A calibration method for zero angle and limit angle of a forklift rudder wheel

Abstract

This invention relates to a calibration method for the 0-angle and limit angles of a forklift steering wheel, belonging to the technical field of all-day operation methods in the steel manufacturing industry. The technical solution of this invention is as follows: A map is constructed using a single-steering-wheel forklift in a test scenario; the position coordinates of the forklift during its movement are collected, along with the parameters corresponding to the steering wheel rotation angle output by the position system; the forklift's trajectory is fitted based on the collected position coordinates during its movement, forming new forklift trajectory generation points; a model function is constructed, and the new forklift trajectory generation points are substituted to calculate the 0-angle position of the forklift steering wheel; the limit rotation radius is determined by least-squares fitting, and the limit angles on both sides are calculated. The advantages of this invention are: it eliminates the need for additional calibration tool templates, demanding calibration environments, and complex spatial perception algorithms; the calibration method is simple, has low requirements for the calibration environment, low calibration costs, and is easy to implement in mass production on assembly lines within a workshop.

Description

Technical Field

[0001] The present invention relates to a calibration method for the zero angle and limit angle of a forklift steering wheel, and belongs to the technical field of all-day operation methods in the iron and steel manufacturing industry. Background Art

[0002] In the iron and steel manufacturing industry, material handling is the core link throughout the entire process from ironmaking, continuous casting, hot rolling, cold rolling to finished product warehousing. The handling objects are characterized by large weight (such as steel coils, slabs), high value, and irregular shapes, and the operating environment is often accompanied by complex conditions such as high-temperature radiation, high dust, ground oil stains, and spatial intersection and limitation. Traditional manual operation not only poses safety risks but also难以满足钢铁制造行业全天作业的生产需求。近年来,随着智慧工厂与“黑灯车间”的推进,采用自动无人叉车实现关键工序间的物料自动转运,已成为行业提升自动化水平、保障作业安全与稳定性的重要发展方向。

[0003] The precise control of an automatic unmanned forklift highly depends on the steering wheel. The steering wheel is an electro-mechanical integration module that integrates drive, steering, and high-precision angle feedback, and its steering angle is precisely commanded by the control system. In this control closed-loop, a core parameter is the "zero angle", that is, the mechanical mid-position that physically ensures the wheels go straight must strictly correspond to the "zero position" signal fed back by the sensor to the control system. If there is a deviation in this reference, the unmanned forklift will generate systematic control errors during actual operation. Specifically, when the vehicle is expected to drive straight, it will continuously deviate, and the control system has to continuously output correction commands, resulting in a snake-like oscillation of the running trajectory and a serious loss of positioning accuracy. It not only cannot complete the precise loading and unloading tasks but also poses a collision safety risk in a dense storage area environment. At the same time, it also causes reactive power loss and abnormal wear of the drive and steering systems. As the other two core parameters, the left and right limit angles of the steering wheel physically control the minimum turning radius of the forklift's left and right turns and also need to strictly correspond to the "left and right limit" signals of the control system to enable the forklift to achieve steering and precise position control in a narrow space.

[0004] Fundamentally speaking, the accurate calibration of the zero angle and left and right limit angles of the steering wheel is the technical cornerstone for constructing the reliability of its "perception-control-execution" digital closed-loop. Only by establishing an accurate angle reference can the upper-layer navigation algorithm, path tracking controller, and the underlying steering wheel actuator of the unmanned forklift be coordinated and unified to ensure that digital commands are accurately converted into linear or curved motions in the physical world. Summary of the Invention

[0005] It should be noted that there is an incomplete sentence in the original text at line 8 which is "难以满足钢铁制造行业全天作业的生产需求。近年来,随着智慧工厂与“黑灯车间”的推进,采用自动无人叉车实现关键工序间的物料自动转运,已成为行业提升自动化水平、保障作业安全与稳定性的重要发展方向。" and it has been translated as best as possible while keeping the context clear. If you can provide the complete correct text, it will be possible to produce a more accurate translation.The purpose of this invention is to provide a calibration method for the 0-angle and limit angles of a forklift steering wheel. By having a single-steering-wheel forklift automatically travel along multiple trajectories on a flat ground area according to upper-level instructions, the automatic calibration of the 0-angle and left and right limit angles of the single-steering-wheel unmanned forklift steering wheel can be completed simultaneously. This method does not require additional calibration tool templates, harsh calibration environments, or complex spatial perception algorithms. The calibration method is simple, has low requirements for the calibration environment, low calibration cost, and is easy to mass-produce on a production line in a workshop, effectively solving the aforementioned problems existing in the background technology.

