GB2049100A - A Method and Apparatus for Unbalance Correction - Google Patents

Abstract

Material is removed from or added to a rotary workpiece to be balanced by a tool of which movement is controlled in dependence not only on the measured imbalance but also on the surface shape of the workpiece so as to blend the altered surface with the original surface. The tool is, therefore, jointly controlled by the imbalance to be reduced and parameters governing the area of the workpiece that can be engaged by the tool and the maximum penetration of the tool thereby. These parameters may be mechanically established by scanning, by means of a pin (4), a contoured body (1) corresponding to the workpiece being balanced or they may be electrically established. The body (1) is axially and angularly adjustable on a shaft (2) and is rotatable in synchronism with the workpiece. The tool (not shown) is controlled from the pin (4) by linkage (18, 19) and therefore its operation is governed by the angular and axial settings of the body (1) and the nature of the machining operation is dictated by the contour of the body (1). A template (15) may be provided to govern the manner in which machining is effected axially of the workpiece. <IMAGE>

Description

SPECIFICATION A Method and Apparatus for Unbalance Correction This invention relates to a method and apparatus for unbalance correction by means of a correction tool movable along a surface of a body requiring balancing, wherein the body and the correction tool move relatively to each other.

Swiss Patent 305,805 discloses apparatus of the type referred to, wherein a tool controlled by the amount of unbalance removes material from, or adds material to, a body requiring balancing until the signal relating to the amount of unbalance and its angular position is no longer measurable. Disadvantages here are that in many equipment procedures the unbalance in the body has to be corrected during the measuring process, and that allowance for the surface of the body during correction is not possible.

German DAS 2,231,226 discloses a method of correcting unbalance in rotary bodies, as determined by measurement, by machining one or more grooves into the periphery of the rotary body. The groove-forming tool is moved along a circular arc whose axis is parallel to the axis of the rotary body, the machining diameter being greater than that of the rotary body at the machining point and the machining feed being effected by parallel displacement of the axis of movement of the tool. Such a method and apparatus are not suitable for use with rotary bodies whose surface contour, where balancing is to take place, can have any desired form, and also such method and device cannot be used when unbalance correction are to be carried out inside a hollow body.

USP 2,474,883 disclose a dynamic balancing apparatus wherein the unbalance is corrected while being controlled by information on unbalance during the testing run on the rotary body. As with Swiss Patent 305,805, this apparatus is unsuitable for providing accurate unbalance correction, since through uncontrolled unbalance correction at the instantaneously determined unbalance angle position a change is produced in this, which because of inertia in the machining tool leads to frequent scrapping of rotary bodies unbalanced in this manner. Aiso allowance for the surface of the body during correction is not possible.

All the methods and devices hitherto referred to, for the correction of unbalance by means of a correction tool movable along a surface of a body requiring balancing, wherein the body and the correction tool move relatively to each other, fail when demands are made in relation to the surface, to the strength, or to a specific flow property of the body. Consequently the problem involved in the invention is to correct the unbalance in a rotary body along a contour which will not affect subsequent usage of the rotary body.

According to one aspect of the present invention we provide a method for unbalance correction by means of a correction tool movable along a surface of a body requiring balancing, wherein the body and the correction tool move relatively to each other, characterised in that the surface of the corrected part of the body is determined in dependence on the unbalance to be corrected and in dependence on the shape of the body surface in the vicinity of the unbalance.

The combined contour of the correction tool in dependence on the body shape and on the unbalance for the first time permits a contour to be produced on the surface of the workpiece, in the area of the unbalance correction, which enables the body concerned to be matched to the shape required in the final machining.

In one embodiment of this method and also independently thereof, the problem on which the invention is based is solved in that in dependence on the shape the body to be corrected has in the vicinity of the unbalance, the surface of the corrected portion of the body, together with the surrounding surface extends without interruption in at least one co-ordinate direction. Due to this control method it becomes possible to provide a contour in the vicinity of the unbalance correction on the surface of the test-body such that premature failure of the balanced rotary body, e.g.

damage through high stress concentration caused by abrupt surface transitions or corners, is fully avoided.

