Magnetic navigation sensor based on tunnel magnetoresistance sensor and detection method thereof

Abstract

The invention belongs to the field of robot control, and particularly relates to a magnetic navigation sensor based on a tunnel magnetoresistance sensor and a detection method of the magnetic navigation sensor. The sensor comprises a tunnel magnetoresistance sensor, an AD peripheral circuit, an MCU and peripheral circuit, and an isolation CAN bus transmit-receive circuit which are connected in sequence. According to the invention, the tunnel magnetoresistance sensor integrated with the conditioning circuit is selected, so that the complexity of a hardware circuit is reduced; the problem that the output voltage of the tunnel magnetoresistance sensor is inconsistent under the zero magnetic field condition is solved through a bias calibration algorithm; the offset proportion of the magnetic strip closest to the sensor chip is solved through a position fusion calculation method, so that the offset is continuously and variably output.

Description

Technical Field

[0001] The invention belongs to the field of robot control, in particular to a magnetic navigation sensor based on a tunnel magnetoresistance sensor and a detection method thereof. Background Art

[0002] A magnetic navigation sensor is a sensor component used for navigation and positioning of mobile robots.

[0003] The magnetic navigation sensor is used to detect the relative position of the vertical magnetic stripe mapped on the sensor. The tunnel magnetoresistive sensor chips are evenly arranged in a row, usually 8 to 32 chips. The magnetic stripe is about 50mm away from the magnetic navigation sensor. The effective magnetic field of the magnetic stripe within this distance is a parabolic curve. The closer the chip is to the center of the magnetic stripe, the higher the voltage value sensed and outputted, thereby determining the relative position of the magnetic stripe in the magnetic navigation sensor.

[0004] Magnetic navigation sensors usually have the following problems:

[0005] 1) The signal output by the magnetic induction chip is a weak signal and cannot be directly read into the MCU controller. It is necessary to add an operational amplifier circuit, which has the disadvantages of complex circuits and high costs.

[0006] 2) The voltage output by the magnetic induction chip is inconsistent in the case of zero magnetic field, resulting in deviation in the detected position.

[0007] 3) Due to cost and size reasons, the number of magnetic sensing chips distributed is limited. In order to obtain continuous position offset, the situation where the magnetic strip falls between two chips needs to be fitted through software algorithms, and the accuracy is not high.

[0008] 4) Only current measurement values ​​can be output in real time, and historical data cannot be reproduced.

[0009] 5) Cannot adapt to different magnetic strips and installation heights.

[0010] 6) Communication has no isolation protection. Summary of the invention

[0011] The present invention aims at the problems of correction of zero magnetic field deviation, position fitting, historical tracing, working condition adaptation, communication isolation, circuit complexity and cost constraints of the sensor, and proposes a magnetic navigation sensor and detection method based on tunnel magnetoresistance sensor. It ensures zero magnetic field deviation correction, improves position fitting accuracy, increases historical data tracing, increases parameter adaptation function, increases communication isolation circuit, reduces circuit complexity, and effectively reduces circuit cost.

[0012] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0013] A magnetic navigation sensor based on a tunnel magnetoresistance sensor comprises a tunnel magnetoresistance sensor, an AD peripheral circuit, an MCU and peripheral circuits connected in sequence, and an isolated CAN bus transceiver circuit.

[0014] The tunnel magnetoresistance sensor has a built-in signal conditioning circuit, which is composed of a tunnel magnetoresistance sensor chip U1 and its peripheral circuits.

[0015] The AD peripheral circuit is a first-order low-pass passive filter circuit composed of a resistor and a capacitor, one end of the resistor serves as the input end of the AD peripheral circuit, the other end is grounded through the capacitor, and the node between the resistor and the capacitor serves as the output end of the AD peripheral circuit.

[0016] The MCU and the peripheral circuits are composed of a digital and analog hybrid single chip microcomputer and its peripheral circuits.

[0017] The isolated CAN bus transceiver and power generation routing is composed of a CAN bus isolation transceiver with an integrated isolation power supply and its peripheral circuits.

[0018] The magnetic stripe detection method based on the magnetic navigation sensor comprises the following steps:

[0019] Calibrate the sensor's zero bias initial value in an electromagnetic environment with zero magnetic field;

[0020] Place the sensor at the set position to detect the magnetic stripe, perform curve fitting, and calculate the gain k and offset coefficient b;

[0021] Compensation is performed based on the gain k and the offset factor b.

[0022] The zero bias initial value calibration is specifically as follows:

[0023] The magnetic field intensity is used as the X-axis and the output voltage value is used as the Y-axis to construct the induction output curve coordinate system, where point A and point B are used as measurement points under two different magnetic field intensities, point C is the measurement point with a magnetic field intensity of 0, and straight line AB is the curve of the transfer function. Assuming that the slope of straight line AB is K and the length of OC is b, the transfer function is y=Kx+b. The offset coefficient b at zero magnetic field is recorded, and each calculation result y1 is corrected, y1=y–b=Kx.

