Abstract:
The invention refers to a device for clamping goods, in particular pallets carrying work pieces, in machine tools during machining. The device comprises several clamping bolts which interact with corresponding recesses of the good. During clamping the good simultaneously the position, respectively the orientation, of the good is determined by introducing the bolt in the recess.

Description:
[0001]     The invention refers to a clamping device for clamping goods, in particular pallets carrying work pieces, in machine tools during machining.  
       BACKGROUND OF THE INVENTION  
       [0002]     Clamping of goods, in particular work pieces, which are mounted on pallets, is an important part for exact machining, for example in cutting machine tools. The clamping device has to take over the considerable machining and cutting forces and simultaneously guarantee the orientation of the work piece. Especially in highly accurate machining therefore the clamping device is extremely important for the exact machining result.  
         [0003]     In the state of the art arrangements are known for that which have a clamping iron. The clamping iron pulls the pallet towards the corresponding contact surfaces. By means of clamping irons the clamping forces are transmitted to the pallet. The clamping irons here embrace the edge of the pallet like a screw clamp. So-called index bolts are used for the exact positioning and orientation of the pallet. The position of the index bolts is exactly reproduced in the machine control. An accurate machining is possible above the work piece which is clamped exactly on the index bolt. The index bolt here interacts with corresponding recesses on the pallet.  
         [0004]     According to the state of the art therefore for example four clamping irons are provided and, separately from them, for example two index bolts. These elements engage on the edge of the pallet. These elements have to be arranged in the working area because the pallet has to be clamped exactly in the working area. The space is already quite cramped anyway in the working area, and each additional element which is arranged in the working area disturbs the movement of the working spindle. Furthermore all supporting surfaces and index points have to be cleaned before clamping as it has to be avoided safely that chips are deposited on the supporting surfaces. A jammed chip may lead to a waste production because of resulting inaccuracies.  
         [0005]     Coming from the cited state of the art it is an object of the invention to improve a clamping device as described in the beginning in such a way that an arrangement is realised which is as space saving as possible.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     This problem is solved by a device as described above, suggesting that the device has several clamping bolts which interact with corresponding recesses of the good in such a way that during clamping the good by means of introducing the bolt in the recess also the positioning, respectively the orientation, of the good is carried out.  
         [0007]     The trick of the invention is to carry out defining (that means the determining of the position and the orientation of the good) and clamping with the same movement. Even the same elements are used for it. The clamping bolt and the recess have the same accuracy as the index bolt and the corresponding recesses according to the state of the art. In addition to indexing also the fixing is carried out by the clamping bolts.  
         [0008]     A spacially separate arrangement of a clamping iron and an index bolt according to the state of the art is not necessary in the solution according to the invention. The arrangement is more space-saving; the saved space is available additionally, for example, for the traverse path of the working spindle. Therefore also the working possibilities are increased. The arrangement according to the invention can also be kept easier free of chips as, for example, only at four clamping points (at each corner of the pallet) an appropriate chip cleaning has to be provided. This is usually carried out by compressed air.  
         [0009]     The solution according to the invention has also advantages in the working time. In the state of the art it was normal first of all to reach the secure indexing of the pallet and only after that, after the pallet had been in position, to clamp it with clamping irons. This sequential procedure of positioning/orientating and, after that, clamping is overcome by the solution according to the invention because now these steps are carried out simultaneously. The change of work pieces therefore is done in shorter time, the efficiency of a machine tool with a device of this kind is increased accordingly.  
         [0010]     However, the object according to the invention is also solved by another concept in the same way. There the invention has in particular several clamping bolts which interact with corresponding recesses of the device in such a way that during clamping the good by means of introducing the bolt in the recess also the positioning, respectively orientation, of the good is carried out. This principle is based on the kinematic reversal of the before mentioned solution according to the invention. The advantages according to the invention can be reached by this concept in the same way. Additionally this variant provides that each good, if necessary thus each pallet, has appropriately movable clamping bolts. The drives of these clamping bolts then can be electrical, hydraulic or pneumatic.  
         [0011]     It is an advantage that the clamping device comprises several holding devices each of them holding a clamping bolt and the holding device is formed like a C in order to embrace the good laterally. The pallet is pushed in the C-shaped holding device by a conveying device and then defined (that means positioned and orientated) by the clamping bolts as well as clamped. The C-shaped holding devices therefore reach in a simple way an embracing of the edge of the pallet, respectively of the good.  
         [0012]     The invention allows here conveying of the good on the pallet suspended as well as upright. Basically it is even possible that the pallet itself is conveyed upright and is clamped exactly positioned with the clamping device according to the invention.  
