KR20060088333A - Method and apparatus for correcting systematic error using magnetic field - Google Patents

Abstract

The present invention relates to a method and apparatus for correcting a system error of a robot using a magnetic field.

A method for correcting a system error of a robot using a magnetic field according to an embodiment of the present invention includes a first calculation step of calculating a difference angle that is a difference between an absolute azimuth angle and a reference coordinate axis at a reference position, and predetermined robots at the reference position. Moving a distance by a distance, calculating a difference angle that is a difference between the absolute azimuth angle of the robot and a reference coordinate axis according to the displacement of the moved robot, and the difference angle and the second calculation step in the first calculation step. Compensating the error of the robot by the difference angle in.

Compass, magnetic field information, dead reckoning

Description

Method and apparatus for correcting system error of a robot using magnetic field {Method and apparatus for correcting systematic error using magnetic field}

1A and 1B illustrate an exemplary method of compensating for a system error occurring in a conventional mobile robot.

2 is an exemplary view of correcting a position by moving a robot equipped with a compass sensor according to an embodiment of the present invention.

3 is a graph showing the characteristics of the compass sensor.

4 is an exemplary view showing an example in which the compass sensor according to an embodiment of the present invention corrects the azimuth angle of the robot.

5 is a flowchart for correcting using a compass sensor according to an embodiment of the present invention.

6 is a block diagram showing some components of the robot according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

130: measurement unit 300: compass sensor unit

510: error correction

In the case of a robot moving by itself, it is essential to know clearly where the current position is. Therefore, much research has been done on the area of localization of robots.

Among them, dead reckoning calculates where the current position is by calculating the position of the starting point and the distance traveled by the robot. If only the information on the reference position is known, it is applied to many robots or mobile devices in that the current position can be arithmetically calculated through the direction in which the robot moves and the distance traveled. However, the movement of the robot is made through a machine, where a difference between the actual information and the calculated information may occur in the information about the wheel or the direction of the robot. This is called a systematic error. On the other hand, when the robot moves, the wheels may slide or the angle may change due to external factors. This is called nonsystematic error.

The cause of a systemic error is a difference in the diameter of the wheel of the robot, measured or estimated, or the wheelbase (Wheelbase), or the angle caused by the device not controlling the direction of movement correctly. Error. If these errors are not corrected, errors can accumulate. Therefore, since the accumulation of errors cannot be avoided only by the dead reckoning, there is a limit in setting and moving the robot by itself.

1A and 1B illustrate an exemplary method of compensating for a system error occurring in a conventional mobile robot.

1A shows the results of arithmetic migration. By arithmetic calculations, if the robot moves a distance of 4m counterclockwise or clockwise and changes its direction at right angles, it will reach its original position. However, when actually moved by the aforementioned system error, the starting point and the arrival point may be changed as shown in FIG. 1B due to the error of the angle and distance.

In order to correct this, the robot is moved as shown in FIG. 1B, and the measured error is calculated to calculate the corrected value during the movement. The measured error may be the diameter of the wheel, the distance between the wheels, and the angle.

If the diameter of the wheel, known as 5cm, is 4.6cm according to the result of the correction, it is possible to know how much distance should be moved when the robot moves by the correction diameter. In addition, if the angle was measured at 90 degrees and 87 degrees, then the next angle can be corrected by this error ("Correction of Systematic Odometry Errors in Mobile Robots", Johann Borenstein, Liquiang Feng).

However, in order to correct the error of the robot in the above-described manner, after moving the robot as shown in FIG. 1B, the position of the robot must be directly measured and calculated. For example, after moving the robot as shown in FIG. 1B, the robot is moved and a process of calculating the position of the center of the robot is compared with the starting point position. Therefore, not only takes a long time to measure one error, but also has a problem that the measurement must be made several times in order to make accurate measurements.

In addition, in order to perform the correction by applying this method to all the robots, it means that the correction must be performed for each robot. That is, in order to examine whether there is an error after producing the robot, it is necessary to calculate the error after moving the robot in the manner shown in FIG. 1B one by one, and it is unreasonable to apply this method when producing a large number of robots. In addition, errors can occur during the movement of the robot even during measurements to calibrate.

