Inductive encoder gap self-adaptive compensation method and encoder system thereof

Abstract

The application discloses a kind of inductance encoder gap adaptive compensation method and its encoder system, it is related to encoder technical field, the method is by applying two specific frequency excitation signals to encoder excitation coil, utilize the different attenuation characteristics of coil to gap change in low frequency band and high frequency band, the amplitude ratio of two-way signal is extracted in real time.The amplitude ratio is used as the "fingerprint" feature of air gap change, for dynamic inversion air gap state, and accordingly reconstruct the virtual orthogonal signal that eliminates the nonlinear influence of air gap.The application breaks through the technical bottleneck that traditional single-frequency automatic gain control (AGC) can only compensate amplitude and cannot correct waveform distortion, realizes high-precision, linearized angle detection in wide gap range, and does not need additional mechanical sensors or complex mechanical structure.

Description

Technical Field

[0001] This invention relates to the field of encoder technology, and in particular to an automated adaptive compensation method for the gap of an inductive encoder and its encoder system. Background Technology

[0002] PCB-type inductive encoders, with their high reliability, strong resistance to oil and dust, and low-cost manufacturing advantages, have been widely used in key areas such as industrial automation servo systems, robot joints, and aerospace actuators. Their working principle is based on electromagnetic induction, calculating angles by detecting changes in the mutual inductance between the stator coil and the rotor. However, in practical engineering applications, the core performance indicator of inductive encoders—measurement accuracy—is highly susceptible to fluctuations in the axial clearance (hereinafter referred to as "air gap") between the stator and rotor.

[0003] According to electromagnetic field theory, the coupling magnetic field strength between coils follows the inverse square law, meaning the magnetic field strength is inversely proportional to the square of the distance. This implies that even a small change in the air gap can lead to a significant change in the coupled inductance and the amplitude of the induced signal. In actual operation, changes in the air gap are unavoidable: the accumulation of tolerances during initial assembly, axial movement during high-speed motor rotation, increased clearance due to bearing wear, and thermal expansion and contraction of materials caused by changes in ambient temperature all contribute to dynamic changes in the air gap. This dynamic change directly manifests as drastic fluctuations in the received signal amplitude, thereby introducing significant position measurement errors.

[0004] To address the air gap sensitivity issue, existing technologies typically employ the following measures: First, automatic gain control (AGC) circuits are used to attempt to stabilize the received signal amplitude at a constant level. However, AGC is essentially a linear amplifier, assuming the signal waveform is an ideal sine wave. In reality, when the air gap changes, the induced signal undergoes waveform distortion due to the nonlinearity of edge and saturation effects, generating higher harmonics. While AGC can adjust the fundamental amplitude, it cannot eliminate these harmonic distortions and may even introduce noise due to over-amplification, leading to decreased solution accuracy. Second, the driving voltage of the excitation signal is increased to improve the signal-to-noise ratio, but this is limited by the voltage withstand capability of power devices, and excessive excitation may cause coil heating, which in turn exacerbates thermal deformation. Third, strict control of mechanical assembly tolerances is implemented, using high-precision bearings and spacers, but this significantly increases manufacturing costs and assembly difficulty, and cannot address dynamic air gap changes during operation.

[0005] Therefore, there is an urgent need for a solution that can sense the air gap state in real time from the signal processing level, adaptively eliminate nonlinear amplitude fluctuations and waveform distortions caused by air gap changes, and does not rely on expensive mechanical structures. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an adaptive compensation method for the air gap of an inductive encoder and its encoder system, so as to solve the problems of decreased measurement accuracy due to changes in the air gap and the inability of traditional AGC to correct waveform distortion.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide an adaptive compensation method for the gap of an inductive encoder, comprising the following steps: A dual-frequency excitation signal is applied to the excitation coil of the inductive encoder. The dual-frequency excitation signal includes a first frequency component f1 and a second frequency component f2. The attenuation response characteristics of the receiving coil of the inductive encoder to changes in the air gap are different under the first frequency component f1 and the second frequency component f2. The received signal generated by the receiving coil is obtained, and the received signal includes a first received component corresponding to the first frequency component f1 and a second received component corresponding to the second frequency component f2; The first amplitude A1 of the first received component and the second amplitude A2 of the second received component are extracted from the received signal, and the amplitude ratio R characterizing the air gap state is calculated based on the first amplitude A1 and the second amplitude A2. Based on the amplitude ratio R, query the air gap and amplitude ratio mapping model to reconstruct a virtual orthogonal signal that eliminates the nonlinear effects of the air gap.

[0008] In one embodiment, the step of reconstructing the virtual orthogonal signal that eliminates the nonlinear effects of the air gap by querying the air gap-to-amplitude ratio mapping model based on the amplitude ratio R includes: Based on the amplitude ratio R, query the air gap and amplitude ratio mapping model to generate the air gap parameter δ; The correction coefficient K_gain is generated based on the air gap parameter δ; The original signal in the received signal is nonlinearly compensated according to the correction coefficient K_gain to obtain a virtual orthogonal signal of reconstructed sine and cosine signals.

