Machine tool

Abstract

The invention relates to a machine tool having a machine body and a tool, wherein an ultrasonic transducer comprising a stacked arrangement of piezoelectric actuators is arranged on a tool side of the machine tool; the machine tool comprises a drive transformer for supplying the ultrasonic transducer with an energy signal, said drive transformer comprising a primary drive coil, which is arranged on the machine body side and is connected to an alternating signal supply device, and a secondary drive coil, which is arranged on the tool side, is separated from the primary drive coil by a first air gap and is connected to the ultrasonic transducer; the machine tool comprises a measuring device comprising at least one piezoelectric sensor arranged on or in a tool holder of the machine tool; wherein the measuring device is connected to a signal transmission device for contactless transmission of a measurement signal from the measuring device to a signal detection device on the machine body side, said signal transmission device comprising signal transmission elements having a second air gap located therebetween and spaced apart from the first air gap. According to the invention, the signal detection device is a voltage measuring device, wherein the at least one piezoelectric sensor is integrated in a measuring circuit comprising the signal transmission device and at least one measuring capacitor connected in parallel with the at least one piezoelectric sensor on the tool side and / or in parallel with the voltage measuring device on the machine body side.

Description

[0001] WO25926IWU / CS.CS

[0002] machine tool

[0003] The present invention relates to a machine tool comprising a machine body and a tool operable by a motor of the machine tool, wherein an ultrasonic transducer having a stacked arrangement of piezoelectric actuators is arranged on a tool side of the machine tool; the machine tool has a drive primary coil arranged on the machine body side and connected to an AC signal supply device, and a drive secondary coil arranged on the tool side and separated from the drive primary coil by a first air gap and connected to the ultrasonic transducer for supplying the ultrasonic transducer with an energy signal; the machine tool has a sensor device comprising at least one piezoelectric sensor arranged on or in a tool holder of the machine tool;wherein the sensor device is connected to a signal transmission element with a signal transmission device having a second air gap located between it and the first air gap, for the contactless transmission of a sensor signal from the sensor device to a signal detection device on the machine body.

[0004] In toolmaking, it is a well-established practice to superimpose ultrasonic vibrations on the rotational movement of a tool. Ultrasound-assisted machining offers advantages such as reduced machining forces, reduced tool wear, increased tool life, and improved chip breaking, thus preventing chip jamming and subsequent tool breakage. For example, ultrasonic assistance reduces cutting forces and improves chip evacuation when drilling deep holes, significantly increasing drilling performance, particularly when machining high-strength and difficult-to-machine materials.

[0005] For example, publication EP 1 763 416 B1 describes a tool holder that is set into vibration by a piezoelectric system. The piezoelectric system comprises a first stationary coil and a second coil spaced apart from it, which engages the tool holder. The second coil is connected to piezoelectric actuators. The piezoelectric actuators encircle a tool holder in a ring-like configuration and vibrate when an alternating voltage is applied.

[0006] From publication EP 2 946 859 B1, a machine tool is known in which the tool side, on which a tool is installed, rotates relative to the machine body side during operation. An ultrasonic transducer installed on the tool side generates a vibration that is superimposed on the rotational movement of the tool.

[0007] In the machine tool described in publication EP 2 946 859 B1, as well as in publication EP 1 763416 B1, the transfer of drive energy from the primary drive coil located on the machine body to the secondary drive coil located on the tool side is contactless. Only the primary drive coil has a ferrite core. An alternating current flowing through the primary drive coil generates a magnetic field around the primary drive coil, which in turn generates an alternating current in the secondary drive coil. This current powers the ultrasonic transducer. The energy required to generate ultrasonic vibrations on the tool side is thus transported by means of inductive energy transfer.

[0008] The ultrasonic transducer can be described as an electrical circuit with a resonant frequency. To effectively drive the transducer and ensure sufficiently high oscillation amplitudes, it is operated with an alternating current whose frequency corresponds to, or is at least close to, the transducer's resonant frequency. At the resonant frequency, the phase difference between the electrical voltage applied to the transducer and the electrical current flowing through it is zero, and the highest current flows through the transducer.However, the resonant frequency, as well as the contact stiffness and damping of the ultrasonic transducer caused by the contact between the tool and the workpiece, change during machine tool operation depending on temperature and mechanical loads. This can alter the vibration status with respect to the resonant frequency and the power required to generate the vibration from the ultrasonic transducer, and consequently, the machining characteristics during machine tool operation. Therefore, frequency and amplitude control is necessary for reliable operation. This, in turn, requires the ability to appropriately acquire physical quantities at the ultrasonic transducer and evaluate them as electrical signals for use in control. A particular challenge here is the transmission of the acquired signals from the rotating tool holder to the signal acquisition device on the machine body.The detected sensor signal typically has the same frequency, but a different amplitude and phase compared to the drive signal. If these signals are used as the basis for the described control system, it is essential that the contactless transmission of the sensor signal is not influenced by the drive signal to ensure reliable operation of the controlled ultrasonic system.

[0009] In the field of conventional ultrasound technology, where the systems do not rotate and are directly connected to the ultrasound transducer, electrical parameters of the ultrasound transducer are used for control. For example, phase control of current and voltage is used for frequency, and current control is used for amplitude.

