WO2012031553A1

WO2012031553A1 - Magnetic encoder with tunnel magnetoresistance effect

Info

Publication number: WO2012031553A1
Application number: PCT/CN2011/079432
Authority: WO
Inventors: 王建国; 薛松生
Original assignee: 江苏多维科技有限公司
Priority date: 2010-09-07
Filing date: 2011-09-07
Publication date: 2012-03-15
Also published as: CN201748928U

Abstract

A magnetic encoder with tunnel magnetoresistance (TMR) effect comprising a magnet (11), a magnetic sensitive element, at least two operational amplifiers (17), a digital signal processing chip (18), and an output display module (19). The magnetic sensitive element uses a TMR biaxial magnetic field chip (15) located below the magnet (11). The operational amplifier (17), the digital signal processing chip (18), and the output display module (19) are arranged on a PCB circuit board (16), the PCB (16) is arranged on the outside of the magnet (11) and the TMR biaxial magnetic field chip (15). Another magnetic encoder with TMR effect comprises a magnetic drum (51), a magnetic grid (52) on the edge of the magnetic drum (51), a magnetic sensitive element, a signal amplifying and shaping module (54), a counting module (55), a computing and processing module (56), and a display module (57). The magnetic sensitive element uses a TMR half-bridge chip (53), the TMR half-bridge chip (53) is arranged on the edge of the magnetic drum (51) and 1-5 mm away from the magnetic grid (52). The signal amplifying and shaping module (54), the counting module (55), and the computing and processing module (56) are arranged on a PCB circuit board (58), the PCB circuit board (58) is arranged on the outside of the magnetic drum (51) and the TMR half-bridge chip (53). Using TMR chips made of TMR material as the magnetic sensitive element enables the magnetic encoder of the present invention to have high sensitivity, optimal temperature stability, high signal to noise ratio, and good noise resistance performance.

Description

Tunnel magnetoresistance effect magnetic encoder

Technical field

The invention relates to the field of magnetic encoders.

Background technique

Tunnel magnetoresistance effect (TMR, Tunnel) Magnetoresistance) is a new magnetoresistance effect newly discovered and started industrial application. It is mainly manifested in the magnetic multilayer film with the change of the magnitude and direction of the external magnetic field. The resistance of the magnetic multilayer film changes significantly. The AMR (anisotropic magnetoresistance effect) and GMR (giant magnetoresistance effect) found and actually applied have a larger rate of change in resistance. TMR materials have the advantages of large resistance change rate, large amplitude of output signal, high resistivity, low power consumption and high temperature stability. Because of these advantages, TMR has replaced the GMR in the read head for hard disk recording data. The magnetic field measuring device made of TMR has higher sensitivity, lower power consumption, better linearity, wider dynamic range, better temperature characteristics and stronger anti-interference ability than AMR, GMR and Hall devices. In addition, TMR can be integrated into existing chip micromachining processes to facilitate the creation of small integrated magnetic field sensors.

In the magnetic encoder, the magnetic sensitive element senses the changing magnetic field and outputs a voltage signal, and then uses the amplification shaping circuit to amplify and shape the voltage signal to output a pulse signal, and finally counts the pulse signal through the gate signal (standard clock), and further According to different applications, the angle, angular velocity, and rotational speed value to be measured are obtained. Generally, magnetic sensitive components in existing magnetic encoders mostly use Hall devices, AMR, and a small number of high-end products adopt GMR. However, since the Hall element has a very small output voltage (about several mV), it requires a subsequent circuit to amplify the signal, and usually has a large zero-point bias voltage, low sensitivity, poor anti-interference ability, and temperature and stress. Very sensitive. AMR and GMR belong to magnetoresistance components, but the resistance change rate of general AMR can only be less than 5%, and the actual industrial application is generally only 2% to 3%. Therefore, the measurement sensitivity is small, the output signal amplitude is small, and the amplification is also required. . The resistance change rate of the GMR component is large, and can reach about 20%. However, due to strong exchange and cooperation, the saturation field of the GMR component is very large, which limits the sensitivity improvement. At the same time, the resistance change rate of the GMR component does not change monotonously with the change of the magnetic field, and there is even symmetry, which makes the switching performance poor. These make them in the application of the magnetic encoder, the signal-to-noise of the output signal is relatively low, and affects its working stability.

