Tool head and method of operating a tool head and gear cutting machine

Abstract

A tool head (300) for a machine tool, particularly for all gear machines, has a first spindle unit (320) and a second spindle unit (330), each having at least one spindle bearing (323, 333) and a spindle member (322, 332), the spindle member being rotatably mounted in the respective spindle bearing about a tool spindle axis (B). The respective spindle bearing can support both radial and axial forces. The spindle units are coaxially arranged, and a tool (340) is axially housed between the spindle members. A controlled clamping device (600) connects the spindle bearings together. A control device (730) activates the clamping device (600) during a machining operation and deactivates it during a machining pause. Alternatively or additionally, the tool head has an axial force element that generates an axial preload force between the spindle bearings.

Description

[Technical Field]

[0001] This invention relates to a cutting tool head. Further, this invention relates to a machine tool having the cutting tool head and a method for operating the cutting tool head. [Previous Technology]

[0002] Small-diameter cutting tools are increasingly used in gear manufacturing. To achieve the required cutting speed, these tools typically operate at relatively high rotational speeds. These tools may be relatively long relative to their diameter. This makes them particularly susceptible to bending and torsional vibrations. Therefore, it is advantageous to house the two ends of such tools on a spindle. Cutting heads with two spindles for gear cutting machines have long been known in the prior art, with the tools housed between these spindles.

[0003] For example, DE4431374A1 discloses a tool head for a contour grinding machine. A tool spindle with a drive motor is located on each of two individual tool slides. Each tool slide can move axially by an individual positioning drive. The spindle members of the two tool spindles are coaxially arranged relative to each other and are connected to each other by a tool holder in a torsional and bending rigid manner. For this purpose, the spindle members have locating pins connected to the tool holder via a radial expansion clamping connection. The positioning drives of the two tool slides can move in a coordinated manner. This configuration may be susceptible to vibration. Furthermore, there is a risk of bearing damage in the tool spindle if the tool thermally expands during machining or if the two tool slides do not accelerate in perfect synchronization when moving axially.

[0004] DE102009039752A1 also discloses a tool head having two tool spindles, with the tool housed between the spindles. The tool spindles are linearly displaceable relative to the base. The tool spindles can be coupled by a motion transmission unit so that the two tool spindles can move together relative to the base using a single positioning drive.

[0005] EP3153277A1 discloses a tool head having a motor spindle and a counter spindle, with the tool housed between the motor spindle and the counter spindle. A balancing device is integrated into the shafts of the motor spindle and the counter spindle. [Summary of the Invention]

[0006] One object of the present invention is to provide a tool head having two spindles, wherein the tool can be housed between the spindles, wherein the tool head has improved vibration characteristics, and wherein the risk of bearing damage is reduced due to thermal expansion.

[0007] This objective is achieved by means of a cutting head as described in technical solution 1 or 7. Other embodiments are given in the appendix.

[0008] A tool head for a machine tool, particularly for all gear machines, is disclosed, comprising: a first spindle unit having at least one first spindle bearing and a first spindle member, the first spindle member being mounted in the first spindle bearing for rotation about a tool spindle axis, the first spindle bearing being configured to absorb both radial and axial forces; and a second spindle unit having a second spindle bearing and a second spindle member, the second spindle member being mounted in the second spindle bearing for rotation about the tool spindle axis, the second spindle bearing being configured to absorb both radial and axial forces, wherein the first spindle unit and the second spindle unit are coaxially arranged relative to each other, in such a way that a tool can be axially housed between the first spindle member and the second spindle member.

[0009] According to a first embodiment of the present invention, the objective is achieved by a tool head including a controllable clamping device for controllably connecting the first spindle bearing and the second spindle bearing to each other, preferably substantially rigidly connecting them to each other, and wherein a control device is associated with the tool head, the control device being configured to activate the clamping device during a machining operation and deactivate the clamping device during a machining pause.

[0010] By carefully connecting the two spindle bearings during machining operations, the tendency for tool head vibration is significantly reduced. During tool head movement, such as during dressing or shifting, the axial force on the spindle bearings generated by the acceleration of the spindle unit can also be significantly reduced by the connection, and / or such forces can be specifically shifted to the spindle unit with a higher preload on the spindle bearings. By carefully releasing this connection during machining interruptions, thermal stresses that may have accumulated during machining can be further reduced. This prevents bearing damage attributable to thermal stress. The machining operation can be machining of a workpiece with a tool, or it can be a dressing operation of a tool with a dressing device.

[0011] The tool head may have at least one sensor for monitoring one of the operating states of the tool head, particularly a temperature sensor, vibration sensor, strain sensor, force sensor, or pressure sensor. The control device can then be configured to read the sensor and deactivate the clamping device taking into account a measurement parameter measured by the sensor. In this way, the connection between the spindle bearings can be released very carefully if necessary.

[0012] The clamping device may particularly include an expansion clamping element. The expansion clamping element may be rigidly connected to the first spindle bearing or the second spindle bearing. The expansion clamping element may cooperate with a mating element rigidly connected to another spindle bearing to connect the first spindle bearing and the second spindle bearing to each other. However, instead of the expansion clamping element, another type of clamping device, such as a mechanical, magnetic, or electrical clamping device, may be used.

[0013] The clamping device can be configured to reduce vibration between the spindle units when the clamping device is in an activated state. For this purpose, the clamping device may have an axial damping element, or the clamping device may cause axial damping due to its design, such as when clamping with a hydraulic or pneumatic cylinder. In this regard, the clamping device may also act as a switchable axial vibration damper.

[0014] In some embodiments, the first spindle unit and the second spindle unit are housed in a common spindle housing. The second spindle bearing may then be held in a bearing housing that is axially displaceable relative to the common spindle housing. The clamping device is then preferably configured to controllably secure the bearing housing to connect the first spindle bearing and the second spindle bearing to each other. If the clamping device includes an expansion clamping element, the expansion clamping element may be configured as an expansion sleeve and radially surround the bearing housing.

[0015] In other embodiments, the two spindle units are housed in individual spindle housings. In this case, the first spindle unit thus includes a first spindle housing in which the at least one first spindle bearing is held, and the second spindle unit includes a second spindle housing in which the at least one second spindle bearing is held. The clamping device is then preferably configured to controllably couple the first spindle housing and the second spindle housing to each other, so as to connect the first spindle bearing and the second spindle bearing to each other. For this purpose, the clamping device preferably connects the two spindle housings directly to each other. For example, if the two spindle housings are displaceably held on a base, it is therefore preferable not to connect them by, or at least not exclusively by, clamping the individual spindle housings to the base, but to connect them directly between the spindle housings.

[0016] The clamping device may include two elements, wherein in the deactivated state of the clamping device, a first of these elements is axially displaceable within a second element (the second element may surround the first element and may include, for example, an expansion sleeve), and wherein in the activated state of the clamping device, the two elements are axially fixed relative to each other. Advantageously, the clamping device is then configured such that the first element cannot extend completely from the second element, for example, even during tool changes, in order to prevent the two elements from blocking each other when pushed together.

[0017] According to a second embodiment of the present invention, the above objective is achieved by a tool head including an axial force element configured to generate an axial preload force between the first spindle bearing and the second spindle bearing.

[0018] According to this configuration, the two spindle units are thus axially clamped to each other on the bearing side. Therefore, the spindle bearings do not move axially relative to each other, but are also not completely rigidly connected. Thus, the spindle bearings are at least partially protected from axial thermal stress. In this way, the tendency for tool tip vibration can also be significantly reduced without the risk of bearing damage attributable to thermal stress.

[0019] Two states can also be combined. Specifically, it is possible to clamp the spindle bearings together using axial force elements, and connect the spindle bearings together in the clamped state during the machining operation using the clamping device, and release this connection again during the machining pause.

