Load proportional antibacklash gear drive system

A novel load proportional antibacklash gear drive system is provided wherein each portion of a split pinion gear is provided with a pressure chamber connected to a torque sensor and servo control unit for controlling the pressure applied individually to each split gear portion, against opposing tooth faces of the driven gear. The servo control unit provides high pressure (hydraulic or pneumatic) to a first split gear portion for drive in one direction while providing low pressure to the second split gear portion in the opposing rotational sense to maintain contact of the split gear with both faces of the driven gear at all times, thereby eliminating backlash. Upon reversal of the direction of rotation of the gear system, the servo unit provides high pressure to the second split gear portion which then acts as the driving gear, and maintains low pressure to the first split gear portion to maintain it in contact with the driven gear to prevent backlash upon reversal of the direction of drive of the gear system.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This invention relates to copending patent application Ser. No. 281,149 
(filed July 7, 1981) to the above named invention, now abandoned. 
BACKGROUND OF THE INVENTION 
This invention relates to gear assemblies and gear drive systems, and more 
particularly to gear drive assemblies configured to reduce or to eliminate 
backlash. 
Considerable amounts of backlash may exist in conventional gear drive 
assemblies resulting from clearances between meshing teeth of gears in the 
drive system. Backlash may be provided in the gears during manufacture to 
avoid binding or excessive wear in the gear system, or may result from 
manufacturing tolerances or design criteria for a particular drive system. 
Backlach may also exist by reason of assembly clearances between bearing 
surfaces of the gears, shafts, and other members within the gear drive 
assembly. 
In gear drive assemblies desired for use in reversible drive systems, the 
existence of backlash within the gear drive may not be tolerable, 
especially where accurate positioning of the drive system is required upon 
reversal of the direction of drive of the component gear members. Prior 
art gear drive assemblies configured to reduce backlash include the use of 
two counteroperating motor drive systems, having the disadvantages of 
significantly higher cost, and of inducing high internal loading and 
friction and commensurate excessive gear wear, especially with the use of 
high output motor drives. Another prior art configuration comprises 
mounting the drive motor pinion gear on a swingarm, preloading the 
swingarm and forcing the pinion into the driven gear, which reduces 
backlash, but at the same time increases friction and strain within the 
bearings, resulting in a relatively short useful life of the system. 
Another category of well known antibacklash gear drive configurations 
utilize split gears, such as disclosed by Bauer (U.S. Pat. No. 3,535,949), 
Eggins (U.S. Pat. No. 3,545,296), and Sutherland (U.S. Pat. No. 
3,512,430), having means to angularly separate the gear teeth of one 
portion from the teeth of the other portion of the split gear, one portion 
of the split gear engaging the driven gear on one face of the teeth, and 
the other portion engaging the other face of the teeth of the driven gear. 
Relative angular or axial displacement of the two portions may be effected 
by various means. For example, in one such split gear configuration, one 
gear portion is fixed to the drive shaft, while the other portion is 
preloaded by means of a spring to achieve the desired degree of angular 
displacement of one portion relative to the other. With either direct 
spring load between the gear portions or with the use of helicoidal 
splines on the shaft, an inherent disadvantage exists that the preload 
must be greater than the maximum torque to be transmitted. The result, as 
in other prior art configurations, is constant high gear tooth loads, high 
friction, excessive tooth wear, and shortened useful gear life. 
The invention described herein eliminates, or substantially reduces in 
critical importance, the foregoing problems in the prior art by providing 
a load proportional antibacklash gear drive system wherein a controlled 
variable force means locks the driving portion of a split gear to the 
drive shaft, while the other portion floats resiliently controlled by low 
pressure means into relative angular misalignment with the driving portion 
to engage both faces of the teeth of the driven gear. In reverse drive, 
the floating gear portion becomes the driving gear portion while the 
former driver portion floats in relative angular displacement to prevent 
backlash. Advantageous attributes of the present invention include the 
elimination of preload, increased efficiency of drive system operation, 
reduced friction and tooth wear, and extended tooth life. 
