed of photosensitive drum 31 becomes "0." Time T1 is an example of a first time, and specifically, is, for example, 1 second.

[0040] When the value of TIMER exceeds time T1 (S16: YES), CPU 101 executes a process for determining the duty ratio of the pulse width modulation signal (S17). FIG. 5 shows the detailed procedure of the duty ratio determination process. In FIG. 5, CPU 101 acquires a temperature signal from temperature sensor 140 and stores it in a predetermined area TE on memory 103 as the ambient temperature of printer 1 (S30). Hereinafter, the ambient temperature stored in the predetermined area TE will also be referred to as ambient temperature TE. Note that the temperature signal output by temperature sensor 140 is a signal whose magnitude corresponds to the ambient temperature, but may not represent the ambient temperature itself. In this case, CPU 101 simply converts the temperature signal acquired from temperature sensor 140 into an ambient temperature and stores it in the predetermined area TE.

[0041] Next, the CPU 101 determines whether the ambient temperature TE is greater than or equal to 10°C (S31). If the ambient temperature TE is less than 10°C (S31: NO), the CPU 101 determines the duty ratio DR_1 of the pulse width modulation signal to be 70% (S32) and then terminates the duty ratio determination process. If the ambient temperature TE is less than 10°C, the ambient temperature TE is low. In this case, the driving load on the black (K) developing roller 33f is also large, so the duty ratio DR_1 needs to be increased and the driving torque transmitted by the first electromagnetic clutch 121 needs to be increased. As a result, although the first electromagnetic clutch 121 generates more heat, since the ambient temperature TE is low, malfunctions due to the heat generated by the first electromagnetic clutch 121, such as a reduction in driving torque, do not occur.

[0042] On the other hand, if the determination in S31 is that the ambient temperature TE is 10°C or higher (S31: YES), the CPU 101 determines whether the ambient temperature TE is 30°C or higher (S33). If the determination is that the ambient temperature TE is lower than 30°C (S33: NO), the CPU 101 sets the duty ratio DR_1 to "60%" (S34) and then ends the duty ratio determination process. Here, if the ambient temperature TE is 10°C ≤ TE < 30°C, the ambient temperature TE is neither low nor high.

[0043] On the other hand, if it is determined in S33 that the ambient temperature TE is equal to or greater than 30°C (S33: YES), the CPU 101 sets the duty ratio DR_1 to 50% (S35) and then terminates the duty ratio determination process. If the ambient temperature TE is equal to or greater than 30°C, the ambient temperature TE is high. In this case, the drive load on the black (K) developing roller 33f is small, so the duty ratio DR_1 may be set low and the drive torque transmitted by the first electromagnetic clutch 121 may be reduced. This suppresses heat generation in the first electromagnetic clutch 121, thereby suppressing malfunctions due to heat generation in the first electromagnetic clutch 121, such as a reduction in drive torque.

[0044] Returning to FIG. 4, the CPU 101 updates the duty ratio DR with the duty ratio DR_1 determined in the duty ratio determination process (S18). After this, the CPU 101 sets the duty ratio of the pulse width modulation signal to the updated duty ratio DR. The duty ratio DR_1 determined in the duty ratio determination process is an example of a second duty ratio. Furthermore, "70%, " "60%, and "50%" determined as the duty ratio DR_1 are all examples, and other values ​​may be determined.

[0045] Next, CPU 101 executes duty ratio change processing (S19). Figure 6 shows the detailed procedure of the duty ratio change processing. In Figure 6, CPU 101 determines whether counter N>30 (S40). If counter N≦30 (S40: NO), CPU 101 waits until printing of the currently printing page is completed (S41: NO). Then, when printing of the currently printing page is completed (S41: YES), CPU 101 increments counter N by "1" (S43) and then terminates the duty ratio change processing.

[0046] On the other hand, if the determination in S40 is that counter N>30 (S40: YES), CPU 101 calculates duty ratio DR_1×0.9, updates duty ratio DR with the calculation result (S41), and then proceeds to S42. The process from S42 onward has been described above and will not be repeated here. Thus, when counter N>30, that is, when the number of pages to be printed exceeds 30, duty ratio DR_1 determined in S17 is further reduced by 10% because, if printing continues so that the number of pages to be printed exceeds 30, the first electromagnetic clutch 121 generates excessive heat. Maintaining the current duty ratio DR_1 could result in malfunctions due to heat generation in the first electromagnetic clutch 121, such as a reduction in drive torque. Therefore, by reducing the current duty ratio DR_1, heat generation in the first electromagnetic clutch 121 is suppressed, thereby preventing malfunctions due to heat generation in the first electromagnetic clutch 121.

