In a patent infringement lawsuit that has survived various rulings and company configurations, a US District Court has ruled that Xerox's patent for its Unistrokes single-stroke handwriting recognition software is invalid and as a result dismissed its suit against PalmOne.

Xerox had contended that Palm's handwriting recognition technology for personal digital assistants (PDAs) violated Xerox US Patent number 5,596,656, which covers Unistrokes symbols. But for the second time a judge for the US District Court for the Western District of New York, Michael Telesca, terminated the patent infringement lawsuit.

Unistrokes was developed in the early 1990s at Xerox's Research Center in California as a technology for allowing users to input information to a computer by printing in special shorthand. Its patent for Unistrokes was granted by the US Patent and Trademark Office in January 1997 and the following April, Xerox sued US Robotics Corp, charging that the Graffiti software used in Palm handheld organisers infringed upon its patent. As the lawsuit made its way thorough the courts, US Robotics was acquired by 3Com, which then spun off Palm in March 2000. Palm in turn spun off PalmSource, the maker of the Palm OS platform, acquired Handspring and renamed the new configuration PalmOne in October 2003. PalmOne retained liability for the Xerox action.

Telesca had first dismissed the ongoing lawsuit in June 2000, when he ruled that Palm's Graffiti did not use the same recognition patterns as Xerox's technology. The lawsuit was revived in October 2001 after the US Court of Appeals for the Federal Circuit ruled that Telesca had misunderstood how and where symbols must be written in order to be recognised by the handheld device.

That December, based on the guidelines put forth by the Court of Appeals, Telesca found in Xerox's favour, stating that its patent was "valid and enforceable" and clearing the way for Xerox to seek damages.

But the appeals and requests for summary judgements continued, and Telesca was required by the Court of Appeals to conduct a full analysis regarding the validity of the patent.

In his ruling, Telesca agreed with PalmOne's contention that the Unistrokes handwriting-recognition software should not have been granted a patent as the technology in question already existed when the patent was applied for, a common anti-patent argument known as "prior art".

In total, PalmOne said there were three cases of prior art that, like Unistrokes, "disclosed spatially independent, graphically separated single-stroke symbols that are recognised immediately upon delimitation," according to the ruling.

Representatives for Xerox and PalmOne could not be reached for comment, though in a statement PalmOne said it was pleased with the ruling.