CN114545913A - Wheel encoder calibration method and system for trolley - Google Patents
Wheel encoder calibration method and system for trolley Download PDFInfo
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- G05D1/02—Control of position or course in two dimensions
- G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
- G05D1/0231—Control of position or course in two dimensions specially adapted to land vehicles using optical position detecting means
- G05D1/0234—Control of position or course in two dimensions specially adapted to land vehicles using optical position detecting means using optical markers or beacons
- G05D1/0236—Control of position or course in two dimensions specially adapted to land vehicles using optical position detecting means using optical markers or beacons in combination with a laser
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
- G05D1/02—Control of position or course in two dimensions
- G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
- G05D1/0212—Control of position or course in two dimensions specially adapted to land vehicles with means for defining a desired trajectory
- G05D1/0223—Control of position or course in two dimensions specially adapted to land vehicles with means for defining a desired trajectory involving speed control of the vehicle
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- G05D1/02—Control of position or course in two dimensions
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- G05D1/0231—Control of position or course in two dimensions specially adapted to land vehicles using optical position detecting means
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- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
- G05D1/02—Control of position or course in two dimensions
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Abstract
The application provides a wheel encoder calibration method and system for a trolley; the wheel encoder calibration method comprises the steps of controlling a trolley to move for multiple times; the trolley is provided with a left wheel and a right wheel which are coaxial; acquiring pose change information of the mark points on the trolley after each movement; and calibrating the corresponding relation between the wheel rotation angle and the trolley rotation angle or calibrating the distance between the left wheel and the right wheel according to the pose change information of the mark point after each movement, the rotation angle of the left wheel and the rotation angle of the right wheel. Compared with the existing laser positioning calibration method, the wheel encoder calibration method and system for the trolley are not affected by ambient light, temperature and the like, and can more conveniently and accurately acquire pose change information of the trolley, so that the wheel encoder is calibrated more accurately.
Description
Technical Field
The application relates to the technical field of encoder calibration, in particular to a wheel encoder calibration method and system for a trolley.
Background
In the related scheme, the moving condition of the AGV is monitored through the infrared laser ranging principle (also called laser positioning), and then the corresponding relation between the moving condition and the output result of the encoder is calibrated according to the monitored moving condition. After calibration is completed, the current moving condition of the AGV can be calculated according to the output result of the encoder in actual use.
However, monitoring the AGV by using the principle of infrared laser ranging is easily affected by light, temperature and the like, so that the actual motion condition of the AGV cannot be accurately reflected, calibration is inaccurate, and the calculated current motion condition error of the AGV is large.
Disclosure of Invention
In order to solve the technical problem of high error rate of the identification result, the invention provides a wheel encoder calibration method capable of obviously improving the identification accuracy, which comprises the following steps:
controlling the trolley to rotate in place for multiple times; the trolley is provided with a left wheel and a right wheel which are coaxial;
acquiring pose change information of a mark point on the trolley after the trolley rotates each time through a visual positioning module, and acquiring a rotating angle of the left wheel and a rotating angle of the right wheel after the trolley rotates each time;
and calibrating the corresponding relation between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark points after the trolley rotates every time, and the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, so as to calibrate the wheel encoder.
Further, the calibrating the corresponding relationship between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark point after the trolley rotates every time, the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time includes:
calculating the rotation angle of the trolley body after each rotation according to the pose change information of the mark points after each rotation of the trolley;
and calibrating the corresponding relation among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley according to the rotation angle of the trolley body after the trolley rotates every time, the rotation angle of the left wheel after the trolley rotates every time and the rotation angle of the right wheel.
Further, calibrating the corresponding relationship among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley according to the rotation angle of the trolley body after the trolley rotates every time, the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, and the calibration method comprises the following steps:
establishing a two-row multi-row matrix representing the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates for multiple times, and a row matrix representing the rotation angle of a trolley body after the trolley rotates for multiple times;
and dividing the column matrix by the two-column multi-row matrix to obtain a two-row matrix which represents the corresponding relation of the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley.
Further, at least three marking points are provided; the three marking points are not on the same straight line, and the distance between each marking point in the three marking points and the other two marking points is unequal; the calculating the rotation angle of the trolley body after the trolley rotates every time according to the pose change information of the mark points after the trolley rotates every time comprises the following steps:
distinguishing different marking points according to the distance between the marking points, and obtaining the position relation of the different marking points after each rotation;
and comparing the position relation of the different mark points after each rotation with the position relation of the different mark points before each rotation to obtain the rotation angle of the vehicle body.
Further, distinguishing different mark points according to the distance between the mark points, and obtaining the position relationship of the different mark points after each rotation, including:
calculating the distance between different mark points in the three mark points after each rotation according to the coordinates of the three mark points after each rotation;
and determining the position relation of different mark points after each rotation according to the distance between the three marks after each rotation.
Further, the wheel encoder calibration method further comprises the following steps:
controlling the trolley to move linearly for multiple times;
acquiring the displacement of the trolley after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley;
and calibrating the distance between the left wheel and the right wheel according to the corresponding relation between the wheel rotation angle and the trolley rotation angle, the displacement of the trolley after each movement, the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley.
