An absolute magnetic grating linear encoder

Abstract

This invention belongs to the field of displacement measurement technology and discloses an absolute magnetic grating linear encoder. Employing a multi-track absolute magnetic grating linear encoder, it determines absolute position information by simultaneously reading the encoded data from the incremental track, the first reference track, and the second reference track, and comparing the phase difference between the three. After a power outage and subsequent power-on, it can accurately read the system's absolute position without requiring calibration at the origin after each power-on. This invention achieves linear absolute encoding of arbitrary length by modifying the magnetic pole pitch of the corresponding tracks, reducing the sensor design complexity of the reading head; the use of a TMR sensor effectively increases magnetic sensitivity, improving the accuracy of the system's linear distance measurement.

Description

Technical Field

[0001] This invention belongs to the field of displacement measurement technology, specifically relating to an absolute magnetic grating linear encoder. Background Technology

[0002] An absolute magnetic grating linear encoder is a device that uses magnetic field measurement technology to achieve position detection. It can provide high-precision position feedback signals and is widely used in CNC machine tools, printing equipment, robots, elevators, and other automated equipment. A commonly used absolute magnetic grating linear encoder consists of incremental tracks and absolute tracks, with the absolute tracks using a pseudo-random number (PRBS) encoding method. The number of absolute head sensors is related to the number of bits in the PRBS. When the absolute magnetic grating is long, more PRBS bits are needed, which increases the number of sensors in the head and places higher demands on data processing. Summary of the Invention

[0003] The purpose of this invention is to provide an absolute magnetic grating linear encoder that can provide high-precision position feedback, does not require pseudo-random number (PRBS) encoding, and only requires three magnetic sensors to process the absolute value of a relatively long magnetic grating, thereby improving the control accuracy of automated equipment.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] An absolute magnetic grating linear encoder is used to measure linear displacement information. The absolute magnetic grating linear encoder includes a magnetic grating scale and a reading head. The magnetic grating scale has three magnetic tracks, namely an incremental magnetic track, a first reference magnetic track, and a second reference magnetic track. The incremental magnetic track, the first reference magnetic track, and the second reference magnetic track are parallel to each other and aligned at their starting positions.

[0006] The pole distance of the incremental magnetic track is P, the pole distance of the first reference magnetic track is M, and the pole distance of the second reference magnetic track is N. The three values ​​of P, M, and N are integers or decimals, with P being the smallest. P, M, and N are coprime after being amplified to integers, either individually or simultaneously. The reading head is equipped with magnetic sensors corresponding to the three magnetic tracks respectively.

[0007] Several alternative methods are provided below, but they are not intended as additional limitations on the overall solution above. They are merely further additions or optimizations. Provided there are no technical or logical contradictions, each alternative method can be combined individually with respect to the overall solution above, or multiple alternative methods can be combined with each other.

[0008] Preferably, the maximum range of the absolute magnetic grating linear encoder is 2*LCM(P,M,N)mm, where LCM(P,M,N) is the length coefficient;

[0009] If the three values ​​P, M, and N are all integers, then the length coefficient is the least common multiple of the three values ​​P, M, and N; otherwise, the three values ​​P, M, and N are magnified by the same factor and converted into integers. The least common multiple of the three converted integers is then taken, and the magnification factor of the least common multiple during the magnification and reduction operation is used as the length coefficient.

[0010] Preferably, the reading head further includes a data processing unit, which is used to receive the angle information of the corresponding magnetic track obtained by the three magnetic sensors, and calculate the displacement information based on the angle information.

[0011] The displacement information is calculated based on the angle information, and the following operations are performed:

[0012] Based on the angle information and periodic change pattern of the three magnetic tracks, the integer period of the magnetic pole change of the incremental magnetic track is calculated.

[0013] The integer period of the magnetic pole change of the incremental magnetic track and the angle information of the incremental magnetic track are converted into displacement information.

[0014] Preferably, the step of calculating the integer period of the magnetic pole change of the incremental magnetic track based on the angle information and periodic change law of the three magnetic tracks includes:

[0015] The periodic variation numbers of the three magnetic tracks have the following relationship:

[0016]

[0017] In the formula, k is the number of periodic changes of the incremental track, k1 is the number of periodic changes of the first reference track, k2 is the number of periodic changes of the second reference track, θ is the angle information of the incremental track, θ1 is the angle information of the first reference track, and θ2 is the angle information of the second reference track.

[0018] Search for k such that k1 and k2 are both integers. The value of k obtained at this time is assigned to parameter K, which serves as the integer period of magnetic pole change of the incremental magnetic track.

[0019] Preferably, the value of k ranges from 0 to... Integers between P, M, and N, where LCM(P, M, N) is the length coefficient.

[0020] Preferably, the step of converting the integer period of the magnetic pole change of the incremental magnetic track and the angle information of the incremental magnetic track into displacement information includes:

[0021]

[0022] In the formula, L represents displacement information in mm, K represents the integer period of magnetic pole change of the incremental track, and θ represents the angle information of the incremental track.

