Abstract:
A toggle clamp comprises a compression spindle assembly with a plunger and a spindle. The plunger has a chamber dimensioned to slidingly receive the spindle in a telescoping arrangement, and a resilient member disposed in the plunger chamber to urge the spindle away from the plunger chamber. A screw extends through a bore of the spindle and the plunger chamber and is threaded into the plunger to bias the resilient member and maintain the spindle in sliding contact with the plunger chamber. The screw has a head abutting a shoulder monolithically formed in the spindle bore. The screw is rotatable to adjust a level of compression of the resilient member. The compression spindle assembly reliably applies a gradual rate of pressure as the compression spindle assembly is compressed.

Description:
RELATED APPLICATION DATA 
   This application is a divisional application of application Ser. No. 10/133,034, filed Apr. 26, 2002, now abandoned. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to clamps for positioning and holding work pieces during manufacturing and, more particularly, to clamps capable of automatically adjusting for holding work pieces of varying thicknesses. 
   2. Related Art 
   Manufacturing operations typically require that a work piece be held in place during machining, assembly and similar operations. Work pieces are held by presses, dies and, most commonly, by clamps. Many of these manufacturing operations are still hand operated. Thus, repetitive clamping of multiple work pieces for repetitive machining or assembly procedures creates predictable needs for efficiency, speed and ease of use. 
   This creates a need for automatic adjustment of a holding device, such as a clamp, to accommodate work pieces of various thicknesses and to thereby avoid the otherwise required re-positioning by hand of a clamp or the like. Work pieces of varying thicknesses necessarily result simply due to manufacturing tolerances. There is a particular need for minimizing or eliminating repetitive adjustments of clamping members when alternating between work pieces intended to be of various thicknesses. 
   Prior art clamps which will securely clamp work pieces having a minimally varying thickness include U.S. Pat. No. 3,212,347 to Robeson. This patent discloses a clamp having a spring to mediate the pressure applied by a plunger to a work piece. However, the plunger in that clamp may not be mounted in other clamps. Moreover, the compression of the spring cannot be readily adjusted and instead is fixed at the time of manufacture. 
   Worker safety is and virtually always has been a serious concern. Work piece holding devices are generally safer to the extent that they can eliminate pinch points where a worker may pinch his hand, especially in those applications where re-positioning of the work pieces into and out of the device may be done repetitively and at speed. Prior art clamps, to the extent that they use springs to compress a plunger and bias it towards a work piece generally do not enclose the spring, and thereby expose workers to pinch points. Another aspect of worker safety involves equipment design that reduces the risk of repetitive motion injury by reducing the necessary amount of force a worker must exert to engage a clamp. The prior art devices not providing some adjustability in spring force, or otherwise not allowing for some mechanical advantage place the worker at risk for this kind of injury as well. 
   There is thus a need in the art for a clamp to apply various degrees of pressure to accommodate work pieces made of various materials in order to prevent damage to the work pieces from excessive pressure. There is also a need to avoid movement of the work piece from its desired position by the type of sudden application of force often produced by toggle clamps or locking clamps. A holding apparatus, such as a clamp, that gradually exerts pressure on a work piece with a “soft start,” is needed. There is also a need for a clamp that will have a totally encapsulated spring, thus avoiding pinch points, but which can provide a soft clamping and accommodate variously sized work pieces. Still further there is a need for a clamp that is easily assembled, and which can be adjusted to provide a different clamping pressure. 
   SUMMARY OF THE INVENTION 
   It is in view of the above needs that the present invention was developed. The invention generally comprises a compression spindle apparatus adaptable for use with manufacturing holding apparatuses, especially clamps. 
   A preferred embodiment of the compression spindle apparatus includes a plunger having an abutment surface at one end for contacting and applying pressure to the work piece. The plunger has an axial bore open at the end of the plunger opposite the abutment surface for receiving a helical compression spring and a spindle. The bore has a first portion wide enough to receive the spring, and the bore transitions to a smaller diameter with a shoulder being formed thereat and against which the spring rests. A threaded screw attaches the spring inside the plunger by extending through the center of the spring and screwing into the smaller diameter of the plunger bore. 
   A spindle encloses the other end and is inserted into the bore over the spring, with the head of the screw engaging a shoulder of the spindle. The spindle is dimensioned to be inserted in close contact with the inside of the bore so that there is no gap or opening through which the spring may be exposed to create a pinch point. The spindle also has an axial bore, with a change in diameter creating the aforementioned annular shoulder much like the plunger bore. Unlike the plunger bore however, the spindle bore is a through hole. Thus, the screw may be inserted entirely through the spindle bore until the head of the screw seats on the annular shoulder of the spindle bore. The screw is then threaded into the plunger bore threads to thereby create the plunger/spring/spindle assembly. 
