Tool head, method of operating a tool head, and machine tool having such a tool head

Abstract

A tool head (300) for a machine tool, in particular a gear cutting machine, has a first spindle unit (320) and a second spindle unit (330), each of which has at least one spindle bearing (323, 333) and a spindle shaft (322, 332) rotatably mounted in each spindle bearing about a tool spindle axis (B). Each spindle bearing can support both radial and axial forces. The spindle units are arranged coaxially with one another, and a tool (340) is received axially between both spindle shafts. A controlled clamping device (600) connects the spindle bearings together. A control device (730) activates the clamping device (600) during machining operations and deactivates the clamping device during machining pauses. Alternatively or additionally, the tool head has an axial force element which generates an axial preload force between both spindle bearings.

Description

[Technical Field]

[0001] The present invention relates to a tool head. The invention further relates to a machine tool comprising such a tool head and to a method of operating such a tool head. [Background technology]

[0002] In gear manufacturing, tools with small diameters are increasingly used. To achieve the desired cutting speed, such tools are usually operated at relatively high rotational speeds. Such tools may be relatively long in relation to their diameter. This makes them particularly susceptible to bending and torsional vibrations. It is therefore advantageous to accommodate such tools in a spindle at both ends. Tool heads for gear cutting machines, which have two spindles between which the tool is accommodated, have been known in the prior art for many years.

[0003] For example, Patent Document 1 discloses a tool head for a form grinding machine. A tool spindle with a drive motor is arranged on each of two separate tool slides. Separate positioning drives allow each tool slide to move axially. The spindle shafts of the two tool spindles are coaxially arranged and connected to each other by tool holders to ensure resistance to twisting and bending. To this end, the spindle shafts have positioning pins connected to the tool holders via radial expansion clamp connections. The positioning drives of the two tool slides can move in unison. This structure may be susceptible to vibration. Furthermore, if the tool thermally expands during machining or if the two tool slides are not accelerated in perfect unison when moving axially, there is a risk of bearing damage in the tool spindle.

[0004] Patent Document 2 also discloses a tool head having two tool spindles with a tool received between them. The tool spindles are linearly displaceable relative to a base. The two tool spindles can be connected by a motion transmission unit so that a single positioning drive moves the two tool spindles together relative to the base.

[0005] Patent Document 3 discloses a tool head having a motor spindle and a counter spindle between which a tool is received, and balancing devices are incorporated into the shafts of the motor spindle and the counter spindle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] DE 4431374 A1 [Patent Document 2] German Patent Application Publication No. 102009039752 [Patent Document 3] European Patent Application Publication No. 3153277 Summary of the Invention

[0007] The object of the present invention is to provide a tool head having two spindles between which a tool can be received, which has improved vibration characteristics and a reduced risk of bearing damage due to thermal expansion.

[0008] This problem is solved by a tool head according to claim 1 or 7. Further embodiments are described in the dependent claims.

[0009] A tool head for a machine tool, in particular a gear cutting machine, comprising: a first spindle unit including at least one first spindle bearing and a first spindle shaft; a second spindle unit including at least one second spindle bearing and a second spindle shaft; and the first spindle shaft is rotatably mounted on a first spindle bearing about the tool spindle axis, the first spindle bearing being configured to absorb both radial and axial forces; the second spindle shaft is rotatably mounted on a second spindle bearing about the tool spindle axis, the second spindle bearing being configured to absorb both radial and axial forces; the first spindle unit and the second spindle unit are coaxially arranged with respect to one another such that a tool is receivable axially between the first spindle shaft and the second spindle shaft; A tool head is disclosed.

[0010] According to a first aspect of the present invention, the above object is achieved by a tool head having a controllable clamping device for controllably connecting a first spindle bearing and a second spindle bearing to one another, preferably for substantially rigidly connecting them to one another, and a control device assigned to the tool head, the control device being configured to activate the clamping device during machining operations and to deactivate the clamping device during machining pauses.

[0011] By intentionally connecting the two spindle bearings during a machining operation, the tendency of the tool head to vibrate is significantly reduced. This connection also significantly reduces the axial forces on the spindle bearings caused by the acceleration of the spindle unit during movement of the tool head, for example during dressing or shifting, and / or allows these forces to be shifted, especially towards the spindle unit containing the more preloaded spindle bearing. By intentionally releasing this connection during machining pauses, thermal stresses that may occur during machining are also eliminated. This prevents damage to the bearings caused by thermal stresses. The machining operation can be the machining of a workpiece with a tool or the dressing operation of a tool with a dressing device.

[0012] The tool head may have at least one sensor for monitoring the operating state of the tool head, in particular a temperature sensor, a vibration sensor, a strain sensor, a force sensor, or a pressure sensor. In this case, the control device may be configured to read the sensor and stop the clamping device taking into account the measurement parameters measured by the sensor. In this way, the connection between the spindle bearings can be released very intentionally, if necessary.

[0013] The clamping device may in particular have an expansion clamping element that may be rigidly connected to the first or second spindle bearing and that connects the first and second spindle bearings together in cooperation with a counterpart that is rigidly connected to the other spindle bearing. However, instead of an expansion clamping element, another type of clamping device may be used, for example a mechanical, magnetic, or electrical clamping device.

[0014] The clamping device may be configured to damp vibrations between the spindle units when the clamping device is in an active state. For this purpose, the clamping device may have an axial damping element or may provide axial damping by its design, for example in the case of clamping by hydraulic or pneumatic cylinders. In this regard, the clamping device may also function as a switchable axial vibration damper.

[0015] In some embodiments, the first spindle unit and the second spindle unit are accommodated in a common spindle housing. In this case, the second spindle bearing can be held in a bearing receptacle that is axially displaceable relative to the common spindle housing. In this case, the clamping device is preferably configured to controllably fix the bearing receptacle to connect the first spindle bearing and the second spindle bearing to each other. When the clamping device has an expanding clamping element, the expanding clamping element can be configured as an expanding sleeve and can radially surround the bearing receptacle.

[0016] In another embodiment, the two spindle units are housed in separate spindle housings. Thus, in this case, the first spindle unit has a first spindle housing in which at least one first spindle bearing is held, and the second spindle unit has a second spindle housing in which at least one second spindle bearing is held. In this case, the clamping device is 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 directly connects the two spindle housings to each other. For example, if the two spindle housings are displaceably held on a base, in this case the connection is preferably made directly between the spindle housings rather than by clamping the individual spindle housings to the base, or at least not exclusively by such clamping.

[0017] The clamping device may have two elements, in which, in the inactive state of the clamping device, a first of these elements is axially displaceable within a second element (which may surround the first element and may, for example, have an expansion sleeve), and in the active state of the clamping device, the two elements are axially fixed to one another. Advantageously, in this case, the clamping device is configured so that the first element cannot be fully extended from the second element, even during a tool change, in order to prevent the two elements from blocking each other when pressed together.

[0018] According to a second aspect of the present invention, the above object is achieved by a tool head comprising an axial force element configured to generate an axial preload force between a first spindle bearing and a second spindle bearing.

[0019] According to this embodiment, the two spindle units are axially clamped to each other on the bearing side. Therefore, the spindle bearings are not free to move axially relative to each other, nor are they completely rigidly connected to each other. As a result, the spindle bearings can at least partially avoid thermal stresses in the axial direction. This also significantly reduces the tool head's tendency to vibrate without the risk of bearing damage due to thermal stresses.

[0020] The two embodiments may also be combined: in particular, it is possible to clamp the spindle bearings to one another by means of an axial force element, which can be connected to one another in a clamped state by a clamping device during the machining operation and which can be released again during machining pauses.

[0021] The axial force element may have a controllable actuator, in particular a pneumatic or hydraulic actuator, for controllably varying, in particular intentionally releasing, the axial preload force. The actuator may be configured to generate an axial preload force that is substantially independent of the axial position of the second spindle bearing relative to the first spindle bearing. This can be easily achieved, for example, by a pneumatic or hydraulic actuator, since with such actuators the axial force often depends only on the applied pressure and not on the position of the actuator.