In addition, a method of measuring a location based on a camera or lighting on the ceiling was also presented. However, there has been a problem in that accurate measurement is required in that an additional microprocessor is required for image processing, and lighting may vary according to objects in a room.

Therefore, there is a need for a method and apparatus that corrects cumulative errors and also improves accuracy without much time and effort in calibration.

The technical problem of the present invention is to easily correct the system errors present in the robot.

Another technical problem of the present invention is to enable dead reckoning while preventing the accumulation of systemic errors.

The objects of the present invention are not limited to the above-mentioned objects, and other objects that are not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention relates to a method and apparatus for correcting a system error of a robot using a magnetic field.

A method for correcting a system error of a robot using a magnetic field according to an embodiment of the present invention includes a first calculation step of calculating a difference angle that is a difference between an absolute azimuth angle and a reference coordinate axis at a reference position, and predetermined robots at the reference position. Moving a distance by a distance, calculating a difference angle that is a difference between the absolute azimuth angle of the robot and a reference coordinate axis according to the displacement of the moved robot, and the difference angle and the second calculation step in the first calculation step. Compensating the error of the robot by the difference angle in.

Prior to the description, the meaning of terms used in the present specification will be briefly described. However, it should be noted that the terminology is used to limit the technical spirit of the present invention unless it is explicitly described as limiting the present invention as an explanation of the present specification.

Compass Sensor

The compass sensor is a sensor that orients itself based on the earth's magnetic field. Since the absolute azimuth angle is measured, the error does not accumulate. In addition, there is very little change over time in the same place. On the other hand, since the error according to the position is large, it is easy to see the difference between the previous position and the current position.

Base Position

Refers to the criteria for measuring position. The current position may be measured by measuring a distance and a direction from the reference position. The reference position in this specification is a point from which the robot starts and returns. Since home robots or mobile devices have a home base for charging or the like, such a home base may be a reference position.

2 is an exemplary view of correcting a position by moving a robot equipped with a compass sensor according to an embodiment of the present invention.

(a) is the situation before leaving home base. Before leaving the home base, the robot records the initial angle difference between the absolute azimuth and the reference home base through the compass sensor.

(b) shows a moving robot. The absolute azimuth angle is not measured during movement. And dead reckoning is performed through the rotation of wheels through odometry.

(c) is the situation where the robot returns to the home base. The robot calculates the current absolute azimuth from the compass sensor. The azimuth angle is corrected by comparing with the angle calculated by the measuring instrument in the process of (b), and the measuring instrument is tuned. Perform the steps (a), (b), and (c) by adjusting the corrected angle and the corrected wheel diameter. This allows for continuous calibration.

3 is a graph showing the characteristics of the compass sensor. The compass sensor shows an error in the measured angle as it travels in a 4m x 4m square area. It can be seen that the magnitude of the error varies greatly depending on the position. This is because the Earth's magnetic field is distorted to varying degrees in indoor environments. However, you can find that the error between the starting point and the ending point of the graph is almost the same, the end point is the point when the vehicle returns to the starting position after driving the 4m x 4m square area. It does not change, it means uniform.

4 is an exemplary view showing an example in which the compass sensor according to an embodiment of the present invention corrects the azimuth angle of the robot.

Initially, the difference between the robot's reference axis and the compass sensor is calculated. In FIG. 4, the angle Θ _i measured by the reference coordinate axis of the robot is 80 degrees. And measuring the angle (Θ _ci ) with a compass sensor is 90 degrees. Therefore, there is an error of 10 degrees between them.

After the robot moves a certain distance, the angle is measured when the robot returns to its original position. Θ _f is the angle based on the reference coordinate axis after the robot moves, and since the robot moved to the initial 80 degrees through dead reckoning, Θ _f is 80 degrees. By the way, the value measured by the compass sensor is 95 degrees. Since there is an error of 10 degrees from the reference sensor axis of the compass sensor and the robot before departure, it can be seen that the actual robot is 85 degrees. Therefore, a system error of 5 degrees has occurred, and the error can be corrected based on this.

5 is a flowchart for correcting using a compass sensor according to an embodiment of the present invention.

