JPS641377B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheet feeding device for an electrostatic copying machine or the like.

When copying is performed using an electrostatic copying machine or the like, a large number of copy sheets stacked on a sheet mounting table are fed out one by one by a feed roller starting with the topmost sheet. The most required performance of the sheet feeding device used for this purpose is reliable sheet feeding and prevention of duplicate feeding.

Various proposals have been made to reliably feed out a large number of stacked sheets one by one from the top. Recent achievements include
This method is disclosed in Japanese Patent No. 56-7847, in which the topmost sheet of the loaded sheets is first sent out with a pick-up roller, and a pair of feed rollers and separation rollers arranged on the downstream side prevent double feeding. . The lower sheet of the sheet that happens to be double-fed is pushed back by the separation roller reversed by the reverse torque stored in the coil spring. This takes advantage of the fact that the sheet-to-sheet friction coefficient is generally smaller than the roller-to-sheet friction coefficient.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved sheet feeding device of the type that feeds the sheet back by reversing the separation roller, and in particular, prevents non-feeding of the sheet by the pick-up roller.

The sheet feeding device according to the present invention includes a feed roller that rotates in one direction at a predetermined timing and rotates overrunning as necessary, and a feed roller that is circumscribed to the feed roller and is constantly driven to rotate in the opposite direction at a contact point, and is capable of applying a constant load. a separation roller that rotates with the feed roller when the feed roller passes over the feed roller; a pick-up roller that is arranged on the upstream side in the rotational direction of the feed roller and rotates in response to a paper feed command to send out a sheet that comes into contact with the separation roller; Pressure means for pressing a roller against the sheet; and means for releasing the pressure after the leading edge of the sheet sent out by the pick-up roller is sandwiched between at least the feed roller and the separation roller. It is equipped with

Hereinafter, the present invention will be described with reference to the accompanying drawings. FIG. 1 schematically shows an embodiment of the invention. The uppermost sheet S of the sheets 2 stacked on the sheet loading table 1 is sent out by the pick up roller 3, held by the feed roller 4 and separation roller 5 disposed downstream of the pick up roller 3, and placed on the guide plate. 6 and 7, and is further sent to a pair of transport rollers 8 and 9. The lower part of the sheet handling table 1 is constantly pressed by a push-up arm 10, which is attached to a shaft 13 provided on a bracket 12 that supports the rotation shaft 11 of the separation roller 5. The upper sheet S is Pick-Up Roller 3
is constantly under pressure. The pick-up roller 3 has a drive shaft 14 as shown in FIG.
It is fixed to a rotating shaft 16 rotatably attached to one end of a pick-up roller arm 15 that rotates around the pick-up roller arm 15. Further, the feed roller 4 is fixed to a rotating shaft 18 that is rotatably attached to one end of a feed roller arm 17 that is rotatable around the same drive shaft 14 . each arm 1
Shafts 19 and 20 are provided at the other ends of 5 and 17, and one end of a tension coil spring 21 and 22 is attached to each shaft 19 and 20, respectively.
The other end of the spring 21 is attached to an actuator 23a of a pressure solenoid 23, as shown in FIG. 1, so that the pick-up roller 3 is pressed against the sheet S when the solenoid 23 is energized. The other end of the other spring 22 is attached to a pin 24 provided on a suitable stationary member, so that the feed roller 4 is always pressed against the outer peripheral surface of the separation roller 5.

As shown in FIG. 2, the drive shaft 14, which serves as a rotational fulcrum for both arms 15 and 17, is rotatably supported by a side plate 25 and an auxiliary side plate 26 via bearings 27 and 28, respectively. axial movement is restricted by A sprocket 32 is attached to the shaft portion of the drive shaft 14 extending from the side plate 25 via an electromagnetic clutch 31.
A chain 33 is connected to the sprocket 32 and receives power from a motor (not shown). On the other hand, a gear 34 is located in the middle of the drive shaft 14.
is fixed to the gear 34, and the gear 3 fixed to the pick-up propeller rotating shaft 16 is connected to the gear 34, respectively.
5 and a gear 36 fixed to the feed roller rotating shaft 18 are engaged with each other. Therefore, when the electromagnetic clutch 31 receives a sheet feeding command and is energized, the sprocket 32 and the drive shaft 14 are connected, the pick up roller 3 and the feed roller 4 rotate in the same direction, and the sheet S is moved in the direction of the arrow. Feed in 37 directions. An overrun clutch is interposed between the feed roller 4 and its rotating shaft 18, if necessary, to stop the rotation of the drive shaft 14 and cause the feed roller 4 to overrun by a certain amount.

