An inductive linear absolute position measuring device

Abstract

The present invention discloses an inductive linear absolute position measuring device, which relates to the field of linear position measurement. The inductive linear absolute position measuring device includes a single-track grating scale and a reading head. The reading head includes: a substrate; an induction coil drawn on the substrate. The induction coil includes an S coil array and an R coil array. Each coil array includes n independent complementary coils. Each independent complementary coil is composed of 2 sub-coils wound in opposite directions in series; an excitation coil surrounding the induction coil. The excitation coil is a multi-turn closed coil connected in series; a hardware processing circuit arranged on the substrate, including an excitation signal driving circuit, a selection switch circuit, a demodulation circuit, an operational amplifier circuit and a programmable logic device. Compared with the prior art, the inductive linear absolute position measuring device provided by the present invention is smaller in size, higher in reliability, higher in measurement accuracy, and stable and accurate in measurement.

Description

Technical Field

[0001] The present invention relates to the field of linear position measurement, and more particularly to an inductive linear absolute position measurement device. Background Art

[0002] In the field of sensors, inductive linear absolute position sensors are widely used in various devices that require precise measurement of linear positions. Conventional such sensors mainly consist of a grating scale and a reading head, where the grating scale adopts a dual-track design. Its working mechanism is as follows: The first group of inductive coils on the main control board moves above the first track, inducing eddy current signals to generate absolute digital signals; the second group of inductive coils slides above the second track, inducing incremental analog signals. Finally, a processing chip on the main control board, such as a single-chip microcomputer, comprehensively resolves these two types of signals to obtain high-resolution absolute position data. However, this dual-track design has obvious drawbacks. On the one hand, the setting of the dual tracks increases the overall size of the grating scale, which is not conducive to the development of devices towards miniaturization and integration; on the other hand, the complex structure of the two tracks reduces the reliability of the product.

[0003] Existing single-track inductive linear absolute position sensors, although simplifying the structure to a certain extent, have poor fault tolerance performance. Since only a single track is relied on to obtain position information, once there is local damage, contamination of the copper foil on the track, or strong external electromagnetic interference during the measurement process, it is very likely to cause abnormal induction signals, and then the position data cannot be accurately obtained, seriously affecting the stability and accuracy of the measurement. In addition, the existing single-track design lacks an effective response mechanism when dealing with position measurement under complex working conditions and is difficult to meet the requirements of high-precision and high-reliability measurement. Summary of the Invention

[0004] Aiming at the above problems, the present invention aims to provide an inductive single-track linear absolute position measurement device to reduce the size of the grating scale, improve the reliability of the product, and at the same time enhance the fault tolerance ability and measurement accuracy of the measurement device.

[0005] The present invention discloses an inductive linear absolute position measuring device, including a single-track grating scale and a read head. The read head includes: a substrate; induction coils drawn on the substrate, the induction coils including an S coil array and an R coil array, and each coil array includes n independent complementary coils, and each independent complementary coil is composed of 2 sub-coils wound in opposite directions in series; an excitation coil surrounding the induction coils, the excitation coil being a multi-turn closed coil in series; a hardware processing circuit disposed on the substrate, including an excitation signal driving circuit, a selection switch circuit, a demodulation circuit, an operational amplifier circuit, and a programmable logic device; the excitation signal driving circuit is used to generate an alternating current; the excitation coil receives the alternating current and generates an alternating magnetic field B1 acting on the single-track grating scale; the single-track grating scale generates an eddy current under the action of the alternating magnetic field B1, and the eddy current generates an alternating magnetic field B2 acting on the induction coils; the S coil array and the R coil array of the induction coils generate an S signal and an R signal under the action of the alternating magnetic field B2, and the S signal and the R signal have a phase difference of a quarter cycle; the selection switch circuit selects to connect the S signal and the R signal; the demodulation circuit receives the S signal and the R signal and outputs a modulation signal; the operational amplifier circuit receives the modulation signal and generates a coded waveform signal; the programmable logic device receives the coded waveform signal, generates coded information, and outputs position information.

[0006] Preferably, the single-track grating scale adopts one of specific designed code values such as a continuous displacement code, a binary code, an M-sequence code, etc.

[0007] Preferably, the sub-coils are wound in a multi-turn rectangular shape or a multi-turn sine half-wave pattern.

[0008] Preferably, both the S signal and the R signal include two complementary signals with a phase difference of 180°.

[0009] Preferably, the excitation signal driving circuit can generate a square wave of 2.5 MHz.

[0010] Preferably, the single-track grating scale adopts a printed circuit board with block copper foils arranged according to a specific code system on the surface.

