Image forming device

An image forming device includes an image carrier, a charging unit, an exposing device, a developing device, a control device and a pair of position adjusting devices. Each of the position adjusting devices is respectively provided at a leading edge and a trailing edge of an output field of the laser light of the exposing device. The position adjusting devices move the exposing device in a direction intersecting with a plane including a rotational center line of the image carrier to adjust a scanning direction of the laser light to be parallel to the rotational center line of the image carrier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming device such as a copying machine, a printer, and a facsimile machine.

2. Description of the Related Art

A known electrophotographic image forming device uses, for example, a photoconductive drum as an image carrier. In such an image forming device, a surface of a charged photoconductive drum is exposed by a laser light, and an electrostatic latent image is formed. Toner adheres to the electrostatic latent image, and the electrostatic latent image is visualized. The visualized image is transferred onto paper, and an image is formed. There exists a demand for an improvement of an image quality in such an image forming device. Accompanying this demand, an improvement in the accuracy of an exposed position of the laser light with respect to the photoconductive drum has been important. However, if errors accumulate in component accuracy or in assembly of the photoconductive drum or an exposing device, which outputs the laser light, accuracy of the exposed position of the laser light with respect to the photoconductive drum decreases. As a result, defects, such as an inclination of an image with respect to a recording paper, are generated. Therefore, after mounting the exposing device, a mounted position of the exposing device is adjusted to improve the accuracy of the exposed position of the laser light with respect to the photoconductive drum.

According to a conventional method for adjusting a mounted position of an exposing device, for example, a fine adjustment is carried out by adding a shim for a position adjustment to the mounted position. When adjusting the mounted position by using the shim, after adding the shim and fixing the exposing device with a screw, it is necessary to check whether or not the accuracy of the position has improved. Therefore, when the accuracy of the position has not improved as expected, it is necessary to remove the fixed screw and replace with a shim having a different thickness and fix the screw again. Each time the shim is replaced, a troublesome operation must be performed because the screw must be removed and then fixed again.

As conventional methods other than the method using the shim for adjusting the position, for example, there are the following two methods. According to a first conventional method, a printer unit includes a Laser Scanning Unit (LSU) and a photoconductive drum, in this order from an upper portion of a frame, and two bar-shaped members are arranged parallel to a driving shaft core of the photoconductive drum and are spaced away from one another by an appropriate distance in a horizontal direction in an upper portion of the printer unit within the frame. The LSU, which is positioned by the bar-shaped members in the same manner, is also positioned highly accurately with respect to the photoconductive drum.

According to a second conventional method, an optical writing unit includes a laser light source and irradiates a light from the laser light source onto a surface of a photoconductive drum via a reflecting mirror. A unit frame including the laser light source and the reflecting mirror are held inside an image forming device such that the unit frame can be pivoted within a plane parallel to an axial line direction of the photoconductive drum. In addition, the rotation of the unit frame is controlled by a cam, which rotates by being driven by a motor, and an elastic member, which urges the unit frame against a cam surface.

According to the first conventional method, the LSU is positioned highly accurately with respect to the photoconductive drum. However, there are cases where after assembling the LSU, the position of the LSU is displaced due to a lack of component accuracy or an accumulated error of the frame itself on which the LSU is mounted or other parts, or the position of the LSU is displaced as a result of a change over time of the frame or the like, or due to vibration. In these cases, since the first conventional method does not provide a mechanism for adjusting the position after the assembling, an exposing position of the LSU cannot be adjusted easily when the accuracy of the exposing position of the LSU has decreased. According to the second conventional method, since the position of the optical unit is adjusted by using the cam, the entire unit is configured to rotate. As a result, it is difficult to make a fine adjustment, and after making an adjustment, the entire unit is prone to move, making the accuracy unstable.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide an image forming device wherein a mounted position of the exposing unit can be adjusted easily and accuracy of an exposed position of the laser light can be stabilized even after an exposing unit, which scans a laser light and forms an electrostatic latent image, is mounted.