[0022] Also in the embodiment according to the second aspect of the invention, the tool head may be assigned a control device which may be configured to control the actuator in order to adjust the axial preload force, for example to keep it constant during machining operations and / or to controllably vary it, in particular to stop it, during machining pauses.

[0023] The tool head may further comprise at least one sensor for monitoring the operating state of the tool head, in particular a temperature, vibration, strain, force or pressure sensor, in which case the control device may be configured to read the sensor and vary the axial preload force taking into account the measurement parameter measured by the sensor.

[0024] In some embodiments, both the first spindle unit and the second spindle unit may be accommodated in a common spindle housing, and a bearing receptacle may be provided that is axially displaceable relative to the spindle housing and holds at least one second spindle bearing therein. In this case, the axial force element may be configured to apply an axial force to the bearing receptacle to generate an axial preload force. For this purpose, the axial force element may be particularly annular and may surround clamping elements for axially clamping the tool to the first spindle shaft and the second spindle shaft. In particular, the axial force element may have an annular actuator.

[0025] In another embodiment, the spindle units may also be housed in separate spindle housings, in which case the axial force element may connect the first and second spindle housings to one another and may be configured to apply an axial force between the first and second spindle housings to generate the axial preload force.

[0026] Particular advantages are achieved when the two spindle shafts are axially clamped to the tool so that axial compression forces act on both sides of the tool. For this purpose, the following design is particularly advantageous: the second spindle shaft has at least one axial bore. Correspondingly, the tool head has at least one pull rod extending through a corresponding axial bore in the second spindle shaft, the pull rod being connectable at a first end to the first spindle shaft. The pull rod is connectable at a second end to the second spindle shaft so that axial compression forces can be exerted on the tool between the first and second spindle shafts. For this purpose, the tool likewise has at least one axial bore through which each pull rod can pass through a corresponding bore in the tool.

[0027] This type of axial pressure creates a unit consisting of two spindle shafts and a tool that is particularly resistant to twisting and bending. The combination of the pull rod and clamping element creates a high axial compression force between the tool and the two spindle shafts. As a result, the unit functions as a single shaft. At the same time, this structure can be extremely compact, making it particularly suitable for tools with small diameters.

[0028] However, the tool may be clamped between the first and second spindle shafts in ways other than by using a continuous pull rod, so long as the result is a tightly clamped, rigid unit consisting of the two spindle shafts and the tool. The clamping of the tool between the two spindle shafts to form a rigid unit is independent of any axial pressure hold-down or clamping of the associated spindle bearings.

[0029] The above described construction is advantageous even if no clamping device or axial force element of the type mentioned above is provided. In this respect, the invention further relates to a tool head for a machine tool, in particular a gear cutting machine, comprising: a first spindle unit having a first spindle shaft, the first spindle shaft being rotatably mounted to the first spindle unit about a tool spindle axis; and a second spindle unit having a second spindle shaft, the second spindle shaft being rotatably mounted on the second spindle unit about the tool spindle axis; It has the first spindle unit and the second spindle unit are arranged such that a tool is axially receivable between the first spindle shaft and the second spindle shaft and such that the tool is rotationally driven about the tool spindle axis; the second spindle shaft has at least one axial bore; The tool head has at least one pull rod extending through an axial bore of the second spindle shaft; the pull rod being connectable at a first end to the first spindle shaft in a tensioning manner; The pull rod is connectable at another end to a second spindle shaft so as to generate an axial compressive force on the tool between the first spindle shaft and the second spindle shaft. Regarding the tool head.

[0030] In this case, it is advantageous if the first spindle unit has at least one first spindle bearing and a first spindle shaft, the first spindle shaft being rotatably mounted in the first spindle bearing about the tool spindle axis, the first spindle bearing being configured to absorb both radial and axial forces, and the second spindle unit correspondingly has a second spindle bearing, the second spindle shaft being rotatably mounted in the second spindle bearing about the tool spindle axis, the second spindle bearing being configured to absorb both radial and axial forces.

[0031] Preferably, there is exactly one pull rod extending through the central axial bore of the second spindle shaft, and therefore the tool also preferably has a central axial bore through which the pull rod can pass.

[0032] In a particularly simple embodiment, the pull rod can be connected to the first spindle shaft by screwing it axially into the first spindle shaft. For this purpose, the corresponding ends of the pull rod and the first spindle shaft can be provided with complementary threads. However, other types of connections, for example bayonet connections, are also conceivable.

[0033] The other free end of the pull rod can be provided with a clamping element forming an annular contact surface that is supported on the second spindle shaft after the pull rod is connected to the first spindle shaft and generates an axial compressive force on the second spindle shaft to press the second spindle shaft in the direction of the first spindle shaft. In the simplest case, the pull rod can be configured for this purpose as a screw with a screw head, for example. In this case, the screw can be screwed into the first spindle shaft, and the screw head can form the clamping element. The axial clamping force is then generated simply by tightening the screw.

[0034] In another, equally simple embodiment, the free end of the pull rod is provided with an external thread onto which a nut can be screwed, the nut then forming the clamping element and the axial compression force being generated simply by tightening the nut.

[0035] Preferably, however, the tool head has a clamping element removably connectable to the pull rod, which preferably generates a compressive force acting purely axially, without clamping of the clamping element generating a torque component about the tool spindle axis. For this purpose, the clamping element has a base element that can be rigidly connected to the pull rod, for example, via a screw connection, a bayonet, or a clamping bushing. The base element may have a central receiving opening for receiving the pull rod or, if there is sufficient space, a pin that can be fixed in the axial bore of the pull rod. The clamping element further comprises an axial pressing element that is axially movable, particularly axially displaceable, relative to the base element in the direction of the second spindle shaft to axially press the second spindle shaft toward the first spindle shaft. The axial pressing element may, in particular, be annular and surround the central receiving opening or pin of the base element; in this case, the axial pressing element may also be called a "pressing ring." The axial pressing element forms the annular contact surface already described. The clamping element further comprises at least one actuating element movable relative to the base element for axially moving the axial pressure element relative to the base element. The actuating element may, for example, be a pressure screw that can be screwed into the base element along the longitudinal or transverse direction. Such clamping elements are known per se from the prior art and are commercially available in many forms.

[0036] In some embodiments, the force transmission from the actuating element to the axial pressure element is purely mechanical. For example, the actuating element may be a plurality of cap screws axially held in the base element and threadable into the axial pressure element to axially displace the axial pressure element relative to the base element. In another embodiment, one or more set screws adjustable in the base element in the direction of the axial pressure element via a threaded connection serve as the actuating element. In yet another embodiment, the actuating element acts, for example, on a gear that advances the axial pressure element. Such clamping elements are available, for example, under the names ESB, ESG, or ESD from Enemac GmbH, Kleinwallstadt, Germany.

[0037] In another embodiment, the force is transmitted from the actuating element to the axial pressure element hydraulically. For this purpose, the actuating element may be configured, for example, as a pressure screw, which generates pressure in a hydraulic system when screwed in, and this pressure acts on the axial pressure element. Such clamping elements are available, for example, from Albert Schrem Werkzeugfabrik GmbH, Herbrechtingen, Germany.

[0038] In order to receive a tool between the spindle shafts and to be able to transmit torque to the tool, it is advantageous if the spindle projections are formed on the first and / or second spindle shafts in such a way that an axial compressive force acting between the tool and the spindle projections can create a non-positive and / or positive connection with the tool at each spindle projection. Preferably, the connection to the tool is formed by a conical connection, more preferably by a conical connection with surface contact. For example, the connection can be formed via one of the forms A, BF, BM, CF, or CM as described in DIN ISO 666:2013-12.

[0039] Advantageously, the two spindle lugs are formed differently from one another so that the tool can only be accommodated in a predefined position between the spindle lugs, for example the diameters of the two spindle lugs may be different.

[0040] To facilitate tool changes, it is advantageous if the second spindle unit is axially displaceable relative to the first spindle unit. If both spindle units are accommodated in a common spindle housing, this can be achieved by having a spindle bearing for the second spindle shaft that is axially displaceable relative to the spindle housing.

