How To Determine Whether a Patent is Infringed

You know the basics of patent litigation, but how do you determine whether a patent is infringed? Here’s an overview and example.

How do I determine whether a patent is infringed?

There are three steps involved:

  1. Discovering the details of the accused activity;
  2. Studying the claims of the patent; and
  3. Comparing the accused activity to the patent claims.

In some cases, the first step is easy. For example, to learn about a mechanical device being sold to the public, you may simply purchase and examine it. In addition, useful information can also be found in advertising materials, on web sites, and in patents owned by the suspected company.

In other cases, more investigation is required, such as when the patent covers a particular manufacturing process that is used in secret to make a product.

Care must be taken when you are investigating a possible infringement, however, so as to not violate any of the competitor’s rights. For example, you may not induce a competitor’s employees or its customers to violate a confidentiality agreement.

Assessing whether an accused activity infringes requires the right expertise. In general terms, a patent’s scope is defined by the limitations of its “claims,” which are listed at the end of the patent. If any one claim is infringed, the patent as a whole is infringed. To literally infringe a claim, each and every limitation of the claim must be met. The analysis proceeds word-by-word or clause-by-clause to see if each is found in an accused device or process.

For a simple example, consider a patent that describes a typical four-legged dining room chair and has a claim for:

a) a sitting device, comprising:

b) a substantially planar surface to support a person; and

c) at least three legs, each coupled to the surface, to support the surface.

You will note that this claim does not recite the back of the chair or four legs. Nonetheless, it still covers a chair with a back and four legs. This is because of the use of the term “comprising” which means “including but not limited to.” Therefore, a stool with three legs would likely infringe, even though its appearance (no back, three legs) is different from that of a dining room chair which has a back and four legs. The stool (a) is a sitting device, (b) has a flat top surface that can support a person and (c) has at least three legs,

connected to the bottom of the flat top surface, to support it. A bean bag chair or a large cylinder, however, likely would not be found to infringe—neither has “at least three legs.”

When a claim limitation is not met literally, a patent owner may have a second chance to prove infringement (depending on the prosecution history of the patent) by asserting the “doctrine of equivalents.” Here, the patent owner would argue that the accused product or process is so close to meeting the literal language of a claim that it would be unreasonable to find no infringement. In other words, the patent owner would assert that it performs substantially the same function in substantially the same way to achieve substantially the same result.

In our example above, if a chair had three legs coupled to a post, or platform, which was coupled to the sitting surface, it might be argued that such a chair infringes the hypothetical patent claim described above under the doctrine of equivalents.

Interested in learning more? Visit our litigation page.