Patent Publication Number: US-8977147-B2

Title: Image forming apparatus capable of computing power consumption thereof, and control method and storage medium therefor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus capable of computing power consumption thereof, and a control method and a storage medium therefor. 
     2. Description of the Related Art 
     In recent years, image forming apparatuses such as printers have been demanded to reduce power consumption thereof for reduction of emission of greenhouse gas such as carbon dioxide. To this end, it is necessary to grasp power consumptions of individual image forming apparatuses at the time of image formation. However, if an externally-attached power meter or a built-in power meter is provided in each of individual image forming apparatuses, a problem of increased cost is caused. 
     Japanese Laid-open Patent Publication No. 2010-4382 discloses a power measurement system including an image forming apparatus with no power meter and an image forming apparatus with power meter, which are network-connected with each other. This system estimates power consumption of the image forming apparatus with no power meter which is consumed when the apparatus is in a sleep state on the basis of power consumption of the image forming apparatus with power meter measured by the power meter and consumed when the apparatus is in a sleep state. 
     With the power measurement system, power consumption of the image forming apparatus consumed when the apparatus is in a sleep state can be estimated, but power consumption thereof consumed when the apparatus executes a print job cannot accurately be computed. 
     Japanese Laid-open Patent Publication No. 2010-72253 discloses a power consumption calculation method in which a work load of a job executed by an image forming apparatus is measured and a power consumption amount corresponding to one job execution is calculated based on the measured work load and state transition data that indicates power consumption and a required time for each of states of the image forming apparatus. 
     Power consumption differs depending on print job contents. For example, power consumption differs between monochrome text printing on an A4 sheet and color graphic printing on a postcard due to a difference in fixing device temperature and a difference in sheet conveyance motor speed. Nevertheless, the above-described power consumption calculation method cannot compute power consumption that reflects factors affecting the power consumption. 
     As described above, conventional techniques have a problem that power consumption of image forming apparatus cannot be computed with accuracy. 
     SUMMARY OF THE INVENTION 
     The present invention provides an image forming apparatus capable of accurately computing power consumption thereof, and a control method and a storage medium therefor. 
     According to one aspect of this invention, there is provided an image forming apparatus having a photosensitive member, an exposure unit that exposes the photosensitive member to light according to an image to be formed to thereby form an electrostatic latent image on the photosensitive member, and a fixing device that fixes onto a recording medium a toner image formed on the photosensitive member by developing the electrostatic latent image and transferred from the photosensitive member to the recording medium, comprising a first computing unit configured to compute first power consumption consumed by the fixing device until the fixing device becomes a state capable of fixing the toner image onto the recording medium, a second computing unit configured to compute, according to at least a type of the recording medium, second power consumption that includes power consumption consumed by the fixing device to fix the toner image onto the recording medium and power consumption consumed to convey the recording medium onto which the toner image is to be fixed, a third computing unit configured to compute, according to the image to be formed, third power consumption consumed by the exposure unit to expose the photosensitive member to light, and a fourth computing unit configured to compute a sum of the first power consumption, the second power consumption, and the third power consumption. 
     With this invention, the first power consumption consumed by the fixing device of the image forming apparatus until the fixing device becomes capable of fixing a toner image onto a recording medium is computed, the second power consumption that includes power consumption consumed by the fixing device to fix the toner image onto the recording medium and power consumption consumed by conveyance of the recording medium onto which the toner image is to be fixed is computed according to a type of the recording medium, the third power consumption consumed by the exposure unit of the image forming apparatus to expose the photosensitive member of the image forming apparatus to light is computed according to an image to be formed, and a sum of the first to third power consumptions is computed. It is therefore possible to compute power consumption of the image forming apparatus with accuracy. 
