Patent Publication Number: US-9891564-B2

Title: Fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 14/856,644 filed on Sep. 17, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a fixing device and an image forming apparatus. 
     BACKGROUND 
     In an image forming apparatus such as a multifunction peripheral, warming-up processing for raising the temperature of a heat roller of a fixing device has been performed. In the warming-up processing, heat generation of a heating device (e.g., a fixing lamp) is maintained until the temperature of the heat roller reaches a target temperature. In recent years, in order to adapt the image forming apparatus to a stricter energy saving standard, there is a demand for a reduction in time until the temperature of the heat roller reaches the target temperature (hereinafter referred to as “reaching time”). Therefore, a configuration for increasing temperature rising speed is adopted. 
     However, if the temperature rising speed is increased, overshoot (over temperature) after the temperature reaching the target temperature is likely to increase. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external view showing an overall configuration example of an image forming apparatus in an embodiment; 
         FIG. 2  is a schematic diagram showing a configuration example of a fixing device; 
         FIG. 3  is a schematic diagram showing a control mechanism of the fixing device; 
         FIG. 4A  is a diagram showing a temperature change of a supply voltage that occurs if alternating-current power is supplied 100% without being subjected to thinning control; 
         FIG. 4B  is a diagram showing a temperature change of a supply voltage that occurs if the alternating-current power is supplied 25% while being subjected to the thinning control; 
         FIG. 5  is a flowchart for explaining an example of a flow of warming-up processing of a the fixing device; 
         FIG. 6  is a diagram showing a temporal change of the temperature of a heat roller that occurs if the thinning control is not performed (a first situation); 
         FIG. 7  is a diagram showing a temporal change of the temperature of the heat roller that occurs if the thinning control is not performed (a second situation); and 
         FIG. 8  is a diagram showing a temporal change of the temperature of the heat roller of the image forming apparatus in the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a fixing device includes a heat roller, a heat generating body, and a controller. The heat roller heats a conveyed sheet. The heat generating body generates heat with electric power in the heat roller. The controller applies thinning control to electric energy supplied to the heat generating body in processing for heating the heat roller. 
     An image forming apparatus  100  in an embodiment is explained with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals and signs. 
       FIG. 1  is an external view showing an overall configuration example of the image forming apparatus  100  in the embodiment. The image forming apparatus  100  is, for example, a multifunction peripheral. The image forming apparatus  100  includes a display  110 , a control panel  120 , a printer section  130 , a sheet storing section  140 , and an image reading section  200 . Note that the printer section  130  of the image forming apparatus  100  may be a device that fixes a toner image or a device of an inkjet type. 
     The image forming apparatus  100  forms an image on a sheet using a developer such as toner. The sheet is, for example, paper or a label sheet. The sheet may be anything as long as the image forming apparatus  100  can form an image thereon. 
     The display  110  is an image display device such as a liquid crystal display or an organic EL (Electro Luminescence) display. The display  110  displays various kinds of information concerning the image forming apparatus  100 . 
     The control panel  120  includes a plurality of buttons. The control panel  120  receives operation of a user. The control panel  120  outputs a signal corresponding to the operation performed by the user to a controller of the image forming apparatus  100 . Note that the display  110  and the control panel  120  may be configured as an integral touch panel. 
     The printer section  130  forms an image on the sheet on the basis of image information generated by the image reading section  200  or image information received via a communication path. The printer  130  forms an image by performing, for example, processing explained below. An image forming device of the printer section  130  forms an electrostatic latent image on a photoconductive drum on the basis of the image information. The image forming device of the printer section  130  forms a visible image by depositing a developer on the electrostatic latent image. One of specific examples of the developer is toner. A transfer device of the printer section  130  transfers the visible image onto the sheet. A fixing device of the printer section  130  heats and pressurizes the sheet to thereby fix the visible image on the sheet. Note that the sheet on which the image is formed may be a sheet stored in the sheet storing section  140  or may be a manually fed sheet. 
     The sheet storing section  140  stores sheets used for the image formation in the printer section  130 . 
