BACKGROUND OF THE INVENTION The present invention relates to a roller for feeding and indexing a sheet, such as a sheet of paper to be printed, that drives the sheet and insures precise indexing of the sheet being driven, without damaging the opposite surface of the sheet that is used, for example, for printing.

Various sheet feed rollers have been advanced in the art for use in printers, and in cutters for cutting large sheets in accordance with a program, and for other applications. Printing a number of labels on a sheet, and then cutting the individual labels from the sheet requires reciprocating the sheet precisely so the printing on each label is correct and so each label is properly positioned on the sheet.

Knurled indexing rollers have been used, but slippage is a problem. The projections tend to damage the paper sheet on the print surface causing unacceptable performance. Also, high friction materials have been used on sections of the drive rollers, but again, indexing the sheet, where precise repeatability in position of the paper for multiple passes is necessary, is hard to achieve with such rollers. Other rough surface sheet drive rollers have been advanced, including random pattern roughening.

SUMMARY OF THE INVENTION The present invention relates to a sheet drive roller that has knurled drive portions forming spaced teeth on the outer surface at least in one portion of the roller. As shown, the drive portions are aligned with edges of the sheet that is to be fed. A pinch roller holds the sheet firmly against the surface in the

drive sections. The drive sections of rollers of the present invention have teeth formed in a pyramidal shape, which are spaced relatively far apart in relation to their height. The pyramids which engage the sheet to be driven have sharp outer ends . The height of the individual pyramids is precisely controlled to be in the range of a known percentage of thickness of the paper so that the teeth or pyramids will not pierce the sheet when held in place with a pinch roller. The pyramidal shape teeth are formed in a conventional manner, with modified knurling tools. The tools used have flat ends to form smooth cylindrical surface portions between the pyramids or teeth so that the sheet may be fully supported on the smooth surface between the teeth. There is an indexing action as the sheet is fed more than once across the roller because if there is slight shifting of the sheet the teeth on the roller will slip into previously formed impressions on the drive side of the sheet. The sheets generally are relatively thick paper sheets, for example sheets used for printing labels.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic perspective view of a sheet drive and indexing roller made according to the present invention and a sheet that is to be fed by such roller;

Figure 2 is a schematic representation of the roller of Figure 1 showing it in connection with a pinch roller urging the sheet to engage drive sections of the indexing roller;

Figure 3 is a sectional view of a portion of a drive section of a roller in greatly enlarged scale to show the teeth formed in the drive sections;

Figure 4 is an enlarged, part perspective view of a roller drive section showing the pyramidal shape of the teeth;

Figure 5 is a schematic representation of a typical knurling operation utilizing right and left-hand oriented knurling tools on the indexing roller; and

Figure 6 is a schematic representation of a flat tipped knurling tool used to form the teeth on the rollers of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to Figure 1, a sheet feed roller indicated generally at 10 is mounted on suitable frame supports 12, that can be selected as desired for the particular printer, cutter or other unit on which the feed roller is to be used. Suitable bearings 14 are used for mounting a center shaft 16 of the feed roller 10. The shaft 16 is driven with a suitable motor 18 (a stepper motor is preferred) in a conventional manner in response to signals from a controller 20. The controller 20 for this type of indexing roller is generally programmed so that a sheet 22 will be fed in one direction, and then reversed, and then fed again in the first direction a sufficient number of times to do four color printing, for example, or a sufficient number of times to cut a periphery of a label that might have been printed on the sheet 22. The sheet 22, as disclosed a sheet of paper, is moved longitudinally by the indexing roller 10, and passes between the indexing roller 10 and a pinch roller 24 as shown in Figures 2 and 3 schematically. The pinch roller 24 is supported relative to a frame portion 26 forming part of the frame having frame supports 12. A pair of arms 28 at opposite ends of the pinch roller are used for rotatably mounting the pinch roller in bearings 30. Springs 27, which are

shown only schematically, spring load the arms 28 and the pinch roller against the drive sections of the indexing roller 10.

The motor 18 drives the indexing roller in either direction of rotation as shown by the double arrow 32. The drive can be at relatively high speeds, particularly when printing small labels with a print head 34 (Figure 1) in multiple colors, where the sheet has to be reversed in direction several times for printing each label on the sheet.

As shown in Figures 1 and 3, the roller 10 is made of metal and has drive sections 32 and 34 at its ends, respectively. The drive sections are made using a knurling process modified to form drive teeth on the roller. A typical cross section through the drive section 32 is shown in Figure 3. The sheet 22 is forced to engage the teeth or projections 36 on the drive sections with the pinch roller 24. The pinch roller 24 has a center shaft and molded end sections 25 of larger diameter than the center shaft that overlie the drive sections 32 and 34. The end sections 25 of the pinch roller are usually an elastomer of suitable hardness.

