Technical Field The invention relates to a headstock for machines or automatic lathes, such as lathes or autolathes and the like machines adapted to carry out such operations, and which comprises a housing with a hollow main spindle, whereby an electric motor and/or a pulley for an electrically powered belt drive is/are mounted on said main spindle, and whereby a hollow pull-push bar is arranged in said main spindle for the control of the jaws of a collet chuck or a draw-in chuck mounted on the front end of said main spin- dle, said pulley being mounted at the rear end of said main spindle.

Background Art A headstock of the above type is known which operates by way of hydraulics for moving the jaws of the collet chuck or the draw-in chuck. This headstock does not operate in a fully satisfactory manner when the lathe or the autolathe is to operate at a number of revolutions of 6,000 rpm and higher, and when the rod-shaped material to be processed on the machine and extending throughout the main spindle is to be temporarily released from the collet chuck or the draw-in chuck so as to allow an advancing of the rod-shaped material and a refixing thereof in said collet chuck or draw-in chuck. Experience has shown that the device advancing the hydraulic liquid runs hot very easily and that metal surfaces running hot seize very quickly. Heat from the roller bearings or the friction bearings or from oil seals etc. in the hydraulic system is transferred to the lathe or to the main spindle of the machine and to the rod-shaped material with the result that it affects the capability of the lathe or the machine, i. e. the capability of meeting the tolerance requirements presented to the completed blanks. In other words the heat causes problems concerning the dimensional stability of the completed blanks.

Brief Description of the Invention The object of the invention is to provide a headstock of the above type which allows a fast engaging and disengaging of a rod-shaped material passing through the hollow main spindle by means of the collet chuck or the draw-in chuck while said main spindle rotates at speeds exceeding 6,000 rpm, and without the rotating members running hot.

The headstock according to the invention is characterised in that a clamping cylinder built of two or more members is mounted on the pulley and/or the rearward surface of the main spindle, said clamping cylinder rotating together with said pulley and/or said main spindle, and that a rotatable cylindrical piston fixedly mounted on the pull-push rod is arranged in the cylindrical cavity of said clamping cylinder, and that a gas valve sleeve is fixedly mounted on the outer side of a coaxial bush rigidly connected to the clamping cylinder, whereby a gas pad is provided between said coaxial bush and some bearing members mounted in the gas valve sleeve and made of a material permeable to gas, and that a first compressed-air pipe system is provided in the wall of the coaxial bush and in the wall of the clamping cylinder for a controlled feeding of compressed air to one side of the piston, and that a second compressed-air pipe system is provided in the wall of the coaxial bush and in the wall of the clamping cylinder for a controlled feeding of compressed air to the opposite side of the piston. As a result a very reliable heat sinking is obtained at the bearing members of the gas valve sleeve and the coaxial bush by means of pneumatics. In addition, a very accurate and reliable control of the axial movement of the piston is obtained with the result that the push-pull rod can be moved very accurately, and the jaws, viz. the claws, of the collet chuck or the draw-in chuck can accordingly be reliably moved radially outwards and inwards, respectively, relative to the rod-shaped material. The latter operation can be carried out while the main spindle rotates at a high number of revolutions.

According to the invention the bearing members of the gas valve sleeve may be made of a sintered material provided with pores with the result that the cooling compressed

air can easily reach the bearing surface between the bearing members and the outer side of the coaxial bush.

Furthermore, the bearing members of the gas valve sleeve may according to the inven- tion be made of a ceramic material, which turned out to be an advantageous bearing material as well.

Moreover, the clamping cylinder may according to the invention comprise two substan- tially pot-shaped members, where the concave surfaces face one another, as well as a radial wall member arranged between said pot-shaped members, all members being bolted or screwed together. As a result the clamping cylinder is provided in a very simple manner.

According to the invention the coaxial bush may be formed by a cylindrical member and a radially extending collar member, where the collar member renders it possible to screw the coaxial bush fixedly onto the clamping cylinder. As a result a very simple structure is obtained.

According to the invention the first channel system may be formed by a first inner annular groove arranged in the gas valve sleeve, a longitudinal, drilled channel pro- vided in the coaxial bush, a radial and an inclined channel in the clamping cylinder and an auxiliary channel in a retention pin arranged on the clamping cylinder for the piston, said auxiliary channel communicating with the side of the piston being farthest away from the gas valve sleeve. As a result a highly reliable feeding of compressed air to the remotest chamber at the piston is obtained.

