Abstract:
In a standby state capable of forming an image, a period of a drive pulse of a heater in a fixing unit is made longer than that of the drive pulse in an image formation state to decrease the number of ON/OFF times of a fixing heater, thereby decreasing a brightness flicker in an illumination equipment which is connected to a power supply system identical with that of an image formation apparatus for ON/OFF controlling the heater to control temperature of the fixing unit to be at a target temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flicker suppression device in an image record apparatus being an electronic equipment such as a copy machine, a printer or the like having a fixing heater. 
     2. Related Background Art 
     In a conventional image record apparatus, for example, in a copy machine having a main heater and a sub heater as fixing heaters, the main heater is lighted (turned on) for, e.g., 240 ms (microsecond) and the sub heater is lighted for, e.g., 160 ms every time a detected temperature of a fixing roller becomes lower than a target temperature. 
     Since a lighting time of the fixing heater is constant (i.e., not varied) in a standby state and also in a copy-sequence state, the fluctuation of power to be supplied to the fixing heater frequently repeats as shown in FIG.  5 . Therefore, voltage change frequently repeats in a power supplying path connected to the fixing heater in the standby state and also in the copy-sequence state. For this reason, a brightness flicker phenomenon is generated in an illumination equipment, a television or the like which is connected to a power supplying system identical with that of the fixing heater. This situation sometimes has brought unpleasant feeling called as a “flicker” for human eyes. It is desirable to decrease the flicker. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide flicker suppression device and method which solve the above-described problem and can decrease a brightness flicker in an illumination equipment, a television or the like connected to a power supplying system identical with that of a fixing heater. 
     Another object of the present invention is to provide the flicker suppression device and method which independently control main and sub heaters to decrease the flicker in an equipment on standby as much as possible. 
     Still another object of the present invention is to provide the flicker suppression device and method which decrease the flicker by minimizing the number of power change times in the standby state. 
     Still another object of the present invention is to provide an image formation apparatus and a control method thereof which decrease the flicker by changing each lighting time of the heater according to an operation condition of the image formation apparatus. 
     Other objects of the present invention will become apparent from the following description based on the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing an embodiment of the present invention; 
     FIG. 2 is a block diagram showing a structure of an image record apparatus; 
     FIG. 3 is a flow chart showing an example of a control program to be stored in a ROM  6  shown in FIG. 1; 
     FIG. 4 is a view showing an example of power change for a main heater control signal and a sub heater control signal; 
     FIG. 5 is a view showing an example of the power change for the main heater control signal and the sub heater control signal in a conventional example; 
     FIG. 6 is a view showing a heater drive condition in a second embodiment; 
     FIG. 7 is a view showing a relation between a heated and/or cooled enclosed temperature and a heater OFF time; 
     FIG. 8 is a flow chart showing a control operation in the second embodiment; 
     FIG. 9 is a flow chart showing the control operation in the second embodiment; and 
     FIG. 10 is a view showing a fixing unit. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1, which shows a first embodiment of the present invention, indicates an example of a copy machine of which structure is shown in FIG.  2 . The copy machine is composed of a reader unit and a printer unit. 
     Initially, the reader unit will be explained. In FIG. 2, numeral  302  denotes an original feeder (or document feeder: DF) which feeds an original to an original mounting glass (platen)  301 . Numerals  303  and  304  denote light sources (halogen lamp or fluorescent lamp) which illuminate the original put on the original mounting glass  301 . Numerals  305  and  306  denote reflectors which are used to condense light from the light sources  303  and  304  on the original. Numeral  314  denotes a carriage which holds the halogen lamps  303  and  304 , the reflectors  305  and  306  and a mirror  307 . Numeral  315  denotes a carriage, which holds mirrors  308  and  309 . 
