Spindle device with overload protection

Abstract

A spindle device (1) with a housing (2) for use on a machine tool (100), comprising: - a spindle shaft (3) arranged in the housing (2) for driving a tool and / or workpiece clamped on the spindle device (1); and - an intermediate chamber (10) formed between the housing (2) and the spindle shaft (3) characterized by a sensor unit connected to the intermediate chamber (10) which is arranged to to detect a volume flow of a medium supplied in the intermediate chamber (10) of the spindle device (1), and to detect a change in the volume flow of the medium in the intermediate chamber (10) for monitoring against spindle and / or tool damage or workpiece damage when the spindle shaft (3) is displaced by a force acting on the tool or workpiece and / or the spindle device (1).

Description

[0001] The present invention relates to a spindle device for use on a machine tool, which is provided with overload protection. background

[0002] Spindle devices for use on machine tools are known in the prior art, in which a spindle shaft of the spindle device is secured by a spring system when subjected to loads.

[0003] With such spindle devices, it has proven impractical that overload conditions occur with tools clamped in the spindle device, which counteract a spring system. In such overload conditions, the front bearings of the spindle device run without preload, so that the bearings can be damaged under sustained load. In spindle devices with clamped end mills, which are becoming increasingly common, overloads can occur even at medium spindle power.

[0004] From DE 10 2018 201 427 A1 a spindle device is known in which force sensors are attached to the spindle device to monitor overloading and determine a force distribution on the spindle device.

[0005] In such a spindle device, it has proven to be disadvantageous that the spindle device equipped with force sensors has a very complex structure, which is also expensive.

[0006] Further prior art is also known from DE 81 31 937 U1 and DE 35 25 691 A1.

[0007] Based on the spindle devices of the prior art, it is an object of the invention to optimize the design of a spindle device for use on a machine tool in such a way that a cost-effective design of a spindle device with overload protection is achieved. Summary of the invention

[0008] To achieve the above-mentioned object, the invention proposes a spindle device according to claim 1 and a system according to claim 14. Dependent claims relate to preferred and exemplary embodiments of the invention.

[0009] According to the present invention, a spindle device with a housing for use on a machine tool is proposed, which comprises an interface for clamping the spindle device on the machine tool, a spindle shaft arranged in the housing for driving a tool and / or workpiece clamped on the spindle device, and an intermediate chamber formed between the housing and the spindle shaft.

[0010] Furthermore, the spindle device comprises a sensor unit arranged in the intermediate chamber, which is configured to detect a volume flow of a medium supplied in the intermediate chamber of the spindle device, and to detect a change in the volume flow of the medium in the intermediate chamber for monitoring against spindle and / or tool damage or workpiece damage when the spindle shaft is displaced by a force acting on the tool or workpiece and / or the spindle device.

[0011] This has the advantage that by detecting the volume flow of the medium, overloads on tools or workpieces clamped to the spindle device can be detected early on via the sensor unit and thus prevented.

[0012] Furthermore, the spindle device according to the invention has the advantage of having the simplest possible structure, which enables real-time monitoring and overload protection without process interruption

[0013] In expedient embodiments, the spindle device comprises bearings arranged in the housing and preloaded by at least one vibration element.

[0014] This has the advantage that the bearings are designed in such a way that the spindle shaft can be driven smoothly. If the spindle shaft moves toward the bearings as a result of tensile forces acting on the tools or workpieces clamped in the spindle fixture, the vibration element prevents direct contact between the bearing and the spindle shaft. Therefore, damage to the bearings caused by tensile forces is minimized or prevented. Furthermore, the vibration element ensures consistent bearing preload.

[0015] In expedient embodiments, the spindle device comprises front bearings preloaded by a first vibration element arranged in a first section of the housing and rear bearings preloaded by a second vibration element arranged in a second section of the housing.

[0016] This has the advantage of providing improved and uniform bearing support in the spindle assembly. The design with front and rear bearings prevents irregularities in the bearing arrangement due to the separation of the bearings.

[0017] In expedient embodiments, the spindle device comprises a sliding element arranged between the oscillating element and the spindle shaft, which sliding element is configured to transmit a spring force of the oscillating element to the rear bearings for preloading the rear bearings.

[0018] This has the advantage that the preload of the vibration element is evenly transmitted to the rear bearings via the sliding element. Excessive compressive force on the vibration element is prevented by the even distribution of forces across the vibration element via the sliding element. This optimizes the transmission of the vibration element's spring force. Furthermore, the even distribution of the spring force prevents excessive loading of individual bearings.

