Advancing material of indeterminate length – With material-responsive control means – To position material laterally
Reexamination Certificate
1998-04-29
2001-08-07
Mansen, Michael R. (Department: 3653)
Advancing material of indeterminate length
With material-responsive control means
To position material laterally
C226S020000, C226S004000, C226S042000, C271S228000
Reexamination Certificate
active
06269995
ABSTRACT:
TECHNICAL FIELD
The present invention relates to friction drive apparatus such as printers, plotters and cutters that feed strip material for producing graphic images and, more particularly, to friction drive apparatus which detect and correct the longitudinal and lateral displacements of the strip material.
BACKGROUND OF THE INVENTION
Friction, grit, or grid drive systems for moving strips or webs of sheet material longitudinally back and forth along a feed path through a plotting, printing, or cutting device are well known in the art. In such drive systems, friction (or grit or grid) wheels are placed on one side of the strip of sheet material (generally vinyl or paper) and pinch rollers, of rubber or other flexible material, are placed on the other side of the strip, with spring pressure urging the pinch rollers and material against the friction wheels. During plotting, printing, or cutting, the strip material is driven back and forth, in the longitudinal or X-direction, by the friction wheels while, at the same time, a pen, printing head, or cutting blade is driven over the strip material in the lateral or Y-direction.
These systems have gained substantial favor due to their ability to accept plain (unperforated) strips of material in differing widths. However, the existing friction feed systems experience several problems. One problem is longitudinal slippage or creep error in the X-direction. The longitudinal slippage or creep occurs when the strip material moves either too slowly or too fast, respectively, in the X-direction. This problem is most pronounced in long plots, i.e. those two or more feet in length, and those in which the strip material moves back and forth in the X-direction with respect to a tool head such as a plotting pen, print head, or cutting blade. Longitudinal slippage or creep is highly undesirable because the operations performed on the strip material become inaccurate.
Another error that occurs in friction feed systems is a skew error. The skew error will arise as a result of strip material being driven unevenly between its two longitudinal edges, causing the strip material to assume a cocked position. The error is integrated in the lateral or Y-direction and produces an increasing lateral position error as the strip material moves along the X-direction. The error is often visible when the start of one object must align with the end of a previously plotted object. In the worst case, such lateral errors result in the strip drifting completely off the friction wheel.
SUMMARY OF THE INVENTION
It is an object of the present invention to detect and correct the longitudinal and lateral displacements of strip material being fed through a friction drive apparatus.
According to the present invention, a friction drive apparatus for feeding strip material in a longitudinal direction along a feed path includes first and second friction wheels associated with first and second longitudinal edges of the strip material, respectively, and a motion processor for rotating the first and second friction wheels independently at different speeds to correct lateral deviation of the strip material from the feed path. The friction drive apparatus also includes first and second motor drives rotating the first and second friction wheels, respectively, and at least one sensor. In the best mode embodiment, the sensor disposed behind the friction wheels, as viewed in the direction of motion of the strip material, detects lateral deviation of the strip material from the feed path. The sensor signal is processed by the motion processor which commands the motor drives to rotate the friction wheels at different speeds to correct the lateral error.
The friction drive apparatus also includes means for detecting the actual longitudinal position of the strip material. The motion processor compares the actual longitudinal position of the strip material with the commanded longitudinal position. In the event of a discrepancy between the two positions, an error signal generated by the processor drives the friction wheels until the actual position and the commanded position of the strip material coincide.
Thus, the friction drive apparatus of the present invention detects both lateral and longitudinal deviations of the strip material from the feed path and corrects both types of errors before a noticeable error occurs in a graphic image of a work operation performed by a tool head on the strip material. The errors are corrected without interrupting the work operation.
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U.S. Patent Application Serial No. 09/217,667, filed Dec. 21, 1998 in the name of Daren Yeo et al.
Guckin Mark E.
Rich Leonard G.
Webster Ronald B.
Gerber Scientific Products, Inc.
Mansen Michael R.
McCormick Paulding & Huber LLP
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