[0006] The technical solution of this invention is: a method for calibrating the zero-angle and limit angle of a forklift steering wheel, comprising the following steps:

[0007] (1) Mapping was performed using a single-steering wheel forklift in a test scenario on a flat ground area;

[0008] (2) Drive the forklift to the starting position, set the parameter of the control wheel rotation angle to the parameter value corresponding to 0 degrees, send the walking command to make the forklift move forward, record the position coordinates of each frame during the forklift's driving process, and the parameter corresponding to the wheel rotation angle output by the position system of each frame during the forklift's driving process.

[0009] (3) Drive the forklift to the starting position, set the control wheel rotation angle parameter in the command system at certain angle intervals to the corresponding parameter value in the range of -40 degrees to 40 degrees, send the travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the wheel rotation angle output by the position system in each frame during the forklift's travel.

[0010] (4) Drive the forklift to the starting position, set the control wheel rotation angle parameter to the maximum pulse of the steering wheel turning to the left, send a travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the steering wheel rotation angle output by the position system in each frame during the forklift's travel.

[0011] (5) Drive the forklift to the starting position, set the parameter for controlling the steering wheel angle to the maximum pulse for steering wheel to the right, send a travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the steering wheel angle output by the position system for each frame during the forklift's travel.

[0012] (6) Fit the forklift running trajectory. Based on the position coordinates of the forklift during the driving process, perform least squares fitting of the circle. Combine the angle corresponding to the current trajectory and the radius value of the fitted circle to form a new forklift trajectory generation point.

[0013] (7) Solve for the position of the forklift steering wheel at 0 deflection angle. Based on the principle that the radius of the forklift's running trajectory is infinite when the steering wheel is at 0 deflection angle and the mathematical model of the forklift steering wheel's steering, construct a model function and substitute the new forklift trajectory generation point to calculate the position of the forklift steering wheel at 0 deflection angle.

[0014] (8) Solve for the position of the forklift steering wheel limit angle, perform least squares fitting of the limit rotation radius, and calculate the limit angles on the left and right sides.

[0015] In step (3), the parameters for controlling the steering wheel angle are set to 2.5 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 30 degrees, 40 degrees, -40 degrees, -30 degrees, -20 degrees, -15 degrees, -10 degrees, -5 degrees and -2.5 degrees respectively, and recorded.

[0016] The specific steps in step (6) are as follows:

[0017] The forklift's trajectory is an arc, where (X, Y) are the forklift's position coordinates during its movement. The forklift lies on a certain arc, and the coordinates of multiple points are considered. , ,…, Perform a least-squares fit on the circle; assume the equation of the circle is... Solve based on the above multiple points. and The value,

[0018] The equation of the circle to be found can be written in general form as follows:

[0019]

[0020] in , ,

[0021] For data points The minimum error function is defined as:

[0022]

[0023] Therefore, there is

[0024]

[0025] If it is sorted out, then there is

[0026]

[0027] This system of linear equations has only three unknowns: D, E, and F. It can be solved using Gaussian elimination, and further solutions can be obtained. and The value;

[0028] Combine the angle corresponding to the current trajectory with the radius value of the fitted circle to form a new pair of points. Each trajectory can yield a set of corresponding points, i.e. , , ..., , ..., .

[0029] The specific steps in step (7) are as follows:

[0030] Points generated by each forklift trajectory , , ..., , ..., Draw to x-axis, radius In a Cartesian coordinate system, when the actual steering wheel deflection angle is 0, the forklift's trajectory is a straight line with an infinite radius. Based on this principle and the mathematical model of forklift steering wheel rotation, a model function is constructed.

