Patent Description:
Industrial power tools such as nutrunners are widely used in the manufacturing industry, e.g. in vehicle manufacturing and the aerospace industry. Power tools of this type typically have a tool head which interacts with the work piece and a main body which is held by the user when operating the power tool. The main body may alternatively form part of a robot.

Manufacturing processes usually require high precision control of the torque applied by the power tool. The power tools therefore typically comprise a torque transducer configured to measure the applied torque. The torque transducer may be provided in the tool head or the main body, or in both.

The torque transducer may for example comprise a strain gauge arranged on a rotating part in the power tool. Slip rings may be used for conveying the measurement signal by the strain gauge to stationary components. <CIT> discloses a power tool of this type. One potential drawback with this configuration is that the measurement signal may be subjected to noise as the slip ring degrades over time. <CIT> discloses a rotary tool using mechanical contactless inductive means to ensure the power supply and communication with the torque measurement means. The tool comprises two support rings, one for the stator and one for the rotor, made out of ferrite, one placed inside of the other, with an air gap in between, in the radial direction.

In view of the above, an object of the present disclosure is to provide a power tool which solves, or at least mitigates, the problems of the prior art.

There is hence provided a power tool comprising a housing, a stationary part, which is stationary relative to the housing, a rotatable part, which is rotatable about a rotation axis relative to the stationary part, and a rotary transformer comprising: a stator attached to the stationary part, the stator comprising a stator coil structure, a stator carrier and a stator screen layer, wherein the stator screen layer is arranged between the stator coil structure and the stator carrier, wherein the stator screen layer is a first ferrite tape; and a rotor attached to the rotatable part, the rotor comprising a rotor coil structure inductively coupled with the stator coil structure, wherein the rotor coil structure and the stator coil structure are arranged with an air gap between them in a direction along the rotation axis, a rotor carrier and a rotor screen layer, wherein the rotor screen layer is arranged between the rotor coil structure and the rotor carrier, wherein the rotor screen layer is a second ferrite tape, wherein the stationary part comprises stationary electronic circuitry connected to the stator coil structure and the rotatable part comprises rotating electronic circuitry connected to the rotor coil structure.

Data transfer and/or power transfer between the stator coil structure and the rotor coil structure may thereby be provided wirelessly. The risk of signal degradation over time may thus be reduced.

Further, the inventors have found that the durability of the stator and the rotor increases by arranging the air gap in the direction of the rotation axis instead of in the radial direction. Components, such as the ferrite tape, in the stator and the rotor may crack if the layers they are formed of are flexed or bent. By placing the rotor coil structure and the stator coil structure with the airgap along the rotation axis, the layers can be arranged in spaced apart radial planes without flexing or bending. This also facilitates the manufacturing process. In power tools, the available space for components is very limited. Screening layers may therefore have to be made very thin in order to fit in the tool. In general, hard ferrite cores traditionally used as screening layers in electronics are very porous and may easily crack if machined very thin. This is specifically a problem in power tools, which are exposed to vibrations and accidental drops on the floor during usage. A ferrite tape can be both thin and flexible with reduced risk of cracking if exposed to vibrations/hits.

The power tool may for example be a nutrunner.

The stator screen layer concentrates the magnetic flux and reduces magnetic losses.

The stator screen layer may be a first ferrite sheet, which may be the first ferrite tape.

The first ferrite tape may be especially sensitive and crack if bent. The configuration with the air gap in the direction of the rotation axis eliminates the risk of cracks, because the first ferrite tape can be arranged planar in a radial plane on the stationary part around the rotatable part.

The first ferrite sheet may for example have a relative permeability of at least <NUM>.

The rotor screen layer concentrates the magnetic flux and reduces magnetic losses.

The rotor screen layer may be a second ferrite sheet, which may be the second ferrite tape.

The second ferrite tape may be especially sensitive and crack if bent. The configuration with the air gap in the direction of the rotation axis eliminates the risk of cracks, because the second ferrite tape can be arranged planar in a radial plane offset from that of the first ferrite tape, around the rotatable part.

The second ferrite sheet may for example have a relative permeability of at least <NUM>.

According to one embodiment the stator is annular and receives the rotatable part, wherein the stator coil structure comprises a spiral coil extending with a plurality of turns spiralling radially outwards around the rotatable part.

According to one embodiment the stator coil structure forms part of a first flexible printed circuit board, PCB.

