Encoder system based on an enhanced robustness inductive encoder chip

Abstract

The application provides an encoder system based on an enhanced robust inductive encoder chip, which is characterized by comprising a rotating motor (1), a rotor PCB (2), a coil PCB (3) and an encoder circuit board (4), wherein the coil PCB (3) comprises a transmitting coil (31) and a receiving coil (32), the encoder circuit board (4) comprises an enhanced robust inductive encoder chip (41) and an encoder chip peripheral working circuit (42), and the enhanced robust inductive encoder chip (41) comprises a transmitting coil driving circuit (411), a receiving coil demodulation circuit (412), a receiving signal feedback circuit (413) and an output signal driving circuit (414). The application can be used for measuring the rotating angle and rotating speed of a motor and can be widely used in the fields of automobile electronics, medical treatment, industrial robots, national defense and aerospace.

Description

(I) Technical Field

[0001] This invention relates to an encoder system based on an enhanced robust inductive encoder chip, applicable to fields such as automotive electronics, medical, industrial robots, defense, and aerospace, and belongs to the field of inductive sensor technology. (II) Background Technology

[0002] Inductive encoders are non-contact position sensors that utilize eddy current induction technology. Also known as inductive encoders, they are a rapidly developing new encoder technology in recent years. Unlike traditional rotary transformers that use copper wire coils to sense position, inductive encoders use dense coil windings implemented on a PCB. Based on this technology, inductive encoders can achieve smaller thickness, lighter weight, lower power consumption, and higher accuracy. Furthermore, compared to optical encoders, they can achieve reliable measurements under harsh conditions. The development of inductive encoder technology has further promoted the development of modern sensing and control fields, utilizing the principle of electromagnetic induction to measure mechanical motion. Currently, the development of this technology mainly shows trends towards miniaturization, high precision, wide application areas, integration, and intelligence.

[0003] Currently, inductive encoders are used in automotive electronics for measuring steering wheel torque and angle, motor speed, and rotation angle; in industrial robotics for measuring robotic arm angles; and in machine tools for measuring position movement. Their wide range of applications is primarily due to their ability to operate in harsh environments and their high precision. However, their application is still limited by installation issues, mainly concerning the relative position of the coil and rotor. In some scenarios, excessive distance between the coil and rotor, or oscillations within a certain range due to installation or usage problems, significantly impact measurement accuracy. Current solutions often involve adding an Automatic Gain Control (AGC) circuit or a digitally programmable gain control circuit after the demodulation circuit of the receiving coil inside the inductive encoder. However, this approach introduces additional delays, which, at ultra-high speeds, affect measurement accuracy and performance, hindering precise feedback control.

[0004] This invention analyzes the relationship between the rotor and the coil, and through formula derivation, confirms that the biggest factors affecting the demodulated waveform quality of the receiving coil are the area of ​​the receiving coil and the physical distance between the receiving coil and the transmitting coil. To address this issue, instead of increasing the delay adjustment gain, this invention chooses to adjust the gain at the source, the transmitting coil. This avoids the problem of automatic gain control (AGC) being limited in its application to certain scenarios and significantly reduces the delay introduced by AGC. Traditional inductive encoder chips have significant limitations in coil area; generally, chips are only designed for a specific area range and cannot be used with multiple coil sizes simultaneously. This necessitates designing multiple chips for different application scenarios, increasing costs. The enhanced robustness inductive encoder chip included in this invention differs from traditional AGC adjustments after receiving the demodulated signal. It analyzes the received signal waveform and adjusts the transmitting coil parameters accordingly. This greatly reduces the overall chip delay and increases robustness in various and unstable application scenarios. (III) Summary of the Invention

[0005] The purpose of this invention is to provide an encoder system based on an enhanced robust inductive encoder chip, which consists of a rotary motor (1), a rotor PCB (2), a coil PCB (3), and an encoder circuit (4). The coil PCB (3) consists of a transmitting coil (31) and a receiving coil (32). The encoder circuit (4) consists of an enhanced robust inductive encoder chip (41) and an encoder chip peripheral circuit (42). The enhanced robust inductive encoder chip (41) consists of a transmitting coil driving circuit (411), a receiving coil demodulation circuit (412), a receiving signal feedback circuit (413), and an output signal driving circuit (414).

