Torque measurement using wireless clock transmission

Abstract

The present invention relates to a sensor device (16), which includes a fixed unit (160) comprising an inductor (162) and a control device (U1) configured to apply a clock to the inductor (162), and a movable unit (161) which is movably mounted relative to the fixed unit (160) and comprises a control device (U3), an inductor (163), and a sensor element (164). The control device (U3) of the movable unit (161) is configured to read pulses by inductive coupling of the inductors (162, 163) and to receive a measurement signal from the sensor element (164).

Description

Technical Field

[0001] The proposed solution relates in particular to a sensor device and a method for determining a measurement signal.

Background Art

[0002] Drive systems for electric bicycles (e.g. e-bikes or pedelecs) are widely known and these comprise at least one electric motor to generate additional drive torque by external power and provide auxiliary power in addition to the driving force by muscle power.

[0003] In practice, it is common to set the auxiliary power and its level according to the rider's preference. The setting according to the rider's preference is determined by measuring the torque currently applied to the bottom bracket shaft of the drive system by muscle power. The harder the rider of the electric bicycle pedals on the pedal connected to the bottom bracket shaft, the higher the auxiliary power selected for acceleration by motor assistance becomes. A torque sensor attached to the bottom bracket shaft is usually used to measure the torque actually applied by muscle power. Thereby, it becomes possible to directly measure the torque actually applied to the bottom bracket shaft, which can be realized by, for example, a method based on the inverse magnetostrictive effect or a method using at least one strain gauge.

[0004] However, measuring the actually applied torque using a torque sensor is usually relatively complex and costly. This also applies to other types of sensor devices with moving parts.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The proposed solution aims to enable measurement by a sensor device with a simple configuration.

[0006] This object is achieved by the subject matter having the features of claim 1.

[0007] The sensor device includes a fixed unit comprising an inductance and a control device configured to apply a clock to the inductance, and a movable unit movably mounted to the fixed unit and comprising a control device, an inductance, and a sensor element. The control device of the movable unit is configured to read the clock applied to the inductance of the fixed unit via inductive coupling between the inductances through the inductance of the movable unit and to receive a measurement signal from the sensor element.

[0008] This is based on the recognition that the functions of a movable unit require a clock periodically, and that components that generate such a clock are usually relatively expensive to manufacture, complex to produce, and require installation space. By using the sensor device described above, it is possible to supply a high-precision clock to the control device of the movable unit with minimal effort and relatively low manufacturing costs, even though the two units of the sensor device are relatively movable. The movable unit does not require its own clock generator. Inductive coupling makes it possible to transmit the clock wirelessly.

[0009] For example, the movable unit is rotatably mounted relative to the fixed unit. In this way, the movable unit can be directly mounted to, for example, an axis, which enables particularly high-precision measurements.

[0010] The measurement signal is based, for example, on the torque acting on the sensor element and / or on components (particularly fixedly) connected to the sensor element. The sensor device may be configured in the form of a torque sensor for measuring torque. In this way, it becomes possible to measure, for example, the torque applied to the pedal shaft with high precision.

[0011] The control unit of the movable unit can receive the power supply voltage through inductive coupling of inductances. In this way, the movable unit can receive both the clock and the power supply voltage through inductive coupling between the same inductances, thereby allowing the inductance to perform a dual function. In this way, the structure can be further simplified.

[0012] For example, the stationary unit includes a clock generator (which may be in the form of a crystal oscillator). The control unit of the stationary unit can determine the clock using the signal from the clock generator. This enables high-precision measurement processing. Alternatively, the stationary unit may be configured to receive a clock from an external device.

[0013] The control device of the stationary unit is configured to periodically open and close a switch, particularly in the form of a semiconductor component, thereby allowing a clock signal to be applied to the inductance of the stationary unit. This makes it possible to transmit the clock signal inductively in a particularly simple manner.

[0014] The control device for the movable unit is electrically connected to the inductance of the movable unit, for example, via a resistor. In this way, the current can be limited while simultaneously allowing for high-precision reading of the clock in a simple manner.

[0015] Selectively, the control device of the movable unit may be configured to encode the measurement signal of the sensor element using the readout clock. Furthermore, the control device of the movable unit may be configured to apply the encoded measurement signal to the inductance of the movable unit. The inductance allows for the transmission of the clock in one direction and the transmission of the encoded measurement signal in the other direction.

