Abstract:
An arrangement for clamping raw materials in a machine tool for machining elongated workpieces is provided. The arrangement comprises a supporting plate with at least one thoroughgoing opening and at least one clamping device arranged in front of one of the openings. The clamping device has a pair of clamping rings that drive pairs of jaws. When a pair of clamping devices are utilized, the first clamping device may be used primarily for the clamping of profiles, while the second clamping device is designated for round bodies.

Description:
The present invention relates to a clamping device and, in particular, to a clamping device well adapted for use in connection with machine tools, including laser machine tools, for machining elongated workpieces. The present application claims the benefit of provisional application No. 60/419,276 filed 17 Oct. 2002. 

   BACKGROUND OF THE INVENTION 
   Elongated work pieces, such as pipes, bars, and flat and hollow profiles, are slid through a chuck of a suitable laser machine and cut and/or welded at their free end by a laser beam. Frequently the workpieces are supported at their free end in order that they do not sag or bend during machining. These known chucks have the disadvantages that they are only suitable for circular cylindrical workpieces. Profile elements and non-symmetrical workpieces cannot be clamped precisely therewith. 
   The problem to be solved with the present invention is to create a universally useable clamping device which can securely clamp elongated full or hollow profile elements of any cross-section during laser machining and the like. The device should be suitable for automated working processes and should permit short spanning and changeover times. 
   BRIEF DESCRIPTIONS OF THE INVENTION 
   The problem is solved by the present invention, which is a clamping device having a supporting plate, preferably vertically oriented, having at least one adjustable workpiece clamping unit and at least one through-going bore for a workpiece. The clamping unit may have clamping rings that support opposed pairs of jaws. The jaw pairs may be advantageously oriented orthogonally to each other. Rotation of a clamping ring causes the respective jaws of a pair to open or close; rotation of both clamping rings allowing the jaw pairs to grip or release a workpiece, accommodating both profile and non-symmetrical workpieces. 
   A second through-going opening in the supporting plate may be provided to allow a workpiece to extend therethrough for engagement with a second clamping unit, which may be of conventional construction, located at a fixed vertical orientation. With provided means to orient the supporting plate vertically, such as a linear drive, the first clamping unit can be positioned as required. 
   The clamping rings may be operated pneumatically, with cylinders having double pistons to control the rotation direction. The rings may be provided with cam or wedge surfaces engaging the jaws to move the jaws radially in response to ring rotation. A two-part jaw construction, in which clamping jaws are positionable upon base jaws, further allow the clamping unit to accommodate a range of workpiece cross-sections and profiles. The use of mating teeth on the base and clamping jaws may provide for quick and secure adjustment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative embodiments of the invention are hereinafter described with reference to the annexed drawings, in which: 
       FIG. 1  is a perspective view of a portion of a laser machine with a clamping device according to the invention; 
       FIG. 2  is a perspective view of the clamping jaws of an upper clamping unit shown in  FIG. 1  with their actuating cylinders and the associated power transmission, a cover ring or flange for the clamping device having been removed; 
       FIG. 3  is a view of the clamping jaws from the opposite side than in  FIG. 2 ; and 
       FIG. 4  is a plan view of the clamping unit of  FIGS. 2 and 3  with a pressurized air supply, also with an outer covering flange being removed. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a simplified representation of a laser machine LM. The laser beam L is guided in known manner by a beam guide and deflecting mirrors S to the working space of the machine. An upper clamping unit  1  for profile elements is arranged on a supporting plate  2 . The power for the clamping unit  1  is supplied by compressed air hoses  3 . 
   The supporting plate  2  is slideably guided laterally by guiding flanges  4  and frontally by guide rails  33  welded to the plate  2  for vertical displacement in the direction Z′. The clamping unit  1  includes clamping jaws  6  with rollers  7 , which clamping jaws are rotatably supported on the supporting plate  2  via respective rings  5 . The clamping jaws  6  are easily exchangeable and are fixed in position on the clamping device  1  by fastening screws  6 ′ on their base bodies. The thoroughgoing openings for the workpieces between the jaw of the upper clamping unit  7  and a second, lower clamping unit are designated D 1  and D 2 , respectively. In the opening D 1  a rectangular hollow profile is shown in phantom, and in the opening D 2  a pipe. The displacement movement of these raw materials is effected in the direction of the respective arrows by a handling system arranged behind the clamping device. The guide rails  33  are protected by a protecting profile  35  against dirt and damage by rebounding workpieces or cut-off parts. 
   The entire clamping device  1  is rotatable in directions which are represented by the arc φ. The position of the clamping device  1  with respect to the machine is continuously monitored by a position sensor  34  and signaled to an NC control unit as known in the art. 
