Patent Publication Number: US-7212750-B2

Title: Image forming device and insertable developing unit with identification protrusions for determining compatibility

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming device such as a copy machine, a printer and a facsimile machine, and more particularly to an image forming device in which a developing unit is inserted removably. 
   2. Description of the Related Art 
   Various types of image forming devices have been developed from a technical aspect to form an image with a high resolution and an aspect of a business use or a domestic use. As a developing unit which can be inserted into various types of image forming devices, various types of developing units have been developed. Therefore, for an image forming device of a prescribed type, a developing unit compliant with the image forming device of the prescribed type is necessary to be inserted. When a noncompliant developing unit is inserted, there are cases in which the image forming device breaks down. Therefore, it is necessary to ensure compatibility between the image forming device and the developing unit to be inserted. 
   For example, in a first conventional device, a fuse and a resistance are mounted on a developing cartridge. In the first conventional device, when the cartridge is inserted into the image forming device frame, by the continuity to the fuse, an initial continuity is detected and the fuse is blown out. In addition, a resistance value is checked and a determination is made as to whether the cartridge complies with the device frame. 
   In a second conventional device, a determination is made as to whether a developing unit is a new one or an old one according to whether a fuse is connected or blown out. 
   In a third conventional device, an antenna is provided on a cartridge for detecting a remaining amount of toner in a developing unit. A fuse is connected between the antenna and ground. When the antenna detects the remaining amount of toner, if the detection result is the same voltage as ground, a determination is made that the cartridge is new. 
   In the above-described first, second and third conventional devices, the fuse is attached to the developing unit. When the developing unit is inserted into the device frame, the fuse is blown out. When a used developing unit is inserted into the device frame, since the fuse is already blown out, the continuity is lost. Therefore, it can be recognized at the device frame that the inserted developing unit is a used developing unit. Such a structure enables an accurate detection of old and new developing units by a simple structure. However, the structure is unsuitable for detections other than the detection of old and new developing units. 
   Therefore, there is a demand for an image forming device which can accurately detect the type of the developing unit by a simple structure. 
   Moreover, it is not sufficient just to ensure the compatibility of the image forming device and the developing unit as described above. It is preferable to enable an operator to recognize the compatibility. Fourth and fifth conventional devices are proposed in consideration to such a demand. 
   In the fourth conventional device, a developing unit and an image forming device are provided with an engaging member and an engaged member to be engaged with one another when the developing unit is inserted into the image forming device frame. Therefore, when a developing unit of a different type is inserted into the image forming device, the engaging member and the engaged member are not engaged with one another. 
   In the fifth conventional device, a developing unit is provided with a connector having contacts of different connections according to a designated image forming device. An image forming device includes an electrical signal relay unit. When the electrical signal replay unit engages with the connector, an electrical signal of a plurality of contacts is read. Then, a determination is made as to whether the inserted developing unit is for that image forming device. 
   In the above-described fourth and fifth conventional devices, the identification of the developing unit is carried out only once. Therefore, when the number of different types of developing units increases, the image forming device cannot handle these increases. That is, when there exists various types of image forming devices, to acquire identification information of an image forming device from the developing unit by carrying out the identification of the developing unit only once, the developing unit is required to be provided with an identifier indicating many pieces of identification information. In addition, the image forming device is required to carry out processes for reading many pieces of identification information. Therefore, the cost for the developing unit and the image forming device increases. 
   Thus, there is a demand for a developing unit which can ensure compatibility for various types of developing units and which the compatibility can be recognized easily by the operator, and a method for distinguishing the type of the developing unit. 
   In the fourth conventional device, a mechanical device and an electrical device are used for ensuring the compatibility. However, when the number of different types of image forming devices increases, the number of patterns relating to the compatibility also increases. Therefore, it is difficult for the fourth conventional device to sufficiently comply with such a large number of patterns. 
   Thus, there is a demand for an image forming device which can flexibly comply with an increase in the number of different types of image forming devices. 
   SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, an image forming device includes a developing unit which is inserted in a prescribed inserting direction into the image forming device. The image forming device includes two terminals provided at the device frame, a metal conduction member and a detecting unit. The conduction member is provided on the developing unit and makes contact with at least one of the terminals. The detecting unit detects a presence or an absence of continuity between the terminals. 
   As the conduction member, a wire rod shaped to make contact with both of the terminals or a wire rod shaped to make contact with one of the terminals is used. 
   The image forming device further includes a determination unit which determines whether the developing unit is for initial mounting or for exchange in accordance with a detection signal from the detecting unit. 
   The developing unit includes a fuse. One terminal of the fuse is connected to one end of the conduction member. Another terminal of the fuse is connected to a different conduction member. In the device frame, a terminal for the fuse is provided to make contact with the different conduction member when the developing unit is inserted. The device frame includes a determination unit which determines whether the developing unit is old or new by energizing between one of the terminals of the fuse and the terminal for the fuse and detecting a presence or an absence of continuity between the terminals. After the detection, the fuse is blown out. 
   According to the present invention, by detecting the presence or the absence of the continuity between the two terminals by a simple structure including the two terminals of the device frame and the conduction member of the developing unit, the compatibility of the developing unit can be detected accurately. Moreover, since the conduction member is not blown out like the fuse, the determination unit can be used for detections other than the detection of whether the developing unit is new or old. 
   When comparing the developing unit for initial mounting and the developing unit for exchange, for example, an amount of toner accumulated inside is different. Therefore, different control operations are required to be carried out for an impressed voltage in a developing process and a remaining state of the toner in a detection process of the remaining amount of toner. If the developing unit for initial mounting and the developing unit for exchange are identified by the presence or the absence of the continuity between the two terminals, the control operations can be changed easily. 
   Since the conduction member is formed of the wire rod and shaped to make contact with both of the two terminals, the continuity state can be established reliably between the two terminals. In case the conduction member is formed to make contact with only one of the two terminals, a non-continuity state can be established reliably. In particular, since the wire rod can be shaped easily by bending, the cost is reduced and an efficiency of work is improved. 
   Furthermore, the developing unit includes a fuse. One terminal of the fuse is connected to one end of the conduction member. Another terminal of the fuse is connected to a different conduction member. In the device frame, a terminal for the fuse is provided to make contact with the different conduction member when the developing unit is inserted. An energization is carried out between one of the two terminals and the terminal for the fuse. Accordingly, the terminal for detecting the presence or the absence of the continuity of the conduction member can also function as a terminal for energizing the fuse. As a result, the detection of the presence or the absence of the continuity of the conduction member and the fuse can be carried out by an extremely simple structure. When the developing unit is inserted, a determination can be made as to whether the developing unit is new or old by detecting the blown out fuse. In addition, at the same time, the type of the developing unit can be determined by the presence or the absence of the continuity of the conduction member. 
