Title of Invention

A DEVICE FOR REDUCING BACKLASH IN GEAR DRIVES

Abstract

A device for reducing backlash in gear drives comprising a casing accommodating first and second gears, the first gear being mounted on a f irst shaft supported in a first set of end bearings, located m directly in the bores on the casing, a set of end caps axially securing the first shaft, the second gear being mounted on a second shaft supported in a second set of end bearings located in a set of end housings, each end housing having an eccentric bore for seating the second shaft, the end housings having a first set of spaced circumferential holes on the exterior corresponding to a mating second * set of spaced circumferential holes on the casing, whereby the end housings are boltable to the casing through said first and second set of holes, in predetermined positions of eccentricity, enabling the second gear to be brought sufficiently close to the first gear, to reduce backlash.

Full Text

This invention relates to a device for reducing backlash in gear drives. "Backlash' in a gear-pair may be described as the shortest (perpendicular) distance between surfaces of the trailing flanks when the driving flanks are in contact. The backlash value can be measured by the rotation angle undergone by the gear when it is rocked within the limits of its play while the other gear remains fixed. The backlash can be measured by a dial indicator with its plunger set normal to the flank surface of the gear being rocked. In a power-transmitting gear drive, loaded uni-directionally, sufficient backlash is provided to cover the effect of manufacturing errors that may act to reduce it. However, when the direction of tooth-loading reverses cyclically as in camshaft drives or in case of precision instruments or drives required to relate or control angular positions, the "gears have to run without backlash". In long gear trains, the effect of backlash is cumulative. The condition of zero-backlash is almost impossible to achieve. It is possible to control the backlash by maintaining all the errors present on the gears to a minimum. It may be necessary, in certain case, to manufacture high-precision gears and match the gears selectively. The manufacture as well as selective assembly of precision type gears is obviously quite expensive. It is well known that the tolerances on gear dimension and center distances influence the backlash in the gear drives. It is possible to use gears such as bevel gears and conical gears whose axial adjustments permit backash to be taken up. In practice, however, drives with other types of gears are used. A number of methods to control backlash in mating gears are reported in the literature. The methods can be grouped into two major categories. 1. Circumferential adjustments 2. Center distance adjustments The following are examples of the methods that result in circumferential adjustments: a) Sandwich gear: A nylon lamination is sandwiched between two phosphor-bronze outer plates. The three layers are machined to the same dimensions but the nylon lamination swells slightly and is larger than the metal sections. This permits tighter meshing with standard pinions because of nylon's high elasticity combined with good abrasive resistance. b) Split gear: The gear is split and the two parts are angularly-adjusted or flexible means like spring-loading etc is used to bring about simultaneous contact on both flanks. The spring loading requires a high driving torque as compared with unloaded gear and adds to tooth wear. c) Double gear trains: In this arrangement, input gear drives two gear trains ending with an output gear. The gear trains are pre-loaded using flexible means so that simultaneous contact with the flanks of the output gear is achieved. Method© that are based on center distance adjustment basically alter the center distance »o that the teeth enter more or less into engagement with each other, such as, the Split Housing. The housing of the gear drive is split and one part of the housing that carries one of the shafts with a gear mounted on it, is provided with a sliding arrangement and an adjustment screi^i. By rotating the screw, the center distance between the mating gears can be varied. It is necessary that the backlash is held, within narrow limits by positive means, since the use of friction or flexible means are objectionable because of the introduction of vibration and chatter or loosening. Use of flexible means also limit the torque transmitting capacity of the gear drive. The known arrangements are complicated in most cashes requiring substantial space and do not satisf actori ly minimize the back lash. The device, according to this invention, for reducing backlash in gear drives comprises, a casing accommi^fttlnf fif^t ifi^ i§g8Rd igiFl^ Ifii first gear being mounted on a first shaft supported in a first set of end bearings, located directly in the bores on the casing, a set of end caps axially securing the first shaft; the second gear being mounted on a second shaft supported in a second set at end bearings located in a set of end housings, i>ach end housing having an eccentric bore for seating the second shaft, the end housings having a first set of spaced circumferential holes on the exterior corresponding to a mating second s#t of ip«€§d circumferential holes on the casing, whereby the end housings are boltable to the casing through defined positions of eccentricity, enabling the second gear to be brought sufficiently close to the first gear, to reduce backlash. This invention will now be described by way of example, and not by way of limitation, with reference to one of possible embodiments thereof, illustrated in the accompanying drawings, in which Fig 