[0010] When inductive transformers are used to power rotating ultrasonic systems, as described in publication EP 2 946 859 B1, they cause a load-dependent phase shift between current and voltage on the primary drive side. Furthermore, the resistances, and thus the current draw, are affected. Consequently, these control approaches lead to faulty control behavior when using inductive transformers in combination with high process loads. For this reason, and for data acquisition for condition and process monitoring and control, additional signals from the rotating ultrasonic system are necessary, capable of detecting or reproducing the mechanical characteristics of the ultrasonic vibration.

[0011] In the machine tool known from publication EP 2 946 859 B1, the vibration status of the ultrasonic transducer is detected by means of a measuring device. The respective measurement signal of the measuring device is transmitted as an electrical signal to a control device located on the machine body via the interaction between the tool-side signal coil and the machine-side signal coil, i.e., by mutual induction. For this purpose, the vibration status of the ultrasonic transducer in the known machine tool is detected by means of a Hall element, which measures both a voltage applied to the ultrasonic transducer and a current flowing through it, from which the vibration status of the ultrasonic transducer is derived. The control device then adjusts the drive energy supplied to the primary drive coil at a frequency depending on the detected vibration status.

[0012] A problem with the machine tool described in publication EP 2 946 859 B1 is that the signal coils used for transmitting the measurement signal are arranged axially between the primary and secondary drive coils of the machine tool. This means that the drive energy and the measurement signal are transmitted across the same air gap between the two signal coils. As a result, the drive signal and the measurement signal interfere with each other in terms of their frequencies. Publication EP 2 946 859 B1 attempts to minimize this effect by using multiple windings with opposing turns, but this is very complex.

[0013] The machine tool described in German publication DE 10 2005 011 197 B4 has a stator section and a rotor section, each with a U-shaped core in cross-section, upon which a winding is wound. Energy is transferred from the stator to the rotor according to the transformer principle. The cores are oriented with their free leg ends facing each other and separated by an air gap. Furthermore, two pairs of coupling windings are provided on the stator and rotor sides for inductive data transmission. These coupling windings are located on the outside of the core legs in both the stator and rotor sections and are thus separated by the same air gap as the energy transmission windings.

[0014] The publication DE 102005 011 197 B4 assumes that the coupling windings arranged on the outer sides of the core legs are shielded from the field of the power transmission windings by the core legs in order to minimize the risk of induced interference signals. However, this does not solve the problem of mutual signal interference when the power and data signals have the same frequency.

[0015] Document US 10903414 B2 describes a radio signal transmission device that prevents mutual interference by modulating the signal to a carrier frequency in the gigahertz range. A disadvantage is that electrical circuits with a power supply are required for both modulation on the transmitter side and demodulation on the receiver side.

[0016] In European patent EP 3 319 748 B1, a generic device for generating an ultrasonic vibration of a tool is disclosed, wherein a piezoelectric ultrasonic transducer installed in the tool holder is supplied with energy via a transformer. In the known device, ultrasonic vibration parameters of the ultrasonic transducer are detected by a piezoelectric sensor device installed in the tool holder. The ultrasonic transducer and a sensor element of the sensor device are arranged stacked one above the other along the tool axis. A transmitter element, located in the tool holder at a distance from the ultrasonic transducer, is connected to the sensor device. A receiver element, spaced apart from the transmitter element, is arranged in a stationary part of the machine tool, and a sensor signal is inductively transmitted from the transmitter element to the receiver element.

[0017] The sensor signal is transmitted from the transmitter element to the receiver element in a direction perpendicular to the direction of energy transmission for the ultrasonic transducer. Specifically, the energy signal is transmitted axially, while the sensor signal is transmitted radially. This ensures that the magnetic fields of the two transformers are oriented perpendicular to each other, thus minimizing any interaction between the energy supply and signal transmission. Alternatively, optical transmission of the sensor signal to the receiver is proposed. However, how the sensor signal is measured at the receiver is not described. Similarly, EP 3 319 748 B1 does not provide a device for reliably and appropriately measuring the phase and voltage of the inductively transmitted sensor signal from the piezoelectric sensor.

[0018] Ultrasound-assisted machine tools, in particular due to the rotating ultrasonic transducer, place high demands on signal transmission, such as high robustness against rotational speeds, latency-free operation and avoidance of phase shifts.

[0019] The object of the present invention is therefore to provide an ultrasound-assisted machine tool which enables, using simple and cost-effective means, a high-quality, as interference-free as possible acquisition of a signal that describes the ultrasonic vibration of the ultrasonic transducer as accurately as possible.

[0020] This problem is solved by a machine tool comprising a machine body and a tool operable by a motor of the machine tool, wherein an ultrasonic transducer having a stacked arrangement of piezoelectric actuators is arranged on a tool side of the machine tool; the machine tool has a drive primary coil arranged on the machine body side and connected to an AC signal supply device, and a drive secondary coil arranged on the tool side, separated from the drive primary coil by a first air gap and connected to the ultrasonic transducer, for supplying the ultrasonic transducer with an energy signal; the machine tool has a sensor device comprising at least one piezoelectric sensor arranged on or in a tool holder of the machine tool;wherein the sensor device is connected to a signal transmission element with a signal transmission device having a second air gap located between it and the first air gap, for the contactless transmission of a sensor signal from the sensor device to a signal acquisition device on the machine body; wherein the signal acquisition device is a voltage measuring device; and wherein the at least one piezoelectric sensor is integrated into a measuring circuit which has the signal transmission device and at least one measuring capacitor connected in parallel to the at least one piezoelectric sensor on the tool side and / or in parallel to the voltage measuring device on the machine body side.