[0047] Returning to FIG. 4, CPU 101 determines whether printing is to be terminated (S20). If this determination indicates that there are remaining pages to be printed based on the acquired print job and printing is not to be terminated (S20: NO), CPU 101 returns the process to S17 and continues the process from S17 onward. On the other hand, if printing is to be terminated (S20: YES), CPU 101 waits until the switching from the pressed state in which developing roller 33f is in pressure contact with photosensitive drum 31 to the separated state is completed (S21: YES), in contrast to S14. Then, when the switching from the pressed state to the separated state is completed (S21: NO), CPU 101 turns off first electromagnetic clutch 121 (disconnected state) (S22), stops driving first motor 111 and second motor 112 (S23), and then terminates the first electromagnetic clutch control process.

[0048] FIG. 7 shows the procedure of a modified example of the duty ratio change process of FIG. 6. In the duty ratio change process of FIG. 6, the process of S41, i.e., the process of decreasing the duty ratio DR_1, is performed when the number of pages to be printed exceeds 30. In contrast, the modified example of the duty ratio change process of FIG. 7 differs in that the process of S41 is performed when the value of TIMER exceeds the time TUP (S50: YES). Here, the time TUP is the time assumed by the developer of the printer 1 as the time that elapses from the start of printing until the first electromagnetic clutch 121 generates excessive heat if printing is performed continuously. The time TUP is an example of the second time, e.g., 180 seconds. Note that 180 seconds is merely an example, and it goes without saying that the time TUP is not limited to this. In this way, even in the modified example of the duty ratio change process, when the value of TIMER exceeds the time TUP, the current duty ratio DR_1 is reduced, thereby suppressing heat generation in the first electromagnetic clutch 121 and preventing malfunctions due to heat generation in the first electromagnetic clutch 121.

[0049] FIG. 8 shows the procedure for the second electromagnetic clutch control process. Like the first electromagnetic clutch control process, the second electromagnetic clutch control process is also started, for example, when the CPU 101 acquires a print job. In other words, the second electromagnetic clutch control process is executed in parallel with the first electromagnetic clutch control process. However, this is not limiting, and the second electromagnetic clutch control process may be configured to be included in the first electromagnetic clutch control process. Note that in FIG. 8, processes similar to those in FIG. 4 are assigned the same step numbers, and descriptions of those processes will be omitted as appropriate.

[0050] 8 controls the second electromagnetic clutch 122. As described above with reference to FIG. 2, the second electromagnetic clutch 122 transmits the driving force of the second motor 112 to the registration roller 15. Unlike the developing roller 33f, the registration roller 15 does not switch between a separated state and a pressed state with respect to another roller (in the case of the developing roller 33f, the photosensitive drum 31). For this reason, the second electromagnetic clutch control process does not include the determination processes of S14 and S21 that are included in the first electromagnetic clutch control process of FIG. 4.

[0051] In the first electromagnetic clutch control process of Fig. 4, the first electromagnetic clutch 121 remains on until printing based on one print job is completed. In contrast, in the second electromagnetic clutch control process of Fig. 8, even while printing based on one print job is continuing, the second electromagnetic clutch 122 is turned off each time printing of the currently printing page is completed (S63). Then, when printing of the next page starts, the second electromagnetic clutch 122 is turned on (S61).

[0052] 8, CPU 101 initializes TIMER1 to "0" (S60). TIMER1 is a timer for measuring the elapsed time since printing based on one print job started. Like TIMER, TIMER1 may be configured as a software timer that uses, for example, a predetermined area on memory 103 as a timer.

[0053] Next, CPU 101 executes the same processes as S11 to S12 of the first electromagnetic clutch control process, and then, with the second electromagnetic clutch 122 still off, the sheet S is fed by the pickup roller 12, and the leading edge of the sheet S is aligned by the registration roller 15, and then CPU 101 turns on the second electromagnetic clutch 122 (S61). Then, similar to S15 of the first electromagnetic clutch control process, CPU 101 initializes the TIMER to "0" (S15). However, unlike the TIMER in the first electromagnetic clutch control process, the TIMER in the second electromagnetic clutch control process measures the elapsed time since the second electromagnetic clutch 122 was turned on.

