JPH0126669Y2 - - Google Patents

Description

[Detailed explanation of the idea]

Technical Field This invention relates to a friction separation type paper feeding device used in copying machines and the like. Prior Art A device that separates sheets of paper one by one from a stack of sheets stacked on the paper feed table of an electrophotographic copier or facsimile machine and feeds them into the machine is a device that abuts the top surface of the stack of sheets and feeds the paper into a predetermined position according to a paper feed signal. A pick-up roller that rotates in the paper feeding direction, a feed roller located downstream of the pick up roller that rotates in the paper feeding direction, and a separation roller that pinches the paper path and presses against it and can rotate in the opposite direction to the paper feeding direction. A well-known friction separation roller paper feeding device that uses the above-mentioned difference in the friction coefficient between the roller and the paper and the friction coefficient between each paper to separate multiple sheets of paper and feed the paper one sheet at a time. There is. In this case, if the separation roller is always rotated at a constant speed in the opposite direction to the paper feeding direction, that is, in the paper return direction, or if it is stationary, the friction coefficient between the separation roller and the paper can be adjusted by adjusting the friction coefficient between the separation roller and the paper. It is essential that the friction coefficient be smaller than the friction coefficient between the paper sheets and larger than the friction coefficient between the paper sheets. Therefore, there are restrictions on the selection of the material of the roller. In addition, when no paper is passing or when one sheet is passing, the separation roller slips against the feed roller or paper, and the roller wears out over time. Also, the separation performance becomes unstable as the coefficient of friction decreases due to the generation and adhesion of paper dust. There are drawbacks. In order to improve this, a torque limiter is installed between the separation roller and its drive source, and a constant torque is always applied to the separation roller in the direction of returning the paper. When only the paper is fed, the frictional force between the rollers or between the paper and the rollers overcomes the above torque, and the separation roller follows the feed roller and rotates without slipping or feeds the paper.
When more than one sheet of paper is fed between the pair of rollers, the torque overcomes the frictional force between the sheets and pushes the second and subsequent sheets back toward the paper feed cassette, separating them and contacting the feed roller. A paper feeding device that feeds only one sheet of paper into the machine has been proposed. According to this method, the selection range of the friction coefficient of the separation roller is considerably wide, the material selection becomes easy, and most paper types can be separated and conveyed. Further, there is no slippage between the paper, the feed roller, and the separation roller, which has the advantage of reducing wear, but it requires an expensive torque limiter, which increases costs. Purpose This invention eliminates the above-mentioned drawbacks of conventionally used or proposed friction separation roller paper feeding devices, and takes into account the friction coefficient of the separation roller to be smaller than that of the feed roller without using a torque limiter. To provide an inexpensive friction separation paper feeding device which can obtain stable separation paper feeding performance for most types of paper without having to pay any additional cost. Configuration Hereinafter, the present invention will be described in detail based on drawings showing embodiments thereof. In the embodiment of the present invention schematically shown in FIG. 1, a pick-up roller 2 presses against the upper surface of a stack of sheets 1 placed on a sheet feed table with a pressing force of P _A , and Rotates a certain amount in the paper feeding direction indicated by the arrow. On the downstream side of the pick-up roller 2, a pair of rollers is provided, including a feed roller 3 that rotates at the same speed and in the same direction as the pick-up roller 2, and a separation roller 4 that pinches the paper path and presses against it with a pressing force P _B. ing. A paper detection means 5 is provided at a position immediately after the nip portion of the pair of rollers 3 and 4. Paper detection means 5
A light-emitting element and a light-receiving element are provided facing each other across a paper path, and can detect no paper, passage of one paper, and passage of two or more papers. At the shaft end of the separation roller 4, as shown in FIG. 2, there is a sprocket gear 8 which is constantly driven by the shaft 6 and a drive source (not shown) in a direction to rotate the separation roller in the return direction via a chain 7. An electromagnetic clutch 9 is provided between the two. A ratchet wheel 10 is also fixed to the separation roller shaft 6, and a locking pawl 12 that locks the ratchet wheel 10 when a solenoid 11 is turned on is provided facing the separation roller shaft 6. FIG. 2b is a side view of the ratchet wheel 10 and the locking pawl 12. The detection signal from the paper detection means 5 is sent to the electromagnetic clutch 9 and solenoid 11, and each is controlled as follows depending on the number of sheets detected.

