Renishaw PLC v. Marposs Societa' per Azioni
| Decision Date | 16 September 1998 |
| Docket Number | No. 98-1007,98-1007 |
| Parties | RENISHAW PLC, Plaintiff-Appellant, v. MARPOSS SOCIETA' PER AZIONI and Marposs Corporation, Defendants-Appellees. |
| Court | U.S. Court of Appeals — Federal Circuit |
Edward P. Walker, Oliff & Berridge, PLC, of Alexandria, Virginia, argued for plaintiff-appellant. With him on the brief was James A. Oliff. Of counsel on the brief were James A. Samborn and Mark K. Riashi, Dickinson, Wright, Moon, Van Dusen & Freeman, of Detroit, Michigan.
Jeffrey M. Johnson, Dickstein, Shapiro, Morin & Oshinsky LLP, of Washington, DC, argued for defendants-appellees. With him on the brief were Charles W. Saber, James W. Brady, Jr., and Laurence E. Fisher. Of counsel was Eric Oliver.
Before PLAGER, CLEVENGER, and GAJARSA, Circuit Judges.
This appeal requires us to determine whether the district court made errors of claim construction that resulted in an erroneous finding of noninfringement at the close of a bench trial. See Renishaw PLC v. Marposs Societa' Per Azioni, 974 F.Supp. 1056 (E.D.Mich.1997). At trial, Renishaw plc (Renishaw) asserted that four claims from three patents were infringed by the Mida product line of touch probes produced by Marposs Societa' per Azioni and Marposs Corporation (collectively Marposs). Renishaw appeals only the finding of noninfringement of claim 2 of its U.S. Patent No. 5,491,904 (the '904 patent). Because we conclude that the district court properly found one limitation of the claim not satisfied, we affirm.
The '904 patent, listing David McMurtry as its inventor, describes and claims an improved touch probe. Touch probes are used in the automated manufacturing and measurement field to check with extreme precision the dimensions of machined parts. A touch probe consists of a long, thin stylus that extends out from a housing and that can deflect in all directions. The probe, which is mounted on a movable arm of a machine, produces an electrical "trigger" signal when the stylus contacts a workpiece to be measured. A computer that controls the movement of the arm uses the trigger signal to calculate the dimensions or location of the workpiece. Although the stylus can be several inches long, a touch probe often exhibits accuracy on the order of one micron (one millionth of a meter) or less. This relatively small dimension must be kept in mind when discussing the attributes of touch probes. Figures 1 and 2 of the '904 patent show one embodiment of the patented touch probe in vertical and horizontal cross-section, respectively:
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE
In these figures, an inverted cup, or stylus holder 12, carries a stylus 14 with a sensing tip 15 at its distal end. The stylus holder is located inside a housing 10 and has an annular skirt 18 that rests against a flat interior surface 20 of the housing. The annular skirt is pushed into tight contact with the housing by a biasing spring 24. When the sensing tip hits an object, the stylus deflects and the stylus holder tilts inside the housing, rotating about a point on the annular skirt where the skirt contacts the housing. A light emitting diode 42 normally shines through an aperture 44 in the stylus to a pair of light detectors 46. However, when the stylus deflects because of contact with an object, the aperture moves and the light beam is deflected. The light detectors sense the change and then send a signal to the computer that runs the machine. When the stylus moves back away from the object, the biasing spring pushes the stylus holder back down into full contact with the housing, and the light beam returns to the undeflected state.
With only the structure described above, the stylus holder is likely to slide around some in the housing so that the probe cannot deliver consistent performance. As a solution to this problem, the figures show the stylus poking through, and connected to, a planar spring 30 which is simply a sheet of flexible material and which is attached at its outer edge to a ring 32. The ring serves as the connecting base for three cylinders 34 which in turn are seated between pairs of balls 36 fixed to the housing. This planar spring assembly, also known as a kinematic mount, can be analogized to a flag pole (i.e., the stylus) stuck through a hole in the surface of a three-legged trampoline. The planar spring prevents the stylus holder from rotating (i.e., about the Z axis) and keeps it from sliding back and forth inside the housing (i.e., in the X and Y axes). When the stylus begins to deflect, the planar spring flexes slightly so that the kinematic mount can remain tightly engaged. With greater deflection, the cylinder on the side opposite the deflection eventually lifts out of its seat, much like a leg on the analogous trampoline would lift off the ground if the flag pole sticking through the flexible surface of the trampoline leaned over too far.
