Patent Publication Number: US-9891575-B2

Title: Image forming device, exchange unit and method for determining exchange unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Application number PCT/JP2014/077713, filed on Oct. 17, 2014. The content of this application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an image forming device, an exchange unit, and a method for determining the exchange unit. 
     An image forming device such as a copying machine, a printer, or the like has a configuration such that a user can exchange an exchange unit including expendable items such as toner. In such a configuration, it is desirable to attach a genuine product of the exchange unit to realize good performance of the image forming device. 
     On the other hand, there is a demand for reusing the exchange unit or the like from the viewpoint of effective utilization of resources, environmental protection, and the like, and a non-genuine product of the exchange units have come to be attached to the image forming device. A method for operating the image forming device to correspond to a non-genuine product when a user intentionally attaches the non-genuine product has been proposed. 
     For example, Japanese Unexamined Patent Application Publication No. 2005-326731 discloses a technique for making an operation mode of the image forming device to which a genuine product of the exchange unit is attached different from the operation mode of the image forming device to which a non-genuine product is attached. Here, whether the exchange unit is genuine or non-genuine is determined by comparing unit information stored in a memory of the exchange unit with corresponding unit information stored in a storage unit of the image forming device. 
     Because a specialist can decode a data code of the unit information stored in the memory of the exchange unit, the same or similar memory can be mounted on a non-genuine product by creating the memory by using the decoded data code. When a non-genuine product on which such a memory is mounted is attached to an image forming device, the image forming device erroneously recognizes it as a genuine product and executes an operation mode corresponding to the genuine product. In such a case, because an inappropriate operation mode is executed, problems such as lowering of printing quality or a failure of the device may occur. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention focuses on these points, and the object of the invention is to appropriately determine whether or not an exchange unit attached to an image forming device is a specific exchange unit. 
     In one aspect of the present disclosure, there is provided an image forming device comprising: an attachment part to which an exchange unit having a fuse that can be molten by being supplied with an electric current is detachably attached; and a control part that applies each of a first conduction signal corresponding to a first current supply state where the fuse of a specific exchange unit is not molten and a second conduction signal corresponding to a second current supply state where the fuse of the specific exchange unit is molten to the fuse, the control part determining that the exchange unit attached to the attachment part is the specific exchange unit when the control part detects that the fuse is not molten by applying the first conduction signal and also detects that the fuse is molten by applying the second conduction signal, and the control part determining that the exchange unit attached to the attachment part is an exchange unit other than the specific exchange unit when the control part detects that the fuse is molten by applying the first conduction signal or when the control part detects that the fuse is not molten by applying the second conduction signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an example of an outline configuration of an image forming device  1  according to one exemplary embodiment of the present invention. 
         FIG. 2  is a schematic view showing an example of a cross-sectional configuration of a fuse  35  of a toner unit  30 . 
         FIG. 3  is a graph showing a pre-arcing time-current characteristic curve of the fuse  35 . 
         FIG. 4  is a diagram for explaining an example of a melting conduction signal and a non-melting conduction signal. 
         FIG. 5  is a block diagram for explaining an example of configurations of a control circuit  90  and a unit-side circuit  80 . 
         FIG. 6  is a diagram showing an example of conduction signal information stored in a storage part  92 . 
         FIG. 7  is a circuit diagram showing a configuration of the unit-side circuit  80 . 
         FIG. 8  is a diagram showing an example of a signal string  1  applied to a fuse  35 . 
         FIG. 9  is a circuit diagram showing an example of a configuration of a determination signal conversion part  96 . 
         FIG. 10  is a flow chart showing an operation example of the image forming device  1  when the toner unit  30  is attached to an attachment part  70 . 
         FIG. 11  is a flow chart showing an example of a detection and determination process of the toner unit  30 . 
         FIG. 12  is a diagram for explaining the melting conduction signal and the non-melting conduction signal according to a first modification example. 
         FIG. 13A  is a diagram showing a signal string according to the first modification example. 
         FIG. 13B  is a diagram showing a signal string according to the first modification example. 
         FIG. 14  is a diagram for explaining the melting conduction signal and the non-melting conduction signal according to a second modification example. 
         FIG. 15  is a diagram showing a signal string according to the second modification example. 
         FIG. 16  is a diagram showing a signal string according to a third modification example. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     &lt;Configuration of an Image Forming Device&gt; 
     A configuration example of an image forming device  1  according to one exemplary embodiment of the present invention is explained with reference to  FIG. 1 .  FIG. 1  is a diagram showing an example of an outline configuration of the image forming device  1 . In  FIG. 1 , the vertical direction is indicated by an arrow and, for example, a paper feed cassette  65  is arranged at the lower part of a device main body  3  and a paper discharge tray  67  is arranged at the upper part of the device main body  3 . 
     Here, the image forming device  1  is an electrophotographic laser beam printer, and forms an image on a paper S by receiving an image signal from an external device such as a computer. As shown in  FIG. 1 , the image forming device  1  includes process units  10 K,  10 Y,  10 M, and  10 C, a transfer unit  40 , a cleaning unit  45 , a fixing unit  50 , a conveyance unit  60 , and a control circuit  90 . 
     The process units  10 K,  10 Y,  10 M, and  10 C have a function of visualizing latent images as toner images using toner as a developer after forming the latent images on photoreceptors  14 K,  14 Y,  14 M, and  14 C. The process units  10 K,  10 Y,  10 M and  10 C are provided corresponding to the respective colors of black (K), yellow (Y), magenta (M), and cyan (C). As shown in  FIG. 1 , the process units  10 K,  10 Y,  10 M, and  10 C are arranged in a row in the horizontal direction. 
     While the process units  10 Y,  10 M, and  10 C from among the four process units  10 K,  10 Y,  10 M, and  10 C have the same size, the process unit  10 K is enlarged so as to cope with a large amount of monochrome printing. Since the four process units  10 K,  10 Y,  10 M, and  10 C have similar basic configurations, the configuration of the process unit  10 K will be explained here. 
     After a latent image is formed on the photoreceptor  14 K, the process unit  10 K visualizes the latent image as a black toner image using black toner. The process unit  10 K includes a photosensitive unit  12 K, an exposure unit  18 K, a developing unit  20 K, and a toner unit  30 K. 
