Apparatus and method for controlling pressing force of separation roller

Abstract

There is provided a method in which a conveyance force of a feed roller applied to recording paper is maintained constant in a period from the start to the end of use of the feed roller and a separation roller. The separation roller pressing force control method according to the present invention is such that a pressing force of the separation roller applied to the feed roller is set to be low in a variable range (Sa) such as the start of use in which the coefficient of friction of the feed roller is high, so that the conveyance force applied to the recording paper is not too large. As the coefficient of friction gradually decreases in accordance with the use of the feed roller, the pressing force of the separation roller is made to be gradually raised, thereby increasing the conveyance force applied to the recording paper and retaining it in a stable area Sb. As a result, reduction in the coefficient of friction and the conveyance force in accordance with the use of the feed roller and the separation roller is canceled or offset by adjusting the pressing force of the separation roller applied to the feed roller, whereby the feed roller can always feed the sheets of recording paper at a constant conveyance force, thus making it possible to prevent defective conveyance and defective separation of the sheets of recording paper.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus for controlling a pressing force of a separation roller, and more particularly, to a separation roller pressing force control apparatus and method for successively feeding sheets of recording paper one by one by passing the sheets between a feed roller and a separation roller in a copying machine or the like.

[0003] 2. Description of the Related Art

[0004] A feed roller and a separation roller, generally used in a copying machine or the like, serve to feed (pass) sheets of recording paper one by one with the sheets being not superposed with each other, by clamping the recording paper sheets between both of the rollers through application of a constant pressing force. In general, EPDMs (ethylene propylene rubbers) and the like are used as materials for the feed roller and the separation roller. However, these materials have a coefficient of friction which is high at the beginning of their use, decrease as the use proceeds, and then become stabilized and settled in a prescribed value. When the pressing force of the separation roller against the feed roller is retained constant, a coefficient of conveyance force with respect to the recording paper based on the coefficient of friction of the feed roller (and the separation roller) provides a conveyance force (conveyance force coefficient×pressing force) more than twice as much as a the pressing force at the beginning, as shown in FIG. 7, but at the time a paper feed of 4K (4,500) sheets or so is executed, the conveyance force produced decreases to about once (one-fold) of the pressing force.

[0005] In the known feed roller and the separation roller as described above, when the setting of the pressing force of the separation roller with respect to the feed roller is low, defective conveyance would result due to slippage between the feed roller and the recording paper, whereas when the pressing force is high, defective sheet separation such as two-sheet feed would take place. Thus, in order to solve this problem, there has been known a technique that a detection means, which detects the number of revolutions per minute of a separation roller, and a special motor are provided for making the conveyance force of the feed roller constant (for instance, Japanese patent application laid-open No. Hei 4-371426). However, there is a demand that defective conveyance and defective separation are wanted to be prevented without using large-scale (additional) members such as a sensor, a motor, etc., for the purposes of reduction in cost and size.

SUMMARY OF THE INVENTION

[0006] The present invention is intended to solve the problems as referred to above, and has for its object to provide a method and apparatus in which the conveyance force of a feed roller with respect to recording paper remains constant during a period from the start to the end of use of the feed roller and a separation roller without using large-scale or additional members.

[0007] In order to solve the above-mentioned problem, the present invention resides in a separation roller pressing force control apparatus for controlling a pressing force of a separation roller applied to a feed roller, the apparatus comprising: a separation roller retention mechanism for retaining the separation roller in such a manner that the separation roller is pressed against the feed roller; and a pressing force adjusting mechanism for maintaining a conveyance force of the feed roller applied to paper substantially constant by changing the pressing force of the separation roller in accordance with a change in the coefficient of friction of the feed roller.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a graph illustrating the concept of a separation roller pressing force control apparatus according to the present invention in an easy-to-understand manner.

[0009] FIG. 2 is a block diagram showing an embodiment of the separation roller pressing force control apparatus according to the present invention.

[0010] FIG. 3 is an enlarged view explaining the relation between a screw shaft and a movable arm shown in FIG. 2.

[0011] FIG. 4 is a view explaining the movements of respective component parts at the time of replacement of a feed roller and a separation roller shown in FIG. 2.

[0012] FIG. 5 is a view explaining the movements of respective component parts at the time of replacement of the feed roller and the separation roller shown in FIG. 2.

[0013] FIG. 6 is a block diagram showing another embodiment of a separation roller pressing force control apparatus according to the present invention.