[0020] The axial force element may include a controllable actuator, particularly a pneumatic or hydraulic actuator, to controllably change the axial preload force, and particularly to carefully release the axial preload force. The actuator can be configured to generate an axial preload force substantially independent of the axial position of the second spindle bearing relative to the first spindle bearing. For example, this can be easily achieved with a pneumatic or hydraulic actuator, since in such actuators the axial force often depends only on the applied pressure, rather than on the position of the actuator.

[0021] In one embodiment of the second aspect of the invention, a control device may also be associated with the tool head. The control device may then be configured to control the actuator to adjust the axial preload force, for example, to keep the axial preload force constant during the machining operation, and / or to controllably change the axial preload force, especially to deactivate the axial preload force during machining pauses.

[0022] The tool head may also have at least one sensor for monitoring one of the operating states of the tool head, particularly a temperature sensor, vibration sensor, strain sensor, force sensor, or pressure sensor. The control device may then be configured to read out the sensor and change the axial preload force in consideration of a measurement parameter measured by the sensor.

[0023] Furthermore, in some embodiments, both the first spindle unit and the second spindle unit may be housed in a common spindle housing, and a bearing housing axially displaceable relative to the spindle housing may be present, in which at least one second spindle bearing is held. The axial force element may then be configured to apply an axial force to the bearing housing to generate the axial preload force. For this purpose, the axial force element may be particularly annular and surround a clamping element for axially clamping the tool to one of the first spindle members and the second spindle member. Specifically, the axial force element may include an annular actuator.

[0024] In other embodiments, the spindle unit may also be housed in a separate spindle housing. The axial force element may then connect the first spindle housing and the second spindle housing to each other and may be configured to apply an axial force between the first spindle housing and the second spindle housing to generate the axial preload force.

[0025] Certain advantages arise when two spindle members are axially clamped to the tool so that axial compressive force acts on both sides of the tool. For this purpose, the following design is particularly advantageous: the second spindle member has at least one axial bore. The tool head correspondingly includes at least one drawbar (traverse bar) extending through the corresponding axial bore of the second spindle member, the drawbar being connectable to the first spindle member at a first end. The drawbar is also connectable to the second spindle member at a second end, such that an axial compressive force can be generated on the tool between the first and second spindle members. For this purpose, the tool also correspondingly has at least one axial bore, allowing individual drawbars to pass through corresponding bores in the tool.

[0026] This type of axial support creates a unit consisting of two spindle shafts and the cutting tool, which is particularly resistant to torsion and bending. The combination of the tie rod and clamping element allows for high axial compressive force to be generated between the cutting tool and the two spindle shafts. Therefore, the aforementioned unit acts as a single shaft. At the same time, this construction can be extremely compact. This makes this construction particularly suitable for cutting tools with small diameters.

[0027] However, the tool can also be clamped between the first and second spindle members in a manner other than the continuous tie rod, as long as this creates a rigid unit consisting of the two spindle members and the tool. Clamping the tool between the two spindle members to form a rigid unit is independent of any axial support or clamping of the associated spindle bearings.

[0028] This configuration is also advantageous in the absence of clamping devices or axial force elements of the type described above. In this regard, the invention also relates to a tool head for a machine tool, particularly for all gear machines, comprising: a first spindle unit having a first spindle member mounted in the first spindle unit for rotation about a tool spindle axis; and a second spindle unit having a second spindle member mounted in the second spindle unit for rotation about the tool spindle axis, wherein the first spindle unit and the second spindle unit are configured such that a tool can be axially received between the first spindle member and the second spindle member to drive the tool to rotate about the tool spindle axis, wherein the second spindle member has at least one axial bore, and wherein the tool head includes at least one pull rod extending through the axial bore of the second spindle member. The pull rod can be connected to the first spindle assembly at a first end for being tightened, and the pull rod can be connected to the second spindle assembly at its other end, in such a way that an axial compressive force can be generated on the tool between the first spindle assembly and the second spindle assembly.

[0029] In this case, it is advantageous that the first spindle unit includes at least one first spindle bearing, the first spindle member being mounted in the first spindle bearing so as to be rotatable about the tool spindle axis, and the first spindle bearing being configured to absorb both radial and axial forces; and the second spindle unit correspondingly includes a second spindle bearing, wherein the second spindle member is mounted in the second spindle bearing so as to be rotatable about the tool spindle axis, and wherein the second spindle bearing is configured to absorb both radial and axial forces.

[0030] Preferably, a tie rod extends through a central axial hole in the second spindle assembly. Therefore, preferably, the tool also has a central axial hole through which the tie rod can pass.

[0031] In a particularly simple embodiment, the tie rod can be connected to the first spindle assembly by axially screwing it into the first spindle assembly. For this purpose, complementary threads can be formed on the corresponding ends of the tie rod and on the first spindle assembly. However, other types of connections, such as bayonet connections, are also conceivable.

[0032] The pull rod may advantageously have a clamping element at its free other end, thereby forming an annular contact surface that is supported on the second spindle shaft after the pull rod has been connected to the first spindle shaft and generates an axial compressive force on the second spindle shaft to push the second spindle shaft in the direction of the first spindle shaft. In its simplest case, the pull rod may be formed for this purpose, for example, as a screw with a screw head. The screw can then be screwed into the first spindle shaft, and the screw head can form a clamping element. An axial clamping force is then easily generated by tightening the screw.

[0033] In another equally simple embodiment, the pull rod has an external thread at its free end, onto which a nut can be screwed. In this case, the nut forms a clamping element, and axial compressive force is generated very easily by tightening the nut.

[0034] However, preferably, the tool head includes a clamping element that is releasably connected to the drawbar and generates a compressive force that preferably acts only axially, and the tightening of the clamping element does not generate a torque component about the tool spindle axis. For this purpose, the clamping element includes a base element that can be rigidly connected to the drawbar, for example, via a screw connection, via a bayonet, or via a clamping bushing. The base element may have a central receiving opening for receiving the drawbar, or (if sufficient space is available) a pin that can be fixed in an axial hole in the drawbar. The clamping element further includes an axially actuating element that is axially movable, particularly axially displaced, relative to the base element in the direction of the second spindle member, in order to axially push the second spindle member in the direction of the first spindle member. The axially actuating element may be particularly annular and surrounds the central receiving opening or the pin of the base element; in this case, the axially actuating element may also be referred to as a "push ring". The axially actuating element forms the aforementioned annular contact surface. The clamping element further includes at least one actuating element movable relative to the base element to move the axial pushing element axially relative to the base element. The actuating element may be, for example, a pressure screw that can be screwed into the base element in a longitudinal or transverse direction. Such clamping elements are known from the prior art and are available in many variations.

[0035] In some embodiments, the transmission of force from the actuating element to the axially actuating element is purely mechanical. For example, the actuating element may be a plurality of headed screws axially held on the base element and screwed into the axially actuating element to displace the axially actuating element axially relative to the base element. In other embodiments, one or more retaining screws act as the actuating element, which can be adjusted in the base element in the direction of the axially actuating element via threaded connections. In still other embodiments, the actuating element acts, for example, on a gear that advances the axially actuating element. Such clamping elements may be available, for example, under the names ESB, ESG, or ESD from Enemac GmbH of Walstadt, Germany.

[0036] In other embodiments, the transmission of force from the actuating element to the axially actuating element is hydraulic. For this purpose, the actuating element can be configured, for example, as a pressure screw, which generates pressure in the hydraulic system when screwed in, and this pressure acts on the axially actuating element. Such clamping elements are available, for example, from Albert Schrem Werkzeugfabrik in Helbrechttingen, Germany.

[0037] To house the tool between the spindle members and to transmit torque to the tool, it is advantageous that the spindle nose is formed on the first and / or second spindle members in such a way that a non-positive and / or positive connection to the tool can be generated at each spindle nose by the axial compressive force acting between the tool and the spindle nose. Preferably, the connection to the tool is made via a conical connector, more preferably via a conical connector having surface contact. For example, the connection can be made via one of the embodiments A, BF, BM, CF or CM mentioned in DIN ISO 666:2013-12.