[0054] Next, the CPU 101 waits until the value of TIMER exceeds time T2 (S62: NO). Here, time T2 is the time assumed by the developer of the printer 1 as the time from when the sheet S, which is in a stationary state in contact with the registration roller 15, is conveyed by the registration roller 15, that the conveying load of the sheet S applied to the registration roller 15 changes from static friction force to kinetic friction force and stabilizes, and is set to about 0.2 seconds. Time T2 is also an example of the first time.

[0055] When the value of TIMER exceeds time T2 (S62: YES), CPU 101 executes a process for determining the duty ratio of the pulse width modulation signal (S17). The processes of S17 to S19 are the same as the processes of S17 to S19 in the first electromagnetic clutch control process, and therefore a description of these processes will be omitted.

[0056] Next, the CPU 101 turns off the second electromagnetic clutch 122 at the timing assumed by the developer of the printer 1 when the trailing edge of the sheet S passes the registration roller 15 (S63), and then determines whether or not to end printing in the same manner as in S20 of the first electromagnetic clutch control process (S20). If this determination determines that printing will not end (S20: NO), the CPU 101 returns the process to S61 and repeats the processes from S61 onwards. On the other hand, if printing will end (S20: YES), the CPU 101 stops driving the first motor 111 and the second motor 112 (S23), and then ends the second electromagnetic clutch control process.

[0057] FIG. 9 shows the procedure of a modified duty ratio change process. The modified duty ratio change process of FIG. 9 corresponds to the modified duty ratio change process of FIG. 7. However, while in the modified duty ratio change process of FIG. 7, a determination is made in S50 as to whether TIMER>TUP?, in the modified duty ratio change process of FIG. 9, a determination is made in S50' as to whether TIMER1>TUP?. This is because the time measured by the TIMER is different between the first electromagnetic clutch control process and the second electromagnetic clutch control process. That is, in the first electromagnetic clutch control process, the TIMER measures the elapsed time since the development roller 33f was switched from the separated state, in which it was separated from the photosensitive drum 31, to the pressed state. In contrast, in the second electromagnetic clutch control process, the TIMER measures the elapsed time since printing based on one print job was started. In the first electromagnetic clutch control process, TIMER is not initialized until printing based on one print job is completed, so TIMER in the first electromagnetic clutch control process could also be used as a timer for measuring the elapsed time since printing based on one print job started, like TIMER1 in the second electromagnetic clutch control process. However, TIMER in the second electromagnetic clutch control process is initialized each time printing of one page is completed, even if printing based on one print job is not yet completed, so TIMER in the second electromagnetic clutch control process can no longer be used as a timer for measuring the elapsed time since printing based on one print job started. Therefore, a new timer, TIMER1, is provided to measure the elapsed time since printing based on one print job started.

[0058] The third electromagnetic clutch control process for controlling the third electromagnetic clutch 123 is executed in parallel with the second electromagnetic clutch control process, but since this can be realized by analogy with the second electromagnetic clutch control process, a detailed description of this process will be omitted.

[0059] In the third electromagnetic clutch control process, at S12 in FIG. 8, the CPU 101 starts driving the first motor 111 and the second motor 112, and then turns on the third electromagnetic clutch 123 at a predetermined timing, and maintains the duty ratio DR of the on time at 100% until time T2 has elapsed, as in the second electromagnetic clutch control process.

[0060] The timing at which the third electromagnetic clutch 123 is turned off is the timing that the developer of the printer 1 assumes when the trailing edge of the sheet S passes the pickup roller 15.

[0061] As described above, printer 1 of this embodiment includes electromagnetic clutches 121-123 that switch between a drive transmission state and a drive disconnection state depending on the power supply from a power source, temperature sensor 140 that detects the ambient temperature, and CPU 101 that controls the amount of power supplied to electromagnetic clutches 121-123 by setting the duty ratio of a pulse width modulation signal. CPU 101 sets the duty ratio of the pulse width modulation signal to a first duty ratio (100%) until a first time (T1 or T2) has elapsed since electromagnetic clutches 121-123 were placed in the drive transmission state, and after the first time has elapsed, sets the duty ratio of the pulse width modulation signal to a second duty ratio (70%, 60%, or 50%) that is smaller than the first duty ratio, depending on the temperature detected by temperature sensor 140.