[0016] The control device of the fixed unit may be configured to read out the encoded measurement signal applied to the inductance of the movable unit by inductive coupling between inductances in the inductance of the fixed unit. The control device of the fixed unit may be configured to output a control signal for controlling the drive motor based on the read-out encoded measurement signal. In this way, for example, torque-dependent drive control can be realized in a simple manner.

[0017] The control device for the movable unit may be configured to read the clock by detecting the zero-crossing of the voltage induced in the inductance of the movable unit. This makes it possible to read the clock simply and with high accuracy.

[0018] The control devices for the movable units and / or the fixed units may be selectively configured as integrated circuit components, respectively. This allows for the use of standard components and particularly reduces the installation space.

[0019] For example, the sensor element includes a strain gauge. This enables robust and highly accurate measurements, especially in small installation spaces.

[0020] In one embodiment, a drive system is provided that includes a sensor device according to any embodiment described herein. The drive system may optionally include, for example, an axis to which a movable unit is attached. For advantages, please refer to the above description of the sensor device.

[0021] The drive system may include a drive motor controlled by a control signal provided by a sensor device. This allows for a simple method of implementing sensor-controlled driving.

[0022] For example, the shaft can be driven by a drive motor and / or a pedal.

[0023] According to one aspect, there is provided an electric bicycle including a sensor device according to any of the embodiments described herein and / or a drive system according to any of the embodiments described herein. Regarding the advantages, please refer to the description of the sensor device mentioned above again.

[0024] According to one aspect, there is provided a method for determining a measurement signal. The method includes the following steps. A step of applying a clock to the inductance of the fixed unit by a control device of the fixed unit of the sensor device (in particular according to any of the embodiments described herein), and a step of reading the clock applied to the inductance of the fixed unit through an inductive coupling between the inductance of the fixed unit and the inductance of the movable unit by a control device of the movable unit of the sensor device that is movably attached to the fixed unit, and a step of receiving a measurement signal from the sensor element by the control device of the movable unit. Regarding the advantages, please refer to the description of the sensor device mentioned above again.

[0025] The method may further optionally include encoding the received measurement signal by the control device of the movable unit using the read clock.

[0026] Furthermore, the method may include the following steps. A step of applying the measurement signal encoded in the inductance of the movable unit by the control device of the movable unit, and a step of reading the encoded measurement signal applied to the inductance of the movable unit through an inductive coupling between the inductance of the movable unit and the inductance of the fixed unit by the control device of the fixed unit, and a step of controlling the drive motor based on the read encoded measurement signal.

Brief Description of the Drawings

[0027] The accompanying drawings show examples of possible embodiments of the proposed solution.

[0028] [Figure 1] It is a diagram schematically showing an electric bicycle including a drive system including a drive motor. [Figure 2] FIG. 1 shows a movable unit relative to a fixed unit of a sensor device of a drive system of an electric bicycle, and shows a state in which the movable unit is attached to a shaft of the drive system and the fixed unit is attached to a frame of the electric bicycle. [Figure 3] FIG. 2 is a circuit diagram of the fixed unit and the movable unit shown in FIG. 2. [Figure 4] FIG. 8 is a diagram showing a method for determining a measurement signal.

[0029] FIG. 1 is a diagram showing an embodiment of a proposed electric bicycle 1 including a front wheel 10 and a rear wheel 11. The rear wheel 11 can be driven with the assistance of an electric motor via at least one drive motor 13 of the drive system A of the electric bicycle 1. Auxiliary power is transmitted to the rear wheel 11 via a power transmission member (e.g., a chain 12, or alternatively or additionally a belt) via the drive motor 13. The rear wheel 11 is rotatably attached to the frame 18 of the electric bicycle 1.

[0030] The auxiliary power by the drive motor 13 of the electric bicycle 1 is provided in addition to the driving force applied by the rider's muscular force via the pedal 17 of the electric bicycle 1. This pedal 17 is connected to a shaft 14 that takes the form of a bottom bracket shaft in this specification. The electronic control unit 15 of the drive system A controls the auxiliary power provided by the drive motor 13 and its level. The provided auxiliary power may be configured to depend on the torque applied by the rider of the electric bicycle 1 to the shaft 14. The battery of the electric bicycle (in the form of a storage battery in this example) supplies energy for operating the drive system A.