[0024] The calculation method of the offset coefficient b is:

[0025] b=((ab) / (ac)) / ((ad) / (ae))

[0026] Among them, a, b, c, d, and e are the detection values ​​of 5 sensors respectively.

[0027] The magnetic navigation sensor saves the original data of the sampling points and automatically saves it in FLASH.

[0028] The present invention has the following beneficial effects and advantages:

[0029] 1. The present invention reduces the complexity of the hardware circuit by selecting a tunnel magnetoresistance sensor with an integrated conditioning circuit; solves the problem of inconsistent output voltage of the tunnel magnetoresistance sensor in a zero magnetic field condition by a bias calibration algorithm; solves the offset ratio of the magnetic strip closest to the sensor chip by a position fusion calculation method, so that the offset value is continuously changed and output.

[0030] 2. Through actual circuit testing, the sensor's initialization voltage output value calibration and continuous output of position sampling offset are realized, and the cost of the hardware circuit is reduced.

[0031] 3. The threshold is adjustable and can be adapted to a variety of magnetic stripes and magnetic nails. Different application sites can update the sensor sensitivity in real time to adapt to the actual application conditions on site. In one site, it can flexibly identify the signals of low-field magnetic tapes indoors and high-strength buried magnetic nails outdoors.

[0032] 4. Sampling value recording facilitates fault tracing and fault reminder. When the sensor encounters abnormal data, it reports the sampling data of the current position corresponding to the time through the bus, which can be used by users to maintain magnetic strips and magnetic nails according to their needs. Or it is convenient for the host computer to diagnose on-site faults and trace problems.

[0033] 5. The CAN isolation driver with integrated isolated power supply is compact in size, has strong field bus anti-interference ability, is convenient for system integration, and has stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Sensor circuit schematic;

[0035] Figure 2 Schematic diagram of zero magnetic field output offset correction;

[0036] Figure 3 Schematic diagram of the method for calculating the offset ratio of the magnetic stripe position;

[0037] Figure 4 Schematic diagram of a specific application example of a magnetic navigation sensor. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0039] The sensor circuit described in the present invention includes four parts, such as Figure 1 As shown, a tunnel magnetoresistance sensor 1, an AD peripheral circuit 2, an MCU and a peripheral circuit 3, and an isolated CAN bus transceiver circuit 4 are connected in series.

[0040] The tunnel magnetoresistance sensor is a tunnel magnetoresistance magnetic linear sensor with a built-in dedicated signal conditioning circuit, which consists of a tunnel magnetoresistance sensor and a dedicated signal conditioning circuit. The built-in dedicated signal conditioning circuit is used to adjust the zero drift and amplification factor parameters of the original signal detected by the tunnel magnetoresistance, and output a corrected linear signal, so the invention eliminates the need for signal conditioning signals. The specific circuit is as follows: Figure 1 As shown in the block diagram 1.

[0041] The AD is surrounded by a filter circuit composed of resistors and capacitors. Specifically, it is a first-order low-pass passive filter circuit. The specific circuit is as follows Figure 1 The block diagram is shown in Figure 2.

[0042] The MCU circuit uses a digital / analog hybrid microcontroller. After the sampling signal passes through the AD peripheral circuit, it can be directly connected to the MCU circuit. The specific circuit is as follows Figure 1 As shown in the block diagram 3.

[0043] The bus communication circuit uses a CAN bus isolation transceiver with an integrated isolated power supply as the bus communication interface. The specific circuit is as follows Figure 1 As shown in the block diagram 4.

[0044] In view of the inconsistent voltage value output by the magnetic induction chip under zero magnetic field, a zero-point bias calibration method is proposed here. Figure 2 , 5 in the block diagram is the induction output curve before calibration, where the X-axis is the magnetic field strength and the Y-axis is the output voltage value. The straight line AB is the curve of the transfer function. Assuming that the slope of the straight line AB is K, the length of OC is b, and the transfer function is y=Kx+b. Record the bias b value at zero magnetic field, and calculate the result y1=y–b=Kx each time. The corrected transfer function is a linear function passing through the origin O, as shown in 6 in the block diagram, which solves the problem of inconsistent voltage output in zero magnetic field.

[0045] The calculation method for position fusion, such as Figure 3 As shown. In the block diagram, 7 is a tunnel magnetoresistance sensor array, which is composed of 5 sensors evenly arranged, and 8 is the distribution of the magnetic field. The detection values ​​of the 5 sensors are a, b, c, d, and e, respectively. The four points b, c, d, and e are perpendicular to the straight line ao1, and four right triangles can be fitted, namely ao1b, ao2c, ao3d, and ao4e. According to the slopes of the hypotenuses of these four right triangles, the offset ratio of the sensor chip closest to the magnetic stripe can be calculated. The calculation formula is: ((ab) / (ac)) / ((ad) / (ae)).

