Image forming device

Abstract

To improve image quality.SOLUTION: A color printer 1 is provided with image forming units 12 each having a photoreceptor drum 30, LED heads 24 each exposing the photoreceptor drum 30, LED head holders 16 each supporting the LED head 24, head springs 26 urging the LED head 24 against the image forming unit 12, and spring receivers 32 receiving the energization of the head springs 26. The head spring 26 has a spring part 26S that is in contact with the spring receiver 32 to provide an urging force and a fitting part 26F that has an outer diameter smaller than the outer diameter of the spring part 26S. The spring receiver 32 has a fitting hole 33A into which the fitting part 26F is inserted, and has a spring receiver constriction part 37 as a wall part that extends in an urging direction of the head spring 26 from a spring contact surface 33S as a contact surface with which the spring part 26S is in contact. The length of the spring receiver constriction part 37 extending in the urging direction is set to be equal to or more than a coil pitch Pw of the fitting part 26F.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and is suitable for application to, for example, an electrophotographic image forming apparatus. [Background technology]

[0002] Conventionally, a widely used image forming apparatus prints an image by irradiating the surface of an image carrier with light from a head unit that emits exposure light emitted from a light-emitting element, such as an LED (Light Emitting Diode), to form an electrostatic latent image on the surface of the image carrier, and then developing the toner image by attaching toner to the electrostatic latent image.

[0003] The head unit may have, for example, a substrate on which an LED array in which multiple LEDs are arranged in a line is mounted, a lens array in which multiple lenses are aligned to focus the light emitted from each LED, and a head frame that holds the substrate and the lens array.The light emitted from the LED array mounted on the substrate passes through the lens array and is focused, and is exposed to the surface of an image carrier disposed at the imaging position of the lens array, thereby forming an electrostatic latent image.

[0004] In such image forming devices, the head unit is held by engaging protrusions formed on both longitudinal ends of the head unit with support holes formed on both longitudinal ends of a head holding unit hanging down from the cover of the image forming device, and a spring member arranged between the head holding unit and the head unit urges the head unit toward the image carrier and abuts it against the image carrier, thereby positioning the head unit relative to the image carrier (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-73041 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in such an image forming device, the spring member and the receiving portion in the head portion that receives the load of the spring member may get caught, causing the spring member to not properly bias the head portion, and there is a risk that image quality may not be maintained.

[0007] The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus that can improve image quality. [Means for solving the problem]

[0008] In order to solve this problem, the image forming apparatus of the present invention comprises an image forming unit having an image carrier, a head portion that exposes the image carrier, a head holding portion that supports the head portion, a spring member that biases the head portion toward the image forming unit, and a receiving portion that receives the bias of the spring member, wherein the spring member has a first portion that abuts against the receiving portion and applies a biasing force, and a second portion that has an outer diameter smaller than that of the first portion, and the receiving portion has an opening into which the second portion is inserted and has a wall portion that extends in the biasing direction of the spring member from the abutment surface where the first portion abuts, and the length of the wall portion extending in the biasing direction is equal to or greater than the coil pitch of the second portion.

[0009] The present invention can prevent the receiving portion from getting caught between the coil windings of the second portion of the head spring member. [Effects of the Invention]

[0010] According to the present invention, it is possible to realize an image forming apparatus capable of improving image quality. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a left side view showing the configuration of the color printer. [Figure 2]FIG. 2 is a perspective view showing the configuration of the LED head unit and the photosensitive drum in an assembled state of the LED unit. [Figure 3] FIG. 2 is a front view showing the configuration of the LED head, the spring, the spring bearing, and the photosensitive drum. [Figure 4] FIG. 2 is a front view showing the configuration of a head spring. [Figure 5] FIG. 2 is a perspective view showing the configuration of a spring bearing. [Figure 6] 4 is a cross-sectional view taken along the line XX in FIG. 3, showing the configuration (1) of the LED head, the spring, and the spring receiver. [Figure 7] 7 is a partial enlarged view of FIG. 6 showing the configuration (2) of the LED head, spring and spring receiver. FIG. [Figure 8] 2 is a cross-sectional view taken along the line XX in FIG. 3, showing the configuration (3) of the LED head, the spring, and the spring receiver. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0013] [1. Color printer configuration] As shown in its left side view in FIG. 1, color printer 1 is a color electrophotographic printer that prints desired color images on paper of, for example, A3 or A4 size. Color printer 1 has various components arranged inside a roughly box-shaped printer housing 2. In the following description, the right end of FIG. 1 is considered to be the front of color printer 1, and the up-down, left-right, and front-rear directions are defined when viewed from the front. Color printer 1 is controlled by a control unit (not shown). This control unit is connected wirelessly or wired to a host device (not shown) such as a personal computer via a communications processing unit (not shown). When image data representing a color image to be printed is provided from the host device and an instruction to print the color image is received, the control unit executes a printing process to form the print image on the surface of the paper.

[0014] The color printer 1 also has a printer cover 2C on the top side of the printer housing 2. LED head holders 16C, 16M, 16Y, and 16K (hereinafter collectively referred to as LED head holders 16) of LED head units 14C, 14M, 14Y, and 14K (hereinafter collectively referred to as LED head units 14) hang down from the underside of the printer cover 2C so as to be supported so as to be able to swing freely around a rotation fulcrum. The LED head holders 16C, 16M, 16Y, and 16K are configured in almost the same way.

[0015] The printer cover 2C is connected to the printer housing 2 via a shaft member provided at the rear end. Therefore, the printer cover 2C can rotate, with the rotation axis of the shaft member as a fulcrum, between a cover closed state (FIG. 1) in which the top of the printer housing 2 is covered, and a cover open state (not shown) in which the top of the printer housing 2 is exposed. At this time, the printer cover 2C rotates along an arc-shaped trajectory around the rotation axis of the shaft member. Furthermore, as the printer cover 2C rotates, each LED head unit 14 provided on the printer cover 2C also rotates along an arc-shaped trajectory around the rotation axis of the shaft member.