[0009] In one embodiment, the amplitude ratio R = A1 / A2, where A1 and A2 are response functions of the air gap parameter δ; wherein A1(δ) = K1 / δ, A2(δ) = K2 / δ^α, K1 and K2 are correlation constants of the receiving coil, and α > 1.

[0010] In one embodiment, the virtual orthogonal signals of the reconstructed sine and cosine signals are: V'_sin = V_sin × K_gain, where V_sin is the original signal received by the receiving coil, and V'_sin is a virtual orthogonal signal of the sinusoidal signal; V'_cos = V_cos × K_gain, where V_cos is the original signal received by the receiving coil, and V'_cos is a virtual orthogonal signal of the cosine signal.

[0011] In one embodiment, after the step of reconstructing the virtual orthogonal signal that eliminates the influence of air gap nonlinearity by querying the air gap and amplitude ratio mapping model according to the amplitude ratio R, the step further includes the following steps: The arctangent function is used to calculate the angle of the compensated virtual orthogonal signal to obtain the calculated angle value θ. θ = arctan(V'_sin / V'_cos).

[0012] In one embodiment, the first amplitude A1 and the second amplitude A2 in the step of extracting the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal are obtained using a DPLL or FFT algorithm.

[0013] In one embodiment, the first frequency component f1 satisfies the following condition: L is the inductance of the excitation coil, and Cpar is the parasitic capacitance of the receiving coil.

[0014] In one embodiment, the second frequency component f2 satisfies the following condition: f2 ≥ 0.6 × f_res, where f_res is the self-resonant frequency of the excitation coil.

[0015] In one embodiment, after the step of using the arctangent function to calculate the angle of the compensated virtual orthogonal signal to obtain the calculated angle value θ, the following step is further included: If the calculated amplitude ratio R exceeds the preset range, it is determined that the receiving coil or the stator and mover are abnormally assembled, triggering an alarm signal.

[0016] In a second aspect, embodiments of the present invention provide an encoder system for implementing the inductive encoder gap adaptive compensation method as described in any of the above claims, comprising: The microcontroller unit is used to generate dual-frequency excitation signals and execute signal processing and angle calculation algorithms. A driving circuit, connected to the microcontroller unit and the excitation coil, is used to amplify the dual-frequency excitation signal and inject it into the excitation coil. An excitation coil, which is used to receive dual-frequency excitation signals and generate an excitation magnetic field; A receiving coil is used to sense changes in rotor position and output the received signal containing position information; An analog-to-digital converter, connected to the receiving coil and the microcontroller unit, is used to sample the received signal at high speed and convert it into a digital signal; The microcontroller unit is further configured to: demodulate the first amplitude A1 and the second amplitude A2 from the digital signal, calculate the amplitude ratio R, invert the air gap state parameter δ, and compensate the original sine / cosine signal to output the position angle value θ.

[0017] The MCU, acting as the microcontroller unit, is responsible for generating dual-frequency signals and executing the compensation algorithm; the drive circuit is responsible for power amplification; and the ADC is responsible for high-speed sampling. This system architecture makes full use of the existing hardware resources of the inductive encoder, eliminating the need for additional displacement sensors or complex mechanical adjustment mechanisms. While maintaining the advantages of low cost and high reliability, it endows the system with intelligent characteristics that adapt to changes in the environment through software algorithms, achieving a balance between hardware simplification and high-end performance.

[0018] Compared with the prior art, this application has the following advantages: Breaking through the technical bottleneck of AGC, unlike traditional AGC which can only adjust the amplitude, this invention accurately inverts the air gap state through the dual-frequency amplitude ratio, which can specifically compensate for nonlinear distortion and significantly improve the orthogonality and purity of the signal.

[0019] It achieves wide-range adaptability and utilizes frequency-dimensional feature decoupling, making the system highly sensitive to air gap changes. It can maintain high-precision measurement over a large air gap fluctuation range and reduce dependence on mechanical assembly accuracy.

[0020] It enhances environmental robustness. The amplitude ratio R is a relative quantity that can effectively offset the impact of common-mode interference such as power supply voltage fluctuations and temperature drift on the amplitude of a single frequency, thereby improving the long-term stability of the system under harsh operating conditions.

[0021] Without requiring additional hardware costs, it fully utilizes the inherent parasitic capacitance and skin effect characteristics of the PCB coil, eliminating the need for additional displacement sensors or complex mechanical adjustment mechanisms, thus maintaining the advantages of low cost and high reliability of inductive encoders.

[0022] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of the present invention more obvious and understandable, preferred embodiments are described in detail below. Attached Figure Description

[0023] Figure 1 This is a block diagram of the encoder system functional modules according to an embodiment of the present invention.

[0024] Figure 2This is the main flowchart of the adaptive compensation method for inductive encoder gap according to an embodiment of the present invention.

[0025] Figure 3 This is a sub-flowchart of the adaptive compensation method for inductive encoder gap according to an embodiment of the present invention.