According to one embodiment the rotor is annular and extends around the rotatable part, wherein the rotor coil structure comprises a spiral coil extending with a plurality of turns spiralling radially outwards around the rotatable part.

According to one embodiment the rotor coil structure forms part of a second flexible PCB.

According to one embodiment each of the stator coil structure and the rotor coil structure has an inductance of at least <NUM>µH. The inductance may for example be at least <NUM>µH.

An inductance of at least <NUM>µH of each of the stator coil structure and the rotor coil structure improves data transfer between the stator and the rotor. However, in case the inductance is too high, the communications bandwidth will be reduced. The inductance may for example be smaller than <NUM>µH, such as smaller than <NUM>µH, such as smaller than <NUM>µH.

According to one embodiment the rotating electronic circuitry comprises a sensor and a modulator circuit, wherein the modulator circuit is configured to modulate a measurement signal received from the sensor to obtain a modulated measurement signal, and to provide the modulated measurement signal to the rotor coil structure to induce the modulated measurement signal in the stator coil structure.

The sensor may be a torque transducer, an angle sensor or a force measurement sensor.

According to one embodiment the stationary electronic circuitry comprises a demodulator circuit configured to demodulate the modulated measurement signal induced in the stator coil structure by the rotor coil structure.

According to one embodiment the stationary electronic circuitry comprises a power transfer circuit configured to generate a power signal and to energise the stator coil structure with the power signal to induce a power signal in the rotor coil structure for powering the rotating electronic circuity.

One embodiment comprises: a voltage sensor configured to measure a rectified voltage of the induced power signal in the rotor coil structure, wherein in case the rectified voltage measured by the voltage sensor is below a threshold value the modulator circuit is configured to generate a modulated voltage sensor measurement signal and feed it to the rotor coil structure to induce the modulated voltage sensor measurement signal in the stator coil structure, and control circuitry connected to the stator coil structure, wherein the control circuitry is configured to control the power transfer circuit to increase a signal strength of the power signal in response to receiving the voltage sensor measurement signal from the stator coil structure.

According to an embodiment, the stator coil structure is a single stator coil and wherein the rotor coil structure is a single rotor coil. This requires less space as compared to double stator and rotor coils, which facilitates fitting the arrangement in the very limited space in the tool.

All references to "a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc.", unless explicitly stated otherwise.

<FIG> shows an example of a power tool <NUM>. The power tool <NUM> may for example be a nutrunner.

The power tool <NUM> has a tool head <NUM> and a main body <NUM>. The tool head <NUM> is attached to the main body <NUM>. The tool head <NUM> is straight but could alternatively be angled.

The tool head <NUM> has an output shaft 3a. The output shaft 3a is configured to be rotatably driven and engage with a fastener such as a nut.

The power tool <NUM> has a housing <NUM>. The power tool <NUM> comprises an electric motor configured to drive the output shaft 3a. The electric motor is arranged in the housing <NUM>.

<FIG> shows the power tool <NUM> with a portion of its housing <NUM> removed to partly expose its interior.

The power tool <NUM> comprises a stationary part <NUM>. The stationary part <NUM> is stationary relative to the housing <NUM>.

The power tool <NUM> comprises a rotatable part <NUM>. The rotatable part is configured to be rotated about a rotational axis A relative to the stationary part <NUM>. The rotational axis A is an axis about which the electric motor provides rotation. The rotational axis A may be the rotor axis of the electric motor or it may be at an angle relative to the rotor axis, for example provided by a crown wheel.

The rotatable part <NUM> may comprise a gear train <NUM> rotatably connecting the output shaft 3a to the electric motor.

<FIG> shows a close-up view of a portion of the region indicating the stationary part <NUM> and the rotatable part <NUM> in <FIG>, with other components removed for reasons of clarity.

The power tool <NUM> comprises a rotary transformer <NUM>. The rotary transformer <NUM> comprises a stator 15a that is attached to the stationary part <NUM>. The stator 15a is fixedly arranged relative to the stationary part <NUM>.

The rotary transformer <NUM> comprises a rotor 15b attached to the rotatable part <NUM>. The rotatable part is fixedly arranged relative to the rotatable part <NUM>. The rotor 15b thus rotates together with the rotatable part <NUM>.

<FIG> shows the components around the rotary transformer <NUM> in more detail. The stationary part <NUM> comprises a stationary electronic circuitry <NUM> and the rotatable part <NUM> comprises rotating electronic circuitry <NUM>.

The stationary electronic circuitry <NUM> is configured to power the rotating electronic circuitry <NUM> via the rotary transformer <NUM>.