[0038] Advantageously, the two spindle noses are configured in a manner that allows the tool to be stored between the spindle noses only in a predetermined position. For example, the diameters of the two spindle noses may be different.

[0039] For ease of tool change, it is advantageous for the second spindle unit to be axially displaced relative to the first spindle unit. If the two spindle units are housed in a common spindle housing, this can be achieved by allowing the spindle bearing used in the second spindle assembly to be axially displaced relative to this spindle housing.

[0040] The first spindle unit and / or the second spindle unit may include a drive motor configured to drive a corresponding spindle member to rotate about the tool spindle axis, thereby driving the tool. In some embodiments, only the first spindle unit includes a drive motor, and the second spindle unit forms a passive docking spindle for the first spindle unit without requiring its own drive motor. In other embodiments, the second spindle unit also includes its own drive motor. The individual drive motors may be, in particular, direct drive devices.

[0041] In order to balance the rotating unit including the cutting tool and two spindle shafts, the cutting tool head may include a first balancing device associated with the first spindle unit and a second balancing device associated with the second spindle unit.

[0042] Preferably, the first balancing device radially surrounds the first spindle member and is axially disposed between the tool-side spindle bearing of the first spindle unit and the tool-side end of the first spindle member, and / or the second balancing device radially surrounds the second spindle member and is axially disposed between the tool-side spindle bearing of the second spindle unit and the tool-side end of the second spindle member.

[0043] Therefore, when the tool is housed between the first spindle assembly and the second spindle assembly, the first balancing device and / or the second balancing device are disposed outside the respective spindle assembly and axially disposed between the tool-side spindle bearing of the associated spindle unit and the tool. The proposed configuration makes it possible to efficiently balance tools with small diameters. By arranging at least one, preferably two, balancing devices around the spindle assembly, the space available for the balancing elements is much larger than if two balancing devices were disposed inside the tool or the spindle assembly. Therefore, even relatively large imbalances can be corrected. By axially distributing the corresponding balancing device between the tool-side spindle bearing and the tool, balancing is performed at a position close to the tool and close to the corresponding bearing. This achieves extremely precise balancing.

[0044] Each spindle unit will typically contain more than one spindle bearing. The term "tool-side spindle bearing" should be understood to refer to the spindle bearing located within the individual spindle unit closest to the tool along the tool spindle axis.

[0045] Specifically, the configuration of the balancing plane relative to the bearing planes of the two spindle units can be as follows: the first spindle bearing on the tool side defines a first bearing plane perpendicular to the tool spindle axis, and the second spindle bearing on the tool side defines a second bearing plane perpendicular to the tool spindle axis. The first balancing device defines a first balancing plane perpendicular to the tool spindle axis, and the second balancing device defines a second balancing plane perpendicular to the tool spindle axis. Preferably, the first balancing plane is disposed between the first bearing plane and the second balancing plane (especially closer to the first bearing plane than the second balancing plane), and / or the second balancing plane is disposed between the second bearing plane and the first balancing plane (especially closer to the second bearing plane than the first balancing plane).

[0046] When the tool is housed between the two spindle members, the tool defines a center-of-gravity plane perpendicular to the tool spindle axis, the center-of-gravity plane containing the center of gravity of the tool. A first balance plane is then preferably located between a first bearing plane and the center-of-gravity plane, and / or a second balance plane is preferably located between a second bearing plane and the center-of-gravity plane. Preferably, each balance plane is closer to the corresponding bearing plane than to the center-of-gravity plane.

[0047] This balance plane configuration achieves efficient dual-plane balance.

[0048] In a preferred embodiment, the first balancing device and / or the second balancing device are configured as a ring balancing system. Ring balancing systems are well known in the prior art (see, for example, DE4337001A1, US5757662A) and achieve highly accurate automatic balancing without stopping the rotation of the spindle. In various embodiments, they are commercially available. However, another type of balancing system may also be used, such as a balancing system with a counterweight that can be moved by an electric motor or a hydraulic balancing system.

[0049] The balancing device can be configured to operate in a numerically controlled (NC) manner. For this purpose, the first balancing device and / or the second balancing device may include at least one actuator for NC adjustment of the imbalance of the respective balancing device.

[0050] At least one vibration sensor may be disposed on the tool head for detecting vibrations caused by imbalance. This sensor may be integrated into one of the balancing devices or configured separately. The tool head may be further associated with a control device configured to detect signals from the at least one vibration sensor and control actuators in the first and / or second balancing devices to adjust the corrective imbalance in the first and / or second balancing devices based on the detected signals. This adjustment may be automatic, thereby reducing imbalance. Preferably, the control device is configured to perform automatic biplane balancing. Corresponding algorithms are well known from the prior art. The control device may be part of a machine control system or may be a separate unit.

[0051] Preferably, the first balancing device and / or the second balancing device are disposed outside the housing of each spindle unit. Specifically, the first spindle unit may include a first housing, and the second spindle unit may include a second housing. The first balancing device and / or the second balancing device are then preferably disposed outside the first housing and the second housing. Alternatively, the first spindle unit and the second spindle unit may include a common spindle housing, and the first balancing device and / or the second balancing device are then preferably disposed outside the common spindle housing.

[0052] In detail, when the tool is housed between the first spindle assembly and the second spindle assembly, the first balancing device is preferably axially disposed between the (first or common) spindle housing of the first spindle unit and the tool, and the second balancing device is axially disposed between the (second or common) spindle housing of the second spindle unit and the tool.

[0053] Preferably, the outer contour of the balancing device is optimized so that interference contour lines are minimized when the workpiece is machined on the workpiece spindle of the machine. Specifically, it is advantageous that the first balancing device and / or the second balancing device have an outer contour that gradually narrows in the direction of the cutting tool.

[0054] The tool head may further include the aforementioned tool, which is axially housed between the first spindle member and the second spindle member and preferably axially clamped. The tool may be an abrasive, particularly a tool for gear grinding. More specifically, the tool may be a grinding worm or a profile grinding wheel, or may include at least one grinding worm and / or at least one profile grinding wheel. The tool may be a one-piece (e.g., in the form of an undressable grinding worm with a hard-coated seat directly housed between the spindle members), or may be two or more pieces (e.g., in the form of a dressable grinding worm or a combined tool with more than one grinding body, wherein one or more grinding bodies are held on individual tool holders and the tool holders are housed between the spindle members).

[0055] The present invention further provides a machine tool comprising a cutting head of the type mentioned above and at least one workpiece spindle for driving a workpiece to rotate about a workpiece axis. The machine tool can be configured as a gear-cutting machine, and more particularly as a gear grinding machine. For this purpose, the machine tool may include a machine control system configured (especially appropriately programmed) to enable the machine to machine the gear teeth of a workpiece housed on at least one workpiece spindle using a cutting tool. Specifically, the machine control system can be configured to enable the machine to machine the gear teeth of the workpiece by profile grinding or generating grinding. For this purpose, the machine control system can be configured to establish a suitable rolling coupling between the workpiece spindle and the cutting head spindle.

[0056] The present invention further provides a method for operating a tool head of the type described above. The method includes: connecting the first spindle bearing and the second spindle bearing during a machining operation and releasing the connection during a machining pause; and / or generating an axial preload force between the first spindle bearing and the second spindle bearing.

[0057] For this method, the other considerations discussed above regarding the tool head are applicable accordingly.

Implementation Method

[0059] [Definition]

[0060] Gear cutting machine: A machine configured to produce or machine gear teeth on a workpiece, particularly internal or external gear teeth. For example, a gear cutting machine can be a machine for precision machining of pre-toothed workpieces, particularly a hardening machine for machining pre-toothed workpieces after hardening. A gear cutting machine includes a programmed machine control system for automatically machining gear teeth.

[0061] Gear generating machining: A type of gear machining in which a cutting tool rolls on a workpiece, thereby producing a cutting motion. Various gear generating machining programs are known, thus distinguishing between programs that utilize geometrically undefined cutting edges, such as gear grinding or boring, and programs that utilize geometrically defined cutting edges, such as gear hobbing, gear peeling, gear scraping, or gear planing.

