Abstract:
An image recording apparatus includes an image forming device, a fixing device, a cooling device and a controller. The image forming device forms an image on a recording medium on the basis of an image signal generated by an image signal generating unit. The fixing device uses heat to fix the image formed on the recording medium, and the cooling device cools the inside of the apparatus. The controller selectively executes either a first economy mode in which the cooling device is activated and the fixing device is inactivated on the basis of a command from the image signal generating unit, or a second economy mode in which both the cooling device and the fixing device are inactivated.

Description:
This application is a division of application Ser. No. 09/123,367, filed Jul. 28, 1998, which issued as U.S. Pat. No. 6,407,826 on Jun. 18, 2002, which is a division of application Ser. No. 08/944,417, filed Oct. 6, 1997, which issued as U.S. Pat. No. 5,828,462 on Oct. 27, 1998, which is a division of application Ser. No. 08/420,802, filed Apr. 12, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to energy saving control of an image recording apparatus which has an interface with an external unit such as a personal computer and records an image on a record sheet based on image information inputted from an external unit through the interface. 
     2. Related Background Art 
     As an image recording apparatus of this type, a laser printer which uses an electrographic process has been known. Many laser printers have the following three types of operation modes. 
     First, a print mode in which a record sheet is transported and a print operation is carried out. 
     Secondly, a stand-by mode in which an immediate print operation is ready. For example, in a laser printer having a thermal fixing unit using a halogen heater, temperature control is effected to maintain the thermal fixing unit at a slightly lower temperature in the stand-by mode than a fixing temperature in the print mode. 
     Thirdly, a sleep mode which is set by a social demand in recent energy saving trend and in which a power consumption is further reduced than that in the stand-by mode. 
     Many prior art laser printers comprise video control means for generating bit map data for each pixel as a video signal from data described by a command scheme such as PDL (page description language) based on a record command from the external unit and record control means for recording an image represented by the video signal. The control of the operation modes is effected by the record control means. A command to shift to the sleep mode and return from the sleep mode is effected from the video control means to the record control means based on information from the external unit. 
     In the prior art sleep mode, however, since the energization and deenergization of the thermal fixing unit used in the laser printer are uniformly set, optimum energy saving control to fit a variety of operation states of the printer is not attained. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an image recording apparatus which permits optimum energy saving control for various operation states of the printer. In particular, it is an object of the invention to provide an image recording apparatus in which execution of energy saving modes is performed selectively. 
     An image recording apparatus in accordance with the present invention includes an image forming means, a fixing means, a cooling means and a control means. The image forming means is for forming an image on a recording medium on the basis of an image signal generated by an image signal generating unit. The fixing device is for heat-fixing the image formed on the recording medium; the cooling means is for cooling the inside of the apparatus. The control means is for selectively executing either a first economy mode, in which the cooling means is activated and the fixing means is inactivated on the basis of a command from the image signal generating unit, or a second economy mode in which both the cooling means and the fixing means are inactivated. 
     Other objects, advantages and effects of the present invention will be apparent from the accompanying drawings, following description and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic sectional view of a laser printer in a first embodiment of the present invention, 
     FIG. 2 shows a block diagram of a video interface of the first embodiment, 
     FIG. 3 shows a timing chart for illustrating serial communication in the video interface of the first embodiment, 
     FIG. 4 shows a timing chart of a print operation in the first embodiment, 
     FIG. 5 shows a timing chart of the print operation in the first embodiment, 
     FIG. 6 shows a state transition chart of sleep control in the first embodiment, 
     FIG. 7 shows a list of command codes relating to the sleep control in the first embodiment, 
     FIG. 8 shows a bit configuration of a sleep mode designation command in the first embodiment, 
     FIG. 9 illustrates a relation between a sleep level code and a process content in the first embodiment, 
     FIG. 10 shows a circuit diagram of a configuration relating to fixing unit control and cooling fan control in the first embodiment, 
     FIG. 11 shows a state transition chart of sleep control in a second embodiment of the present invention, 
     FIG. 12 shows a circuit diagram of a configuration relating to fixing unit control, cooling fan control and photo-sensor control in a third embodiment of the present invention, 
     FIG. 13 illustrate a relation between a sleep level code and a process content in the third embodiment, 
     FIG. 14 shows a timing chart of a detection timing of a photo-sensor in the third embodiment, 
     FIG. 15 shows a bit configuration of a sleep mode designation command in a fourth embodiment, 
     FIG. 16 shows a state transition chart relating to sleep control in a fifth embodiment, 
     FIG. 17 shows a circuit diagram of a principal part of the fifth embodiment, 
     FIG. 18 shows a timing chart illustrating a relation between CPRDY and a printer state in a sixth embodiment of the present invention, 
     FIG. 19 shows a state transition chart for sleep control in a seventh embodiment, 
     FIG. 20 shows a list of command codes relating to the sleep control in the seventh embodiment, 
     FIG. 21 shows a bit configuration of a sleep-in delay time designation command in the seventh embodiment, 
     FIG. 22 illustrates a bit configuration of a sleep time designation command in the seventh embodiment, 
     FIG. 23 illustrates a list of command codes relating to sleep control in an eighth embodiment of the present invention, 
     FIG. 24 illustrates a bit configuration of a sleep-in delay time designation/sleep time designation command in the eighth embodiment, 
     FIG. 25 shows a block diagram of a video interface in a ninth embodiment of the present invention, 
     FIG. 26 shows a state transition chart relating to the sleep control in the ninth embodiment, 
     FIG. 27 illustrates a relation between a sleep level code and a process content in the ninth embodiment, 
     FIG. 28 shows a circuit diagram of a configuration relating to fixing unit control and cooling fan control in the ninth embodiment, 
     FIG. 29 shows a block diagram of a configuration of a control circuit of a clock oscillation circuit of an MPU of the ninth embodiment, 
     FIG. 30 shows a block diagram of a configuration of a control circuit of a clock oscillation circuit of an MPU of a tenth embodiment of the present invention, and 
     FIG. 31 shows a state transition chart relating to sleep control in an eleventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are now described in conjunction with the accompanying drawings. 