Further, calibrating the distance between the left wheel and the right wheel according to the corresponding relationship between the wheel rotation angle and the trolley rotation angle, the displacement of the trolley after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley, comprising:
establishing a plane rectangular coordinate system which comprises a transverse axis and a longitudinal axis and covers the moving area of the trolley;
respectively representing the moving distance along the transverse axis and the moving distance along the longitudinal axis after each movement of the trolley by using the corresponding relation between the wheel rotation angle and the trolley rotation angle, the distance representation between the left wheel and the right wheel, the rotating angular velocity of the left wheel, the rotating angular velocity of the right wheel, the moving time length of the trolley after each movement of the trolley and the included angle between the moving direction of the trolley and the transverse axis;
and the array formed by the moving distance along the transverse axis and the moving distance along the longitudinal axis after the trolley moves every time is equal to the array formed by the moving distance along the transverse axis and the moving distance along the longitudinal axis after the trolley moves every time, which are obtained by the vision positioning module, and the distance between the left wheel and the right wheel is calculated by a least square method.
Further, after calibrating the distance between the left wheel and the right wheel according to the corresponding relationship between the wheel rotation angle and the trolley rotation angle, the displacement of the trolley after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley, the method further comprises:
and calibrating the radius of the left wheel and the radius of the right wheel according to the corresponding relation between the wheel rotation angle and the trolley rotation angle and the distance between the left wheel and the right wheel.
Further, acquiring pose change information of the mark point on the trolley after the trolley rotates every time through a vision positioning module, and acquiring the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, wherein the pose change information comprises:
acquiring the rotating angular speed and the corresponding rotating time of the left wheel, and the rotating angular speed and the corresponding rotating time of the right wheel;
and calculating the rotation angle of the left wheel according to the rotation angular speed and the corresponding rotation time of the left wheel, and calculating the rotation angle of the right wheel according to the rotation angular speed and the corresponding rotation time of the right wheel.
The present application further provides a wheel encoder calibration system, including:
the control unit is used for controlling the trolley to rotate in place for multiple times; the trolley is provided with a left wheel and a right wheel which are coaxial;
the acquisition unit is used for acquiring pose change information of a mark point on the trolley after the trolley rotates every time through the visual positioning module, and acquiring the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time;
and the calibration unit is used for calibrating the corresponding relation between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark points after the trolley rotates every time, the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, so as to calibrate the wheel encoder.
According to the technical scheme, the method has at least the following advantages and positive effects:
compared with the existing laser positioning calibration method, the method and the system for calibrating the wheel encoder of the trolley are not affected by ambient light, temperature and the like, and can more conveniently and accurately acquire pose change information of the trolley, so that the wheel encoder is calibrated more accurately.
Drawings
Fig. 1 is a flow chart of a wheel encoder calibration method according to an embodiment of the present application.
Fig. 2 is a schematic flow chart of encoder calibration and accuracy evaluation according to an embodiment of the present application.
Fig. 3 is a block diagram illustrating a structure of a wheel encoder calibration system according to an embodiment of the present disclosure.
Fig. 4 is a schematic diagram of a hardware structure of an electronic device in an embodiment of the present application.
Fig. 5 is a schematic structural diagram of an appearance of a storage medium in an embodiment of the present application.
Detailed Description
Exemplary embodiments that embody features and advantages of the present application will be described in detail in the following description. It is to be understood that the present application is capable of various modifications in various embodiments without departing from the scope of the application, and that the description and drawings are to be taken as illustrative and not restrictive in character.
In the description of the present application, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a particular orientation, be constructed in a particular orientation, and be operated, and thus should not be construed as limiting the present application.
In the embodiments shown in the drawings, directional references (such as up, down, left, right, front, and rear) are used to explain the structure and movement of the various elements of the present application not absolutely, but relatively. These descriptions are appropriate when the elements are in the positions shown in the drawings. If the description of the positions of these elements changes, the indication of these directions changes accordingly.
The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless otherwise specified.
In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.
An AGV, i.e., an automatic guided vehicle, also called an automated guided vehicle, is a vehicle equipped with an automatic guide device such as an electromagnetic or optical device and having various transfer functions. Can detect wheel pivoted speed through wheel encoder, and then can calculate the removal condition such as moving distance, turned angle of AGV according to parameters such as wheel radius, two-wheeled interval.
Although parameters such as the radius of the wheels and the distance between the two wheels are preset before the AGV is produced and assembled, the actual moving condition of the AGV and the displacement condition calculated according to design parameters and the rotating speed of the wheels have errors due to machining and assembling errors, thermal expansion and cold contraction of the actual using environment, abrasion in the using process, micro structural deformation generated by pressure and the like.
In the related scheme, the actual displacement condition of the AGV is monitored through the infrared laser ranging principle (which can be called laser positioning), and then related parameters are calibrated according to the monitored displacement condition as reference, so that the current movement condition of the AGV calculated according to the wheel rotating speed and the like detected by an encoder is adjusted. However, monitoring the AGV by using the infrared laser ranging principle is easily affected by ambient light and temperature, and thus the actual position of the cart cannot be reflected well, and the calibration method also combines laser positioning and utilizes the nearest iteration point to calculate the transformation angle between the two positions, so that the positioning and calibration method has large errors.
The wheel encoder calibration method and system for a vehicle proposed in the present application will be described in detail with specific embodiments.
Referring to fig. 1, fig. 1 is a flow chart illustrating a method for wheel encoder calibration according to an exemplary embodiment.
In this example, a plurality of mark points are fixedly arranged on the body of the trolley. The trolley is provided with at least two coaxial left wheels and right wheels. The left wheel and the right wheel are respectively provided with a corresponding encoder. The trolley may in particular be an AGV (automatic guided vehicle).
The wheel encoder calibration method for the trolley at least comprises the following steps of S1 to S3, and the detailed description is as follows:
step S1, controlling the trolley to rotate in place for a plurality of times; the trolley is provided with a left wheel and a right wheel which are coaxial;
step S2, acquiring pose change information of the mark points on the trolley after each rotation of the trolley through a vision positioning module, and acquiring the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the trolley;
and step S3, calibrating the corresponding relation between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark points after the trolley rotates every time, the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, so as to calibrate the wheel encoder.
