Note: Descriptions are shown in the official language in which they were submitted.
109010~
BACXGRO[iND OF TI~R INVENTION
This invention relates to automatic machining centers and has as
its principal object to provide a machining center which is so com-
pletely automated that it can be reliably operated unattended and un-
watched for an entire shift.
Numerically controlled automatic machining centers have been man-
ufactured in the past which can automatically perform a preprogrammed
sequence of machining operations. Such machining centers have a plur-
ality of tools which are stored in a tool magazine and are automatic-
1~ ally inserted into and removed from the spindle to perform the corres-
ponding machining operations. A machining center of this type is dis-
closed in U.S. Patent No. 3,704,510, issued to Robert K. Sedgwick et
al, for a "MACHINE TOOL WITH TOOL CHANGER". However, this type of
automatic machining center requires the services of a full time oper-
ator for loading and unloading the workpieces, starting and stopping
the machine for each machining cycle, cleaning out chips, inspecting
the tools for excessive wear and breakage, replacing broken or ex-
cessively worn tools, compensating for tool wear, etc.
Automatic workpiece handling apparatus has been manufactured in
the past, as disclosed in U.S. Patent No. 3,825,245, issued to John
G. Osburn et al, for a nWORXPIECE CHANGER MECHANISM FOR A MACHINE
TOOLn, and in U.S. Patent No. 3,796,163, issued to Ronald E. Meyer
et al, for a "MANUFACTURING SYSTEM", but such apparatus also requires
the services of one or more full time operators.
Apparatus for automatically inspecting tools for excessive wear
and breakage and for automatically replacing broken or excessively
- worn tools has beer devised in the past as disclosed in U.S. Patent
No. 3,817,647, issued to Jerome H. Lemelson, for a "TOOL CONTROL AR-
RANGEMENT", and in U.S. Patent No. 3,963,364, issued to Jerome H.
Lemelson, for a ~TOOL CONTROL SYSTEM AND METHOD". However, the ma-
chine tools disclosed in the Lemelson patents also require the atten-
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tion of an operator. In spite of the great strides that have
been made in automating machining operations, no prior art
machine tool or machining center is known which is capable of
operating unattended and unwatched for an entire shift or longer.
This invention provides an automatic machining center
capable of completely unmanned operation for an entire shift or
longer~ The unmanned machining center of this invention includes
a workpiece support, a spindle adapted to hold a cutting tool
and to rotate the tool, means for moving the workpiece support
and spindle relative to each other to machine a workpiece on the
workpiece support with a tool in the toolholder, a tool magazine
for storing a plurality of tools each of which is mountable in
the spindle, a tool changer for transferring selected tools from
the tool magazine to the spindle and from the spindle back to --
the tool magazine, a workpiece magazine for storing a plurality
of workpieces each of which is mountable on the workpiece support,
shuttle means for transferring selected workpieces from the work-
piece magazine to the workpiece support and for removing
finished workpieces from the workpiece support, a~d tool check-
~ .
ing means for checking to verify the presence of an unbroken
tool in the spindle.
In particular the tool checking means includes means
for counting the number of teeth on a tool in the spindle, means
for comparing the counted number of teeth to a recorded number
which signifies the number of teeth that should be on the tool,
and means for automatically replacing a broken or incorrect tool
- wi'ch another tool of the same type from the tool magazine.
In another aspect of the invention there is provided
~ a method of checking the condition of the cutting tools in the
rotary spindle of a machine tool comprising the steps of, count-
ing the number of teeth on a tool in the spindle, comparing the
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number of teeth counted with a recorded number that indicates
the number of teeth that should be on the specific tool in the
spindle, and replacing the tool in the qpindle with a new tool
: whenever the number of counted teeth differs from the number of
recorded teeth.
In a particular embodiment the method includes the
steps of checking for broken or incorrect tools by moving the
tool tip to a position adjacent to a proximity switch, rotating
the tool through one complete revolution, counting the number
of output pulses from the proximity switch for one complete
revolution of the tool, comparing the total number of output
pulses from the proximity switch for one complete revolution
: of the tool to the number of teeth that should be on the tool,
and replacing the tool or suspending the machining operation
if the total number of output pulses from the proximity switch
for one complete revolution of the tool is different from the
number of teeth that should be on the tool as entered into the
control system.
