GB2141692A - Friction roller pair for moving paper and the like - Google Patents

Abstract

Rollers (12, 14) of substantially different hardness, rotatably mounted in contact with and at fixed distance from each other provide frictional force to move one or more sheets or a web of paper, one of the rollers being deformable to the contour of the other. <IMAGE>

Description

SPECIFICATION Friction roller pair for moving paper and the like This invention is concerned with a friction roller pair for moving paper and the like.

The need for moving paper, whether as single sheets or a continuous web, of varying thickness and including multi-part forms, is well known. Newspaper presses, office typewriters and printers used as computer system output devices all require that the paper on which they print be moved in reliable, timely fashion to facilitate good printed copy.

Usually, pairs of rollers, frequently referred to as pinch rollers, are used to move paper. The paper to be moved is inserted between the rollers and, as the rollers rotate in opposite directions, the paper is moved. The speed of the paper movement is determined by the rotational speed of the rollers, providing, of course, that the force applied to the paper by the "pinch" of the rollers is sufficient to maintain friction between the rollers and the paper. In order to ensure that frictional force is adequate, pinch rollers typically require spring loading or some other mechanism for providing the force for urging one roller against the other.

Obviousiy, the spring loading of pinch rollers requires parts in addition to those required for simply rotatably mounting the rollers. Depending on the configuration, the force imparted to the rollers by the spring system may increase or decrease as the thickness of the paper to be moved increases or decreases, or as the number of sheets of paper to be moved at the same time increases.

In typical prior art pinch roller paper moving systems, only one roller is driven and the other roller is spring loaded into contact with it. As the thickness of the paper to be moved thickens (or additional sheets to be moved are simultaneously added), the amount of force provided by the spring loaded roller may vary. If the force decreases below the amount needed to maintain frictional engagement between the surfaces of the rollers and the paper, the paper being moved may become skewed, wrinkled or both. In the case of a multipart form, sheets of the form may become skewed with respect to one another if the force is insufficient to maintain frictional engagement between the sheets of paper. This last condition is particularly noticeable where the relative surface speeds of the rollers are significantly different.

It should also be noted that by the very nature of a spring loaded pinch loaded system for moving paper, the distance between centers of the shafts of the rollers is not fixed. Thus, without substantiai addition of moving parts to the system, only one roller can be driven. If the frictional engagement between the roller is uneven or interrupted, the surface speed of the rollers will not remain equal. Unequal surface speed of the rollers also causes skewing and wrinkling of the paper to be moved. When both rollers can be driven in a paper moving system, their speed can be controlled and the surface speed of the rollers can be made equal.

This present invention provides apparatus for moving a thin sheet of material comprising first roller means rotatably mounted in a chassis; second roller means rotably mounted in the chassis in contact with the first roller means; and drive means coupled to the first and second roller wheels for positively rotatably driving the rollers in opposite directions; said first roller being constructed of substantially harder material than said second roller; and said second roller being deformed to the contour of the surface of the first roller in response to its contact therewith.

In a paper moving system constructed according to the principles of the present invention, paper is driven between two rollers of substantially different hardness or durometer rating. The two rollers are rotatably mounted in contact with one another. Both are driven. The relative position of the rollers is fixed and cause deformation of the surface of the soft or low durometer roller. Since the low durometer roller is constructed of a resilient material, its deformation essentially determines the force imparted to the paper for movement as the rollers rotate. Of course, the apparatus of the present invention can provide for adjustment of the amount of deformation desired.

The surface of the hard or high durometer roller is essentially undeformed by the urging force developed by the deformation of the soft roller. By proper selection of the material from which the low durometer roller is constructed, the amount of deformation may vary conveniently as the thickness of the paper varies or more sheets to be moved simultaneously are added. The amount of force developed by the deformation of the soft roller also varies to ensure substantially continuous frictional engagement with the paper.

There now follows a detailed description which is to be read with reference to the accompanying drawings of apparatus according to the present invention; it is to be clearly understood that the apparatus has been selected for description to illustrate the invention by way of example and not by way of limitation.

In the accompanying drawings: Figure 1 is a schematic side view of two rollers constructed and disposed in contact with one another for moving a sheet of paper in accordance with the principles of the present invention; and Figure 2 is a front view of the rollers of Fig. 1 employed in a typical paper moving system.

Referring to Fig. 1, paper 10 moves in response to rotation of rollers 1 2 and 14. The roller 1 2 is softer than the roller 14, its surface being deformed to the contour of the roller 14 as shown when mounted in contact therewith.

An indication of the relative hardness of the rollers 1 2 and 14 is given in units of Shore A.

The roller 1 2 is approximately 2 Shore A and the roller 1 4 is about 60 Shore A. Since the roller 1 4 is essentially undeformed by its contact with the roller 12, the paper tends to ride on the roller 14, the frictional force being provided by the thermal force necessary to deform the roller 12.

