Abstract:
An image forming apparatus includes an image forming mechanism, a fixing roller, a heater, a sensor, a warm-up mechanism, and a controller. The image forming mechanism forms a toner image on a recording medium according to image data. The fixing roller fixes the toner image on the recording medium by applying heat. The heater heats the fixing roller to warm up the fixing roller. The sensor detects a temperature of the fixing roller. The warm-up mechanism warms up the fixing roller by using the heater. The controller performs a first warm-up control that finishes the warm-up of the fixing roller and a second warm-up control that continues the warm-up of the fixing roller.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority to Japanese patent application No. 2005-125279 filed on Apr. 22, 2005 in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for image forming, and more particularly to a method and an apparatus for image forming with an improved warm-up control for fixing a toner image on a recording medium. 
     2. Description of the Background Art 
     A background electrophotographic image forming apparatus, such as a copying machine, a printer, or a facsimile machine, generally forms an electrostatic latent image on a photoconductor according to image data. The electrostatic latent image is visualized with toner to form a toner image on the photoconductor. The toner image is transferred onto a sheet and the sheet having the toner image is conveyed to a fixing unit in which heat and pressure fix the toner image on the sheet. 
     Such a background image forming apparatus is being required to save energy for environmental protection or compliance with various standards or regulations. To cope with such requirements, the fixing unit needs to be quickly heated to a predetermined temperature at which a proper fixing can be performed. 
     One example of such a background image forming apparatus includes a sensor for detecting a temperature of the fixing unit to attempt to shorten a warm-up time of the fixing unit. However, the sensor may detect the increasing temperature of the fixing unit with a delay while the fixing unit is warming up. Specifically, the temperature of the fixing unit detected by the sensor may be lower than an actual temperature of the fixing unit. Namely, even when the temperature of the fixing unit actually reaches the predetermined temperature at which a proper fixing can be performed, the image forming apparatus may judge that the temperature of the fixing unit has not reached the predetermined temperature based on the temperature detected by the sensor. As a result, the start of fixing operations of the image forming apparatus may be delayed. 
     In another example of such a background image forming apparatus, a time period required for the temperature of the fixing unit to reach the predetermined temperature is calculated in advance. When the calculated time period elapses, the image forming apparatus judges that the warm-up of the fixing unit is finished. However, the temperature of the fixing unit may not reach the predetermined temperature even when the calculated time period elapses when an input voltage of the fixing unit is not sufficiently high. As a result, a proper fixing cannot be performed. 
     SUMMARY OF THE INVENTION 
     This specification describes a novel image forming apparatus. In one aspect of the present invention, the novel image forming apparatus includes an image forming mechanism, a fixing roller, a heater, a sensor, a warm-up mechanism, and a controller. The image forming mechanism is configured to form a toner image on a recording medium according to image data. The fixing roller is configured to fix the toner image on the recording medium by applying heat. The heater is configured to heat the fixing roller to warm up the fixing roller. The sensor is configured to detect a temperature of the fixing roller. The warm-up mechanism is configured to warm up the fixing roller by using the heater. The controller is configured to perform a first warm-up control that finishes the warm-up of the fixing roller on either one of conditions that the temperature of the fixing roller detected by the sensor reaches a predetermined first temperature or that a predetermined time period elapses. The controller is also configured to perform a second warm-up control that continues the warm-up of the fixing roller until the temperature of the fixing roller detected by the sensor reaches a predetermined third temperature, which is not lower than the predetermined first temperature, when the temperature of the fixing roller detected by the sensor does not reach a predetermined second temperature, which is not higher than the predetermined first temperature, even when the predetermined time period elapses. 