1 illustrates (in section) the said embodiment, Fig.2 illustrates the bearing cap and Fig.3 illustrates the eccentric bearing housing. As shown in Fig.l, the input shaft (2) carries a pinion (4) secured to it by spacer (6), circlip (7) and key (8) arrangement. The gear (5) is mounted on the output shaft (3) similarly. The method of securing the pinion or gear can vary depending on the designer's choice. In the proposed method, a positive means is used to adjust the center distance. Eccentric bearing housing, proposed herein by the inventors, combines the ftanctions of a bearing cap and an eccentric bush. The bearing cap (10,11) is used to arrest the axial play in the shaft and bearing assembly. The bearing cap is provided with a number of equi-spaced holes and it is secured to the housing (1) by screws (15). The step length shown as a critical dimension (Fig.2) is adjusted during the assembly by machining. In the present invention, the bearings (9) are housed in the inner cylindrical surface of the aimular feature of eccentric bearing housings (12, 13). As shown in Fig.3, the distance between the flange face and the step on the inner cylindrical feature is the critical dimension to control the axial play. The outer cylindrical surface is machined with an eccentricity. As shown in Fig.l, two such eccentric bearing housings (12,13) are used at both ends of the output shaft (3) carrying the gear (5). Seals (14) are used at the input and output ends of the shafts, by fixing them on bearing cap (10) and eccentric bearing housing (13) respectively. When these eccentric bearing housings are rotated within the bore of the casing (1), the center distance is varied. An index is provided on the flange portion of each bearing housing to show the point of maximum eccentricity. The holes in the flange are also machined with equal angular spacing and with reference to this marking. After rotating the eccentric bearing housings through the same angle to bring the gear pair into close or near close mesh, the bearing housings are secured by screws after matching the holes with the correct or nearest threaded holes on the casing. The angular adjustment possible depends on the number of threaded holes provided on the casing. The angular adjustment possible depends on the number of threaded holes on the casing. For example, if there are six threaded holes on the casing and corresponding number of holes on the eccentric bearing housing, the incremental angular adjustment is 360/6=60 deg. If an eccentricity of 0.1 mm is provided on the outer cylindrical surface of the bearing housing, this angular adjustment would correspond to 0.0167 mm. If it is possible to increase the number of holes on the eccentric bearing housing to say 12, maintaining six threaded holes on the casing, the center distance adjustment can be carried out in steps of 0.0083 mm. It may be noted that only six screws can be used, leaving out remaining holes of the bearing housing. In practice, the magnitude of eccentricity provided in the bearing housings depends on the gear accuracy, center distance and the other factors. The arrangement proposed herein is positive and the torque transmitting capacity is not affected by this method. As the eccentric bearing housings on either side of the shaft is adjusted by the same rotation angle, the gears or bearings are not subjected to unfavourable loading conditions. The readjustment necessitated by the wear of gear tooth can be readily made. The present arrangement lead® to a compact gear box with less number of parts. This arrangement also ensures proper stiffness of the gear train- By the very nature of bearing housing, the leak proof design is realized facilitating effective lubrication. The gearboM with this arrangement is easy to manufacture and the assembly is also simple. The backlash minimization method proposed herein can be used for motion control in high-torque as well as high-speed applicat ions. The bearing housing also reduces the axi al play that is an important factor in the high-torque and high-speed gear boxes. Though the arrangement is explained for a single-stage gear box, it can readily be extended to multi-stage gearbox. It wi11 be appreci ated from the foregoing description that various other embodiments of the proposed device are possible without departing from the scope and ambit of this invention. We Claims 1- A device for reducing backlash in gear drives comprising a casing accommodating first and second gears, the first gear being mounted on a first shaft supported in a first set of end bearings, located directly in the bores on the casing, a set of end caps axially securing the first shaft; the second gear being mounted on a second shaft supported in a second set of end bearings located in a set of end housings, each end housing having an eccentric bore for seating the second shaft, the end housings having a first set of spaced circumferential holes on the exterior corresponding to a mating second set of spaced circumferential holes on the casing, whereby the end housings are boltable to the casing through said first and second set of holes, in predetermined positions of eccentricity, enabling the second gear to be brought sufficiently close to the first gear, to reduce back1ash. 2. A device for reducing backlash in gear drives substantially as herein described and illustrated with reference to the accompanying drawings. Dated this the 4th day of August 2003.

Documents:

636-che-2003-abstract.pdf

636-che-2003-claims.pdf

636-che-2003-correspondnece-others.pdf

636-che-2003-correspondnece-po.pdf

636-che-2003-description(complete).pdf

636-che-2003-drawings.pdf

636-che-2003-form 1.pdf

636-che-2003-form 19.pdf

636-che-2003-form 26.pdf