In the above steps S1 and S2, the test site may be a flat ground. The trolley is placed in a test field, then the trolley is controlled to rotate in place for at least 180 degrees for many times, and meanwhile, the visual positioning module is used for capturing the rotation motion of the trolley every time according to the movement information of the mark points on the trolley. The pose change information of the mark points on the trolley after each rotation is the pose change generated after the mark points rotate around the rotation central point of the trolley, and the pose change information of the mark points on the trolley is obtained, namely the pose change information of the trolley is obtained. Wherein the pose change information may be a rotation angle on a plane. Meanwhile, the rotation angle of the left wheel after the trolley rotates every time is obtained by using the feedback information of the wheel encoder corresponding to the left wheel, and the rotation angle of the right wheel after the trolley rotates every time is obtained by using the feedback information of the wheel encoder corresponding to the right wheel.
The method comprises the following steps of obtaining the rotation angle of a left wheel and the rotation angle of a right wheel after each rotation of the trolley, and specifically carrying out the following steps:
acquiring the rotating angular speed and the corresponding rotating time of the left wheel, and the rotating angular speed and the corresponding rotating time of the right wheel;
and calculating the rotation angle of the left wheel according to the rotation angular speed and the corresponding rotation time of the left wheel, and calculating the rotation angle of the right wheel according to the rotation angular speed and the corresponding rotation time of the right wheel.
In the above steps, the left wheel rotation angular velocity corresponding to each rotation of the trolley can be obtained through the left wheel encoder, and the right wheel rotation angular velocity corresponding to each rotation of the trolley can be obtained through the right wheel encoder. And then, multiplying the rotating angular speed of the left wheel corresponding to each rotation of the trolley by the rotating time to obtain the rotating angle of the left wheel of each rotation of the trolley. And multiplying the rotation angular speed of the right wheel corresponding to each rotation of the trolley by the rotation time to obtain the rotation angle of the right wheel of each rotation of the trolley.
In step S3, the corresponding relationship between the wheel rotation angle and the trolley rotation angle can be calibrated according to the pose change information of the mark point after each rotation of the trolley collected by the vision positioning module in the above steps and the rotation angle of the left wheel and the right wheel after each rotation of the trolley obtained by the information fed back by the wheel encoder.
The corresponding relation between the wheel rotation angle and the trolley rotation angle, namely the corresponding relation between the rotation angle of the left wheel, the rotation angle of the right wheel and the trolley rotation angle. After the corresponding relation between the wheel rotation angle and the trolley rotation angle is calibrated, the next step of calibrating such as the distance between the left wheel and the right wheel, the radius of the left wheel, the radius of the right wheel and the like can be carried out.
In some embodiments, the calibrating the corresponding relationship between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark point after each rotation of the trolley, and the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the trolley may specifically be performed according to the following steps:
calculating the rotation angle of the trolley body after each rotation according to the pose change information of the mark points after each rotation of the trolley;
and calibrating the corresponding relation among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley according to the rotation angle of the trolley body after the trolley rotates every time, the rotation angle of the left wheel after the trolley rotates every time and the rotation angle of the right wheel.
In the above steps, the trolley rotates in situ each time, and the pose change information of the mark points on the trolley after each rotation is the position change generated after the plurality of mark points rotate around the rotation central point of the trolley. Furthermore, the rotation angle of the trolley can be calculated through the position change of each mark point. According to the calculated rotation angle of the trolley after each rotation, the corresponding relation among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley can be calibrated by combining the corresponding rotation angle of the left wheel after each rotation and the corresponding rotation angle of the right wheel after each rotation.
In some embodiments, at least three marker points are fixed on the body of the trolley. The three marking points are not on the same straight line, and the distance between each marking point and the other two marking points is unequal. The method comprises the following steps of calculating the rotation angle of a vehicle body after the trolley rotates every time according to the pose change information of the mark points after the trolley rotates every time, wherein the step comprises the following steps:
distinguishing different marking points according to the distance between the marking points, and obtaining the position relation of the different marking points after each rotation;
and comparing the position relation of the different mark points after each rotation with the position relation of the different mark points before each rotation to obtain the rotation angle of the vehicle body.
In the above steps, different mark points can be distinguished according to the distance relationship of the at least three mark points. The visual positioning module does not have the function of distinguishing different marking points, but can acquire the position coordinates of the marking points in the area. According to the scheme, the plurality of mark points are fixedly arranged on the trolley according to a specific rule, so that different mark points are distinguished, and further the position and pose of the trolley are monitored.
Specifically, the following steps can be performed:
and calculating the distance between different mark points in the three mark points after each rotation according to the coordinates of the three mark points after each rotation. In this step, after the coordinates of the three moved mark points are obtained, the distances between the three mark points can be calculated.
And determining the position relation of different mark points after each rotation according to the distance between the three marks after each rotation. Because the distance and the position relation between the three mark points fixed on the trolley can not be changed, different mark points can be judged by comparing the distance between the three moved marks with the distance between the set mark points, and the position relation of the different moved mark points is further determined.
For example, points A and B are arranged longitudinally (in the front-rear direction of the cart) side by side on the cart, the distance between points A and B being 10 cm. With respect to the trolley body, point a is located directly in front of point B. The point B and the point C are arranged on the trolley in parallel in the transverse direction (in the left-right direction of the trolley), and the distance between the point B and the point C is 5 cm. Relative to the trolley body, the point C is positioned right to the point B. Therefore, no matter what pose state the trolley is in, the position coordinates of the three marking points can be obtained A, B, C, the distances among the three marking points are calculated to distinguish the three different marking points, and the position relations of the three different marking points are further determined.