     This specification further describes a novel image forming method. In one aspect of the present invention, the novel image forming method includes forming a toner image on a recording medium according to image data, warming up a fixing roller by heating the fixing roller with a heater, performing a first warm-up control that finishes the warm-up of the fixing roller on either one of conditions that a temperature of the fixing roller detected by a sensor reaches a predetermined first temperature or that a predetermined time period elapses, performing a second warm-up control that continues the warm-up of the fixing roller until the temperature of the fixing roller detected by the sensor reaches a predetermined third temperature, which is not lower than the predetermined first temperature, when the temperature of the fixing roller detected by the sensor does not reach a predetermined second temperature, which is not higher than the predetermined first temperature, even when the predetermined time period elapses, and fixing the toner image on the recording medium by applying heat of the fixing roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram of an electrical structure of the image forming apparatus shown in  FIG. 1 ; 
         FIG. 3  is a graph illustrating temperature increase of a fixing roller of the image forming apparatus shown in  FIG. 1 ; 
         FIG. 4  is a flowchart illustrating operations of a CPU (central processing unit) of the electrical structure shown in  FIG. 2 ; 
         FIG. 5  is a graph illustrating another temperature increase of the fixing roller of the image forming apparatus shown in  FIG. 1 ; 
         FIG. 6  is a flowchart illustrating operations of the CPU of the electrical structure shown in  FIG. 2  according to an exemplary embodiment of the present invention; 
         FIG. 7  is a flowchart illustrating operations of the CPU of the electrical structure shown in  FIG. 2  according to another exemplary embodiment of the present invention; 
         FIG. 8  is a flowchart illustrating operations of the CPU of the electrical structure shown in  FIG. 2  according to yet another exemplary embodiment of the present invention; and 
         FIG. 9  is a flowchart illustrating operations of the CPU of the electrical structure shown in  FIG. 2  according to yet another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and particularly to  FIG. 1 , an image forming apparatus  101  according to an exemplary embodiment of the present invention is explained. 
     As illustrated in  FIG. 1 , the image forming apparatus  101  includes a photoconductor  1 , a charger  2 , an exposure unit  4 , a development unit  6 , a paper tray  10  including a bottom plate  11 , a feeding roller  12 , a separating pad  13 , a registration roller pair  20 , a transferor  7 , a cleaning unit  3 , a fixing unit  30  (including a heater  31 , a fixing roller  32 , a sensor  35 , and a pressure roller  33 ), an ejecting roller  34 , and an output tray  40 . 
     The image forming apparatus  101  forms an image in an electrophotographic method. According to this non-limiting embodiment, the image forming apparatus  101  functions as a digital copying machine. The photoconductor  1  rotates in a rotating direction A. The charger  2 , the exposure unit  4 , the development unit  6 , the transferor  7 , and the cleaning unit  3  are disposed around the photoconductor  1 . The charger  2  uniformly charges a surface of the photoconductor  1 . The exposure unit  4  irradiates light L onto the surface of the photoconductor  1  to form an electrostatic latent image according to image data. The development unit  6  visualizes the electrostatic latent image formed on the surface of the photoconductor  1  with toner to form a toner image. 
     A recording medium is placed on the bottom plate  11  of the paper tray  10 . The recording medium includes sheets and OHP (overhead projector) transparencies and is hereinafter referred to as “the sheet”. The paper tray  10  is disposed in a lower portion of the image forming apparatus  101  and is attachable to and detachable from the lower portion. The bottom plate  11  moves upward to cause an uppermost sheet of the sheets placed on the bottom plate  11  to pressingly contact the feeding roller  12 . The feeding roller  12  rotates to feed the sheets placed on the bottom plate  11  toward the registration roller  20 . While the feeding roller  12  rotates, the separating pad  13  separates the uppermost sheet from the other sheets. The registration roller pair  20  feeds the uppermost sheet toward the transferor  7  at a timing when the toner image formed on the surface of the photoconductor  1  is properly transferred onto the sheet. The transferor  7  transfers the toner image formed on the surface of the photoconductor  1  onto the fed sheet. The cleaning unit  3  removes residual toner not transferred and remaining on the surface of the photoconductor  1 . The sheet having the toner image transferred thereto is further fed toward the fixing unit  30 . 