     The photosensitive unit  12 K includes the photoreceptor  14 K and an electrifier  16 K. The photoreceptor  14 K has a photosensitive layer on the outer periphery of a drum and carries a latent image on the surface of the photosensitive layer. The photoreceptor  14 K is rotatably supported by the device main body  3  and rotates clockwise in  FIG. 1 . The electrifier  16 K electrifies the photoreceptor  14 K. 
     The exposure unit  18 K forms a latent image on the electrified photoreceptor  14 K by irradiating the photoreceptor  14 K with a laser. That is, an electrostatic latent image corresponding to the print image is formed on the photoreceptor  14 K. 
     The developing unit  20 K contains black toner, and develops (visualizes) the latent image formed on the photoreceptor  14 K as a black toner image using the black toner. The developing unit  20 K has a developing roller  21 K carrying the black toner, and develops the latent image on the photoreceptor  14 K as a toner image by applying a developing bias to the developing roller  21 K. 
     The toner unit  30 K contains the black toner to be supplied to the developing unit  20 K. The toner unit  30 K is detachably attached to an attachment part  70 K. Between the toner unit  30 K and the developing unit  20 K, a supply mechanism, which is not shown in figures, for supplying the black toner in the toner unit  30 K to the developing unit  20 K is provided. Further, a fuse  35 K, whose details will be described later, for determining whether the toner unit  30 K is a genuine product or a non-genuine product is attached to the toner unit  30 K. 
     The transfer unit  40  transfers the toner images of the respective colors carried by the four photoreceptors  14 K,  14 Y,  14 M, and  14 C onto the paper S. The transfer unit  40  includes a transfer belt  41 , a driving roller  42 , a transfer roller  43 , and a transfer back-up roller  44 . The transfer belt  41  is stretched around the driving roller  42  and the transfer roller  43 , and is rotated by the driving roller  42  in the direction of the arrow shown in  FIG. 1 . The transfer belt  41  is in contact with the photoreceptors  14 K,  14 Y,  14 M, and  14 C, and the toner images on the photoreceptors are primarily transferred onto the transfer belt  41  by applying a primary transfer bias at the contact part between the transfer belt  41  and the photoreceptors. The transfer belt  41  moves the primarily transferred toner images by rotating in a state of carrying the toner images. The transfer roller  43  and the transfer back-up roller  44  sandwich the paper S conveyed from the paper feed cassette  65 . By applying a secondary transfer bias to the transfer roller  43  and the transfer back-up roller  44 , single-color toner images or full-color toner images on the transfer belt  41  are secondarily transferred to the paper S. 
     The cleaning unit  45  removes residual toner that is not secondarily transferred to the paper S and remains on the transfer belt  41 . The cleaning unit  45  has a cleaning roller  46  and a bias roller  47 , and mechanically and electrically cleans the transfer belt  41 . The cleaning roller  46  is a brush roller that is in contact with the transfer belt  41  while rotating. It should be noted that the cleaning unit  45  may have a cleaning blade instead of the brush roller. 
     The fixing unit  50  heats and presses the single-color toner images or the full-color toner images transferred onto the paper S and fuses the images to the paper S to form a permanent image. The fixing unit  50  includes a heat roller  51  and a fixing back-up roller  53 , and sandwiches the paper S using them. The heat roller  51  heats and presses while contacting the toner image transferred onto the paper S. 
     The conveyance unit  60  draws out the papers S stacked in the paper feed cassette  65  one by one, conveys the delivered paper S, and discharges the paper S to the paper discharge tray  67 . The conveyance unit  60  includes a conveyance path  61  through which the paper S is conveyed and a plurality of conveyance rollers  62  provided in the conveyance path  61 . When the conveyance roller  62  conveys the paper S, the transfer unit  40  performs the above-described secondary transfer of the toner image, and the fixing unit  50  performs the above-described fixing of the toner image. 
     The control circuit  90  controls each unit described above. An image signal and a control signal are inputted to the control circuit  90  from, for example, a computer connected to the image forming device  1 . The control circuit  90  controls each unit to form an mage on the basis of the inputted image signal and control signal. Further, the control circuit  90  is electrically connected to each unit and controls each unit while detecting the state of each unit by receiving a signal from a sensor or the like. 
     &lt;Operation of the Image Forming Device at Image Formation&gt; 
     The image forming device  1  having the above-described configuration can form a monochrome image or a color image on the paper S. In the following, an example of operation of the image forming device  1  at color image formation will be described with reference to  FIG. 1 . 
     First, when the image signal and the control signal from the computer are inputted to the control circuit  90 , the photoreceptors  14 K,  14 Y,  14 M,  14 C, the transfer belt  41 , and the like are rotated under the control of the control circuit  90 . 
     The photoreceptors  14 K,  14 Y,  14 M, and  14 C are uniformly electrified by the electrifiers  16 K,  16 Y,  16 M, and  16 C at the electrifying position while rotating. The electrified areas of the photoreceptors  14 K,  14 Y,  14 M and  14 C that are electrified reach the exposure positions in accordance with the rotation of the photoreceptors, and latent images corresponding to image information of black (K), yellow (Y), magenta (M), and cyan (C) are formed in the electrified areas by the exposure units  18 K,  18 Y,  18 M, and  18 C. 
     The latent images formed on the photoreceptors  14 K,  14 Y,  14 M, and  14 C reach the developing positions in accordance with the rotation of the photoreceptors, and the latent images are developed into toner images by the developing units  20 K,  20 Y,  20 M, and  20 C. When the toner is consumed by the development performed by the developing units  20 K,  20 Y,  20 M, and  20 C, the toner is replenished to the developing units from the toner units  30 K,  30 Y,  30 M, and  30 C. 
     Single-color toner images (a black toner image or the like) formed on the photoreceptors  14 K,  14 Y,  14 M, and  14 C reach the primary transfer positions where the primary transfer bias is applied between the photoreceptors and the transfer belt  41  in accordance with the rotation of the photoreceptors  14 K,  14 Y,  14 M, and  14 C, and the single-color toner images are primarily transferred to the transfer belt  41 . Then, a full-color toner image is formed on the transfer belt  41  by primarily transferring the toner images carried by the four photoreceptors  14 K,  14 Y,  14 M, and  14 C. 
     The full-color toner image formed on the transfer belt  41  reaches the secondary transfer position where the secondary transfer bias is applied between the transfer roller  43  and the transfer back-up roller  44  in accordance with the rotation of the transfer belt  41 , and the full-color toner image is secondarily transferred to the paper S conveyed from the paper feed cassette  65 . It should be noted that the toner that is not secondarily transferred to the paper S and remains on the transfer belt  41  is moved in accordance with the rotation of the transfer belt  41  and is removed by the cleaning roller  46 . 