[0021] The machine tool according to the invention is suitable for all ultrasonically assisted workpiece machining processes in which the tool and the ultrasonic transducer are rotatable relative to the stationary side of the machine body around the longitudinal axis of the machine tool, which in this case is its axis of rotation, for example for ultrasonically assisted machining processes or for ultrasonically assisted friction stir welding.

[0022] The machine tool according to the invention can also be used in ultrasonic-assisted workpiece machining processes in which the ultrasonic transducer does not rotate but is supplied with electrical energy without contact. In both variants, it is possible with the aid of the present invention to measure parameters of the ultrasonic transducer and to transfer them to the machine body for the purpose of setting up a control system for the ultrasonic transducer and / or a process monitoring system for a process carried out on the machine tool.

[0023] In the present invention, the electrical energy signal with which the piezoelectric actuators of the ultrasonic transducer are operated is transmitted contactlessly from the machine body side to the tool side of the machine tool via the drive transformer. The drive transformer comprises the primary drive coil located on the machine body side and the secondary drive coil located directly opposite the primary drive coil and separated from it by the first air gap.

[0024] In this process, at least one piezoelectric sensor detects a strain or vibration and converts it into an electrical sensor signal that has a frequency and an amplitude and may be phase-shifted relative to the energy signal.

[0025] The at least one piezoelectric sensor uses the same physical principle for detecting sensor signals at the ultrasonic transducer, namely the piezoelectric principle, which the ultrasonic transducer also uses to generate the ultrasonic vibrations transmitted to the tool. This makes the at least one piezoelectric sensor particularly suitable for detecting essential measured quantities at the ultrasonic transducer. For example, quantities such as forces, strains, or vibrations can be detected with the at least one piezoelectric sensor, which are suitable for controlling the ultrasonic transducer and thus the ultrasonic-assisted workpiece machining by the machine tool, or for process monitoring at the machine tool.

[0026] The at least one piezoelectric sensor used for vibration detection according to the invention can either be integrated into the stack of piezoelectric elements of the ultrasonic transducer or be provided at at least one end of this stack and / or at another position on the tool holder of the machine tool. This means that the at least one piezoelectric sensor is directly connected to the ultrasonic transducer or at least very close to it, so that any vibration of the ultrasonic transducer or other force acting on the ultrasonic transducer is directly transmitted to the at least one piezoelectric sensor and can be measured by it. As a result, the sensor signal has the same frequency as the energy signal, but a different amplitude and phase, which are suitable for describing the vibration characteristics of the ultrasonic unit.

[0027] The electrical sensor signal is transmitted contactlessly via the signal transmission device from the tool side, on which the tool holder, subjected to ultrasonic vibrations by the ultrasonic transducer, is provided for holding the tool, to the machine body side of the machine tool, on which the signal acquisition device is provided, in analog form.

[0028] In the machine tool according to the invention, the sensor signal is transmitted via the second air gap, which is located away from the first air gap, through which the energy signal is transmitted.

[0029] Both the first and second air gaps are small; preferably, the distance between the drive coils and between the signal coils is less than 2 mm. This ensures reliable energy and signal transmission.

[0030] The components used for signal transmission in the present invention can be simple and cost-effective in design, yet still guarantee high signal quality on both the tool side and the machine body side.

[0031] The voltage measurement signal acquired on the machine body side forms the basis for controlling the ultrasonic-assisted workpiece machining on the machine tool or for monitoring a machining state or a system state on the machine tool.

[0032] The machine tool according to the invention makes it possible to perform vibration detections directly at the tool holder – i.e., where the vibration generated by the ultrasonic transducer is effective – and to acquire the sensor signals almost flawlessly and in real time, in order to then effectively control the ultrasonic vibration by means of the control device. In contrast to the radio signal transmission known from the prior art, the present invention requires no energy for signal transmission, since the at least one piezoelectric sensor itself forms a voltage source. The energy of the AC signal supply device can therefore be used exclusively to power the ultrasonic transducer in the present invention.

[0033] Furthermore, in the present invention, the signal transmission is analogous compared to digital radio applications known from the prior art, which results in no latency times in the signal transmission.

[0034] It has been shown that voltage signals are better suited than current signals for evaluating the sensor signals transmitted to the machine body. Therefore, the voltage measuring device is used as the signal acquisition device in the present invention. A measuring voltage drops across the measuring capacitor, depending on the number of electrical charges detected by the at least one piezoelectric sensor, and this voltage can be measured by the voltage measuring device. The capacitance of the respective measuring capacitor can be selected such that the measuring voltage lies within a targeted measuring range.

[0035] The measuring circuit used in the present invention covers both a part of the rotating tool side and a part of the machine body side of the machine tool.

[0036] The at least one measuring capacitor can be arranged on either the rotating tool side or the stationary side of the machine tool. If the at least one measuring capacitor is located on the tool side of the machine tool, it is connected in parallel to the at least one piezoelectric sensor and in parallel to the tool-side signal transmission element. If the at least one measuring capacitor is located on the machine tool body side of the machine tool, it is connected in parallel to the signal acquisition device and in parallel to the machine-side signal transmission element.

[0037] The respective transmission element arranged on the machine body, i.e. the drive primary coil and / or the signal transmission element arranged on the machine body, can be installed in the machine tool in a fixed, pivotable or removable manner, or be mounted on an environmental component of the machine tool, or be connected to a tool holder of the machine tool via a rolling bearing or be arranged on it in a replaceable manner.