     [First Embodiment] 
     FIG. 1 shows a schematic sectional view of a construction of an image recording apparatus in an embodiment of the present invention. 
     A laser printer main unit  1  (hereinafter referred to as a main unit  1 ) has a cassette  2  for accommodating record sheets S, a cassette sheet sensor  3  for sensing the presence or absence of the record sheet S in the cassette  2 , a cassette size sensor  4  (comprising a plurality of microswitches) for detecting a size of the record sheet S of the cassette  2  and a sheet feed roller  5  for feeding the record sheet S from the cassette  2 . 
     A pair of registration rollers  6  for synchronously feeding the record sheet S is arranged downstream the sheet feed roller  5 . An image forming unit  8  for forming a toner image on the record sheet S based on a laser beam from a laser scanner unit  7  is arranged downstream the pair of registration rollers  6 . 
     A fixing unit  9  for thermally fixing the toner image formed on the record sheet S is arranged downstream the image forming unit  8 , and a sheet ejection sensor  10  for sensing the sheet transport state of a sheet ejection unit, a sheet ejection roller  11  for ejecting the record sheet S and a stack tray  12  for stacking recorded sheet S are arranged downstream the fixing unit  9 . 
     The laser scanner unit  7  comprises a laser unit  13  for emitting a laser beam modulated with an image signal (VDO) sent from an external unit  28  to be described later, a polygon motor  14  for scanning the laser beam from the laser unit  13  onto a photoconductor drum  17  to be described later, a group of focusing lenses  15  and a deflection mirror  16 . 
     The image forming unit  8  comprises the photoconductor drum  17 , a pre-exposure lamp  18 , a primary charger  19 , a developing unit  20 , a transfer charger  21  and a cleaner  22  which are required in a known electrographic process. The fixing unit  9  comprises a heat roller  9   a , a pressure roller  9   b , a halogen heater  9   c  arranged in the heat roller and a thermistor  9   d  for detecting a surface temperature of the heat roller. 
     A main motor  23  is energized through a sheet feed roller clutch  24  and the pair of registration rollers  6  are energized through a registration roller  25 , and units in the image forming units  8 , the fixing unit  9  and the sheet ejection roller  11  are also energized. 
     An engine controller  26  controls the electrographic process by the laser scanner unit  7 , the image forming unit  8  and the fixing unit  9  and controls the feed of the record sheet in the main unit  1 . 
     A video controller  27  is connected to the external unit  31  such as a personal computer through a general purpose interface (Centronics, RS232C, etc.)  30  and develops image data sent from the general purpose interface  30  into bit data which is converted to a VDO signal and sent to the engine controller  26 . 
     A video interface  28  is communication means between the video controller  27  and the engine controller  26 . 
     A cooling fan  29  is rotated and stopped by the engine controller  26  to cool the interior of the printer, particularly the video controller  27 . 
     FIG. 2 shows a block diagram of a configuration of the video interface  28  shown in FIG.  1 . 
     In FIG. 2, CPRDY is a signal indicating that the external unit  3  is ready to communicate, and it is sent from the video controller  27  to the video controller  26 . 
     PPRDY is a signal indicating that the engine controller  26  is ready to communicate and it is sent from the engine controller  26  to the video controller  27 . 
     SBSY is a status valid signal which is sent from the engine controller  26  to the video controller  27 . 