   The plunger/spring/spindle assembly allows the plunger and spindle to move relative to each other while compressing the spring, when the plunger abuts a work piece to hold it. At a rest position the screw head engaging the spindle annular shoulder limits the extension of the plunger and spindle. Thus, the plunger/spring/spindle assembly provides a telescoping assembly that is self contained and modular. This plunger/spring/spindle assembly of the present invention may thus be mounted in a variety of clamps, dies and presses. This adaptability is not found in prior art devices. 
   The telescoping action of the compression spring assembly allows it to be used on work pieces of varying thicknesses without adjustment between uses. 
   As noted, in the preferred embodiment, the spring is entirely encapsulated by the plunger and the spindle. Thus the spring is not exposed and no pinch points are created to cause worker injury. 
   The screw also serves to allow for adjustment of the spring compression, and thereby the pressure exerted by the plunger. The screw can be tightened to compress the spring and loosened to release pressure on the spring, to thereby provide for an adjustable pre-load. Of course, various kinds of springs may also be used, each of which could exhibit different compression characteristics. The ability to adjust the spring compression characteristics and pre-load a desired pressure is a good and valuable feature. 
   In a preferred embodiment the end of the spindle not engaged with the plunger bore has a through hole perpendicular to its longitudinal axis. A lever pin may be inserted through this hole to mount the assembly in a clamp or other holding device. 
   In operation, the plunger/spring/spindle assembly, or simply the compression spindle assembly, is preferably mounted on a clamp or other holding device to allow movement in an axial direction, but to limit movement in other directions. The spindle preferably has an actuation means, such as a toggle clamp lever, attached to it via the pin extending through the perpendicular through hole. To clamp a work piece, pressure is applied to the spindle via a lever pin or other force application mechanism. The compression spring assembly moves as a unit towards the work piece. Upon the plunger contacting the work piece, the spindle moves along the plunger axis, through the plunger bore in a telescoping action towards the work piece. The movement of the spindle towards the work piece compresses the spring until the full travel position of the lever or other holding mechanism is reached. The amount of pressure created by the spring is that degree of pressure preselected by a worker&#39;s adjustment of the screw. The spring compression allows the assembly to accommodate differences in work piece size or positioning without re-adjustment. Further, the spring mediates the application of pressure to the work piece. 
   Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  is a cutaway side view of the compression spindle apparatus. 
       FIG. 2  is a cutaway top view of the compression spindle apparatus as installed with a typical toggle clamp. 
       FIG. 3  is a side view of the compression spindle apparatus as installed with a typical toggle clamp. 
       FIG. 4  is a partially cutaway side view of the compression spindle apparatus as installed with an alternative type of clamp. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , wherein like reference numbers identify like parts, the compression spindle assembly  10  of the present invention has a plunger  12  with an abutment surface end  14  for holding a work piece (not shown). A bore  16  is formed at the end  18  of the plunger opposite the abutment surface end  14 . The bore  16  has a spring mount portion  20  with a larger diameter and a screw mount portion  22  with a smaller diameter. The screw mount portion  22  is closer to the plunger abutment surface end  14 . Plunger  12  and bore  16  are preferably coaxial. The step transition between the spring mount portion  20  and the screw mount  22  forms an annular shoulder  32 . Spring  30  is disposed in spring mount portion  20  and one end thereof rests against shoulder  32 . Spindle  40  is preferably sized to closely fit within the inner diameter of spring mount portion  20  and has a through hole  42  with an opening  44  at one end and a screw inlet  46  at its opposite end. In the depicted embodiment, opening  44  has an optional cap  60 . Spindle  40  also preferably has a perpendicular through hole  52  for receiving a drive pin for linking the compression spindle assembly of the present invention to a clamp lever. 
   Screw inlet  46  preferably has a smaller diameter than through hole  42  so that a step transition formed at their juncture creates a screw cap seat  48 . A threaded screw  28  has a cap  50  at one end and threads  26  along its shank and preferably near its outboard end. Screw mount portion  22  preferably has threads  24  formed to receive and fixedly secure corresponding threads  26  to thereby retain screw  28  within bore  16 . Screw  28  has sufficient threads  26 , and screw mount portion  22  is sufficiently long, to allow screw  28  to be reliably retained and secured within bore  16  without driving screw  28  fully into screw mount portion  22 , as shown in FIG.  1 . This allows the spring loading to be adjusted, both with respect to the spring parameters and the pre-load or initial compression set as the compression spindle assembly  10  is first made or later adjusted. In  FIG. 1 , gap  31  indicates the space into which the screw  28  may be turned in order to further compress the spring  30 . 
