CA1185681A

CA1185681A - Gap control system

Info

Publication number: CA1185681A
Application number: CA000408965A
Authority: CA
Inventors: Rhual L. Guerguerian
Original assignee: Dominion Engineering Works Ltd
Current assignee: Dominion Engineering Works Ltd
Priority date: 1982-08-06
Filing date: 1982-08-06
Publication date: 1985-04-16

Abstract

GAP CONTROL SYSTEM
ABSTRACT OF THE DISCLOSURE

The gap between the stator and the rotor of a gearless type drive, (i.e. where the rotor forms part of and is rigidly connected to the driven part of the equipment and wherein the equipment is mounted for rotation about an axis of rotation on a pair of spaced apart bearings) is controlled by sensing the clearance between the rotor and the stator at spaced locations about the stator and adjusting the position of the axis of rotation of the equipment by positioning means in at least one of the bearings controlled in accordance with the sense location of the rotor to maintain the clearances substantially constant.

Description

GAP CONTROL SYSTEM
FIELD OF THE INVENTIOM
The present invention relates to a gap control for a gearless drive, more particularly the present invention relates to a gap control wherein bearing support clearance is adjusted to maintain a desired clearance between the rotor and the stator providing the drive to the equipment.
BACKGROUND OF THE INVENION
Much consideration has been given recently to substituting gearless drives for the conventional ring gear and pinion drives used on heavy equipment such as grinding mills where the torque loads on the pinion are extremely high. One such device is shown for example British Patent Number 1,290,069 published September 20, 1972.
An inherent problem associated with such gearless drives is maintenance of uniform relatively small clearances between the rotor and stator since the efficiency of the drive motor is in part determined by these clearances. The British Patent attempted to solve this problem by mounting of the mill on huge roller bearings extending completely about the maximum periphery of the mill, i.e. instead of mounting the mill on trunnions the huge roller bearings were used and the rotor was connected to the drum periphery immediately adjacent one of the ~8~

_~_ bearings. Such a solution severely limits the type of mill that might use gearless drives i~e. it does not solve the problem of incorporating a gearless drive on trunnion supported mill.
The principal relied on in this application is simply increasing the rigidity of drum structure adjacent the bearing to maintain very limited change in position of the rotor.
It is also well known to support such a mill or piece of heavy equipment on adjustable bearings the position of which m~y be changed, for example, by means of adjustable bearing pads as described in United States Patent Number 3,984,159 issued October 5~ 1976 to Jenness, or U.S. Patent Number 3,909,080 issued September 30, 1975 to Hallnor, et al. The latter patent discloses a hydrostatic type bearing wherein the position of the pads may be changed by a mechanical mechanism.
German Pat~nt Number 2,049,402 issued April 29, 1971, also diæcloses hydrostatic bearing with bearing pads spaced around the rotating member. This particular device provides means for adjusting the pressure exerted by each group of pads on the rotating member independently of the other group and also in conjunction therewith.
In all of the above di~cussed adjustable bearings the adjustment is generally made once at or before start up for each major change in mill loading and there is no continuous monitoring.
Thus means are available for changing the position of the bearing or alternatively the forces applied to the journal by the bearing in both a hydrostatic bearing or a hydrodynamic type bearing.
BRIEF DESCRIPTION OF THE INVENTION
~ .
It is an object of the present invention to provide a method and apparatus for controlling the gap or clea~ance between a rotor and a stator of a gearles~ drive applied to heavy equipment that tends i8~.