First, the initial position of the robot is measured (S110). It means to measure the reference position like the groove base. The azimuth angle θ _ci is measured through the compass sensor (S112). And the difference (θ _offset = θ _ci -θ _i ) and the reference coordinate axis of the robot is recorded (S114). This is to obtain a standard for correcting an error in the reference coordinate axis measured when the robot returns to the home base.

After the measurement is completed, the robot is moved (S120). The robot performs dead reckoning using an odometry while moving (S122). As a result, xd, yd, and angle information θd, which are distance information about coordinates, are calculated. The distance information can be obtained through the accumulated rotation angles of the left wheel and the right wheel. The moved angle can be obtained by using the difference between the accumulated moving distances of the left wheel and the right wheel.

The robot returns to the home base by the dead reckoning of step S122 (S124). The absolute azimuth angle θ _cf is measured by the compass sensor at the returned position (S126). And azimuth is corrected (S128). The correction of the azimuth angle uses θ _f which is the result of subtracting the azimuth data θ _cf measured in step S126 and θ _offset calculated in step S114. If θ _f is different from the previous θ _i , an error has occurred, and the left and right diameters of the wheels are corrected by obtaining er and el, which are errors with respect to the diameters of the left and right wheels, based on this error (S130).

The following formula shows the process of correcting the error.

First, the moving distance U _r of the right wheel and the moving distance U _l of the left wheel can be obtained through Equation 1. k is a conversion factor, and N _r and N _l represent the accumulated angles as the right and left wheels rotate. In addition, D _r and D _l are the diameters of the right and left wheels, respectively, and D ' _r and D' _l are the actual diameters of the right and left wheels, respectively. Therefore, the error between the actual wheel diameter and the arithmetic wheel diameter is e _Dr , e _Dl . The distance traveled is the product of the conversion factor, the accumulated angle and the wheel diameter multiplied by π.

The angle after the movement may be calculated by calculating a cumulative difference between the movement distances of the left wheel and the right wheel at the initial angle. This is shown in equation (2).

Initially, the angle measured by the instrument relative to the robot's direction is Θ ₀ and the angle measured by the compass sensor is Θ _C0 . After moving, the angle measured by the instrument is Θ and the angle measured by the compass sensor is Θ _C.

As shown in Equation 2, when the left and right wheels are rotated and the robot moves, the cumulative distance and the distance between the two wheels are accumulated and added to obtain an angle changed by the movement. When Equation 1 is applied to U _r and U _l in Equation 2, Equation 3 can be calculated.

는 나침반 센서로 측정한 결과이며

는 각도에 있어서의 오류(e_Θ)이다. The first half of the equation

Is the result measured by the compass sensor

Is the error in angle (e _Θ ).

In order to solve the error in the angle is developed as shown in equation (4).

On the other hand, in the present experiment, assuming that there is no error when going straight, that is, assuming that an error occurs only during rotation, the equation (5) can be derived. This means that going straight does not compensate.

The result calculated by substituting Equation 5 into Equation 4 is expressed as Equation 6.

In Equation 5, it can be seen that e _Dr and e _Dl have only opposite signs. Accordingly, e _Dl may be calculated as in Equation 7 through Equation 6.

On the other hand, since the error between the angle previously measured by the compass sensor and the angle measured by the robot is Θ _offset is the same as Equation 8.

As a result, the error of the angle can be obtained by subtracting Θ _offset from the compass sensor from the current angle of the robot as shown in Equation (9).

6 is a block diagram showing some components of the robot according to an embodiment of the present invention.

The term '~ part' used in this embodiment, that is, '~ module' or '~ table' means a hardware component such as software, FPGA or ASIC, and '~ module' or '~ part' Perform the functions. However, the term 'module' or 'unit' is not limited to software or hardware. The '~ module' or '~ part' may be configured to reside in an addressable storage medium or may be configured to play one or more processors. Thus, as an example, '~ module' or '~' means components such as software components, object-oriented software components, class components, and task components, processes, functions, attributes, and the like. , Procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided within the components and modules may be combined into a smaller number of components and modules or further separated into additional components and modules. In addition, the components and modules may be implemented to play one or more CPUs in a device or secure multimedia card.

6 is largely divided into three components. Compass sensor unit 300 for measuring the absolute azimuth angle, the moving unit 100 in charge of driving and measuring the mileage, and collects the data generated by the compass sensor unit 300 and the moving unit 100, the error And a controller 500 to correct.