[0026] Figure 4 The image shows the actual experimental results of the adaptive compensation method for inductive encoder gap according to an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures: The encoder system 100, microcontroller 101, drive circuit 102, excitation coil 103, receiving coil 104, and analog-to-digital converter 105 are included. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In this invention, terms such as "installed," "connected," "joined," and "fixed" should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0032] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] PCB-type inductive encoders, with their high reliability, strong resistance to oil and dust, and low-cost manufacturing advantages, have been widely used in key areas such as industrial automation servo systems, robot joints, and aerospace actuators. Their working principle is based on electromagnetic induction, calculating angles by detecting changes in the mutual inductance between the stator coil and the rotor. However, in practical engineering applications, the core performance indicator of inductive encoders—measurement accuracy—is highly susceptible to fluctuations in the axial clearance (hereinafter referred to as "air gap") between the stator and rotor.

[0034] According to electromagnetic field theory, the coupling magnetic field strength between coils follows the inverse square law, meaning the magnetic field strength is inversely proportional to the square of the distance. This implies that even a small change in the air gap can lead to a significant change in the coupled inductance and the amplitude of the induced signal. In actual operation, changes in the air gap are unavoidable: the accumulation of tolerances during initial assembly, axial movement during high-speed motor rotation, increased clearance due to bearing wear, and thermal expansion and contraction of materials caused by changes in ambient temperature all contribute to dynamic changes in the air gap. This dynamic change directly manifests as drastic fluctuations in the received signal amplitude, thereby introducing significant position measurement errors.

[0035] To address the air gap sensitivity issue, existing technologies typically employ the following measures: First, automatic gain control (AGC) circuits are used to attempt to stabilize the received signal amplitude at a constant level. However, AGC is essentially a linear amplifier, assuming the signal waveform is an ideal sine wave. In reality, when the air gap changes, the induced signal undergoes waveform distortion due to the nonlinearity of edge and saturation effects, generating higher harmonics. While AGC can adjust the fundamental amplitude, it cannot eliminate these harmonic distortions and may even introduce noise due to over-amplification, leading to decreased solution accuracy. Second, the driving voltage of the excitation signal is increased to improve the signal-to-noise ratio, but this is limited by the voltage withstand capability of power devices, and excessive excitation may cause coil heating, which in turn exacerbates thermal deformation. Third, strict control of mechanical assembly tolerances is implemented, using high-precision bearings and spacers, but this significantly increases manufacturing costs and assembly difficulty, and cannot address dynamic air gap changes during operation.

[0036] Therefore, there is an urgent need for a solution that can sense the air gap state in real time from the signal processing level, adaptively eliminate nonlinear amplitude fluctuations and waveform distortions caused by air gap changes, and does not rely on expensive mechanical structures.

[0037] Example 1 Please see Figures 1 to 4 In this embodiment, the adaptive compensation method for the gap of the inductive encoder includes the following steps: Step S100: Apply a dual-frequency excitation signal to the excitation coil of the inductive encoder. The dual-frequency excitation signal includes a first frequency component f1 and a second frequency component f2. The attenuation response characteristics of the receiving coil to the air gap change are different under the first frequency component f1 and the second frequency component f2. Specifically, the first frequency component f1 is a low-frequency signal and the second frequency component f2 is a high-frequency signal. The different attenuation characteristics of the receiving coil of the inductive encoder to the gap change under the high-frequency signal and the low-frequency signal provide compensation reference information.

[0038] Step S200: Obtain the received signal induced by the receiving coil. The received signal includes a first received component corresponding to the first frequency component f1 and a second received component corresponding to the second frequency component f2. In this step, a high-speed ADC is used to sample the received signal of the receiving coil. The first received component generated by the excitation of the first frequency component f1 and the second received component generated by the excitation of the second frequency component f2 are obtained from the sampled signal as intermediate data for subsequent adaptive compensation. Both the first received component and the second received component are sinusoidal or cosine periodic AC signals.

[0039] In the step of extracting the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal, the first amplitude A1 and the second amplitude A2 are respectively extracted using a digital phase-locked loop (DPLL) or fast Fourier transform (FFT) algorithm.

[0040] A digital phase-locked loop (DPLL) is a closed-loop control system that uses digital circuits to achieve phase synchronization. It includes a phase detector, a digital loop filter, and a digitally controlled oscillator.

[0041] A phase detector (PD) compares the phase difference between the input signal and the output signal of the local oscillator to generate a digitized phase error signal. A digital loop filter (LF) is used to filter and accumulate the phase error, remove high-frequency noise, and control the loop dynamic response (such as bandwidth and damping coefficient).

[0042] A digitally controlled oscillator (NCO) is used to adjust the frequency and phase of the output signal based on the filtered error signal, gradually synchronizing the output signal with the input signal. A digital phase-locked loop (DPLL) works by continuously detecting, filtering, and adjusting errors until the output signal is locked to the frequency and phase of the input signal, achieving stable tracking. DPLLs offer advantages such as high precision, strong anti-interference capabilities, and ease of integration, and are widely used in communications, clock recovery, and frequency synthesis.

[0043] The Fast Fourier Transform (FFT) is an efficient algorithm for computing the Discrete Fourier Transform (DFT). Its core principle is to use the periodicity and symmetry of the twitch factor to decompose the DFT of a long sequence into multiple short sequences, thereby significantly reducing the amount of computation.

[0044] The first frequency component f1 satisfies the following condition: L is the inductance of the excitation coil, and Cpar is the parasitic capacitance of the receiving coil. At this frequency f1, the impedance of the receiving coil is mainly inductive, and the signal amplitude decreases approximately linearly by 1 / δ as the air gap parameter δ increases.