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Other objects and advant~yes of the invention will be apparent
from the detailed description herein.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of one preferred embodiment of the inven-
tion;
Fig. 2 is a side elevation view and longitudinal sectional view
taken on the line 2-2 of Fig. l;
Fig. 3 is a fragmentary front elevation view of the mechanism for
opening and closing the coolant enclosure doors taken on the line 3-3
of Fig. 2;
Fig. 4 is a fragmentary plan view taken on the line 4-4 of Fig. 3;
Fig. 5 is a front elevation view of the housing containing the
calibration bushing and proximity switches; ~-
Fig. 6 is a side elevation view taken on the line 6-6 of Fig. 5;
Fig. 7 is a cross-sectional view taken on the line 7-7 of Fig. 5
and showing a probe tip within the calibration bushing;
Fig. 8 is a plan view of the housing of Figs. 5 to 7 showing a -
probe tip contacting the Z calibration surface thereof; -
Fig. 9 is a block diagram of the spindle position feedback system ~-
for the embodiment of Figs. 1 to 8;
Fig. 10 is a block diagram of the broken tool detector for the em-
bodiment of Figs. 1 to 8; and
Fig. 11 is a flow chart of the program for checking for broken or
incorrect tools.
DESCRIPTION OF THE PR ~RRED EMBODIMENTS -
Referring to Figs. 1 and 2, one preferred embodiment of the inven-
tion includes a horizontal machining center 10 which has a first bed ~-
portion 12 that supports horizontal ways 14. A worktable carriage 16
is slidably mounted on ways 14 for movement along a horizontal X-axis
18 (Fig. 1). A workta~le 2~ (Fig. 2) is rotatably mounted on work-
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table carriage l6 for ro~ation about a vertical B-axis 22. Worktable
20 is adapted to slidably receive a conventional pallet 24 and to
clamp pallet 24 thereto in position to machine a workpiece (not shown)
which lS clamped to pallet 24 by conventional means (not shown). Work-
table 20 can be indexed to a desired rotary position about B-axis 22
to present any desired face of the workpiece to the cutting tool.
Machining center 10 nas a second bed 26 which supports horizontal
ways 28. An upright 30 is slidably mounted on ways 28 for movement
along a horizontal Z-axis 32 (Fig. l) which is perpendicular to both
X-axis 18 and B-axis 22. Upright 30 supports vertical ways 34 (Fig.
- 2). A spindlehead 36 is slidably mounted on ways 34 for movement
along a vertical Y-axi-s 38 (Fig. 2~ which is perpendicular to both
X-axis 18 and Z-axis 32. A spindle 40 which is adapted to receive a
cutting tool 42 is rotatably mounted on spindlehead 36 for rotation
; 15 about Z-axis 32. Rotation of spindle 40 and movement of the other
machine tool parts alonq or around their respective axes is effected
by electric motors (not shown) which are controlled by conventional
electrical controls (not shown) mounted in a machine control unit and
; power distribution panel 44 (Fig. 1). A hydraulic unit 46 (Fig. l)
provides hydraulic fluid under pressure for the hydraulic components
of the system.
A conventional tool magazine 48 (Fig. 2) having a plurality of
tool sockets 49 and a conventional tool changer 50 having a pair of
tool change arms 51 are mounted on upright 30 for storing a plurality
of cutting tools and for transferring the tools from tool magazine 48
to spindle 40 and vice versa. The tools include a special probe (not
`~ shown) which is mounted in a standard toolholder and can be clamped
in spindle 40 for calibration purposes as described in later para-
graphs.