[0019] In expedient embodiments, the sliding element is designed such that the rear bearings are at least partially enclosed by the sliding element to protect the rear bearings.

[0020] This has the advantage that the rear bearings are protected in such a way that the service life of the bearings is extended and maintenance of the spindle device due to bearing changes is reduced.

[0021] In expedient embodiments, the spindle device is designed such that when tensile forces act on the clamped tool or workpiece during machining and the spindle shaft moves in the direction of the front bearings, the sliding element is moved in the direction of the front bearings and the intermediate chamber occupies a smaller volume than in the pre-tensioned state.

[0022] This has the advantage that the design of the spindle device is kept compact and the determination of overloads is realized cost-effectively.

[0023] In expedient embodiments, the sensor unit is configured to detect the volume flow of the medium supplied to the intermediate chamber of the spindle device by means of a flow measurement.

[0024] This has the advantage that the functionality of the spindle device is improved or at least maintained, while the structure for detecting overloads has been simplified.

[0025] In expedient embodiments, the spindle device further comprises a nozzle with throttle geometry, wherein the medium flows to the nozzle through a line arranged in the housing and the sensor unit is designed to measure the flow rate or to measure a dynamic pressure of the medium supplied to the intermediate chamber of the spindle device at the nozzle and thus infers the volume flow.

[0026] This has the advantage that the medium is fed into the intermediate chamber evenly and in a controlled manner via the line and the nozzle with throttle geometry, and the volume flow can be precisely recorded and detected by the sensor unit. Furthermore, the design of the spindle device is kept compact, and if the sensor unit is configured to measure back pressure, a more cost-effective back pressure measurement can be achieved compared to flow meters.

[0027] In expedient embodiments, the sensor unit is configured such that a safety measure is carried out to protect against spindle and / or tool damage when the volume flow of the medium reaches a predetermined critical value.

[0028] This has the advantage that overloads on the spindle device are efficiently prevented and the safety measure leads to the protection of the spindle device.

[0029] In expedient embodiments, the sensor unit is configured such that a first signal is detected when the measured volume flow of the medium assumes a value that lies in a first value range, a second signal is detected when the measured volume flow of the medium assumes a value that lies in a second value range, and a third signal is detected when the measured volume flow of the medium assumes a value that lies in a third value range, wherein the third value range lies in a range that is smaller than the first and second value ranges, and the second value range lies in a range that is smaller than the first value range.

[0030] This has the advantage that the functionality of the sensor unit is improved so that different signals can be detected and assigned to a range of values, thus improving the accuracy of the measurement.

[0031] In expedient embodiments, the sensor unit is configured such that the machining is carried out by means of the machine tool when the sensor unit detects the first signal.

[0032] This has the advantage that the signal alerts a user that the tools or workpieces clamped to the spindle device are exerting a load on the spindle device that is not critical for the spindle device, so that the spindle device can continue to perform a machining process without interruption.

[0033] In expedient embodiments, the sensor unit is configured such that, as a safety measure to protect against spindle and / or tool damage, a warning appears on the machine tool when the sensor unit detects the second signal.

[0034] This has the advantage that a warning is sent to the user before overloads occur, allowing precautions to be taken to protect the spindle device. This allows the user to react early to tensile forces during the machining process and protect the spindle device from overloads.

[0035] In expedient embodiments, the sensor unit is configured such that, as a safety measure to protect against spindle and / or tool damage, the machine tool is switched off when the sensor unit detects the third signal.

[0036] This has the advantage that in the event of an overload, the spindle is immediately shut down, thus protecting the spindle assembly from potential damage. This prevents excessive tensile forces, which could lead to overloading, from acting on the spindle assembly.

[0037] According to the present invention, a system is proposed which comprises a numerically controlled machine tool and a spindle device mounted on the machine tool according to one of the above expedient embodiments.

[0038] In expedient embodiments, the machine tool comprises a control device configured to control a movement of the spindle device, and the spindle device has a transmission unit for transmitting signals to the control device of the machine tool.

[0039] This has the advantage that the spindle device can communicate with the machine tool to prevent overloading. Detected signals can be quickly transmitted to the machine tool via the spindle device's transmission unit, and the machine tool can receive the detected signals and process them via the control device, allowing the machine tool to react to overloads and control the movement or feed motion of the spindle device.