[0038] Preferably, the at least one piezoelectric sensor is arranged so close to the piezoelectric actuators of the ultrasonic transducer that the sensor signal of the at least one piezoelectric sensor, which describes the mechanical ultrasonic vibration, has the same frequency as the energy signal supplied to the ultrasonic transducer, i.e., the current or voltage with which the piezoelectric actuators of the ultrasonic transducer are operated. The frequency of the sensor signal is thus also in the ultrasonic range. This fact presents a problem in the prior art, since if the energy signal and the sensor signal have the same frequency, the two signals tend to interfere with each other. In EP 3 319 748 B1, an attempt is made to circumvent this problem by placing the sensor signal transmission at a distance from the energy signal transmission.The latter is not necessary in the present invention, since the drive transformer and the measuring circuit can be electrically designed in such a way as to ensure that no mutual interference occurs between the energy signal and the sensor signal. The amplitude and / or phase or phase angle of the sensor signal, which differs from the energy signal in the present invention, can thus be used for frequency-independent control of the ultrasonic transducer or the ultrasonic workpiece processing.

[0039] In a preferred embodiment of the present invention, the signal transmission elements comprise a tool-side signal coil and a machine-body-side signal coil of a signal transmission transformer. In this embodiment of the invention, the combination of the at least one measuring capacitor and the signal transmission elements used in the measuring circuit results in a resonant circuit whose frequency should be adjusted by appropriately selecting the capacitance of the at least one measuring capacitor and the inductances of the signal coils such that it lies outside the ultrasonic frequency of the ultrasonic transducer, preferably less than half or greater than twice the ultrasonic frequency.This results in a particularly high transmission power if the tool-side signal coil, i.e., the one located on the rotating side of the machine tool, is a solid ring arranged concentrically to a longitudinal axis of the machine tool, and the machine body-side signal coil is a solid ring or a partial ring, i.e., a ring segment, arranged concentrically to the longitudinal axis of the machine tool.In contrast to the device described in EP 3319748 B1, which proposes either a transmitter-receiver arrangement on one side of the tool holder or a plurality of circumferentially arranged transmitter and / or receiver elements, this embodiment of the present invention can generate a higher inductance necessary for transmission and avoid both imbalance and inaccuracy of signal transmission due to inaccurate relative positioning of the multiple transmitter and / or receiver elements.

[0040] High-quality signal transmission is achieved when both the tool-side signal coil and the machine body-side signal coil each have at least one ferrite core on which at least one winding is located.

[0041] The at least one piezoelectric sensor, with respect to its electrical behavior, is a charge source and thus generates a voltage. This voltage is well suited for signal transmission between the signal coils, which together, optionally with at least one ferrite core, form a transformer arrangement. This voltage can be tapped as a measuring voltage across the measuring capacitor used in the present invention.

[0042] In another, equally advantageous embodiment of the machine tool according to the invention, the signal transmission elements comprise tool-side plate elements and machine-body-side plate elements of a signal transmission capacitor device. At least one of the tool-side plate elements is connected to a positive terminal of the at least one piezoelectric sensor and at least one of the tool-side plate elements is connected to a negative terminal of the at least one piezoelectric sensor, while at least one of the machine-body-side plate elements is connected to a positive terminal of the voltage measuring device and at least one of the machine-body-side plate elements is connected to a negative terminal of the voltage measuring device.The opposing plate elements on the tool and machine body sides thus form two parallel capacitors, via which a voltage, which is built up by the electrical charges accumulated by the at least one piezoelectric sensor, can be detected as a measurement signal by the voltage measuring device.

[0043] In a preferred embodiment of the present invention, interactions between the drive transformer and the signal transmission device can be prevented even more effectively if an electrically and / or magnetically shielding material, such as a metal screen, is arranged between the drive transformer and the signal transmission transformer. The metal screen is electrically conductive and can therefore dissipate electric and electromagnetic fields.

[0044] The shielding material can be part of the housing of the machine tool, into which the drive transformer and / or the signal transmission device are at least partially installed. The housing can be made entirely of metal. However, it is also possible that only an intermediate section of the housing, located between the drive transformer and the signal transmission device, is made of the shielding material.

[0045] If the signal transmission elements are the plate elements of a signal transmission capacitor, it is particularly convenient to use these signal transmission elements as a measuring capacitor. In this case, an additional measuring capacitor is unnecessary. However, inductive signal transmission using signal coils preferably utilizes the measuring capacitor as the electrical component of the measuring circuit for the measurement task.

[0046] Regardless of on which side of the machine tool the measuring capacitor is located, inductive signal transmission creates a resonant circuit through the combination of inductances and capacitance(s). This resonant circuit generates resonant frequencies that alter the amplitude and phase response of the measuring circuit within the measuring range. To avoid influencing the measurement, the electrical frequencies must lie outside the measuring range. In the present invention, this can be achieved by appropriately selecting the inductances of the signal coils and the capacitance of the at least one measuring capacitor. In addition to the at least one measuring capacitor and the signal coils, the machine tool according to the invention can have additional capacitances and / or inductances installed in parallel and / or in series on its machine body side and / or its tool side to adjust the resonant frequency of the resonant circuit.

[0047] In both inductive and capacitive signal transmission, there is another way to adapt the measuring circuit by connecting at least one fixed or adjustable resistor in parallel to the voltage measuring device and / or in series with the measuring capacitor. This allows the measuring voltage to be specifically set to a desired measuring range.