     In the fixing unit  30 , the pressure roller  33  faces the fixing roller  32  including the heater  31  to apply pressure to the fixing roller  32 . The heater  31  heats the fixing roller  32 . The sensor  35  detects a temperature of the fixing roller  32 . While the sheet is conveyed through a nip formed between the fixing roller  32  and the pressure roller  33 , heat applied by the fixing roller  32  and pressure applied by the pressure roller  33  fix the toner image on the sheet. The ejecting roller  34  feeds the sheet having the fixed toner image onto the output tray  40  with the fixed toner image facing down. 
     As illustrated in  FIG. 2 , the image forming apparatus  101  further includes a CPU (central processing unit)  51 , a ROM (read-only memory)  52 , a RAM (random-access memory)  53 , a bus  54 , a motor  55 , a motor driving circuit  56 , a sensor circuit  57  connected to the temperature sensor  35 , and a heater driving circuit  58  connected to the heater  31 . 
     The CPU  51  controls operations of the image forming apparatus  101 . The ROM  52  stores various programs executed by the CPU  51  and fixed data. The RAM  53  provides an operation area for the CPU  51 . The motor driving circuit  56  drives the motor  55 . The motor  55  drives the fixing roller  32 . The sensor circuit  57  drives the sensor  35 . The heater driving circuit  58  drives the heater  31 . 
     The CPU  51 , the ROM  52 , and the RAM  53  are connected to the bus  54 . The motor  55 , the sensor  35 , and the heater  31  are connected to the bus  54  via the motor driving circuit  56 , the sensor circuit  57 , and the heater driving circuit  58  respectively. Further, various other sensors and actuators (not shown) are connected to the bus  54 . 
     The CPU  51  turns on and off the heater  31  based on the temperature of the fixing roller  32  detected by the sensor  35  to maintain the temperature of the fixing roller  32  within a desired temperature range. 
     The image forming apparatus  101  is configured to shorten a warm-up time of the fixing unit  30 . To achieve that benefit the temperature of the fixing roller  32  is increased at a high speed. However, in that circumstance the sensor  35  may detect with a delay that the temperature of the fixing roller  32  reaches a desired fixing temperature. When the sensor  35  is strained due to continuous use of the image forming apparatus  101 , the sensor  35  may detect a temperature with even more of a delay. 
     Referring to  FIG. 3 , the following describes the delay in temperature detection.  FIG. 3  is a graph illustrating the temperature of the fixing roller  32  changing with time. A curve  61  represents an actual temperature of the fixing roller  32  and a curve  62  represents a temperature of the fixing roller  32  detected by the sensor  35 . The actual temperature of the fixing roller  32  reaches a predetermined first temperature T 1  within a predetermined time period P 1 . However, the temperature of the fixing roller  32  detected by the sensor  35  does not reach the first temperature T 1  when the time period P 1  elapses. Thus, the CPU  51  may judge that the actual temperature of the fixing roller  32  does not reach the first temperature T 1  even when the time period P 1  (i.e., the warm-up time) elapses. 
     In the above-described configuration of the image forming apparatus  101 , the image forming apparatus  101  may not provide the standardized warm-up time if the heater  31  is turned off at time period P 1 . An output of the heater  31  and a thickness of the fixing roller  32  are generally set to or near limit values in terms of an amount of heat. Therefore, it may be difficult to set the output of the heater  31  and the thickness of the fixing roller  32  by considering the delay in detection by the sensor  35 . 
     To cope with such a condition, the CPU  51  may be configured to judge that the warm-up of the fixing roller  32  is finished when the time period P 1  elapses based on a prediction that the actual temperature of the fixing roller  32  reaches the first temperature T 1  within the time period P 1 , regardless of the delay in detection by the sensor  35 . 
       FIG. 4  is a flowchart illustrating operations of the CPU  51  configured as described above. In step S 101 , a counter starts counting after a count C of the counter is reset to “0”. In step S 102 , the CPU  51  monitors whether a temperature T of the fixing roller  32  reaches the first temperature T 1  or not. If the temperature T of the fixing roller  32  reaches the first temperature T 1  (i.e., if YES in step S 102 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 104 . If the temperature T of the fixing roller  32  does not reach the first temperature T 1  (i.e., if NO in step S 102 ), the CPU  51  monitors whether the time period P 1  elapses or not in step S 103 . If the time period P 1  elapses (i.e., if YES in step S 103 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 104 . 
