CAPACITIVE TURN ANGLE MEASURING SYSTEM AND METHOD FOR ADAPTING A CAPACITIVE TURN ANGLE MEASURING SYSTEM

Description

[0001] The present invention relates to a capacitive rotary angle measuring system for detecting a rotary movement of a shaft, comprising a capacitive sensor unit with a transmitting electrode arrangement, a receiving electrode arrangement capacitively coupled to the transmitting electrode arrangement, and a rotatable coupling arrangement that can be mounted rotating with the shaft and configured to change the electrical capacitance between the receiving electrode arrangement and the transmitting electrode arrangement depending on the rotational position of the coupling arrangement, a carrier signal generator electrically connected to the transmitting electrode arrangement and configured to generate an electrical carrier signal with a carrier signal frequency defined by a carrier signal frequency value and to feed it into the transmitting electrode arrangement, and an evaluation unit electrically connected to the receiving electrode arrangement and configured toThe present invention relates to the method of adapting a capacitive angle measurement system. This method involves tapping an electrical measurement signal generated by feeding the carrier signal into the transmitting electrode arrangement of the capacitive sensor unit at the receiving electrode arrangement of the capacitive sensor unit and determining a current rotation angle measurement value by evaluating the measurement signal.

[0002] Such capacitive rotary angle measuring systems are well known from the prior art, for example from EP 2 733 468 A1, and are often also referred to as capacitive angle measuring devices, capacitive rotary angle sensors, or capacitive rotary encoders. These systems are used in particular for controlling and monitoring electric motors, especially servo motors, in machines, plants, or vehicles. Capacitive rotary angle measuring systems are characterized in particular by their contactless and therefore wear-free sensor technology, which enables a long service life.

[0003] Typically, such capacitive rotary angle measurement systems operate with a carrier signal frequency in the low kHz range, for example, a carrier signal frequency of 25 kHz. However, PWM signal generators, which generate a pulse-width modulated PWM signal with a defined PWM signal frequency, also typically operate in this frequency range. Such PWM signal generators are frequently used in electric motors for the electronic control of drive power. Typical PWM signal frequencies used in electric motors are, for example, 4 kHz or 8 kHz. A harmonic of these typical PWM signals is at 24 kHz, and thus close to the typical carrier signal frequency of 25 kHz.

[0004] When using typical capacitive rotary encoders to monitor electric motors, the PWM signal used to control the drive power, or rather its harmonics, can generate significant signal noise in the encoder's measurement signal. This signal noise can, in turn, significantly impair the accuracy and reliability of the capacitive rotary encoder.

[0005] From DE 10 2011 087 493 A1 a capacitive rotary angle measuring system of the type mentioned above is known, wherein a carrier signal frequency is varied when a reference signal deviates from a predetermined value.

[0006] From US 2019 / 0011291 A1, a capacitive sensor is known wherein a carrier frequency is modified when it is found that noise in a modulated signal is caused by interference approximately at the carrier frequency.

[0007] The task, therefore, is to create a reliable and versatile capacitive rotary angle measuring system.

[0008] This problem is solved by a capacitive rotary angle measuring system with the features of claim 1 and by a method for adapting a capacitive rotary angle measuring system with the features of claim 4.

[0009] According to the invention, a carrier signal adaptation unit is provided to which an interference frequency value is supplied during operation of the rotary angle measuring system. This unit is configured to adapt the carrier signal frequency value, which defines the carrier signal frequency, based on the interference frequency value. According to the invention, the interference frequency value is supplied to the carrier signal adaptation unit via a data storage device, which the carrier signal adaptation unit has access to and in which the interference frequency value is stored. The interference frequency value can, for example, be written to the data storage device during initialization before commissioning or during maintenance of the rotary angle measuring system, or it can be supplied via the data storage device in another way. Alternatively, automatic determination and supply of the interference frequency value via the data storage device during operation of the rotary angle measuring system can also be provided.

