Patent Publication Number: US-2023161280-A1

Title: Image forming apparatus

Description:
BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to an image forming apparatus including a circuit board. 
     Description of the Related Art 
     An electrophotographic image forming apparatus forms an electrostatic latent image on a photosensitive member charged by a charging unit, develops the electrostatic latent image into a toner image at a development unit, and transfers the developed toner image onto a recording material at a transfer unit, thereby forming an image. At this time, a high voltage of several hundred volts to several kilovolts is applied to the charging unit, the development unit, and the transfer unit. Therefore, the image forming apparatus includes a circuit board equipped with a high-voltage power supply circuit that generates the high voltage. 
     Japanese Patent No. 6104189 discusses a configuration in which an electric contact is formed by a jumper wire provided on a circuit board and a torsion coil spring provided on a main body side to supply a high voltage generated by a high-voltage power supply circuit to each process member. 
     The configuration discussed in Japanese Patent No. 6104189 may lead to limitations on the method for mounting the circuit board onto the image forming apparatus. More specifically, the circuit board in Japanese Patent No. 6104189 needs to be mounted onto the image forming apparatus while the jumper wire provided on the circuit board is pressed against an arm portion of the torsion coil spring that is biased in a predetermined direction. For example, the circuit board needs to be mounted onto the image forming apparatus in such a manner that the circuit board is inserted from the opposite side from the direction in which the arm portion of the torsion coil spring is biased. Due to the limitation on the mounting method, the configuration discussed in Japanese Patent No. 6104189 may be unusable depending on the configuration of the image forming apparatus or the circuit board. 
     SUMMARY 
     Aspects of the present disclosure provide for forming an electric contact using an elastic member such as a torsion coil spring regardless of a method of mounting a circuit board. 
     According to an aspect of the present disclosure, an image forming apparatus includes an image forming unit configured to form an image on a recording material, a printed circuit board including a voltage generation unit mounted thereon and configured to generate a voltage to be applied to the image forming unit, a conductive member provided on the printed circuit board, to which the voltage generated by the voltage generation unit is applied, an elastic member including an arm portion configured to be biased toward the conductive member, and configured to connect the conductive member and the image forming unit, and a holding unit configured to hold the arm portion of the elastic member at a position where the arm portion is not in contact with the conductive member. 
     Further features of the present disclosure will become apparent from the following description of embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an image forming apparatus. 
         FIG.  2    is a cross-sectional view of the image forming apparatus. 
         FIG.  3    is a perspective view illustrating the position of a circuit board. 
         FIG.  4    is a front perspective view illustrating the position of the circuit board. 
         FIG.  5    is a perspective view of the circuit board and members disposed near the circuit board. 
         FIG.  6    is a side view of the circuit board and the members disposed near the circuit board. 
         FIG.  7    is a top view of the circuit board and the members disposed near the circuit board. 
         FIG.  8    is a perspective view illustrating configurations that hold an optical box and a driving motor. 
         FIG.  9    illustrates electronic components on the circuit board. 
         FIG.  10    is a block diagram illustrating functions of the circuit board. 
         FIG.  11    is a perspective view illustrating the configuration of an electric contact. 
         FIG.  12    is a cross-sectional view illustrating the configuration of the electric contact. 
         FIG.  13    is a top view illustrating a wiring route of a harness. 
         FIG.  14    is a side view illustrating a first stage of a process of mounting the circuit board. 
         FIG.  15    is a side view illustrating a second stage of the process of mounting the circuit board. 
         FIG.  16    is a side view illustrating a third stage of the process of mounting the circuit board. 
         FIG.  17    illustrates the positions of cutout portions for electric contacts on the circuit board. 
         FIG.  18    is a perspective view illustrating the configuration of a holding unit for an arm portion of a torsion coil spring according to a first embodiment. 
         FIG.  19    is a perspective view illustrating the configuration of a holding unit for the arm portion of the torsion coil spring according to a second embodiment. 
         FIG.  20    is a perspective view illustrating the configuration of a holding unit for the arm portion of the torsion coil spring according to a third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following description, configurations for implementing the present disclosure will be described in detail based on embodiments thereof with reference to the drawings. Dimensions, materials, shapes, a relative layout, and the like of components that will be described in these embodiments may be changed as appropriate in accordance with the configuration of an apparatus to which the present disclosure is applied and various kinds of conditions. They are not intended to limit the scope of the present disclosure to the embodiments that will be described below. 
     Overall Configuration of Image Forming Apparatus 
     The overall configuration of an image forming apparatus  1  according to a first embodiment will be described. The image forming apparatus  1  according to the present embodiment is a monochrome laser beam printer using the electrophotographic process, and is configured to form an image on a recording material P with toner (a developer) in accordance with image information transmitted from an external apparatus such as a personal computer. Examples of the recording material P include recording paper, label paper, an overhead projector (OHP) sheet, and a cloth. 
     Further, in the following description, a Z direction will be defined as the height direction of the image forming apparatus  1  when the image forming apparatus  1  is set up on a horizontal surface (a direction opposite from the direction of gravitational force). An X direction will be defined as a direction intersecting with the Z direction and extending in parallel with an axial direction (a main scanning direction) of a photosensitive drum  11 , which will be described below. A Y direction will be defined as a direction intersecting with the X direction and the Z direction. Desirably, the X direction, the Y direction, and the Z direction perpendicularly intersect with one another. Further, for the sake of convenience, a positive side and a negative side in the X direction will be referred to as a right side and a left side, respectively. A positive side and a negative side in the Y direction will be referred to as a front side or a front surface side and a back side or a back surface side, respectively. A positive side and a negative side in the Z direction will be referred to as an upper side and a lower side, respectively. 
