Patent Publication Number: US-2013250340-A1

Title: Detection apparatus and method and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-067531 filed Mar. 23, 2012. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a detection apparatus and method and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a detection apparatus including the following elements. Plural terminals are connected to plural contact points in a one-to-one correspondence, the plural terminals and the plural contact points being arranged in a predetermined direction. A power feeding unit feeds power to a substrate via, among the plural terminals, a first terminal positioned at one end in the predetermined direction and a contact point connected to the first terminal. A detector detects a signal which is supplied from the substrate as a result of feeding power to the substrate and which is received by, among the plural terminals, a second terminal positioned at the other end opposite the first terminal in the predetermined direction, via a contact point connected to the second terminal. A determining unit determines whether there is an occurrence of a connection abnormality between the plural terminals and the plural associated contact points on the basis of whether the signal detected by the detector satisfies a predetermined condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates an example of the entire configuration of an apparatus according to an exemplary embodiment; 
         FIGS. 2A ,  2 B, and  2 C illustrate arrangements of terminals or pins provided in a connecting unit or a cable; 
         FIGS. 3A through 3D  illustrate examples of the connection state between a connecting unit and a cable; 
         FIG. 4  illustrates a functional configuration of a control unit; 
         FIG. 5  is a flowchart illustrating the flow of an operation performed by an apparatus according to this exemplary embodiment; 
         FIGS. 6 and 7  illustrate examples of the related art; 
         FIG. 8  illustrates an example of the entire configuration of an apparatus according to a first modified example; 
         FIG. 9  illustrates a range of an output voltage in which the connection state between substrates is considered to be normal; 
         FIG. 10  is a flowchart illustrating the flow of an operation performed by an apparatus according to the first modified example; and 
         FIG. 11  illustrates an example of the entire configuration of an image forming apparatus according to a second modified example. 
     
    
    
     DETAILED DESCRIPTION 
     1. Exemplary Embodiment 
     1-1. Entire Configuration 
       FIG. 1  illustrates the entire configuration of an apparatus  9  according to an exemplary embodiment of the invention. In order to discuss the arrangement of elements which form the apparatus  9 , hereinafter, in the drawings, the space in which the elements are disposed is represented using a right-handed xyz coordinate space. Among the coordinate symbols shown in  FIG. 1 , the symbol represented by a black circle within a white circle indicates an arrow directing from the far side to the near side in the plane of the drawings. The symbol represented by two lines crossing each other within a white circle indicates an arrow directing from the near side to the far side in the plane of the drawings. In the xyz coordinate space, the directions along the x axis are the x axis directions. Among the x axis directions, the direction in which the x component increases will be referred to as a +x direction, while the direction in which the x component decreases will be referred to as a −x direction. Likewise, concerning the y and z components, the y axis directions, the +y direction, the −y direction, the z axis directions, the +z direction, and the −z direction will also be defined in the same manner as those of the x component. 
     The apparatus  9  is, for example, an image forming apparatus that forms images on a medium, such as paper, by using an electrophotographic system, or an image reading apparatus that optically reads images formed on a medium. The apparatus  9  may be a receiving apparatus that receives broadcast waves and that plays back images and sound corresponding to the received broadcast waves. The apparatus  9  may also be a computer or one of various communication apparatuses. In short, the apparatus  9  may be of any type as long as it has plural substrates connected to each another by using cable lines and implements a certain function as a result of being controlled. 
     In addition to various elements for implementing the above-described function, the apparatus  9  includes, as shown in  FIG. 1 , a first substrate  1 , a second substrate  2 , and a notification unit  3 . The first substrate  1  serves to control the apparatus  9  by sending and receiving signals to and from the second substrate  2 . The first substrate  1  includes a control unit  11 , a connecting unit  12 , a power feeding unit  13 , and a cable  14 . 
     The notification unit  3  is connected to the control unit  11  of the first substrate  1 , and, under the control of the control unit  11 , it notifies a user about whether the first substrate  1  and the second substrate  2  are correctly connected. More specifically, the notification unit  3  includes two light emitting elements that emit light of different colors, e.g., green and red, and more specifically, one light emitting element emits light in red and the other light emitting element emits light in green when receiving power. Upon receiving a signal indicating that the first and second substrates  1  and  2  are correctly connected, the notification unit  3  causes a light emitting element to emit light of a color indicating the normal connection state (e.g., green). In contrast, upon receiving a signal indicating the first and second substrates  1  and  2  are not correctly connected, the notification unit  3  causes the other light emitting element to emit light of a color indicating the abnormal connection state (e.g., red). 
     The control unit  11  includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). The CPU of the control unit  11  reads and executes a computer program (hereinafter simply referred to as a “program”) stored in a storage device (not shown), such as a hard disk drive, or the ROM, thereby controlling the elements of the apparatus  9 . 
     The first substrate  1  and the second substrate  2  are aligned in the x axis direction and are connected to each other via the cable  14  extending in the x axis direction. The cable  14  is a cable line set or a cable harness through which signals are sent and received between the first and second substrates  1  and  2  and power is supplied from the first substrate  1  to the second substrate  2 . The cable  14  includes a power feeding line  141 , an inspection signal line  142 , and a signal line set  143 . The power feeding line  141  is a line through which power is supplied (fed). The inspection signal line  142  is a cable line for transmitting a signal which represents information to be supplied from the second substrate  2  to the first substrate  1  and which is also used for inspecting whether the first and second substrates  1  and  2  are connected is transmitted. 
