An unmanned forklift adaptive posture calibration method and system

Abstract

The application discloses a self-adaptive posture calibration method and system for an unmanned forklift, and the method comprises the following steps: acquiring the coordinates of two end points of a target pallet facing the forklift in a world coordinate system; calculating a perpendicular bisector L1 of the two end points according to the coordinates of the two end points; acquiring the coordinates of a midpoint A of a connecting line of two steering wheels of the forklift and a perpendicular bisector L2; drawing an auxiliary circle 1; drawing an auxiliary circle 2; acquiring the coordinates of a point B where the auxiliary circle 1 and the auxiliary circle 2 are tangent to each other and the coordinates of a point C where the auxiliary circle 2 and the perpendicular bisector L1 are tangent to each other; intercepting a circular arc AB on the auxiliary circle 1 and a circular arc BC on the auxiliary circle 2; and driving the forklift in a reverse direction along the curve ABC and then driving the forklift in a forward direction, so that the pallet can be inserted and taken. The application has the advantages of short time consumption, high efficiency and cost saving.

Description

Technical Field

[0001] This invention relates to a method and system for calibrating the attitude of an unmanned forklift. Background Technology

[0002] The demand for automated integrated smart warehouses is constantly increasing, and the demand for driverless forklifts is also rising, with increasingly higher requirements for the precision of forklift insertion. Existing driverless forklifts often experience deviations when first arriving at the designated picking point due to environmental factors, insufficient mechanical assembly precision, or positioning accuracy. When the deviation is too large, they cannot properly insert and pick up goods. Therefore, a path point generation and path planning algorithm with low memory consumption and the ability to quickly calculate the optimal adjustment route is a pressing issue that needs to be addressed. Summary of the Invention

[0003] In view of this, the present invention provides an adaptive attitude calibration method for unmanned forklifts, which can quickly calculate the optimal adjustment route to calibrate the forklift attitude when positioning deviation occurs, so as to facilitate pallet insertion and removal.

[0004] To solve the above technical problems, the technical solution of the present invention is to adopt an adaptive attitude calibration method for an unmanned forklift, comprising:

[0005] Obtain the coordinates of the two endpoints of the target pallet facing the forklift in the world coordinate system;

[0006] Calculate the perpendicular bisector L1 of the line connecting the two endpoints;

[0007] Obtain the coordinates of the midpoint A of the line connecting the two steering wheels of the forklift and the perpendicular bisector L2;

[0008] If the perpendicular line L1 and the perpendicular line L2 coincide, the forklift posture is considered to be no need to be adjusted; if the perpendicular line L1 and the perpendicular line L2 do not coincide, then take the midpoint A as the foot of the perpendicular and draw the perpendicular line L3 of the perpendicular line L2. The perpendicular line L3 is located on the side of the forklift teeth that are biased when the perpendicular line L1 is used as the reference.

[0009] Find a point O1 on the perpendicular line L3 such that the distance between O1 and the median perpendicular line L2 is R1. Draw an auxiliary circle 1 with O1 as the center and R1 as the radius, where R1 is not less than the minimum turning radius of the forklift.

[0010] Make an auxiliary circle 2, the center O2 of which is located on both sides of the perpendicular bisector L1 of the auxiliary circle 1; the radius of the auxiliary circle 2 is R2, and the auxiliary circle 2 is tangent to the auxiliary circle 1 and the perpendicular bisector L1 respectively, and R2 is not less than the minimum turning radius of the forklift.

[0011] Obtain the coordinates of point B where auxiliary circle 1 and auxiliary circle 2 are tangent, and the coordinates of point C where auxiliary circle 2 is tangent to the perpendicular bisector L1. Then, extract the arc AB on auxiliary circle 1 and the arc BC on auxiliary circle 2.

[0012] After reversing along curve ABC, the forklift can move forward to pick up the pallet.

[0013] As an improvement, a world coordinate system is obtained through laser SLAM or multi-sensor fusion SLAM, and all coordinates are transformed to the world coordinate system.