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to overcome the deficiencies in the prior art and to provide a magnetic encoder capable of improving the signal-to-noise ratio and operational stability of an output signal of a magnetic encoder.

In order to achieve the above object, an aspect of the present invention provides a tunnel magnetoresistance effect magnetic encoder, comprising a magnetic block, a magnetic sensitive component, at least two operational amplifiers, a digital signal processing chip, an output display module, and a magnetic sensing component. TMR dual-axis magnetic field chip, The TMR biaxial magnetic field chip is located below the magnetic block; at least two operational amplifiers, a digital signal processing chip, and an output display module are located on a PCB circuit board. The PCB board is located outside the magnet block and the TMR biaxial magnetic field chip.

Preferably, the TMR biaxial magnetic field chip comprises two TMR full bridges, and the two TMR full bridges are placed orthogonally to each other.

Further optimized, in the TMR full bridge, the magnetic pinning layers of the opposite two TMR elements have the same magnetic moment direction and are anti-parallel to the direction of the pinning layers of the other two opposite TMR elements, and the magnetic freedom of the four TMR elements The layer magnetic moments are parallel.

Another aspect of the present invention provides a tunnel magnetoresistance effect magnetic encoder, comprising a magnetic drum, a magnetic grid located on an edge of the drum, a magnetic sensitive component, a signal amplification shaping module, a counting module, a calculation processing module, A display module, the magnetic sensitive component uses a TMR half-bridge chip, and the TMR half-bridge chip is located at the edge of the drum and is spaced 1-5 mm from the magnetic grid. The signal amplification shaping module, the counting module, and the calculation processing module are located on a PCB circuit board, and the PCB circuit board is located outside the drum and the TMR half bridge chip.

Preferably, the magnetic pinning layers of the two TMR elements in the TMR half-bridge chip are antiparallel to each other, and the magnetic moment directions of the magnetic free layers of the two TMR elements are parallel to each other. The TMR half-bridge chip operates in a switching state.

Compared with the prior art, the beneficial effect of the invention is that the tunnel magnetoresistance effect encoder has high sensitivity, good temperature stability, high signal to noise ratio and anti-noise performance due to the TMR chip made of TMR material as the magnetic sensitive component. it is good. In addition, TMR is sensitive to magnetic fields. Unlike photoelectric sensors, it is non-contact and has strong environmental resistance such as dust and oil.

In addition, the second type of tunnel magnetoresistance effect encoder using TMR half-bridge chip as magnetic sensitive component, TMR half-bridge chip works in the switching state, which has strong anti-interference ability and higher working stability. From the above scheme, combined with TMR material has the advantages of large resistance change rate, large output signal amplitude, high resistivity, low energy consumption and high temperature stability. TMR is applied to existing magnetic encoders as magnetic coding. The magnetic sensitive component of the device can effectively improve the signal-to-noise ratio, working stability, anti-interference ability and comprehensive performance of the magnetic encoder. Compared with the traditional magnetic encoder, the signal-to-noise ratio is higher, the anti-interference ability is stronger, and the sensitivity is more. High, work more stable advantages.

DRAWINGS

1 is a schematic diagram showing the structure and working principle of a magnetic encoder according to a first embodiment of the present invention;

2 is a schematic diagram of a TMR biaxial magnetic field chip constructed by using two TMR full bridges in the magnetic encoder shown in FIG. 1;

3 is a schematic diagram of a TMR full bridge structure used in the TMR biaxial magnetic field chip shown in FIG. 2;

4 is a schematic diagram showing the output characteristics of the TMR full bridge shown in FIG. 3;

FIG. 5 is a schematic diagram showing the structure and working principle of another magnetic encoder according to Embodiment 2 of the present invention; FIG.

