Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to power drawbolts which are
rotatably ~ounted within a machine tool spindle and are ro-
tated by an electric motor to screw into a threaded opening
in a toolholder to secure the toolholder within a socket on
the front end of the spindle. The drawbolt rotates with the
spindle during machining operations, and therefore, in the
past, it was believed to be necessary to couple the motor to
- the drawbolt through a clutch since the motor was mounted on
the spindle head.
The principal object of this invention is to provide a
motor drawbolt coupling which eliminates the need for a
clutch. An additional object of this invention is to pro-
vide a motor drawbolt coupling containing a more compact
speed reducing gear arrangement than heretofore known in the
art.
In accordance with the invention, first and second spur
gears are formed on the rear end of a spindle and drawbolt,
respectively. The gears are positioned side by side and are
equal in diameter, but have a differing number of teeth. A
planetary gear cage surrounds the spur gears and has pinion
gears which mesh with both of the spur gears. The planetary
gear cage is attached to the armature of an electric motor
which, when energized, rotates the gear cage and thus causes
the drawbolt to rotate at a reduced speed. The speed reduc-
tion depends on the difference in the number of teeth in the
two spur gears. In the preferred embodiment, the motor arma-
ture is axially shiftable to move a locking ring on the plane-
tary gear cage into and out of engagement with the spur gear
on the spindle.
Y ~ ~!
In the drawings:
Figure 1 is an axial sectional view of the rear end of
a spindle and drawbolt incorporating the motor drawbolt
coupling of this invention;
Fig. 2 is an axial sectional view of the front end of
the spindle and drawbolt shown in Fig. l;
Fig. 3 is a cross-sectional view taken on the line 3-3
of Fig. l; and
Fig. 4 is a schematic circuit diagram of a motor con-
trol circuit for the embodiment of Figs. 1 to 3.
Referring to Figs. 1 and 2, a hollow, cylindrical spin-
dle 10 is journaled for rotation within a spindle head 12 by
bearings 14. Spindle head 12 is mounted on a machine tool
upright (not shown) by conventional means (not shown) and is
movable along the axis of spindle 10. The machine tool up-
right is movable along the conventional X and Y axes. The
front end of spindle 10 is adapted to receive a cutting tool
16 (Fig. 2) which is mounted on a toolholder 18. Toolholder
18 has a conical rear surface 20 which mates with a conical
socket 22 in the front end of spindle 10.
A drawbolt 24 is rotatably mounted within the hollow in-
terior of spindle 10 by bearing sleeves 26 (Fig. 1). The
front end of drawbolt 24 carries threads 28 (Fig. 2) which
match a threaded opening 30 in toolholder 18. To insert a
toolholder 18 into socket 22, drawbolt threads 28 are engaged
in threaded opening 30 and drawbolt 24 is rotated while spin-
dle 10 remains stationary to screw threads 28 into opening 30,
which draws the conical rear surface 20 of toolholder 18 into
contact with toolholder socket 22. A spring 32 (Fig. 1)
urges drawbolt 24 rearwardly by bearing against washer 34
that rests on a pin 36. Pin 36 extends through a bore in
drawbolt 24. The front end of spring 32 is supported by a
shoulder 37 on a sleeve 38 that rests on the rear edge of one
of the bearing sleeves 26. A pin 40 projects from the outer
surface of drawbolt 24 and rides in a slot 42 in sleeve 38.
Pin 40 limits the forward movement of drawbolt 24 by abutting
against the rear edge of the adjacent bearing sleeve 26.
1~l lL~893
A first spur gear 44 is formed on the rear end of spin-
dle ln and a second spur gear 46 is formed on a sleeve 48
which is rotatably mounted in rear bearing sleeve 26 and is
slidably coupled to drawbolt 24 by splines S0. Spur gears
44 and 46 are positioned side by side and are equal in diam-
eter, but have a differing number of teeth to provide for a
speed reduction. A planetary gear cage 52 having pinion
gears 54 journaled therein surrounds the spur gears 44 and
46. Pinion gears 54 mesh with both of the spur gears 44 and
46. When planetary gear cage 52 is rotated, it causes rota-
tion of sp~r gear 46 at a greatly reduced speed which de-
pends on the difference in the number of teeth between gears
44 and 46. The direction of rotation depends upon which
gear has the most teeth and on the direction of rotation of
planetary gear cage 52. ~,ear 44 remains stationary during
rotation of planetary gear cage 52 because of the greater
mass connected to it. Planetary gear cage 52 is coaxial with
drawbolt 24.
Planetary gear cage 52 is rigidly attached to the shaft
56 of a three phase induction motor 58 and rotates therewith.
Motor 58 is mounted in a housing 60 which is rigidly attached
to spindle head 12. Armature shaft 56 is coaxial with draw-
bolt 24 and is axially slidably mounted within housing 60 by
means of sleeves 62 in end plates 64. The motor armature 66
is normally pushed axially off center by a spring 68 which
extends between the rear of drawbolt 24 and a collar 70 hav-
ing a conical central depression 72 in which a ball 74 is
seated. Ball 74 also bears against a conical depression 76
in armature shaft 56 and serves to couple the force of spring
68 to shaft 56 without preventing rotation of shaft 56.