     CBSY is a command valid signal which is sent from the video controller  27  to the engine controller  26 . 
     SC is a status/command signal. When the status valid signal SBSY is true, it is sent from the engine controller  26  to the video controller  27  as status data indicating the internal status of the printer, and when the command valid signal CBSY is true, it is sent from the video controller  27  to the engine controller  26  as command data indicating a command from the video controller  27  to the engine controller  26 . 
     CLK is a synchronization clock of the status/command signal SC and it is sent from the video controller  27  to the engine controller  26 . The engine controller  26  sends back a corresponding status to each command from the video controller. 
     Namely, the signals SBSY, CBSY, SC and CLK conduct the hand shaking serial communication. 
     RDY is a ready signal which is true when the engine controller  26  is ready to print and it is sent from the engine controller  26  to the video controller  27 . 
     PRINT is a print signal which is true when the video controller  27  indicates the start of print and it is sent from the video controller  27  to the engine controller  26 . 
     VSREQ is a vertical synchronization request signal by which the engine controller  26  requests the output of a vertical synchronization signal VSYNC to be described later to the video controller  27 . 
     VSYNC is the vertical synchronization signal for vertically (sub-scan direction/sheet feed direction) synchronizing the image output sent from the video controller  27  to the engine controller  26 . 
     BD is a horizontal synchronization signal for horizontally (main scan direction/laser scan direction) synchronizing the image output sent from the engine controller  26  to the video controller  27 . 
     VDO is an image signal by which the video controller  27  serially sends a dot image to the engine controller  26  in synchronism with the vertical synchronization signal VSYNC and the horizontal synchronization signal BD. 
     FIG. 3 shows a timing chart of a serial communication operation. 
     When the main unit  1  is powered and the engine controller  26  is initialized and is ready for the serial communication, the engine controller  26  renders the PPRDY true. 
     On the other hand, when the video controller  27  is powered, initialized and is ready for the serial communication, the video controller  27  renders CPRDY true. The video controller  27 , after confirming that the PPRDY is true for a predetermined time period, determined that it is ready for the serial communication, and renders CBSY true if necessary, and sends an 8-bit command through the SC line in synchronism with CLK. Then, it renders CBSY false and waits for the send-back of the status from the engine controller  26 . 
     When the engine controller  26  receives the command, it renders SBSY true to send back the status in accordance with the content of the command. When the video controller  27  detects the true state of SBSY, it starts the transmission of CLK and the engine controller  26  sends back the status through the SC line in synchronism with CLK and renders SBSY false. 
     When the engine controller  26  confirms the true state of CPRDY for a predetermined time period, it is determined that the serial communication is ready and the command is valid. 
     FIGS. 4 and 5 show timing charts of a print operation of the main unit  1 . Referring to those figures, the print operation is explained. 
     When the engine controller  26  is ready for the print operation, it renders RDY true and informs the print ready state to the video controller  27 . In response thereto, the video controller  27  renders PRINT true if a print request is issued to indicate the start of printing. 
     When the engine controller  26  detects the true state of PRINT, it starts to drive the main motor  23  and the polygon motor  14 . When the main motor is driven, the photoconductor drum  17 , the fixing roller (in the fixing unit  9 ) and the sheet ejection roller  11  are rotated. The engine controller  26  activates the high voltage for the primary charger  19 , the developing unit  20  and the transfer charger  21 , turns on the sheet feed clutch  24  to drive the sheet feed roller  5  t1 second after the steady state of the rotation of the polygon motor  14  (see FIG.  4 ), and feeds the record sheet S toward the pair of registration rollers  6 . 
     At the timing when the leading edge of the record sheet S reaches the pair of registration rollers  6  (t2 second after the drive of the sheet feed roller  5 ), the engine controller  26  sends the vertical synchronization request signal VSREQ to the video controller  27  and turns off the sheet feed clutch  24  to stop the drive of the sheet feed roller  5 . 
     When the video controller  27  completes the development of the image information into the dot image and the image signal VDO is ready to output, it confirms that the vertical synchronization request signal VSREQ is true and renders the vertical synchronization signal VSYNC true, and starts to output one page of image signal VDO tV second later in synchronism thereto. 
     The engine controller  26  turns on the registration roller clutch  25  t3 second after the rise of the vertical synchronization signal VSYNC to drive the pair of registration rollers  6 . The pair of registration rollers  6  are driven for t4 second until the trailing edge of the record sheet S is fed past the pair of registration rollers  6 . 
     During this period, the engine controller  26  sends the horizontal synchronization signal BD to the video controller  27  at a predetermined timing in synchronism with the laser scan and modulates the laser beam emitted from the laser unit  13  based on the image signal VDO. 