[0023] This invention provides an absolute magnetic grating linear encoder, employing a multi-track absolute magnetic grating linear encoder. It determines absolute position information by simultaneously reading the encoded data from the incremental track, the first reference track, and the second reference track, and comparing the phase difference between the three. After a power outage and subsequent power-on, the track angles can be directly read for calculation, accurately determining the system's absolute position. This eliminates the need for calibration at the origin after each power-on, resulting in a simpler structure and magnetization method. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an absolute magnetic grating linear encoder according to the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the three magnetic tracks in the magnetic grating ruler of the present invention;

[0026] Figure 3 This is a schematic diagram of the reading head of the present invention. Detailed Implementation

[0027] 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.

[0028] It should be noted that when a component is said to be "connected" to another component, it can be directly connected to the other component or it can be connected to a component in between; when a component is said to be "fixed" to another component, it can be directly fixed to the other component or it can be connected to a component in between.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0030] To overcome the shortcomings of existing technologies, this embodiment provides an absolute magnetic grating linear encoder for measuring linear displacement information and achieving high-precision position feedback. For example... Figure 1 As shown, the absolute magnetic grating linear encoder of this embodiment includes a magnetic grating scale and a reading head.

[0031] (1) Magnetic scale: such as Figure 2As shown, in order to break away from the limitations of the pseudo-random number (PRBS) encoding method, the magnetic grating ruler in this embodiment has three magnetic tracks: an incremental magnetic track, a first reference magnetic track, and a second reference magnetic track. Specifically, the magnetic grating ruler includes a substrate and a magnetized layer, wherein the magnetized layer includes the aforementioned three magnetic tracks, which are composed of alternating N and S magnetic poles.

[0032] To ensure reading accuracy, the incremental track, the first reference track, and the second reference track are parallel to each other and aligned at their starting positions. The pole distance of the incremental track is P mm, the pole distance of the first reference track is M mm, and the pole distance of the second reference track is N mm. P, M, and N are all integers or decimals, with P being the smallest. This means the incremental track has the smallest pole distance, and P, M, and N are coprime after being magnified to integers. For example, P = 2, M = 3, and N = 5, or P = 5.1, M = 6.1, and N = 7.3. When P = 5.1, M = 6.1, and N = 7.3, after magnification by 10 times, these become 51, 61, and 73, which are coprime, thus meeting the requirements.

[0033] Based on this, the maximum range of the absolute magnetic grating linear encoder in this embodiment is 2*LCM(P,M,N)mm, where LCM(P,M,N) is the length coefficient.

[0034] Since P, M, and N are either integers or decimals, when determining the length coefficient, if all three values ​​are integers, the length coefficient is the least common multiple (LCM) of P, M, and N. Otherwise, P, M, and N are magnified by the same factor and converted to integers. The LCM of these three converted integers is then taken, and the magnification factor used in the magnification operation is reduced from the LCM to obtain the length coefficient. For example, when calculating the length coefficient for P = 1.5, M = 2.3, and N = 2.6, they are first magnified by a factor of 10 and converted to 15, 23, and 26. The LCM of 15, 23, and 26 is 8970. After reducing the LCM by a factor of 10, the length coefficient is 897.

[0035] (2) Reading head: such as Figure 3 As shown, the reading head is equipped with magnetic sensors corresponding to three magnetic tracks. These can be TMR sensor units, such as dual-axis TMR angle sensors using TMR3002 and TMR3005, or other magnetic sensors such as AMR and GMR. It also includes a data processing unit, which receives the angle information of the corresponding tracks from the three magnetic sensors and calculates the displacement information based on the angle information. The data processing unit is a main controller with logic operation capabilities, such as an STM32 series chip.

[0036] The data processing unit calculates the displacement information based on the angle information and performs the following operations:

[0037] A. Based on the angle information and periodic change pattern of the three magnetic tracks, the integer period of the magnetic pole change of the incremental magnetic track is calculated.

[0038] The TMR sensor unit consists of three sensors: TMR sensor S1 corresponding to the incremental track, TMR sensor S2 corresponding to the first reference track, and TMR sensor S3 corresponding to the second reference track. The three TMR sensors are initially aligned with no phase difference. With each cycle of magnetic pole change, the phase of each TMR sensor changes by 2π, meaning the angle is obtained from the periodic change of the magnetic poles. After the reading head moves a certain distance relative to the magnetic scale, the three TMR sensors respectively obtain the angle information of the corresponding track. TMR sensor S1 obtains the angle information θ corresponding to the incremental track, TMR sensor S2 obtains the angle information θ1 of the first reference track, and TMR sensor S3 obtains the angle information θ2 of the second reference track.

[0039] Considering the periodic changes in magnetic poles along the tracks, let θ′ = 2kπ + θ, where the incremental track undergoes k cycles, and k is a non-negative integer. θ′1 = 2k1π + θ1, where the first reference track undergoes k1 cycles, and k1 is a non-negative integer. θ′2 = 2k2π + θ2, where the second reference track undergoes k2 cycles, and k2 is a non-negative integer. Then the number of cycles for the three tracks has the following relationship:

[0040]

[0041] Therefore:

[0042]

[0043] In the formula, k is the periodic change number of the incremental track, and the value of k ranges from 0 to... The integers between k1 and k2 represent the number of periodic changes of the first reference track, k2 represent the number of periodic changes of the second reference track, θ represents the angle information of the incremental track, θ1 represents the angle information of the first reference track, and θ2 represents the angle information of the second reference track.

