EP1293848B1

EP1293848B1 - Image forming device

Info

Publication number: EP1293848B1
Application number: EP02020654.6A
Authority: EP
Inventors: Yasushi Okabe
Original assignee: Brother Industries Ltd
Current assignee: Brother Industries Ltd
Priority date: 2001-09-13
Filing date: 2002-09-13
Publication date: 2019-11-06
Anticipated expiration: 2022-09-13
Also published as: CN2627544Y; CN100451857C; CN1428666A; EP1293848A3; EP1293848A2; HK1055803A1

Description

The present invention relates to an electrophotographic image forming device, such as a laser beam printer, a copying machine, or a facsimile device. More particularly, the invention relates to a process unit detachably loaded into the image forming device and a structure of the image forming device for receiving and accommodating the process unit.
Conventional image forming devices, such as a laser beam printer, uses a process unit. The process unit is, for example, a combined unit of a photosensitive unit and a developing unit. The photosensitive unit includes a photosensitive drum and a charger. The developing unit includes a developing roller and a toner cartridge containing developing agent (toner) therein.
During the printing operation, the developing roller is urged against the photosensitive drum, so that the developing roller transfers toner onto the photosensitive drum. Also, the transfer roller is urged against the photosensitive drum.
For the sake of maintenance and for facilitating paper jam resolving job, the process unit is detachably mounted on the image forming device. That is, the process unit is unloaded from and loaded into the image forming device when paper jam occurs, for example.
U.S. Patent No. 6,101,350 proposes horizontally loading the process unit. The horizontally loading type requires a locking mechanism to prevent the loaded process unit from being accidentally detached. To withstand strong detaching force to be imparted upon the process unit, a rigid locking mechanism is needed. However, the image forming device cannot be structurally simplified and made compact in size and also the cost of the image forming device cannot be lowered if the rigid locking mechanism is employed.
US 5,353,100 A discloses a generic image forming device according to the preamble of claim 1. Other image forming devices are known from EP 1 031 894 A1 and EP 0 708 387 A2 .
The present invention has been made to solve the aforementioned problems, and accordingly it is the object of the invention to provide an image forming device in which a process unit can be easily loaded into the image forming unit and the process unit thus loaded cannot be easily detached, wherein the image forming device has a simple structure for receiving the process unit and urging a developing roller against a photosensitive drum once the process unit is received and accommodated in a process unit accommodating section.
This object is achieved by the image forming device having the features of claim 1. The invention is further developed as defined in the dependent claims.
With the image forming device thus constructed, the process unit can be easily accommodated in the process unit accommodating section. This can be done by engaging the protrusions with the first guide and placing the process unit on the second guide. When the protrusions formed in the process unit are brought into abutment with the terminals, the trailing end of the process unit is automatically rotated downward due to its own weight and accommodated into the accommodating section. Also, the process unit can be easily unloaded from image forming device by lifting the trailing end of the process unit, placing it on the second guide, and moving up along the second guide.
A posture maintaining member may be formed on the process unit for maintaining a posture of the process unit when accommodated in the process unit accommodating section.
Preferably, the first guide is in the form of an elongated U-shaped groove into which the protrusion is inserted, and the second guide is in the form of a rail having an upper flat surface on which the process unit
slidably moves.
A locking means may further be provided for locking the process unit to the housing. It is desirable that the locking means be provided in the process unit accommodating section. The locking means may be constructed to resiliently engage the trailing end of the process unit.
The process unit includes a photosensitive unit and a developing unit. The developing unit is detachably mounted on the photosensitive unit. The photosensitive unit includes a photosensitive drum, and the developing unit includes a developing roller. The protrusions are provided to the photosensitive unit. The rotational shaft of the photosensitive drum may be provided to project from the photosensitive unit. In such a case, the projected portions of the rotational shaft may be used as the protrusions.
A latching means may be further provided for latching the process unit to the process unit accommodating section.
The process unit includes a photosensitive drum and developing roller. It is desirable that the process unit is accommodated in the process unit accommodating section while being urged toward a predetermined direction to urge the developing roller against the photosensitive drum
The process unit may be formed with auxiliary guide members for determining a loading direction and unloading direction of the process unit when loading into and unloading from the housing.
It is desirable that the developing unit have a bottom surface on which a first posture maintaining member is formed for maintaining a posture of the developing unit when mounted on the photosensitive unit and that the photosensitive unit have a bottom surface on which a second posture maintaining member is formed for maintaining a posture of the photosensitive unit when accommodated in the process unit accommodating section. Preferably, the first posture maintaining member and the second posture maintaining member are mated with each other.
