We Claim :
1. An anti-backlash device for preventing backlash in a screw and nut mechanism having a helical screw thread and used in converting rotary motion into linear motion, said anti-backlash device comprising:
a cylindrical, pressure actuator integrally formed with a helical thread;
a cylindrical cradle integrally formed with a helical, internal thread for meshing with said helical screw thread, said cradle being mounted around said screw, exterior to and in close proximity to said pressure actuator,
wherein both said pressure actuator and cradle each have only one accurately machined face axially oriented inward toward said screw, and
wherein when said screw is operated to rotate within said cradle, said helical, pressure actuator thread is loaded on said helical screw thread so as to exert pressure thereon in a first axial direction, while simultaneously pressure is applied in an opposing, second axial direction by said cradle internal thread when loaded on said helical screw thread, thereby applying a predetermined, axial, balanced force on said screw so as to prevent backlash.
2. The anti-backlash device as claimed in claim 1, wherein said pressure actuator and said cradle have at least a single-turn helical thread formed in about a 360-degree arc.
3. The anti-backlash device as claimed in claim 1, wherein said anti-backlash device further comprises an active, preloading means housed in a compact case comprising said cradle.
4. The anti-backlash device as claimed in claim 3, wherein said preloading means, supported by a retainer, axially backs said pressure actuator in a predetermined force on said screw to prevent backlash.
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5. The anti-backlash device as claimed in claim 1, wherein said screw comprises an Acme lead screw.
6. The anti-backlash device as claimed in claim 1, wherein said screw comprises a roller screw configured with roller screw threads for providing races for continuously rolling a plurality of shaped rollers in about a 360-degree arc active helical circle and about a 360-degree arc returning circuit around said roller screw in conjunction with said internal cradle thread when said roller screw rotates.
7. The anti-backlash device as claimed in claim 6, wherein said cylindrical pressure actuator has an axial degree of freedom, in order to act as an active preloading means when axially loading said plurality of shaped rollers against said roller screw in order to prevent backlash.
8. The anti -backlash device as claimed in claim 6, wherein said plurality of shaped rollers in both a single-start and a multiple start roller screw are profile-compatible with the profile of said internal cradle threads and said roller screw threads conjoined to form said races in given mechanical applications for use with said anti-backlash device to prevent backlash.
9. The anti-backlash device as in claim 6, wherein said plurality of shaped rollers are arranged around said roller screw in parallel, helical pathways to each other.
10. The anti-backlash device as in claim 6, wherein said plurality of shaped rollers in said active circle are arranged around said roller screw at a 90 degree angle to each other.
11. The anti -backlash device as in claim 6, wherein said plurality of shaped rollers is selected from at least one of the group comprising: balls, cylinders, coins, and diamond-shaped elements disposed in a variety of orientations as required by given mechanical applications.
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12. The anti-backlash device as claimed in claim 6, wherein said preloading means and retainer are utilized to back said pressure actuator and control the axial freedom of said plurality of shaped rollers and the predetermined amount of load exerted on said plurality of shaped rollers among said pressure actuator, cradle and roller screw.
13. The anti-backlash device as in claim 6, wherein said roller screw is provided with a pitch and profile, wherein the outside diameter of said roller screw is provided with a larger outside diameter that is bigger than the inside diameter of said cradle and the pressure actuator, resulting in a low pressure angle of about 10-30 degrees of arc to the axis of said roller screw.
14. The anti-backlash device as in claim 13, wherein said larger outside diameter of said roller screw thread profile effects a reduction of Hertz effects among said shaped rollers, said roller screw and said cradle while reducing rolling friction, and increasing the system efficiency and longevity of said pressure actuator device.
15. The anti-backlash device as in claim 6, wherein said returning circuit for said plurality of shaped rollers further comprises: an extraction means, embedded slots disposed about the outer surface of said cradle, and an outer cover that covers said embedded slots.