[0014] As a further improvement, a forklift model is constructed based on the dimensions of the forklift, wherein the forklift body is constructed from rounded rectangles and the forklift teeth are constructed from two rounded rectangles.

[0015] As another further improvement, both R1 and R2 are equal to the forklift's minimum turning radius.

[0016] As an improvement, the method for obtaining the midpoint A of the line connecting the two steering wheels of the forklift is as follows:

[0017] Obtain the coordinates and wheelbase of the forklift's center point P;

[0018] The midpoint A is calculated using trigonometric functions based on the coordinates of the forklift's center point P and the wheelbase.

[0019] As an improvement, the method for calculating the midpoint A using trigonometric functions is as follows:

[0020] Given that the coordinates of the forklift's center point P are (x, y, R), and the distance between center point P and midpoint A is L / 2, and the coordinates of center point P are (x1, y1, R1), the formula is:

[0021] x1 = x - cosR*(L / 2)

[0022] y1 = y - sinR*(L / 2)

[0023] R1=R.

[0024] As an improvement, the arcs AB and BC are the shorter arcs on auxiliary circles 1 and 2, respectively.

[0025] The present invention also provides an adaptive attitude calibration system for an unmanned forklift, comprising:

[0026] The target pallet endpoint acquisition module is used to acquire the coordinates of the two endpoints of the target pallet facing the forklift in the world coordinate system, and calculate the perpendicular bisector L1 of the line connecting the two endpoints based on their coordinates.

[0027] The forklift steering wheel midpoint acquisition module is used to obtain the coordinates of the midpoint A of the line connecting the two steering wheels of the forklift and the perpendicular bisector L2;

[0028] The auxiliary circle 1 acquisition module is used to draw a perpendicular line L3 to the perpendicular line L2 with the midpoint A as the foot of the perpendicular. The perpendicular line L3 is located on the side where the fork fork teeth are biased when the perpendicular line L1 is used as the reference. The module acquires a point O1 on the perpendicular line L3 such that the distance between O1 and the perpendicular line L2 is R1. The auxiliary circle 1 is drawn with O1 as the center and R1 as the radius. R1 is not less than the minimum turning radius of the forklift.

[0029] The auxiliary circle 2 acquisition module is used to create auxiliary circle 2. The center O2 of auxiliary circle 2 and the center O1 of auxiliary circle 1 are located on opposite sides of the perpendicular bisector L1, and the center O2 is located behind the midpoint A. The radius of auxiliary circle 2 is R2, and auxiliary circle 2 is tangent to auxiliary circle 1 and perpendicular bisector L1 respectively. R2 is not less than the minimum turning radius of the forklift.

[0030] The route generation module is used to obtain the coordinates of point B where auxiliary circle 1 and auxiliary circle 2 are tangent, and the coordinates of point C where auxiliary circle 2 is tangent to the perpendicular bisector L1. It then extracts arc AB on auxiliary circle 1 and arc BC on auxiliary circle 2 to generate the forklift reversing path curve ABC.

[0031] As an improvement, a world coordinate system construction module is also included, which is used to obtain the world coordinate system through laser SLAM or multi-sensor fusion SLAM and transform all coordinates to the world coordinate system.

[0032] As an improvement, a forklift model building module is also included, which is used to build a forklift model according to the size of the forklift, wherein the forklift body is constructed from rounded rectangles and the forklift teeth are constructed from two rounded rectangles.

[0033] The advantages of this invention are:

[0034] Short processing time, high efficiency, and cost savings: Precise cargo insertion requires only one or fewer adjustments; the vehicle body does not need to spin, and smooth curves are sufficient for attitude adjustment. It is suitable not only for Ackerman chassis but also for any chassis type, eliminating the need to modify an Ackerman chassis with a spin offset radius into an expensive full-size chassis without one. It also reduces wheel wear caused by spin, extending the lifespan of rubber wheels. 2. Non-repetitive calculations and low system overhead: There is no redundant computation, resulting in minimal memory consumption. It can be integrated into complex path generation, improving generation efficiency.