On the other hand, as shown in FIGS. 3 and 4, the separation roller 5 is rotatably attached to the side plate 25 and the auxiliary side plate 38 via bearings 39 and 40, respectively, and has a sprocket 41 at each extending end. , is attached via a torque limiter 43 to the rotating shaft 11 to which an E-ring 42 is attached. This torque limiter 43 has a rubber separation roller 5 fixedly attached to the rotating shaft 11.
A driven hub 44 is rotatably attached to the driven hub 44, and a driving hub 45 having the same diameter and fixed to the rotating shaft 11.
and a coil spring 46 attached around both hubs 44 and 45, and movement in the axial direction is restricted by fixing thrust stops 47 to the shaft 11 on opposite sides. Since the coil spring 46 is slightly frictionally connected to both hubs 44 and 45, the sprocket 41 is rotated clockwise in FIG. When driven in the opposite direction, the drive hub 45, coil spring 46, and driven hub 44 also rotate in the same direction. When the load on the separation roller 5 increases above a certain level, the drive hub 45 rotates in a direction to unwind the coil spring 46, so the frictional connection between the drive hub 45 and the coil spring 46 slips, causing the drive hub 45 to unwind. No power is transmitted from the separation roller 5 to the separation roller 5.
Therefore, when the load on the separation roller 5 is small, the separation roller 5 is driven in the opposite direction to the feed roller 4 at its contact point, and when the load is large, the separation roller 5 is not driven and rotates along with the feed roller 4. and rotate in the same direction at the point of contact.

Generally, the friction coefficient between paper and paper is smaller than the friction coefficient between paper and a rubber roller, so when two or more sheets of paper are interposed between the separation roller 5 and the feed roller 4, the separation roller The load on the separation roller 5 is relatively small, so the separation roller 5 receives the power transmitted from the sprocket 41 and pushes back the paper in contact with it in a direction opposite to the paper feeding direction by the feed roller 4. On the other hand, if there is no paper between the spallation roller 5 and the feed roller 4, or if there is only one paper,
Since the load applied to the separation roller 5 is relatively large, the power from the sprocket 41 is not transmitted to the separation roller 5, and the separation roller 5 rotates together with the feed roller 4, so that when there is paper between them, cooperates with the feed roller 4 to convey this in the paper feeding direction.

In this manner, sheet separation is performed by the separation roller 5 and the feed roller 4.Next, the paper feeding conditions in this invention will be theoretically considered. It should be noted that this consideration ignores the influence of the gear train. First, considering the requirements for feeding the sheet S by the pick-up roller 3, the force F ₀ required for the pick-up roller 3 to feed the top sheet S in FIG. 5 is as follows.

F ₀ = (μO−μP) M−α …(1) μO: Coefficient of friction between pick-up roller 3 and sheet S μP: Coefficient of friction between sheets S M: Pressure force of pick-up roller 3 against sheet S α: Electrostatic force between sheets Next, in FIG. 6, the necessary force F ₁ for the feed roller 4 to convey the sheet S is as follows.

F ₁ > T F ₁ =μRN ∴T<μRN (2) T: Force of separation roller 5 pushing back sheet S μR: Coefficient of friction between feed roller 4 and sheet S N: Separation roller 5 of feed roller 4 Pressure force against the feed roller 4 as shown in FIG.
and the separation roller 5.
When S ₁ and S ₂ intervene, the separation roller 5 stops or pushes back the lower sheet S ₂ in response to the force F ₂ by which the feed roller 4 conveys the upper sheet S ₁ to separate both sheets. The requirements are as follows.

F ₂ ≦T F ₂ =μPN+μP(M+m) +μR(M+2m) =μPN+μP(2M+3m) ∴T≧μPN+μP(2M+3m) …(3) m: Weight per sheet S Equation (2) and (3) above The formula can be summarized as follows.

μRN>T≧μPN+μP (2M+3m) …(4) From this equation (4), the force T for separating the sheets
is required to be larger than the load μPN when the number of sheets interposed on the separation roller 5 is two or more, and smaller than the load μPN when the number of sheets is one or less. This T has a relationship of T=τ/r, where r is the radius of the separation roller 5 and τ is the torque of the torque limiter 43. Therefore, the torque τ of the torque limiter 43 is expressed as (4) above.
If the equation is determined to satisfy the equation, good sheet feeding can be achieved.

On the other hand, when formulas (2) and (3) above are obtained for N and combined into one, the following is obtained.

T/μR<N≦T/μP−(2M+3m) …(5) Therefore, if T is fixed, N
By adjusting within the range of formula (5), reliable single-sheet feeding can be achieved while preventing duplicate feeding. Note that when two torque limiters 43 are used, T, N, and M in the above equation become 2T, 2N, and 2M, respectively, so 3m in equation (5) only changes to 3m/2.

By the way, as is clear from the above equation (1), as the pressing force M of the pick-up roller 3 against the sheet S increases, the sheet conveyance force F ₀ also increases,
The sheet S is reliably sent out from its stacking position. The sheets used in recent copying machines have a wide variety of properties, and the sheet feeding device that feeds these sheets has a system that can handle any type of sheet without causing misfeeding. Reliable feeding performance is required. In particular, since the electrostatic force α in equation (1) above changes due to the influence of the environment, etc., in order to overcome this change and ensure reliable feeding, the pressing force M on the sheet S by the pick-up roller 3 is changed.
is the preferred measure. However, if the pressing force M of the pick-up roller 3 is increased, 2M in the above equation (4) or (5) also increases, the appropriate range of T or N becomes narrower, and the margin for design or adjustment becomes smaller accordingly. . Therefore, if the pressure of the pick-up roller is increased,
Although the pick-up roller 3 can reliably feed the paper, there is a risk that the separation roller 5 will not function sufficiently to prevent duplicate feeding.

