Ball screw drive with dynamically adjustable preload

A method of controlling linear motion and position of a moving working element carried on a movably mounted carrier operable for carrying the working element along a line of action, comprising the steps of:

• (a) providing a threaded screw fixedly non-rotatably mounted parallel to and at least coextensive with the line of action to be traversed by the carrier;
• (b) providing first and second threaded nuts laterally restrained in and mounted for free rotation thereof in the carrier and threadably and concentrically engaging the screw in laterally spaced apart relationship axially therealong and with a given maximum backlash thread clearance between said nuts and screw;
• (c) providing first and second electric drive motors for supplying rotational torque power to the first and second nuts respectively;
• (d) individually operably mechanically coupling the first and second motors respectively to the first and second nuts in operable rotational driving relationship therewith for individually imparting rotational torque to the nuts;
• and
• (e) individually regulating the power input to the first and second motors for causing the nuts to conjointly produce linear motion and positioning of the carrier along the screw and for controllably varying the backlash thread clearance from said maximum clearance to zero clearance to effect one or more of the following operational modes:
• (1) developing anti-backlash pre-load forces between the first and second nuts relative to the screw;
• (2) producing an electromotive and/or frictional braking force for holding the carrier in a selected stationarily fixed position along the line of action;
• (3) causing the first and second motor rotors to simultaneously exert rotational torque on the respectively associated first and second nuts in the same or opposite rotary directions;
• (4) dynamically adjusting pre-load forces exerted between the first and second nuts via the screw by monitoring the load and/or position of each of the first and second motors and adjusting the power input thereto individually to thereby adjust the pre-loading forces dynamically while producing conjoint motion of the motors and carrier along the screw, and
• (5) controlling the angular phase relationship between the motors and hence between the nuts to thereby variably control the amount of backlash between the nuts within the range of system screw-to-nut backlash clearance.

A method of constructing a drive mechanism system operable for controlling linear motion and position of a drive unit and an associated linear member relative to one another along a line of action, comprising the steps of:

• (a) providing an elongated rigid linear member having a row of teeth and being non-rotatably mounted parallel to and extending linearly along the line of action;
• (b) providing a drive unit having first and second threaded nuts laterally restrained in and mounted for free rotation thereof in the drive unit and individually threadably engaging the teeth of the linear member in laterally spaced apart relationship with a given maximum backlash clearance between the nuts and teeth;
• (c) providing first and second electric drive motors in the drive unit for supplying rotational torque power to the first and second nuts respectively;
• (d) individually operably mechanically coupling the first and second motors respectively to the first and second nuts in operable rotational driving relationship therewith for individually imparting rotational torque to the associated nuts;
• and
• (e) providing a power control system operable for individually regulating the power input to the first and second motors for causing the nuts to conjointly produce relative linear motion and relative positioning of the drive unit relative to the linear member and for controllably varying the backlash clearance from maximum to zero to effect one or more of the following operational modes:
• (1) developing anti-backlash pre-load forces between the first and second nuts relative to the linear member;
• (2) producing an electromotive and/or frictional braking force for holding drive unit and the linear member in a selected stationarily fixed position relative to one another along the line of action;
• (3) causing the first and second motor rotors to simultaneously exert rotational torque on the respectively associated first and second nuts in the same or opposite rotary directions;
• (4) dynamically adjusting pre-load force exerted between the first and second nuts via the linear member by monitoring the load and/or position of the drive unit relative to the screw and adjusting the power input thereto individually to thereby adjust the pre-loading forces dynamically while producing conjoint motion of drive unit relative to the linear member, and
• (5) controlling the angular phase relationship between the motors and hence between the nuts to thereby variably control the amount of backlash between the nuts within the range of system linear member teeth-to-nut backlash clearance.