The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a cross-sectional view showing a laser beam printer according to an embodiment of the present invention;
Fig. 2 is an enlarged cross-sectional view showing essential portions of a process unit of the printer shown in Fig. 1;
Fig. 3 is a side view showing a process of combining a developing unit to a photosensitive unit;
Fig. 4 is a plan view showing a process unit receiving portion;
Fig. 5 is a side view showing first guides, second guides, and a pressing mechanism;
Fig. 6 is a side view showing a locking mechanism for locking the process unit;
Fig. 7 is a side view showing a process of combining the developing unit to the photosensitive unit loaded into the process unit receiving portion;
Fig. 8 is an enlarged side view showing a locking mechanism for locking the developing unit to the photosensitive unit;
Fig. 9 is a perspective view showing the photosensitive unit;
Fig. 10 is a perspective view showing the developing unit;
Fig. 11 is a perspective view showing a process unit in which the developing unit shown in Fig. 10 is mounted on and combined to the photosensitive unit shown in Fig. 9.

A laser beam printer according to a preferred embodiment of the invention will be described with reference to the accompanying drawings. In the following description, the terms "downward", "front", "rear", "above", "below", "beneath" and the like will be used assuming that the laser beam printer is disposed in an orientation in which it is intended to be used.
Fig. 1 is a cross-sectional view showing the laser beam printer. As shown in this figure, the laser beam printer 1 has a housing 2 in which a sheet feed section 4 and an image forming section 5 are disposed. The image forming section 5 forms images on paper sheets supplied by the sheet feed section 4.
The sheet feed section 4 includes a sheet feed tray 6, a sheet urging plate 7, a sheet feed roller 8, a sheet feed pad 9, a pair of paper dust removing rollers 10, a pair of sheet feed rollers 11, and a pair of registration rollers 12. The sheet feed tray 6 is detachably provided on the bottom portion of the housing 2. The sheet feed roller 8 is rotatably disposed above one end of the sheet feed tray 6. The paper dust removing rollers 10 are disposed downstream from the sheet feed roller 8 with respect to a sheet transport direction in which the sheets of paper are transported. The registration rollers 12 are disposed downstream from the sheet feed rollers 11.
The sheet urging plate 7 is disposed in the sheet feed tray 6. The sheet urging plate 7 is pivotally movably supported about its end portion remote from the sheet feed roller 8 and is upwardly biased by springs (not shown) provided on the lower side of the urging plate 7. A stack of sheets 3 is adapted to be placed on the urging plate 7. The free end portion of the urging plate 7 moves downward against the biasing force of the springs to an extent that depends upon how many sheets of paper are stacked in the sheet urging plate 7.
The sheet feed roller 8 and the sheet feed pad 9 are disposed in confronting relation with each other. The sheet feed pad 9 is pressed against the sheet feed roller 8 by a spring 13 disposed in the rear surface of the sheet feed pad 9. The tip end of the uppermost sheet 3 stacked in the sheet feed tray 6 is pressed against the sheet feed roller 8 by the spring biasing the sheet urging plate 7 upward, is gripped by the sheet feed roller 8 and the sheet feed pad 9, and then is transported by rotation of the sheet feed roller 8. The sheet of paper fed by the sheet feed roller 8 passes through the nip between the paper dust removing rollers 10 where the paper dust removing rollers 10 remove paper dust from the sheet to a certain extent. Then, the sheet of paper is further transported by the sheet feed rollers 11 to the registration rollers 12, where the sheet of paper is subjected to registration, and then fed to the image forming section 5.
The sheet feed section 4 further includes a multi-purpose tray 14, a multi-purpose sheet feed roller 15, and a multi-purpose sheet feed pad 25. The multi-purpose sheet feed roller 15 and the multi-purpose sheet feed pad 25 supply sheets 3 that are stacked on the multi-purpose tray 14. The multi-purpose sheet feed roller 15 and the multi-purpose sheet feed pad 25 are disposed in mutual confrontation with each other. A spring disposed to the undersurface of the multi-purpose sheet feed pad 25 presses the multi-purpose sheet feed pad 25 toward the multi-purpose sheet feed roller 15. Rotation of the multi-purpose sheet feed roller 15 sandwiches sheets 3 that are stacked on the multi-purpose tray 14 between the multi-purpose sheet feed roller 15 and the multi-purpose sheet feed pad 25 and then feeds the sheets 3 one at a time to the registration rollers 12.
The image forming section 5 includes a scanner unit 16, a process unit 17, and a fixing unit 18. The scanner unit 16 is provided in the upper section of the housing 2 and includes a polygon mirror 19, lenses 20 and 22, and a reflection mirror 21. A laser source emits a laser beam modulated based on image data. As indicated by single-dot chain line in Fig. 1, the laser beam is reflected by the rotating polygon mirror 19, passes through the lens 20, is reflected by the reflection mirror 21, and passes through the lens 22. The laser beam that has passed through the lens 22 scans across the surface of a photosensitive drum 27 in the process unit 17. The term "process unit" as used in the following description refers to a combined unit of a developing unit 28 and a photosensitive unit 26.