[0016] When color printer 1 is performing a printing operation, the front end of printer cover 2C is pushed down using a shaft member as a fulcrum, closing the interior of printer housing 2 from the outside, thereby protecting the interior (FIG. 1). On the other hand, when color printer 1 is performing maintenance work such as replacing image forming units 12C, 12M, 12Y, and 12K (hereinafter collectively referred to as image forming units 12) or removing jammed paper inside, the front end of printer cover 2C is lifted using a shaft member as a fulcrum, opening the interior of printer housing 2 to the outside, thereby enabling easy access to each internal component. In this cover-open state, LED head unit 14 is retracted and separated upward from image forming units 12.

[0017] A paper storage cassette 3 that stores paper is provided at the bottom of the printer housing 2. A pickup roller 5 is located above the front end of the paper storage cassette 3 and pulls paper from inside the paper storage cassette 3. A paper feed roller 6 and a separation roller 7 are arranged in pair in contact with each other in front of the pickup roller 5. For example, when multiple sheets of paper are pulled out at the same time, the paper is sequentially fed one by one into the conveyance section 4 toward a conveyance roller pair 8 located downstream. The conveyance section 4 has conveyance roller pairs 8 and 9 arranged in order from upstream to downstream. The conveyance roller pairs 8 and 9 sandwich and convey the paper fed from the paper feed roller 6 and separation roller 7, correcting any skew of the paper and conveying it along the conveyance direction toward the transfer belt 10.

[0018] A transfer belt 10 is provided above the paper cassette 3 within the printer housing 2, and extends across the printer housing 2 from front to back. The transfer belt 10 has its central axis oriented left to right and is stretched so that it goes around rollers arranged one at the front and one at the back. The transfer belt 10 is wide in the left to right direction and is formed as an endless belt, and by running in conjunction with the rotation of the rollers, it places the paper handed over from the transport roller pair 9 on its top surface and transports it rearward.

[0019] Meanwhile, above the transfer belt 10, i.e., above the center of the printer housing 2, four image forming units 12C, 12M, 12Y, and 12K are arranged in order from rear to front. That is, the image forming units 12 for each color are arranged in a so-called tandem configuration. These image forming units 12C, 12M, 12Y, and 12K correspond to the colors cyan (C), magenta (M), yellow (Y), and black (K), respectively. The image forming units 12C, 12M, 12Y, and 12K are configured identically, differing only in the color of the corresponding toner. The image forming units 12 are formed in a generally box-like shape that is relatively long in the left-right direction to accommodate the left-right width of the paper.

[0020] Photosensitive drums 30C, 30M, 30Y, and 30K (hereinafter collectively referred to as photosensitive drum 30) are provided near the lower center of each of image forming units 12C, 12M, 12Y, and 12K. Photosensitive drum 30 is cylindrical with its central axis oriented in the left-right direction and is rotatably supported. When image forming unit 12 is installed in printer housing 2, the underside of photosensitive drum 30 contacts transfer belt 10 or paper placed on transfer belt 10. Image forming unit 12 is also capable of moving up and down so that photosensitive drum 30 approaches or moves away from transfer roller 13.

[0021] Furthermore, spacers 30S (FIGS. 2 and 3) are provided on both the left and right sides above the photosensitive drum 30. The size and mounting position of the spacers 30 are optimized, and the lower surfaces of the LED heads 24C, 24M, 24Y, and 24K (hereinafter collectively referred to as LED heads 24) are brought into contact with the upper surface of the spacers 30, thereby adjusting the distance between the circumferential side surface of the photosensitive drum 30 and the LED heads 24 to a desired length. The positional relationships between the photosensitive drums 30C, 30M, 30Y, and 30K and the LED head units 14C, 14M, 14Y, and 14K in all image forming units 12C, 12M, 12Y, and 12K are all configured in the same way.

[0022] Also within the printer housing 2, LED head units 14C, 14M, 14Y, and 14K are provided above and facing the photosensitive drums 30C, 30M, 30Y, and 30K of the image forming units 12C, 12M, 12Y, and 12K, respectively. The LED head units 14C, 14M, 14Y, and 14K are configured substantially identically. As shown in FIG. 2, the LED head unit 14 is composed of an LED head holder 16, an LED head 24, a head spring 26, and a spring receiver 32. Each LED head unit 14 exposes the photosensitive drum 30 to light in accordance with image data for each color to form an electrostatic latent image. When installed in the printer housing 2, each image forming unit 12 is positioned very close to the LED head 24 of the LED head unit 14, and exposure processing is performed using light from the LED head 24. The LED head 24 is configured as a rectangular parallelepiped that is elongated in the left-right direction, and has multiple LEDs arranged inside it in a row along the left-right direction, and each LED is illuminated in an illumination pattern that corresponds to image data supplied from the control unit.

[0023] Toner cartridges 18C, 18M, 18Y, and 18K (hereinafter collectively referred to as toner cartridges 18) are connected to the upper portions of the image forming units 12C, 12M, 12Y, and 12K, respectively. The toner cartridges 18 are hollow containers elongated in the left-right direction, containing powdered toner of each color and incorporating a predetermined stirring mechanism. Directly below each image forming unit 12 are four transfer rollers 13C, 13M, 13Y, and 13K (hereinafter collectively referred to as transfer rollers 13). Each image forming unit 12 sandwiches the upper portion of the transfer belt 10 between itself and the transfer roller 13. Incidentally, the transfer rollers 13 are configured to be electrically charged.