[0014] FIG. 7 is a graph illustrating a change in a conveyance force for recording paper in a known feed roller.

DESCRIPTION OF THE PREFERRED ENBODIMENTS

[0015] Now, preferred embodiments of the present invention will be described below based on the accompanying drawings. FIG. 1 is a graph illustrating the concept of a separation roller pressing force control apparatus according to the present invention in an easy-to-understand manner. FIG. 2 is a block diagram showing an embodiment of the separation roller pressing force control apparatus according to the present invention. FIG. 3 is an enlarged view explaining the relation between a screw shaft and a movable arm shown in FIG. 2. FIGS. 4 and 5 are views explaining the movements of respective component parts when a feed roller and a separation roller shown in FIG. 2 are replaced with new ones. FIG. 6 is a block diagram showing another embodiment of a separation roller pressing force apparatus according to the present invention. Here, note that the embodiments shown in FIG. 2 through FIG. 6 are implementations of the contents of the invention to be described later and illustrated in FIG. 1 as apparatuses.

[0016] First of all, reference will be made to the adjustment of the pressing force of the separation roller applied to the feed roller according to the present invention while using FIG. 1. As already explained with reference to FIG. 7, the coefficient of friction of the feed roller gradually decreases in accordance with the number of sheets of recording paper being fed in a variable range Sa at the start of use of the roller. Accordingly, the coefficient of conveyance force based on the coefficient of friction also decreases gradually, and when the number of paper sheets fed becomes around 4.5 K, the coefficient of conveyance force enters a stable area Sb and becomes substantially constant. Therefore, in the variable range Sa, the pressing force of the separation roller against the feed roller is gradually increased so that the reduction in the coefficient of conveyance force of the feed roller can be canceled out or offset, whereas when the coefficient of conveyance force has entered the stable area Sb, the pressing force of the separation roller is kept constant.

[0017] The separation roller pressing force control apparatus shown in FIG. 2 is used for feeding sheets of paper in a copying machine or the like. In the case of this example, a drive motor 10 is mounted on a motor mounting frame 11. A feed roller 20 has a rotating shaft 21 with its one end supported by the motor mounting frame 11, and a roller portion 22 attached to the other end of the rotating shaft 21. This rotating shaft 21 is supported by a support plate 24 with a bearing 23 attached thereto at a location near the roller portion 22. In this case, the support plate 24 is fixedly secured to an upper frame (not shown).

[0018] A separation roller 30 has a rotating shaft 31 with its one end supported by the motor mounting frame 11, a torque limiter 39 arranged at the other end of the rotating shaft 31, and a roller portion 32 attached to the torque limiter 39. This rotating shaft 31 is supported by a support plate 34 with a bearing 33 attached thereto at a location near the roller portion 32. In this case, the support plate 34 is fixedly secured to a lower frame 90, but the bearing 33 is arranged in an elongated hole formed in the support plate 34 for vertical movement. A release lever 40 is arranged along the separation roller 30 on the lower frame 90 below the separation roller 30 in such a manner that it is rotatable about a support shaft 41 within a vertical plane. In this case, the support plate 34 is arranged so as not to obstruct the rotation of the release lever 40.

[0019] A pressure arm 50 is rotatably mounted on a support shaft 51, which is fixedly secured to a cut-out and bent-up or upright portion 91 formed on the lower frame 90, in such a manner that it is rotatable on a vertical plane parallel to the plane of rotation on which the release lever 40 is rotatable. A pressure spring 55 in the form of a coil or helical spring has one end thereof attached to a lower end of the pressure arm 50 so that the pressure arm 50 is thereby pulled in a direction toward the motor mounting frame 11. The pressure arm 50 has an upper end in abutment with a lower end of the bearing 33 so as to apply a pressing force corresponding to the tensile force of the pressure spring 55 to the bearing 33 and hence the separation roller 30, thereby pushing it up toward the feed roller 20. A screw shaft 60 has one end thereof rotatably mounted on the motor mounting frame 11, and the other end thereof rotatably mounted on a cut-out and bent-up or upright portion 92 formed on the lower frame 90. A screw groove 61 with a gradually changing screw pitch is formed on the surface of the screw shaft 60. The screw shaft 60 is driven to rotate in a direction indicated by an arrow RA at a location near the motor mounting frame 11 by means of the drive motor 10, which drives the feed roller, etc., through a speed reduction mechanism 80 using gears.