     The paper S on which the full-color toner image is secondarily transferred is conveyed to the fixing unit  50  by the conveyance roller  62 . The full-color toner image is fused on the paper S by being heated and pressed by the heat roller  51 . As a result, the image is formed on the paper S. The paper S, on which the image is formed, is further conveyed and is discharged from the paper discharge tray  67 . 
     &lt;Fuse of an Exchange Unit&gt; 
     The image forming device  1  has a configuration by which an exchange unit is detachably attached. The exchange unit is an item similar to consumable supplies whose lifetime is shorter than the service lifetime of the main device main body  3  of the image forming device  1 , and is a unit assumed to be exchanged by a user or a service person. 
     In the present exemplary embodiment, the photosensitive units  12 K,  12 Y,  12 M,  12 C, the developing unit  20 K,  20 Y,  20 M,  20 C, the toner unit  30 K,  30 Y,  30 M,  30 C, the cleaning unit  45 , the fixing unit  50 , and the like shown in  FIG. 1  correspond to the exchange unit. The device main body  3  is provided with an attachment part to which the exchange unit is detachably attached. For example, the toner units  30 K,  30 Y,  30 M, and  30 C are respectively attached to the attachment parts  70 K,  70 Y,  70 M, and  70 C shown in  FIG. 1  in a detachable manner. 
     The exchange unit is provided with a fuse that can be molten by being supplied with a current in order to determine whether or not the exchange unit attached to the attachment part is a specific exchange unit. A fuse is a component having a predetermined pre-arcing time-current characteristic, and is molten depending on a combination of a predetermined conduction current and conduction time. In the following description, the toner units  30 K,  30 Y,  30 M, and  30 C will be described as the exchange units. The fuses  35 K,  35 Y,  35 M, and  35 C are provided in the toner units  30 K,  30 Y,  30 M, and  30 C as shown in  FIG. 1 . The fuses  35 K,  35 Y,  35 M, and  35 C have the same configuration. For convenience of explanation, the toner units  30 K,  30 Y,  30 M, and  30 C will be generally referred to as a toner unit  30 , and the fuses  35 K,  35 Y,  35 M, and  35 C will be generally referred to as a fuse  35 . 
       FIG. 2  is a schematic view showing an example of a cross-sectional configuration of the fuse  35  of the toner unit  30 . As shown in  FIG. 2 , the fuse  35  has a substrate  36 , a fuse element  37 , a terminal  38 , and an overcoat  39 . 
     The substrate  36  is an insulating substrate made of, for example, ceramics or the like. The fuse element  37  is a fuse element which generates heat and melts by being supplied with an electric current. When the fuse element  37  generates heat and the temperature thereof rises to the melting point, the fuse element  37  melts. The terminal  38  is connected to both ends of the fuse element  37 . The terminal  38  is connected to the unit-side circuit  80  (see  FIG. 5 ) of the toner unit  30 . The overcoat  39  is made of, for example, an insulating resin material and covers the upper part of the fuse element  37 . The fuse  35  having the above-described configuration has a unique pre-arcing time-current characteristic as shown in  FIG. 3 . 
       FIG. 3  is a graph showing a pre-arcing time-current characteristic curve G of the fuse  35 . The pre-arcing time-current characteristic curve G shows the relationship between the conduction current and the conduction time for melting the fuse  35 . In the graph of  FIG. 3 , the horizontal axis represents the conduction time T, and the vertical axis represents the conduction current I. The horizontal axis and the vertical axis both have a logarithmic scale. Generally, the fuse  35  is molten after a short conduction time T when the conduction current I is large, and is molten after a long conduction time T when the conduction current I is small. 
     The calorific value Q 0  of the fuse element  37  of the fuse  35  is related to the resistivity of the fuse element  37 , the conduction current density (a current-carrying cross-sectional area of the fuse element  37  with the conduction current I), the conduction time T, and the like. On the other hand, the calorific value Q x  that is necessary for melting the fuse  35  is determined from the amount of heat required to raise the temperature of the fuse element  37  to the melting point and the amount of heat absorbed by the substrate  36 , the terminal  38 , and the overcoat  39 . The fuse  35  is molten when the condition Q 0 &gt;Q x  is satisfied, but the conduction current I and the conduction time T for actually melting the fuse  35  are determined by many factors related to a melting mechanism of the fuse  35 . By quantitatively managing each factor, the pre-arcing time-current characteristic curve G of the fuse  35  as shown in  FIG. 3  is obtained. 
     As shown in  FIG. 3 , the fuse  35  has a basic nature of increasing the conduction time T required for melting when the value of the conduction current I is decreased. When the value of the conduction current I is further decreased, the pre-arcing time-current characteristic curve G often becomes a substantially horizontal straight line. The pre-arcing time-current characteristic curve G of a typical fuse has a substantially horizontal straight line in a region where the conduction time T is from about 10 msec to 100 sec. This region is called the minimum melting current region, and the current value of the conduction current I representing the minimum melting current region is called the minimum melting current value. 
     In this exemplary embodiment, it is determined whether or not the toner unit  30  attached to the attachment part  70  is a specific toner unit (more specifically, a genuine toner unit) by effectively utilizing the pre-arcing time-current characteristic of the above-described fuse  35 . Specifically, a conduction signal is applied to the fuse  35  of the toner unit  30 , and the toner unit  30  is determined to be genuine or non-genuine by detecting whether or not the fuse  35  is molten by the applied conduction signal. Such determination is realized by cooperation of the control circuit  90  of the device main body  3  and the unit-side circuit  80  including the fuse  35  of the toner unit  30 . 
     The conduction signal applied to the fuse  35  is a signal string in which the non-melting conduction signal and the melting conduction signal are combined and arrayed. The non-melting conduction signal is a first conduction signal corresponding to a first current supply state where the fuse  35  is not molten, and the melting conduction signal is a second conduction signal corresponding to a second current supply state where the fuse  35  is molten. The non-melting conduction signal and the melting conduction signal correspond to characteristic points on the pre-arcing time-current characteristic curve. 
