Push-pull plunger clamp

Abstract: A plunger clamp capable of locking in either a retracted or extended position having a rigid body slidably supporting an elongated plunger. A bifurcated lever is pivotally connected inside the body and to a V shaped link arm, the link arm is pivotally connected to the plunger where the link arm translates the angular motion of the lever to drive the plunger between the retracted and extended positions. Essentially the entire linkage assembly is housed in cavities formed by the body during actuation of the lever.

Description: The present invention broadly relates to a plunger clamp apparatus, and more particularly, relates to a plunger clamp assembly having a body for support and stability. Plunger clamps have been long known in the industry and act to provide a lever arm connected through a linkage to move a cylindrical plunger. The linkage generally consists of three pivot points all in the same plane as the motion of the plunger. Additionally, the linkage members all have substantially linear designs with longitudinal axes in line with the pivot points when the plunger is in either a push or pull position. An example of this type of device is manufactured by De-Sta-Co company, Model 604. The design of such devices create problems. First, the mechanical advantage of the typical plunger clamp, that is, the correlation between the force applied to the handle and resulting reaction force to the plunger, is so great that the linkage is routinely overstressed during normal use causing the linkage to fail. Second, the linkage design of the typical plunger clamp uses rivets to make pivotal connections, routinely connecting only two members at a time. This type of connection has unbalanced forces resulting in a torquing force on the rivet. Accordingly, if the connected members of the plunger are not machined properly, within low tolerances, the stress on the rivets during normal use is increased to a level resulting in rivet failure. US 3,926,418 discloses a plunger clamp in accordance with the pre-characterising portion of claim 1. The hereinafter described and illustrated embodiment of a plunger clamp in accordance with the present invention has a mechanical advantage that does not over-stress the linkage during normal use. It also uses full cross pins to lessen torquing forces at the pivotal connections to reduce the risk of failure of the pivotal connections. According to the present invention there is provided a hand-operated plunger clamp according to claim 1. A link arm essentially shaped as a V is pivotally connected to a lateral extension of the lever at a second axis and pivotally connected to the plunger at a third axis in which the link arm translates the angular motion of the lever to drive the plunger along a longitudinal axis between a retracted and extended position responsive to movement of the lever. The plunger has a rectangular forked end with the link arm positioned between the forked ends for the pivotal connections at the third axis, the forked ends having smaller dimensions than the diameter of the plunger to allow this pivotal connection to enter the linear bearing. Accordingly, the linear bearing need not be enlarged to accommodate this pivotal connection effectively maximizing support for the plunger. This linkage design: the V-shaped link arm, the forked plunger end, and the lateral extension of the lever reduces stress in the linkage by decreasing the mechanical advantage of the clamp and allows for full cross pins to be used as pivotal connections. Additionally, this design has three pivotal connections instead of five to simplify the. manufacture of the clamp. Finally, a substantial portion of the linkage is housed in the cavity of the body to protect the linkage during use of the present invention in the work place. The present invention will be further described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a side view of the present invention with the plunger clamped in a retracted position. Figure 2 is a side view similar to Figure 1 showing the plunger clamped in an extended position. Figure 3 is a top view of Figure 1. Figure 4 is a side view of the body of the present invention. Figure 5 is a bottom view of the body in Figure 4. Figure 6 is an end view of Figure 5. Figure 7 is a side view of the link arm of the present invention. Figure 8 is top view of the link in Figure 7. Referring now in greater detail to the drawings, Figure 1 illustrates a plunger clamp 20 in accordance with the present invention. Said clamp 20 includes a body 26 having a threaded end 39, said body 26 forms a linear bearing 36 to slidably support an elongated plunger 28, said plunger 28 actuated by a link arm 24 pivotally connected at full cross pin 34 to plunger 28 and pivotally connected to a bifurcated lever 40 at full cross pin 32 of a lateral extension 38 of said lever 40, said lever 40 having a second pivotally connection at full cross pin 30 to end of said body 26 opposite to threaded end 39. Figures 7-8 illustrates an embodiment of the actuating link arm 24 having essentially a V-shape with an inside curvature 42. Fig. 1 illustrates the present invention in a retracted position where lever 40 is essentially perpendicular to the longitudinal axis of plunger 28, with cross pin 32 slightly above a plane formed by cross pins 30, 34 and the longitudinal axis of plunger 28 effectively locking the plunger over center. In this position, curvature 42 of link arm 24 rests securely against cross pin 30 to prevent further movement of lever 40 toward the body 26. Figures 2-3 illustrate the plunger clamp 20 in the extended position. From the position of Figure 1, lever 40 is rotated about the axis of cross pin 30 through a path away from the body 26 such that the lever 40 is once again essentially perpendicular to the longitudinal axis of plunger 28. This actuation of the lever translates the axis of cross pin 32 from a point outside body 26 as positioned in Figure 1 through a path with a final position inside body 26 between cross pins 30 and 34. Cross pin 32 moves slightly past a plane defined by pins 30, 34 and the longitudinal axis of plunger 28 to lock the plunger over center with end 50 of link 24 resting against cavity 46 of body 26. Figures 4-6 illustrates cavities 46, 52 and a linear bearing 36 formed by the body 26 to allow maximum travel of the link arm 24 and plunger 28 and to house the linkage assembly. This embodiment of body 26 is essentially rectangular with linear bearing 36 traversing half the length of body 26, with linear bearing 36 having a rectangular cavity portion 52 to allow link arm 24 to move through body 26. The rest of body 26 is essentially open having two sides 54, 56 where lever 40 is pivoted at cross pin 30 inside body 26. Plunger 28 is essentially cylindrical with the end at cross pin 34 having a pair of rectangular forks 58 of smaller dimensions than the diameter of plunger 28 allowing the forks 58 to travel through the linear bearing 36 uninhibited. The forks are spaced apart leaving just enough room for link arm 24 to be securely positioned between the forks and pivotally fastened with cross pin 34. The present embodiment of plunger 28 is internally threaded capable of receiving threaded adjustment knobs (not shown) allowing adjustment of the throw of plunger 28.

