Note: Descriptions are shown in the official language in which they were submitted.
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The present invention concerns a control systern for
machine tools or the like, and more particularly to a
control system for machine tools which regulate spindle
bearing lubrication in accordance with bearing ternpera-
ture and which regulates the spindle bearing preload
and the spindle axis feedrate in accordance with spindle
bearing thrust to assure optimum machine tool performance.
Modern machining practices dernand rnachine tools
with rotary spindles for rotating a cutter having greater
ranges of operation. Such spindles are capable of being
driven at higher rates of rotation while at the same time
they are required to accept heavy loads at slower speeds.
The present invention is directed toward achieving these
improved results.
The cutter carrying spindles in machine tools are
rotatably supported by the machine in antifriction bear-
ings which have to be preloaded in order to support the
spindle with the precision required for machine tool
accuracy. In the past it has been the practice to apply
the preload to the bearings during the original assembly
and retain such load for all operations. However, in
order to meet the expanding requirements for machine
tool spindle operations, the present invention provides
for automatically varying the preload on the spindle
bearings in response to the varying conditions under
which the spindle is being operated.
When the spindle is being rotated at the higher
speeds with lighter loads, the preload pressure is auto-
matically relieved for reducing the tightness of the
bearing to enable it to be operated at the high speed
without excessive heating. On the other hand when the
spindle is operating at a relatively low speed with
higher cutting forces being developed, the preload pres-
sure is increased in order to maintain the desired
accuracies despite the high loading. This arrangement
contributes substantially to increasing the range of
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operation of machine tool spindles~
Further efficiency in the operation of a machine
tool spindle can be achieved by lubricating the spindle
antifriction bear:ings with an oil mist applied to the
bearing and varylng the mixture of oil and air in such
mist in response to the bearing temperature. The pre-
sent invention includes means for constantly monitoring
the bearing temperature and automat:ically varying the
ratio of air to oil in the mist to accommodate the
]0 conditions. As the temperature of the bearings
increases the amount of oil in the mixture is increased
and as the temperature drops the amount of oil is
reduced so that the mixture contains a higher percent-
age of air. Thus, the oil mist applied to the bearings
is ideal for all conditions to further improve the
operation of the spindle.
In accordance with the invention there is provided
an apparatus for rotatably supporting a member journaled
in a frame by antifriction bearings; sensing means in
position to sense the thrust imposed upon said rotatable
member and produce a signal representing the sensed
thrust; pressure means disposed to apply a pressure to
said bearings for preloading the bearings; adjusting
means connected to regulate said pressure for varying
the preloading of said bearings; a control connected to
receive the signal from said sensing means representing
the thrust on the rotatable member; and means connect-
ing said control to said adjusting means for regulating
the oper~ation of said adjusting means in accordance with
the signal received from said sensing means so that the
preload pressure applied to said bearings is continually
adjusted to suit the prevailing conditions.
In a particu]ar embodiment thrust sensors are
mounted in position to measure both the axial and
radial thrusts on the spindle. The sensors produce
electrical signals representing the amount of thrust
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measured and these signals are transmitted to a
control. The control in turn operates a pressure
regulator that regulatrs the hydraulic pressure to a
piston and cylinder mechanism which is coupled to apply
the pressure to one of the races of the antifriction
bearings for varying the preloading of the bearing.
To further improve the efficiency cf the spindle,
the temperature of` the bearings is rnonitored by
thermi~stors or other suitable ternperature sensitive
electrical elements. The thermistors produce an
electrical signal representing the temperature and the
signal is transmitted to a control which regulates an
oil valve and an air valve for controlling the amount
of air and oi] f]owing to an atomizer which sprays the
mist onto the bearings. With this arrangement the
ratio of air to oil is regulated so that the lubrication
is maintained at an ideal level for all conditions of
operation.
Ihe featuresof the invention believed to be novel
are set forth with particularity in the appended claims.
