Note: Descriptions are shown in the official language in which they were submitted.
GOK 103-107
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
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GOK 103-107
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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
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GOK 103-107
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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
GOK 103-107
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.
GOK 103-107
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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
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GOK 103-107
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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
GOK 103-107
-7
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
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GOK 103-107
--8--
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~ ~
GOK 103--107
_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
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GOK 103-107
--10--
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
GOK 103 107
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
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GOK 103-107
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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.
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GOK 103-107
-13-
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.