[0031]

[0032] in and These are the parameters to be solved, when hour, As the radius approaches infinity, the forklift's turning radius becomes infinite, meaning the forklift's trajectory becomes a straight line. This refers to the 0 deflection angle of the steering wheel to be calibrated;

[0033] Will , , ..., , ..., Substituting into the equation, we can obtain

[0034]

[0035] Construct the error function as follows

[0036]

[0037] Due to the existence of absolute value and the singularity of the tangent function, the error function It is not differentiable, therefore it is not possible to use parameters. The solution is obtained by finding the derivative, and the specific algorithm is as follows:

[0038] Step 1 Fix Solving for the optimal

[0039] For any given , to obtain smallest ,at this time yes Quadratic function:

[0040]

[0041] right Take the derivative and set it to zero:

[0042]

[0043] Solving

[0044]

[0045] get yes The function;

[0046] Step 2 Transform into Univariate function

[0047] Will Substitute return , get about The function is as follows:

[0048]

[0049] Indicates that in a given The minimum sum of squared residuals;

[0050] Step 3: Search for the optimal

[0051] Need to find in one-dimensional real space Make Minimum, because the model is in or Strange, and It should be near the origin, and the search interval should be set to... , A small positive number, such as 0.1; uniform sampling within this interval. A point, such as Calculate each point Find the point with the smallest value; thus obtain the minimum value. The best estimate made , It is the estimated value of the forklift steering wheel's 0 deflection angle;

[0052] Then Substituting into formula (10), we get

[0053] (12).

[0054] The specific steps in step (8) are as follows:

[0055] Confirmed and Then, according to the formula

[0056]

[0057] The limiting rotation radius of the least squares fit based on the collected data. Solve for the limiting angles on both the left and right sides.

[0058] (14).

[0059] The beneficial effects of this invention are: by having a single-steering wheel forklift automatically travel along multiple trajectories on a flat ground area according to instructions from the upper level, the automatic calibration of the 0-angle and left and right limit angles of the single-steering wheel unmanned forklift can be completed simultaneously. It does not require additional calibration tool templates, harsh calibration environments, or complex spatial perception algorithms. The calibration method is simple, has low requirements for the calibration environment, low calibration cost, and is easy to mass produce on a production line in the workshop. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the planar structure of a forklift steering wheel in the background art of this invention;

[0061] Figure 2 This is a three-dimensional structural diagram of a forklift steering wheel, which is part of the background technology of this invention.

[0062] Figure 3 This is a schematic diagram of forklift operation when the parameters are set to 0 degrees according to an embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram of the data storage format according to an embodiment of the present invention;

[0064] Figure 5 This is a schematic diagram of forklift travel when the parameter setting is 2.5 degrees according to an embodiment of the present invention;

[0065] Figure 6 This is a schematic diagram illustrating the relationship between the steering wheel angle and the forklift turning radius according to an embodiment of the present invention;

[0066] Figure 7 This is a schematic diagram illustrating the relationship between the steering wheel angle and the forklift's travel trajectory according to an embodiment of the present invention;

[0067] Figure 8 These are the extreme angle position curves on the left and right sides of an embodiment of the present invention;

[0068] In the diagram: 1. Steering wheel; 2. Fork arm; 3. Fork arm wheel assembly; 4. Angle. Detailed Implementation

[0069] To make the purpose, technical solutions, and advantages of the invention's embodiments clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only a small part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0070] A method for calibrating the zero-angle and limit angle of a forklift steering wheel includes the following steps:

[0071] (1) Mapping was performed using a single-steering wheel forklift in a test scenario on a flat ground area;

[0072] (2) Drive the forklift to the starting position, set the parameter of the control wheel rotation angle to the parameter value corresponding to 0 degrees, send the walking command to make the forklift move forward, record the position coordinates of each frame during the forklift's driving process, and the parameter corresponding to the wheel rotation angle output by the position system of each frame during the forklift's driving process.

[0073] (3) Drive the forklift to the starting position, set the control wheel rotation angle parameter in the command system at certain angle intervals to the corresponding parameter value in the range of -40 degrees to 40 degrees, send the travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the wheel rotation angle output by the position system in each frame during the forklift's travel.

[0074] (4) Drive the forklift to the starting position, set the control wheel rotation angle parameter to the maximum pulse of the steering wheel turning to the left, send a travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the steering wheel rotation angle output by the position system in each frame during the forklift's travel.

