Abstract:
A work table is provided with a housing ( 10, 23 ) and a rotary element ( 11, 12, 24 ) mounted rotatably at the housing ( 10, 23 ) as well as with a locking device ( 22, 23, 26 ) for fixing the particular angle of rotation position of the rotary element ( 11, 12, 24 ) in relation to the housing ( 10, 23 ). To provide the work table with a fail-safe behavior the locking device ( 22, 23, 26 ) is released by a first actuating member when the energy supply is switched on and is activated by means of a restoring member when the energy supply is switched off. An additional actuating member may be provided to boost the locking force.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of priority under 35 U.S.C. § 119 of German Application DE 103 58 943.0-14 filed Dec. 15, 2003, the entire contents of which are incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention pertains to a work table with a housing and with a rotary element mounted rotatably at the housing as well as with a locking means for fixing the particular angle of rotation position of the rotating element in relation to the housing.  
       BACKGROUND OF THE INVENTION  
       [0003]     Such a work table is disclosed, for example, in DE 202 02 998 U1. This work table has a round table mounted rotatably at a housing, which is called substructure in the document. Workpieces are clamped on the round table in the usual manner in order to subject them to machining, especially cutting. Consequently, the round table is a workpiece mount arranged rotatably at the housing. The workpieces mounted on the round table can be rotated by means of the round table driven by a rotating drive into predetermined positions favorable for the particular machining step and then machined.  
         [0004]     Considerable forces, which must be diverted via the round table, act on the workpiece during the machining of workpieces, especially by milling, planing or the like. These forces apply a considerable torque on the round table, so that it may inadvertently rotate in relation to the housing. This is prevented by means of the locking means.  
         [0005]     Motor-driven worm gear mechanisms were originally used as the rotating drive. These had the advantage of locking the particular angular position of the rotary element (round table) by means of a self-locking design. The worm gear mechanism was consequently also the locking means at the same time.  
         [0006]     There has more recently been a change to providing the round tables with a so-called direct drive via a torque motor, as it is offered, for example, by the firm of Eberle. The possibility of locking the rotary element by means of self-locking is eliminated here. A clamping is therefore provided between the housing (substructure) and the rotary element (round table) in the work table according to DE 202 02 998 U1. A disk arranged at the round table is now clamped, and it is clamped such that the clamping is activated by admitting a pressurizing agent into hydraulic cylinders after the angular position of the round table has been set in relation to the housing.  
         [0007]     The drawback of this procedure is that the clamping is released in case of failure of the pressurizing agent supply for the hydraulic cylinders. This may lead to an inadvertent rotation of the round table and consequently to a crash of the workpiece and even to a risk of injury to personnel due to breaking tools and/or workpieces.  
         [0008]     Locking means similar to those described in DE 202 02 998 U1 are disclosed in U.S. Pat. No. 6,457,383 B1 and U.S. Pat. No. 6,001,145 A.  
         [0009]     DE 195 15 085 C2 shows a locking means for a belt drive. Should a drive belt break, a spring-loaded locking lever is pivoted and it engages a locking wheel as a result. The locking lever can be pivoted back and the locking abolished by a cylinder.  
         [0010]     In the locking means shown in DE 42 14 947 A1, a bar or shaft is clamped by means of a clamping lever. The clamping lever has a hole, in which the bar or shaft is guided. The hole becomes eccentric in relation to the bar or shaft due to the pivoting of the clamping lever, so that the bar or shaft is clamped.  
       SUMMARY OF THE INVENTION  
       [0011]     The basic object of the present invention is to improve a work table of the type described in the introduction such that the clamping will be reliably preserved even in case of failure of the energy supply, especially the pressurizing agent supply (fail-safe behavior).  
         [0012]     To accomplish this object, the work table according to the present invention is characterized in that the locking means is released when the energy supply is switched on and activated when the energy supply is switched off.  
         [0013]     Hydraulic oil/fluid is used predominantly for the energy supply in machine tools, and pneumatic energy supply by means of, e.g., compressed air is used less frequently. The locking means is consequently designed according to the present invention such that it fixes the rotary element in the pressureless state. If a pressurizing agent is admitted to actuating cylinders of the locking means, the locking means is released and the rotary element can be rotated. If the pressurizing agent supply fails for whatever reason, the locking means remains fully active. The rotary element cannot rotate inadvertently.  
