This invention relates to an apparatus for controlling the angular displacement or relative angular position of a sprocket wheel in a device for feeding or guiding media such as paper, vinyl, etc. More specifically, the apparatus relates to adjusting the angular position of a sprocket which to adjust the tension of the media in the device.

BACKGROUND OF THE INVENTION Devices such as printers, plotters, cutters or the like, are frequently provided with sprocket wheels for feeding a media, wherein the media is provided with sprocket holes along at least one edge for receiving the sprocket teeth of the sprocket wheels. On occasion the tension of the media may vary, especially when the media is a stretchable material, such as vinyl, resulting in improper drive of the media.

SUMMARY OF THE INVENTION The present invention is therefore directed to the provi¬ sion of a sprocket control apparatus adapted to overcome the above discussed problem

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Briefly stated, in accordance with the invention, an ar¬ rangement is provided for adjusting the angular displacement or relative angular position of a sprocket wheel that is rotatably mounted on a first axis. The arrangement includes a pulley mounted for rotation with the sprocket wheel, λ holding arrange¬ ment is spaced from the first axis, and a belt extends around the pulley from the holding means. First and second courses or runs of the belt thus extend between the pulley and the holding ar¬ rangement and the belt is held by said holding arrangement. Ad- justment means are provided for simultaneously changing the lengths of the belt in opposite directions in the first and sec¬ ond courses.

In a preferred embodiment of the invention, the device is a media driving device which has first and second sprocket wheels mounted on parallel spaced apart first and second rotatable shafts, respectively. The pulleys are fixed to the respective shafts to rotate therewith by, for example, a spline arrangement. A first pulley is mounted on the first shaft, a second pulley is mounted on the second shaft, and a belt extends around the pul¬ leys. The belt also engages a drive roller mounted to be driven by a motor, so that rotation of the motor causes the belt to rotate and drive the pulleys to effect rotation of the rotatable shafts, and hence the sprocket wheels affixed thereto. In this arrangement, the belt thus has first and second courses extending between the two pulleys, with the drive roller engaging the first course. The drive roller preferably engages the belt on the in-

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side of the loop formed by the belt. The drive roller is held fixed by the motor when the motor is stopped, and the belt engaged by the drive roller holds the first sprocket wheel (part of the holding arrangement) at a fixed position when the motor is 5 stopped.

In accordance with the invention, a first roller engages the first course of the belt between the drive roller and the second pulley, and a second roller engages the second course of the belt between the first and second pulleys. The first and sec- - . ond rollers preferably engage the outer circumferential surface of the belt, i.e. the outside of the loop formed by the belt.

The first and second rollers are mounted on a pivoted control lever to be simultaneously movable under the control of the operator. The control lever is positioned so that pivoting of the lever effects the changing of the relative lengths of the belt in the first and second courses, in opposite directions, in substantially equal amounts. This enables the second sprocket wheel to be angularly displaced without rotation of the first sprocket wheel. A clamping arrangement, such as a thumb wheel, enables the lever to be held at any adjustment position.

It is of course apparent that the belt may be supported and guided by additional _. rollers.

The minimum adjustment range is an angular displacement of the sprocket wheel corresponding to the distance between two adjacent sprocket teeth.

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BRIEF DESCRIPTION OF THE DRAWING In order that the invention may be more clearly un¬ derstood, it will now be disclosed in greater detail with reference to the accompanying drawing, wherein:

Fig. 1 is simplified illustration of elements of a ^' sprocket control apparatus of the invention before adjustment of the angular displacement of one of the sprocket wheels, for ex¬ plaining the operational concept of the invention;

Fig. 2 is a simplified illustration corresponding to that of Fig. 1, but wherein the angular displacement of the sprocket wheel has been adjusted in accordance with the invention; and Fig. 3 is a top view of portions of the arrangement of Figs. 1 and 2.

DETAILED DISCLOSURE OF THE INVENTION

Referring now to the drawings, a pair of parallel spaced apart splined shafts 10, 11 are rotatably mounted to a machine frame 12 (Fig. 3) of a device such as printer, plotter, cutter or the like, adapted to feed a media 13 such as paper, vinyl, etc. It will be apparent that the invention is not limited to this selection of devices or media.

Sprocket wheels 14, 15 are mounted on the shafts 10, 11, respectively, for rotation therewith by a spline arrangement which enables the sprocket wheels to be axially displaced on the shafts, in conventional manner, in order to adapt the device for the feeding of different widths of media. The media may be

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further guided by a conventional platen arrangement 16 (il¬ lustrated oniy in Fig. 1) . The invention is not limited to the provision of these features. λ pulley 20 is mounted on the shaft 10, for rotation therewith, and a pulley 21 is mounted on the shaft 11, for rota¬ tion therewith. The mounting arrangement of these pulleys is con¬ ventional.

A belt 22 extends around the two pulleys 20 and 21, the belt having a course 23 extending for example between the upper sides of the two pulleys and a course 24 extending between the lower sides of the two pulleys. The course 23 of the belt is guided by a pair of rollers 30, 31 journaled in the machine frame 12 on parallel spaced apart fixed axes, and the course 24 of the belt is guided by a pair of rollers 32, 33 journaled in the ma- chine frame 12 on parallel spaced apart fixed axes.