         [0013]     In another variant of the invention it is provided that on the holding device a supporting surface is provided for the good which takes over the clamping forces of the clamping bolt. Clamping is carried out in that way that the good, respectively the edge of the good is gripped in the manner of a screw clamp by two “jaws” and fixed. On the one side here the clamping bolt acts as described, on the other side, a supporting surface is provided the position of which can be positioned appropriately accurately.  
         [0014]     It is an advantage here that the position of the supporting surface can be adjusted by means of adjustment washers on the holding device. By means of that an exact spacial orientation of the supporting surface is possible. The supporting surface is part of the clamping plane and defines the machining position of the work piece.  
         [0015]     An advantageous development of the invention is characterised by the fact that a drive is provided for the clamping bolt.  
         [0016]     It is convenient that a separating stopper is provided in order to reach a safe releasing of the clamping bolt from the good. Because of the automatic lock, in particular with a conical design of the clamping bolt, it is possible that the clamping bolt which has to be released cannot be released from the pallet. The pallet then moves towards the separating stopper which causes the clamping bolt to be released from the pallet.  
         [0017]     Even if in this application the pallet is often mentioned as an example of a good the invention should be in no way limited to that. For all exemplary descriptions of the use of a pallet of course every other good is meant in the same way, which is also clear for the expert.  
         [0018]     It is an advantage that the clamping bolt is designed like a cone, truncated cone or cylinder on the end which engages in the good. The recess of the good is, correspondingly, also designed like a cone, truncated cone or cylinder. In particular the designs of the clamping bolt as a cone or truncated cone make for an introduction of the clamping bolt in the recess without clearance. A cylindrical design, if necessary a conical turned off front end of the clamping bolt, is, for example, used when this clamping bolt is needed only for fastening purposes, but not at the same time for indexing purposes. It is provided here that not necessarily all clamping bolts of the clamping device carry out clamping and a simultaneous exact orientation of the good/pallet, but only a few because this could lead geometrically otherwise to disadvantageous over-determinations. Of course, the invention allows also an arrangement with a geometrical over-determination, for example in order to be able to check the exact position of the pallet at several positions.  
         [0019]     It is an advantage if the clamping bolt is supported with as little clearance as possible or without any clearance. The clearance of the bolt has to be kept as low as possible as it also takes care of the indexing in order not to risk the accuracy of the complete arrangement.  
         [0020]     In another variant of the invention it is provided that the device has a clamping crosshead and the clamping crosshead acts on several clamping bolts. A drive is provided for the movement of the clamping bolt. In order to reach a movement as even as possible it is convenient to provide a central drive which operates all clamping bolts of a clamping arrangement. The pallet is usually clamped on its lateral edge. This means that two clamping holding devices have to be arranged on each side. These two clamping holding devices are cleverly collected by operating the clamping bolts of these holding devices by means of the common clamping crosshead. The movement of the crosshead can be derived there, for example, by a central crankshaft which drives in a similar way also the clamping bolts on the other side of the pallet.  
         [0021]     In addition to that the arrangement of the clamping crosshead allows a certain compensation of tolerances in the position of the pallet. Namely it is provided to connect the clamping crosshead flexibly with the clamping drive, for example a clamping rod. Therefore it is possible to compensate appropriately certain position tolerances which the conveyed in pallet may have.  
         [0022]     Furthermore the invention relates to a machine tool with a clamping device as mentioned before. The machine tool according to the invention gains space in the working area by the use of the clamping device as described above. Furthermore the efficiency increases, respectively the performance of a machine tool, as described.  
         [0023]     According to the invention it is provided that the machine tool is designed as a cutting, forming, assembling or separating machine or the machine tool is designed as testing, mounting, adjustment, surface treatment, packing or unpacking station, indicating or cleaning station. The machine tool according to the invention is in no way tied to the machining which has to be carried out. All machining possibilities mentioned before necessitate positioning of the work piece. Basically the positioning of the work piece should be carried out in a time as short and as accurate as possible which is solved, independently from the actual machining, by the invention. Therefore the invention can be used for any purpose of a machine tool. On the one hand, it is possible that the machine tool actually machines the work piece, this means for example, cuts, forms, assembles or separates. Furthermore, however, it is also an advantage that the machine tool is designed as a test station, for example to check corresponding machinings of a previous machine tool. It is an advantage here to provide corresponding tests as early as possible so that not in the final inspection after a number of machining steps, it has to be realised that already in an early machining a fault has occurred and the complete work piece is waste. It is also possible to design the machine tool as mounting station. For example, it is possible to cut a thread into a boring which has been provided earlier, and then to mount another component in this thread in the mounting station. However it is also possible to carry out a change of the work piece carriers in a mounting station, that means for example to mount another work piece carrier.  
         [0024]     In the same way it is convenient to provide the mounting station for an exact positioning, respectively orientation, of the work piece. Furthermore it is possible that the machine tool is designed as a surface treatment station. It serves for example for lacquering, electroplating, printing and so on. Also packing or unpacking stations are seen as machine tools which, for example, pack the work piece after machining or unpack it before machining.  