[0020] A movable arm 70 has one end thereof mounted on a support shaft 94 fixedly secured to the lower frame 90, and in this case, the mounting of the movable arm 70 to the support shaft 94 is made such that an angle of the movable arm 70 relative to the support shaft 94 can be varied in the vertical direction to some extent so as to permit the movable arm 70 to freely rotate in the horizontal direction. A protrusion 71 (FIG. 3) is formed on a lower surface of the movable arm 70 at the other end thereof, and it is placed into fitting engagement with the screw groove 61 of the screw shaft 60. This protrusion 71 extends to some extent in the longitudinal direction of the movable arm 70. In addition, the other end of the pressure spring 55 is attached to the movable arm 70 at a location slightly closer to the support shaft 94 from the protrusion 71. In this case, the movable arm 70 operates between the rotating shaft 31 and the release lever 40 when operating normally as shown in FIG. 2, but it is pushed toward the screw shaft 60 under the action of the resilient force of the pressure spring 55.

[0021] Now, reference will be made to the successive operation of the separation roller pressing force control apparatus of FIG. 2 while referring to FIG. 3. At the time when a new feed roller 20 and a new separation roller 30 begin to be used, the movable arm 70 has been turned to the side of the pressure arm 50, with the protrusion 71 being in engagement with a start groove MS, as shown in FIG. 3. Accordingly, the protrusion 71 of the movable arm 70 is located at a position nearest to the pressure arm 50, so the force applied to the pressure arm 50 through the pressure spring 55 is smallest and hence the pressing force applied to the separation roller 30 by the pressure arm 50 is least or minimum. On the other hand, the coefficients of friction of the new feed roller 20 and the new separation roller 30 (and the conveyance force coefficient or conveyance force based on the coefficients of friction force) are greatest, so the large coefficients of friction are offset by the small pressing force, whereby the conveyance force becomes a desired value.

[0022] As the feed roller 20 and the separation roller 30 are started to be used, they serve to separate and convey sheets of recording paper one by one. At this time, the screw shaft 60 is driven to rotate in the direction of the arrow RA (FIG. 2) at a low speed through the speed reduction mechanism 80, so that the protrusion 71 of the movable arm 70 is caused to move from the start groove MS to a variable pitch groove MV. Thus, the protrusion 71 of the movable arm 70 is advanced in a direction indicated by an arrow DA (FIG. 3) to finally enter an end groove MZ. The variable pitch groove Ml has a pitch which is coarse at a location near the start groove MS, and which becomes finer and finer as the distance thereof from the start groove MS increases. Therefore, while the protrusion 71 is moving within the variable pitch groove MV, the pressure spring 55 is stretched or expanded at a fast speed at first (i.e., in the variable range Sa of FIG. 1), and hence the force applied to the pressure arm 50 through the pressure spring 55 is also increased at a fast speed. The rate of stretching or expansion of the pressure spring 55 is gradually slowed down, so the force applied to the pressure arm 50 through the pressure spring 55 gradually increases at a slower speed, and finaly becomes constant.

[0023] As described above, by changing the pitch of the screw groove formed in the screw shaft 60 in a manner as shown in FIG. 3, the pressing force of the roller portion 32 of the separation roller 30 applied to the roller portion 22 of the feed roller 20 can be changed in a manner as shown in a characteristic curve of FIG. 1. Accordingly, the conveyance force applied to the recording paper by the roller portion 22 of the feed roller 20 does not change in accordance with the number of sheets of paper being fed (i.e., the number of sheets passed), thus making it possible to feed the sheets of recording paper with a constant force. As the conveyance force applied to the recording paper remains constant, there will not be any defective conveyance and defective separation of the recording paper. Moreover, since the apparatus is constructed of mechanical component members of simple structure alone, it is simple in construction, low in cost and small in space, as compared with the known one using a detection means for detecting the number of revolutions per minute of a separation roller as well as a special motor.

[0024] Next, reference will be made to the case in which in the separation roller pressing force control apparatus of FIG. 2, the feed roller and the separation roller after having been fully used are replaced with new ones, while referring to FIG. 4 and FIG. 5. When the feed roller 20 and the separation roller 30 have been fully used, the mountings (for instance, E rings) of the rotating shafts 21, 31 of the feed roller 20 and the separation roller 30 to the motor mounting frame 11 are removed (in this connection, note that the separation roller 30 and the feed roller 20 are generally replaced with new ones at the same time). At this time, the protrusion 71 of the movable arm 70 is usually in engagement with the end groove MZ of the screw shaft 60. First of all, the feed roller 20 is pulled out in a direction indicated by an arrow DB, and then the separation roller 30 is pulled out in the direction of the arrow DB. When the separation roller 30 is pulled out, the roller portion 32 abuts against a lamp 42 of the release lever 40, whereby the lamp 42 is depressed in a direction indicated by an arrow RB, as shown in FIG. 5.

