Spindle system and method for clamping a tool and machine

Abstract

Spindle system (10) with a motor spindle (11) and an actuating device (12), wherein the motor spindle (11) comprises a hollow shaft (13) with a motor for driving the hollow shaft (13) and a clamping device (15), wherein the clamping device (15) comprises a collet chuck (16), an actuating rod (18) movable in the direction of a longitudinal axis (17) of the hollow shaft (13), and a spring device, wherein the spring device holds the collet chuck (16) in a closed position (19) for clamping a tool (20) by means of a spring force exerted on the actuating rod (18), wherein a translational movement can be exerted on the actuating rod (18) against the spring force by means of the actuating device (12), such that the collet chuck (16) can be transferred into an open position for releasing the tool (20), characterized inthat the actuating device (12) comprises an electric motor (21) and a gear (22) for converting a rotary movement of the electric motor (21) into the translatory movement, wherein the gear (22) has a transmission gear connected to the electric motor (21) for translating the rotary movement, wherein the transmission (22) has a spindle drive (23) with a threaded spindle (24) and a spindle nut (25) for converting the rotary movement into the translatory movement, wherein the threaded spindle (24) or the spindle nut (25) can be driven by the electric motor (21).

Description

[0001] The invention relates to a spindle system according to the preamble of claim 1, a machine with such a spindle system and a method for clamping a tool according to the preamble of claim 12.

[0002] Such spindle systems and methods are well known in the art and are regularly used to clamp a tool in the collet of a motor spindle. Motor spindles of this type are used for milling or grinding molds in the dental field. These motor spindles can reach speeds between 5,000 and 120,000 revolutions per minute, and tools or milling cutters with a diameter of up to 10 mm can be clamped with the collet. The hollow shaft of the motor spindle, within which the collet is housed, is mounted on ball bearings and is directly driven by a motor or electric motor, which can be a synchronous or an asynchronous motor. This electric motor is therefore arranged around and surrounds the hollow shaft, so that the hollow shaft simultaneously forms a drive shaft for the electric motor of the motor spindle.

[0003] The collet is actuated via an actuating rod in the hollow shaft such that the collet can be opened or closed by moving the actuating rod in the direction of the longitudinal axis of the hollow shaft. A spring device provided on the actuating rod exerts a spring force on the collet such that the collet is held in a closed position for clamping a tool. To release the tool, the actuating rod must then be actuated against the spring force.

[0004] In the spindle systems known from the prior art, an actuating device is usually designed with a pneumatic drive. This means that the respective actuating rod is driven by a pneumatically driven piston. However, a disadvantage is that a pneumatically driven piston cannot exert excessive forces on the spring device. To ensure that the tool can still be released, the tool can only be clamped with a low spring force.

[0005] DE 20 2014 104 118 U1 discloses a clamping device for clamping a tool and comprises a mechanical clamping unit, by means of which the tool is clamped in a clamping position, and an actuating device comprising an electric motor and a gear, by means of which the clamping unit is released and closed. The gear converts a rotary movement of the electric motor into a translatory movement of an actuating device, which interacts with a spring device and a collet chuck such that the tool can be fixed by means of a clamping cartridge, which is coupled to the collet chuck via a drawbar. Furthermore, the clamping device has a cooling pipe through which compressed air can be fed into the area of ​​the clamping unit for cooling and cleaning purposes.

[0006] Furthermore, DE 10 2006 017 645 A1 discloses a machine tool which comprises a motor spindle and a clamping device for clamping a tool.

[0007] DE 101 01 093 A1 discloses a spindle system with a motor spindle and an actuating device, wherein the motor spindle comprises a hollow shaft and a clamping device, wherein the clamping device comprises a collet chuck and an actuating rod movable in the direction of a longitudinal axis of the hollow shaft, wherein a translational movement or a tensile force can be exerted on the actuating rod by means of the actuating device such that the collet chuck can be transferred into a closed position for clamping a tool or can be held in the closed position, wherein the actuating device comprises an electric motor and a gear for converting a rotary movement of the electric motor into the translational movement. The gear is designed as a reduction gear, for example with a planetary roller thread spindle, so that a fast rotary movement can be converted into a slow linear movement with low friction losses and thus with low friction.

[0008] It is therefore an object of the invention to propose a spindle system, a machine with a spindle system, and a method for clamping a tool that enables the development of a clamping force adapted to requirements. This object is achieved by a spindle system having the features of claim 1, a machine having the features of claim 11, and a method having the features of claim 12.