         [0014]     It is, of course, also conceivable to actuate the locking means by means of electromagnets, which are to be supplied with electric energy in this case. The locking means is designed in this case as well such that it is released only when the electromagnet is switched on.  
         [0015]     It is common to the locking means known from DE 202 02 998 U1, U.S. Pat. No. 6,457,383 B1 and U.S. Pat. No. 6,001,145 A that they operate by clamping, i.e., in a nonpositive manner. This has the advantage that locking is possible continuously in any desired angular position. However, if continuous locking is unimportant and, in particular, very high torques are to be absorbed by means of the locking means, a positive-locking fixation may also be performed within the framework of the present invention. Hirth rings are especially suitable in this case, because they permit very small angle increments.  
         [0016]     An additional actuating member, which further boosts the locking force applied by the restoring member, is preferably provided. This would be especially suitable when the workpiece mounted on the work table is exposed to especially strong machining forces. Even though the locking force is reduced to the locking force applied solely by the restoring member in case of a failure of the rest of the actuating member, this force is sufficient to allow sufficient time for the human operator or the electronic system for an emergency shut-off of the machining, without a dangerous rotation of the workpiece mount occurring during this time.  
         [0017]     For example, springs or the force of gravity are used as the restoring member. The actuating members are preferably actuated by pressurizing medium. Hydraulics, in particular, but also compressed air are usually available at all machine tools.  
         [0018]     The suitable actuating members are especially annular pistons. These may be led on the outside around the workpiece mount and thus have the greatest possible lever arm and consequently the strongest possible locking force at a predetermined pressure. The annular piston may be designed as a plastic part and press-fit into an annular groove acting as a cylinder housing, so that no separate sealing elements are necessary.  
         [0019]     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The present invention will be explained in greater detail below on the basis of exemplary embodiments shown in the drawings. In the drawings:  
         [0021]      FIG. 1  is a vertical sectional view of a first work table having the features of the present invention;  
         [0022]      FIG. 2  is a horizontal sectional view of another work table having the features of the present invention; and  
         [0023]      FIG. 3  is a view of the work table according to  FIG. 2  in a section plane rotated in relation to  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Referring to the drawings in particular, the work table shown in  FIG. 1  has a housing  10  and, as a first rotary element, a pivoting housing  11  mounted rotatably at the housing  10 . A face plate  12 , at which workpieces can be mounted for machining in the known manner, is mounted rotatably as an additional rotary element at the pivoting housing  11 . The pivoting housing  11  is rotatable around a first pivot axis  13  in relation to the housing  10 , and the face plate  12  is rotatable around a second pivot axis  14  positioned at an angle in relation to the first pivot axis  13  in relation to the pivoting housing  11 . The pivoting housing  11  is mounted at the housing  10  and the face plate  12  is mounted at the pivoting housing  11  by means of prior-art pivot bearings  15  and  16 . A respective torque motor  17  and  18  is used as the rotating drive. The particular angular position of the pivoting housing  1  in relation to the housing  10  can be detected by means of a measuring system  19 . Another measuring system  20  is used to detect the angle of rotation position of the face plate  12  in relation to the pivoting housing  11 .  
         [0025]     A locking means  21  is provided to fix the pivoting housing  11  in its angular position in relation to the housing  10 . Another locking means  22  is used to fix the angular position of the face plate  12  in relation to the pivoting housing  11 . The two locking means  21 ,  22  have, in principle, the same design and will be described below on the basis of  FIGS. 2 and 3 .  
         [0026]      FIGS. 2 and 3  show another work table, namely, a round table. This has a housing  23  and a face plate  24 , which is mounted at the housing  23  rotatably around the axis of rotation  25 . The face plate  24  can again be fixed in relation to the housing  23  by means of a locking means  26 . This locking means has a design analogous to that of the locking means  21  and  22  for the work table according to  FIG. 1 , so that it is sufficient to describe below this locking means  26  only in greater detail.  
         [0027]     A housing ring  27  is arranged, for example, screwed, on the housing  23 . This housing ring  27  has an annular groove  28 , into which an annular piston  29  is inserted. The annular piston  29  is made of a plastic and has a press fit in relation to the annular groove  28 , so that it is automatically sealed against the annular groove  28 . Pressurizing agent, specifically hydraulic oil, can be admitted into a pressure space  32  under the annular piston  29  via a connection hole  30  and an ascending pipe  31 . As a result, the annular piston  29  is lifted out of the annular groove. As a result, the annular piston  29  raises a fixed disk  33 . An outer edge of a rotating disk  34 , which said disk is nonrotatably connected with the face plate  24  and rotates together with same, is arranged on the inner side of the annular piston  29  under the fixed disk  33 .  