[0010] The interference frequency value can, for example, correspond to the PWM signal frequency of an electric motor that is to be monitored by the rotary angle measurement system. However, the interference frequency value can also refer to the frequency of any other interference signal typically present during the operation of the rotary angle measurement system. The carrier signal adaptation unit can also be provided with multiple interference frequency values ​​or even an interference frequency band, in which case the carrier signal adaptation unit is configured to adapt the carrier signal frequency value based on the multiple interference frequency values ​​or on the interference frequency band.

[0011] The carrier signal adaptation unit is specifically designed to adapt the carrier signal frequency value such that the carrier signal frequency value is different from the interference frequency value and preferably also different from all integer multiples of the interference frequency value. This minimizes the expected interference from a noise signal with a frequency determined by the interference frequency value. Furthermore, the carrier signal adaptation unit according to the invention enables easy adaptation of the rotary angle measurement system to different applications with different interference signals, thus creating a reliable and versatile capacitive rotary angle measurement system.

[0012] Preferably, an interference frequency detection unit is provided, which is configured to automatically determine an interference frequency value and provide the determined interference frequency value to the carrier signal adaptation unit. The interference frequency detection unit can, for example, be configured to detect potentially present interference radiation by means of an antenna device and to determine the interference frequency value based on the frequency of the detected interference radiation. The automatic determination of the interference frequency value enables automatic adaptation of the rotary angle measurement system to interference sources present at the installation site. The interference frequency detection unit according to the invention thus creates a particularly reliable and versatile rotary angle measurement system.

[0013] Rotary angle measurement systems typically have a data interface through which the current rotary angle measurement can be read by an external readout device, such as a motor controller of an electric motor. In electric motors, the motor controller and PWM signal generator often operate at a common clock rate, so the readout frequency used to retrieve the current rotary angle measurement from the rotary angle measurement system via the data interface during operation typically corresponds, at least approximately, to the PWM signal frequency of a PWM signal generated by the PWM signal generator.

[0014] In a preferred embodiment of the present invention, the interference frequency detection unit is therefore connected to the data interface and configured to detect the readout frequency at which the current rotation angle measurement can be read out via the data interface. The interference frequency detection unit is further configured to determine the interference frequency value based on the detected readout frequency, wherein the determined interference frequency value is preferably equal to the detected readout frequency. Alternatively, the interference frequency detection unit can also be configured to determine the interference frequency value using a mathematical formula or a stored characteristic map based on the detected readout frequency. The interference frequency detection unit is further configured to provide the determined interference frequency value to the carrier signal adaptation unit.According to the invention, the interference frequency detection unit is configured to write the determined interference frequency value to a data storage device, which the carrier signal adaptation unit can access. The interference frequency detection unit according to the invention enables automatic determination of the interference frequency value during operation of the rotary angle measurement system, thus creating a particularly reliable and versatile rotary angle measurement system.

[0015] The inventive method for adapting a capacitive rotary angle measuring system comprises the following process steps: Providing a disturbance frequency value by writing the disturbance frequency value to a data storage device, determining a carrier signal frequency value based on the disturbance frequency value, providing the carrier signal frequency value to a carrier signal generator, generating an electrical carrier signal with a carrier signal frequency specified by the carrier signal frequency value using the carrier signal generator, feeding the carrier signal into a transmitting electrode arrangement of a capacitive sensor unit, and evaluating an electrical measurement signal generated by feeding the carrier signal into the transmitting electrode arrangement at a receiving electrode arrangement of the capacitive sensor unit to determine a current rotation angle measurement value.

[0016] Preferably, an interference frequency detection unit is provided to determine the interference frequency value, enabling automatic determination of the interference frequency value during operation of the rotary angle measurement system. Alternatively, the interference frequency value can also be provided manually, for example, during initialization or maintenance of the rotary angle measurement system.

[0017] For determining the carrier signal frequency value, a carrier signal adaptation unit according to the invention, as described above, is preferably provided. This unit is configured to determine a carrier signal frequency value for which the expected interference from a disturbance signal with a disturbance frequency specified by the disturbance frequency value is as low as possible. In particular, the determined carrier signal frequency value is not equal to the disturbance frequency value and preferably also not equal to all integer multiples of the disturbance frequency value.