       FIG.  1    illustrates a perspective view of the image forming apparatus  1 , and  FIG.  2    illustrates a cross-sectional view taken along a plane perpendicular to the X direction of the image forming apparatus  1  (the direction of the rotational axis of the photosensitive drum  11 ). In  FIG.  1   , the image forming apparatus  1  includes a feeding cassette  4 , in which the recording material P is contained, and a discharge tray  14 , on which the discharged recording medium P is stacked. Insertion of the feeding cassette  4  in a feeding port  81  brings the image forming apparatus  1  into a state that the recording material P contained in the feeding cassette  4  can be fed into the image forming apparatus  1 . 
     Further, the feeding cassette  4  is configured to be pulled out from the feeding port  81  in the Y direction, and a user can replenish the recording material P thereto. The recording material P fed from the feeding cassette  4  and subjected to image formation thereon is discharged from a discharge port  15  toward a discharge direction illustrated in  FIG.  1    (a direction toward the positive side of the Y axis), and is stacked onto the discharge tray  14 . 
     A front cover  70  is provided at a part of the end surface (a part of the front surface) of the image forming apparatus  1  on the downstream side in the discharge direction, and covers a circuit board  100 , which will be described below. An exterior cover  71  is provided on a part of the front surface, the side surfaces and the top surface of the image forming apparatus  1 . The front cover  70 , the exterior cover  71 , and the foregoing discharge tray  14  form a housing  75  of the image forming apparatus  1  together. The housing  75  is a member covering the image forming apparatus  1 , and includes therein process members such as an optical box  50 , which will be described below. The foregoing feeding port  81  and discharge port  15  are openings formed on a part of the housing  75 , and the recording material P is inserted into the image forming apparatus  1  through the feeding port  81  and is discharged out of the image forming apparatus  1  through the discharge port  15 . 
     A flow of an image forming operation on the recording material P will be described with reference to the cross-sectional view of  FIG.  2   . When the image information is transmitted to the image forming apparatus  1 , the photosensitive drum  11  (an image bearing member), which is a rotational member, is rotationally driven at a predetermined circumferential speed (a process speed) in a direction indicated by an arrow R based on a print start signal. The optical box  50  irradiates the photosensitive drum  11  with laser light based on the input image information. The optical box  50  is a box-like unit including therein members such as a laser oscillator that outputs the laser light, a polygon mirror and a lens for irradiating the photosensitive drum  11  with the laser light, and a scanner motor for rotating the polygon mirror. The photosensitive drum  11  is charged by a charging roller  17  in advance, and an electrostatic latent image is formed on the photosensitive drum  11  with the laser light irradiated on the photosensitive drum  11 . After that, the electrostatic latent image is developed with toner by a development roller  12 , and then a toner image is formed on the photosensitive drum  11 . 
     The recording material P is fed from the feeding cassette  4  in parallel with the above-described image forming process. A pickup roller  3 , a feeding roller  5   a , and a conveyance roller pair  5   c  are provided on a conveyance path in the image forming apparatus  1 . The pickup roller  3  (a feeding member) comes into contact with a recording material P located at the uppermost position among the recording materials P contained in the feeding cassette  4 , and feeds the recording material P in a feeding direction (a direction toward the negative side of the Y axis) with the rotation of the roller itself. The feeding roller  5   a  and a separation pad  5   b  that is in pressure contact with the feeding roller  5   a  form a separation nip. If a plurality of recording materials P is undesirably fed to the separation nip due to the influence of a frictional force between the recording materials P, the feeding roller  5   a  and the separation pad  5   b  separate the plurality of recording materials P one by one, and feed only the recording material P located at the uppermost position to the downstream side. 
     The recording material P fed from the feeding cassette  4  is conveyed toward a transfer roller  7  by the conveyance roller pair  5   c . The toner image formed on the photosensitive drum  11  is transferred onto the recording material P due to application of a transfer bias to the transfer roller  7 . The recording material P with the toner image transferred thereon by the transfer roller  7  is subjected to heating and pressing processing by a fixing device  9 , and then the toner image is fixed onto the recording material P. The fixing device  9  includes a heating roller  9   a , which includes a not-illustrated heater built therein, and a pressing roller  9   b , which is biased toward the heating roller  9   a . Then, the recording material P with the toner image fixed thereon is discharged onto the discharge tray  14  by a discharge roller pair  10 . 
     When images are formed on the both surfaces of the recording material P, the discharge roller pair  10  guides the recording material P to a two-sided conveyance path  16  by causing the recording material P with the image formed on a first surface thereof to be switched back. 
     The recording material P guided to the two-sided conveyance path  16  is conveyed toward the transfer roller  7  again by a two-sided conveyance roller pair  5   d . The recording material P is discharged out of the apparatus by the discharge roller pair  10  after an image is formed on a second surface of the recording material P by the transfer roller  7 . Further, after the toner image is transferred on the recording material P, the toner remaining on the photosensitive drum  11  is removed by a cleaning unit  13 . 