[0006] The objective of this invention is achieved as follows:

[0007] The rotating motor (1) drives the rotor PCB (2) to rotate. The coil PCB (3) is driven by the encoder circuit (4) and coupled with the rotor PCB (2) through the electromagnetic induction eddy current field. The sensed motor position signal is sent to the encoder circuit (4) and delivered to the enhanced robust inductive encoder chip (41) in the encoder circuit (4). After being demodulated by the receiving coil demodulation circuit (412) inside the chip, the sine and cosine signals containing the motor position are output to the receiving signal feedback circuit (413) and the output signal drive circuit (414). The receiving signal feedback circuit (413) analyzes the signal and adjusts the parameters of the transmitting coil drive circuit (411) according to the characteristics of the signal so that the system can work in a better state. The output signal drive circuit (414) drives the received signal to the subsequent stage for use, so as to sense the motor rotation position, calculate the motor rotation speed and other information.

[0008] The circuit includes a receiving signal feedback circuit (413). This circuit analyzes the signal after the receiving coil input signal is demodulated by the receiving coil demodulation circuit (412) to make corresponding adjustments to the transmitting coil drive circuit (411). The transmitting coil and the receiving coil induce each other through the principle of electromagnetic induction. The transmitting coil drive circuit (411) drives the transmitting coil to generate an alternating voltage value. According to the principle of mutual induction, the receiving coil is induced with an alternating voltage value. When there is no rotor PCB (2), due to the characteristic that the receiving coil is a combination of two sets of reverse coils, they cancel each other out, and the voltage value input to the receiving coil demodulation circuit (412) is 0V. When the rotor PCB (2) is present, due to the special shape of the copper foil on the PCB, it generates an eddy current electric field under the influence of the magnetic field of the transmitting coil. The eddy current electric field generates a magnetic field in the opposite direction, which cancels out part of the original magnetic field. This causes the inductance, impedance, and quality factor of the coil to change. When the copper foil completely blocks the forward or reverse coil, the induction coil outputs the maximum or minimum voltage value. The inductance of the receiving coil to the rotor PCB (2) is affected by the following factors:

[0009]

[0010] Where L is the self-inductance of the receiving coil, δ is the air gap length, and μ is the air permeability, which is a fixed value of 4π*10⁻⁶. -7 H / m, S is the cross-sectional area of ​​the air gap. From the formula, it can be seen that the self-inductance of the receiving coil is affected by the position of the rotor PCB (2), where the coverage area S and the air gap length δ are influencing factors. The relationship between the induced voltage at the receiving coil and the induced voltage at the transmitting coil is affected by mutual inductance, and the mutual inductance electromotive force at the receiving coil is...

[0011]

[0012] Where ε is the induced electromotive force, Ψ 12 Let I be the flux linkage of the induction coil. I1 is the current in the transmitting coil. Since the transmitting circuits are mutually inverted, their currents are affected by voltage. The formula for calculating the mutual inductance coefficient M is:

[0013]

[0014] Where M is the mutual inductance coefficient, k is the coupling factor, L1 is the inductance of the transmitting coil, and L2 is the inductance of the receiving coil. Therefore, the main factors affecting the induced electromotive force of the receiving coil are the air gap length δ and the coverage area S.

[0015] The transmitting coil is a multi-turn toroidal coil, which, together with the transmitting drive circuit, forms the transmitting circuit. The formula for calculating the self-inductance L1 of the transmitting coil is as follows:

[0016]

[0017] The induced electromotive force of the receiving coil is affected by the air gap length δ. Therefore, the installation distance between the rotor PCB (2) and the coil PCB (3) in the entire system is a sensitive factor, and the change in distance will have a significant impact on the system accuracy. To reduce this impact, the peak-to-peak value Vpprx of the AC signal of the transmitting coil can be adjusted, thereby affecting the current I1 of the transmitting coil, so that the maximum peak-to-peak value max(Vpprx) of the signal received by the demodulation circuit (412) of the receiving coil remains stable. Specifically, the demodulation circuit (412) inputs the maximum peak-to-peak value max(Vpprx) of the received signal to the receiving signal feedback circuit (413). This part of the circuit makes a judgment: if max(Vpprx) is greater than the reference peak-to-peak value (Vppref), the value of the coefficient K input to the transmitting coil drive circuit (411) is reduced; if max(Vpprx) is less than the reference peak-to-peak value (Vppref), the value of the coefficient K input to the transmitting coil drive circuit (411) is increased; if they are equal, K remains unchanged.