     The signal line set  143  is constituted by plural cable lines through which plural signals that are sent and received between the first and second substrates  1  and  2  are transmitted. In this exemplary embodiment, as shown in  FIG. 1 , the signal line set  143  is a bundle of six signal lines. All the signal lines extend in the x axis direction and are arranged in the y axis direction. The power feeding line  141  is positioned on the +y direction side of the signal line set  143 , while the inspection signal line  142  is positioned on the −y direction side of the signal line set  143 . At both ends of the cable  14 , pins corresponding to the power feeding line  141 , the inspection signal line  142 , and the individual cable lines of the signal line set  143  are provided. These pins are contact points formed in a projecting shape and are inserted into terminals provided in the connecting unit  12  of the first substrate  1  and into terminals provided in a connecting unit  22  of the second substrate  2 . 
     The power feeding unit  13  feeds power to the second substrate  2  via the power feeding line  141 . The connecting unit  12  is a connector for connecting the control unit  11  and the second substrate  2  via the cable  14 . The connecting unit  12  includes a power feeding terminal  121 , an inspection signal terminal  122 , and a signal terminal set  123 . 
     The power feeding terminal  121  is a terminal formed in a recessed shape, and receives a pin provided in the power feeding line  141  of the cable  14 . With the connection of the terminal and the pin, the power feeding terminal  121  and the power feeding line  141  are connected. The power feeding terminal  121  is connected to the power feeding unit  13  and feeds power supplied from the power feeding unit  13  to the power feeding line  141 . 
     The inspection signal terminal  122  is a terminal formed in a recessed shape, and receives a pin provided in the inspection signal line  142  of the cable  14 . With the connection of the terminal and the pin, the inspection signal terminal  122  and the inspection signal line  142  are connected. The inspection signal terminal  122  is connected to a predetermined port of the control unit  11 , and receives a signal output from the second substrate  2  via the inspection signal line  142  and transmits the received signal to the control unit  11 . 
     The signal terminal set  123  includes plural (six in this case) terminals formed in a recessed shape, and the terminals receive pins provided in the associated signal lines of the signal line set  143  of the cable  14 . With the connection of the terminals and the pins, the terminals of the signal terminal set  123  and the associated signal lines of the signal line set  143  are connected. The terminals of the signal terminal set  123  are connected to the control unit  11  (not shown), and receive various signals output from the second substrate  2  via the signal line set  143  and transmit the received signals to the control unit  11 . 
     The second substrate  2  causes a certain element of the apparatus  9  to perform signal processing so as to control the element. The second substrate  2  includes an inspection unit  21  and the connecting unit  22 . The inspection unit  21  is an oscillation circuit that generates a signal for inspecting whether the first and second substrates  1  and  2  are connected (hereinafter such a signal will be referred to as an “inspection signal”). The inspection unit  21  includes a sensor  211  and an inverter  212 . The sensor  211  is, for example, a humidity sensor, and measures the humidity around the sensor  211  and outputs a measurement result in the form of a digital signal. The inverter  212  converts a digital signal output from the sensor  211  into a square wave inspection signal. That is, upon receiving power, the inspection unit  21  generates, as an inspection signal, a signal which has been adjusted such that a change in the signal is contained within a predetermined range. 
     The connecting unit  22  includes a power feeding terminal  221 , an inspection signal terminal  222 , and a signal terminal set  223 . The power feeding terminal  221  is a terminal formed in a recessed shape, and receives a pin provided in the power feeding line  141  of the cable  14 . With the connection of the terminal and the pin, the power feeding terminal  221  and the power feeding line  141  are connected. The power feeding terminal  221  is connected to the inspection unit  21 , and feeds power supplied from the power feeding unit  13  of the first substrate  1  via the power feeding line  141  of the cable  14  to the inspection unit  21 . 
     The inspection signal terminal  222  is a terminal formed in a recessed shape, and receives a pin provided in the inspection signal line  142  of the cable  14 . With the connection of the terminal and the pin, the inspection signal terminal  222  and the inspection signal line  142  are connected. The inspection signal terminal  222  is connected to the inspection unit  21 , and supplies an inspection signal output from the inspection unit  21  to the first substrate  1  via the inspection signal line  142 . 
     The signal terminal set  223  includes plural (six in this case) terminals formed in a recessed shape, and the terminals receive pins provided in the associated signal lines of the signal line set  143 . With the connection of the terminals and the pins, the terminals of the signal terminal set  223  and the associated signal lines of the signal line set  143  are connected. The terminals of the signal terminal set  223  are connected to certain elements of the second substrate  2  which implement various functions, and send and receive control signals and signals representing various items of information to and from the elements of the second substrate  2 . 
     1-2. Connecting Unit 
       FIGS. 2A and 2C  respectively illustrate the arrangements of the terminals provided in the connecting units  12  and  22  of the first and second substrates  1  and  2 .  FIG. 2B  illustrates the pins provided in the cable  14 . When viewing the connecting unit  12  of the first substrate  1  from the second substrate  2 , as shown in  FIG. 2A , the power feeding terminal  121 , the inspection signal terminal  122 , and the signal terminal set  123  are sequentially disposed in the order of the inspection signal terminal  122 , the signal terminal set  123 , and the power feeding terminal  121  in the +y direction. 