In order for the device to properly feed the media, the sprocket holes of the media should be spaced such that the media lays directly against the platen 16, and is not stretched too tight or too slack, in this position. For example, due to tolerances of or improper spacing between the sprocket holes in the media, or due to εtretching or contracting of the media, the media may be excessively loose between the sprocket wheels, as illustrated in Fig. 1, or may be stretched too tight or loose be¬ tween the sprocket teeth for proper feeding, or may be too taut between the sprocket wheels.

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In order to avoid this problem, in accordance with the invention, a lever 40 is pivoted to the machine frame, on an axis 41 that will be discussed hereafter in greater detail. The lever extends sufficiently in one direction to provide a handle 42 that can be manipulated by an operator. The other end of the lever supports two parallel spaced apart rollers 44 and 45. λs illustrated in the drawings, the upper course 23 of the belt extends inwardly of the rollers 30, 31 toward the course 24,, i.e. in a reentrant manner, so that its outer surface is guided by the roller 45. Similarly the lower course 24 of the belt extends inwardly of the rollers 32, 33, i.e. toward the course 23, i.e. in a reentrant manner, so that its outer surface is guided by the roller 44. It is thus apparent that, upon rota¬ tion of the lever 40, e.g. in the counter-clockwise direction from the Fig. 1 condition to the Fig. 2 condition, the length of the belt 22 in the lower course 24 will increase, while the length of the belt 22 in the upper course 23 thereof will decrease.

For example, as shown in Fig. 1, the lever is illustrated as having an angular displacement such that the media extends loosely between the sprocket wheels. By pivoting the lever 40 in the counter-clockwise direction, the length of the course 23 has decreased and the length of the course 24 has increased, as il¬ lustrated in Fig. 2. If this pivoting of the lever 40 is effected while holding the pulley 20 fixed, it is apparent that the belt will rotate the pulley 21, and hence the sprocket wheel 15, in

the counter-clockwise direction. As a result, the slack in the media 13 can be removed, so that the media runs smoothly on the platen 16.

Adjustment of the sprocket in this manner is of course not effected by changes in the length of the belt itself, but only by changing the proportions of the belt that extend in the upper and lower courses. It is hence necessary, in accordance with the invention, to locate the pivot axis 41 at a location such that decreases in the length of one course of the belt are substantially equal to increases in the length of the other course of the belt, as the lever 40 is pivoted. It is apparent that the selection of the position of the axis 41 is also depen¬ dent upon the relative locations of the rollers 44, 45. As an ex¬ ample, in the illustrated embodiment of the invention, the axis 41 is along the line extending between the axes of the shafts 10, 11. The invention is not limited, however, to this specific loca¬ tion of the axis 41. Further, while in the illustrated embodiment of the invention, the axis 41 and the axis of the roller 45 are on arms extending from the lever, the invention is not limited to this configuration.

Lever 40, pivot axis 41 and the rollers are selected and positioned to permit the angular displacement or angular position of sprocket wheel 15 relative to a given angular position to be adjusted by a minimum adjustment distance or displacement. A minimum adjustment distance of about 0.5 inch or at least the spacing between adjacent sprocket wheel teeth has been found to be suitable for adjusting the tension of media 13. As il-

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lustrated by the positions of reference line 60 in Figs. 1 and 2, the adjustment distance equals the spacing between adjacent sprocket wheel teeth, which for sprocket wheel 15 is about 0.5 inch. This minimum adjustment distance allows the media to be properly tensioned practically regardless of initial machine set¬ up.

In the arrangement in accordance with the invention, the roller 30 is a drive roller, being driven for example by a motor 50 mounted on the machine frame 12 and controlled by a control system 51, as illustrated in Fig. 3. The pivotal mounting of the lever 40 about the axis may include a thumbscrew 52, as seen in Fig. 3, in order to enable the operator to release the lever dur¬ ing an adjustment process, and the fixedly hold the lever at the desired angular displacement after it has been properly adjusted. The thumbscrew is positioned to tighten the lever firmly against the machine frame.

In normal operation, the roller 30 is driven by the motor 50. Rotation of the roller 30 drives the belt 22, whereby the belt effects the rotation of the pulleys 20, 21 and other rol- lers, so that the sprocket wheels 14, 15 are rotated to drive the media in the desired direction and at the desired speed. Since the forces for driving the media pass via the belt 22, it is desirable that the belt 22 engage the drive roller 30 for at least 180 degrees. When a new media is to be assembled on the device, the motor 50 is stopped. The stopping of the motor fixes the angular

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displacement of the pulley 21, and hence the sprocket wheel 14. If, after the media is assembled on the device with the sprocket holes thereof receiving the sprockets of the sprocket wheels 14, 15, it is found that the media is too loose or too tight, the 5 thumbscrew 52 may be released to permit pivoting of the lever 40. The pivoting of the lever effects its angular displacement, and hence the angular displacement of the sprocket wheel 15. When the sprocket wheel 15 has been rotated to a position at which the sprockets thereof are properly received by the holes of the 10 media, and the media has the desired tension, the thumb wheel is tightened to hold the lever 40 at the adjusted position. The device may now be operated to drive the media in the desired man¬ ner.

The belt 22 is preferably a timing belt, e.g. a toothed 15 belt that does not permit any slip. It may be comprised, for ex¬ ample, of Kevlar, polyester or fiberglass tension material bound by polyurethane, neoprene or other suitable material.

While the invention has been disclosed and described with reference to a single embodiment, it will be apparent that varia¬

*>n tions and modification may be made therein, and it is therefore intended in the following claims to cover each such variation and modification as falls within the true spirit and scope of the in¬ vention.

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