     Reflection light (transmission light) from the original put on the original mounting glass  301  is guided to a condenser lens  310  by the mirrors  307 ,  308  and  309  to be guided on a CCD  101  by the condenser lens  310 . The CCD  101 , which is mounted on a substrate, converts a light signal into an electrical signal. The carriage  314  moves at a speed V in an orthogonal direction to an electrical scan (main scan) direction of the CCD  101  and the carriage  315  moves at a speed V/2, thereby scanning (sub scan) an entire surface of the original. Numeral  312  denotes an image process unit, which performs a drive control of the CCD  101  and processes the obtained electrical signal. Numeral  313  denotes an interface (I/F) unit, which interfaces with an another IPU or the like. 
     Subsequently, the printer unit will be explained. In FIG. 2, numerals  340  and  441  denotes cassettes, which hold therein recording paper sheets. Numerals  338  and  339  denote pickup rollers, which respectively pick up the sheets one by one from the cassettes  340  and  441 . Numerals  336  and  337  denote paper feed rollers, which feed the sheets picked up by the pickup rollers  338  and  339  on a transfer belt  333 . Numeral  446  denotes an adsorption charger, which charges the sheets fed by the paper feed rollers  336  and  337  cooperating with a transfer belt roller  448  used for driving the transfer belt  333 . Numeral  447  denotes a paper leading edge sensor, which detects a leading edge of the sheet on the transfer belt  333 . A detection signal from the paper leading edge sensor  447  is transmitted from the printer unit to a color reader unit, and is used as a sub-scan sync signal when a video signal is transmitted to the printer unit from the color reader unit. 
     Numeral  317  denotes an M (magenta) image formation unit,  318  denotes a C (cyan) image formation unit,  319  denotes a Y (yellow) image formation unit, and  320  denotes a K (black) image formation unit. These units are arranged opposite to the transfer belt  333  from an upstream side to a downstream side. The M image formation unit  317 , the C image formation unit  318 , the Y image formation unit  319  and the K image formation unit  320  substantially have the same structure except for colors of development agents used in development units  322 ,  325 ,  328  and  331 . 
     The M image formation unit  317  charges a surface of a photosensitive drum  341  up to a predetermined potential by using a primary charger  321  and scans the surface of the photosensitive drum  341  by driving an LED array  210  based on first color image data, after a latent image formation to form a latent image on the surface of the photosensitive drum  341  is prepared. The latent image is developed by the development unit  322  to form an M toner image. The development unit  322  contains a sleeve  345  which is used for performing a development by applying a development bias. The M toner image on the photosensitive drum  341  is to be transferred on the recording paper sheet put on the transfer belt  333  by discharging electricity from a back side of the transfer belt  333  by using a transfer charger  323 . 
     The C image formation unit  318  charges a surface of a photosensitive drum  342  up to a predetermined potential by using a primary charger  324  and scans the surface of the photosensitive drum  342  by driving an LED array  211  based on first color image data, after a latent image formation to form a latent image on the surface of the photosensitive drum  342  is prepared. The latent image is developed by the development unit  325  to form a C toner image. The development unit  325  contains a sleeve  346  which is used for performing a development by applying a development bias. The C toner image on the photosensitive drum  342  is to be transferred on the sheet put on the transfer belt  333  by discharging electricity from the back side of the transfer belt  333  by using a transfer charger  326 . 
     The Y image formation unit  319  charges a surface of a photosensitive drum  343  up to a predetermined potential by using a primary charger  327  and scans the surface of the photosensitive drum  343  by driving an LED array  212  based on first color image data, after a latent image formation to form a latent image on the surface of the photosensitive drum  343  is prepared. The latent image is developed by the development unit  328  to form a Y toner image. The development unit  328  contains a sleeve  347  which is used for performing a development by applying a development bias. The Y toner image on the photosensitive drum  343  is to be transferred on the sheet put on the transfer belt  333  by discharging electricity from the back side of the transfer belt  333  by using a transfer charger  329 . 
