An anti-backlash gear assembly includes a drive gear that is fixably mountable on a drive shaft that drives the drive gear and has a plurality of drive gear clearance holes. A rod ring is fixed to one side of the drive gear. A flank gear having a plurality of flank gear clearance holes corresponding to the drive gear clearance holes is also mounted on the drive shaft adjacent to the drive gear. A force ring having a plurality of receiving holes is mounted to the flank gear. Springs having a first end fixed to the rod ring and extend through the drive gear clearance holes, the flank gear clearance holes, and into the receiving holes. The springs exert a force biasing the flank gear and the drive gear to rotate in opposite directions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates, generally, to an anti-backlash gear and more 
specifically, to anti-backlash gears for industrial machinery such as 
printing presses. 
2. Description of the Related Art 
Anti-backlash gearing is commonly used in gear trains of instruments and in 
mechanical computing devices. Gears of this type are well known and are 
sold in numerous instrument related catalogues. However, these classes of 
anti-backlash gears are not useful in power transmissions of high speed 
machinery. 
High performance, high horsepower, servo motors used in printing presses 
create a requirement for gearing that can apply both accelerating and 
decelerating torque without introducing a following positional error such 
as would be introduced by normal gear backlash. The gear teeth that mesh 
between a first gear and a corresponding second gear, such as between a 
driving gear and a driven gear of a gear train, have a tendency to 
separate circumferentially when the gears rotate at very high speeds and 
have backlash problems when torque values are changed on the drive gear. 
U.S. Pat. No. 5,813,335 to Burke et al. (Burke) exemplifies the prior art 
developments to eliminate the backlash problem. Burke teaches a drive gear 
and a supplemental gear. The supplemental gear has a recess formed therein 
for housing a leaf spring assembly. The leaf spring assembly biases the 
teeth of the supplemental gear to rotate opposite the teeth of the drive 
gear in order to prevent backlash with the teeth of a driven gear. 
However, the supplemental gear has to be of a minimum size (diameter) in 
order to house the leaf spring and the leaf springs for developing the 
anti-backlash forces are short in length and therefore have a high spring 
rate which is undesirable. In addition, the complexity of the accuracy 
requirements of the configuration leads to high production costs. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide an anti-backlash 
gear which overcomes the herein-mentioned disadvantages of the 
heretofore-known devices of this general type, in which a less complex 
construction is provided, the diameter of the gear can be reduced, and the 
spring rate of the springs can also be reduced. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, an anti-backlash gear assembly, including: 
a drive gear having a plurality of drive gear clearance holes formed 
therein and fixably mountable on a drive shaft for driving the drive gear; 
a rod ring fixed to the drive gear; a flank gear having a plurality of 
flank gear clearance holes formed therein and corresponding to the drive 
gear clearance holes; a force ring having a plurality of receiving holes 
formed therein and mounted to the flank gear; and cantilever rod springs 
having a first end fixed to the rod ring and extending through the 
plurality of drive gear clearance holes, the plurality of flank gear 
clearance holes and into the plurality of receiving holes, the springs 
exerting a force biasing the flank gear and the drive gear to rotate in 
opposite directions. 
In accordance with an additional feature of the invention, the plurality of 
drive gear clearance holes, the plurality of flank gear clearance holes, 
and the plurality of receiving holes are all rotationally offset with 
respect to each other. 
In accordance with another feature of the invention, the springs extend 
through the plurality of drive gear clearance holes without contacting the 
drive gear and through the plurality of flank gear clearance holes without 
contacting the flank gear. 
In accordance with a further added feature of the invention, the flank gear 
has a hub mounting the force ring. 
In accordance with a further additional feature of the invention, the 
springs are spring rods, and the spring rods are deflected in a 
cantilevered fashion as the rod springs extend from the rod ring to the 
force ring for exerting the force biasing the flank gear and the drive 
gear to rotate in opposite directions. 
In accordance with another added feature of the invention, the force ring 
has a circumference with a notch formed therein shaped to receive a wrench 
for rotating the force ring. 
In accordance with another additional feature of the invention, the flank 
gear is mounted on the drive shaft coaxially and adjacent the drive gear, 
the flank gear rotating freely about the drive shaft. 
In accordance with an added feature of the invention, the drive gear has a 
bore formed therein, and including a bushing disposed in the bore of the 
drive gear. 
In accordance with an additional feature of the invention, the bushing has 
a conically, step-shaped interior hole formed therein and the flank gear 
has a threaded pin bore formed therein, and including a threaded pin 
having a guide end matching the conically, step shaped interior hole of 
the bushing and a threaded end disposed in the threaded pin bore, the 
threaded pin acting in conjunction with the bushing for the dual purposes 
of, in a first position, aligning the flank gear with the drive gear, and, 
in a second position, limiting a movement of the flank gear relative to 
the drive gear. 
In accordance with a concomitant feature of the invention, the force ring 
has a force ring bore formed therein alignable with the threaded pin bore 
of the flank gear for allowing access to the pin disposed in the threaded 
pin bore. 
Other characteristic features of the invention are set forth in the 
appended claims. 
Although the invention is illustrated and described herein as embodied in 
an anti-backlash gear, it is nevertheless not intended to be limited to 
the details shown, since various modifications and structural changes may 
be made therein without departing from the spirit of the invention and 
within the scope and range of equivalents of the claims. 