The process unit 17 is disposed below the scanner unit 16. As shown in Fig. 2, the process unit 17 includes the photosensitive drum 27, a scorotron charge unit 29, a transfer roller 30, a cleaning roller 51, a secondary roller 52, and a sliding member 53. These components of the process unit 17 are housed in a photosensitive unit 26, which is freely detachably mounted on the housing 2.
The laser beam printer 1 primarily uses the developing roller 31 to collect residual toner from the surface of the photosensitive drum 27. That is, the developing roller 31 collects the toner that remains on the photosensitive drum 27 after toner is transferred onto the sheet 3. As such, there is no need to provide a cleaning blade and a means for holding waste toner. Therefore, the printer can be made with a simpler configuration, more compact, and less expensive.
As best shown in Fig. 2, the photosensitive drum 27 has a rotational shaft 27a extending in parallel with a rotational shaft of the developing roller 31 and is disposed in contact with the developing roller 31. The photosensitive drum 27 is rotatable in the counterclockwise direction and the developing roller 31 is rotatable in the opposite direction, i.e., clockwise direction, as indicated by arrows in Fig. 2. The photosensitive drum 27 includes a drum connected to ground and a photosensitive layer covering the outer surface of the drum. The photosensitive layer is made from a material selected from an amorphous silicon group, such as α-Si:H, from a cadmium sulfide group, such as CdS, from a zinc oxide group, such as ZnO, from a selenium group, such as selen, or is made from organic photosensitive materials, such as polycarbonate. Such photosensitive materials have a property to be positively charged.
As shown in Figs. 3 and 4, the rotational shaft 27a of the photosensitive drum 27 extend outwardly from the photosensitive unit 26 and is rotated by a main motor (not shown).
The scorotron charge unit 29 is disposed above the photosensitive drum 27 and separated from the photosensitive drum 27 by a predetermined distance so as not to contact the photosensitive drum 27. The scorotron charge unit 29 is of a positively-charging type that generates a corona discharge from a charge wire made from tungsten, for example. The scorotron charge unit 29 uniformly charges the surface of the photosensitive drum 27 to a positive polarity. The scorotron charge unit 29 is turned ON and OFF by a charge power source (not shown).
In association with rotation of the photosensitive drum 27, the surface of the photosensitive drum 27 is uniformly charted to a positive polarity by the scorotron charge unit 29, and is then exposed to light by the laser beam. The laser beam is emitted from the scanner unit 16 while being modulated by image data and scanned in the widthwise direction of the photosensitive drum 27 at a high speed. As a result of exposure by the laser beam, an electrostatic latent image is formed on the surface of the photosensitive drum 27.
The transfer roller 30 is disposed below the photosensitive drum 27 while contacting the photosensitive drum 27. The transfer roller 30 is supported on the photosensitive unit 26 so as to be rotatable in the clockwise direction as indicated by an arrow in Fig. 2. The transfer roller 30 consists of a metal roller and an ion conductive rubber material covering the metal roller. A transfer bias application power source applies a forward bias to the transfer roller 30 when toner is to be transferred from the photosensitive drum 27. The visible toner image on the surface of the photosensitive drum 27 is transferred onto a sheet 3 when the sheet 3 passes between the photosensitive drum 27 and the transfer roller 30.
The developing unit 28 is detachably mounted to the photosensitive unit 26. The developing unit 28 includes a developing roller 31, a layer-thickness regulating blade 32, a supply roller 33, and a toner box 34.
The toner box 34 is filled with non-magnetic single-component toner having a positively charging nature. In the present example, the toner filling the toner box 34 is a polymer toner obtained by co polymerization of a monomer with a polymerizing nature. The co polymerization can be performed by a well-known polymerization method such as suspension polymerization. Examples of monomers that can be used include a styrene monomer, such as styrene, or an acrylic monomer, such as acrylic acid, alkyl (C1-C4) acrylate, and alkyl (C1-C4) meta acrylate. The polymer toner particles are spherical so that the toner has extremely high fluidity. Also, coloring agents, such as carbon black, and wax are dispersed in the toner. Also, an external additive such as silica is added to increase fluidity of the polymer toner. The toner particles have a particle size of between about 6 to 10 micrometers.
A rotation shaft 35 is provided in the center of the toner box 34. An agitator 36 is supported on the rotation shaft 35. The agitator 36 rotates in the counterclockwise direction as indicated by an arrow in Fig. 2. This stirs up the toner in the toner box 34 and also pushes the toner out through a toner supply opening 37 that is opened in the side of the toner box 34. A window 38 is formed in the side wall of the toner box 34. The window 38 is provided for detecting how much toner remains in the toner box 34. Also, a cleaner 39 is supported on the rotation shaft 35 for cleaning the window 38.