[0075] (5) Drive the forklift to the starting position, set the parameter for controlling the steering wheel angle to the maximum pulse for steering wheel to the right, send a travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the steering wheel angle output by the position system for each frame during the forklift's travel.

[0076] (6) Fit the forklift running trajectory. Based on the position coordinates of the forklift during the driving process, perform least squares fitting of the circle. Combine the angle corresponding to the current trajectory and the radius value of the fitted circle to form a new forklift trajectory generation point.

[0077] (7) Solve for the position of the forklift steering wheel at 0 deflection angle. Based on the principle that the radius of the forklift's running trajectory is infinite when the steering wheel is at 0 deflection angle and the mathematical model of the forklift steering wheel's steering, construct a model function and substitute the new forklift trajectory generation point to calculate the position of the forklift steering wheel at 0 deflection angle.

[0078] (8) Solve for the position of the forklift steering wheel limit angle, perform least squares fitting of the limit rotation radius, and calculate the limit angles on the left and right sides.

[0079] In step (3), the parameters for controlling the steering wheel angle are set to 2.5 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 30 degrees, 40 degrees, -40 degrees, -30 degrees, -20 degrees, -15 degrees, -10 degrees, -5 degrees and -2.5 degrees respectively, and recorded.

[0080] The specific steps in step (6) are as follows:

[0081] The forklift's trajectory is an arc, where (X, Y) are the forklift's position coordinates during its movement. The forklift lies on a certain arc, and the coordinates of multiple points are considered. , ,…, Perform a least-squares fit on the circle; assume the equation of the circle is... Solve based on the above multiple points. and The value,

[0082] The equation of the circle to be found can be written in general form as follows:

[0083]

[0084] in , ,

[0085] For data points The minimum error function is defined as:

[0086]

[0087] Therefore, there is

[0088]

[0089] If it is sorted out, then there is

[0090]

[0091] This system of linear equations has only three unknowns: D, E, and F. It can be solved using Gaussian elimination, and further solutions can be obtained. and The value;

[0092] Combine the angle corresponding to the current trajectory with the radius value of the fitted circle to form a new pair of points. Each trajectory can yield a set of corresponding points, i.e. , , ..., , ..., .

[0093] The specific steps in step (7) are as follows:

[0094] Points generated by each forklift trajectory , , ..., , ..., Draw to x-axis, radius In a Cartesian coordinate system, when the actual steering wheel deflection angle is 0, the forklift's trajectory is a straight line with an infinite radius. Based on this principle and the mathematical model of forklift steering wheel rotation, a model function is constructed.

[0095]

[0096] in and These are the parameters to be solved, when hour, As the radius approaches infinity, the forklift's turning radius becomes infinite, meaning the forklift's trajectory becomes a straight line. This refers to the 0 deflection angle of the steering wheel to be calibrated;

[0097] Will , , ..., , ..., Substituting into the equation, we can obtain

[0098]

[0099] Construct the error function as follows

[0100]

[0101] Due to the existence of absolute value and the singularity of the tangent function, the error function It is not differentiable, therefore it is not possible to use parameters. The solution is obtained by finding the derivative, and the specific algorithm is as follows:

[0102] Step 1 Fix Solving for the optimal

[0103] For any given , to obtain smallest ,at this time yes Quadratic function:

[0104]

[0105] right Take the derivative and set it to zero:

[0106]

[0107] Solving

[0108]

[0109] get yes The function;

[0110] Step 2 Transform into Univariate function

[0111] Will Substitute return , get about The function is as follows:

[0112]

[0113] Indicates that in a given The minimum sum of squared residuals;

[0114] Step 3: Search for the optimal

[0115] Need to find in one-dimensional real space Make Minimum, because the model is in or Strange, and It should be near the origin, and the search interval should be set to... , A small positive number, such as 0.1; uniform sampling within this interval. A point, such as Calculate each point Find the point with the smallest value; thus obtain the minimum value. The best estimate made , It is the estimated value of the forklift steering wheel's 0 deflection angle;

[0116] Then Substituting into formula (10), we get

[0117] (12).

[0118] The specific steps in step (8) are as follows:

[0119] Confirmed and Then, according to the formula

[0120]

[0121] The limiting rotation radius of the least squares fit based on the collected data. Solve for the limiting angles on both the left and right sides.