     As illustrated in  FIG.  2   , the image forming apparatus  1  includes the circuit board  100 . The circuit board  100  includes a printed circuit board  101  made of an insulating material, and electronic component groups  111  and  121  soldered on the printed circuit board  101 . Conductor wiring is laid on the printed circuit board  101 , and thus the electronic component groups  111  and  121  are electrically connected to each other. The circuit board  100  is equipped with a not-illustrated converter circuit that rectifies a voltage supplied from the outside of the image forming apparatus  1  and converts the voltage to acquire a predetermined voltage value necessary for the image forming process. 
     As illustrated in  FIG.  2   , the circuit board  100  is disposed in such an orientation that the surface of the printed circuit board  101  with the electronic component groups  111  and  121  mounted thereon intersects with the discharge direction. Further, the printed circuit board  101  is provided between the front cover  70  and the optical box  50  in the discharge direction. The electronic component groups  111  and  121  are disposed on the surface of the printed circuit board  101  which faces the optical box  50 . 
     Layout of Circuit Board 
     The layout of the circuit board  100  according to the present embodiment will be described in detail with reference to  FIGS.  3  to  8   .  FIG.  3    is a perspective view of the image forming apparatus  1  illustrating the layout of the circuit board  100 , and the front cover  70  and the exterior cover  71  are omitted in the  FIG.  3    unlike  FIG.  1   . As illustrated in  FIG.  3   , the circuit board  100  is set up on the front surface side, and the optical box  50  and a driving motor  60  are disposed on the inner side behind the circuit board  100  (the negative side in the Y direction). In  FIG.  3   , the optical box  50  and the driving motor  60  are illustrated with dotted lines because they are located at positions that cannot be seen actually. 
     As illustrated in  FIG.  3   , the image forming apparatus  1  includes a right-side plate frame  72  (a first-side plate frame), a left-side plate frame  73  (a second-side plate frame), and a base frame  74 . The right-side plate frame  72  supports the right-side end portion (a first end portion) of the photosensitive drum  11  in the X direction, and the left-side plate frame  73  supports the left-side end portion (a second end portion) of the photosensitive drum  11  in the X direction. The base frame  74  is provided on the bottom surface, and supports the right-side plate frame  72  and the left-side plate frame  73  from below. 
     The circuit board  100  is supported by these frame members, and is mounted on the image forming apparatus  1  in such a manner that the circuit board  100  extends substantially in parallel with the XZ plane. Bent portions  72   a  and  73   a  are provided for reinforcement at the respective end portions of the right-side plate frame  72  and the left-side plate frame  73  in the Y direction. The bent portion  72   a  is bent toward the positive side in the X direction so as to extend substantially in parallel with the XZ plane, and the bent portion  73   a  is bent toward the negative side in the X direction so as to extend substantially in parallel with the XZ plane. In other words, the bent portions  72   a  and  73   a  are bent so as to extend along the surface of the printed circuit board  101 . The plate frames on the both sides are bent toward outside the image forming apparatus  1  (in directions away from the photosensitive drum  11  in the X direction) in this manner, and thus the present configuration allows electronic components to be mounted on a further large region of the printed circuit board  101 . 
       FIG.  4    is a front perspective view of the image forming apparatus  1  illustrating the layout of the circuit board  100 . As illustrated in  FIG.  4   , a distance L 1  between the inner surfaces of the right-side plate frame  72  and the left-side plate frame  73  in the X direction is shorter than a length L 2  of the circuit board  100  in the X direction. The printed circuit board  101  is arranged on the positive side (the front surface side) in the Y direction relative to the bent portions  72   a  and  73   a , and the printed circuit board  101  is in contact with each of the bent portions  72   a  and  73   a . The circuit board  100  overlaps the bent portions  72   a  and  73   a  when viewed from the front surface side. In  FIG.  4   , parts of the bent portions  72   a  and  73   a , the optical box  50 , and the driving motor  60  are illustrated with dotted lines to illustrate they are located at positions that are normally covered. Positional Relationship between Electronic Members and Optical Box 
     Next, the positional relationship between the electronic component group  111  and the optical box  50  will be described in detail with reference to  FIGS.  5  to  7   . 
       FIG.  5    is a perspective view illustrating the circuit board  100  when viewed from behind the main body. The electronic component group  111  having a larger size in the Y direction than other members is collectively placed together on the lower side of the printed circuit board  101  and is mounted so as to be contained below the optical box  50  for the purpose of effectively utilizing the space. More specifically, the electronic component group  111  is provided on the lower side with respect to the center of the printed circuit board  101  in the vertical direction. A power supply input unit  115  is provided at the end portion of the printed circuit board  101 . The power supply input unit  115  is connected to a not-illustrated inlet, and receives power supply from a commercial power source. 
       FIG.  6    is an enlarged side view illustrating the circuit board  100  when viewed from the left side surface of the main body. The optical box  50  is disposed at an optimum position for irradiating the photosensitive drum  11  with the laser light indicated with a chain line. Further, a member such as the electronic component group  111  that significantly protrudes from the plate surface is not disposed at a portion where the optical box  50  and the printed circuit board  101  are located closest to each other in the Y direction. In other words, the optical box  50  and the electronic component group  111  are disposed at respective positions that are different from each other in the Z direction so as not to interfere with each other. 