The supply roller 33 is disposed at the side of the toner supply opening 37. The supply roller 33 is rotatable in the clockwise direction as indicated by an arrow in Fig. 2. The developing roller 31 is disposed in confrontation with the supply roller 33 and is rotatable in the clockwise direction as indicated by an arrow in Fig. 2. The supply roller 33 and the developing roller 31 abut against each other so that each is compressed by a certain extent.
The supply roller 33 is a conductive foam roller that covers a metal roller shaft. The developing roller 31 is a conductive rubber roller that covers a metal roller shaft. More specifically, the foam roller portion of the developing roller 31 includes a roller body with a coat layer covering its surface. The roller body is made from conductive silicone rubber or urethane rubber including carbon particles. The coat layer is silicon rubber or urethane rubber including fluoride. The developing roller 31 is applied with a developing bias by a developing bias application power source (not shown).
The layer-thickness regulating blade 32 is disposed in the vicinity of the developing roller 31. The layer-thickness regulating blade 32 includes a blade body and a pressing portion 40. The blade body is made from a metal leaf spring. The pressing portion 40 is provided on the free tip of the blade body. The pressing portion 40 is dome-shaped in cross-section and is made from silicone rubber with electrically insulating properties. The layer-thickness regulating blade 32 is supported on the developing unit 28 at a position near the developing roller 31. The resilient force of the blade body presses the pressing portion 40 against the surface of the developing roller 31.
The toner pushed out from the toner supply opening 37 is supplied to the developing roller 31 by rotation of the supply roller 33. The toner is charged to a positive polarity by friction between the supply roller 33 and the developing roller 31. As the developing roller 31 rotates, the toner on the developing roller 31 enters between the developing roller 31 and the pressing portion 40 of the layer-thickness regulating blade 32. The toner is further charged by friction between the developing roller 31 and the layer-thickness regulating blade 32 and regulated into a thin layer of uniform thickness on the developing roller 31.
When rotation of the developing roller 31 brings the positively charged toner borne on the developing roller 31 into confrontation with and contact with the photosensitive drum 27, the toner selectively clings to the electrostatic latent image on the surface of the photosensitive drum 27, thereby developing the electrostatic latent image into a visible toner image. As a result, inverse development is achieved.
As shown in Fig. 1, the fixing unit 18 is disposed at the downstream of the process unit 17. The fixing unit 18 includes a thermal roller 41, a pressing roller 42, and a pair of transport rollers 43. The pressing roller 42 presses against the thermal roller 41. The transport rollers 43 are disposed at the downstream side of the thermal roller 41 and the pressing roller 42. The thermal roller 41 is made from metal and includes a halogen lamp for heating up. After toner is transferred onto a sheet 3 in the process unit 17, the sheet 3 passes between the thermal roller 41 and the pressing roller 42. Heat from the thermal roller 41 melts and fixes the toner onto the sheet 3. Afterward, the transport rollers 43 transport the sheet 3 to a discharge path 44. The sheet 3 transported to the discharge path 44 is transported to sheet-discharge rollers 45 and discharged onto a sheet-discharge tray 46.
Referring next to Figs. 3, 4 and 9-11, description will be made with respect to mounting the developing unit 28 on and dismounting the developing unit 28 from the photosensitive unit 26.
Fig. 9 shows the photosensitive unit 26 and Fig. 10 shows the developing unit 28. The developing unit 28 is mounted on the photosensitive unit 26 to form the process unit 17 as shown in Fig. 11.
The photosensitive unit 26 has side walls 26a apart from each other by a predetermined distance. Both end portions of the rotational shaft 27a of the photosensitive drum 27 project out from the side walls 26a. A guide plate 60 also projects out from the side wall 26a near the rotational shaft 27a. The guide plates 60 determine a loading direction of the photosensitive unit 26 or the process unit 17 in cooperation with the rotational shaft 27a when the unit 26 or 17 is loaded into the housing 2. The photosensitive unit 26 has a drum unit accommodating section that is defined by the side walls 26a and a bridging frame 26b bridged between the side walls 26a at the developing unit receiving side. The upper surface of the dveloping unit mounting section is open to allow the developing unit 28 to be mounted thereon. A developing unit guide groove 61 is formed in each side wall 26a and is used when the developing unit 28 is mounted on and dismounted from the photosensitive unit 26. In mounting the developing unit 28, it is disposed so that its developing roller side faces the photosensitive unit 26, and then the developing unit 28 is moved toward the photosensitive unit 26. At this time, the developing unit guide groove 61 guides the roller shaft 31a of the developing roller 31 until the developing roller 31 is brought into abutment wit the photosensitive drum 27. When the developing roller 31 is in abutment with the photosensitive drum 27, the shaft 31a of the developing roller 31 is located in the terminal 61a, i.e., the end position of the guide groove 61.