[0025] When the roller portion 32 has depressed the lamp 42 of the release lever 40, the release lever 40 is rotated about the support shaft 41, thereby pushing up the movable arm 70. When the movable arm 70 has been pushed up, the protrusion 71 of the movable arm 70 is released from the end groove MZ of the screw shaft 60, whereby the protrusion 71 of the movable arm 70 is returned to the position of the start groove MS under the action of the resilient force of the pressure spring 55, as shown by an arrow RC in FIG. 5. When the separation roller 30 is further pulled out so that the roller portion 32 has passed through the lamp 42, the protrusion 71 of the movable arm 70 is brought into engagement with the start groove MS. When the separation roller 30 is freshly installed, the protrusion 71 of the movable arm 70 comes off from the start groove MS, similar to the time when the separation roller 30 is pulled out, but it is again placed into engagement with the start groove MS. Accordingly, when the separation roller 30 (the feed roller 20) is replaced with a new one, the initial setting of the pressing force of the new separation roller 30 is automatically carried out with a simple structure. However, it is of course possible, if necessary, to set the position of the protrusion 71 of the movable arm 70 to a desired position on the screw shaft by pressing the lamp 42 of the release lever 40 with a finger, etc., to release the protrusion 71 of the movable arm 70 from the screw groove, in the state shown in FIG. 2.

[0026] Now, reference will be made to another embodiment of a separation roller pressing force control apparatus according to the present invention while referring to FIG. 6. In the separation roller pressing force control apparatus of FIG. 6, a rotating plate 160 with a spiral groove is used instead of the screw shaft 60 of FIG. 2. The rotating plate 160 is driven to rotate by means of a drive motor 110 through a speed reduction mechanism 180. A protrusion (not shown) is provided on a lower surface of a movable arm 170 at a free end thereof, and it is in engagement with a spiral groove 161 in the rotating plate 160. At the start of use of a separation roller 130 (and a feed roller 120), the protrusion on the movable arm 170 is in engagement with an outermost spiral groove 161 at a location near a pressure arm 150. The protrusion on the movable arm 170 is caused to gradually move to a center portion of the rotating plate 160 in accordance with the increasing number of sheets of paper being fed. Thus, a pressure spring 155 is caused to expand in accordance with the increasing number of sheets of paper being fed, so the pressing force of the separation roller 130 applied to the feed roller 120 is accordingly increased by means of the pressure arm 150. In this connection, note that the function of a release lever 140 is the same as that of the release lever 40 of FIG. 2.

[0027] As described above, in the variable range Sa shown in FIG. 1, the coefficient of conveyance force based on the coefficient of friction of the feed roller gradually decreases in accordance with the characteristic curve in the variable range Sa shown in FIG. 1, that is, the coefficient of conveyance force with respect to the recording paper gradually decreases in accordance with the characteristic curve. The separation roller pressing force control apparatuses shown in FIG. 2 and FIG. 6 increase the pressing force of the separation roller applied to the feed roller in accordance with the decreasing conveyance force (conveyance force coefficient×pressing force) applied to the recording paper, whereby reduction in the coefficient of friction of the feed roller in the variable range Sa is canceled or offset to keep the conveyance force of the feed roller applied to the recording paper at a constant value in a period from the start of use of the feed roller to the end of use thereof. In addition, since such operation is achieved by simple mechanical or structural members, the apparatuses are low in cost, and advantageous for the reduction in size.

[0028] Since a method and apparatus for controlling the pressing force of a separation roller according to the present invention are constructed in a manner as described above, when the coefficient of friction of a feed roller is high, the conveyance force applied to recording paper can be controlled so as not to be too large by setting the pressing force of the separation roller against the feed roller to a small value, whereas when the coefficient of friction gradually decreases in accordance with the use of the feed roller, the pressing force of the separation roller against the feed roller is gradually raised to increase the conveyance force applied to the recording paper. As a result, reduction in the coefficient of friction and the conveyance force in accordance with the use of the feed roller and the separation roller is canceled or offset by adjusting the pressing force of the separation roller applied to the feed roller, whereby the feed roller can always have a constant conveyance force. Thus, it is possible to prevent defective conveyance and defective separation with respect to the recording paper. Moreover, such operation can be achieved by simple mechanical or structural members, and hence the apparatus is low in cost and advantageous for the reduction in size. Furthermore, in a development example, the initial setting of the pressing force of the separation roller applied to the feed roller is automatically carried out at the time when the feed roller and the separation roller are replaced with new ones, thereby providing ease of use.