According to a preferred embodiment of the present invention, an image forming device includes an image carrier, a charging unit, an exposing unit, a developing unit, a control unit, and a pair of position adjusters. The charging unit charges a surface of the image carrier. The exposing unit scans a laser light on the charged surface of the image carrier and forms an electrostatic latent image. The developing unit adheres toner onto the electrostatic latent image formed on the surface of the image carrier to visualize the electrostatic latent image. The control unit controls a rotation of the image carrier and controls each of the above-mentioned units for forming an image onto paper. In the image forming device, each of the position adjusters is respectively provided at a leading edge and a trailing edge of an output field of the laser light output by the exposing unit. The position adjusters move the exposing unit in a direction intersecting with a plane including a rotational center line of the image carrier. Accordingly, the position adjusters adjust a scanning direction of the laser light to be parallel or substantially parallel to the rotational center line of the image carrier.

According to the above-described preferred embodiment, each of the position adjusters is provided respectively at the leading edge and the trailing edge of the output field of the laser light of the exposing unit. Therefore, an adjustment of the movement of the exposing unit in the direction intersecting with the plane including the rotational center line of the image carrier can be carried out easily and accurately. That is, when the output field of the laser light output from the exposing unit is inclined with respect to the plane including the rotational center line of the image carrier, by adjusting the position adjuster at the leading edge and the position adjuster at the trailing edge in opposite directions from one another, the inclination can be adjusted easily within a short period of time. As a result, an adjustment operation can be carried out efficiently. Moreover, since the adjustment operation is carried out while moving both of the position adjusters simultaneously, the position can be adjusted accurately.

According to a preferred embodiment of the present invention, each of the position adjusters preferably includes a cam member and a position adjusting member. The cam member is mounted rotatably on a main body frame. The position adjusting member is mounted on the exposing unit and includes a hole where the cam member is loosely inserted. Accompanying the rotation of the cam member, both the position adjusting member and the exposing unit move.

According to the above-described preferred embodiment, each of the position adjusters includes the cam member, which is mounted rotatably on the main body frame, and the position adjusting member, which is mounted on the exposing unit and includes a hole where the cam member is loosely inserted. Therefore, a position adjustment can be carried out continuously by rotating the cam member. As a result, a highly accurate position adjustment can be carried out easily and reliably.

According to another preferred embodiment of the present invention, an image forming device includes an image carrier, a charging unit, an exposing unit, a developing unit, a control unit, a supporting body, and a pair of position adjusters. The charging unit charges a surface of the image carrier. The exposing unit scans a laser light on the charged surface of the image carrier and forms an electrostatic latent image. The developing unit adheres toner to the electrostatic latent image formed on the surface of the image carrier and visualizes the electrostatic latent image. The control unit controls a rotation of the image carrier, and controls each of the above-mentioned units for forming an image onto paper. The exposing unit is placed and fixed on the supporting body. Each of the position adjusters is respectively provided on a main body frame at a leading edge and a trailing edge of an output field of the laser light of the exposing unit. Each of the position adjusters includes an urging member and a cam member. A portion of the supporting body is urged against a cam surface of the cam member by the urging member of the position adjuster. Accompanying a rotation of the cam member, the exposing unit moves in a direction intersecting with a plane including the rotational center line of the image carrier. Accordingly, a position adjustment of the supporting body is carried out so that a scanning direction of the laser light becomes parallel or substantially parallel to the rotational center line of the image carrier. Further, the position adjustment of the supporting body is preferably carried out by the position adjusters in a state in which the supporting body is held on the main body frame such that the supporting body can be pivoted.