[0009] The spindle system according to the invention comprises a motor spindle and an actuating device, wherein the motor spindle comprises a hollow shaft with a motor for driving the hollow shaft and a clamping device, wherein the clamping device comprises a collet, an actuating rod movable in the direction of a longitudinal axis of the hollow shaft, and a spring device, wherein the spring device holds the collet in a closed position for clamping a tool by means of a spring force exerted on the actuating rod, wherein a translational movement can be exerted on the actuating rod against the spring force, such that the collet can be transferred into an open position for releasing the tool, wherein the actuating device comprises an electric motor and a gear for converting a rotary movement of the electric motor into the translational movement,wherein the transmission comprises a transmission gear connected to the electric motor for translating the rotary movement, wherein the transmission comprises a spindle drive with a threaded spindle and a spindle nut for converting the rotary movement into the translatory movement, wherein the threaded spindle or the spindle nut is drivable by the electric motor.

[0010] Accordingly, the actuating device has an electric motor for generating a rotary movement, wherein the rotary movement of the electric motor is converted into a translatory movement by means of the actuating device's gearing. This translatory movement then essentially corresponds to the translatory movement exerted on the actuating rod by means of the actuating device against the spring force. Consequently, the translatory movement of the actuating rod is carried out via the actuating device's gearing. By using the electric motor with the gearing instead of a pneumatic piston, a large number of revolutions of the electric motor are converted or reduced into the translatory movement or a linear distance. Depending on the design of the gearing, it is then possible to exert a particularly large force on the actuating rod.The spring device can then also exert a comparatively greater spring force on the collet and thus securely clamp a tool with an even greater clamping force. Furthermore, the fact that the actuating device consists of an electric motor and a gearbox offers the advantage that a compressed air line to the spindle system or a milling machine with the spindle system does not necessarily have to be laid. Operating costs for the spindle system can also be saved by replacing comparatively expensive compressed air with electrical energy. The actuating device can then also be easily supplied with electrical energy via supply lines of the motor spindle. The electric motor can in particular be a synchronous motor, asynchronous motor, torque motor or stepper motor.In contrast to a pneumatic piston, such an electric motor enables a much more precise execution of the translational movement and the generation of a force on the actuating rod.

[0011] According to the invention, the transmission comprises a transmission gear connected to the electric motor for transmitting the rotary motion. The transmission gear can be, for example, a planetary gear, with which a rotary motion of the electric motor can be reduced to a speed suitable for conversion into translational motion.

[0012] According to the invention, the gear unit comprises a spindle drive with a threaded spindle and a spindle nut for converting the rotary movement into the translatory movement, wherein the threaded spindle or the spindle nut can be driven by the electric motor. For example, the threaded spindle can be coupled to a shaft of the electric motor, so that a rotary movement of the shaft can cause a translatory movement of the spindle nut. Depending on the thread pitch of the spindle nut, a gear ratio can then be easily formed, with which a large force can be generated to actuate the actuating rod. Furthermore, it is also possible to vary a clamping force or to determine an adjustment path of the spindle nut or the actuating rod with such an actuating device. If the spindle drive is designed to be self-locking, the electric motor does not need to be permanently supplied with electrical energy.This means that the collet can be kept open in the open position for any length of time without the use of energy.

[0013] The threaded spindle or spindle nut can form a tappet that can act on the actuating rod. The tappet can be sealed with a ring seal to prevent dirt from entering the hollow shaft with the actuating rod. Furthermore, it is then also possible to seal the hollow shaft from the environment in the area of ​​the actuating device.

[0014] The spindle drive can have an anti-rotation device for the threaded spindle or the spindle nut. If the threaded spindle is driven by the electric motor, the spindle nut preferably has the anti-rotation device, and if the spindle nut is driven by the electric motor, the threaded spindle has the anti-rotation device. The anti-rotation device can be implemented, for example, by a simple pin that prevents the threaded spindle or the spindle nut from rotating.

[0015] The actuating device can have a housing, whereby the actuating device can be detachably attached to a spindle housing of the motor spindle with the housing. This then makes it possible to design a modular spindle system such that motor spindles of very different designs can always be combined with a similarly designed actuating device. The housing of the actuating device can then simply be flanged to the spindle housing. A connection between the housing and the spindle housing can be formed by a simple screw thread or a flange with a number of screws. The motor spindle can have a spindle housing with a compressed air connection. Furthermore, the spindle housing can have a connection for connecting to a line for power supply and data transmission. The compressed air connection can be used to supply the spindle housing with compressed air for a wide variety of purposes.

