The United States Patent and Trademark Office classifies all inventions into one or more of about 450 different classes. Each class is further divided into numerous subclasses. There may be up to a 1000 subclasses per class. The classes describe a generic category. The subclasses describe specific features of each of the categories.
Benefit of searching within a class and subclass
By searching within one or more class and subclass combination, the patent search process is more efficient. If you perform a keyword based search without specifying the class and subclass, the search results will include references that are in other unrelated technical fields which must be manually eliminated. By searching within a particular class and subclass, irrelevant references are less likely to be included in the search results. No time is wasted manually eliminating these irrelevant references.
Danger of searching within a class and subclass
If all of the relevant classes and subclasses are not searched, then the most relevant reference may be missed even if you have the right keywords. Accordingly, it is important to determine all of the relevant classes and subclasses. The search for all relevant classes and subclasses is an ongoing and iterative process. Just like keywords, as you review patents and published patent applications, review the list of classes and subclasses of the relevant documents to check whether you can identify more relevant classes and subclasses.
Finding relevant classes and subclasses
To find relevant classes and subclasses go to the Patent Classification Main Menu.
Go to Option B. Search USPTO. (see below). Look up your search terms in the index with the alphabetical index. You can alternatively browse all of the classes by selecting “class numbers and titles“. In our example, Class 24 may be relevant to paper clips.
Go back to the Patent Classification Main Menu. In option A. 2., click the radio button Class Definition. (see below).Type in 24 in the first box in option A and click submit under A.3. Read through the definition of Class 24. Try different keywords until you find a relevant class. If Class 24 is relevant to paper clips, then type in 24 in the first box and click the radio button for class schedule to look for relevant subclasses. Identify as many relevant subclasses.
You can identify relevant subclasses by doing a text search. Once the class schedule is shown, press “ctrl-f” to perform a text search for “paper clips”. This search term will not show up. You must look for “clips” or “clip”. Remember this is a keyword based search. Sometimes, you have to split up the phrase to find the right class or subclass.
Once you have found potentially relevant classes and subclasses, type in the class and subclass in option A.1., click the Class Schedule radio button and click submit. Read through the class and subclass definition to check for relevance.
Updating class and subclass list
During the database search, relevant references may be found which solves the problem that your invention solves or is similar to your invention. For these references, check the other classes and subclasses listed on these documents. Check for relevance. If relevant, add these classes and subclasses to your list.
In the example shown below, U.S. Patent No. 7793449 is also classified in U.S. Class/Subclass 40/641, 40/360, 24/67R. Read through the definition of these classes and subclasses to check for relevancy. If relevant, add them to the list of classes and subclasses.
Other related blog posts:
1. Overview: How to conduct a DIY patent search
2. Basics of a DIY Patent Search
3. Brainstorming keywords for the DIY patent search
4. Finding the right class and subclass for the DIY patent search
5. Search databases for both the issued patents and published patent application for your DIY patent search
I invite you to contact me with your patent questions at (949) 433-0900 or [email protected]. Please feel free to forward this article to your friends. As an Orange County Patent Attorney, I serve Orange County, Irvine, Los Angeles, San Diego and surrounding cities.