In a further embodiment of the method of the invention it is proposed that a further weight change be superimposed on the change in the weight of the body caused by unbalance correction. This superimposition for the first time means that flanges hitherto provided for correcting unbalance, for instance on extended shafts in flow-sensitive rotary bodies, can be eliminated to such an extent that interfering flange edges are no longer encountered and that only the amount of material to be removed in correcting unbalance is left as a raised or lowered portion with a steady transition surface, in the vicinity of the flange originally present.

In accordance with a second aspect of the invention there is provided apparatus for carrying out the method of invention including a tool for correcting the unbalance and means for controlling the tool in synchronism with the rotary speed of the workpiece being balanced, said apparatus being characterised in that the means for controlling the tool includes a contoured body which is adjustable in relation to the workpiece requiring balancing by being turned about a rotation axis, and is rotatable in synchronism with the workpiece being balanced, said body having on its surface an axially extending line determining the maximum change that can be effected by the tool to the surface of the workpiece, and other lines having a form differing therefrom, and in that the axial extension of the contoured body represents an unbalance range and controls the machining tool during rotation of the workpiece and said contoured body.

This axially extending line may have a shape differing from a straight line, if for exact unbalance correction by changing the surface of the workpiece in the unbalance direction, or by changing the surface of the workpiece displaced therefrom by a predetermined angle, it becomes necessary to consider the effective radius which defines the distance from the rotation axis of the centre of gravity of the material removed or added. In order to perform a mass balance in a number of stages, without having to change again the surface of the workpiece already altered by the first correction stage, the axially extending line on the surface of the rotating contoured body may consist for instance of sequentially following straight lines in the axial direction, interconnected by arcs.This enables the surface of the subsequently finally corrected workpiece to be used for the envelope line of the contoured body, or as a pattern or model for the minimum flow resistance of the workpiece being balanced.

In order to reduce the flow resistance, e.g. with a view to uniformly supplying corresponding parts of bearings, disposed adjacent the correction plane and which have to be supplied with oil, the peripheral envelope lines of the contoured body can also be formed with an elliptic shape or an extra cam-like projection or recess.

Hence this apparatus is not limited to the correction of unbalance along the peripheral surface of a workpiece, but may very well be utilised in the machining of inclined surfaces, for end surfaces, and also for correcting unbalance inside hollow bodies.

In one particularly effective embodiment of the apparatus, the axially-extending line is an envelope line of the contoured body. This embodiment is particularly suitable when cylindrical surfaces are to be treated in accordance with the invention.

The contoured body may be mounted on a shaft in such a way that it can be rotated, shifted and locked. With the mobility of the contoured body and with an axially but radially movable fixed sensor pin for controlling the tool, it is possible to sense the axial extension of the contoured body which corresponds to one unbalance zone, and through rotation and subsequent locking of the contoured body brought into coincidence with the position on the workpiece whereat the unbalance is to be corrected, by surface machining or by internal machining the case of hollow bodies.

In yet a further embodiment of the device it is proposed that the contoured body has an angle scale on its periphery and the shaft has a reference scale extending lengthwise. Because of the angle scale on the contoured body whereby said body can be rotated from its zero setting in the direction of the unbalance angle position, and because of the lengthened reference scale provided on the shaft, it becomes possible to pre set the correction tool to the correct angular position corresponding to the unbalance, with the maximum penetration depth, when unbalance is being corrected by removing material.

For this purpose however the reference scale may also be disposed on the contoured body in order to move this along the shaft away from a fixed reference point. It is also possible to provide the angle scale on a fixed portion and with a single marking on the contoured body bring this into the required unbalance angle position.

In one embodiment of the apparatus the axis of the shaft carrying the contoured body is parallel to the axis of rotation of the workpiece. This embodiment is especially useful where the correction plane forms a cylindrical surface round the axis of rotation of the body being balanced. If the axis of the shaft carrying the contoured body is not parallel to the axis of rotation of the workpiece, then in accordance with the method provided by the invention it is possible to machine any other suitable surface of a workpiece, especially an end surface perpendicular to the rotation axis, or an inclined end surface, as met for example in fans and pumps, when top surfaces are used as correction planes.

