Mechanical centering apparatus and method

A centering apparatus for a workpiece having a periphery, comprising:

• a workplace spindle operable to rotate the workpiece about a rotational axis;
• and
• a centering head, comprising
• a mount movable in a movement direction lying in a plane perpendicular to the rotational axis, the movement direction being generally a radial line extending outwardly from the rotational axis, and
• a swivel head, comprising
• a central body, pivotably connected to the mount and pivotable about a pivot axis parallel to the rotational axis,
• a pair of arms extending outwardly on opposite sides of the body and parallel to the plane,
• a pair of rotating bearings, one of the bearings being mounted on each of the arms and having a bearing axis parallel to the rotational axis;
• a pivot structure extending between the mount and the central body of the pivot head, the pivot structure being operable to pivot the swivel head about the pivot axis parallel to the rotational axis;
• and
• a distance measuring device operable to measure the distance between the periphery of the workpiece and a measurement location on the mount, and
• a centering drive operable to contact the bearings to the workpiece and thereafter to move the mount along the movement direction responsive to the distance measuring device, until the workpiece is centered.

A method for centering a workpiece, comprising the steps of

• furnishing a workpiece having a periphery;
• providing a centering apparatus comprising
• a workpiece spindle operable to rotate the workpiece about a rotational axis;
• and
• a centering head comprising
• a mount movable in a movement direction lying in a plane perpendicular to the rotational axis, the movement direction being generally a radial line extending outwardly from the rotational axis, and
• a swivel head pivotably supported on the mount and pivotable about a pivot axis parallel to the rotational axis, the swivel head comprising a pair of bearings spaced apart along a direction lying generally perpendicular to the movement direction, each of the bearings having a bearing axis parallel to the rottional axis,
• a distance measuring device operable to measure the distance between the periphery of the workpiece and a measurement location on the mount;
• mounting the workpiece on the spindle;
• positioning the centering head at a location adjacent to the periphery of the workpiece;
• rotating the spindle to rotate the workpiece;
• positioning the centering head at a location adjacent to the periphery of the workpiece;
• rotating the spindle to rotate the workpiece;
• measuring a runout curve using the distance measuring device of the centering head, the runout curve having a constant term and a variable term;
• moving the centering head along the movement direction until the bearings contact the workpiece;
• and
• centering the workpiece by pushing against the periphery of the workpiece with the bearings in a direction and by an amount so as to reduce the constant term of the runout curve toward zero.