[0016] For example, the motor spindle can be equipped with a cleaning device, whereby a tool holder of the collet chuck can be cleaned using compressed air from the cleaning device. For example, compressed air can then be used to blow out the tool holder of the collet chuck through the hollow shaft and thereby clean it of chips, for example.

[0017] Furthermore, the motor spindle can have a probing device, which can be used to measure electrical contact between the hollow shaft and a reference body. The reference body can also be, among other things, an electrically conductive workpiece that can be machined using the spindle system. The probing device can then transmit an electrical current between the hollow shaft and the reference body. For example, if the resistance is low, contact with the reference body and thus the distance between the hollow shaft and the reference body can be measured.

[0018] The motor spindle can have an overpressure device, whereby compressed air from the overpressure device can be used to create an overpressure in the spindle housing and / or the hollow shaft relative to the ambient pressure. The creation of the overpressure can then ensure that no contaminants, such as chips, can penetrate the spindle housing and / or the hollow shaft.

[0019] The motor spindle can have a cooling device, wherein compressed air from the cooling device can be delivered to a tool and / or workpiece. For example, a compressed air stream can be directed onto the tool and / or workpiece via a nozzle or a plurality of nozzles arranged concentrically adjacent to the tool or collet. In addition to cooling the tool or workpiece, chips generated during machining of the workpiece can also be easily removed into the environment. In addition, the cooling device can have nozzles for applying cooling lubricant to the tool and / or workpiece.

[0020] It is particularly advantageous if the spring device is constructed from disc springs. Disc springs can exert a relatively large spring force on the collet or actuating rod in a small installation space.

[0021] The machine according to the invention, in particular a milling machine or grinding machine, has a spindle system according to the invention. Further advantageous embodiments of the machine are evident from the subclaims referring back to device claim 1.

[0022] In the method according to the invention for clamping a tool, a motor spindle of a spindle system comprises a hollow shaft with a motor for driving the hollow shaft and a clamping device, wherein the clamping device comprises a collet, an actuating rod movable in the direction of a longitudinal axis of the hollow shaft, and a spring device, wherein the spring device exerts a spring force on the actuating rod, which holds the collet in a closed position in which a tool is clamped, wherein a translational movement is exerted on the actuating rod counter to the spring force by means of an actuating device of the spindle system, such that the collet is transferred into an open position for releasing the tool, wherein the actuating device has an electric motor and a gear, wherein a rotary movement of the electric motor is converted into the translational movement by means of the gear.The transmission comprises a transmission gear connected to the electric motor for transmitting the rotary motion, the transmission comprising a spindle drive with a threaded spindle and a spindle nut for converting the rotary motion into the translatory motion, the threaded spindle or the spindle nut being drivable by the electric motor. For the advantages of the method according to the invention, reference is made to the description of the advantages of the spindle system according to the invention. Further advantageous embodiments of the method emerge from the subclaims referring back to device claim 1.

[0023] The invention is explained in more detail below with reference to the drawing.

[0024] The figure shows a partial longitudinal section of a spindle system 10 with a motor spindle 11 and an actuating device 12. The motor spindle 11 comprises a hollow shaft 13 with a motor (not shown in detail here) for driving the hollow shaft 13 within a spindle housing 14. The motor spindle 11 also has a clamping device 15, which in turn comprises a collet 16 and an actuating rod 18 movable in the direction of a longitudinal axis 17 of the hollow shaft 13, and a spring device (not visible here) formed by disc springs. The spring device exerts a spring force on the actuating rod 18, which holds the collet 16 in the closed position 19 shown here for clamping a tool 20.A translational movement of the actuating rod 18 along the longitudinal axis 17 and against the spring force causes the collet 16 to be pushed out of the hollow shaft 13 and thus the collet 16 to spread into an open position (not shown here), in which the tool 20 is released.

[0025] The actuating device 12 has an electric motor 21 with a gear 22, which can convert a rotary movement of the electric motor 21 into a translational movement. The gear 22 is formed from a spindle drive 23 with a threaded spindle 24 and a spindle nut 25. The threaded spindle 24 is driven by the electric motor 21 and then causes a translational movement of the spindle nut 25, with an anti-rotation device 28 being formed on the spindle nut 25 by means of a pin 26 that engages in a bore 27. The gear 22 also comprises a transmission gear (not shown in detail here) within the electric motor 21. A plunger 29 is formed on the spindle nut 25 and acts on one end 30 of the actuating rod 18. The plunger 29 is sealed against the spindle housing 14 by means of an annular seal 31.The electric motor 21 with the gear 22 is housed in a housing 32, which is easily screwed onto the spindle housing 14 via a thread 33. Furthermore, a compressed air connection 34 and an electrical connection 35 for supplying the motor spindle 11 with compressed air and electrical energy are formed on the spindle housing 14.