to be distorted in operation.
Broadly the present invention comprises a machine mounted for rotation about an axis of rotation on a pair of spaced bearings, a rotor of an electric motor drive rigidly connected to said machine, a stator surrounding said rotor, means to substantially continously sense the clearance between the said stator and rotor at spaced locations about the periphery of said stator thereby to determine the position of said rotor relative to said stator, positioning means associated with at least one of said bearings and ad~pted to adjust the position oE said axis of rotation, control means controlling said positioning means to maintain clearance between said rotor and ætator as measured by said sensing means within pre-set limits.
The positioning means may comprise means for adjusting the oil pressure at discrete locations around a bearing and thereby adjusting the position of the axis of rotation or means for bodily moving a bearing shoe to adjust the axis of rotation.
In some cases it may be desirable to utilize proximitors within the bearing to ensure that the required amount of lubrication is always present in the bearing and that the adjustments made by changing bearing pressure locally does not result in damage to the bearing.
As the equipment is s~lpported on a pair of spaced bearin~s the positioning means may be provided on one or more of the bearings and each of these positioning means be operated individually or in concert.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features, objects and advantages will be evident from the following detailed description of the prefered embodiments of the present invention taken in conjunction with the accompanying drawings in which -Figure 1 is a sche~atic isometric view ofone type of mill equipped with a gearless drive.
Figure 2 is a perspective view of one type of hydrostatic bearing incorporating detectors for determining the position of the bearing runner in the bearing and/or the thickness of the oil film in the various circumferential positions around the bearing.
Figure 3 schematically illustrates control arrangement that may be used with the present invention.
Figure 4 is a schematic layout of a control arrangement for controlling one or more hydrostatic bearings to adjust the position of the axis of rotation and thereby the clearance hetween the stator and rotor~
Figure 5 schematically illustrates one technique for adjusting the position of bearing shoes relative to the bearing runner to thereby adjust the position of the bearing runner and the axis of rotation of the mill to adjust the clearance.
Figuxe 6 schematically illustrates a temperature control to adjust the position of the runner in the bearing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 is a schematic ilustration depicting a grinding mill 10, one particular application of the present invention, supported on spaced trunnions 12 and 14 which in turn are supported by bearing structures (not shown in Figure 1). A
torque cone 16 extends from the trunnion 14 and is connected by suitable means, not illustrated, to a rotor 18 orming part o the electrical drive of the mill.
The rotor 18 is driven by a stator 20 that is anchored in some suitable manner to resist the torque generator by rotation of the mill 10.

Suitable sensors such as proximity sensors, which will deter~ine the spacing bet~een the rotor 18 and stator 20, are provided at space locations around the stator 20. Such pro~imity sensors have been ~chematically indicated at 22, 24, 26 and 28 spaced at 90 degree intervals around the stator with the sensors 22 and 26 being positioned in the vertical plane and 24 and 28 in a horizon~al plane. At least 4 sensors normally will be used to define the location of the rotor relative to the stator, however, if desired, more such sensors may be used and in an economical version fewer sensors may be used, for example a pair of sensors spaced 90 degress apart will giv~ some indication o-f the relative position of the rotor and stator and in some cases even one such proximity sensors could be used, however the accuracy of this type of equipment would be limited and for most practical operations 4 such sensors will normally be used.
Each of the sensors send out instantaneous signals defining the specific clearance between the rotor and stator at the location of that particular sensor at that particular timeO
This information is supplied to a suitably programmed computer and it i8 a simple matter to determine the relative position of the rotor and stator.
Each of the two trunnions 12 and 14 are supported in suitable bearings. These may be the static type bearings or the dynamic type bearing, i.e.
hydrostatic or hydrodynamic bearings. Figure 2 shows one form of hydrostatic bearing. Figure 5 schematically shows an arrangement that could be used with either a hydrodynamic or hydrostatic bearing.
In the arrangement shown in Figure 2 sensors are incorporated into the bearing so that they can monitor and control the mill bearing clearance, however, ~uch sensors are not essential to the ~p~