     As shown in FIG. 5, the video controller  27  outputs one scan of image signal VDO in synchronism with the rise of the horizontal synchronization signal BD. 
     When the next page is to be printed, the print signal PRINT is rendered true t5 second later. Then, the same operation as that for the first page is carried out. 
     Through the above operation, the record sheet S is sequentially fed to the sheet feed roller  5 , the pair of registration rollers  6 , the image forming unit  8 , the fixing unit  9  and the sheet ejection roller  11  so that the image is recorded. 
     The energy saving, that is, the sleep control in the present embodiment is now explained. 
     The printer  1  is either in the stand-by mode or in the sleep mode except in the print mode and provided that no abnormal state such as failure occurs. 
     In the stand-by mode, it may be immediately shifted to the print mode upon the print request. Specifically, a temperature of the fixing unit  9  is set to a lower temperature than a temperature in the print mode (for example, the fixing unit temperature in the stand-by mode is 150° C. while the fixing unit temperature in the print mode is 190° C.) and the cooling fan  29  is energized to cool the video controller. 
     On the other hand, in the sleep mode, the power consumption is more reduced than that in the stand-by mode. The sleep mode has a sleep level 0 and a sleep level 1. In the level 0, the energization to the fixing unit  9  is stopped, and in the level 1, the energization to the fixing unit  9  is stopped as well as the energization of the cooling fan  29  is stopped. The shift from the stand-by mode to the sleep mode is controlled by a command sent from the video controller  27  to the engine controller  26  through the video interface  28 . 
     FIG. 6 shows a state transition chart illustrating the state transition for the sleep control of the main unit  1 . 
     As shown, the transition from the stand-by mode to the sleep level 0 mode is effected by the sleep designation command and the designation of the sleep level 0 by the sleep mode designation command. 
     The transition from the stand-by mode to the sleep level 1 mode is effected by the sleep designation command and the designation of the sleep level 1 mode by the sleep mode designation command. 
     The mode is shifted to the stand-by mode from the level 0 or level 1 sleep mode by a wake-up designation command. 
     FIG. 7 shows command codes relating to the sleep control. 45H in a hexadecimal code is allocated to the sleep designation, and 46H is allocated to the wake-up designation. 
     The sleep mode designation is made by a 2-byte command. The video controller  27  sends a command code 80H at the first byte, and sends a predetermined command code at the second byte to designate the sleep level. 
     FIG. 8 shows a bit configuration of the second byte of the sleep mode designation command. 
     The command designates the sleep level by the three bits (5th to 7th bits) of the eight bits. 
     FIG. 9 illustrates a relation between the sleep level code and a process content. A code 000 designates the sleep level 0, that is, the deenergization of the fixing unit. A code 001 designate the sleep level 1, that is, the deenergization of the fixing unit and the deenergization of the cooling fan. Codes 010 to 111 are unused. 
     FIG. 10 shows a circuit diagram of a halogen heater drive circuit for controlling the temperature of the fixing unit  9  shown in FIG. 1 and a drive circuit for the cooling fan  29 . 
     In FIG. 10, the halogen heater  9   c  in the fixing unit  9  is connected to a commercial power source (AC power source)  32  through a TRIAC  33   a  in a SSR  33  which is a solid state relay comprising the TRIAC  33   a , a LED  33   b  and a zero-crossing detection circuit (not shown). When the LED  33   b  emits a light, the TRIAC  33   a  conducts and the halogen heater is turned on. The LED  33   b  is connected to a +5V power supply (generated from the commercial power source by a low voltage power circuit (not shown)) which powers the DC-powered engine controller  26  and has a cathode thereof connected to a collector of a grounded emitter NPN transistor  37 . A base of the transistor  37  is connected to an output port (OUT 1 ) of the MPU  26   a  through a grounded resistor  39  and a resistor  38 . 
     The MPU  26   a  is a microcomputer which controls the engine controller  26 . When the MPU  26   a  renders the output port (OUT 1 ) to L (off), the LED  33   b  is not turned on and the halogen heater  9   c  is not turned on. When it renders an output port (OUT 2 ) to H (on), the LED  33   b  is turned on and the halogen heater  9   c  is turned on. 
     The thermistor  9   d  in the fixing unit  9  has one end thereof connected to the DC +5V power supply and the other end thereof connected to a resistor  35 . 
     An analog voltage Vt determined by the thermistor  9   d  and the resistor  35  is supplied to an A/D conversion input port of the MPU  26   a  and the MPU  26   a  detects the fixing unit temperature. 
     In the above arrangement, the MPU  26   a  monitors the fixing unit temperature by the analog voltage Vt and changes an on/off duty factor of the output port to control the temperature of the fixing unit  9 . 