The present invention employs two portions of a split pinion mounted on a 
common drive shaft to deliver torque to an engaged gear. Each pinion 
portion includes a pressure chamber. Hydraulic or pneumatic pressure moves 
the pinion portions axially apart and into relative angular misalignment 
upon engagement of the portions with a collar having V-shaped face teeth. 
The two pinion portions deliver torque in opposing directions, and 
therefore, full contact on both tooth faces of the driven gear results. At 
any given time during operation of the gear drive system of this 
invention, one of the pinion portions acts as the driver, while the other 
portion supplies minimum opposing torque to eliminate backlash, which 
minimizes gear tooth loading. The difference in pressure applied 
separately to the two pinion portions is proportional to the delivered 
torque. 
The present invention therefore provides an antibacklash gear drive system 
utilizing a split pinion configuration wherein no mechanical preload on 
the two pinion portions is required to effect the angular displacement of 
the two portions sufficient to eliminate backlash, but wherein the applied 
pressure to effect the displacement is a proportionally controlled 
function of the applied torque. The applied pressure may be switched 
hydraulically or pneumatically from one pinion portion to the other upon 
reversal of the drive system. 
It is, therefore, an object of this invention to provide a gear drive 
system having no backlash in the gears. 
It is a further object of this invention to provide an antibacklash gear 
drive system using a split gear configuration not requiring mechanical 
preload on the two portions of the split gear. 
It is a still further object of this invention to provide an antibacklash 
gear drive system wherein hydraulic or pneumatic pressure is applied to 
the split gear portions to effect relative angular displacement of the two 
portions to eliminate backlash, and wherein the applied pressure is 
proportional to the torque delivered to the drive system, to minimize gear 
tooth loading and tooth wear. 
These and other objects of the invention will become apparent as the 
detailed description of certain preferred embodiments thereof proceeds. 
SUMMARY OF THE INVENTION 
In accordance with the foregoing principles and objects of the present 
invention, a novel load proportional antibacklash gear drive system is 
provided wherein each portion of a split pinion gear is provided with a 
pressure chamber connected to a torque sensor and servo control unit for 
controlling the pressure applied individually to each split gear portion, 
against opposing tooth faces of the driven gear. The servo control unit 
provides high pressure (hydraulic or pneumatic) to a first split gear 
portion for drive in one direction while providing low pressure to the 
second split gear portion in the opposing rotational sense to maintain 
contact of the split gear with both faces of the driven gear at all times, 
thereby eliminating backlash. Upon reversal of the direction of the gear 
system, the servo unit provides high pressure to the second split gear 
portion which then acts as the driving gear, and maintains low pressure to 
the first split gear portion to maintain it in contact with the driven 
gear to prevent backlash upon reversal of the direction of drive of the 
gear system.

DETAILED DESCRIPTION 
Referring now to the drawings, the invention may be conveniently understood 
by examination of the embodiment shown in FIG. 1. A composite of two split 
pinion gear portions 10-10' are piloted on drive shaft 11 and drive driven 
gear 12. Torque is delivered by drive shaft 11 from a motor system (not 
shown). Shaft 11 carries toothed rings or clutches 13-13' which are 
rigidly fixed to drive shaft 11 by suitable means such as diametric bores 
14-14' and pins 15-15'. Rings 13-13' have on their confronting faces 
radially cut V-shaped face teeth 16-16'. Split pinion gear portions 10-10' 
have on their sides facing toothed rings 13-13' matching radial V-shaped 
face teeth 17-17', such that torque delivered to drive shaft 11 is 
transmitted to split gear portions 10-10' through the meshing of face 
teeth 16 of ring 13 with matching face teeth 17 of gear portion 10, and 
the meshing of face teeth 16' of ring 13' with matching face teeth 17' of 
gear portion 10'. 
Rings 13-13' are secured to shaft 11 in a spaced relationship from full 
engagement with their mating gear portions 10-10' to yield a gap A larger 
than the backlash between gear portions 10-10' and driven gear 12 to be 
corrected. Centering springs 19-19' are disposed around shaft 11 within 
annular spaces 21-21' to center gear portions 10-10' between the 
confronting faces of rings 13-13' when the system is not pressurized as 
hereinbelow described. 