[0122] (14).

[0123] Example:

[0124] In practical applications, this invention includes a data acquisition method and a data analysis algorithm.

[0125] Data acquisition methods

[0126] (1) Mapping is performed using a single-steering wheel forklift in a test scenario with a flat ground surface;

[0127] (2) For example Figure 3 The forklift is driven to a starting point A. The parameter controlling the steering wheel angle is set to the value corresponding to 0 degrees in the command system and then fixed. The command system sends a travel command to make the forklift move forward, automatically traveling from point A to point B. The distance between points A and B is approximately 8 meters, and the travel speed is slow and steady (approximately 0.2 meters / s). The position coordinates (x, y, theta) of the forklift in each frame during its movement, as well as the parameter corresponding to the steering wheel angle output by the position system in each frame (wheel_theta), are recorded and saved in a txt file in the following format: Figure 4 As shown, each row of data is separated by a tab.

[0128] (3) such as Figure 5 As shown, drive the forklift to the starting storage position A. Set the control wheel angle parameter to the theoretical value corresponding to 2.5 degrees and fix it. The command system sends a travel command to make the forklift move, that is, automatically travel from point A to point B'. The arc length between points A and B' should be as far as possible, preferably 1 / 4 of a circle, at a slow and steady speed (about 0.2 m / s). Similarly, record the parameters corresponding to the control wheel angle output by the position system for each frame during the forklift's movement, as well as the position coordinates of the forklift in each frame during the movement, and save them to a txt file in the following format: Figure 4 As shown;

[0129] (4) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the parameter value corresponding to the theoretical steering wheel angle of 5 degrees, repeat step (3), and save the data with the same requirements as step (3).

[0130] (5) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the parameter value corresponding to the theoretical steering wheel angle of 10 degrees, repeat step (3), and save the data with the same requirements as step (3).

[0131] (6) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the parameter value corresponding to the theoretical steering wheel angle of 15 degrees, repeat step (3), and save the data with the same requirements as step (3).

[0132] (7) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the parameter value corresponding to the theoretical steering wheel angle of 20 degrees, repeat step (3), and save the data with the same requirements as step (3).

[0133] (8) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the parameter value corresponding to the theoretical 30 degrees of the steering wheel, repeat step (3), and save the data with the same requirements as step (3).

[0134] (9) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the parameter value corresponding to the theoretical 40 degrees of the steering wheel, repeat step (3), and save the data with the same requirements as step (3).

[0135] (10) Repeat steps (3) to (9). At this time, set the parameters for controlling the steering wheel angle to the theoretical values ​​corresponding to -40 degrees, -30 degrees, -20 degrees, -15 degrees, -10 degrees, -5 degrees and -2.5 degrees respectively. Save the data for each corresponding angle as required in step (3).

[0136] (11) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the maximum pulse for steering wheel to turn left, repeat step (3), and save the data required in step (3), but the last column is not needed.

[0137] (12) Drive the forklift to the starting storage location A, set the parameter for controlling the steering wheel angle to the maximum pulse of the steering wheel turning to the right, repeat step (3), and save the data that is required in the same way as in step (3), but the last column is not needed.

[0138] At this point, we have obtained 15 txt files showing the running trajectory of the forklift steering wheel at different angles, as well as txt files showing the steering angles of the left and right steering wheels.

[0139] Solving the problem

[0140] (1) Fitting of forklift running trajectory

[0141] Because the steering angle given by the steering wheel is fixed during the forklift's movement, the forklift's trajectory is an arc. Without loss of generality, for data in a txt file at a certain angle, (X, Y) represents the forklift's position coordinates during movement, and it should lie on a certain arc. For multiple coordinate points... , ,…, Perform a least-squares fit on the circle. Assume the equation of the circle is... The solution requires considering multiple points mentioned above. and The value of .

[0142] The equation of the circle to be found can be written in general form as follows:

[0143]

[0144] in , ,

[0145] For data points The minimum error function is defined as:

[0146]

[0147] Therefore, there is

[0148]

[0149] If it is sorted out, then there is

[0150]

[0151] This system of linear equations has only three unknowns: D, E, and F. It can be solved using Gaussian elimination. Further solutions can be derived... and The value of .

