WORKING UNIT FOR A MACHINE OPERATED TOOL CARRIER

Abstract: A working unit intended to be mounted on a movable machine operated tool support comprises a casing (10) which is attached to the tool support and which supports a pneumatic turbine motor (23, 24, 51) with a rotor (19), and an end mill type machining tool (22,21) with a cutter portion (21) extending out of the casing (10) and a shank portion (22) rotatively journalled in the casing (10), whereing the machining tool shank portion (22) is rigidly integrated with a turbine whell (24) to form the turbine rotor (19), a flow control valve (48) is arranged to deliver pressure air to the turbine motor (23, 24, 51), and the turbine rotor (19) is provided with a generator device for delivering a speed responsive output voltage to a control unit (55) which is arranged to make the flow control valve 848) adjust the power supply to the rotation motor (23, 24, 51) so as to maintain the rotation speed at a desired predetermined level.

Description: Working unit for a machine operated tool carrier. The invention relates to a working unit intended to be mounted on a movable machine operated tool carrier and comprises a casing attached to the tool carrier, a rotation motor supported in the casing, and a machining tool rotatively journalled relative to the casing and driven by the motor. Previously known working units of the type having a motor and a machining tool carrying output spindle suffer from a rather slow working action. This is due both to the fact that the working unit has a relatively large mass and to the fact that the speed of the motor is relatively low. By nature, a heavy working unit is difficult to move at high velocity either in a plain reciprocating movement or in a more or less complicated working pattern, which means that the working process time will be undesirably long. Also, a relatively slow motor limits the maximum feed speed of the working tool relative to the work piece. A heavy output spindle unit including a tool chuck also means a large rotating mass, which tends to create vibration problems at high speed rotation. It is difficult to avoid resonance frequencies in such a known device. One reason why previously known movable working units has a relatively large mass is a rather complex design of the motor and output spindle arrangement . Another reason why previous working units has a large mass is the use of electric motors with all their heavy iron cores and copper windings . Electric motors also have a limited rotation speed which limits the rotation speed of the working tool, and, thereby, the possible feed speed of the working tool . The main object of the invention is to solve the above problems by accomplishing an improved working unit for mounting on a movable machine operated tool carrier which due to a simple design, a low weight and a high machining tool rotation speed provides a fast working action and, thereby, shortened working process times. Further objects and advantages of the invention will appear from the following specification and claims. A preferred embodiment of the invention is below described in detail with reference to the accompanying drawing figures . In the drawings Fig. 1 shows a longitudinal section through a working unit according to the invention and illustrates schematically a speed control system connected to the working unit . Fig. 2 shows another longitudinal section through the working unit in Fig. 1. The working unit illustrated in the drawings comprises a casing 10 with a rear mounting neck 11 for attaching the working unit to a movable machine operated tool carrier (not shown) . The casing 10 is divided into a central section 12 and a front section 13. The front section 13 is clamped to the central section 12 by a nut 14. The rear mounting neck 11 is secured to the central section 12 by screws 15. In the casing 10 there is provided a rotation motor in the form of a pressure air operated turbine 18 with a rotor 19, and a machining or milling tool 20 in the form of an end cutter. At its forward end, the milling tool 20 is formed with a cutter portion 21 extending out in front of the casing 10, and a shank 22 extending into the casing 10. A turbine wheel 24 carrying a circumferential row of drive blades 23 is rigidly secured to the inner end of the shank 21, which means that milling tool 20 and the turbine wheel 24 together form the turbine rotor 19 and the shank 22 forms the rotation axle of the rotor 19. The turbine wheel 24 is secured to the milling tool shank 22 by a press and/or shrinkage fit . By forming the motor rotor as a separate turbine wheel 24 rigidly mounted on the tool shank 22 as described above a standard type end mill can be used as machining tool 20. This means that a working unit according to the invention is simple and inexpensive to manufacture. The turbine rotor 19, i.e. the tool shank 22, is radially supported relative to the casing 10 by two hydro-dynamic bearings 25,26. These bearings 25,26 comprise two bushings 27,28 which are rigidly secured in a support sleeve 29 which in turn is rigidly secured in the front section 13 of the casing 10. As illustrated in Fig.2, both bushings 27,28 are supplied with a liquid via two radial passages 31,32, an axially extending passage 33 and a supply opening 34 in the casing 10. Preferably, the liquid being used as bearing medium is the liquid used for lubricating and cooling the cutter end portion 21 of the milling tool 20 during operation. 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Lubricating and cooling liquid is also supplied to the radial bearings 25,26 via passages 33,31,32 and openings 35,36 where the liquid creates a hydrodynamic radial support for the milling tool shank 22, i.e. the turbine rotor 19. The liquid is drained successively to the outlet passage 39 via the radial opening 38. Now, the rotor 19 is properly supported in the radial as well as in the axial directions and the supplied pressure air makes the turbine rotate at an increasing speed. As long as the speed has not reached the desired level, the output voltage from the generator winding coil 53 is below the desired certain magnitude, and the flow control valve 48 is kept open to a relatively large extent to make the turbine 24 accelerate. However, as the desired speed level is reached and exceeded to some extent the generator voltage becomes too high, and the control unit 55 will start deliver a negative output voltage to the flow valve servo-motor 54 such that the latter will start moving the flow control valve 48 towards a smaller opening area to reduce the pressure air flow to the turbine nozzles 52 and, thereby, reducing the turbine speed. Should the turbine speed decrease too much under the desired predetermined level, the control unit 55 would again change the output voltage to be positive and make the servo-motor 54 rotate in the opposite direction, thereby shifting the flow control valve 48 to a larger opening area to increase the turbine speed. When the turbine 24 is running at the desired predetermined rotation speed, the control unit 55 will not deliver any voltage at all. By the working unit according to the invention there is obtained a structurally simple and light device which is capable of operating at a very high speed thanks to a rotor spindle which is not only small and light but which is fully integrated with the turbine motor to an integrated unit. The device according to the invention is also capable of high speed rotation and long service life because of the frictionless bearings supporting the rotor both in the radial direction and the axial direction. By forming the turbine motor as a separate turbine wheel rigidly mounted directly on the machining tool shank portion by a simple press fit or a shrinkage fit a standard type end mill may be used without any special adaptation for this particular purpose .