[0040] In expedient embodiments, the transmission unit is configured to transmit a control signal to the control device of the machine tool, wherein the signal indicates the change in the volume flow of the medium detected by the sensor unit.

[0041] In expedient embodiments, the control device of the machine tool is configured to control or regulate a movement of the spindle device mounted on the machine tool on the basis of the control signal received from the transmission unit of the spindle device.

[0042] This has the advantage that the machine tool and spindle assembly form a system that enables simple and economical real-time monitoring of overloads. The spindle assembly is protected from mechanical overloads that occur when high process forces are applied during radial or axial processes. The signals detected by the sensor unit, which represent the loads on the spindle assembly, can be visually displayed on the control device. Furthermore, the feed motion of the machine tool can be regulated to prevent overloading, thus preventing bearing damage to the spindle assembly due to overloading.

[0043] The spindle device according to the invention and the system comprising machine tool and spindle device according to the invention realize an economical and functionally integrated overload protection. Short description of the characters Fig. 1 shows an embodiment of a spindle device with overload protection according to the invention. Fig. 2 shows a diagram of the embodiment of the spindle device according to the invention. Fig. 3 shows a numerically controlled machine tool with a spindle device according to the invention. Detailed description of the figures and preferred embodiments

[0044] Examples and embodiments of the present invention are described in detail below with reference to the accompanying figures. Identical or similar elements in the figures may be designated by the same reference numerals, although sometimes different reference numerals may be used.

[0045] It should be emphasized, however, that the present invention is in no way limited or restricted to the exemplary embodiments and their embodiment features described below, but further comprises modifications of the exemplary embodiments, in particular those which are encompassed by modifications of the features of the described examples or by combination of one or more of the features of the described examples within the scope of protection of the independent claims.

[0046] Fig. Figure 1 shows an embodiment of a spindle device 1 according to the invention. The spindle device 1 comprises a housing 2 and a spindle shaft 3 arranged in the housing 2. The spindle device 1 has a rotary feedthrough 4 at one end of the housing 2 for the internal supply of a cooling lubricant.

[0047] The spindle device 1 comprises a drawbar 5 by means of which tools or workpieces can be clamped into the spindle device 1. The drawbar 5 is arranged within the housing 2 within the spindle shaft 3. The drawbar 5 is designed such that it is movable in the axial direction, so that tools or workpieces are clamped or released into the spindle device 1 via the movement of the drawbar 5 in the axial direction.

[0048] Between the housing 2 and the spindle shaft 3, front bearings 6a are arranged in a first section 2a of the housing 2, and rear bearings 6b are arranged in a second section 2b to support the spindle shaft 3. The front bearings 6a and the rear bearings 6b are designed, for example, as bearing assemblies and are preloaded via vibration elements. The front bearings 6a and rear bearings 6b are preloaded via the vibration elements in such a way that the spindle shaft 3 transmits tensile loads as efficiently as possible to the housing 2 via the front and / or rear bearings 6a, 6b.

[0049] The rear bearings 6b are preloaded via a vibration element 7 to protect the rear bearings 6b from tensile loads during machining with the machine tool. The vibration element 7 is arranged on the housing 2 in the second section 2b of the housing 2. The vibration element 7 is designed, for example, as a compression spring.

[0050] In the second section 2b of the housing 2, a sliding element 8 is arranged, which comprises a cylindrical main section 8a and an end section 8b, wherein the end section 8b is wider than the main section 8a, so that the sliding element 8 has an L-shaped cross-section. An outer peripheral surface of the sliding element 8 borders the housing 2 and an outer side of the end section 8b of the sliding element 8 is in contact with the vibration element 7. The rear bearings 6b are arranged within the sliding element 8 such that the sliding element 8 frames the rear bearings 6b in an L-shape and the rear bearings 6b are at least partially enclosed by the sliding element 8. The sliding element 8 is designed such that the vibration element 7 presses against the sliding element 8 and the spring force for preloading the rear bearings 6b is exerted on the rear bearings 6b by the sliding element 8.The sliding element 8 is sealed against the housing 2 by seals 9.

[0051] Between the housing 2 and the end section 8b of the sliding element 8, the spindle device 1 comprises an intermediate chamber 10, which is formed by the preload generated by the vibration element 7 on the sliding element 8 or the rear bearings 6b. The intermediate chamber 10 is designed, for example, as a block gap, and the sliding element 8 is designed, for example, as a sliding bushing.

