1. Field of the Invention
The present invention relates to an image forming apparatus, in particular, an image forming apparatus to which sheet containing means containing sheets is detachably attached.
2. Related Background Art
A conventional image forming apparatus allows sheet containing means containing sheets to be detachably attached to the main body of the image forming apparatus. In such an image forming apparatus, sheets contained in a sheet containing cassette serving as the sheet containing means are successively conveyed to an image forming portion, where image recording is effected on the sheets.
Incidentally, the sheet containing cassette is attached and detached for the purpose, for example, of filling it with sheets or effecting a change in sheet size. When the attachment operation is conducted on the sheet containing cassette after filling it with sheets, the sheet containing cassette, which has become heavy due to the sheets, puts a significant burden upon the user. Further, when the sheet containing cassette is heavy, the user may exert an excessive force at the time of attachment to give the cassette great momentum in the attachment direction thereof, resulting an impact at the time of attachment. This impact may lead to positional deviation of the sheets filling the sheet containing cassette or damage to the sheet containing cassette.
As means for solving this problem, there is known, for example, an automatic sheet containing cassette conveying mechanism, which, when the insertion of the sheet containing cassette is detected, automatically conveys the sheet containing cassette by the drawing portion, thereby sparing the user the trouble of performing the operation of inserting the sheet containing cassette. In the case of this mechanism, however, automatic conveyance is impossible in a state in which no power is supplied to the apparatus main body. In view of this, there is provided charge means for storing driving power, making it possible to perform automatic conveyance even when no power is being supplied. The provision of such charge means, however, results in a very complicated apparatus construction.
In view of this, Japanese Patent Application Laid-open No. H4-85220, for example, discloses, instead of an automatic sheet containing cassette conveying mechanism using electric power, a mechanical automatic sheet containing cassette conveying mechanism using a spring and needing no electric power. As shown in
However, in this conventional image forming apparatus adopting a mechanical automatic sheet containing cassette conveying mechanism, when drawing the sheet containing cassette through the engagement pin 113, the arm 118 makes a rotating motion, whereas the movement route for the engagement pin 113 formed by a groove 124 defined by the guide 123 extends linearly in the direction in which the sheet containing cassette is inserted, so that the engagement pin 113 is guided linearly.
Here, when the engagement pin 113 is thus guided linearly, the position of the point of action of the moment on the arm transmitting force to the engagement pin 113 changes every moment as the sheet containing cassette is drawn, and in the end region of the sheet cassette conveyance section, the point of action of the moment with respect to the engagement pin 113 moves away from the shaft 119, the point of action of the moment having been moving toward the shaft 119 of the arm 118 due to the configuration of a grasping groove 118a for grasping the engagement pin 113, which is formed at the rotation end of the arm 118.
Further, when the point of action of the moment thus moves away from the shaft 119, which is the rotation center of the arm 118, the conveyance force for drawing the sheet containing cassette is weakened as indicated by symbol a in
It might be possible to prevent this shortage of conveyance force by using a strong toggle spring. In this case, however, the requisite operating force for pulling back the toggle spring when drawing out the sheet containing cassette increases, resulting in a deterioration in usability.
The present invention has been made in view of the above problems in the prior art. It is an object of the present invention to provide an image forming apparatus allowing the sheet containing cassette (sheet containing means) to be reliably drawn without involving a deterioration in usability.
According to the present invention, an image forming apparatus, in which sheet containing means containing a sheet is detachably attached to a containing portion provided in an apparatus main body, includes: an engagement portion provided on the sheet containing means; drawing means which is rotatably provided in the containing portion as a pivot, the drawing means being engaged with the engagement portion and being rotated to draw-the sheet containing means in the containing portion by a spring when the sheet containing means is inserted to the containing portion; and guide means which, when the drawing means being rotated to draw the sheet containing means, guides a movement of the engagement portion in a drawing direction of the sheet containing means, wherein the guide means is composed of: a linear portion parallel to the drawing direction of the sheet containing means; and a curved portion which is provided on the downstream side of the linear portion with respect to the drawing direction, the curved portion being curved not to be away from the pivot of the drawing means.
