Image Forming Apparatus Including a Developer Device Engaging and Disengaging Mechanism

1. Field of the Invention

The present invention relates to a developer device engaging and disengaging mechanism for an image forming apparatus.

2. Description of the Related Art

As use of office automation systems has become widespread in recent years, demand for image forming apparatus which can form varied and quality characters and images on ordinary paper with low noise, has increased. To meet this demand, image forming apparatuses utilizing electrophotography which is also used in copying machines and facsimile equipment, has been widely used. An image forming apparatus which has components divided into replaceable functional units such as a photoconductive drum and a developer device, is desired, so that those functional units can easily be removed and inserted when the life of the photoconductive drum expires or when toner needs to be replenished in the toner hopper of the developer device.

The developer device is typically positioned near the photoconductive drum and is coupled thereto through a gear. Accordingly, in order to easily insert and remove the developer device to and from an image forming apparatus, a mechanism which can properly engage and disengage the developer device in the apparatus, is in great demand.

FIG. 1 is a side view of an electrophotographic recording unit which consists mainly of a laser beam scanner 1, photoconductive drum 2a, cleaner 3, charger 4, developer station 5a, transfer station 6, discharger 7, fuser station 8a, paper transport path 9, paper stacker 11, and paper hoppers 10a and 10b for recording paper of different sizes.

When a print command is issued to the recording unit in a print-ready state with the power turned on and with a heat roller R1 of the fuser station 8a heated up to a predetermined temperature, the recording unit starts a print operation. That is, a sheet of recording paper 12 of a command-designated size is fed onto the paper transport path 9 and transported in the direction of arrow A, toward the photoconductive drum 2a. By this time, the photoconductive drum 2a has been discharged by the discharger 7, cleaned by the cleaner 3 and newly charged by the charger 4.

The laser beam scanner 1 including a laser oscillator, exposes and scans image data-modulated light onto the photoconductive drum 2a to form an electrostatic latent image thereon. The electrostatic latent image formed on the photoconductive drum 2a is developed by toner 52 which is picked up from a toner container 50 and attached to a developing roll 51a. The toner 52 which is composed of ferromagnetic powder, is charged while being mixed and stirred in the toner container 50. Then, the transfer station 6 transfers the toner-developed image to the recording paper 12 fed from the paper hoppers 10a or 10b. The image transferred is fused by the heat roller R1 and a pressure roller R2 in the fuser station 8a. Finally, the recording paper 12 is fed to the stacker 11.

The recording unit has an upper cover 13, which is on the upper side of the paper transport path 9. The upper cover 13 opens backward by swinging about a shaft (see cover supporting shaft 131 in FIG. 4) positioned to the right of the structure illustrated in FIG. 1.

FIG. 2 is a perspective view of developer station 5a which includes guide pins 54a-54d on the lower part of both sides of a housing 53. A handle 55, provided on the upper part of the housing 53, is used to remove the developer station 5a for maintenance or when the toner 52 needs to be changed (e.g., after 4000-6000 sheets of recording paper have been printed). The developer station 5a also has gap rolls 56a and 56b on the ends of the developer roll 51a.

FIG. 3 is a sectional view of a unit frame 14a, showing guide grooves 15a-15d which are provided perpendicularly in the unit frame 14a of the recording unit. The guide grooves 15a-15d each have at their lowermost end, a hooked portion (e.g., 10 mm-long) which turns at a right angle toward the photoconductive drum 2a. The developer station 5a is mounted on the unit frame 14a by inserting the guide pins 54a-54d along the guide grooves 15a-15d.

FIG. 4 is a side view of a developer station engaging and disengaging mechanism of the related art. A leaf spring 16a is coupled at one end to a shaft 17. An arm 18a is connected at one end to the shaft 17, and at the other end to a spring 19. The spring 19 forces upward the arm 18a and a link bar 20a whose lower end contacts the arm 18a. Thus, when the upper cover 13 is closed with the cover-supporting shaft 131 serving as a rotational axis, a protruding portion 130 provided on the back of the upper cover 13, presses down the link bar 20a. The link bar 20a rotates the arm 18a counterclockwise against the elasticity of the spring 19, and the leaf spring 16a swings in the direction of the arrow B, pressing the rear side 5a' of the developer station 5a. Accordingly, the developer station 5a slides in the direction of the arrows shown in FIG. 3 along the hooked portion of the guide grooves 15a-15d to the far end. Thus, the gap rollers 56a and 56b (see FIG. 2) provided at both ends of the developer roll 51a contact the photoconductive drum 2a at both ends so as to position the developer roll 51a at a predetermined distance from the photoconductive drum 2a.

