Patent Application
20070151379
The present application is related to a backlash reducing mechanism for a gearbox or the like, and in particular to a backlash reducer that incorporates opposed pairs of interlocking, tapered rings at opposite ends of the gearbox hollow output shaft.
Mechanical loss motion (resulting from backlash) is of concern in servo drive line components; positioning errors, changes to systems dynamics, and mechanical component failures are all attributed to system backlash. To minimize loss motion designers look for ways to reduce or completely eliminate the backlash in each component in the system. This can affect the economy of the design, or introduce added complexity that may make implementation impossible.
Loss motion often occurs where a shaft (not shown) goes thru such a hollow bore gearbox 10. Typically, the shaft is held tightly in place within the hollow bore or hub 22 by a key (not shown). In such a system, a simple fit of the shaft, key and hub 22 is often the major factor determining the amount of loss motion in the system. In addition to loss motion, it is important to consider the failure modes of the connection. Because keyed connections are mechanically dimensioned for slip fit assembly they will fail from wear when undergoing reciprocating motions. The constant sliding of these surfaces can also result in fretting corrosion that leads to cracking of metal surfaces and ultimately a broken shaft/hub/key system. Key connections can also fatigue fail and break due to cyclic torque reversals on the key.
Technologies exist to eliminate the keys and their failings. The currently accepted design used by many gearbox manufactures implements a means to squeeze the hollow gearbox hub down over the shaft. Although this concept works well, it comes with complexity and high cost.
Internal locking devices such as the Ringfeder GSA-1000 locking ring elements (Ringfeder Corporation, 165 Carver Ave., Westwood, N.J. 07675) (
Rather than use locking rings, the industry standard for gearboxes is to use a shrink disk. A shrink disk 30 (
There is a need for an improved backlash reducer for gearboxes and the like that overcomes the above problems using locking elements within the hollow bore of a gearbox.
A backlash reducing apparatus for a gearbox, the gearbox having a hollow bore and a shaft therethrough, the hollow bore having a counter-bore at each end thereof, the apparatus comprising:
(a) a first pair of tapered, interlocking rings engaging the shaft within the hollow bore at one end of the hollow bore;
(b) a second pair of tapered, interlocking rings engaging the shaft within the hollow bore at the opposite end of the hollow bore; and
(c) a fastener engaging the shaft and applying axial pressure to the first and second pairs of tapered, interlocking rings to thereby force the first and second pairs of tapered, interlocking rings against the shaft and the hollow bore.
A method for reducing backlash in a gearbox, the gearbox having a hollow bore and a shaft therethrough, comprising the steps of:
(a) engaging a first pair of tapered, interlocking rings against the shaft within the hollow bore at one end of the hollow bore;
(b) engaging a second pair of tapered, interlocking rings against the shaft within the hollow bore at the other end of the hollow bore; and
(c) applying axial pressure to the first and second pairs of tapered, interlocking rings to thereby force the first and second pairs of tapered, interlocking rings against the shaft and the hollow bore.
The present invention includes placing locking elements into the hollow bore of a gearbox. The ratio of hub outside diameter to shaft diameter is such that the hub wall thickness may be very thin. This is a very clean, simple, and low cost design that has been needed for continuous motion packaging machinery and other industries.
A simple counter bore is made at each end of the hollow bore where the locking elements will be installed. Two simple rings are machined so that the bolt's axial clamping force is applied to the locking rings.
A principal object and advantage of the present invention is that with locking elements installed on both ends of the hollow bore the design inherently centers the thru shaft so that runout (wobble) is virtually eliminated from the design.
Another principal object and advantage of the present invention is that the concentric tapered locking rings located on both ends of the hollow bore within the hollow bore make the runout of the shaft independent of the assembly operations. This is true since the tapered locking rings always center themselves exactly under any bolt loading condition.
Another principal object and advantage of the present invention is a specially designed key. A key is still used so it is impossible for the shaft to slip in extreme overload jam conditions. The keyseat is end milled into the shaft (in contrast to a sled runner type) so that it is not free to move around causing difficult assembly and disassembly.
Another principal object and advantage of the present invention is that it is also more compact than a shrink disk design. The space savings is often very important when designing machines where factory floor space demands a small machine.
Another principal object and advantage of the present invention is that both ends of the gearbox are sealed, keeping out the environment.
Another principal object and advantage of the present invention is that the low profile and uncomplicated design is suitable for dirty environments since it is easily cleaned—not a lot of crevices to collect debris.
Another object and advantage of the present invention is that the key is completely sealed inside the gearbox. This is of added value to ensure the key and shaft do not rust, causing the shaft to stick inside the gearbox.
Another principal object and advantage of the present invention is manufacturing cost savings. This cost savings approaches a factor of 10 over the shrink disk design. The shrink disk cost approaches that of the gearbox. The internal locking design also allows for a shaft tolerance that is less costly to machine than the same shaft if used with the shrink disk design.
The present invention is generally shown in the Figures as reference numeral 110.
The present invention 110 is a gearbox 110 having a housing 112, an input shaft 120, and an output shaft 114 journalled within a hollow bore 122.
A backlash reducing apparatus 130 comprises a first pair 132 of interlocking rings engaging the shaft 114 within the hollow bore 122 at one end of the hollow bore 122; a second pair 134 of interlocking rings engaging the shaft 114 at the opposite end of the hollow bore 122; and a fastener 136 engaging the shaft 114 and applying axial pressure to the first 132 and second 134 pairs of interlocking rings to thereby force the first 132 and second 134 pairs of interlocking rings against the shaft 114 and hollow bore 122.
As shown in
Preferably, each of the pairs 132 and 134 of interlocking rings are mounted within a counter-bore or recess 140 within the hollow bore 122 at each end of the hollow bore 122. The counter-bore or recess 140 has a lip or flange 142 against which the pairs of interlocking rings are forced by axial pressure, as is explained below.
A fastener 136 such as a bolt or screw 150 is inserted into a threaded aperture 152 which has been tapped into the shaft 114. Suitably, a washer 154 surrounds the head 151 of the bolt 150.
Preferably, a compression disk 160, sized to substantially match the diameter of the hollow bore 122, is used to force the pairs 132 and 134 against the lip or flange 142. An adapter ring 162 of diameter substantially the same as that of the pairs 132 and 134 is used between the compression disk 160 and the pairs 132 and 134.
Preferably, a key 170 is inserted into a key seat 172 which has been suitably milled into the shaft 114. The key retains the shaft 114 within the hollow bore 122 against slippage during extreme overload jam conditions.
To assemble the apparatus 110, one of the adapter rings 162 is slid onto the shaft 114 so that it butts against a stop 121 on the shaft. Then, the slit nested interlocking rings 134 are slid onto the shaft, making sure that the inner ring goes on first, then the outer ring is slid onto the shaft 114. Next, the optional key 170 is inserted into the key seat 172. The shaft 114 is then slid into the hollow bore 122.
Next, the other pair of interlocking rings 132 is inserted into the counter-bore or recess 140 at the opposite end of the gearbox's hollow bore output 122. When performing this step, the inner ring must go in first, then the outer ring is inserted. The other adapter ring 162, compression disk 160, washer 154, and fastener 150 are then mounted and the fastener is torqued to produce an axial force to the interlocking rings 132 and 134 as they bear against the flanges 142 within the counter-bores 140. This axial force results in inward and outward radial forces on the shaft 114 and hollow bore 122, creating a backlash free connection between the shaft 114 and bore 122.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar to or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety to the extent allowed by applicable law and regulations. In case of conflict, the present specification, including definitions, will control.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.