   At the lower part of the supporting plate  2  a horizontal support  8  is arranged on the lower portion of the machine base  32 . A pair of steady supports  12  with steadies  11  and embedded spheres  11 ′ are horizontally displaceably mounted on the support  8 . The displacement motion of the steady supports  12  is shown by the double-headed arrows. A manometer  31  for monitoring of optimal air supply pressure is mounted on a face of the support  8 . 
   Angle profile members  2 ′ on opposite sides of the supporting plate  2  are arranged on the plate  2  and provide vertical adjustment. As can be seen, a counterbearing  9 ′ of pushing bar  10  of electromagnetic linear drive  9  is mounted on the middle part of the front of angle profile  2 ′. The drive  9  can move the upper, first clamping unit from an initial position HO into a lowered working position H 1 . The movement is marked by the arrow Z′. 
   The clamping rings  5  visible in  FIG. 1  comprise, according to  FIG. 2 , a first ring  5   a  and a second ring  5   b . The ring  5   a  effects an adjustment of a first pair of opposed base jaws  16  associated with, for example, the vertical jaws in  FIG. 1 . The ring  5   b  effects the adjustment of a second pair of opposed jaws  16  associated with the horizontal jaws in  FIG. 1 . Both rings  5   a  and  5   b  are rotatable independently of each other and each have roller supports  13   a ,  13   b , respectively, shifted against each other by an angle of 90°. Roller shaft bearers  14  with rollers  15  at one end are inserted in the roller supports  13   a, b.    
   The outer rings of rollers  15  each bear against a pair of opposed cam or wedge surfaces  17  formed in each of the base jaws  16 , and drive the base jaws radially inward or outward depending on the direction of rotation of the corresponding clamping ring. Each clamping ring has a pair of piston supports  22 , located between the respective roller shaft bearers, which connect to an axially displaceable piston  25 ′ in a piston cylinder  25 . Preferably, as shown, the piston is a double piston. The pistons are secured to the piston supports by piston bolts  23  and standard securing rings  24  called “Seegerrings”. 
   The base jaws  16  have on their face side a central fastening groove  20  and lateral toothings  18 . The grooves  20  facilitate the positioning and mounting of the clamping jaws  6  on the base jaws, such as by retaining screws  6 ′. The lateral grooves  19  mate with corresponding grooves in chuck body  29  and maintain the base jaws in register when the clamping rings rotate. 
     FIG. 3  shows the arrangement described above from the opposite side. Visible are the wedge surfaces  17  and the lateral grooves  19  in the base jaws  16 . The rollers  15  can be seen as well between the embedded wedge surfaces  17 , as well as the screw connection  21  for the roller shaft bearers  14 . 
   The plan view of  FIG. 4  shows the same arrangement, equally with the outer covering ring removed, mounted on the chuck body  29 . Cylinder covers  27  are screwed onto the ends of cylinders  25 . The cylinders  25  are maintained in defined positions on the chuck body by positioning rings  26  fitting into accommodating recesses  37  in the chuck body  29 . On their back side (as seen in  FIG. 4 ) the cylinders  25  each have two connections for compressed air, these connections ending in thoroughgoing openings  36  in the chuck body  29 , and are supplied with energy via the compressed air hoses  3  through air tight flanges with cavities as known in the art. The chuck body  29  is screwed onto a driven hollow spindle (not shown) by bolts through centering borings  30 . 
   The function of the clamping unit according to  FIGS. 2–4  is as follows: 
   Depending on the profile to be clamped (workpiece/blank) the clamping jaws  6  are screwed onto the base jaws  16  with clearance against the profile. The positioning and maintenance of the clamping jaws  6  upon the corresponding base jaws  16  is facilitated by the base jaw toothing  18 , the clamping jaws  6  having corresponding teeth. The hoses  3  are supplied with compressed air (controlled by the NC program) and the compressed air act on the pistons  25 ′ ( FIG. 2 ), closing the clamping unit, i.e. the clamping jaws  6  clamp the profile with a force of about 60 kg per jaw. The force transmission is easily seen; two opposing double pistons each move the ring  5   a  and/or  5   b  such that the rollers  15  roll on the wedge surfaces  17  thereby moving the base jaws  16  radially in their lateral grooves  19  in respective grooves of the outer chuck body  29 . 
   The embodiment shown allows very short clamping and opening times which enables shorter working cycles. 
   The second clamping unit  11 ,  11 ′,  12  (see  FIG. 1 ) works similar to a known steady rest and is designed for rotationally symmetric workpieces. It is operated pneumatically as well and can easily be moved away from the vertical support when the first clamping unit is in operation. A conventional drive is associated with the first clamping unit  1  such that workpieces can be cut by the laser beam L around the entire circumference of the profile supplied and clamped. The rotational speed of the clamping unit  1  can be increased in a short time to several hundred rpm. Thereby cut-out parts of the workpiece can be ejected by centrifugal action.