[0018] According to the invention, the determined carrier signal frequency value is provided to a carrier signal generator, which generates an electrical carrier signal with a carrier signal frequency defined by the determined carrier signal frequency value. The carrier signal frequency value is written to a data memory to which the carrier signal generator has access.

[0019] The carrier signal is fed into the transmitting electrode arrangement of a conventional capacitive sensor unit known from the prior art. This generates a measurement signal at the receiving electrode arrangement of the capacitive sensor unit, from which a current rotation angle measurement value is determined using evaluation arrangements / methods well known from the prior art.

[0020] The method according to the invention generates a carrier signal from the carrier signal generator, which has a carrier signal frequency that enables interference-free and reliable rotation angle measurement. Furthermore, the method according to the invention allows for easy adaptation of the rotation angle measurement system to different applications with different interference signals.

[0021] Advantageously, the inventive method for adapting a capacitive rotary angle measuring system further comprises the following method steps: Determining a readout frequency at which a current rotation angle measurement value is read out via a data interface of the rotation angle measurement system, and determining a disturbance frequency value based on the detected readout frequency.

[0022] Preferably, the determined interference frequency value is equal to the detected readout frequency. Alternatively, the interference frequency value can also be determined using a mathematical formula or a stored characteristic map based on the detected readout frequency. This enables, as described above, automatic determination of the interference frequency value during operation of the rotary angle measuring system.

[0023] Two exemplary embodiments of a capacitive rotary angle measuring system according to the invention for detecting a rotary movement of a shaft are described below with reference to the accompanying figures, wherein Figure 1 a schematic representation of a capacitive rotary angle measuring system according to the invention, which is arranged on a shaft driven by an electric motor, and Figure 2 a schematic representation of an alternative capacitive rotary angle measuring system according to the invention is shown.

[0024] Figure 1shows a capacitive rotary angle measuring system 10, which is arranged on a shaft 12 driven by an electric motor 14.

[0025] The capacitive rotary angle measuring system 10 comprises a capacitive sensor unit 16 with a transmitting electrode arrangement 18, a receiving electrode arrangement 20, and a rotatable coupling arrangement 22. The transmitting electrode arrangement 18 and the receiving electrode arrangement 20 are fixedly arranged, for example, on a housing or on a stator unit of the capacitive rotary angle measuring system 10, and each has one or more typically metallic electrodes. In the present embodiment, the coupling arrangement 22 is arranged on a rotor disk 24, which is fixedly attached to the shaft.The receiving electrode arrangement 20 is capacitively coupled to the transmitting electrode arrangement 18 via the coupling arrangement 22, wherein the capacitive sensor unit 16 - as is well known from the prior art - is designed such that the electrical capacitance measurable between the receiving electrode arrangement 20 and the transmitting electrode arrangement 18 changes depending on the current rotational position of the coupling arrangement 22.

[0026] The capacitive rotary angle measurement system 10 includes a data storage device 26 in which at least one disturbance frequency value SF, one carrier signal frequency value TF and one current rotary angle measurement value DW can be stored.

[0027] The capacitive rotary angle measuring system 10 comprises a carrier signal generator 28, which is electrically connected to the transmitting electrode arrangement 18 and has access to the data storage 26. The carrier signal generator 28 is configured to read the carrier signal frequency value TF from the data storage and to generate an electrical carrier signal TS with a carrier signal frequency specified by the carrier signal frequency value TF and to feed this signal into the transmitting electrode arrangement 18. By feeding the carrier signal TS into the transmitting electrode arrangement 18, a measurement signal MS is generated at the receiving electrode arrangement 20, which depends on the current rotational position of the coupling arrangement 22 – as is well known from the prior art.

