A claim reads like this.
An apparatus for feeding humans, the apparatus comprising:
item A;
item B;
item C.
Another claim reads like this.
An apparatus for feeding aliens, the apparatus comprising:
item A;
item B;
item C.
Both claims have the same items, but only the "subject" differs in the preamble.
Is preamble offers any limitation OR only offers some description about the invention?
In the US, it depends on the case. In Europe, the preamble limits more or less depending on what is claimed: most of the times methods are limited by the preamble (please check out explanation in the "more" link), whereas devices/systems are limited such that they must be suitable for the stated purpose (please check out explanation in the "less" link). The scope of the two examples you have provided is the same if aliens are fed like humans are fed, but if they are fed differently, then the scopes may be different.
In the U.S. having details in a preamble is usually not a good idea. During prosecution an examiner is likely to not credit the preamble as actually proving a limitation that helps you with patentablity. However, during an infringement proceeding a preamble might be given strong weight by a judge or jury.
A patent has a preamble in its specification. The preamble is an introductory phrase to introduce the subject matter of the claims, defines a work concept or states of purpose or use of the invention. The preamble does not define the scope of invention rather it is an introduction to body of that claim which serves the function.
The preambles can be of any length; however, shorter preambles are mostly preferred. The preamble is similar to the preambles of the claims, but can vary as needed. In one example, a preamble such as, i) ‘an apparatus comprising’ can be considered overly broad or ii) composition of matter that describe a new material.
Typically, claims of patent specification contain three major components which are i) a preamble, ii) a transition term and iii) a body. The preamble should not embrace unnecessary limitations; if a constraint is needed for the claim, it should be included in the body of the claim, using ‘whereby’ or wherein clause. Further, it is important that the preamble should match the invention described in the patent specification. If the specification describes ‘a chain’, then the claim should not specify ‘a bracelet’; similarly, if the invention can be used in headphone or watch, the claim should not specify just ‘headphone’ or ‘watch’.
A good strategy for drafting a preamble is to include preamble terms that make the claim scope seems rational, however it can be drafted that these limitations may not construe to narrow the claim.