[0035] 3. Innovation: Unlike traditional traversal path finding, it generates the optimal adjustment path by autonomously calculating the target point, and is also applicable to the generation of optimal paths for autonomous vehicles such as lane changing and merging. Attached Figure Description

[0036] Figure 1 This is a flowchart of the present invention.

[0037] Figures 2-4 This is a schematic diagram illustrating the construction process of path ABC.

[0038] Figure 5 This is a schematic diagram of the structural principle of the present invention. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0040] Traditional driverless forklifts, due to limitations in Ackerman chassis or positioning accuracy, may have low accuracy when reaching designated storage locations, leading to deviations. When inserting or picking up goods, they cannot achieve precise insertion with one or fewer adjustments, often requiring external physical intervention or even manual intervention, which deviates from the original intention of automated operation.

[0041] As a low-cost chassis, the Ackerman chassis has the disadvantage of a large spin radius and low point accuracy, which often cannot be solved by pure spin lateral movement. Most existing solutions modify the Ackerman chassis into a more expensive omnidirectional chassis, which increases the cost.

[0042] In addition, most existing solutions require the vehicle body to rotate to correct the attitude during small attitude adjustments. For chassis that are not omnidirectional or have insufficient machining and assembly precision, vehicle body rotation often results in additional displacement due to assembly precision issues. Therefore, attitude adjustments need to be performed repeatedly, and it is even possible that the target attitude cannot be achieved in the end.

[0043] The present invention aims to adjust the posture of the forklift when there is a deviation in its positioning, so that it can face the target pallet and easily insert the target pallet.

[0044] like Figure 1 As shown, this invention provides an adaptive attitude calibration method for an unmanned forklift, taking an Ackerman chassis that uses rear-wheel steering as an example. Of course, this invention can also be applied to chassis with other steering configurations. Specifically, it includes:

[0045] S1 obtains the coordinates of the two endpoints of the target pallet facing the forklift in the world coordinate system.

[0046] First, a world coordinate system should be constructed. In this embodiment, a world coordinate system (right-handed coordinate system) is obtained through laser SLAM (simultaneous localization and mapping) or multi-sensor fusion SLAM, and all subsequent coordinates are transformed to the world coordinate system. After constructing the world coordinate system, a forklift model needs to be constructed according to the forklift's dimensions. In this embodiment, the forklift body is constructed from rounded rectangles, and the forklift teeth are constructed from two rounded rectangles.

[0047] S2 calculates the perpendicular bisector L1 of the line connecting the two endpoints.

[0048] When a forklift needs to adjust its posture to pick up or drop a pallet, the world coordinates of the two endpoints of the pallet are obtained through depth camera analysis. The line connecting the two endpoints, endpoint 1 and endpoint 2, and the perpendicular bisector L1 of that line are then calculated. Given two known points, obtaining the connecting line and the perpendicular bisector is a purely mathematical problem, which will not be elaborated upon in this invention.

[0049] S3 obtains the coordinates of the midpoint A of the line connecting the two steering wheels of the forklift and the perpendicular bisector L2.

[0050] The center point P and wheelbase L of the forklift are known. For the Ackerman chassis, which uses rear-wheel steering, the center point A is located L / 2 behind the center point of the forklift.

[0051] like Figure 2 As shown, the coordinates of the forklift's center point P are (x, y, R), and the distance between center point P and midpoint A is L / 2. Find the coordinates of center point P (x1, y1, R1). In this embodiment, trigonometric functions are used for calculation. The specific formula is as follows:

[0052] x1 = x - cosR*(L / 2)

[0053] y1 = y - sinR*(L / 2)

[0054] R1=R.

[0055] S4 If the perpendicular line L1 and the perpendicular line L2 coincide, it is considered that the forklift posture does not need to be adjusted; if the perpendicular line L1 and the perpendicular line L2 do not coincide, then take the midpoint A as the foot of the perpendicular and draw the perpendicular line L3 of the perpendicular line L2. The perpendicular line L3 is located on the side of the forklift teeth that are biased when the perpendicular line L1 is used as the reference.