     On the other hand, a transistor for driving the cooling fan  29  is connected to the output port (OUT 2 ) of the MPU  26   a  through a base resistor  41 . A counter emf absorbing diode  43  for the cooling fan  29  is connected to a DC +24V power supply which powers to a collector of the transistor  43  and the cooling fan. Accordingly, when the MPU  26   a  renders the output port (OUT 2 ) to H (on), the cooling fan is energized, and when it renders the output port (OUT 2 ) to L (off), the cooling fan is deenergized. 
     In the above arrangement, the video controller  27  may arbitrarily designates the sleep level 0 mode in which the cooling fan is energized and the sleep level 1 mode in which the cooling fan is deenergized. 
     [Second Embodiment] 
     A second embodiment of the present invention is now explained. A difference between the second embodiment and the first embodiment resides in that the sleep level may be changed only by the sleep mode designation command. 
     FIG. 11 shows a state transition chart relating to the sleep control in the second embodiment. 
     When the printer is in the sleep level 0 state and the video controller  27  sends the sleep mode designation command to the engine controller  26  while designating the sleep level 1, the printer is shifted to the sleep level 1 mode. On the other hand, when the printer is in the sleep level 1 mode and the sleep mode designation command is sent while designating the sleep level 0, the printer is shifted to the sleep level 0 mode. 
     In this manner, the video controller  27  may omit the wake-up designation command and the sleep designation command when the sleep level is to be changed so that a process load is reduced. 
     [Third Embodiment] 
     A third embodiment of the present invention is now explained. A difference between the third embodiment and the first embodiment resides in the addition of photo-sensor control to the control in the sleep mode. 
     FIG. 12 shows a circuit diagram of the halogen heater drive circuit, the cooling fan drive circuit and the photo-sensor control circuit. 
     In FIG. 12, the halogen heater drive circuit and the cooling fan drive circuit are identical to those of FIG. 10 shown for the first embodiment and the explanation thereof is omitted. 
     The photo-sensor control circuit is now explained. 
     The laser printer of the present embodiment uses two photo-sensors, one being a cassette sheet sensor  3  and the other being a sheet ejection sensor  10 . The cassette sheet sensor  3  comprises an LED  3   a  and a photo-transistor  3   b  and detects the status by checking if a light from the LED  3   a  impinges to the photo-transistor  3   b  or not. 
     An anode of the LED  3   a  is connected to the DC +24V power supply through a resistor  47  and a cathode thereof is connected to a collector of a transistor  45 . An emitter of the transistor  45  is connected to GND and a base thereof is connected to an output port (OUT 3 ) of the MPU  26   a  through a base resistor  44 . 
     Accordingly, when the MPU  26   a  renders the output port (OUT 3 ) to H, the LED  3   a  is turned on and the detection by the photo-sensor is enabled, and when it renders the output port (OUT 3 ) to L, the LED  3   a  is turned off and the detection is disabled. 
     An emitter of the photo-transistor  3   b  is connected to GND and a collector thereof is connected to an input port (IN 1 ) of the MPU  26   a  and a pull-up resistor  46 . When the light from the LED  3   a  is impinged to a base of the photo-transistor  3   b , the input port (IN 1 ) is rendered to L, and if it is not impinged, the input port (IN 1 ) is rendered to H. 
     The same connection is made for the sheet ejection sensor  10 , and the LED  3   a  in the above description corresponds to an LED  10   a , the photo-transistor  3   b  corresponds to a photo-transistor  10   b , the resistor  47  corresponds to a resistor  49 , the pull-up resistor  46  corresponds to a pull-up resistor  48 , and the input port (IN 1 ) corresponds to an input port (IN 2 ). 
     FIG. 13 illustrates a relation between the sleep level code and a process content in the third embodiment. 
     In addition to the first embodiment, a photo-sensor intermittent detection process for the sleep level 0 mode and a photo-sensor detection stop process for the sleep level 1 mode are added. 
     FIG. 14 shows a timing chart of the photo-sensor detection process in the respective modes. 
     In the stand-by mode, the MPU  26   a  renders to output port (OUT 3 ) to H to turn on the LED  3   a  and the LED  10   a  so that the detection by the photo-sensor is continuously effected. In the sleep level 0 mode, the LED is turned on at an interval of a period t10 (for example, 10 seconds) and the intermittent detection is made only during that period. In the sleep level 1 mode, the LEDs are turned off and the detection is stopped. 
     Through this control, the power consumption by the light emission of the LED in the photo-sensor is reduced or eliminated during the sleep mode so that further energy saving is attained. [Fourth Embodiment] 
     A fourth embodiment of the present invention is now explained. A difference between the fourth embodiment and the third embodiment resides in that the setting of the sleep level is controlled by controlling the energization to the load in accordance with the sleep mode designation command bit. 