The invention itself, however, both as to organization
and the method of operation, together with further
objects and advantages thereof, may best be understood
by reference to the following description taken in
conjunction with the accompanying drawings in which:
Fig. 1 is a block diagram of the control apparatus
of the present invention;
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Fig. lA is an alternate embodiment of the lubrication
system of Fig. 1;
Fig. 2 is a graphical representation of how bearing
temperature varies in accordance w:ith the percentage volume of
oil in the oil-air mist lubrication mixture;
Fig. 3 is a side elevational view of a high speed machine
tool spindle of a machine tool;
Fig. 4 is an enlarged view of a portion of the high speed
spindle illustrated in Fig. 3; and
Fig. 5 is a block diagram of a modification of the control
apparatus of Fig. 1 for controlling a machine tool embodying
the spindle of Eigs. 3 and ~.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Fig. 1 illustrates a block diagram of a control appara-
tus 10 for rotating machinery, such as a machine tool, for
regulating the lubrication supplied to machinery bearings 12
which journal a rotating machinery member such as a shaft 14
to a stationary member (not shown). Control apparatus 10
comprises a temperature sensor 16, typicalLy configured of a
thermistor or the like, mounted adjacent to bearing 12 for
providing an electrical output signal indicative of bearing
temperature. In certain instances, it may be desirable to
employ a pair of thermistors to measure the temperature of the
fluid (either air or oil, for example) entering and exiting
the bearing for determining bearing temperature exactly. The
output signal of thermistor 16 is supplied to an analog to
digital (A/D) converter 18 which converts the analog thermistor
output signal into a digital signal which is supplied to an
electronic processing circuit 20, typically a microcomputer.
Microcomputer 20 is responsive to the output signal of A/D
converter 18, and in accordance therewith, determines the
proper volume of lubrication fluid supplied by lubrication
apparatus 22 to lubricate beariny 12.
In the presently preferred embodiment, lubrication system
22 is configwred to provide an oil-air lubrication mist mixture
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and includes a pair o electrically controlled valves 24a and
2~b, each valve being electrically connected to and controlled
by microcomputer 20. Valve 24b is coupled between a supply of
pressuri~ed air 25b and an atomizer 26 and con'crols the amount
or volume of air admitted to atomizer 26 in accordance with
signals from microcomputer 20. Valve 24a is coupled between a
supply of pressurized lubricating oil 25a and atomizer 26 and
controls the volume of oil a~mittecl to the atomizer in accor~
dance with signals from microcomputer 20. Typically, each of
valves 24a and 24b comprises an ASC0 model TX8262208 valve
manuactured by Automatic Switch Company, Florheim Park, New
Jersey. Atomi~er 26 atomizes the oil supplied thereto from
oil supply 25a through valve 24a with air supplied thereto
from air supply 25b through valve 24b to produce the oil-air
mist mixture which is sprayed on bearing 12.
A better understanding of how microcomputer 20 regulates
the percentage volume of oil in the oil~air lubrlcation mist
mixture may be gained by reference to Fig. 2 which illustrates
the relationship between the percentage volume of oil in the
oil-air lubrication mist mixture and the bearing temperature.
As can be seen, the relationship between the percentage volume
of oil in the lubrication mist mixture and the bearing tempera-
ture is concave upwards, having a relative minimum identified
by the point X. With the knowledge that the relationship
between the perc~ntage volume of oil in the lubrication mist
mixture and the bearing temperature is concave upwards, micro-
computer 20 is programmed to calculate the ratio of the rate
of change of bearing temperature to the rate of change of the
percentage volume of oil in the lubrication mist mix-ture
( T %~. If T is made sufficiently small, then dT/d%, the
first derivative of the bearing temperature-~ oil relationship
can be approximated. Since, from elementary calculus, the
first derivative (dT/d%) of the beariTlg temperature-% oil
relationship is representative o the slope of the curve, and
since the slope of the bearing temperature-% oil curve of
Fig. 2 is equal to zero at the point X on the curve, it follows
that dT/d% is zero at the relative minimum (point X) on the
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curve of Fig. 2. From the calculated va.lues of dT/d%, micro-
computer 20 can determine the percentage volume of oil neces-
sary to maintain minimum beariny temperature.
The process by which microcomputer 20 regulates the ~
volume of oil in the oil-air bearing lubrication mist mixture
is a dynamic rather than a static process. Since bearing
temperature does not remain constant, but varies in accordance
with such factors as shaft speed and bearing load, among
others, microcomputer 20 continually monitors bearing tempera-
tures so that the % volume of oil can be continuous]y reyulated
to assure proper bearing lubrication. Microcomputer 20's fast
processing speed allows it to respond to very rapid incremented
changes in bearing temperature, thereby assuring proper bearing
lubrication at all times.
It may be desirabLe in some applications to lubricate the
rotating machinery bearings with a single lubricating fluid
such as oil or air in contrast to lubricating the bearings
with a mixture of lubricating fluids such as air and oil.