     Further features of the present invention will become apparent from the following description of an exemplary embodiment with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically showing the construction of an image forming apparatus according to one embodiment of this invention; 
         FIG. 2  is a view showing a fixing-device power consumption table and a sheet-conveyance power consumption table, which are provided in a printer engine controller of the image forming apparatus; 
         FIG. 3  is a schematic view showing the construction of an essential part of the image forming apparatus; 
         FIG. 4  is view showing a time-dependent change of power consumption consumed by the image forming apparatus to execute print jobs; 
         FIG. 5A  is a view showing a difference between power consumptions consumed by execution of two print jobs where the same print content is printed on an A4 normal sheet and on a postcard, respectively; 
         FIGS. 5B and 5C  are views schematically showing the print content printed on the A4 normal sheet and on the postcard when the print jobs shown in  FIG. 5A  are executed; 
         FIG. 5D  is a view showing a difference between power consumptions consumed by execution of two print jobs where different print contents are printed on A4 normal sheets; 
         FIGS. 5E and 5F  are views schematically showing print contents printed on the respective A4 normal sheets when the print jobs shown in  FIG. 5D  are executed; 
         FIG. 6  is a flowchart showing procedures of a power consumption computing process executed by a main controller of the image forming apparatus while the fixing device temperature is increased at a predetermined temperature increase rate; and 
         FIG. 7  is a flowchart showing procedures of a power consumption computing process executed by the main controller while the fixing device temperature is increased to a predetermined temperature in a predetermined time period. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention will now be described in detail below with reference to the drawings showing a preferred embodiment thereof. 
       FIG. 1  schematically shows in block diagram the construction of an image forming apparatus according to one embodiment of this invention. 
     As shown in  FIG. 1 , the image forming apparatus  100  includes amain controller  1000  that controls the entire image forming apparatus  100 , a printer engine  2000  that forms or prints an image on a recording medium such as a sheet of paper, and a panel  3000  that provides a user interface for displaying information to a user and for being used by a user to operate the image forming apparatus  100 . 
     The main controller  1000  includes an ASIC  1100  that controls the main controller  1000 , a RAM  1300  that is a volatile memory having a control program execution area, a work data area, and an output data storage area, and a ROM  1400  that is a nonvolatile memory storing control programs. 
     The ASIC  1100  includes a CPU  1110  that controls respective parts of the main controller  1000 , an image processor  1120  that performs image processing on a print job sent from a PC  200 , and a PC interface  1130  that receives the print job from the PC  200 . The ASIC  1100  also includes a RAM interface  1140 , a panel interface  1150 , and a ROM interface  1160  that respectively perform data communication with the RAM  1300 , the panel  3000 , and the ROM  1400 . The ASIC  1100  further includes a printer interface  1200  that transfers image data to the printer engine  2000  and performs control communication with the printer engine  2000 . The printer interface  1200  includes a video count unit  1210  that counts a video count value, which will be described later. 
     The printer engine  2000  includes a controller interface  2100  that performs data communication with the main controller  1000 , and a printer engine controller  2200  that controls the printer engine  2000  and has a fixing-device power consumption table  2210  and a sheet-conveyance power consumption table  2220 . 
     The printer engine  2000  also includes a fixing device  2300  that becomes a state capable of fixing a toner image onto a sheet when the actual temperature of the fixing device  2300  is increased to a predetermined temperature. The fixing device  2300  includes a temperature detection unit  2310  that detects an actual temperature of the fixing device  2300 . 
     The printer engine  2000  further includes a sheet conveyance motor controller  2400  that includes a speed controller  2410  for controlling the speed of a sheet conveyance motor (not shown). 
       FIG. 2  collectively shows the fixing-device power consumption table  2210  and the sheet-conveyance power consumption table  2220 , which are provided in the printer engine controller  2200 . 
     The fixing-device power consumption table  2210  shows a relation between sheet type and fixing-device power consumption. The term “fixing-device power consumption” refers to power consumption consumed by the fixing device  2300  to fix an image onto a sheet. The fixing-device power consumption table  2210  includes a “sheet type” field in which there are indicated sheet sizes A3, B4, A4, B5, letter, regal, and postcard that represent sheet types and a “fixing-device power consumption” field in which there are indicated values “PW_F (sheet type)_image type” that represent fixing-device power consumptions corresponding to combinations of sheet types and image types (monochrome image BW or color image CL). For example, a value “PW_F B4_BK” represents a fixing-device power consumption that corresponds to a combination of sheet size B4 and monochrome image BK. In an actual table, concrete numerical values are indicated instead of the values “PW_F (sheet type)_image type”. 