As described in the above steps, the position relationship of the different mark points after rotation reflects the orientation of the trolley after rotation. The position relation of different mark points before rotation reflects the orientation of the trolley before rotation. In the above steps, the position relationship of three different mark points, that is, the position and orientation of the cart, is determined. And then the orientation of the trolley after rotation is compared with the orientation of the trolley before rotation, so that the rotation angle of the trolley body can be realized.
In some embodiments, the step of calibrating the corresponding relationship between the rotation angle of the left wheel, the rotation angle of the right wheel, and the rotation angle of the cart according to the rotation angle of the cart body after each rotation of the cart, the rotation angle of the left wheel after each rotation of the cart, and the rotation angle of the right wheel may specifically be performed according to the following steps:
establishing a two-row multi-row matrix representing the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates for multiple times and a row matrix representing the rotation angle of the trolley body after the trolley rotates for multiple times;
and dividing the column matrix by the two-column multi-row matrix to obtain a two-row matrix which represents the corresponding relation of the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley.
In the above steps, the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the cart are taken as one row of a multi-row matrix, and then the logarithm values obtained after the cart is rotated for many times can be combined into a two-column multi-row matrix, for example:
the rotation angle of the left wheel after the first rotation is recorded as thetaL0And the rotation angle of the right wheel is recorded as thetaR0；
The rotation angle of the left wheel after the second rotation is recorded as thetaL1And the rotation angle of the right wheel is recorded as thetaR1；
And so on, after the n +1 th rotation, the rotation angle of the left wheel is recorded as thetaLnAnd the rotation angle of the right wheel is recorded as thetaRn；
The two-column multi-row matrix representing the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the trolley is shown as the following formula 1:
the rotation angle of the car body after each rotation of the trolley is established into a column matrix corresponding to the two-column multi-row matrix, for example, the rotation angle of the car body after each rotation of the trolley is S in sequenceθ0To SθnThen, the column matrix is established as shown in the following formula 2:
the numerical values of each row in the two-row multi-row matrix and the numerical values of the corresponding row in the column matrix are obtained in the same rotation of the trolley.
And dividing the column matrix by the two-column multi-row matrix to obtain a two-row matrix representing the corresponding relation of the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley. The two-row matrix representing the corresponding relation between the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley can be used as J21And J22The formed column matrix is expressed, namely, a two-column multi-row matrix which expresses the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the trolley, a column matrix which is formed by the rotation angle of the trolley body after each rotation of the trolley captured by the visual positioning module, and the J21And J22The relationship of the formed column matrix is shown in the following formula 3:
therefore, after data obtained by each rotation of the trolley is substituted according to the relation, the least square method is used for solving, and J can be obtained21And J22The corresponding relation between the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley is calibrated.
The correspondence between the two-column multi-row matrix representing the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates for many times and the column matrix representing the rotation angle of the trolley body after the trolley rotates for many times can be derived by the following method:
the spacing between the left and right wheels is denoted b. Where b is equal to the left and right wheels up to twice the center of the vehicle body. The radius of the left wheel is denoted as rL. The radius of the right wheel is denoted rR. The forward speed of the left wheel is denoted as vL. The forward speed of the right wheel is denoted vR. The rotational angular velocity of the left wheel is represented as ωL. The rotational angular velocity of the right wheel is represented as ωR. The forward speed of the vehicle body center is denoted by v. The forward speed v of the center of the vehicle body can be regarded as the forward speed of the trolley. The rotational angular velocity of the vehicle body is denoted by ω.
the following formula 6 is obtained according to formula 4 and formula 5:
let the transformation matrix of the forward speed and the rotational speed of the vehicle body center be J,
the rotation angular velocity of the trolley is integrated to obtain the rotation angle of the trolley at each moment, namely, as shown in formula 9:
θ (t) ═ ω (t) dt (formula 9)
From formula 7, it can be obtained:
wherein, J21Representing the second row and first column values of the J matrix, J22Representing the values of the second row and the second column of the J matrix, J11Representing the first row and column values of the J matrix, J12Representing the first row and second column values of the J matrix.
Further, J can be replaced by11And J12Respectively with J21And J22To give the following formulae 11 and 12:
will omegatBy omegaLAnd omegaRIs represented by the following formulae 13 and 14:
ω(t)＝ω＝J21ωL+J22ωR(formula 13)
v(t)＝v＝J11ωL+J12ωR(formula 14)
Substituting formula 11 and formula 12 into formula 14 results in formula 15 shown below:
substituting formula 13 for formula 9 to obtain:
θ(t)＝∫ω(t)dt＝∫J21ωL+J22ωRdt
further, the following formula 16 can be obtained,
the rotation angle obtained by the visual positioning module is represented as Sθ. Initial J21And J22Can be obtained by actually measuring the radius and the distance between two wheels.
By the formula 16, the corresponding relation of the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle obtained by the corresponding relation vision positioning module is constructed according to a plurality of groups of experimental arrays by combining the rotation angles of the left wheel and the right wheel, and the corresponding relation is shown as the following formula 17:
wherein, ω isL0ΔT0Indicating the angle of rotation, omega, of the left wheel after the first rotation of the trolleyR0ΔT0Indicating the angle of rotation, omega, of the right wheel after the first rotation of the trolleyL1ΔT1Indicating the angle of rotation, omega, of the left wheel after the second rotation of the trolleyR1ΔT1The turning angle of the right wheel after the trolley turns for the second time is shown, and so on.
Further, equation 17 is solved by using the least square method according to the acquired experimental data, and J can be obtained21And J22The corresponding relation between the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley is calibrated.