     The K image formation unit  320  charges a surface of a photosensitive drum  344  up to a predetermined potential by using a primary charger  330  and scans the surface of the photosensitive drum  344  by driving an LED array  213  based on first color image data, after a latent image formation to form a latent image on the surface of the photosensitive drum  344  is prepared. The latent image is developed by the development unit  331  to form a K toner image. The development unit  331  contains a sleeve  348  which is used for performing a development by applying a development bias. The K toner image on the photosensitive drum  344  is to be transferred on the sheet put on the transfer belt  333  by discharging electricity from the back side of the transfer belt  333  by using a transfer discharger  332 . 
     Numeral  349  denotes a discharge charger, which discharges electricity from the sheet in order to easily separate the sheet, which flows through the K image formation unit  320 , from the transfer belt  333 . Numeral  350  denotes a separation charger, which prevents an image confusion due to separation discharge when the sheet is separated from the transfer belt  333 . Numerals  351  and  352  denote pre-fixing chargers, which charge the sheet separated from the transfer belt  333  to prevent the image confusion by reinforcing adsorption of a toner. Numeral  334  denotes a fixing unit, which thermally fixes a toner image formed on the sheet by heat of rollers  903  and  904  heated by fixing heaters  901  and  902 . Numeral  335  denotes a paper discharge tray, which receives discharged sheets. 
     Subsequently, FIG. 1 will be explained. In FIG. 1, numeral  1  denotes a RAM (random access memory), which stores a heater lighting time setting table. Numeral  6  denotes a ROM (read only memory), which stores a control program. Numeral  3  denotes a CPU (central processing unit), which detects if the copy machine is in a heat-up state, a standby state or a copy operation state according to the control program stored in the ROM  6 . A heater lighting time and a heater lighting off time corresponding to the state of the copy machine detected by the CPU  3  or periodicity of a heater drive pulse are captured from the heater lighting time setting table stored in the RAM  1  to set them in a heater control unit  4 . Numeral  4  denotes the heater control unit, which controls drives of the fixing heaters  901  and  902  based on the lighting time or the periodicity which is set after capturing it from the RAM  1  by the CPU  3 . 
     FIG. 3 is a flow chart showing an example of the control program stored in the ROM  6  shown in FIG.  1 . When the power is supplied, ordinary lighting times of the fixing heaters and periodic data are captured from the RAM  1  to set a time 240 ms as a lighting time of the main heater  901  and a time 160 ms as a lighting time of the sub heater  902  in the heater control unit  4 , in a step S 201 . In a step S 202 , the heater control unit  4  is caused to execute a heat-up process. A timing is controlled such that the sub heater  902  is not lighted concurrently with the main heater  901 . 
     When a heat-up process by the heater control unit  4  is terminated, a flow advances to a step S 203 . In the step S 203 , it is judged whether or not the copy machine ready for copying is in the standby state. If not in the standby state, the flow advances to a step S 204 . In the step S 204 , it is judged whether or not the copy machine is in the copy operation state. If in the copy operation state, the flow returns to the step S 203 . If not in the copy operation state, the control is terminated. 
     On the other hand, in a case where the judged result in the step S 203  indicates the standby state, the flow advances to a step S 205 . In the step S 205 , changed lighting times of the fixing heaters and periodic data are captured from the RAM  1  to set a time 7200 ms as the lighting time of the main heater  901  and a time 4800 ms as the lighting time of the sub heater  902  in the heater control unit  4 . Then, in a step S 206 , wait until a copy start key  5  is depressed. In this case, also the timing is controlled such that the sub heater  902  is not lighted concurrently with the main heater  901 . When the copy start key  5  is depressed, the flow advances to a step S 207 . In the step S 207 , the ordinary lighting times of the fixing heaters and the period data are captured from the RAM  1  to set the time 240 ms as the lighting time of the main heater  901  and the time 160 ms as the lighting time of the sub heater  902 . Then the flow returns to the step S 203 . 
