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Can 3DSystems sue Formlabs over US Patent 5597520? If it was issued in 1997, wouldn't it have expired in 2007?

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This patent was filed before June 8, 1995. Its term should be at least 17 years after its issue date. The issue date was January 28, 1997, so the patent should be valid until January 28, 2014. – Mark Nowotarski patent agent Nov 21 '12 at 23:13
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@MarkNowotarskipatentagent That is right; you should submit it as an answer. – kinkfisher Nov 21 '12 at 23:18
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The expiry date should have been April 24, 2014. Patents filed before June 8, 1995 have a term which is the longer of 17 years from the date of grant or 20 years from the date of filing. In this case the 20 years is longer. And the final maintenance fee has been paid so it will remain in force until that date. See: ramps.uspto.gov/eram/… – Doug Calhoun Nov 27 '12 at 3:37
The truth is I was assuming 20 years and did the arithmetic in my head wrong. Thanks for all your help, everyone! – Dave Menninger Nov 28 '12 at 14:16

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I don't know about the first question, but the second is no. Calculating a patent term can be complicated, but assuming the maintenance fees were paid, etc., there's no reason it should have expired in 2007.

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