[0018] The induced electromotive force (EMF) of the receiving coil is affected by the coverage area S. Therefore, different coil sizes in different application scenarios will affect the mutual induced EMF at the receiving coil. In extreme cases where the required area is too large or too small in high-precision scenarios, ordinary inductive encoder chips cannot fully meet the working requirements, resulting in reduced accuracy or failure to work. In this case, the enhanced robust inductive encoder chip with a receiving signal feedback circuit (413) used in this patent automatically adjusts the transmission power at the transmitting coil. It can automatically adjust for cases where the induced EMF of the receiving coil is too weak or too strong to achieve the chip's preset accuracy. First, the coil area is estimated according to the application scenario, and the coil area is divided into 4 ranges to preset different initial circuit parameters K0, achieving applicability under various areas and universality in various cases such as sector, ring, and linear shapes. (iv) Description of the attached drawings

[0019] Figure 1 This is a schematic diagram of an encoder system based on an enhanced robust inductive encoder chip, consisting of a rotary motor (1), a rotor PCB (2), a coil PCB (3), and an encoder circuit (4). The coil PCB (3) consists of a transmitting coil (31) and a receiving coil (32). The encoder circuit (4) consists of an enhanced robust inductive encoder chip (41) and an encoder chip peripheral circuit (42). The enhanced robust inductive encoder chip (41) consists of a transmitting coil drive circuit (411), a receiving coil demodulation circuit (412), a receiving signal feedback circuit (413), and an output signal drive circuit (414).

[0020] Figure 2This is an equivalent model circuit of the transmitting coil, receiving coil, and metal rotor. When the coil PCB (3) is confirmed, the parasitic internal resistance R of the transmitting coil in the circuit is... LR The self-inductance LT of the transmitting coil is fixed, but its value varies for different coils. The equivalent circuit on the receiving coil side is the same as that on the transmitting side. After the coils are fixed, the variable factors in the circuit model are the distance d between the coils and the position of the metal rotor. Changing the coils mainly alters the transmitting coil inductance LT and the parasitic resistance R of the transmitting coil circuit. LT Receiver coil inductance LR, receiver coil circuit parasitic resistance R LR The model is simplified to the principle of a transformer. For an inductive encoder chip, the adjustable parameter is Vtx. Therefore, this invention analyzes the received voltage value Vrx of the induction coil, and adjusts the parameters of the transmitting coil drive circuit through the chip's internal demodulation circuit and feedback current, thereby adjusting the transmitting coil drive voltage Vtx to ensure that the maximum value of the peak-to-peak value of the receiving coil Vrx remains constant.

[0021] Figure 3 This is a flowchart of an encoder system method based on an enhanced robust inductive encoder chip. The key process is divided into steps S1-S6. Through the internal adjustment of the inductive encoder chip, a stable maxVpprx is finally obtained in the receiving coil circuit, thereby improving the robustness of the system.

[0022] Figure 4 This is a schematic diagram of the positional relationship between the coil PCB and the rotor PCB. The rotor PCB can rotate and be in different positions, while the coil PCB is relatively fixed. Different positions correspond to different self-inductances L2 of the receiving coil, and therefore have different mutual inductance coefficients M. As a result, the induced electromotive force at the receiving coil changes with the position. This change information includes the rotor's position information. By analyzing this information, we can obtain information such as the motor's rotational position and rotational speed. (V) Detailed Implementation

[0023] Example 1:

[0024] Figure 3 A flowchart of an encoder system method based on an enhanced robust inductive encoder chip is presented, including the following steps:

[0025] In S1, the rotor PCB and coil PCB are designed according to the requirements of the application scenario. After the design is completed, the rotating motor and various circuits and PCBs are deployed, and the approximate value of the receiving coil area S is recorded. The transmitting coil is a multi-turn toroidal coil, which, together with the transmitting drive circuit, forms the transmitting circuit. The formula for calculating the self-inductance L1 of the transmitting coil is as follows:

[0026]

[0027] The receiving coil is a combination of two sets of reverse coils, which cancel each other out. The final voltage input to the receiving coil demodulation circuit (412) is 0V. When the rotor PCB (2) is present, due to the special shape of the copper foil on the PCB, it generates an eddy current electric field under the influence of the magnetic field of the transmitting coil. The eddy current electric field generates a magnetic field in the opposite direction, which cancels out part of the original magnetic field. This causes changes in the inductance, impedance, and quality factor of the coil. When the copper foil completely blocks the forward or reverse coil, the induction coil outputs the maximum or minimum voltage value. The inductance of the receiving coil is affected by the rotor PCB (2), and the influencing factor formula is as follows:

[0028]

[0029] S2 controls the rotary motor to rotate and enables the inductive encoder chip circuit to operate normally. The inductive encoder chip circuit is used to measure the rotation angle and rotation speed.