The function served by rings 13-13' may alternatively be served by 
providing helicoidal splines (not shown) on drive shaft 11 for mating with 
splines which may be provided on the inside bores of gear portions 10-10' 
adjacent shaft 11, although the use of V-shaped faced teeth as described 
is preferred. 
Drive shaft 11 has intermediate the gear portions 10-10' a diametric 
enlargement in the form of piston 18. Gear portions 10-10' have 
cylindrical cavities or chambers 20-20' for receiving piston 18 as shown. 
Means (not shown in FIG. 1) are provided, such as by passages in the drive 
shaft as hereinbelow discussed with relation to FIG. 2, to impart 
hydraulic or pneumatic pressure to the pressure chambers defined by piston 
18 and chambers 20-20'. As pressure is applied to the chambers, gear 
portions 10-10' are forced axially separate into engagement with rings 
13-13'. As gear portions 10-10' mesh with rings 13-13', the relative 
positions of the teeth on the faces of rings 13-13' cause gear portions 
10-10' to rotate in opposite directions until the peripheral meshing teeth 
of gear portion 10 engage one face of the peripheral gear teeth on driven 
gear 12 and the peripheral teeth of gear portion 10' engage the other face 
of the peripheral teeth of driven gear 12, at which point gear portions 
10-10' are restrained from further relative rotation and the backlash 
between driven gear 12 and the composite of gear portions 10-10' is 
eliminated. 
Referring now to FIG. 2 of the drawings, wherein like numerals refer to 
like parts of FIG. 1, a typical single mesh gear train is shown including 
the novel antibacklash gear drive configuration of this invention. As 
shown in FIG. 2, motor 22 may be provided to drive drive shaft 11 which 
may be journalled into housing 23 conventionally, such as through bearings 
24-24'. Unconventional split gear portions 10-10' and rings 13-13' are 
driven by shaft 11 in the manner described above in relation to FIG. 1, to 
impart drive to driven gear 12. Assuming a counterclockwise drive, torque 
is applied by motor 22 to drive shaft 11. Torque sensor and servo control 
unit 25 directs pressure (either hydraulic or pneumatic) proportional to 
the torque applied by motor 22 by way of line 26, rotary union 27 and 
passageway 28 in shaft 11 to pressure chamber 20' formed by the recess 
cavity in split pinion gear portion 10' and enlarged shaft portion or 
piston 18. Gear portion 10' in this configuration therefore acts as the 
driver for counterclockwise rotation of drive shaft 11. While pressure is 
applied to chamber 20' for drive by gear portion 10', corresponding 
pressure chamber 20 associated with the other gear portion 10 is vented to 
the return line 29 of servo control unit 25 via passageway 30 provided 
within shaft 11 and rotary union 27. Low pressure is maintained throughout 
operation in return line 29 to maintain gear portion 10 meshed with ring 
13 to maintain controlled pressure meshing of gear portion 10 with driven 
gear 12. When motor 22 is commanded into clockwise drive, servo control 
unit 25 senses the torque and reverses the pressure applied to chambers 
20-20', allowing high pressure into chamber 20 of gear portion 10, which 
then assumes the role as driver for clockwise drive on driven gear 12. 
During clockwise drive, chamber 20' of gear portion 13' sees low pressure 
from servo control unit 25 and thus contact is maintained between gear 
portion 13' with driven gear 12 in the counterclockwise sense to eliminate 
backlash. 
The present invention as hereinabove described therefore provides a novel 
load proportional antibacklash gear drive system wherein loading on the 
driven gear is proportional to the applied torque. 
It is understood that the invention described herein may be alternatively 
configured within the scope of the appended claims, as might occur to one 
with skill in the field of the present invention. Therefore, all 
embodiments contemplated hereunder have not been shown in complete detail. 
Other embodiments may be developed without departing from the spirit and 
scope of the appended claims.