GB1599905A

GB1599905A - Apparatus and a method for monitoring gear teeth profiles

Info

Publication number: GB1599905A
Application number: GB1663277A
Authority: GB
Original assignee: English Electric Co Ltd
Current assignee: English Electric Co Ltd
Priority date: 1978-04-21
Filing date: 1978-04-21
Publication date: 1981-10-07

Description

(54) IMPROVEMENTS IN OR RELATING TO APPARATUS AND A METHOD FOR MONITORING GEAR TEETH PROFILES (71) We, THE ENGLISH ELECTRIC COMPANY LIMITED, of 1 Stanhope Gate, London W1A lEH, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to apparatus and a method for monitoring profiles of gear teeth.

It is particularly, but not exclusively, concerned to provide a relatively simple method and apparatus for achieving this.

In geared transmissions, uniformity of relative rotation, silence in operation and optimum distribution of load over the tooth surfaces depend to a large extent on the accuracy of gear tooth form as produced in the gear cutting and finishing processes.

One major constituent of tooth form is the profile of the surface from tip to root of the tooth flank. Commonly this corresponds basically to the involute derived from the base circle of the gear, and monitoring has as its aim the detection of departure from this involute form in a particular transverse plane.

Machines are commonly available on which small gears may be mounted, to provide in autographic form a record of departure from involute profile. On large gears, however, the measurement is frequently carried out laboriously by plotting of the co-ordinates of individual points on the profile.

Mechanical instruments are available, which register departure from straight line or circular arc for subsequent interpretation or electronic processing to give departure from the involute curve. These suffer from difficulty in accurate location of the instrument which prevents accurate interpretation of the measurement.

One object of this invention is therefore to provide a method and apparatus whereby the tooth profile accuracy of gears may be monitored rapidly and accurately in such a manner that interpretation of the readings is, within an easily attained range, independent of the instrument location.

According to one aspect of the present invention, a gear tooth profile monitoring apparatus comprises a master gear wheel having one or more teeth of model tooth profile, mounting means for mounting the master gear wheel in driving engagement with a test gear, the master gear wheel being so formed that each of the model profile teeth is engageable by the test gear over substantially the whole driven flank of the model profile tooth, first means for producing a signal representative of the movement of the master gear wheel, second, reference, means for producing a signal which varies linearly with movement of the test gear, and comparison means for deriving from the two signals a representation of the extent to which driven movement of the master gear wheel is non-linear with driving movement of the test gear.

The master gear wheel may be of either spur or helical form.

Where the apparatus is for use with a helical test gear, the master gear wheel may be a spur gear, the mounting means then being adapted to permit the spur gear wheel to lie with its teeth parallel to the teeth of the test gear at the position of engagement.

The reference means may comprise frictional drive means for engagement with a plane, cylindrical or conical surface of, or fixedly associated with, the test gear and a transducer for converting the driven movement of the frictional drive means to an electrical signal.

The means for producing a signal representative of the movement of the master gear wheel, and the reference means, may produce cyclically varying signals of equal frequency whose relative phase is compared by the comparison means, the instantaneous phase error representing the non-linearity of the test gear.

The teeth of model profile preferably each have following and preceding teeth which are relieved in such manner as to cause the master gear wheel to be driven by test gear engagement with the intervening tooth over sub stantially the whole of its flank.

According to another aspect of the invention a method of monitoring a gear tooth profile includes the steps of mounting the test gear for operational movements, mounting a master gear wheel having one or more teeth of model tooth profile for operational engagement with the test gear, the master gear wheel being so formed that each of the model profile teeth is engageable by the test gear over substantially the whole driven flank of the model profile tooth, deriving from the driven movement of the master gear wheel a signal which varies linearly with the movement of the master gear wheel, deriving a signal which varies linearly with the driving movement of the test gear, and comparing the two signals to provide a representation of the non-linearity of the test gear.

One embodiment of apparatus according to the invention and a method of operating ahe apparatus will now be described, by way of example, with reference to the accompanying drawings, of which Figure 1 is a partly diagrammatic perspective view of the apparatus in operation; Figure 2 is a profile view of meshing gear teeth and corresponding error records; and Figure 3 shows a profile of a master gear having alternate teeth relieved.

