Rapid advancing and retracting mechanism for clamping device

The present invention relates to an improved mechanism for clamping means comprising a pair of split nuts resiliently retained in place inside a hollow cylindrical body by spring means, which mechanism can either slidably hold the screw spindle to allow the latter to be rapidly pushed to its working position or retracted to dismount the workpiece when the threads of split nuts are not in mesh with the screw spindle, or offer a snug, complete engagement between the split nuts and screw spindle in which the load is equally distributed, thereby largely reducing the wear thereof, and allowing the device to be fabricated relatively small in size.

The parent application related to a rapid operating mechanism for advancing 
or retracting the screw spindle of clamping means, for example clamps, 
vises, and suchlike. The improvement of this invention over its prototype 
resides in replacing the latter's springs by springs and stop pieces, so 
as to facilitate the production, and more effectively release the split 
nuts. 
Yet known clamping devices fall into two categories: manual type, and 
hydraulic type. Despite its relatively high cost of production, the 
application of the former is much limited due to the structure thereof, 
and adapted only to special c-clamps. Moreover, such device entails a 
preparatory step to set the screw in operating position and is therefore 
inconvenient. For this reason, it is not preferably accepted by the 
public. While the cost of production of the latter is also high, it is not 
adapted to ordinary use. Provided with hydraulic chamber, the layout of 
such device is inconveniently bulky, thus limiting its application to some 
specialized works. 
A yet known means to obtain a rapid advance or retract of clamping means to 
fasten or release the workpiece is accomplished by an eccentric nut 
provided with thread means on half of its internal surface, which nut, 
normally does not engage with the screw spindle, yet when turned forwardly 
about half a round inside a hollow cylindrical body in the frame, will 
produce a radial displacement such that its half-threads engage with the 
screw spindle penetrating through it. Rapidly as it can fasten or release 
the workpiece, such device suffers several disadvantages as follows: 
1. Since only half of the inner wall is provided with thread, the load is 
mostly exerted on the threaded portion in operation, therefore largely 
increasing the wear of the thread and screw spindle. Moreover, such device 
cannot convert the torsion of the operator completely and efficiently into 
the pressure against the workpiece, particularly when the load is heavy. 
2. The provision of a cylindrical body and the eccentric nut renders the 
inconveniently large size of the resulting assembly, which largely limits 
the use of such device. Also, the nut must provide enough number of 
threads to convert the angular torque into axial thrust, thus the required 
length is also inconveniently long. 
3. In operation, only three effort points are bearing the propulsion of the 
screw spindle, thus causing the wear of the entrance and the exit of the 
cylindrical body, and enlarging the size of the opening thereof after long 
use, so that the screw spindle is liable to slacken during operation and 
fails to hold the workpiece snugly and securely in place. 
Accordingly, it is the chief object of this invention to provide a rapid 
advancing and retracting mechanism to supercede the yet known means, 
thereby curing the deficiecies of the latter. 
This invention concerns an improved rapid mechanism for advancing and 
retracting the screw spindle by means of a pair of split nuts which 
constrict to knuckle the screw spindle when the latter is turned in 
obverse direction (i.e. the direction which results in advance) and expand 
to release the screw spindle when the latter is turned in reverse 
direction (i.e. the direction which results in retract). Unlike the 
aforementioned prior art, the load is equally distributed to the two split 
nuts as well as the periphery of the screw spindle, thus largely reducing 
the wear thereof.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIGS. 1A and 1B, this invention comprises substantially a 
hollow cylindrical body (1) for receiving a pair of split nuts (3) (3') 
resiliently retained in place. The inner side of each split nut (3) (3') 
is provided with female threads (31) (31') which exactly match the male 
threads (21) of screw spindle (2). Note that the thickness of each nut is 
not uniform. Due to the crescent profile of the female thread the nuts are 
thicker in the portion of the middle part of the crescent thread. In other 
words, the "inner diameter" near the split faces of each split nut is 
larger than that near the middle line due to the different thread depth 
thereof. The outer walls (32) (32') of split nuts (3) (3') are 
respectively provided with notches (33) (33'), into which insert the ends 
of springs (4a) (4b) (4c) (4d) as well as the front ends of stop pieces 
(5) (5'). The tail ends (51) (51') of stop pieces urge against pins (11) 
(11'). 
As shown in FIG. 3, spring (4) is formed by folding the two ends of a strip 
of highly tough steel inwardly along the dash lines and bending the whole 
length into an arc. The arcs thus formed is fitted into the cylinder with 
their folded ends inserted into corresponding notches. Likewise, as shown 
in FIG. 4, stop piece (5) is formed by curling a slotted blank into an 
arc, with its head end (51) folded inwardly. The slot has two ends, 
including an open end (55) and a close end (54), and allows pin (11) to be 
inserted thereinto. 
In FIG. 1A and FIG. 1B, the screw spindle is only resiliently and slidably 
retained by, but not engaged with split nuts, so it can slide axially (in 
the direction of the arrow in FIG. 1A) to any desired operating position. 
Yet when the screw spindle is turned an angle in clockwise direction (as 
shown by the arrow in FIG. 2A and FIG. 2B), the split nuts are forced to 
frictionally co-rotate through an angle and their outer walls (32) (32') 
now lean against pins (11) (11'), so that their split faces meet to 
construct a complete nut, and their threads now mate the threads of screw 
spindle. The split nuts only co-rotate with the screw spindle to the 
position of FIG. 2B. Now the screw spindle can only be advanced by 
screwing. No axial sliding is possible now, as in ordinary clamps. The 
reason why the co-rotation of split nuts (3) (3') and screw spindle (2) 
optimally stops in the position of FIG. 2B is that at this position the 
closed end (54) of the slot of each stop piece meet its corresponding pin 
(11) or (11'), and therefore prevents further co-rotation thereof. So the 
optimal, snuggest engaging position can be designed by properly selecting 
the length of slot. For this reason, the operator can rapidly secure a 
workpiece by firstly pushing the screw spindle to the approximate working 
position, and next turning it an angle in clockwise position. 
To release a workpiece, the screw spindle is turned an angle in reverse 
(counterclock) direction. The splits nuts thus co-rotate an angle until 
the tail ends (51) (51') respectively meet pins (11') (11). Now the split 
nuts (5) (5') are no longer urged by pins (11) (11'), and the resilience 
and the springs and stop pieces pulls them apart from each other, resuming 
the state of FIG. 1B. Now the operator can directly pull the screw spindle 
backward to unload the workpiece. 
FIG. 5 is an embodiment of this invention applied to an equidistant device. 
After improved, this invention exhibits the following advantages over its 
precursor: 
1. The spring of the parent application is divided into two separate parts 
which are much easier to fabricate; 
2. The new design of spring can more reliably slacken the two split nuts 
when dismounting the workpiece; 
3. When the split nuts are being released, the tail ends of stop pieces 
also meet the pins, therefore imparting the pins the function to release 
the nut. 
It will be apparent from the foregoing description of my invention, that 
the same is subject to alteration and modification without departing from 
the underlying principles involved, and I accordingly, do not desire to be 
limited to the specific details illustrated and described except as may be 
necessitated by the appended claims.