         [0025]     Furthermore also a device for indicating work pieces can be provided as machine tool. In an indicating station it is provided, for example, that labels or other indications, if necessary even electronically legible indications like bar codes or transponders are fastened or fixed to the work piece, respectively its work piece carrier or its pallet, in order to identify the respective work piece for the control. As a rule a corresponding identification step precedes that (however, this is not compulsory).  
         [0026]     It is also convenient here that as a machine tool a cleaning station, respectively a rinsing or washing station, is provided. Frequently the work pieces are soiled during machining, for example by lubricants, which have to be removed especially at the end of a corresponding process line. Neither is it convenient to leave appropriate oily emulsions on the work pieces if afterwards a surface treatment, like a lacquering or other coating, has to be carried out.  
         [0027]     In the machine tools mentioned before automatically working systems or also manual work places in the sense of the invention should be comprised. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0028]     In the drawing the invention is shown schematically. In the drawings:  
         [0029]      FIG. 1 a  side view of the machine tool according to the invention with the clamping device according to the invention,  
         [0030]      FIG. 2 a  detail of the clamping device according to the invention,  
         [0031]      FIG. 3 a  top view of the pallet according to the invention,  
         [0032]      FIGS. 3   a  and  3   b  details according to  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     The invention is shown schematically in  FIG. 1 .  FIG. 1  shows the machine tool according to the invention with the clamping device according to the invention. The machine tool  1  is, for better understanding, only drawn partly. In particular the frame is only indicated partly. The working area  16  is limited, on the one hand, by the housing and, on the other hand, by doors  10 ,  10 ′.  
         [0034]     The machine tool serves for carrying out certain machinings on goods  2 . The goods  2  are conveyed here by a conveying device  4  in the working area  16 . In the example shown here a good is suspended as work piece  2  on a pallet  20 . In  FIG. 1  three goods  2 ,  2 ′,  2 ″ are indicated altogether. The good  2  is here in the center in the machine tool, the good  2 ″ has already been removed from the working area, the working door  10  has been closed again already. The next work piece  2 ′ is already in front of the door  10 ′ ready for further machining. The conveying device  4  is formed for example by a roller conveyor consisting of rollers  40 .  
         [0035]     In the example shown here the clamping device  5  according to the invention serves for clamping the pallet  20  in the working area  16 . Even if here the interacting of the clamping device  5  with a pallet  20  is shown, the invention is not limited to that. The pallet  20  is a special case of the good  2 . The work piece  2  can also be clamped directly.  
         [0036]     The clamping device  5  is formed by several holding devices  53  which themselves have the clamping bolt  55 . The exact embodiment of the holding device  53  is shown in  FIG. 2 .  
         [0037]     For clamping, respectively indexing, the clamping bolts  55  carry out a vertical movement  59 . For that purpose a drive  7  is used. The drive  7  is formed by a motor  70  which drives a drive shaft  72  via a gear  71 . A connecting rod  54 , which transforms the rotational movement of the drive shaft into a linear movement, is located on the drive shaft  72 . Eventually the connecting rod  54  acts on the clamping rod  57  which finally operates the clamping bolt  55  (if necessary guided restrictedly). The drive shaft  72  provides in this case several clamping bolts  55  with the necessary movement. Naturally, it is also possible that an independent, autonomous drive is provided for each clamping bolt.  
         [0038]     It is convenient in this embodiment that the clamping rod  57  acts on a clamping crosshead  50  and the clamping crosshead  50  moves in the example shown here two clamping bolts  55 . Between the connecting rod  54  and the clamping rod  57  a spring assembly  52  is provided for a compensation of the clamping forces as per clamping device there are two clamping crossheads  50  in order to reach four clamping points which are operated by a motor.  
         [0039]     The clamping crosshead  50  is connected here via a joint  51  with the clamping rod  57  which can compensate certain position tolerances easily. If necessary the crosshead  50  also acts flexibly on the respective clamping bolt  55 .  
         [0040]     Instead of a mechanical drive for the clamping bolt  55  it is also possible to drive the clamping bolts for example hydraulically or pneumatically.  
         [0041]     In the example shown here the machine frame  11  has a guide frame  56  for guiding the clamping bolt  55 . If necessary, also the holding device  53  is connected with it.  
         [0042]     The guide frame  56  holds the bolt guides  58  for the clamping bolts  55 .  