     When viewing one end of the cable  14  from the first substrate  1 , as shown in  FIG. 2B , the power feeding line  141 , the inspection signal line  142 , and the signal line set  143  are sequentially disposed in the order of the inspection signal line  142 , the signal line set  143 , and the power feeding line  141  in the +y direction. 
     When viewing the connecting unit  22  of the second substrate  2  from the first substrate  1 , as shown in  FIG. 2C , the power feeding terminal  221 , the inspection signal terminal  222 , and the signal terminal set  223  are sequentially disposed in the order of the inspection signal terminal  222 , the signal terminal set  223 , and the power feeding terminal  221  in the +y direction. 
       FIGS. 3A through 3D  illustrate examples of the connection state between the connecting unit  12  and the cable  14 . Although a description will be given of the connection between the connecting unit  12  and the cable  14 , the connection between the connecting unit  22  and the cable  14  is similar to that between the connecting unit  12  and the cable  14 . A description will be given below, assuming that the connecting unit  22  and the cable  14  are correctly connected. 
     Assuming that the cable  14  belongs to the second substrate  2 , plural pins which are provided in the cable  14  and which are to be connected to the associated terminals provided in the connecting unit  12  are examples of plural contact points which are arranged in a predetermined direction and which are to be connected to the associated terminals of the first substrate  1  in one-to-one correspondence. 
     Conversely, assuming that the cable  14  belongs to the first substrate  1 , plural pins which are provided in the cable  14  and which are to be connected to the associated terminals provided in the connecting unit  22  are examples of plural terminals which are provided in the first substrate  1  and which are arranged in a predetermined direction. In this case, the terminals provided in the connecting unit  22  of the second substrate  2  are examples of contact points which are arranged in a predetermined direction and which are to be connected to the associated terminals of the first substrate  1  in one-to-one correspondence. 
     When viewing the connecting unit  12  and the cable  14  from above, i.e., from the +z direction to the −z direction, as shown in  FIG. 3A , the terminals provided in the connecting unit  12  and the pins provided in the cable  14  are all arranged in the y axis direction. The cable  14  is inserted into the connecting unit  12  such that the pins of the cable  14  fit into the associated terminals of the connecting unit  12 . 
     If the cable  14  is obliquely inserted into the connecting unit  12 , the cable  14  and the connecting unit  12  are partially connected, as shown in  FIG. 3B . In the connection state shown in  FIG. 3B , although the inspection signal terminal  122  and the inspection signal line  142  are connected, the power feeding terminal  121  and the power feeding line  141  are not connected. Accordingly, since power is not supplied to the inspection unit  21 , an inspection signal is not output from the inspection unit  21 , and thus, the inspection signal terminal  122  does not receive an inspection signal. As a result, the control unit  11  does not detect any inspection signal. 
     The cable  14  may be obliquely inserted into the connecting unit  12  in a direction opposite to that shown in  FIG. 3B , in which case, the cable  14  and the connecting unit  12  are partially connected, as shown in  FIG. 3C . In the connection state shown in  FIG. 3C , although the power feeding terminal  121  and the power feeding line  141  are connected, the inspection signal terminal  122  and the inspection signal line  142  are not connected. Accordingly, although power is supplied to the inspection unit  21 , an inspection signal output from the inspection unit  21  is not transmitted to the inspection signal terminal  122 . As a result, the control unit  11  does not detect any inspection signal. 
     The connection state between the cable  14  and the connecting unit  12  obtained as a result of inserting the cable  14  into the connecting unit  12  in such a manner that that all the terminals of the connecting unit  12  are connected to the pins of the cable  14  is shown in  FIG. 3D . In the connection state shown in  FIG. 3D , the power feeding terminal  121  and the power feeding line  141  are connected, and also, the inspection signal terminal  122  and the inspection signal line  142  are connected. Accordingly, power is supplied to the inspection unit  21 , and an inspection signal output from the inspection unit  21  is supplied to the control unit  11  via the inspection signal terminal  122 , thereby allowing the control unit  11  to detect the inspection signal. Additionally, the terminals of the signal terminal set  123  disposed between the power feeding terminal  121  and the inspection signal terminal  122  are all connected to the associated pins of the cable  14 . Thus, the elements provided in the second substrate  2  are controlled by the control unit  11  of the first substrate  1 . 
     1-3. Functional Configuration of Control Unit 
       FIG. 4  illustrates the functional configuration of the control unit  11 . The control unit  11  functions as a detector  111 , a determining section  112 , and an output section  113  by executing a program. The detector  111  detects a signal transmitted from the inspection signal terminal  122 . The determining section  112  determines whether a signal detected by the detector  111  satisfies predetermined conditions. More specifically, the determining section  112  determines whether a change in the signal detected by the detector  111  is contained within a predetermined range. A change in the signal is a fluctuation in a potential or a current represented by the signal. If a change in the signal is contained within a predetermined range, the determining section  112  determines that the signal satisfies the predetermined conditions and that the detector  111  has detected an inspection signal supplied from the second substrate  2 . 