     The sheet-conveyance power consumption table  2220  shows a relation between sheet type and sheet conveyance power consumption (i.e., power consumption consumed by the sheet conveyance motor to convey a sheet when an image is fixed onto the sheet by the fixing device  2300 ). The sheet-conveyance power consumption table  2220  includes a “sheet type” field in which there are indicated sheet sizes that represent sheet types and a “sheet conveyance power consumption” field in which there are indicated values “PW_C (sheet type)” that represent sheet conveyance power consumptions corresponding to sheet types. For example, a value “PW_C B4” represents a fixing-device power consumption that corresponds to the sheet size B4. In an actual table, concrete numerical values are indicated instead of the values “PW_C (sheet type)”. 
       FIG. 3  schematically shows the construction of an essential part of the image forming apparatus  100 . 
     In  FIG. 3 , reference numerals  20 C,  20 M,  20 Y, and  20 K respectively denote color toner cartridges for cyan, magenta, yellow, and black colors. Each toner cartridge includes a photosensitive member  50 , an exposure unit  30  that exposes the photosensitive member  50  to light according to an image to be formed, thereby forming an electrostatic latent image on the photosensitive member  50 , a developing device (not shown) that develops the electrostatic latent image to form a toner image on the photosensitive member  50 , a cleaner (not shown) that removes residual toner on the photosensitive member  50 , and the like. 
     In the case of color printing, the toner cartridges  20 Y,  20 M,  20 C, and  20 K are used. In the case of monochrome printing, the toner cartridge  20 K alone is used. 
     In the image forming apparatus  100 , a sheet transfer system that includes conveyance roller pairs  70 ,  80  is driven by sheet conveyance motors (not shown) under the control of the sheet conveyance motor controller  2410 , and sheets  40  are transferred one by one from a sheet cassette  60  to the toner cartridge  20 K or to the toner cartridges  20 C,  20 M,  20 Y and  20 K. A toner image formed on the photosensitive member  50  is transferred to the sheet  40  and then fixed onto the sheet  40  by the fixing device  2300 . 
     The PC  200  generates and compresses bitmap data (which is image data), and transmits a print job including the compressed bitmap data and additional sheet type information to the image forming apparatus  100 . 
     In a case that the image forming apparatus  100  is implemented by a printer that uses a page description language, the PC  200  generates page description language code data instead of bitmap data, and transmits a print job including the code data to the image forming apparatus  100 . The image forming apparatus  100  interprets the code data and generates bitmap data. 
     In the main controller  1000 , the PC interface  1130  receives the compressed bitmap data, and the image processor  1120  decompresses the compressed bitmap data. The bitmap data is comprised of ON pixel data representing pixels on which toner is to be adhered and OFF pixel data representing pixels on which no toner is to be adhered. 
     The bitmap data is transferred to the printer engine  2000 . At that time, the video count unit  1210  adds up the number of pieces of ON pixel data (hereinafter, referred to as the video count value) in the image data. The total number of pixels on the entire A4 sheet is equal to about the product of 5000 and 7000 in the case of 600 dpi. In the case of color image data, the video count unit  1210  adds up video count values in image data for respective CMYK colors. 
       FIG. 4  shows a time-dependent change of power consumption consumed by the image forming apparatus  100  to execute print jobs. 
     In  FIG. 4 , there is shown an example in which a first print job whose execution is started from a sleep state of the image forming apparatus  100  and a second print job whose execution is started from a standby state of the apparatus  100  are executed in sequence. Elapsed time is shown along the abscissa, and power consumption of the image forming apparatus  100  is shown along the ordinate. 
     When receiving the first print job, the image forming apparatus  100  wakes up from the sleep state and increases the temperature of the fixing device  2300  to a predetermined temperature where the fixing device  2300  becomes capable of performing a fixing operation, while consuming power. This power consumption, i.e., the power consumption consumed to bring the fixing device  2300  into a state capable of performing the fixing operation (hereinafter, referred to as the first power consumption) is represented by PWpre 1 . The first power consumption PWpre 1  corresponds to the area of a hatched triangular region shown in  FIG. 4  in association with the first print job. 