[0048] In practical applications, the at least one piezoelectric sensor may exhibit manufacturing tolerances. For example, several piezoelectric sensors, each with different manufacturing tolerances, may be provided on the tool holder. Furthermore, the machine tool according to the invention can be designed such that it incorporates several tool holders that are changed during workpiece machining. The tool-side components of the signal transmission device are also changed during this process. To nevertheless ensure reproducible behavior, particularly when using multiple tool holders and changing them during workpiece machining, the measuring circuit used in the machine tool according to the invention can include at least one compensating capacitor, switchable in series with the at least one piezoelectric sensor, to compensate for manufacturing tolerances. Thus, depending on the tool used, the measurement can be adjusted accordingly.Tool holder, to which at least one compensating capacitor of the measuring circuit can be connected or disconnected.

[0049] In particular, structural advantages arise when the drive transformer is arranged radially and / or axially and / or angularly offset from the signal transmission device.

[0050] The drive transformer can be arranged radially inside and the signal transmission device radially outside, or the signal transmission device radially inside and the drive transformer radially outside. It is also possible that the drive transformer and the signal transmission elements are not radially offset, but offset from each other in the axial orientation of the machine tool. In the latter case, however, the signal transmission elements are not enclosed by the drive coils of the drive transformer, as in the device described in EP 2 946 859 B1, but are separated from each other by a different air gap than the drive coils of the drive transformer, namely by a second air gap arranged concentrically to the first.

[0051] The drive transformer can be located closer to the tool side than the signal transmission device, or the signal transmission device can be located closer to the tool side than the drive transformer.

[0052] Furthermore, in the present invention it is possible for the drive transformer and the signal transmission device to overlap each other in the axial direction of the machine tool by means of a combination of radial and axial offset.

[0053] Depending on the arrangement of the drive transformer and the signal transmission device, the first and second air gaps in the machine tool according to the invention can be arranged on the same plane, i.e., merge into one another in the radial direction of the machine tool. The first and second air gaps can also be arranged on different planes, i.e., axially offset from each other. Furthermore, the first and second air gaps can be arranged both radially and axially offset from each other, so that a step is formed between the first and second air gaps. The first and second air gaps can also be oriented at an angle to each other other than 90° or 180°.

[0054] In a preferred embodiment of the present invention, the drive secondary coil and the tool-side signal transmission element are arranged in one and the same rotor housing. The rotor housing can be made in one piece or in multiple parts, i.e., from several interconnected housing parts.

[0055] Preferred embodiments of the present invention are explained in more detail below with reference to figures, wherein figure 1 schematically shows a tool holder of an embodiment of a machine tool according to the invention in a sectional side view; figures 2 to 6 schematically show principle representations of possible arrangements of a drive transformer and a signal transmission device in different embodiments of the machine tool according to the invention, each in a sectional side view;

[0056] Figure 7 shows a block diagram of a system in which an embodiment of the machine tool according to the invention is integrated; Figures 8 to 13 show schematic diagrams of measuring circuits of various embodiments of the machine tool according to the invention;

[0057] Figure 14 schematically shows a tool holder with a stator designed as a solid ring according to an embodiment of the machine tool according to the invention in a perspective side view; and

[0058] Figure 15 schematically shows a tool holder with a stator formed from a ring segment according to an embodiment of the machine tool according to the invention in a perspective side view.

[0059] Figure 1 schematically shows a tool holder 1 of an embodiment of a machine tool according to the invention in a sectional side view. The machine tool has a longitudinal axis A. In the embodiment shown, the longitudinal axis A forms a rotational axis A for the tool holder 1.

[0060] The tool holder 1 has a machine interface 2 via which it is connected to a machine body side 11 of the machine tool. The tool holder 1 also has a tool interface 3 with a chuck 31 on its side opposite the machine interface 2, into which a tool (not shown here) can be inserted.

[0061] In the description of the present invention, the side of the machine tool to which the tool holder 1 is connected via the machine interface 2 is referred to as the machine body side 11, while the side of the machine tool to which the tool is coupled is referred to as the tool side 12. In the illustrated embodiment, the machine body side 11 is stationary during operation, and the tool side 12 is rotatable relative to the machine body side 11 during operation. However, in other embodiments of the invention, the tool side 12 may also be non-rotatable.

[0062] An ultrasonic transducer 4 is arranged in the tool holder 1 on the tool side 12. The ultrasonic transducer 4 has a stacked arrangement of piezoelectric actuators (not shown) with which a movement of the tool is superimposed with an ultrasonic vibration. In the illustrated embodiment, the piezoelectric actuators are disc-shaped. The ultrasonic transducer 4 also has electrodes (not shown) connected to the piezoelectric actuators, through which the energy signal is supplied to each of the piezoelectric actuators.

[0063] The ultrasonic transducer 4 is supplied with electrical energy, i.e., an energy signal, from the machine body side 11. The energy signal is transmitted from the machine body side 11 to the tool side 12 via a drive transformer 5.

[0064] For this energy transmission, the drive transformer 5 has a primary drive coil 51 arranged on the machine body and a secondary drive coil 52 located opposite the primary drive coil 51 across a first air gap 53. The primary drive coil 51 and the secondary drive coil 52 are arranged concentrically to the longitudinal axis A of the machine tool. In the illustrated embodiment, the primary drive coil 51 and the secondary drive coil 52 are annular in shape. In the illustrated embodiment, the first air gap 53 extends radially along the machine tool. In the illustrated embodiment, the primary drive coil 51 and the secondary drive coil 52 each have a ferrite core onto which at least one winding is wound.