       FIG.  7    is an enlarged top view illustrating the circuit board  100  when viewed from the upper surface of the main body. Referring to this drawing, the optical box  50  and the electronic component group  111  are disposed at positions where they partially overlap each other. The optical box  50  is located above the electronic component group  111  as described above, and thus the electronic component group  111  cannot be visually confirmed from this direction actually.  FIG.  7    illustrates the electronic component group  111  in a see-through manner with the optical box  50  indicated with a dotted line so as to indicate the positional relationship between the two members in an easily understandable way. 
     The electronic component group  111  is disposed at the above-described position in this manner, and thus the present configuration can reduce the distance between the circuit board  100  and the optical box  50  in the Y direction (the front-back direction), thereby reducing the size of the image forming apparatus  1 . 
     Positional Relationship between Electronic Components and Driving Motor 
     Next, the positional relationship between the electronic component group  111  and the driving motor  60  will be described in detail with reference to  FIGS.  5  to  7   . The driving motor  60  assumes the role of rotating members for feeding and conveying the recording material P (the pickup roller  3 , the feeding roller  5   a , the conveyance roller pair  5   c , and the like) and the photosensitive drum  11 . 
     As illustrated in  FIG.  5   , the driving motor  60  protrudes toward the negative side in the X direction, and the printed circuit board  101  is disposed on the front side of the main body relative to the driving motor  60 . It can be understood that the electronic component group  111  is mounted to avoid the driving motor  60  so as not to interfere with the driving motor  60 . As illustrated in  FIG.  6   , the driving motor  60  and the electronic component group  111  are disposed at positions where they partially overlap each other when viewed from the left side surface of the main body. Then, as illustrated in  FIG.  7   , the driving motor  60  and the electronic component group  111  are disposed at respective positions that are different from each other in the X direction so as not to interfere with each other when viewed from the upper surface of the main body. 
     The electronic component group  111  is disposed at the above-described position in this manner, and thus the present configuration can reduce the distance between the circuit board  100  and the driving motor  60  in the Y direction (the front-back direction), thereby reducing the size of the image forming apparatus  1 . 
     Mounting of Optical Box and Driving Motor on Main Body 
     Next, configurations for mounting the optical box  50  and the driving motor  60  on the main body will be described in detail with reference to  FIG.  8   .  FIG.  8    corresponds to the perspective view illustrated in  FIG.  5    with the right-side plate frame  72  and a scanner holding member  40  added thereto. The left-side plate frame  73  and the base frame  74  are omitted in  FIG.  8   . 
     The optical box  50  is held by the scanner holding member  40 . The scanner holding member  40  is fixed to the right-side plate frame  72  and the left-side plate frame  73  (not illustrated in  FIG.  8   ), and is configured to bridge the space between the two frame walls. The driving motor  60  is attached to the right-side plate frame  72 , and a gear coupled with the driving motor  60  is provided on the positive side of the right-side plate frame  72  in the X direction. The driving force of the driving motor  60  is transmitted to the feeding roller  5   a  and the photosensitive drum  11  via this gear. 
     Configuration of Circuit Board 
     Next, the configuration of the circuit board  100  will be described with reference to  FIG.  9   .  FIG.  9    is a back view of the circuit board  100  when viewed from the back side of the main body.  FIG.  9    illustrates not only the circuit board  100  but also the optical box  50  and the driving motor  60  in addition thereto. 
     The circuit board  100  includes the power supply input unit  115 , which receives an alternating-current voltage from the commercial power source serving as an external power source, a low-voltage power supply unit  110 , which converts the alternating-current voltage into a direct-current voltage, and a high-voltage power supply unit  120  for supplying a high voltage necessary for the image formation to each process member. In the case of the circuit board  100  according to the present embodiment, the low-voltage power supply unit  110  and the high-voltage power supply unit  120  are mounted on the same board. 
     The low-voltage power supply unit  110  includes a low-voltage power supply transformer  112 , a heat sink  113 , and an electrolytic capacitor  114  as the electronic component group  111  having a large size in the Y direction. The high-voltage power supply unit  120  includes a charging transformer  122 , a development transformer  123 , and a transfer transformer  124  as the electronic component group  121  having a large size in Y direction. As described above, both the electronic component groups  111  and  121  large-sized in the Y direction are mounted on the surface of the image forming apparatus  1  on the inner side (the negative side in the Y direction) while being arranged so as to avoid the positions of the optical box  50  and the driving motor  60  for the purpose of making good use of the space inside the image forming apparatus  1 . 
     Function of Circuit Board 
     Next, the functions of the low-voltage power supply unit  110  and the high-voltage power supply unit  120  will be described with reference to  FIGS.  9  and  10   .  FIG.  10    is a block diagram illustrating the functions of the circuit board  100 . 