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A workpie~e ma(3~.ine 52 is mounted on a frame 54 adjacent to bed
12. Workpiece magazine S2 contains a track 56 upon which wheeled
carts 58 are movably mounted and can be rnoved around track 56 by means
of a conventional drive chain 60 (Fig. 2) which is driven by conven-
tional means (not shown). Each of the carts 58 is adapted to slidably
' receive a pallet 24 upon which a workpiece (not shown) is clamped. A
:
pallet loading and unloading station 62 (Fig. 1) is mounted adjacent
to track 56 and a hydraulic ram 64 is mounted in position to pull pal-
lets 24 from station 62 to an adjacent cart 58 and to push pallets 24
from cart 58 to station 62. A similar hydraulic ram 66 is mounted in
position to push pallets 24 from cart 58 to worktable 20 and to pull
pallets 24 from worktable 20 to cart 58. ~ydraulic rams 64 and 66
~ have extendible piston rods which terminate in latch members 68 and
- 70, respectively, which are shaped to engage a T-shaped recess in pal-
lets 24 for pushing and pulling pallets 24. The electrical controls
for rams 64 and 66 and for the workpiece magazine drive are housed in
a cabinet 71. - -~
Pallet guideways 72 and 74 are mounted adjacent to worktable 20
to support pallets 24 when they are being transferred from a cart 58
to worktable 20 or vice versa. Guideway 72 is supported by frame 54
while guideway 74 is supported by bed 12.
An enclosure 76 which is closed on three sides by transparent
rectangular panels 78 and has a pair of sliding doors 80 on one closed
side is mounted on bed 12 in position to enclose worktable 20. The
~25 fourth side of enclosure 76 which faces spindle 40 is open to permit
machining of the workpiece on pallet 24 inside of enclosure 76. The -
~ top of enclosure 76 is also open. Referring to Fig. 2, the side panels
!.; 78 are supported by uprights 82 which are attached a~ their bottom ends ;-
to bed 12 and are attached at their top end to cross members 84.
Referring to Fig. 3, a portion of the side of enclosure 76 which
~ faces workpiece magazine 52 is closed by side panels 78 and the cen-
j tral portion thereof is closed by two sliding doors 80. Both sliding
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doors 80 are identical and therefore only one door 80 will be described
in detail~ Each slicling door 80 includes a rectangular frame 86 which
is covered by a transparent rectangular panel 88 and is bolted at its
top edge to a rectangular support plate 90. A pair of rollers 92 are
rotatably attached to support plate 90 and roll on a support rod 94
which is attached to uprights 82 and spans the upper edge of the side
of enclosure 76 which faces workpiece magazine 52. Support plate 90
is moved laterally between an open and a closed position by a pneumatic
ram 96 which is attached at one end to upright 82 by bracket 98 and is
attached at the other end to support plate 90 by bracket 100. Pneu-
matic ram 96 is shown in its fully extended position in Figs. 3 and 4.
This corresponds to the closed position of sliding door 80. In the
fully retracted position ofpneumatic ram 96, sliding door 80 is moved
to the right in Figs. 3 and 4 to form an opening through which pallets
-15 24 can be moved from worXpiece magazine 52 to worktable 20 or vice
versa.
The opening and closing of sliding doors 80 is electrically indi-
cated by a three position limit switch 102 having an actuating arm 103
which is spring biased to a central neutral position. W~en sliding
20 - door 80 is fully closed, as shown in Fig. 3, a lug 104 on one end of
support plate 90 moves limit switch arm 103 to a first actuated posi-
tion indicating that door 80 is fully closed. When sliding door 80 is ~ ~
fully opened, a second lug 106 on the other end of support plate 90 -
moves limit switch arm 103 to a second actuated position indicating
that door 80 is fully opened.
The purpose of enclosure 76 is to permit theworkpieceon pallet
24 to be sprayed with coolant after it has been machined to wash chips
off the workpiece and off pallet 24. The coolant is sprayed from an
upstanding conduit 108 (Fig. 2) which ha~ a plurality of orifices (not
shown) spaced along its length on the side thereof adjacent to pallet
24. Coolant under pressure is supplied to conduit 108 by a conven- -
tional pump (not shown) and is controlled by a conventional solenoid
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lO~J~108
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valve (not shown). An uprigl~t compr~ssed air conduit 110 (Fig. 2) is
mounted beside coolant conduit 108 and also has a plurality of orifi-
ces (not shown) spaced along its length on the side thereof adjacent
to pallet 24. Compressed air is supplied to conduit 105 by a con-
S ventional air compressor (not shown) and is controlled by a conventionalsolenoid valve (not shown). The purpose of the compressed air is to
blow coolant off the workpiece and off pallet 24 after they have been
sprayed with coolant to wash away the chips.