FIGS. 9 is a perspective view of a drawing portion according to another embodiment of the present invention;
In the following, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
In
In the image forming portion 1A constructed as described above, when image forming operation is started, a beam corresponding to an image signal is first applied to the photosensitive drum 2 by a laser scanner 4. By thus applying a beam corresponding to an image signal, a latent image is formed on the photosensitive drum 2. Next, this latent image is developed by toner contained in a process cartridge 5, thereby forming a toner image (visible image) on the photosensitive drum.
In parallel with this toner image forming operation, a sheet S is fed from a sheet containing cassette 6. The sheet S is conveyed to a transferring portion formed by the photosensitive drum 2 and the transferring roller 3 by means of conveying rollers 7 and registration rollers 7A in synchronism with the image formed on the photosensitive drum 2. Then, in this transferring portion, a bias is applied to the transferring roller 3, thereby transferring the toner image to the sheet S.
After this, the sheet S, to which the toner image has been transferred, is conveyed to fixing means 8, where the sheet S is heated and pressurized, thereby fixing the toner image to the sheet, which is then discharged onto a delivery portion 10 in the upper portion of the apparatus by delivery rollers 9.
The pin retaining arm 14 retaining the engagement pin 13 is rotatable in the lateral direction (direction perpendicular to the attachment direction) with respect to the sheet containing cassette 6 through a shaft 17 described below (shown in
When it is attached to the containing portion 1B, the sheet containing cassette 6 is detachably mounted to the apparatus main body 1 along slide guides 15 shown in
Incidentally, in
Here, the operation of attaching the sheet containing cassette 6 is conducted by the user. When, as a result of the attaching operation, the engagement pin 13 and the pin retaining arm 14 both mounted to the back surface of the sheet containing cassette 6 reach the position of the drawing portion 16, the drawing portion 16 is engaged with the engagement pin 13. When, after this, the sheet containing cassette 6 is further inserted, the pin 13 is drawn in by the drawing portion 16, and the sheet containing cassette 6 is drawn to the feed position.
When, as in the case, for example, of
In view of this, in this embodiment, in the drawing portion 16, which draws the sheet containing cassette 6 by the spring force of the toggle mechanism, the downstream end portion with respect to the inserting direction of the guide groove 24 of the guide member 23 corresponding to the end region of the drawing section, which is a portion where the conveyance resistance to the sheet containing cassette increases due to a spring component, etc. of a detecting sensor or the like, is formed as an arc whose center is the shaft 19 of the arm 18. As a result, the point of action of the moment of the engagement pin 13 is prevented from being moved away from the shaft 19, which is the rotation center of the arm.
That is, as shown in
Next, the operation of drawing the sheet containing cassette 6 performed at the drawing portion 16 thus constructed will be illustrated.
First, the sheet containing cassette 6 is inserted into (attached to) the containing portion 1B through manipulation by the user. When the engagement pin 13 reaches the position as shown in
Next, when the sheet containing cassette 6 in this state is further inserted, the engagement pin 13 gradually moves to the depth side of the grasping groove 18a while pressurizing the arm 18. Then, by being thus pressurized by the engagement pin 13, the arm 18 rotates using the shaft 19 as the pivot. Further, by this rotation of the arm 18, the toggle spring peg 21 is caused to move in the inserting direction. When the toggle spring peg 21 moves in this way, the arm 18 soon reaches a predetermined rotating position as shown in
Next, when, after this position is reached, the sheet containing cassette 6 is further inserted, the neutral positional relationship of the toggle mechanism is dissolved, and thereafter, the arm 18 starts to rotate by the contracting force of the toggle spring 20, using the shaft 19 as the pivot, with the engagement pin under the influence of the action force due to the rotation moment being drawn along the guide groove 24. That is, when the neutral positional relationship of the toggle mechanism is dissolved, the engagement pin 13 is drawn along the guide groove 24 by the contracting force of the toggle spring 20.