     The image reading section  200  reads reading target image information as contrast of light. The image reading section  200  records the read image information. The recorded image information may be transmitted to another information processing apparatus via a network. The recorded image information may be formed as an image on the sheet by the printer section  130 . 
       FIG. 2  is a schematic diagram showing a configuration example of a fixing device  30 . The fixing device  30  includes a fixing unit  50  and an energization controller  60 . The fixing unit  50  fixes a visible image on a conveyed sheet. The energization controller  60  controls electric power supplied to a lamp of the fixing unit  50 . 
     Details of the fixing unit  50  are explained below. The fixing unit  50  is a part of the fixing device  30  included in the printer section  130 . The fixing unit  50  includes a heat roller  501 , an HR lamp  502 , an HR thermistor  503 , a pressurizing belt  510 , a pressurizing pad  511 , a pad holder  512 , a pressurizing roller  513 , a tension roller  514 , a belt heat roller  515 , a pressurizing belt lamp  516 , and a pressurizing thermistor  517 . 
     The heat roller  501  is a fixing member formed in a cylindrical shape. The HR lamp  502  is provided on the inside of the heat roller  501 . The HR lamp  502  generates heat to thereby heat the heat roller  501 . The HR lamp  502  is configured using, for example, a halogen lamp. The HR thermistor  503  measures the surface temperature of the heat roller  501 . 
     The pressurizing belt  510  is held by the pressurizing roller  513 , the tension roller  514 , and the belt heat roller  515 . The pressurizing belt  510  is brought into pressurized contact with the heat roller  501  by the pressurizing pad  511  and the pressurizing roller  513 . A fixing nip portion is formed between the pressurizing belt  510  and the heat roller  501  by this pressurized contact. 
     The pressurizing pad  511  is held in a state in which the pressurizing pad  511  is in pressurized contact with the heat roller  510  via the pressurizing belt  510 . The pad holder  512  holds the pressurizing pad  511  in a state in which the pressurizing pad  511  is in pressurized contact with the heat roller  501 . 
     The pressurizing roller  513  is disposed downstream in a conveying direction of the sheet. The pressurizing roller  513  brings the pressurizing belt  510  into pressurized contact with the heat roller  501 . An exit of the fixing nip portion is formed by the pressurizing roller  513 . The tension roller  514  is disposed in a position away from the pressurizing roller  513  and the belt heat roller  515  to thereby apply tension to the pressurizing belt  510 . The belt heat roller  515  is disposed upstream in the conveying direction of the sheet. The belt heat roller  515  is formed in a hollow cylindrical shape. The pressurizing belt lamp  516  is provided on the inside of the belt heat roller  515 . The pressurizing belt lamp  516  generates heat to heat the belt heat roller  515 . The pressurizing belt lamp  516  is configured using, for example, a halogen lamp. The pressurizing thermistor  517  measures the surface temperature of the pressurizing belt  510  near the belt heat roller  515 . 
       FIG. 3  is a diagram showing the configuration of a control mechanism of the fixing device  30 . The HR lamp  502  includes a plurality of lamps. The HR lamp  502  includes a first HR lamp  502 A and a second HR lamp  502 B. The first HR lamp  502 A includes a heat generating unit in the vicinity of the center in the length direction of the heat roller  501 . The first HR lamp  502 A generates heat to thereby heat the vicinity of the center in the length direction of the heat roller  501 . The second HR lamp  502 B includes heat generating units in the vicinities of both the ends in the length direction of the heat roller  501 . The second HR lamp  502 B generates heat to thereby heat the vicinities of both the ends in the length direction of the heat roller  501 . The pressurizing belt lamp  516  includes a heat generating unit over the entire length direction of the belt heat roller  515 . The pressurizing belt lamp  516  generates heat to thereby heat the entire length direction of the belt heat roller  515 . 
     The first HR lamp  502 A includes the heat generating unit having, for example, width substantially the same as the sheet width of the A4 portrait size. The second HR lamp  502 B includes the heat generating units, for example, in positions corresponding to the vicinities of both the ends of a sheet of the A4 landscape size. The first HR lamp  502 A, the second HR lamp  502 B, and the pressurizing belt lamp  516  may be configured using lamps having the same power (e.g., 300 W). The first HR lamp  502 A, the second HR lamp  502 B, and the pressurizing belt lamp  516  may be configured using lamps having different powers. 