[0024] Color printer 1 supplies toner from toner cartridge 18 to image forming units 12. At the same time, color printer 1 causes LED head 24 to emit light so as to form an emission pattern corresponding to image data supplied from a host device (not shown). In response, each image forming unit 12 uses toner supplied from toner cartridge 18 to form a toner image corresponding to the emission pattern of LED head 24 on the circumferential surface of photosensitive drum 30, and transfers this toner image onto paper. In this way, four-color toner images corresponding to the image data are sequentially transferred onto paper being transported by transfer belt 10.

[0025] A fuser unit 20 is provided behind the transfer belt 10, i.e., near the vertical center near the rear end of the printer housing 2. The fuser unit 20 is made up of a pair of rollers: a heating roller located above the conveyance section 4 and having an internal heater and a surface made of an elastic material, and a pressure roller located below the conveyance section 4 and pressing its upper surface against the heating roller. The fuser unit 20 applies heat and pressure to the toner image on the paper sent out from the transfer belt 10, fixing the toner image to the paper. The paper is then conveyed by a pair of discharge rollers 21 and eventually discharged onto a discharge tray 2T formed on the top surface of the printer cover 2C.

[0026] Furthermore, a double-sided transport unit 22 is provided below the transfer belt 10, i.e., below the center of the printer housing 2. The double-sided transport unit 22 turns the paper over and then transports the paper to the transport roller pair 8 again.

[0027] [2. LED head unit configuration] As described above, the LED head unit 14 (FIG. 2) is composed of the LED head holder 16, the LED head 24, the head spring 26, and the spring bearing 32. Hereinafter, the state in which the spring bearing 32 is attached to the LED head frame 50 of the LED head 24 as shown in FIG. 3 will be referred to as the "spring bearing attached state," and the state in which the spring bearing 32 attached to the LED head 24 is attached to the LED head holder 16 with the head spring 26 sandwiched between the spring bearing 32 and the LED head holder 16 as shown in FIG. 2 will be referred to as the "LED unit assembled state." Note that FIGS. 4, 6, and 7 only show the head spring 26 schematically, and FIG. 6 does not show the board 52, lens array 54, and other components inside the LED head frame 27. Also, for the sake of convenience in explaining the coil pitch Pw, FIG. 7 illustrates only a portion of the coil winding of the head spring 26, as shown in FIG. 8.

[0028] [2-1. LED head holder configuration] The LED head holder 16 is made by molding a mixed resin of polycarbonate and ABS, and is configured as a plate that is long and narrow in the left-right direction and thin in the front-to-back direction, and has posts (not shown) at both left and right ends into which the head spring 26 is fitted.

[0029] The LED head holder 16 hangs down while being supported so as to be able to swing freely relative to the printer cover 2C (Fig. 1) as the shafts provided at both left and right ends are rotatably supported in support holes in the printer cover 2C. The LED head holder 16 also suspends the LED head 24 by fitting the support protrusions of the LED head 24 into the support holes provided at both left and right ends.

[0030] [2-2. LED head configuration] As shown in a schematic cross-sectional view of the LED head 24 in Figure 8, the LED head 24 is formed as a rectangular parallelepiped elongated in the left-right direction as a whole, and is configured by attaching various components such as a substrate 52 and a lens array 54 to an LED head frame 50. Hereinafter, the downward direction in Figure 8 will also be referred to as the irradiation direction (biasing direction), and the upward direction will also be referred to as the counter-irradiation direction. Also, below, the left-right direction, which is the arrangement direction of the LED array 56, will also be referred to as the arrangement direction (longitudinal direction, main scanning direction), the front-rear direction intersecting with this left-right direction will be referred to as the sub-scanning direction, and the up-down direction, which is the optical axis direction of the lens array 54, will also be referred to as the optical axis direction.

[0031] The LED head frame 50 is fabricated by pressing, for example, a galvanized steel sheet. Its overall shape resembles a hollow rectangular prism with the side opposite the illumination direction removed, and the head frame internal space 50IS, which is an internal space extending in the left-right direction, forms a cross section resembling the capital letter "U." The LED head frame 50 is centered around a bottom portion 50B that is elongated in the left-right direction and thin in the up-down direction. Furthermore, the LED head frame 50 has two plate-like side portions 50W that are elongated in the left-right direction and thin in the front-to-back direction, extending parallel to each other from both front and rear edges of the bottom portion 50B and perpendicular to the bottom portion 50B. A head frame opening 50A is formed at the top end. A slit-shaped lens array hole 50H, elongated in the left-to-right direction and penetrating vertically, is drilled approximately in the center of the bottom portion 50B.

[0032] Furthermore, stopper holes 50WA are formed above the base plate 52 near both the left and right ends of the pair of front and rear side portions 50W, penetrating from the outside of the side portion 50W to the head frame internal space 50IS. These stopper holes 50WA are rectangular in front and rear views, and engage with a stopper 36 (described below) of the spring bearing 32. A first engagement surface 50S is formed in the upper linear portion of the stopper hole 50WA. The first engagement surface 50S is a flat surface facing downward and formed parallel to the second engagement surface 36S of the stopper 36 along the left-right direction. When the spring bearing is attached (FIG. 3), the first engagement surface 50S faces and abuts against the second engagement surface 36S of the stopper 36 in the up-down direction.

[0033] A lens array 54 is inserted into the lens array hole 50H and attached thereto. This allows the lens array 54 to be supported by the LED head frame 50. The lens array 54 is formed as a rectangular parallelepiped elongated in the left-right direction as a whole, and holds a large number of tiny lenses aligned in the left-right direction. These lenses have optical properties that converge the light emitted from the LED array 56, which will be described later. The lens array 54 is fixed to the LED head frame 50 so that the incident distance between the upper surface, which is the end face of the lens array 54 where the light is incident, and the lower surface, which is the surface of the LED array 56, is optimal for the characteristics of the lens array 54. The light emitted from the LED array 56 is converged by the lens array 54 and exposed onto the charged photosensitive drum 30 (FIG. 3), thereby forming an electrostatic latent image.