     When the fixing device  2300  becomes a state capable of performing the fixing operation, the image forming apparatus  100  executes the first print job, while consuming power. This power consumption is represented by PWjob 1 . During the execution of the first print job, the exposure unit  30  exposes the photosensitive member  50  to light to thereby form an electrostatic latent image on the photosensitive member  50 , and the electrostatic latent image is developed into a toner image. On the other hand, a sheet is conveyed from the sheet cassette  60  to the toner cartridge (s) and is further conveyed to the fixing device  2300  where the toner image is fixed onto the sheet. Hereinafter, power consumption including power consumption consumed by the toner image fixing and power consumption consumed by the sheet conveyance will be referred to as the second power consumption, and power consumption consumed by exposure of the photosensitive member  50  to light will be referred to as the third power consumption. The power consumption PWjob 1  is represented by the sum of the second and third power consumptions, and corresponds to the area of a hatched rectangular region shown in  FIG. 4  in association with the first print job. 
     When the first print job is complete, the image forming apparatus  100  shifts to a standby state. When receiving the second print job, the image forming apparatus  100  wakes up from the standby state and increases the temperature of the fixing device  2300  to the predetermined temperature, while consuming power. This power consumption (i.e., the first power consumption consumed by the fixing device  2300  to become a state capable of performing the fixing operation) is represented by PWpre 2 . 
     Since the fixing device temperature is higher when the image forming apparatus  100  is in the standby state than when the apparatus  100  is in the sleep state, the first power consumption PWpre 2  consumed to increase the fixing device temperature from the standby state is smaller than the first power consumption PWpre 1  consumed to increase the fixing device temperature from the sleep state. 
     When the fixing device  2300  becomes a state capable of performing the fixing operation, the image forming apparatus  100  executes the second print job, while consuming power. This power consumption is represented by PWjob 2 . In the example of  FIG. 4 , the power consumption PWjob 2  consumed to execute the second print job is smaller than the power consumption PWjob 1  consumed to execute the first print job. 
     In the following, a power consumption difference observed between different print jobs will be described. First, a description will be given of a power consumption difference observed when the same print content is printed on sheets of different types. Then, a description will be given of a power consumption difference observed when different print contents are printed on sheets of the same type. 
       FIG. 5A  shows a difference between power consumptions consumed by execution of two print jobs where the same print content is printed on an A4 normal sheet and on a postcard, and  FIGS. 5B and 5C  show the print content printed on the A4 normal sheet and on the postcard.  FIG. 5D  shows a difference in power consumptions consumed by execution of two print jobs where different print contents are printed on A4 normal sheets, and  FIGS. 5E and 5F  show the print contents printed on the respective A4 normal sheets. 
     In the two print jobs shown for comparison in  FIG. 5A , the same print content (which is shown by each of rectangular hatched regions in  FIGS. 5B and 5C ) is printed on sheets of different types, i.e., on the A4 normal sheet and on the postcard. A predetermined temperature of the fixing device  2300  at which the fixing device  2300  becomes a state capable of performing a fixing operation is higher when an image is fixed to the postcard than when fixed to the A4 normal sheet since the postcard is thicker than the A4 normal sheet. Thus, power consumption consumed to increase the fixing device temperature to the predetermined temperature to bring the fixing device  2300  to a state capable of performing the fixing operation is higher when the image is fixed to the postcard than when fixed to the A4 normal sheet. 
     The sheet conveyance speed is lower when the postcard thicker than the A4 normal sheet is conveyed than when the A4 normal sheet is conveyed. Accordingly, power consumption for sheet conveyance is larger when the postcard is conveyed than when the A4 normal sheet is conveyed. 
     As apparent from the foregoing description and from  FIG. 5A , power consumption for execution of the print job on the postcard is larger than power consumption for execution of the print job on the A4 normal sheet. In other words, power consumption for execution of a print job varies depending on sheet type, even if print content remains the same. 
