US3499252A - Means for generating involute gears - Google Patents

Description

March 10, 1970 P. H. CLEFF MEANSI'OR GENERATING INVOLUTE GEARS 4 Sheets-Sheet 1 Filed Dec. 26, 1967 H61 PRIOR ART FIG] March 10, 1970 P. H. CLEFF 3,

MEANS ;FOR GENERATING INVOLUTE GEARS Filed Dec. 26, 1967 4 Sheets-Sheet 2 March 10, 1970 P. H. CLEFF' 3,499,252

MEANS,.FOR GENERATING INVOLUTE GEARS Filed Dec. 26, 1967 4 Sheets-Sheet 5 l I l E ERROR IN 10-6MM.UN/TS NEGATIVL PER MM RAD/US R0 Pas/m5 4: u m Q Q 9 9 W? all;

March 10, 1970 P. H. CLEI'L'F 3,499,252

MEANSI'OR GENERATING INVOLUTE GEARS Filed Dec. 26, 1967 4 Sheets-Sheet 4 y Wis T Q OF WORK- GEAR United States Patent US. Cl. 51-123 2 Claims ABSTRACT OF THE DISCLOSURE For involute gear grinding and the like machines, a mechanism for producing relative movement between a workgear and a grinding wheel comprises an arrangement of rotation and sliding members designed to produce the required movement in accordance with a given basic equation.

This invention relates to means for generatively finishing, for example by grinding, the pre-cut tooth flanks of external or internal cylindrical gear Wheels or pinions having either straight spur orhelical teeth of either involu'.e or modified involute form.

Although in what follows reference will be made mainly to a grinding process, it must be clearly understood that metal removal processes such as spark-erosion, electro-chemical machining and the like may be adapted to the purpose of this invention and are included within the meaning of the term grinding.

The principal object of the invention is to provide improved means for the involute generative movement of a work-gear past stationary grinding wheels or, inversely, the involute generative movement of grinding wheels past a stationary work-gear.

In most known gear grinding machines of the involute generating type, such as MAAG, KOLB and HURTH machines, the generative movement between the Workgear, i.e. the gear to be ground, and grinding wheels, usually of rectilinear generatrix, is produced by means of a circular pitch block and a pair of steel tapes, these being the equivalents respectively of the familiar disc and string of the theoretical involute construction.

FIG. 1 of the accompanying drawings illustrates this principle of involute generation diagrammatically. Grinding wheels 1 and 2 are motor-driven to rotate round their respective axes of rotation 1a and 2a, but are otherwise stationary relative to the main machine bed 8. Work-gear 3, i.e. the gear to be ground, is firmly mounted on an arbor or spindle 4 rotatably journalled in a rectilinearly reciprocating slide 5, the direction of said reciprocation being at right angles to the axis of workgear rotation. A pitch block or roll segment 6 of the required size is drive-connected to, and co-axial with, arbor 4. Thin, flexible steel tapes (at least two in number) 7a and 7b are wrapped around the roll segment in a respectively right-about and left-about manner and fastened at their respective inner ends to the roll segment or pitch block 6. The outer ends of the tapes are anchored to the stationary main machine bed 8 on which aforesaid slide is recirprocated by means of a power driven Scotch Yoke mechanism 9, 9a and 10.

It will be readily understood by those versed in the art that any rectilinear movement of slide 5 by an amount As will be accompanied by a rotation through A of roll segment 6, and work-gear 3 drive-connected thereto, such that with R operative radius of roll segment 6, and A=angular rotation of the roll segment in radians, and

that the operative rectilinear generatrices of the grinding wheels will envelope as line curves involute tooth profiles on work-gear 3 during such movement.