When coolant is sprayed through the orifices of coolant conduit
108 to wash away the chips from the workpiece and from the p~llet 24
within enclosure 76, worktable 20 is rotated through 360 to present
every side of the workpiece and pallet 24 to the jets of coolant is-
suing from coolant conduit 108. After worktable 20 has rotated through
360, the flow of coolant is switched off and the compressed air is
~!15 switched on while worktable 20 continues to rotate through a second
360 to present every side of the workpiece and pallet 24 to the air
jets issuing from compressed air conduit.
The chips washed away by the coolant fall into a drain trough
112 (Fig. 2) whose lower surface is part of a chip conveyor belt 114
-20 (Fig. 1) which carries the chips to a chip cart 116 beside the ma-
chining center 10. The coolant that was used to wash the chips off
the workpiece and off pallet 24 is collected in a conventional drain -
, .
(not shown) under chip conveyor 114 and is returned to a coolant tank ~ -
117 (Fig. 1) by conventional means (not shown). The provision of
~ 25 means for automatically disposing of the chips produced by the ma-
;j chining operation is an important feature of this invention since
there is no operator to remove the chips and since a build-up of chips
could interfere with the proper functioning of the machining center.
It should be noted that machining center 10 also contains a con-
ventional coolant system tnot shown) for applying coolant streams to
the cutting tool and to the portion of the workpiece being cut during
the machining operation. The purpose of coolant conduit 108 is not
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to cool the cutting tool during the m~chining operation, but rather,
to wash away the chips after the machining operation is completed.
A small housing 118 (Figs. 2 and 5 to 8) containing two proxim-
ity switches 120 (Fig. 5) and a calibration bushing 122 is rigidly at-
tached to worktable carriage 16 (Fig. 2). Calibration bushing 122 is
recessed in a flat plate 124 (Figs. 5 to 8) which is bolted to hous-
ing 118 by bolts 126 (Figs. 5 and 71. Proximity switches 120 are re-
sponsive to the presence of a metallic object within a predetermined
distance therefrom and produce an output signal whenever a metallic
object is moved within the predetermined distance therefrom.
Figure 10 shows the electrical circuit used in combination with
proximity switches 120 to check for broken or incorrect tools and Fig.
11 is a flow chart of the program for checking for broken or incorrect
tools. Referring to Fig. 10, the output of both proximity switches
lS 120 are connected in parallel to a counter 128. The two switches 120
are oriented at right angles to each other (see Fig. 6) for checking
different types of tools. Only one of the switches 120 is used for
checking any given tool. In the example shown in Fig. 10, the tool
to be checked is a milling cutter 130 which has a plurality of cutting
teeth 132 projecting radially therefrom. In this particular example,
there are ten radially projecting teeth 132 on cutter 130.
The first step of the tool checking program (Fig. 11) is step 134
in which tool 130 is positioned adjacent to the appropriate proximity
switch 120 such that a tooth 132 adjacent to proximity switch 120 will
cause an output signal while the valley between teeth 132 will not
cause an output signal. Step 134 ~s initiated in response to a com-
mand programmed on the N.C. tape. The command which initiates step
134 includes the X, Y and Z coordinates that spindle 40 must be moved
to place tool 130 in the correct position relative to the selected
30 proximity sensor 120. The particular X, Y and Z coordinates will vary -
for each different tool depending on the dimensions and configuration
of the tool.
nlos
In the next pr~ram step 136, the tool 130 is either rotated
through 360 if it has a plurality of teeth or is rotated to position
its single tooth opposite proximity switch 120 and is ~eylocked in
that position.
In the next program step 138, the command G38Si is received from
the N.C. controls where i = the number of teeth on the selected tool.
Step 138 follows step 136 but occurs before rotation of tool 130 is
completed. The 36Q of rotation through which cutting tool 130 ro-
tates in this example is timed from the trailing edge of a pulse out-
put from counter 128 (Fig. 10) which indicates a valley between two
of the teeth 132. Starting from the first detected valley, the tool
is rotated for 360 and the number of pulses occurring during the 360
rotation is counted by counter 128. -
In the next program step 140, the number in counter 128 is com- ~
pared to the number received in step 138 to see if the tool under test ~ -
has the correct number of teeth. If the measured number of teeth is -
less than it should be, this implies that one or more of the teeth are ~ -
broken. If the measured number of teeth is greater than it should be,
this implies that the wrong tool is in the spindle. In either of these
20 incorrect instances, step 140 selects the NO branch 142 which leads to
step 144. If the number in counter 128 is equal to the number received -~
in step 138, step 140 selects YES branch 146 which returns control to
the machining operation. This comparison is made in comparator circuit
141 ~Fig. 10).