[0045] In one embodiment, the second frequency component f2 satisfies the following condition: f2 ≥ 0.6 × f_res, where f_res is the self-resonant frequency of the excitation coil. At this frequency f2, due to the resonance effect of parasitic capacitance and inductance, the signal amplitude decays nonlinearly and rapidly with the increase of air gap parameter δ, and the slope of its decay curve is significantly different from that of the low-frequency component.

[0046] Step S300: Extract the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal, and calculate the amplitude ratio R that characterizes the air gap state based on the first amplitude A1 and the second amplitude A2; that is, extract the amplitude of the AC signal of each of the first received component and the second received component from the information extracted from the sampled signal, that is, the maximum value of the instantaneous voltage is the first amplitude A1 and the second amplitude A2.

[0047] Step S400: Query the air gap and amplitude ratio mapping model based on the amplitude ratio R to reconstruct a virtual orthogonal signal that eliminates the nonlinear effects of the air gap. Based on experimental values, a mapping data table between the amplitude ratio R and the air gap is pre-constructed. Different amplitude ratios R correspond to different stator and rotor rotational clearance values. Through experiments, the quantitative relationship between the amplitude ratio R and the clearance is formed into a complete mapping data correspondence table. This table includes the air gap parameter δ and its corresponding correction coefficient K_gain, which is used to directly call the corresponding air gap value after obtaining the amplitude ratio R in real time, thereby performing vibration elimination compensation.

[0048] The above signal processing principle is as follows: The dual-frequency excitation signal, formed by the superposition of the first frequency component f1 and the second frequency component f2 output by the microcontroller unit, is amplified by the drive circuit and injected into the excitation coil. The receiving coil generates an induced signal, which contains position information of the two frequency components. The high-speed ADC (analog-to-digital converter) samples the induced signal and demodulates the amplitude A1 and phase φ1 of the first frequency component signal, and the amplitude A2 and phase φ2 of the second frequency component signal, respectively, through a digital phase-locked loop (DPLL) or a fast Fourier transform (FFT).

[0049] The above scheme decouples the air gap information by utilizing the differentiated response in the frequency dimension, avoids the problem of common-mode interference on single-frequency amplitude, and achieves accurate perception of the air gap state.

[0050] Specifically, step S400, which involves querying the air gap and amplitude ratio mapping model based on the amplitude ratio R to reconstruct a virtual orthogonal signal that eliminates the nonlinear effects of the air gap, includes: Step S401: Query the air gap and amplitude ratio mapping model according to the amplitude ratio R to generate the air gap parameter δ; the air gap and amplitude ratio mapping model is also the mapping data table between the amplitude ratio R and the gap mentioned above. The air gap parameter δ can be directly obtained from the mapping data table obtained in advance. The relationship between the air gap parameter δ and the amplitude ratio R is determined, so the mapping data table between the two can be determined in advance through experiments.

[0051] Step S402: Generate the correction coefficient K_gain based on the air gap parameter δ; using a preset air gap to amplitude ratio R mapping model, retrieve the current air gap parameter δ in real time based on the calculated amplitude ratio R. Specifically, establish the mapping function between the amplitude ratio R and the correction coefficient K_gain through calibration experiments: K_gain = f_model(R) Where f_model(R) is a mapping function established through calibration experiments, which can be stored in the microcontroller in the form of a lookup table or polynomial fitting.

[0052] Step S403: Perform nonlinear compensation on the original signal in the received signal according to the correction coefficient K_gain to obtain a virtual orthogonal signal of the reconstructed sine and cosine signals.

[0053] This physical mechanism ensures a strict one-to-one monotonic relationship between the amplitude ratio R and the air gap parameter δ, laying a solid physical foundation for subsequent inversion compensation and effectively solving the technical problem of the amplitude-air gap relationship being easily affected by environmental interference and unstable at a single frequency. Preferably, the mapping model is established through factory calibration experiments and stored in non-volatile memory. By transforming the complex nonlinear inversion process into table lookup or simple polynomial operations, the complexity of online calculations is greatly reduced, meeting the real-time requirements of the encoder's high-frequency response. Simultaneously, the calibration model can cover individual coil differences and assembly tolerances, achieving personalized and precise compensation, eliminating consistency errors in mass production, and significantly improving product yield and long-term stability.

[0054] Furthermore, the amplitude ratio R = A1 / A2, where A1 and A2 are response functions of the air gap parameter δ; where A1(δ) = K1 / δ, A2(δ) = K2 / δ^α, K1 and K2 are correlation constants of the receiving coil, and α > 1. Therefore, the function of the amplitude ratio R can be expressed as: R(δ) = A1 / A2 = (K1 / K2) · δ^(α-1).

[0055] Specifically, the virtual orthogonal signals of the reconstructed sine and cosine signals are: V'_sin = V_sin × K_gain, where V_sin is the original signal received by the receiving coil, and V'_sin is a virtual orthogonal signal of the sinusoidal signal; V'_cos = V_cos × K_gain, where V_cos is the original signal received by the receiving coil, and V'_cos is a virtual orthogonal signal of the cosine signal.