After the corresponding relation among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley is calibrated, in the actual use of the trolley after leaving a factory, the data representing the position and the posture of the trolley can be calculated according to the rotation parameters of the left wheel and the right wheel.
With continued reference to fig. 1, in some embodiments of the present application, after calibrating the corresponding relationship between the wheel rotation angle and the trolley rotation angle, the wheel encoder calibration method for the trolley further includes the following steps:
step S4, controlling the trolley to move linearly for multiple times;
step S5, obtaining the displacement of the trolley after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley;
and step S6, calibrating the distance between the left wheel and the right wheel according to the corresponding relation between the wheel rotation angle and the trolley rotation angle, the displacement of the trolley after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley.
In the above steps S4 and S5, the test site may be a flat ground. And placing the trolley in a test field, and then controlling the trolley to linearly move for multiple times. And capturing the movement of the trolley every time by using the visual positioning module according to the movement information of the mark points on the trolley, thereby obtaining the displacement of the trolley after each movement. The left wheel rotating angle corresponding to each movement of the trolley can be obtained through the left wheel rotating angular speed and the rotating time of each movement of the trolley fed back by the encoder of the left wheel. The right wheel rotation angle corresponding to each movement of the trolley can be obtained through the right wheel rotation angular speed and the rotation time of each movement of the trolley fed back by the encoder of the right wheel.
In the step S6, the distance between the left wheel and the right wheel can be calibrated according to the corresponding relationship between the wheel rotation angle and the trolley rotation angle, the displacement of the trolley after each movement obtained in the steps S4 and S5, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley.
In some embodiments, the specific steps for calibrating the distance between the left and right wheels are as follows:
establishing a plane rectangular coordinate system which comprises a transverse axis and a longitudinal axis and covers the moving area of the trolley;
respectively representing the moving distance along the transverse axis and the moving distance along the longitudinal axis after each movement of the trolley by using the corresponding relation between the wheel rotation angle and the trolley rotation angle, the distance representation between the left wheel and the right wheel, the rotating angular velocity of the left wheel, the rotating angular velocity of the right wheel, the moving time length of the trolley after each movement of the trolley and the included angle between the moving direction of the trolley and the transverse axis;
and the array formed by the moving distance along the transverse axis and the moving distance along the longitudinal axis after the trolley moves every time is equal to the array formed by the moving distance along the transverse axis and the moving distance along the longitudinal axis after the trolley moves every time, which are obtained by the vision positioning module, and the distance between the left wheel and the right wheel is calculated by a least square method.
As described in the above steps, a rectangular plane coordinate system covering the moving area of the cart is established, including a horizontal axis and a vertical axis, so that the displacement in the re-area of the cart can be represented in the rectangular plane coordinate system.
In the above steps, the calibrated correspondence between the wheel rotation angle and the trolley rotation angle, the distance representation between the left wheel and the right wheel, the left wheel rotation angular velocity, the right wheel rotation angular velocity, the trolley moving time length, and the included angle between the trolley moving direction and the horizontal axis after each trolley moving can be used for respectively representing the moving distance along the horizontal axis and the moving distance along the longitudinal axis after each trolley moving, and the specific process is as follows:
in a rectangular coordinate system with the x axis as the horizontal axis and the y axis as the vertical axis, the advance speed of the trolley at each moment is integrated to obtain:
the displacement of the trolley along the x-axis direction is as shown in formula 18:
x (t) ═ v (t) cos θ (t) dt (formula 18)
Substituting the formula 1 in the above embodiment into the formula 18 in the embodiment, the following formula 19 is obtained
Wherein, cxRepresents a known or obtainable quantity in equation 19.
The displacement of the trolley along the y-axis direction is as shown in formula 20:
y (t) ═ v (t) sin θ (t) dt (formula 20)
Substituting equation 15 in the above embodiment into equation 20 in this embodiment yields equation 21 as follows:
wherein, cyRepresents a known or obtainable quantity in equation 21.
In the above steps, the displacements of the cart in the x-axis direction and the y-axis direction obtained by the vision positioning module can be specifically represented as Sx0And Sy0. The array formed by the moving distance along the horizontal axis and the moving distance along the vertical axis after each moving of the trolley is equal to the array formed by the moving distance along the horizontal axis and the moving distance along the vertical axis after each moving of the trolley obtained according to the visual positioning module. The corresponding relationship is constructed from multiple sets of experimental data as shown in the following formula 22:
equation 22 is solved using a least squares method to obtain b, thereby completing the calibration of the distance between the left and right wheels.
With continued reference to fig. 1, in some embodiments of the present application, after completing the calibration of the correspondence relationship between the wheel rotation angle and the trolley rotation angle and the calibration of the distance between the left wheel and the right wheel, the calibration method for the encoder of the trolley further includes:
and step S7, calibrating the radius of the left wheel and the radius of the right wheel according to the corresponding relation between the wheel rotation angle and the trolley rotation angle and the distance between the left wheel and the right wheel. The method comprises the following specific steps:
from equation set 10 in the above example, equation 23 below is derived:
rL＝-J21b rR＝J22b (type 23)
From which it can be based on the calibrated J21And J22And b is calculated to obtain rLAnd rR。
To this end, the radius r of the left wheel of the trolleyLAnd the radius r of the right wheelRAnd the distance b between the two wheels is calibrated.
Referring to fig. 2, in some embodiments, after the calibration of the distance b between two wheels and the radius r of the wheel is completed, the calibration accuracy can be evaluated as follows.