[0034] A substrate 52 is attached to the LED head frame 50 above the lens array 54, with its longitudinal direction aligned with the left-right direction. The substrate 52 is made of a so-called glass epoxy substrate and is formed as a plate that is elongated in the left-right direction and thin in the up-down direction, with multiple wiring layers with predetermined wiring patterns formed thereon stacked vertically. On the lower surface (the illumination direction side) of the substrate 52, an LED array 56 is mounted along the longitudinal direction of the substrate 52, approximately at the center in the front-to-back direction, facing the lens array 54. The LED array 56 has LED elements that emit light downward and are arranged at predetermined small intervals along the arrangement direction (the left-to-right direction). The length of the substrate 52 in the front-to-back direction is shorter than the distance between the side portions 50W of the LED head frame 50.

[0035] [2-3. Spring bearing configuration] [2-3-1. Overall structure of spring holder] Near both left and right ends on the upper side of the LED head frame 50, spring bearings 32 are detachably attached one on each side, laterally inward of both left and right ends of the substrate 52. As shown in Fig. 5, the spring bearings 32 are made by, for example, sheet metal pressing a thin metal plate of a predetermined thickness, such as stainless steel, and are rigid enough not to deform even when subjected to the biasing force of the head spring 26. As a whole, the spring bearings 32 have an internal space, a spring bearing internal space 32IS, and have a shape that resembles an upside-down capital letter "U" when viewed from the left and right.

[0036] When the LED unit is assembled (FIG. 2), the spring bearing 32 is urged downward, i.e., toward the photosensitive drum 30, by the head spring 26 disposed between the LED head holder 16 and the spring bearing 32, thereby urging the LED head 24 downward (urging direction). Furthermore, the spring bearing 32 abuts against the head spring 26 and the LED head frame 50, thereby establishing electrical continuity between the head spring 26 and the LED head frame 50. Furthermore, the LED head frame 50 is electrically connected to the LED head holder 16 due to the abutment between the head spring 26 and the LED head holder 16.

[0037] [2-3-2. Configuration of spring contact plate] The spring bearing 32 is centered around a spring contact plate 33 formed in the shape of a thin, generally square plate in the vertical direction. A flat spring contact surface 33S is formed on the upper side of the spring contact plate 33. A circular fitting hole 33A is drilled in the center of the spring contact plate 33 so as to penetrate therethrough in the vertical direction. A fitting portion 26F (described later) of the head spring 26 is loosely fitted into this fitting hole 33A.

[0038] [2-3-3. Arm board configuration] The spring bearing 32 has thin, approximately square, plate-like arm plates 35 extending downward from both front and rear sides of the spring abutment plate 33 so as to be approximately parallel to each other and perpendicular to the spring abutment plate 33, with spring bearing openings 32A formed at the lower ends. A spring bearing inner wall surface 35S, which is a flat surface extending in the vertical and horizontal directions, is formed on the surfaces of the pair of front and rear arm plates 35 facing the spring bearing internal space 32IS, i.e., on the rear surface of the front arm plate 35 and the front surface of the rear arm plate 35. The arm plate 35 is composed of an arm main body 35M and an arm tip portion 35T. Arm plate main body 35M is disposed in the upper portion of arm plate 35 and occupies most of arm plate 35, and its lower end is slightly inclined inward in the front-to-rear direction (toward spring bearing internal space 32IS) from both front and rear sides of spring abutment plate 33 in a direction perpendicular to spring abutment plate 33. Therefore, the distance between the pair of arm plate main bodies 35M at their lower ends in the front-to-rear direction is slightly narrower than the distance between their upper ends in the front-to-rear direction.

[0039] Arm plate tip 35T is inclined from the lower end of arm plate main body 35M so that its lower end faces outward in the front-to-back direction relative to arm plate main body 35M. Furthermore, because arm plate 35 is a thin metal plate, it can be deformed so that its lower end moves in the front-to-back direction, with the connection point with spring abutment plate 33 as a fulcrum, that is, it can bend relative to spring abutment plate 33 so as to widen or narrow the front-to-back width of spring receiving opening 32A.

[0040] The distance between the spring receiver inner wall surfaces 35S facing each other in the front-to-rear direction at the upper ends of the pair of arm body portions 35M is slightly wider than the LED head frame side width, which is the width in the front-to-rear direction from the front surface of the front side portion 50W of the LED head frame 50 to the rear surface of the rear side portion 50W. Furthermore, when the spring receiver 32 is detached from the LED head frame 50, the distance between the spring receiver inner wall surfaces 35S facing each other in the front-to-rear direction at the lower ends of the pair of arm body portions 35M is slightly narrower than the LED head frame side width.

[0041] [2-3-4. Configuration of the spring receiving throttle section] The spring bearing 32 has a cylindrical spring bearing throttle portion 37 extending downward (toward the spring bearing opening 32A) from an edge along the outer periphery of the fitting hole 33A in the spring abutment plate portion 33 so as to be perpendicular to the spring abutment plate portion 33. The lower end of the spring bearing throttle portion 37 is open.

[0042] [2-3-5. Tapered section configuration] Furthermore, a tapered portion 34, which is a flat surface that slopes downward toward the central axis of the fitting hole 33A relative to the spring abutment plate portion 33, is formed at the upper end of the spring receiver tapered portion 37. This tapered portion 34 is a portion that is formed during the manufacturing process of the spring receiver 32 when the spring receiver tapered portion 37 is pressed out from the upper side of the spring abutment plate portion 33 toward the spring receiver internal space 32IS.