The construction of the invention, however, together with additional 
objects and advantages thereof will be best understood from the following 
description of specific embodiments when read in connection with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In all the figures of the drawing, sub-features and integral parts that 
correspond to one another bear the same reference symbol in each case. 
Referring now to the figures of the drawings in detail and first, 
particularly, to FIG. 1 thereof, there is shown an exploded, perspective 
view of an anti-backlash gear assembly. The anti-backlash gear assembly 
includes a drive gear 1 having teeth 1' and a flank gear 2 having teeth 2' 
that develops an anti-backlash torque component. The drive gear 1 and the 
flank gear 2 are to be coaxially mounted on a common shaft adjacent one 
another, and commonly meshing with a non-illustrated driven third gear 
having sufficient face width to engage the teeth 1', 2' of both of the 
coaxially mounted gears 1, 2. The teeth 1' of the drive gear 1 bear 
against one side of the teeth of the third gear while the teeth 2' of the 
flank gear 2 bear against the opposite side of the teeth of the third 
gear. The drive gear 1 is rigidly fixed to the common shaft and the flank 
gear 2 is free to rotate. 
A rod ring 4 is mounted to one side of the drive gear 1 via shoulder bolts 
9 which accurately lock the rod ring 4 in place on the drive gear 1. A 
plurality of spring rods 8 are rigidly mounted in the rod ring 4 and 
extend in a cantilevered fashion from the rod ring 4 into clearance holes 
13, 17 formed in both the drive gear 1 and the flank gear 2, respectively. 
The spring rods 8 pass through the clearance holes 13, 17 of the drive 
gear 1 and the flank gear 2 without touching either gear 1, 2 and function 
as a cantilever beam or spring for providing the anti-backlash torque. The 
clearance holes 13, 17 in each gear 1, 2 are rotationally offset to allow 
for the bending of the spring rods 8. A force ring 3 is rotationally 
located around a hub 12 of the flank gear 2 and further rotationally 
positioned by a locating pin 10 insertable through the force ring 3 and 
into a bore formed in the flank gear 2. The force ring 3 is further held 
in place on the flank gear 2 by two screws 11. The force ring 3 also has a 
plurality of rotationally offset receiving holes 14 corresponding to the 
clearance holes 17 of the flank gear 2 and receives the spring rods 8 
protruding from the flank gear 2. The force ring 3 is mounted on the flank 
gear 2 such that the receiving hole locations require that the spring rods 
8 bend in the manner of a cantilever in order to pass through the 
receiving holes 14. The plane of deflection of the cantilevered spring rod 
8 is perpendicular to the radial of the anti-backlash gear assembly. The 
deflection results in a torque between the two adjacent gears 1, 2. By 
placing a plurality of the spring rods 8 in a circular array, a large 
anti-backlash torque value is generated. 
The spring rods 8 between the two coaxially mounted gears 1, 2 provide a 
torsional force between the gears 1, 2. In a static condition each gear 1, 
2 applies the same tooth contact force to the teeth of the non-illustrated 
third gear, but in opposite directions so that there is no net driving 
force of the third gear. When a driving force is applied to the drive gear 
1, this balance is removed and a net driving force causes motion and an 
increase in tooth contact of the rigidly fixed drive gear 1. If an 
opposite torque is applied, the tooth contact force of the drive gear 1 
decreases but remains greater than zero to maintain tooth contact up to 
the limit of the spring force of the spring rods 8. 
For performing the functions of aligning the flank gear 2 during the 
installation or removal procedure of the anti-backlash gear assembly, and 
to limit the maximum displacement of the gear teeth 1', 2' relative to 
each other there is provided a hardened bushing 7 and a pin 6. The 
hardened bushing 7 is pressed into a counter bore 18 formed in the side of 
the drive gear 1. The hardened bushing 7 has a lead-in conical surface 15 
matching one end of the pin 6 to provide for the transition between the 
functions of flank gear alignment and limiting the travel of the teeth 1', 
2' relative to each other. The pin 6 is installed in a threaded hole 19 
formed in the flank gear 2. The travel path of the pin 6 away from the 
hardened bushing 7 is limited by the force ring 3. The force ring 3 has a 
hole 20 formed therein which is large enough to allow access to a hex head 
of the pin 6 but is narrower than the pin 6. In this manner, the position 
of the pin 6 can be adjusted by an adjusting wrench via the hole 20 in the 
force ring 3. This assures that the pin 6 can be properly adjusted in its 
location to provide proper travel so that its dual functions can be 
performed. 
The force ring 3 is formed with a notch 16. The notch 16 is configured to 
be engaged by a wrench for rotating the force ring 3. 
FIG. 2 shows a perspective view of the anti-backlash gear assembly in an 
assembled state. 
FIG. 3 shows a front elevational view of the assembled anti-backlash gear 
assembly as viewed from the force ring 3. 
FIG. 4 is a side elevational view of the assembled anti-backlash gear 
assembly. 
FIG. 5 is a rear elevation view of the assembled anti-backlash gear 
assembly as viewed from the ring rod 4 mounted on a drive shaft 21. 
A further application of the invention would be for use in soft, quiet, 
compliant type drive applications. In such an environment, the spring rods 
8 would transmit torque between a driven gear and a driving gear. The low 
spring rate coupled with a large driven mass would provide a low resonant 
frequency that is desirable for attenuating drive disturbances.