[0052] The spindle device 1 comprises a line 11 for supplying air in the housing 2. The line 11 comprises an inlet opening 11a formed on the outside of the housing 2 and an outlet opening 11b formed between the housing 2 and the sliding element 8. The line 11 comprises a first line section 11a1 in the region of the inlet opening 11a and a second line section 11b1 in the region of the outlet opening 11b, wherein the two line sections 11a1, 11b1 of the line 11 are formed perpendicular to each other.

[0053] At the outlet opening 11b of the line 11, between the outlet opening 11b and the sliding element 8, the spindle device 1 comprises a nozzle 12. The nozzle 12 has a throttle geometry by means of which the flow rate of the supplied air is regulated. The air is guided into the intermediate chamber 10 via the line 11 and the nozzle 12. The air supplied to the intermediate chamber 10 is sealed in the intermediate chamber 10 by the seals 9 such that the supplied air cannot escape via the sliding element 8.

[0054] The spindle device 1 comprises a sensor unit connected to the intermediate chamber 10 and configured to detect an air volume flow supplied into the line 11. The sensor unit can be configured as a flow meter, but can also be configured as any other sensor unit capable of measuring an air volume flow and / or a dynamic pressure.

[0055] The sensor unit is designed, for example, in such a way that the change in air flowing from the line 11 arranged in the housing 2 to the nozzle 12 and into the intermediate chamber 10 is detected by means of the sensor unit by a dynamic pressure arising at the throttle geometry.

[0056] A tool or workpiece is clamped to the spindle device 1 by the drawbar 5. When tensile forces act on the clamped tool or workpiece during machining, the spindle shaft 3 moves toward the front bearings 6a, and the oscillating element 7 is moved from a preloaded state to a state in which the oscillating element 7 is compressed. The change from the preloaded state to the state in which the oscillating element 7 is compressed is detected by the sensor unit as a change in the air volume flow. The tensile force acting on the tool or workpiece causes a displacement of the spindle shaft 3, whereby the sliding element 8 is moved toward the front bearings 6a, and the intermediate chamber 10 therefore has a smaller volume than in the preloaded state. This change in the intermediate chamber 10 is detected by the sensor unit as a change in the air volume flow.The air volume flow detected by the sensor unit is evaluated to prevent overloads during processing.

[0057] Fig. Figure 2 shows a diagram of an embodiment according to the invention. The diagram shows the size of the intermediate chamber 10 as the width of the block gap on a horizontal axis. The vertical axis represents the air flow rate supplied through line 11 via nozzle 12 and detected by the sensor unit.

[0058] The horizontal axis is further divided into a first area A, labeled “Normal,” a second area B, labeled “Critical,” and a third area C, labeled “Overload.”

[0059] The first region A defines a first machining state in which no or only a minimal tensile force acts on the spindle device 1, so that no or only a minimal change in the size of the volume of the intermediate chamber 10 occurs and the flow rate detected by the sensor unit is at a sufficiently large value. The flow rate detected by the sensor unit is assigned to a first signal, which is interpreted as normal.

[0060] The second region B defines a second machining state in which a tensile force acts on the spindle device 1 that is greater than the tensile force acting in the first state. The volume of the intermediate chamber 10 is smaller than the size of the volume of the intermediate chamber 10 in the first state. Due to this reduction in the volume of the intermediate chamber 10, the air volume flow decreases, and the sensor unit detects a smaller value in the second state than in the first state. The flow rate detected by the sensor unit is assigned to a second signal, which is interpreted as critical.

[0061] The third area C defines a third state during machining in which a tensile force acts on the spindle device 1 that is greater than the tensile force acting in the first state and the second state. The volume of the intermediate chamber 10 is smaller than the size of the volume of the intermediate chamber 10 in the first state and the second state. Due to this reduction in the volume of the intermediate chamber 10, the air volume flow decreases further, and the sensor unit detects a smaller value in the third state than in the first state and the second state. The flow rate detected by the sensor unit is assigned to a third signal, which is interpreted as an overload.

[0062] The spindle device 1 is monitored by the air volume flow detected by the sensor unit and overloads can be detected at an early stage so that an early response to overloads can be achieved.

[0063] Fig. Figure 3 shows a numerically controlled machine tool 100 with a spindle device 1 according to the invention, wherein, for example, a tool is accommodated on the spindle device 1. The spindle device 1 is, for example, the spindle devices 1 shown in the Fig. 1 is shown.