[0056] For a forklift to successfully pick up a pallet, its centerline must coincide with the pallet's centerline. At this point, the forklift can move forward straight to pick up the pallet. The forklift's centerline is the perpendicular bisector L2, and the pallet's centerline is the perpendicular bisector L1. Therefore, if the perpendicular bisectors L1 and L2 coincide, no adjustment to the forklift's posture is needed, and no further steps are required.

[0057] like Figure 3 As shown, if the perpendicular bisectors L1 and L2 do not coincide, subsequent attitude calibration is required. In actual use, the forklift's positioning error will not be too large; generally, the forklift body will still be on the perpendicular bisector L1, only with a slight offset in position and direction.

[0058] At this point, with the midpoint A as the foot of the perpendicular, draw the perpendicular line L3 to the perpendicular line L2. The perpendicular line L3 is located on the side to which the fork teeth of the fork are biased when the perpendicular line L1 is used as the reference.

[0059] For example, if the fork teeth of the forklift are facing to the left of the perpendicular bisector, then draw a perpendicular line L3 from the midpoint A to the left of the perpendicular bisector L1. If the fork teeth are facing to the right of the perpendicular bisector, then draw a perpendicular line L3 from the midpoint A to the right of the perpendicular bisector L2.

[0060] S5 obtains point O1 on the perpendicular line L3 such that the distance between O1 and the middle perpendicular line L2 is R1. An auxiliary circle 1 is drawn with O1 as the center and R1 as the radius, and R1 is not less than the minimum turning radius of the forklift. In this embodiment, R1 is equal to the minimum turning radius of the forklift, so that the final planned path is the shortest and most economical.

[0061] S6 constructs an auxiliary circle 2, with its center O2 aligned with the center O1 of auxiliary circle 1 on either side of the perpendicular bisector L1. The radius of auxiliary circle 2 is R2, and it is tangent to both auxiliary circle 1 and the perpendicular bisector L1. R2 is not less than the minimum turning radius of the forklift. Similarly, in this embodiment, R2 is equal to the minimum turning radius of the forklift for the same reason.

[0062] In addition, there are two circles that satisfy the condition of radius R2 and are tangent to both auxiliary circle 1 and perpendicular bisector L1. However, in order to generate a smooth path, the auxiliary circle 2 selected in this invention should be one that is far away from the target pallet.

[0063] S7 obtains the coordinates of point B, where auxiliary circle 1 and auxiliary circle 2 are tangent, and the coordinates of point C, where auxiliary circle 2 is tangent to the perpendicular bisector L1. It then extracts arc AB from auxiliary circle 1 and arc BC from auxiliary circle 2. Arc AB and arc BC are the shorter arcs on auxiliary circle 1 and auxiliary circle 2, respectively. Figure 4 As shown.

[0064] The S8 forklift can reverse along curve ABC and then move forward to pick up the pallet.

[0065] like Figure 5 As shown, connecting arcs AB and BC forms the calibration path. After the forklift reverses along curve ABC, its centerline coincides with the centerline of the target pallet, so it can simply move forward to pick up the target pallet.

[0066] like Figure 6 As shown, the present invention also provides an adaptive attitude calibration system for an unmanned forklift, comprising:

[0067] The target pallet endpoint acquisition module is used to acquire the coordinates of the two endpoints of the target pallet facing the forklift in the world coordinate system, and calculate the perpendicular bisector L1 of the line connecting the two endpoints based on their coordinates.

[0068] The forklift steering wheel midpoint acquisition module is used to obtain the coordinates of the midpoint A of the line connecting the two steering wheels of the forklift and the perpendicular bisector L2.

[0069] The auxiliary circle 1 acquisition module is used to draw a perpendicular line L3 to the perpendicular line L2 with the midpoint A as the foot of the perpendicular. The perpendicular line L3 is located on the side where the fork teeth of the fork are biased when the perpendicular line L1 is used as the reference. The module acquires a point O1 on the perpendicular line L3 such that the distance between O1 and the perpendicular line L2 is R1. The auxiliary circle 1 is drawn with O1 as the center and R1 as the radius, and R1 is not less than the minimum turning radius of the forklift.