According to a further aspect of the invention there is provided apparatus for carrying out the method, comprising a tool for correcting unbalance and means for controlling the tool in synchronism with the rotation of the workpiece being balanced, said apparatus being characterised in that the means for controlling the tool includes a sine generator which is rotatable in locked phase relation with the rotary body, the sinusoidal output signal from the sine generator is combined with a signal electrically representing the unbalance, and in a computer the contour of a correction plane in the rotary body being balanced and the pre-set value deviating from the rotary body contour are stored with the combined signals and control the machining tool.

With this electrical control of the machining tool unbalance may also be corrected independently of any mechanical shaft.

In an embodiment of this electrical control apparatus provided by the invention it is proposed that a sine-cosine generator be coupled in lockedphase relation with the workpiece being balanced, with the output signals therefrom being combined with the signals electrically representing the unbalance. With use of a sine-cosine generator, rotation of the generator relative to its initial angular position becomes unnecessary, since any angular unbalance position can be represented by appropriately combining sine and cosine values.

To provide locked-phase rotation with no coupling between the sine-cosine generator and the workpiece being balanced, there is provided in accordance with yet another aspect of the invention apparatus for performing the method, comprising a tool for correcting unbalance and means for controlling the tool in synchronism with the rotation speed of the workpiece being balanced, said apparatus being characterised in that through one control impulse per revolution of the rotary body being balanced, a sine-cosine generator produces a signal at the same frequency as the workpiece rotates, that the output signal from said generator is combined with the signals corresponding electrically to the unbalance, in that in a computer the contour of a correction plane in the workpiece and the predetermined value deviating from the contour of the workpiece are stored with the combined signals and control the machining tool. Digital components in particular may be used in emitting impulses for controlling the amount removed and for the value of the predetermined contour.

Another alternative form of apparatus for performing the method is characterised in that in dependence on a reference mark on the workpiece an impulse source emits impulses in locked-phase relation with the rotary body being balanced, in that the impulses are combined with the signals which represent the unbalance electrically in magnitude and position, and in that in dependence on the contour of at least one correction plane in the workpiece being balanced, the signals thus combined control a machining tool for that plane. In this apparatus, workpiece being corrected may be used as a contoured body to enable an unbalance to be corrected with the method of the invention. In one embodiment of this device the correction plane contour is mechanically sensed.Through mechanical sensing of the unmachined workpiece contour in the vicinity of a correction position, the actual surface contour is put without transfer error into relation with the removal or addition of material needed in correcting an unbalance.

In performing a multi-plane correction, only the contoured body needed for each correction plane, or the appropriate number of mechanical sensors needed for sensing the surface of the workpiece and the stored contour for each plane, in conjunction with the information on the magnitude and angular location of unbalance for each correction plane separately are required to enable the correction in the various planes according to the unbalance angles involved to be carried out in one simultaneous operation.

The invention is explained in more detail with reference to the attached drawings. In these:- Figure 1 a shows schematically mechanical control means in accordance with the invention for correcting unbalance; Figure 1 b shows schematically allowance for surface contour in accordance with the invention, through machining in dependence on two contoured bodies allowing for co-ordinate directions; Figure 1 c shows various cross-sections for contoured bodies; Figure 2 is a block circuit diagram of electrical control of unbalance correction, as provided by the invention; Figure 3 is a block circuit diagram of a further electrical control of unbalance correction, as provided by the invention; Figure 4 is a schematic view of a two-plane unbalance correction, using mechanical sensing, provided by the invention.

According to Figure 1 a contoured body 1 can be axially shifted along a shaft 2. The shaft 2 carries a reference scale 3 whereby the depth of penetration of a correcting tool, not shown, can be controlled and measured by moving a contact pin 4. The contoured body 1 also carries an angle scale 5 whereby it can be rotated in relation to a fixed mark 6. Thus the angular location of unbalance and hence the operating area of the machining tool can be determined. In the case of a combined removal of material to include both unbalance correction and surface adjustment, maximum penetration of the machining tool into the workpiece being balanced is thus brought about in the area of the unbalance location.