As shown in Fig. 3, the developing unit 28 is pivotally movable about the roller shaft 31a in a position where the shaft 31a is located in the terminal 61. By rotating the trailing end of the developing unit 28 downward, the developing unit 28 is accommodated into the dveloping unit mounting section. A support 28c formed in the bottom surface of the developing unit 28 is brought into abutment with the surface of the dveloping unit mounting section and support the developing unit 28 therein in cooperation with the roller shaft 31a supported on the terminal 61a. Likewise, a support 26d is formed in the bottom surface of the photosensitive unit 26 in the position where the support 28c is seated. The support 26d protrudes outwardly, so its inner surface is configured to be concave capable of receiving the support 28c. The developing unit 28 is thus properly positioned on the developing unit mounting section when the support 28c is mated with the support 26d from the back side.
The bridging frame 26b has its outer surface provided with a locking mechanism 62. The locking mechanism 62 includes a locking lever 62a which, as shown in Fig. 8, is pivotally movable about a shaft 62b formed in the bridging frame 26b. The locking lever 62a is biased by a torsion spring 63 in a direction in which the locking lever 62a engages a locking protrusion 64 formed in the rear end of the developing unit 28. Engaging the locking lever 62a with the locking protrusion 64 locks the developing unit 28 to the photosensitive unit 26.
As shown in Figs. 4, 10 and 11, a gripping portion 65 is provided at the rear side, that is the same side as the side where the locking protrusion 64 is formed, of the developing unit 28 for operator's gripping convenience. The operator can lift the combined developing unit 28 and the photosensitive unit 26, i.e., the process unit 17, while gripping the upper surface of the developing unit 28 and the gripping portion 65. In this case, because engagement of the roller shaft 31a of the developing roller 31 with the terminal 61a of the guide groove 61 is being maintained when the developing unit 28 is lifted, the photosensitive unit 26 is not separated from the developing unit 28. In this manner, the developing unit 28 can be mounted on and dismounted from the photosensitive unit 26 regardless of whether the photosensitive unit 26 is loaded in the laser beam printer 1 or the photosensitive unit 26 is placed outside the laser beam printer 1.
As shown in Figs. 1, 2 and 4, a process cartridge insertion opening is formed in an upper surface of the housing 2 in a position frontwardly of the sheet discharge tray 46. The opening is defined by the front plate 2a, left and right side walls 2b. A lid 54 that is pivotally movable about a shaft 54a covers the opening.
As shown in Figs. 4 and 5, first guides 55 are formed in the inner surfaces of the side plates 2b of the housing 2. The first guides 55 are sloped down toward their end positions or terminals 55a. When viewed from the side, the first guide 55 is seen to be an elongated U-shaped groove into which the rotational shaft 27a of the photosensitive drum 27 is inserted. The rotational shaft 27a of the photosensitive drum 27 is slidably moved down toward the lowest end position, i.e., the terminal 55a, of the first guide 55 where the photosensitive drum 27 can be rotatably supported.
A pair of second guides 56 is provided between the first guides 55. Like the first guide 55, the second guide 56 is also sloped down in the same direction as the direction in which the first guide 55 is sloped down. However, unlike the first guide 55, the second guide 56 is in the form of a rail with a flat upper surface, along which the photosensitive unit 26 moves. Between the second guides 56, a photosensitive unit accommodating section 57 is formed for receiving the photosensitive unit 26.
To load the photosensitive unit 26 or the process unit 17 into the laser beam printer 1, the rotational shaft 27a of the photosensitive drum 27 is slidably moved down along the first guides 55. When the rotational shaft 27a has reached the terminals 55a of the first guides 55, the trailing end of the photosensitive unit 26 is rotated downward about the rotational shaft 27a. In this manner, the photosensitive unit 26 is placed on the photosensitive unit accommodating section 57.
As shown in Fig. 6, a seat 58 is provided below the photosensitive unit accommodating section 57 for seating the photosensitive unit 26 thereon. When the photosensitive unit 26 is placed on the accommodating section 57, a protruded portion 26d formed on the bottom wall of the photosensitive unit 26 is brought into abutment with the seat 58. Due to the protruded portion 26d and the seat 58, the posture of the photosensitive unit 26 can be maintained on the accommodating section 57.