     The output section  113  outputs a signal indicating a determination result obtained from the determining section  112  to the notification unit  3 . For example, if the determining section  112  determines that a change in the signal is contained within a predetermined range, the output section  113  outputs a signal indicating that the first substrate  1  and the second substrate  2  are correctly connected to the notification unit  3 . If the determining section  112  determines that a change in the signal is not contained within a predetermined range, the output section  113  outputs a signal indicating the occurrence of an abnormality in the connection state between the first and second substrates  1  and  2  to the notification unit  3 . The notification unit  3  then causes the light emitting element of the color corresponding to the received signal to emit light, thereby notifying a user about whether the first substrate  1  and the second substrate  2  are correctly connected. The notification unit  3  may cause a light emitting element to emit light only when the connection state between the first and second substrates  1  and  2  is normal. Alternatively, only when the connection state between the first and second substrates  1  and  2  is abnormal, may the notification unit  3  cause the corresponding light emitting element to emit light. In short, upon receiving a signal indicating an abnormality of the connection, the notification unit  3  lets the user recognize such an abnormality. 
     1-4. Operation 
       FIG. 5  is a flowchart illustrating the flow of an operation performed by the apparatus  9  according to this exemplary embodiment. In step S 11 , the control unit  11  of the first substrate  1  detects an inspection signal output from the inspection unit  21  provided in the second substrate  2 . Then, in step S 12 , the control unit  11  determines whether the detected inspection signal has a predetermined change and whether the predetermined change is contained within a predetermined range. If the control unit  11  determines in step S 12  that the predetermined change is contained within a predetermined range, the process proceeds to step S 13 . In step S 13 , the control unit  11  executes processing which is to be executed when the connection state between the first and second substrates  1  and  2  is normal. The processing executed in step S 13  may be the measurement of the frequency of the inspection signal. Alternatively, the control unit  11  may cause the notification unit  3  to notify a user that the connection state is normal. 
     On the other hand, if the control unit  11  determines in step S 12  that the predetermined change is not contained within a predetermined range, the process proceeds to step S 14 . In step S 14 , the control unit  11  executes processing which is to be executed when the connection state between the first and second substrates  1  and  2  is abnormal. In the processing executed in step S 14 , the control unit  11  causes the notification unit  3  to notify a user about the occurrence of an abnormality in the connection state between the first and second substrates  1  and  2 . 
     In order to discuss the features of the apparatus  9  of this exemplary embodiment, the apparatus  9  will be compared with those of the related art. If the control unit  11  merely determines whether none of the terminals of the connecting unit  12  are connected to the pins of the cable  14 , as shown in  FIG. 3A , it is sufficient that any combination of a terminal and a pin be used for detecting the connection state. In reality, however, as shown in  FIG. 3B  or  3 C, the connecting unit  12  and the cable  14  are partially connected such that the cable  14  is obliquely inserted into the connecting unit  12 . In such an obliquely connected state, even if some terminals are connected to the associated pins at one end in the arrangement direction of the cable lines, some terminals are not correctly connected to the associated pins at the other end in the arrangement direction of the cable lines. Accordingly, if only one combination of a terminal and a pin is used for detecting the connection state, such an obliquely connected state may be wrongly recognized as the correct connection state. 
     In view of this situation, the following technique has been developed in the related art. The connection state at both ends in the arrangement direction of the cable lines is monitored, and only when both the connection state is normal, will it be determined that the connection state of the cable lines is normal.  FIG. 6  illustrates an apparatus  9   a  of an example of the related art. The apparatus  9   a  shown in  FIG. 6  includes a first substrate  1   a , a second substrate  2   a , and a notification unit  3   a.    
     The first substrate  1   a , which controls the apparatus  9   a , includes a control unit  11   a , a connecting unit  12   a , and a cable  14   a . The control unit  11   a  includes a CPU, a ROM, and a RAM, and controls the elements forming the apparatus  9   a  as a result of the CPU reading and executing a program stored in, for example, the ROM. 
     The cable  14   a  is a cable line set or a cable harness through which signals are sent and received between the first and second substrates  1   a  and  2   a  and power is supplied from the first substrate  1   a  to the second substrate  2   a . The cable  14   a  includes a first inspection signal line  141   a , a second inspection signal line  142   a , and a signal line set  143   a.    
     The connecting unit  12   a  includes a first inspection signal terminal  121   a , a second inspection signal terminal  122   a , and a signal terminal set  123   a . The first inspection signal terminal  121   a  is connected to the first inspection signal line  141   a . The second inspection signal terminal  122   a  is connected to the second inspection signal line  142   a . The terminals of the signal terminal set  123   a  are connected to the associated signal lines of the signal line set  143   a.    
     The second substrate  2   a  causes a certain element provided in the apparatus  9   a  to perform signal processing so as to control the element. The second substrate  2   a  includes a first inspection unit  21   a , a second inspection unit  23   a , and a connecting unit  22   a . Both of the first and second inspection units  21   a  and  23   a  are circuits that generate signals for inspecting whether the first and second substrates  1  and  2  are connected. 