         [0028]     In the lowered state, when the pressure space  31  under the annular piston  29  is pressureless, the fixed disk  33  clamps the rotating disk  34  between itself and the housing ring  27 . The face plate  24  is fixed and workpieces mounted on it can be machined. If pressurizing agent is admitted into the pressure space  32 , the annular piston  29  raises the fixed disk  33 , so that the rotating disk  34  can rotate freely under the fixed disk  33 . The face plate  24  can be rotated in this position. As soon as the desired angle of rotation of the face plate  24  in relation to the housing  23  has been set, the pressure is released from the pressure space  32 . The fixed disk  33  is lowered by means of suitable restoring members and clamps the rotating disk  34 . Suitable restoring members may have the following design:  
         [0029]     Weights, for example, in the form of a ring that lies on the fixed disk  33  and is connected with the fixed disk  33  and/or the housing ring  27  in a suitable manner, may be located on the fixed disk  33  in case of work tables in which the disks  33  and  34  are located in a plane that is sloped at a sufficient angle in relation to the force of gravity. If this solution is not sufficient or is even impossible, e.g., when the plane of the disks  33  and  34  is located in the direction of the force of gravity, it is also possible to provide restoring members. It is possible, for example, for this purpose to screw the above-mentioned ring to the annular housing  27  and to provide compression springs between the heads of the screws and the ring, on the one hand, and/or between the ring and the fixed disk  33 , on the other hand.  
         [0030]     Another variant is shown in  FIG. 3 . A ring  35  is provided here on the side of the fixed disk  33  facing away from the annular housing  27  and is connected with the annular housing  27  and/or the fixed disk  33  in a suitable manner. An annular groove  36 , into which a second annular piston  37  is inserted, is provided in the ring  35  on the side facing the fixed disk  33 . This annular piston  37  has exactly the same design as the annular piston  29 , so that the same component can be used, which minimizes the manufacturing and stocking costs. The annular piston  37  is again press-fitted in relation to the annular groove  36 , so that it is sealed against the annular groove  36 .  
         [0031]     A pressure space  38  above the annular piston  37  is supplied with pressurizing agent, specifically hydraulic oil, via supply holes  39 ,  40 ,  41 ,  42 ,  43 . Of these supply holes  39  . . .  43 , the supply hole  42  can be drilled only from the outside, as can be recognized from  FIG. 2 . It is therefore closed by a plug  44  toward the outside. Furthermore, the supply holes  40  and  41  are connected with one another via a grommet  45  in order to establish a sealed transition through the fixed disk  33  from the housing ring  27  to the ring  35  for the pressurizing agent supply.  
         [0032]     If the pressurizing agent is admitted into the pressure space  38 , the annular piston  37  presses the fixed disk  33  in the direction of the housing ring  27 . The rotating disk  34  is clamped by the fixed disk  33 . This variant has the advantage that the clamping force can be set continuously by varying the pressure in the pressure space  38 .  
         [0033]     Nonreturn valves, not shown, which ensure that the pressure in the pressure space  28  continues to be maintained in case of failure of the pressurizing agent supply, are provided in the pressurizing agent line in order to achieve the desired fail-safe behavior in this variant.  
         [0034]     The variant shown in  FIG. 3  can be readily combined with other variants of a restoring element, especially the above-described ones, and it will thus have a clamping force-increasing effect.  
         [0035]     Wile specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.  
       APPENDIX  
       [0036]     List of Reference Numbers: 
     10  Housing      11  Pivoting housing      12  Face plate      13  Pivot axis      14  Pivot axis      15  Pivot bearing      16  Pivot bearing      17  Torque motor      18  Torque motor      19  Measuring system      20  Measuring system      21  Locking means      22  Locking means      23  Housing      24  Face plate      25  Axis of rotation      26  Locking means      27  Housing ring      28  Annular groove      29  Annular piston      30  Connecting hole      31  Ascending hole      32  Pressure space      33  Fixed disk      34  Rotating disk      35  Ring      36  Annular groove      37  Annular piston      38  Pressure space      39  Supply hole      40  Supply hole      41  Supply hole      42  Supply hole      43  Supply hole      44  Plug      45  Grommet