       FIG. 4  is a diagram for explaining an example of the melting conduction signal and the non-melting conduction signal. The characteristic point P 1  shown in  FIG. 4  is set in the minimum melting current region of the pre-arcing time-current characteristic curve described above. The conduction current of the characteristic point P 1  is the minimum melting current value I 1 , and the conduction time of the characteristic point P 1  is T 1 . For example, the conduction current I 1  is about 200 mA and the conduction time T 1  is about 0.5 sec. 
     The melting conduction signal and the non-melting conduction signal are each set by the current value of the conduction current and the conduction time based on the pre-arcing time-current characteristic curve G of the fuse  35 . For example, the melting conduction signal corresponds to a characteristic point PB having a current value larger than the characteristic point P 1  on the graph, and is composed of the conduction time T 1  of the characteristic point P 1  and a conduction current I B  larger than the conduction current I 1  of the characteristic point P 1 . The non-melting conduction signal corresponds to a characteristic point PA having a current value smaller than the characteristic point P 1  on the graph, and is composed of the conduction time T 1  of the characteristic point P 1  and a conduction current I A  which is smaller than the conduction current I 1  of the characteristic point P 1 . Hence, the current value of the melting conduction signal is different from the current value of the non-melting conduction signal. 
     When the melting conduction signal of the conduction current I B  is applied to the fuse  35 , the fuse  35  is molten after the conduction time T B  that is shorter than the conduction time T 1 , as can be seen from the graph. It should be noted that the conduction current I B  of the melting conduction signal is set so that the conduction time T B  is sufficiently smaller than the conduction time T 1 . 
     It should be noted that, in the minimum melting current region, the fluctuation of the current value is small due to the characteristics of the pre-arcing time-current characteristic curve G of the fuse  35 . Therefore, fuses having different pre-arcing time-current characteristic curves can be appropriately distinguished by setting the characteristic point P 1  in the minimum melting current region and by making the voltages of the non-melting conduction signal and the melting conduction signal different from the current value of the characteristic point P 1 . 
     &lt;Configuration of the Control Circuit  90  and the Unit-Side Circuit  80 &gt; 
     With reference to  FIG. 5 , configurations of the control circuit  90  and the unit-side circuit  80  for determining whether or not the exchange unit is the specific exchange unit will be described.  FIG. 5  is a block diagram for explaining an example of the configurations of the control circuit  90  and the unit-side circuit  80 . 
     In the present exemplary embodiment, the unit-side circuit  80  to which the above-described fuse  35  is connected is attached to the toner unit  30 . The unit-side circuit  80  is electrically connected to the control circuit  90  of the device main body  3  via a connector  75 . As shown in  FIG. 5 , the control circuit  90  includes a control part  91 , a storage part  92 , a D/A conversion part  93 , a waveform generation part  94 , a voltage-current conversion part  95 , and a determination signal conversion part  96 . 
     The control part  91  applies a signal string obtained by combining the non-melting conduction signal and the melting conduction signal to the fuse  35 , and detects each of whether or not the fuse  35  is molten due to the application of the non-melting conduction signal and whether or not the fuse  35  is molten due to the application of the melting conduction signal. Then, the control unit  91  determines whether or not the toner unit  30  attached to the attachment part  70  is a genuine product (a specific exchange unit) on the basis of the detection result of whether or not the fuse  35  is molten. 
     The control part  91  outputs a digital voltage signal to the D/A conversion part  93 . In addition, the control part  91  outputs, to the waveform generation part  94 , a conduction time signal for determining a conduction time and a conduction timing of the conduction signal to the fuse  35 . The digital voltage signal and the conduction time signal are set on the basis of the conduction signal information stored in the storage part  92 . 
     The storage part  92  stores programs executed by the control part  91  and data to be used when the control part  91  performs control. Further, the storage part  92  stores conduction signal information on conduction signals to be applied to the fuse  35  of the toner unit  30 , which is an exchange unit. Specifically, the storage part  92  stores a plurality of pieces of signal string data whose patterns of conduction signals are different from each other. 
       FIG. 6  is a diagram showing an example of the conduction signal information stored in the storage part  92 . The conduction signal information is the information in which a signal string number n and signal string data are associated. The signal string number n is a number (1 to N) for specifying a conduction signal that is actually applied to the fuse  35  from among a plurality of stored signal strings. One piece of signal string data is set for each of the signal string numbers n. The signal string data is composed of a signal array number m, a voltage code V (n, m), a conduction time code T (n, m), and a comparison code J (n, m). It should be noted that the signal string data corresponding to the signal string numbers 2 to N−1 are omitted in  FIG. 6  for convenience of explanation. 
     The signal array number m indicates the arrayed position in the signal string of the melting conduction signal and the non-melting conduction signal composing the signal string. The voltage code V (n, m) indicates a value for determining the voltage outputted from the control part  91  to the D/A conversion part  93 . The conduction current value of the melting conduction signal or the conduction current value of the non-melting conduction signal is determined on the basis of the value of the voltage code V (n, m). The conduction time code T (n, m) indicates a numerical value for determining the signal outputted from the control part  91  to the waveform generation part  94 . The conduction time or the like of the conduction signal are determined on the basis of the numerical value of the conduction time code T (n, m). 
     The comparison code J (n, m) is a code indicating the fuse  35  being molten or the fuse  35  not being molten. Here, the code of the comparison code J (n, m) is 0 or 1. The comparison code J (n, m)=1 indicates that the fuse  35  was molten, and the comparison code J (n, m)=0 indicates that the fuse  35  was not molten. That is, the storage part  92  stores setting information on whether or not the fuse  35  is molten corresponding to each of the applications of the melting conduction signal and of the non-melting conduction signal to the fuse  35 . 
     Returning to  FIG. 5 , the D/A conversion part  93  converts the digital voltage signal inputted from the control part  91  into an analog voltage signal. The D/A conversion part  93  outputs the converted analog voltage signal to the waveform generation part  94 . 
     The waveform generation part  94  generates a voltage signal waveform in which the analog voltage signal inputted from the D/A conversion part  93  and the conduction time signal inputted from the control part  91  are synchronized. The waveform generation part  94  outputs the generated voltage signal waveform to the voltage-current conversion part  95 . It should be noted that the D/A conversion part  93  and the waveform generation part  94  includes, for example, a Pulse Width Modulation (PWM) signal output circuit and a smoothing circuit. 
     The voltage-current conversion part  95  converts the voltage signal waveform inputted from the waveform generation part  94  into a predetermined current signal waveform. The voltage-current conversion part  95  outputs the converted current signal waveform to the unit-side circuit  80  via the connector  75  as a conduction signal. 