The stationary electronic circuitry <NUM> and the rotating electronic circuitry <NUM> are configured to communicate with each other via the rotary transformer <NUM>, as will be explained in more detail in the following.

<FIG> show various views of the rotary transformer <NUM>.

The stator 15a comprises a stator carrier 21a. The stator carrier 21a is annular and configured to receive the rotatable part <NUM> by means of its through-opening.

The stator carrier 21a may for example comprise metal such as stainless steel, or a polymeric material.

As better seen in <FIG>, the stator 15a comprises a stator screen layer 23a and a stator coil layer 25a.

The stator screen layer 23a may for example be a first ferrite sheet. The first ferrite sheet may for example be a first ferrite tape.

The stator coil layer 25a is provided with a stator coil structure 31a, shown in <FIG>. The stator coil structure 31a is in the example a single stator coil. The stator coil layer 25a may for example be formed by a first flexible or standard PCB. The stator coil structure 31a is a spiral coil extending with a plurality of turns spiralling radially outwards around the rotatable part <NUM>.

The stator screen layer 23a is arranged between the stator carrier 21a and the stator coil layer 25a. The stator screen layer 23a is thus arranged between the stator coil structure 31a and the stator carrier 21a.

The stator 15a comprises a stator connection 27a which electrically connects the stator coil structure 31a to the stationary electronic circuitry <NUM>.

The stator carrier 21a may be fixedly attached to the stationary part <NUM>.

The rotor 15b comprises a rotor carrier 21b. The rotor carrier 21b is annular and extends around the rotatable part <NUM>.

The rotor carrier 21b may for example comprise metal such as stainless steel, or a polymeric material.

The rotor 15b comprises a rotor screen layer 23b and a rotor coil layer 25b.

The rotor screen layer 23b may for example be a second ferrite sheet. The second ferrite sheet may for example be a second ferrite tape.

The rotor coil layer 25b is provided with a rotor coil structure 31b. The rotor coil structure 31b is in the example a single rotor coil. The rotor coil layer 25b may for example be formed by a second flexible or standard PCB. The rotor coil structure 31b is a spiral coil extending with a plurality of turns spiralling radially outwards around the rotatable part <NUM>.

The rotor screen layer 23b is arranged between the rotor carrier 21b and the rotor coil layer 25b. The rotor screen layer 23b is thus arranged between the rotor coil structure 31b and the rotor carrier 21b.

The rotor 15b comprises a rotor connection 27b which electrically connects the rotor coil structure 31b to the rotating electronic circuitry <NUM>.

The rotor carrier 21b may be fixedly attached to the rotatable part <NUM>.

The stator coil structure 31a and the rotor coil structure 31b are inductively coupled to each other.

The stator coil structure 21a and the rotor coil structure 31b are arranged with an airgap <NUM> between them. The airgap <NUM> is an axial airgap and thus defines a spacing between the stator coil structure 21a and the rotor coil structure 31b in a direction along the rotation axis A.

<FIG> schematically shows a circuit diagram of the rotary transformer <NUM>, the rotating electronic circuitry <NUM> and the stationary electronic circuitry <NUM>.

The rotating electronic circuitry <NUM> comprises a modulator circuit <NUM> and a sensor <NUM>.

The modulator circuit <NUM> is electrically connected to the rotor coil structure 31b.

The modulator circuit <NUM> is configured to send signals such as measurement signals from the rotating electronic circuitry <NUM> to the stationary electronic circuitry <NUM>.

The sensor <NUM> is electrically connected to the modulator circuit <NUM>.

The sensor <NUM> may for example be a torque transducer, an angle sensor or a force measurement sensor. The sensor <NUM> may thus, for example, be configured to measure a torque, an angle, or a force related to rotation of the rotatable part <NUM>.

The sensor <NUM> is configured to send measurement signals to the modulator circuit <NUM>. The modulator circuit <NUM> is configured to modulate the measurement signal received from the sensor <NUM> to obtain a modulated measurement signal. Further, the modulator circuit <NUM> is configured to feed the modulated measurement signal to the rotor coil structure 31b to induce the modulated measurement signal in the stator coil structure 31a.

The modulator circuit <NUM> may for example be configured to perform modulation using amplitude-shift keying (ASK) modulation. The ASK modulation may for example be on-off keying (OOK) modulation.

The stationary electronic circuitry <NUM> comprises a power transfer circuit <NUM> and a stator side-demodulator circuit <NUM>.