     Since it is not required to precisely perform temperature controls of the fixing heaters in the standby state as compared with the copy operation state, the number of lighting times are to be decreased instead of extending the lighting times of the heaters by performing such a control as the lighting time of the main heater  901  is set the time 7200 ms and the lighting time of the sub heater is set the time 4800 ms in the standby state, as described above. As a result, power changes for a main heater control signal and a sub heater control signal come to be in such a state as shown in FIG.  4 . As apparent from FIG. 4, a power change range is decreased and the number of power change times can be considerably decreased. Therefore, an obtained value can clear a flicker standardized value of IEC555-3 (IEC1000-3-3) defining the limits of voltage change and flicker in a commercially available power supply system. The voltage change and flicker occur when electrical loads of an electrical and electronic equipment are switched. 
     In the first embodiment of the present invention, an example of an image record apparatus having the two fixing heaters is described. However, the same effect as above can be obtained in case of having only one fixing heater. 
     The number of power change times can be considerably decreased by changing the lighting time of the main heater  901  and the lighting time of the sub heater  902  respectively in an image record operation state and the standby state. Therefore, since the number of power change times in the commercially available power supply system can be decreased, the obtained value can clear the above flicker standardized value. 
     FIG. 10 is a cross-sectional view of the fixing unit. 
     Numeral  11  denotes a main heater,  12  denotes a sub heater,  13  denotes a thermistor,  14  denotes a thermostat, and  15  denotes a fixing roller. 
     Hereinafter, a second embodiment of the present invention will be described. 
     FIG. 6 indicates a relation among a power variation a in case of controlling an OFF time of a fixing heater according to a sequence, a control signal b of a fixing main heater and a control signal c of a fixing sub heater. Hereinafter, the second embodiment will be explained according to an actual operation. 
     In the second embodiment, during an image formation apparatus is in a standby state, the OFF time of the fixing heater is set. For example, if a heated and/or cooled enclosed temperature is 190° C., the OFF time of the fixing main heater (500 W) is set 10,000 ms (A in FIG. 6) and the OFF time of the fixing sub heater (600 W) is set 13,000 ms (B in FIG. 6) as shown in FIG.  7 . Data corresponding to the OFF time of each heater shown in FIG. 6 is stored in the ROM  6 . Since the OFF time of the heater in the standby state is set sufficiently longer as compared with a driving period of the heater in an image formation operation state, entire number of lighting times of the heater can be reduced. If the image formation apparatus is in the standby state, since it is not required that a surface temperature of a fixing roller always reaches the heated and/or cooled enclosed temperature, there occurs no problem in this control. However, if the heated and/or cooled enclosed temperature in the standby state is not maintained at a certain level, heat quantity required in a fixing can not be immediately obtained after depressing a copy start key. Therefore, the OFF time of the fixing heater has to be properly changed according to power of the heater or the heated and/or cooled enclosed temperature as in a characteristic table indicating a relation between the heated and/or cooled enclosed temperature and the OFF time of the heater shown in FIG.  7 . 
     Lighting times of the fixing main heater and the fixing sub heater in the standby state are determined due to the fact that whether or not the temperature reaches the heated and/or cooled enclosed temperature (lighting time is not controlled in this case). That is, when each fixing heater is once lighted, the heater is lighted throughout until it reaches the heated and/or cooled enclosed temperature. If the fixing heater reaches that temperature, the heater is turned off, and the setting OFF time is counted. 
     As shown in FIG. 6, when a copy is started upon depressing the copy start key during OFF time counting, the OFF time counting is released (A″, B″). 
     In this manner, by controlling the OFF time of the fixing heater, the number of lighting times of the heater can be entirely reduced. Therefore, since the number of power change times can be considerably reduced, the obtained value can clear the flicker standardized value. 
     Since a value of the OFF time in the second embodiment is merely an example, the value can be changed according to another consideration. Further, the same effect as above can be obtained in case of the one fixing heater. 