     FIG. 15 shows a bit configuration of the second byte of the sleep mode designation command in the fourth embodiment and a process for the bit. 
     As shown, when the fifth bit is 1, the detection by the photosensor is stopped, when the sixth bit is 1, the cooling fan is deenergized, and when the seventh bit is 1, the fixing unit is deenergized. 
     By this process, the video controller  27  may designate any combination of sleep modes. 
     [Fifth Embodiment] 
     A fifth embodiment of the present invention is now explained. A difference between the fifth embodiment and the first embodiment resides in the addition of the detection of the direct access to the printer by a user as a condition to transit from the sleep mode to the stand-by mode. 
     FIG. 16 shows a state transition chart indicating the state transition relating to the sleep control in the fifth embodiment. 
     In the sleep level 0 mode and the sleep level 1 mode, the mode is shifted to the stand-by mode when the wake-up designation command is received as well as when the open state of a door (not shown) of the printer which is opened when jam is to be processed or when the user depresses a test print switch (not shown) to print. In the test print, the mode is then shifted to the print mode from the stand-by mode for effecting the test print. 
     FIG. 17 shows a circuit diagram of a principal portion of the fifth embodiment. 
     A door switch  50  is opened when the door is opened and closed when the door is closed. One terminal of the door switch  50  is connected to GND and the other terminal is connected to a pull-up resistor  51  and the input port (IN 3 ) of the MPU  26   a . Accordingly, the MPU  26   a  determines that the door is closed when the input port (IN 3 ) is L, and the door is open when the input port (IN 3 ) is H. 
     A test print switch  52  is normally open and closed when the user depresses the test print switch  52 . One terminal of the test print switch  52  is connected to GND and the other terminal is connected to a pull-up resistor  53  and an input port (IN 4 ) of the MPU  26   a . Accordingly, the MPU  26   a  determines that the test print is requested when the input port (IN 4 ) is L, and the test print is not requested when the input port (IN 4 ) is H. 
     [Sixth Embodiment] 
     A sixth embodiment of the present invention is now explained. A difference between the sixth embodiment and the first embodiment resides in the control which does not accept soft reset by the signal CPRDY in the sleep mode. 
     FIG. 18 illustrates a relation between the signal CPRDY and the printer state in the sixth embodiment. 
     In the sleep level 0 mode and the sleep level 1 mode, the sleep mode is maintained whether the state of CPRDY is true (H) or false (L). The video controller  27  renders CPRDY true (H) and sends the wake-up designation command, and after the printer state has been shifted to the stand-by mode, it renders CPRDY false (L) so that the engine controller  26  is reset and the printer is initialized. 
     Accordingly, even if CPRDY is rendered false by the energy saving control (partial deenergization in the video controller) of the video controller  27  when the printer is in the sleep mode, the engine controller  26  is not reset and the sleep mode is maintained. 
     [Seventh Embodiment] 
     A seventh embodiment of the present invention is now explained. A difference between the seventh embodiment and the first embodiment resides in that a time from the transmission of the sleep designation command to the transition to the sleep mode and a time from the transition to the sleep mode to the automatic wake-up are settable. 
     FIG. 19 shows a state transition chart indicating the state transition relating to the sleep control in the seventh embodiment. 
     As shown, when the sleep designation command is received in the stand-by mode, the mode is shifted to the sleep mode designated by a sleep mode designation command after a delay time designated by a sleep-in delay time command to be described later. 
     On the other hand, the mode is shifted from the sleep mode to the stand-by mode after the elapse of the sleep time (the time elapsed after the transition to the sleep mode) designated by a wake-up designation command of a sleep time designation command to be described later. 
     The sleep-in delay time designation and the sleep time designation are now described. 
     FIG. 20 illustrates the commands relating to the sleep control in the seventh embodiment. 
     The sleep-in delay time designation is effected by the sleep-in delay time designation command which is the second byte command as is the sleep mode designation command. The first byte of the sleep-in delay designation command is 83H and the second byte is configured as shown in FIG.  21 . The binary value of the six bits, second to seventh bits of the second byte indicates a time with one bit corresponding to ten minutes. 
     Namely, if it is 000111 (B), it represents 6×10 minutes so that the delay time of 60 minutes is designated. 
     On the other hand, the sleep-in time is designated by the sleep time designation command which is the second byte command. The first byte of the sleep time designation command is 85H and the second byte is configured as shown in FIG.  22 . The binary value of six bits, the second to seventh bits of the second byte indicates a time with one bit corresponding to ten minutes. 
     For example, if it is 001000 (B), it indicates 8×10 minutes so that the sleep time of 80 minutes is designated. 
     By this arrangement, the video controller  27  may reduce the time management process for the sleep control. 