[0062] Generating Grinding: The generating grinding program is a continuous chip removal program using a geometrically undefined cutting edge to produce axially symmetrical periodic structures, wherein a grinding wheel ("grinding worm") with a worm-shaped outer profile is used as the cutting tool. The cutting tool and the workpiece are mounted on a rotating spindle. The typical rolling motion of the program is achieved by coupling the rotational movement of the cutting tool and the workpiece about the axis of rotation. This rolling motion and the axial feed motion of the cutting tool or workpiece along the workpiece axis produce the cutting motion.

[0063] Tool Head: In this document, the term "tool head" refers to an assembly configured to house and drive the rotation of a machining tool. Specifically, the tool head may be mounted on a rotating body and / or one or more slides to align and position the tool relative to the workpiece.

[0064] Spindle Unit: In machine tool construction, a rotatable shaft on which a tool or workpiece is held is generally referred to as a "spindle". However, in addition to the rotatable shaft, the assembly that includes the associated spindle bearings and associated housings for rotatably supporting the shaft is also frequently referred to as a "spindle". In this document, the term "spindle" is used in this sense. A single shaft is referred to as a "spindle shaft". An assembly that includes at least the associated spindle bearings in addition to the spindle shaft is referred to as a "spindle unit". A "spindle unit" may contain its own housing, but it may also be housed in a common housing together with another spindle unit.

[0065] Ring Balancing System: The ring balancing system has two adjacent balancing rings that surround and are driven by the shaft. Each balancing ring has a predetermined additional imbalance of the same magnitude. The orientation of the balancing rings about the axis of rotation of the shaft is adjustable. If the additional imbalances of the two balancing rings are diametrically opposed, their effects cancel each other out. If the two additional imbalances have the same angular position, maximum balancing capability is achieved. By setting other angles, the resulting corrective imbalance can be freely adjusted in magnitude and direction within these limitations. Example machine tool configuration

[0066] Figure 1 shows an example of a machine tool for hard machining gears by generating grinding. The machine includes a machine bed 100, a tool holder 200 disposed on the machine bed for displacement along the horizontal feed direction X. A Z-slide 210 is disposed on the tool holder 200 for displacement along the vertical direction Z. The Z-slide 210 carries a rotating body 220, which is pivotable relative to the Z-slide 210 about a horizontal axis of rotation A. The axis of rotation A is parallel to the feed direction X. A tool head 300, shown only symbolically, is disposed on the rotating body 220 and will be described in more detail below.

[0067] Furthermore, a pivotable workpiece holder in the form of a rotary table 400 is mounted on the machine bed 100. The rotary table 400 can pivot between several rotational positions about a vertical axis of rotation C3. It carries two workpiece spindles 500, on which a workpiece 510 can be clamped. Each of the workpiece spindles 500 can be driven to rotate about a workpiece axis. In Figure 1, the workpiece axis of the visible workpiece spindle 500 is designated as C2. The workpiece axis of the invisible workpiece spindle in Figure 1 is designated as axis C1. The two workpiece spindles are located on the rotary table 400 in diametrically opposed positions (i.e., offset by 180° relative to the axis of rotation C3). In this way, when a workpiece is being machined on one of the two workpiece spindles, the other workpiece spindle can be loaded and unloaded. This largely avoids undesirable non-productive time. This machine concept is known, for example, from WO 00 / 035621 A1.

[0068] The machine has a machine control system 700, shown only symbolically, which includes a plurality of control modules 710 and a control panel 720. Each of the control modules 710 controls the machine axis and / or receives signals from a self-sensor. [Cutter head according to the first embodiment]

[0069] Figures 2 to 4 illustrate the tool head according to the first embodiment. The tool head includes a base 310 rigidly connected to a rotating body 220. A linear guide 311 is formed on the base 310. The spindle housing 380 is displaceably guided along the displacement direction Y on the linear guide 311. For this purpose, the spindle housing 380 has a corresponding guide block 386. The displacement direction Y is perpendicular to the X-axis and forms an angle with the Z-axis, which can be adjusted about the A-axis. In order to controllably adjust the position of the spindle housing 380 along the displacement direction Y, a ball screw drive device 312 that interacts with a displacement drive device not shown in the figures is used.

[0070] Two spindle units 320 and 330 are housed within the spindle housing 380. A tool 340 is held between spindle units 320 and 330. In this example, the tool 340 is a grinding worm gear. [Spindle Unit Configuration]

[0071] Figures 3 and 4 illustrate the configuration of spindle units 320 and 330 in more detail.

[0072] In this example, the spindle unit 320 is a motorized spindle with a drive motor 324, which directly drives the first spindle member 322 to rotate around the tool spindle axis B. The tool spindle axis B is parallel to the displacement direction Y.

[0073] The first spindle assembly 322 is supported at three bearing positions within the spindle bearings 323. These bearing positions are located at different axial positions along the first spindle assembly 322. Two of these bearing positions are located between the drive motor 324 and the tool-side end of the first spindle unit 320. The corresponding spindle bearings form a positioning-non-positioning bearing or a support bearing; that is, at at least one of these bearing positions, the spindle bearing can absorb both radial and axial forces. The other bearing position is located on the side of the drive motor 324 opposite to the tool. The spindle bearing located at this bearing position is configured as a non-positioning bearing, meaning it absorbs radial forces but allows axial movement. All three spindle bearings 323 are fixedly disposed within the spindle housing 380. Specifically, they cannot be axially displaced relative to the spindle housing 380.

[0074] In this example, the second spindle unit 330 is a non-drive docking spindle. The second spindle unit 330 has a second spindle member 332, which is supported in the spindle housing 380 at two bearing positions along the spindle member in the spindle bearing 333. These spindle bearings form a positioning-non-positioning bearing or a support bearing, that is, at at least one of these bearing positions, the spindle bearing 333 can absorb both radial and axial forces.

[0075] The second spindle unit 330 is axially displaceable relative to the spindle housing 380 between the operating position shown in FIG. 3 and the tool change position shown in FIG. 4. For this purpose, the spindle bearing 333 of the second spindle unit is housed in a bearing housing 391. In this example, the bearing housing 391 is a bearing bushing, which may be, for example, a sliding bearing bushing or a ball bearing bushing. The bearing housing 391 is guided in the spindle housing 380 so that it is axially displaceable. In the operating position of FIG. 3, the second spindle unit 330 advances in the direction of the first spindle unit 320, such that the tool 340 is held between the first spindle member 322 and the second spindle member 332. In contrast, in the tool change position of FIG. 4, the second spindle unit 330 has been axially retracted a sufficient distance to allow removal of the tool 340. [Axial clamping of the tool]

[0076] In this example, the tool 340 has a tool holder 341 that supports a worm gear-formed dressable abrasive body 342. In this example, the tool holder 341 is formed as a retaining flange for the grinding body according to DIN ISO 666:2013-12. For connection to the spindle shafts 322, 332, the tool holder 341 has a tapered seat (also called a tapered socket or tapered support) with surface contact at each end, such as a short tapered seat of 1:4 according to DIN ISO 702-1:2010-04.

[0077] Spindle noses 325 and 335 are formed at the tool-side ends of spindle members 322 and 332. The shapes of spindle noses 324 and 325 are complementary to the shape of the tapered seat of the tool holder 341. Each has a conical shape pointing towards the tool 340 and a planar contact surface on its respective end face. For example, each spindle nose may be formed as a 1:4 tapered shank according to DIN ISO 702-1:2010-04.

[0078] Therefore, in the operating position shown in Figure 3, there is a conical connector with surface contact between each of the tool 340 and the spindle members 322 and 332. The conical connector may have different diameters at the two ends of the tool to ensure that the tool 340 can only be correctly oriented and housed between the spindle members 322 and 332.

