Bi-directional snap-action register display mechanism

A bi-directional snap-action register mechanism for a mechanical register display comprising:

• at least one register display wheel having at least one display position provided thereon:
• guide means disposed coaxially along a common rotational axis with the register display wheel;
• a bi-directional cam disposed about the guide means, the bi-directional cam comprised of two spiral surfaces, each spiral surface having a smooth portion and a step transition portion provided thereon, the two spiral surfaces being oriented symmetrically mirror-reversed with respect to each other and arranged along a portion of a common shaft having guide means formed thereon, the bi-directional cam having means cooperating with the guide means to allow lateral displacement of the bi-directional cam in a direction parallel to the common rotational axis;
• a pin biased by biasing means into contact with one of the spiral surfaces of the bi-directional cam;
• and
• means for coupling the bi-directional cam to the register display wheel;
• whereby rotation of the guide means causes the biased pin to engage one of the two spiral surfaces of the bi-directional cam and causes the cam to abruptly rotate through a predetermined angular distance when the point of contact of the biased pin with the engaged spiral surface moves from the smooth portion of the engaged surface to the step transition portion of the engaged surface, the abrupt rotation of the cam being communicated to the register display wheel by the coupling means to cause a new display position to be moved into view.