[0056] Furthermore, for higher accuracy, the compensation process also includes dynamic suppression of the third harmonic based on the A1 and A2 ratios to further correct waveform distortion. Preferably, the third harmonic content is predicted using air gap state parameters to generate a reverse compensation signal. By introducing a high-order harmonic suppression mechanism, not only is the nonlinear variation of the fundamental amplitude compensated, but also the high-order harmonic distortion caused by magnetic circuit saturation and edge effects is actively eliminated. This allows the reconstructed virtual orthogonal signal to maintain extremely high sinusoidality even under extreme conditions such as very small air gaps or large eccentricities, reducing the periodic error of angle calculation to the sub-angular fraction level, thus meeting the stringent requirements for extreme stability in high-end equipment such as precision radar.

[0057] Example 2 In this second embodiment, the adaptive compensation method for the gap of the inductive encoder includes the following steps: Step S100: Apply a dual-frequency excitation signal to the excitation coil of the inductive encoder. The dual-frequency excitation signal includes a first frequency component f1 and a second frequency component f2. The attenuation response characteristics of the receiving coil to the air gap change are different under the first frequency component f1 and the second frequency component f2. Specifically, the first frequency component f1 is a low-frequency signal and the second frequency component f2 is a high-frequency signal. The different attenuation characteristics of the receiving coil of the inductive encoder to the gap change under the high-frequency signal and the low-frequency signal provide compensation reference information.

[0058] Step S200: Obtain the received signal induced by the receiving coil. The received signal includes a first received component corresponding to the first frequency component f1 and a second received component corresponding to the second frequency component f2. In this step, a high-speed ADC is used to sample the received signal of the receiving coil. The first received component generated by the excitation of the first frequency component f1 and the second received component generated by the excitation of the second frequency component f2 are obtained from the sampled signal as intermediate data for subsequent adaptive compensation. Both the first received component and the second received component are sinusoidal or cosine periodic AC signals.

[0059] In the step of extracting the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal, the first amplitude A1 and the second amplitude A2 are respectively extracted using a digital phase-locked loop (DPLL) or fast Fourier transform (FFT) algorithm.

[0060] A digital phase-locked loop (DPLL) is a closed-loop control system that uses digital circuits to achieve phase synchronization. It includes a phase detector, a digital loop filter, and a digitally controlled oscillator.

[0061] A phase detector (PD) compares the phase difference between the input signal and the output signal of the local oscillator to generate a digitized phase error signal. A digital loop filter (LF) is used to filter and accumulate the phase error, remove high-frequency noise, and control the loop dynamic response (such as bandwidth and damping coefficient).

[0062] A digitally controlled oscillator (NCO) is used to adjust the frequency and phase of the output signal based on the filtered error signal, gradually synchronizing the output signal with the input signal. A digital phase-locked loop (DPLL) works by continuously detecting, filtering, and adjusting errors until the output signal is locked to the frequency and phase of the input signal, achieving stable tracking. DPLLs offer advantages such as high precision, strong anti-interference capabilities, and ease of integration, and are widely used in communications, clock recovery, and frequency synthesis.

[0063] The Fast Fourier Transform (FFT) is an efficient algorithm for computing the Discrete Fourier Transform (DFT). Its core principle is to use the periodicity and symmetry of the twitch factor to decompose the DFT of a long sequence into multiple short sequences, thereby significantly reducing the amount of computation.

[0064] The first frequency component f1 satisfies the following condition: L is the inductance of the excitation coil, and Cpar is the parasitic capacitance of the receiving coil. At this frequency f1, the impedance of the receiving coil is mainly inductive, and the signal amplitude decreases approximately linearly by 1 / δ as the air gap parameter δ increases.

[0065] In one embodiment, the second frequency component f2 satisfies the following condition: f2 ≥ 0.6 × f_res, where f_res is the self-resonant frequency of the excitation coil. At this frequency f2, due to the resonance effect of parasitic capacitance and inductance, the signal amplitude decays nonlinearly and rapidly with the increase of air gap parameter δ, and the slope of its decay curve is significantly different from that of the low-frequency component.

[0066] Step S300: Extract the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal, and calculate the amplitude ratio R that characterizes the air gap state based on the first amplitude A1 and the second amplitude A2; that is, extract the amplitude of the AC signal of each of the first received component and the second received component from the information extracted from the sampled signal, that is, the maximum value of the instantaneous voltage is the first amplitude A1 and the second amplitude A2.

[0067] Step S400: Query the air gap and amplitude ratio mapping model based on the amplitude ratio R to reconstruct a virtual orthogonal signal that eliminates the nonlinear effects of the air gap. Based on experimental values, a mapping data table between the amplitude ratio R and the air gap is pre-constructed. Different amplitude ratios R correspond to different stator and rotor rotational clearance values. Through experiments, the quantitative relationship between the amplitude ratio R and the clearance is formed into a complete mapping data correspondence table. This table includes the air gap parameter δ and its corresponding correction coefficient K_gain, which is used to directly call the corresponding air gap value after obtaining the amplitude ratio R in real time, thereby performing vibration elimination compensation.

