Patents protect inventions by giving the patent owner the right to sue anyone who makes, uses or sells the patented product without the owner's permission. Of course, this raises the question, what exactly constitutes patent infringement?
When can you tell if a patent is or is not infringed? Before discussing this topic, let's get some nomenclature out of the way. For the purposes of this article, let's call the product which allegedly infringes the patent the "offending product" and let's call the person (or persons) who put that offending product on the market the "patent offender". Of course, patent infringement is not a criminal matter, so by "offender" we mean someone who has caused harm to the patent owner by taking some action such as manufacturing or selling the offending product. Also, when we say that an offending product "infringes" a patent, what we actually mean is that the offender would be committing patent infringement by making, using and selling the offending product in the jurisdiction where the patent was granted. The mere existence of the product does not actually constitute patent infringement, only its sale, use or manufacture does that.
Now that we have the nomenclature out of the way, let's start our examination by stating what patent infringement does NOT include.
Creating the Same Product as Shown in the Patent Drawings
This might come as a surprise to some people, but a patent is not necessarily infringed if the offending product looks like the product depicted in the patent drawings. The scope of the patent - i.e. the type of product which is actually protected by the patent - is defined by the claims of the patent, not the drawings. The claims literally define what specifically has to be included in the product to constitute patent infringement. Those features may, or may not, be clearly discernible from the drawings; therefore, it is quite possible that a product which looks like the product depicted in the patent drawings may, in fact, not infringe. Conversely, it is quite possible for a product which looks very different from the product illustrated in the patent may, in fact, fall within the scope of the patent claims and infringe the patent.
Creating the Same Product that the Patent Owner Sells
Patent owners are not required to sell the products they patent. While it's often the case that a patented invention will be found in the patent owner's inventory of products, there are numerous examples where the patent owner does not in fact sell or manufacture the patented invention. Conversely, if the offender copies a product which the patent owner produces, this does not necessarily mean that the offender infringes any patents. From a patent infringement perspective, it is completely irrelevant what products the patent owner sells. Again, the scope of the patent is defined in the claims of the patent, not in the patent owner's product inventory.
Creating the Same Product that is Described in the Patent
It may sound counter-intuitive, but the description of the invention does not, in itself, define what the invention is and therefore cannot, by operation of law, define what does and does not infringe the patent. Again, only the claims of the patent actually define what the invention is and what does and does not constitute patent infringement. So now that we know what does not constitute patent infringement, lets take a close look at what actually does determine whether a patent has been infringed.
The invention is literally defined by the exact wording of the patent claims. Roughly speaking, each and every claim in a patent is essentially a check list of the features which the offending product has to include in order to "pass" the test of infringement. Think of a claim as a numbered list of features, and if the offending product has all of the features listed in the claim, then the offending product "infringes" that claim in the patent. This is what is generally referred to in patent circles as "literal infringement". If there is more than one claim (and there usually is), then the total number of claims infringed does not matter. Infringing one claim or infringing all of them makes no difference from a legal point of view.
Let's consider this principle of literal patent infringement with a hypothetical example. Let's assume the patent owner has a patent for a desk lamp having seven specific features, namely:
A first offending product up for consideration is a lamp and has all of the features (1) through (6) but it does not have feature (7), the control circuit for automatically turning the lamp off after 30 minutes. In this example the first offending product does not literally infringe the claim because it is missing a listed feature. However, a second offending product which does have all the features listed would be considered infringing. If the offending product has other features in addition to features (1) through (7), such a dimmer switch, then it is still considered to infringe the claim. Generally, claims are written with inclusive language so that patent infringement is not avoided by the addition of non-listed features.
Now, let's consider a third offending product - one which has all of the listed features except for the LED bulb. Instead of an LED bulb, the third offending product has an incandescent bulb. Does this third product still infringe? From a literal infringement point of view, no it does not since the claim specifies an LED bulb. However, many jurisdictions, including the United States and Canada, have additional legal doctrines which, when applied, would render this third offending product as also infringing. In the United States it is quite likely that the third offending device would be considered to infringe the patent because while the offending device does not have an LED bulb, it does have something which works in substantially the same way to give substantially the same result. Both LED bulbs and incandescent bulbs are "functional equivalents" because they both work in substantially the same way to give substantially the same results. They both turn electricity into light. Therefore, it is quite likely that a court in the United States would view the third offending product as infringing. The law in Canada, while not exactly the same, is similar and would likely yield a similar result.
Now let's stretch this reasoning a little further and consider the case of a fourth offending product, a lamp with all of the claimed features except for the auto shut off feature. In place of the auto shut off circuit, this fourth lamp has a circuit which is designed to shut the lamp on or off simply by touching. If the lamp is off, touching it will turn it on; however, if the lamp is already on, touching it will shut it off. This "improved" lamp does away with the auto shut off feature by providing an extended touch feature.
Applying the analysis of "functional equivalents" we can agree that the "extended touch feature" is not a functional equivalent to the auto shut off timer. The fourth offending lamp would remain on all night long provided it was not touched again. Therefore we can say with some confidence that the fourth offending product does not infringe the claim under the US doctrine of equivalents.
The above example illustrates the possible difficulty if applying the United States principle of "functional equivalence" (and the Canadian tests of "substantive infringement" and "purposive construction"). Whether or not two features are considered "functional equivalents" largely depends on the relative importance of the missing feature. In the above examples, the LED bulb, while important to the lamp over all, is essentially the same thing as an incandescent bulb. Essentially, these legal doctrines boil down to extending patent protection to situations where a relatively minor and unimportant feature of a claim is missing in the offending product being considered.
Of course, determining whether or not a specific feature is important or not is often no small task. But that's a topic for another day.