Elastic biasing element and encoder arrangement for precise control of force or torque

A bore finishing tool comprising:

• a feed system for a feeding and applying a feed force to an abrasive element of the bore finishing tool in a lateral direction relative to an axis of rotation thereof, the feed system comprising:
• a drive element supported for movement in a first direction and an opposite second direction and a drive apparatus connected to the drive element and controllably operable to move the drive element in the first direction and the opposite second direction within a predetermined range for generating the feed force;
• at least one elastic biasing element having a first end and a second end, the first end disposed in predetermined relation to the drive element so as to be displaced by the movement thereof to cause the at least one biasing element to elastically store a quantity of energy proportional to the displacement and representative of the feed force, and the second end being disposed in predetermined relation to an output element disposed to move generally axially in cooperation with a feed element of the bore finishing tool when the output element is positioned to bear thereagainst, to transfer and apply the feed force laterally to the abrasive element and to displace jointly with the output element responsive to changes in the applied force;
• and
• a first sensor positioned and operable to measure a value representative of the displacement of the second end of the biasing element and output a signal representative thereof, a second sensor positioned and operable to measure a value representative of the displacement of the first end of the biasing element and output a signal representative thereof, and a processor connected to the first sensor and to the second sensor to receive the signals outputted thereby and configured to determine a responsive value for moving the drive element of the drive apparatus to apply a selected feed force.

A method of controlling a feed force applied to an abrasive element of a bore finishing tool laterally relative to an axis of rotation of the tool, comprising steps of:

• providing a drive apparatus controllably operable to move a drive element in a first direction and an opposite second direction within a predetermined range;
• providing an elastic biasing element having a first end and a second end, the first end disposed in predetermined relation to the drive element so as to be displaced by the movement thereof to cause the biasing element to elastically store a quantity of energy proportional to the displacement and representative of the feed force, and the second end being disposed in predetermined relation to an output element disposed to move generally axially in cooperation with an element of the bore finishing tool to transfer and apply the feed force laterally to the abrasive element and to transfer changes in the applied force from the abrasive element to the second end of the biasing element so as to cause displacement thereof representative of the changes;
• and
• during rotation of the tool in a bore with the abrasive element in contact with a surface bounding the bore, measuring positions of the output element or the second end of the biasing element and responsively determining displacements of the second end of the biasing element, and controlling the drive apparatus to move the drive element as required to variably displace the first end of the biasing element responsive to changes in the applied feed force as represented by the displacements of the second end thereof, to apply a predetermined feed force to the abrasive element.