Referring to the embodiment shown in Figure 1, a large test gear 1 is mounted on a horizontal bed 2 for rotation about the gear axis 3.

A master gear wheel 4 is of relatively small axial width (i.e. thickness) so as in effect to be able to 'sample' the tooth profile of the test gear in a particular transverse plane of that gear. The master gear wheel has an accurately machined tooth profile in which any errors are negligible in comparison with the tolerance limits that are acceptable in the test gear wheel. The master gear wheel thus has a model tooth profile.

A selection of such master gears would of course be necessary so that a match is available for any test gear that may be provided.

The master gear wheel 4 is mounted on a shaft 5 which drives a transducer 6, either the shaft or the transducer being fixedly mounted so that the master gear 4 is in engagement with the test gear 1 so as to be driven thereby.

An important feature of the present invention is that the centre spacing of the test gear 1 and the master gear 4 is not at all critical in relation to the magnitude of error that is being monitored.

Where the test gear -1 is a spur gear the master gear 4 is also a spur gear, but in the case of a helical test gear the master gear 4 may be either a helical gear or a spur gear.

In the latter case the shaft 5 is angled so that the teeth of the two gears are parallel at the point of engagement. The master gear will still, of course, engage the test gear in a particular transverse plane of the test gear.

The transducer 6 may be one of various known forms. In the present instance it is assumed to convert the shaft (5) rotary position into an electric signal of cyclically varying magnitude. The phase of this signal provides a representation of the shaft, and thus master gear, position. If, of course, the velocity ratio of the gear coupling is not constant, that is, if the driven movement of the master gear 4 is non-linear with the driving movement of the test gear, then the phase of the output signal from the transducer 6 will not truly represent the rotational position of the test gear.

A linear representation of the rotational position of the test gear is obtained by friction drive means comprising a friction wheel 7 and a further transducer 8. The friction wheel 7 bears upon a plane surface which in this example is the rotary supporting bed 2 which does of course rotate in unison with the test gear 1. The output signal of the transducer 8 is an analogue signal varying cyclically with the rotational position of the test gear and thus is similar to the first output signal. If the two signals have the same average spatial frequency, i.e. undergo the same number of cycles in one revolution of the test gear, then any local non-linearities between the gear movements will be reflected in small changes of the phase relation between the two signals.

A zero-ing adjustment may be provided on one or both transducers to bring the two signals into phase synchronism at some point of the rotation.

The two signals are applied to an electronic phase comparator 11 which plroduces a phasedifference error signal. This signal drives a chart recorder 12 which produces a trace of error against angular rotation of the test gear.

It was assumed above that the cyclic frequency of the two signals would on average, be identical. Clearly, the velocity ratio of the friction wheel coupling will depend upon the radial distance of the point of engagement from the axis 3. Where the bed 2 has a horizontal plane or conical face this radial distance may be easily adjusted. Alternatively a rim surface of predetermined radius may be used so that the average master gear angular velocity equals the friction wheel angular velocity.

A selection of rims or a selection of friction wheels would then be required for different diameters of the test gear.

If only the overall errqr in the velocity ratio were of interest then a master gear as described above would suffice. A typical error trace from such an arrangement would be the solid line in Figure 2(b). It may be seen, however, from Figure 2(a) that in general, each tooth engagement is interrupted, before it has come to the limiting position, by the following tooth engagement which takes over from it.

The broken lines in Figure 2(b) show typlical error traces that are lost by this overlap.

The non-linearity error for the whole engageable portion of the flank of a tooth, can be determined, as illustrated in Figure 3, by relieving the driven surface 13 of alternate teeth of the master gear by an amount such as just to permit engagement of the unrelieved teeth over substantially the whole of the flank profile.

In a variation of this method only one or some of the alternate teeth may have following and preceding teeth so relieved. Again, as long as the master gear can be kept in mesh, the relieving of the teeth need not be restricted to the driven flank only.

In operation of the apparatus the various components are set up and the bed 2 is rotated at a low speed. Variations in the speed will not matter since, apart from profile errors the signals from the two transducers 6 and 8 will vary in synchronism. The comparison circuit produces a continuous phase error signal which is displayed by the chart recorder 12.