[0043] [2-3-6. Stopper configuration] The spring bearing 32 has a stopper 36 protruding from approximately the center of the spring bearing inner wall surface 35S of the arm plate 35 toward the spring bearing internal space 32IS, i.e., from the spring bearing inner wall surface 35S of the front arm plate 35 toward the rear, and from the spring bearing inner wall surface 35S of the rear arm plate 35 toward the front. The stopper 36 as an engagement portion has an overall quarter-sphere shape and is formed at a location that fits into the stopper hole 50WA of the LED head frame 50 when the spring bearing is attached (FIG. 3). That is, the distance from the lower surface of the spring abutment plate 33 to the second engagement surface 36S is equal to the distance from the upper end surface of the LED head frame 50 to the first engagement surface 50S. The stopper 36 on the front arm plate 35 and the stopper 36 on the rear arm plate 35 are arranged as a pair so that their positions in the up-down and left-right directions are the same.

[0044] The stopper 36 is composed of a spherical portion 36B formed on its lower side (the side toward the irradiation direction) and a second engagement surface 36S formed on its upper side (the side opposite the irradiation direction). The spherical portion 36B as a protrusion has a quarter-sphere shape with an open upper side and an open outer side in the front-to-rear direction, and the connection point with the spring bearing inner wall surface 35S is semicircular with a diameter slightly shorter than the left-to-right length of the stopper hole 50WA in the LED head frame 50. The second engagement surface 36S is a flat surface facing upward and formed parallel to the spring abutment surface 33S at the upper end of the spherical portion 36B, and abuts against the first engagement surface 50S of the stopper hole 50WA in the up-down direction when the spring bearing is attached (FIG. 3). Specifically, in the spring bearing attached state (FIG. 3), the inner front-rear direction tip of the spherical portion 36B of the stopper 36 extends into the stopper hole 50WA of the LED head frame 50 toward the head frame internal space 50IS to a position approximately half the thickness of the side portion 50W. Furthermore, by making the stopper 36 shaped like a quarter sphere as a whole, both left and right ends of the lower side of the second engagement surface 36S can be connected to the arm plate portion 35. Therefore, the spring bearing 32 can hold the stopper 36 with the arm plate portion 35 and maintain its strength. This prevents the stopper 36 from being deformed when the second engagement surface 36S abuts against the first engagement surface 50S of the stopper hole 50WA and an upward force is applied.

[0045] This stopper 36 is formed in the manufacturing process of the spring receiver 32 by pushing out the arm plate portion 35 from the outer surface side in the front-rear direction of the arm plate portion 35 toward the spring receiver internal space 32IS side.

[0046] [2-3-7. Installation to LED head frame] The spring bearing 32 is moved in the mounting movement direction from the top to the bottom of the LED head 24, and is attached to the LED head frame 50 in a state in which the spring abutment plate portion 33 covers a portion of the head frame opening 50A of the LED head frame 50 in the left-right direction, and the arm plate portion 35 faces the outside of the side portion 50W of the LED head frame 50 in the front-to-back direction, thereby entering a spring bearing mounting state (Figure 3).

[0047] Here, when viewed from the left-right direction, the spherical portion 36B of the stopper 36 has a surface that curves inward in the front-rear direction and upward in the opposite direction to the mounting movement direction from a lower end, which is the mounting movement direction side when the spring bearing 32 is mounted to the LED head 24. That is, the portion of the stopper 36 that faces the outside of the side portion 50W of the LED head frame 50 in the front-rear direction is shaped so that the end on the opposite side to the mounting movement direction is closer to the side portion 50W in the front-rear direction than the end on the mounting movement direction side. In other words, the inner surface of the spherical portion 36B of the pair of stoppers 36 in the front-rear direction is inclined in a curved shape that curves inward in the front-rear direction from the mounting movement direction side toward the opposite side to the mounting movement direction. For this reason, when the spring receiver 32 is attached to the LED head frame 50, the vicinity of the lower end of the stopper 36 first abuts against the LED head frame 50, and as the spring receiver 32 further moves in the attachment movement direction toward the LED head frame 50, the spacing between the arm plate portions 35 in the front-to-rear direction widens, causing the inner ends of the spherical portions 36B in the left-to-right direction to abut against the outside of the side portions 50W of the LED head frame 50. This allows the stopper 36 to easily attach the spring receiver 32 to the LED head frame 50.

[0048] In the spring bearing attached state (FIG. 3), the lower end of the spring bearing 32 moves inward in the front-to-rear direction to narrow the front-to-rear width of the spring bearing opening 32A as the arm plate portion 35 attempts to return to its natural state, thereby sandwiching the side portion 50W of the LED head frame 50 from the outside. Furthermore, in the spring bearing attached state (FIG. 3), the stopper 36 of the spring bearing 32 enters through the stopper hole 50WA toward the head frame internal space 50IS, and the second engagement surface 36S abuts against the first engagement surface 50S of the stopper hole 50WA, thereby preventing the spring bearing 32 from moving upward away from the LED head 24 and falling off the LED head 24.

[0049] [2-4. Spring configuration] [2-4-1. Overall structure of the spring] As shown in Figures 4 and 8, the head spring 26 has a cylindrical shape that extends in the vertical direction (also called the coil extension direction) as a whole, and is formed by winding a single cylindrical coil winding into a coil shape, and is composed of a spring portion 26S and a fitting portion 26F.

[0050] [2-4-2. Spring configuration] The spring portion 26S is disposed in the upper portion of the head spring 26, occupies most of the head spring 26 in the coil extension direction, and functions as a compression coil spring.

