I have an idea for a new product and did a patent search and found someone who has a patent on it already, however my idea would require an additional part that adds more functionality to this device, is this infringement?

Don't go to an attorney first. First determine if your improvement INCLUDES the use of the other patent. Read the claims to make sure. Often, it will not. If it does then your improvement would not infringe if you purchased the underlying patented product from an authorized source. That is called, "license is inferred". If you produce the same product without permission, then you're infringing. However, the other patented product cannot use your improvement if you get a patent on it. The owner of the underlying patent must have your permission.

To file for a patent, you should go through a lawyer for several reasons. First reason is that they can answer this question. A slight variation on a design may be valid for a seperate patent. Also, the lawyer will be responsible to ensure that everything is filed correctly.

Most patents are not entirely new ideas, but rather enhancements upon existing ideas/devices, there's nothing wrong with that as one patent can reference many others. The ballpoint pen for instance was an enhancement upon liquid ink reservoir pens. If you were to set up a factory to produce your invention, you would have to negotiate royalties to the first patent holder.

Sorry.

If you are thinking of marketing your idea without a patent, I believe that:

1. someone else could copy your idea without being liable to you for infringement, and,

2. you are risking, an infringement lawsuit which only a court could decide.

I will repeat my original statement. Consulting an experienced patent attorney is best. The fee is nothing compared to either:

1. the rewards of marketing a patented idea, or,

2. the agony of an infringement lawsuit.

You don't need a lawyer to apply for a patent. A person familiar with the process who can word and illustrate the application properly can do this. Assuming that the Patent Office grants you a patent is not a guarantee that infringement has not occurred. Your patent will not need defending if nobody challenges it. Infringement is often a gray area that must be worked out in a legal environment including a court of law and lawyers.

With all due respect to "Bobdem", I would suggest consulting an experience patent attorney first.

Legal terminology is often difficult to interpret.

http://www.uspto.gov/web/offices/ac/qs/ope/fee2009january01_2009may01.htm#patapp

The above site lists current filing fees. If the expense of an attorney consultation is more than the patent fees (assuming one is preparing the application oneself [the language and format of the "claims" referred to by "Bobdem" are, to me, devilishly confusing] you might consider submitting the application yourself.

To the best of my knowledge, the worst that could happen is a denial, and loss of your:

1. time, and,

2. application fees, [I'm quite certain.].

If your additional part's function works with the patent's function to do something new, then your idea is probably patentable. The new function can't be an easily separated into your part's function and the patent's function. The whole is greater than the sum of the parts. 2+2=4 isn't patentable. But 2+2=5 is.