An Indian Patent titled "A compact drive mechanism of a reciprocating machine" was granted to IIT Bombay on 5 June 2006. According to the inventor, Prof S L Bapat, Department of Mechanical Engineering, the objective of the invention is to provide a compact and efficient drive mechanism for a reciprocating machine that is free from side thrust. The utility of this drive mechanism ranges from reciprocating compressor and pump (also vacuum pump) to stirling cycle machines (coolers as well as engines), internal combustion engines and pulse tube cryocoolers. The drive mechanism consists of two horizontal circular discs parallel to each other, both having a coinciding circumferential groove of same size and shape. One of these discs is stationary while the
other (driving disc) is rotated using a prime mover. A vertical (driven) disc with external surface matching the curvature of the grooves is placed in between the two horizontal plates. It rotates in the grooves about the central axis of the mechanism and also about its own horizontal axis, which ends up in a planetary motion. This vertical disc has equally spaced circular holes, with same pitch circle diameter through it. Similarly, the horizontal
stationary disc has same number of holes to hold tubes acting as cylinders. Two circular rods are coupled to each other at right angle to obtain a L-shaped member. The horizontal limbs of such L-shaped members are inserted through holes in the vertical disc and the guide sleeve where they rotate and reciprocate and act as load bearing limbs. The vertical limbs act as pistons and reciprocate (and simultaneously rotate) in the respective cylinders mounted on horizontal stationary disc. One rotation of the vertical disc is equivalent to two strokes (one upward and one downward) of each piston. Thus, the rotary motion is converted to reciprocating one using this compact drive mechanism. The drive mechanism enable it to have large stroke to diameter ratio. Moreover, the orientation of the drive mechanism has no effect on the performance of the application for which it is used. The line contact between the mating members ensures least frictional loss. The number of piston-cylinder combinations and angular phase difference between them can be adjusted within the geometrical constraints.

Contact: slbapat@iitb.ac.in.