The opinion of the court was delivered by: Paul Barbadoro United States District Judge
Markem-Imaje Corporation ("Markem"), a manufacturer of thermal transfer printers, seeks a declaratory judgment that a series of patents held by Zipher Ltd. and Videojet Technologies, Inc. (collectively "Zipher") are invalid, unenforceable, and have not been infringed by Markem or its customers. For the reasons detailed below, I determine that the broad functional claim language in Zipher's patents fails to satisfy the definiteness requirement of 35 U.S.C. 112, ¶ 2. On that basis, I grant Markem's motion for summary judgment, and declare the challenged patent claims invalid.
This dispute involves the tape drive systems used in industrial thermal transfer printers. Product manufacturers use these printers to rapidly print unique information onto individual labels or packaging material. For example, a potato chip manufacturer might use a thermal transfer printer to stamp expiration dates onto a roll of flat potato chip packages before separating the roll into individual bags and filling the bags with potato chips.
The act of thermal transfer printing consists of pressing a print head against an inked tape that contacts the printing medium (the potato chip bag) and using the print head to selectively heat the tape, thereby transferring the desired ink pattern to the printing medium (e.g., "BEST IF USED BY 08.29.2012"). The basic principle is similar to that of a typewriter or dot matrix printer, except that the print head uses heat rather than the force of the impact to transfer the ink from the ribbon to the printing medium.
The printer may be required to operate in intermittent mode or continuous mode, depending on how the production line is set up in a particular factory. In intermittent mode, the printing medium is advanced into position and remains stationary during the printing process. In continuous mode, the printing medium advances through the printer at a constant rate throughout the printing process; as the printing medium moves forward, the printing head moves with it. Once the current sheet has been printed, the printing head then rapidly returns to its home position and the printing ribbon briefly rewinds so that the printing head is lined up with the boundary between the used and unused sections of ribbon.
As with any industrial application, reliability is extremely important in a thermal transfer printer. Some of the failures that can interrupt the operation of such a printer include excessive tape tension (which can cause the tape to break, forcing the operator to halt the production line to respool the tape), insufficient tape tension (which can interfere with the printer's ability to position the tape properly), wastage of unused tape (which forces the operator to replace the tape spools more frequently), and mechanical failures caused by wear and tear on the tape drive system. Accordingly, tape drives must be designed to maintain tape tension within an acceptable range.
For two reasons, simply rotating each spool the same number of degrees for each printing cycle will not produce consistent tape tension. First, even in perfect conditions, rotating a given spool by a given number of degrees will result in a different length of ribbon advance depending on the diameter of ribbon on the spool. For example, a one-degree rotation of a spool 100 mm in diameter will result in about 0.9 mm of ribbon advance, whereas a one-degree rotation of a spool 50 mm in diameter will result in only about 0.4 mm of ribbon advance. Thus, the rotation of each spool must be adjusted according to the amount of ribbon remaining on the spool. Second, real-world conditions can interfere with the ideal mathematical relationship between spool diameter, spool rotation, and ribbon advance. For example, ribbon may stretch unevenly over time, causing unpredicted slack to develop. Additionally, if the ribbon breaks, operators may take actions (such as taping two sections of ribbon together or tying off the ribbon) that make it even more difficult to measure how much ribbon remains on each spool.
The most common form of prior art relies upon a single motor to drive the take-up spool (the spool onto which used ribbon is taken up), with tension control provided by some form of "slipping clutch" arrangement on the supply spool (the spool from which fresh ribbon is drawn). As the take-up motor pulls more ribbon from the supply spool, the slipping clutch provides a resistive force that maintains an appropriate level of tension in the ribbon. The slipping clutch becomes less reliable, however, as it wears out over time. Additionally, a slipping clutch system's reliance on friction for tension control limits the acceleration, deceleration, and maximum speed capability of the ribbon transport system.
Other prior art uses two motors, with one motor driving the ribbon in a tape-transport direction and the other functioning solely for tension control, not ribbon advance. For example, U.S. Patent No. 5,366,303 (filed May 11, 1993) ("Barrus") discloses a printer that employs a take-up motor and a supply motor. Barrus, however, is a "pull-drag" device in that only the take-up motor provides rotational torque in the direction of ribbon transport; the supply motor merely provides a variable drag on the other motor.
At issue in this case are U.S. Patent No. 7,150,572 ("the '572 Patent") and four patents that are continuations of the '572 Patent: U.S. Patent Nos. 7,682,094 ("the '094 Patent"), 7,722,268 ("the '268 Patent"), 7,748,917 ("the '917 Patent"), and 7,753,605 ("the '605 Patent"). Although the claims of the continuation patents differ from the '572 Patent, each patent's specification is necessarily the same as the one filed with the '572 Patent. The patents disclose a tape drive intended for use in a thermal transfer printer.
The tape drive described in the common specification consists of two spools of tape, each mounted on a spool support. The exemplary embodiment energizes both motors to drive the spools in a tape transport direction, drives the spools to add or subtract appropriate lengths of ribbon for tension control purposes, uses the operation of the motors to measure tape tension without making physical contact with the tape, and switches easily between continuous and intermittent operation.
For purposes of the analysis that follows, claim 1 of the '572 Patent is representative. It is directed to "[a] tape drive ...