[0065] The primary drive coil 51 is electrically connected to an AC signal supply unit located on the machine body (not shown here). The secondary drive coil 52 is electrically connected to the electrodes of the ultrasonic transducer 4.

[0066] In the illustrated embodiment, a piezoelectric sensor 6 is arranged axially at each end of the ultrasonic transducer 4. In the illustrated embodiment, the piezoelectric sensors 6 are disc-shaped.

[0067] In other embodiments of the present invention, not shown here, at least one piezoelectric sensor 6 can be installed in the ultrasonic transducer 4 and / or arranged at another location of the tool holder 1.

[0068] The piezoelectric sensors 6 detect the vibration signals from the ultrasonic transducer 4 as electrical sensor signals. These sensor signals are then electrically transmitted to a signal transmission device 7.

[0069] In the illustrated embodiment, the signal transmission device 7 is a signal transmission transformer. The signal transmission transformer has a tool-side signal coil 71 and a machine-body-side signal coil 72, which are directly opposite each other across a second air gap 75. In the illustrated embodiment, the second air gap 75 extends radially along the machine tool. The second air gap 75 is a direct extension of the first air gap 53, but spaced apart from it, and is located on the same plane as the first air gap 53.

[0070] The signal transmission device 7 is arranged concentrically to the longitudinal axis A of the machine tool. In the illustrated embodiment, the signal transmission device 7 is also arranged concentrically to the drive transformer 5. The drive transformer 5 is arranged radially offset from the signal transmission device 7. An electrically and / or magnetically shielding material, such as a metal screen 29, is arranged between the drive transformer 5 and the signal transmission device 7.

[0071] As can also be seen in the enlarged representation of the area of ​​the tool holder 1 from Figure 1, designated Z, shown schematically in Figure 2, in the embodiment shown in Figure 1 the signal transmission device 7 is arranged closer to the longitudinal axis A than the drive transformer 5.

[0072] However, it is also possible that, as shown schematically in Figure 3, the drive transformer 5 is arranged closer to the longitudinal axis A than the signal transmission device 7 in another embodiment of the invention.

[0073] In another embodiment, shown schematically in Figure 4, the drive transformer 5 is arranged not only radially but also axially offset from the signal transmission device 7. As a result, the first air gap 53 is also arranged axially offset from the second air gap 75.

[0074] Figure 5 schematically shows another embodiment in which the drive transformer 5 is arranged not only radially but also axially offset from the signal transmission device 7. As a result, the first air gap 53 is also arranged axially offset from the second air gap 75.

[0075] In the embodiment shown in Figure 6, the signal transmission device 7 is arranged at an obtuse angle relative to the drive transformer 5. As a result, the first air gap 53 is also arranged at an angle to the second air gap 75.

[0076] In the embodiment shown in Figure 1, the stationary coils, i.e., the primary drive coil 51 of the drive transformer 5 and the machine-body-side signal coil 72 of the signal transmission device 7, are located in a stator housing 81. The coils rotatable with the tool, i.e., the secondary drive coil 52 of the drive transformer 5 and the tool-side signal coil 72 of the signal transmission device 7, are located in a rotor housing 82. The rotor housing 82 is separated from the stator housing 81 at least by the first air gap 53 and the second air gap 75 and is open to both air gaps 53 and 75.

[0077] In all embodiments shown in Figures 2 to 6, the drive secondary coil 52 and the tool-side signal transmission element 71 are each arranged in one and the same rotor housing 82, 82', 82", 82"', 82"".

[0078] The entire assembly consisting of the piezoelectric actuators of the ultrasonic transducer 4 and the piezoelectric sensors 6, which is hereinafter referred to as the ultrasonic unit and which borders an inner wall of the tool holder 1 at its first end, is subjected to a mechanical preload by a clamping device in the form of a clamping nut 9 acting at its second end.

[0079] In this process, a further piezoelectric sensor 6 is arranged between the first end of the ultrasound unit and the inner wall of the tool holder 1 for recording a mechanical stress or force.

[0080] In addition, another piezoelectric sensor 6 is arranged on an outer wall of the lining 31.

[0081] Figure 7 shows a block diagram of a system 10, in which an embodiment of the machine tool according to the invention is integrated. The system 10 includes the tool holder 1 described above, which functions as a rotor, and a stator 15 attached to a spindle 14 and located opposite the tool holder 1, with a tool 13 attached to the tool holder 1. The stator 15 includes the primary drive coil 51 of the drive transformer 5 and the machine-side signal coil 72 of the signal transmission device 7. The secondary drive coil 52 of the drive transformer 5, the tool-side signal coil 72 of the signal transmission device 7, and the ultrasonic unit are provided on the tool holder 1.

[0082] As shown schematically in Figure 7, the stator 15 is electrically connected to machine-body-side components of a measuring circuit 17 located in an ultrasonic control cabinet 24. These components serve to acquire the measurement signal. In particular, these components include a voltage measuring device 21. The ultrasonic control cabinet 24 also contains a control device 25 connected to the measuring circuit 17. The components located in the ultrasonic control cabinet 24 are powered via a main control cabinet 26, which contains a power supply 27 for an AC signal supply device located in the ultrasonic control cabinet 24. The system also includes a display device 28 connected to the control device 25, which can be used, for example, to display measurement signals.