If NO branch 14~ is selected, control passes to step 144 in which
the tool failure is recorded and the tool selector circuits 145 (Fig.
10) are activated to seek an alternate tool in tool magazine 48. For
the purpose of replacing a broken tool, at least two identical tools
are stored in tool magazine 48 for any tool that is subject to break-
age. If a given tool is liable to break more than once during a shift,
three or more of that tool can be stored in tool magazine 48.
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Step 144 leads to step 148 in which the availability of an alter-
nate tool is determined. If an alternàte tool is available, YES branch
150 is selected which leads to step 152 in which the defective tool is
replaced with an alternate tool of the same type. Tle machining oper-
ation is then continued. If an alternate tool is not available, NObranch 154 is selected which leads to step 156 in which an alarm is
activated and the machining operation is suspended by emergency stop
circuits 157 (Fig. 10).
The use of the previously noted special probe to calibrate the
N.C. circuits is illustrated in Figs. 7 and 8. The probe158is moved
into contact with th~ front of plate 124 (see Fig. 8) to calibrate the
Z-axis dimension and compensate for temperature expansion or contrac-
tion along the Z-axis. To calibrate the X and Y axes dimension and
.~ .
- compensate for temperature expansion or contraction along the X and Y
;~15 axes, probe 158 is moved into contact with the interior of calibration
bushing 122, as shown in Fig. 7. Opposite sides of the bushing are
contacted for X-axis calibration and the top and bottom are contacted
for the Y-axis calibration. By periodically moving probe 158 into con-
tact with the above-noted calibration surfaces and comparing the posi- - -
tion of the spindle along the appropriate axis with the position pre-
viously recorded for the same calibration surface, thermal growth or
contraction can be detected and the N.C. circuits can be recalibrated
; to compensate for the thermal changes.
j As an example of this calibration process, a specific compensation
for Z-axis temperature growth will be given. Suppose that the Z-axis
displacement of the probe is 87.8976" when the machine lS started, i.e.,
that the Z-axis displacement is 87.8976" at the time that the probe
!~ makes contact with the Z-axis calibration surface 124. Suppose that one
hour later the measurement is repreated and the Z-axis displacement has
3~ changed to 87.8971", indicating a thermal growth along the Z-axis of
0.0005". The N.C. controls will then be programmed to subtract 0.0005"
- from every Z-ax~s posit~on reading to compensate for this thermal growth.
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1(~901~
Compensation for the tl-ermal growth or contraction along the X and Y
axes is accomplished in the same manner. All three axes are checked
and recalibrated periodically. It is important to recalibrate the
machine tool automatically during its unmanned operation to prevent
errors from creeping in due to thermal growth or contraction. Accord-
ingly, the machine program inc~udes the steps of periodically recali-
brating the machine tool at regular intervals, e.g., once an hour.
This is an important feature in the unmanned operation because it en-
ables the machine to automatically compensate for temperature changes
without the need for an operator for relatively long period of time.
Fig. 9 shows the position feedback and torque feedback for spindle
40. Spindle 40 is rotated by a D.C. motor 168 through gears 170. ~otor
168 is controlled by a conventional motor control circuit 172 which is ~
under the control of computer 167. The armature current IA of motor ~ -
15 168 is applied-via conductors 176 and 178 to computer 167. A resolver
180 is coupled to gears 170 and produces an anguiar position signal for
~ spindle 40 which is applied to computer-167. This angular position
i! signal is used to determine when spindle 40 has rotated through 360
when the number of-teeth on the tool is being~checked.
Although the illustrative embodiments of the invention have been
described in considerable detail for the purpose of disclosing a prac-
tical operative structure by which the invention may be practiced ad-
vantageously, it is to be understood that the particular apparatus
described is intended to be illustrative only and that the novel char-
acteristics of the invention may be incorporated in other structural
forms without departing from the spirit and scope of the invention, as
defined in ~:he sub-joined claims.
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