     First, the low-voltage power supply unit  110  receives power from the commercial power source via the power supply input unit  115  mounted at the end portion of the circuit board  100 , and converts an alternating-current voltage into a stable direct-current voltage by using a rectification and smoothing circuit including the electrolytic capacitor  114 . After that, the low-voltage power supply unit  110  converts the direct-current voltage into a high-frequency alternating-current voltage by using a switching element such as a transistor, and then inputs the high-frequency alternating-current voltage into the low-voltage power supply transformer  112  after that. The low-voltage power supply transformer  112  converts the high-frequency alternating-current voltage, which is input from the low-voltage power supply unit  110 , into an alternating-current voltage having a desired voltage value. The low-voltage power supply unit  110  converts the alternating-current voltage into the direct-current voltage again and outputs the acquired direct-current voltage to the high-voltage power supply unit  120  and the optical box  50 . Further, the low-voltage power supply unit  110  is equipped with the heat sink  113  manufactured using aluminum or iron for heat dissipation because a power loss at the individual circuit components emerges as heat. 
     Direct-current voltages of 24 V, 3.3 V, and 5 V are output from the converter circuit of the above-described low-voltage power supply unit  110 . The direct-current voltage of 24 V is supplied to the high-voltage power supply unit  120 , and the direct-current voltages of 3.3 V and 5V are supplied to the optical box  50 , the driving motor  60 , an engine control unit  130 , and a video controller  140 . The direct-current voltages output from the low-voltage power supply unit  110  are supplied to the high-voltage power supply unit  120 , the optical box  50 , the driving motor  60 , the engine control unit  130 , and the video controller  140  via a wiring component such as a pattern on the printed circuit board  101 , a harness, and the like. 
     The high-voltage power supply unit  120  converts the voltage supplied from the low-voltage power supply unit  110  (for example, 24 V) into a high voltage necessary for the image forming process such as the charging, the development, and the transfer. The charging transformer  122  converts the voltage supplied from the low-voltage power supply unit  110  into a voltage for the charging, and the converted voltage is then supplied to the charging roller  17 . The development transformer  123  converts the voltage supplied from the low-voltage power supply unit  110  into a voltage for the development, and the converted voltage is then supplied to the development roller  12 . The transfer transformer  124  converts the voltage supplied from the low-voltage power supply unit  110  into a voltage for the transfer, and the converted voltage is then supplied to the transfer roller  7 . 
     The optical box  50 , the driving motor  60 , the engine control unit  130 , and the video controller  140  operate using the voltage (for example, 3.3 V or 5 V) supplied from the low-voltage power supply unit  110 . Now, the engine control unit  130  assumes the role of comprehensively controlling various kinds of process members. The engine control unit  130  includes, for example, a central processing unit (CPU) (not illustrated), a random access memory (RAM) (not illustrated) used to, for example, calculate and temporarily store data necessary to control the image forming apparatus  1 , and a read only memory (ROM) (not illustrated) storing therein a program for controlling the image forming apparatus  1  and various kinds of data. The engine control unit  130  may be provided on another board different from the circuit board  100  or may be provided on the same board as the circuit board  100 . The video controller  140  assumes the role of communicating with the external apparatus such as the personal computer to receive print data, and notifying the engine control unit  130  of a result of analyzing the print data. 
     Configuration of Electric Contact 
     Next, the configuration of an electric contact for supplying the voltage output from the high-voltage power supply unit  120  to each process member will be described with reference to  FIGS.  11  and  12   .  FIG.  11    illustrates a perspective view of a charging contact portion  159  provided at the edge of the printed circuit board  101 , and  FIG.  12    illustrates a cross-sectional view of the charging contact portion  159  provided at the edge of the printed circuit board  101 . The configuration of an electric contact for the charging will be described here, although electric contacts for the development and the transfer are also configured similarly thereto. 
     As described above, the high-voltage power supply unit  120  converts the voltage supplied from the low-voltage power supply unit  110  into the high voltage for the charging by using a converter circuit for the charging (not illustrated) including the charging transformer  122 . 
     In other words, the high-voltage power supply unit  120  functions as a voltage generation unit that generates the high voltage for the charging. Then, the high voltage is supplied to a jumper wire  150  illustrated in  FIG.  11   . The jumper wire  150  (a conductive member) is disposed so as to extend across a cutout portion  153  formed through the component surface and the soldered surface of the printed circuit board  101 . This cutout portion  153  is structured to allow an arm portion  152  of a charging contact spring  151  (an elastic member) to enter it, and the jumper wire  150  and the arm portion  152  are brought into contact with each other when the arm portion  152  enters the cutout portion  153 . 
     As illustrated in  FIG.  12   , the charging contact spring  151  is shaped as a torsion coil spring, and is configured such that a force acts on the arm portion  152  in a direction toward the jumper wire  150 . As a result, the arm portion  152  is configured to press the jumper wire  150  in a direction indicated by an arrow  155  illustrated in  FIGS.  11  and  12   , thereby being designed to be stabilized as an electric contact. 
     Further, as illustrated in  FIG.  12   , the charging contact spring  151  includes two arm portions  152  and  154 . The arm portion  152  is structured to come into contact with the jumper wire  150  as described above, and an arm portion  154  is connected to the charging roller  17  (not illustrated in  FIG.  12   ). Therefore, when the arm portion  152  functions as the electric contact in contact with the jumper wire  150 , this allows the high voltage generated by the converter circuit for the charging to be supplied to the charging roller  17  via the jumper wire  150  and the charging contact spring  151 . 
     Mounting of Circuit Board 
     Next, a method for mounting the circuit board  100  onto the image forming apparatus  1  will be described with reference to  FIG.  13   .  FIG.  13    is a top view of the circuit board  100  when viewed from above the image forming apparatus  1 . 