6 is a schematic view showing the structure of a TMR half bridge used in the magnetic sensor of the magnetic encoder shown in FIG. 5;

Fig. 7 is a schematic diagram showing the output characteristics of the TMR half bridge shown in Fig. 6.

detailed description

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

Figures 1-7 reflect an alternate embodiment of a magnetic encoder in accordance with the present invention.

Embodiment 1

A tunnel magnetoresistance effect magnetic encoder shown in FIG. 1 includes a magnetic block 11, a magnetic sensitive component, two operational amplifiers 17, a digital signal processing chip 18, and an output display module 19, and the magnetic sensitive component adopts TMR. The biaxial magnetic field chip 15 and the TMR biaxial magnetic field chip 15 are located below the magnetic block 11.

The two operational amplifiers 17, the digital signal processing chip 18, and the output display module 19 are located on a PCB circuit board 16, which is located outside the magnetic block 11 and the TMR biaxial magnetic field chip 15.

As shown in FIG. 2, the TMR biaxial magnetic field chip 15 is composed of two TMR

full bridges

21, 22, and the two TMR

full bridges

21, 22 are placed orthogonally to each other. The two TMR

full bridges

21, 22 simultaneously sense the magnetic field components generated by the moving magnetic blocks in the two orthogonal directions X, Y, and convert them into two voltage output signals.

The magnetic pinning layers of the opposite two TMR elements in the TMR

full bridges

21, 22 have the same magnetic moment direction and are anti-parallel to the direction of the pinning layers of the other two opposite TMR elements, and the magnetic free layer magnetic of the four TMR elements The directions of the moments are parallel.

The PCB circuit board 16 is located outside the magnet block 11 and the TMR biaxial magnetic field chip 15; the magnetic block 11 generates an alternating magnetic field on the TMR biaxial magnetic field chip 15 when moving.

The operational amplifier 17 amplifies the voltage output signal to a level that matches the DSP input. The DSP chip has an analog to digital conversion function, as well as digital filtering, and computational processing functions.

The output display module 19 can display the output information.

The magnetic encoder using a single TMR dual-axis magnetic field chip is mainly used for the measurement of the angle value. Its outstanding features are high signal-to-noise ratio, high precision, simple structure and low cost. Working principle: the magnetic block follows the moving object to be tested Moving together, an alternating magnetic field is generated at the TMR biaxial magnetic field chip. The TMR chip senses the orthogonal X, Y direction magnetic field changes and outputs two voltage signals, and then amplifies through two operational amplifiers, and then inputs to the DSP. The chip performs analog-to-digital conversion, digital filtering, and calculation processing to obtain changes in magnetic field strength and angle, and finally displays through the display module. Since the analog-to-digital conversion has been performed, the digital angle value and the magnetic field strength are output, that is, the encoding of the angle of the moving magnet block is realized.

The structure and working principle of the magnetic encoder are shown in Figure 1. The magnetization direction of the magnet block 11 shown in the figure is shown by the arrow 12. The magnet block rotates about its axis 14, and the direction of rotation shown in Fig. 1 is as indicated by arrow 13, either clockwise or counterclockwise. A magnetic sensitive component, namely a TMR biaxial magnetic field sensing chip 15, is disposed on the lower end surface of the magnetic block. Two operational amplifiers 17, a DSP digital signal processing chip 18, and a display module 19 On a PCB circuit board 16. The output of the TMR biaxial magnetic field chip 15 is connected via wires 20 to an operational amplifier 17 on the PCB circuit board 16.

When the magnet block 11 rotates, it generates an alternating magnetic field on the TMR biaxial magnetic field chip 15, and its components in two orthogonal directions also alternately change. The output voltage caused by the change of the magnetic field in the X and Y directions is input to the two operational amplifiers 17 via the wire 20 for amplification, and a voltage signal matching the analog-to-digital conversion ADC input of the DSP digital signal processing chip 18 is obtained. The voltage is subjected to analog-to-digital conversion (ADC), digital filtering, and arithmetic processing by the DSP digital signal processing chip 18, and the amplitude and angle of the alternating magnetic field at the TMR biaxial magnetic field chip 15 are outputted in real time by the display module 19 display.