     In the two print jobs shown for comparison in  FIG. 5D , different print contents (i.e., a monochrome image denoted by symbol BW in  FIG. 5E  and a color image denoted by symbol CL in  FIG. 5F ) are printed on sheets of the same type, i.e., on A4 normal sheets. The predetermined temperature of the fixing device  2300  at which the fixing device  2300  becomes a state capable of performing a fixing operation is higher when the color image CL is fixed than when the monochrome image BW is fixed since a toner amount used for formation of the color image CL is larger than that used for formation of the monochrome image BW. Thus, power consumption consumed to increase the fixing device temperature to the predetermined temperature is higher when the color image CL is formed than when the monochrome image BW is formed. 
     The number of ON pixels (i.e., video count value) in image data of the same size is larger in the color image CL than in the monochrome image BW. Thus, the third power consumption consumed by exposure of the photosensitive member  50  to light for electrostatic latent image formation and hence power consumption for execution of a print job (i.e., the sum of the first, second, and third power consumptions) are larger in the case of the color image CL than in the case of the monochrome image BW. In other words, the third power consumption and hence the power consumption for execution of a print job vary depending on the print content (the number of ON pixels in image data), even if the sheet type remains the same. 
     As described above, power consumption for execution of a print job varies depending on print content, especially, the number of ON pixels in image data (video count value). Thus, this embodiment computes the third power consumption based on a video count value counted by the video count unit  1210 , thereby eliminating a power consumption computing error from occurring. 
       FIG. 6  shows in flowchart the procedures of a power consumption computing process executed by the controller  1000  while the fixing device temperature is increased at a predetermined temperature increase rate. 
     A program for the power consumption computing process is read from the ROM  1400  and developed in the RAM  1300  for execution by the main controller  1000 . 
     In the power consumption computing process of  FIG. 6 , the main controller  1000  of the image forming apparatus  100  receives a print job from the PC  200  through the PC interface  1130 , acquires information indicating a sheet type to be used for the print job, and determines from the received print job whether an image type to be formed by the print job is monochrome image or color image (step S 301 ). Next, based on the sheet type and the image type determined in step S 301 , the main controller  1000  reads from e.g., the ROM  1400  information representing the predetermined temperature of the fixing device  2300 , and starts temperature increase control for increasing the temperature of the fixing device  2300  up to the predetermined temperature at a predetermined temperature increase rate. The main controller  1000  also starts a time measurement and notifies the printer engine  2000  through the printer interface  1200  that the main controller has received the print job (S 302 ). 
     Next, the main controller  1000  determines whether an actual temperature of the fixing device  2300  detected by the temperature detection unit  2310  reaches the predetermined temperature (step S 303 ). If the answer to step S 303  is NO, the process returns to step S 303 . When the actual temperature of the fixing device  2300  reaches the predetermined temperature (i.e., if the answer to step S 303  is YES), the main controller  1000  determines that the fixing device  2300  becomes a state capable of performing a fixing operation, and completes the time measurement and the temperature increase control (step S 304 ). 
     Based on the measured time, a difference between the predetermined temperature and the actual temperature detected for the first time by the temperature detection unit  2310 , and the predetermined temperature increase rate, the main controller  1000  (first computing unit) computes the first power consumption PWpre consumed to bring the fixing device  2300  to a state capable of performing the fixing operation (step S 305 ). 
     Next, the main controller  1000  starts executing the print job (step S 306 ), and determines whether the print job is complete (step S 307 ). If the answer to step S 307  is NO, the process returns to step S 307 . 
     If the print job is complete (i.e., if the answer to step S 307  is YES), the main controller  1000  (second computing unit) decides fixing device power consumption that corresponds to the information representing sheet type acquired in step S 301  and the image type determined in step S 301 , while referring to the fixing-device power consumption table  2210  of  FIG. 2 , and also decides sheet conveyance power consumption that corresponds to the information representing sheet type acquired in step S 301 , while referring to the sheet-conveyance power consumption table  2220  of  FIG. 2 . Then, the main controller  1000  adds together the fixing device power consumption and the sheet conveyance power consumption, thereby computing second power consumption. The main controller  1000  (third computing unit) reads a video count value from the video count unit  1210  in the printer I/F  1200 , computes third power consumption consumed by exposure of the photosensitive member  50  to light based on the video count value, and adds together the second and third power consumptions to thereby compute the power consumption PWjob consumed by execution of the print job (step S 308 ). 