The basic problem of producing involute generative movements between work-gear and grinding wheels will thus be seen to be one of rectification of a circle over a usually limited arc length Steel tape drives of the type just described can be made to work with a high degree of accuracy, provided R is held to close tolerances and the steel tapes are C I- rectly positioned and tightened. They have, however, a number of disadvantages of which a major one is the necessity to provide a new roll segment or pitch block 6 for every change in roll radius R of the gear to be ground. Another disadvantage is the impossibility of running gear grinding machines of this type at high, or very high, generating speeds because of the dynamic stretch of the steel tapes and consequent profile errors on the gear being ground, especially when grinding gears having a high mass-moment of inertia.

It is the purpose of the present invention to provide a simple but very accurate, robust and steplessly adjustable link mechanism of low compliance and comprising only cylindrical pivots and straight slides, as a means for overcoming the above-mentioned limitations of the steel tape drives, and applying it, by way of example and inter alia, to gear grinding machines of the type depicted diagrammatically in FIG. 1 and described in the preceding paragraphs.

One form of construction of such link mechanism in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an end view of an involute generative gear grinding machine using pitch block and steel tapes as means of involute generation, as described above.

FIG. 2 shows the basic mechanism according to the invention, FIG. 2(L), and the underlying mathematical and kinematical principles, FIG. 2(R),

FIG. 3 illustrates the complete roll-generating mechanism in accordance with the invention, FIG. 3(L), and the underlying mathematical and kinematical principles, FIG. 3(R),

FIG. 4 shows the structural errors of the complete roll-generating mechanism of FIG. 3(L) for roll-angle ranges of respectively plus/minus 30 and plus/minus 40 arcdegrees, and

FIG. 5 is an end view of an involute generative gear grinding machine similar to that of FIG. 1, but with the roll-generating mechanism of FIG. 3 having replaced the steel tape drive.

Referring to FIG. 2 of the drawings, the roll-generating mechanism in accordance with the invention and in its basic form is essentially a turning block slider crank whose output member drives through a slide/pivot member a main output slide which is slidably guided in a direction at right angles to the line joining the centres of the first and second main pivot of the aforementioned turning block slider crank mechanism.

Considering the plane of the paper as stationary base there is provided a first main pivot 11 round which a crank 12 of radius R may rotate through plus/minus 4). Attached to the outer end of said crank 12 and at a distance R from the centre of the first main pivot 11, is a pivot 13 carrying rotatable thereon a slide block 14. Said slide block 14 is in drive engagement with rectilinear inner guides 15 machined into a lever 16 which is rotatably held by a second main pivot 17 secured to the base of the mechanism and a certain vertical distance away from the first main pivot 11. Lever 16 is in drive engagement with a guide block 18 by means of its rectilinear outer guides 19. Said guide block 18 is pivotally connected to a main output slide 20 by means of a pivot 21, enabling the main output slide 20 to be moved along a fixed rectilinear guide bar 22 whose centre line runs at right angles to the line joining the centres of the first main pivot 11 and second main pivot 17 and lies a certain pie-determined vertical distance away from the first main pivot 11.

To those versed in the art it will be apparent that a rotation of crank 12 by plus/minus will be accompanied by a linear movement of main output slide 20 through plus/minus s, with the relationship s=f() being uniquely determined by the dimensions selected for the primary members of the mechanism. It can now be shown by limit calculations of the type 1c0s +sin R 11m 1 c0s 3R that if main pivot centre distance 11-17 is made equal to 2R then the linear travel of main output slide 20 will be equal to are to a high degree of accuracy for small values of plus/minus arc-degrees and R =l.

In order to extend the useful range (plus/minus 5) of the basic mechanism shown in FIG. 2, whilst maintaining its very high small g5 accuracy, in accordance with the invention a simple slider crank mechanism has been added to result in the configuration illustrated in FIG. 3. All the elements of the basic mechanism of FIG. 2 are still evident and have, therefore, been given the same identification numbers. Crank 12 has been extended radially to form small crank 23 of radius r with pivot 24 at that distance from the first main pivot 11, and with all three pivots 13, 11 and 24 lying in line. Hinged to pivot 24 is a connecting rod 25 of length 1 whose other end is movably connected to an extension pivot 26 of second main pivot 17. Second main pivot 17 is now no longer fixed, but has been made movable in the direction of a line passing through first main pivot 11 and being at right angles to the centre line of fixed rectilinear guide bar 22, by means of slide 27 and therewith associated rectilinear guide bars 28.

