The driving gear of the compressor converts the rotating motion of the crank into the oscillating motion of the piston and also transmits work.
It usually works according to the kinematic principle of the connecting rod mechanism.
For single acting compressors usually the connecting rod is directly linked to the piston (plunger type piston – fig. a), whereas for double acting compressors linear reciprocating motion is achieved by linking the connecting rod to the cross head (crosshead design – fig.b).
On very small compressors (for example with household refrigerators) the kinematic principle of the cross slide (fig. c) will find application. It is a four member link with two linear guidances. Small fast running units can be designed as axial compressors (fig. d). Thereby several pistons are runnig parallel to the axis of the drive of the machine. The pistons are moved via a disc fitted at an angle to the drive shaft (wash plate).
For (combustion) engine driven compressors the free piston execution is an interesting alternative (fig. g): The reciprocating action of the combustion engine is directly linked to the oscillating motion of the compressor. As the combustion engine is double acting motion control entirely is enabled by proper timing of the counteracting combustion processes in the two combustion chambers.