an automatic tool - exchanging device can be set on a robot for exchanging tools . it mainly comprises an upper and lower assemblies , and an engaging mechanism . the engaging mechanism includes a cam , which is to be driven with a double - acting pneumatic cylinder assembly . when the double - acting pneumatic cylinder is turned on , the upper and lower assemblies will be engaged together and generate a self - lock effect for safety ; when the double - acting pneumatic cylinder is turned off , the two assemblies will be disengaged from each other .