[0062] In this way, in the printer 1 of this embodiment, the duty ratio of the pulse width modulation signal can be set to an appropriate second duty ratio that is smaller than the first duty ratio in accordance with the load to be driven by the clutches 121 to 123 that changes depending on the ambient temperature of the printer 1, thereby reducing the power consumption of the entire printer 1 and preventing the temperature of the electromagnetic clutches 121 to 123 from rising.

[0063] Furthermore, the CPU 101 sets the second duty ratio to a larger value as the temperature detected by the temperature sensor 140 decreases (S32). When the ambient temperature of the printer 1 is low, the load on the objects driven by the electromagnetic clutches 121-123 is also large, so it is necessary to increase the second duty ratio and increase the drive torque transmitted by the electromagnetic clutches 121-123. As a result, although the electromagnetic clutches 121-123 generate more heat, malfunctions due to heat generated by the electromagnetic clutches 121-123 do not occur because the ambient temperature of the printer 1 is low.

[0064] The printer 1 further includes a print engine 20 capable of printing on a sheet S, and the CPU 101 acquires the temperature detected by the temperature sensor 140 (S30) each time the print engine 20 prints one page on the sheet S, and sets the second duty ratio according to that temperature (S32, S34, S35). This makes it possible to set an appropriate second duty ratio according to the temperature environment, even when the temperature environment around the printer 1 changes during mass printing.

[0065] Furthermore, when the print engine 20 is printing based on one print job and the number of pages printed exceeds a predetermined number (S40: YES), the CPU 101 sets the second duty ratio to a value smaller than the currently set duty ratio (S41). As continuous printing continues, the driven object generates heat and the required drive torque decreases, so by setting the second duty ratio to a more optimal value, it is possible to reduce the power consumption of the entire printer 1 and prevent the temperature of the electromagnetic clutches 121-123 from rising.

[0066] Furthermore, when a second time (time TUP) has elapsed since print engine 20 started printing on a sheet (S50: YES), CPU 101 sets the second duty ratio to a value smaller than the currently set duty ratio (S41). As continuous printing continues, the driven object generates heat and the required drive torque decreases, so by setting the second duty ratio to a more optimal value, it is possible to reduce the power consumption of printer 1 as a whole and prevent the temperature of electromagnetic clutches 121-123 from rising.

[0067] The print engine 20 also has a photosensitive drum 31, a charger 32 that charges the photosensitive drum 31, and a developing roller 33f that supplies toner to an electrostatic latent image formed on the charged photosensitive drum 31 to form a toner image on the photosensitive drum 31, and the first electromagnetic clutch 121 drives the developing roller 33f, and the CPU 101 sets the end timing of the first time to the timing when it is estimated that the developing roller 33f is pressed against the photosensitive drum 31 and the relative peripheral speed between them becomes "0" (S16). Immediately after the developing roller 33f is pressed against the photosensitive drum 31, there is a slight relative speed difference between the peripheral speed of the developing roller 33f and the peripheral speed of the photosensitive drum 31, so the driving torque transmitted by the first electromagnetic clutch 121 is unstable. However, after some time has passed since the pressing, the driving torque required for driving stabilizes, so even if the second duty ratio is reduced, the first electromagnetic clutch 121 can provide stable driving to the developing roller 33f.

[0068] Printer 1 further includes supply tray 11 on which sheets S are placed, print engine 20 capable of printing on sheets S, and transport unit 10 that transports sheets S toward print engine 20, transport unit 10 having pickup roller 12 that picks up sheets placed on supply tray 11, third electromagnetic clutch 123 being the driving target for pickup roller 12, and CPU 101 setting the end timing of the first period to the timing at which pickup roller 12 is estimated to pick up the sheet and start moving the sheet S. In this way, because the end timing of the first period is set to the timing at which pickup roller 12 is estimated to pick up the sheet and start moving the sheet S, even if the duty ratio of the pulse width modulation signal is set to a second duty ratio that is smaller than the first duty ratio, third electromagnetic clutch 123 can stably drive pickup roller 12.

[0069] The printer 1 further includes a print engine 20 capable of printing on sheets, and a transport unit that transports the sheet S toward the print engine 20, the transport unit 10 having a registration roller 15 that aligns the direction of the leading edge of the sheet S before transporting the sheet to the print engine 20, the second electromagnetic clutch 122 being the driving target for the registration roller 15, and the CPU 101 setting the end timing of the first time period to the timing when it is estimated that the registration roller 15 will start transporting the sheet S (S52). In this way, since the end timing of the first time period is set to the timing when it is estimated that the registration roller 15 will start transporting the sheet S, even if the duty ratio of the pulse width modulation signal is set to a second duty ratio that is smaller than the first duty ratio, the second electromagnetic clutch 122 can stably drive the registration roller 15.