   According to an aspect of the present invention, a developing unit is inserted in a prescribed inserting direction into an image forming device. The developing unit includes at least one identification protrusion. The identification protrusion is fixed on an upper surface of the developing unit so as to protrude upward, at a plurality of attaching portions arranged in a direction approximately orthogonal to the inserting direction. The developing unit includes a protrusion formed on the upper surface of the developing unit so as to protrude upward at a front side of the inserting direction than the identification protrusion. The developing unit also includes a metal conduction member which makes contact with the terminal of the image forming device. 
   An inner part of the protrusion is preferable to be a gap connected to an inner part of the developing unit. The identification protrusion is preferable to be fixed on a position of the attaching portion of a combination determined according to the type of developing unit. Furthermore, the conduction member is preferable to be set at a length to bring between the two terminals of the image forming device into conduction or non-conduction. 
   According to an aspect of the present invention, a method for distinguishing a type of developing unit is a method for distinguishing the type of the above-described developing unit. Two large groups are distinguished according to a presence or an absence of a leveled part. Intermediate groups are distinguished according to the position where the identification protrusion is fixed. Two small groups are distinguished according to the presence or the absence of the continuity of the conduction member. 
   According to the present invention, when inserting the developing unit into the image forming device, the operator recognizes the compatibility by the protrusion formed on the upper surface of the developing unit. When the compatibility of the protrusion coincides, the operator recognizes the compatibility by the identification protrusion also fixed on the upper surface of the developing unit. When the compatibility of the identification protrusion coincides, the developing unit is inserted and the conduction member makes contact with the terminal of the image forming device. Accordingly, the compatibility is recognized by the image forming device. 
   The compatibility is recognized in three stages as described above. Therefore, many types of developing units can be identified. Furthermore, the various types of developing units can be classified in a hierarchy. As a result, the identification of the developing units can be carried out easily. With respect to the protrusion and the identification protrusion, the developing unit cannot be inserted when there is no compatibility. Therefore, the operator can easily recognize that there is no compatibility. In addition, at a stage that the developing unit fails to be inserted, the operator can recognize the type of developing unit. Since the image forming device carries out only the recognition of the conduction member, the image forming device is not required to carry out a large number of processes for the type of developing unit. 
   Furthermore, the inner part of the protrusion is formed as a gap connected to the inner part of the developing unit. Therefore, when inserting the developing unit forcibly by cutting off the protrusion, the cut part opens. As a result, the toner inside the developing unit leaks. Thus, such an injustice can be prevented. 
   The identification protrusion is fixed on the position of the attaching portion of the combination determined according to the type of developing unit. Therefore, by increasing the number of attaching portions, a larger number of combinations can be set. As a result, the image forming device can easily respond to the number of types of developing units. 
   By setting the length of the conduction member at the length to bring between the two terminals of the image forming device into conduction or non-conduction, the presence or the absence of the continuity can be set easily and reliably. 
   According to the method for distinguishing the type of developing unit of the present invention, the developing unit can be distinguished into two large groups by the protrusion. Each of the large groups can be distinguished into intermediate groups by the combination of the identification protrusion. Furthermore, each of the intermediate groups can be distinguished further by the conduction member. 
   According to an aspect of the present invention, an image forming device includes a developing unit which is inserted in a prescribed inserting direction into the image forming device. The image forming device includes two terminals provided at the device frame, a metal conduction member, a detecting unit, a storage unit and a determination unit. The conduction member is provided on the developing unit and makes contact with at least one of the terminals. The detecting unit detects a presence or an absence of continuity between the terminals. The storage unit stores an identification flag identifying a type of image forming device and compatibility information indicating compatibility between the image forming device and the developing unit. The determination unit determines whether a detection signal from the detecting unit and the compatibility information correspond with one another when there is the identification flag. 
   As the conduction member, a wire rod shaped to make contact with both of the terminals or a wire rod shaped to make contact with only one of the terminals is preferable to be used. 
   When there is no identification flag, the determination unit is preferable to determine whether the developing unit is a developing unit for initial mounting or a developing unit for exchange in accordance with the detection signal from the detecting unit. 
   According to an aspect of the present invention, the image forming device stores an identification flag for identifying the type of image forming device. When there is an identification flag, as the data indicating the compatibility, the detection signal indicating the presence or the absence of the continuity of the conduction member of the developing unit is compared with the compatibility information, and the compatibility of the developing unit is determined. That is, when there is no identification flag, the detection signal from the detecting unit is used as the data indicating characteristics of the developing unit. When there is an identification flag, the detection signal of the detecting unit is used as the data indicating the compatibility. Accordingly, the detection signal from the detecting unit can be used for different purposes according to the type of developing unit. For example, as for the various types of image forming devices, in case there is a type which uses both the developing unit for initial mounting and the developing unit for exchange and a type which uses only the developing unit for initial mounting, an image forming device of the type which uses two types of developing units uses the detection signal of the detecting unit for identifying the type of developing unit. However, in case of an image forming device of the type which uses only one type of developing unit, it is not necessary to use the detection signal for such a purpose. Therefore, the detection signal from the detecting unit can be used as the data indicating the compatibility between the developing unit and the device frame. As described above, one detection signal can be used differently according to the type of image forming device. In addition, the type of image forming device can be dealt with easily by the setting of the identification flag. Therefore, the image forming device can comply flexibly with various types of developing units. 
   The conduction member is formed of the wire rod. By shaping the conduction member so as to make contact with both of the two terminals, a continuity state can be established reliably between the two terminals. By shaping the conduction member so as to make contact with only one of the terminals, a non-continuity state can be established reliably. In particular, since the wire rod can be shaped easily by bending, the costs can be reduced and the efficiency of the work can be improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view of the entire image forming device according to an embodiment of the present invention. 
       FIG. 2  is an enlarged cross-sectional view of a printing unit. 
       FIG. 3  is an enlarged cross-sectional view of a developing unit. 
       FIG. 4  is an exterior perspective view of the entire developing unit. 
       FIG. 5  is a perspective view of a state in which the developing unit is inserted in a main frame viewed from a front side. 
       FIG. 6A  and  FIG. 6B  are views for describing when a leveled part of the developing unit is cut off. 