[0083] Figure 8 schematically shows a basic representation of the measuring circuit 17. Instead of the measuring circuit 17, one of the measuring circuits 17a, 17b, 17c, 17d, 17e shown schematically in Figures 8 to 13 can also be used in the machine tool according to the invention.

[0084] Each of the measuring circuits 17, 17a, 17b, 17c, 17d, 17e has a piezoelectric sensor 6, whereby instead of a single piezoelectric sensor 6, several piezoelectric sensors 6 can also be used. The piezoelectric sensor 6 is located on the tool side 12 or on the side of the tool holder 1.

[0085] In the measuring circuit 17 of Figure 8, a measuring capacitor 20 is connected in parallel to the piezoelectric sensor 6. The tool-side signal coil 71 of the signal transmission transformer 7 is connected in parallel to this parallel circuit consisting of the piezoelectric sensor 6 and the measuring capacitor 20. Opposite the tool-side signal coil 71, the machine-side signal coil 72 is arranged. The measuring circuit 17 thus uses inductive coupling for sensor signal transmission. The voltage measuring device 21 is connected in parallel to the machine-side signal coil 72 on the machine body side 12, or on the side of the stator 15 of the machine tool.

[0086] In the measuring circuit 17a of Figure 9, the tool-side signal coil 71 of the signal transmission transformer 7 is connected in parallel to the piezoelectric sensor 6. Opposite the tool-side signal coil 71, the machine-body-side signal coil 72 is arranged. The measuring circuit 17a thus also uses inductive coupling for sensor signal transmission. A measuring capacitor 20' is connected in parallel to the machine-body-side signal coil 72 on the machine body side 12, or on the side of the stator 15 of the machine tool. The voltage measuring device 21 is connected in parallel to the parallel circuit consisting of the machine-body-side signal coil 72 and the measuring capacitor 20'.

[0087] In the measuring circuit 17b of Figure 10, the tool-side signal coil 71 of the signal transmission transformer 7 is connected in parallel to the piezoelectric sensor 6. Opposite the tool-side signal coil 71, the machine-side signal coil 72 is arranged. The measuring circuit 17b thus also uses inductive coupling for sensor signal transmission. The measuring capacitor 20' is connected in parallel to the machine-side signal coil 72 on the machine body side 12, or on the side of the stator 15 of the machine tool. A variable resistor 22 is connected in parallel to the parallel circuit consisting of the machine-side signal coil 72 and the measuring capacitor 20'. The voltage measuring device 21 is connected in parallel to the resistor 22.

[0088] In the measuring circuit 17c of Figure 11, the tool-side signal coil 71 of the signal transmission transformer 7 is connected in parallel to the piezoelectric sensor 6. Opposite the tool-side signal coil 71, the machine-side signal coil 72 is arranged. The measuring circuit 17c thus also uses inductive coupling for sensor signal transmission. The measuring capacitor 20' is connected in parallel to the machine-side signal coil 72 on the machine body side 12, or on the side of the stator 15 of the machine tool. A variable resistor 22' is connected in series with the measuring capacitor 20'. The voltage measuring device 21 is connected in parallel with the series connection of the resistor 22' and the measuring capacitor 20'.

[0089] The measuring circuits 17b and 17c can also be combined, using both resistors 22, 22'.

[0090] In the measuring circuit 17d of Figure 12, a compensating capacitor 23 is connected in series with the piezoelectric sensor 6. The compensating capacitor 23 can also be disconnected from the measuring circuit, or a differently dimensioned compensating capacitor can be connected to the measuring circuit 17d instead of the compensating capacitor 23. The tool-side signal coil 71 of the signal transmission transformer 7 is connected in parallel with the series connection of the piezoelectric sensor 6 and the compensating capacitor 23. Opposite the tool-side signal coil 71, the machine-side signal coil 72 is arranged. The measuring circuit 17d thus also uses inductive coupling for sensor signal transmission. The measuring capacitor 20' is connected in parallel with the machine-side signal coil 72 on the machine body side 12, or on the side of the stator 15 of the machine tool.The voltage measuring device 21 is connected in parallel to the parallel circuit consisting of the machine body-side signal coil 72 and the measuring capacitor 20'.

[0091] In the measuring circuit 17e of Figure 13, the measuring capacitor 20 is connected in parallel to the piezoelectric sensor 6. A tool-side plate element 73 of a first signal transmission capacitor 7' is connected to a positive terminal of the piezoelectric sensor 6. A tool-side plate element 73' of a second signal transmission capacitor 7" is connected to a negative terminal of the piezoelectric sensor 6. Furthermore, in the measuring circuit 17e shown, a positive terminal of a voltage measuring device 21 is connected to a machine-side plate element 74 of the first signal transmission capacitor 7', and a negative terminal of the voltage measuring device 21 is connected to a machine-side plate element 74' of the second signal transmission capacitor 7'.The first signal transmission capacitor 7' has plate elements 73, 74 arranged opposite each other, while the second signal transmission capacitor 7" has plate elements 73', 74' arranged opposite each other. Plate elements 73, 73' are located on the tool side 12, i.e., on the side of the rotor 16 of the machine tool, while plate elements 74, 74' are located on the machine body side 11, i.e., on the side of the stator 15 of the machine tool. The measuring circuit 17e uses capacitive coupling for sensor signal transmission via the signal transmission capacitors 7', 7".