     Factors affecting the increase in the temperature of the fixing roller  32  may include the output of the heater  31  and the thickness of the fixing roller  32 . Factors affecting the increase in the temperature of the fixing unit  30  may include conditions of the fixing unit  30 . Therefore, the time period P 1  may be set by considering the worst imaginable conditions caused by those factors. However, the worst imaginable conditions may not be properly determined due to other factors including an output voltage and an environment where the image forming apparatus  101  is located. In this case, the actual temperature of the fixing roller  32  may not reach the first temperature T 1  even when the time period P 1  elapses. Thus, fixing may not be properly performed when the sheet is fed into the fixing unit  30  immediately after the time period P 1  elapses. 
       FIG. 5  is a graph illustrating the increase in the temperature of the fixing roller  32  in other circumstances. A curve  63  represents the temperature of the fixing roller  32  when a rated voltage is applied. A curve  64  represents the temperature of the fixing roller  32  when a lower voltage is applied. 
     The image forming apparatus  101  includes the sensor  35 . Therefore, the CPU  51  may control the operations of the image forming apparatus  101  in accordance with conditions (e.g., temperature) of the environment where the image forming apparatus  101  is located. For example, if the image forming apparatus  101  is powered on when the sensor  35  detects the temperature of the fixing roller  32  is below an allowable limit, the warm-up will not be finished even when the time period P 1  elapses. Therefore, an additional sensor, such as a voltage sensor, may be required, resulting in an increase in manufacturing costs and layout modification of the image forming apparatus  101 . Particularly, it may be difficult to provide the additional sensor in the compact, low-cost image forming apparatus  101 . 
     The following describes operations for controlling a fixing temperature of the fixing unit  30 , particularly when the fixing unit  30  is turned on, so as to solve the above-described problems without increasing manufacturing costs caused by needing the additional voltage sensor. 
       FIG. 6  is a flowchart illustrating operations for controlling the fixing temperature of the fixing unit  30  according to an exemplary embodiment of the present invention. The operations illustrated in  FIG. 6  may be performed when the fixing temperature detected when the time period P 1  elapses is low enough to be below an allowable limit of error and a faulty image may be produced if the sheet is fed into the fixing unit  30  at that too low fixing temperature. 
     In step S 201 , the counter starts counting after the count C of the counter is reset to “0”. In step S 202 , the CPU  51  monitors whether the temperature T of the fixing roller  32  reaches the first temperature T 1  or not. If the temperature T of the fixing roller  32  reaches the first temperature T 1  (i.e., if YES in step S 202 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 206 . If the temperature T of the fixing roller  32  does not reach the first temperature T 1  (i.e., if NO in step S 202 ), the CPU  51  monitors whether the time period P 1  elapses or not in step S 203 . If the time period P 1  elapses (i.e., if YES in step S 203 ), the CPU  51  monitors whether the temperature T of the fixing roller  32  reaches a predetermined second temperature T 2 , which is not higher than the first temperature T 1 , or not in step S 204 . If the temperature T of the fixing roller  32  reaches the second temperature T 2  (i.e., if YES in step S 204 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 206 . The second temperature T 2  is determined based on whether a faulty image may be produced or not if the sheet is fed into the fixing unit  30  when at that second temperature T 2  and whether the CPU  51  may judge that the input voltage of the heater  31  is substantially low or not. If the temperature T of the fixing roller  32  does not reach the second temperature T 2  (i.e., if NO in step S 204 ), the CPU  51  monitors whether the temperature T of the fixing roller  32  reaches the first temperature T 1  or not in step S 205 . When the temperature T of the fixing roller  32  reaches the first temperature T 1  (i.e., when YES in step S 205 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 206 . 