[0030] In step S3, the initial power-on parameter K0 of the inductive encoder chip is selected based on the receiving coil area S recorded in step S1. The selection relationship is as follows:

[0031]

[0032] In the formula, A, B, C, and D are calculated and experimentally corrected empirical values, which are stored inside the chip. The external circuit parameters are matched according to the area S of the receiving coil, so that the chip selects the value.

[0033] S4 represents the voltage Vpprx continuously received by the receiving coil during rotation. The chip's internal feedback circuit filters out the maximum value maxVpprx within this time period and calculates the change in the transmitting coil parameters ΔK. Upon receiving this parameter, the transmitting coil drive circuit adjusts the transmitting coil drive accordingly.

[0034] Due to the change in the parameters of the transmitting coil drive circuit in S5, the induced voltage value of the receiving coil changes. This change makes the maximum value of the induced voltage of the receiving coil, Vpprx, closer to the reference value, Vppref.

[0035] After a period of adjustment, the entire system in S6 becomes stable, and the motor rotation status and speed can be accurately fed back from the output signal of the inductive encoder.

[0036] Example 2:

[0037] Figure 4 This paper presents a simplified design for an inductive encoder coil and a possible rotor PCB placement. The receiving coils are divided into two groups, RX1 and RX2, with a 90° phase difference. Each group of coils consists of two coils of different polarities connected in series.

[0038] Without a rotor PCB, the positive and negative phases of the receiving coil cancel each other out, resulting in an induced voltage of 0V. With a rotor PCB, due to its special design containing magnetic copper foil and rotating simultaneously with the motor, the shaded area represents the rotor PCB when the rotor rotates to the angle shown in the diagram. At this point, the positive terminal of coil RX1 experiences its maximum induced voltage, while the negative terminal experiences zero induced voltage. At this time, coil RX1 induces its maximum electromotive force (EMF) maxε. After the rotor rotates 180 degrees, coil RX1 induces its minimum EMF minε. At this point…

[0039] Vpprx = maxε - minε

[0040] Ideally, this formula can be derived as Vpprx = 2maxε = Vppref. Inductive encoder chips adjust the parameters of their internal feedback circuits to make the measured values ​​approximate this value.

[0041] In some embodiments, the coil and PCB are designed as a ring, or a group of coils includes multiple positive and negative coils, where the number of positive coils equals the number of negative coils. Specifically, when there are 9 positive and negative coils, it can be understood that one turn outputs 9 points per cycle. The RX1 coil includes RX10p, RX11p, RX12p, RX13p, RX14p, RX15p, RX16p, RX17p, RX18p, RX10n, RX11n, RX12n, RX13n, RX14n, RX15n, RX16n, RX17n, and RX18n. The maximum electromotive force reached by the rotor PCB during rotation is...

[0042] maxε=RX10p+RX11p+RX12p+RX13p+RX14p+RX15p+RX16p+RX17p+RX18p

[0043] At this point, the sum of the areas of all positive polarity coils is considered, and the sum of the areas of all smaller coils is also taken into account. After selecting the corresponding parameter K0 based on the sum of the areas in step S3, the system operates normally. During system operation, automatic adjustments are made based on the air gap between the rotor PCB and the coil PCB to achieve a more accurate response to the current rotational position and speed.

Claims

1. An encoder system based on an enhanced robust inductive encoder chip; characterized in that: The robust inductive encoder system consists of a rotary motor (1), a rotor PCB (2), a coil PCB (3), and an encoder circuit (4). The coil PCB (3) consists of a transmitting coil (31) and a receiving coil (32). The encoder circuit (4) consists of a robust inductive encoder chip (41) and peripheral circuits (42). The robust inductive encoder chip (41) consists of a transmitting coil drive circuit (411), a receiving coil demodulation circuit (412), a receiving signal feedback circuit (413), and an output signal drive circuit (414). In the system, the rotary motor (1) drives the rotor PCB (2) to rotate. The coil PCB (3) is driven by the encoder circuit (4) and coupled with the rotor PCB (2) through the electromagnetic induction eddy current field. It sends the sensed motor position signal to the encoder circuit (4) and to the enhanced robust inductive encoder chip (41) in the encoder circuit (4). After being demodulated by the receiving coil demodulation circuit (412) inside the chip, it outputs a sine and cosine signal containing the motor position to the receiving signal feedback circuit (413) and the output signal drive circuit (414). The receiving signal feedback circuit (413) is used to obtain the peak-to-peak value max(Vpprx) of the receiving coil demodulated signal and compare the peak-to-peak value with the preset reference peak-to-peak value Vppref. According to the comparison result, the drive coefficient K of the transmitting coil drive circuit (411) is adjusted so that the peak-to-peak value of the receiving coil demodulated signal is stable within the preset range. The output signal drive circuit (414) drives the received signal to the subsequent stage for use in order to sense the motor rotation position and calculate the motor rotation speed.

