Gear cutting – milling – or planing – Gear cutting – Gear tooth shape generating
Reexamination Certificate
2000-05-11
2001-09-04
Howell, Daniel W. (Department: 3722)
Gear cutting, milling, or planing
Gear cutting
Gear tooth shape generating
C033S628000, C033S638000, C033S641000, C279S136000, C409S061000, C409S034000, C409S062000, C409S042000
Reexamination Certificate
active
06283686
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns a supporting and centering device for use in the production of double-toothing sprocket wheels or pulleys and method of using same.
The sprocket wheels or pulleys to which the invention refers include a central groove which separates the two toothed rings and whose teeth are usually inclined from 2° to 60°, but can be straight. The sprocket wheels or pulleys to which the invention refers are advantageously of the type used together with the so-called positive drive belts such as those produced by the Goodyear Company and known by the trade name of “EAGLE”.
The invention seeks to enable sprocket wheels to be produced using generating blades or pinion instruments which move along an axis parallel to the axis of the sprocket wheel and rotate in coordination therewith, both in the forward and in the return movement, the axes being perpendicular to the plane of the workpiece-bearing table. The sprocket wheels to which the invention relates may include teeth which coincide with respect to the center line or are offset, the offset distance being advantageously 50% of the pitch.
The invention is used to correctly position a workpiece in order to obtain the desired reciprocal positioning of the two mating rings of teeth of the sprocket wheel. The state of the art covers sprocket wheels with a straight or bi-helical double-toothing. Reference is made, for example, to DE-A1-2717515 where one positioning method for carrying out toothing is described. The wheels comprise two coaxial rings of oblique and converging teeth, arranged substantially symmetrically with respect to an intermediate plane of separation, in a substantially herringbone design. Double-toothing wheels are normally worked by positioning and clamping a workpiece and subsequently activating a generating blade or cutting instrument to act on the periphery of the workpiece. Depending on the shape of the teeth, the sprocket wheels may be used to transmit movement by means of positive drive belts.
On the one hand it is not normally possible to work small double-toothing wheels on a large scale with machines having a single positioning, and on the other hand such a machine involves prohibitive production costs and low productivity. There have also been proposals to work the double-toothing sprocket wheels using machines with a supporting base or workpiece-bearing table and with a generating blade or pinion instrument cutting tool which works with a to-and-fro movement parallel to the axis of the piece and rotates at the same time in a coordinated manner with the piece to be worked.
In this case the unworked workpiece is placed with its axis vertical and associated with a shaft, cooperating with the supporting base or piece-bearing table, which determines the starting position with respect to the position of the generating blade or pinion instrument. In this procedure, two rings of teeth are made in two successive steps; the first step leads to formation of teeth on a first ring and the second step is for formation of the teeth on the other ring.
However, with this procedure there is the problem of correctly positioning the workpiece on the machine for the second ring of teeth to be made so as to achieve the precise respective positions of the first and second ring of teeth. It should be noted that in order to obtain a satisfactory result the axes of the teeth must necessarily meet along the center line of the sprocket wheel within extremely limited tolerances.
The play in the connection between the workpiece to be worked and the shaft which clamps the workpiece to the supporting base makes it even more difficult to achieve the correct positioning. Therefore it becomes necessary to carry out long and complex operations to adapt the position of the generating blade or pinion instrument with respect to the workpiece and vice versa, according to data and measurements monitored by specific equipment.
Also with this method, the cost of production of the sprocket wheels is very high and one of the reasons for this is simply because of the additional operations of removing the shavings.
The smaller the sprocket wheel to be made, the greater the problem; even though it is possible to achieve larger sprocket wheels with a sufficient degree of precision, and with overall production times which are reasonable with respect to the total cutting time, until now it has been practically impossible to make small sprocket wheels of this type with any guarantee of reliability and at reasonable cost.
An object of the invention is to achieve a device which will allow the precise positioning and centering of the workpieces required for producing a second ring of teeth in the production of double-toothing sprocket wheels.
SUMMARY OF THE INVENTION
Another object of the invention is to obtain the precise positioning of the teeth of the second ring with respect to the teeth of the first ring cheaply and in a short time.
A further object is to provide a simple, functional device which will allow the workpiece to form the sprocket wheel to be centered precisely with respect to a cutting blade or pinion instrument, and which will allow the correlated centered position to be maintained throughout the working step.
The invention is set forth and characterised in the respective independent claims, while the dependent claims describe other characteristics of the idea of the main embodiment.
The invention is applied to production of double-toothing sprocket wheels generated typically by generating blades or pinion instruments.
This invention also provides a method of producing double-toothing sprocket wheels which will allow a drastic reduction in the time required to center and correctly position the workpiece and therefore, more generally, reduce the times and costs of production, while at the same time guaranteeing extreme precision and reliability even for smaller sprocket wheels.
The centering device according to the invention operates in association with the shaft of the supporting base of the workpiece to be worked and is placed, for any size of sprocket wheel, in a pre-set position with respect to the start-of-work position of the blade device or pinion instrument. The device cooperates with any tooth, or with any pair of teeth, of the first ring of teeth.
The pre-set position is correlated to the extent of the desired staggering, or alignment, of the teeth of the first and second ring of the sprocket wheel.
The centering device comprises at least one retractable pin arranged with its axis substantially parallel to the axis of rotation of the sprocket wheel and cooperating with the separating grooves between the teeth of the first ring of the sprocket wheel which is to be made.
According to one variant, the centering device has a fork element which cooperates with a tooth of the first ring.
According to another variant, the pin or fork element cooperates with the groove, or with two teeth, substantially along the pitch circle of the teeth.
Hereinafter, for simplicity of explanation, we shall describe only the situation with the retractable pin, but the situation with the fork element cooperating with a tooth shall be considered equivalent thereto.
According to the invention, the retractable pin can assume at least a first position, or waiting position, wherein it is arranged in a high position above the support surface of the supporting base and a second position, or operating position, wherein it cooperates with two teeth of the first ring, then protruding to a small extent from the said surface.
According to a variant, the retractable pin cooperates with spring means which is able, when compressed or released, to define respectively the waiting position or the operating position.
The centering device is kinematically connected to the supporting base so that it rotates together with the base, with the sprocket wheel and possibly with the axial positioning and clamping shaft; the sprocket wheel is mounted coaxially with respect to the base and the shaft.
According to another variant, the position of the
Akin Gump Strauss Hauer & Feld L.L.P.
Howell Daniel W.
Technologies Research Holding S.A.
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