[0031] To measure the torque applied to the shaft 14 (e.g., the torque applied by the rider's muscular force), the drive system A includes at least one sensor device 16 in the form of a torque sensor. FIG. 2 is a diagram schematically showing an exemplary configuration of the sensor device 16 of the electric bicycle 1. In this embodiment, the sensor device 16 is provided on the shaft 14.

[0032] Figure 2 shows a portion of the shaft 14, and for simplification, the two pedals 17 rotatably mounted on the shaft 14 are not shown again here. The shaft 14 is functionally connected to a power transmission member (in this case, a chain 12). Therefore, a gear (not shown in Figure 2) is attached to the shaft 14 and meshes with the chain 12. Furthermore, a drive motor 13 is functionally connected to the shaft 14 and is configured to rotate the shaft 14 relative to the frame 18.

[0033] The sensor device 16 includes a fixed unit 160 and a movable unit 161. The movable unit 161 is movable relative to the fixed unit and, in this example, is rotatably mounted. In this embodiment, the fixed unit 160 is fixed to the frame 18 and is mounted on the frame 18. The movable unit 161 is mounted on the shaft 14.

[0034] The movable unit 161 includes, for example, at least one strain gauge 165. In the example in Figure 2, the strain gauge 165 is wrapped around the shaft 14, but it can be mounted in other ways. When torque is applied to the shaft 14, a twist occurs in the shaft 14, and this twist can be measured by the strain gauge 165.

[0035] The fixed unit 160 and the movable unit 161 each have disc-shaped portions that are arranged adjacent to each other.

[0036] Figure 3 is a diagram that further illustrates the details of the fixed unit 160 and the movable unit 161.

[0037] The fixed unit 160 includes an inductor 162 and a control device U1. The control device U1 is configured to apply a clock to the inductor 162.

[0038] The movable unit 161 includes a control device U3, an inductance 163, and a sensor element 164. The control device U3 of the movable unit 161 is configured to read the induced clock that is electrically applied to the inductance 162 of the fixed unit 160, which is induced in the inductance 163 of the movable unit 161 by the inductive coupling of inductances 162 and 163.

[0039] Inductors 162 and 163 each take the form of an electric coil. Inductors 162 and 163 are arranged adjacent to each other, and the alternating current flowing through one inductor 162 or 163 induces an alternating voltage in the other. In this embodiment, inductors 162 and 163 are arranged in the disc-shaped portions of their respective units 160 and 161.

[0040] Furthermore, the control device U3 of the movable unit 161 is configured to receive measurement signals from the sensor element 164. In the illustrated example, the sensor element 164 includes a strain gauge 165.

[0041] The control device U1 of the fixed unit 160 is in the form of a microchip. The control device U1 of the fixed unit 160 is equipped with an integrated electronic circuit. The control device U1 requires a clock to operate. This clock is provided (with high precision) by the clock generator Q1 of the fixed unit 160. In this embodiment, the clock generator Q1 includes a crystal oscillator. The clock generator Q1 has two electrical terminals. Both electrical terminals of the clock generator Q1 are electrically connected to the ground GND1 of the fixed unit 160 via capacitors C1 and C2, respectively. Furthermore, both terminals of the clock generator Q1 are electrically connected to the control device U1 of the fixed unit 160. The control device U1 of the fixed unit 160 includes a clock determination unit Q_OSC. The clock determination unit Q_OSC is configured to cause the clock generator Q1 to oscillate and read out its oscillation frequency.

[0042] The switch controller SWC of the control device U1 of the fixed unit 160 is configured to output a switching signal SWD based on the read oscillation frequency. The switching signal SWD is a logic signal that switches between the states of "1" and "0" in the period already described in this embodiment. This clock is based on the read oscillation frequency. The clock may correspond to the oscillation frequency, or, for example, to a multiple thereof, or vice versa. Since the clock generator outputs an accurate signal, the clock also has high temporal accuracy.