       FIG. 7  is an exterior view showing a rear part of the developing unit. 
       FIG. 8  is an enlarged view showing a structure of an electrical connection of the developing unit. 
       FIG. 9  is an enlarged view showing a part for carrying out an electrical identification and detection. 
       FIG. 10  is a circuit diagram of  FIG. 9 . 
       FIG. 11  shows a detection operation of a remaining toner detecting sensor. 
       FIG. 12  shows a circuitry for carrying out an electrical detection of the developing unit. 
       FIG. 13  shows examples of settings of leveled parts and identification protrusions of the developing unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described. Further, the embodiments to be described below are preferable specific examples for implementing the present invention. Therefore, there are various technical limitations in the description. However, unless explicitly stated in the following description to limit the present invention, the present invention shall not be limited to the embodiments. 
     FIG. 1  is a schematic cross-sectional view of the entire image forming device according to an embodiment of the present invention. In an upper part of an image forming device  1 , a document scanning unit  2  is disposed. In a lower part of the image forming device  1 , a paper feed unit  3  and a printing unit  4  are disposed in this order from a bottom surface. 
   In the document scanning unit  2 , an original document placed on a document tray  11  is transported to a scanning position by a document transportation device  12  and discharged onto a document discharge tray  13 . Further, the document tray  11  is provided on a document cover  10 . A scanning device  16  is disposed to face the original document at the scanning position. The scanning device  16  includes a reading device  15  which scans an original document optically. When scanning a book or the like, the document cover  10  is swung upward and a part of the book or the like to be scanned is placed on a flatbed platen  14 . Then, the scanning device  16  is moved in a direction shown with the arrow in the drawing and a scanning operation is carried out. The above-described configuration is the same as a conventional document scanning device known as an Auto Document Feeder (ADF) and a flat bed type. 
   In the paper feed unit  3 , a paper feed cassette  17  is provided and a plurality of papers of a prescribed size are stacked on a flapper  18 . A pickup roller  19  is provided at a right end of the paper feed cassette  17 . The flapper  18  is urged upward by a spring member (not shown) so that an upper surface of the stacked papers makes contact with the pickup roller  19 . Under this state, when the pickup roller  19  rotates, the papers are fed one sheet at a time into a paper transportation path by a frictional force. 
   The fed paper is transported to the printing unit  4  by a feed roller  20  and a press roller  21 . For printing an image onto the transported paper, the printing unit  4  includes a developing unit  22 , a paper dust removing roller  23 , a corona charger  24 , a photoconductive drum  25 , a transfer roller  26 , an exposure head  27  and a fuser roller  28 . 
   The paper dust removing roller  23  is formed of an electrically conductive sponge or the like. The paper dust removing roller  23  traps toner or paper dust adhered on a surface of the photoconductive drum  25  after a transfer process. The corona charger  24  uniformly charges the surface of the photoconductive drum  25  by a discharge from a corotron. By exposing the photoconductive drum  25  by the exposure head  27  according to an image printing signal, an electrostatic latent image is formed on the photoconductive drum  25 , which is charged uniformly by the paper dust removing roller  23  and the corona charger  24 . Then, although details will be described later, the toner in the developing unit  22  is transferred onto the electrostatic latent image formed on the photoconductive drum  25 , and the electrostatic latent image is visualized. 
   The transfer roller  26  is disposed at a position facing the photoconductive drum  25  across the paper. When a prescribed voltage is impressed to the transfer roller  26 , a toner image formed on the surface of the photoconductive drum  25  is transferred onto the paper. Then, the transferred toner image is nipped and heat-pressed by the fuser roller  28  and a press roller  29  to be fixed onto the paper. The paper on which the toner image is fixed is nipped between a paper discharge roller  30  and a press roller  31  and transported out onto a paper discharge tray  32 . 
   In  FIG. 1 , the paper transportation path is shown with dashed lines between the paper feed unit  3  and the paper discharge tray  32 . Transportation rollers and a paper guide disposed along the paper transportation path constitute a paper transportation unit. 
   A reverse transportation unit  40  is attached removably at a side surface of the image forming device  1 . At the side surface where the reverse transportation unit  40  is attached, a paper transportation outlet  41  and a paper transportation inlet  42  are formed. In the reverse transportation unit  40 , a feed roller  43  and a press roller  44 , and a feed roller  45  and a press roller  46  are disposed vertically. A reverse transportation path shown with double dashed lines in  FIG. 1  is formed to diverge from the paper transportation path between the paper discharge roller  30  and the fuser roller  28 , to pass between the two pairs of the transportation rollers and to converge the paper transportation path between the roller pairs  20  and  21  and the pickup roller  19 . 
   When printing onto both sides of the paper, the paper is transported through the paper transportation path shown with the dashed lines in  FIG. 1  and a printing process is executed on one side of the paper. Then, the paper is transported out onto the paper discharge tray  32  by the paper discharge roller  30 . Under a state in which a trailing edge of the paper is nipped by the paper discharge roller  30  and the press roller  31 , the transportation operation is stopped once. Then, the paper discharge roller  30  rotates in a reverse direction, and the paper is transported into the reverse transportation path from the trailing edge. Under a state in which the paper is nipped by the feed roller  43  and the press roller  44 , the paper is transported through the reverse transportation path. Next, the paper is nipped by the feed roller  45  and the press roller  46  and transported further so that the paper makes contact with the roller pairs  20  and  21 . When the paper is transported through the paper transportation path under this state, another side of the paper faces the photoconductive drum  25  and the printing process is executed on the other side of the paper. Accordingly, both sides of the paper are printed. 
     FIG. 2  is an enlarged cross-sectional view of the printing unit  3  of  FIG. 1 .  FIG. 3  is an enlarged cross-sectional view of the developing unit  22 .  FIG. 4  is a perspective view showing the developing unit  22  viewed from an upper side. 
   As described above, the developing unit  22 , the paper dust removing roller  23 , the corona charger  24  and the transfer roller  26  are disposed around the photoconductive drum  25 . Between the corona charger  24  and the developing unit  22 , a laser light from the exposure head  27  is irradiated on the surface of the photoconductive drum  25  according to the image printing signal. 
   The developing unit  22  is formed by fixing a cover  51  on an upper part of a container  50  by welding or with a screw and by sealing the container  50 . Three toner chambers  52 ,  53  and  54  are formed as toner replenish chambers in the container  50 . At a region of the container  50  located on the photoconductive drum  25 , a supply chamber  57  having a developing roller  55  and a supply roller  56  is formed. The first toner chamber  52  and the supply chamber  57  are partitioned by a partition plate  58  that extends downward from a lower surface of the cover  51 . A replenish opening  59  is formed through the partition plate  58 . 