For simplicity, Figure 1 shows an envelope line 7 as being parallel to the axis 8 of shaft 2. This straight envelope line 7 is the representation for a cylindrical balancing surface about an axis of rotation of the workpiece being balanced. It will readily be realised that the form of the envelope line 7 may be selected to represent, for example, the contour of the top surface of a fan blade or a pump blade. The surface line 7 could also represent the optimum flow surface line on the workpiece being balanced. Similarly the other envelope lines, represented in the illustrated embodiment by a conical envelope line 9, may have a non-straight contour and be correspondingly formed so that in cross-section the contoured body has the form of a circle 11, an ellipse 12, or a raised cam contour 13, all as shown in Figure ic.

The mechanical control means represented in Figure 1 b shows how while maintaining the conical surface line 9, any desired contour on the surface of the rotary body being balanced can be produced, preparatory to correcting the unbalance, by means of a fixed template 1 5 along which a sensing pin 16 is slidable, the pin 16 being connected to a shaft 18 of a machining device (not shown) by a transmission lever 1 9.

Figure 1 b illustrates the simplest case of axial displacement on a smooth shaft in order to give a surface contour a specific treatment by removing or applying material. Here the shaft 2, the contoured body 1, the contact pin 4, the transmission lever 19 and the sensing pin 1 6 are moved either to left or right, in the direction of double arrows 20, depending on the particular area in a flange, not shown but which is provided as the correction plane, wherein the unbalance is present, whereby after the unbalance correction has been made the machined surface will exhibit a steady transition both axially and in the peripheral direction, especially when as disclosed under the invention the additional removal of weight has also been inciuded.

From the foregoing, it will be seen that the movement of the tool can be co-ordinated with the rotating workpiece in such a way that, depending on the angular setting and axial displacement of the contoured body and the shape of the latter, the tool can remove material from the workpiece (or add material thereto, as the case may be) along a peripheral zone or zones thereof while blending the resulting depression or projection with the contiguous non-machined peripheral zones of the workpiece. Also, where desired, the machining can take place axially of the workpiece under the control of the template 1 5. Such peripheral and axial machining may be executed simultaneously.

In Figure 2 a sine generator 21 is driven with angular velocity W in locked phase relation with the workpiece being balanced, and on rotation with the aid of an angle scale 22 is brought into the unbalance position in relation to a fixed mark 23. Output voltages 24 will give information on the precise angular position of the unbalance. A calculator 25 makes allowance electrically for a preset value of the predetermined final contour in conjunction with the expected contour of a correction plane in the workpiece being balanced.

The resulting voltage taken from a terminal 27 in calculator 25 is fed to a device 28 wherein the voltage from terminal 27 is combined with a voltage related to the unbalance means to provide a control voltage to the input of the controller 30 of a machining tool 31.

The electrical control for unbalance correction represented in Figure 3 is synchronised via an electronic sine-cosine generator 32 by one impulse per rotation of the workpiece being balanced, this being in the phase position corresponding to the angular position of unbalance. Using a calculation circuit 33 the amount of unbalance is treated, according to the amplitude changes. Further processing in view of the required contour is electronically performed as already described with reference to Figures 1 and 2. Digitally operating components are especially suitable for this purpose. Block 36 represents the tool controller.

According to Figure 4 a rotary body 100 requiring balancing, is mounted on an auxiliary shaft 101 and set in rotation. This is effected via drive 102, locked in phase with impulse source 110.

In a preliminary run the position and magnitude of unbalance have been separately determined for each plane and stored in a device 108. The unbalance information is now fed separately for each plane, to a calculator 109 for the left-hand plane and calculator 1 09a for the right-hand plane. The calculators 109, 1 09a are connected to the impulse source 11 0, and thus at each rotation receive information on the angular position of workpiece 100 at that instant, related to a fixed zero point on the workpiece.