The compass sensor unit 300 measures the absolute azimuth angle. Absolute azimuth is an angle based on magnetic north pole and magnetic south pole and always shows the same value in the same place. Compass sensor unit 300 may be configured as a sensor for detecting the magnetized metal and the rotation angle.

The moving unit 100 largely includes a driving unit 110 and a measuring unit 130. Although not shown in the drawings may further include a power transmission unit for transmitting power to the driving unit. The driving unit 110 includes a member that enables movement such as a wheel. The measurement unit 130 calculates the rotation speed of the driving unit 110 to calculate how much the moving distance is. Including the measuring instrument mentioned herein, the error of the movement distance calculated by the measuring unit 130 is incorrectly calculated the size of the diameter of the driving unit 110, or the rotation speed calculated by the measuring unit 130 is different from the actual Can occur in such cases.

The controller includes an error corrector 510, an absolute azimuth controller 530, an angle measurer 540, and a distance measurer 560.

The absolute azimuth control unit 530 stores the absolute azimuth angle sensed by the compass sensor 100 and compares the absolute azimuth angles of the compass sensor 100 measured after the movement.

The distance measuring unit 560 collects the moving distances of the driving unit 110 measured by the measuring unit 130 and measures the distance. In the case of the driving unit 110 composed of left and right wheels, since a difference in rotation of the left and right wheels occurs, various calculations are required to calculate the moving distance.

The angle measuring unit 540 measures the moving angle of the robot in the difference between the moving distances of the left and right sides measured by the measuring unit 130. It also measures the robot's reference coordinate axis.

The error correction unit 510 compares the absolute azimuth angle measured by the absolute azimuth angle controller 530 with values obtained from the results measured by the angle measuring unit 540 and the distance measuring unit 560 to correct the error when the error occurs. Do the work.

Table 1 is a table showing the azimuth correction performance of the compass sensor used in the present invention.

Counterclockwise Clockwise Instrument (without tuning) Instrument (UMB) Compass Instrument (without tuning) Instrument (UMB) Compass One 4.09 0.49 0.15 4.57 0.89 0.45 2 4.59 0.99 0.6 4.56 0.89 0.01 3 4.09 0.49 0.29 4.58 0.91 0.23 4 5.07 1.47 0.01 4.57 0.89 0 5 5.06 1.46 0.49 3.91 0.23 0.36 6 5.06 1.46 0.57 3.96 0.29 0.8 7 4.06 0.45 0.25 3.93 0.25 2.12 8 5.25 1.65 0.28 3.94 0.27 0.97 Average 4.66 1.06 0.33 4.25 0.58 0.62

After running the robot in a certain direction, that is, counterclockwise or clockwise, the experiment compares the accuracy of the azimuth measured by each sensor. The number of experiments is 8 times counterclockwise and 8 times clockwise. Each experiment measures the difference between the angle measured by the odometry, the difference between the angle of the compass sensor, and the instrument tuned by the compass sensor. The difference in angle is shown.

If the robot is run counterclockwise, the instrument's error is 4.66 degrees on average without tuning. The error when tuning through the instrument is 1.06. However, it can be seen that the compass sensor has an average error of 0.33 degrees. It can be seen that the error of the compass sensor is lower than the error of the instrument.

On the other hand, if the robot is driven in the clockwise direction, the average error of the instrument without tuning is 4.25 degrees, and if tuned, the error is 0.58 degrees. The compass sensor has an average error of 0.62 degrees.

Eight times, experiments counterclockwise and clockwise showed less error when using a compass sensor than when using a meter.

Table 2 is an experimental result comparing the performance of the embodiment of the present invention and the conventional UMB method.

Counterclockwise Clockwise Ex (mm) Ey (mm) EΘ (deg) Ex (mm) Ey (mm) EΘ (deg) UMB Mark 39.96 28.24 1.06 37.51 30.95 0.58 Example 15.28 11.37 0.47 13.90 18.82 0.64 Improve performance 61.8% 59.7% 55.7% 62.9% 39.2% -10.6%

The experiment is based on the measurement data obtained by driving the robot clockwise or counterclockwise in a 4m x 4m square area, using the tuning factor calculated using the UMB mark test and applying the method presented here. Comparing the results.