This may be readily accomplished by employing the alternate
lubrication system embodiment 22' illustrated in Fig. lA in
place of lubrication system 22 in Fig. 1. Lubrication system
22 7 comprises a single electrically controlled valve 24' which
is coupled to a supply of pressuriæed lubrication fluid 25'
(which fluid may be either a gas, such as air or a liquid such
as oil~ for regulating the volum2 lubricating fluid supplied
to bearing 12 (Fig. 1) in accordance wlth signals from micro-
computer 20 (Eig. 1). The volume of lubrication fluid carried
by valve 24' from lubricating fluid supply 25' is controlled
by microcomputer 20 in accordance wi th bearing ternperature in
exactly the same manner in which microcomputer 20 controls
valves 24a and 24b of lubrication system 22 of Fig. 1, since
the bearing temperature wlll vary in accordance with the
volume of fluid supplied from lubrication supply ~5' in exactly
the same way the bearing temperature varies in accordance with
the percentage volume of oil as depicted in Fig. 2.
The control apparatus of Fig. l is well suited for use
with numerically controlled machine tools for automatically
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reyulating spindle bearing lubrication. The control apparatus
allows higher machine tool spindle speeds and hlgher spindle
loads to be reached than would otherwise be possible. ~'urther,
as detailed hereinafter, the control apparatus described above
can be modi1ed to control not only machine tool spindle
bearing lubrication but the spindle bearing preload and the
spindle axis feedrate which allows attainment of still highar
spindle speeds and spindle loads as well. This may be better
understoocl by reference to Figs. 3 and 4 which illustrate a
portion of a high speed spindle assembly 100 of a numerically
controlled r~lachine tool. Spindle assembly 100 is typically
disposec3 in a frame such as the machine tool spindlehead (not
shown), which is linearly movable on the machine tool along an
axis at a rate referred to as the spindle axis feedrate. The
high speed spindle assembly 100 comprises a spindle 110 having
an axially extending bore therethrough dimensioned to receive
the shank 112 of a cutting tool therein. Spindle 110 is
in~egral with the shaft of a motor 114 comprised of a stator
114a and a rotor 114b. A key 115 extending from spindle 110
engages a complementary keyway in the rotor (not shown) to
lock the spindle to the rotor so that spindle 110 rotates
co-jointly with rotor 114b.
Spindle 110 extends through the case 116 of motor 114 and
is journaled to the front and rear of motor case 116 by front
and rear spindle bearings 118 and 120, respectively, which are
each carried on spindle 110 adjacent to a separate one of the
ends thereof. Front spindle bearing 118 comprises a pair of
ball bearings 124a and 124b, respectively, which are carried
on spindle 110 hetween a shoulder or flange 126 and threads
127. A nut lZ8 engages threads 127 to urge the lower races of
ball bearings 124a and 124b against shoulder 126. Adjusting
the displacement o nut 128 from shoulder 126 serves to vary
the force against, or the preloading on, the lower ball bearing
races~ The upper races of ball bearings 24a and 124b are
uryed against a vertical wall in motor case 116 by an annular
ring piston 129 which is reciprocally disposed in a piston
chamber 130 wi thin a front bearing cap 132 fastened to motor
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case 116 by bolts 134 which are disposed through passages
spaced e~uidistantly about the bearing cap circumference.
The amount of force or preloadiny on the upper races of
ball bearlngs 124a and 124b varies ln accordance with the
pressure of hydraulic fluid admitt:ed into piston chamber 130
through a connecting pa~sage 136 f rorn a source of hydraulic
1uid ~not shown) which is couplecl to connecting passage 136
through a pressure regulator (d~sc:ribed hereinafter). The
pressure of hydraulic fluid admitt:ed through connecting passage
136 from the source of hydraulic fluid is varied by the pres-
sure regulator in accordance with radial and axial spindle
bearing thrust. To this end, two pairs oî spindle thrust
sensors 137a and 137b, respectively, whose sensors are typi
cally comprised of a magnetic or capacitive transducer, are
dispvsed within bearing cap 132 adjacent to spindle shoulder
126 to measure radial and axial spindle thrust, respectively.