[0046] Record tracing

[0047] The sensor can save the original data of the sampling point and automatically save it in FLASH. After a fault occurs, the data before and after the fault time point can be read through bus instructions, thereby solving faults that are difficult to find on site.

[0048] Threshold Adjustment

[0049] The sensitivity threshold of the sensor can be set through bus commands. Due to the difference in magnetic field strength of different magnetic stripes, there is a difference in field strength between indoor magnetic tapes and outdoor magnetic nails. The sensor threshold can be updated in real time through bus commands and saved in FLASH to adapt to different working conditions and applications of different magnetic stripes or magnetic nails.

[0050] Example

[0051] The present invention is applied to an intelligent mobile robot as a sensor of the robot to detect the position of a magnetic strip on the ground. Figure 4 As shown, the magnetic navigation sensor (Figure 9) is evenly distributed with 15 tunnel magnetoresistance sensor chips (Figure 11). When the robot is working, the sensor chip (Figure 11) periodically samples the magnetic field value generated by the magnetic strip (Figure 10).

[0052] The sensor is initialized and calibrated in an environment without strong electromagnetic fields. The sensor is perpendicular to the ground plane and the zero bias is initialized through the host computer bus command. Then the sensor is parallel to a 50mm wide tape and 50mm above the tape surface. The curve is fitted again through the host computer bus command. The program automatically calculates the gain k and offset b coefficients according to the correction scheme and saves them in FLASH.

[0053] The present invention eliminates the need for an analog signal conditioning circuit, and the overall circuit is simple and low in cost.

[0054] The present invention realizes zero magnetic field output offset correction through a software method.

[0055] The present invention realizes the calculation of the offset ratio of the magnetic stripe position by a software method.

[0056] The present invention stores the original data of the sensor sampling points for tracing the fault points and backtracking the problems.

[0057] The present invention can flexibly adjust the threshold value to adapt to the change of the magnetic stripe field strength, and is suitable for the application of buried rollers, magnetic nails, and magnetic stripes of different widths.

[0058] The present invention has the advantages of CAN bus isolated transmission and reception, and stable industrial field communication.

Claims

1. A magnetic navigation sensor based on a tunnel magnetoresistance sensor, characterized in that: It includes a tunnel magnetoresistance sensor, an AD peripheral circuit, an MCU and peripheral circuits connected in sequence, and an isolated CAN bus transceiver circuit.

2. A magnetic navigation sensor based on a tunnel magnetoresistance sensor according to claim 1, characterized in that: The tunnel magnetoresistance sensor has a built-in signal conditioning circuit, which is composed of a tunnel magnetoresistance sensor chip U1 and its peripheral circuits.

3. The magnetic navigation sensor based on the tunnel magnetoresistance sensor according to claim 1, characterized in that: The AD peripheral circuit is a first-order low-pass passive filter circuit composed of a resistor and a capacitor, one end of the resistor serves as the input end of the AD peripheral circuit, the other end is grounded through the capacitor, and the node between the resistor and the capacitor serves as the output end of the AD peripheral circuit.

4. The magnetic navigation sensor based on the tunnel magnetoresistance sensor according to claim 1, characterized in that: The MCU and the peripheral circuits are composed of a digital and analog hybrid single chip microcomputer and its peripheral circuits.

5. The magnetic navigation sensor based on the tunnel magnetoresistance sensor according to claim 1, characterized in that: The isolated CAN bus transceiver and power generation routing is composed of a CAN bus isolation transceiver with an integrated isolation power supply and its peripheral circuits.

6. The magnetic stripe detection method based on the magnetic navigation sensor according to claim 1 is characterized in that: The following steps are involved: Calibrate the sensor's zero bias initial value in an electromagnetic environment with zero magnetic field; Place the sensor at the set position to detect the magnetic stripe, perform curve fitting, and calculate the gain k and offset coefficient b; Compensation is performed based on the gain k and the offset factor b.

7. The magnetic stripe detection method of the magnetic navigation sensor according to claim 6, characterized in that: The zero bias initial value calibration is specifically as follows: The magnetic field intensity is used as the X-axis and the output voltage value is used as the Y-axis to construct the induction output curve coordinate system, where point A and point B are used as measurement points under two different magnetic field intensities, point C is the measurement point with a magnetic field intensity of 0, and straight line AB is the curve of the transfer function. Assuming that the slope of straight line AB is K and the length of OC is b, the transfer function is y=Kx+b. The offset coefficient b at zero magnetic field is recorded, and each calculation result y1 is corrected, y1=y–b=Kx.

8. The magnetic stripe detection method of the magnetic navigation sensor according to claim 6, characterized in that: The calculation method of the offset coefficient b is: b=((ab) / (ac)) / ((ad) / (ae)) Among them, a, b, c, d, and e are the detection values ​​of five sensors respectively.

9. The magnetic stripe detection method of the magnetic navigation sensor according to claim 6, characterized in that: The magnetic navigation sensor saves the original data of the sampling points and automatically saves it in FLASH.

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