Chuck with centrifugal force compensation

A centrifugal force compensated chuck (12) using a moderately sized counterweight (60) and force multiplication to achieve proper compensation. Each counterbalance assembly includes a pair of levers (32, 40) pivotable about a common axis (34). One of the levers (32) is connected through an appropriate mechanical interconnection to an associated chuck jaw (15), the other lever (40) engages a counterweight (60) which moves out from the center of the chuck (12) during rotation. A ratchet (36) and pawl (42) mechanism is provided between the first and second levers. When the chuck (16) is stopped, the counterweight (60), which is spring biased, moves to a position disengaging the ratchet and pawl. With the ratchet and pawl disengaged the pair of levers are free for independent movement about their pivot axis. When the chuck is rotated the counterweight mechanism moves outward and the ratchet (36) and pawl (42) engage causing the pair of levers to move in unison. As the counterweight (60) moves outward the second lever (40 ) engages a sloped surface (42) on the counterweight and transmits compensating force thru the first lever to the chuck jaw (15). In another embodiment the ratchet and pawl assembly can be eliminated and levers (32, 40) can be formed on a common member.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention relates to turning machines and more particularly to a power 
chuck having centrifugal force compensation. 
2. Background Art 
Centrifugal counter balance systems are well known in chucks for turning 
machines. In the usual application a large weight is attached to or made 
part of each actuating lever which moves an associated chuck jaw. The 
centrifugal force exerted by this counterweight balances the centrifugal 
force of the chuck jaw and maintains the desired clamping force on the 
workpiece at all speeds. The body of the chuck must usually be 
considerably enlarged to accommodate the counterbalance weights. U.S. Pat. 
Nos. 2,784,977; 2,839,307; 2,861,471; 2,982,558; 3,370,859; 3,597,822; 
3,938,815; 3,984,114; 4,009,888 and 4,040,315 illustrate various prior art 
chucks having centrifugal force compensation. 
DISCLOSURE OF THE INVENTION 
The present invention teaches a centrifugal force compensated chuck using a 
moderately sized counterweight and force multiplication to achieve the 
desired force compensation. The disclosed chuck has an improved 
counterbalancing mechanism for use on a high speed turning machine to 
counteract the centrifugal force tending to move the chuck jaws outward. 
The counterbalance uses low friction wedge to achieve a large force 
multiplication from moderately sized counterbalance weight. The disclosed 
construction does not require changing the proportion of the chuck to 
accommodate the counterbalance mechanism. 
The disclosed chuck has a plurality of chuck jaws and a centrifugal 
counterweight associated with each chuck jaw. The counterweight mechanism 
consists of a double ended lever which is movable with the associated 
chuck jaw, wherein the primary lever is actuated by a central draw bar in 
the chuck. The secondary lever, integral with the primary level but 
extended beyond the pivot axis, carries a low friction roller which 
engages an inclined ramp on counterweight. 
When the chuck rotates, the counterweight is moved outward by centrifugal 
force to engage in the roller on the secondary lever. The centrifugal 
force of the counterweight is magnified through the inclined ramp and 
applied to the secondary lever, thus compensating for the centrifugal 
force of the chuck slide and chuck jaw. 
Another embodiment of the invention separates the primary and secondary 
levers. These two lever arms pivot about the same axis; the primary lever 
has a ratchet formed on its outward surface and the secondary lever has a 
spring-biased pawl adjacent to the ratchet. With the chuck stopped the 
counterweight is at a stopped position disengaging the ratchet and pawl. 
When the chuck rotates the counterweight moves to release the pawl which 
then engages the ratchet and causes the two levers to move together. This 
mechanism allows for a longer stroke of the primary lever than does the 
one-piece, double-ended lever. Once the pawl is engaged, the centrifugal 
force of the counterweight, magnified by the inclined ramp, is transmitted 
through the secondary lever to the chuck slide and chuck jaw. Suitable low 
friction bearings can be provided to assure low friction movement of the 
counterweight.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings there is shown, a turning machine 10 having a 
chuck 12 which utilizes a counter balance mechanism according to the 
teaching of the present invention. A workpiece to be machined is supported 
by chuck 12 and rotated therewith. Suitable drive means 13 are provided 
for rotating chuck 12. A tool turret 14 is indexable to bring various 
tools into position for machining the supported workpiece. Turret 14 is 
supported on vertical and horizontal ways for movement along two axes by 
appropriate drives. 
Chuck 12 consists of a plurality of chuck jaws 15 which are moved to engage 
a workpiece. Jaws 15 are bolted to and move with chuck slides 16 which are 
connected to chuck slide nuts 18. A central actuating rod 30 moves 
vertically to raise or lower a primary lever arm 32. When the primary 
lever arms 32, one associated with each jaw 15, are raised the chuck 
slides 16 move outward, when primary lever arms 32 are lowered the chuck 
slides 16 are moved inward. Thus, workpieces may be engaged and held in 
either an outward or inward direction depending on the machining operation 
to be performed. The location of each chuck slide 16 may be adjusted 
independently by manually turning chuck screw 74 so that the slide moves 
inward or outward relative to chuck slide nut 18. This adjustment is 
sometimes necessary to center an irregularly-shaped part about the axis of 
rotation. Chuck screw 74 is attached to chuck slide 16 by fitted cap 75. 