[0092] Figure 14 schematically shows a tool holder 1 with a stator 15 designed as a solid ring according to an embodiment of the machine tool according to the invention in a perspective side view. The stator 15 includes the primary drive coil 51 of the drive transformer 5 and the machine-side signal coil 72 of the signal transmission device 7. The stator 15 is rigidly connected to the machine body side 11 by means of fixing elements 19. The tool holder 1 is arranged opposite the stator 15. The tool holder 1 carries the secondary drive coil 52 of the drive transformer 5, the tool-side signal coil 72 of the signal transmission device 7, and the ultrasonic unit. In the illustration shown, the stator 15 is fixedly and removablely attached to the machine tool, but it can also be pivotable or connected to the tool holder 1 via rolling bearings and thus be replaceable.

[0093] The tool holder 1 is connected to the machine body side 11 of a machine tool using the machine interface 2. A tool (not shown here) is inserted into the chuck 31.

[0094] Figure 15 schematically shows a tool holder T with a stator 15' designed as a partial ring according to an embodiment of the machine tool according to the invention in a perspective side view. The stator 15' includes the primary drive coil 51 of the drive transformer 5 and the machine-side signal coil 72 of the signal transmission device 7. The stator 15' is rigidly connected to the machine body side 11 by means of fixing elements 19. The tool holder T is arranged opposite the stator 15'. The tool holder T carries the secondary drive coil 52 of the drive transformer 5, the tool-side signal coil 72 of the signal transmission device 7, and the ultrasonic transducer 4.

[0095] The tool holder T is connected to the machine body side 11 of a machine tool using the machine interface 2. A tool (not shown here) is inserted into the chuck 31.

Claims

Patent claims 1. Machine tool comprising a machine body and a tool operable by a motor of the machine tool, wherein an ultrasonic transducer (4) having a stack arrangement of piezoelectric actuators is arranged on a tool side (12) of the machine tool; the machine tool has a drive primary coil (51) arranged on the machine body side and connected to an AC signal supply device and a drive secondary coil (52) arranged on the tool side, separated from the drive primary coil (51) by a first air gap (53) and connected to the ultrasonic transducer (4) for supplying the ultrasonic transducer (4) with an energy signal; the machine tool has a sensor device comprising at least one piezoelectric sensor (6) arranged on or in a tool holder (1, 1') of the machine tool; and the sensor device comprising a signal transmission element (71, 72;73, 73', 74, 74') with a signal transmission device (7, 7') located between the first air gap (53) and having a second air gap (75) spaced apart from the first air gap (53) for contactless transmission of a sensor signal from the sensor device to a signal acquisition device on the machine body, characterized in that the signal acquisition device is a voltage measuring device (21); wherein the at least one piezoelectric sensor (6) is integrated into a measuring circuit (17, 17a, 17b, 17c, 17d, 17e) which has the signal transmission device (7, 7') and at least one measuring capacitor (20, 20') connected on the tool side (12) of the machine tool in parallel to the at least one piezoelectric sensor (6) and / or on the machine body side (11) of the machine tool in parallel to the voltage measuring device (21).

2. Machine tool according to claim 1, characterized in that the at least one piezoelectric sensor (6) is arranged so close to the piezoelectric actuators of the ultrasonic transducer (4) that the sensor signal of the at least one piezoelectric sensor (6) has the same frequency as the energy signal provided to the ultrasonic transducer (4).

3. Machine tool according to claim 1 or 2, characterized in that the signal transmission elements comprise a tool-side signal coil (71) and a machine body-side signal coil (72) of a signal transmission transformer.

4. Machine tool according to claim 3, characterized in that the tool-side signal coil (71) is a solid ring arranged concentrically to a longitudinal axis (A) of the machine tool and the machine body-side signal coil (72) is a solid ring or partial ring arranged concentrically to a longitudinal axis (A) of the machine tool.

5. Machine tool according to claim 3 or 4, characterized in that both the tool-side signal coil (71) and the machine body-side signal coil (72) each have at least one ferrite core on which at least one winding is located.

6. Machine tool according to claim 1 or 2, characterized in that the signal transmission elements comprise tool-side plate elements (73, 73') and machine-side plate elements (74, 74') of a signal transmission capacitor device.

7. Machine tool according to one of the preceding claims, characterized in that an electrically and / or magnetically shielding material is arranged between the drive transformer (5) and the signal transmission device (7, 7').

8. Machine tool according to claim 4, characterized in that the signal transmission elements (73, 73', 74, 74') form the measuring capacitor (20, 20').

9. Machine tool according to one of the preceding claims, characterized in that at least one fixed or adjustable resistor (22, 22') is connected in parallel to the voltage measuring device (21) and / or in series to the measuring capacitor (20, 20').

10. Machine tool according to one of the preceding claims, characterized in that the measuring circuit (17d) has a compensating capacitor (23) which can be switched in series with the at least one piezoelectric sensor (6).

11. Machine tool according to one of the preceding claims, characterized in that the drive transformer (5) is arranged radially and / or axially and / or angularly offset to the signal transmission device (7, 7').

12. Machine tool according to one of the preceding claims, characterized in that the drive secondary coil (52) and the tool-side signal transmission element (71 , 73, 73') are arranged in one and the same rotor housing (82, 82', 82", 82'", 82"").

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