~6--operation of the device it being only essential to be able to controllably position the trunnion supported by the bearing and thereby adjust the position of the rotor 18 (without damage to the mill~.
When it is desired to know precisely the location of the trunnion in a bearing runner of a hydrostatic hearing, a system such as that illustrated in Figure 2 may be used. In that arrangement a bearing element 30 is provided with sensors that may sense the proximity of the trunnion and if desired the oil pressure in the bearing pockets 34 and 36 on the leading and trailing side of the bearings respectively (assuming trunnion rotation in the counterclockwise direction).
Proximity sensors 38 and 40 are positioned preferably at diagonally opposite sides of the trunnion on a horizontal line extending across the trunnion preferably intersecting the axis of rotation. Obviously, since the axis of rotation moves, they cannot always be precisely aligned with the axis of rotation. These proximity sen~ors 38 and 40 indicate the location of the trunnion relative to the sensors in the horizontal direction.
Proximity sensors 42 and 44 are positioned one at the mill sida 46 and the other at the outer side of the bearing and in a vertical plane passing along the axis of the bearing. These sensors may be used to determine the slope o the trunnion across the bearing and in many cases may simply be averaged to give the average bearing clearance of the trunnion in the vertical direction.
Suitable pressure sensors 48 and 50 may be provided within the bearing recesses 34 and 36 respectively. Similarly te~perature sensors 52 and 54 may also be provided in the bearing recessesO The pressure sensors obviously sense the oil pressure in the bearing on the leading and trailing sides respectively while the temperature sensors 52 and 54 indicate the oil temperature which indicates oil viscoslty.
In the preferred arrangement the bearing supporting the trunnions 12 and 14 will be equipped with the appropriate sensors as described above in relation to the bearing 30.
Referring to Figure 4 the output from each of the sensors of each of the bearings has been indicated by lines with arrows feeding into the computer 56, the vertical arrows indicating the control from bearing supporting trunnion 1~ and the horizontal arrows indicating similar inputs ~rom the bearing supporting trunnion 12.
- 15 As indicated in Figure 3 the output from the proximity sensors 22, 24, ~6 and 28 which determine the radial clearance between the rotor and stator are fed into the computer control 56 via lines designated at 22C, 24C, 26C and 28C respectively. Similarly the output from the various sensors in the bearing supporting trunnion 14 have been indicated (by vertical lines entering the computer 56~ using the same number as used to designate the respective sensor followed by the letter A and the output from the bearing supporting trunnion 12 have been indicated in a similar manner but with the letter B following each numerical designation.
The computer 56 will be programmed in any well known manner to determine the position of the rotor 18 relative to the stator 20 and to determine the bearing clearances in the two bearings as well as the oil pressures and oil temperatures. This information in hand it is a simple matter for a properly programmed computer to adjust the bearing to maintain clearances sensed by the sensors 22, 24, 26 and 28 witllin pre-set ranges by adjusting the axis of rotation of the equipment in a suitable manner. It r~

will be apparent to those skilled in the art that the axis of rotation will, due to the tumbling action in the mill, travel in an orbit and it is the function of the control to keep this orbit within acceptable limits. If the limits are exceeded the mill automatically will be shut down by built in safety features (not illustrated).
The computer may be programmed based on known computer technology combined with practical experience with a mill to recognize a trend and react to the trend rather than an event.
Figure 4 shows one technique for adjusting the axis o rotation of the equipment, in this case a grinding mill. In this arrangement oil is pumped by the sump 55 via a suitable pump 58 to distributing lines to the various oil recesses in the two bearings designated 12A and 14A for the trunnions 12 and 14 respectively. Suitable flow distributing equipment designated at 60, is used to distribute the flow from a main positive displacement supply pump 58 as required to each of the re~esses 34 and 36 of each of the bearings 12A and 14A via the lines 62, 64, 66 and 68 respectively. The required flows to the bearings are calculated when the mill is designed and the flow to each bearing pocket is adjusted accordingly.
The actual oil pressures in the pockets 34 and 36 and the bearings 12A and 14A are controlled by pressure relief valves 70, 72, 74 and 76 connected to the lines 62, 64, 66 and 68 respectively. These pressure relief valves are respectively controlled by controlled lines WXYZ shown in dotted lines in Figures 3 and 4 which control the relief pressure and thus the actual pressure in the pocket to which the line controlled by relief valve is connected. Relief flows from these relief valves are fed by suitable means generally indicated at 78, 80, 82 and 84 back to the sump 55. The simple supply pump 58 may be replaced 18 ~D~ ~

