Automatic dynamic error compensator

A method for automatically and dynamically adjusting for position errors arising in the movement of a movable member of a machine in accordance with a specific program as the movable member is being driven by a servo drive system having a feedback system with a transducer comprising the steps of

• precisely verifying the passage of said movable member past a precisely known location along its fixed path of travel to determine its actual position,
• determining the indicated position of said movable member as indicated by said servo system at the time said movable member passes by said location on said fixed path,
• generating an error value in accordance with the difference between said indicated movable member position and the actual movable member position at the time said movable member passed by said precisely known location,
• and adjusting the indicated movable member position in accordance with the established error value.

In a machine tool controlled by a numerical control circuit comprising:

• a base,
• a movable member carried by said base for movement in a prescribed path of travel,
• a servo positioning system connected to drive the movable member along its path of travel in accordance with commands received from a recorded program,
• a transducer responsive to the movement of the movable member for producing a position signal which represents the indicated position of the movable member at any instant of time,
• the improvement comprising, a vane detector housing supported for movement with said movable member,
• a pair of magnets supported in said housing in spaced relationship,
• a Hall effect sensor mounted opposite each of said magnets in the path of the magnetic flux emanating from its cooperating magnet,
• a marker vane mounted on said base along the path of travel of said movable member in position to be straddled by each of said magnets and their cooperating Hall effect sensor as the movable member moves along its path of travel for interrupting the passage of the magnetic flux to the Hall effect sensor, said marker vane being of a length that is less than the spacing between said two Hall effect sensors so that both Hall effect sensors cannot be activated simultaneously by said marker vane,
• means connected to produce said verifier signal when said marker vane interrupts the passage of the magnetic flux from a magnet to its cooperating Hall effect sensor,
• an overtravel vane at each limit of movement of said movable member having a length that is greater than the spacing between said two Hall effect sensors so that the passage of magnetic flux to both Hall effect sensors can be interrupted simultaneously by said overtravel vane,
• and means connected to produce a stop signal for stopping the travel of the movable member at its limits of movement when both Hall effect sensors are activated simultaneously.

In a machine tool controlled by a numerical control circuit comprising,

• a base,
• a movable member carried by said base for movement in a prescribed path of travel,
• a servo positioning system connected to drive the movable member along its path of travel in accordance with commands received from a recorded program,
• a transducer responsive to the movement of the movable member for producing a position signal which represents the indicated position of the movable member at any instant of time,
• the improvement comprising,
• a pair of sensors mounted in spaced relationship for movement with said movable member,
• a marker vane mounted on said base along the path of travel of said movable member in position to actuate said sensors as they move past said marker vane, said marker vane having a length that is less than the spacing of said sensors so that the marker vane can only actuate said sensors sequentially,
• means responsive to the individual actuation of said sensors to produce a verifier signal and connected to transmit it to the numerical control circuit to establish a precise actual position of said movable member in relation to said base,
• an overtravel vane mounted on said base at each limit of movement of said movable member, each of said overtravel vanes having a length that is at least equal to the spacing of said sensors so that said overtravel vanes will actuate both of said sensors simultaneously, and
• means responsive to the simultaneous actuation of both of said sensors to produce a stop signal and connected to transmit it to the numerical control circuit for stopping the movement of said movable member when it arrives at either of its limits of travel.