The photosensitive unit 26 is loaded into the laser beam printer 1 in the following manner. First, the photosensitive unit 26 is oriented in a direction in which the photosensitive drum side faces the inner portion of the housing 2. Both end portions of the rotational shaft 27a projecting out from the photosensitive unit 26 are inserted into the first guides 55. The guide plates 60 formed next to the rotational shaft 27a also slide along the first guides 55 following the rotational shaft 27a. The process unit 17 is obliquely downwardly moved into the housing 2. At this time, left and right side portions of the photosensitive unit 26 are disposed on the second guides 56 and are slidably moved down while being guided by the second guides 56.
When the rotational shaft 27a has reached the terminal 55a of the first guides 55, the photosensitive unit 26 is disengaged from the second guides 56. As a result, the rear end portion of the photosensitive unit 26 rotates downward about the rotational shaft 27a and the photosensitive unit 27 is placed on the photosensitive unit receiving portion 57. At this time, the protrusion 26d on the bottom surface of the photosensitive unit 26 brought into abutment with the seat 58. The photosensitive unit 26 is stably supported at three points, that is, left and right sides of the rotational shaft 27a and the seat 58.
As shown in Fig. 4, a boss 26e is formed on one side wall (right side wall in the figure) of the photosensitive unit 26. An electrically driven urging unit (not shown) disposed in the housing 2 urges the opposite side wall (left side wall in the figure) of the photosensitive unit 26 toward the right side wall so that the boss 26e is in abutment with the right side inner surface of the housing 2. A gear (not shown) is provided at the right side of the photosensitive unit 26. The photosensitive unit 26 is urged toward the right side of the housing 2 by the force created by the rotations of the gear. With the electrically driven urging unit and the gear, the photosensitive unit 26 is positioned in the same location on the process unit accommodating section 57. Similarly, the developing unit 28 is positioned so that the right side of the developing unit 28 is urged in the same direction.
As described, the photosensitive unit 26 is loaded on the process unit accommodating section 57 by downwardly rotating (counterclockwise direction in Fig. 6) the trailing side about the rotational shaft 27a located at the terminal 55a. In the positions near the terminals 55a of the first guides 55, stepped portions 59 are engraved. When the trailing end of the photosensitive unit 26 is rotated downward about the rotational shaft 27a, the guide plates 60 are fitted into the stepped portions 59. Thus, the photosensitive unit 26 cannot easily be taken out from the accommodating section 57.
As shown in Figs. 6 and 7, locking units are provided in the accommodating section 57 at positions beneath the second guides 56. Each locking unit includes a torsion spring 66 having a rounded head 66c and a pair of legs extending from the head 66c. Ring-shaped foot portions 66a, 66b are provided at the ends of the legs, which are supported by pins 67, 68, respectively. When the photosensitive unit 26 is accommodated in the accommodating section 57, the rounded head 66c of the torsion spring 66 engages a dimple 26c formed in the rear wall of the photosensitive unit 26 and urges the photosensitive unit 26 toward the terminal 55a of the first guide 55. By virtue of the urging force of the torsion spring 66, the photosensitive unit 26 is firmly held and supported at three points as mentioned above.
In order to unload, the photosensitive unit 26 from the accommodating section 57, the operator grasps the grip 65 and lifts the photosensitive unit 26. Lifting the unit 26 causes the rounded head 66c of the torsion spring 66 to disengage from the dimple 26c. To completely unload the photosensitive unit 26, the photosensitive unit 26 is further lifted while directing the trailing end upward and slidably moving back the photosensitive unit 26 along the second guides 56. Loading and unloading the photosensitive unit 26 can be performed regardless of whether the developing unit 28 is combined to the photosensitive unit 26. That is, not only the photosensitive unit 26 alone but also the process unit 17 can be loaded into and unloaded from the laser beam printer 1 in such a manner as described above. Another locking unit can be employed instead of the locking unit using the torsion spring 66.
Next, an urging mechanism 70 will be described while referring to Figs. 4, 5 and 7. The urging mechanism 70 is operable only when the photosensitive unit 26 and the developing unit 28 as combined are loaded into the laser beam printer 1, because the urging mechanism 70 is used for urging the developing roller 31 contained in the developing unit 28 against the photosensitive drum 27 contained in the photosensitive unit 26.
The urging mechanism 70 is disposed in a space between the first guide 55 and the second guide 56, and includes a pair of nipping levers 72, 73 and a lever moving mechanism 77 for moving one nipping lever 73 toward and away from another nipping lever 72. A teardrop-shape engagement protrusion 71, that is formed in the rear portion of each of the side walls of the developing unit 28, is inserted between the nipping levers 72, 73 when the developing unit 28 is mounted on the photosensitive unit 26. The engagement protrusion 71 is nipped by the nipping levers 72, 73 and is urged toward the terminal 55a, so that the developing roller 31 is urged against the photosensitive drum 27.