16. The anti-backlash device as claimed in claim 6, wherein said screw is a ball roller screw provided with a combination of a first and a second anti-backlash device mounted on the same said screw, but oriented in opposing axial directions,
wherein said first anti-backlash device is disposed on a threaded end of said screw and is operable on a load,
wherein said second anti -backlash device is disposed on an unthreaded end of said ball roller screw and provided with a screw support bearing, and
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wherein when said second anti-backlash device is mechanically connected to a fixed work bed in alignment with the axis of said ball roller screw, said combination enables greater stability and control over the anti-backlash operation of said ball roller screw when rotated.
17. The anti-backlash device as claimed in claim 16, wherein said screw support bearing comprises an annular ring of a plurality of ball rollers partially embedded in said ball roller screw at said unthreaded end thereof and housed in an inner race of said second anti-backlash device, said plurality of ball rollers being confined between inner faces of the cradle and pressure actuator of said second anti-backlash device, said screw support bearing providing stable axial support to said ball roller screw.
18. A method for anti-backlash operation of a screw having helical threads and used in converting rotary motion into linear motion, said method comprising:
providing a cylindrical, pressure actuator formed integrally with a helical thread, said pressure actuator being axially disposed around said screw;
providing a cylindrical cradle integrally formed with a helical, internal thread, said cylindrical cradle being externally disposed axially around said pressure actuator and said screw to form a housing for both;
providing a preloading means for applying a predetermined pressure on said cylindrical, pressure actuator;
operating said screw to rotate within said cradle;
activating said preloading means;
applying a predetermined pressure from said preloading means upon said pressure actuator and consequently also on said helical thread;
loading said helical pressure actuator thread on said screw threads so as to exert pressure in a first axial direction, while said cradle internal thread is simultaneously loaded
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on said screw threads in a second, opposing axial direction, thereby applying a predetermined, balanced force on said screw so as to prevent backlash.
19. The method for anti-backlash operation of a screw as claimed in claim 18, wherein said screw is a roller screw having helical threads with grooves, said method comprising:
providing a plurality of shaped rollers arranged in a predetermined orientation in a series along said roller screw grooves to form a continuous pathway around said roller screw;
providing a cylindrical, pressure actuator integrally formed with a helical thread having a rolling surface; and
providing a cradle integrally formed with internal helical threads and having a rolling surface, said cradle serving as a housing for said roller screw and said pressure actuator;
providing a preloading means with a retainer for securing said preloading means on said cradle;
activating said preloading means to apply a predetermined pressure on one face of said cylindrical pressure actuator;
loading said pressure actuator helical thread on said plurality of shaped rollers in a first direction; and
loading said cradle helical thread in a second, opposing direction on said plurality of shaped rollers, wherein said loading in said first and second opposing directions on said roller screw and said plurality of shaped rollers applies a predetermined axial, balanced force on said roller screw so as to preclude any backlash effect.
20. The method for anti-backlash operation of a screw as claimed in claim 18, wherein said screw is an Acme lead screw having helical threads with grooves forming teeth, said method comprising:
providing a cradle for housing said Acme lead screw therein,
wherein said cradle is formed with an inner helical thread;
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providing a cylindrical pressure actuator assembly axially oriented toward and disposed between said cradle and said Acme lead screw, said pressure actuator assembly comprising:
a cylindrical pressure actuator provided with a helical thread; and
a pre-loading means for applying a predetermined pressure on said cylindrical pressure actuator, said preloading means having a retaining ring to secure said preloading means on said cradle;
loading said pressure actuator helical thread upon said cradle sleeve and said Acme lead screw teeth utilizing said preloading means so that said helical pressure actuator thread exerts pressure in a first axial direction; and
loading said helical, inner cradle thread upon said helical threads of said Acme lead screw in a second, axial direction opposed to said first, axial direction as a counterforce,
wherein said helical pressure actuator thread; said at least one cradle inner helical thread; and said Acme lead screw thread all combine to achieve a predetermined axial, balanced force on said Acme lead screw when rotated, so as to preclude any backlash effect.