Controller for automatic tool changer

A chucking repeat controller used for a work machine having a main spindle adapted for chucking a tool, a drive motor for said main spindle, a transfer arm assembly for replacing one tool on said main spindle with another tool reserved at a given stand-by position by its horizontal turning and vertical reciprocation, and a numerical control device for controlling operation of said transfer arm assembly according to a given programme, comprising:

• a limit switch arranged at a check point position right below said main spindle and generative of a chucking start signal every time said transfer arm assembly arrives at said check point position,
• a motor control circuit connected to said drive motor and including a current sensor which is attached to said drive motor and generative of a chucking complete signal upon defection of success in each chucking operation by said main spindle,
• an arm control circuit connected to said transfer arm assembly in order to control movement thereof between said main spindle and said check point position, and
• a chucking repeat circuit connected to said numerical control device, said limit switch, said motor control circuit and said arm control circuit, and including a timer and a chucking repeat fixer connected to said timer;
• said timer and said chucking repeaat fixer clearing up the chucking repeat mode of said chucking repeat circuit, and said motor control circuit stopping rotation of said drive motor, both upon receipt of said chucking complete signal from said current sensor which is concurrent by passed to said numerical control device as a work continuation order in order to enable subsequent operation of said transfer arm assembly as programmed,
• said timer generating, when no chucking complete signal is received from said current sensor within a prescribed set time after receipt of said chucking start signal from said limit switch, a time-up signal which is passed to said motor control circuit as a reverse rotation order for said drive motor, and to said arm control circuit as a descent order for said transfer arm assembly, and
• said chucking repeat fixer further generating, when chucking operation by said main spindle has ended in failure for prescribed times in succession, an interception signal which is passed to said motor control circuit as a stop order to said drive motor, and to said numerical control device as a work stop order to ban said subsequent operation of said transfer arm assembly as programmed.