     The configuration of the unit-side circuit  80  will be described with reference to  FIG. 7 .  FIG. 7  is a circuit diagram showing the configuration of the unit-side circuit  80 . The unit-side circuit  80  has an input terminal A, an output terminal B, a power supply terminal C, and the fuse  35 . Between the output terminal B and the fuse  35 , there is provided a pull-down resistor having one end connected to the ground of the device main body  3  side via a terminal F. 
     The input terminal A is connected to the voltage-current conversion part  95  of the control circuit  90  via the connector  75 . A conduction signal from the voltage-current conversion part  95  is inputted to the input terminal A. The fuse  35  is connected in series between the input terminal A and the power supply terminal C connected to the power supply part  97  of the device main body  3 , and the fuse  35  receives the conduction signal from the input terminal A. 
     The fuse  35  receives a non-melting conduction signal, which is a first conduction signal corresponding to the first current supply state where the fuse  35  is not molten, and a melting conduction signal, which is a second conduction signal corresponding to the second current supply state where the fuse  35  is molten, which are inputted from the control circuit  90 . The fuse  35  melts when the conduction signal is the melting conduction signal, and the fuse  35  does not melt when the conduction signal is the non-melting conduction signal. The voltage between the terminals  38  in a state where the fuse  35  does not melt is larger than the voltage between the terminals  38  in a state where the fuse  35  melts. 
     A signal string applied to the fuse  35  will be described with reference to  FIG. 8 .  FIG. 8  is a diagram showing an example of the signal string  1  applied to the fuse  35 . The signal string  1  is set on the basis of the conduction time T 1  and the conduction current I 1  corresponding to the characteristic point P 1  shown in  FIG. 4 . The signal string  1  is composed of five conduction signals M 1  to M 5 , and is applied to the fuse  35  in the order of the conduction signal M 1 , the conduction signal M 2 , . . . , and the conduction signal M 5 . The conduction signal M 4  is the melting conduction signal, and has the conduction current I B  and the conduction time T 1 . The conduction signals M 1 , M 2 , M 3 , and M 5  are non-melting conduction signals, and each has the conduction current I A  and the conduction time T 1 . 
     Here, the signal string  1  is configured on the basis of the signal string data (the signal array number m is 1 to 5) of the signal string number n=1 in  FIG. 6 . Specifically, the conduction signal M 1  is configured on the basis of the data described in the row of the signal array number m=1 in  FIG. 6 , and the conduction signal M 2  is configured on the basis of the data described in the row of the signal array number m=2. At this configuration, 1 (melting) is allocated to the comparison code J (1, 4) corresponding to the conduction signal M 4  (m=4), which is the melting conduction signal, and the comparison code J (1, 5) corresponding to the conduction signal M 5  arrayed after the conduction signal M 4  in the comparison code J corresponding to the signal string  1 . On the other hand, 0 (non-melting) is allocated to the comparison codes J (1, 1), J (1, 2), and J (1, 3) corresponding to the other three conduction signals M 1  to M 3 . 
     In the present exemplary embodiment, the signal string is applied to the fuse  35  by being selected from a plurality of pieces of signal string data stored in the storage part  92 . At this time, the control part  91  randomly selects one signal string from a plurality of signal strings and applies it to the fuse  35 . For example, the control part  91  can select a signal string at random by determining the signal string number n by using software regarding random numbers. This makes it difficult to decode the signal string selected from the plurality of signal strings. Here, one signal string is selected, but a plurality of signal strings may be randomly selected. 
     Further, as can be seen from  FIG. 8 , the control part  91  applies the melting conduction signal to the fuse  35  after applying at least one non-melting conduction signal (here, three non-melting conduction signals) to the fuse  35 . This makes it possible to reliably detect whether or not the fuse  35  is molten by the non-melting conduction signal and whether or not the fuse  35  is molten by the melting conduction signal. 
     Returning to  FIG. 7 , the output terminal B is connected to the determination signal conversion part  96  ( FIG. 5 ) of the control circuit  90  via the connector  75 . The output terminal B outputs i) the first voltage signal corresponding to the voltage between the terminals  38  when the fuse  35  is not molten and ii) the second voltage signal corresponding to the voltage between the terminals  38  when the fuse  35  is molten to the determination signal conversion part  96  via the connector  75 . In the present exemplary embodiment, the first voltage signal has a voltage substantially equal to the voltage applied from the power supply part  97  to the power supply terminal C. Further, the second voltage signal has a voltage substantially equal to the ground voltage. 
     In the present exemplary embodiment, the region surrounded by a dashed line in  FIG. 7  is a voltage signal output part  82  that is connected to the fuse  35 . The voltage signal output part  82  has a function to output the first voltage signal to the control circuit  90  of the device main body  3  in a state where the fuse  35  is not molten, and to output the second voltage signal to the control circuit  90  of the device main body  3  in a state where the fuse  35  is molten. 
     Returning to  FIG. 5 , the determination signal conversion part  96  of the control circuit  90  converts the voltage signal inputted from the unit-side circuit  80  (specifically, the output terminal B) into the voltage signal of a level that can be determined by the control part  91  (that is, the determination signal). The determination signal conversion part  96  outputs the converted determination signal to the control part  91 . 
       FIG. 9  is a circuit diagram showing an example of a configuration of the determination signal conversion part  96 . The determination signal conversion part  96  includes an input terminal D and an output terminal E. A first voltage signal corresponding to a state where the fuse  35  is not molten and a second voltage signal corresponding to a state where the fuse  35  is molten are inputted to the input terminal D from the unit-side circuit  80 . The inputted first voltage signal is converted into a first converted signal, which is sufficiently larger than a threshold voltage at which the control part  91  can determine ON/OFF, and the second voltage signal is converted to a second converted signal, which is sufficiently smaller than the threshold voltage. The output terminal E outputs the first converted signal and the second converted signal to the control part  91 . 
