Protective system for automatic tool changing apparatus

Claim 1

A protective system for automatic tool changing apparatus which provides protection against an interference between a tool and a work during the tool changing operation by an automatic tool changing apparatus for a machine tool which performes through a driving electric motor a series of tool changing cyclic operations including lowering and raising of a tool magazine, etc., between a socket of a machining head spindle and the tool magazine, said protective system comprising: a current detecting circuit for detecting a load current of said driving motor; a first comparator circuit for generating an output when said current detecting circuit detects a current which is greater than a warning current value preset to a current level greater than a maximum steady-state load current value of said motor; a second comparator circuit for generating an output when said current detecting circuit detects a current which is greater than an irregularity protection current value preset to a second current level higher than said first current level; a timer circuit for preventing a detection output of said current detecting circuit from being applied to said comparator circuits for a predetermined time interval during a starting period between the starting of said motor and a time that said load current is stabilized at a steady-state value; warning relay means operable in response to an output of said first comparator circuit to give an overload warning; and protective action relay means operable in response to an output of said second comparator circuit and an actuation signal from said warning relay means to reverse the direction of rotation of said driving motor thereupon.