     The above-noted operation as discussed with respect to  FIG. 6  may be particularly beneficial in a case in which an environmental temperature or an insufficient input voltage prevents the fixing roller  32  from increasing to an appropriate temperature by the time P 1 . More particularly, in the operation shown in  FIG. 6  if the temperature of the fixing roller  32  does not reach the second temperature T 2  at the time P 1  in step S 204 , that may indicate that an environmental temperature or an insufficient input voltage is preventing the increase in temperature of the fixing roller  32  and it may therefore take a longer time before the temperature of the fixing roller  32  reaches an appropriate temperature for fixing (i.e., the first temperature T 1 ). Therefore, in the operation in  FIG. 6  in such situations the warm-up continues until the temperature of the fixing roller  32  reaches the first temperature T 1 , i.e., until YES in step S 205 . 
       FIG. 7  is a flowchart illustrating the operations for controlling the fixing temperature of the fixing unit  30  by using a temperature gradient according to another exemplary embodiment of the present invention. The CPU  51  periodically monitors a temperature gradient K of the temperature of the fixing roller  32  detected by the sensor  35  during the warm-up of the fixing roller  32 . The temperature gradient K is compared with a gradient K 1 . The gradient K 1  is determined based on whether a faulty image may be produced or not if the sheet is fed into the fixing unit  30  when at that gradient K 1  and whether the CPU  51  may judge that the input voltage of the heater  31  is substantially low or not. 
     In step S 301 , the counter starts counting after the count C of the counter is reset to “0”. In step S 302 , the CPU  51  monitors whether the temperature gradient K reaches the gradient K 1  or not. If the temperature gradient K reaches the gradient K 1  (i.e., if YES in step S 302 ), the CPU  51  monitors whether the temperature T of the fixing roller  32  reaches the first temperature T 1  or not while continuously monitoring the temperature gradient K in step S 303 . If the temperature T of the fixing roller  32  does not reach the first temperature T 1  (i.e., if NO in S 303 ), the CPU  51  monitors whether the time period P 1  elapses or not while continuously monitoring the temperature gradient K in step S 304 . If the temperature T of the fixing roller  32  reaches the first temperature T 1  (i.e., if YES in step S 303 ) or if the time period P 1  elapses (i.e., if YES in step S 304 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 306 . If the temperature gradient K does not reach the gradient K 1  (i.e., if NO in step S 302 ), the CPU  51  monitors whether the temperature T of the fixing roller  32  reaches the first temperature T 1  or not in step S 305 , without monitoring whether the time period P 1  elapses or not. When the temperature T of the fixing roller  32  reaches the first temperature T 1  (i.e., when YES in step S 305 ), the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 306 . 
     The temperature of the fixing roller  32  at which the CPU  51  judges that the warm-up of the fixing roller  32  is finished is usually preset lower than the temperature at which fixing can be performed, because the temperature of the fixing roller  32  may further increase while the sheet fed after the CPU  51  judges that the warm-up of the fixing roller  32  is finished is conveyed to the fixing unit  30 . This shortens the warm-up time. 
     When the input voltage of the heater  31  is not sufficient, it may take longer for the temperature of the fixing roller  32  to reach the temperature at which the CPU  51  judges that the warm-up of the fixing roller  32  is finished. The temperature of the fixing roller  32  may also not sufficiently increase while the sheet fed after the CPU  51  judges that the warm-up of the fixing roller  32  is finished is conveyed to the fixing unit  30 . Thus, the temperature of the fixing roller  32  may not reach the preset temperature when the sheet is fed into the fixing unit  30 . 
       FIGS. 8 and 9  are flowcharts illustrating operations of further exemplary embodiments of the present invention that solve the above-described problems. In  FIG. 8 , steps S 401 , S 402 , S 403 , S 404 , and S 406  respectively replace S 201 , S 202 , S 203 , S 204 , and S 206 . However, S 205  is replaced by S 405  in which a predetermined third temperature T 3  is preset instead of the first temperature T 1 . The third temperature T 3  is not lower than the first temperature T 1 . In  FIG. 9 , steps S 501 , S 502 , S 503 , S 504 , and S 506  respectively replace S 301 , S 302 , S 303 , S 304 , and S 306 . However, S 305  is replaced by S 505  in which the third temperature T 3  is preset instead of the first temperature T 1 . 