[0041] The first and / or second spindle units may include a drive motor configured to drive the corresponding spindle shaft in rotation about the tool spindle axis, thereby driving the tool. In some embodiments, only the first spindle unit has a drive motor, and the second spindle unit forms a passive counter-spindle for the first spindle unit without its own drive motor. In other embodiments, the second spindle unit also has its own drive motor. Each drive motor may, in particular, be a direct drive.

[0042] To balance a rotary unit having a tool and two spindle shafts, the tool head may have a first balancing device assigned to the first spindle unit and a second balancing device assigned to the second spindle unit.

[0043] Preferably, the first balancing device radially surrounds the first spindle shaft and is arranged axially between the tool-side spindle bearing of the first spindle unit and the tool-side end of the first spindle shaft, and / or the second balancing device radially surrounds the second spindle shaft and is arranged axially between the tool-side spindle bearing of the second spindle unit and the tool-side end of the second spindle shaft.

[0044] Thus, when a tool is received between the first and second spindle shafts, the first and / or second balancing devices are axially arranged outside each spindle shaft, between the tool and the spindle bearing on the tool side of the assigned spindle unit. This proposed arrangement allows tools with small diameters to be effectively balanced. By arranging at least one balancing device, preferably two balancing devices, surrounding the spindle shaft, significantly more space is available for balancing elements than if both balancing devices were arranged inside the tool or the spindle shaft. As a result, even relatively large imbalances can be corrected. By axially arranging the corresponding balancing device between the tool-side spindle bearing and the tool, balancing by the balancing device occurs both near the tool and near the corresponding bearing position. This allows for extremely accurate balancing.

[0045] Each spindle unit often has more than one single spindle bearing, and the term "tool-side spindle bearing" in this case should be understood to relate to the spindle bearing that is located closest to the tool in each spindle unit along the tool spindle axis.

[0046] In particular, the balancing surfaces may be arranged relative to the bearing surfaces of the two spindle units as follows: the first spindle bearing on the tool side defines a first bearing surface perpendicular to the tool spindle axis, and the second spindle bearing on the tool side defines a second bearing surface perpendicular to the tool spindle axis; the first balancing device defines a first balancing surface perpendicular to the tool spindle axis, and the second balancing device defines a second balancing surface perpendicular to the tool spindle axis. In this case, it is preferred that the first balancing surface is arranged between the first bearing surface and the second balancing surface (in particular, closer to the first bearing surface than the second balancing surface) and / or that the second balancing surface is arranged between the second bearing surface and the first balancing surface (in particular, closer to the second bearing surface than the first balancing surface).

[0047] When the tool is received between two spindle shafts, the tool defines a centroid plane perpendicular to the tool spindle axis that includes the center of gravity of the tool. In this case, the first balancing surface is preferably located between the first bearing surface and the centroid plane, and / or the second balancing surface is preferably located between the second bearing surface and the centroid plane. Preferably, each balancing surface is closer to the corresponding bearing surface than to the centroid plane.

[0048] This arrangement of balancing surfaces allows for effective two-plane balancing.

[0049] In a preferred embodiment, the first balancing device and / or the second balancing device are configured as ring balancing systems. Ring balancing systems have been known in the prior art for a long time (see, for example, DE 4337001 A1 and U.S. Pat. No. 5,757,662) and allow highly accurate automatic balancing without the need to stop the spindle rotation. Such ring balancing systems are commercially available in various embodiments. However, alternatively, other types of balancing systems can also be used, for example balancing systems with balancing weights that can be moved by an electric motor or hydraulic balancing systems.

[0050] The balancing devices may be configured to operate in a numerically controlled (NC) manner, and for this purpose the first and / or second balancing devices may comprise at least one actuator for adjusting the corrective imbalance of the balancing devices in a numerically controlled manner.

[0051] At least one vibration sensor may be provided in the tool head to detect vibrations caused by the imbalance. This sensor may be integrated into one of the balancing devices or configured separately. The tool head may further include a control device assigned to the tool head, which is configured to detect signals from the at least one vibration sensor and control actuators in the first and / or second balancing devices to adjust a corrective imbalance in the first and / or second balancing devices in response to the detected signals. Such adjustments may be automated so that the imbalance is reduced. Preferably, the control device is configured to perform automatic two-plane balancing. Corresponding algorithms are known in the art. The control device may be part of the machine control system or may be a separate unit.

[0052] Preferably, the first and / or second balancing devices are arranged outside the housing of each spindle unit. In particular, the first spindle unit may have a first housing and the second spindle unit may have a second housing. In this case, the first and / or second balancing devices are preferably arranged outside the first and second housings. Alternatively, the first and second spindle units may have a common spindle housing, in which case the first and / or second balancing devices are preferably arranged outside the common spindle housing.

[0053] In particular, when a tool is received between the first spindle shaft and the second spindle shaft, the first balancing device is preferably arranged axially between the tool and a (first or common) spindle housing surrounding the first spindle unit, and the second balancing device is arranged axially between the tool and a (second or common) spindle housing surrounding the second spindle unit.

[0054] Preferably, the outer contour of the balancing device is optimized in such a way that interference contours are minimized when machining a workpiece in the workpiece spindle of the machine, and it is particularly advantageous if the first and / or second balancing device has an outer contour that tapers in the direction of the tool.

[0055] The tool head may further comprise a tool as described above, which is axially received between the first and second spindle shafts and preferably axially clamped. The tool may be a grinding tool, in particular a tool for gear grinding. More specifically, the tool may be a grinding worm or a shaping wheel, or may comprise at least one grinding worm and / or at least one shaping wheel. The tool may be one-piece (e.g., in the form of a non-dressable grinding worm with a hard-coated substrate received directly between the spindle shafts) or may consist of two or more parts (e.g., in the form of a dressable grinding worm or a combination tool with two or more grinding bodies, where the grinding bodies are held in separate tool holders and the tool holders are received between the spindle shafts).

[0056] The invention further provides a machine tool comprising a tool head of the above-mentioned type and at least one workpiece spindle for driving a workpiece in rotation about the workpiece axis. The machine tool may be configured as a gear cutting machine, in particular as a gear grinding machine. For this purpose, the machine tool may include a (in particular suitably programmed) machine control system configured to cause the machine to machine, by means of a tool, gear teeth of a workpiece received in the at least one workpiece spindle. In particular, the machine control system may be configured to cause the machine to machine gear teeth of the workpiece by form grinding or generating gear grinding. For this purpose, the machine control system may be configured to establish a suitable rotational connection between the workpiece spindle and the tool spindle.

[0057] The present invention further provides a method of operating a tool head of the type described above, the method comprising: connecting the first spindle bearing to the second spindle bearing during machining operations and releasing this connection during machining pauses; and / or Generating an axial preload force between the first spindle bearing and the second spindle bearing. Includes.

[0058] With respect to this method, the further considerations discussed above with respect to the tool head apply as appropriate.

[0059] Preferred embodiments of the present invention are described below with reference to the drawings, which are for illustrative purposes only and should not be construed as limiting. [Brief explanation of the drawings]

[0060] [Figure 1] FIG. 1 is a schematic perspective view showing an example of a machine tool equipped with a tool head according to a first embodiment for hardening and finishing gears by generating gear grinding. [Figure 2] FIG. 1 is a schematic perspective view showing a tool head of a first embodiment. [Figure 3] FIG. 1 is a perspective cross-sectional view showing a tool head according to a first embodiment. [Figure 4] FIG. 2 is a perspective cross-sectional view of the tool head of the first embodiment after the tool has been removed. [Figure 5] FIG. 10 is a schematic perspective view of a tool head according to a second embodiment. [Figure 6] FIG. 10 is a perspective cross-sectional view showing a tool head according to a second embodiment. [Figure 7] FIG. 10 is a perspective cross-sectional view of the tool head of the second embodiment after the tool has been removed. [Figure 8] FIG. 10 is a central vertical cross-sectional view showing a clamping device for a tool head according to a second embodiment. [Figure 9] FIG. 10 is a perspective cross-sectional view of a tool head according to a third embodiment. [Figure 10] FIG. 10 is a perspective cross-sectional view of the tool head of the third embodiment after the tool has been removed. [Figure 11] FIG. 10 is a schematic perspective view of a tool head according to a fourth embodiment. [Figure 12]FIG. 10 is a perspective cross-sectional view showing a tool head according to a fourth embodiment. [Figure 13] FIG. 2 is a central vertical cross-sectional view showing a clamp nut. [Figure 14] FIG. 14 is a perspective view showing the clamp nut of FIG. 13. DETAILED DESCRIPTION OF THE INVENTION

[0061] [Definition] Gear cutting machine: a machine configured to produce or machine gear teeth, especially internal or external gear teeth, on a workpiece. For example, a gear cutting machine may be a fine machining machine for machining pre-toothed workpieces, and in particular a hardening and finishing machine for machining pre-toothed workpieces after hardening. The gear cutting machine is equipped with a machine control system programmed to control the automatic machining of gear teeth.

