Source: {"pile_set_name": "USPTO Backgrounds"}

As the search for oil and gas, as well as other subterranean deposits, has increased, the need for a portable self-contained drilling rig capable of drilling to the depths required has arisen.
Prior art drilling rigs were either large complicated relatively immovable structures or were small relatively unsophisticated apparatus, and of which Leonard, U.S. Pat. No. 2,904,310 is a good example. Leonard discloses a truck mounted drilling rig in which the drilling frame is at an incline relative to the truck body when in operation. Leonard employs a pair of cooperating cylinders mounted to the upper end of the drilling frame with the swivel mounted at the lower end of the pistons. The disadvantage of an assembly such as Leonard is the use of the pair of cylinders suspended from the upper end of the drilling rig and the fact that the drilling frame may become bent or distorted because of the rotary action of the power swivel being transmitted to the frame and causing distortion thereof.
Consequently, a lightweight portable drilling apparatus having a minimal number of parts is desirable. The added capability of directly connecting the rotary power swivel to a length of drill pipe is desirable and results in a further decreased amount of necessary equipment and also results in decreased amount of labor. Such a drilling rig is highly desirable for the foregoing reasons and also because the resulting structure minimizes the risk of injury to the drilling rig operating personnel.