A sensor or switch mechanism for a gripper mechanism having a gripper body, an actuator one of connected to and integrated with said gripper body, a driving member connected to said actuator, and at least one movable jaw (26, 28) operably connected to said driving member, comprising: a pivotal cam link, said pivotal cam link having a cam slot; a drive pin connectable to the driving member and engaged with said cam slot, said drive pin and said cam slot configured to convert linear reciprocal motion of the driving member to rotational motion of said pivotal cam link; a target one of attached to and integrated with said pivotal earn link; a sensor or switch positioned proximate to an arc described by said target upon said rotation of said pivotal cam link; and the pivotal cam link is provided with a curved cam slot shaped so that a small change in the position of the driving member corresponds to a large angular displacement of the pivotal cam link, said pivotal cam link, said cam slot, said target, and said sensor or switch being arranged so that: said pivotal cam link pivots to place said target in a first position on said arc upon the at least one movable jaw (26, 28) closing upon no workpiece, said first position resulting in a first output of said sensor or switch; said pivotal cam link pivots to place said target in a second position on said arc upon said at least one movable jaw (26, 28) closing upon a single workpiece, said second position resulting in a second output of said sensor or switch; said pivotal cam link pivots to place said target in a third position on said arc upon said at least one movable jaw (26, 28) closing upon at least two workpieces, said third position resulting in a third output of said sensor or switch; and said first output of said sensor or switch being one of the same as and different from said third output of said sensor or switch. a pivotal cam link, said pivotal cam link having a cam slot; a drive pin connectable to the driving member and engaged with said cam slot, said drive pin and said cam slot configured to convert linear reciprocal motion of the driving member to rotational motion of said pivotal cam link; a target one of attached to and integrated with said pivotal earn link; a sensor or switch positioned proximate to an arc described by said target upon said rotation of said pivotal cam link; and the pivotal cam link is provided with a curved cam slot shaped so that a small change in the position of the driving member corresponds to a large angular displacement of the pivotal cam link, said pivotal cam link, said cam slot, said target, and said sensor or switch being arranged so that: said pivotal cam link pivots to place said target in a first position on said arc upon the at least one movable jaw (26, 28) closing upon no workpiece, said first position resulting in a first output of said sensor or switch; said pivotal cam link pivots to place said target in a second position on said arc upon said at least one movable jaw (26, 28) closing upon a single workpiece, said second position resulting in a second output of said sensor or switch; said pivotal cam link pivots to place said target in a third position on said arc upon said at least one movable jaw (26, 28) closing upon at least two workpieces, said third position resulting in a third output of said sensor or switch; and said first output of said sensor or switch being one of the same as and different from said third output of said sensor or switch. said pivotal cam link pivots to place said target in a first position on said arc upon the at least one movable jaw (26, 28) closing upon no workpiece, said first position resulting in a first output of said sensor or switch; said pivotal cam link pivots to place said target in a second position on said arc upon said at least one movable jaw (26, 28) closing upon a single workpiece, said second position resulting in a second output of said sensor or switch; said pivotal cam link pivots to place said target in a third position on said arc upon said at least one movable jaw (26, 28) closing upon at least two workpieces, said third position resulting in a third output of said sensor or switch; and said first output of said sensor or switch being one of the same as and different from said third output of said sensor or switch.