     [Eighth Embodiment] 
     An eighth embodiment of the present invention is now explained. A difference between the eighth embodiment and the seventh embodiment resides in the consolidation of the sleep-in delay time designation command and the sleep time designation command. 
     FIG. 23 illustrates commands relating to the sleep control in the eighth embodiment. 
     The sleep-in delay time designation and the sleep time designation are effected by a sleep-in delay time designation/sleep time designation command which is a 2-byte command. The first byte of the command is 83H and the second byte is configured as shown in FIG.  24 . The binary value of three bits, second to fourth bits of the second byte indicates the sleep-in delay time and the binary value of three bits, fifth to seventh bits indicates the sleep time, with one bit corresponding to 30 minutes. 
     For example, if it is 010100 (B), it indicates 4×30 minutes so that the delay time of 2 hours is designated, and 8×30 minutes so that the sleep time of 4 hours is designated. 
     Thus, both the sleep-in delay time and the sleep time can be designated by the single command so that the command configuration and the exchange thereof are simplified. 
     [Ninth Embodiment] 
     A ninth embodiment of the present invention is now explained. In the present embodiment, the construction of the laser beam printer is common to that shown in FIG.  1  and the explanation thereof is omitted. A basic operation is also common to that described in connection with FIGS. 3 to  5  and the explanation thereof is omitted. 
     FIG. 25 shows a block diagram of a configuration of the video interface  28  shown in FIG.  1 . 
     In FIG. 25, RESET is a reset signal by which the video controller  27  hard-resets the engine controller  26 . Others are common to those shown in FIG.  2  and the explanation thereof is omitted. 
     The energy saving or the sleep control in the present embodiment is now explained. 
     The printer  1  is either in the stand-by mode or in the sleep mode except in the print mode provide that no abnormal state such as failure occurs. 
     In the stand-by mode, the mode may be immediately shifted to the print mode upon print request. Specifically, the temperature of the fixing unit  9  is set to a lower temperature than that in the print mode (for example, the fixing unit temperature in the standby mode is 150° C. while the fixing unit temperature in the print mode is 190° C.) and the cooling fan  29  is energized to cool the video controller. 
     On the other hand, in the sleep mode, the power consumption is further reduced than that in the stand-by mode. The sleep mode includes three levels, sleep level 0, sleep level 1 and sleep level 2. In the level 0, the fixing unit is deenergized, in the level 1, the fixing unit  9  is deenergized as well as the cooling fan  29  is deenergized, and in the level 2, in addition to the level 1, the clock of the MPU  26   a  in the engine controller is stopped. The transition from the stand-by mode to the sleep mode is effected in accordance with a command sent from the video controller  27  to the engine controller  26  through the video interface  28 . 
     FIG. 26 shows a state transition chart illustrating the state transition relating to the sleep control of the main unit  1 . 
     As shown, the mode is shifted from the stand-by mode to the sleep level 0 mode by the sleep designation command and the designation of the sleep level 0 by the sleep mode designation command. 
     The mode is shifted from the stand-by mode to the sleep level 1 mode by the sleep designation command and the designation of the sleep level 1 by the sleep mode designation command. 
     Further, the mode is shifted from the stand-by mode to the sleep level 2 mode by the sleep designation mode and the designation of the sleep level 2 by the sleep mode designation command. 
     The mode is shifted from the level 0 or level 1 sleep mode to the stand-by mode by the wake-up designation command. 
     When hard-reset is applied in the level 2 sleep mode, the mode is shifted to the stand-by mode through the initial reset. 
     In the commands relating to the sleep control, 45H of the hexadecimal code is allocated to the sleep designation and 46H is allocated to the wake-up designation, as shown in FIG.  7 . 
     The sleep mode designation is of 2-byte command configuration. The video controller  27  sends the command code 80H at the first byte and sends a predetermined command at the second byte to designate the sleep level. 
     The second byte of the sleep mode designation command is configured as shown in FIG.  8 . 
     The command designates the sleep level by the 3-bit (fifth to seventh bits) of the 8 bits. 
     FIG. 27 illustrates a relation between the sleep level code and a process content in the present embodiment. The code 000 designates the sleep level 0, that is, the deenergization of the fixing unit. The code 001 designates the sleep level 1, that is, the deenergization of the fixing unit and the deenergization of the cooling fan. The code 010 designates the sleep level 2, that is, the stop of the clock of the MPU  26   a . The codes 011-111 are unused. 
     FIG. 28 shows a circuit diagram of the halogen heater drive circuit for controlling the temperature of the fixing unit  9  shown in FIG.  1  and the drive circuit for the cooling fan  29 . 
     Basically, it is identical to that shown in FIG. 1 for the first embodiment but in the present embodiment, the MPU  26   a  uses the NEC μPD78214 and has a crystal oscillator  68  shown and RESET * terminal (where * indicates a negative logic). 