[0043] The switching signal SWD is applied to the switch S1 of the fixed unit 160. In this embodiment, the switch S1 is a semiconductor component, specifically a transistor. The first terminal of the switch S1 is electrically connected to the ground GND1 of the fixed unit 160. The second terminal of the switch S1 is connected to the power supply voltage VCC1 of the fixed unit 160 via the inductance 162 of the fixed unit 160 and another capacitor C3. The power supply voltage VCC1 of the fixed unit 160 is supplied by the battery of the electric bicycle 1. The capacitor C3 and the inductance 162 form a resonant circuit. When the switch is closed, i.e., the first and second terminals of the switch S1 are electrically connected, current flows (from the terminal of the power supply voltage VCC1) through the inductance 162 (to ground GND1). By periodically opening and closing the switch S1, a time-varying current flows through the inductance 162 of the fixed unit 160, which induces an AC voltage in the inductance 163 of the movable unit 161. This induced AC voltage is based on the time pattern of the switching operation of switch S1 of the fixed unit 160.

[0044] The frequency of this AC voltage is read by the control device U3 of the movable unit 161. Therefore, the control device U3 of the movable unit 161 is electrically connected to the inductance 163 of the movable unit 161 via resistor R1, thereby receiving the signal Z_DET corresponding to the induced AC voltage. The encoding element ENC of the control device U3 of the movable unit 161 receives the signal Z_DET and reads the clock transmitted by the fixed unit 160 from it. To do this, the encoding element ENC counts the zero crossings of the signal Z_DET. Because the control device U3 processes logic signals, the encoding element ENC receives only the positive half-waves of the signal Z_DET. Therefore, the electrical connection between the encoding element ENC and resistor R1 is connected to two diodes D2 and D3, as will be described later.

[0045] Capacitor C4 of the movable unit 161 is connected in parallel with inductor 163 of the movable unit 161. Diode D1 is connected between inductor 163 and capacitor C4. Diode D1 allows current to flow from the first terminal to the second terminal. In this case, the current flows from inductor 163 to capacitor C4. Diode D1 and capacitor C4 form a rectifier, specifically a half-wave rectifier. Voltage regulator U2 is connected to the second terminal of diode D1. Voltage regulator U2 controls the input voltage to a predetermined maximum value and outputs the limited voltage as the power supply voltage VCC2 of the movable unit 161. Voltage regulator U2 is also connected to the ground GND2 of the movable unit 161. Inductor 163 and capacitor C4 are also each connected to the ground GND2.

[0046] The Z_DET signal line is connected to the power supply voltage VCC2 via diode D3. This diode allows current to flow in the direction of the voltage regulator U2. A second diode D2 connects ground GND2 to the signal line Z_DET and allows current to flow in the direction of the signal line Z_DET. Diodes D2 and D3 act as protection diodes to protect the encoding element ENC from the negative half-wave of the signal Z_DET.

[0047] The encoding element ENC further receives measurement signals from the sensor element 164. These measurement signals indicate the applied torque. The encoding element ENC encodes these measurement signals in time. For example, lower frequencies correspond to low torque, and higher frequencies correspond to high torque (or vice versa). The encoding element ENC outputs the time-encoded measurement signals to the switch S2 of the movable unit. In this embodiment, the switch S2 is a semiconductor component, specifically a transistor. The switch S2 is connected in parallel with the inductance 163. Closing the switch S2 increases the load, resulting in a voltage deviation at the inductance 162 of the fixed unit 160. The two inductors 162 and 163 constitute a transformer. In the illustrated example, the inductors 162 and 163 have the same number of turns.

[0048] The signal conditioning element CON of the fixed unit 160 is electrically connected to the inductor 162 of the fixed unit 160. Specifically, it is connected to the terminal of the inductor 162 which is connected to ground GND1 via switch S1. The signal conditioning element CON detects the received measurement signal TRQ_REC. The signal conditioning element CON scales the received measurement signal TRQ_REC to a predetermined voltage range. Furthermore, the signal conditioning element CON filters the received measurement signal TRQ_REC, specifically using a low-pass filter. This makes it possible to remove disturbances. The measurement signal thus generated and processed is output by the signal conditioning element CON to the decoding element DEC of the control device U1 of the fixed unit 160. The decoding element DEC decodes the received time-encoded measurement signal and determines the measured value (in this example, the torque measurement) based on it.

[0049] The control device U1 of the fixed unit 160 can control the drive motor 13 based on this measurement. The sensor device 16 may be part of the electronic control unit 15, or it may be connected to the electronic control unit 15 in communication.