Claims

1. A separation roller pressing force control apparatus for controlling a pressing force of a separation roller applied to a feed roller,

said apparatus comprising:

a separation roller retention mechanism for retaining said separation roller in such a manner that said separation roller is pressed against said feed roller; and

a pressing force adjusting mechanism for maintaining a conveyance force of said feed roller applied to paper substantially constant by changing the pressing force of said separation roller in accordance with a change in the coefficient of friction of said feed roller.

2. The separation roller pressing force control apparatus as set forth in claim 1, wherein said pressing force adjusting mechanism changes the pressing force of said separation roller applied to said feed roller by using a driving force of said feed roller.

3. The separation roller pressing force control apparatus as set forth in claim 2, wherein said pressing force adjusting mechanism comprises:

a pressure arm having its one end held for rotation about a pressure arm support shaft so as to press said separation roller toward said feed roller;

a pressure spring having its one end attached to the other end of said pressure arm;

a movable arm having one end thereof held for rotation about a movable arm support shaft and the other end thereof to which is attached the other end of said pressure spring;

a speed reduction mechanism for performing transmission of the driving force of said feed roller; and

a pressure spring expansion mechanism adapted to receive the driving force transmitted from said speed reduction mechanism to set a tensile force of said pressure spring to a low value at the start of use of said feed roller, and to increase the tensile force of said pressure spring applied to said pressure arm in accordance with the increasing number of sheets of paper being fed thereby to gradually increase the pressing force applied to said separation roller by said pressure arm.

4. The separation roller pressing force control apparatus as set forth in claim 3, wherein when the number of sheets of paper being fed has reached a threshold, said pressure spring expansion mechanism maintains the pressing force which is applied to said separation roller by said pressure arm at that time.

5. The separation roller pressing force control apparatus as set forth in claim 3, wherein said pressure spring expansion mechanism comprises a screw shaft which is arranged to extend in a direction toward said pressure arm, and which is driven to rotate under the action of the driving force from the speed reduction mechanism, and a screw groove of an irregular pitch is formed on the outer periphery of said screw shaft, so that the one end of said movable arm is engageable with said screw groove.

6. The separation roller pressing force control apparatus as set forth in claim 5, wherein said screw shaft has a start groove formed on the outer periphery thereof at an end portion thereof near said pressure arm, an end groove formed on the outer periphery thereof at an end portion thereof away from said pressure arm, and a screw groove formed on the outer periphery thereof between said start groove and said end groove, said screw groove starting from said start groove with a coarse pitch, and being connected with said end groove with its pitch becoming gradually finer and finer.

7. The separation roller pressing force control apparatus as set forth in claim 3, wherein said pressure spring expansion mechanism comprises a rotating plate which is formed on its surface with a spiral groove extending from its center of rotation, and which is caused to rotate by the driving force from said speed reduction mechanism, and a screw groove of an irregular pitch is formed on the surface of said rotating plate, with the other end of said movable arm being engageable with said screw groove.

8. The separation roller pressing force control apparatus as set forth in claim 7, wherein said rotating plate is formed on its surface with a spiral groove extending from its center of rotation and is caused to rotate by the driving force from said speed reduction mechanism, and said rotating plate has a start groove formed on its outermost periphery, and an end groove formed at its center of rotation, and a screw groove of an irregular pitch formed on its outer periphery between said start groove and said end groove, said screw groove starting from said start groove with a coarse pitch, and being connected with said end groove with its pitch gradually becoming finer and finer.

9. A separation roller pressing force control method in which sheets of recording paper are passed between a feed roller and a separation roller with a pressing force of said separation roller applied to said feed roller being controlled so as to feed the sheets of recording paper one by one,

said method comprising:

retaining said separation roller so as to permit said separation roller to move toward said feed roller; and

maintaining the pressing force of said separation roller applied to said feed roller at a constant value by changing the pressing force of said separation roller applied to said feed roller by the use of a driving force of said feed roller so as to offset a change in the coefficient of friction of said feed roller which changes in accordance with the number of sheets of paper being fed.