     The HR thermistor  503  includes a plurality of thermistors. In this embodiment, the HR thermistor  503  includes a first HR thermistor  503 A and a second HR thermistor  503 B. The first HR thermistor  503 A is disposed in the vicinity of the center in the length direction of the heat roller  501 . The first HR thermistor  503 A measures the surface temperature in the vicinity of the center in the length direction of the heat roller  501 . The second HR thermistor  503 B is disposed in the vicinity of one end in the length direction of the heat roller  501 . The second HR thermistor  503 B measures the surface temperature in the vicinity of one end in the length direction of the heat roller  501 . The pressurizing thermistor  517  is disposed in the vicinity of the belt heat roller  515 . For example, the pressurizing thermistor  517  is disposed in the vicinity of the center in the length direction of the belt heat roller  515 . In this case, the pressurizing thermistor  517  measures the surface temperature of the pressurizing belt  510  in the vicinity of the center in the length direction of the belt heat roller  515 . 
     The energization controller  60  includes a first switching element  61 , a second switching element  62 , a third switching element  63 , and a controller  64 . For example, the first switching element  61 , the second switching element  62 , and the third switching element  63  are configured using bidirectional thyristors. 
     The first switching element  61  is provided between a power supply and the first HR lamp  502 A. The first switching element  61  takes an ON or OFF state. A state of the first switching element  61  is controlled by the controller  64 . If the first switching element  61  is in the ON state, alternating-current power is supplied to the first HR lamp  502 A from the power supply. The second switching element  62  is provided between the power supply and the second HR lamp  502 B. The second switching element  62  takes an ON or OFF state. A state of the second switching element  62  is controlled by the controller  64 . If the second switching element  62  is in the ON state, alternating-current power is supplied to the second HR lamp  502 B from the power supply. The third switching element  63  is provided between the power supply and the pressurizing belt lamp  516 . The third switching element  63  takes an ON or OFF state. A state of the third switching element  63  is controlled by the controller  64 . If the third switching element  63  is in the ON state, alternating-current power is supplied to the pressurizing belt lamp  516  from the power supply. 
     The controller  64  acquires signals output from the first HR thermistor  503 A, the second HR thermistor  503 B, and the pressurizing thermistor  517 . The controller  64  acquires a measurement result of temperature (hereinafter referred to as “measured temperature”) on the basis of the acquired signals. The controller  64  controls the first switching element  61 , the second switching element  62 , and the third switching element  63  according to the acquired measured temperature. For example, the controller  64  may acquire an average of measurement values of the first HR thermistor  503 A and the second HR thermistor  503 B as the measured temperature. 
     The controller  64  controls the switching elements to thereby perform thinning control of power supply to the lamps. When performing the thinning control, the controller  64  controls ON and OFF of the switching elements at a short cycle. According to such control, alternating-current electric energy per time supplied to the lamps is adjusted. The control of ON and OFF may be performed at a zero cross of an alternating-current voltage. Since such control is performed, it is possible to perform safe thinning control with less energy loss. The thinning control may be applied to only the first HR thermistor  503 A and the second thermistor  503 B. 
       FIGS. 4A and 4B  are schematic diagrams showing the thinning control.  FIG. 4A  is a diagram showing a temperature change of a supply voltage that occurs if alternating-current power is supplied 100% without being subjected to the thinning control.  FIG. 4B  is a diagram showing a temperature change of a supply voltage that occurs if the alternating-current power is supplied 25% while being subjected to the thinning control. Waveforms shown in  FIGS. 4A and 4B  indicate temporal changes of a voltage value supplied from the power supply to the fixing device  30 . Black portions on the inner sides of the waveforms indicate a voltage supplied to the lamps. White portions on the inner sides of the waveforms indicate a voltage not supplied to the lamp by the thinning control. 