   As shown in  FIG. 3 , the three toner chambers  52 ,  53  and  54  are disposed to be in parallel with one another in a horizontal direction under a state in which the developing unit  22  is inserted in the image forming device  1 . At approximately the center part of each of the toner chambers, paddles  60 ,  61  and  62  are respectively provided as a means for agitating and transferring. Suppose that a perpendicular direction of the page of  FIG. 2  is in a front-back direction of the developing unit  22 . Then, both end parts of a rotational shaft of each of the paddles in the front-back direction are supported by front and back frames of the container  50 . The rotational shafts are aligned in the front-back direction. At a tip end of the paddle  60 , a blade  63  made of a flexible resin film is attached along a rotational direction of the paddle  60 . In the same manner, a blade  64  is attached to the paddle  61  and a blade  65  is attached to the paddle  62 . A common member is used for the blades  63 ,  64  and  65 . Sliding surfaces  66 ,  67  and  68  are formed on a bottom surface of the container  50 . The sliding surfaces  66 ,  67  and  68  are curved outward to have an arc-shape in cross-section so as to follow along a path of rotational movements of the blades attached to the paddles. 
   The toner replenished in each of the toner chambers  52 ,  53  and  54  is accumulated on the sliding surfaces  66 ,  67  and  68 . When the paddles  60 ,  61  and  62  are rotated, the blades  63 ,  64  and  65  are rotated to slide against the sliding surfaces  66 ,  67  and  68 , respectively. By the sliding movement of each of the blades, the toner is scooped and the toner is agitated in each of the toner chambers. As a result, the deterioration of the toner due to aggregation of the toner can be prevented. Moreover, as shown in  FIG. 2 , when the blades  63 ,  64  and  65  are rotated counterclockwise, the toner in the third toner chamber  54  is transferred into the second toner chamber  53 , and the toner in the second toner chamber  53  is transferred into the first toner chamber  52 . Then, the toner in the first toner chamber  52  is replenished into the supply chamber  57  through the replenish opening  59  of the partition plate  58 . At this time, the replenished toner is agitated by the paddle  60  in the first toner chamber  52  and a preliminary charging is carried out. The replenish opening  59  is opened as a slit in the front-back direction. By adjusting the width and the position of the opening, the amount of the toner replenished from the first toner chamber  52  into the supply chamber  57  can be adjusted. 
   While the supply roller  56  is rotated, the supply roller  56  is rubbed against the developing roller  55 , and the toner replenished into the supply chamber  57  is rubbed and charged. Then, the toner is carried on the surface of the developing roller  55 . A developing blade  69  is disposed in proximity to or in contact with the surface of the developing roller  55 . The developing blade  69  controls the layer thickness of the supplied toner. By the developing roller  55  and the photoconductive drum  25  being rubbed against one another while rotating, the toner layer controlled to have a prescribed layer thickness by the developing blade  69  is adhered onto the electrostatic latent image formed on the surface of the photoconductive drum  25 , and the electrostatic latent image is developed. 
   The developing unit  22  can be inserted or removed with respect to the image forming device  1  in the front-back direction. In  FIG. 2 , it is defined that a front side in the perpendicular direction of the page is a front side of the developing unit  22  and the opposite is a rear side of the developing unit  22 . The developing unit  22  is inserted from the rear side into an installation space formed in a main frame  70  of the image forming device  1 . A pressing mechanism  71  is provided on the main frame  70  of the image forming device  1 . The container  50  is pushed upward from a lower side by the pressing mechanism  71 . Then, the developing unit  22  is set to the main frame  70  so that the developing roller  55  makes contact with the photoconductive drum  25 . In response to the pressing movement of the pressing mechanism  71 , a remaining toner detecting sensor  72  is elevated and set in a concave groove  73 . Further, the concave groove  73  is formed of a transparent member and provided on the sliding surface  67 . In the same manner, in response to the inserting movement of the developing unit  22 , a remaining toner detecting sensor  74  is elevated and set in a concave groove  75 . Further, the concave groove  75  is formed of a transparent member and provided on the sliding surface  68 . 
   In the pressing mechanism  71 , a bottom surface of a pressing body  79  provided slidable on a plate  78  makes contact with a cam member  77  fixed on a rotational shaft  76 . When the developing unit  22  is inserted, an upper surface of the pressing body  79  faces a rib-shaped contact portion  80  formed on the bottom surface of the developing unit  22 . When an operator swings a lever (not shown) fixed on an end part of the rotational shaft  76 , the cam member  77  rotates clockwise and pushes the pressing body  79  upward in the direction of the arrow. Then, the pressing body  79  presses the contact portion  80  and the developing roller  55  makes contact with the photoconductive drum  25 . 
   The remaining toner detecting sensor  72  is fixed on one end part of a swing lever  81 . Another end part of the swing lever  81  is urged downward by a compressing spring (not shown) so as to make contact with the cam member  77 . When the cam member  77  rotates clockwise, the swing lever  81  rotates clockwise with a shaft  82  as the center and the remaining toner detecting sensor  72  is elevated. The remaining toner detecting sensor  74  can be elevated in response to the pressing movement of the pressing mechanism  71  in the same manner. 
   As shown in  FIG. 4 , the cover  51  of the developing unit  22  is formed in a plate-shape so as to seal the upper opening of the container  50 . On the cover  51 , a leveled part  83  protruding upward is provided at a position located off centered, towards the developing roller  55 . A slanting part  84  slanting downward from the leveled part  83  toward the developing roller  55  is also formed on the cover  51 . The leveled part  83  is formed from a front edge toward a rear edge of the cover  51  along the inserting direction of the developing unit  22 . 
   As shown in  FIG. 3 , an inner surface of the cover  51  is formed to spread upward from the leveled part  83  to the slanting part  84  to form a space  85 . Guide protrusions  86   a  and  86   b  protruding upward are formed on an end part of the slanting part  84  located above the developing roller  55 . The guide protrusions  86   a  and  86   b  are arranged in the inserting direction of the developing unit  22  on a part of the cover  51  located above the developing roller  55 . The guide protrusion  86   a  is disposed at a rear side of the inserting direction. The guide protrusion  86   b  is disposed at a front side of the inserting direction. An interval between the guide protrusion  86   a  and the developing roller  55  is set slightly larger than an interval between the guide protrusion  86   b  and the developing roller  55 . A cavity is formed inside the guide protrusions  86   a  and  86   b . Ribs are formed at a center part of the cavity along the inserting direction. Between the guide protrusions  86   a  and  86   b , a plurality of ribs are formed along the inserting direction. Side surfaces  87   a  and  87   b  of the guide protrusions  86   a  and  86   b  facing one another are slanted to widen toward the developing roller  55  according to an irradiating range of the laser light irradiated by the exposure head  27  shown in  FIG. 2 . 