Evaluating the linear precision calibrated by the wheel encoder:
controlling the trolley to do linear motion with a certain distance on the flat ground, capturing the linear motion by using the visual positioning module, and acquiring the rotating angular speed omega of the left wheel of the trolley from the wheel encoderLAnd right wheel turning angular velocity ωR. And repeating the steps to obtain multiple groups of data. Then, the distance S traveled by the trolley from the start to the stop is calculated by using the calibrated two-wheel distance b and the wheel radius rv. The distance S of the trolley running is obtained by the vision positioning modulemI.e. the distance the vehicle actually travels. The running distance S calculated by the encodervAnd the driving distance S obtained by the vision positioning modulemAnd comparing and analyzing the errors so as to obtain the linear running precision calibrated by the wheel encoder. The specific evaluation formula is shown in the following formula 24:
wherein S isv0To SvnAnd the running distances calculated according to the calibration and the left and right wheel rotation angular speeds in a plurality of experiments are shown. Sm0To SmnRepresenting a plurality of driving distances acquired by the visual positioning module in a plurality of experiments. e.g. of the typeL0To eLnError for each experiment is indicated. If the error is within the allowable range, the calibration precision can be considered to meet the use requirement. If the error exceeds a certain range, the calibration precision can be considered to fail to meet the use requirement. Under the condition that the calibration precision cannot meet the use requirement, the encoder with higher precision can be replaced to carry out calibration again.
And (3) evaluating the rotation precision of the wheel encoder calibration:
controlling the trolley to do in-situ rotation movement of not less than 180 degrees on a flat ground, capturing the rotation movement by using a visual positioning module, and acquiring the left wheel rotation angular speed omega of the trolley from a wheel encoderLAnd right wheel turning angular velocity ωR. And repeating the steps to obtain multiple groups of data. Then, the angle θ v through which the cart is turned from start to stop is calculated using the two-wheel pitch b and the wheel radius r at which the calibration is completed. The visual positioning module acquires the rotating angle theta of the trolleymI.e. the angle the trolley actually turns through. The angle thetav calculated by the encoder and the angle theta obtained by the visual positioning module are comparedmAnd comparing and analyzing the errors so as to obtain the calibrated rotation angle precision of the wheel encoder. The specific evaluation formula is as follows 25:
wherein, thetam0To thetamnAnd the running distances calculated according to the calibration and the left and right wheel rotation angular speeds in a plurality of experiments are shown. Sv0To SvnThe multiple driving distances obtained by the vision positioning module in multiple experiments are shown. e.g. of the typew0To ewnError for each experiment is indicated. If the error is within the allowable range, the calibration precision can be considered to meet the use requirement. If the error exceeds a certain range, the calibration precision can be considered to fail to meet the use requirement. Under the condition that the calibration precision cannot meet the use requirement, the encoder with higher precision can be replaced to carry out calibration again.
Fig. 2 shows the whole process of encoder calibration and evaluation of calibration accuracy in the present application:
the trolley is controlled to rotate in situ for a plurality of times, and the encoder 1 obtains the rotating speed omega of the left wheel in each rotation through the process 2LAnd right wheel speed omegaRThen according to the left wheel rotation speed omega of each rotationLAnd right wheel speed omegaRThe angle of rotation of the car body at each turn of the car is shown in flow 3. Visual localization of motion capture system 4The module captures the original-place rotation movement of the trolley every time through the process 5, and the captured angle of the trolley body every time is obtained. In the process 6, J is obtained from the angle of rotation of the vehicle body per rotation shown in the process 3 and the angle of rotation of the vehicle body per rotation captured by the motion capture system 4 in the process 521And J22The corresponding relation between the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley is calibrated.
The trolley is controlled to do linear motion for a plurality of times, and the encoder 1 obtains the left wheel rotating speed omega of the trolley in each linear motion through the process 7LAnd right wheel speed omegaRThen according to the rotating speed omega of the left wheel in each linear motionLAnd right wheel speed omegaRThe distance traveled by the car body during each linear movement of the car is shown in flow 8. The vision positioning module of the motion capture system 4 captures each linear motion of the trolley through the process 9, and obtains the displacement/distance of each linear motion of the captured trolley body. In the process 10, the distance b between the left wheel and the right wheel of the trolley can be calculated according to the distance traveled by the trolley in each linear motion shown in the process 8 and the distance traveled by the trolley in each linear motion captured by the motion capture system 4 in the process 9, that is, the distance calibration of the wheels is completed.
In the process 11, the method is based on the J calibrated in the process 621And J22And the distance b between the left wheel and the right wheel, as specified in the process 10, the radius r of the left wheel can be calculatedLAnd the radius r of the right wheelRThereby completing the calibration of the left wheel radius and the right wheel radius. After the above calibrations are completed, in flow 12, the calibration accuracy is evaluated.
After the encoder is calibrated, even if all calibration accuracies can meet the use requirements, the wheels may be worn and the distance between the left wheel and the right wheel may be changed after the trolley is used for a period of time. Thus, the calibration accuracy needs to be re-evaluated periodically or aperiodically depending on the use case. When the calibration accuracy is re-evaluated, according to the method in the above embodiment, after a plurality of mark points are fixedly arranged on the trolley, the calibration accuracy can be re-evaluated by the visual positioning module in cooperation with the encoder to output data. If the accuracy is found to be not enough to meet the use requirement, the encoder may be recalibrated according to the method in the above embodiment.
Referring to fig. 3, the present application further provides a wheel encoder calibration system including a control unit 810, an acquisition unit 820, and a calibration unit 830.
The control unit 810 is used to control the cart to rotate in place multiple times. In some embodiments, the control unit 810 may also be used to control the cart to move in a straight line or to control the cart to move in a curved line.