         [0043]     In  FIG. 2 a  holding device  53  of the clamping device  5  according to the invention is shown in a detail. The holding device  53  is here formed like a C in order to embrace the good  2 ,  20  laterally. The conveying device is, for example, vertical to the plane of the paper. The C-like embodiment embraces cleverly the edge of the good  2 , respectively the pallet  20 , which is here, for example, pushed in for clamping and indexing. In the example, above the pallet  20 , the clamping bolt  55  is provided which can be introduced by a vertical movement  59  with the bottom end  61  in a recess  21  of the pallet  20 . The guide of the clamping bolt  55  has no clearance or very little clearance. Below the pallet  20  a supporting surface  62  is provided which can be orientated exactly. It is part of the clamping plane. The exact position of the support  62  can be adjusted by adjustment washers  63  which can be built in. The pallet is held non-positive and positive locking by the clamping bolt  55 , driven in the recess  21 , between the clamping bolt  55  and the support  62  for machining purposes.  
         [0044]     As it may be that, for example because of the automatic lock, the front end of the bolt cannot simply be released from the recess, a separating stopper  60  is provided. This separating stopper  60  is arranged laterally on the right hand side beside the guide for the clamping bolt. In case that, if the clamping device  5  is opened, the front end  61  of the clamping bolt  55  is not freed from the recess  21 , the pallet  20  is pushed upstairs until it comes into contact with the separating stopper  60 . Then the clamping bolt is pulled out of the recess  21  by force.  
         [0045]     The clamping bolt  55  has an axial boring  64 . This boring  64  is connected with supply lines  65  for compressed air. However, it is possible, before and after introducing the clamping bolt, to clean the recess  21  for example from chips and the like.  
         [0046]     In  FIG. 3  the pallet  20  is shown schematically. The pallet is here an essentially square pallet which has recesses  21  on its edges in the corner. The recesses  21  are, for example, designed like cones, truncated cones or cylinders. The work piece  2  is mounted on the pallet  20 .  
         [0047]     Advantageously the pallet has at least at each of its corners a recess  21 . In the shown embodiment of the invention the recesses  21  have clearance on the left hand side and on the top of the right hand side while the recess  21  which is coloured dark on the bottom of the right hand side is without clearance.  
         [0048]     According to the invention the good is not only clamped by means of the clamping device, but simultaneously fixed in its position and orientation, that means it is determined. As the four supporting points have the effect that the complete arrangement is geometrically over-determined, in a variant according to the invention it is provided that not necessarily all recesses  21  have to be included in the definition of the pallet. According to the invention, however, it is provided that a certain over-determination is actually desired.  
         [0049]     In  FIG. 3   b  in a detailed view the introduction of the clamping bolt  55  in the recess  21  is shown schematically. This is a first holding device which serves for positioning the pallet in a clamping plane.  
         [0050]     Conveniently the front end of the clamping bolt is designed here as a complete cone which is introduced in the recess  21 . By means of that the pallet is determined defined in the clamping plane. However, the possibility of a rotational movement in this clamping plane around this clamping bolt still remains.  
         [0051]     In order to eliminate also this degree of freedom a second holding device is provided which is used preferably opposite diagonally ( FIG. 3 ) on the pallet, which causes the determination of the pallet in the clamping plane. In order to avoid an over-determination the clamping bolt of this second holding device has lateral flattenings  65 . The flattenings  65  are arranged here in such a way that they are on the connection line of the recesses  21 ,  21 ′ interacting with the first and the second holding device. The embodiment is shown in  FIG. 3   a  schematically. The situation in the recess is shown in each of the two enlarged sections in  FIG. 3   a.  Therefore the clamping bolt  55 ′ only causes a determination in one direction rectangular to the diagonal line of the pallet. It is convenient that the clamping bolts  55  and  55 ′ of the first and second holding device engage more or less simultaneously in the respective recess  21 ,  21 ′ in the pallet. The spacial determination of the pallet with regard to the clamping plane as well as fixed in the clamping plane is thus carried out simultaneously automatically.  
         [0052]     The arrangement in  FIG. 3  shows clearly that the recesses  21  in the pallet  20  are different. In  FIG. 3   b  a cone-like recess has been chosen, in recess  21 ′ according to  FIG. 3   a  it is an embodiment like a truncated cone. In use this does not cause any problems as long as the pallet is not rotated during operation. In the case that the pallet is rotated it is an advantage if all recesses  21  are identical. Furthermore it is provided to arrange grooves  66  on the pallet in a region on the recess  21  of the pallet. They allow a certain chance for compensation. Cleverly these grooves are not arranged at these recesses which are provided for the determination of the position, respectively orientation. Flattenings of the truncated cones, respectively the guides, are also embodiments provided according to the invention which allow certain chances of compensation.  
         [0053]     Although the invention has been described by exact examples which are illustrated in the most extensive detail, it is pointed out that this serves only for illustration and that the invention is not necessarily limited to it because alternative embodiments and methods become clear for experts in view of the disclosure. Accordingly changes can be considered which can be made without departing from the contents of the described invention.