A variety of spindle mounted balancers have been designed over the years having the meaning to simplify and improve the accu-- racy of manual balancing methods. Attention shall be given to those designed to operate while the spindle is revolving. Such balancers, generally known as unbalance compensators, can be broadly classified into two categories; mechanical and fluid operated. The mechanical types cannot, however, do both large and fine balance corrections at the same time. Such balancing arrangements have been illustrated for example in US the pat- ents 2,518,226 (Drake), 4,683,681 (Russ) and the PCT publica- tion number W082/00353.

Also the following publications present structures belonging to this technological field. The US patent publications 5,174,585 (Rinne), 2,324,225 (Mueller), 2,553,990 (Vidal), 2,652,749 (Hagmeister), 2,794,661 (Sears), 2,826,420 (Klinger), 2,852,287 (Baker), 2,911,222 (Eve), 3,259,020 (Walker), 4,430,017 (Ste- fanicich) and the UK patent publication 2007550 disclose fas- tening means for axial bodies based on the idea of using hy- draulic pressure in a closed cylindrical space to deform fas- tening sleeve and to clamp said tool accurately with high torque.

Releasable hydraulic chucks are widely used to clamp tools and workpieces. However, these clamping means involve problem of oil leaks and they require big size which is causing weight and therefore unbalances.

An object of the present invention is to avoid the drawbacks of the known technology and to provide a well balanced toolholder whereby its own design is so well balanced that only the addi- tional unbalance of the tool or workpiece to be clamped need to be balanced. The object mentioned above includes quickly oper- able pressurizing means and an unleakable piston and seal ar- rangement for a clamping device, whereby said problems can be eliminated. On order to achieve the objects mentioned above the invention is characterized in what is mentioned in the charac- terizing part of claim 1. The advantageous embodiments of the invention are characterized in what is mentioned in the other claims.

A guide surface which is inclined or bent with respect to the moving direction is moved via an actuating element, particu- larly designed as a ring. On this guiding surface an actuator is sliding which in turn moves a pressure transfer piston which is movable in a pressure cylinder to a clamping means. The ac- tuator is advantageously a ball, which rolls on the guiding surface. In the pressure transfer piston the actuator is sup- ported by means of a support element, particularly made of a slippery PTFE-material which is able to creep under pressure.

The pressure transfer piston further comprises a sealing to maintain the pressure applied by the actuator in the pressure cylinder.

By the help of the present invention a new and improved design and way to use a piston and seal arrangement for a clamping de- vice can be achieved. As an advantage the invention provides a fast way to clamp a toolholder or the like. Further the device is light weight, accurate, symmetrical and has automatic bal- ancing properties.

As the pressurizing ring of the toolholder is floating on the pressurized bearing balls the ring can find the best balance position for itself when the spindle is turning with high speed and still at the same time the ring is functioning as a pres- surizing device of the clamping tool. The balancing ability is, of course, depending on the weight of the ring and the gap be- tween the body and the ring which is defines possible movement of the ring.

The invention is described in detail on the following pages by the help of the enclosed drawings in which: FIG. 1 shows a sectional side view of the present invention, FIG. 2 shows a sectional side view of an embodiment of the present invention, FIG. 3 shows a sectional side view of further another em- bodiment of the present invention having a different tool fastening system, FIG. 4 shows a sectional side view of further another em- bodiment of the present invention having a booster for tool fastening system, FIG. 5 shows a sectional side view of the embodiment of fig.

4 where the clamped piece is locked, FIG. 6 shows a cross sectional view of the present inven- tion, whereby the hydraulic bearing ball piston and seal arrangement are shown, FIG. 7 shows a cross sectional view of the present inven- tion, whereby several hydraulic pistons are pushed in by the eccentric ring and fastening the tool with hy- draulic pressure, FIG. 8 shows an exaggerated illustration of the balancing situation of the ring, and FIG. 9 a further embodiment of the invention with axially inclined surfaces.

Figure 1 shows a sectional side view of a toolholder having a body section 1 connected to a fastening device 2, the latter comprising a turnable pressurizing ring 3 which has on its in- ner circumference for instance three low angle eccentric sur- faces 11. The pressurizing ring 3 fits on its smallest diameter accurately onto the body section 1. Further the pressurizing ring 3 has more than one, preferably three pistons 4, each of the pistons comprising a bearing ball 4a rolling along the cor- responding eccentric surface 11 of the pressurizing ring 3 when the ring is rotated and thus working as power intensifier of the hydraulic pressure.

The fastening device 2 comprises further an axial bore 12 for a tool or a workpiece 7 to be fastened, the bore 12 being coaxial with the toolholder. The bore is surrounded by pressure chan- nels 5 filled with pressure medium and connected with the pres- sure side of the pistons 4 of the pressurizing ring 3. Between the pressure channels 5 and the bore 12 there is a tubular steel sleeve 6 which is fixedly connected to the body of the toolholder. The sleeve 6 can be deformed by the pressure caused by the turning of the pressurizing ring 3 and conducted to the sleeve by the pressure medium in the pressure channels. When deforming the sleeve presses towards the bore 12 thus decreas- ing the diameter of the bore causing the tool or workpiece 7 inside the bore to be securely fastened.