     Next, the controller  1000  (fourth computing unit) computes a sum of the first power consumption PWpre and the second and third power consumptions PWjob (step S 309 ), and completes the present process. 
     According to the power consumption computing process of  FIG. 6 , the first power consumption corresponding to sheet type and image type is computed based on the measured time period of temperature increase, the second power consumption is computed by adding together the fixing device power consumption corresponding to sheet type and image type and decided referring to the fixing-device power consumption table  2210  and the sheet conveyance power consumption decided referring to the sheet-conveyance power consumption table  2220 , and the third power consumption is computed based on the video count value. The first to third power consumptions are added together, thereby computing power consumption consumed by execution of the print job. Accordingly, the power consumption of the image forming apparatus  100  can be computed with accuracy. 
       FIG. 7  shows in flowchart the procedures of a power consumption computing process executed by the main controller  1000  while the fixing device temperature is increased to a predetermined temperature in a predetermined time period. 
     A program for the power consumption computing process is read from the ROM  1400  and developed in the RAM  1300  for execution by the main controller  1000 . 
     In the power consumption computing process of  FIG. 7 , the main controller  1000  of the image forming apparatus  100  receives a print job from the PC  200  through the PC interface  1130 , acquires, from the received pint job, information representing a sheet type to be used for the print job, and determines from the print job an image type to be formed by the print job (step S 701 ). Next, the main controller  1000  acquires information representing the predetermined temperature of the fixing device  2300  (corresponding to the sheet type and the image type determined in step S 701 ), acquires information representing an actual temperature of the fixing device  2300  and detected by the temperature detection unit  2310 , and notifies the printer engine  2000  that the main controller  1000  has received the print job (step S 702 ). 
     Based on the information representing the predetermined temperature and the information representing the actual temperature of the fixing device  2300 , which are acquired in step S 702 , the main controller  1000  starts temperature increase control to increase the fixing device temperature to the predetermined temperature in the predetermined time period (step S 703 ). 
     Next, the main controller  1000  determines whether the actual temperature of the fixing device  2300  reaches the predetermined temperature (step S 704 ). If the answer to step S 704  is NO, the process returns to step S 704 . If the actual temperature of the fixing device  2300  reaches the predetermined temperature (i.e., if the answer to step S 704  is YES), the main controller  1000  completes the temperature increase control, and computes power consumption PWpre consumed to bring the fixing device  2300  to a state capable of performing a fixing operation based on the temperature difference between the predetermined temperature and the actual temperature of the fixing device  2300  detected for the first time (step S 705 ). 
     In steps S 706  to S 709 , the main controller  1000  performs the same processing as that performed in steps S 306  to S 309  in  FIG. 6 . Specifically, the main controller  1000  starts executing the print job (step S 706 ), and if the print job is complete (if the answer to step S 707  is YES), decides fixing device power consumption and sheet conveyance power consumption, and adds together these power consumptions to thereby compute second power consumption. The main controller  1000  computes third power consumption based on the video count value, adds together the second and third power consumptions to thereby compute power consumption PWjob consumed by the execution of the print job (step S 708 ), and computes the sum of the first power consumption PWpre and the second and third power consumptions PWjob (step S 709 ), whereupon the present process is completed. With the power consumption computing process of  FIG. 7 , effects similar to those achieved by the power consumption computing process of  FIG. 6  can be achieved. 
     Other Embodiments 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment, and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment. For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium). 
     While the present invention has been described with reference to an exemplary embodiment, it is to be understood that the invention is not limited to the disclosed exemplary embodiment. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2010-240921, filed Oct. 27, 2010, which is hereby incorporated by reference herein in its entirety.