[0050] To perform temporal encoding, the encoding element ENC requires a time reference. This time reference also needs to be known on the fixed unit 160 side in order to re-evaluate the measured value. For this reason, a crystal oscillator is usually connected to the clock determination unit Q_OSC of the movable unit 161, so that the control device U3 of the movable unit 161 can also generate a corresponding high-precision clock. However, such a crystal oscillator leads to increased costs and a more complex configuration. Therefore, such a clock generator can be omitted in the movable unit 161.

[0051] The control device U3 of the movable unit 161 further includes a built-in clock determination unit RC_OSC. However, the accuracy of this unit itself is insufficient, and it cannot encode the measurement signal in time. The control device U3 can correct the clock signal of the built-in clock determination unit RC_OSC based on the clock received from the fixed unit 160. Alternatively, the control device U3 may not use the (inaccurate) clock signal of the built-in clock determination unit RC_OSC at all in the temporal encoding of the measurement signal, and may simply count the clock pulses included in the signal Z_DET, for example. In this embodiment, the control device U3 is operated using the (inaccurate) clock signal of the built-in clock determination unit RC_OSC.

[0052] Therefore, the clock is transmitted from the fixed unit 160 to the movable unit 161 via inductors 162 and 163, and the encoded measurement signal is transmitted in the reverse direction. Furthermore, the movable unit 161 receives the power supply voltage VCC2 for operating the movable unit 161 via inductors 162 and 163.

[0053] Figure 3 does not show all the components of the fixed unit 160 and the movable unit 161 for illustrative purposes, and the fixed unit 160 and the movable unit 161 may further comprise other components.

[0054] The ground GND1 of the fixed unit 160 is electrically isolated from the ground GND2 of the movable unit 161. Resistor R1 protects against overcurrent.

[0055] Figure 4 shows a method for determining the measurement signal, specifically a method for determining the torque of an electric bicycle. This method is carried out, for example, by the sensor device 16 described above, and includes the following steps.

[0056] Step S1: The control device U1 of the fixed unit 160 of the sensor device 16 applies a clock to the inductance 162 of the fixed unit 160.

[0057] Step S2: The control device U3 of the movable unit 161 of the sensor device 16, which is movably attached to the fixed unit 160, reads the clock applied to the inductance 162 of the fixed unit 160 via the inductive coupling between the inductance 162 of the fixed unit 160 and the inductance 163 of the movable unit 161.

[0058] Step S3: The control device U3 of the movable unit 161 receives a measurement signal from the sensor element 164. Step S3 may be performed before or after steps S1 and / or S2.

[0059] Step S4: The control device U3 of the movable unit 161 encodes the received measurement signal using the readout clock.

[0060] Step S5: The control device U3 of the movable unit 161 applies the encoded measurement signal to the inductance 163 of the movable unit 161.

[0061] Step S6: The control device U1 of the fixed unit 160 reads out the encoded measurement signal applied to the inductance 163 of the movable unit 161 via the inductive coupling between the inductance 163 of the movable unit 161 and the inductance 162 of the fixed unit 160.

[0062] Step S7: The drive motor 13 is controlled based on the read-out encoded measurement signal.

[0063] Steps S1 to S7 may be performed sequentially and iteratively. [Explanation of symbols]

[0064] 1. Electric bicycle 10 Front Wheel 11 Rear wheels 12 chain 13 Drive motor 14 axes 15 Electronic control unit 16 Sensor device 160 Fixed Unit 161 Movable Unit 162, 163 Inductance 164 sensor elements 165 Strain Gauges 17 pedals 18 frames A Drive System C1-C4 Capacitors CON signal conditioning element D1-D3 Diodes DEC decoding element ENC encoding element GND1, GND2 grounding Q1 Clock generator Q_OSC Clock Determination Unit RC_OSC Clock Determination Unit R1 Resistor S1, S2 Switch SWC Switch Controller SWD switching signal TRQ_REC Received measurement signal U1, U3 control devices U2 Voltage Regulator VCC1, VCC2 Power supply voltage Z_DET signal

Claims

1. Sensor device (16), A fixed unit (160) having an inductor (162) and a control device (U1) configured to apply a clock to the inductor (162), The system comprises a movable unit (161) which is movably mounted relative to the fixed unit (160) and has a control device (U3), an inductance (163), and a sensor element (164), The sensor device (16) is characterized in that the control device (U3) of the movable unit (161) is configured to read the clock applied to the inductance (162) of the fixed unit (160) by inductive coupling of the inductances (162, 163), and to receive a measurement signal from the sensor element (164).