     A control taken measures for the flicker will be described hereinafter with reference to a flow chart shown in FIG.  8 . 
     When the power is supplied in a step S 301 , the fixing heaters are simultaneously lighted for the purpose of heating up and a lighting time in an ordinary copying state is set. Then, a flow advances to a step S 302  to judge whether or not the process of heating up is terminated (reaches heated and/or cooled enclosed temperature). After terminating the process of heating up, the flow advances to a step S 303  to judge whether or not the image formation apparatus is in the standby state. If not in the standby state, the flow advances to a step S 304 . On the other hand, if in the standby state, the flow advances to a step S 305 . In the step S 305 , the OFF time of the heater read from the ROM  6  is set, and the flow advances to a step S 306 . A detailed flow chart at this time will be described later with reference to FIG.  9 . In the step S 306 , it is judged whether or not the copy start key is depressed. If the key is depressed, the flow advances to a step S 307 . In the step S 307 , the lighting time of the heater is reset (OFF time setting is released), and the flow advances to the step S 304 . In the step S 304 , it is again judged whether or not the apparatus is in a copy operation state. If not in the copy operation state, the flow advances to a step S 308  to judge whether or not the apparatus is in the standby state. In the step S 308 , if in the standby state, the flow advances to the step S 305  to perform the control after the step S 305  described above. If not in the standby state, the operation is terminated. 
     Subsequently, a control when the OFF time of the heater is set will be described with reference to FIG.  9 . 
     In a step S 401 , when the OFF times of the main and sub heaters in the standby state are set, a flow advances to a step S 402  to judge whether or not the temperature of a fixing unit reaches the heated and/or cooled enclosed temperature. If it reaches the heated and/or cooled enclosed temperature, the flow advances to a step S 403 . On the other hand, if it does not reach, the flow advances to a step S 406 . In the step S 406 , the main heater is lighted to judge whether or not the temperature of the fixing unit reaches the heated and/or cooled enclosed temperature in a step S 407 . If it reaches the heated and/or cooled enclosed temperature, the flow advances to the step S 403 . If it does not reach, the main heater is continuously lighted in the step S 406 . In the step S 403 , the main heater is turned off and the sub heater is lighted to start to count the OFF time of the main heater set in the step S 401 . Then, in a step S 404 , it is judged whether or not the copy start key is depressed. If the key is not depressed, the flow advances to a step S 405 . In this step, the main heater is forcedly maintained in an OFF state until the count terminates. If the key is depressed, the flow advances to a step S 408 . In this step, an OFF time set of the heater is released, and then operation terminates. The same control as that of the main heater is performed to the sub heater. 
     As a result, by the above control, the obtained value can clear the flicker standardized value. 
     As described above, it is needless to say that the object of the present invention can be also attained when a storage medium storing a program code of software for realizing the function in the above embodiments is supplied to a system or an apparatus, and a computer (CPU or MPU) provided in the system or the apparatus reads the program code stored in the medium and executes it. 
     In this case, the program code itself read from the storage medium realizes a new function of the present invention, and the storage medium storing therein the program code constitutes the present invention. 
     As the storage medium for supplying the program code, e.g., a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM (compact disk ROM), a CD-R (compact disk recordable), a magnetic tape, a non-volatile memory card, a ROM (read-only memory), or the like can be used. 
     It is needless to say that the functions of the above embodiments can be realized not only in the case where the computer reads and executed the program code but also in a case where an OS (operating system) or the like operating on the computer executes a part or all of the actual processes based on instructions of the program code. 
     Further, it is needless to say that the functions of the above embodiments can be realized also in a case where the program code read from the storage medium is written in a memory provided in a function expansion board inserted in the computer or a function expansion unit connected to the computer, and then on the basis of the instruction of the program code, a CPU or the like provided in the function expansion board or the function expansion unit executes a part or all of the actual processes. 
     The present invention is not limited to the above embodiments, but can be modified variously within the scope of the appended claims.