_9_ with individual supply purnps~ Such individual pumps may be controlled by computer 56 in the manner the relief valves would be controlled and then the relief valves 70, 72, 74 and 76 may also be eliminated (compare Figure 5 embodiment).
In the operation of the feed control system, based on the simplest mode of control, one of the bearings 12A or 14A, probably bearing 12A, will not be controlled and will simply operate in the conventional manner to support the trunnion 12. Trunnion 14 will be manipulated by changing pressures in the bearing 14A thus in the event the clearance between the rotor and stator changes significantly, i.e. assuming the rotor moves upwardly beyond its normal limit then the oil pressure in the bearing 14 in both the pocket 34 and 36 would be reduced to lower the axis of rotation and thus the rotor 200 Similarly if the clearance is diminished adjacent to sensor 22 the oil pressure on the same side of the bearing 14 will be increased and tend to shift the centre of rotation in the opposite direction. This type of control operates to maintain the clearances between the rotor and the stator within prescribed limits~
In som,e cases it may be desirable to amplify the control by putting similar controls in the bearing 12A supporting the trunnion 12. In this case it is likely the control will still be via the bearing 14A
until such time as the bearing clearances are approaching the minimum pre-set level sensed via the proximity sensors located within the bearing itself.
Under these conditions the control would then be instituted by adjusting the total pressure or the pressure on opposite sides of the bearing 12, i.e. the pockets 34 and 36 individually to shift the axis of rotation. Obviously shifting the axis of rotation of the stator in the arrangement shown in Figure 1 5~

using bearing 12A will require changes opposite to those instituted with respect to the bearing 14A for shi-fting the axis of rotation in the same direction.
It w;ll be apparent tha-t if th~ stator and rotor are located in a different location than that indicated in Figure 1 the manner in which the beaxings would be manipulated to adjust the clearance may require changing, i.e. if the stator was positioned between the two outboard of bearings 12, 14 the shifting of the trunnion in the bearings by local adjustment of the clearance would be changed.
Arrangement shown in Figure 5 may be used for either hydrostatic or hydrodynamic bearings.
The bearings have been very schematically indicated to - 15 show the principle of operation of the control. In the arrangement a trunnion 14 is supported on a plurality of bearing pads or shoes in the illustrated arrangement, 4 shoes namely two bottom shoes 86 and 88 and the pair of control shoes 90 and 92~ Each of these shoe~ as above indicated are schematically illustrated and could be either dynamic or hydrostatic bearings subject to appropriate modifications.
In the illustrated arrangement shoes 90 and 92 are supported by pistons 94 and 96 respectively that in turn are received in cylinders 98 and 100.
Hydxaulic fluid ~rom the reservoir 102 is pumped to the cylinder 98 via a positive displacement of pump 104 which is controlled by a suitable speed controller 106 which in turn is controlled by the input from th~ computer in line X, and from pump 104 via line 108 into the cylinder 98. Positive displacement pump 110 is controlled via controller 112 which in turn is controlled by the computer by a control line W, pump 110 feeds oil to the cylinder 100 via line 114.
A~suming positive displacement pumps are used each of these cylinders 98 and 100 will be connected by bleed lines 116 and 118 respectively back to the reservoir 102. Each of these :Lines 116 and 118 will be restricted so that the positive displacement pumps 104 and 110 can accurately control the pressure within the cylinders 98 and 100 respectively.
A similar arrangement can be obtained by bleeds in the lines 108 and 114 in the manner described hereinabove with respect to Figure 4. In Figure 4 the bleed val~es were adjuRtable and the flow of oil was constant whereas in Figure 5 the bleeds are constant and the flow~ of oil are adjusted to change the pressure applied to the trunnion by the two bearingsO
In the operation of Figure 5 arrangement - 15 clearances between the rotor and the stator are sensed by the various sensors 22, 24, 26 and 28 and the posit~on of the rotor relative to the stators is determined by the computer control 56. In the event the clearances are outside the pre-set ranges for any one of the sensors the pressure in the cylinders 9B
and 100 will be adjusted as required to shift the axis of rotation of the trunnion 14 and thus of the rotor 20.
In this case, assuming the trunnion 14 is to be shifted to the left in Figure 5 the output of pump 110 will be increased to increase the pressure in the cylinder 100 and thereby shit the axis of rotation of the trunnion 14 (alternatively or in conjunction therewith output of pump 104 may be adjusted (decreased).
~ he Figure 5 arrangement has been shown with respsct to a single trunnion bearing but may equally well be applied to the other trunnion bearing or to both bearings to adjust the location of the axis of rotation, thus the clearance between the rotor and stator.
As ahove indicated the specific ~ 3~ ~