[0011] Preferably, the excitation coil is connected to a frequency-selective capacitor to form an LC circuit.

[0012] Preferably, the excitation coil includes 2n multi-turn closed coils in series, and each closed coil surrounds each independent complementary coil.

[0013] Preferably, the programmable logic device is a single-chip microcomputer with multiple ADCs.

[0014] Compared with the prior art, an inductive linear absolute position measuring device provided by the present invention can meet the requirements. Compared with a conventional dual-track grating scale, the size of the grating scale is reduced, which is beneficial to the miniaturized design of the product. The S coil array and the R coil array with a phase difference of a quarter cycle between the two output signals can accurately output the code value signal. At the same time, only relying on the above-mentioned S coil array and R coil array can further output high-resolution information by subdivision modulation within each code value.

[0015] In addition, since n independent complementary coils can independently output analog signals for resolving high-resolution position information, according to the design of specific sequence code values, it can be ensured that two independent coils simultaneously output analog signals for resolving high-resolution position information, so that the above-mentioned redundant analog signals can generate high-resolution position information with mutual error correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of an inductive linear absolute position measuring device.

[0017] Figure 2 is a circuit principle block diagram of an inductive linear absolute position measuring device.

[0018] Figure 3 is a signal schematic diagram of the induction coil of an inductive linear absolute position measuring device.

[0019] Figure 4 is a schematic diagram of the coding waveform of an inductive linear absolute position measuring device.

[0020] DESCRIPTION OF THE REFERENCE NUMERALS:

[0021] 1. Read head, 11. Induction coil, 12. Excitation coil, 13. Selection switch circuit, 14. Demodulation circuit, 15. Operational amplifier circuit, 16. Single-chip microcomputer, 17. Excitation signal drive circuit;

[0022] 2. Grating scale, 21. Copper foil. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be further described in detail below with reference to the accompanying drawings.

[0024] An embodiment of the present invention discloses an inductive linear absolute position measuring device including a read head 1 and a grating scale 2. Refer to Figure 1 , Figure 2 .

[0025] On the substrate of the reader head 1 (not shown in the figure), 16 series-connected exciting coils 12 are evenly spaced and drawn. Each exciting coil 12 is a rectangular coil wound with multiple turns, surrounding the induction coil 11. The induction coils 11 are independent of each other and include an S coil array composed of S1 to S8 and an R coil array composed of R1 to R8. Each induction coil 11 contains two multi-turn sine half-waveform wound sub-coils. The winding directions of the two sub-coils are opposite, showing central symmetry to form complementary coils. The induction coils 11 are arranged horizontally in parallel at intervals. For the S coil array and the R coils, the distance from the center point of the previous coil to the center point of the next coil is λ. That is, the distance from the center point of the S1 coil to the center point of the S2 coil is λ, the distance from the center point of the S2 coil to the center point of the S3 coil is λ, and so on. The distance from the center point of the R7 coil to the center point of the R8 coil is λ. However, the distance between the S8 coil and the R1 coil is (1 + 1 / 2)λ.

[0026] A hardware circuit is also provided on the substrate, including a selection switch circuit 13, a demodulation circuit 14, an operational amplifier circuit 15, a single-chip microcomputer 16, and an exciting signal driving circuit 17.

[0027] The grating scale 2 uses a PCB board, and block copper foils 21 are etched on the PCB board according to the pre-designed 8-bit displacement continuous code.

[0028] When the inductive linear absolute position measuring device operates, that is, the grating scale 2 moves inside the reader head 1. At this time, the copper foil 21 moves under the exciting coils 12. The exciting signal driving circuit 17 generates a driving alternating current for the exciting coils 12, so that the exciting coils 12 radiate an alternating magnetic field. Since the exciting coils 12 surround the induction coils 11, the induction coils 11 are affected by the alternating magnetic field, and thus an alternating current is generated inside the induction coils 11. The exciting signal driving circuit is capable of generating a square wave of 2.5 MHz. Through the LC circuit composed of the exciting coils 12 and the frequency-selective capacitor, the sine and cosine waves of the same frequency in the square wave are output.

