Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd

Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd.
535 U.S. 722 (2002)

Stoll invented a kind of piston and tried to get two patents on it. When the USPTO rejected the original applications, Stoll went back and added a new limitation, and the patents were approved.

The limitation that the patent specified used a pair of sealing rings and that the outer shell must be made out or magnetizing metal.

Stoll sold the patent to Festo who began manufacturing the pistons. When SMC entered the market with a very similar product, Festo sued for infringement.

SMC argued that their piston used a different kind of sealing ring and was made out of non-magnetizing metal, therefore it was outside of the scope of Stoll's patent.
Festo argued that the differences were very minor, and so it was still infringing via the Doctrine of Equivalents.

The Doctrine of Equivalents says that a product or process that does not literally infringe upon the express terms of a patent claim may nonetheless be found to infringe if there is an equivalence between the elements of the accused product or process and the claimed elements of the patented invention.
See Graver Tank v. Linde Air Products Co. (339 U.S. 605 (1950)).

The Appellate Court found that Festo could not argue the Doctrine of Equivalents because of Prosecution History Estoppel.

Prosecution History Estoppel says that if you added a new limitation to get your claim approved, then you can't go back later and make an equivalents argument later.

The Court found that Prosecution History Estoppel was a complete bar, and there was no wiggle room for Festo.

The US Supreme Court found that Prosecution History Estoppel is not a complete bar, and that the amendments to the original patent must be viewed in light of the reason for the change.

So, if the amendments were made to the patent application just to clarify a translation, then there would be no bar. On the other hand, if the amendments purposely limited the claims in order to get around some prior art, then they would be a bar to asserting equivalence.

For example, if you have a chemical process that you original claim works up to a pH of 10, but there is prior art at pH 10, so you limit your claim to pH of 9 or lower, you can't then sue someone for making a process at pH 10.

The Court found that you have to look at the prosecution history (letters between the USPTO and the inventor, the first office action, lab notes, etc), to determine why someone amended their claim.

The Court found that there is a presumption that an amendment that limits a claim will bar bringing infringement claims via Prosecution History Estoppel. However, in the very narrow case that the infringer is using some variation that was unforeseeable at the time the original patent was filed, then the Doctrine of Equivalents might still apply.

"The equivalent may have been unforeseeable at the time of the application; the rationale underlying the amendment may bear no more than a tangential relation to the equivalent in question; or there may be some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question. In those cases the patentee can overcome the presumption that prosecution history estoppel bars a finding of equivalence."

The Court remanded back to the Trial Court to determine the exact reasons for why Stoll amended his patent.

The Courts eventually determined that Stoll amended his patents to get around the prior art, and that SMC's design was not unforeseeable. Therefore Festo could not use the Doctrine of Equivalents because of Prosecution History Estoppel.

Is there really any difference between what you originally put into the patent application and what you add by amendment?

Using the above example, if you knew about the prior art and filed your original patent at pH 9, you could sue someone for making a process at pH 10. Does that make sense?

According to my professor, this case is the "Mani-Festo" for how to understand prosecution history estoppel.