     The connecting unit  22   a  includes a first inspection signal terminal  221   a , a second inspection signal terminal  222   a , and a signal terminal set  223   a . The first inspection signal terminal  221   a  is connected to the first inspection signal line  141   a . The second inspection signal terminal  222   a  is connected to the second inspection signal line  142   a . The terminals of the signal terminal set  123   a  are connected to the associated signal lines of the signal line set  143   a.    
     The notification unit  3   a  is connected to the control unit  11   a  of the first substrate  1   a , and, under the control of the control unit  11   a , it notifies a user about whether the first substrate  1   a  and the second substrate  2   a  are correctly connected. 
     An inspection signal output from the first inspection unit  21   a  (hereinafter referred to as a “first inspection signal”) is received by the first inspection signal terminal  121   a  of the connecting unit  12   a  after passing through the first inspection signal terminal  221   a  of the connecting unit  22   a  and the first inspection signal line  141   a  of the cable  14   a . The first inspection signal received by the first inspection signal terminal  121   a  is detected by the control unit  11   a  of the first substrate  1   a.    
     An inspection signal output from the second inspection unit  23   a  (hereinafter referred to as a “second inspection signal”) is received by the second inspection signal terminal  122   a  of the connecting unit  12   a  after passing through the second inspection signal terminal  222   a  of the connecting unit  22   a  and the second inspection signal line  142   a  of the cable  14   a . The second inspection signal received by the second inspection signal terminal  122   a  is detected by the control unit  11   a  of the first substrate  1   a.    
     The control unit  11   a  monitors the first and second inspection signals and determines whether each of the first and second inspection signals has a predetermined change. If at least one of the first and second inspection signals does not have a predetermined change, the control unit  11   a  determines that the connection state between the first and second substrates  1   a  and  2   a  is abnormal. If a predetermined change is identified in both the first and second inspection signals, the control unit  11   a  determines that the connection state between the first and second substrates  1   a  and  2   a  is normal. 
     In the related art shown in  FIG. 6 , two inspection units are provided in the second substrate  2   a . Accordingly, in order to send first and second inspection signals from the first and second inspection units  21   a  and  23   a , respectively, to the first substrate  1   a , it is necessary to assign different cable lines to the first and second inspection units  21   a  and  23   a . Both of the first and second inspection units  21   a  and  23   a  may be used as a sensor provided in the second substrate  2   a , in which case, however, at least two signals are necessary to be sent from the second substrate  2   a  to the first substrate  1   a . That is, more restrictions are imposed on the configuration of the apparatus  9   a  shown in  FIG. 6  than that of the apparatus  9 . Accordingly, in order to send and receive the same amount of signals in the apparatus  9   a  shown in  FIG. 6  as that in the apparatus  9 , it is necessary that the number of signal lines of the signal line set  143   a  be greater than that of the signal line set  143  by one, the number of terminals of the signal terminal set  123   a  be greater than that of the signal terminal set  123  by one, and the number of terminals of the signal terminal set  223   a  be greater than that of the signal terminal set  223  by one. Additionally, in the related art shown in  FIG. 6 , it is necessary to provide ports used for individually detecting the first and second inspection signals for the control unit  11   a  of the first substrate  1   a.    
       FIG. 7  illustrates an apparatus  9   b  of another example of the related art, which is different from that shown in  FIG. 6 . The apparatus  9   b  shown in  FIG. 7  includes a first substrate  1   b , a second substrate  2   b , and a notification unit  3   b . In the apparatus  9   b , the first substrate  1   b  includes a control unit  11   b , a connecting unit  12   b , a power feeding unit  13   b , a pull-up resistor R, and a cable  14   b . The second substrate  2   b  includes a connecting unit  22   b  but does not have an inspection unit. 
     The cable  14   b  is a cable line set or a cable harness through which signals are sent and received between the first and second substrates  1   b  and  2   b  and power is supplied from the first substrate  1   b  to the second substrate  2   b . The cable  14   b  includes a first inspection signal line  141   b , a second inspection signal line  142   b , and a signal line set  143   b.    
     The connecting unit  12   b  includes a first inspection signal terminal  121   b , a second inspection signal terminal  122   b , and a signal terminal set  123   b . The first inspection signal terminal  121   b  is connected to the first inspection signal line  141   b . The second inspection signal terminal  122   b  is connected to the second inspection signal line  142   b . The terminals of the signal terminal set  123   b  are connected to the associated signal lines of the signal line set  143   b.    
     The connecting unit  22   b  includes a first inspection signal terminal  221   b , a second inspection signal terminal  222   b , and a signal terminal set  223   b . The first inspection signal terminal  221   b  is connected to the first inspection signal line  141   b . The second inspection signal terminal  222   b  is connected to the second inspection signal line  142   b . The terminals of the signal terminal set  223   b  are connected to the associated signal lines of the signal line set  143   b.    
     In the second substrate  2   b , the first inspection signal terminal  221   b  is connected to the second inspection signal terminal  222   b . Accordingly, if there is an abnormality of the connection in at least one of the path “first inspection signal terminal  121   b →first inspection signal line  141   b →first inspection signal terminal  221   b ” and the path “second inspection signal terminal  222   b →second inspection signal line  142   b →second inspection signal terminal  122   b ”, a high level voltage is applied to the port of the control unit  11   b  of the first substrate  1   b  by a combination of the power feeding unit  13   b  and the pull-up resistor R. Conversely, if the terminals and the lines are correctly connected in both of the above-described paths, a low level voltage is applied to the port of the control unit  11   b  since the distal end of these paths is connected to a grounding point G. In this manner, the control unit  11   b  detects an abnormality of the connection state between the first and second substrates  1   b  and  2   b  by monitoring the level of the voltage applied to the port of the control unit  11   b.    