[0062] Gear generating: Gear machining in which a tool rolls on the workpiece and performs a cutting action. Various gear generating processes are known, where a distinction is made between processes with a geometrically non-defined cutting edge, such as gear grinding or gear honing, and processes with a geometrically defined cutting edge, such as gear hobbing, gear skiving, gear shaving or gear shaping.

[0063] Generating Gear Grinding: The generating gear grinding process is a continuous chip removal process in which axisymmetric periodic structures are produced using a geometrically variable cutting edge, using a grinding wheel with a worm-shaped outer contour ("grinding worm") as the tool. The tool and workpiece are mounted on a rotating spindle. The rotational motion typical of the process is achieved by combining the rotational motion of the tool and workpiece about the rotation axis. This rotational motion, together with the axial feed motion of the tool or workpiece along the workpiece axis, produces the cutting action.

[0064] Tool Head: As used herein, the term "tool head" refers to an assembly configured to receive and rotationally drive a machining tool. In particular, the tool head may be mounted on a rotating bed and / or one or more slides for aligning and positioning the tool relative to a workpiece.

[0065] Spindle Unit: In machine tool construction, a rotatable shaft onto which a tool or workpiece can be clamped is typically referred to as a "spindle." However, an assembly including a rotatable shaft, as well as an associated spindle bearing for rotatably supporting the shaft and an associated housing, is also often referred to as a "spindle." The term "spindle" is used in this context herein. A shaft alone is referred to as a "spindle shaft." An assembly having a spindle shaft and at least an associated spindle bearing is referred to as a "spindle unit." A "spindle unit" may have its own housing, or may be housed in a common housing with another spindle unit.

[0066] Ring balancing system: A ring balancing system has two adjacently arranged balancing rings that surround and are driven by a shaft. Each balancing ring has a predefined additional unbalance of the same size. The orientation of the balancing rings around the rotation axis of the shaft is adjustable. If the additional unbalances of the two balancing rings are diametrically opposed, their effects cancel each other out. If both additional unbalances have the same angular position, maximum balancing capacity is achieved. By setting other angles, the resulting corrective unbalance can be freely adjusted in magnitude and direction within these limits.

[0067] [Example machine tool structure] 1 shows an example of a machine tool for hard-finishing gears by generating gear grinding. The machine has a machine bed 100 on which a tool support 200 is arranged so as to be displaceable along a horizontal feed direction X. A Z-slide 210 is arranged on the tool support 200 so as to be displaceable along a vertical direction Z. The Z-slide 210 supports a pivoting bed 220 which is pivotable relative to the Z-slide 210 about a horizontal pivot axis A. The pivot axis A is parallel to the feed direction X. A tool head 300, shown only diagrammatically, is arranged on the pivoting bed 220 and will be described in more detail below.

[0068] Additionally, a pivotable workpiece support in the form of a rotary turret 400 is disposed on the machine bed 100. The rotary turret 400 is pivotable about a vertical pivot axis C3 between a plurality of rotational positions. The rotary turret supports two workpiece spindles 500, each of which can clamp a workpiece 510. Each of the workpiece spindles 500 is drivable to rotate about a workpiece axis. In FIG. 1, the workpiece axis of the visible workpiece spindle 500 is designated C2. The workpiece axis of the workpiece spindle not visible in FIG. 1 is referred to as the C1 axis. The two workpiece spindles are disposed on the rotary turret 400 at diametrically opposite positions (i.e., offset by 180° with respect to the pivot axis C3). In this way, one of the two workpiece spindles can be loaded and unloaded while a workpiece is being machined on the other workpiece spindle. This significantly avoids undesirable non-productive time. The concept of such a machine is known, for example, from WO 00 / 035621.

[0069] The machine has a machine control system 700, shown only diagrammatically, which includes a number of control modules 710 and a control panel 720. Each control module 710 controls a machine axis and / or receives signals from sensors.

[0070] [Tool head according to the first embodiment] 2 to 4 show a tool head according to a first embodiment. The tool head includes a base 310 rigidly connected to the swivel bed 220. A linear guide 311 is formed in the base 310. In the linear guide 311, a spindle housing 380 is guided so as to be displaceable along the shift direction Y. For this purpose, the spindle housing 380 has a corresponding guide shoe 386. The shift direction Y is perpendicular to the X axis and forms an adjustable angle with the Z axis about the A axis. For controlled adjustment of the position of the spindle housing 380 along the shift direction Y, a ball screw drive 312 is used, which interacts with a shift drive (not shown).

[0071] The spindle housing 380 contains two spindle units 320 and 330. A tool 340 is held between the spindle units 320 and 330. In this example, the tool 340 is a grinding worm.

[0072] Spindle unit structure 3 and 4 show the structure of the spindle units 320, 330 in more detail.

[0073] In this example, the spindle unit 320 is a motor-driven spindle having a drive motor 324 that directly drives a first spindle shaft 322 to rotate about a tool spindle axis B. The tool spindle axis B is parallel to the shift direction Y.

[0074] The first spindle shaft 322 is supported at three bearing positions in spindle bearings 323. These bearing positions are located at different axial positions along the first spindle shaft 322. Two of the three 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 fixed-free or support bearings, i.e., at least one of these bearing positions can absorb both radial and axial loads. An additional bearing position is located on the tool-side side of the drive motor 324. The spindle bearing located at this bearing position is configured as a free bearing, i.e., it absorbs radial loads but allows axial movement. All three spindle bearings 323 are fixedly arranged in the spindle housing 380. In particular, these bearings are not axially displaceable relative to the spindle housing 380.

[0075] In this example, the second spindle unit 330 is a non-driven counter-spindle. The second spindle unit 330 has a second spindle shaft 332 supported in a spindle housing 380 in spindle bearings 333 at two bearing locations along the spindle shaft. In this case, these spindle bearings form fixed-free or support bearings, i.e., at at least one of these bearing locations, the spindle bearing 333 can absorb both radial and axial load forces.

[0076] The second spindle unit 330 is axially displaceable relative to the spindle housing 380 between an operating position shown in FIG. 3 and a tool change position shown in FIG. 4. To this end, the spindle bearing 333 of the second spindle unit is received in a bearing receptacle 391. In this example, the bearing receptacle 391 is a bearing bush, which may be, for example, a plain bearing bush or a ball bearing bush. The bearing receptacle 391 is guided in the spindle housing 380 so as to be axially displaceable. In the operating position of FIG. 3, the second spindle unit 330 is advanced toward the first spindle unit 320 so that the tool 340 is held between the first spindle shaft 322 and the second spindle shaft 332. In contrast, in the tool change position of FIG. 4, the second spindle unit 330 is axially retracted sufficiently to allow the tool 340 to be removed.

[0077] Axial clamping of tools In this example, tool 340 has a tool holder 341 which has a worm-shaped, dressable grinding body 342. In this example, tool holder 341 is formed as a retaining flange for the grinding body in accordance with DIN ISO 666:2013-12. To connect to spindle shafts 322, 332, tool holder 341 has a tapered receptacle (known as a tapered socket or conical seat) with face contact at each end, for example a short tapered receptacle 1:4 in accordance with DIN ISO 702-1:2010-04.