[0079] The cutting tool 340 is axially compressed between spindle members 332 by a pull rod 370 and a clamping nut 372. For this purpose, the cutting tool 340 and the second spindle member 332 each have a central axial bore extending through them. The first spindle member 322 also has a central axial bore at its cutting tool end. In this example, this bore is not continuous. The bore is open on the cutting tool side, and an internal thread is formed in the bore. The pull rod 370 is inserted through the central bore of the spindle member 332 and the cutting tool 340. The pull rod 370 has an external thread at its end facing the first spindle unit 320 that screws into the internal thread of the first spindle member 322. The pull rod also has an external thread at its other end. The clamping nut 372 is screwed onto this external thread. By tightening the clamping nut 372, the clamping nut 372 applies axial pressure to the second spindle member 332 in the direction of the cutting tool 340. This allows the tool 340 to be axially clamped between the spindle members 332, creating a single, continuous shaft with high rigidity. [Axial support for the bearing housing]

[0080] The bearing housing 391, which houses the spindle bearing 333 of the second spindle unit 330, is axially clamped relative to the spindle housing 380. In general, the second spindle unit 330 is thus axially clamped not only at the spindle members 322, 323 relative to the first spindle unit 320 via the tool 340, but also axially clamped at the bearing side. In this way, an axial compressive or tensile force can be generated between the spindle bearing 323 of the first spindle unit 320 and the spindle bearing 333 of the second spindle unit to preload these bearings. An annular actuator 390 (in this example, a pneumatic actuator) is used to generate the axial compressive or tensile force. The actuator 390 has an annular actuator housing 393, which is rigidly connected to the spindle housing 380. A piston element 392, also annular, is displaceably guided within the actuator housing 393. The piston element 392 is rigidly connected to the bearing housing 391. The actuator housing 393 and the piston element 392 together define an annular space, the volume of which depends on the axial position of the piston element 392 within the actuator housing 393. By introducing compressed air into the annular space, the piston element 392 is pushed toward or away from the first spindle unit 320, thereby generating an axial compressive or tensile force between the spindle bearing 333 of the second spindle unit 330, which is held in the bearing housing 391, and the spindle bearing 323 of the first spindle unit 320 when the tool 340 is clamped.

[0081] The control device 730 controls the actuator 390 in a manner known per se. For example, the control device 730 interacts with a pneumatic valve (not shown) in a pressure line to the actuator 390 to change the pressure in the actuator 390.

[0082] By arranging the actuator 390 in a ring shape, the rear end of the second spindle member 332 can still be approached from the outside via the actuator 390, so that the tool 340 can be axially clamped between the first spindle member 322 and the second spindle member 332. The clamping nut 372 can be located in the area surrounded by the ring actuator 390. [Operation of the tool spindle]

[0083] To clamp the tool 340 between the spindle units 320 and 330, the second spindle unit 330 is first moved to the tool changing position shown in FIG. 4, and the clamping nut 372 is removed from the pull rod 370. The tool 340 is inserted, and the pull rod 370 is inserted through the tool into the hole of the first spindle member 322, wherein the pull rod is fixed by screwing it into the appropriate position. The second spindle unit 330 is now moved to the operating position shown in FIG. 3. In this position, the clamping nut 372 is placed on the pull rod 370, and the tool 340 is axially clamped to the first spindle member 321 and the second spindle member 332 by means of the clamping nut 372. The actuator 390 is not operated until this point to avoid interfering with the axial displacement of the second spindle unit 330. After clamping the tool 340, the actuator 390 is activated to axially clamp the spindle bearing 333 of the second spindle unit 330 relative to the spindle housing 380.

[0084] The tool 340 is now rotated by a drive motor 324 and used to machine a workpiece. During machining, both the spindle housing 380 and the unit comprising two spindle shafts 322, 332 and the tool 340 axially clamped between these spindle shafts become hot. Therefore, the spindle housing 380 and the unit thermally expand. The thermal expansion of these parts usually differs. During machining, the pneumatic pressure acting on the actuator remains constant. In this way, the spindle bearing 333 of the second spindle unit 330 can follow the thermal expansion of the spindle shafts 322, 332 and the rotor 340, and the axial clamping force on the spindle bearing remains constant even if the thermal expansion differs.

[0085] Depending on the situation, the control device 730 can be configured to change the pressure in the actuator 390 based on one or more measurement parameters. For this purpose, for example, a sensor 731, shown only symbolically, can be disposed on the spindle housing 380, and this sensor is read by the control device 370. The sensor 731 can be, for example, a temperature sensor, a vibration sensor, a strain gauge, or a force sensor for measuring axial clamping force. The control device 730 can then change the pressure in the actuator based on the measurement parameters from the sensor 731, for example, to reduce vibration or selectively increase the axial clamping force in the event of increased spindle load (such as indicated by increased temperature or thermal expansion). [Alternative to pneumatic clamping]

[0086] Instead of a pneumatic actuator, another type of actuator can be used to generate axial compressive or tensile force between the spindle bearings; for example, a hydraulic actuator can also be used. The above considerations for pneumatic actuators similarly apply to hydraulic actuators. However, the actuator can also be a mechanical actuator. A mechanical actuator may, for example, include a helical spring that generates axial tensile or compressive force between the spindle housing 380 and the bearing housing 391. The degree of compression of the helical spring and thus the axial force generated by the helical spring can then be changed by a suitable actuator. Alternatively, the axial force can be generated by a piezoelectric element. Various other embodiments are conceivable.

[0087] In addition to axially supporting or replacing the bearing housing 391 by means of an actuator, it is conceivable to axially fix ("clamp") the bearing housing 391 relative to the spindle housing 380 in a controlled manner. For this purpose, a clamping device not shown in the figure may be provided, such as an expansion sleeve mounted in the spindle housing 380 and surrounding the bearing housing 391. With the aid of the clamping device, the bearing housing 391 can be carefully fixed to the spindle housing 380 during workpiece machining to minimize vibration, and this fixation can be briefly released during machining pauses, such as after each tool stroke or after machining each workpiece, to reduce excessive axial bearing forces. A control device 730 may be used for this purpose. The release may be controlled based on measurement parameters. For example, the control device 730 may use a sensor 731 to detect temperature, vibration, thermal expansion and / or axial force between the spindle bearings for this purpose, and release the clamping device from time to time based on the measured measurement parameters. If both an actuator for generating axial force and a clamping device are present, clamping can occur after the spindle bearings 323 and 333 have been preloaded by the actuator.

[0088] The actuator 390 can also be operated to provide a releasable clamping force without generating an axial preload. If the actuator is a pneumatic or hydraulic actuator, the fluid simultaneously generates a restoring action combined with damping, i.e., the clamping has limited stiffness. This can further help prevent spindle bearing overload. Advantageously, the actuator 390 can also be used to retract the bearing housing 391 during tool changes. [Second Embodiment]

[0089] Figures 5 to 8 illustrate the cutter head according to the second embodiment. The same or similar functional parts have the same reference numerals as in the first embodiment.

[0090] Compared to the first embodiment, the first spindle unit 320 has its own first housing 321, and the second spindle unit 330 has its own second housing 331. The housings 321 and 331 are independently guided along the displacement direction Y on the linear guide 311 of the base 310. For this purpose, each housing includes guide blocks 326 and 336. The position of the first housing 321 can be adjusted along the displacement direction Y by means of a displacement actuator and a ball screw drive device 312 (not shown in the figures). The second housing 331 can be coupled to the first housing 321 in a manner described in more detail below, such that the second housing is held by the first housing 321 when the first housing 321 moves along the displacement direction Y. The spindle bearings remain non-axially displaceable in the respective housings 321 and 323. Compared to the first embodiment, the axially displaceable bearing housing for the spindle bearings of the second spindle unit 330 is omitted. The actuator for axially adjusting the displaceable bearing housing is also omitted. In addition, the two spindle units 320 and 330 are configured in the same manner as in the first embodiment.