Figure 2 shows another type of a toolholder. The fastening sys- tem is basically the same as in figure 1. However, in this type the tool or workpiece 7 is not inserted inside the bore but onto the cylindrical projection of the fastening device 2 which cylindrical projection is coaxial with the toolholder. The pressure in channels 5 presses the steel sleeve around the cy- lindrical projection now outwards and the sleeve expands thus fastening the tool or workpiece 7 securely onto the cylindrical projection when the pressurizing ring 3 is turned to the fas- tening position. The angle of rotation from loose position to fastened position can be between 600 to 1800, for example 900.

Figure 3-5 show further another types of a toolholder. The tool or workpiece 7 is now form locked to its position when the pressurizing ring 3 is turned to the fastening position. Form locking is applied with hydraulically operated pistons 8 com- prising bearing balls 8a which are moved by the pressure caused by the pistons 4 and which bearing balls 8a press towards the matching semi-circular groove 9 encircling the tubular locking projection of the tool or the workpiece. The groove 9 is better seen in figure 4 where the locking process is just beginning and the bearing balls 8a have not yet pressed completely into the bottom of the groove 9. Small arrows in figure 4 show the directions of the motions of the tool or the workpiece and the bearing balls 8a when turning the pressurizing ring 3 to the fastening direction. The pressure medium 10 conveys the pres- sure from the pistons 4 to the bearing balls 8a.

Figure 4 and 5 show a special embodiment of the invention where the diameter of the bearing ball 8a is bigger than that of bearing ball 4a. In this structure the piston system acts as a pressure booster or amplifier for the clamping device causing bigger pressure for locking the tool or the workpiece.

Figure 6 and 7 present a cross sectional view of the invention, where the hydraulic bearing ball piston and seal arrangement are shown.-In figure 6 the bearing balls 4a are further out in the eccentric surfaces 11 and thus the tool or workpiece is not fastened into its position. The system has its minimum pressure on. Piston 4 comprises the bearing ball 4a supported by a slip- pery supporting part 4b against which the bearing ball 4a is rolling when the pressurizing ring 3 is turned. The supporting part 4b consists of e.g. PTFE plastic or another similar slip- pery material. In order to achieve sufficient sealing in the piston bore the piston 4 is further equipped with a lip seal 4c which is situated on the pressure side of the piston arrange- ment 4 adjacent to the supporting part 4b.

When turning the pressurizing ring 3 to the position of figure 7, for instance 60°-180° (depending from the design) manually or with some known mechanical device the eccentric surfaces 11 press the bearinq balls 4a in the piston bore towards the cen- tral axis thus causing a required hydraulic pressure to achieve the deformation of the steel sleeve 6 or the necessary locking power to clamp the tool or workpiece 7.

When the soft PTFE supporting parts 4b and 8b are used under the bearing balls 4a and 8a the PTFE supporting parts compen- sate their own wearing as they form and tend to creep against the bearing balls under a very high pressure. Thanks to the self compensating wearing property of the PTFE supporting parts the working pressure remain constant throughout the whole ac- tive working life of the toolholder.

Figure 8 shows an exaggerated illustration of the balancing situation of the pressurizing ring 3. When rotating with a high speed the pressurizing ring balances the toolholder by moving to its best balanced position and thus working as an automatic balancing device at the same time as causing the necessary fas- tening pressure to the tool or the workpiece 7. When rotating with a high speed the pressurizing ring 3 is floating in a bal- anced position on the bearing balls 4a. The movement to the best balanced position happens to in the radial direction of the pressurizing ring 3.

When having two piston systems 4 and 8 they both comprises ba- sically similar parts. They both are situated in the same pis- ton bore so that the bearing balls 4a and 8a are further apart from each other thus each situating at its own end of the pis- ton bore. Adjacent to the bearing ball 4a and 8a to inwards di- rection there are slippery supporting parts 4b and 8b and be- tween the both supporting parts there is hydraulic pressure me- dium 10.

It is, of course, possible to design various combinations with slight modifications for diverse purposes without departing from the spirit and scope of the protection of the enclosed claims. For example the number of pistons 4 and 8 can vary de- pending on the embodiment. Also the connection of the pressur- izing ring 3 with the body of the toolholder can be different from the structures shown in this description.

In the embodiment of Fig. 9 the turnable ring 3 is supported at the toolholder (not shown) by means of axial threads 30. A ro- tation of the ring in direction a is transformed by the threads in an axial movement according to arrow b. The guiding surface at the inner diameter of ring 3 is designed as axial cone with axially inclined guiding surfaces, whereon the balls 4a or other actuators of the pressure transfer pistons are sliding when the clamping means is operated.

The above illustrated invention in form of a hydraulically op- erated clamping means and arrangement for applying pressure to a piston sealing system is designed for an axially shaped cy- lindrical or spherical tool or workpiece or machine part of a desired shape. The device comprises a closed hydraulically op- erated system in a body part 1 and an eccentric clamping or pressurizing ring 3 located in the body part. This eccentric pressurizing ring 3 actuates bearing balls and associated pres- sure transferring pistons for applying pressure to a pressure channel 5 of a hydraulically operated device. This device may be a hydraulically operated toll holder, a clutch, a chuck or similar clamping means. This device is designed for clamping and releasing machine parts.