[0078] Opposing spindle protrusions 325, 335 are formed on the tool-side ends of the spindle shafts 322, 332. The shape of the spindle protrusions 324, 325 is complementary to the shape of the tapered receptacle of the tool holder 341. Each spindle protrusion has a shape that conically tapers toward the tool 340 and has a flat contact surface on each end face. For example, each spindle protrusion may be formed as a tapered shank 1:4 in accordance with DIN ISO 702-1:2010-04.

[0079] 3, there is therefore a conical connection with face contact between each tool 340 and the spindle shafts 322, 332. The conical connection may have different diameters at the two ends of the tool to ensure that the tool 340 can only be received between the spindle shafts 322, 332 in the correct orientation.

[0080] The tool 340 is clamped between the spindle shafts 332, 332 while being compressed in the axial direction by a pull rod 370 and a clamping nut 372. To this end, the tool 340 and the second spindle shaft 332 each have a central axial bore extending therethrough. The first spindle shaft 322 also has a central axial bore at its tool-side end. In this example, this bore is not continuous. This bore is open on the tool side and has an internal thread formed therein. The pull rod 370 is inserted through the central bore of the spindle shaft 332 and the central bore of the tool 340. At the end of the pull rod 370 facing the first spindle unit 320, it has an external thread that screws into the internal thread of the first spindle shaft 322. The pull rod also has an external thread at the other end. A 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 shaft 332 in the direction of the tool 340. This clamps the tool 340 axially between the spindle shafts 332, 332. This results in a single continuous shaft with high rigidity.

[0081] Axial pressure on bearing receptacle The bearing receptacle 391, in which the spindle bearing 333 of the second spindle unit 330 is housed, can be axially clamped to the spindle housing 380. In this way, the second spindle unit 330 as a whole is axially clamped to the first spindle unit 320 via the tool 340, not only on the spindle shafts 322, 323 but also on the bearing side. In this way, an axial compression or tension force can be generated between the spindle bearing 323 of the first spindle unit 320 and the front spindle bearing 333 of the second spindle unit, and these can be preloaded. To generate the axial compression or tension force, an annular actuator 390, which in this example is a pneumatic actuator, is used. The actuator 390 has an annular actuator housing 393 rigidly connected to the spindle housing 380. A similarly annular piston element 392 is displaceably guided within the actuator housing 393. The piston element 392 is rigidly connected to the bearing receptacle 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 forced towards or away from the first spindle unit 320, which generates an axial compression or tension force between the spindle bearing 333 held in the bearing receptacle 391 of the second spindle unit 330 and the spindle bearing 323 of the first spindle unit 320 when the tool 340 is clamped.

[0082] The controller 730 controls the actuator 390 in a manner known per se. For example, the controller 730 interacts with a pneumatic valve, not shown, in the pressure line to the actuator 390 in order to vary the pressure in the actuator 390.

[0083] By having the annularly formed actuator 390, the rear end of the second spindle shaft 332 can still be operated from the outside via the actuator 390, thereby allowing the tool 340 to be clamped axially between the first spindle shaft 322 and the second spindle shaft 332. The clamping nut 372 can be disposed in an area surrounded by the annular actuator 390.

[0084] Tool spindle movement To clamp the tool 340 between the spindle units 320, 330, the second spindle unit 330 is first moved to the tool change position of FIG. 4, and then 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 shaft 322, where the pull rod is secured in place by screwing it in. The second spindle unit 330 is then moved to the operating position of FIG. 3. In this position, the clamping nut 372 is attached to the pull rod 370, and the tool 340 is axially clamped to the first spindle shaft 321 and the second spindle shaft 332 by the clamping nut 372. The actuator 390 remains deactivated until this point so as not to interfere with the axial displacement of the second spindle unit 330. After the tool 340 is clamped, the actuator 390 is actuated to axially clamp the spindle bearing 333 of the second spindle unit 330 to the spindle housing 380 .

[0085] Here, the tool 340 is rotated by the drive motor 324 and used to machine a workpiece. During machining, both the spindle housing 380 and the unit including the two spindle shafts 322, 332 and the tool 340 clamped axially between them are heated. As a result, the spindle housing 380 and the unit undergo thermal expansion. The thermal expansion of these components generally differs from each other. During machining, the air pressure acting on the actuator is maintained constant. This allows the spindle bearing 333 of the second spindle unit 330 to follow the thermal expansion of the spindle shafts 322, 332 and the rotor 340, and the axial clamping force of the spindle bearing remains constant despite the differing thermal expansion.

[0086] Optionally, controller 730 may be configured to vary the pressure in actuator 390 as a function of one or more measured parameters. To this end, for example, a sensor 731, shown only schematically, may be located in spindle housing 380 and read by controller 370. Sensor 731 may be, for example, a temperature sensor, a vibration sensor, a strain gauge for measuring axial clamping force, or a force sensor. In this case, controller 730 may vary the pressure in the actuator as a function of the measured parameter from sensor 731, for example to reduce vibration or selectively increase axial clamping force, in the event of increased spindle load, as indicated by elevated temperature or thermal expansion.

[0087] · Alternative to pneumatic clamps Instead of a pneumatic actuator, another type of actuator can be used to generate an axial compression or tension force between the spindle bearings; for example, a hydraulic actuator may be used. The above discussion regarding pneumatic actuators applies equally to hydraulic actuators. However, the actuator may also be a mechanical actuator. The mechanical actuator may, for example, have a coil spring that generates an axial tension or compression force between the spindle housing 380 and the bearing receptacle 391. The degree of compression of the coil spring, and therefore the axial force generated by the coil spring, can be varied by a suitable actuator. Alternatively, the axial force may be generated by a piezoelectric element. Various further embodiments are contemplated.

[0088] In addition to or as an alternative to the axial pressing of the bearing receptacle 391 by the actuator, it is also conceivable to fix ("clamp") the bearing receptacle 391 in an axially controlled manner relative to the spindle housing 380. For this purpose, a clamping device (not shown) may be provided, for example an expansion sleeve attached to the spindle housing 380 and surrounding the bearing receptacle 391. By means of the clamping device, the bearing receptacle 391 may be intentionally fixed to the spindle housing 380 to minimize vibrations during the machining of the workpiece, and this fixation may be temporarily released during machining pauses, for example after each tool stroke or after the machining of each workpiece, to reduce excessive axial support forces. A control device 730 may be used for this purpose. The release may be controlled based on measured parameters. For example, the control device 730 can use sensors 731 for this purpose to detect temperature, vibration, thermal expansion and / or axial force between the spindle bearings and release the clamping device from time to time as a function of the measured parameters. If both an actuator for generating the axial force and a clamping device are present, the spindle bearings 323, 333 can be preloaded by the actuator before clamping is performed.

[0089] The actuator 390 may be operated to provide a releasable clamp without generating an axial preload force. If the actuator is a pneumatic or hydraulic actuator, the fluid simultaneously provides a restoring action combined with damping, i.e., the clamp has a finite hardness. This may additionally help prevent overloading of the spindle bearing. Advantageously, the actuator 390 may also be used to retract the bearing receptacle 391 during tool changes.

[0090] [Second embodiment] 5 to 8 show a tool head according to a second embodiment, in which actuating members that are the same as or similar to those in the first embodiment are given the same reference numerals.

[0091] Unlike 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, 331 are guided independently of each other by linear guides 311 of the base 310 along the shift direction Y. For this purpose, each housing has guide shoes 326, 336. The position of the first housing 321 can be adjusted along the shift direction Y by a shift actuator and a ball screw drive 312 (not shown). The second housing 331 can be coupled to the first housing 321 in a manner described in more detail below, so that the second housing is entrained by the first housing 321 when the first housing 321 is moved along the shift direction Y. Spindle bearings are held axially undisplaceable within each housing 321, 323. Unlike the first embodiment, the axially displaceable bearing receptacle for the spindle bearing of the second spindle unit 330 is omitted. The actuator for axially adjusting the displaceable bearing receptacle is also omitted. In other respects, the two spindle units 320, 330 are formed similarly to the first embodiment.