A notched locking ring 78 (Figs. 1 and 3) is attached to
the front end of planetary gear cage 52 and engages spur gear
44 when armature 66 is in its rearward off center position as
shown in solid lines in Fig. 1. When armature 66 is moved
axially to its central position, to the right in Fig. 1, lock-
ing ring 78 moves to the position shown in broken lines in
Fig. 1 and disengages from spur gear 44. Since armature 66
1~16B~3
is normally spring biased to its rearward off center posi-
tion, locking ring 78 is normally locked to spur gear 44
which means that the planetary gear cage 52 and motor arma-
ture 66 rotate with spindle 10 during machining operations.
This is an important feature of the invention since it elim-
inates the need for a clutch between armature shaft 56 and
drawbolt spur gear 46.
When it is desired to rotate drawbolt 24, a single
phase excitation is first applied to stator windings 80 to
magnetically draw armature 66 to its central position and
thus to disengage locking ring 78 from spur gear 44. The
reason that the magnetism from the stator windings 80 draws
armature 66 to its central position is that armature 66 is
off center with respect to stator 80 in its rearward posi-
tion, which is shown in solid lines in Fig. 1. With only a
single phase of stator winding 80 energized, armature 66
will move axially to its central position but will not ro-
tate. After enough time has elapsed to permit disengagement
of locking ring 78, three phase excitation is applied to
stator windings 80 to cause rotation of planetary gear cage
52 and thus to rotate drawbolt 24 at a reduced speed. After
drawbolt 24 is screwed into or unscrewed from toolholder 18,
motor 58 is deenergized and armature shaft 56 is pushed back
to its rearward position by spring 68 thereby engaging lock-
ing ring 78 with spur gear 44.
Figure 4 is a schematic circuit diagram of a motor con-
trol circuit for implementing the above-described motor ac-
tion. The motor is energized by a manually actuated single
pole triple throw switch S which is spring-biased to normally
rest in its central position Sl. To cause motor 58 to rotate
in the direction which clamps a toolholder in socket 22,
switch S is manually moved to its S2 position and is held
there until the clamping action is completed. In the S2 po-
sition, switch S energizes the clamping relay C which closes
normally open contacts Cl, C2 and C3. Contacts Cl and C2
connect a single phase of the three phase source across sta-
tor windings Wl and W3 of three phase motor 58. This single
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phase excitation creates a magnetic field which draws the
off center armature 66 forwardly to a central position with
respect to stator windings Wl, W2 and W3. However, the
single phase excitation does not cause armature 66 to ro-
tate. For armature rotation, three phase excitation is re-
quired.
When contacts C3 close, they energize a time delay re-
lay TD which delays three phase excitation of stator wind-
ings 80 for a short time (e.g. 1 second) to permit locking
ring 78 (Fig. 1) to disengage from spur gear 44 due to the
forward motion of armature 66 caused by the single phase ex-
citation of windings Wl and W3. After the time delay, nor-
mally open contacts TDl close and apply three phase excita-
tion to stator windings Wl, W2 and W3 thereby rotating ar-
mature 66, planetary gear cage 52 and drawbolt 24.
When the threaded end of the drawbolt 24 ~Fig. 2) is
fully screwed into toolholder 18, motor 58 will stall due
to the fact that the conical rear surface 20 of toolholder
18 abuts against the conical socket 22 in the front end of
spindle 10 and prevents further rotation of dra~7bolt 24.
After the motor stalls, switch S is released and automati-
cally returns to its central position Sl. This deenergizes
clamping relay C and time delay relay TD and thus deener-
gizes stator windings Wl, W2 and W3.
For rotation of motor 58 in the opposite direction to
unscrew the threaded end of drawbolt 24 from the toolholder
18, switch S is manually moved to its S3 position. This en-
ergizes unclamp relay U which closes normally open contacts
Ul, U2 and [J3. Contacts Ul and U2 apply single phase exci-
tation to stator windings Wl and W3. Contact U3 energizes
time delay relay ~D. When time delay relay contacts TDl
close, three phase excitation is applied to windings Wl, W2
and W3 with power input lines Ll and L2 reversed from the
connection used for clamping. This causes armature 66 (Fig.
1) to rotate in the opposite direction from that used for
clamping and thus unscrews the threaded end of drawbolt 24
from toolholder 18. After toolholder 18 is unscrewed from
ii 8 ~1~
--6--
the threaded end of drawbolt 24, switch S is released and
automatically returns to its central position Sl thereby
deenergizing relays U and TD and windings Wl, W2 and W3.
Although the illustrative embodiment of the invention
has been described in considerable detail for the purpose
of fully disclosing a practical operative structure incor-
porating the invention, it is to be understood that the
particular apparatus shown and described is intended to be
illustrative only and that the various novel features of the
invention may be incorporated in other structural forms with-
out departin~ from the spirit and scope of the invention.