[0068] The above signal processing principle is as follows: The dual-frequency excitation signal, formed by the superposition of the first frequency component f1 and the second frequency component f2 output by the microcontroller unit, is amplified by the drive circuit and injected into the excitation coil. The receiving coil generates an induced signal, which contains position information of the two frequency components. The high-speed ADC (analog-to-digital converter) samples the induced signal and demodulates the amplitude A1 and phase φ1 of the first frequency component signal, and the amplitude A2 and phase φ2 of the second frequency component signal, respectively, through a digital phase-locked loop (DPLL) or a fast Fourier transform (FFT).

[0069] The above scheme decouples the air gap information by utilizing the differentiated response in the frequency dimension, avoids the problem of common-mode interference on single-frequency amplitude, and achieves accurate perception of the air gap state.

[0070] Step S500: Use the arctangent function to calculate the angle of the compensated virtual orthogonal signal to obtain the calculated angle value θ. θ = arctan(V'_sin / V'_cos). The calculated angle value θ obtained by solving the angle using virtual orthogonal signals can yield a high-precision position angle value.

[0071] Example 3 In this second embodiment, the adaptive compensation method for the gap of the inductive encoder includes the following steps: Step S100: Apply a dual-frequency excitation signal to the excitation coil of the inductive encoder. The dual-frequency excitation signal includes a first frequency component f1 and a second frequency component f2. The attenuation response characteristics of the receiving coil to the air gap change are different under the first frequency component f1 and the second frequency component f2. Specifically, the first frequency component f1 is a low-frequency signal and the second frequency component f2 is a high-frequency signal. The different attenuation characteristics of the receiving coil of the inductive encoder to the gap change under the high-frequency signal and the low-frequency signal provide compensation reference information.

[0072] Step S200: Obtain the received signal induced by the receiving coil. The received signal includes a first received component corresponding to the first frequency component f1 and a second received component corresponding to the second frequency component f2. In this step, a high-speed ADC is used to sample the received signal of the receiving coil. The first received component generated by the excitation of the first frequency component f1 and the second received component generated by the excitation of the second frequency component f2 are obtained from the sampled signal as intermediate data for subsequent adaptive compensation. Both the first received component and the second received component are sinusoidal or cosine periodic AC signals.

[0073] In the step of extracting the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal, the first amplitude A1 and the second amplitude A2 are respectively extracted using a digital phase-locked loop (DPLL) or fast Fourier transform (FFT) algorithm.

[0074] A digital phase-locked loop (DPLL) is a closed-loop control system that uses digital circuits to achieve phase synchronization. It includes a phase detector, a digital loop filter, and a digitally controlled oscillator.

[0075] A phase detector (PD) compares the phase difference between the input signal and the output signal of the local oscillator to generate a digitized phase error signal. A digital loop filter (LF) is used to filter and accumulate the phase error, remove high-frequency noise, and control the loop dynamic response (such as bandwidth and damping coefficient).

[0076] A digitally controlled oscillator (NCO) is used to adjust the frequency and phase of the output signal based on the filtered error signal, gradually synchronizing the output signal with the input signal. A digital phase-locked loop (DPLL) works by continuously detecting, filtering, and adjusting errors until the output signal is locked to the frequency and phase of the input signal, achieving stable tracking. DPLLs offer advantages such as high precision, strong anti-interference capabilities, and ease of integration, and are widely used in communications, clock recovery, and frequency synthesis.

[0077] The Fast Fourier Transform (FFT) is an efficient algorithm for computing the Discrete Fourier Transform (DFT). Its core principle is to use the periodicity and symmetry of the twitch factor to decompose the DFT of a long sequence into multiple short sequences, thereby significantly reducing the amount of computation.

[0078] The first frequency component f1 satisfies the following condition: L is the inductance of the excitation coil, and Cpar is the parasitic capacitance of the receiving coil. At this frequency f1, the impedance of the receiving coil is mainly inductive, and the signal amplitude decreases approximately linearly by 1 / δ as the air gap parameter δ increases.

[0079] In one embodiment, the second frequency component f2 satisfies the following condition: f2 ≥ 0.6 × f_res, where f_res is the self-resonant frequency of the excitation coil. At this frequency f2, due to the resonance effect of parasitic capacitance and inductance, the signal amplitude decays nonlinearly and rapidly with the increase of air gap parameter δ, and the slope of its decay curve is significantly different from that of the low-frequency component.

[0080] Step S300: Extract the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal, and calculate the amplitude ratio R that characterizes the air gap state based on the first amplitude A1 and the second amplitude A2; that is, extract the amplitude of the AC signal of each of the first received component and the second received component from the information extracted from the sampled signal, that is, the maximum value of the instantaneous voltage is the first amplitude A1 and the second amplitude A2.

[0081] Step S400: Query the air gap and amplitude ratio mapping model based on the amplitude ratio R to reconstruct a virtual orthogonal signal that eliminates the nonlinear effects of the air gap. Based on experimental values, a mapping data table between the amplitude ratio R and the air gap is pre-constructed. Different amplitude ratios R correspond to different stator and rotor rotational clearance values. Through experiments, the quantitative relationship between the amplitude ratio R and the clearance is formed into a complete mapping data correspondence table. This table includes the air gap parameter δ and its corresponding correction coefficient K_gain, which is used to directly call the corresponding air gap value after obtaining the amplitude ratio R in real time, thereby performing vibration elimination compensation.