In the configuration of Fig. 2, the amount of deformation of the rollers 1 2 when in contact with the roller 14, is determined by the spacing between drive shafts 15 and 17. The spacing between the drive shafts 1 5 and 1 7 is influenced by the selection of the low durometer material used for foring the rollers 1 2.

In the preferred embodiment, the distance between the roller centers 11 and 13, hereinafter designated CD, Is fixed, thus facilitating convenient drive of either roller. According to the principles of the present invention, that distance is given by

Where D, = diameter of roller 1 2 D2 = diameter of roller 14 tp = paper thickness Fs = ,uN, force exerted on paper by rollers, where y = coefficient of friction between paper and roller pair and N = Normal force to produce desired deflection of roller 1 2 and K, = spring constant of roller pair.

It should be noted that slightly greater force is actually applied to thicker paper by the rollers 1 2 and 14. However, owing to the low spring constant of the foam material used to construct the roller 12, the incremental increase of force is small enough to be practical in the mechanism.

Values for ,up and Kf are typically determined experimentally using exact roller configura tion and materials for the roller pair. For configurations involving multiple roller pairs on long shafts, the total force applied to the paper is the sum of forces developed by each roller pair. Furthermore, to determine the distance between roller centers, the deflection of the shaft on which the rollers are mounted must be accounted for since that deflection reduces the amount of deformation of the roller 12. Thus, in the absence of an undeflected center shaft, the determination of distance between center shafts for locating multiple roller pairs is an iterative solution for each change in normal force, and corresponding to a change in shaft deflection.

Fig. 2 shows the rollers 1 2 and 14 mounted to rotate about parallel axes, in contact with each other on drive shafts 1 7 and 1 5, respectively, in a chassis 20. In this configuration, the roller 14 is substantially longer along its longitudinal axis than the rollers 12, and is constructed of high durometer elastomer material, such as a hard synthetic plastics material (e.g., polyurethane) or hard natural or synthetic rubber (e.g., neoprene). The rollers 1 2 are constructed of low durometer foam material, such as a polyurethane foam or other similar material.

Other configurations should be noted, including lengthening the rollers 1 2 and 14 along their longitudinal axes or adding more roller pairs along center shafts 1 5 and 1 7.

A drive gear 21 is coaxially mounted on the drive shaft 15 and engages a drive gear 22 which is coaxially mounted on the drive shaft 1 7. The drive shafts 1 5 and 1 7 are in turn rotatably mounted in the chassis 20 through any suitable bushing or bearing arrangement.

Connected also to the shaft 1 7 is a pulley 23 to receive a toothed timing belt from a stepper motor (not shown) for automatic operation. The pulley 23 includes a manually operable knob portion for manual operation of the assembly.

The rollers 1 2 provide nearly contant normal force against the roller 1 5 thus providing nearly constant frictional force to the paper which tends to ride on the roller 14. The rollers 1 2 are approximately 1 7.8 mm in diameter and contructed of soft (approximately 2 Shore A) polyurethane foam of 240.3Kg/m3. The roller 14 is approximately 10.8 mm in diameter and constructed of a hard elastomer (approximately 60 Shore A). The center-to center spacing of the shafts 1 5 and 1 7 is about 13.33 mm. The range of paper thickness which can be accommodated by such a configuration of roller pairs is .076 mm to .508 mm.

The ratio of the gears 21 and 22 is set to rotatably drive the shafts 15 and 17 so that the surface speeds of the roller 14 and the rollers 1 2 are equal. The surface speed of the rollers 1 2 remains equal to that of the roller 14 even though its surface is deformed by its contact with the rollers 14 and the passage of paper between the rollers, since the gear ratio of the gears 21 and 22 is matched to the ratio of the diameter of the rollers where the diameter of the roller 1 2 is undeformed by its contact with the roller 14. Thus the roller 14 in combination with the rollers 1 2 move multipart forms without skewing sheets of the forms relative to one another. In addition, the roller drive system of the present invention will accommodate a wide range of paper thickness and number of parts of multipart forms without adjusting the force between the rollers or distance between the shafts on which the rollers are mounted.

Claims (2)

1. Apparatus for moving a thin sheet of material comprising: first roller means rotatably mounted in a chassis; second roller means rotatably mounted in the chassis in contact with the first roller means; and drive means coupled to the first and second roller wheels for positively rotatably driving the rollers in opposite directions; said first roller being constructed of substantially harder material than said second roller; and said second roller being deformed to the contour of the surface of the first roller in response to its contact therewith.

2. Apparatus for moving a thin sheet of material substantially as hereinbefore described with reference to the accompanying drawings.