   In assembly, spring  30  is inserted into spring mount portion  20  of plunger  12 . Spindle  40  is then inserted into spring mount portion  20 , contacting the top of spring  30  and encapsulating it. Preferably, the longitudinal opening through spring  30  substantially aligns with through hole  42  and screw inlet  46  such that screw readily slides into place. Screw  28  may then be inserted first through the wide opening  44 , through hole  42 , and then through the narrow screw inlet  46  of spindle  40 . Screw  28  is further inserted through spring  30  arid threaded into the screw mount portion  22  of bore  16 . Screw  28  is preferably turned at least until screw cap  50  seats against screw cap seat  48  in spindle  40 . Screw  28  then retains the spindle  40  in the bore  16  of plunger  12 , and contains both ends of spring  30 . Screw  28  can thereafter be further turned to adjust and to set a predetermined compression of spring  30 . 
   In operation, spindle  40  is driven towards a work piece in a manner described below. When the abutment surface  14  contacts the work piece, telescoping of the spindle  40  within plunger  12  compresses spring  30  until the mechanical driver reaches its locked position. At that position, the work piece is reliably held in position under pressure of the compressed spring  30 . Preferably, the compression spindle assembly is adjusted, by choosing the spring and screw position with respect to the spring, so that the desired amount of spring compression is achieved for the work piece being held by the clamp within which the compression spindle assembly is used. As the plunger is spring loaded, the work piece is not shifted or damaged by being engaged with a “hard” mechanical linkage type clamp, and instead is locked in place under spring pressure. 
   With the present invention, the worker need not continuously adjust the stroke of the clamp, or other mechanical structure of the clamp, thereby minimizing the amount of hand movement needed to process successive work pieces and diminishing the risk of repetitive motion injuries. Furthermore, the spring is completely encapsulated, hidden from view and shielded from workers fingers and clothes, thus eliminating pinch points and the reducing risk of injury. 
   It will be readily apparent to those of skill in the art that various design alternatives are available without departing from the scope of the present invention. For example, the helical compression spring  30  may be replaced with a grommet of rubber or other resilient material. It may also be replaced with a spring washer or a series of spring washers. Still any other type of resilient type of material may be used which provides for relative movement between the plunger and spindle and which applies a force under compression. 
   The plunger, bore and spindle may be rectangular or other shapes in cross section besides the preferred cylindrical shape. The plunger may comprise the male portion and the spindle the female member, so that telescoping movement between the two is reversed. 
   Likewise, the spindle and spring may be retained by means other than screw  28 . These means may include a center post extending through the spring with a nut for fastening at the end of the center post, a center post with a rivet, or a screw extension machined into the spindle. An annular ring may be used between the bore  16  of plunger  12  and the exterior surface of the spindle  40 , with seating of the annular ring in a step or detent in the interior surface of bore  16  or the exterior surface of spindle  40 . Design alternatives also include inserting and retaining an adjustment screw  28  from the opposite direction, i.e., by boring through the center of the abutment surface  14  of plunger  12 . A screw would then be inserted through that bore, and through the helical compression spring to engage the threads of a female mount in spindle  40 . The screw cap would then seat in a recess in the abutment surface  14 . Even further design alternatives are possible by using press fittings assembled by force and without threads. 
     FIGS. 2 and 3  depict the compression spindle apparatus as installed with a typical toggle or over center clamp. Plunger  12  is oriented in the clamp assembly with abutment surface  14  oriented towards a work station for holding a work piece therein. Plunger  12  must preferably be free to move axially towards a work piece and thereafter away from it. However, it must preferably simultaneously be restrained from uncontrolled movement in any other direction. Accordingly, in the depicted structure, housing  150  includes a channel  152  to receive the compression spindle assembly. Of course, housing  150  may be designed in any of a variety of configurations, with channel  152  open or fully circumscribing the compression spindle assembly. In the depicted embodiment, housing  150  is cylindrical, closes entirely around the compression spindle assembly, and further has a step to a wider portion  154  which serves as a mount for brackets  156 . 
     FIG. 3  depicts the clamp components in their closed position with solid lines and, alternatively, in their open position with broken lines. Nut  180  is a lock nut for mounting the clamp on a block, on a wall or for otherwise mounting the clamp on a work platform. Bilateral brackets  156  are attached to housing  150  by pivot posts  158  so that the brackets  156  may rotate around posts  158 . The other ends of brackets  156 , oriented to the right in FIGS.  2  and  3 , also have through holes  168  for receiving lever pins  160 , thus providing a linkage between the lever  162  and the compression spindle assembly  10 . 
   The lever  162  has a handle end  164  and an L-shaped foot  166 . The foot  166  has two through holes; one at its heel  168  and one at its toe  170 . One through hole,  168 , receives lever pins  160  so that lever  162  may rotate around the axis of through hole  168 . Second through hole  170 , at the toe of foot  166 , receives spindle pin  172  so that lever  162  may also rotatively engage the spindle pin  172  for driving the spindle  40 . 
