Determining whether or not a design patent would be infringed by a particular device is a very subjective decision. The scope of a design patent is normally best determined through a careful analysis, including comparing the disclosed invention with prior devices. In very general and simplified terms, a court will often consider the issue of design patent infringement by asking the question, for example, "would an ordinary observer be likely to purchase the 'supposedly infringing' design thinking that it was the one protected by the subject design patent?"
On the other hand, the protection that a utility patent affords is primarily defined by the claims of the patent, located at the end of the patent. The claims are the entering arguments defining the metes and bounds of the property right protected by the patent, yet must be read in light of the entire patent and the prosecution history of the patent. Also, regarding claim interpretation, you must recognize that regardless of your opinion, or our opinion, the trier of fact (judge or jury) will have their own opinion if a patent is taken to court. For the owner of a utility patent to have the right to keep others from making, using, or selling particular subject matter, at least one claim of the patent must "read on" that particular subject matter. Generally, for a claim of a utility patent to read on particular subject matter, the subject matter must include every element in the claim (and the elements in any base and intervening claims).
Please understand, however, that claim interpretation encompasses a wide variety of issues which are not addressed here since this information is not directed toward any specific inventions or circumstances. Furthermore, this information should not be relied upon as legal advice.