[0082] The above signal processing principle is as follows: The dual-frequency excitation signal, formed by the superposition of the first frequency component f1 and the second frequency component f2 output by the microcontroller unit, is amplified by the drive circuit and injected into the excitation coil. The receiving coil generates an induced signal, which contains position information of the two frequency components. The high-speed ADC (analog-to-digital converter) samples the induced signal and demodulates the amplitude A1 and phase φ1 of the first frequency component signal, and the amplitude A2 and phase φ2 of the second frequency component signal, respectively, through a digital phase-locked loop (DPLL) or a fast Fourier transform (FFT).

[0083] The above scheme decouples the air gap information by utilizing the differentiated response in the frequency dimension, avoids the problem of common-mode interference on single-frequency amplitude, and achieves accurate perception of the air gap state.

[0084] Step S500: Use the arctangent function to calculate the angle of the compensated virtual orthogonal signal to obtain the calculated angle value θ. θ = arctan(V'_sin / V'_cos). The calculated angle value θ obtained by solving the angle using virtual orthogonal signals can yield a high-precision position angle value.

[0085] Step S600: If the calculated amplitude ratio R exceeds the preset range, it is determined that the receiving coil or the stator and mover assembly is abnormal, and an alarm signal is triggered.

[0086] An alarm is triggered when the amplitude ratio R exceeds the normal threshold range. Preferably, the physical boundary characteristics of the R value are used as a health status monitoring indicator. Since the R value is only related to the air gap electromagnetic coupling state and is not affected by common-mode factors such as power supply voltage and temperature, it is an ideal characteristic quantity for judging coil short circuits, open circuits, rotor detachment, or serious mechanical assembly failures. Through this mechanism, the system can provide early warnings before faults occur, avoiding equipment loss of control accidents caused by sensor failure, significantly enhancing the safety and reliability of the entire servo system, and achieving deep integration of measurement and diagnostic functions.

[0087] In a second aspect, embodiments of the present invention provide an encoder system 100, the encoder system 100 being used to implement the inductive encoder gap adaptive compensation method as described in any of the above claims, comprising: The microcontroller unit 101 is used to generate dual-frequency excitation signals and execute signal processing and angle calculation algorithms; The driving circuit 102 is connected to the microcontroller unit 101 and the excitation coil, and is used to amplify the dual-frequency excitation signal and inject it into the excitation coil. Excitation coil 103, which is used to transmit excitation signals; The receiving coil 104 is used to sense changes in rotor position and output the received signal containing position information; An analog-to-digital converter 105, connected to the receiving coil and the microcontroller unit 101, is used to sample the received signal at high speed and convert it into a digital signal. The microcontroller unit 101 is further configured to: demodulate the first amplitude A1 and the second amplitude A2 from the digital signal, calculate the amplitude ratio R, invert the air gap state parameter δ, and compensate the original sine / cosine signal to output the position angle value θ.

[0088] The MCU, acting as the microcontroller unit, is responsible for generating dual-frequency signals and executing the compensation algorithm; the drive circuit is responsible for power amplification; and the ADC is responsible for high-speed sampling. This system architecture makes full use of the existing hardware resources of the inductive encoder, eliminating the need for additional displacement sensors or complex mechanical adjustment mechanisms. While maintaining the advantages of low cost and high reliability, it endows the system with intelligent characteristics that adapt to changes in the environment through software algorithms, achieving a balance between hardware simplification and high-end performance.

[0089] Please see Figure 4The figure shows the experimental results of the adaptive gap compensation method for inductive encoders. Inductive encoders are highly sensitive to changes in the gap between the rotor and stator, which directly affects the amplitude of the induced signal. For example, in the figure, when the original induced signal amplitude is 0.5V, after being amplified three times by the operational amplifier, the output is 1.5V. However, when the gap decreases and the induced signal amplitude increases to 1V, the amplified signal will rise to 3V. But because the input limit of the ADC is 2.5V, the signal will experience clipping distortion, leading to abnormal position calculations. By employing dual-frequency modulation technology, the impact of gap changes on the amplitude of the induced signal can be effectively reduced, thereby improving the system's anti-interference capability and calculation stability.

[0090] Compared with the prior art, the embodiments of this application have the following beneficial effects: Breaking through the technical bottleneck of AGC, unlike traditional AGC which can only adjust the amplitude, this invention accurately inverts the air gap state through the dual-frequency amplitude ratio, which can specifically compensate for nonlinear distortion and significantly improve the orthogonality and purity of the signal.

[0091] It achieves wide-range adaptability and utilizes frequency-dimensional feature decoupling, making the system highly sensitive to air gap changes. It can maintain high-precision measurement over a large air gap fluctuation range and reduce dependence on mechanical assembly accuracy.

[0092] It enhances environmental robustness. The amplitude ratio R is a relative quantity that can effectively offset the impact of common-mode interference such as power supply voltage fluctuations and temperature drift on the amplitude of a single frequency, thereby improving the long-term stability of the system under harsh operating conditions.

