Safety lock system for test head mount

1. A safety lock system for preventing unlocking of a balanced loaded unit which includes a load mounted on and locked to a vertical guide rail when said loaded unit becomes unbalanced, said safety lock system comprising:

a plurality of calipers situated on opposite sides of said guide rail for simultaneously applying pressure on opposite sides of said rail;

a lock block for coupling said load to at least one of said calipers for movement of said load along said guide rail;

a rotatable handle coupled to said calipers by means of a shaft for increasing pressure by said calipers of said guide rail upon rotation of said handle in one direction in order to lock said lock block against vertical movement along said shaft and for decreasing pressure by said calipers of said guide rail from said guide rail upon rotation of said handle in an opposite direction; and

a safety block coupled to said loaded unit and moveable with said loaded unit for preventing rotation of said handle upon a preselected movement of said loaded unit relative to said lock block.

2. A safety lock system according to claim 1 , wherein a first axis extends from said guide rail to said load; and said shaft is orthogonal to said first axis and said guide rail.

3. A safety lock system according to claim 1 , wherein said calipers exerts pressure against said rail without completely surrounding said rail.