[0091] To controllably couple or release housings 321 and 331, the tool head in this example includes two clamping devices 600. One of these clamping devices is positioned above the central mid-plane of the tool head, and the other is positioned below this mid-plane. Here, the central mid-plane is a plane containing the workpiece spindle axis B in the XY direction. Only the upper clamping device is visible in Figures 6 and 7. The clamping device 600 is shown separately in Figure 8.

[0092] The clamping device 600 includes an axially extending rod 620 connected to the second spindle housing 331 via a mounting flange 621. A damping ring 622 is disposed between the mounting flange 621 and the second spindle housing 331. Another damping ring 622' is located on the other axial side between the mounting flange 621 and the push ring 623. The damping rings 622 and 622' are compressed in the axial direction by screws 624 when the rod 620 is mounted, and reduce vibration between the rod 620 and the second spindle housing 331. They may also be omitted.

[0093] The clamping device 600 further includes an expansion sleeve 610 connected to the first spindle housing 621 via screws 614. The expansion sleeve 610 can be hydraulically actuated to selectively clamp the rod 620 in the expansion sleeve 610 or release such clamping.

[0094] The clamping device 600 is controlled by the control device 730. Depending on the situation, for this purpose, a sensor 731 may also be disposed on the first spindle housing 321 and / or the second spindle housing 331, and this sensor is read by the control device 370. The sensor 731 may be, for example, a temperature sensor, vibration sensor, strain sensor, or force sensor as in the first embodiment. The control device 730 may then be configured to actuate the clamping device 600 based on one or more measurement parameters from the sensors. The two clamping devices 600 may be actuated together or independently. For example, for certain types of vibration, actuating only one of the two clamping devices 600 may be suitable.

[0095] When the clamping of the two clamping devices 600 is released, the second spindle unit 320 can be manually moved along the Y direction between the operating positions in Figures 5 and 6 and the tool change position in Figure 7. [Operation of the tool spindle]

[0096] Before starting workpiece machining, the clamping device 600 is activated to secure the second spindle housing 331 to the first spindle housing 321. The tool 340 is now rotated by the drive motor 324 and used to machine the workpiece. During machining, the second spindle housing 331 remains fixed to the first spindle housing 321 to prevent vibration. However, both the spindle housings 321 and 331, and the unit comprising the two spindle shafts 322 and 332 and the tool 340 axially clamped between these spindle shafts, become hot. To avoid excessive axial bearing force due to different thermal expansion, the control device 730 releases the clamping device 600 periodically during machining pauses, such as after each tool stroke or after machining each workpiece. This can be done based on measurement parameters, as appropriate. For example, the control device 730 may detect temperature, linear expansion, or axial bearing force for this purpose and release the clamping device 600 periodically based on the measured parameters. [Balancing device]

[0097] The first balancing unit 350 is disposed on the first spindle member 322 in the axial region between the housing 321 of the first spindle unit 320 and the tool 340. The second balancing unit 360 is axially disposed on the second spindle member 332 between the housing 331 of the second spindle unit 330 and the tool 340. The balancing units 350 and 360 surround the respective spindle members 322 and 332 outside the housings of the respective spindle units 320 and 330. Each of them includes a housing that gradually narrows from the associated spindle unit toward the tool 340. The tapered outer contours of the balancing units 350 and 360 reduce the risk of collision between the balancing unit and the workpiece 510.

[0098] Each of the balancing units 350 and 360 is configured as a ring balancing system. For this purpose, each of the balancing units 350 and 360 has a rotor having two balancing rings surrounding and driven by the respective spindle shaft. Each of the balancing units 350 and 360 also has a stator. The stator is connected to the respective spindle housings 321 and 331. On one hand, the stator includes sensors for detecting vibrations of the respective spindle housings, rotational speeds of the respective spindle shafts, and the angular position of each balancing ring. On the other hand, the stator includes actuators with coil configurations for changing the angular position of the balancing rings on the respective spindle shafts upon contact.

[0099] The balancing unit can be used to compensate for the static and dynamic imbalance of the system including the tool 340 and the spindle shafts 322 and 332 clamped thereon, so as to balance the system in two balancing planes.

[0100] The ring balancing system for automatic dual-plane balancing is known and available from various suppliers. An example is the AB 9000 electromagnetic ring balancing system from Hofmann Mess- und Auswuchttechnik in Pfonsstadt, Germany.

[0101] Such a balancing unit can also be provided in the first embodiment. In order to enable the second spindle unit 330 to retract for tool change, the rotor of the second balancing unit 360 can be axially displaced relative to the stator of this balancing unit. The outer diameter of the rotor can be selected to be smaller than the inner diameter of the portion of the spindle housing 380 in which the guide bearing housing 391 is located. When the second spindle unit 330 retracts axially from the spindle housing 380, the second spindle unit carries the rotor of the second balancing unit 360 in the axial direction, such that the rotor, together with the second spindle unit 330, retracts into the spindle housing 380. In contrast, the stator of the second balancing unit 360 is fixed to the spindle housing 380 and remains stationary during the retraction of the second spindle unit 330.

[0102] Alternatively, it is also conceivable that the second balancing unit 360 (i.e., both the rotor and the stator) can be retracted together with the second spindle unit 330 to facilitate tool replacement.

[0103] The type of balancing unit described herein also exists in other embodiments discussed below. [Third Embodiment]

[0104] Figures 9 and 10 illustrate the third embodiment. The third embodiment differs from the second embodiment in that the second spindle housing 320 is not fixed to the first spindle housing 310 by a controlled, releasable clamp, but is axially clamped relative to the first spindle housing 310. Two pneumatic actuators 630, disposed between the two spindle housings 310 and 320 rather than the clamping device 600, are used to generate corresponding axial compressive or tensile forces. In Figures 9 and 10, only one of these two actuators is visible.

[0105] In order to further consider the effects of operation, axial clamping of the spindle bearing, and alternatives to the pneumatic actuator used to generate axial force, refer to the description of the first embodiment.

[0106] Clamping and axial support can also be combined. For this purpose, the tool head may include both a controlled, releasable clamping device as in the second embodiment and an actuator for generating axial force. Clamping may then occur after the spindle bearings 323, 333 have been preloaded using the actuator.

[0107] Where appropriate, actuator 630 can also be operated to provide releasable clamping without generating axial offset force. When the actuator is pneumatic or hydraulic, the fluid generates a certain spring action in combination with damping during clamping. When the actuator is pneumatic or hydraulic, the fluid generates a specific restoring action in combination with damping during clamping, meaning that the clamping has limited stiffness. This can further help prevent spindle bearing overload. Advantageously, actuator 630 can also be used to push back the second spindle unit 330 during tool change. [Fourth Embodiment]

[0108] Figures 11 to 13 illustrate the cutter head according to the fourth embodiment.

[0109] The first spindle unit 320 and the second spindle unit 330 each have their own spindle housings 321 and 331, which are independently guided on the linear guide 311 by guide blocks 326 and 336. Each spindle unit has its own positioning drive 328 and 338 for moving the individual spindle unit independently of the other spindle unit along the Y direction. For this purpose, each positioning drive 328 and 338 has a torque motor that drives a backlash-free preloaded ball nut to rotate about the rotation axis B'; the ball nut extends on a fixed ball screw spindle 313 positioned along the rotation axis B'. The rotation axis B' is parallel to the Y direction and parallel to the tool spindle axis B.

[0110] Each of the two spindle housings 321, 322 may be clamped to the base 310 via clamping devices 327, 337, as appropriate. In some embodiments, the clamping devices 327, 337 establish a connection between the respective spindle housing and the base that is not entirely rigid but elastically damped in the axial direction. For this purpose, each of the two spindle housings has: an auxiliary body that can be releasably fixed to the base 310 by clamping and is movable relative to the base 310 together with the respective spindle housings 321, 331 in the released state; and at least one vibration damper disposed between the auxiliary body and the movable body. For details of this embodiment, refer to WO2020038751A1.