[0051] [2-4-3. Configuration of fitting part] The fitting portion 26F is disposed below the spring portion 26S, coaxial with the spring portion 26S, and is formed by tightly wound coil windings. Therefore, the fitting portion 26F does not function as a spring. Therefore, the fitting portion 26F has a shorter coil pitch than the spring portion 26S. Furthermore, the fitting portion 26F has an outer diameter that is approximately half that of the spring portion 26S, making it smaller than the spring portion 26S. Because the fitting portion 26F is formed by tightly wound coil windings, the coil pitch Pw is the same as the winding diameter Dw.

[0052] [2-4-4. Installing the spring] When the LED unit is assembled (Figure 2), the head spring 26, which is a compression coil spring, is positioned between the spring holder 32 and the LED head holder 16 in a more compressed state than in its normal state, with the lower end of the spring portion 26S abutting against the spring abutment surface 33S of the spring abutment plate portion 33 of the spring holder 32 and the upper end abutting against a post (not shown) of the LED head holder 16.

[0053] Therefore, in the assembled state of the LED unit (FIG. 2), the spring bearing 32 is urged downward, i.e., in the direction toward the photosensitive drum 30, by the head spring 26 disposed between the LED head holder 16 and the spring bearing 32. As a result, the LED head 24 to which the spring bearing 32 is attached is also urged downward, i.e., in the direction toward the photosensitive drum 30, by the urging force of the head spring 26. Hereinafter, the downward direction in which the head spring 26 urges the spring bearing 32 and the LED head 24 will also be referred to as the urging direction.

[0054] Furthermore, in the assembled state of the LED unit (FIG. 2), fitting portion 26F of head spring 26 fits into fitting hole 33A of spring receiver 32, with its lower end positioned lower than the upper end of spring receiver narrowing portion 37. Therefore, in the assembled state of the LED unit, when head spring 26 moves in the front-rear, back-rear, left-right directions, spring receiver 32 causes the inner wall surface of spring receiver narrowing portion 37 to abut against the outer circumferential surface of fitting portion 26F of head spring 26, thereby restricting the front-rear, left-right movement of head spring 26 relative to LED head 24.

[0055] The outer diameter of the fitting portion 26F is shorter than the inner diameter of the spring receiver tapered portion 37. This allows the head spring 26 to have a certain degree of play with respect to the LED head 24 and the spring receiver 32. In other words, the head spring 26 is loosely fitted into the spring receiver 32.

[0056] The LED head 24 is positioned in the up-down direction, which is the direction in which it moves toward and away from the circumferential surface of the photosensitive drum 30, by abutting against the spacer 30S of the photosensitive drum 30. This keeps the relative position between the LED head 24 and the photosensitive drum 30 constant.

[0057] As described above, the LED head holder 16 suspends the LED head 24, and in the LED unit assembled state (FIG. 2), the head spring 26, which is a compression coil spring, is disposed between the spring receiver 32 and the LED head holder 16 in a state where it is more compressed than in its normal state. For this reason, when the LED head holder 16 is lifted when the printer cover 2C transitions from the cover closed state (FIG. 1) to the cover open state, although the LED head holder 16 and the LED head 24 are integrated, the head spring 26 extends and the LED head holder 16 lifts the LED head 24. For this reason, the head spring 26 expands and contracts as the LED head unit 14 moves up and down.

[0058] [2-5. Dimensional Relationships] 7, when the length in the vertical direction from the spring abutment surface 33S of the spring bearing 32 to the lower end surface of the spring bearing tapered portion 37 is defined as the spring bearing tapered height H, the relationship between the spring bearing tapered height H and the coil pitch Pw is set to "spring bearing tapered height H≧coil pitch Pw." In other words, the spring bearing tapered height H is set to be equal to or greater than the coil pitch Pw.

[0059] Furthermore, when the inner diameter of the spring receiving tapered portion 37 of the spring receiving 32 is defined as the spring receiving hole diameter D1, the outer diameter of the fitting portion 26F of the head spring 26 is defined as the fitting portion outer diameter D2, and the coil pitch of the fitting portion 26F of the head spring 26 is defined as the coil pitch Pw, the relationship between the spring receiving hole diameter D1 and the fitting portion outer diameter D2 is set to "spring receiving hole diameter D1 - fitting portion outer diameter D2 ≦ coil pitch Pw." In other words, the value obtained by subtracting the fitting portion outer diameter D2 from the spring receiving hole diameter D1 is set to be equal to or less than the winding diameter Dw.

[0060] Furthermore, when the diameter of the upper end of the tapered portion 34 in the spring seat 32, i.e., the diameter of the opening at the upper end of the spring seat throttle portion 37, is defined as the spring seat throttle opening diameter D3, and the inner diameter of the spring portion 26S in the head spring 26 is defined as the spring portion inner diameter D4, the relationship between the spring seat throttle opening diameter D3 and the spring portion inner diameter D4 is set to "spring seat throttle opening diameter D3 < spring portion inner diameter D4." In other words, the spring seat throttle opening diameter D3 is set to be smaller than the spring portion inner diameter D4.

[0061] [3. Actions and Effects] In the above configuration, color printer 1 is configured so that spring receiver tapered height H is set to be equal to or greater than coil pitch Pw. This prevents spring receiver tapered portion 37 from getting caught in the gap between the coil windings at fitting portion 26F of head spring 26. This prevents color printer 1 from lifting spring receiver 32 upward and away from LED head 24, causing it to fall off LED head 24, when spring receiver tapered portion 37 is caught in the gap between the coil windings at fitting portion 26F of head spring 26 and part of head spring 26 is caught on spring receiver 32 and the head spring 26 extends.

