Abstract:
The invention relates to an actuating device for a tool or a workpiece tensioning jack in a machine tool spindle. The actuating device includes a pressure piston which is arranged inside a housing for actuating the tool or workpiece tensioning jack. In order to provide a compact, space-saving actuating device enabling leakage fluid to be drained off in a simple manner, several interspaced continuous bores are arranged concentrically around a center axis in a side wall of the housing. Pressure plungers which are axially displaceable with the aid of the pressure piston are disposed therein and the housing contains at least one leakage channel with a section extending between the pressure plungers in a radially outer direction.

Description:
FIELD OF THE INVENTION 
     The invention pertains to an actuating device for a tool or a workpiece tensioning jack in a machine tool spindle. 
     BACKGROUND OF THE INVENTION 
     The working spindles of machine tools or processing centers as a rule have an integrated tool tensioning jack for automatic tensioning and release of the processing tools. In the conventional tool tensioning jacks, the tools are usually held by a tensioning grasper which is located at the front end of a tensioning rod which is tensioned by a cup spring packet and engages in a corresponding tightening bolt of the tools or tool holder. To release the tools, the tensioning rod is displaced by a usually hydraulically actuated piston-cylinder unit opposite the tensioning force of the cup spring packet, so that the tensioning jaw is opened and the tool is released. Often an inner coolant inlet is provided so that the lubricating coolant can be directed to the tool, for example, via the hollow tensioning rod through the interior of the working spindle. But in this case, the lubricating coolant has to be sent through a suitable device from a stationary connecting piece into the rotating parts during the processing. As a rule, this occurs through so-called rotary lead throughs, in which the transition between the fixed and rotating parts takes place by means of sealing rings that slide upon each other. In order to achieve a particularly space-saving and compact design, the rotary lead through can be integrated within the actuating device for the tool tensioning jack. However, since this kind of rotary lead through is not entirely leak-proof and leakage of the lubricating coolant may occur in particular at the connecting point between the stationary and rotating parts, the problem that occurs primarily in the compact design is to ensure a suitable removal of the leakage fluid. 
     From DE 195 43 612 C1 a similar actuating device is known for a tool or workpiece tensioning jack which contains a pressure piston which is arranged inside a housing for actuating the tensioning rod which is pretensioned by a set of springs. Integrated into this actuating device there is a rotary lead through which contains a first slide washer joined with the tensioning rod, and a second slide washer located in a separate sealing part. The pressure piston designed as ring piston is located in a cylinder that will move axially in a fixed machine part. If the ring piston is placed under pressure within the cylinder, then the piston will be braced against the spindle by means of internal engaging elements and exert a corresponding counter-force on the axially moving cylinder. In this manner, the tension rod and also the rotary lead through will be moved along. 
     It is the purpose of the invention to create a compact and space-saving actuating device of the kind described above, which makes possible a simple removal of leakage fluid. 
     SUMMARY OF THE INVENTION 
     The invention relates to an actuating device for a tool or a workpiece tensioning jack in a machine tool spindle. The actuating device includes a pressure piston which is arranged inside a housing for actuating the tool or workpiece tensioning jack. In order to provide a compact, space-saving actuating device enabling leakage fluid to be drained off in a simple manner, several interspaced continuous bores are arranged concentrically around a center axis in a side wall of the housing. Pressure plungers which are axially displaceable with the aid of the pressure piston are disposed therein and the housing contains at least one leakage channel with a section extending between the pressure plungers in a radially outer direction. 
     Due to the interspaced placement of the pressure plungers there will be space between them for the passage of one or more leakage bores or channels, into which any leakage fluid can flow off without back-pressure and it can be collected there or removed through corresponding lines. In particular in the vertical position of a machine tool spindle, the leakage fluid will flow by gravity downward and can be released at appropriate intervals or it can be moved off continuously through suitable lines as needed. The actuating device according to this invention is a particularly compact device and is thus also highly suited for machine tools with little available space. 