[0111] For workpiece machining, as in the second or third embodiment, the second spindle housing 331 is fixed to the first spindle housing 321 and / or axially clamped relative to the first spindle housing 321 by clamping in a controllable release manner. For possible implementations of the connection between the spindle housings and operational considerations, refer to the above explanation of the second and third embodiments.

[0112] During workpiece machining, clamping devices 327 and 337 can be activated as needed to fix the two spindle housings 321 and 331 to the base 310. In order to change the position of the tool 340 relative to the workpiece along the Y-axis, clamping devices 327 and 337 are released, and two positioning drive devices 328 and 338 are controlled synchronously to make the spindle housings 321 and 331 move synchronously relative to the base 310.

[0113] The second spindle assembly 332 is driven independently by a second drive motor 334. Preferably, the second drive motor 334 is sized smaller than the first drive motor 324, such that the torque it generates is less than half of the total torque on the tool 340, for example, between 30% and 45% of the total torque. This asymmetrical torque distribution between the two drive motors 324 and 334 avoids virtual resonance. However, the second drive motor can also be omitted. [Clamping Nut]

[0114] Figures 13 and 14 illustrate an exemplary clamping nut 372, such as that which can be used in the embodiments described above.

[0115] The clamping nut 372 includes a base element 373 defining a central hole having internal threads for screwing the base element 373 onto a pull rod having corresponding external threads. At one end, the base element 373 is externally formed as a hexagonal nut. A support ring 374 is mounted on the base element 373. The support ring abuts against a collar of the base element 373 in such a way that it prevents axial movement of the support ring in one direction (to the left in FIG. 9). Furthermore, an annular axially actuating element 375 is guided on the base element 373 in an axially displaceable manner. A plurality of actuating elements 376, in the form of pressure screws, are screwed into the axially actuating element 375 and axially supported on the support ring 374 in such a way that they prevent axial movement of these actuating elements in one direction (to the left in FIG. 9). By unscrewing the pressure screw from the axial push element 375, the axial push element 375 moves forward relative to the base element 373 in a direction opposite to the support direction (to the right in Figure 9).

[0116] To clamp the tool 340 between the two spindle members 322 and 332, the axial push element 375 is first moved back completely relative to the base element 373 by tightening the pressure screw as much as possible into it. Now, the clamping nut 372 is screwed onto the pull rod 370, and adjusted against the second spindle member 332 by means of the hexagonal shape formed on the outside of the base element 373. This is accomplished with relatively low torque. Subsequently, by means of the pressure screw, the annular axial push element 375 advances in a controlled manner in the direction of the second spindle member 332 until the required clamping force is applied to the tool 340. Thus, the axial push element 375 is supported on the second spindle member 332 by the annular contact surface.

[0117] Of course, other constructions for clamping the nut can also be used, as are known from the prior art. For example, force transmission can be achieved in a manner different from that described. Specifically, a hydraulically clamped nut can be used.

[0118] Instead of a threaded clamping nut, a clamping element that can be connected to the pull rod by means other than screws, such as via a bayonet or a clamping bushing. [Other variations]

[0119] The interface between the spindle members 322, 332 and the tool 340 can also be formed in a manner different from that described in the embodiments above. Specifically, different types of conical connectors and / or surface contacts can be used. Specifically, any known conical connector can be used, such as embodiments A, BF, BM, CF or CM mentioned in DIN ISO 666:2013-12. For details, refer to DIN ISO 666:2013-12 and other standards mentioned therein, such as DIN EN ISO 1119:2012-04, DIN ISO 702-1:2010-04, ISO 12164-1:2001-12 and ISO 12164-2:2001-12.

[0120] In any embodiment, the pull rod 370 may extend through the first spindle member 322 rather than through the second spindle member 332, and may be connected at its end to the second spindle member 332. Thus, the clamping element then applies an axial force to the first spindle member in the direction of the second spindle member.

[0121] In order to axially clamp the tool 340 between the first spindle member 322 and the second spindle member 332, two or more tie rods may be used instead of the central tie rod, which extend parallel to each other and are radially spaced from the tool spindle axis B, and are arranged at different angular positions relative to the tool spindle axis B.

[0122] The cutting tool can also be fixed between the first and second spindle members in a manner other than using a continuous tie rod, for example, by using a clamping system disposed inside the respective spindle members. For this purpose, the connection between the cutting tool and the spindle members can be achieved, for example, by means of a hollow shank tapered connection according to ISO 12164-1:2001-12 and ISO 12164-2:2001-12.

[0123] Alternatively, clamping between the spindle bearings on both sides of the tool can be achieved by means of a combination of rack and pinion, mechanical means, eccentric rotating lever, pawl, or electromagnetic means, rather than by using a hydraulic expansion clamping element.

[0124] In the embodiments described above, the tool 340 includes a worm-formed dressable abrasive body 342 interchangeably mounted on the tool holder 341. However, the tool may also have different configurations, particularly a one-piece configuration. For example, the tool may be an undressable CBN grinding worm with a CBN coating directly applied to the tool holder body. The interfaces of the spindle noses 325, 335 are then formed on the tool holder body. The tool is not necessarily a grinding worm. The tool may also be, for example, a profile grinding wheel, a combination of two or more profile grinding wheels, or a combination of one or more grinding worms and one or more profile grinding wheels.

[0125] In the embodiment described above, the spindle bearing 323 is a rolling bearing. Alternatively, other types of spindle bearings, such as hydrostatic, hydrodynamic, or aerodynamic bearings, may be used, as are known in the prior art.

[0126] In the embodiments described above, the direct drive device is used as a drive motor. Alternatively, a gear motor may also be used.

[0127] The second drive motor, as in the fourth embodiment, may also be provided in the first to third embodiments.

[0128] While ring balancing systems are preferred as balancing devices, other types of balancing devices are also conceivable, such as hydraulic balancing systems known from the prior art. In such balancing systems, balancing is achieved by injecting fluid into balancing chambers distributed in a circumferential direction. [Simplified Explanation of the Diagram]

[0058] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, which are for illustrative purposes only and should not be interpreted in a limiting manner. In these figures, [Figure 1] schematically shows an example of a machine tool for hard machining gears by generating grinding, the machine tool having a tool head according to a first embodiment; [Figure 2] schematically shows a perspective view of the tool head of the first embodiment; [Figure 3] shows a perspective sectional view of the tool head of the first embodiment; [Figure 4] shows a perspective sectional view of the tool head of the first embodiment after tool removal; [Figure 5] schematically shows a tool head according to a second embodiment; [Figure 6] shows a perspective sectional view of the tool head of the second embodiment; [Figure 7] shows a perspective sectional view of the tool head of the second embodiment after tool removal; [Figure 8] shows a central longitudinal section of the clamping device of the tool head of the second embodiment; [Figure 9] shows a perspective sectional view of the tool head according to a third embodiment; [Figure 10] shows a perspective sectional view of the tool head of the third embodiment after tool removal; [Figure 11] schematically shows a perspective view of the tool head according to a fourth embodiment; [Figure 12] The cutting head of the fourth embodiment is shown in a perspective cross-sectional view; [Fig. 13] shows the central longitudinal section of the clamping nut; and [Fig. 14] shows the clamping nut of Fig. 13 in perspective view.

Claims

1. A tool head (300) for a machine tool, comprising: a first spindle unit (320) having at least one first spindle bearing (323) and a first spindle member (322), the first spindle member being mounted in the first spindle bearing (323) for rotatability about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; and a second spindle unit (330) having at least one second spindle bearing (333) and a second spindle member (332), the second spindle member being mounted in the second spindle bearing (333) for rotatability about the tool spindle axis (B), the second spindle bearing (333) being configured to absorb both radial and axial forces. The first spindle unit (320) and the second spindle unit (330) are coaxially arranged relative to each other, in such a way that a tool (340) can be axially housed between the first spindle member (322) and the second spindle member (332). The tool head (300) includes a controlled clamping device for controllably connecting the first spindle bearing (323) and the second spindle bearing (333) to each other. A control device (730) is associated with the tool head (300) and is configured to activate the clamping device during a machining operation and deactivate the clamping device during a machining pause. The cutting head (300) includes at least one sensor (731) for monitoring the operating state of one of the cutting heads (300), and the control device (730) is configured to read the sensor (731) and deactivate the clamping device in consideration of a measurement parameter measured by the sensor (731).