According to the above-described preferred embodiment, each of the position adjusters is respectively provided at the leading edge and the trailing edge of the output field of the laser light of the exposing unit. Therefore, the adjustment of the movement of the exposing unit in the direction intersecting with the plane including the rotational center line of the image carrier can be carried out easily and accurately. That is, when the output field of the laser light output from the exposing unit is inclined with respect to the plane including the rotational center line of the image carrier, the inclination can be adjusted easily within a short period of time by adjusting the position adjuster at the leading edge and the position adjuster at the trailing edge in opposite directions from one another. As a result, an adjusting operation can be carried out efficiently. In addition, since the adjustment operation is carried out while operating both of the position adjusters simultaneously, the position can be adjusted accurately.

Each of the position adjusters preferably includes an urging member and a cam member, which are provided on the main body frame supporting the supporting body. A portion of the supporting body is urged against a cam surface of the cam member by the urging member. Therefore, a fine adjustment can be carried out by a movement of the cam member. Since the supporting body is sandwiched between the cam surface and the urging member, the supporting body is held in a stable state. In particular, when one of the position adjusters is moved, the supporting body is prevented from moving unexpectedly by the other position adjuster, and the adjustment operation can be carried out in a stable state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below. Further, the preferred embodiments to be described below are only preferred specific examples for implementing the present invention. Therefore, there are various technical limitations in the following description. However, unless explicitly stated in the following description, the present invention shall not be limited to the preferred embodiments described herein.

FIG. 1is a schematic cross-sectional view of the entire image forming device according to a preferred embodiment of the present invention. A paper discharge tray10is arranged in an upper portion of an image forming device1. A printer unit2and a paper feed unit3are arranged in a lower portion of the image forming device1.

A paper feed cassette11is provided in the paper feed unit3. A plurality of sheets of paper of a prescribed size is stacked on a flapper12. A pickup roller13is disposed at a right end portion of the paper feed cassette11. The flapper12is urged upward by a spring member (not shown). Accordingly, an upper surface of the stacked papers makes contact with the pickup roller13. When the pickup roller13is driven and rotates in this state, the paper is transported one sheet at a time into a paper transportation path by a frictional force.

The fed paper is transported to the printer unit2by a feed roller14and a press roller15. The printer unit2includes a developing unit16, a cleaning mechanism17, a corona charger18, a photoconductive drum19, a transfer roller20, an exposing head21, and a fixing roller22for printing onto the transported paper. The cleaning mechanism17includes a cleaning roller. The cleaning roller traps a foreign substance, such as remaining toner and paper dust, adhered on a surface of the photoconductive drum19after a transfer process and cleans the surface of the photoconductive drum19. The corona charger18includes a discharge wire. The surface of the photoconductive drum19is charged uniformly by corona discharge from the discharge wire. The exposing head21exposes the uniformly charged photoconductive drum19according to an image printing signal and an electrostatic latent image is formed. Toner in the developing unit16transfers onto the electrostatic latent image formed on the photoconductive drum19. Accordingly, the electrostatic latent image is visualized as a toner image. The transfer roller20is disposed at a position facing the photoconductive drum19across the paper. When a prescribed voltage is applied to the transfer roller20, the toner image formed on the surface of the photoconductive drum19is transferred onto the paper. The transferred toner image is fixed onto the paper by being sandwiched, heated, and pressed by the fixing roller22and a press roller23. The paper on which the toner image is fixed is sandwiched between a paper discharge roller24and a press roller25and transported out onto the paper discharge tray10.

A manual paper feeding mechanism and a reversal transportation mechanism are provided at a side of a device main body. A manual paper feeding operation is carried out by opening a side cover26and inserting paper to a paper feed roller27. A printing operation is carried out onto the inserted paper while the inserted paper is being transported by the paper feed roller27to the feed roller14and the press roller15. When carrying out a reversal transportation, the paper on which an image is printed on one side is sandwiched between the paper discharge roller24and the press roller25and partially transported out. Then, the paper discharge roller24rotates in a reverse direction, and the paper is transported into a reversal transportation path. Two pairs of transportation rollers, i.e. a feed roller28and a press roller29, and a feed roller30and a press roller31, transport the paper downward. The feed roller14and the press roller15transport the paper again and a printing operation is carried out onto another side of the paper. Accordingly, an image is printed onto both sides of the paper.