     In the operations in  FIGS. 8 and 9  the third temperature T 3  is used for an image forming apparatus which, for example, is located in a low-temperature environment in which the temperature of the fixing roller  32  may decrease when plural sheets are continuously fed to the fixing roller  32  after the warm-up is finished. The first temperature T 1  can then be used for an image forming apparatus that is not located in such a low-temperature environment. That is, in the operation in  FIGS. 8 and 9  when the temperature T 2  is not reached at the time P 1 , i.e., when NO at step S 404 , the third temperature T 3  is then used. 
     As illustrated in  FIG. 8 , when the temperature of the fixing roller  32  detected by the sensor  35  after the time period P 1  elapses (i.e., if YES in step S 403 ) does not reach the second temperature T 2  (i.e., if YES in step S 404 ), the warm-up of the fixing roller  32  continues until the temperature of the fixing roller  32  reaches the third temperature T 3  (i.e., until YES in step S 405 ). As illustrated in  FIG. 9 , the temperature gradient K is calculated until the time period P 1  elapses. When the calculated temperature gradient K does not reach the gradient K 1  (i.e., if NO in step S 502 ), the warm-up of the fixing roller  32  continues until the temperature of the fixing roller  32  reaches the third temperature T 3  (i.e., until YES in step S 505 ). The third temperature T 3 , which is not lower than the first temperature Ti, may be used instead of the first temperature T 1  by the CPU  51  to judge that the warm-up of the fixing roller  32  is finished. 
     Thus, even if the temperature of the fixing roller  32  does not reach the desired temperature due to an insufficient input voltage of the heater  31  when the sheet is fed onto the fixing roller  32 , the image forming apparatus  101  may provide the shortened warm-up time while providing improved image quality producing no faulty image caused by improper fixing without an increase in manufacturing costs. 
     The above-described operations may be effective when the sheet is fed onto the fixing roller  32  immediately after the CPU  51  judges that the warm-up of the fixing roller  32  is finished in step S 406  or S 506 . When no sheet is fed onto the fixing roller  32  immediately after the CPU  51  judges that the warm-up of the fixing roller  32  is finished, fixing may be properly performed if the CPU  51  judges that the warm-up of the fixing roller  32  is finished when the time period P 1  elapses, even if the temperature of the fixing roller  32  does not reach the first temperature T 1 , the second temperature T 2 , or the third temperature T 3 . The operations illustrated in  FIGS. 6 to 9  may be performed only when a sheet feeding signal for feeding the sheet onto the fixing roller  32  is output while the fixing roller  32  is warmed up. 
     Thus, the image forming apparatus  101  may provide the shortened warm-up time while providing improved image quality producing no faulty image caused by improper fixing without an increase in manufacturing costs. 
     The sheet feeding signal may not be output while the fixing roller  32  is warmed up, but output immediately after the CPU  51  judges that the warm-up of the fixing roller  32  is finished when the time period P 1  elapses while the temperature of the fixing roller  32  does not reach the first temperature T 1 . In this case, the temperature of the fixing roller  32  may not sufficiently increase, resulting in improper fixing. 
     To solve this problem, the CPU  51  may judge whether the temperature of the fixing roller  32  reaches the first temperature T 1  or the third temperature T 3  simultaneously with the sheet feeding signal output after the warm-up of the fixing roller  32  is finished. When the temperature of the fixing roller  32  does not reach the first temperature T 1  or the third temperature T 3  but reaches the second temperature T 2 , feeding the sheet onto the fixing roller  32  may start after the temperature of the fixing roller  32  reaches the first temperature T 1  or the third temperature T 3 . 
     Thus, the image forming apparatus  101  may provide the shortened warm-up time while providing improved image quality producing no faulty image caused by improper fixing without the increase in manufacturing costs. 
     The present invention has been described above with reference to specific embodiments. Note that the present invention is not limited to the details of the embodiments described above, but various modifications and improvements are possible without departing from the spirit and scope of the invention. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention and appended claims.