WHAT WE CLAIM IS:- 1. A gear tooth profile monitoring apparatus comprising a master gear wheel having one or more teeth of model tooth profile, mounting means for mounting the master gear wheel in driving engagement with a test gear, the master gear wheel being so formed that each of said model profile teeth IS engageable by the test gear over substantially the whole driven flank of the model profile tooth, first means for producing a signal representative of the movement of the master gear wheel, second, reference, means for producing a signal which varies linearly with movement of the test gear, and comparison means for deriving from the two signals a representation of the extent to which driven movement of the master gear wheel is non-linear with driving movement of the test gear.

2. Apparatus according to Claim 1, for use with a spur test gear, wherein said master gear wheel is a spur gear.

3. Apparatus according to Claim 1, for use with a helical test gear, wherein said master gear wheel is a helical gear.

4. Apparatus according to Claim 1, for use with a helical test gear, said master gear wheel being a spur gear and said mounting means being adapted to permit the spur gear wheel to lie with its teeth parallel to the teeth of the test gear at the position of engagement.

5. Apparatus according to any preceding claim, wherein said first means for producing a signal representative of the driven movement of the master gear wheel comprises a transducer coupled to said master gear wheel for converting the driven movement thereof to an electrical signal.

6. Apparatus according to any preceding claim, wherein said second means comprises frictional drive means for enaggement with a plane or conical surface of, or fixedly associated with, the test gear and a transducer for converting the driven movement of the frictional drive means to an electrical signal.

7. Apparatus according to any of Claims 1-6, wherein said first and second means produce cyclically varying signals of equal frequency whose relative phase is compared by said comparison means, the instantaneous phase error representing the non-linearity of the test gear.

8. Apparatus according to any preceding claim wherein said teeth of model profile each have following and preceding teeth which are relieved in such manner as to cause the master gear wheel to be driven by test gear engagement with the intervening tooth over substantially the whole of its flank.

9. Apparatus according to Claim 8, wherein said following and preceding teeth are relieved over their driven flanks only.

10. Apparatus according to Claim 8 or Claim 9 wherein alternate teeth of the master gear wheel are so relieved.

11. A method of monitoring the tooth profile of a test gear including the steps of mounting the test gear for operational movement, mounting a master gear wheel having one or more teeth of model tooth profile for operational engagement with the test gear, the master gear wheel being so formed that each of said model profile teeth is engageable by the test gear over substantially the whole driven flank of the model profile tooth, deriving frm the driven movement of the master gear wheel a signal which varies linearly with the movement of the master gear wheel, deriving a signal which varies linearly with the driving movement of the test gear, and comparing the two signals to provide a representation of the non-linearity of the test gear.

12. Gear tooth profile monitoring apparatus substantially as hereinbefore described with reference to Figures 1 and 2 as modified in accordance with Figure 3.

13. A method of monitoring a gear tooth profile substantially as hereinbefore described, with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. error traces that are lost by this overlap. The non-linearity error for the whole engageable portion of the flank of a tooth, can be determined, as illustrated in Figure 3, by relieving the driven surface 13 of alternate teeth of the master gear by an amount such as just to permit engagement of the unrelieved teeth over substantially the whole of the flank profile. In a variation of this method only one or some of the alternate teeth may have following and preceding teeth so relieved. Again, as long as the master gear can be kept in mesh, the relieving of the teeth need not be restricted to the driven flank only. In operation of the apparatus the various components are set up and the bed 2 is rotated at a low speed. Variations in the speed will not matter since, apart from profile errors the signals from the two transducers 6 and 8 will vary in synchronism. The comparison circuit produces a continuous phase error signal which is displayed by the chart recorder 12. WHAT WE CLAIM IS:-

1. A gear tooth profile monitoring apparatus comprising a master gear wheel having one or more teeth of model tooth profile, mounting means for mounting the master gear wheel in driving engagement with a test gear, the master gear wheel being so formed that each of said model profile teeth IS engageable by the test gear over substantially the whole driven flank of the model profile tooth, first means for producing a signal representative of the movement of the master gear wheel, second, reference, means for producing a signal which varies linearly with movement of the test gear, and comparison means for deriving from the two signals a representation of the extent to which driven movement of the master gear wheel is non-linear with driving movement of the test gear.