2. The tool head (300) of claim 1, wherein the clamping device includes an expanding clamping element.

3. The tool head (300) of claim 1 or 2, wherein the clamping device is configured to reduce vibration between the first spindle unit (320) and the second spindle unit (330) when the clamping device is in an activated state.

4. The tool head (300) of claim 1 or 2, comprising: a common spindle housing (380) in which both the first spindle unit (320) and the second spindle unit (330) are housed; a bearing housing (391) axially displaceable relative to the common spindle housing (380); and at least one second spindle bearing (333) held in the bearing housing; wherein the clamping device is configured to controllably fix the bearing housing (391) relative to the common spindle housing (380) to connect the first spindle bearing (323) and the second spindle bearing (333) to each other.

5. The tool head (300) of claim 1 or 2, wherein the first spindle unit (320) includes a first spindle housing (321) and the at least one first spindle bearing (323) is held in the first spindle housing, wherein the second spindle unit (330) includes a second spindle housing (331) and the at least one second spindle bearing (333) is held in the second spindle housing, and wherein the clamping device is configured to controllably couple the first spindle housing (321) and the second spindle housing (331) to each other to connect the first spindle bearing (323) and the second spindle bearing (333) to each other.

6. A tool head (300) for a machine tool, comprising: a first spindle unit (320) having at least one first spindle bearing (323) and a first spindle member (322), the first spindle member being mounted in the first spindle bearing (323) for rotatability about a tool spindle axis (B), the at least one first spindle bearing (323) being configured to absorb both radial and axial forces; and a second spindle unit (330) having a second spindle bearing (333) and a second spindle member (332), the second spindle member being mounted in the second spindle bearing (333) for rotatability about the tool spindle axis (B), the at least one second spindle bearing (333) being configured to absorb both radial and axial forces. The first spindle unit (320) and the second spindle unit (330) are coaxially arranged relative to each other, in such a way that a tool (340) can be axially housed between the first spindle member (322) and the second spindle member (332). The tool head (300) includes an axial force element configured to generate an axial preload force between the first spindle bearing (323) and the second spindle bearing (333). The axial force element includes an actuator (390; 630) to controllably change the axial preload force. The tool head (300) is associated with a control device (730) configured to actuate the actuator (390; 630) to adjust and / or controllably change the axial preload force in a controlled manner. The tool head (300) includes at least one sensor (731) for monitoring the operating state of one of the tool heads (300), and the control device (730) is configured to read the sensor (731) and change the axial preload force in consideration of a measurement parameter measured by the sensor (731).

7. The tool head (300) of claim 6, comprising: a common spindle housing (380) in which both the first spindle unit (320) and the second spindle unit (330) are housed, a bearing housing (391) axially displaceable relative to the common spindle housing (380), and at least one second spindle bearing (333) held in the bearing housing, wherein the axial force element is configured to apply an axial force on the bearing housing (391) to generate the axial preload force.

8. The tool head (300) of claim 7, wherein the actuator (390) is annular and surrounds a support element for axially securing the tool (340) between the first spindle member (322) and the second spindle member (332).

9. The tool head (300) of claim 6 or 7, wherein the first spindle unit (320) includes a first spindle housing (321), wherein the second spindle unit (330) includes a second spindle housing (331), and wherein the axial force element connects the first spindle housing (321) and the second spindle housing (331) to each other, and is configured to apply an axial force between the first spindle housing (321) and the second spindle housing (331) to generate the axial preload force.

10. The tool head (300) of claim 1, 2, 6, 7 or 8, wherein the tool (340) is axially secured between the first spindle member (322) and the second spindle member (332), such that an axial compressive force is applied to the tool (340) between the first spindle member (322) and the second spindle member (332).

11. The tool head (300) of claim 10, wherein the second spindle member (332) has at least one axial bore, wherein the tool head (300) includes at least one pull rod (370) extending through the axial bore of the second spindle member (332), the pull rod (370) being connectable at a first end to the first spindle member (322) for tensioning, and wherein the pull rod (370) is connectable at a second end to the second spindle member (332) such that an axial compressive force can be generated on the tool (340) between the first spindle member (322) and the second spindle member (332).

12. The tool head of claim 11, wherein the tool head (300) includes a support element that can be connected to the second end of the pull rod (370) and configured to axially push the second spindle member (332) toward the first spindle member (322).

13. The tool head of claim 12, wherein the support element comprises: a base element rigidly connected to the pull rod (370); an axial push element axially displaceable relative to the base element in the direction of the second spindle member (332) to axially push the second spindle member (332) toward the first spindle member (322); and at least one actuating element movable relative to the base element to generate an axial compressive force on the axial push element relative to the base element.

14. The tool head (300) of claim 1, 2, 6, 7 or 8, wherein a first spindle nose (325) is formed at a tool-side end of the first spindle member (322) in such a way that an axial compressive force can be generated at the first spindle nose (325) to a non-positive and / or positive connection to the tool (340), and wherein a second spindle nose (335) is formed at a tool-side end of the second spindle member (332) in such a way that an axial compressive force can be generated at the second spindle nose (335) to a non-positive and / or positive connection to the tool (340).

15. The tool head (300) of claim 1, 2, 6, 7 or 8, wherein the first spindle unit (320) includes a first drive motor (324) configured to drive the first spindle member (322) to rotate about the tool spindle axis (B), and / or wherein the second spindle unit (330) includes a second drive motor (334) configured to drive the second spindle member (332) to rotate about the tool spindle axis (B).

16. The tool head (300) of claim 1, 2, 6, 7 or 8 comprises: a first balancing unit (350) associated with the first spindle unit (320); and a second balancing unit (360) associated with the second spindle unit (330).

17. The tool head (300) of claim 16, wherein the first balancing unit (350) radially surrounds the first spindle member (322) and is axially disposed between a tool-side spindle bearing (323) of the first spindle unit (320) and a tool-side end of the first spindle member (322), and / or wherein the second balancing unit (360) radially surrounds the second spindle member (332) and is axially disposed between a tool-side spindle bearing (333) of the second spindle unit (330) and a tool-side end of the second spindle member (332).

18. The tool head (300) of claim 17, wherein the first balancing unit (350) and / or the second balancing unit (360) are configured as a loop balancing system.

19. The tool head (300) of claim 1, 2, 6, 7 or 8 further comprises a tool (340) axially housed between the first spindle member (322) and the second spindle member (332) and axially fastened such that an axial compressive force is applied to the tool (340) between the first spindle member (322) and the second spindle member (332).

20. The tool head (300) of claim 1, 2, 6, 7 or 8, wherein the sensor (731) is a temperature sensor, vibration sensor, strain sensor, force sensor or pressure sensor.

21. The tool head (300) as requested in item 6, 7 or 8, wherein the actuator is a pneumatic actuator or a hydraulic actuator.

22. The tool head (300) of claim 6, 7 or 8, wherein the control device (730) is configured to activate the axial force element during a machining operation and deactivate the axial force element during a machining pause.

23. A gear cutting machine comprising: a cutter head (300) as claimed in any one of claims 1 to 22; and at least one workpiece spindle (500) for driving a workpiece (510) to rotate about a workpiece axis (C1).

24. A method of operating a tool head (300) as claimed in any one of claims 1 to 22, comprising: connecting the first spindle bearing (323) and the second spindle bearing (333) during a machining operation and releasing the connection during a machining pause; and / or generating an axial preload force between the first spindle bearing (323) and the second spindle bearing (333).

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