     In the related art shown in  FIG. 7 , it is sufficient that only one port for detecting inspection signals be provided in the control unit  11   b , and no inspection unit is provided in the second substrate  2   b . In the related art shown in  FIG. 7 , however, a determination as to whether the connection state between the first and second substrates  1   b  and  2   b  is normal is made by using a current flowing back and forth between the first and second substrates  1   b  and  2   b . Thus, as in the related art shown in  FIG. 6 , in order to determine the connection state, two signal lines are necessary. Accordingly, in order to send and receive the same amount of signals in the apparatus  9   b  shown in  FIG. 7  as that in the apparatus  9 , it is necessary that the number of signal lines of the signal line set  143   b  be greater than that of the signal line set  143  by one, the number of terminals of the signal terminal set  123   b  be greater than that of the signal terminal set  123  by one, and the number of terminals of the signal terminal set  223   b  be greater than that of the signal terminal set  223  by one. That is, in the related art shown in  FIG. 6  or  7 , the two cable lines positioned at the ends in the arrangement direction of the cable lines are used only for detecting the connection state between the terminals and lines. Accordingly, communication between the first substrate  1   a  or  1   b  and the second substrate  2   a  or  2   b  has to be made by using the remaining cable lines other than the above-described two cable lines. 
     Unlike the above-described related art, in the apparatus  9 , the connection state on the +y direction side is detected by the power feeding line  141  through which power is supplied from the first substrate  1  to the second substrate  2 , while the connection state on the −y direction side is detected by the inspection signal line  142  through which an inspection signal is sent from the second substrate  2  to the first substrate  1 . The inspection unit  21  may supply any signal to be sent from the second substrate  2  to the first substrate  1 , and thus, it may be used for purposes other than the detection of inspection signals. For example, the inspection unit  21  may supply humidity information to the control unit  11 , as described above. That is, in the apparatus  9 , two cable lines positioned at two ends in the arrangement direction of the cable lines are used for detecting the connection state, however, one of the two cable lines may also be used for another purpose. Accordingly, a smaller number of cable lines are required than in the related art. Additionally, in the apparatus  9 , in order to detect inspection signals, the provision of only one port is sufficient for the control unit  11 . 
     2. Modified Examples 
     The exemplary embodiment has been discussed above. This exemplary embodiment may be modified as in the following modified examples. The following modified examples may also be combined. 
     2-1. First Modified Example 
     In the above-described exemplary embodiment, an inspection signal is a square wave signal converted from a digital signal. However, an inspection signal does not have to be a digital signal which changes in a manner as described above, for example, it may be a signal indicating an analog value.  FIG. 8  illustrates the entire configuration of an apparatus  9   c  according to a first modified example in which an analog signal is utilized. The configuration of the apparatus  9   c  is the same as that of the apparatus  9 , and the individual elements forming the apparatus  9   c  are denoted by like reference numerals appended with “c”. The apparatus  9   c  is different from the apparatus  9  in that an inspection signal output from an inspection unit  21   c  is an analog signal. The inspection unit  21   c  is a circuit that generates an inspection signal for inspecting whether first and second substrates  1   c  and  2   c  are correctly connected. The inspection unit  21   c  includes a sensor  211   c  and an amplifier  212   c.    
     The sensor  211   c  is, for example, a humidity sensor, and measures the humidity around the sensor  211   c  and outputs a voltage indicating a measurement result to the amplifier  212   c . The amplifier  212   c  amplifies the voltage supplied from the sensor  211   c  and outputs the amplified voltage. In the amplifier  212   c , the offset voltage is adjusted so that the voltage output from the inspection unit  21   c  (hereinafter referred to as an “output voltage”) is contained within a range from V 1  to V 2 . The output voltage is transmitted to a control unit  11   c  via an inspection signal terminal  222   c , an inspection signal line  142   c , and an inspection signal terminal  122   c . The control unit  11   c  determines on the basis of the value of the received voltage whether the connection state between the first and second substrates  1   c  and  2   c  is normal. 
       FIG. 9  illustrates a range of the output voltage (hereinafter referred to as the “normal range”) in which the connection state of the first and second substrates  1   c  and  2   c  is considered to be normal. If there is a break between a power feeding terminal  121   c  and a power feeding line  141   c  or between the power feeding line  141   c  and a power feeding terminal  221   c , power is not supplied to the inspection unit  21   c , and thus, the voltage output to the control unit  11   c  becomes 0 V. If there is a break between the inspection signal terminal  222   c  and the inspection signal line  142   c  or between the inspection signal line  142   c  and the inspection signal terminal  122   c , power is supplied to the inspection unit  21   c  and a voltage which is not 0 V is output from the inspection unit  21   c . However, since there is a break on the downstream side of the inspection unit  21   c , the voltage supplied to the control unit  11   c  becomes 0 V. That is, regardless of whether there is the occurrence of an abnormality in the path “power feeding terminal  121   c →power feeding line  141   c →power feeding terminal  221   c ” or the path “inspection signal terminal  222   c →inspection signal line  142   c →inspection signal terminal  122   c ”, a voltage of 0 V is detected by the control unit  11   c.    