   The foot  166  of lever  162  has an offset  174  dimensioned to allow brackets  156  to override the outside dimension of spindle pin  172 , so that spindle pin  172  may travel between the inside dimensions of brackets  156 . 
   In operation, a work station adjacent to the toggle clamp depicted in  FIGS. 2 and 3  is empty, lever  162  and handle  164  are down, in the position indicated by the broken lines in  FIG. 3 , and both spindle  40  and plunger  12  are retracted away from the work station, shown towards the left of  FIGS. 2 and 3 . Upon insertion of a work piece into the work station, an operator manually swings handle  164  upwards towards the position indicated by the solid lines in FIG.  3 . Lever foot  166  simultaneously pivots around lever pin  160  and spindle pin  172 . Lateral translation of the lever heel at pin  160  is restrained by solid brackets  156 . Accordingly, the upward, arcuate motion of lever  162  drives spindle  40  to translate towards the work station while the toe of the lever foot  166  rotates around spindle pin  172  simultaneously. This translation continues until the lever  162  is in its fully upright position. Optionally, any of a variety of known locking mechanisms, such as an abutment, a hook, a boss and detent arrangement or a spring (not shown) may arrest and hold lever  162  in its fully upright position. 
   The translation of spindle  40 , driven by lever  162  through spindle pin  172 , is in a direction towards the work piece. When the abutment surface  14  first contacts the work piece, it applies a small amount of pressure to the work piece. As the spindle  40  continues to travel towards the work piece, it further compresses the spring  30 . The compression of spring  30  increases the force urging plunger  12  against the work piece and gradually continues to increase that pressure until the lever  162  is in its fully upright position. Thereafter, the spring maintains the preconfigured degree of pressure holding the plunger against the work piece, thus securing the work piece for machining, assembly or other manufacturing operations. 
     FIG. 4  depicts the compression spindle assembly disposed in a clamp with a different configuration. Plunger  12  is still oriented horizontally with the abutment surface  14  facing towards a work station. Spindle  40  still faces away from the work station where it is to be engaged with a clamp. Plunger  12  is again slidingly disposed within a housing  250 . Housing  250  is either a part of, or attached to a mounting base  252 , which includes a mounting plate  254  for attaching the entire clamp assembly to a bench or other work platform. A lever  262  again has a handle end  264  and two through holes  268  and  270 . 
   In the embodiment depicted in  FIG. 4 , both through holes  268  and  270  are in line with the longitudinal axis of the lever  262 . Through hole  268  receives a pin  272  which holds lever  262  in pivoting attachment with mounting base  252 . Lever through hole  270  receives a pin  274  pivotally linking lever  262  with bracket  280 . Bracket  280  has two through holes at either end. One of the through holes also receives insertion of pin  274 . The through hole  282  at the other end of bracket  280  receives insertion of pin  284 , which is also inserted within through hole  52  of spindle  40 . Pin  284  puts bracket  280  in pivoting engagement with spindle  40 , providing a linkage between the lever  262  and the compression spindle assembly  10 . 
   In operation, a worker pulls lever  262  away from the work station. The lever pivots around its mount at pin  272 . Through hole  270  of lever  262  is thereby moved through an arcuate path towards the work station. Through pivoting communication with the lever by pin  274  and pivoting communication with spindle  40  through pin  284 , bracket  280  transfers the arcuate motion of lever  262  into driving translation of spindle  40  towards the work piece. Thereafter, in the manner previously described, spindle  40  drives abutment surface  14  into holding contact with a work piece in a gradual manner mediated by spring  30  of the compression spindle assembly. 
   Those of skill in the art will recognize the variety of linkage assemblies with which the compression spindle assembly may be engaged with a clamp. The spindle  40  may have a slot perpendicular to both the through hole  52  and the axis of spindle  40  for linking a single bracket  156  or  280  between the spindle and the lever pins. Similarly levers  162  or  262  or mounts may be bifurcated to accommodate single bracket linkages. 
   It will be readily apparent to those of skill in the art that the operation of the compression spindle assembly as combined with the toggle levers described above creates a graduating pressure upon a work piece during clamping. The graduation of this pressure effected by the compression spindle assembly avoids shifting of the work piece during clamping, avoids damaging the work piece and makes the clamping movement easy to execute for a worker. Injury risk is further reduced by encapsulation of spring  30 . Moreover, the interaction of the spring between the spindle and plunger, allows the plunger pressure to be applied to work pieces of varying thickness without a worker having to make an adjustment of the length of the plunger for each new differently sized work piece. 
   In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.