GB2435915A

GB2435915A - Backlash-free gearbox

Info

Publication number: GB2435915A
Application number: GB0604959A
Authority: GB
Inventors: Timothy John Sweatman
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-03-11
Filing date: 2006-03-11
Publication date: 2007-09-12
Also published as: GB0604959D0

Abstract

A backlash free gearbox transmits power through one of two alternative gear paths (1, 2A, 3A and 4 or 1, 2B, 3B and 4) depending upon the direction of the torque being transmitted, ie whether the gears are being driven or reversed. The adjustment to reduce or eliminate the backlash being by means of a movable layshaft 7 (see fig 3). Therefore there is no backlash in the gearbox when the gears are driven clockwise or anticlockwise.

Description

Backlash-Free Gearbox This invention relates to a gearbox which

eliminates backlash and permits full torque reversal.

It is well know that in any system of gears, backlash exists between any pair of gearwheels. In Figure 1 gearwheel 1 is rotating in an anticlockwjse direction and driving gearwheel 2 in a clockwise direction. If the direction of rotation of gearwheel 1 is reversed, it will rotate through a small angle 3 (clockwise) before engaging with gearwheel 2. This angle of free rotation is called the "backlash".

Backlash can be a serious problem in some types of mechanical system where a positive drive and accurate angular relationship is required between the shafts of the gearwheels. Important examples of this occur in servo gearboxes and the cam shaft drive systems of a internal combustion engines.

Numerous systems have been devised for reducing backlash, but none eliminate it completely without imposing the penalty of imposing high friction forces on the system. Examples of such systems include split toothed wheels and systems wherein the meshing between the wheels is reduced to minimise backlash. These systems have applications in which the improvements obtained are acceptable, but for high torque or high angular accuracy situations they are often unsatisfactory.

According to the present invention an arrangement of gears is such that power is transmitted from the input shaft to the output shaft through different gear trains, depending on the angular sense of the torque between the input and output shafts. The advantage of this system is that backlash may be eliminated by adjusting the position of a lay shaft such that on reversal of torque, power is immediately transferred through an alternate gear train. As the inoperative gear train is then transmitting no power, the friction forces associated with it are extremely small. If required the amount of backlash may be adjusted even while the gearbox is running, thus permitting dynamic control over the amount of backlash.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates backlash between a pair of gear wheels Figure 2 shows the arrangement of gears in the invention Figure 3 shows the lay shaft adjustment arrangements (1) Figure 4 shows The meshing gear train and the effect of adjustment of the lay shaft With reference to Figure 2 the arrangement of gears in the present invention can be seen in plan view. An input shaft 4 is attached to the first gear in the train, "Gear 1". If Gear 1 is rotating clockwise power is transmitted through Gears 2A and 3A and the lay shaft 6 to Gear 4 and the output shaft 5. The speed of the output shaft 5 relative to the input shaft 4 is determined by the ratios of the gears in the train. The only constraint in principle is that the arrangement must permit the input and output shafts to be co-linear.

The reverse torque situation is best understood by reference to Figures 3 and 4. The lay shaft 7 is mounted in such a way that its position may be varied in an arc centred on the common axes of the input and output shafts 4 and 5. This may for example be achieved by mounting the pivots for lay shaft 7 on a moveable plate (not illustrated) which pivots about the shaft 4. The said plate may be clamped in the desired position with a multiplicity of clamping screws. To progressively adjust backlash removal the lay shaft 7 it is rotated in an anticlockwise direction about the axis of the input shaft 4 until there is no backlash between Gear 1 and Gear 2B and also between Gear 4 and Gear 3B.

With this setting, when the torque on the input shaft 4 is reversed, the power will immediately be transmitted through Gears 2B and 3B and lay shaft 7 to Gear 4 and the output shaft 5. With this arrangement of alternative power train paths, the gearbox will be seen to operate in both directions of rotation without backlash.

If the lay shaft 7 is rotated in a clockwise direction torque will be transferred from lay shaft 6 to lay shaft 7 for a given direction of rotation of the input and output shafts 4 and 5. This exchange of roles of the lay shafts may be desirable if it is required to equate wear between the two gear trains or to replace one of the lay shafts to change the gear ratios while the gearbox is in use. (It should be noted that for situations where there is a constant torque in one direction, the backlash can be adjusted so that one of the lay shafts can be totally unloaded.) (2)

Claims

CLAIMS: 1. A zero-backlash gearbox wherein the transmission of power

occurs through one of two alternative gear train paths depending upon the direction of torque being transmitted the adjustment to eliminate backlash being by means of a moveable lay shaft in one of the said gear trains.

2. A zero-backlash gearbox as described in Claim 1 wherein co-axial input and output shafts are driven by gears mounted on two alternative lay shafts wherein the axis of one lay shaft may be adjusted in an arc centred on the axes of the coaxial input and output shafts such that power is transmitted through one lay shaft in one direction and through the other lay shaft when the torque is reversed.

3. A zero-backlash gearbox as described in Claims 1 and 2 wherein backlash is removed progressively and (if required) dynamically by adjusting the position of the moveable lay shaft to a multiplicity of intermediate positions such that the amount of backlash in the system may be varied.

4. A zero-backlash gearbox as described in Claims 1, 2 and 3 wherein for a given direction of torque the position of the moveable lay shaft may be adjusted such that the roles of the two lay shafts are exchanged and torque transmission is transferred from one gear train to the other.

5. A zero-backlash gearbox substantially as described herein with reference to Figures 1 to 4 attached hereto.