The embodiment just described purportedly solves two problems in the prior art: lobing and hysteresis. Lobing occurs when, because of the way the stylus holder is mounted in the housing, a greater amount of stylus deflection is required to trigger the probe in some directions than in others. The pictured embodiment reduces lobing because the annular skirt results in equal deflection in every direction. Because the probe triggers upon relatively equal deflection in any direction, it can achieve micron-level accuracy by signaling soon after the stylus contacts a workpiece.
Hysteresis occurs when the stylus returns to a different position after each deflection (i.e., the stylus does not center fully); it is caused primarily by friction between the probe components. The pictured embodiment reduces hysteresis because the biasing spring pushes the cylinders tightly into their seats between the balls, returning the stylus to the same rest position each time. The key issue on appeal is whether the claimed touch probe solves both these problems. Claim 2 recites (emphasis added):
2. A touch probe, for use on a movable arm of a position determining apparatus, the probe having a housing with an axis and a stylus holder located within the housing, the stylus holder carrying an elongate stylus which projects through an aperture in the housing, and which has a sensing tip at a free end thereof, the probe generating a trigger signal when said sensing tip contacts an object and said stylus holder is thereby deflected relative to said housing, the trigger signal being used by the position determining apparatus to take a reading of an instantaneous position of the movable arm, the touch probe comprising:
biasing means for applying an axial biasing force to said stylus holder;
a device acting between said stylus holder and said housing for constraining said stylus holder relative to the housing, the device including a seating and at least one constraining spring distinct from the biasing means, said seating including at least one pair of mutually engageable elements, each mutually engageable element having a surface inclined relative to the axis of the housing and providing lateral constraint from axial biasing;
an annular member retained in a predetermined relationship with the stylus holder and having an annular surface facing in a direction of said aperture, said annular member being tiltable relative to the housing, and said stylus holder being tiltable with said annular member relative to said housing about a point on said annular surface; and
a transducer for generating said trigger signal, said transducer being actuable by tilting of said stylus holder with said annular member about said point on said annular surface, wherein said tilting of said stylus holder relative to the housing is accommodated by flexing of said at least one constraining spring and said mutually engageable elements coming out of contact with each other.
Renishaw asserts infringement of claim 2 by Versions 4 and 5 from Marposs's Mida line of touch probes. The Version 5 probe is illustrated in vertical and oblique cross-section in plaintiff's exhibits below:
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE
In the Mida probes, the stylus holder ("armset" in the diagram) has a spherical surface that rests in a conical seat in the housing and a central extension that rises toward a microswitch. The stylus holder also has an annular member ("disk" in the diagram), but unlike the annular skirt in the preferred embodiment of the '904 patent, it does not normally rest flat against the housing. Rather, it rests above a shelf built into the side of the housing and is separated from the shelf by a small gap. Thus, when the stylus contacts an object, the stylus holder does not immediately move upward toward the microswitch. Instead, it first rotates inside the conical seat (like a ball-and-socket joint). Once the annular disk hits the shelf, the stylus holder tips upward and its central extension hits the microswitch. 1
The annular ring cannot rest in flat contact with the shelf, and therefore, the spring can only force the stylus to return to a "neutral zone" rather than to a single precise rest position. As a result, the Mida probes are not designed to signal as soon as the stylus begins to move. Instead, they do not signal until the probe reaches the edge of the neutral zone. Because the size of the neutral zone is known, the location of the object being measured can be calculated. Thus, although the Mida probes do not eliminate hysteresis, they nonetheless provide precise readings.
Renishaw sued Marposs in July 1994, and a bench trial on infringement was held in March 1997. During the trial, Marposs presented no evidence regarding invalidity. At the close of the evidence, the district court took the case under advisement and requested proposed findings and post-trial briefs from both...
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