Wherein, the dolly is equipped with coaxial left wheel and right wheel. The trolley may in particular be an AGV (automatic guided vehicle).
The obtaining unit 820 is configured to collect pose change information of the marker point on the trolley after each rotation of the trolley through the vision positioning module, and obtain a rotation angle of the left wheel and a rotation angle of the right wheel after each rotation of the trolley. In some embodiments, the obtaining unit 820 may also be configured to collect, through the vision positioning module, pose change information of the marker point on the trolley after each linear movement or curvilinear movement of the trolley, and obtain a rotation angle of the left wheel and a rotation angle of the right wheel after each rotation of the trolley.
The obtaining unit 820 may specifically include a visual positioning module and an obtaining module. The visual positioning module can sense the pose change of the mark points on the trolley, so that the pose change information of the mark points on the trolley after each rotation or movement is acquired. The pose change information of the mark points on the trolley after each rotation or movement can be acquired in each rotation or movement process of the trolley, and the pose change information corresponding to each rotation or movement can be acquired at one time through the record of each rotation or movement after the trolley rotates or moves for many times. The pose change information of the mark points can specifically comprise information such as displacement and rotation angle of the mark points. The acquisition module is used for acquiring the rotation angle of the left wheel and the rotation angle of the right wheel according to the angular speed of the left wheel, the angular speed of the right wheel and the corresponding rotation time detected by the wheel encoder during each rotation or movement.
The calibration unit 830 is configured to calibrate a corresponding relationship between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark point after each rotation of the trolley, and the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the trolley, so as to calibrate the wheel encoder.
The calibration unit 830 may calibrate the corresponding relationship between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark point obtained by the obtaining unit after each rotation, and by combining the rotation angle of the left wheel after each rotation and the rotation angle of the right wheel after each rotation. The rotation angle of the trolley can be obtained through the pose change information of the mark points on the trolley. The corresponding relation between the wheel rotation angle and the trolley rotation angle, namely the corresponding relation between the rotation angle of the left wheel, the rotation angle of the right wheel and the trolley rotation angle. The corresponding relation can be represented by a matrix through data/information obtained by the trolley through multiple rotations.
The calibration unit 830 may also calibrate the distance between the left wheel and the right wheel according to the pose change information of the marker point after each movement, the rotation angle of the left wheel after each movement, and the rotation angle of the right wheel after each movement. For example, according to the displacement of the mark point after each movement, the rotation angle of the left wheel after each movement and the rotation angle of the right wheel after each movement, and by combining the known or pre-calibrated corresponding relationship among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley, the distance between the left wheel and the right wheel can be calibrated. The distance of the calibrated left wheel from the right wheel can also be represented by a matrix.
In one embodiment, the present application further provides an electronic device including a memory and a processor, where the memory stores computer readable instructions, and the computer readable instructions, when executed by the processor, implement the wheel encoder calibration method for a vehicle as described above.
Fig. 4 is a schematic diagram of a hardware structure of an electronic device according to an exemplary embodiment.
It should be noted that the electronic device is only an example adapted to the application and should not be considered as providing any limitation to the scope of the application. The electronic device is also not to be construed as requiring reliance on, or necessity of, one or more components of the exemplary electronic device illustrated in fig. 4.
The hardware structure of the electronic device may have a large difference due to the difference of configuration or performance, as shown in fig. 4, the electronic device includes: a power supply 910, an interface 930, at least one memory 950, and at least one Central Processing Unit (CPU) 970.
The power supply 910 is used for providing an operating voltage for each hardware device on the electronic device.
The interfaces 930 include at least one wired or wireless network interface 931, at least one serial-to-parallel conversion interface 933, at least one input/output interface 935, and at least one USB interface 937, etc. for communicating with external devices.
The storage 950 is used as a carrier of resource storage, and may be a read-only memory, a random access memory, a magnetic or optical disk, etc., on which the stored resources include an operating system 951, application programs 953 or data 955, etc., which may be stored in a transient or permanent manner.
The operating system 951 is used to manage and control hardware devices and application programs 953 on the electronic device, so as to implement calculation and processing of the mass data 955 by the central processor 970, and may be Windows server, Mac OS XTM, unix, linux, and the like. The application programs 953 are computer programs that perform at least one particular task over the operating system 951 and may include at least one module (not shown in fig. 4) that may each include a sequence of computer-readable instructions for an electronic device. Data 955 may be http protocol data stored on disk, etc.
As described in detail above, an electronic device to which the present application is applied will read a series of computer readable instructions stored in the memory 950 by the central processor 970 to implement the wheel encoder calibration method for a vehicle as described in the previous embodiments.
Furthermore, the present application can also be implemented by hardware circuitry or by a combination of hardware circuitry and software instructions, and thus the implementation of the present application is not limited to any specific hardware circuitry, software, or combination of both.
Referring to fig. 5, in an embodiment, the present application further provides a computer readable storage medium 1000 having stored thereon a computer program which, when executed by a processor, implements the wheel encoder calibration method for a vehicle as described above.
While the present application has been described with reference to several exemplary embodiments, it is understood that the terminology used is intended to be in the nature of words of description and illustration, rather than of limitation. As the present application may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.
Claims (10)
1. A wheel encoder calibration method for a trolley is characterized in that a mark point is fixedly arranged on the trolley, and the calibration method comprises the following steps:
controlling the trolley to rotate in place for multiple times; the trolley is provided with a left wheel and a right wheel which are coaxial;
acquiring pose change information of a mark point on the trolley after the trolley rotates each time through a visual positioning module, and acquiring a rotating angle of the left wheel and a rotating angle of the right wheel after the trolley rotates each time;
and calibrating the corresponding relation between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark points after the trolley rotates every time, and the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, so as to calibrate the wheel encoder.