Claims: A hand-operated plunger clamp (20) comprising: a body (26); an elongated plunger (28) slidably held within said body (26); a lever (40) pivotally connected to said body (26) at a first axis (30); and a link arm (24) pivotally connected to said lever (40) at a second axis (32) and said link arm (24) pivotally connected to said plunger (28) at a third axis (34), said link arm (24) being arranged to translate the angular motion of said lever (40) to drive said plunger (28) along its longitudinal axis between first and second positions responsive to movement of said lever (40); characterised in that : said plunger (28) has an offset forked end of smaller dimensions than the diameter of said plunger (28) where said link arm is pivotally connected at said third axis (34) between said forked end; in that said body (26) is essentially rectangular, with a square cross-section and a threaded end (39); and in that said plunger (28) is internally threaded and full cross pins are used at each pivotal connection (30,32,34). The plunger clamp of claim 1, wherein said lever (40) is a bifurcated lever having an extension (38). The plunger clamp of claim 2, wherein said extension (38) is located adjacent the pivotal connection (30) at said first axis, said pivotal connection (32) at said second axis positioned in said extension (38) whereby said first position of said lever (40) positions the second axis (32) above a plane established by the first axis (30), third axis (24) and the longitudinal axis of the plunger (40) to lock the plunger (28) over center, a concave portion of said link arm (42) rests against said pivotal connection at said first axis (30) to lock the plunger (28) in said first position. The plunger clamp of any one of the preceding claims, wherein said link arm (24) has major dimensions shaped as a V forming a seat at the concave portion (42) of the V-shape. The plunger clamp of any one of claims 1 to 3, wherein said link arm (24) has measured dimensions shaped as a V forming a seat at a concave portion (42) of the V shape. The plunger clamp of any one of the preceding claims, wherein said body forms a first cavity (52) to allow the link arm to move inside said body (26) during the angular motion of said lever (40) between first and second positions of said plunger (28). The plunger clamp of claim 6, wherein said body (26) forms a second cavity (46) to allow the extension (38) of said lever (40) to move into a position inside the body which positions said second axis (32) between first and third axes (30,34) just above a plane established by the first axis (30), third axis (34) and the longitudinal axis of the plunger (28) to lock the plunger (28) over center, one end of said link arm (24) resting against said second cavity (46) to lock the plunger (28) in said second position.

Inventors: DYKSTRA HENRY, DYKSTRA, HENRY
Applicants: CAPITAL FORMATION INC, DELAWARE CAPITAL FORMATION, INC.
Application year: 1998
Main classification: B25B5
IPC codes: B25B5