Next, referring toFIG. 2throughFIG. 9, a description will be made of one of the unique features of the image forming device according to a first preferred embodiment of the present invention.FIG. 2is a perspective view illustrating where the exposing head21is mounted. Optical components, such as a laser light source, a polygon mirror and a plurality of lenses, are unitized and provided in the exposing head21. The exposing head21is fixed at mounting holes of a mounting bracket33that is preferably formed from a metal plate. A plurality, e.g., three, fixing portions34are arranged to protrude horizontally from side surfaces of the exposing head21. The fixing portions34are fixed by a screw, a pin, or other suitable fixing element at a periphery of the mounting holes of the mounting bracket33.

A fixing portion36and a locking portion47are arranged on both sides of the mounting bracket33, respectively. The fixing portion36is bent substantially perpendicularly from both sides of the mounting bracket33. The locking portion47protrudes horizontally from both sides of the mounting bracket33. Two screw holes36aand36bare arranged on each of the fixing portions36at a prescribed interval between one another in a horizontal direction. One of the screw holes36ais arranged at a position that is spaced away from the photoconductive drum19. The other screw hole36bis arranged at a position located closer to the photoconductive drum19. The mounting bracket33is mounted onto side frames (not shown) by a holding screw screwed into the screw hole36a, to be described later, such that the mounting bracket33can be pivoted. The mounting bracket33is fixed onto the side frames by a fixing screw screwed into the screw hole36b.

Since the locking portions47preferably have a substantially flat rectangular shape, for example, the locking portions47can be fit into locking holes (not shown) arranged on the side frames of a main body frame. The locking holes arranged on the side frames are preferably larger than the locking portions47to enable a vertical movement of the locking portions47.

A procedure for mounting the mounting bracket33onto the side frames includes, first, fitting the locking portions47into the locking holes of the side frames and screwing the holding screws into the screw holes36a. Accordingly, the mounting bracket33is held temporarily on the side frames. In this state, the mounting bracket33can be pivoted around the screw holes36a. Therefore, an inclined position of the exposing head21can be adjusted easily by position adjusters37, described later. After the adjustment of the inclined position of the exposing head21by the position adjusters37has been completed, the mounting bracket33is fixed completely on the side frames by screwing the fixing screws into the screw holes36b.

A base frame35, which is a part of the main body frame, is disposed above a side of the exposing head21located closer to the photoconductive drum19. The base frame35is preferably formed from a metal plate in the shape of a cross-section of the letter-L. The base frame35is fixed on the side frames (not shown). A vertical portion of the base frame35is disposed substantially parallel to a side surface of the mounting bracket33located closest to the photoconductive drum19. A horizontal portion of the base frame35protrudes above an output field of the laser light from the exposing head21and towards the photoconductive drum19.

A light path of the laser light output from the exposing head21sequentially moves within the output field from a leading edge Ls to a trailing edge Le. Accordingly, the laser light is irradiated along a scanning line S on the surface of the photoconductive drum19.FIG. 3is a view illustrating a relationship between a rotational center line P of a rotational shaft of the photoconductive drum19and the scanning line S. To form an electrostatic latent image accurately on the surface of the photoconductive drum19, the rotational center line P and the scanning line S are required to be parallel or to coincide with one another. As illustrated inFIG. 3, when the scanning line S is inclined by an angle θ with respect to the rotational center line P, an electrostatic latent image is also inclined on the surface of the photoconductive drum19. To adjust such an inclination, each of the position adjusters37is provided respectively at the leading edge Ls and the trailing edge Le.