The nipping levers 72, 73 are supported by pins 74, 75, respectively, and are pivotally movable about the respective pins 74, 75. A spring 76 having one end fixed to the housing 2 and another end fixed to the movable end portion of the nipping lever 73 exerts urging force upon the nipping lever 73. Thus, the nipping lever 73 is rotated counterclockwise and nips the engagement protrusion 71 in cooperation with another nip lever 73.
The lever moving mechanism 77 includes a cam 78 and a cam shaft 79 to which the cam 78 is fixed. The cam shaft 79 is connected to a motor (not shown) and rotated thereby. The cam 78 is in contact with one end of the nipping lever 72, so that rotations of the cam 72 move opposite end of the nip lever 72 toward and away from the movable end of the counterpart nip lever 71. Instead of moving the cam shaft 79 by the motor, the cam shaft 79 can be moved manually.
The process unit 17 can be loaded into the laser beam printer 1. Also, the developing unit 28 can be separately loaded into the laser beam printer 1 if the photosensitive unit 26 has already been set to the printer 1. In the former case, when the trailing end of the photosensitive unit 26 is rotated downward about the rotational shaft 27a with the rotational shaft 27a being fitted to the terminals 55a of the first guides 55, the engagement protrusion 71 moves downward and is inserted between the pair of nipping levers 72, 73 against the urging force of the spring 76 urging the nipping lever 73 toward the counterpart nipping lever 72. At this time, the upper end of the nipping lever 72 has been moved toward the free end of the nipping lever 73. In this case, the engagement protrusion 71 moves downward and is inserted between the pair of nipping levers 72, 73 when the trailing end of the loaded developing unit 28 is rotated downward about the roller shaft 31a located in the terminal 56a of the guide groove 61.
As shown in Fig. 5, when the photosensitive unit 26 is accommodated in the accommodating section 57, the roller shaft 31a of the developing roller 31 is located in the terminal of the guide groove 61 formed in the side wall of the photosensitive unit 26. In this condition, the roller shaft 31a is on or along the line connecting the rotational shaft 27a of the photosensitive drum 27 and the engagement protrusion 71. Therefore, the engagement protrusion 71 traces substantially the same locus at the time of downward movement of the process unit 17 and of downward movement of only the developing unit 28. Therefore, not only the process unit 17 but also the developing unit 28 alone can be loaded into and unloaded from the printer 1 as shown by two-dotted-chain line in Fig. 7.
When the photosensitive unit 26 is unloaded from the accommodating section 57, the unit 26 is not capable of rotating about the guide shaft 27a in the unloading direction more than a limited extent due to the guide plate 60. Accordingly, the upper portion of the photosensitive unit 26 does not impinge upon the lower cover of the scanner unit 16, so the scanner unit 16 or other components are not damaged.
At the time of printing, the motor is driven by a controller (not shown) to thereby rotate the cam 78. Abutment of the small-diameter portion of the cam 78 with the lower portion of the nip lever 72 moves the upper portion of the nipping lever 72 toward the photosensitive drum 27. On the other hand, the nipping lever 73 urges the engagement protrusion 71 toward the photosensitive drum 27 by the urging force of the spring 76. As a result, the developing roller 31 is urged against the peripheral surface of the photosensitive drum 27.
When the printing operation is not performed, the large-diameter portion of the cam 78 is brought into abutment with the lower portion of the nipping lever 72, thereby moving the upper portion of the nip lever 72 away from the photosensitive drum 27. Accordingly, the engagement protrusion 71 is moved toward the nipping lever 73 and so the developing unit 28 is separated from the photosensitive drum 27.
As described above, the developing unit 28 and the photosensitive unit 26 can be combined into a single unit outside the printer 1. This can be done outside the printer 1 by inserting the developing unit 28 into the guide groove 61 of the photosensitive unit 26 and mounting the developing unit 28 on the developing unit mounting section of the photosensitive unit 26. The combined unit (process unit) can also be easily loaded into and unloaded from the laser beam printer 1. Furthermore, only the developing unit 28 can be loaded into the laser beam printer 1, mounted on the photosensitive unit 26 that has already been set in position in the laser beam printer, and dismounted from the photosensitive unit 26 while leaving the photosensitive unit 26 inside the laser beam printer 1.
The roller shaft 31a of the developing roller 31 and the rotational shaft 27 of the photosensitive drum 27 protrude out from the units 26 and 28, respectively, and are rotated by a drive motor (not shown) disposed in the housing 2 via couplings and a transmission gear mechanism. Counterclockwise rotational moments (Fig. 2) imparted upon the roller shaft 31a and the rotational shaft 27 (the rotational moments imparted toward the bottom of the accommodating section 57) cause the photosensitive unit 26 and the developing unit 28 to move toward their accommodating sections. Accordingly, by utilizing the rotational moments of the roller shaft 31a and the rotational shaft 27 and also owing to the weights of the units 26, 28, mounting the units 26, 28 on their accommodating sections can be performed smoothly.