[0029] Reference Figure 3 、 Figure 4When an alternating current is generated inside the induction coil 11 under the influence of the excitation coil 12, since it is composed of complementary coils, when there is no conductor in the outside world, the alternating current in the induction coil 11 is in a counterbalanced state, so the value of the alternating current is 0. When a metal copper foil 21 appears below the induction coil 11, due to the eddy current effect generated by the metal copper foil 21 under the influence of the excitation coil 12, the current counterbalance state formed by the complementary effect of the induction coil 11 is broken, and thus the alternating current inside the induction coil 11 changes with the change of the projected area of the metal copper foil 21 on the induction coil 11. To prevent the position of the copper foil 21 and the induction coil 11 from being exactly symmetrical, that is, the areas of the copper foil 21 corresponding to the two sub-coils of the complementary coil are equal. This special state will cause the current inside the entire induction coil 11 to also be in a counterbalanced state, resulting in a code value jump during the signal demodulation of the output. Therefore, it is necessary to design an S coil array composed of S1 to S8 and an R coil array composed of R1 to R8. Since both the S coil and the R coil are composed of independent complementary coils, each coil array generates a waveform separately. For each complete single-cycle waveform output by the coils S[1:8] and R[1:8], the corresponding travel of the grating scale 2 in the read head 1 is 2λ. Since the R coil array lags behind the S coil array by a distance of 1 / 2λ, the two coil arrays output two sets of envelope carrier signals with a phase difference of one-quarter cycle, namely the R signal and the S signal.

[0030] When the inductive linear absolute position measuring device operates, that is, when the grating scale 2 moves in the read head 1, the R signal and the S signal are respectively generated by 8 independent complementary coils. It can be seen on the time axis that during operation, the waveforms of 2 different coils are changing. Each selection switch circuit 13 selects and connects an independent complementary coil of the S coil array and the R coil array. The R signal and the S signal generated by the S coil array and the R coil array are amplitude-modulated by the demodulation circuit 14, that is, the carrier signal is filtered out, and the demodulated envelope sine and cosine signals are input into the operational amplifier circuit 15 to form amplitude-amplified sine and cosine signals. The ADC module of the single-chip microcomputer circuit 16 samples the amplitude-amplified sine and cosine signals, and then through filtering and algorithm demodulation, during the operation of the inductive linear absolute position measuring device on the grating scale, a complete high-resolution absolute value signal is quickly obtained, and finally the position information is output.

[0031] The above are all the preferred embodiments of this application, and the protection scope of this application is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. An inductive linear absolute position measuring device, comprising a single-track grating scale and a read head, characterized in that: The read head includes: A substrate; Induction coils, drawn on the substrate, the induction coils include an S coil array and an R coil array, both the S coil array and the R coil array contain n independent complementary coils, and each of the independent complementary coils is composed of 2 sub-coils wound in opposite directions in series; An excitation coil, surrounding the induction coils, the excitation coil is a multi-turn closed coil connected in series; A hardware processing circuit, arranged on the substrate, including an excitation signal driving circuit, a selection switch circuit, a demodulation circuit, an operational amplifier circuit and a programmable logic device; The excitation signal driving circuit is used to generate an alternating current; The excitation coil receives the alternating current and generates an alternating magnetic field B1 acting on the single-track grating scale; The single-track grating scale generates an eddy current under the action of the alternating magnetic field B1, and the eddy current generates an alternating magnetic field B2 acting on the induction coils; The S coil array and the R coil array of the induction coils generate an S signal and an R signal under the action of the alternating magnetic field B2, and the phase difference between the S signal and the R signal is one-quarter cycle; The selection switch circuit selects to connect the S signal and the R signal; The demodulation circuit receives the S signal and the R signal and outputs a modulation signal; The operational amplifier circuit receives the modulation signal and generates an encoded waveform signal; The programmable logic device receives the encoded waveform signal, generates encoded information and outputs position information.

2. The inductive linear absolute position measuring device according to claim 1, wherein The single-track grating scale adopts one of a continuous displacement code, a binary code, and an M-sequence code.

3. An inductive linear absolute position measuring device according to claim 1, characterized in that, The sub-coils are wound in a multi-turn square shape or a multi-turn sine half-wave pattern.

4. An inductive linear absolute position measuring device according to claim 1, characterized in that Both the S signal and the R signal include two complementary signals with a phase difference of 180°.

5. An inductive linear absolute position measuring device according to claim 1, characterized in that The excitation signal driving circuit can generate a square wave of 2.5 MHz.

6. The inductive linear absolute position measuring device according to claim 1, wherein The excitation coil is connected to a frequency-selective capacitor to form an LC circuit.

7. An inductive linear absolute position measuring device according to claim 1, characterized in that, The excitation coil includes 2n multi-turn closed coils connected in series, and each of the closed coils surrounds each independent complementary coil.

8. An inductive linear absolute position measuring device according to claim 1, wherein, The programmable logic device is a single-chip microcomputer with multiple ADCs.

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