[0092] To controllably couple or uncouple the housings 321, 331, the tool head in this example has two clamping devices 600. One of these clamping devices is located above a central mid-plane of the tool head, and the other clamping device is located below this mid-plane. In this case, the central mid-plane is a plane in the XY direction that contains the workpiece spindle axis B. Only the upper clamping device is visible in Figures 6 and 7. In Figure 8, clamping device 600 is shown by itself.

[0093] 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 disposed on the other axial side between the mounting flange 621 and a push ring 623. The damping rings 622, 622' are axially compressed by screws 624 when the rod 620 is mounted, and damp vibrations between the rod 620 and the second spindle housing 331. These may be omitted.

[0094] The clamping device 600 further includes an expansion sleeve 610 connected to a first spindle housing 621 via a screw 614. The expansion sleeve 610 can be hydraulically actuated to selectively cause clamping of the rod 620 within the expansion sleeve 610 or release of such clamping.

[0095] The clamping device 600 is controlled by a control device 730. Optionally, for this purpose, a sensor 731 can be arranged on the first and / or second spindle housing 321, 331, which is read by the control device 370. The sensor 731 can be, for example, a temperature sensor, a vibration sensor, a strain sensor, or a force sensor, as in the first embodiment. In this case, the control device 730 can be configured to activate the clamping device 600 as a function of one or more measured parameters from the sensor. The two clamping devices 600 can be activated together or independently of each other. For example, it may be appropriate to activate only one of the two clamping devices 600 for a given type of vibration.

[0096] Once both clamping devices 600 are unclamped, the second spindle unit 320 can be manually moved along the Y direction between the working position of FIGS. 5 and 6 and the tool change position of FIG.

[0097] Tool spindle movement Before starting machining of the workpiece, the clamping device 600 is activated to secure the second spindle housing 331 to the first spindle housing 321. Here, the tool 340, rotated by the drive motor 324, is used to machine the workpiece. During machining, the second spindle housing 331 remains fixed to the first spindle housing 321 to prevent vibrations. However, both the spindle housings 321, 331 and the unit with the two spindle shafts 322, 332 and the tool 340 axially clamped therebetween heat up. To avoid excessive axial support forces due to differential thermal expansion, the control device 730 occasionally releases the clamping device 600 during pauses in machining, for example after each tool stroke or after machining of each workpiece. This may optionally be done based on measured parameters. For example, the control device 730 can for this purpose detect temperature, linear expansion or axial bearing force and release the clamping device 600 from time to time as a function of the measured parameter.

[0098] Balancing equipment A first balancing unit 350 is arranged on the first spindle shaft 322 in the axial region between the housing 321 of the first spindle unit 320 and the tool 340. A second balancing unit 360 is arranged on the second spindle shaft 332 in the axial region between the housing 331 of the second spindle unit 330 and the tool 340. The balancing units 350, 360 surround each spindle shaft 322, 332 outside the housing of each spindle unit 320, 330. Each balancing unit has a housing that tapers from its assigned spindle unit toward the tool 340. The tapered outer contour of the balancing units 350, 360 reduces the risk of collision between the balancing units and the workpiece 510.

[0099] Each of the balancing units 350, 360 is configured as a ring balancing system. To this end, it has a rotor with two balancing rings that surround and are driven by the respective spindle shaft. Each balancing unit 350, 360 also has a stator connected to the respective spindle housing 321, 331. On the one hand, the stator has sensors for detecting the vibrations of the respective spindle housing, the rotational speed of the respective spindle shaft, and the angular position of the respective balancing ring. On the other hand, the stator includes an actuator with a coil arrangement for contactlessly changing the angular position of the balancing ring on the respective spindle shaft.

[0100] The balancing unit may be used to compensate for static and dynamic imbalances of the system comprising the tool 340 and the spindle shafts 322, 332 clamped to the tool, and to balance the system in two balancing planes.

[0101] Ring balancing systems for automated two-plane balancing are known per se and are commercially available from various sources, one example being the AB 9000 electromagnetic ring balancing system manufactured by Hofmann Mess- und Auswuchttechnik GmbH & Co KG of Pfungstadt, Germany.

[0102] Such a balancing unit may also be provided in the first embodiment. The rotor of the second balancing unit 360 may be axially displaceable relative to the stator of this balancing unit so that the second spindle unit 330 can be retracted for tool changes. The outer diameter of the rotor may be selected to be smaller than the inner diameter of the spindle housing 380, in which the bearing receptacle 391 is guided. When the second spindle unit 330 is retracted axially from the spindle housing 380, the rotor of the second balancing unit 360 is entrained axially together with the second spindle unit 330, so that the rotor of the second balancing unit 360 is retracted into the spindle housing 380 together with the second spindle unit 330. In contrast, the stator of the second balancing unit 360 is fixed to the spindle housing 380 and remains stationary during retraction of the second spindle unit 330.

[0103] Alternatively, it is also conceivable to position the second balancing unit 360 so that the entire second balancing unit 360, i.e., both the rotor and the stator, can be retracted together with the second spindle unit 330 for tool changes.

[0104] Balancing units of the type described here are also present in other embodiments described below.

[0105] [Third embodiment] A third embodiment is shown in Figures 9 and 10. This 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 instead axially clamped relative to the first spindle housing 310. Two pneumatic actuators 630, located between the two spindle housings 310, 320, act in place of the clamping device 600 to generate the corresponding axial compression or tension forces. Only one of these two actuators is visible in Figures 9 and 10.

[0106] For further consideration of operation, the effect of axial clamping of the spindle bearings, and alternatives to pneumatic actuators for generating axial force, reference is made to the description in the first embodiment.

[0107] Clamping and axial pressure may also be combined. For this, the tool head may have both a controlled releasable clamping device and an actuator for generating an axial force, as in the second embodiment. In this case, the spindle bearings 323, 333 may be preloaded by use of the actuator before clamping.

[0108] If desired, the actuator 630 may be operable to provide a releasable clamp without generating an axial biasing force. If the actuator is a pneumatic or hydraulic actuator, the fluid creates some spring action combined with damping during clamping. If the actuator is a pneumatic or hydraulic actuator, the fluid creates a predetermined return action combined with damping during clamping, meaning the clamp has a finite hardness. This can additionally help prevent overloading of the spindle bearings. Advantageously, the actuator 630 can also be used to push back the second spindle unit 330 during a tool change.

[0109] [Fourth embodiment] 11 to 13 show a tool head according to a fourth embodiment.

[0110] In this case, the first and second spindle units 320, 330 each have their own spindle housing 321, 331, which are guided independently of one another along the linear guide 311 by guide shoes 326, 336. Each spindle unit has its own positioning drive 328, 338 for moving it along the Y direction independently of the other spindle unit. For this purpose, each positioning drive 328, 338 has a torque motor that drives a preloaded ball screw nut in rotation about a rotation axis B' without backlash. The ball screw nut moves along a fixed ball screw spindle 313 arranged along the rotation axis B'. The rotation axis B' is parallel to the Y direction and parallel to the tool spindle axis B.

[0111] Each of the two spindle housings 321, 322 may optionally be connected to the base 310 in a clamping manner via a clamping device 327, 337. In some embodiments, the clamping device 327, 337 establishes a connection between each spindle housing and the base that is not completely rigid but is elastically damped in the axial direction. To this end, each of the two spindle housings has an auxiliary body that can be releasably fixed to the base 310 by a clamp and that is movable together with the respective spindle housing 321, 331 relative to the base 310 in the released state, and at least one vibration damper arranged between the auxiliary body and the movable body. For details of such embodiments, reference is made to WO2020038751.

[0112] For machining of the workpiece, similar to the second or third embodiment, the second spindle housing 331 is controllably and releasably fixed to the first spindle housing 321 by a clamp and / or is axially clamped relative to the first spindle housing 321. For possible embodiments of the connection between the spindle housings and for operational considerations, reference is made to the above description for the second and third embodiments.