Comparison between the momentary angular position of the workpiece and the angle information stored in the calculators 109, 1 09a relating to the balance arising in that particular plane produces a control signal 111 or 112 which determines the start of machining on the workpiece surfaces in the correction planes. In the simplest form for instance these control signals can operate a specific initial angle before the actual angular position of unbalance to ensure machining tools 107, 1 07a engage with the workpiece 100, remain penetrated to a specific depth over the actual unbalance sector, hence removing material, and emerge again at an angle which, taken in relation to the position of unbalance, is symmetrical to the angle of initial approach.The machining tools 107, 1 07a are each mounted on tool-slides 103, 1 03a movable transverse to the axis of rotation, and can be moved axially when actuated via the control signals 111, 112. Sensors 104, 104a are moved on workpiece surface positions 105, 106 along the correction planes which are not altered by the? unbalance correction. This ensures that by means of the momentary position of sensors 104, 1 04a in conjunction with the stored information on unbalance, the tool penetration depth and the machined length along the perimeter can be controlled as desired in symmetry with the particular angular unbalance position. Through shifting of the tool-slides 103, 1 03a machining can be carried out not only on a peripheral line in workpiece 100, but spatially extended depressions can be made during machining, or elevated portions when material feeding devices are used instead of the machining tools.

Claims (14)

Claims

1. A method for unbalance correction by means of a correction tool movable along a surface of a body requiring balancing, wherein the body and the correction tool move relatively to each other, characterised in that the surface of the corrected part of the body is determined in dependence on the unbalance to be corrected and in dependence on the shape of the body surface in the vicinity of the unbalance.

2. A method for unbalance correction by means of a correction tool movable along a surface of a body requiring balancing, wherein the body and the correction tool move relatively to each other, especially as claimed in Claim 1, characterised in that in dependence on the shape the body to be corrected has in the vicinity of the unbalance, the surface of the corrected portion of the body, together with the surrounding surface extends without interruption in at least one coordinate direction.

3. A method as in Claim 1 or 2, characterised in that a further weight change is superimposed on the change in the weight of the body caused by unbalance correction.

4. Apparatus for performing the method according to any one or more of the preceding claims with a tool for correcting the unbalance and means for controlling the tool in synchronism with the rotary speed of the workpiece being balanced, characterised in that the means for controlling the tool includes a contoured body which is adjustable in relation to the workpiece requiring balancing by being turned about a rotation axis, and is rotatable in synchronism with the workpiece being balanced, said body having on its surface an axially extending line determining the maximum change that can be effected by the tool to the surface of the workpiece, and other lines having a form differing therefrom, and in that the axial extension of the contoured body represents an unbalance range and controls the machining tool during rotation of the workpiece and said contoured body.

5. Apparatus as claimed in Claim 4, characterised in that the axially-extending line is an envelope line of the contoured body.

6. Apparatus as claimed in Claim 4 or 5, characterised in that the contoured body is mounted on a shaft and is angularly and axially adjustable relative to the shaft.

7. Apparatus as claimed in any one of Claims 4-5, characterised in that the contoured body has an angle scale on its periphery and the shaft has an axially extending reference scale.

8. Apparatus as claimed in any one of Claims 4-7, characterised in that the axis about which the contoured body can be turned is parallel to the axis of rotation of the workpiece.

9. Apparatus for performing the method according to any one of Claims 1-3, with a tool correcting the unbalance, and means controlling the tool in synchronism with the speed of rotation of the rotary body being balanced, characterised in that the means for controlling the tool includes a sine generator which is rotatable in locked phase relation with the rotary body, the sinusoidal output signal from the sine generator is combined with a signal electrically representing the unbalance, and in a computerthe contour of a correction plane in the rotary body being balanced and the pre-set value deviating from the rotary body contour are stored with the combined signals and control the machining tool.

10. Apparatus as claimed in Claim 9, characterised in that the generator is a sinecosine generator coupled in locked-phase relation with the rotary body being balanced, and in that the output signal therefrom is combined with the signal electrically representing the unbalance.

11. Apparatus for performing the method according to any one of Claims 1-3, with a tool correcting the unbalance, and means controlling the tool in synchronism with the speed of rotation of the rotary body being balanced, characterised in that through one control impulse per revolution of the rotary body being balanced, a sine-cosine generator produces a signal at the same frequency as the work-piece rotates, that the output signal from said generator is combined with the signals corresponding electrically to the unbalance, in that in a computer the contour of a correction plane in the workpiece and the predetermined value deviating from the contour of the workpiece are stored with the combined signals and control the machining tool.