Referring now to Fig. 4, which is an enlarged fragmentary view
of a portit~n OI the spindle assembly ilLustrated in Fig. 3, to
measure radial spindle thrust, one thrust serlsor of thrust
sensor pair 137a i5 vertically disposed in bearing cap 132
adjacent to flange 126 above the axis 138 OI spindle 110; the
other thrust sensor (not shown) of thrust sensor pair i37a is
vertically disposed in bearing cap 132 so as to be adjacent to
1ange 126 b low the spindle axis. To measure axial bearing
thrust, one thrust sensor of thrust sensor pair 137b is hGri-
zontally mounted in bearing cap 132 adjacent to the flange so
as to be above the spindle axis while the other thrust sensor
(not shown) of thrust sensor pair 137b is horizontally mounted
in the bearing cap adjacent to flange 126 below spindle axis
138. The thrust sensors of thrust sensor pairs 137a and 137b
are connected differentially to produce a signal varying in
accordance with radial and axial spindle thr~st, respectively.
The output signal produced by each of thrust sensor pairs
137a and 137b, which varies in accordance with radial and
axial spindle thrust, respectively, is supplled to a control
apparatus 2t)0 illustrated in Fig. 5 which controls the spindle
axis rate and bearing preload as well as the percentage volume
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of oll in the oil-air lubrlcation mist mixture. Control
apparatus 200 comprises an analog to digital (A/D) converter
218, for converting the analog signal from each of thrust
sensor pairs 137a and 137b (Figs. 3 and 4) into a digital
signal which is transmitted to a microcomputer 220. Micro-
computer 220 is respon~ive to the output signals from A/D
converter 218 and, during intervals when the radial and axial
thrusts on spindle 110 (Fig. 3) are large, as will likely
occur when spindle speeds are low and the force on the cuttin~
tool is disposed within the spindle is large, microcomputer
220 modulates the output signal supplied to a pressure regu-
lator 225, coupled between the source of pressurized hydraulic
fluid and passage 136 (Fig. 3) to increase the pressure of
hydraulic fluid admitted through connecting passage 136 to
piston chamber 130 (Fig. 3) so as to increase the force of
piston 130 against the upper races of bearings 124a and 124b
(Fi~. 3), accordingly, thereby increasing bearing preload to
reduce bearing chatter. In addition, during intervals of
large radial and axial spindle thrusts, microcomputer 220 also
supplies an output signal to the spindlehead axis drive motor
ampli~ier (not shown) to reduce the axis feedrate accordingly.
At high spindle speeds when the force on the cutting tool held
in spindle 110 (Fig. 3) is likely to be much lower, thereby
resulting in lower radial and axial thrusts on spindle 110
(Fig. 3), microcomputer 220, in response, commands pressure
regulator 225 to reduce the pressure of fluid admitted into
piston chamber 130 through connecting passage 136, thereby
reducing the preload on bearings 124a and 12gb (Fiys. 3 and 4).
During this same interval of lower radial and axial spindle
bearing thrusts, microcomputer 220 also supplies an output
signal to the spindlehead axis drive system motor amplifier to
command an increase in the spindle feedrate accordingly. In
this way, microcomputer 220 dynamically regulates the preload-
iny on spindle bearings 124a and 124b.
In addition to being responsive to radial and axial
spindle thrust, microcomputer 220 is also responsive to machine
tool spindle speed, as sensed by a tachometer, or as determined
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by the machine tool control system. During intervals when
machine tool spindle speed is increased, it may be desirable
to decrease bearing preload. This is readily accomplished by
microcomputer 220 in response to an increase in magnitude o
the speed signal supplied thereto. Conversely, when spindle
speed decreases, microcomputer 220 increases the volume of
~luid admitted by the pressure re~llated into piston chamber
130 (Fig. 4) through connecting passage 136 (Fig. 4) to in-
crease bearing preload.
Referring back to Fig~. 3 and 4 jolntly, a lubrication
passage 139 is disposed through bearing cap 132 to carry an
oil-air lubrication mist mixture to bearings 1~4a and 124b
from a lubrication system 230 illustrated in Fig. 5, which is
configured identically to lubrication system 22 described
previously with respect to Fig. 1. A temperature sensor 140
(best illustrated in Fig. 4) is disposed in bearing cap 132
adjacent to bearing 124a and supplies A/D converter 218 illus
trated in Fig. 5 with a signal varying in accordance with
bearing temperature. In accordance with the digital output
signal from A/D converter 218, microcomputer 220 (Fig. 5),
while regulating bearing preload and the spindle axis feedrate,
also supplies a pair of control signals to lubrication system
230 to regulate the percentage volume of oil in the oil-air
mist mixture supplied through lubrication passage 139 to
bearings 124a and 124b in the manner described previously with
respect to Figs. 1 and 2. To provide for aster lubrication
system response, microcomputer 220 (Fig. 5) utilizes the
output signals from each of thrust sensor pairs 137a and 137b
to sense variations in radial and axial thrust, respectively,
which in practice precedes changes in spindle bearing tempera-
ture. By anticipating changes in spindle bearing temperature
prior to their occurrence, microcomputer 220 is better able to
regulate spindle bearing lubrication.