[0093] Without requiring additional hardware costs, it fully utilizes the inherent parasitic capacitance and skin effect characteristics of the PCB coil, eliminating the need for additional displacement sensors or complex mechanical adjustment mechanisms, thus maintaining the advantages of low cost and high reliability of inductive encoders.

[0094] The above examples are merely illustrative of the technical content of the present invention to facilitate easier understanding by the reader, but do not imply that the implementation of the present invention is limited to these examples. Any technical extensions or re-creations made based on the present invention are protected by the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for adaptive compensation of gap in an inductive encoder, characterized in that, Includes the following steps: A dual-frequency excitation signal is applied to the excitation coil of the inductive encoder. The dual-frequency excitation signal includes a first frequency component f1 and a second frequency component f2. The attenuation response characteristics of the receiving coil of the inductive encoder to changes in the air gap are different under the first frequency component f1 and the second frequency component f2. The received signal generated by the receiving coil is obtained, and the received signal includes a first received component corresponding to the first frequency component f1 and a second received component corresponding to the second frequency component f2; The first amplitude A1 of the first received component and the second amplitude A2 of the second received component are extracted from the received signal, and the amplitude ratio R characterizing the air gap state is calculated based on the first amplitude A1 and the second amplitude A2. Based on the amplitude ratio R, query the mapping model between the air gap and the amplitude ratio, and reconstruct a virtual orthogonal signal to eliminate the nonlinear effects of the air gap.

2. The adaptive compensation method for inductive encoder gap according to claim 1, characterized in that, The step of reconstructing a virtual orthogonal signal that eliminates the nonlinear effects of the air gap by querying the air gap-amplitude mapping model based on the amplitude ratio R includes: Based on the amplitude ratio R, query the air gap and amplitude ratio mapping model to generate the air gap parameter δ; The correction coefficient K_gain is generated based on the air gap parameter δ; The original signal in the received signal is nonlinearly compensated according to the correction coefficient K_gain to obtain a virtual orthogonal signal of reconstructed sine and cosine signals.

3. The adaptive compensation method for inductive encoder gap according to claim 2, characterized in that, The amplitude ratio R = A1 / A2, where A1 and A2 are response functions of the air gap parameter δ; where A1(δ) = K1 / δ, A2(δ) = K2 / δ^α, K1 and K2 are correlation constants of the receiving coil, and α > 1.

4. The adaptive compensation method for inductive encoder gap according to claim 3, characterized in that, The virtual orthogonal signal of the reconstructed sine and cosine signals is: V'_sin = V_sin × K_gain, where V_sin is the original signal received by the receiving coil, and V'_sin is a virtual orthogonal signal of the sinusoidal signal; V'_cos = V_cos × K_gain, where V_cos is the original signal received by the receiving coil, and V'_cos is a virtual orthogonal signal of the cosine signal.

5. The adaptive compensation method for inductive encoder gap according to claim 4, characterized in that, Following the step of reconstructing the virtual orthogonal signal that eliminates the nonlinear effects of the air gap by querying the air gap-to-amplitude ratio mapping model based on the amplitude ratio R, the following steps are also included: The arctangent function is used to calculate the angle of the compensated virtual orthogonal signal to obtain the calculated angle value θ. θ = arctan(V'_sin / V'_cos).

6. The adaptive compensation method for inductive encoder gap according to claim 1, characterized in that, The first amplitude A1 and the second amplitude A2 in the step of extracting the first amplitude A1 of the first received component and the second amplitude A2 of the second received component from the received signal are obtained by using DPLL or FFT algorithm.

7. The adaptive compensation method for inductive encoder gap according to claim 1, characterized in that, The first frequency component f1 satisfies the following condition: L is the inductance of the excitation coil, and Cpar is the parasitic capacitance of the receiving coil.

8. The adaptive compensation method for inductive encoder gap according to claim 7, characterized in that, The second frequency component f2 satisfies the following condition: f2 ≥ 0.6 × f_res, where f_res is the self-resonant frequency of the excitation coil.

9. The adaptive compensation method for inductive encoder gap according to claim 5, characterized in that, After the step of using the arctangent function to calculate the angle of the compensated virtual orthogonal signal to obtain the calculated angle value θ, the following steps are also included: If the calculated amplitude ratio R exceeds the preset range, it is determined that the receiving coil or the stator and mover are abnormally assembled, triggering an alarm signal.

10. An encoder system, said encoder system being used to implement the adaptive compensation method for the gap of an inductive encoder as described in any one of claims 1 to 9, characterized in that, include: The microcontroller unit is used to generate dual-frequency excitation signals and execute signal processing and angle calculation algorithms. A driving circuit, connected to the microcontroller unit and the excitation coil, is used to amplify the dual-frequency excitation signal and inject it into the excitation coil. An excitation coil, which is used to receive dual-frequency excitation signals and generate an excitation magnetic field; A receiving coil is used to sense changes in rotor position and output a received signal containing position information. An analog-to-digital converter, connected to the receiving coil and the microcontroller unit, is used to sample the received signal at high speed and convert it into a digital signal for transmission to the microcontroller unit; The microcontroller unit is further configured to: demodulate the first amplitude A1 and the second amplitude A2 from the digital signal, calculate the amplitude ratio R, invert the air gap parameter δ, and compensate the original sine / cosine signal to output the position angle value θ.

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