Opinion ID: 613378
Heading Depth: 1
Heading Rank: 1

Heading: the patented invention

Text: The '572 patent, entitled Tape Drive and Printing Apparatus, describes and claims a device for transfer printing. In transfer printing, ink is carried by a ribbon that is moved into contact with the substrate to be printed, and a print head impresses upon the ribbon and causes the ink to transfer from the ribbon to the substrate. In thermal transfer printing, the print head is heated, facilitating transfer and adherence of the ink to the substrate. Thermal transfer printers are used for such tasks as printing on plastic packaging and other surfaces to which ink does not readily adhere. In systems where the thermal printing is part of a mechanized and automated process, the printing step must keep pace with the production line, with minimal down time. The '572 patent is directed to a heat transfer printing apparatus that provides increased control over the acceleration, deceleration, speed, and positional accuracy of the printing operation, while minimizing waste of unused portions of the ink ribbon. In transfer printers in general, the ink ribbon is wound on two spools, one spool for supplying the ribbon for positioning on the substrate, and the other spool for taking up the ribbon after use. The '572 patent explains that prior art transfer printers rely upon a wide range of different approaches to the problem of how to drive the ribbon spools. Some rely upon stepper motors, others on DC motors to directly or indirectly drive the spools. Generally the known arrangements drive only the spool onto which ribbon is taken up (the take-up spool) and rely upon some form of slipping clutch arrangement on the spool from which ribbon is drawn (the supply spool) to provide a resistive force so as to ensure that the ribbon is maintained in tension during the printing and ribbon winding processes and to prevent ribbon overrun when the ribbon is brought to rest. '572 patent col.1 ll.33-44. The patent states that It will be appreciated that maintaining adequate tension is an essential requirement for proper functioning of the printer. Id. col.1 ll.44-46. The '572 patent is directed to an improvement in controlling the movement and tension of the ribbon. Figure 1 of the '572 patent shows the two ribbon spools 7 and 11, with ribbon 6 extending between them and passing under the print head at 4: The patent specification explains the problems with the slipping clutch that has been used to provide ribbon tension in prior art printers. A slipping clutch provides a constant resistive torque to the supply spool, and the constant torque causes the tension in the ribbon to vary as the supply spool outer diameter changes with the draw of ribbon. The patent states that such dynamically changing ribbon tension requires tight tolerances in clutch force, which is difficult to maintain because wear in the clutch tends to change the resistive force of the clutch. Too much clutch force can break the ribbon or require more power to drive the ribbon, and too little clutch force can cause the supply spool to overrun. The patent states: Given these constraints, typical printer designs have compromised performance by way of limiting the rate of acceleration, the rate of deceleration, and the maximum speed capability of the ribbon transport system. Overall printer performance has as a result been compromised. Id. col.1 l.66-col.2 l.4. Examples of conventional clutch or drag-type drive mechanisms are discussed in the '572 patent, including mechanisms in which, instead of a slipping clutch, a motor connected to the supply spool supplies a resistive force to provide ribbon tension. In another prior apparatus, a motor coupled to the supply spool act[s] as a feedback transducer to enable appropriate control of the motor driving the take-up spool to take account of changing spool diameters while maintaining a constant ribbon speed. Id. col.2 ll.39-42. The '572 patent distinguishes this prior apparatus from what the '572 patent calls the push-pull mechanism of the '572 apparatus, explaining that although this [prior art] arrangement does avoid the need for example of a capstan drive interposed between the two spools so as to achieve reliable ribbon delivery speeds, only one of the motors is driven to deliver torque to assist ribbon transport. There is no suggestion that the apparatus can operate in push-pull mode, that is the motor driving the take-up spool operating to pull the ribbon and the motor driving the supply spool operating to push the associated spool in a direction which assists tape transport. Id. col.2 ll.43-51. In accordance with the push-pull mode of the '572 patent, both the take-up spool and the supply spool are driven to particular angular positions by stepper motors that receive commands from a microcontroller. The take-up spool rotates and takes up a given length of ribbon per rotation, while the supply spool is rotated to feed out the same length of ribbon, independent of the constantly changing spool diameter. Such an arrangement is not provided in the prior devices, and is described as solving various problems encountered with prior devices. As described in the '572 patent, stepper motors rotate by selectively energizing electromagnets around the outside of the