[0064] The machine tool 100 comprises a machine bed 102 and a machine stand 101 arranged on the machine bed 102. The machine stand 101 can, for example, be arranged on the machine bed 102 so that it can move in one or more directions. A spindle device carrier 104, which supports the spindle device 1, is arranged on the machine stand 101. The spindle device carrier 104 can, for example, be movable in one or more directions. The spindle device 1 is driven by a drive 1a. The machine tool 100 further comprises a workpiece table 105 arranged on the machine bed 102, with a workpiece clamping device 106 in which a workpiece 107 is clamped. The workpiece table 105 can, for example, be designed as a rotary table or as a swivel rotary table. The workpiece table 105 can be arranged on the machine bed 102 so that it can move in one or more directions.

[0065] The machine tool 100 comprises a control device 91 configured to cause the spindle device 1 to execute a feed movement. The control device 91 controls the drive 1a of the spindle device 1. The spindle device 1 is configured vertically, for example, but can also be configured horizontally or at an angle.

[0066] The spindle device 1 comprises a transmission unit 92 that transmits signals to the control device 91 of the machine tool 100. The transmission unit 92 of the spindle device 1 transmits a signal indicating the change in the air volume flow detected by the sensor unit to the control device 91. The control device 91 of the machine tool 100 receives the signal and can then control or regulate the movement of the spindle device 1 mounted on the machine tool 100.

[0067] If the first signal is detected at the sensor unit of the spindle device 1, in which no tensile force or a minimal tensile force acts on the tool or workpiece mounted on the spindle device 1 and the air volume flow corresponds to a normal value, so that no or minimal changes are detected, the first signal is transmitted via the transmission unit 92 to the control unit 91 and the movement of the spindle device 1 mounted on the machine tool 100 remains unchanged due to the first signal received by the control device 91.

[0068] If the second signal is detected on the sensor unit of the spindle device 1, in which a greater tensile force than in the first signal acts on the tool or workpiece held on the spindle device 1 and the air volume flow corresponds to a critical value, wherein a greater change in the air volume flow is detected than in the first signal, the second signal is transmitted to the control unit 91 via the transmission unit 92. The received second signal can be used to display a warning for a user of the machine tool 100 on a display device of the machine tool 100, which alerts the user that a tensile force critical for the spindle device 1 is acting on the tool or workpiece held on the spindle device 1.Workpiece and based on the first signal received by the control device 91, the movement of the spindle device 1 mounted on the machine tool 100 and / or the speed of the spindle shaft 3 and / or the movement of the workpiece table 105 can be changed.

[0069] If the third signal is detected at the sensor unit of the spindle device 1, in which a greater tensile force than in the first signal and the second signal acts on the tool or workpiece mounted on the spindle device 1 and the air volume flow corresponds to an "overload" value, wherein a greater change in the air volume flow is detected than in the first signal and the second signal, the third signal is transmitted via the transmission unit 92 to the control unit 91. The received third signal can be used to display an overload for the user of the machine tool 100 on the display device of the machine tool 100, which alerts the user that a tensile force that is excessive for the spindle device 1 is acting on the tool or workpiece mounted on the spindle device 1.The machining by means of the spindle device 1 mounted on the machine tool 100 can be stopped based on the first signal received by the control device 91 and the machine tool 100 can be switched off.

[0070] By controlling the machine tool using the above solution, overloads can be prevented in a simple and cost-effective way.

[0071] Examples and embodiments of the present invention and their advantages have been described in detail above with reference to the accompanying figures. It should be emphasized again that the present invention is in no way limited or restricted to the above-described embodiments and their design features, but rather further encompasses modifications of the embodiments, in particular those encompassed by modifications of the features of the described examples or by combining one or more of the features of the described examples within the scope of the independent claims. List of reference symbols 1 spindle device 1a drive 2 housings 2a first section 2b second section 3 spindle shaft 4 rotary union 5 Drawbar 6a front bearing 6b Rear bearing 7 Vibration element 8 sliding element 8a Main Section 8b final section 9 Seals 10 Intermediate chamber 11 Line 11a Entrance opening 11b Exit opening 12 nozzles 91 Control device 92 transmission unit 100 machine tools 101 Machine stands 102 Machine bed 104 spindle fixture carriers 105 Workpiece table 106 Workpiece clamping device 107 Workpiece