The present invention solves this dilemma by providing a pressure means for pressing the pick-up roller 3 against the sheet S during feeding, and at the same time, the leading edge of the sheet sent out by this roller is at least separated from the feed roller 4. This is overcome by releasing the pressure applied to the sheet by the pressure means after the sheet is caught between the rollers 5 and the roller 5. Although such a pressurizing means is a pressurizing solenoid 23 provided at the upper end of the pick-up roller arm 15 via a spring 21 in FIG. 1, other methods and types may be used. For example, pressure may be applied according to the sheet feeding timing by the sheet push-up arm 10.

In normal conditions, the pick-up roller 3 rests on the sheet S due to its own weight. When the solenoid 23 is energized by a paper feed command, the pick-up roller arm 15 swings around the shaft 14, and the pick-up roller 3 is pressed against the sheet S. At the same time, the pick-up roller 3 is rotated by the motor, and the sheet S is sent out in the paper feeding direction. When the leading edge of the fed sheet S is detected by a sheet sensor 46 such as a photo sensor provided on the window 6a of the conveyance guide 6 downstream of the feed roller 4, the signal is applied to the sheet S as shown in FIG. The pressure solenoid 23 is demagnetized, the pressure on the pick-up roller 3 is released, and the pick-up roller 3 is placed on the sheet S again by its own weight, and separation by the separation roller 5 occurs when two or more sheets are fed. Make it easier.

As the sheet sensor 48, a micro switch or the like can be used in addition to a photo sensor. Further, without using such a sheet sensor, a timer may be used to turn off the solenoid 23 after the leading edge of the sheet is caught between the feed roller 4 and the separation roller 5. moreover,
When the copy switch of a copier, etc. is turned on, the solenoid 23 is immediately turned on and the pick-up roller 3 is turned on.
After the leading edge of the sheet S is caught between the feed roller 4 and the separation roller 5, the pressure is released, and when the rear end of the sheet S comes out of the pick-up roller 3, the pressure is applied again. It is also possible to do so. Furthermore, the pick-up roller 3 may be held in a state floating above the sheet S under normal conditions, and may be brought into pressure contact with the sheet S after receiving a paper feeding command. In this case, when using two or more rollers as the pick-up roller 3, care must be taken to prevent the sheet from skewing due to uneven contact when pressed against the sheet.

When we actually tested the pick-up roller by changing its pressing force, as shown in Figure 9, the pressure at which the pick-up roller does not cause non-feeding is approximately
200g or more (especially for OHP and peeler paper) is required, and the pressing force of the pick-up roller when the separation roller pushes back the second and subsequent sheets is 50g or less (especially for OHP and peeling paper), as shown in Figure 10. Good results were obtained for thin paper (30Kg to 45Kg). For this reason, when feeding paper using the pick-up roller as in the present invention, a high pressure is applied to it, and when the paper feeding by the pick-up roller is finished and the paper is fed by the feed roller,
It will be appreciated that releasing pressure on the pick-up roller is a highly preferred measure.

[Brief explanation of drawings]

1 is a schematic configuration diagram showing an embodiment of a sheet feeding device according to the present invention, FIG. 2 is a perspective view showing a pick-up and feed roller unit of the device shown in FIG. 1, and FIG. 1 is an exploded perspective view showing the separation roller unit of the apparatus shown in FIG. 1, FIG. 4 is a sectional view of the unit shown in FIG. 3, and FIGS. FIG. 8 is a diagram for explaining the conditions, and FIG. 8 is a diagram showing the operation timing of the pick-up roller pressing means of the apparatus shown in FIG. 1. FIG. 9 is a diagram showing the pressing force of the pick-up roller and the sheet feeding performance by the pick-up roller. FIG. 10 is a diagram showing the relationship between the pressing force of the pick-up roller and the separation performance of the separation roller. 3... Pick up roller, 4... Feed roller, 5... Separation roller, 23... Pressure solenoid, 48... Sheet sensor.

Claims (1)

[Claims] 1. A feed roller 4 that rotates in one direction at a predetermined timing and rotates overrunning as necessary, and a feed roller 4 that is circumscribed to the feed roller 4 and is constantly driven to rotate in the opposite direction at its contact point, and when a certain load is exceeded. a separation roller 5 that rotates together with the feed roller 4; a pick-up roller 3 that is arranged on the upstream side in the rotational direction of the feed roller 4 and rotates in response to a paper feed command to send out a sheet that comes into contact with the separation roller 4; A pressure means 23 presses the pick-up roller 3 against the sheet, and the leading edge of the sheet fed out by the pick-up roller 3 is sandwiched between the feed roller 4 and the separation roller 5. and means for releasing the pressure applied to the sheet by the pressure means 23 when the sheet is reversely fed.