     Conversely, if an abnormality is occurring in neither of the two paths, the output voltage output from the inspection unit  21   c  is adjusted to a range from V 1  to V 2  by the amplifier  212   c . Accordingly, if the received voltage is in a normal range from V 1  to V 2 , as shown in  FIG. 9 , the control unit  11   c  determines that the connection state between the first and second substrates  1   c  and  2   c  is normal, and if the received voltage is outside this normal range, the control unit  11   c  determines that the connection state between the first and second substrates  1   c  and  2   c  is abnormal. If the control unit  11   c  determines that the connection state is normal, it obtains a value measured by the sensor  211   c  of the inspection unit  21   c  (e.g., a humidity value) on the basis of the value of the above-described voltage. 
       FIG. 10  is a flowchart illustrating the flow of an operation performed by the apparatus  9   c  according to the first modified example. In step S 21 , the control unit  11   c  of the first substrate  1   c  detects an output value represented by an inspection signal output from the inspection unit  21   c  of the second substrate  2 . In step S 22 , the control unit  11   c  determines whether the output value is contained within the normal range. If the result of step S 22  is YES, the process proceeds to step S 23 . In step S 23 , the control unit  11   c  executes processing which is to be executed when the connection state between the first and second substrates  1   c  and  2   c  is normal. The processing executed in step S 23  may be the measurement of the frequency of the inspection signal. Alternatively, the control unit  11  may cause a notification unit  3   c  to notify a user that the connection state is normal. If the apparatus  9   c  is an image forming apparatus, in step S 23 , image forming processing may be continued. 
     On the other hand, if the control unit  11   c  determines in step S 22  that the output value is not contained within the normal range, the process proceeds to step S 24 . In step S 24 , the control unit  11   c  executes processing which is to be executed when the connection state between the first and second substrates  1   c  and  2   c  is abnormal. In the processing executed in step S 24 , the control unit  11   c  causes the notification unit  3   c  to notify a user about the occurrence of an abnormality in the connection state between the first and second substrates  1   c  and  2   c.    
     In the above-described configuration, as well as in the first exemplary embodiment, an output value detected by the control unit  11   c  is used for detecting the connection state and also for another purpose. Accordingly, only one cable line is sufficient for transmitting the output value. That is, with this configuration, a smaller number of cable lines are required than in the related art. 
     2-2. Second Modified Example 
     In the above-described exemplary embodiment, the function and the type of the apparatus  9  are not particularly restricted. If the apparatus  9  is applied to an image forming apparatus  9   d  that forms images on a medium, the image forming apparatus  9   d  may be configured as follows. 
       FIG. 11  illustrates the entire configuration of the image forming apparatus  9   d  according to a second modified example. As shown in  FIG. 11 , the image forming apparatus  9   d  includes a first substrate  1   d , a second substrate  2   d , a notification unit  3   d , and an image forming unit  8 . The image forming unit  8  includes developing units  4 Y,  4 M,  4 C, and  4 K, a transfer unit  5 , a fixing unit  6 , and a transport unit  7 . The alphabetical characters Y, M, C, and K appended to reference numerals  4 Y,  4 M,  4 C, and  4 K for the developing devices represent colors of toners, i.e., yellow, magenta, cyan, and black, respectively. The configurations of the developing units  4 Y,  4 M,  4 C, and  4 K are roughly the same, except that the colors of toners used in the individual developing units are different. Hereinafter, the developing units  4 Y,  4 M,  4 C, and  4 K will be simply referred to as the “developing unit  4 ” or “developing units  4 ” by omitting the alphabetical characters unless it is necessary to distinguish between them. 
     The first substrate  1   d  serves to control the image forming apparatus  9   d  and includes a control unit  11   d , a connecting unit  12   d , a power feeding unit  13   d , and a cable  14   d . The configurations of the elements forming the first substrate  1   d  are the same as those of the first substrate  1  of the apparatus  9 , and an explanation thereof will thus be omitted. 
     The second substrate  2   d  causes the developing unit  4 , the transfer unit  5 , the fixing unit  6 , or the transport unit  7 , which forms the image forming apparatus  9   d , to perform signal processing so as to control the element that has performed signal processing. The second substrate  2   d  includes an inspection unit  21   d  and a connecting unit  22   d . The configurations of the elements of the second substrate  2   d  are the same as those of the second substrate  2  of the apparatus  9 , and an explanation thereof will thus be omitted. 
     The notification unit  3   d  is connected to the control unit lid of the first substrate  1   d , and, under the control of the control unit  11   d , it notifies a user about whether the first and second substrates  1   d  and  2   d  are correctly connected. The configuration of the notification unit  3   d  is the same as that of the notification unit  3  of the apparatus  9 , and an explanation thereof will thus be omitted. 
     The transport unit  7  includes a housing section and a transport roller. In the housing section, sheets of paper P, which serve as a medium and which are cut into a predetermined size, are stored. The sheets of paper P are extracted one by one by the transport roller in response to an instruction from the control unit  11   d  of the first substrate  1   d , and are transported to the transfer unit  5  via a sheet transport path. The medium is not restricted to sheets of paper, and may be resin sheets. In short, any type of medium may be used as long as images can be recorded on the surface of a medium. 