Here, at the stage of drawing up to the moment that the state as shown in
Incidentally, during the drawing in the end region of the sheet containing cassette drawing section from the position shown in
In this way, on the downstream side with respect to the attaching direction of the linear portion 24a (which is parallel to the cassette inserting direction) of the guide groove 24 provided in the guide member 23, there is provided the curved portion 24b curved so as not to extend away from the shaft 19 of the arm 18. As a result, it is possible to prevent a reduction in the conveyance force for the sheet containing cassette 6, and to secure a sufficient conveyance force to cope with the increase in conveyance resistance in this section.
Due to this construction, it is possible to increase the conveyance force solely in the portion where the conveyance resistance increases without increasing the spring pressure of the toggle spring 20, with the result that the sheet containing cassette 6 can be reliably drawn. Further, by making the center of the arcuate configuration of the curved portion 24b of the guide groove 24 identical with the shaft 19 of the arm 18, the sliding friction between the guide member 23 and the engagement pin 13 is substantially reduced, making it possible to draw the sheet containing cassette 6 efficiently. Further, due to the efficient transmission of force, there is no need to make the toggle spring 20 unnecessarily strong, so there is no fear of a deterioration in usability when the user draws out the sheet containing cassette 6.
This embodiment differs from the above embodiment in that there is provided a mechanism for slowly rotating the arm 18 so as not to rotate fast, and that there is provided a restoring mechanism for restoring the arm 18 forcibly to the home position. Otherwise, this embodiment is of the same construction and operation as the above embodiment, so the components that are the same as or equivalent to those of the above embodiment are indicated by the same reference symbols, and a description thereof will be omitted.
First, as a mechanism for slowly rotating the arm 18 so as not to rotate fast, a rotary damper 92 (shown in
This construction, which employs the rack 94 and the rotary damper 92, is also applicable to the above-described embodiment.
Next, the restoring mechanism for forcibly restoring the arm 18 to the home position will be described with reference to
In the above embodiment, when a vibration or shock is applied to the apparatus main body, with the sheet containing cassette 6 drawn out, the vibration or shock may be transmitted to the arm 18, and there is a fear of a movement of the sheet containing cassette 6 in the drawing direction occurring although the sheet containing cassette 6 has not been inserted beyond the neutral point of the toggle spring 20 yet. In this case, the arm 18 is not at the home position, where it ought to be situated, so no cassette drawing operation is effected when the sheet containing cassette 6 is to be inserted. Further, even if the sheet containing cassette 6 is pushed in, the sheet containing cassette 6 cannot be inserted so as to reach the feed position due to interference of the engagement pin 13 and the arm 18.
In order that the arm 18 may not be moved by a vibration or shock, it might be possible to set the standby position for the arm 18 at a position greatly deviated in phase from the neutral position of the toggle spring 20. In that case, however, a great force would be exerted in a direction opposite to the cassette inserting direction. Thus, when inserting the sheet containing cassette, the user would have to push the cassette in with a great force, resulting in a deterioration in usability.
In view of this, this embodiment employs a restoring mechanism for the toggle mechanism as described below for coping with such a situation.
As shown in
When a vibration or shock is applied to the apparatus main body, with the sheet containing cassette 6 detached, the vibration/shock may be transmitted to the arm 18, causing the arm 18 to be deviated from the home position and to move to the position as shown in
While in this embodiment, as described above, the hole 114 is used as the restoring means, it is also possible to adopt a protruding configuration as long as it effects engagement when a bar-like object is inserted.
This application claims priority from Japanese Patent Application Nos. 2004-313526 filed Oct. 28, 2004 and 2005-290534 filed on Oct. 3, 2005, which are hereby incorporated by reference herein.
Number | Date | Country | Kind |
---|---|---|---|
2004-313526 | Oct 2004 | JP | national |
2005-290534 | Oct 2005 | JP | national |