The structure of the TMR biaxial magnetic field sensor chip 15 is as shown in FIG. A TMR dual-axis magnetic field sensing chip 15 is constructed by placing two mutually perpendicular TMR

full bridges

21, 22 orthogonally perpendicularly. The TMR

full bridges

21 and 22 respectively measure the orthogonal Y-direction magnetic field Hy The magnetic field Hx 24 in the 23 and X directions is converted into an output voltage, respectively.

The structure of the TMR

full bridges

21, 22 is shown in FIG. The TMR full bridge 21 is composed of four TMR elements, which are an upper left element 211, an upper right element 212, a lower left element 213, and a lower right element 214, respectively. The

magnetic moment directions

221, 224 of the magnetically pinned layer of the upper left element 211 and the lower right element 214 are the same, and are antiparallel to the

magnetic moment directions

222, 223 of the magnetic upper layer of the upper right element 212 and the lower left element 213. The

magnetic moment directions

231, 232, 233, 234 of the magnetic free layer of the TMR upper left element 211, the upper right element 212, the lower left element 213, and the lower right element 214 are parallel to each other. The

electrodes

215, 216 are the voltage input terminals Vi+, Vi- of the TMR full bridge; the

electrodes

217, 218 are the voltage output terminals Vo+, Vo- of the TMR full bridge.

The full bridge output characteristics of the TMR full bridge are shown in Figure 4. The output voltage of the TMR full bridge is V=Vo+-Vo-.

The change occurs as the direction and magnitude of the external magnetic field 7 changes. When the direction of the applied magnetic field 7 is negative (-) and the magnetic field strength is greater than the reverse saturation field H1, the output voltage of the TMR full bridge is the lowest and saturated. When the direction of the applied magnetic field 7 is positive (+) and the magnetic field strength is greater than the forward saturation field H2, the output voltage of the TMR full bridge is the highest and reaches saturation. The magnetic field range between -H1 and H2 is the measurement range of the TMR full bridge. Between -H1 and H2, the output voltage varies linearly with the applied magnetic field 7.

Embodiment 2

Referring to FIG. 5, another tunnel magnetoresistance effect magnetic encoder (also referred to as a magnetic encoder) includes a drum 51, a magnetic grid 52 on the edge of the drum, a magnetic sensitive component, and a signal amplification and shaping. The module 54 , a counting module 55 , a computing processing module 56 , a display module 57 , the magnetic sensitive component uses a TMR half bridge chip 53 , and the TMR half bridge chip 53 is located at the edge of the magnetic drum 51 and spaced apart from the magnetic gate 52 . -5mm The signal amplification shaping module 54, the counting module 55, and the calculation processing module 56 are located on a PCB circuit board 58 which is located outside the drum 51 and the TMR half bridge chip 53.

As shown in FIG. 6, the magnetic pinning layers of the two

TMR elements

614, 615 in the TMR half-bridge chip 53 are antiparallel to each other, and the magnetic moment directions of the magnetic free layers of the two TMR elements are parallel to each other. The TMR half-bridge chip operates in a switching state.

In actual operation, the drum 51 moves with the object to be tested, and the magnetic grid 52 thereon generates an alternating magnetic field on the TMR half bridge chip 53, and the TMR half bridge chip 53 operates in the switching state.

The magnetic grid encoder of TMR half-bridge magnetic field chip working in the switching state is mainly used for measuring angle, angular velocity and rotational speed. Its outstanding features are stable operation, good resistance to harsh working environment and strong anti-interference ability. Working principle: The magnetic drum engraved with the magnetic grid moves along with the coded object to be tested, and the magnetic grid motion on the magnetic drum generates a changing magnetic field. The TMR half bridge chip senses the magnetic field generated by the magnetic grid and outputs a voltage signal. The signal amplification and shaping module is used to amplify and shape the voltage signal to obtain a pulse signal, and the pulse signal is counted by the counting module, and then processed by the calculation processing module to obtain the encoded value of the moving object, and the encoded value may be angle, angular velocity, speed, and finally Displayed by the display module.