According to the invention the second channel system may be formed by a second inner annular groove arranged in the gas valve sleeve, a longitudinal, drilled second channel arranged in the coaxial bush, a second radial channel in the clamping cylinder and a substantially longitudinal channel between the radial channel and the piston

chamber extending adjacent the coaxial bush. As a result a highly reliable feeding of compressed air is obtained to the piston chamber adjacent the coaxial bush.

Moreover the gas valve sleeve may according to the invention be retained in position on the coaxial bush by means of an axial bearing ring arranged on said coaxial bush, whereby a very reliable retaining of said gas valve sleeve on the coaxial bush is ob- tained.

According to the invention the bearing members of the valve sleeve may be arranged opposite wide, circumferential grooves provided in the interior of the gas valve sleeve, said bearing members being made of a material permeable to gas, where said cir- cumferential grooves communicate with one or more compressed air sources at a working pressure of 5 to 8 bars by means of substantially radial channels and pressure connecting pieces connected thereto. As a result, a particularly severe cooling of the bearing material and consequently of the bearing is obtained.

Finally, a pressure switch may according to the invention be connected to the pressure connecting pieces, said pressure switch being adapted and arranged such that it stops the electric motor when the pressure of the compressed air drops during the operation of the headstock below a predetermined limit, such as 4.5 bars, whereby programming means can be provided in connection with the compressed air sources for the control of the air pressure to the pressure connecting pieces. As a result, the main spindle stops immediately when the compressed air sources disclose a dropping pressure. The above programming means allow the engaging and disengaging of the rod-shaped material to take place in accordance with an accurately determined processing procedure on the lathe or the lathe machine.

Brief Description of the Drawing The invention is explained in detail below with reference to the accompanying draw-

ing, in which The Figure is a longitudinal sectional view of an embodiment of the headstock accord- ing to the invention.

Best Mode for Carrying Out the Invention The headstock shown in the Figure is intended for machines or automatic lathes per- forming lathe processing, such as for instance autolathes or lathe machines, such as CNC machines. The headstock comprises a housing 1 with a hollow main spindle 2, a pulley 3 for an electrically powered belt drive not shown being mounted on said main spindle 2. The electric motor can optionally be connected directly to the main spindle.

A hollow pull-push bar 5 is arranged in the main spindle 2, said pull-push bar 5 con- trolling several jaws inter alia 7a, 7b of a collet chuck, viz. a universal chuck, 7 mount- ed on the front end 2a of the main spindle 2. These jaws can, if desired, also be the jaws of a collet chuck. As illustrated, the pulley or optionally the electric motor is mounted at the rear portion 2b of the main spindle 2.

A clamping cylinder 13 comprising two or more parts 10,11,12 rotates together with the pulley and/or the main spindle and is mounted on the rearward surface 9 of said pulley and/or the rearward surface 2c of the main spindle 2. A rotatable cylindrical piston 14 is arranged in the cylindrical, optionally stepped cavity of the main spindle, cf. the Figure, and this piston 14 can be stepped in the same manner as said cavity. The piston is rigidly connected to the pull-push rod 5. A gas valve sleeve 18 is fixedly mounted on the outer side of a coaxial bush rigidly connected to the clamping cylinder 13. Bearing members in form of bearing rings 19 and 20 are mounted inside the gas valve sleeve 18, said bearing rings extending directly on the outer cylindrical bearing surface of the coaxial bush. The bearing members 19 and 20 are made of a material permeable to air. Compressed air is fed to the latter material through pressure connect- ing pieces 22 and 23 and further to the outer surfaces of the coaxial bush and the inner

surfaces of the bearing members with the result that a compressed air pad is formed.

A first compressed-air pipe system is provided in the coaxial bush 15, said first com- pressed-air pipe system comprising channels 25,26,27,28 and 29 for a controlled feeding of compressed air to one side 14a of the piston. A second compressed-air pipe system 31, 32, 33, 34 is provided in the wall of the coaxial bush 15 and in the wall 12 of the clamping cylinder, said second compressed-air pipe system ensuring a controlled feeding of compressed air to the opposite side 14b of the piston 14.

The bearing members 19 and 20 of the gas valve sleeve 18 can be made of sintered material provided with many pores in such a manner that the air can easily ooze through the bearing members. The number of pores must not, however, be so high that the mechanical strength of the bearing members is strongly weakened.

Another possibility is that the bearing members 19,20 are made of a ceramic material preferably provided with pores.

The clamping cylinder 13 can be made of two substantially pot-shaped members 10 and 12, where the concave surfaces thereof face one another, as well as of a radial wall portion 11 arranged between said members 10 and 12. As illustrated, the members 10, 11 and 12 can be joined by means of bolts or screws 37 and 38.

