System for automatically positioning the carriage of a machine in numerical control system at a reference point

A system for automatically positioning a carriage at the reference point of a machine using a numerical control system and having a machine bed, a platform mounted with respect to the machine bed, a carriage adapted to move along said machine bed, a first sensor disposed on said system to detect whether the carriage is on the platform to provide coarse positioning of the carriage with respect to a predetermined point on the machine bed, a second sensor disposed on said system for detecting a fine positioning of the carriage, control means for controlling the movement of the carriage characterized in that said control means comprises

• means for producing a positioning command,
• decode means for decoding said positioning command and activating said control unit,
• decode/count means responsive to changes in the output signal of said first sensor for producing first, second and third status signals,
• means for determining the direction of movement of said carriage in response to said first sensor and said decode/count means,
• rapid travelling means for moving the carriage in a first direction at high speed in response to said first status signals from said decode/count means,
• slow feed means for moving said carriage in a second direction opposite to that of said first direction at slow speed in response to said second status signals from said decode/count means when said carriage passes a predetermined point,
• means for producing fine positioning of said carriage in response to said third status signals from said decode/count means, and
• means coupled to said determining means, said rapid travelling means, said slow feed means and said actuating means for driving said carriage.