[0070] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0071] (1) In the above embodiment, a color laser printer was described as an example of an image forming apparatus, but the image forming apparatus is not limited to this and may be a monochrome laser printer. Also, the image forming apparatus is not limited to a printer and may be a multifunction machine or a copier.

[0072] (2) In the above embodiment, a printer 1 that can print only on one side of a sheet S and cannot print on both sides of the sheet S was used as an example of an image forming device, but this is not limited to this, and a printer that has a mechanism that can print on both sides of a sheet S and can print on both sides of a sheet S may also be used.

[0073] (3) In the above embodiment, an example was described in which the processes shown in Figures 4 to 9 are executed by CPU 101. However, these processes may be executed not only by CPU 101 but also by ASIC or other logic integrated circuits, or these processes may be executed by cooperation between CPUs, ASICs, and other logic integrated circuits.

[0074] (4) In the above embodiment, in both the first electromagnetic clutch control process of FIG. 4 and the second electromagnetic clutch control process of FIG. 8, a temperature signal is acquired from the temperature sensor 140 each time printing of one page is completed. However, this is not limited to this, and a temperature signal may be acquired from the temperature sensor 140 only once when printing based on one print job is started. [Explanation of symbols]

[0075] 1...printer, 10...conveying section, 11...supply tray, 15...registration roller, 20...printing engine, 31...photosensitive drum, 33f...developing roller, 60...fuser, 61...heating roller, 62...pressure roller, 65...discharge roller, 101...CPU, 102...user IF, 103...memory, 111...first motor, 112...second motor, 121...first electromagnetic clutch, 122...second electromagnetic clutch, 123...third electromagnetic clutch, 133...developing roller moving mechanism, 140...temperature sensor, S...sheet.

Claims

1. a clutch that switches between a drive transmission state and a drive disconnection state by power supply from a power source; a temperature sensor for detecting the ambient temperature; a control unit that controls the amount of power supplied to the clutch by setting a duty ratio of a pulse width modulation signal; Equipped with The control unit setting the duty ratio of the pulse width modulation signal to a first duty ratio until a first time period has elapsed since the clutch was put into a driving force transmission state; after the first time period has elapsed, the duty ratio of the pulse width modulation signal is set to a second duty ratio smaller than the first duty ratio in accordance with the temperature detected by the temperature sensor. An image forming apparatus characterized by:

2. The control unit the second duty ratio is set to a larger value as the temperature detected by the temperature sensor decreases.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The image forming apparatus further comprises: A printing engine capable of printing on sheets, Equipped with The control unit a temperature detected by the temperature sensor is acquired each time the print engine prints one page on a sheet, and the second duty ratio is set in accordance with the temperature; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The control unit When the print engine is printing based on one print job and the number of print pages exceeds a predetermined number, the second duty ratio is set to a value smaller than the currently set duty ratio.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

5. The control unit When a second time has elapsed since the print engine started printing on a sheet, the second duty ratio is set to a value smaller than the currently set duty ratio.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

6. The print engine includes: a photosensitive drum, a charger for charging the photosensitive drum, and a developing roller for supplying toner to an electrostatic latent image formed on the charged photosensitive drum to form a toner image on the photosensitive drum; and the clutch drives the developing roller, The control unit The end timing of the first time period is set to a timing when it is estimated that the developing roller is brought into pressure contact with the photosensitive drum and the relative peripheral speed between them becomes "0".

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

7. The image forming apparatus further comprises: a supply tray on which sheets are placed; a print engine capable of printing on the sheet; a conveying unit that conveys the sheet toward the print engine; Equipped with the conveying section has a pickup roller that picks up the sheet placed on the supply tray, the clutch drives the pickup roller, The control unit The end timing of the first time period is set to the timing when it is estimated that the pickup roller will pick up the sheet and the sheet will start moving.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. The image forming apparatus further comprises: a print engine capable of printing on sheets; a conveying unit that conveys the sheet toward the print engine; Equipped with the transport section includes registration rollers that align the leading edge of the sheet before transporting the sheet to the print engine; the clutch drives the registration roller; The control unit setting an end timing of the first time period to a timing when it is estimated that the registration rollers will start conveying the sheet; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

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