RE: Ampex versus Mitsubishi (the appeal)
This is my understanding of the basis of AXC's appeal. Again, this is largely based on that piece of analysis I referred to earlier.
Prosecution History Estoppel
Finally, the Supreme Court provided some guidance with respect to the effect of claim amendments under the doctrine of prosecution history estoppel, which precludes a patentee from recapturing, in an infringement action, matter surrendered to obtain the patent.
The court rejected the broad rule proposed by Warner-Jenkinson that any claim amendments made during patent prosecution should give rise to an estoppel--regardless of the reason for the amendment--and adopted a more flexible approach.
The court held that if, on one hand, the prosecution history shows that an amendment was made to overcome prior art, the claims cannot be interpreted under the doctrine of equivalents to recapture the subject matter surrendered by the amendment.......
If, on the other hand, the prosecution history shows that there were other reasons for the amendment, such as merely to improve the form of the claim, the permissible range of equivalents is not limited by the amendment.....
In a novel twist, the Supreme Court added that if the reason for the amendment is not clear from the prosecution history, it will be presumed that the Patent and Trademark Office had a substantial reason related to patentability for including the elements added by amendment, and a rebuttable presumption of estoppel will apply.
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