Claims: CΛ ms . 1. Working unit intended for mounting on a movable machine operated tool carrier, comprising a casing (10), a turbine motor (23,24,51) supported in said casing (10) and having a rotor (19), and a machining tool (22,21) driven by said motor (23,24,51), c h a r a c t e r i z e d in that said machining tool (22,21) comprises a cutter portion (21) extending out of said casing (10), and a shank portion (22) extending into and being rotatively journalled relative to said casing (10), wherein said turbine motor (23,24,51) comprises a drive blade (23) carrying turbine wheel (24) rigidly mounted on said shank portion (22) to form said rotor (19) . 2. Working unit according to claim 1, wherein said machining tool (22,21) comprises a standard type end mill. 3. Working unit according to claim 1 or 2, wherein said turbine wheel (24) is secured to said shank portion (22) by a press fit. 4. Working unit according to claim 1 or 2 , wherein said turbine wheel (24) is secured to said shank portion (22) by a shrinkage fit. 5. Working unit according to anyone of claims 1-4, wherein said casing (10) comprises a turbine stator (40,51) including a pressure air supply passage (41,47,50), one or more nozzles (51) communicating with said air supply passage (41,47,50) and arranged to direct motive pressure air onto said turbine wheel (24) , a speed governing device (48,52-55) including an air flow control valve (48) communicating with said air supply passage (41,47,50), and a motor speed responsive activation device (52-55) arranged to accomplish adjustment of the opening area of said air flow control valve (48) in response to the actual motor speed so as to maintain the motor speed at a predetermined level . 6. Working unit according to claim 5, wherein said activation device (52-55) comprises a generator (52,53) connected to said rotor (19) and arranged to deliver an electric voltage in response to the actual motor speed, and an electric servo motor (54) connected to said generator (52,53) and arranged to accomplish adjustment of said air flow control valve (48) in response to the magnitude of the voltage delivered by said generator (52,53) . 7. Working unit according to claim 6, wherein said generator (52,53) has a rotor (52) which is formed as a rigid unit with said turbine rotor (19) . 8. Working unit according to anyone of claims 1-7, wherein said turbine rotor (19) is radially supported in two hydrodynamic bearings (25,26) which are fed with hydraulic pressure fluid from a cutting fluid source supplying cutting fluid to the machining tool cutter portion (21) .

Inventors: JACOBSSON ROLF ALEXIS, JACOBSSON, ROLF, ALEXIS
Applicants: ATLAS COPCO TOOLS AB, JACOBSSON ROLF ALEXIS, JACOBSSON, ROLF, ALEXIS
Application year: 2001
Main classification: B23Q5
IPC codes: B23Q5, B23Q15, B23Q17, G05B19