Work clamping fixture

A workholding fixture for clamping a workpiece for rotation about a selected axis comprising at least one throwblock for receiving a workpiece portion to be clamped, a clamp arm associated with the throwblock including a jaw at one end and a control surface at the other end, means for pivotally supporting the clamp arm intermediate the ends, means for selectively displacing the pivotally supporting means along an arc from a predetermined advanced position to a predetermined retracted position, means for pivotally displacing the clamp arm about the pivotally supporting means including cylinder means having bearing surface means selectively displaceable from a retracted position to an advanced position, the bearing surface means having a selected length to permit engagement with the control surface means as the pivotally supporting means and the bearing surface means are displaced between the advanced and retracted positions, and means for maintaining the bearing and control surfaces in engagement.

The present invention relates to workholding fixtures, and more 
particularly, to workholding fixtures for holding a workpiece in a 
cylindrical grinding machine. 
Workholding fixtures for cylindrical grinding machines generally include 
one or a plurality of bearing blocks for receiving cylindrical portions 
such as bearings of a workpiece. A jaw associated with each bearing block 
is mounted for pivotal displacement to selectively clamp the bearings 
within the bearing blocks. Such a workholding fixture is disclosed in U.S. 
Pat. No. 4,003,721. 
Since workpieces are usually automatically loaded into and removed from the 
workholding fixture, the jaws must be pivotally displaced through a 
substantial arc to clear a displacement path for the crankshaft. 
It is, accordingly, an object of the present invention to provide a 
workholding fixture wherein a displacement path can be established with 
very limited displacement of the jaw elements. 
Other objects and advantages of the present invention will become apparent 
from the following portion of this specification and from the accompanying 
drawings which illustrate, in accordance with the mandate of the patent 
statutes, a presently preferred embodiment incorporating the principles of 
the invention.

A cylindrical grinding machine includes one or a pair of workholding 
fixtures 10 supporting a workpiece for rotation about a predetermined axis 
of rotation. The illustrated workpiece is a crankshaft 12 for a four 
cylinder engine having pairs of 180.degree. related crankpins P1, P2, and 
the work fixture supports one of these pairs so that the axis of rotation 
of the work fixture is coaxial to the axis of this pin pair. Stock is 
removed by one or more rotatable grinding wheels 14 selectively 
advanceable into abrasive engagement with one or both of these crankpins. 
The workholding fixture includes a drive plate 16 and a clamping assembly 
18 secured to the drive plate, which includes a base 20 supporting two 
bearing blocks 22 operatively associated with clamp arms 24. A yoke member 
26 extends between and is pivotally supported by an upstanding side wall 
portion 28 of the base and the flange 29. Bushings 30, lubricated by oil 
supplied through suitable conduits 32, minimize wear. The end of the yoke 
proximate the drive plate includes a pinion 34. The piston 36 of a yoke 
control cylinder 38, which is supported by the flange, includes a rack 
portion 40, which drivingly engages the pinion 34. The piston 36 is biased 
towards an advanced position by a compression spring 42. 
The clamp arms 24 are pivotally supported on a pivot shaft 44 which extends 
through and is fixedly secured to the downwardly extending legs 46 of the 
yoke member. Bushings 48, lubricated by oil supplied by suitable conduits 
49, minimize wear. Pivotal movement of the yoke member 26, by advancement 
or retraction of the control cylinder, accordingly, displaces the clamp 
arm pivot shaft 44 along an arc between retracted and advanced positions. 
The clamp arms 24 include a hardened workshoe 50 at one end and a bearing 
surface or button 52 at the other end. The button 52 is maintained in 
continuous engagement with a bearing surface 54 of a block or piston head 
56 by a tension spring 58 extending between the end of the clamp and the 
block. 
The clamp arm control cylinder 60 includes a piston 62 to which the block 
is secured, which is retained in a retracted position by a heavy 
compression spring 64. Advancement of the piston 62 pivots the clamp arms 
24 counterclockwise about the clamp arm pivot shaft 44. 
In the fully retracted condition illustrated in FIG. 3, with the clamp and 
unclamp solenoid deenergized and the unclamp and retract solenoid 
energized, the yoke control cylinder is fully retracted and the clamp 
control cylinder is fully retracted. When these conditions are reversed, 
the yoke control cylinder piston will be advanced to its fully advanced 
position whereat a conduit to the clamp control cylinder will be opened. 
The elevation of this piston to its advanced or elevated position rotates 
the advanced clamp arm downwardly to clamp the workpiece. 
When these conditions are again changed, yoke cylinder spring 42 will 
momentarily maintain the clamp arms in their advanced position and clamp 
arm cylinder spring 64 will retract the clamp arm piston to pivot the 
clamps slightly away from the workpiece. The pressure will then retract 
the yoke member cylinder and, hence, the clamp arm to the retracted 
position.