[Table] Therefore, when the paper detection means 5 does not detect any paper, the separation roller 4 becomes free and rotates following the feed roller 3, and when one paper is detected, the locking pawl 12 is attached to the ratchet wheel 10. engages and the separation roller stops, and when two or more sheets of paper are detected, the sprocket wheel, which is constantly rotating by the chain 7, is connected to the separation roller shaft 6 by the electromagnetic clutch 9, and the separation roller is rotated. 4 rotates in the return direction. Although the pick up roller and the feed roller are provided separately in the above embodiment, they may be used as one roller, or an endless belt may be used instead of the roller. Since this device is constructed as described above, the separation roller 4 follows the feed roller 3 until the paper arrives, so that there is no slippage and friction is prevented as much as possible. Next, in order to separate and convey the sheets, P _A and P _B can be set as shown below. As shown in Figure 3, to feed one sheet of paper between the feed roller 3 and separation roller 4 using the pick-up roller 2, the coefficient of friction between the paper and the roller is μ _R The coefficient of friction between the sheets is μ _P One sheet of paper If the weight of is m, then μ _R P _A > μ _P (P _A + m) ∴μ _R > μ _P (1 + m/P _A ) Since m is sufficiently small compared to P _A , μ _R > μ _PThe leading edge of the paper When the sheet passes through the feed roller 3 and the separation roller 4 and is detected by the paper sensor 5, the separation roller stops. Therefore, a frictional force μ _R P _B acts in the conveying direction between the paper and the feed roller 3, and a frictional force μ _R P _B acts in the opposite direction between the separation roller 4 and the paper, so that the two are in equilibrium. However, since the conveyance force by the pick-up roller 2 is greater than the frictional force between the first and second sheets of the sheet bundle, the sheet is conveyed passing between the feed roller 3 and the separation roller 4. Note that if the paper is weak, it may bend between the pick-up roller 2 and the feed roller 3, so it is necessary to provide an appropriate paper guide. As shown in FIG. 4, when two sheets of paper are fed by the pick-up roller 2, the first sheet passes through the nip between the feed roller 3 and separation roller 4 and is detected by the paper sensor 5. When the nip is opened, the leading edge of the second sheet of paper is often located at the nip. In this case, in the apparatus of the present invention, the separation roller 4 is stopped, so that the second sheet is not conveyed and only the first sheet is conveyed. If the separation roller is not stopped when one sheet is detected, the second sheet will also move forward, and the paper sensor 5 will detect double feeding and reverse the separation roller, resulting in the paper being returned more frequently. Buckling, etc. are more likely to occur. Next, as shown in FIG. 5, the paper sensor 5 detects two sheets of paper, and the separation roller 4 reverses to separate them and return the second sheet of paper to below the first sheet of the paper stack. In order to do this, μ _R P _B > μ _P P _B + μ _P (P _A + m) + μ _P (P _A +2m) P _B > μ _P / μ _R − μ _P (2P _A +3 m) In this case, also use an appropriate guide plate. By providing this, even paper with weak stiffness can be returned. Normally, the friction coefficient μ _R between the paper and the roller is approximately 1.2, the friction coefficient μ _P between the sheets is approximately 0.5, and P _B is approximately 1.5 times that of P _A. At maximum, μ _R min is 1.1 μ _P max is approximately 0.8. Therefore, if P _B is set to about 6 times P _A , almost all paper types can be separated. Effects As described above, according to the present invention, almost all paper types can be separated with high accuracy by simply setting the pressing force of the separation roller and pick-up roller appropriately, without changing the coefficient of friction between the feed roller and the separation roller. and can be transported. In addition, since a torque limiter or the like is not used, manufacturing costs are reduced, and excellent effects such as improved durability can be expected.

[Brief explanation of the drawing]

Fig. 1 is a sectional view schematically showing an embodiment of the configuration of the present invention, Fig. 2a is a front view showing the separation roller control mechanism, and Fig. 2b is a view taken along the line B-B in Fig. a. 3 to 5 are schematic diagrams illustrating the operation of the apparatus of the present invention. 3...Feed roller, 4...Separation roller, 5...Paper detection means, 9-12...Separation roller control means.

Claims (1)

[Scope of utility model registration request] It has a feed roller that rotates in the paper feeding direction, and a separation roller that pinches the paper path and comes into pressure contact with it and can be driven to rotate in the opposite direction to the paper feeding direction. In a paper feeding device that separates and feeds double-fed sheets due to the difference in When the detection means does not detect any paper, the separation roller is set free, when one paper is detected, the separation roller is stopped, and when two or more papers are detected, the separation roller is moved in the opposite direction to the paper feeding direction. 1. A paper feeding device comprising: a control means for controlling the drive so as to drive the paper feeding device.