[0152] Combine the angle corresponding to the current trajectory with the radius value of the fitted circle to form a new pair of points. Each trajectory can yield a set of corresponding points, i.e. , , ..., , ..., .

[0153] (2) Solving for the 0-angle position of the forklift steering wheel

[0154] Points generated by each forklift trajectory , , ..., , ..., Draw to x-axis, radius In a rectangular coordinate system, it should be similar to... Figure 6 As shown by the curve in the middle.

[0155] Since when the actual steering wheel deflection angle is 0, the forklift's trajectory should be a straight line, and the corresponding trajectory radius should be infinite. Figure 7 As shown.

[0156] Based on this principle and the mathematical model of forklift steering wheel, a system is constructed. Figure 6 Model function of relations

[0157]

[0158] in and These are the parameters to be solved. It's not difficult to analyze that when... hour, As the radius approaches infinity, the forklift's turning radius becomes infinite, meaning the forklift's trajectory becomes a straight line. This refers to the 0-angle deflection of the steering wheel to be calibrated.

[0159] Will , , ..., , ..., Substituting into the equation, we can obtain

[0160]

[0161] Construct the error function as follows

[0162]

[0163] It is not difficult to see from the form of the error function that, due to the existence of the absolute value and the singularity of the tangent function, the error function... It is not differentiable, therefore it is not possible to use parameters. The solution is obtained by finding the derivative. The specific algorithm is as follows:

[0164] Step 1 Fix Solving for the optimal

[0165] For any given We can analytically obtain that makes smallest ,at this time yes Quadratic function: (8)

[0166] right Take the derivative and set it to zero:

[0167]

[0168] Solving

[0169]

[0170] get yes The function.

[0171] Step 2 Transform into Univariate function

[0172] Will Substitute return , get about The function is as follows:

[0173]

[0174] Indicates that in a given The minimum sum of squared residuals.

[0175] Step 3: Search for the optimal

[0176] Need to find in one-dimensional real space Make Minimum. Because the model is in or Strange, and It should be near the origin, and the search interval should be set to... , Let it be a small positive number, such as 0.1. Sample evenly within this interval. A point, such as Calculate each point Find the point with the minimum value. This will give you the minimum value. The best estimate made . It is the estimated value of the forklift steering wheel deflection angle at 0.

[0177] Then Substituting into formula (10), we get

[0178]

[0179] (3) Determining the extreme angle position of the forklift steering wheel

[0180] Confirmed and Then, according to the formula

[0181]

[0182] The limiting rotation radius of the least squares fit is obtained from the data in steps (11) and (12) of the data acquisition. This allows us to calculate the limiting angles on both sides, similar to... Figure 8 The two positions are shown.

[0183]

[0184] This completes the calibration of the forklift steering wheel's 0-angle deflection and left and right limit angles.

[0185] This invention calibrates the 0-angle and left and right limit angles of a single-steering-wheel forklift by simply traversing a few paths without the aid of calibration templates or other calibration tools. The calibration method is simple, has low requirements for the calibration environment, resulting in low calibration costs and ease of mass production on assembly lines within a workshop.

Claims

1. A method for calibrating the zero-angle and limit angle of a forklift steering wheel, characterized in that... Includes the following steps: (1) Mapping was performed using a single-steering wheel forklift in a test scenario on a flat ground area; (2) Drive the forklift to the starting position, set the parameter of the control wheel rotation angle to the parameter value corresponding to 0 degrees, send the walking command to make the forklift move forward, record the position coordinates of each frame during the forklift's driving process, and the parameter corresponding to the wheel rotation angle output by the position system of each frame during the forklift's driving process. (3) Drive the forklift to the starting position, set the control wheel rotation angle parameter in the command system at certain angle intervals to the corresponding parameter value in the range of -40 degrees to 40 degrees, send the travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the wheel rotation angle output by the position system in each frame during the forklift's travel. (4) Drive the forklift to the starting position, set the control wheel rotation angle parameter to the maximum pulse of the steering wheel turning to the left, send a travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the steering wheel rotation angle output by the position system in each frame during the forklift's travel. (5) Drive the forklift to the starting position, set the parameter for controlling the steering wheel angle to the maximum pulse for steering wheel to the right, send a travel command to make the forklift move forward, record the position coordinates of each frame during the forklift's travel, and the parameters corresponding to the steering wheel angle output by the position system for each frame during the forklift's travel. (6) Fit the forklift running trajectory. Based on the position coordinates of the forklift during the driving process, perform least squares fitting of the circle. Combine the angle corresponding to the current trajectory and the radius value of the fitted circle to form a new forklift trajectory generation point. (7) Solve for the position of the forklift steering wheel at 0 deflection angle. Based on the principle that the radius of the forklift's running trajectory is infinite when the steering wheel is at 0 deflection angle and the mathematical model of the forklift steering wheel's steering, construct a model function and substitute the new forklift trajectory generation point to calculate the position of the forklift steering wheel at 0 deflection angle. (8) Solve for the position of the forklift steering wheel limit angle, perform least squares fitting of the limit rotation radius, and calculate the limit angles on the left and right sides.