[0044] The search for k such that k1 and k2 are both integers is performed. The resulting value of k is assigned to parameter K, serving as the integer period of the incremental magnetic track's pole changes, i.e., the integer period traversed by the incremental magnetic track. In this embodiment, a brute-force search is directly used, i.e., k is traversed from 0 within its range until a value is found that makes both k1 and k2 integers. In other embodiments, the search method can be changed; this embodiment does not limit the search method.

[0045] B. Convert the integer period of magnetic pole change of the incremental magnetic track and the angle information of the incremental magnetic track into displacement information.

[0046]

[0047] In the formula, L represents displacement information in mm, K represents the integer period of magnetic pole change of the incremental track, and θ represents the angle information of the incremental track.

[0048] It should be noted that a basic logic circuit unit is also required for the operation of the magnetic sensor and data processing unit. The most basic function of this logic circuit unit is to provide power to the magnetic sensor and data processing unit to ensure their normal operation. A conventional power supply circuit can be used for this purpose. Alternatively, a filtering circuit and a signal amplification circuit can be added to filter and amplify the angle information acquired by the magnetic sensor. In this case, conventional filtering and signal amplification circuits can be added. During signal amplification, the phase difference within a single magnetic track is adjusted to 90 degrees, and the amplitudes (maximum and minimum amplitudes) of two signals with a 90-degree phase difference within a single magnetic track are adjusted to be the same.

[0049] This embodiment presents an absolute magnetic grating linear encoder. Employing a multi-track absolute magnetic grating linear encoder, it determines absolute position information by simultaneously reading the encoded data from the incremental track, the first reference track, and the second reference track, and comparing the phase difference between the three. After a power outage and subsequent power-on, it can accurately read the system's absolute position without requiring calibration back to the origin after each power-on. By modifying the pole pitch of the corresponding tracks, linear absolute encoding of arbitrary lengths can be achieved, reducing the sensor design complexity of the readout head. Using a TMR sensor effectively increases magnetic sensitivity, improving the accuracy of the system's linear distance measurement.

[0050] In this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number or order of the indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0051] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0052] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. An absolute magnetic grating linear encoder for measuring linear displacement information, characterized in that, The absolute magnetic grating linear encoder includes a magnetic grating scale and a reading head. The magnetic grating scale has three magnetic tracks, namely an incremental magnetic track, a first reference magnetic track, and a second reference magnetic track. The incremental magnetic track, the first reference magnetic track, and the second reference magnetic track are parallel to each other and aligned at their starting positions. The pole moment of the incremental track is The pole moment of the first reference track is The pole moment of the second reference track is ,and , and The three values ​​are either integers or decimals, among which Minimum, and , and The reading head is equipped with magnetic sensors corresponding to three magnetic tracks, and the reading head also includes a data processing unit. The data processing unit is used to receive the angle information of the corresponding magnetic tracks obtained by the three magnetic sensors and calculate the displacement information based on the angle information. The displacement information is calculated based on the angle information, and the following operations are performed: Based on the angle information and periodic variation pattern of the three magnetic tracks, the integer period of the magnetic pole change of the incremental magnetic track is calculated, including: The periodic variation numbers of the three magnetic tracks have the following relationship: ； ； In the formula, This represents the number of periodic changes in the incremental magnetic track. The periodic variation number of the first reference track. The periodic variation number of the second reference track. For incremental track angle information, For the angle information of the first reference track, This provides the angle information for the second reference track. search , making and All are integers, and the result is... The value is assigned to the parameter , which is the integer period of the magnetic pole change of the incremental magnetic track; The integer period of the magnetic pole change of the incremental magnetic track and the angle information of the incremental magnetic track are converted into displacement information.

2. The absolute magnetic grating linear encoder according to claim 1, characterized in that, The maximum range of the absolute magnetic grating linear encoder is: mm, where This is the length coefficient; like , and If all three values ​​are integers, then the length coefficient is... , and The least common multiple of the three values; otherwise, both will be... , and After the three values ​​are magnified by the same factor, they are all converted into integers. The least common multiple of the three converted integers is taken, and the magnification factor of the magnification operation is reduced based on the least common multiple taken as the length coefficient.

3. The absolute magnetic grating linear encoder according to claim 1, characterized in that, The value range is 0 to Integers between, where This is the length coefficient.

4. The absolute magnetic grating linear encoder according to claim 1, characterized in that, The process of converting the integer period of the magnetic pole change of the incremental magnetic track and the angle information of the incremental magnetic track into displacement information includes: ； In the formula, This is displacement information, in mm. For the integer period of the magnetic pole change of the incremental magnetic track. This is the angle information for the incremental magnetic track.

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