[0062] Furthermore, in color printer 1, the value obtained by subtracting fitting portion outer diameter D2 from spring receiving hole diameter D1 is set to be equal to or less than winding diameter Dw. Therefore, color printer 1 can prevent the lower end of spring receiving tapered portion 37 from getting caught in the gap between the coil windings at fitting portion 26F of head spring 26, even when LED head 24 swings. This prevents color printer 1 from lifting spring receiving portion 32 upward and away from LED head 24, causing it to fall off LED head 24, when spring receiving tapered portion 37 is caught in the gap between the coil windings at fitting portion 26F of head spring 26 and the head spring 26 expands with a portion of the head spring 26 caught on spring receiving portion 32.

[0063] Furthermore, in color printer 1, spring receiving throttle opening diameter D3 is set smaller than spring portion inner diameter D4, so that color printer 1 can stably receive the load of head spring 26 on spring contact surface 33S of spring contact plate portion 33.

[0064] Furthermore, in color printer 1, spring bearing 32 is configured to be detachable from LED head frame 50. Therefore, in the process of assembling LED head 24, color printer 1 allows substrate 52 to be fixed to LED head frame 50 from the head frame opening 50A side in a state where spring bearing 32 does not interfere with the movement path of substrate 52, and then spring bearing 32 is attached to LED head frame 50, thereby facilitating assembly of LED head 24. Furthermore, color printer 1 allows the longitudinal length of LED head 24 to be reduced compared to a case where spring bearing 32 is integrally molded with LED head frame 50 so that spring bearing 32 is positioned outward in the left-right direction from both left and right ends of substrate 52, so that spring bearing 32 does not interfere with the movement path of substrate 52 when substrate 52 is fixed to LED head frame 50 in the process of assembling LED head 24.

[0065] In the above configuration, the color printer 1 includes an image forming unit 12 having a photosensitive drum 30 as an image carrier, an LED head 24 that exposes the photosensitive drum 30, an LED head holder 16 that supports the LED head 24, a head spring 26 that biases the LED head 24 toward the image forming unit 12, and a spring retainer 32 that receives the bias of the head spring 26. The head spring 26 has a spring portion 26S that abuts against the spring retainer 32 and applies a biasing force, and a fitting portion 26F that has an outer diameter smaller than that of the spring portion 26S. The spring retainer 32 has a fitting hole 33A into which the fitting portion 26F is inserted and which has a spring retainer throttle portion 37 as a wall portion extending in the biasing direction of the head spring 26 from a spring abutment surface 33S as an abutment surface against which the spring portion 26S abuts, and the length extending in the biasing direction of the spring retainer throttle portion 37 is equal to or greater than the coil pitch Pw of the fitting portion 26F.

[0066] This makes it possible for the color printer 1 to prevent the spring receiver 32 from getting caught between the coil windings of the fitting portion 26F of the head spring 26.

[0067] 4. Other Embodiments In the above-described embodiment, the fitting portion 26F of the head spring 26 is formed by tightly winding the coil winding. However, the present invention is not limited to this. A gap may be formed between adjacent coil windings in the vertical direction in the fitting portion 26F. In this case, the coil pitch Pw is greater than the winding diameter Dw.

[0068] In the above embodiment, the stopper 36 is in the shape of a quarter sphere, but the present invention is not limited to this, and the stopper 36 may have various other shapes.

[0069] Furthermore, in the above-described embodiment, the stopper 36 is provided below the center in the vertical direction of the arm plate portion 35. However, the present invention is not limited to this, and the stopper 36 may be provided at any position in the vertical direction of the arm plate portion 35, or the lower end of the arm plate portion 35 may be folded inward in the front-to-rear direction to function as a stopper.

[0070] Furthermore, in the above-described embodiment, the case has been described in which, in the spring bearing attached state (FIG. 3), the inner front-rear direction tip of the spherical portion 36B of the stopper 36 is inserted into the stopper hole 50WA of the LED head frame 50 toward the head frame internal space 50IS to a position approximately half the thickness of the side portion 50W. The present invention is not limited to this, and, in the spring bearing attached state (FIG. 3), the inner front-rear direction tip of the spherical portion 36B of the stopper 36 may be inserted further into the head frame internal space 50IS than the side portion 50W of the LED head frame 50.

[0071] Furthermore, in the above-described embodiment, the case where one spring receiver 32 is fixed to each of the left and right ends of the LED head frame 50 has been described. However, the present invention is not limited to this, and any number of spring receivers 32, three or more, may be fixed to the LED head frame 50.

[0072] Furthermore, in the above-described embodiment, the spring bearing 32 is fabricated by sheet metal press working a thin metal plate such as stainless steel and attached to the LED head frame 50. However, the present invention is not limited to this, and the spring bearing 32 may be integrally molded with the LED head frame 50 using various other materials that are rigid enough not to deform even when subjected to the biasing force of the head spring 26. In this case, if the spring bearing 32 is positioned outside the left and right ends of the substrate 52 in the left-right direction, the spring bearing 32 will not interfere with the movement path of the substrate 52 when the substrate 52 is fixed to the LED head frame 50 from the head frame opening 50A side during the assembly process of the LED head 24.

[0073] Furthermore, in the above-described embodiment, the LED head frame 50 is made of a liquid crystal polymer resin. However, the present invention is not limited to this, and the LED head frame 50 may be made of a resin made of various other materials. Alternatively, the LED head frame 50 may be made by aluminum die casting, or by outsert molding resin onto sheet metal.

[0074] Furthermore, in the above-described embodiment, the LED head holder 16 is manufactured by molding a mixed resin of polycarbonate and ABS. However, the present invention is not limited to this, and the LED head holder 16 may be manufactured using resin made of various other materials.

[0075] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the LED head units 14 of each color that correspond to the image forming units 12 of each color that are arranged in series along the front-to-rear direction in a tandem color printer 1. However, the present invention is not limited to this, and may be applied to LED head units mounted in color printers of various other types, such as a four-cycle type.