As illustrated, the coaxial bush 15 can be formed by a cylindrical member 15 a and a radially extending collar member 15b, which allows said coaxial bush to be screwed fixedly onto the clamping cylinder 13, i. e. actually on the member 12, by means of screws 39 and 40.

As illustrated, the first channel system can be formed by a first inner annular groove 42 arranged in the gas valve sleeve 18, a longitudinal, drilled channel 26 arranged in the coaxial bush member 15a, a radial channel 27 and an inclined channel 28 in the

clamping cylinder 13 and an auxiliary channel 29 in a retention pin 44 for the piston, said retention pin 44 being arranged on the clamping cylinder 13. The auxiliary channel 29 communicates with the side 14a of the piston 14 farthest away from the gas valve sleeve 18.

The second channel system of the headstock can be formed by a second inner annular groove 46 arranged in the gas valve sleeve 18, a longitudinal, drilled second channel 32 arranged in the coaxial bush 15a, a second radial channel 33 in the clamping cylin- der 13, i. e. at the member 12 thereof, and a substantially longitudinal channel 34 ex- tending between the channel 27 and the piston chamber adjacent the coaxial bush, said piston chamber being the chamber at the piston side 14b.

As illustrated, the gas valve sleeve 18 can be retained in position on the coaxial bush member 15a by means of an axial bearing ring 47 and the radial member 15b of said coaxial bush, said axial bearing ring 47 being arranged on said coaxial bush member.

Axial bearings 50,51 are also provided at the ends of the gas valve sleeve.

The bearing members 19 and 20 of the gas valve sleeve 18 are positioned opposite some inner, rather wide circumferential grooves 55 and 56. These grooves can be supplied with a gas, such as compressed air, through substantially radial channels 59 and 60 and the pressure connecting pieces 22 and 23 connected thereto, cf. the Figure.

These pressure connecting pieces communicate with one or more compressed air sources not shown. These compressed air sources can operate at a working pressure of preferably 5 to 8 bars. It should be noted that when the headstock is operating, the air heated at the bearings oozes away from said headstock through narrow clearances between the members of said headstock.

The compressed air sources are usually associated with programming means 22a, 23 a, 62a and 63 a for the control of the air pressure to the pressure connecting pieces 22,23, 62 and 63. These pressure connecting pieces can be associated with a pressure switch

not shown in order to ensure that the previously described electric motor stops in case the pressure of the compressed air drops below a predetermined limit, such as 4.5 bars.

As a result the main spindle stops the rotations and the lathe or the lathe machine stops.

As it appears, it is possible to regulate the radial movement of the piston 14 by means of the feeding of compressed air to the pressure connecting pieces 62 and 63 while the main spindle and the pull-push rod rotate. It should be noted that the pull-push rod is forced to rotate together with the main spindle through the retention pin 44. The retro- grade movement of the pull-push rod 2 causes changes of the radial position of the jaws 7a, 7b on the collet chuck 7, and this adjustment of the jaws is carried out while the main spindle rotates at a high speed, typically 6,000 rpm or more. The rod-shaped rod-shaped material not shown is positioned inside the pull-push rod 2 and accordingly it can be gripped by the jaws 7a, 7b and fixed while the rod-shaped material rotates.

While the rod-shaped material is in this state, a processing can be carried out on the lathe or the lathe machine. When the material for a new blank is to be advanced, the piston 14 is set in a position in which the j aws release the rod material. A length of rod material of a suitable size can then be advanced through the pull-push rod by means of means not shown. When the correct amount of rod material has left the collet chuck to the left in the Figure, the jaws 7a, 7b are moved radially inwards by means of the piston 14 and the pull-push rod 2 so as to fix the material, whereafter lathe operations can again be carried out on the lathe or the lathe machine. In addition the machine presents the following advantages: -infinitely variable clamping force at the jaws 7a and 7b during operation from 0 to maximum value, where the maximum clamping force depends on the diameter of the clamping cylinder chosen, -short building length preventing an outward bending of the main spindle 2, -no load of the bearings of the main spindle,

-no generation of heat originating from the clamping cylinder, -no loss at the cycle period in connection with the advancing of the rod-shaped material, as a deacceleration and an acceleration of the main spindle is unnecessary even at the highest spindle speeds, -the building costs associated with the machine are rather low because a cost-inten- sive hydraulic assembly is avoided, -low operational costs due to a low consumption of compressed air, said consump- tion typically being approximately 25 1/min.

The invention may be modified in many ways without thereby deviating from the scope of the invention.