       FIG.  13    illustrates a board-side connector  161  mounted on the printed circuit board  101 , motor-side connectors  162  of the driving motor  60 , and a harness  160  connecting the board-side connector  161  and the motor-side connectors  162 . The space inside the housing  75  can be effectively utilized by disposing the board-side connector  161  to which the harness  160  is connected on the same surface as the electronic component groups  111  and  121  and arranging the wiring route of the harness  160  so as to avoid the positions of the process members, such as the optical box  50 . Further, a reduction in the distance between the board-side connector  161  and the motor-side connectors  162  leads to a reduction in the length of the harness  160 , thereby contributing to a reduction in the space for the wiring. Therefore, it is desirable that the board-side connector  161  is located near the motor-side connectors  162  in terms of the reduction in the size of the image forming apparatus  1 . 
     In the case where the board-side connector  161  is disposed at a position near the motor-side connectors  162 , it may be difficult for a worker to perform the operation to connect the board-side connector  161  and the motor-side connectors  162  in the state that the circuit board  100  is mounted on the image forming apparatus  1  as described with reference to  FIGS.  3  to  6   . The board-side connector  161  is hidden behind the printed circuit board  101  when viewed from the front surface side, and is also hidden behind the driving motor  60  when viewed from the right side. Further, the optical box  50  and the tall electronic component group  121  are disposed above the driving motor  60 , and this also undesirably limits the space through which the worker can access the board-side connector  161  from above. 
     In this manner, in the case in which the wiring route of the harness  160  is designed in such a manner that the space in the housing  75  is effectively utilized to reduce the size of the image forming apparatus  1 , it is difficult to perform the wiring work of the harness  160  in the state that the circuit board  100  is mounted on the image forming apparatus  1 . Therefore, in the present embodiment, the wiring work of the harness  160  is performed before the circuit board  100  is mounted. 
       FIGS.  14  to  16    are side views illustrating the procedure of mounting the circuit board  100  onto the image forming apparatus  1  while connecting the harness  160 . Since the wiring work cannot be performed in the state that the circuit board  100  is mounted on the image forming apparatus  1  as described above, first, wiring work at the lower stage portion of the image forming apparatus  1  is performed in a state that the circuit board  100  is laid down as illustrated in  FIG.  14   . In the state that the circuit board  100  is laid down, a work space can be secured on the top surface side of the image forming apparatus  1  (the positive side in the Z direction), and therefore wiring work can be performed to connect the harness  160  to the board-side connector  161  at the lower stage portion. 
     The electronic component group  111  is disposed on the left side (the negative side in the X direction) of the board-side connector  161  as illustrated in  FIG.  13   .  FIGS.  14  to  16    illustrate the board-side connector  161  as if seeing it through the electronic component group  111  for illustrative purposes. 
     Next, the circuit board  100  is erected halfway as illustrated in  FIG.  15   , and wiring work at a middle stage portion is performed to connect a harness  163  to a board-side connector  164 . Lastly, wiring work at an upper stage portion is performed in the state that the circuit board  100  is mounted on the image forming apparatus  1  as illustrated in  FIG.  16    to connect a harness  166  to a board-side connector  167 . The method of mounting the circuit board  100  onto the image forming apparatus  1  while erecting the circuit board  100  allows the wiring work of connecting the harness  160  to the board-side connector  161  to be performed while the length of the harness  160  is reduced. 
     The mounting method has been described here focusing on the connector  161  and the harness  160  connected to the driving motor  60  as an example, but the procedure of the wiring work is not limited thereto. For example, in a case where the image forming apparatus  1  is configured in such a manner that the board-side connector  164  connected to the connector  165  of the optical box  50  and the board-side connector  167  connected to a connector  168  of a not-illustrated process member are disposed on the lower stage side, the wiring work to connect these connectors may be performed before the wiring work for the driving motor  60 . 
     Positions of Cutout Portions on Circuit Board 
     Next, the positions of the cutout portions on the circuit board  100 , which are provided for electric contacts, will be described with reference to  FIG.  17   .  FIG.  17    is a back view of the circuit board  100  when viewed from the back side of the main body. 
     As illustrated in  FIG.  17   , the cutout portion  153 , which forms a part of the charging contact portion  159  described with reference to  FIGS.  11  and  12   , is provided at the edge of the circuit board  100  on the positive side in the X direction. Then, the jumper wire  150  is disposed so as to extend across this cutout portion  153 . In addition to the cutout portion  153 , a jumper wire  200  and a cutout portion  201  for the development, and a jumper wire  202  and a cutout portion  203  for the transfer are provided at the edge of the circuit board  100  on the positive side in the X direction. Hereinafter, when the “cutout portion” is simply used, the term is referred to as including the cutout portions  153 ,  201 , and  203  forming the respective electric contacts for the charging, the development, and the transfer. 
     In such a configuration, conventionally, the circuit board  100  has been mounted by, for example, a method like inserting it into the image forming apparatus  1  from the negative side in the X direction. In the case where the circuit board  100  is mounted according to the procedure described with reference to  FIGS.  14  to  16   , the circuit board  100  and the arm portion of the torsion coil spring may interfere with each other when the circuit board  100  is being erected. 