12. Apparatus for performing the method according to any one of Claims 1-3, with a tool correcting the unbalance, and means controlling the tool in synchronism with the speed of rotation of the rotary body being balanced, characterised in that in dependence on a reference mark on the workpiece an impulse source emits impulses in locked-phase relation with the rotary body being balanced, in that the impulses are combined with the signals which represent the unbalance electrically in magnitude and position, and in that in dependence on the contour of at least one correction plane in the workpiece being balanced, the signals thus combined control a machining tool for that plane.

13. Apparatus as claimed in Claim 12, characterised in that the contour of the correction plane is mechanically sensed.

14. A process for reducing imbalance in a rotational body having a surface which is reacted upon by a tool to obtain an ultimate shape for the surface in accordance with the relative distance of the tool from the surface, comprising the steps of predetermining a minimum limit for the distance, and operatively traversing the tool relative to the body toward reducing the inbalance whereby the ultimate shape of the surface of the body is governed by the imbalance and minimum limit for the distance.

1 5. A process as set forth in Claim 14, wherein the body has an original surface, a portion of the body reacted upon by the tool having an altered surface, and the altered surface being smoothly blended with the original surface in at least one co-ordinate direction.

1 6. Apparatus for reducing imbalance in a rotational body having a surface which is reacted upon by a tool in accordance with the relative distance of the tool from the surface to obtain an ultimate shape for the surface, comprising a contoured body of rotation corresponding to the rotational body having the inbalance, synchronous drive means rotating the body of rotation and contoured body of rotation in coordinated phase relationship, drive means connected to the tool for traversing the tool relative to the body of rotation toward reducing the inbalance, control means connected to the drive means for governing the relative distance of the tool from the surface, scanning means operatively connected with the contoured body and axially movable relative thereto, and inbalance input means connected to the control means for governing the relative distance of the tool from the rotational body to reduce the imbalance, and the scanning means also being connected to the control means whereby the contoured body establishes a minimum distance between the tool and the rotational body in conjunction with the distance established by the inbalance input means.

1 7. Apparatus for reducing imbalance in a rotational body having a surface which is reacted upon by a tool in accordance with the relative distance of the tool from the surface to obtain an ultimate shape for the surface, comprising drive means connected to the tool for traversing it relatively to the body of rotation toward reducing the imbalance, control means connected to the drive means for governing the relative distance of the tool from the surface, imbalance input means connected to the control means for governing the relative distance of the tool from the surface of the rotational body in accordance with the imbalance, limit input means connected to the control means for providing a limit control signal establishing a predetermined minimum distance between the tool and the rotational body, and the control means being constructed and arranged to combine the imbalance input and the limit input whereby the ultimate shape for the surface is a function of the inbalance being reduced and the predetermined minimum distance between the tool and the surface.

1 8. An apparatus for reducing imbalance in a rotational body having mass and a surface which is reacted upon by a tool to obtain an ultimate shape of the surface in accordance with the relative distance of the tool from the surface, the body having an original surface, a portion of the body reacted upon by the tool having an altered surface, the altered surface being smoothly blended with the original surface in at least one co-ordinate surface, the mass of the body also being altered while the imbalance is being reduced, comprising a control device synchronously connecting the tool with the rotational speed of the body whose imbalance is being reduced, the control device emitting a control pulse per revolution of the rotational body, a sine-cosine generator emitting voltages having the same frequency as the rotational body, imbalance signalling means generating imbalance voltages electrically representing the imbalance, summing means combining the electrical voltages from the sine-cosine generator with those emitted from the imbalance signalling means, a computer circuit storing the contour of a correction plane of the rotational body, and a derived value deviating from the contour of the rotational body stored with the combined voltages whereby the tool is controlled.

1 9. An apparatus as set forth in Claim 1 6, wherein a reference mark is provided on the surface of the rotational body, a pulse transmitted locked in phase with the rotational body, summing means combining the pulses from the pulse transmitter with the voltages electrically representing the imbalance in accordance with their position and magnitude whereby the voltages are combined in accordance with the contour of at least one correction plane of the rotational body to control the tool for such correction plane.