Interlock mechanism

An interlock mechanism for use with a plurality of vertically stacked units each unit capable of being horizontally movable into and out of the stack, with said mechanism comprising:

• pin means maintained on each unit respectively and movable therewith;
• slide means which includes respective slot means having respective camming surfaces engageable with the respective pin means upon movement of the respective units in and out of the stack with said engagement causing the slide means to move vertically between a first position and a second position;
• said slide means having means which allows a unit to be withdrawn from the stack when in said first position with the withdrawing therefrom causing the pin means of the unit withdrawn to engage the respective slot means on the slide means moving the slide means from the first position to the second position;
• said slide means capable of preventing the units remaining in the stack from being horizontally withdrawn from the stack when in said second position;
• and
• insertion of the withdrawn unit into the stack causes the pin means of said unit to engage the slot means moving the slide means from the second position to the first position.