Claims

[1] A spindle system (10) with a motor spindle (11) and an actuating device (12), wherein the motor spindle (11) comprises a hollow shaft (13) with a motor for driving the hollow shaft (13) and a clamping device (15), wherein the clamping device (15) comprises a collet chuck (16), an actuating rod (18) movable in the direction of a longitudinal axis (17) of the hollow shaft (13), and a spring device, wherein the spring device holds the collet chuck (16) in a closed position (19) for clamping a tool (20) by means of a spring force exerted on the actuating rod (18), wherein a translational movement can be exerted on the actuating rod (18) against the spring force by means of the actuating device (12), such that the collet chuck (16) can be transferred into an open position for releasing the tool (20), characterized bythat the actuating device (12) comprises an electric motor (21) and a gear (22) for converting a rotary movement of the electric motor (21) into the translatory movement, wherein the gear (22) has a transmission gear connected to the electric motor (21) for translating the rotary movement, wherein the gear (22) has a spindle drive (23) with a threaded spindle (24) and a spindle nut (25) for converting the rotary movement into the translatory movement, wherein the threaded spindle (24) or the spindle nut (25) can be driven by the electric motor (21). [2] Spindle system (10) according to claim 1, characterized by that the threaded spindle (24) or the spindle nut (25) forms a plunger (29) which acts on the actuating rod (18). [3] Spindle system (10) according to claim 1 or 2, characterized bythat the spindle drive (23) has an anti-twist device (28) for the threaded spindle (24) or the spindle nut (25). [4] Spindle system (10) according to one of the preceding claims, characterized by that the actuating device (12) has a housing (32), wherein the actuating device (12) is detachably fastened to the housing (32) on a spindle housing (14) of the motor spindle (11). [5] Spindle system (10) according to claim 4, characterized by that the motor spindle (11) has the spindle housing (14) with a compressed air connection (34). [6] Spindle system (10) according to one of the preceding claims, characterized by that the motor spindle (11) has a cleaning device, wherein a tool holder of the collet chuck (16) can be cleaned by means of compressed air from the cleaning device. [7] Spindle system (10) according to one of the preceding claims, characterized bythat the motor spindle (11) has a probing device, wherein an electrical contact between the hollow shaft (13) and a reference body can be measured by means of the probing device. [8] Spindle system (10) according to one of claims 4 to 7, characterized by that the motor spindle (11) has an overpressure device, wherein an overpressure compared to an ambient pressure can be formed in the spindle housing (14) and / or the hollow shaft (13) by means of compressed air from the overpressure device. [9] Spindle system (10) according to one of the preceding claims, characterized by that the motor spindle (11) has a cooling device, wherein compressed air from the cooling device can be delivered to the tool (20) and / or a workpiece. [10] Spindle system (10) according to one of the preceding claims, characterized by that the spring device is made of disc springs. [11] Machine, in particular a milling machine or grinding machine, with a spindle system (10) according to one of the preceding claims. [12] A method for clamping a tool, wherein a motor spindle (11) of a spindle system (10) comprises a hollow shaft (13) with a motor for driving the hollow shaft (13) and a clamping device (15), wherein the clamping device (15) comprises a collet chuck (16), an actuating rod (18) movable in the direction of a longitudinal axis (17) of the hollow shaft (13), and a spring device, wherein a spring force is exerted on the actuating rod (18) by the spring device, which holds the collet chuck (16) in a closed position (19) in which a tool (20) is clamped, wherein by means of an actuating device (12) of the spindle system (10), a translational movement is exerted on the actuating rod (18) against the spring force, such that the collet chuck (16) is transferred into an open position for releasing the tool (20), characterized byin that the actuating device (12) has an electric motor (21) and a gear (22), wherein by means of the gear (22) a rotary movement of the electric motor (21) is converted into the translatory movement, wherein the gear (22) has a transmission gear connected to the electric motor (21) for translating the rotary movement, wherein the gear (22) has a spindle drive (23) with a threaded spindle (24) and a spindle nut (25) for converting the rotary movement into the translatory movement, wherein the threaded spindle (24) or the spindle nut (25) can be driven by the electric motor (21).

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