As shown in Fig. 4, a latching means is provided to latch the process unit 17 to the accommodating section 57. Specifically, a protrusion 80 is formed on the accommodating section 57. An engaging portion 81 is formed on the bottom surface of the process unit 17 in the position corresponding to the position of the protrusion 80. When the process unit 17 is placed on the accommodating section 57, the engaging portion 81 is brought into engagement with the protrusion 80. By the provision of the engaging portion 81 in the process unit 17, improper process unit with no such protrusion or with the protrusion in a position offset from the correct position is not allowed to be properly accommodated in the accommodating section 57. That is, the protrusion 80 serves as a discriminating means for discriminating a type of process unit. The discriminating means is used by an image forming device to determine if a process unit loaded thereinto is proper or not. In a modification, the protrusion 80 may be formed in the bottom surface of the process unit 17 and the engaging portion 81 for receiving the protrusion 80 may be formed in the accommodating section 57.
While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention, which is defined by the attached claims.
For example, instead of using the rotational shaft of the photosensitive drum as a guide shaft for loading the photosensitive unit into the printer, a pair of protrusions may be formed on outer surfaces of the side walls for use as the guide shaft. In this case, it is desirable that the protrusions be in alignment with the longitudinal axis of the shaft. The same is true with respect to the guide shaft for mounting the developing unit on the photosensitive unit.

Claims

An image forming device comprising:
a housing (2);

a pair of first guides (55) extending down to terminals (55a);

a process unit (17) having a bottom wall and side walls formed with protrusions (27a) protruding outward from the side walls, the protrusions (27a) being engageable with the pair of first guides (55), the protrusions (27a) being guided down along the pair of first guides (55) toward the terminals (55a) when the process unit (17) is loaded into the housing (2); and

a process unit accommodating section (57) for receiving and accommodating the process unit (17),
characterized by

a second guide (56) formed between the pair of first guides (55) configured to guide the bottom surface of the process unit (17) from a top open space of the housing (2) toward the terminal (55a), wherein the process unit (17) is accommodated in the process unit accommodating section (57) when the protrusions (27a) of the process unit (17) have been brought into abutment with the terminals (55a), the process unit (17) is disengaged from the second guide (56) and a trailing end of the process unit (17) is rotated downward about an imaginary line connecting the protrusions (27a).
The image forming device according to claim 1, further comprising a posture maintaining member (26d) formed on the process unit (17) for maintaining a posture of the process unit (17) when accommodated in the process unit accommodating section (57).
The image forming device according to claim 1 or 2, wherein each of the pair of first guides (55) is in the form of an elongated U-shaped groove into which each protrusion is inserted, and the second guide (56) is in the form of a rail having an upper flat surface on which the process unit (17) slidably moves.
The image forming device according to claim 1, further comprising locking means (66) for locking the process unit (17) to the housing (2), the locking means (66) being provided in the process unit accommodating section (57).
The image forming device according to claim 4, wherein the locking means (66) resiliently engages the trailing end of the process unit (17).
The image forming device according to claim 1, wherein the process unit (17) comprises a photosensitive unit (26) and a developing unit (28) detachably mounted on the photosensitive unit (26), the photosensitive unit (26) including a photosensitive drum (27), the developing unit (28) including a developing roller (31).
The image forming device according to claim 6, wherein the protrusions (27a) are provided to the photosensitive unit (26).
The image forming device according to claim 7, wherein the photosensitive drum (27) has a rotational shaft having two end portions projecting from the process unit, the two end portions of the rotational shaft being used as the protrusions (27a).
The image forming device according to claim 1, further comprising latching means (80, 81) for latching the process unit (17) to the process unit accommodating section (57).
The image forming device according to claim 1, wherein the process unit (17) includes a photosensitive drum and developing roller, the process unit (17) being accommodated in the process unit accommodating section (57) while being urged toward a predetermined direction to urge the developing roller against the photosensitive drum.
The image forming device according to claim 1, wherein the process unit (17) is formed with an auxiliary guide member (60) for determining a loading direction and unloading direction of the process unit (17) when loading into and unloading from the housing (2).
The image forming device according to claim 6, wherein the developing unit (28) has a bottom surface on which a first posture maintaining member (28c) is formed for maintaining a posture of the developing unit (28) when mounted on the photosensitive unit (26), the photosensitive unit (26) has a bottom surface on which a second posture maintaining member (26d) is formed for maintaining a posture of the photosensitive unit (26) when accommodated in the process unit accommodating section (57), wherein the first posture maintaining member (28c) and the second posture maintaining member (26d) are mated with each other.