A schematic diagram of the structure and working principle of the tunnel magnetoresistance effect magnetic encoder according to the second embodiment is shown in FIG.

In operation, the drum 51 is mounted on a moving object by a mounting rod to move together with the moving object. During the movement, the magnetic grid 52 on the drum 51 generates a magnetic field on the magnetic sensitive element, i.e., the TMR half bridge 53, and outputs an alternating voltage signal. The voltage signal is input to the signal amplification shaping module 54 through the wire 59 for amplification and shaping, and a pulse signal is obtained, and then counted by the counting module 55. The count value is then input to the calculation processing module 56 for computational processing, displayed by the display module 57 or directly output to other control modules for use in controlling the motion of the moving object.

The structure of the TMR half bridge chip 53 is as shown in FIG. 6. The TMR half-bridge chip body shown in the figure is composed of two TMR elements, a left element 614 and a right element 615, respectively. The direction of the magnetic moment of the magnetic pinned layer of the left element 614 and the right element 615 is the

arrow

616 and 617 are opposite and parallel to each other. The directions of the magnetic free layers of left element 614, right element 615, i.e.,

arrows

618 and 619, are parallel to each other. The electrodes 611 and 612 are the voltage input terminals Vin+, Vin- of the TMR half bridge, the electrode 613 is the voltage output terminal of the TMR half bridge, and the voltage input terminal 612 is also the reference terminal of the TMR half bridge voltage output, and its output voltage is Vout.

Schematic diagram of the output characteristics of the TMR half bridge, as shown in Figure 7. The output voltage Vout of the TMR half bridge changes as the direction and magnitude of the external magnetic field 7 changes. When the direction of the applied magnetic field 7 is negative (-) and the magnetic field strength is greater than the reverse saturation field H1, the TMR half bridge outputs a low level 321. When the direction of the applied magnetic field 7 is positive (+) and the magnetic field strength is greater than the forward saturation field H2, the TMR half bridge outputs a high level 320, that is, the TMR half bridge operates in the switching state. The range of the magnetic field between -H1 and H2 is the measurement range of the TMR half bridge.

Claims

A tunnel magnetoresistance effect magnetic encoder comprising a magnetic block, a magnetic sensitive component, at least two operational amplifiers, a digital signal processing chip, and an output display module, wherein the magnetic sensitive component adopts TMR dual An axial magnetic field chip, the TMR biaxial magnetic field chip is located below the magnetic block; at least two operational amplifiers, a digital signal processing chip, and an output display module are located on a PCB circuit board, and the PCB circuit board is located on the magnetic block and the TMR dual axis The outside of the magnetic field chip.

2. A tunnel magnetoresistance effect magnetic encoder according to claim 1, wherein the TMR biaxial magnetic field chip comprises two TMR full bridges, and the two TMR full bridges are placed orthogonally to each other.

3. The tunnel magnetoresistance effect magnetic encoder of claim 2, wherein: In the TMR full bridge, the magnetic pinning layers of the opposite two TMR elements have the same magnetic moment direction and are anti-parallel to the direction of the pinning layers of the other two opposite TMR elements, and the magnetic free layer magnetic moment directions of the four TMR elements parallel.

4. A tunnel magnetoresistance effect magnetic encoder comprising a magnetic drum, a magnetic grid located on an edge of the drum, a magnetic sensitive component, a signal amplification shaping module, a counting module, a computing processing module, and a display module. The utility model is characterized in that: the magnetic sensitive component adopts a TMR half bridge chip, and the TMR half bridge chip is located at an edge of the magnetic drum and is spaced apart from the magnetic grid by 1-5 mm. The signal amplification shaping module, the counting module, and the calculation processing module are located on a PCB circuit board, and the PCB circuit board is located outside the drum and the TMR half bridge chip.

5. A tunnel magnetoresistance effect magnetic encoder according to claim 4, wherein: The magnetic pinning layers of the two TMR elements in the TMR half-bridge chip are antiparallel to each other, and the magnetic moment directions of the magnetic free layers of the two TMR elements are parallel to each other. The TMR half-bridge chip operates in a switching state.