When driving in the counterclockwise direction (CCW), there is an error of 39.36 mm for the UMB mark test based on the x coordinate, but an error of 15.28 mm when using the compass sensor, and there is an improvement of about 61.8%. There is an error of 28.24 mm for the UMB mark test based on the y-coordinate, but an error of 11.37 mm for the compass sensor, and an improvement of about 59.7%. There is an error of 1.06 degrees in the UMB mark test, but an error of 0.47 degrees in the compass sensor, and an improvement of about 55.7%.

When driving clockwise (CW), there is an error of 37.51 mm for the UMB mark test based on the x-coordinate, but an error of 13.90 mm for the compass sensor, and an improvement of about 62.9%. There is an error of 30.95 mm for the UMB mark test based on the y-coordinate, but an error of 18.82 mm for the compass sensor, and an improvement of about 39.2%. On the other hand, there is an error of 0.58 degrees in the UMB mark test in the error of the angle, but there is an error of 0.64 degrees in the compass sensor. However, this difference is a very slight difference.

Those skilled in the art will appreciate that the present invention can be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and the equivalent concept are included in the scope of the present invention. Should be interpreted.

 By implementing the present invention it is possible to implement a dead reckoning robot that does not accumulate errors.

By implementing the present invention can provide a robot that automatically corrects the error.

Claims (13)

A first calculating step of calculating a difference angle that is a difference between the absolute azimuth angle and the reference coordinate axis at the reference position; Moving the robot by a predetermined distance from the reference position; A second calculating step of calculating a difference angle which is a difference between an absolute azimuth angle of the robot and a reference coordinate axis according to the displacement of the moved robot; And Correcting the error of the robot by the difference angle in the first calculation step and the difference angle in the second calculation step. The method of claim 1, The absolute azimuth angle is measured using a compass sensor, using a magnetic field to correct the system error of the robot. The method of claim 1, And the moving step is a step of returning the robot to the reference position. The method of claim 1, The moving step And recording the cumulative travel distance of the left wheel and the cumulative travel distance of the right wheel. The method of claim 4, wherein The correcting step Calculating a moving angle by the recorded cumulative moving distance; And And calculating the error of the cumulative movement distance by comparing the calculated movement angle with the difference angle calculated in the first calculation step. The method of claim 1, The correcting step And correcting an error between the diameter of the left wheel and the diameter of the right wheel of the robot. An angle measuring unit for controlling the information about the reference coordinate axis and measuring the moved angle; And A robot for correcting a system error by using a magnetic field, comprising an error correction unit for calculating the difference angle between the reference coordinate axis and the absolute azimuth angle measured by the angle measuring unit before and after the movement. The method of claim 7, wherein Compass sensor unit for measuring the absolute azimuth angle; And And storing an absolute azimuth angle measured by the compass sensor unit and controlling the compass sensor unit. The error compensator is a robot for correcting a system error using a magnetic field, to obtain information about the absolute azimuth angle through the absolute azimuth control unit. The method of claim 7, wherein A measuring unit measuring a moving distance; And Further comprising a distance measuring unit for calculating the moving distance through the measuring unit, The angle measuring unit measures an angle moved through the distance measured by the distance measuring unit, The error compensating unit corrects a system error using a magnetic field to obtain an error by comparing the absolute azimuth angle and the results measured by the angle measuring unit and the distance measuring unit. The method of claim 7, wherein The measuring unit calculates the accumulated rotation angle during movement to measure the movement distance, the robot for correcting the system error using a magnetic field. The method of claim 7, wherein It includes a driving unit for moving the robot by a predetermined distance, And the distance measuring unit corrects a system error by using a magnetic field to record the accumulated moving distance of the driving unit. The method of claim 11, And the traveling unit corrects a system error by using a magnetic field to return the robot to a starting position. The method of claim 7, wherein The error correction unit calculates the cumulative movement distance of the robot recorded by the distance measuring unit and the cumulative movement angle of the angle measuring unit, and calculates an error of the driving unit by a difference angle between the absolute azimuth angle measured by the compass sensor unit. Robot that corrects system errors.

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