   As shown in  FIG. 4 , a flat plate  88  extends in a horizontal direction at the front side of the container  50 . A grasping part  89  is formed downward on a lower surface of the flat plate  88 . The grasping part  89  is a rectangular parallelepiped having an upper opening. A plurality of reinforcement ribs  90  are provided in the front-back direction in a gap inside the grasping part  89 . On an upper surface of the flat plate  88 , rectangular frame-shaped attaching portions  91   a  through  91   e  are arranged in a direction approximately orthogonal to the inserting direction of the developing unit  22 . Identification protrusions  92  are fit and fixed in the attaching portions  91   a  through  91   e . The identification protrusions  92  identify compatibility of the developing unit  22  and the device frame. The identification protrusions  92  are fixed in the attaching portions  91  selected according to a type of developing unit. Therefore, when there is no compatibility between the positions of the identification protrusions  92  and the device frame, the developing unit cannot be inserted. 
     FIG. 5  is a perspective view showing a state in which the developing unit  22  is inserted in the main frame  70 . A space for inserting the developing unit  22  is provided between a bottom surface part  93  and an upper surface part  94  of the main frame  70 . The height of the guide protrusions  86   a  and  86   b  is set so that when the developing unit  22  is inserted, a slight gap is formed between the developing unit  22  and a lower surface of the upper surface part  94 . Accordingly, the developing unit  22  is prevented from moving vertically when inserting or removing the developing unit  22 . 
   On the lower surface of the upper surface part  94 , a regulatory member  95  and an identification engaging portion  96  are formed protruding downward along an edge of a front opening at the front side of the page of  FIG. 5 . A guide surface  97  slanted in the inserting direction is formed on the regulatory member  95  at the front opening. A regulatory surface  98  located on the opposite side of the photoconductive drum  25  is positioned so that the developing unit  22  is inserted apart from the photoconductive drum  25 . When the guide protrusion  86   a  or  86   b  reaches a position regulated by the regulatory surface  98 , since there is only a slight gap between the side surface of the developing unit  22  and a side surface  99  of the main frame  70 , the developing unit  22  is inserted and removed without being moved to the left or the right. 
   The identification engaging portion  96  can be fixed at five attaching positions corresponding to the attaching portions  91   a  through  91   e . The position of the identification engaging portion  96  has consistency with the positions of the identification protrusions  92  protruding from the developing unit  22  which can be inserted into the device frame and which has compatibility. Accordingly, when the developing unit  22  is inserted, the identification protrusions  92  and the identification engaging portion  96  do not collide with one another. When a developing unit not having compatibility with the device frame is inserted, the identification protrusions  92  and the identification engaging portion  96  collide with one another. However, as described above, there is only a slight gap between the side surface of the developing unit  22  and the side surface  99  of the main frame  70 . Therefore, the identification protrusions  92  and the identification engaging portion  96  cannot be prevented from colliding with one another by displacing the developing unit  22  to the left or to the right. As a result, a developing unit not having compatibility cannot be inserted. 
   In the above-described example, the leveled part  83  is formed on the cover  50  of the developing unit  22 . According to the presence or the absence of the leveled part  83 , the compatibility of the developing unit  22  can be provided. That is, in  FIG. 5 , a gap  100  for permitting the leveled part  83  to pass through is formed between the attached position of the identification engaging portion  96  and the position of the restriction member  95 . Therefore, when inserting a developing unit having the leveled part  83  larger than the gap  100 , the leveled part  83  collides with the device frame and the developing unit fails to be inserted. When inserting the developing unit forcibly by cutting off the leveled part  83 , for example, when the leveled part  83  is cut off at cutting lines A—A as shown in  FIG. 6A , an opening is formed through the developing unit and the gap  85 , and the inner side of the developing unit is connected to the outside as shown in  FIG. 6B . The toner spouts out from the opening and the developing unit becomes incapable of being used. 
   As described above, to ensure the compatibility between the developing unit and the device frame, a physical device such as (1) the combinations of the identification protrusions  92  fixed on the attaching portions  91   a  through  91   e  of the developing unit and (2) the presence or the absence of the leveled part  83  of the developing unit are used. 
   For identifying the compatibility between the developing unit and the device frame, an electrical device can also be used. First, a structure of an electrical connection between the developing unit  22  and the device frame when inserting the developing unit  22  will be described. 
     FIG. 7  is an exterior view showing a rear side of the developing unit  22 . On a rear frame  101  of the container  50 , a rotational shaft  102  of the developing roller  55 , a rotational shaft  103  of the supply roller  56  and rotational shafts  104  of the paddles  60  through  62  are supported rotatably, respectively. An end part of each of the rotational shafts  102 ,  103  and  60 – 62  protrudes outward from the rear frame  101 . Gears  105  for transmitting a drive force are mounted on the protrusions. When the developing unit  22  is inserted, a drive shaft  106  is connected to a drive mechanism of the device frame. A drive force from the drive shaft  106  is transmitted to each of the rotational shafts by the transmitting gears. A cover member  107  is attached to the rear frame  101 . The cover member  107  covers a part of the rear frame  101  located at the developing roller  55  including the rotational shafts  102  and  103 . 
     FIG. 8  is an enlarged view of the cover member  107  attached on the rear side of the developing unit  22 . Mounting holes  108   a  and  108   b  are formed on the cover member  107  for screwing the cover member  107  onto the rear frame  101 . Circular openings  109 ,  110  and  111  are formed through the cover member  107  at positions corresponding to the rotational shaft  103  of the-supply roller  56  and the drive shaft  106 , respectively. On the reverse side of the cover member  107 , a first contact member  112 , a second contact member  113  and a third contact member  115  are mounted. The first contact member  112  makes contact with the rotational shaft  102  of the developing roller  55 . The second contact member  113  makes contact with the rotational shaft  103  of the supply roller  56 . The third contact member  113  makes contact with the pressing plate  114  of a blade which makes contact with the surface of the developing roller  55 . 