The demodulator circuit <NUM> is connected to the stator coil structure 31a and configured to demodulate the modulated measurement signal induced in the stator coil structure 31a by the rotor coil structure 31a, to recover the measurement signal.

The power transfer circuit <NUM> is configured to energise the stator coil structure 31a with a power signal to provide wireless power transfer to the rotating electronic circuitry <NUM> via the rotor coil structure 31b.

The power transfer circuit <NUM> may for example comprise switching circuit, such as a flyback converter, an H-bridge or a class-E amplifier. The switching circuit is configured to generate the power signal by switching a voltage, which when induced in the rotor coil structure 31b can drive the rotating electronic circuitry <NUM>.

The rotating electronic circuitry <NUM> may comprise a rectifier (not shown) configured to rectify the power signal induced in the rotor coil structure 31b by the stator coil structure 31a. The rectified voltage is used to power the rotating electronic circuitry <NUM>, such as the modulator circuit <NUM>.

The rotating electronic circuitry <NUM> may comprise a voltage sensor <NUM>. The voltage sensor <NUM> is configured to measure the rectified voltage of the rotor coil structure 31b induced by the stator coil structure 31a when the stator coil structure 31a is fed with the power signal. The rectified voltage provides a measure of the air gap <NUM>. A decrease in the rectified voltage is an indication that the air gap <NUM> has widened. This could for example potentially occur due to vibrations or due to an impact to the power tool <NUM>.

The modulator circuit <NUM> is configured to generate a modulated voltage sensor measurement signal based on measurement of the rectified voltage and feed it to the rotor coil structure 31b to induce the modulated voltage sensor measurement signal in the stator coil structure 31a if the rectified voltage measured by the voltage sensor <NUM> falls below a threshold value.

The stationary electronic circuitry <NUM> may comprise control circuitry <NUM> configured to control the power transfer circuit <NUM> to increase the signal strength of the power signal in response to receiving the voltage sensor measurement signal from the stator coil structure 31a. An increase in the air gap <NUM> may thereby be compensated for.

The same rotor coil structure 31b and stator coil structure 31a may for example be used for transmission of measurement signals by the sensor <NUM>, for voltage measurement signals by the voltage sensor <NUM>, and for power signals. The signals are preferably transmitted alternatingly and not simultaneously. Thus, for a first period of time, only the power signal may be transmitted, and for a second period of time only a measurement signal may be transmitted, followed by only the power signal and so on.

As an alternative to having a single stator coil, the stator coil structure may comprise two stator coils, one for the power signal transfer and one for receiving measurement signals. The rotor coil structure may in this case instead of a single rotor coil comprise two rotor coils, one for the power signal reception and one for the measurement signal transmission. In this case, the two stator coils may be provided in different stator coil layers or in the same stator coil layer. The two rotor coils may be provided in different rotor coil layers or in the same rotor coil layer.

According to another variation, the power tool may comprise two rotary transformers of the type disclosed herein, one handling power signal transmission and the other handling measurement signal transmission.

Claim 1:
A power tool (<NUM>) comprising:
- a housing (<NUM>),
- a stationary part (<NUM>), which is stationary relative to the housing (<NUM>),
- a rotatable part (<NUM>), which is rotatable about a rotation axis (A) relative to the stationary part (<NUM>), and
- a rotary transformer (<NUM>) comprising:
a stator (15a) attached to the stationary part (<NUM>), the stator (15a) comprising a stator coil structure (31a), a stator carrier (21a) and a stator screen layer (23a), wherein the stator screen layer (23a) is arranged between the stator coil structure (35a) and the stator carrier (21a), wherein the stator screen layer (23a) is a first ferrite tape, and
a rotor (15b) attached to the rotatable part (<NUM>), the rotor (15b) comprising a rotor coil structure (31b) inductively coupled with the stator coil structure (31a), a rotor carrier (21b) and a rotor screen layer (23b), wherein the rotor screen layer (23b) is arranged between the rotor coil structure (31b) and the rotor carrier (21b), wherein the rotor screen layer (23b) is a second ferrite tape,
wherein the rotor coil structure (31b) and the stator coil structure (31a) are arranged with an air gap (<NUM>) between them in a direction along the rotation axis (A),
wherein the stationary part (<NUM>) comprises stationary electronic circuitry (<NUM>) connected to the stator coil structure (31a) and the rotatable part (<NUM>) comprises rotating electronic circuitry (<NUM>) connected to the rotor coil structure (31b).