FIG. 5 is a side view of the developer station 5a of the related art in the engaged position. The developer station 5a is provided with a developer gear 57a which transmits a rotational force from a power transmission mechanism 21 to the developer roll 51a and the toner mixer in the toner container 50 (see FIG. 1). The power transmission mechanism 21 consists of a bracket 22a, gears 25a, G1 and G2, motor gear G3, pulleys P1 and P2, belt B1, motor M, tension roller R and spring SP. The bracket 22a is rotatably-coupled to the unit frame 14a (FIG. 3) via an axis 23a. Coaxially-coupled gear 25a and pulley P1 are rotatably-coupled to one end of the bracket 22a. A spring 26a is provided at the other end of the bracket 22a to force the gear 25a to engage the developer gear 57a. Thus, a driving force is transmitted through the gears 25a and 57a to the developer station 5a as it is engaged properly with the recording unit. Accordingly, when the upper cover 13 (FIG. 4) is opened, the spring 19 causes the arm 18a to rotate, and the leaf spring 16a swings in the direction of an arrow C so that the guide pins 54a-54d of the developer station 5a are released from the hooked portions of the guide grooves 15a-15d. As a result, the developer station 5a can be removed from the apparatus using the handle 55. However, gears 25a and 57a tend to remain engaged until the developer station 5a is manually removed from the image forming apparatus.

As described above, in order to smoothly engage or disengage the developer station 5a by sliding it along the hooked portions of the guide grooves 15a-15d, it is necessary that the gear 25a and the developer gear 57a rotate while being engaged with each other, because of a large rotational torque which the gears provide. Accordingly, it is difficult to engage and disengage the developer station smoothly when the developer station is removed from or inserted into an image forming apparatus when maintenance is required.

It is an object of the present invention to provide a developer device engaging and disengaging mechanism which can smoothly engage and disengage a developer device.

It is another object of the present invention to provide a developer engaging and disengaging mechanism which can economically and reliably engage and disengage a developer device.

To achieve the above and other objects, the present invention moves the developer device between a first position where the developer device is capable of being mounted or dismounted, with the first gear for driving the developer device disengaged from the second gear, and a second position where the developer device faces the image forming device at a predetermined distance, with the first gear engaged with the second gear. In the second position, the second gear which is coupled to a frame of the image forming apparatus, transmits power from a power source to the first gear. In accordance with the present invention, the first gear engages the second gear when the developer device has been moved from the first position to the second position, and the first gear is disengaged from the second gear when the developer device is in the second position.

FIG. 1 is a side view of an electrophotographic recording unit;

FIG. 2 is a perspective view of a developer station;

FIG. 3 is a sectional view of a unit frame, showing guide grooves;

FIG. 4 is a side view of a developer station engaging and disengaging mechanism of the related art;

FIG. 5 is a side view of the developer station of the related art in the engaged position;

FIG. 6 is a side view of a developer station and its engaging and disengaging mechanism in accordance with an embodiment of the present invention;

FIG. 7 is a diagram illustrating the operation of the developer station engaging and disengaging mechanism of the present invention; and

FIG. 8 is a side view of a modification to the embodiment of the present invention.

Throughout the above-mentioned drawings, identical reference numerals are used to designate the same or similar component parts.

FIG. 6 is a side view of a developer station and its engaging and disengaging mechanism in accordance with an embodiment of the present invention, as it is installed in an electrophotographic recording unit in accordance with the related art.

A developer station 5b, including a developer gear 57a and a developer roll 51a, is constructed such that it is capable of being mounted on and dismounted from the unit frame 14a (FIG. 3) which is coupled to axis 23a. The developer roll 51a develops an electrostatic latent image formed on the photoconductive drum 2a. The developer gear 57a transmits rotational power to the developer roll 51a. A leaf spring 16a presses or biases the developer station 5b toward the photoconductive drum 2a to a position where developer roll 51a is spaced by a predetermined distance from the photoconductive drum 2a.

A bracket 22b, which is provided with gears 25a and 24a, spring 26a and link block 27a, is supported on and rotatably-coupled to the unit frame 14a via an axis 23a. The gear 24a is rotatably-coupled to the axis 23a and is engaged with a power transmission mechanism 21a including a motor M, and gears G3, G2 and G1. The gear 25a is rotatably-coupled to the bracket 22b and is engaged with the gear 24a. The spring 26a pulls the bracket 22b to rotate it about the axis 23a and forces the gear 25a toward the developer gear 57a, so that the gears 25a and 57a engage each other.

The link block 27a, which is a protruding lower part of the bracket 22b, is provided with a follower rod 270 at one end. One end of an arm 18b is coupled to a shaft 17 to which the leaf spring 16a is connected, and the other end is positioned under the follower rod 270. The lower end of a link bar 20a contacts the surface of the arm 18b, and a spring 19a presses against the bottom of the arm 18b. Accordingly, when downward pressure from the link bar 20a is removed (e.g., when the cover 13 is opened), the end of the arm 18b contacts and links the follower rod 270. The elastic force of the spring 19a is set such that the value of torque provided by the spring 19a to rotate the bracket 22b via the follower rod 270 in the direction of arrow F, is larger than the torque provided by the spring 26a to rotate the bracket 22b in the direction of arrow G.