   The first contact member  112  is a metal wire rod formed in a hook shape by being bent once at the center part. One end of the first contact member  112  is inserted and held at a holder  116  of the cover member  107 . The holder  116  is formed to protrude toward the reverse side of the cover member  107  with a height difference. The holder  116  has an opening for inserting the first contact member  112  into the holder  116 . Another end of the first contact member  112  is bent twice into a shape of a bracket to form a contact portion  117 . The contact portion  117  is engaged and fixed in a narrow inserting hole  118  and a circular engaging hole  119  formed through the cover member  107 . 
   When mounting the contact portion  117  onto the cover member  107 , first, the contact portion  117  is inserted into the inserting hole  118  from the reverse side and protrudes to the front side. Then, the bent tip end of the first contact member  112  is inserted into the engaging hole  119 . By mounting the contact portion  117  as described above, the contact portion  117  is set under a state protruding from the front side of the cover member  107 . The contact portion  117  reliably makes contact with an electrode of the image forming device  1 , and can be connected electrically with the image forming device  1 . Since a diameter of the engaging hole  119  is formed approximately the same as the diameter of the first contact member  112 , the other end of the first contact member  112  is fixed tightly. Furthermore, the one end of the first contact member  112  is held by the holder  116 . Therefore, the first contact member  112  is not displaced from the cover member  107 . The first contact member  112  is contacted against the rotational shaft  102  by an elastic force which urges the first contact member  112  upward. The first contact member  112  and the rotational shaft  102  are maintained under a stable contacting state and the electrical contacting state can be established reliably. 
   The second contact member  113  is also made of a metal wire rod formed in a hook shape by being bent once like the first contact member  112 . Another end of the second contact member  113  is bent twice to form a contact portion  120  having a shape of a bracket. One end of the second contact member  113  is inserted and held at a holder  121  provided in the same manner as the holder  116 . In the same manner as the contact portion  117 , the contact portion  120  is engaged and fixed in a narrow inserting hole  122  and a circular engaging hole  123  provided on the cover member  107 . Therefore, the second contact member  113  is held reliably without being displaced from the cover member  107 . In addition, the contact portion  120  is set under a state protruding from the front side of the cover member  107 . The second contact member  113  reliably makes contact with the electrode of the image forming device  1  and can be connected electrically. The second contact member  113  is contacted against the rotational shaft  103  by an elastic force which urges the second contact member  113  upward. In the same manner as the first contact member  112 , the second contact member  113  and the rotational shaft  103  are maintained under a stable contacting state and the electrical contacting state can be established reliably. 
   The third contact member  115  is made of a metal wire rod having a small diameter. One end of the third contact member  115  is formed in a shape of a coil spring. Another end of the third contact member  115  is bent perpendicularly in the shape of the letter L to form a contact portion  124 . A tip end of the contact portion  124  is bent further into a hook shape. When mounting the third contact member  115  onto the cover member  107 , the other end of the third contact member  115  is inserted from the reverse side into a circular inserting hole  125  formed on the cover member  107 . The contact portion  124  is exposed on the front side of the cover member  107 . The bent part at the tip end is inserted and fixed in a circular engaging hole  126 . 
   The diameter of the engaging hole  126  is formed approximately the same as the diameter of the third contact member  115 . Therefore, the other end of the third contact member  115  is held reliably without being displaced from the cover member  107 . The contact portion  124  is set under a state protruding from the front side of the cover member  107 . The third contact member  115  reliably makes contact with the electrode of the image forming device  1  and can be connected electrically. Moreover, when mounting the cover member  107  onto the rear frame  101 , the part of the one end formed in the shape of the coil spring makes contact with the edge of the pressing plate  114  of the blade and is maintained under a compressed state. Therefore, the third contact member  115  and the pressing plate  114  can be maintained under a stable contacting state and the electrical contacting state can be established reliably. 
   A fourth contact member  127  and a fifth contact member  128  for identifying the developing unit  22  are provided on the cover member  107 . The fourth contact member  127  is a metal wire rod having a small diameter. One end of the fourth contact member  127  is bent in a hook shape and inserted toward the reverse side of a protector  129  mounted removably on the cover member  107 . A center part of the fourth contact member  127  is exposed on the front side of the cover member  107 . Another end of the fourth contact member  127  is bent and inserted on the reverse side of the cover member  107  via a narrow inserting hole  130  formed on the cover member  107 . An inserting hole  131  like the inserting hole  130  is formed on the cover member  107 . When the length of the fourth contact member  127  is short, the other end of the fourth contact member  127  is inserted into the inserting hole  131 . 
   The fifth contact member  128  is made of a metal wire rod having a small diameter. In the same manner as the fourth contact member  127 , one end of the fifth contact member  128  is bent in a hook shape and inserted toward the reverse side of the protector  129 . Another end of the fifth contact member  128  is bent and inserted on the reverse side of the cover member  107  via a narrow inserting hole  132  formed on the cover member  107 . 
   The end of the fourth contact member  127  bent in the hook shape is disposed facing the bent end of the fifth contact member  128 . Metal coil springs  133  are set on both ends. A fuse member  134  is held between the two coil springs  133 . 
   As shown in  FIG. 9 , when the developing unit  22  is inserted into the device frame, two connection terminals  135   a  and  135   b  of the device frame make contact with the fourth contact member  127 . The connection terminal  135   a  is disposed so as to make contact with the fourth contact member  127  in proximity to the inserting hole  131 . The connection terminal  135   b  is disposed so as to make contact with the fourth contact member  127  in proximity to the inserting hole  130 . When the fourth contact member  127  has a length to reach the inserting hole  130 , both of the connections terminals  135   a  and  135   b  make contact with the fourth contact member  127 . However, when the fourth contact member  127  has a short length to reach just the inserting hole  131 , only the connection terminal  135   a  makes contact with the fourth contact member  127 . A connection terminal  135   c  of the device frame makes contact with the fifth contact member  128  in proximity to the inserting hole  132 . 
     FIG. 10  is a circuit diagram showing a state in which the developing unit  22  is inserted into the device frame and makes contact with the connection terminals of the device frame. The connection terminal  135   a  is set at a ground potential, and the presence or the absence of continuity between the connection terminals  135   a  and  135   b  is detected. When the continuity is detected, the fourth contact member  127  is identified to have a length to reach the inserting hole  130 . When the continuity is not detected, the fourth contact member  127  is identified to have a length to reach the inserting hole  131 . Therefore, by changing the length of the fourth contact member  127  according to the type of the developing unit  22 , the type of the developing unit  22  can be identified. By applying an electric current between the connection terminals  135   a  and  135   c  sufficient for blowing out the fuse member  134 , the fuse member  134  is cut when the developing unit  22  is inserted. Therefore, a developing unit, which has been inserted into the device frame even for once, cannot bring the connection terminals  135   a  and  135   c  into conduction. Thus, by detecting the presence or the absence of the continuity between the connection terminals  135   a  and  135   c,  the developing unit  22  can be identified to be new or used. 