Each of the position adjusters37preferably includes a position adjusting plate38and a cam member39. A lower portion of the position adjusting plate38is fixed on the mounting bracket33. The cam member39is loosely inserted in a hole arranged through an upper portion of the position adjusting plate38. The cam member39is mounted rotatably on the base frame35.

FIG. 4is an enlarged cross-sectional view of the position adjuster37at the trailing edge Le taken along lines A-A ofFIG. 2, viewed from a direction of arrows when cut at a vertical plane.FIG. 5is an enlarged view of the position adjuster37at the trailing edge Le viewed from a side of the photoconductive drum19inFIG. 2. InFIG. 5, the base frame35is illustrated by dashed lines so that a structure of the position adjuster37can be understood more easily.

The position adjusting plate38includes a substantially rectangular plate shaped member. A semicircular guide portion46extends from an upper portion of the plate shaped member. Both sides of the position adjusting plate38are bent in the shape of a cross-section of the letter-L and function as reinforcement portions45. A positioning hole40is arranged as a long and thin slit through a lower portion of the position adjusting plate38. A protrusion41provided on the mounting bracket33is inserted into the positioning hole40, and the position adjusting plate38is attached to the mounting bracket33. A screw hole is arranged below the positioning hole40. By inserting a screw42into the screw hole, the position adjusting plate38is fixed onto a side plate of the mounting bracket33arranged at a side of the photoconductive drum19. An oblong guide hole43is provided in the guide portion46arranged on the upper portion of the position adjusting plate38.

The cam member39includes a knob portion39a, a cam portion39b, an inserting portion39c, and an operation portion39d. The knob portion39ais preferably substantially cylindrical. The substantially cylindrical cam portion39bprotrudes from a reverse side of the knob portion39aand eccentrically from a center of the knob portion39a. The substantially cylindrical inserting portion39cprotrudes from the cam portion39b. A center of the inserting portion39cis provided at the same position as the center of the knob portion39a. The operation portion39dis fixed on an edge of the knob portion39aand disposed about a center of the knob portion39a. A mounting hole44is arranged in a vertical portion of the base frame35. The inserting portion39cis inserted into the mounting hole44from the side of the exposing head21. Accordingly, the cam member39is mounted rotatably within the mounting hole44. In this case, the cam portion39bfits loosely in the guide hole43of the position adjusting plate38, and a semicircular outer circumference of the guide portion46makes contact with the operation portion39d. Therefore, when the operation portion39dis rotated along the outer circumference of the guide portion46, the entire cam member39rotates. However, since the cam portion39bis eccentrically arranged with respect to the knob portion39aand the inserting portion39c, a contact portion of the cam portion39band the guide hole43moves vertically accompanying the rotation of the cam member39.

InFIG. 5, the contact portion of the cam portion39band the guide hole43is at a highest position. By rotating the operation portion39dclockwise, the position of the contact portion gradually descends as illustrated inFIG. 6. Then, as illustrated inFIG. 7, when the operation portion39dis rotated clockwise to its limit, the position of the contact portion is at a lowest position. Therefore, by rotating the operation portion39d, the position adjusting plate38continuously moves vertically, and the vertical position of the mounting bracket33on which the position adjusting plate38is fixed can be adjusted.

When adjusting the vertical position of the mounting bracket33by using the pair of the position adjusters37, in a state in which the scanning line S is inclined as illustrated inFIG. 3, the scanning line can be easily adjusted to be parallel to the rotational center line according to the following procedure. For example, first, the operation portion39dof the leading edge Ls is adjusted and the position adjusting plate38at the leading edge Ls is lowered. Then, the operation portion39dof the trailing edge Le is adjusted and the position adjusting plate38at the trailing edge Le is elevated. As a result, the position adjusting plate38is provided in a state as illustrated with dotted lines inFIG. 8. Since the position adjusting plate38continuously moves vertically accompanying the rotation of the operation portion39d, a fine adjustment can be carried out. In addition, each of the position adjusters is disposed at the leading edge and the trailing edge of the output field of the laser light, respectively. Therefore, compared with a case where only one adjuster is provided, by simultaneously adjusting both of the position adjusters, an adjustment operation can be carried out easily and reliably.