motor, referred to as the stator, to interact with permanent magnets or electromagnets on the shaft or rotor of the motor. Id. col.20 ll.38-41. Unlike DC (direct current) motors, which are analog devices that simply rotate when power is supplied, stepper motors have discrete angular positions or steps and can be forced or driven to stay in particular step positions. Zipher's expert witness, Professor Kuc, explained that an advantage of a stepper motor is that when it's still, it's got a holding torque to keep the ribbon in place. Hearing Tr. 40:21-23 (J.A. 340). The holding torque results from the electromagnetic attraction between poles of the rotor and poles of the stator in an energized stepper motor at rest. When an external torque (resulting from tension in the print ribbon) is applied to the spools, these electromagnetic forces create an opposing torque to keep the motor in its current angular position, thereby maintaining tension in the print ribbon. If the motor's maximum holding torque is exceeded by the external torque, the motor shaft will rotate; thus holding torque also specifies the minimum amount of external torque needed to rotate the shaft of a stepper motor commanded to hold steady in its current position. Markem's expert witness, Peter Landers, agreed with Zipher's expert that when power is applied to a stepper motor it is held in position so that even when the spool of the printer is not rotating it will hold the [ribbon] tension to the level it was set before. Hearing Tr. 21:6-23:1 (J.A. 321-23). The '572 patent describes optically monitoring the radii of the spools and using the data to calculate the step rate and the number of steps required by each motor to drive the spools in an appropriate manner so as to feed the ribbon a predetermined distance. Col.20 ll.25-28. The patent explains that [t]ension in the ribbon between the two spools must however be closely controlled to avoid the tension becoming too high (resulting in over tightening of the ribbon on the spools or even ribbon breakage) or the tension becoming too low (resulting in loss of positional control as a result of the ribbon becoming slack). Id. col.19 ll.32-38. The '572 patent describes its method of estimating ribbon tension ( t ), and explains how tension is maintained within predetermined limits: If the derived value of t is too high (above a predetermined limit), then a small step adjustment can be made to either or both of the motors to add a short section of ribbon to the length of ribbon between the spools. If the derived value of t is too low (below a different predetermined limit), then a short section of ribbon can be removed from the length of ribbon between the spools. . . . [M]athematical processing results in a correction amount of ribbon that needs to be added to or removed from the ribbon path between the spools during the next ribbon feed. This addition or removal of ribbon maintains ribbon tension within acceptable limits. Id. col.22 ll.16-42. Claim 1, the broadest claim of the '572 patent, is directed to a tape drive that corrects tension divergences from the predetermined limit in this manner: 1. A tape drive comprising: two motors, at least one of which is a stepper motor; two tape spool supports on which spools of tape are mounted, each spool being driveable by a respective one of said motors; a controller adapted to control energization of said two motors such that tape is transported in at least one direction between spools of tape mounted on the spool supports; wherein the controller energizes both said motors to drive the spools in a tape transport direction, and said controller calculates a length of tape to be added to or subtracted from tape extending between said spools in order to maintain tension in said tape between predetermined limit values and controls said motors to drive the spools to add or subtract the calculated length of tape to or from the tape extending between said spools. Following a claim construction hearing, the district court construed driveable and drive to mean rotateable and rotate, as proposed by Markem, rejecting Zipher's broader construction. Markem, 2008 WL 4116666, at . The district court explained in its reconsideration opinion that the use of the plural word spools in the claim clause to drive the spools to add or subtract the calculated length of tape means that both spools must rotate. Markem, 2009 WL 2855011, at . The court further explained that both spools must rotate to add or subtract a single calculated length of tape. Markem-Imaje, 2010 WL 114947, at . The operation of Markem's accused devices was not disputed, as the district court explained: Although Markem's tape drives rotate both spools during the tape tension adjustment process, only a single spool is rotated to achieve each adjustment. If tape tension is too low, the take-up spool is rotated to decrease the length of tape between the spools and if tape tension is too high, the supply spool is rotated to increase the length of tape between the spools. Id. Based on the district court's ruling that the term drive in the '572 claims requires that both spools are rotated together to adjust the tape, the court granted summary judgment of non-infringement. Zipher appeals, stating that the judgment was based on an erroneous claim construction.