     The developing units  4  each include a photoconductor drum  41 , a charging device  42 , an exposure device  43 , a developing device  44 , a first transfer roller  45 , and a drum cleaner  46 . The photoconductor drum  41  is an image carrier including a charge generating layer and a charge transport layer, and is rotated in the direction indicated by the arrow D 4  in  FIG. 11  by a driver (not shown). The charging device  42  charges the surface of the photoconductor drum  41 . The exposure device  43  includes a laser emitting source, a polygon mirror (neither of which is shown), etc., and under the control of the control unit  11   d , it irradiates the photoconductor drum  41  charged by the charging device  42  with laser light corresponding to image data. Then, an electrostatic latent image is formed on each of the photoconductor drums  41 . The above-described image data may be obtained from an external device via a communication unit (not shown) by the control unit  11 . The external device is, for example, a reader that reads an original image or a storage device that stores therein data representing images. 
     The developing device  44  includes a two-component developer containing toner of one of Y, M, C, and K colors, and a magnetic carrier, such as ferrite powder. Then, the head of a magnetic brush formed in the developing device  44  is brought into contact with the surface of the photoconductor drum  41 , causing toner to adhere to a portion on the surface of the photoconductor drum  41  exposed by the exposure device  43 , i.e., image lines of the electrostatic latent image, thereby forming (developing) an image on the photoconductor drum  41 . 
     The first transfer roller  45  generates a predetermined potential difference at a position at which an intermediate transfer belt  51  of the transfer unit  5  opposes the photoconductor drum  41 , and whereby transfers an image onto the intermediate transfer belt  51 . The drum cleaner  46  removes toner remaining on the photoconductor drum  41  which has not been transferred to the intermediate transfer belt  51  after an image has been transferred, thereby discharging the surface of the photoconductor drum  41 . That is, the drum cleaner  46  removes unnecessary toner or electric charge from the photoconductor drum  41  for a subsequent image forming operation. 
     The transfer unit  5  includes the intermediate transfer belt  51 , a second transfer roller  52 , belt transport rollers  53 , and a backup roller  54 . The transfer unit  5  transfers an image formed by the developing unit  4  on a sheet P, the type of which is determined by an operation performed by a user. The intermediate transfer belt  51  is an endless belt member and is stretched by the belt transport rollers  53  and the backup roller  54 . At least one of the belt transport rollers  53  and the backup roller  54  is provided with a driver (not shown), and moves the intermediate transfer belt  51  in the direction indicated by the arrow D 5  shown in  FIG. 11 . The belt transport rollers  53  or the backup roller  54  which is not provided with a driver is rotated as a result of being driven by the movement of the intermediate transfer belt  51 . By the movement and the rotation of the intermediate transfer belt  51  in the direction indicated by the arrow D 5  in  FIG. 11 , an image on the intermediate transfer belt  51  is moved to a region sandwiched between the second transfer roller  52  and the backup roller  54 . 
     The second transfer roller  52  transfers the image on the intermediate transfer belt  51  onto a sheet P transferred from the transport unit  7 , due to a potential difference between the second transfer roller  52  and the intermediate transfer belt  51 . A belt cleaner  59  removes toner remaining on the surface of the intermediate transfer belt  51  which has not been transferred to the sheet P. Then, the transfer unit  5  or the transport unit  7  transports the sheet P on which the image has been transferred to the fixing unit  6 . The fixing unit  6  fixes the image transferred onto the sheet P by heating. Then, the sheet P is placed on a sheet discharge section provided on the top surface of the image forming apparatus  9   d  by the transport unit  7 . 
     When the second substrate  2   d  causes the developing unit  4 , the transfer unit  5 , the fixing unit  6 , or the transport unit  7 , which forms the image forming unit  8 , to perform signal processing, operating conditions may be changed depending on the humidity of an environment around which the corresponding element is disposed. For example, the developing unit  4  includes the developing device  44  in which toner is contained. Depending on the humidity within the developing device  44 , it may be necessary to increase the temperature within the developing device  44  in order to prevent condensation. If the second substrate  2   d  includes the inspection unit  21   d  that measures the humidity within the developing device  44  and also includes a controller for controlling a heating element that heats the inside of the developing device  44 , the control unit  11   d  of the first substrate  1   d  obtains a measurement result output from the inspection unit  21   d  on the basis of an inspection signal, and sends a control signal to the controller for controlling the heating element in accordance with the obtained measurement result. Then, if the control unit  11   d  determines on the basis of the inspection signal that the connection state between the first and second substrates  1   d  and  2   d  is abnormal, it causes the notification unit  3   d  to notify a user about the occurrence of an abnormality in the connection state. 
     2-3. Third Modified Example 
     In the above-described exemplary embodiment, the notification unit  3  notifies a user about whether the connection state between substrates is normal by using two light emitting elements which emit light in different colors. Alternatively, the notification unit  3  may notify a user in another manner. For example, the notification unit  3  may notify a user about whether the connection state is normal by using sound or images or characters displayed on a liquid crystal panel. 
     The foregoing description of the exemplary embodiment and the modified examples of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment and the modified examples chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.