     This may necessitate a measure such as increasing the size of the cutout portion or shaping the arm portion of the torsion coil spring so as to conform with the trajectory of the circuit board  100  when it is erected. 
     On the other hand, even if the size of the cutout portion provided to the circuit board  100  is increased so as to prevent the interference between the circuit board  100  and the torsion coil spring, this may bring about such a state that the jumper wire and the arm portion obliquely contact each other, thereby resulting in an unstable connection at the electric contact. Further, when increasing the size of the cutout portion for example, the rigidity of the circuit board  100  may reduce and the mounting space on the circuit board  100  may be limited. Further, the wiring work is performed in parallel when the circuit board  100  is being erected in the configuration according to the present embodiment, and therefore it is undesirable to perform the wiring work in an unstable state that the circuit board  100  is subjected to resilience from the torsion coil spring. 
     For these reasons, a holding unit for holding the arm portion of the torsion coil spring is provided to the image forming apparatus  1  in the present embodiment. 
     Configuration of Holding Unit for Holding Arm Portion of Torsion Coil Spring 
       FIG.  18    is a perspective view illustrating the configuration of the holding unit for the arm portion of the torsion coil spring according to the present embodiment. The configuration of the holding unit at the electric contact for the charging described with reference to  FIGS.  11  and  12    will be described here, but the holding units at the electric contacts for the development and transfer are also configured similarly thereto. 
       FIG.  18    illustrates a holding unit  170  that holds the arm portion  152 , which is a part of the charging contact spring  151  (not illustrated in  FIG.  18   ) shaped as a torsion coil spring. The holding unit  170  temporarily holds the arm portion  152  at a position where the arm portion  152  does not come into contact with the jumper wire  150  (hereinafter referred to as a retracted position) so as to prevent the arm portion  152  from entering the trajectory of the circuit board  100  when the circuit board  100  is mounted. 
     The holding unit  170  is provided to the main body of the image forming apparatus  1 , and is fixed to, for example, the right-side plate frame  72  (illustrated in  FIG.  8    and the like). The holding unit  170  includes a reception portion  171 , which receives a force acting on the arm portion  152  in a direction indicated by an arrow  175 , and an L-shaped cutout portion  172  is formed in the holding unit  170 . As described above, the arm portion  152  is biased in the direction toward the jumper wire  150  under the influence of the torsion coil spring. 
     The worker performs the operation of mounting the circuit board  100  onto the image forming apparatus  1  according to the procedure illustrated in  FIGS.  14  to  16    in the state that the arm portion  152  is held by the holding unit  170 , and detaching the arm portion  152  from the holding unit  170  after that. As a result, the arm portion  152  and the jumper wire  150  can be brought into contact with each other in a stable state as illustrated in  FIG.  11   . 
     Further, the cutout portion  153  provided to the printed circuit board  101  has a shape flaring out toward the edge of the printed circuit board  101 . This flared portion serves as a guide portion  156 , and is configured to guide the arm portion  152  detached from the holding unit  170  to the jumper wire  150 . 
     In this manner, according to the present embodiment, the electric contact can be formed using an elastic member such as a torsion spring coil regardless of the method for mounting the circuit board  100 . 
     Further, the space in the housing  75  of the image forming apparatus  1  can be effectively utilized by mounting the circuit board  100  according to the procedure illustrated in  FIGS.  14  to  16   . Further, an area for the electric contact of the circuit board  100  can be reduced by forming the electric contact using the torsion coil spring. As a result, the size of the image forming apparatus  1  can be further reduced. 
     A second embodiment will be described. As described in the first embodiment, the arm portion  152  is held at the retracted position by the holding unit  170  until the circuit board  100  is mounted on the image forming apparatus  1  and the arm portion  152  is connected to the jumper wire  150 . In some cases, the arm portion  152  may be accidentally detached from the holding unit  170  due to vibration at the time of the assembling work or if the assembling worker unintentionally touches the arm portion  152 . 
       FIG.  19    is a perspective view illustrating the configuration of a holding unit for holding the arm portion of the torsion coil spring according to the present embodiment. The holding unit according to the present embodiment will be described focusing on differences from the first embodiment, and the description of a similar configuration to the first embodiment will be omitted. 
       FIG.  19    illustrates a holding unit  180  that holds the arm portion  152 , which is a part of the charging contact spring  151  (not illustrated in  FIG.  19   ) shaped as a torsion coil spring. In addition to a reception portion  181  and a cutout portion  182  as in the first embodiment, the holding unit  180  includes a protrusion portion  183  extending from a part of the reception portion  181  in the direction opposite from the jumper wire  150 . The protrusion portion  183  prevents the arm portion  152  held by the holding unit  180  from being accidentally detached from the holding unit  180  due to a vibration or the like. 
     In this manner, according to the present embodiment, the following advantageous effects can be further achieved in addition to the advantageous effects of the first embodiment. That is, the provision of the protrusion portion  183  can prevent the arm portion  152  from being easily detached from the holding unit  180  due to vibration or if the assembling worker unintentionally touches the arm portion  152  when the circuit board  100  is mounted onto the image forming apparatus  1 . 
     The shape of the protrusion portion  183  according to the present embodiment is an example, and is not limited thereto. The protrusion portion  183  may have any shape as long as it can inhibit unintentional detachment of the arm portion  152  from the holding unit  180 . 
