US Patent 10117996 State changing appliance for a drug delivery device

A system comprising a state changing appliance and a drug delivery device, the state changing appliance comprising first interface means for rotationally locking to a first exterior portion of the drug delivery device, second interface means for rotationally locking to a second exterior portion of the drug delivery device, the first exterior portion and the second exterior portion being angularly displaceable relative to one another from a first relative position to a second relative position, which second relative position defines a set dose to be expelled by the drug delivery device, and limiter means for limiting a relative angular displacement between the first interface means and the second interface means.