FIG. 7 is a diagram illustrating the operation of the developer station engaging and disengaging mechanism in accordance with the present invention. When the upper cover 13 is opened and the pressure which the link bar 20a exerts on the arm 18b is removed, the spring 19a rotates the arm 18b in the direction of the arrow D and the shaft 17 rotates accordingly. The leaf spring 16a swings in the direction of the arrow C and, simultaneously, the bracket 22b, which is linked to the follower rod 270, rotates in the direction of the arrow F. Thus, the gear 25a disengages the developer gear 57a. That is, when the upper cover 13 is opened, the leaf spring 16a and gear 25a move from the normal position (i.e., the position of leaf spring 16a and gear 25a when the recording unit is operable), whether or not the developer station 5b is mounted on the unit frame 14a.

Therefore, the developer station 5b is engaged in the following order:

(1) Guide pins 54a-54d of the developer station 5b are inserted along the guide grooves 15a-15d of the unit frame 14a, and into the bottoms as illustrated in FIG. 3.

(2) Closing the upper cover 13 causes the link bar 20a to press the arm 18b and rotate arm 18b in the direction of the arrow E.

(3) The leaf spring 16a presses the developer station 5b in the direction of the arrow B and moves it to the position where the developer roll 51a and the photoconductive drum 2a are spaced apart by a predetermined distance.

(4) The arm 18b is released from linkage with the follower rod 270 and the spring 26a pulls and rotates the bracket 22b in the direction of the arrow G, to engage the gear 25a with the developer gear 57a.

In contrast, the developer station 5b is disengaged in reverse order. When the upper cover 13 is opened, the leaf spring 16a swings in the direction of the arrow C and, at the same time, the gear 25a is released from engagement with the developer gear 57a. Accordingly, the developer station 5b slides along the hooked portions of the guide grooves 15a-15d to the corner portions thereof. Then, the developer station 5b can be removed from the unit frame 14a by pulling up on the handle 55. Since the gear 25a of the bracket 22b is disengaged from the developer gear 57a beforehand, the developer station 5b can be inserted into and removed from the recording unit easily and smoothly.

The above embodiment describes an example where the arm 18b is rotated by the pressure from the link bar 20a, which is caused by closing the upper cover 13. However, the arm 18b may be rotated by other means, e.g., manually or by rotating the shaft 17 using a motor.

FIG. 8 is a diagram of a modification to the embodiment of FIG. 6 and particularly to the mechanism including the arm 18b and the link bar 20a in FIG. 6. The arm 18b in FIG. 6 corresponds to an arm 18c in FIG. 8, and the link bar 20a in FIG. 6 corresponds to a set of arms 18d and 18e and link bar 20b in FIG. 8. In FIG. 8, the L-shaped arm 18c is rotatably-coupled to a shaft 17b and one side of the arm 18c is provided almost in parallel to the leaf spring 16a. The ends of the arm 18d are rotatably-coupled to one end of the arm 18c and one end of the arm 18e, respectively. The other end of the arm 18e is also rotatably-coupled to the unit frame 14a so that the arms 18d and 18e become upwardly doglegged. When the upper cover 13 is closed, the link bar 20b presses down on the joint of the arms 18d and 18e and causes the other end of the arm 18d to extend leftward because the arm 18e is fixed at one end. The link 20b also causes the arm 18c and thus the shaft 17b to rotate counterclockwise. The leaf spring 16b swings in the direction shown by an arrow H and presses the developer station 5b toward the photoconductive drum 2a so that the gear 25a engages the developer gear 57a. Thus, the developer station 5b is secured there stably.

With the arms 18c, 18d and 18e so-constructed, the vertical component of a restoring force of the leaf spring 16b which is provided to the arms 18d and 18e is reduced sharply (e.g., to zero when the arms 18d and 18e are straightened). Therefore, the force with which the link bar 20b presses up against the upper cover 13 is minimized.

A stopper may be provided under the joint of the arms 18d and 18e, to prevent the link bar 20b from being pressed further down when the arms 18d and 18e become slightly doglegged downwardly. In this state, the above-mentioned vertical component of the force is downward, which allows the link bar 20b to stay where it is pressed down and to cause no upward pressure against the upper cover 13. To disengage the developer station 5b, it is only necessary to release the above-mentioned state. Thus, the improvement can prevent the upper cover 13 from being deformed and can prevent wear on mechanical parts which are subject to sliding due to opening and closing the upper cover 13.

As is apparent from the above description, since the gear 25a disengages from the developer gear 57a and the developer station 5b moves from the normal operating position automatically just by opening the upper cover 13, for example, the developer station 5b can be inserted into and removed from the recording unit easily and smoothly.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be resorted to as falling within the scope of the invention in the appended claims and their equivalents.