     For example, in a simple design and low-cost embodiment, the housing contains an inner housing part and an outer housing part securely attached to it such that an annular compression space for the pressure piston is defined. The leakage channel is formed preferably by bores which run parallel and perpendicular to the center axis of the housing. The bores can be sealed at their outward open ends by stopper plugs or drain screws or be connected to corresponding outlet lines. 
     Within the housing of the actuating device there is a rotary lead through for the inlet of a working fluid and/or cleaning fluid for the machine tool spindle which is rotating during operation. The rotary lead through is located preferably in a separate housing and can thus be installed or removed in a simple manner. 
     In addition, an air inlet channel for the cleaning of clamping surfaces or such can be provided in the housing of the actuating device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional details and advantages are indicated from the following description of one preferred design example with reference to the following figures: 
     FIG. 1 is a portion of a tool tensioning jack with an actuating device according to this invention, presented in cross section; 
     FIG. 2 is a side view of the actuating device illustrated in FIG. 1; 
     FIG. 3 is a cross sectional view of the actuating device in a plane offset to that presented in FIG. 1; and 
     FIGS. 4A,  4 B are an assembly of the pressure plunger to the pressure piston. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 presents a part of a tool tensioning jack  2  built into a machine tool spindle  1  and an actuating device  3  with a so-called rotary lead through  4  for the inlet of a working fluid and/or cleaning fluid to the machine tool spindle  1 . The illustrated parts of the tool tensioning jack  2  and of the actuating device  3  in the top half of FIG. 1 are shown in a release setting and in the lower half, in a tensioned setting. 
     As is evident in FIG. 1, the actuating device  3  contains a hollow, cylindrical housing which consists of an inner housing part  5  and an outer housing part  6  tightly screwed thereto. A pressure chamber  9  is bounded by the inner and outer housing part  5  and  6  and is sealed externally by means of gaskets  7  or  8 . A ring-shaped pressure piston  10  can slide in an axial direction of the housing within this pressure chamber. The pressure piston  10  is sealed against the inner and outer wall of the ring-shaped compression chamber  9  by means of inner and outer sealing elements  11  and  12 . The inner ends of several cylindrical pressure plungers  14  which are interspaced at the same angle in the circumferential direction are located at the front side  13  of the pressure piston  10  which front side is directed toward the tool tensioning jack  2 . The other ends protrude outward from the housing in the release setting illustrated in the top half of FIG.  1 . The pressure plungers  14  are located in several interspaced continuous bores  16  located concentrically around a center axis  15  of the housing in a radial flange  17  formed on the housing part  5 , which flange forms one side wall of the housing. In addition, the pressure plungers  14  are sealed against the housing by suitable sealing rings  18  in the radial flange  17  and can be axially displaced in corresponding guide bores  19  of a guide ring  20  located within the compression chamber  9 . 
     The housing part  5  equipped with a central bore opening  21  contains several leakage channels  22  which lead from a ring groove  23  at the inner wall of the bore opening  21  to an outlet opening  24  sealed by means of a screw  46  at the outer perimeter of the radial flange  17 . The leakage channel  22  is formed by a section  25  in the radial flange  17 , running transverse to the center axis  15  between two pressure plungers radially outward to the outlet opening  24 , and by a section  26  at a right angle to it, and said section runs parallel to the center axis  15  between the inner wall of the bore opening  21  and the compression chamber  9 . Preferably, the leakage channel  22  is produced by bores which run from the rear side and the outside of the housing part  5  and which are sealed by a stopper plug  27  or the screw  46 . An additional drain bore  28  opens into the section  25  at the front side of the radial flange  17 , which likewise can be sealed by a sealing screw. 
     At the perimeter wall of the outer housing part  6  there is a first, radial inlet opening  29  which leads via a bore  30  to a rear end of the ring-shaped compression chamber  9 . Via the inlet opening  29  the ring-shaped pressure piston  10  can be supplied with hydraulic fluid as pressuring agent for extension of the pressure plunger  14 . From a second radial inlet opening  31  at the housing part  6  another inlet bore  32  runs parallel to the center axis  15  and leads to the front end of the compression chamber  9 . The pressure plunger  10  can be supplied with hydraulic fluid via the inlet opening  31  and the inlet bore  32  for retraction of the pressure plunger  14 . 