2. The method for calibrating the wheel encoder of the trolley according to claim 1, wherein calibrating the corresponding relationship between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark point after each rotation of the trolley and the rotation angle of the left wheel and the rotation angle of the right wheel after each rotation of the trolley comprises:
calculating the rotation angle of the trolley body after each rotation according to the pose change information of the mark points after each rotation of the trolley;
and calibrating the corresponding relation among the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley according to the rotation angle of the trolley body after the trolley rotates every time, the rotation angle of the left wheel after the trolley rotates every time and the rotation angle of the right wheel.
3. The wheel encoder calibration method for a cart according to claim 2, wherein calibrating the correspondence among the rotation angle of the left wheel, the rotation angle of the right wheel, and the rotation angle of the cart according to the rotation angle of the cart body after each rotation of the cart, the rotation angle of the left wheel, and the rotation angle of the right wheel after each rotation of the cart comprises:
establishing a two-row multi-row matrix representing the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates for multiple times and a row matrix representing the rotation angle of the trolley body after the trolley rotates for multiple times;
and dividing the column matrix by the two-column multi-row matrix to obtain a two-row matrix which represents the corresponding relation of the rotation angle of the left wheel, the rotation angle of the right wheel and the rotation angle of the trolley.
4. The method for calibrating a wheel encoder for a vehicle as claimed in claim 2, wherein there are at least three marking points; the three marking points are not on the same straight line, and the distance between each marking point in the three marking points and the other two marking points is unequal; the calculating the rotation angle of the trolley body after the trolley rotates every time according to the pose change information of the mark points after the trolley rotates every time comprises the following steps:
distinguishing different marking points according to the distance between the marking points, and obtaining the position relation of the different marking points after each rotation;
and comparing the position relation of the different mark points after each rotation with the position relation of the different mark points before each rotation to obtain the rotation angle of the vehicle body.
5. The method for calibrating a wheel encoder for a vehicle as claimed in claim 4, wherein the step of distinguishing the different marked points according to the distance between the marked points and obtaining the position relationship of the different marked points after each rotation comprises:
calculating the distance between different mark points in the three mark points after each rotation according to the coordinates of the three mark points after each rotation;
and determining the position relation of different mark points after each rotation according to the distance between the three marks after each rotation.
6. The wheel encoder calibration method for a vehicle as set forth in claim 1, further comprising:
controlling the trolley to move linearly for multiple times;
acquiring the displacement of the trolley after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley;
and calibrating the distance between the left wheel and the right wheel according to the corresponding relation between the wheel rotation angle and the trolley rotation angle, the displacement of the trolley after each movement, the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the trolley.
7. The method for calibrating a wheel encoder for a vehicle as claimed in claim 6, wherein calibrating the distance between the left wheel and the right wheel according to the correspondence between the wheel rotation angle and the vehicle rotation angle, the displacement of the vehicle after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the vehicle comprises:
establishing a plane rectangular coordinate system which comprises a transverse axis and a longitudinal axis and covers the moving area of the trolley;
respectively representing the moving distance along the transverse axis and the moving distance along the longitudinal axis after each movement of the trolley by using the corresponding relation between the wheel rotation angle and the trolley rotation angle, the distance representation between the left wheel and the right wheel, the rotating angular velocity of the left wheel, the rotating angular velocity of the right wheel, the moving time length of the trolley after each movement of the trolley and the included angle between the moving direction of the trolley and the transverse axis;
and the array formed by the moving distance along the transverse axis and the moving distance along the longitudinal axis after the trolley moves every time is equal to the array formed by the moving distance along the transverse axis and the moving distance along the longitudinal axis after the trolley moves every time, which are obtained by the vision positioning module, and the distance between the left wheel and the right wheel is calculated by a least square method.
8. The method for calibrating a wheel encoder for a vehicle as claimed in claim 6, wherein after calibrating the distance between the left wheel and the right wheel according to the correspondence between the wheel rotation angle and the vehicle rotation angle, the displacement of the vehicle after each movement, and the rotation angle of the left wheel and the rotation angle of the right wheel after each movement of the vehicle, the method further comprises:
and calibrating the radius of the left wheel and the radius of the right wheel according to the corresponding relation between the wheel rotation angle and the trolley rotation angle and the distance between the left wheel and the right wheel.
9. The wheel encoder calibration method for the trolley according to claim 1, wherein the acquiring, by a vision positioning module, pose change information of the marking point on the trolley after each rotation of the trolley and the acquiring a rotation angle of the left wheel and a rotation angle of the right wheel after each rotation of the trolley comprises:
acquiring the rotating angular speed and the corresponding rotating time of the left wheel, and the rotating angular speed and the corresponding rotating time of the right wheel;
and calculating the rotation angle of the left wheel according to the rotation angular speed and the corresponding rotation time of the left wheel, and calculating the rotation angle of the right wheel according to the rotation angular speed and the corresponding rotation time of the right wheel.
10. A wheel encoder calibration system for a cart, comprising:
the control unit is used for controlling the trolley to rotate in place for multiple times; the trolley is provided with a left wheel and a right wheel which are coaxial;
the acquisition unit is used for acquiring pose change information of a mark point on the trolley after the trolley rotates every time through the visual positioning module, and acquiring the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time;
and the calibration unit is used for calibrating the corresponding relation between the wheel rotation angle and the trolley rotation angle according to the pose change information of the mark points after the trolley rotates every time, the rotation angle of the left wheel and the rotation angle of the right wheel after the trolley rotates every time, so as to calibrate the wheel encoder.
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