[0028] The capacitive rotary angle measuring system 10 comprises an evaluation unit 30, which is electrically connected to the receiving electrode arrangement 20 and has access to the data storage 26. The evaluation unit 30 is configured to tap and evaluate the measurement signal MS generated at the receiving electrode arrangement 20. Specifically, the evaluation unit 30 is configured to determine the current rotary angle measurement value DW by evaluating the measurement signal MS. This value indicates the current rotational position of the coupling arrangement 22 and thus the current rotation angle of the shaft 12. The evaluation unit 30 is further configured to write the determined current rotary angle measurement value DW to the data storage 26.

[0029] The capacitive rotary angle measuring system 10 includes a data interface 32 that has access to the data memory 26. The data memory 26 can be read and written to externally via the data interface 32. In the present embodiment, the data interface 32 establishes a data connection to a motor controller 34 of the electric motor 14, via which the motor controller 34 periodically reads the current rotary angle measurement value DW.

[0030] In the present embodiment, the capacitive rotary angle measuring system 10 comprises an interference frequency detection unit 36 ​​which is connected to the data interface 32 and has access to the data memory 26. The interference frequency detection unit 36 ​​is configured to detect a readout frequency AF, with which the current rotary angle measurement value DW is read from the motor control 34 via the data interface 32. The interference frequency detection unit 36 ​​is further configured to determine the interference frequency value SF based on the readout frequency AF and to write the determined interference frequency value SF to the data memory 26. In the present embodiment, the determined interference frequency value SF specifies the readout frequency AF. However, it is also conceivable that the interference frequency value SF is determined from the readout frequency AF using a defined mathematical formula or a stored characteristic map.

[0031] However, a rotary angle measurement system that does not require a disturbance frequency detection unit is also conceivable. For example, the disturbance frequency value can be written to the data memory via the data interface by an external programming device during initialization or maintenance of the rotary angle measurement system.

[0032] The capacitive rotary angle measuring system 10 comprises a carrier signal adaptation unit 38, which has access to the data memory 26. The carrier signal adaptation unit 38 is configured to read the interference frequency value SF from the data memory 26 and to adapt the carrier signal frequency value TF stored in the data memory 26 based on the interference frequency value SF. Specifically, the carrier signal adaptation unit 38 is configured to determine a carrier signal frequency value TF that is not equal to the interference frequency value SF and not equal to any integer multiples of the interference frequency value SF, and to write the determined carrier signal frequency value TF to the data memory 26.

[0033] During operation, the current rotation angle measurement value DW is periodically read out by the motor control 34 via the data interface 32, whereby the interference frequency detection unit 36 ​​records the readout frequency AF.

[0034] The interference frequency determination unit 36 ​​determines the interference frequency value SF based on the readout frequency AF and writes the determined interference frequency value SF to the data memory 26.

[0035] The carrier signal adaptation unit 38 reads the determined interference frequency value SF from the data memory 26, determines the carrier signal frequency value TF based on the interference frequency value SF, and writes the determined carrier signal frequency value TF to the data memory 26.

[0036] The carrier signal generator 28 reads the determined carrier signal frequency value TF from the data storage 26, generates the carrier signal TS with the carrier signal frequency specified via the carrier signal frequency value TF and feeds the carrier signal TS into the transmitting electrode arrangement 18 of the capacitive sensor unit 16.

[0037] The evaluation unit 30 reads the carrier signal frequency value TF from the data memory and taps the measurement signal MS generated at the receiving electrode arrangement 20 of the capacitive sensor unit 16. The evaluation unit 30 evaluates the measurement signal MS based on the carrier signal frequency value TF to determine the current rotation angle measurement value DW and writes the determined current rotation angle measurement value DW to the data memory 26.

[0038] Figure 2 shows an alternative capacitive rotary angle measuring system 10' according to the invention.

[0039] The capacitive rotary angle measuring system 10' differs from the capacitive rotary angle measuring system 10 by an alternative interference frequency detection unit 36' with an antenna device 40.

[0040] The interference frequency detection unit 36' is designed to detect potentially present interference radiation via the antenna device 40 and to determine the frequency of the interference radiation.