     The sleep mode 2 is now explained in detail. 
     The sleep modes 0 and 1 are designated by the MPU  26   a  and the MPU  26   a  continues its operation even during the sleep mode while the MPU  26   a  per se does not operate in the sleep mode 2. In the sleep mode 2, the MPU  26   a  stops the oscillation and stops the overall operation. 
     The MPU  26   a  may be operated with a very small power consumption with a leakage current only. This is referred to as a stop mode of the MPU. 
     FIG. 29 shows a block diagram of a configuration of a control circuit of a clock oscillation circuit of the MPU  26   a . Referring to FIG. 29, an internal operation of the MPU  26   a  is explained. 
     When the MPU  26   a  receives the sleep mode 2 request, it carries out the sleep mode process, that is, deenergizes the fixing unit  9  and deenergizes the fan  29  and renders PPRDY of the interface signal  28  false and then sets the bit  1  of a stand-by control register STBC  61  through an internal bus. Thus, a stop flip-flop  62  is set and stops the operation of a system clock oscillator  64  which generates a clock by using the crystal oscillator  63 . 
     When the oscillator  64  is stopped, a frequency divider  65  which divides the output of the oscillator  64  is also stopped and the clock supplied to the MPU  26   a  is stopped so that the entire MPU  26   a  is stopped. Thus, the stop mode is entered. 
     In order to wake up from the stop mode, the system should be hard-started up. The start-up may be effected by a non-maskable interrupt terminal NMI or a reset signal. In the ninth embodiment, a method by the reset signal is explained. 
     When a signal RESET of the interface signal  28  of FIG. 25 is applied to the terminal RESET * of the MPU  26   a , the stop flip-flop  62  is reset through an inverter  66  and an OR circuit  67  of FIG.  29  and the system clock oscillator  64  is started and the MPU  26   a  is started. 
     The MPU  26   a  is reset simultaneously with the start so that it is initialized such as memory clear and port initialization. To start up from the sleep mode, whether a command  46 H, the wake-up designation is to be used or the reset signal is to be used is stored by the video controller  27 . 
     If PPRDY signal is false, the reset signal from the video controller  27  may be outputted. 
     [Tenth Embodiment] 
     A tenth embodiment of the present invention is now explained. 
     In the tenth embodiment, another start-up method from that of the ninth embodiment is explained. In the ninth embodiment, the signal RESET is applied to the terminal RESET * of the MPU  26   a . Thus, the initialization operation is started simultaneously with the start-up from the sleep mode and the memory is cleared. 
     Thus, when the signal PPRDY of the interface signal  28  is rendered true after the start-up, it is necessary for the video controller  27  to conduct the entire communication protocol from the beginning. 
     In the tenth embodiment, as shown in FIG. 30, the signal RESET for the start-up is applied to the non-maskable interrupt terminal NMI of the MPU  26   a.    
     In this case, the MPU  26   a  is started up without being reset. After the start-up, the engine controller  26  is immediately set to the stand-by mode and the signal PPRDY of the interface signal  28  is rendered true. Thus, the video controller  27  need not conduct the initial protocol to start the communication with the printer and the data in the memory of the MPU  26   a  is maintained. Accordingly, the retransmission of the data prior to the sleep is not necessary. 
     The signal RESET is not the reset function and it may be correctly referred to as a signal WAKE-UP. 
     [Eleventh Embodiment] 
     An eleventh embodiment of the present invention is now explained. 
     FIG. 31 illustrates a state transition relating to the sleep control capable of changing the level during the sleep. 
     When the printer is in the sleep level 0 or 1 and the video controller  27  sends the sleep mode designation command to the engine controller  26 , and if the sleep level 2 is designated, the printer is shifted to the sleep level 2 mode. 
     When a printer is in the sleep level 0 and the sleep level 1 is designated, the printer is shifted to the sleep level 1, and when the printer is in the sleep level 1 and the sleep level 0 is designated, the printer is shifted to the sleep level 0. 
     However, when the printer is in the sleep level 2, it is not possible to change the sleep level by the command because the MPU  26   a  is not operating and the signal RESET is applied to the terminal RESET * or the terminal NMI to reset it to the stand-by mode. 
     Since the wake-up designation command and the sleep designation command may be omitted in changing the sleep level, the process load is reduced. 
     In accordance with the present invention, the function to designate the mode from the video control means for a plurality of sleep modes in the recording means is provided in the communication means so that optimum energy saving control to various operation conditions of the printer such as the frequency of use and the reduction of the financial burden of the power consumption is attained. 
     The present invention should not be limited to the above illustrated embodiments but many modifications thereof may be made. The above embodiments may be combined in any manner and they are within the scope of the present invention.