The drive sections have a series of pyramidal shaped teeth 36 shown in Figures 3 and 4. These teeth 36 are spaced apart a selected distance both in the axial direction of the roller, that is, parallel to the axis of the shaft 16, and in the circumferential or peripheral direction of the indexing roller 10. The teeth extend around the entire circumference of the roller 10. As shown in Figure 3, the teeth 36 are restricted in height indicated by the arrows 40 to be less than the thickness of the sheet to be driven, and preferably in the range of 1/2 of the thickness of the sheet. Thus, the teeth can be in the range of 0.0035 to

0.004 inches in height, when utilized for driving a sheet that is in the range of 1 1/2 to 2 times the height of the teeth.

When teeth in the drive sections 32 and 34 have a height of .0035 to .004 inches, approximately 50 teeth per inch are formed on the drive sections. While the drive sections are shown adjacent the roller ends, one or more drive sections may be located at any desired location on the roller. The teeth may also be formed along the entire length of the roller.

The teeth 36 are formed by a recessed space between the individual teeth, which is a flat surface in cross section as indicated at 42, between the teeth 36. This surface forms a straight line in the cross section of Figure 3, and it is a smooth cylindrical surface in the annular direction between the teeth 36 as indicated at 44 in Figure 4.

This tooth spacing is made by having a flat end on the teeth of a knurling tool so that there is a substantial amount of smooth surface between the formed teeth. The smooth surface is sufficiently large in area so that the sheet to be driven can be forced down to be supported on the smooth surface between the teeth. At the same time the pointed ends of the generally pyramidal shaped teeth penetrate the sheet and form indentations in the sheet that provide for indexing and drive recesses. When the sheet is reciprocated in forward and reverse direction for printing or cutting, the teeth will tend to slide into recesses previously formed by the teeth and if there is any slight slippage or misalignment of the sheet, the pressure from the pinch roller will cause the sheet to slide slightly and center the recesses in the sheet on the individual teeth

over which the sheet is passing, to form a positive drive and centering action.

The use of the spaced teeth with a smooth surface between them that is adequate to permit the paper to be compressed to conform to the full depth of the teeth insures that good indexing action will occur as well as a satisfactory driving action.

The diameter of the smooth surface between the teeth 36 is substantially the same diameter as the smooth center part of the roller.

Also, the pyramidal shape is formed preferably approximately at an angle of 60° between the opposite sides, as shown in Figure 3. While equal sides (square) pyramids are shown, other shapes of teeth can be used. The teeth should be made with points and then tapered outwardly from a center axis formed by a radial line passing through the point. The teeth height is less than the thickness of the sheet being indexed and preferably is in the range of one half of the sheet thickness. If the teeth are too high the printing surface of the sheet will be damaged. The including angle of the teeth should be in the range of 60° but can range from about 45° to 90°. An angle that is too large reduces the drive capabilities of the teeth, and results in a tendency to slip.

The teeth are preferably formed by being knurled, or using a standard knurling process with modified knurling tools. Knurling occurs as is schematically shown in an end view of Figure 5, by supporting the roller blank 50 in a machine that will move it axially, and at the same time will rotate the roller as indicated by the arrow 52.

As shown, right and left-hand knurling tools 54 and 56 are mounted in the machine and are forced

against the surface of the roller blank as shown by the arrows on the axes of these knurling tools. The pressure exerted by the knurling tools 54 and 56 is great enough to force the material of roller blnk 50 into the grooves of the knurling tools.

The roller blank 50 is driven in direction indicated by arrow 52 and is also moved axially, so that a valley that is formed by one of the tools will form a path between the teeth at the angle illustrated in Figure 4 at 56. The other knurling tool will move a ^' Ong the shaft at an angle that is substantially equal, and is indicated at 58. As shown, these angles are substantially 30° and equal.

In Figure 6, a knurling tool 60 is illustrated, and it can be seen that the grooves 62 in the tool are very narrow and small, and the ends 63 are quite smooth and wide to provide for the wide spaces between the teeth 36 as the knurling operation progresses . Knurling tools are conventional, but in this form, the surfaces 63 are made so that the teeth 36 will have a substantial space of smooth material between them. The grooves 62 are made to have a depth that is equal to the desired height of the teeth 36. While the teeth 36 are shown as being sharp pointed, they could have rounded ends or plateaus on the top of them. It is preferred to have a base that has straight lines along a plurality of sides to form the teeth in order to provide a good driving and indexing function.

Other than the modified tool 60 (and the opposite hand tool used on the opposite side of the roller blank) the knurling tools and the knurling process are conventional. The space between the teeth

36 from one tooth to the next is generally in the range of between 10 and 20 times the height of the teeth. As can be seen the teeth height is relatively low so that the grooves in the forming tool are also relatively shallow.

The term penetration includes compressing the sheet to receive the teeth without actually slitting or partially cutting the sheet.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.