Is this patent already expired? The original patent was filed way back on Sept. 4, 1990 but as you can see there have been a number of continuations and continuations in part over the years since then. How do these continuations affect the patent expiry date?
I guess my overall question, is whether I am opening myself up to patent infringement issues if I design something very similar to the device in this patent. Any help/advice would be appreciated.
You're thinking along the right lines, but the answer in this case is "not until October 2014". Part of the patent law allows for the term of a patent to be extended to the extent that the delay-in-granting over a certain point is attributable to patent office delay. In this case, the patent granted as US patent 7,666,104 and the patentee asked for the term adjusment to be re-calculated, which came out to a term adjustment of 1,503 days
(i.e., 4 years & about 6 wks).
This time is added to the end of what would have been the normal term. This information is available from the public record database at http://portal.uspto.gov/external/portal/pair
(go through the challenge screen then plug in any of the application serial number, the publication number or the patent number - all will point you to the same record).
But you should also look at the claims of the granted patent 7,666,104, not at the application publication (what you had linked was only the published application - not a patent). Once you compare the two, you'll see that the granted patent claims are much
longer and more detailed than those of the publication. Generally speaking, a more detailed claim is "harder" to infringe because there are more elements required to be present before infringement exists. So you have to go through each independent claim-as-granted and for each element required by that claim ask, "would I have this element?" (or for method claims, "would I be doing this step?"). Sometimes it can be tough to parse your way through claim language and understand fully what it means, which is why it's a good idea to have a patent attorney review the situation with you. And in your shoes, I'd probably also ask the attorney to look at some of the other granted patents in that family on the chance that some of them are relevant and may also have been able to take advantage of term adjustment.
Good luck to you.