     The control part  91  determines whether the toner unit  30  is a genuine product or not by detecting whether or not the fuse  35  is molten on the basis of the inputted first converted signal and the second converted signal. For example, when the fuse  35  is not detected to be molten by the application of the non-melting conduction signal and is also detected to be molten by the application of the melting conduction signal, the control part  91  determines that the toner unit  30  attached to the attachment part  70  is the specific exchange unit (a genuine product). On the other hand, when the fuse  35  is detected to be molten by the application of the non-melting conduction signal or when the fuse  35  is not detected to be molten by the application of the melting conduction signal, the control part  91  determines that the toner unit  30  attached to the attachment part  70  is an exchange unit other than the specific exchange unit (a non-genuine product). Accordingly, it is possible to determine whether the toner unit  30  is a genuine product or a non-genuine product according to a detection of whether or not the fuse  35  is molten with respect to the application of the conduction signal. 
     Further, the control part  91  determines whether or not the toner unit  30  attached to the attachment part  70  is a genuine product by comparing the detection result of whether or not the fuse  35  is molten with the comparison code J (n, m) stored in the storage part  92 . Specifically, the control part  91  determines that the toner unit  30  is a genuine product when the detection result of whether or not the fuse  35  is molten matches the comparison code J (n, m), and the control part  91  determines that the toner unit  30  is a non-genuine product when the detection result of whether or not the fuse  35  is molten does not match the comparison code J (n, m). Accordingly, it is possible to easily and appropriately determine whether the toner unit  30  is a genuine product or a non-genuine product. 
     In the present exemplary embodiment, when the toner unit  30  is attached to the attachment part  70 , the control part  91  determines whether or not the fuse  35  is molten by detecting the voltage between the terminals  38  of the fuse  35  of the toner unit  30  on the basis of whether the signal inputted from the toner unit  30  is the first voltage signal or the second voltage signal. When it is determined that the fuse  35  is not molten, the control part  91  determines whether or not the toner unit  30  is a genuine product by applying the non-melting conduction signal and the melting conduction signal to the fuse  35 . In this way, there is no need to perform a determination process on the non-genuine toner unit  30  for which the fuse  35  is molten. 
     &lt;Determination Process when an Exchange Unit is Attached&gt; 
     A determination process at the time when an exchange unit is attached to an attachment part will be described with reference to  FIG. 10  and  FIG. 11 . By taking the toner unit  30  as an example of an exchange unit, a process of determining whether the exchanged toner unit  30  is a genuine product or a non-genuine product will be described in the following. 
       FIG. 10  is a flow chart showing an operation example of the image forming device  1  when the toner unit  30  is attached to the attachment part  70 . The flow chart shown in  FIG. 10  starts from the time when the toner in the toner unit  30  is consumed and the amount thereof becomes equal to or less than a predetermined amount, and “toner empty” is detected by a sensor (the sensor is mounted inside the toner unit  30 ) that is not shown in figures (step S 102 ). When “toner empty” is detected, the control circuit  90  displays a message urging the exchange of the toner unit  30  on an operation panel which is not shown in the figures. 
     In accordance with the content displayed on the operation panel, a user removes the toner unit  30  attached to the attachment part  70  and attaches a new toner unit  30  to the attachment part  70  (step S 104 ). When the control circuit  90  detects that the toner unit  30  is attached to the attachment part  70  by using a sensor or the like, the control circuit  90  detects whether the fuse  35  of the toner unit  30  is molten before starting the image forming operation (step S 106 ). The control circuit  90  can determine whether or not the fuse  35  is molten on the basis of the magnitude of the voltage of the signal corresponding to the voltage between the terminals  38  of the fuse  35  outputted from the unit-side circuit  80 . 
     When it is determined that the fuse  35  is molten in step S 106  (Yes), the control circuit  90  determines that the toner unit  30  attached to the attachment part  70  is a non-genuine product (step S 110 ). Then, the control circuit  90  displays a message that the attached toner unit  30  is a non-genuine product on, for example, the operation panel. 
     On the other hand, when it is determined that the fuse  35  is not molten in step S 106  (No), the control circuit  90  executes a detection/determination process of the toner unit  30  shown in  FIG. 11  (step S 108 ). Thus, it can be determined whether the toner unit  30  attached to the attachment part  70  is a genuine product or a non-genuine product. 
       FIG. 11  is a flow chart showing an example of the detection/determination process of the toner unit  30 . First, the control circuit  90  starts outputting the conduction signal (step S 202 ). Next, the control circuit  90  determines the signal string number n (step S 204 ). Here, the signal string applied to the fuse  35  is assumed to be the signal string  1  shown in  FIG. 8 . Then, the signal string number n is “1” and the signal array number M is “5.” 
     Subsequently, the control circuit  90  sets the signal array number m to “I” (step S 206 ). Then, the control circuit  90  determines whether or not the value of the signal array number m is equal to or less than M (=5) (step S 208 ). Here, since the signal array number m is “1,” the control circuit  90  converts a digital voltage signal corresponding to the voltage code V (1, 1) into an analog voltage signal using the D/A conversion part  93  and outputs it to the waveform generation part  94  (step S 210 ). Further, the control circuit  90  outputs the conduction time signal corresponding to the conduction time code T (1, 1) to the waveform generation part  94  (step S 212 ). The waveform generation part  94  generates the voltage signal waveform in which the analog voltage signal and the conduction time signal are synchronized. 
     Next, the control circuit  90  applies the conduction signal M 1  obtained by converting the voltage signal waveform into the current signal waveform using the voltage-current conversion part  95  to the fuse  35  via the unit-side circuit  80  (step S 214 ). Upon receipt of the conduction signal M 1 , the fuse  35  is molten or not molten. 
     Next, the control circuit  90  obtains the voltage signal between the terminals  38  of the fuse  35  that receives the conduction signal M 1  from the unit-side circuit  80  (step S 216 ). That is, the control circuit  90  obtains the first voltage signal corresponding to the voltage at which the fuse  35  is not molten or the second voltage signal corresponding to the voltage at which the fuse  35  is molten. The control circuit  90  determines whether or not the fuse  35  is molten on the basis of the obtained voltage signal (step S 218 ). 
     Because the conduction signal M 1  is a non-melting conduction signal, the value of the comparison code J (1, 1) previously stored in the storage part  92  is “0.” When the control circuit  90  receives the second voltage signal from the unit-side circuit  80 , the control circuit  90  determines that the exchanged toner unit  30  is a non-genuine product because the detection result and the comparison code J (1, 1) do not match in step S 218  (step S 224 ). When the exchanged toner unit  30  is determined as a non-genuine product, the control circuit  90  displays a message that the attached toner unit  30  is a non-genuine product on, for example, the operation panel. In addition, the control circuit  90  displays a message urging the exchange of the toner unit  30  with a genuine product or executes a process of changing the operation condition of the image forming device  1  to the process corresponding to a non-genuine product. 