[0076] Furthermore, in the above-described embodiment, four LED heads 24 corresponding to the colors yellow, magenta, cyan, and black are attached to the printer housing 2 of the color printer 1 that performs color printing. However, the present invention is not limited to this, and for example, three or fewer or five or more LED heads 24 may be attached to the printer housing 2 depending on the number of toner colors used in the color printer, or one LED head 24 may be attached to a monochrome printer that performs monochrome printing.

[0077] Furthermore, in the above-described embodiment, the present invention has been described as being applied to color printer 1. However, the present invention is not limited to this, and may be applied to devices that have an LED head 24 similar to color printer 1, such as facsimiles, MFPs (Multifunction Printers), copiers, and digital printing machines.

[0078] Furthermore, the present invention is not limited to the above-described embodiments and other embodiments. That is, the scope of application of the present invention also extends to embodiments in which the above-described embodiments are combined in part or in whole with any of the above-described other embodiments. Furthermore, the scope of application of the present invention also extends to cases in which part of the configuration described in any of the above-described embodiments and other embodiments is extracted and replaced or diverted with part of the configuration of any of the above-described embodiments and other embodiments, or where part of the extracted configuration is added to any of the above-described embodiments.

[0079] Furthermore, in the above-described embodiment, color printer 1 as an image forming apparatus is configured with image forming unit 12 as an image forming unit, LED head 24 as a head portion, LED head holder 16 as a head holding portion, head spring 26 as a spring member, and spring holder 32 as a receiving portion, and the spring member is configured with spring portion 26S as a first portion and fitting portion 26F as a second portion, and the receiving portion is configured with fitting hole 33A as an opening. The present invention is not limited to this, and an image forming apparatus may be configured with an image forming unit, head portion, head holding portion, spring member, and receiving portion having various other configurations, the spring member may be configured with a first portion and a second portion having various other configurations, and the receiving portion may be configured with an opening having various other configurations. [Industrial Applicability]

[0080] The present invention can be used in, for example, an LED head mounted on an electrophotographic printer. [Explanation of symbols]

[0081] 1...Color printer, 2...Printer housing, 2T...Ejection tray, 2C...Printer cover, 3...Paper storage cassette, 4...Transport unit, 5...Pickup roller, 6...Paper feed roller, 7...Separation roller, 8, 9...Pair of transport rollers, 10...Transfer belt, 12...Image forming unit, 13...Transfer roller, 14...LED head unit, 16...LED head holder, 18...Toner cartridge, 20...Fuser unit, 21...Pair of ejection rollers, 22...Duplex transport unit, 24...LED head, 26...Head spring, 26S...Spring portion, 26F...Fitting portion, 30...Photosensitive drum, 30S...Spacer, 32...Spring receiver, 32A...Spring receiver opening, 32IS...Spring receiver internal space, 33... ...spring abutment plate portion, 33S...spring abutment surface, 33A...engagement hole, 34...tapered portion, 35...arm plate portion, 35M...arm plate main body portion, 35T...arm plate tip portion, 35S...spring receiver inner wall surface, 36...stopper, 36B...spherical portion, 36S...second engagement surface, 37...spring receiver throttle portion, 50...LED head frame, 50IS...head frame internal space, 50B...bottom, 50W...side portion, 50A...head frame opening, 50H...lens array hole portion, 50WA...stopper hole portion, 50S...first engagement surface, 52...substrate, 54...lens array, 56...LED array, D1...spring receiver hole diameter, D2...engagement portion outer diameter, D3...spring receiver throttle opening diameter, D4...spring portion inner diameter, Dw...winding diameter, Pw...coil pitch.

Claims

1. an image forming unit having an image carrier; a head unit that exposes the image carrier; a head holding portion that supports the head portion; a spring member that biases the head portion toward the image forming unit; a receiving portion that receives the bias of the spring member; and The spring member a first portion that abuts against the receiving portion and applies a biasing force; a second portion having an outer diameter smaller than an outer diameter of the first portion; The receiving portion is an opening into which the second portion is inserted and which has a wall extending in the biasing direction of the spring member from a contact surface against which the first portion contacts; have The length of the wall portion extending in the biasing direction is equal to or greater than the coil pitch of the second portion. An image forming apparatus characterized by:

2. The value obtained by subtracting the outer diameter of the second portion from the inner diameter of the wall portion is equal to or less than the coil pitch of the second portion.

2. The image forming apparatus according to claim 1, wherein:

3. The diameter of the opening on the abutment surface side of the wall portion is less than the inner diameter of the first portion.

2. The image forming apparatus according to claim 1, wherein:

4. The receiving portion is detachable from the head portion.

2. The image forming apparatus according to claim 1, wherein:

5. The receiving portion has an engaging portion that engages with the head portion.

5. The image forming apparatus according to claim 4, wherein:

6. the head portion has a hole portion on a side surface thereof, the hole portion having a first engagement surface formed therein that engages with the engagement portion; The engaging portion has a second engaging surface that abuts against the first engaging surface.

6. The image forming apparatus according to claim 5, wherein:

7. The engaging portion is a protrusion that protrudes from the side surface toward the inside of the head portion and extends from the second engaging surface in a direction of attachment movement when the receiving portion is attached to the head portion.

7. The image forming apparatus according to claim 6, further comprising:

8. The end of the protrusion on the side opposite to the mounting movement direction is located more inside the head portion than the end on the mounting movement direction side.

8. The image forming apparatus according to claim 7, wherein:

9. The protrusion is quarter spherical in shape.

9. The image forming apparatus according to claim 8, wherein:

10. The head holding portion supports the head portion in a state in which the spring member is expandable and contractible, and moves toward and away from the image forming unit.

2. The image forming apparatus according to claim 1, wherein:

11. The receiving portions are provided near both longitudinal ends of the head portion, one on each side.

2. The image forming apparatus according to claim 1, wherein:

Images