Angular movement of crank 12 plus crank 23 round first main pivot 11 by an amount plus/minus will produce a linear movement of main output slide 20 of plus/ minus with R =1. The accuracy of circle rectification, by a mechanism constructed in accordance with the invention, is extremely high. This is illustrated in FIG. 4 and shows that for a total maximum angular swing of crank 12 by 60 arcdegrees (plus/minus 30 arcdegrees) the maximum structural erroris of the order of +0.7-l0 inch/inch of radius R or less than 0.15 arcsecond. Even for a maximum swing of 80 arcdegrees the maximum structural error does not exceed the linear equivalent of 1 arcsecond.

FIG. 5 shows, in accordance with the invention, the mechanism of FIG. 3 suitably adapted by inversion to the requirements of a gear grinding machine similar to that illustrated in FIG. 1. Essentially the mechanism is now carried on reciprocating slide 5 as'the base. Cranks 12+23 are drive-connected to work-gear spindle 4, and main output slide 20 has become integral with the rectilinear guide bar 22 such that pivot 18 is now rendered stationary on the centre line of the machine.

It will be apparent to those versed in the art that the mechanism above described, by way of example only, may be constructed in several different configurations all based, however, on the basic turning block slider crank mechanism and its kinematic inversions. The application of mechanisms in accordance with the invention is not limited to the type of machine selected, i.e. gear grinding machines, but may usefully be employed in other machines and apparatus whenever a constant ratio transformation from linear to angular, or angular to linear, motion is required and particularly so if such transformation has to be mechanised with a high degree of accuracy and with an absolute minimum of dynamic compliance.

I claim:

1. A mechanism for use in an involute-generating gear grinding machine to produce roll-rectilinear relative movement between a workgear carried on a reciprocating generating slide and a rotatable grinding wheel of rectilinear generatrix, comprising a turning block slider crank and a slider crank mechanism so arranged in compound that, upon a reciprocation (s) of said workgear-carrying generating slide of generative radius (R said workgear is rotated relatively to said generating slide through an angle (arc such that the arrangement of said turning block slider crank mechanism comprising, a crank of radius R co-axially and drivingly-connected to said workgear, a first slide-block pivoted at the outer end of said crank and engaging internal rectilinear guide-ways of a lever constrained to slide at its upper end, by means of a pair of external rectilinear guide-ways, through a second slide-block pivotally mounted on a stationary main machine frame above the workgear axis, the lower end of said lever being constrained to oscillate about a main pivot mounted on said generating slide below the workgear axis, said main pivot being moved reciprocatingly relative to said generating slide by means of said slider crank mechanism which comprises a crank of radius r as an integral extension of aforementioned crank R, but arc-degrees out of phase therewith, a connecting rod of length l pivotally connected at its one end to said crank and to said main pivot at its other end, and a slide carrying said main pivot reciprocatingly movable in a pair of rectilinear guideways secured to said generating slide, all said cranks, levers, connecting rods, pivots, guide-ways and slides being in line in the central position of the compound mechanism and from which central position the said compound mechanism may be moved to either side in conformance with above basic equation.

2. A mechanism for use in an involute-generating gear grinding machine as claimed in claim 1, in which for the central position of said mechanism the distance of said main pivot of said turning block slider crank mechanism from the common workgear and R -crank axis is exactly References Cited UNITED STATES PATENTS 2,388,173 10/1945 Miller 51-123 1,187,616 6/1916 Grannis 51123 1,515,281 11/1924 Schurr 5l123 HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R.

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