[0041] The interference frequency detection unit 36' determines the interference frequency value SF based on the frequency of the detected interference radiation and writes this to the data storage unit 26. Reference symbol list

[0042] 10;10' Capacitive rotary angle measuring system 12 Shaft 14 Electric motor 16 Capacitive sensor unit 18 Transmitting electrode assembly 20 Receiving electrode assembly 22 Coupling assembly 24 Rotor disk 26 Data storage 28 Carrier signal generator 30 Evaluation unit 32 Data interface 34 Motor control 36;36' Interference frequency detection unit 38 Carrier signal adaptation unit 40 Antenna device AF Readout frequency DW Rotation angle measurement value MS Measurement signal SF Interference frequency value TFT Carrier signal frequency value TST Carrier signal

Claims

1. Capacitive rotary angle measurement system (10; 10') for detecting a rotary movement of a shaft (12), comprising: - a capacitive sensor unit (16) with • a transmitting electrode arrangement (18), • a receiving electrode arrangement (20) which is capacitively coupled to the transmitting electrode arrangement (18), and • a rotatable coupling arrangement (22) which can be mounted so as to rotate with the shaft (12) and which is configured to vary the electrical capacitance between the receiving electrode arrangement (20) and the transmitting electrode arrangement (18) as a function of the rotational position of the coupling arrangement (22), - a carrier signal generator (28) which is electrically connected to the transmitting electrode arrangement (18) and which is configured to generate and to feed into the transmitting electrode arrangement (18) an electrical carrier signal (TS) having a carrier signal frequency which is predetermined by a carrier signal frequency value (TF), and - an evaluation unit (30) which is electrically connected to the receiving electrode arrangement (20) and which is configured to detect an electrical measurement signal (MS) generated at the receiving electrode arrangement (20) by feeding the carrier signal (TS) into the transmitting electrode arrangement (18), and to determine a current rotary angle measurement value (DW) by evaluating the measurement signal (MS), characterized in that a carrier signal adaptation unit (38) is present, to which, during operation, an interference frequency value (SF) is provided via a data memory (26) and which is configured to adapt the carrier signal frequency value (TF) on the basis of the interference frequency value (SF).

2. Capacitive rotary angle measurement system (10; 10') according to claim 1, wherein an interference frequency determination unit (36; 36') is present which is configured to automatically determine an interference frequency value (SF) and to provide the determined interference frequency value (SF) to the carrier signal adaptation unit (38).

3. Capacitive rotary angle measurement system (10) according to claim 2, wherein - a data interface (32) is present via which the current rotary angle measurement value (DW) can be read out by an external read-out device (34), and - the interference frequency determination unit (36) is connected to the data interface (32) and is configured to • detect a read-out frequency (AF) at which the current rotary angle measurement value (DW) can be read out via the data interface (32), and • determine the interference frequency value (SF) on the basis of the detected read-out frequency (AF).

4. Method for adapting a capacitive rotary angle measurement system (10; 10'), comprising: - providing an interference frequency value (SF) by writing the interference frequency value (SF) into a data memory (26), - determining a carrier signal frequency value (TF) on the basis of the interference frequency value (SF), - providing the carrier signal frequency value (TF) to a carrier signal generator (28), - generating an electrical carrier signal (TS) having a carrier signal frequency predetermined by the carrier signal frequency value (TF) by means of the carrier signal generator (28), - feeding the carrier signal (TS) into a transmitting electrode arrangement (18) of a capacitive sensor unit (16), and - evaluating an electrical measurement signal (MS), which is generated at a receiving electrode arrangement (20) of the capacitive sensor unit (16) by feeding the carrier signal (TS) into the transmitting electrode arrangement (18), in order to determine a current rotary angle measurement value (DW).

5. Method for adapting a capacitive rotary angle measurement system (10) according to claim 4, further comprising: - detecting a read-out frequency (AF) at which a current rotary angle measurement value (DW) is read out via a data interface (32) of the rotary angle measurement system (10), and - determining an interference frequency value (SF) on the basis of the detected read-out frequency (AF).