Claims

[1] A spindle device (1) with a housing (2) for use on a machine tool (100), comprising: - a spindle shaft (3) arranged in the housing (2) for driving a tool and / or workpiece clamped on the spindle device (1); and - an intermediate chamber (10) formed between the housing (2) and the spindle shaft (3) characterized by a sensor unit connected to the intermediate chamber (10) which is arranged to to detect a volume flow of a medium supplied in the intermediate chamber (10) of the spindle device (1), and to detect a change in the volume flow of the medium in the intermediate chamber (10) for monitoring against spindle and / or tool damage or workpiece damage when the spindle shaft (3) is displaced by a force acting on the tool or workpiece and / or the spindle device (1). [2] Spindle device (1) according to claim 1, which comprises bearings (6a; 6b) arranged in the housing (2) and preloaded by at least one vibration element (7). [3] Spindle device (1) according to claim 1 or 2, wherein the spindle device (1) comprises front bearings (6a) arranged in a first section (2a) of the housing (2) and preloaded by a first vibration element, and a rear bearing (6b) arranged in a second section (2b) of the housing (2) and preloaded by a second vibration element (7). [4] Spindle device (1) according to claim 3, wherein the spindle device (1) comprises a sliding element (8) arranged between the vibration element (7) and the spindle shaft (3), which is designed to transmit a spring force of the vibration element (7) to the rear bearings (6b) for preloading the rear bearings (6b). [5] Spindle device (1) according to claim 4, wherein the sliding element (8) is designed such that the rear bearings (6b) are at least partially enclosed by the sliding element (8) to protect the rear bearings (6b). [6] Spindle device (1) according to claim 4 or 5, wherein the spindle device (1) is designed such that when tensile forces act on the clamped tool or workpiece during machining and the spindle shaft (3) moves in the direction of the front bearings (6a), the sliding element (8) is moved in the direction of the front bearings (6a) and the intermediate chamber (10) occupies a smaller volume than in the pre-tensioned state. [7] Spindle device (1) according to claim 6, wherein the sensor unit is configured to detect the volume flow of the medium supplied to the intermediate chamber (10) of the spindle device (1) by a flow measurement. [8] Spindle device (1) according to one of the preceding claims, wherein the spindle device (1) further comprises a nozzle (12) with throttle geometry and the medium flows to the nozzle (12) in a line (11) arranged in the housing (2) and the sensor unit is set up to measure the flow rate or to measure a dynamic pressure applied to the nozzle (12) of the medium supplied to the intermediate chamber (10) of the spindle device (1) and thus infers the volume flow. [9] Spindle device (1) according to one of the preceding claims, wherein the sensor unit is arranged such that a safety measure is carried out to protect against spindle and / or tool damage when the volume flow of the medium reaches a predetermined critical value. [10] Spindle device (1) according to one of the preceding claims, wherein the sensor unit is arranged such that a first signal is detected when the measured volume flow of the medium assumes a value that lies within a first value range, a second signal is detected when the measured volume flow of the medium assumes a value that lies within a second value range, and a third signal is detected when the measured volume flow of the medium assumes a value that lies within a third value range, where the third value range is in a range that is smaller than the first and second value ranges, and the second range of values ​​lies in a range that is smaller than the first range of values. [11] Spindle device (1) according to claim 10, wherein the sensor unit is arranged such that the machining is carried out by means of the machine tool (100) when the sensor unit detects the first signal. [12] Spindle device (1) according to claim 10, wherein the sensor unit is arranged such that, as a safety measure to protect against spindle and / or tool damage, a warning appears on the machine tool (100) when the sensor unit detects the second signal. [13] Spindle device (1) according to claim 10, wherein the sensor unit is arranged such that, as a safety measure to protect against spindle and / or tool damage, the machine tool (100) is switched off when the sensor unit detects the third signal. [14] System comprising: - a numerically controlled machine tool (100), and - a spindle device (1) mounted on the machine tool (100) according to at least one of the preceding claims. [15] System according to claim 14, wherein the machine tool (100) comprises a control device (91) which is designed to control a movement of the spindle device (1) and / or a workpiece table (105) of the machine tool (100), and the spindle device (1) has a transmission unit (92) for transmitting signals to the control device (91) of the machine tool (100). [16] System according to claim 15, wherein the transmission unit (92) is configured to transmit a signal to the control device (91) of the machine tool (100), wherein the control signal indicates the change in the volume flow of the medium detected by means of the sensor unit. [17] System according to claim 16, wherein the control device (91) of the machine tool (100) is adapted to control or regulate a movement of the spindle device (1) accommodated on the machine tool (100) on the basis of the signal received from the transmission unit (92) of the spindle device (1).

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