FIG. 9is an enlarged cross-sectional view at a plane passing through the screw holes36aand36bin a state in which the fixing portion36of the mounting bracket33is fixed on a side frame50. A holding screw51is inserted through a mounting hole52arranged through the side frame50, and screwed in the screw hole36a. A diameter of the mounting hole52is larger than a diameter of the screw hole36a. A fitting portion53of the holding screw51fits in the mounting hole52. A screw portion54extends from the fitting portion53is screwed in the screw hole36a. Therefore, the fixing portion36is not fixed on the mounting hole52, and is capable of rotating about the mounting hole52.

Meanwhile, a fixing screw55is inserted through a mounting hole56arranged through the side frame50, and screwed in the screw hole36b. The fixing screw55is screwed together with both the mounting hole56and the screw hole36b. The fixing portion36is, thus, fixed on the side frame50.

The mounting bracket33is temporarily held on the side frame50by the holding screw51in a state in which the mounting bracket33can be pivoted. After adjusting the inclined position by the position adjusters37, the mounting bracket33is fixed completely on the side frame50by the fixing screw55. Accordingly, the position of the mounting bracket33can be maintained stably in an adjusted state.

Next, with reference toFIG. 10throughFIG. 18, a description will be made of another unique feature of an image forming device according to a second preferred embodiment of the present invention.FIG. 10is a perspective view illustrating a mounted portion of the exposing head21according to the second preferred embodiment of the present invention. To facilitate comprehension of the drawing, side frames137are omitted in FIG.10(an outline of the side frames137is indicated by dashed lines). Optical components, such as a laser light source, a polygon mirror and a plurality of lenses, are unitized and provided in the exposing head21. The exposing head21is fixed at mounting holes of a mounting bracket133. Three fixing portions34are arranged to protrude horizontally from a side surface of the exposing head21. The fixing portions134are fixed by a screw, a pin, or other suitable fixing element at a periphery of the mounting holes of the mounting bracket33.

A fixing portion135and a locking portion136are arranged on both sides of the mounting bracket133, respectively. The fixing portion135is bent perpendicularly from both sides of the mounting bracket133. The locking portion136protrudes horizontally from both sides of the mounting bracket133. Two screw holes135aand135bare arranged on each of the fixing portions135at a prescribed interval between one another in a horizontal direction. One of the screw holes135ais arranged at a position located away from the photoconductive drum19. The other screw hole135bis arranged at a position located closer to the photoconductive drum19. The mounting bracket133is mounted onto the side frames137by a holding screw screwed into the screw hole135a, to be described later, such that the mounting bracket133can be pivoted. The mounting bracket133is fixed onto the side frames137by a fixing screw screwed into the screw hole135b.

The locking portions136preferably have a substantially flat rectangular shape, for example. The locking portions136can be fit into locking holes138arranged on the side frames137(illustrated with dashed lines) of a main body frame. The locking portions136can be moved vertically by being held by a pair of position adjusters139provided on the side frames137. The locking holes138on the side frames137are arranged as elongated holes so that the locking portions136can move towards the photoconductive drum19. Accordingly, an interval between the exposing head21and the photoconductive drum19can be adjusted.

When mounting the mounting bracket133onto the side frames137, first, the locking portions136are fit into the locking holes138of the side frames137, and the interval between the exposing head21and the photoconductive drum19is adjusted. Then, the holding screws are screwed into the screw holes135a. Accordingly, the mounting bracket133is held temporarily onto the side frames137. In this state, the mounting bracket133can be pivoted around the screw holes135a. As to be described later, by vertically moving the locking portions136by the position adjusters139, an inclined position of the exposing head21can be easily adjusted. Then, after the adjustment of the inclined position of the exposing head21by the position adjusters139has been completed, the mounting bracket133is fixed completely on the side frames137by screwing the fixing screws into the screw holes135b.