     On the other hand, when the control circuit  90  receives the first voltage signal from the unit-side circuit  80 , the control circuit  90  determines that the detection result and the comparison code J (1, 1) match in step S 218  and sets the value of m as “2” (step S 220 ). Then, the control circuit  90  returns to the process of step S 208  and repeats the processes of steps S 208  to S 218 . 
     In the signal string  1  shown in  FIG. 8 , the conduction signal M 4  applied in the fourth order is the melting conduction signal. For this reason, when the toner unit  30  is a genuine product, the fuse  35  is not molten when the conduction signals M 2  and M 3  are applied to the fuse  35 , and the detection result and the comparison code match in the routine of m=2, 3. Then, the fuse  35  is molten when the conduction signal M 4  is applied to the fuse  35 , and the detection result and the comparison code J (1, 4) match in the routine of m=4. That is, the control circuit  90  determines that the fuse is molten with the first melting conduction signal included in the signal string  1 . 
     The conduction signal M 5  applied in the fifth order in the signal string  1  is a non-melting conduction signal, but since it is a conduction signal after the conduction signal M 4 , the comparison code J (1, 5) is stored as “1” (melting) in the storage part  92 . Therefore, the detection result and the comparison code J (1, 4) match with each other in the routine of m=5, and the control circuit  90  determines that the toner unit  30  is a genuine product when it determines that m=M+1 (=6) (step S 222 ). 
     It should be noted that, in the above description, the routine of m=5 is performed after it is determined that the fuse  35  is molten in the routine of in =4, but it is not so limited and the routine of m=5 does not have to be performed. That is, the routine of m=5 does not have to be performed in a case when the toner unit  30  is a genuine product since the toner unit  30  can be determined as a genuine product when the fuse  35  is molten in the routine of m=4. That is, the process of  FIG. 11  may be ended at the timing when the toner unit is determined to be a genuine product or a non-genuine product before all conduction signals included in the signal string are applied to the fuse  35 . 
     In the above description, the melting conduction signal was configured to be the fourth order in the signal string, but it is not so limited and it may be configured to be the second order or the third order of the signal string. Further, in the above description, the signal string includes five conduction signals, but it is not so limited and the number of conduction signals included in the signal string may be any of 2 to 4. In addition, the signal string includes one melting conduction signal, but it is not so limited and a plurality of melting conduction signals may be included. 
     Furthermore, in the above description, a signal string including the melting conduction signal and the non-melting conduction signal is applied to the fuse  35 , but it is not so limited. For example, the melting conduction signal and the non-melting conduction signal may be independently applied to the fuse  35  without constituting a signal string. 
     &lt;Effect of the Present Exemplary Embodiment&gt; 
     As described above, the image forming device  1  according to the present exemplary embodiment applies the non-melting conduction signal and the melting conduction signal to the fuse  35 , and detects each of whether or not the fuse  35  is molten by the non-melting conduction signal and whether or not the fuse  35  is molten by the melting conduction signal. Then, the image forming device  1  determines whether or not the toner unit, which is an exchange unit attached to the attachment part  70 , is a specific exchange unit (a genuine product or a non-genuine product) on the basis of the detection result of whether or not the fuse is molten. 
     In such a configuration, by using the pre-arcing time-current characteristic of the fuse  35  having analog characteristics rather than using memory information stored in a memory chip mounted on a conventional toner unit, it is difficult even for a specialist to decode the conduction signal applied to the fuse  35  mounted on the toner unit  30  (that is, the non-melting conduction signal and the melting conduction signal having different current values). Particularly, it is difficult to detect the current value and the conduction time of the conduction signal applied to the fuse  35  in practical limitations. Further, the determination criterion can be flexibly changed by changing the position of the characteristic point on the pre-arcing time-current characteristic curve of the fuse  35  and changing the melting conduction signal and the non-melting conduction signal corresponding to the characteristic point. As a result, it is possible to appropriately determine whether the toner unit  30  mounted on the attachment part  70  is a genuine product or a non-genuine product. 
     Furthermore, in the present exemplary embodiment, because the signal string obtained by combining the melting conduction signal and the non-melting conduction signal is applied to the fuse  35 , it is difficult for a specialist to decode the conduction information. Moreover, it is further difficult for the specialist to decode the conduction information because the signal string randomly selected from the plurality of signal strings stored in the storage part  92  is applied to the fuse  35 . 
     Further, according to the present exemplary embodiment, because it is possible to appropriately determine whether the toner unit  30  attached to the attachment part  70  is a genuine product or a non-genuine product, it is possible to appropriately manage the image forming condition and the operating conditions of the image forming device  1  in accordance with the exchange of the toner unit  30 . Accordingly, even when a non-genuine toner unit  30  is attached, the image forming device  1  can perform image formation under appropriate operating conditions corresponding to non-genuine products. As a result, image quality can be secured and maintenance of the image forming device  1  becomes possible, and so it is possible to ameliorate the disadvantage that has occurred to users and the like. 
     MODIFICATION EXAMPLES 
     In the above description, the control part  91  sets the melting conduction signal and the non-melting conduction signal to one characteristic point P 1  on the pre-arcing time-current characteristic curve as shown in  FIG. 4 , but it is not so limited. For example, the control part  91  may set the melting conduction signal and the non-melting conduction signal on the basis of the current value and conduction time corresponding to each of two characteristic points. 
     The First Modification Example 
       FIG. 12  is a diagram for explaining the melting conduction signal and the non-melting conduction signal according to a first modification example. In the first modification example, the melting conduction signal and the non-melting conduction signal are set for the characteristic point P 2  in the minimum conduction current region and the characteristic point P 3  having a current value larger than the characteristic point P 2 . 
     Specifically, as shown in  FIG. 12 , the melting conduction signal at the point P 22  corresponding to the characteristic point P 2  is composed of the conduction time T 2  of the characteristic point P 2  and the conduction current I 22  which is larger than the conduction current I 2  of the characteristic point P 2 . The non-melting conduction signal at the point P 21  corresponding to the characteristic point P 2  is composed of the conduction time T 2  of the characteristic point P 2  and the conduction current I 21  which is smaller than the conduction current I 2  of the characteristic point P 2 . Similarly, the melting conduction signal at the point P 32  corresponding to the characteristic point P 3  is composed of the conduction time T 3  of the characteristic point P 3  and the conduction current I 32  which is larger than the conduction current I 3  of the characteristic point P 3 . 