One embodiment of the centrifugal force multiplication principle is 
illustrated in FIG. 5. Lever arm 31 engages central actuating rod 30, 
which moves vertically to raise or lower the lever arm and move chuck 
slide 18 which engages an upward extension 33 of lever arm 32. An outward 
extension 41 of lever arm 31 carries a roller 46 mounted on a low friction 
bearing. This roller 46 is positioned to engage inclined ramp 66 of 
counterweight 60 when the counterweight moves outward under centrifugal 
force. The centrifugal force of counterweight 60 is thus transmitted 
through lever arm extension 41 to lever arm 31 and to chuck slide nut 18 
to balance the centrifugal force of chuck slide 16 and chuck top jaw 
assembly 15. 
Inclined ramp 66 of counterweight 60 allows for a moderate vertical stroke 
of actuating rod 30. Roller 46 on lever extension 41 will still engage 
inclined ramp 66 when actuating rod 30 is anywhere within its moderate 
stroke. In cases where a long operating stroke is needed, FIGS. 2 and 3 
show another embodiment where lever arm 31 and outward extention 41 are 
separate levers 32 and 40 respectively. 
Primary lever arm 32 pivots around a pivot connection 34. A secondary lever 
arm 40 is arranged to pivot around pivot support 34, around which primary 
lever arm 32 also pivots. A ratchet section 36 is formed on primary lever 
arm 32. An upward extending portion 33 of lever 32 engages chuck slide 16. 
A pawl 42 is disposed on secondary lever 40. Pawl 42 is spring biased by a 
spring 44 towards engagement with the ratchet sections 36 formed on 
primary lever 32. The outer end of lever arm 40 carries a roller 46 
mounted on a low friction bearing. Counterbalance weight 60, one of which 
is provided for each centrifugal compensating mechanism, is mounted on 
linear anti-friction recirculating rolling contact bearings 62 and 64. An 
inclined ramp 66 is provided on counterweight 60. The outer end of lever 
arm 40 carries a roller 46 which rests on the inclined portion of 66 of 
counterbalance weight 60. Weight spring 68 is provided for biasing 
counterweight 60 into engagement with a stop surface 70. Stop surface 70 
is formed on the mounting flange 72 to stop the counterweight 60 in the 
proper relationship to secondary lever arm 40. In the stop position as 
shown in FIG. 3 pawl 42 is engaged and forced out of engagement with the 
ratchets 36 on primary lever arm 32. Thus, secondary lever arm 40 with 
counterweight 60 in the stop position, is not connected to primary lever 
arm 32. Motion of the primary lever arm 32 to engage and disengage the 
workpiece, with the chuck in a standstill position, may thus proceed in a 
normal manner. 
When chuck 12 starts to rotate counterbalance weight 60 moves outward under 
centrifugal force. When pawl 42 is released by the outward motion of 
counterweight 60 spring 44 urges pawl 42 into engagement with one of the 
ratchet notches 36 formed on primary arm 32. This engaged position as 
shown in FIG. 2 causes primary lever arm 32 and secondary lever arm 40 to 
move in unison. The centrifugal force of counterweight 60 is thus 
transmitted through secondary lever arm 40 to primary lever arm 32 and 
chuck slides 16 thus balancing the centrifugal force of the chuck slide 16 
and top chuck jaw 15 assembly. 
It is important that counterweight 60 move with minimum friction. The angle 
of the inclined plane and the frictional forces resisting movement 
determine the ratio of the centrifugal force of the weight to the force 
transmitted to secondary arm 40. The force pattern in the mechanism is 
illustrated in FIG. 6. Inclined ramp 66 is elevated from the horizontal 
plane by angle .theta.. Centrifugal force Fc on counterweight 60 is 
balanced by a Force Fn/cos.psi..sub.1, where Fn is the force normal to 
inclined ramp 66 and .psi..sub.1 is the angle whose tangent is equal to 
the friction coefficient between roller 46 and inclined ramp 66, and by a 
force Fv tan.psi..sub.2, where Fv is the force in the vertical direction 
and .psi..sub.2 is the angle whose tangent is equal to the coefficient of 
friction between roller bearings 62 and 64 and horizontal surface 73. 
Thus: 
EQU Fc=(Fn/cos .psi..sub.1) sin (.theta.+.psi..sub.1)+Fv tan .psi..sub.2 
and since Fv=(Fn/cos .psi..sub.1) cos (.theta.+.psi..sub.1) 
EQU Fc=(Fn/cos .psi..sub.1) sin (.theta.+.psi..sub.1)+(Fn/cos .psi..sub.1) cos 
(.theta.+.psi..sub.1) tan .psi..sub.2 
With a secondary lever arm having the proportions illustrated in FIG. 2 and 
an inclined plane slope of 1/3 (the tangent of the angle .theta.), the 
centrifugal force of the counterweight is increased by a factor of almost 
10. This allows a moderately sized counterweight and requires no 
additional space within the chuck. 
The arrangement shown in the figures is adapted specifically to vertical 
boring and turning machines. A similar arrangement can be provided for a 
horizontal turning machine by rearranging the guide bearings for the 
counterbalance weight and adding a spring bias to the secondary lever arm 
to maintain contact with the counterbalance weight.