-12~
instrumentation in the bearings themselves to determine oil temperature and/or pressure within the bearings and clearances of the hearings are not absolutely essential and the present invention may be practised using conventional bearings modified to adjust the pressuxe in a hydrostatic bearing while maintaining a certain minimum bearing pressure at all locations.
The use of ~he temperature sensor is simply to indicate the temperature of the oil in the bearing since the viscosity of the oil changes significantly with changes in oil tempexature and the pressure signals may require appropriate adjustments. This control may be used in conjunction with other of the - 15 sensors to detect problems in the lubricating system such as lubricating pump problems, etc.
The temperature control of the oil fed to each of the various pockets in a hydrostatic bearing may be used to adjust the position of the runner in ~0 the bearing. It is conventional in many mills to control the average temperature of the oil, with the present invention, as shown in Figure 6, the temperature of the oil in lines 120 and 122 leading to the pockets 34 and 36 respectively are individually controlled via coolers 124 and 126 respectively.
Cooling fluid is pumped to cooler 124 by pump 128 the speed o which is controlled by control motor 130 in accordance with say control signal X. Similarly cooling fluid is pumped through cooler 126 via pump 132 the speed of which is controlled by control motor in accordance with say control signal Y. As above indicated oil viscosity changes significantly with te~perature and as a result a significant change in oil temperature will affect a significant change in oil pressure in the bearing at the selected pocket 34 or 36 thereby shifting the trunnion or runner in the bearing.

~5~

Having described the invention modifications will be evident to those skilled in the art without departing fro~ the spirit of the invention as defined in the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A clearance control system for a gearless drive comprising a machine mounted for rotation about an axis on a pair of spaced bearings, electric rotor rigidly connected to said machine, a stator surrounding said rotor, a control means, means to sense the clearance between said stator and said rotor at spaced locations around the periphery of said stator and to transmit signals indicative of the position of said rotor relative to said stator to said control means, a positioning means associated with at least one of said bearings to adjust the position of a runner in said one bearing and thereby said axis of rotation, said control means controlling said positioning means in accordance with said transmitted signals to maintain pre-set clearances between said stator and said rotor.

2. Apparatus as defined in Claim 1 wherein said positioning means comprises means to locally adjust the flow of oil to said at least one bearing thereby to influence the position of said runner in said one bearing and thereby said axis of rotation.

3. An apparatus as defined in Claim 1 wherein said at least one bearing comprises at least two bearing shoes positioned on opposite sides of a vertical plane passing through the axis of rotation and wherein said positioning means comprises means for independently adjusting the pressure applied by each of said shoes.

4. An apparatus as defined in Claim 1 wherein said positioning means comprises means to locally adjust the oil temperature in said at least one bearing thereby to locally change the viscosity of the oil and influence the position of said runner.

5, An apparatus as defined in Claims 1, 2 or 3 comprising another positioning means in the other of said two bearings, means connecting said control means to said other positioning means to control the operation of said other positioning means to adjust the position of said axis of rotation.

6. An apparatus as defined in Claim 4 comprising another positioning means in the other of said two bearings, means connecting said control means to said other positioning means to control the operation of said other positioning means to adjust the position of said axis of rotation.

7. An apparatus as defined in Claims 1, 2 and 3 further comprising means to sense the location of said runner in said one bearing and generating a location signal and means for delivering said location signal to said control means.

8. An apparatus as defined in Claims 1, 2 and 3 further comprising pressure sensors in said one bearing sensing the oil pressure between said bearing and said runner supported in said bearing at spaced locations around said bearing thereby to generate pressure signals and means for delivering said pressure signals to said control means.

9. An apparatus as defined in Claims 1, 2 and 3 further comprising another positioning means in the other of said pair of bearings, means for sensing location of said runner in said one bearing and generally a location signal and feeding said location signal to said control means, means connecting said other positioning means to said control means, the position of said runner in said one bearing as determined by said location signal regulating the operation of said control means on said other positioning means.
10. Method of controlling the clearance of a rotor relative to a stator in a gearless drive to rotating equipment supported by runners rotating in bearings comprising detecting the relative location of

Claim 10 continued:
said rotor to said stator and adjusting the position of at least one of said runners and its respective bearing to maintain the spacing between said stator and said rotor within pre-set limits.