     The non-melting conduction signal at the point P 31  corresponding to the characteristic point P 3  is composed of the conduction time T 3  of the characteristic point P 3  and the conduction current I 31  which is smaller than the conduction current I 3  of the characteristic point P 3 . It should be noted that, in the first modified example, the characteristic point P 3  corresponds to the first characteristic point, and the characteristic point P 2  corresponds to the second characteristic point. 
       FIG. 13  is a diagram showing a signal string according to the first modification example.  FIG. 13A  is a diagram showing a signal string  2  obtained by combining the melting conduction signal and the non-melting conduction signal corresponding to the characteristic point P 2  in  FIG. 12 .  FIG. 13B  is a diagram showing a signal string  3  obtained by combining the melting conduction signal and the non-melting conduction signal corresponding to the characteristic point P 3  in  FIG. 12 . In the signal string  2 , the conduction signals M 21 , M 22 , M 23 , and M 25  are the non-melting conduction signals and the conduction signal M 24  is the melting conduction signal. Similarly, in the signal string  3 , the conduction signals M 31 , M 32 , M 33 , and M 35  are the non-melting conduction signals and the conduction signal M 34  is the melting conduction signal. 
     The control part  91  applies the signal string  2  and the signal string  3  to the fuse  35 . For example, the control part  91  alternately applies the conduction signal of the signal string  2  and the conduction signal of the signal string  3  (for example, applying the conduction signals in the order of M 21 , M 31 , M 22 , M 32 , M 23 , . . . ) and detects whether or not the fuse  35  is molten. As described above, by applying the conduction signal corresponding to the plurality of characteristic points, even a non-genuine product, whose current value in the minimum melting current region is similar to a genuine product, can be properly specified by the signal string  3  corresponding to characteristic point P 3 . It should be noted that, in the above description, the melting conduction signal and the non-melting conduction signal are set for the two characteristic points P 2  and P 3 , but it is not so limited and the melting conduction signal and the non-melting conduction signal may be set for three or more characteristic points. 
     The Second Modification Example 
       FIG. 14  is a diagram for explaining the melting conduction signal and the non-melting conduction signal according to a second modification example. In the second modification example, the melting conduction signal is set with respect to the characteristic point P 4  in the minimum melting current region, and the non-melting conduction signal is set with respect to the characteristic point P 5  whose current value is larger than the characteristic point P 4 . 
     Specifically, as shown in  FIG. 14 , the melting conduction signal at point P 42  is composed of a conduction time T 4  at the characteristic point P 4  and the conduction current  42  which is larger than the conduction current I 4  at the characteristic point P 4 . The non-melting conduction signal at point P 51  is composed of a conduction time T 5  at the characteristic point P 5  and the conduction current I 51  which is smaller than the conduction current I 5  at the characteristic point P 5 . 
       FIG. 15  is a diagram showing a signal string according to the second modification example. As shown in  FIG. 15 , the control part  91  applies the signal string  4  obtained by combining the melting conduction signal and the non-melting conduction signal of  FIG. 14  to the fuse  35 . In the signal string  4 , the conduction signals M 41 , M 42 , M 43 , and M 45  are non-melting conduction signals, and the conduction signal M 44  is a melting conduction. 
     In the case of the second modification example, by setting the conduction current of the melting conduction signal to be larger than the conduction current of the characteristic point P 4  and by setting the conduction current of the non-melting conduction signal to be smaller than the conduction current of the characteristic point P 5 , the fuse  35  with the pre-arcing time-current characteristic curve having a large slope between the characteristic point P 4  and the characteristic point P 5  can be properly distinguished from the other fuses. Because it is easier to determine whether the toner unit  30  is a genuine product or a non-genuine product when, in particular, the toner unit  30  on which the fuse  35  having a steep pre-arcing time-current characteristic curve is mounted is a genuine product, the present example is more effective. 
     The Third Modification Example 
     In the above description, the melting conduction signals of the signal string and the non-melting conduction signal each has one current value, but it is not so limited. For example, as shown in  FIG. 16 , there may be a plurality of current values of the non-melting conduction signal and the melting conduction signal. 
       FIG. 16  is a diagram showing a signal string according to the third modification example. The signal string  5  shown in  FIG. 16  includes five conduction signals, and conduction signals M 51 , M 52 , and M 53  are the non-melting conduction signals and conduction signals M 54  and M 55  are the melting conduction signals. The five conduction signals are set for, for example, one characteristic point on the pre-arcing time-current characteristic curve. As can be seen in  FIG. 16 , the current values of the conduction signals M 51 , M 52 , M 53 , M 54 , and M 55  are respectively different from each other and set stepwise. The conduction times of the five conduction signals are the same. 
     The control part  91  sequentially applies conduction signals constituting the signal string  5  to the fuse  35 , and determines whether the toner unit  30  is a genuine product or a non-genuine product by detecting whether or not the fuse  35  is molten. In this manner, since it is possible to detect whether or not the fuse  35  is molten by subdividing the current value, a genuine toner unit  30  and a non-genuine toner unit  30  can be determined with high accuracy. 
     It should be noted that, in the above description, the determination of whether the toner unit  30  is a genuine product or a non-genuine product is described as an example of the determination as to whether or not the exchange unit is the specific exchange unit, but it is not so limited. For example, it may be determined whether the toner unit is a high-definition image forming toner unit (specific exchange unit) or a standard image forming toner unit. 
     Further, in the above description, an electrophotographic printer is described as an example of an image forming device, but it is not so limited. The image forming device may be a copying machine, a facsimile, a multifunctional printer, or the like. Furthermore, the printer may adopt a so-called ink jet system. 
     Moreover, in the above description, the control circuit  90  of the device main body  3  is connected to the unit-side circuit  80  of the toner unit  30 , which is the exchange unit, via the connector  75 , but it is not so limited. For example, the control circuit  90  may be wirelessly connected to the unit-side circuit  80 . 
     The present invention is explained with the exemplary embodiments of the present invention but the technical scope of the present invention is not limited to the scope described in the above embodiment. It is apparent for those skilled in the art that it is possible to make various changes and modifications to the embodiment. It is apparent from the description of the scope of the claims that the forms added with such changes and modifications are included in the technical scope of the present invention.