   As described above, as the electric device for identifying the developing unit at the device frame, there are (3) the detection of the presence or the absence of the continuity between the connection terminals  135   a  and  135   b , and (4) the detection of the presence or the absence of the continuity between the connection terminals  135   a  and  135   c.    
   Next, the structure of the remaining toner detecting sensors  72  and  74  will be described. As shown in  FIG. 2 , when the developing unit  22  is inserted, the remaining toner detecting sensors  72  and  74  are set in the concave grooves  73  and  75  formed on the bottom surface of the replenish chambers of the developing unit  22 , respectively. The mechanisms of the remaining toner detecting sensors  72  and  74  are the same mechanism. Therefore, the mechanism of the remaining toner detecting sensor  72  will be described, and a description of the mechanism of the remaining toner detecting sensor  74  will be omitted. 
     FIG. 11  is a cross-sectional view showing the state in which the center part of the concave groove  73  is cut in the vertical direction orthogonal to the page of  FIG. 2 . Two concave grooves  73  are provided at both sides of a remaining amount detecting unit  136 . The concave grooves  73  and the remaining amount detecting unit  136  are formed integrally by a transparent member made of synthetic resin. As shown in  FIG. 2 , the remaining amount detecting unit  136  having a prescribed groove width is formed along a rotational track of a cleaning member  137  mounted on the paddle  61 . The toner in the remaining amount detecting unit  136  is discharged once to the outside of the remaining amount detecting unit  136  each time the cleaning member  137  slides inside the remaining amount detecting unit  136 . The cleaning member  137  is formed of a plurality of rectangular rubber sheets stacked one on the other. The width of each sheet is slightly larger than the groove width of the remaining amount detecting unit  136 . The rubber sheets are mounted on surfaces orthogonal to the direction in which the cleaning member  137  proceeds. Therefore, the sheets of the cleaning member  137  slide in a close contact against both sides  138  of the remaining amount detecting unit  136  at all times, and the toner is removed once. Meanwhile, in the remaining toner detecting sensor  72 , a light emitter  140  is fixed on a protrusion  139  set in one of the concave grooves  73 . A light receiver  142  is fixed on a protrusion  141  set in the other concave groove  73 . The light receiver  142  outputs a detection signal according to whether or not the light receiver  142  receives the light from the light emitter  141  that penetrates through the remaining amount detecting unit  136 . 
   Each time the cleaning member  137  slides inside the remaining amount detecting unit  136  in synchronism with the rotation of the paddle  61 , the light from the light emitter  140  penetrates through the remaining amount detecting unit  136  and the light receiver  142  outputs the detection signal. When a sufficient amount of toner is accumulated in the replenish chamber, after the cleaning member  137  slides, the inner part of the remaining amount detecting unit  136  is filled in with the toner again. Therefore, the light receiver  142  does not detect the light from the light emitter  140 . However, when the remaining amount of the toner in the replenish chamber becomes small, the inner part of the remaining amount detecting unit  136  cannot be filled in with the toner. Accordingly, the light receiver  142  continues to detect the light. In accordance with such a change in the detection signal, the remaining toner detecting sensor  72  transmits to a control unit of the image forming device, a detection signal indicating the remaining amount of toner. 
   As a method for detecting the remaining amount of the toner, other than the detection signal indicating the detection of the light by the light receiver  142 , a timing signal indicating the rotation of the paddle  61  can be considered. For example, a period of time from when the cleaning member  137  passes the remaining amount detecting unit  136  until the light receiver  142  no longer detects the light can be detected. In addition, a correlation between the detected period of time and the remaining amount of the toner can be tested and determined in advance. Then, in accordance with the correlation, the remaining amount of the toner can be detected. Moreover, a number of times the light from the light emitter  140  is shielded by the toner can be counted by the presence or the absence of the detection signal indicating the detection of the light by the light receiver  142 . The counted number of times the toner is agitated can be used as an index for indicating the degree of deterioration of the toner. 
   The remaining toner detecting sensor  74  detects the remaining amount of the toner in a toner chamber  54  located farthest away from the supply chamber  57 . The remaining toner detecting sensor  72  detects the remaining amount of the toner in a toner chamber  53  located second farthest away from the supply chamber  57 . Therefore, the remaining amount of the toner can be detected even under a state in which the toner remains to some extent. That is, the toner is transferred sequentially to the supply chamber by the paddles. Therefore, the remaining amount of the toner becomes larger in the toner chamber  52  than in the toner chamber  54  located farthest away from the supply chamber  57 . Thus, by detecting the change in the remaining amount of the toner in the toner chambers  54  and  53  in which the change in the toner amount is most likely to generate, the state of the remaining toner in the developing unit  22  can be grasped accurately. 
   Therefore, according to the state of the remaining toner in the developing unit  22 , a time to replace the developing unit  22  can be notified.  FIG. 12  shows an example of such circuitry. The detection signals from the remaining toner detecting sensors  72  and  74  are input via detecting circuits  143  and  144  to a control circuit  145 . A storage circuit  146  stores in advance, data indicating a correlation between a detection pattern of the presence or the absence of the toner from the remaining toner detecting sensors  72  and  74 , and the state of the remaining toner in the developing unit  22 . The control circuit  145  retrieves the correlation data from the storage circuit  146 . Then, the control circuit  145  compares the correlation data with the input data from the detecting circuits  143  and  144  and monitors the state of the remaining toner in the developing unit  22 . Meanwhile, the detection signals relating to the presence or the absence of the continuity between the connection terminals  135   a  and  135   b  and the presence or the absence of the continuity between the connection terminals  135   a  and  135   c  are input from the detecting circuit  147  into the control circuit  145 . 
   When detecting the presence or the absence of the continuity between the connection terminals  135   a  and  135   c,  the control circuit  145  detects whether or not both of the terminals are energized and brought into conduction. When there is continuity, the control circuit  145  determines that a new developing unit has been inserted and the process proceeds onto a subsequent process. Then, an electric current sufficient for the fuse member  134  to be blown out is supplied, and both of, the terminals are brought into a non-continuity state. When there is no continuity between the terminals, the control circuit  145  determines that a used developing unit has been inserted and the process does not proceed onto a subsequent process. For example, the control circuit  145  controls to display an error on a display circuit  148 . 