A base frame140, which is a part of the main body frame, is disposed above a side of the exposing head21located closer to the photoconductive drum19. The base frame140is preferably a metal plate arranged in the shape of a cross-section of the letter-L. The base frame140is fixed between the side frames137. A vertical portion of the base frame140is disposed substantially parallel to a side surface of the bracket133located closest to the photoconductive drum19. A horizontal portion of the base frame140protrudes above an output field of the laser light from the exposing head21and towards the photoconductive drum19.

A light path of the laser light output from the exposing head21sequentially moves within the output field from a leading edge Ls to a trailing edge Le. Accordingly, the laser light is irradiated along a scanning line S on the surface of the photoconductive drum19.FIG. 11illustrates a relationship between a rotational center line P of a rotational shaft of the photoconductive drum19and the scanning line S. To form an electrostatic latent image accurately on the surface of the photoconductive drum19, the rotational center line P and the scanning line S are required to be parallel or to coincide with one another. As illustrated inFIG. 11, when the scanning line S is inclined at an angle θ with respect to the rotational center line P, an electrostatic latent image is also inclined on the surface of the photoconductive drum19. To adjust such an inclination, each of the position adjusters139is provided respectively at the leading edge Ls and the trailing edge Le.

FIG. 12is a cross-sectional view taken along lines A-A ofFIG. 10, and is across-sectional view of a portion of the position adjuster139at the trailing edge Le cut at a vertical plane.FIG. 13is a view of the position adjuster139viewed from an outer side of the side frame137. Further, since the position adjuster139at the leading edge Ls also has the same structure, a description thereof will be omitted.

The position adjuster139includes a knob member141, a cam member142and an urging member143. The substantially cylindrical knob member141has an end surface144as a bottom surface. The end surface144makes contact with the side frame137. An opposite end surface of the end surface144is open. A shaft supporting portion145protrudes inwards from a center of the end surface144. A shaft hole146is arranged in the shaft supporting portion145. The shaft hole146penetrates from the end surface144and along the shaft supporting portion of the knob member141.

The cam member142has a bar-shaped shaft portion148. The shaft portion148protrudes from a bottom surface of the cam member142at a position that is spaced from a center of a cylindrical portion of the cam member142. A cam surface147is arranged on an outer circumference of the cylindrical portion. The center of the shaft portion148is parallel or substantially parallel to the center of the cylindrical portion. The shaft portion148is inserted into a mounting hole149arranged in the side frame137, and into the shaft hole146of the knob member141. An inner diameter of the mounting hole149is approximately the same size as an outer diameter of the shaft portion148to prevent jouncing. The shaft portion148preferably has a substantially D-shaped cross section and an inner surface of the shaft hole146also has a substantially D-shaped cross section. Therefore, in a state in which the shaft portion148is inserted in the shaft hole146, the knob member141and the cam member142are integrally rotatable.

When the shaft portion148is inserted into the shaft hole146, a tip end portion of the shaft portion148protrudes from the shaft supporting portion145. A coil spring150and a washer151are provided on the protruding portion and attached immovably by a screw152.FIG. 14is an exploded perspective view of the knob member141and the cam member142. A tip end of the screwed shaft portion148is urged against a tip end of the shaft supporting portion145via the coil spring150. Therefore, the knob member141and the cam member142are biased to the side frame137, and a bottom surface of the knob member141and a bottom surface of the cam member142make contact with the side frame137. As illustrated inFIG. 14, a plurality of positioning holes153are arranged on the surface of the side frame137facing the knob member141with a prescribed angle displaced between each of the positioning holes153. A pair of positioning protrusions154protrudes from the bottom surface of the knob member141. The positioning protrusions154fit into the positioning holes153, and the knob member141is thus positioned.