2. The encoder system based on an enhanced robust inductive encoder chip according to claim 1; characterized in that: The inductive encoder chip includes a characteristic part receiving signal feedback circuit (413). This part of the circuit analyzes the signal after the receiving coil input signal is demodulated by the receiving coil demodulation circuit (412) to make corresponding adjustments to the transmitting coil drive circuit (411). The transmitting coil and the receiving coil induce each other through the principle of electromagnetic induction. The transmitting coil drive circuit (411) drives the transmitting coil to generate an alternating voltage value at both ends. According to the principle of mutual induction, the alternating voltage value is induced in the receiving coil. When there is no rotor PCB (2), since the receiving coil consists of two sets of reverse coils... The combined characteristics cancel each other out, and the final input voltage to the receiving coil demodulation circuit (412) is 0V. When the rotor PCB (2) is present, due to the special shape of the copper foil on the PCB, it generates an eddy current electric field under the influence of the magnetic field of the transmitting coil. The eddy current electric field generates a magnetic field in the opposite direction, which cancels out part of the original magnetic field. This causes the inductance, impedance, and quality factor of the coil to change. When the copper foil completely blocks the forward or reverse coil, the induction coil outputs the maximum or minimum voltage value. The inductance of the receiving coil is affected by the rotor PCB (2), and the formula for its influencing factors is: Where L is the self-inductance of the receiving coil. The length of the air gap. The air permeability is a fixed value. S is the cross-sectional area of ​​the air gap, and N is the effective number of turns of the receiving coil; as can be seen from the formula, the receiving coil is affected by the position of the rotor PCB (2), where the coverage area S and the air gap length are... : These are influencing factors; the relationship between the induced voltage at the receiving coil and the induced voltage at the transmitting coil is affected by mutual inductance. The mutual induced electromotive force at the receiving coil is: in To induce electromotive force. For the flux linkage of the induction coil, : This represents the current in the transmitting coil; due to the mutual inductance between the transmitting and receiving circuits, and the fixed parasitic resistance of the receiving circuit, its current is affected by voltage. The formula for calculating the mutual inductance coefficient M is: Where M is the mutual inductance coefficient and k is the coupling factor. This is the inductance value of the transmitting coil. The inductance of the receiving coil is given; therefore, the main factor affecting the induced electromotive force of the receiving coil is the air gap length. and coverage area S; The induced electromotive force of the receiving coil is affected by the length of the air gap. Therefore, the mounting distance between the rotor PCB (2) and the coil PCB (3) in the entire system is a sensitive factor, and changes in the distance will have a significant impact on the system accuracy. To reduce this impact, the peak-to-peak value Vpptx of the AC signal of the transmitting coil can be adjusted, thereby affecting the transmitting coil current. This ensures that the peak-to-peak value of the signal received by the receiving coil demodulation circuit (412) is kept stable, specifically, the receiving demodulation circuit (412) inputs the peak-to-peak value of the received signal, max(Vpprx), to the receiving signal feedback circuit (413). This part of the circuit makes a judgment: if max(Vpprx) is greater than the reference peak-to-peak value Vppref, then the value of the coefficient K input to the transmitting coil drive circuit (411) is reduced; if max(Vpprx) is less than the reference peak-to-peak value Vppref, then the value of the coefficient K input to the transmitting coil drive circuit (411) is increased; if they are equal, then K remains unchanged. The induced electromotive force of the receiving coil is affected by the coverage area S. Therefore, in different application scenarios, the combination of different coil sizes will affect the mutual induced electromotive force at the receiving coil. In extreme cases where the area required for high-precision scenarios is too large or too small, ordinary inductive encoder chips cannot fully meet the working requirements, resulting in reduced accuracy or failure to work. At this time, the enhanced robust inductive encoder chip with receiving signal feedback circuit (413) used in this patent automatically adjusts the transmission power at the transmitting coil. It can automatically adjust for situations where the induced electromotive force of the receiving coil is too weak or too strong, achieving the chip's preset accuracy. First, the coil area is estimated according to the application scenario, and the coil area is divided into 4 ranges to preset different initial circuit parameters K0, achieving applicability under various areas, as well as universality in various cases such as sector, ring, and linear shapes.

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