     A third embodiment will be described. As described in the first embodiment, the arm portion  152  of the torsion coil spring needs to be moved to the retracted position in advance before the circuit board  100  is mounted onto the image forming apparatus  1 . When the mounted circuit board  100  is dismounted, the arm portion  152  needs to be moved from the position where the arm portion  152  is in contact with the jumper wire  150  (a contact position) to the retracted position. At the same time, the size of the holding unit  170  also needs to be reduced as much as possible to reduce the size of the image forming apparatus  1 . The reduction in the size of the holding unit  170  naturally leads to a reduction in the size of the cutout portion  172 , thereby possibly making it difficult for the worker to perform the work of inserting the arm portion  152  into the holding unit  170 . 
       FIG.  20    is a perspective view illustrating the configuration of a holding unit for holding the arm portion of the torsion coil spring according to the present embodiment. The holding unit according to the present embodiment will be described focusing on differences from the first embodiment, and the description of a similar configuration to the first embodiment will be omitted. 
       FIG.  20    illustrates a holding unit  190  that holds the arm portion  152 , which is a part of the charging contact spring  151  (not illustrated in  FIG.  20   ) shaped as a torsion coil spring. In addition to a reception portion  191  and a cutout portion  192  as in the first embodiment, the holding unit  190  includes a guide portion  193  near the opening of the cutout portion  192 . The cutout portion  192  according to the present embodiment has a shape flaring out toward the jumper wire  150 , and this flared portion serves as the guide portion  193 . The shape of the guide portion  193  facilitates the operation of moving the arm portion  152  from the contact position to the retracted position (facilitates the placing of the arm portion  152  on the holding unit  190 ), thereby being expected to improve the workability. 
     In this manner, according to the present embodiment, the following advantageous effects can be further achieved in addition to the advantageous effects of the first embodiment. That is, the provision of the guide portion  193  can improve the workability when the circuit board  100  is dismounted from the image forming apparatus  1 . 
     The shape of the guide portion  193  according to the present embodiment is an example, and is not limited thereto. 
     The guide portion  193  may have any shape as long as the shape can guide the arm portion  152  into the cutout portion  192  of the holding unit  190 . 
     (Exemplary Modifications) 
     The first to third embodiments have been described on the case that all the electric contacts for the charging, the development, and the transfer are similarly configured; however, only one of the electric contacts may be configured according to the above-described first to third embodiments and the others may be configured differently. Further, in the above-described first to third embodiments, the jumper wires and the cutout portions for the respective electric contacts for the charging, the development, and the transfer are provided at the edge of the circuit board  100  on the positive side in the X direction, as described with reference to  FIG.  17   . However, the jumper wires and the cutout portions are not limited thereto. For example, only the jumper wire and the cutout portion for the charging may be provided at the edge on the positive side in the X direction and the jumper wires and the cutout portions for the development and the transfer may be provided at the edge on the negative side in the X direction. 
     Further, the above-described first to third embodiments have been described using the charging roller  17 , the development roller  12 , and the transfer roller  7  as the image forming unit as an example, but the image forming unit is not limited thereto. For example, the configurations according to the embodiments of the present disclosure may be applied to an electric contact for applying a voltage to a member such as the driving motor  60  and the optical box  50 . In other words, the configurations according to the embodiments of the present disclosure may be applied to not only the electric contact of the high-voltage power supply unit  120  but also an electric contact of the low-voltage power supply unit  110 . 
     Further, the above-described first to third embodiments have been described using the torsion coil spring as the elastic member, but the elastic member is not limited thereto and may be, for example, a conducting member having an elastic structure such as a plate spring. Then, the conductive member may also be, for example, a metal member shaped like a flat plate without being limited to a liner member like the jumper wire. Further, the shape of the cutout portion is not limited to a square shape and may be, for example, a circular shape, an elliptic shape, or a polygonal shape. 
     Further, the above-described first to third embodiments have been described using the case where the circuit board  100  is mounted onto the image forming apparatus  1  while erecting the circuit board  100 , but the mounting method is not limited thereto. For example, the circuit board  100  may be mounted onto the image forming apparatus  1  in such a manner that the circuit board  100  is inserted into the image forming apparatus  1 , or such the circuit board  100  may be mounted onto the image forming apparatus  1  while rotating the circuit board  100  relative to the image forming apparatus  1 . 
     Further, the above-described first to third embodiments have been described based on the configuration in which the low-voltage power supply unit  110  and the high-voltage power supply unit  120  are disposed on the same board (the circuit board  100 ), but the configuration is not limited thereto. The two power supply units may be disposed on different boards. Then, both the board on which the low-voltage power supply unit  110  is provided and the board on which the high-voltage power supply unit  120  is provided may be disposed on the front surface side of the image forming apparatus  1  illustrated in  FIG.  3   . Alternatively, only the board on which the low-voltage power supply unit  110  is provided may be disposed on the front surface side, and the board on which the high-voltage power supply unit  120  is provided may be disposed at a different position. Alternatively, only the board on which the high-voltage power supply unit  120  is provided may be disposed on the front surface side, and the board on which the low-voltage power supply unit  110  is provided may be disposed at a different position. 
     While the present disclosure has been described with reference to embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of priority from Japanese Patent Application No. 2021-190757, filed Nov. 25, 2021, which is hereby incorporated by reference herein in its entirety.