     In a state of 100% supply, the thinning control is not performed. Therefore, all the voltage supplied from the power supply to the fixing device  30  is supplied to the lamps. On the other hand, in a state of 25% supply (a state of a thinning ratio of 75%), the alternating-current power supply is stopped for time equivalent to 75% in total in a predetermined time. As the time in which the alternating-current power supply is stopped, time equivalent to 25% is not continuously provided but time equivalent to less than 25% is intermittently provided a plurality of times. 
       FIG. 5  is a flowchart for explaining an example of a flow of warming-up processing of the fixing device  30 . When warming-up of the fixing device  30  is started, the controller  64  controls the lamps to be ON (ACT  101 ). The lamps controlled to be ON in ACT  101  are the first HR lamp  502 A, the second HR lamp  502 B, and the pressurizing belt lamp  516 . At this point in time, the controller  64  does not execute the thinning control on the lamps controlled to be ON in ACT  101 . That is, the controller  64  controls the switching elements to set a power supply ratio to 100% (ACT  102 ). Thereafter, the controller  64  determines on the basis of measurement results output from the thermistors whether a measured temperature exceeds a first threshold (ACT  103 ). If the measured temperature does not exceed the first threshold (NO in ACT  103 ), the controller  64  does not start the thinning control. If the measured temperature exceeds the first threshold (YES in ACT  103 ), the controller  64  starts the thinning control (ACT  104 ). In this case, the controller  64  performs the thinning control at a predetermined thinning ratio (e.g. 75%). The lamps subjected to the thinning control in ACT  104  are the first HR lamp  502 A and the second HR lamp  502 B. The first threshold is smaller than a target value (a READY temperature) of the temperature of the heat roller  501 . 
     Thereafter, the controller  64  determines on the basis of measurement results output from the thermistors whether a measured temperature exceeds a second threshold (Act  105 ). If the measured temperature does not exceed the second threshold (NO in ACT  105 ), the controller  64  continues the thinning control while keeping the lamps in the ON state. If the measured temperature exceeds the second threshold (YES in ACT  105 ), the controller  64  controls the lamps to be OFF (ACT  106 ). The lamps controlled to be OFF in ACT  106  are the first HR lamp  502 A, the second HR lamp  502 B, and the pressurizing belt lamp  516 . The second threshold is a value close to or the same as the target value (the READY temperature) of the temperature of the heat roller  501 . The second threshold is larger than the first threshold. The second threshold is closer to the READY temperature than the first threshold. 
     Thereafter, the controller  64  determines on the basis of measurement results output from the thermistors whether a measured temperature falls below the second threshold (ACT  107 ). If the measured temperature does not fall below the second threshold (NO in ACT  107 ), the controller  64  maintains the lamps in the OFF state. If the measured temperature falls below the second threshold (YES in ACT  107 ), the controller  64  controls the lamps to be ON (ACT  108 ). The lamps controlled to be ON in ACT  108  are the first HR lamp  502 A, the second HR lamp  502 B, and the pressurizing belt lamp  516 . The controller  64  starts heat insulation control (ACT  109 ). The lamps subjected to the heat insulation control in ACT  109  are the first HR lamp  502 A, the second HR lamp  502 B, and the pressurizing belt lamp  516 . Then, the warming-up processing ends. 
     In the image forming apparatus  100  configured in this way, the lamps of the fixing device  30  are subjected to the thinning control. For example, the thinning control is performed when the heat roller  501  is heated in the warming-up processing. Therefore, it is possible to reduce overshoot that occurs in the heating of the heat roller  501 . Such an effect is useful, in particular, in a situation explained below. In recent years, in apart of countries including Japan, new standards for energy saving have been specified. In such standards, improvement of heat efficiency of a heat roller is decided for a reduction of electric power required for the warming-up processing. Specifically, a reduction in the thickness of the heat roller, improvement of a heat insulation effect, and the like are decided. As a result, temperature rising speed increases. Therefore, large overshoot is likely to occur in a short time (a first situation). In some case, the temperature of the heat roller rises to temperature for disconnecting a relay and a failure of the fixing device is caused (a second situation). The image forming apparatus in the embodiment is capable of reducing the overshoot. 