When rotating the knob member141and changing a position of the knob member141, as illustrated inFIG. 15, the knob member141is pulled in a direction to be separated from the side frame137against the urging force of the coil spring150, and the positioning protrusions154are separated from the positioning holes153. Then, in a state in which the positioning protrusions154and the positioning holes153are separated from one another, by rotating the knob member141for a prescribed angle, the knob member141can be returned to an original state.

A bottom surface of the locking portion136of the mounting bracket133is placed on an upper portion of the cam surface147of the cam member142. The urging member143having a coil spring is urged against an upper surface of the locking portion136. The upper portion of the urging member143is fit in a locking protrusion155arranged on an upper portion of the locking hole138of the side frame137. A lower portion of the urging member143is urged against the upper surface of the locking portion136at all times. Therefore, the locking portion136is sandwiched between the cam surface147of the cam member142and the urging member143at all times.

FIG. 16illustrates a state in which the knob member141is rotated by a prescribed angle from the state illustrated inFIG. 13. Accompanying the rotation of the knob member141, the cam member142also rotates integrally. However, since the shaft portion148is arranged eccentrically with respect to the substantially cylindrical portion of the cam member142, a portion of the cam surface147making contact with the locking portion136moves vertically. InFIG. 13, the locking portion136of the mounting bracket133makes contact with a bottom portion of the locking hole138of the side frame137. However, inFIG. 16, the locking portion136is pushed upward by the cam member142against the urging force of the urging member143. Thus, the position adjustment of the locking portion136is carried out by rotating the knob member141as described above.

The locking portion136is sandwiched between the cam surface147of the cam member142and the urging member143at all times. Therefore, the locking portion136is reliably maintained in a desired position and is stable throughout operation. The positioning protrusions154of the knob member141fit into the positioning holes153of the side frames137and are maintained at a prescribed position. When adjusting the vertical position of the mounting bracket133by using the pair of the position adjusters139, for example, in a state in which the scanning line S is inclined as illustrated inFIG. 11, the scanning line can be easily adjusted to be parallel to the rotational center line according to the following procedure. For example, first, the knob member141of the leading edge Ls is adjusted and the cam member142of the leading edge Ls is lowered. Then, the knob member141of the trailing edge Le is adjusted and the cam member142of the trailing edge Le is elevated. As a result, the cam member142is provided in a state as illustrated with dotted lines inFIG. 17. Moreover, each of the position adjusters139is disposed at the leading edge and the trailing edge of the output field of the laser light, respectively. Therefore, compared with a case where only one adjuster is provided, by simultaneously adjusting both of the position adjusters, the adjustment operation can be carried out easily and reliably.

FIG. 18is an enlarged cross-sectional view at a plane passing through both the screw holes135aand135bin a state in which the fixing portion135of the mounting bracket133is fixed on the side frame137. A holding screw160is inserted through a mounting hole161arranged through the side frame137, and screwed into the screw hole135a. A diameter of the mounting hole161is larger than a diameter of the screw hole135a. A fitting portion162of the holding screw160fits in the mounting hole161. A screw portion163fixed on the fitting portion162is screwed in the screw hole135a. Therefore, the fixing portion135is not fixed on the mounting hole161, and is capable of rotating.

Meanwhile, a fixing screw164is inserted through the mounting hole165arranged through the side frame137, and screwed in the screw hole135b. The fixing screw164is screwed together with both the mounting hole165and the screw hole135b. The fixing portion135is thus fixed on the side frame137.

The mounting bracket133is temporarily held on the side frame137by the holding screw160in a state in which the mounting bracket133can be pivoted. Then, as described above, after adjusting the inclined position by the position adjusters139, the mounting bracket133is fixed completely on the side frame137by the fixing screw164. Accordingly, the position of the mounting bracket133can be reliably maintained in an adjusted state.