   Among new developing units, when comparing a developing unit for initial mounting inserted initially into the image forming device and a developing unit for exchange inserted after removing the developing unit for initial mounting, the amount of the toner filled in the developing unit is set larger in the developing unit for exchange than in the developing unit for initial mounting. Therefore, as shown in the above (3), by using the fact that the presence or the absence of the continuity state between the connection terminals  135   a  and  135   b  is determined by the length of the fourth connection member  127 , a setting can be made in advance that when the fourth connection member  127  is long (when there is continuity), the inserted developing unit is a developing unit for initial mounting, and when the fourth connection member  127  is short (when there is no continuity), the inserted developing unit is a developing unit for exchange. Therefore, when the developing unit is inserted, in accordance with the detection data regarding the presence or the absence of the continuity state between the connection terminals  135   a  and  135   b , a determination is made as to whether the inserted developing unit is a developing unit for initial mounting or a developing unit for exchange. 
   The storage circuit  146  stores in advance, data regarding a remaining state of the toner when the developing unit for initial mounting and the developing unit for exchange are necessary to be replaced. The control circuit  145  fetches data of the remaining state of the toner of a corresponding developing unit in accordance with the detection data regarding the presence or the absence of the continuity state between the connection terminals  135   a  and  135   b . Then, the data regarding the current remaining state of the toner in the abovementioned developing unit and the detection data are compared. When the current remaining state of the toner is small, the control circuit  145  transmits data to the display circuit  148  to display a time to replace the developing unit. 
   In case of the developing unit for exchange, since a filled amount of the toner is large, even when the remaining state of the toner is large, the toner deteriorates by being agitated. Therefore, a time to replace the developing unit is notified at a stage when the remaining state of the toner is still large. On the contrary, in case of the developing unit for initial mounting, since a filled amount of the toner is small, a time to replace the developing unit is notified at a stage when the remaining state of the toner is small. 
     FIG. 13  shows examples of ensuring the compatibility between the device frame and the developing unit by using the above (1) and (2). In the examples shown in  FIG. 13 , as the types of device frame, a group containing M 1  to M 3  and a group containing P 1  to P 3  are set. First, between each of the groups, a setting of the toner of the developing unit and the printing unit such as the photoconductive drum of the device frame is adjusted. For example, when forming an image with a high resolution, characteristics such as a diameter of a particle of the toner and the printing unit are adjusted to be optimum in response to the image forming process. Therefore, when a toner inappropriate for the image forming process is supplied, a sufficient resolution cannot be obtained. Thus, to distinguish the two groups, the compatibility is ensured by using the presence or the absence of the leveled part  83 . The presence or the absence of the leveled part  83  can be recognized when inserting the developing unit into the device frame. Therefore, when there is no compatibility between the developing unit and the device frame, the developing unit cannot be inserted. In the group containing P 1  to P 3 , only a developing unit without the leveled part  83  can be inserted. A developing unit with the leveled part  83  having compatibility with the group containing M 1  to M 3  cannot be inserted. Even when the developing unit is inserted forcibly by cutting off the leveled part  83 , as described with reference to  FIG. 6 , a hole is formed through the developing unit and the toner leaks from the hole to cause troubles in the device frame. Moreover, the developing unit without the leveled part can be inserted in the device frame of the group containing M 1  to M 3 . Therefore, two types of developing units can be used in the device frame of the group containing M 1  to M 3 . 
   In each of the groups, when setting the compatibility by distinguishing the group into smaller groups, the compatibility can be set by combinations of the identification protrusions  92  fixed on the attaching portions  91   a  through  91   e  of the developing unit. When the compatibility of the leveled part  83  coincides, the developing unit can be inserted. However, when the compatibility of the identification protrusions  92  do not coincide with the device frame, the developing unit cannot be inserted completely into the device frame. Therefore, at this point in time, the developing unit is recognized to have no compatibility. In the examples shown in  FIG. 13 , by using two identification protrusions  92 , three types of developing units within the group can be identified. In M 1  and P 1 , the identification protrusions  92  are fixed on the attaching portions  91   c  and  91   d . In M 2  and P 2 , the identification protrusions  92  are fixed on the attaching portions  91   a  and  91   c . In M 3  and P 3 , the identification protrusions  92  are fixed on the attaching portions  91   c  and  91   e . Therefore, as shown in  FIG. 5 , by fixing the identification engaging portion  96  on the device frame at a part corresponding to the position where the identification protrusion  92  is not fixed, only the developing unit having compatibility can be inserted into each type of device frame. Moreover, by reducing the number of the identification engaging portions  96  to be fixed, the number of types of developing units having compatibility can be increased. The patterns of the compatibility can be changed variously according to necessity. 
   The identification of the developing unit according to the detection of the presence or the absence of the continuity between the connection terminals  135   a  and  135   b  of the above (3) has been described to be used for the identification of the developing unit for initial mounting and the developing unit for exchange. When the compatibility of the leveled part  83  coincides and the compatibility by the combination of the identification protrusions  92  coincides, the developing unit is set at a prescribed inserting position. Then, the fourth connection member  127  makes contact with the connection terminals  135   a  and  135   b . Therefore, the compatibility of the developing unit is ensured by triple identifications. 
   In case of the type which does not use the developing unit for exchange and uses only the developing unit for initial mounting, the detection of the presence or the absence of the above (3) is not necessary to be used for identifying the developing unit for initial mounting and the developing unit for exchange. In this case, as a default value, a flag identifying that the device is the type which uses only the developing unit for initial mounting and the data indicating the compatibility between the device frame and the developing unit can be stored in the storage circuit  146  of  FIG. 12 . When the identification flag is stored, the control circuit  145  compares the detection signal of the presence or the absence of-the continuity of the above (3) and the data indicating the compatibility. When the detection signal and the data correspond with one another, the control circuit  145  determines that there is compatibility between the device frame and the developing unit, and the subsequent process is executed. When the detection signal and the data do not correspond with one another, the subsequent process stops, and the control circuit controls to display an error on the display circuit  148 . Other than the device for ensuring the compatibility mechanically as in the above (1) and (2), the compatibility can be ensured by the electrical device. Therefore, for example, by identifying the type of toner according to the detection of the presence or the absence of the continuity of the above (3), the compatibility of the type of toner can be ensured by both the mechanical and the electrical devices. As a result, the safety can be improved even more.