     Effects of the image forming apparatus  100  in the embodiment are explained below with reference to  FIGS. 6 to 8 .  FIG. 6  is a diagram showing a temporal change of the temperature of the heat roller that occurs if the thinning control is not performed (the first situation).  FIG. 7  is a diagram showing a temporal change of the temperature of the heat roller that occurs if the thinning control is not performed (the second situation). In  FIGS. 6 and 7 , the lamps are controlled to be ON according to the start of the warming-up processing. Thereafter, 100% electric power is supplied to the lamps until a measured temperature reaches the READY temperature (equivalent to the second threshold). If the measured temperature reaches the READY temperature, the lamps are controlled to be OFF. However, thereafter, the heat roller is still heated by residual heat of the lamps. The temperature rises for a fixed time. The temperature rise is the overshoot. In  FIG. 7 , a gradient of a rise in the temperature is steep compared with  FIG. 6 . Therefore, the overshoot also increases and the temperature of the heat roller exceeds a relay disconnection temperature. In this case, the heat roller is likely to be damaged. 
       FIG. 8  is a diagram showing a temporal change of the temperature of the heat roller  501  of the image forming apparatus  100  in the embodiment. Time t 0  indicates time when the warming-up processing is started. When the warming-up processing is started, the controller  64  controls the first HR lamp  502 A and the second HR lamp  502 B to be ON. That is, at time t 0 , the controller  64  causes the first HR lamp  502 A and the second HR lamp  502 B to start heat generation. At this point, the thinning control is not executed. Therefore, electric energy supplied to the first HR lamp  502 A and the second HR lamp  502 B is electric energy equivalent to 100% of a predetermined value. The predetermined value is, for example, a value supplied to a lamp of a fixing device of an image forming apparatus in the past. 
     If a measured temperature exceeds the first threshold at time t 1 , the controller  64  starts the thinning control. In the thinning control, the electric energy supplied to the first HR lamp  502 A and the second HR lamp  502 B is less than 100%. Therefore, after time t 1 , a temperature rising gradient is gentle compared with before time t 1 . 
     If the measured temperature exceeds the second threshold at time t 2 , the controller  64  controls the first HR lamp  502 A and the second HR lamp  502 B to be OFF. Thereafter, the measured temperature still rises with residual heat for a certain degree of time (between t 2  and t 3 ). However, the temperature rising gradient at time t 2  is gentle compared with  FIGS. 6 and 7 . Therefore, the overshoot is also small compared with  FIGS. 6 and 7 . 
     After time t 3 , the measured temperature starts to drop. Thereafter, if the measured temperature falls below the second threshold at time t 4 , the controller  64  starts heat insulation control. 
     Modifications 
     The second HR thermistor  503 B may be disposed in the vicinities of both the ends in the length direction of the heat roller  501 . 
     In the thinning control, the controller  64  may control electric energy using a plurality of kinds of thinning ratios. For example, the controller  64  may perform the thinning control at a lower thinning ratio for a predetermined time after the measured temperature exceeds the first threshold and thereafter perform the thinning control at a higher thinning ratio. With such a configuration, it is possible to reduce time required until the measured temperature reaches the READY temperature. 
     The controller  64  may determine, according to time rather than the measured temperature, a period in which the thinning control is performed. For example, the controller  64  may execute the warming-up processing as explained below. The controller  64  does not perform the thinning control until a first time elapses after the warming-up processing is started. If the first time elapses after the warming-up processing is started, the controller  64  starts the thinning control. If a second time elapses after the thinning control is started, the controller  64  controls the first HR lamp  502 A and the second HR lamp  502 B to be OFF. 
     Timing when the thinning control is executed does not need to be limited to timing during the warming-up processing. The thinning control may be performed at any timing as long as the timing is timing during processing for heating a member of the fixing device with a heat generating body such as a lamp. 
     In the flowchart of  FIG. 5 , the thinning control may be started at the timing of ACT  102 . In this case, the thinning ratio of the thinning control performed in ACT  102  is lower than the thinning ratio of the thinning control performed in ACT  104 . That is, the electric energy supplied by the thinning control in ACT  102  is larger than the electric energy supplied by the thinning control in ACT  104 . 
     While certain embodiments have been described these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms: furthermore various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and there equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.