2. The calibration method for the 0-angle and limit angle of a forklift steering wheel according to claim 1, characterized in that: In step (3), the parameters for controlling the steering wheel angle are set to 2.5 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 30 degrees, 40 degrees, -40 degrees, -30 degrees, -20 degrees, -15 degrees, -10 degrees, -5 degrees and -2.5 degrees respectively, and recorded.

3. The method for calibrating the 0-angle and limit angle of a forklift steering wheel according to claim 1, characterized in that: The specific steps in step (6) are as follows: The forklift's trajectory is an arc, where (X, Y) are the forklift's position coordinates during its movement. The forklift lies on a certain arc, and the coordinates of multiple points are considered. , ,…, Perform a least-squares fit on the circle; assume the equation of the circle is... Solve based on the above multiple points and The value, The equation of the circle to be found can be written in general form as follows: in , , For data points The minimum error function is defined as: Therefore, there is If it is sorted out, then there is This system of linear equations has only three unknowns: D, E, and F. It can be solved using Gaussian elimination, and further solutions can be obtained. and The value; Combine the angle corresponding to the current trajectory with the radius value of the fitted circle to form a new pair of points. Each trajectory can yield a set of corresponding points, i.e. , , ..., , ..., .

4. The method for calibrating the 0-angle and limit angle of a forklift steering wheel according to claim 3, characterized in that: The specific steps in step (7) are as follows: Points generated by each forklift trajectory , , ..., , ..., Draw to x-axis, radius In a Cartesian coordinate system, when the actual steering wheel deflection angle is 0, the forklift's trajectory is a straight line with an infinite radius. Based on this principle and the mathematical model of forklift steering wheel rotation, a model function is constructed. in and These are the parameters to be solved, when hour, As the radius approaches infinity, the forklift's turning radius becomes infinite, meaning the forklift's trajectory becomes a straight line. This refers to the 0 deflection angle of the steering wheel to be calibrated; Will , , ..., , ..., Substituting into the equation, we can obtain Construct the error function as follows Due to the existence of absolute value and the singularity of the tangent function, the error function It is not differentiable, therefore it is not possible to use parameters. The solution is obtained by finding the derivative, and the specific algorithm is as follows: Step 1 Fix Solving for the optimal For any given , to obtain smallest ,at this time yes Quadratic function: right Take the derivative and set it to zero: Solving get yes The function; Step 2 Transform into Univariate function Will Substitute return , get about The function is as follows: Indicates that in a given The minimum sum of squared residuals; Step 3: Search for the optimal Need to find in one-dimensional real space Make Minimum, because the model is in or Strange, and It should be near the origin, and the search interval should be set to... , A small positive number, such as 0.1; uniform sampling within this interval. A point, such as Calculate each point Find the point with the smallest value; thus obtaining the minimum value. The best estimate made , It is the estimated value of the forklift steering wheel's 0 deflection angle; Then Substituting into formula (10), we get (12)。 5. The calibration method for the 0-angle and limit angle of a forklift steering wheel according to claim 4, characterized in that: The specific steps in step (8) are as follows: Confirmed and Then, according to the formula The limiting rotation radius of the least squares fit based on the collected data. Solve for the limiting angles on both sides. (14)。

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