2. The sensor device (16) according to claim 1, characterized in that the movable unit (161) is mounted so as to be rotatable relative to the fixed unit (160).

3. The sensor device (16) according to claim 1 or 2, characterized in that the sensor device (16) is configured in the form of a torque sensor for measuring torque, and the measurement signal is based on the torque acting on the sensor element (164) and / or a component connected to the sensor element (164).

4. A sensor device (16) according to any one of claims 1 to 3, characterized in that the control device (U3) of the movable unit (161) receives a power supply voltage (VCC2) through inductive coupling of the inductances (162, 163).

5. The fixed unit (160) includes a clock generator (Q1) in the form of a crystal oscillator. A sensor device (16) according to any one of claims 1 to 4, characterized in that the control device (U1) of the fixed unit (160) determines the clock based on a signal from the clock generator (Q1).

6. The sensor device (16) according to any one of claims 1 to 5, characterized in that the control device (U1) of the fixed unit (160) is configured to periodically open and close a switch (S1) in order to apply a clock to the inductance (162) of the fixed unit (160).

7. A sensor device (16) according to any one of claims 1 to 6, characterized in that the control device (U3) of the movable unit (161) is electrically connected to the inductance (163) of the movable unit (161) via a resistor (R1).

8. The sensor device (16) according to any one of claims 1 to 7, characterized in that the control device (U3) of the movable unit (161) is configured to encode the measurement signal of the sensor element (164) using the read-out clock, and to apply the encoded measurement signal to the inductance (163) of the movable unit (161).

9. The sensor device (16) according to claim 8, characterized in that the control device (U1) of the fixed unit (160) reads out the encoded measurement signal applied to the inductance (163) of the movable unit (161) by inductive coupling of the inductances (162, 163) in the inductance (162) of the fixed unit (160), and outputs a control signal for controlling the drive motor (13) based on the read-out encoded measurement signal.

10. The sensor device (16) according to any one of claims 1 to 9, characterized in that the control device (U3) of the movable unit (161) is configured to read a clock by detecting a zero crossing of the voltage induced in the inductance (163) of the movable unit (161).

11. A sensor device (16) according to any one of claims 1 to 10, characterized in that the control devices (U1, U3) of the movable unit (161) and / or the fixed unit (160) are configured in the form of integrated circuit components.

12. A sensor device (16) according to any one of claims 1 to 11, characterized in that the sensor element (164) includes a strain gauge.

13. A drive system (A) comprising a shaft (14) and a sensor device (16) as described in any one of claims 1 to 12, A drive system (A) characterized in that the movable unit (161) is fixed to the shaft (14).

14. The drive system (A) according to claim 13, characterized by comprising a drive motor (13) controlled by a control signal provided by the sensor device (16).

15. The drive system (A) according to claim 14, characterized in that the shaft (14) is drivable by the drive motor (13) and / or pedal (17).

16. An electric bicycle (1) characterized by comprising a sensor device (16) according to any one of claims 1 to 12 and / or a drive system (A) according to any one of claims 13 to 15.

17. A method for determining a measurement signal, Step (S1) of applying a clock to the inductance (162) of the fixed unit (160) of the sensor device (16) using the control device (U1) of the fixed unit (160), The control device (U3) of the movable unit (161) of the sensor device (16), which is movable relative to the fixed unit (160), reads a clock applied to the inductance (162) of the fixed unit (160) via inductive coupling between the inductance (162) of the fixed unit (160) and the inductance (163) of the movable unit (161) (S2), A method characterized by including the step (S3) of receiving a measurement signal from the sensor element (164) using the control device (U3) of the movable unit (161).

18. The method according to claim 17, further comprising the step (S4) of encoding the received measurement signal using the readout clock by the control device (U3) of the movable unit (161).

19. The control device (U3) of the movable unit (161) applies the encoded measurement signal to the inductance (163) of the movable unit (161) (S5), Step (S6) of reading the encoded measurement signal applied to the inductance (163) of the movable unit (161) via the inductive coupling between the inductance (163) of the movable unit (161) and the inductance (162) of the fixed unit (160) by the control device (U1) of the fixed unit (160), The method according to claim 18, further comprising the step (S7) of controlling a drive motor (13) based on the read-out encoded measurement signal.

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