     By means of the pressure plungers  14  actuated by the pressure piston  10 , a pressure disk  33  is displaced which is attached to the rear end of a tension rod  34  equipped with a continuous bore. The tension rod  34  can be displaced axially within the operating spindle  1  and is tensioned by a schematically illustrated cup spring packet  35  in the tensioned position illustrated in the bottom half of FIG.  1 . In this setting a tool installed in the tool spindle will be pulled into a cone by a tensioning jack (not shown). To release the tool, the pressure piston  10  is supplied with a compressed fluid via the first radial inlet opening  29  and the bore  30 , and then it will be moved together with the pressure plungers  14  from the tensioned setting illustrated in the lower half of FIG. 1, into the released setting illustrated in the upper half of the figure. Thus, the tensioning rod  34  will be displaced to the left via the pressure ring  33  according to FIG. 1, and the cup spring packet  35  will be compressed. Thus, the tensioning jack located at the front end of the tension rod will release the tool. 
     For tensioning of the tool, the pressure piston  10  is supplied with compressed fluid via the second, radial inlet opening  31  and the inlet bore  32 , and the pressure piston  10  will move back from its released setting into the tensioned setting and the tension rod  34  will be pulled back into the tensioned position under the effect of the cup spring packet  35 . Thus, a tool installed in the tool spindle will be clamped by the clamping jack (not shown). 
     The rotary lead through  4  is located in the central passage opening  21 . It contains a stationary connecting part  36  for connection of a fixed supply line and of a rotating connection pipe  37 , which can slide axially with a hollow connecting part  38  and is sealed. The hollow connecting part  38  is screwed into the continuous bore of the tensioning rod  34 . From the housing of the rotary lead through  4  a radial leakage bore  39  runs outward and it is in connection with the ring channel  23 . The leakage fluid can be removed to the outside via this leakage bore and the leakage channel  22  from the interior of the rotary lead through  4 . 
     As is evident in FIG. 2, in the illustrated design eight pressure plungers  14  located coaxially to the center axis  15  of the housing are provided, together with four leakage channels  22  each offset to one another by 90 degrees and each provided with front-side outlet bore  28 . The number of pressure plungers  14  and leakage channels  22  can be varied as desired. Four continuous bores  40  are supplied on the outside, each one for a screw  41  illustrated in FIG. 3, so that the housing can be secured to a spindle head or such. In addition, FIG. 3 shows an inlet channel for a cleaning fluid; this channel contains an inlet opening  42  positioned radially in the outer housing part  6 , and an inlet bore  43  running parallel to the center axis  15 , and also a radial bore  45  in the inner housing part  5 . This radial bore is connected to the inlet bore and opens via a slanting inlet bore  44  at the inner wall of the passage opening  21 . Cleaning air for cleaning of clamping surfaces or such can be supplied via this inlet channel. 
     In FIGS. 4A and 4B we see the assembly of the pressure plungers  14  to the pressure piston  10 . The cylindrical pressure plungers  14  have two mutually opposing flattened sides  47  on their ends facing the pressure piston  10  for insertion into corresponding T-grooves  48  at the front side of the pressure piston  10  directed toward the pressure plungers  14 . The pressure plungers  14  can thus be inserted into the corresponding T-groove  48  by a simple displacement in the radial direction, as is shown in FIG.  4 A. In the installed position illustrated according to FIG. 4B, the pressure plungers  14  can then be easily locked in place in the axial direction with respect to the pressure piston  10 . In this manner, with little manufacturing expense, a fast and simple assembly of the pressure plungers to the pressure piston can be obtained. 
     The invention is characterized by a very compact design which allows a space-saving construction of an automatically actuated machine tool jack in a machine tool spindle. 
     However, the invention is not restricted to the illustrated design example. It can be employed in a corresponding manner, e.g., as an actuating device for a workpiece tensioning jack.