[0113] During machining of the workpiece, clamping devices 327, 337 can be optionally activated to secure the two spindle housings 321, 331 to the base 310. To change the position of the tool 340 along the Y axis relative to the workpiece, the clamping devices 327, 337 are released and the two positioning drives 328, 338 are controlled synchronously to move both spindle housings 321, 331 synchronously relative to the base 310.

[0114] The second spindle shaft 332 is driven separately by a second drive motor 334. Preferably, the second drive motor 334 is designed to be smaller than the first drive motor 324, and the second drive motor generates less than half of the total torque in the tool 340, for example, 30% to 45% of the total torque. Such an asymmetric torque generation distribution between the two drive motors 324, 334 avoids spurious resonances. However, the second drive motor may be omitted.

[0115] [Clamp nut] 13 and 14 show an exemplary clamp nut 372 that may be used in the embodiments described above.

[0116] The clamping nut 372 includes a base element 373 defining a central bore with an internal thread for screwing the base element 373 onto a pull rod with a corresponding external thread. At one end, the base element 373 is externally formed in the form of a hexagonal nut. A support ring 374 is attached to the base element 373. The support ring abuts against a collar of the base element 373 so that axial movement in one direction (toward the left in FIG. 9) is prevented. Furthermore, an annular axial pressure element 375 is guided axially displaceably in the base element 373. A plurality of actuating elements 376 in the form of pressure screws are screwed into the axial pressure element 375 and are axially supported by the support ring 374 so that axial movement in one direction (toward the left in FIG. 9) is prevented. By loosening the pressure screw from the axial pressing element 375, the axial pressing element 375 is advanced relative to the base element 373 in the direction opposite to the support direction (to the right in FIG. 9).

[0117] To clamp the tool 340 between the two spindle shafts 322, 332, the axial pressure element 375 is first moved completely backward relative to the base element 373 by screwing the pressure screw into the axial pressure element 375 as far as possible. The clamping nut 372 is then screwed onto the pull rod 370 and adjusted relative to the second spindle shaft 332 by the hexagonal external shape of the base element 373. This is done with a relatively low torque. The pressure screw then advances the annular axial pressure element 375 in a controlled manner toward the second spindle shaft 332 until the desired clamping force acts on the tool 340. The axial pressure element 375 is thereby supported by the annular contact surface on the second spindle shaft 332.

[0118] Of course, other constructions of clamping nuts may also be used, as are known per se from the prior art, for example the force transmission may take place in a manner different from that shown, in particular hydraulic clamping nuts may be used.

[0119] Instead of a clamping nut with an internal thread, a clamping element may also be used which can be connected to the pull rod in a manner other than a threaded connection, for example via a bayonet or clamping bush.

[0120] [Other changes] The interface between the spindle shafts 322, 332 and the tool 340 may be configured differently from the embodiment described above. In particular, different types of conical connections and / or surface contacts may be used. In particular, any known conical connection may be used, for example, forms A, BF, BM, CF or CM as described in DIN ISO 666:2013-12. For further details, reference is made to DIN ISO 666:2013-12 and other standards as described in DIN EN ISO 1119:2012-04, DIN ISO 702-1:2010-04, ISO 12164-1:2001-12 and ISO 12164-2:2001-12.

[0121] In any embodiment, the tension rod 370 may extend through the first spindle shaft 322 rather than through the second spindle shaft 332 and may be connected at its end to the second spindle shaft 332. In this case, the clamping element therefore applies an axial force to the first spindle shaft in the direction of the second spindle shaft.

[0122] To axially clamp the tool 340 between the first spindle shaft 322 and the second spindle shaft 332, two or more pull rods extending parallel to each other and spaced radially from the tool spindle axis B and positioned at different angular positions relative to the tool spindle axis B may be used instead of or in addition to one central pull rod.

[0123] The fixing of the tool between the first and second spindle shafts may be achieved in a way other than by means of a continuous pull rod, for example by means of a clamping system arranged inside the respective spindle shafts, for which purpose the connection between the tool and the spindle shafts may be achieved, for example, by means of a hollow shank taper connection in accordance with ISO 12164-1:2001-12 and ISO 12164-2:2001-12.

[0124] Clamping between the spindle bearings on either side of the tool may be effected in ways other than by hydraulic expansion clamping elements, for example mechanically by means of a rack and pinion combination, an eccentric rotating lever, a pawl, or electromagnetically.

[0125] In the embodiment described above, the tool 340 has a dressable grinding body 342 formed in the shape of a worm, which is replaceably mounted in a tool holder 341. However, the tool may have a different structure, in particular a monolithic structure. For example, the tool may be a non-dressable CBN grinding worm with a CBN coating applied directly to the tool substrate. The interface to the spindle projections 325, 335 is in this case formed in the tool substrate. The tool does not necessarily have to be a grinding worm. The tool may, for example, be a forming wheel, a combination of two or more forming wheels, or a combination of one or more grinding worms and one or more forming wheels.

[0126] In the embodiment described above, the spindle bearing 323 is a rolling bearing. Instead of a rolling bearing, other types of spindle bearings may be used, such as hydrostatic, hydrodynamic or aerodynamic bearings, as known per se in the art.

[0127] In the above-described embodiment, a direct drive motor is used as the drive motor. Instead of the direct drive motor, a geared motor may be used.

[0128] The second drive motor as in the fourth embodiment may be provided in the first to third embodiments.

[0129] Preferably, a ring balancing system is used as the balancing device, but other types of balancing devices are also conceivable, such as hydrobalancing systems known per se from the prior art, in which balancing is carried out by injecting a fluid into balancing chambers distributed around the circumference. [Explanation of symbols]

[0130] 100 Machine Bed 200 Tool support 210 Z-slide 220 Rotating body 300 Tool Head 310 Base 311 Linear Guide 312 Ball screw drive unit 313 Ball screw spindle 320 First Spindle Unit 321 First spindle housing 322 First spindle shaft 323 First Spindle Bearing 324 First drive motor 325 First spindle protrusion 326 Guide shoe 327 Clamping Device 328 Positioning drive unit 330 Second Spindle Unit 321 Second spindle housing 332 Second spindle shaft 333 Second Spindle Bearing 334 Second drive motor 335 Second spindle protrusion 336 Guide shoe 337 Clamping Device 338 Adjustment drive 340 Tools 341 Tool holder 342 Grinding body 350 First balancing device 351 Vibration Sensor 352 Actuator 360 Second Balancing Device 361 Vibration Sensor 362 Actuator 370 Pull rod 372 Clamp nut 373 Base Element 374 Support Ring 375 Axial pressing element 376 Actuating Elements 380 common spindle housing 386 Guide shoe 390 Bearing clamping device 391 Bearing Guide 392 Bearing Receptacle 400 rotation turret 500 Workpiece Spindle 510 workpieces 600 Clamping Device 610 Expandable Sleeve 620 rod 621 Mounting flange 622 Damping Ring 623 Push Ring 630 Actuator 700 Machine Control System 710 Control Module 720 Control Panel 730 Control Device X,Y,Z linear axis A Swivel Axis B Tool axis C1,C2 workpiece axis C3 Tower rotation axis

Claims

1. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation 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 with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); the tool head (300) has a controlled clamping device (600) for controllably connecting the first spindle bearing (323) and the second spindle bearing (333) to one another; a control device (730) assigned to the tool head (300), the control device being configured to activate the clamping device (600) during machining operations and to deactivate the clamping device during machining pauses; The tool head (300) has at least one sensor (731) for monitoring the operating state of the tool head (300); the control device (730) is configured to read the sensor (731) and stop the clamping device (600) taking into account the measurement parameters measured by the sensor (731); The sensor (731) is a temperature sensor, a vibration sensor, a strain sensor, a force sensor or a pressure sensor. A tool head (300).

2. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation 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 with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); the tool head (300) has a controlled clamping device (600) for controllably connecting the first spindle bearing (323) and the second spindle bearing (333) to one another; a control device (730) assigned to the tool head (300), the control device being configured to activate the clamping device (600) during machining operations and to deactivate the clamping device during machining pauses; The clamping device (600) includes an expanding clamping element (610). A tool head (300) characterized in that:

3. 3. The tool head (300) of claim 1 or 2, wherein the clamping device (600) is configured to damp vibrations between the first spindle unit (320) and the second spindle unit (330) when the clamping device (600) is in an activated state.

4. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation about the tool spindle axis (B), the second spindle bearing (333) being configured to absorb both radial and axial forces; a common spindle housing (380) in which both the first spindle unit (310) and the second spindle unit (320) are housed; a bearing receptacle (391) axially displaceable relative to said common spindle housing (380) and in which at least one said second spindle bearing (333) is held; a controlled clamping device (600) for controllably connecting said first spindle bearing (323) and said second spindle bearing (333) to one another; the first spindle unit (320) and the second spindle unit (330) are coaxially arranged with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); a control device (730) assigned to the tool head (300), the control device being configured to activate the clamping device (600) during machining operations and to deactivate the clamping device during machining pauses; the clamping device (600) is configured to controllably secure the bearing receptacle (391) relative to the common spindle housing (380) to connect the first spindle bearing (323) and the second spindle bearing (333) together; A tool head (300) characterized in that:

5. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation about the tool spindle axis (B), the second spindle bearing (333) being configured to absorb both radial and axial forces; a controlled clamping device (600) for controllably connecting said first spindle bearing (323) and said second spindle bearing (333) to one another; the first spindle unit (320) and the second spindle unit (330) are coaxially arranged with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); a control device (730) assigned to the tool head (300), the control device being configured to activate the clamping device (600) during machining operations and to deactivate the clamping device during machining pauses; The first spindle unit (320) has a first spindle housing (321) in which at least one first spindle bearing (323) is held; The second spindle unit (330) has a second spindle housing (331) in which at least one second spindle bearing (333) is held; the clamping device (600) 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; A tool head (300) characterized in that:

6. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) including a second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearings (323) for rotation about a tool spindle axis (B), and the at least one first spindle bearing (323) is configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearings (333) for rotation about the tool spindle axis (B), and at least one second spindle bearing (333) is configured to absorb both radial and axial forces; the first spindle unit (320) and the second spindle unit (330) are coaxially arranged with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); The tool head (300) an axial force element (390; 630) configured to generate an axial preload force between the first spindle bearing (323) and the second spindle bearing (333); the axial force element (390; 630) having an actuator for controllably varying the axial preload force; said tool head (300) is assigned a control device (730) configured to operate said actuator to adjust and / or controllably vary said axial preload force in a controlled manner; at least one sensor (731) for monitoring the operating state of the tool head (300); The control device (730) is configured to read the sensor (731) and vary the axial preload force taking into account the measurement parameters measured by the sensor (731). A tool head (300).

7. The tool head of claim 6 , wherein the actuator is a pneumatic or hydraulic actuator.

8. 8. The tool head (300) of claim 7, wherein the controller (730) is configured to operate the actuator to activate the axial force element (390; 630) during machining operations and to deactivate the axial force element during machining pauses.

9. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation about the tool spindle axis (B), the second spindle bearing (333) being configured to absorb both radial and axial forces; an axial force element (390; 630) configured to generate an axial preload force between the first spindle bearing (323) and the second spindle bearing (333); a spindle housing (380) in which both the first spindle unit (320) and the second spindle unit (330) are housed; a bearing receptacle (391) that is axially displaceable relative to the spindle housing (380) and in which at least one second spindle bearing (333) is held; It has the first spindle unit (320) and the second spindle unit (330) are coaxially arranged with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); the axial force element (390) is configured to apply an axial force to the bearing receptacle (391) to generate the axial preload force. A tool head (300) characterized in that:

10. 10. The tool head (300) of claim 9, wherein the axial force element (390) is annular and surrounds a clamping element (372) for axially clamping the tool (340) to the first spindle shaft (322) and the second spindle shaft (332).

11. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation about the tool spindle axis (B), the second spindle bearing (333) being configured to absorb both radial and axial forces; an axial force element (390; 630) configured to generate an axial preload force between the first spindle bearing (323) and the second spindle bearing (333); the first spindle unit (320) and the second spindle unit (330) are coaxially arranged with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); The first spindle unit (320) has a first spindle housing (321); The second spindle unit (330) has a second spindle housing (331); the axial force element (630) 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. A tool head (300) characterized in that:

12. 12. The tool head (300) of claim 1, wherein the tool (340) is clampable axially between the first spindle shaft (322) and the second spindle shaft (332) such that an axial compressive force acts on the tool (340) between the first spindle shaft (322) and the second spindle shaft (332).

13. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation 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 with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); the tool head (300) has a controlled clamping device (600) for controllably connecting the first spindle bearing (323) and the second spindle bearing (333) to one another; a control device (730) assigned to the tool head (300), the control device being configured to activate the clamping device (600) during machining operations and to deactivate the clamping device during machining pauses; The second spindle shaft (332) has at least one axial bore; the tool head (300) has at least one pull rod (370) extending through the axial bore of the second spindle shaft (332), the pull rod (370) being connectable at one end to the first spindle shaft (322) in a tensioning manner; the pull rod (370) is connectable at a second end to the second spindle shaft (332) such that an axial compressive force can be exerted on the tool (340) between the first spindle shaft (322) and the second spindle shaft (332); A tool head (300) characterized in that:

14. 14. The tool head of claim 13, wherein the tool head includes a clamping element connectable to a second end of the pull rod, the clamping element configured to axially urge the second spindle shaft toward the first spindle shaft.

15. The clamping element a housing rigidly connectable to said pull rod (370); an axial pressing element that is axially displaceable relative to the housing in the direction of the second spindle shaft (332) and presses the second spindle shaft (332) axially toward the first spindle shaft (322); at least one actuating member movable relative to the housing for generating an axial compressive force on the axial pressing element relative to the housing; The tool head of claim 14, comprising:

16. A tool head (300) for a machine tool, comprising: a first spindle unit (320) comprising at least one first spindle bearing (323) and a first spindle shaft (322); a second spindle unit (330) comprising at least one second spindle bearing (333) and a second spindle shaft (332); and the first spindle shaft is mounted in the first spindle bearing (323) for rotation about a tool spindle axis (B), the first spindle bearing (323) being configured to absorb both radial and axial forces; the second spindle shaft is mounted in the second spindle bearing (333) for rotation 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 with respect to one another such that a tool (340) is receivable axially between the first spindle shaft (322) and the second spindle shaft (332); the tool head (300) has a controlled clamping device (600) for controllably connecting the first spindle bearing (323) and the second spindle bearing (333) to one another; a control device (730) assigned to the tool head (300), the control device being configured to activate the clamping device (600) during machining operations and to deactivate the clamping device during machining pauses; a first spindle protrusion (325) is formed on the tool-side end of the first spindle shaft (322) such that a non-positive and / or positive connection with the tool (340) can be created at the first spindle protrusion (325) by an axial compressive force; a second spindle projection (335) is formed on the tool-side end of the second spindle shaft (332) so that a non-positive and / or positive connection with the tool (340) can be created at the second spindle projection (335) by an axial compressive force; A tool head (300) characterized in that:

17. the first spindle unit (320) comprises a first drive motor (324) configured to drive the first spindle shaft (322) in rotation about the tool spindle axis (B); and / or the second spindle unit (330) has a second drive motor (334) configured to drive the second spindle shaft (332) in rotation about the tool spindle axis (B); The tool head (300) according to any one of the preceding claims.

18. The tool head (300) of any one of claims 1 to 17, further comprising a tool (340), the tool (340) being axially received between the first spindle shaft (322) and the second spindle shaft (332).

19. A machine tool, A tool head (300) according to any one of claims 1 to 18, at least one workpiece spindle (500) for driving a workpiece (510) to rotate about a workpiece axis (C1); It has Machine tools.

20. A method for operating a tool head (300) according to any one of claims 1 to 18, comprising the steps of: - connecting the first spindle bearing (323) and the second spindle bearing (333) during machining operations and releasing said connection during machining pauses; and / or generating an axial preload force between said first spindle bearing (323) and said second spindle bearing (333); A method of operating a tool head (300), comprising:

Images