Spindle 110 has a pair of tool gripping collets 140a and
140b, which are each integrated to a separate one of the
spindle ends, respectively. Each of tool gripping collets
140a and 140b, respectively, is urged radially inward to grip
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shank llZ of the cutting tool by a separate one of collet nuts
142a and 142b which are each ln threaded engagement with
spindle llO adjacent to a separate one of collets 140a and
140~. To prevent the collet nut at each end of the spindle
from loosening during high speed rotation of spindle 110, the
spindle carries a pair of hollow bore collet nut drivers 145a
and 145~, khe collet nut drivers each being carried on the
spindle adjacent to a separate one of the spindle ends so as
to be coaxial with, and adjacent to, a separate one of collet
nuts 142a and 142b, respectlvely. The bore through each
collet nut driver is dimensioned to receive a respective one
of the collet nuts. The interior surface of the bore through
each collet nut driver, such as collet nut driver 145a, for
example, carries a set of splines 146a, which splines are
complementary to the exterior splines 146b carried on the
rearward end of each o the collet nuts, such as collet nut
142a, and are complementary to the exterior splines 146c
carried on each end of spindle 110 adjacent to a separate one
of collet~ 140a and 140b. Each collet nut driver, such as
collet nut driver 145a, is slidable along the spindle between
a first or inwardmost position at which location the collet
nut driver is adjacent to an associated one of bearing caps
132 and 160, respectively, and a second or outwardmost position
at which location the collet nut driver is distal from the
corresponding bearing cap. When the collet nut driver is
displaced along the spindle to its first or inwardmost posi-
tion adjacent to its corresponding bearing cap, the splines on
the interior surface of the collet nut driver engage th~
exterior splines on both the collet nut and the spindle, thus
preventing the collet nut from rotating independently of the
spindle. When the collet nut driver is slid outwardly along
the spindle away from its corresponding spindle bearing cap to
its second position, then the splines on the interior surface
of the collet nut driver engage only the exterior splines on
the collet nut thus permitting the collet nut and its associ-
ated collet nut driver to be threaded off of the corresponding
collet at the end of the spindle. Each collet nut driver is
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restralned from axial movement, once slidably moved to its
inw~rdmost position to engage both the spindle splines and the
splines on the corresponding collet nut, by a pair of Vlier
screws 1~8, only one of which is shown, the Vlier screws being
threaded into the spindle to extend radially therefrom so that
each engages a circumferential groove circumscribiny the inner
bore of a corresponding collet nut driver.
Proximity switches 150a and l!;Ob are each mounted in a
separate one of front and rear bearing caps 137. and 160,
respectively, so that each switch :is adjacent to a separate
one o front and rear collet nut drivers 145a and 145b, respec-
tively. Each of proximity switches 150a and 150b, respective-
ly, is actuated when a separate one of collet nut drivers 145a
and 145b, respectively, is slidably moved inwardly to be
adjacent to a separate one of bearing caps 132 and 160, respec
tively, to jointly engage a separate one of collet nuts 1~2a
and 142b, respectively, with the spindle~ When actuated, each
proximity switch supp]ies microcomputer 220 with a signal
indicative of the engagement of the corresponding collet nut
and the spindle. Should one of collet nut drivers 145a and
145b be slldably moved outwardly causing a corresponding one
of proximlty switches 150a and 150b, respectively, to cease
being actuated, then microcomputer 220 supplies an inhibit
signal to the drive amplifier controlling motor 114 to prevent
spindle rotation. In this manner, damage to the cutting tool
as well ~s the machine tool operator is prevented when -the
cutting tool is not firmly held in the spindle.
It is apparent that the present invention provides a
novel arrangement for automatically varying the preloading of
spindle bearings to accommodate the operating conditions being
encountered. In addition, the lubrication to the bearings is
automatically controlled to provide the ideal lubrication for
the existing situation to further improve the efficiency of
-the spindle.
Although the illustrative embodiment of the lnvention has
been described in considerable detail for the purpose of
disclosing a practical operative structure incorpora-ting the
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i.nvention, it i5 to be understood that the particular apparatus
shown and described is intended to be illustrative only and
various novel featuxes of the invention may be incorporated in
other structural forms without departing from the spirit and
scope of the invention as defined :in the subjoined claims.
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