There are many crankless engine designs for over a century but none of these have been commercially viable - one of the main reasons being that the rollers often track both an internal cam surface and an external cam surface (i.e. one roller is often tracking within a "groove"). A roller which is supported on one side only would cause "bending" of the connecting rod and therefore will not track properly (especially when under load during a power stroke) - resulting in excessive radial and axial loads on the rollers. This is mitigated using a TCK design because rollers are correctly supported.
The TCK Engine crankless mechanism is unique in that: different size rollers can be used; rollers are supported on each side; rollers each track an external cam surface (thus can track properly even under engine load); multi lobed cams can be used (odd or even number lobes) and the piston movement profile can both be spatially and temporally engineered. Only the piston rings are in contact with the cylinder bore. The mechanism can also be applied to drive the valves as well as the pistons. Valve control is fully desmodromic and controls valve timing, valve actuation and valve duration. The compression ratio can be varied within a stroke of the piston.