[0070] The auxiliary circle 2 acquisition module is used to create the auxiliary circle 2. The center O2 of the auxiliary circle 2 is located on both sides of the perpendicular bisector L1, and the center O2 is located behind the midpoint A. The radius of the auxiliary circle 2 is R2, and the auxiliary circle 2 is tangent to both the auxiliary circle 1 and the perpendicular bisector L1. R2 is not less than the minimum turning radius of the forklift.

[0071] The route generation module is used to obtain the coordinates of point B where auxiliary circle 1 and auxiliary circle 2 are tangent, and the coordinates of point C where auxiliary circle 2 is tangent to the perpendicular bisector L1. It then extracts arc AB on auxiliary circle 1 and arc BC on auxiliary circle 2 to generate the forklift reversing path curve ABC.

[0072] The world coordinate system construction module is used to obtain the world coordinate system through laser SLAM or multi-sensor fusion SLAM, and transform all coordinates to the world coordinate system.

[0073] The forklift model building module is used to build a forklift model based on the size of the forklift. The forklift body is constructed from rounded rectangles, and the forklift teeth are constructed from two rounded rectangles.

[0074] This invention can automatically plan the optimal and shortest adjustment target point and target path when a forklift is unable to pick up goods on its first arrival at a storage location due to accuracy issues, based on the pallet position returned by the camera sensor. The target path is a smooth curved path that does not require the forklift body to rotate, thus achieving the purpose of rapid attitude calibration and reducing wear on the rubber wheels caused by rotation.

[0075] In addition, this invention not only provides a path generation approach and calculation method for attitude adjustment, but also, when combined with visualization editing software, can be used for pre-planning of complex trajectories. Secondary optimizations that cannot be achieved using traditional path planning algorithms can be accomplished by combining this method.

[0076] Traditional obstacle avoidance algorithms generate paths with randomness. Embedding this method can resolve this randomness and find the optimal planned path. Even with small-distance attitude adjustments, the planned path is continuous and smooth, better simulating real human driving and significantly improving the level of intelligence.

[0077] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An adaptive posture calibration method for unmanned forklifts, characterized by The method comprises the following steps: acquiring the coordinates of two end points of a target pallet facing a forklift in a world coordinate system; calculating a perpendicular bisector L1 of the two end points according to the coordinates of the two end points; acquiring the coordinates of a midpoint A of a line connecting two steering wheels of the forklift and a perpendicular bisector L2; if the perpendicular bisector L1 and the perpendicular bisector L2 coincide, it is considered that the posture of the forklift does not need to be adjusted; if the perpendicular bisector L1 and the perpendicular bisector L2 do not coincide, a perpendicular line L3 of the perpendicular bisector L2 is drawn with the midpoint A as a foot, and the perpendicular line L3 is located on a side to which a fork tooth of the forklift deviates when the perpendicular bisector L1 is used as a reference; acquiring a point O1 on the perpendicular line L3 so that the distance between the point O1 and the perpendicular bisector L2 is R1, and an auxiliary circle 1 is drawn with the point O1 as a center and R1 as a radius, and R1 is not less than a minimum turning radius of the forklift; an auxiliary circle 2 is drawn, a center O2 of the auxiliary circle 2 is located on a side opposite to the center O1 of the auxiliary circle 1 with the perpendicular bisector L1 as a reference, a radius of the auxiliary circle 2 is R2, and the auxiliary circle 2 is tangent to the auxiliary circle 1 and the perpendicular bisector L1, and R2 is not less than the minimum turning radius of the forklift; coordinates of a point B at which the auxiliary circle 1 and the auxiliary circle 2 are tangent and a point C at which the auxiliary circle 2 and the perpendicular bisector L1 are tangent are acquired, and an arc AB on the auxiliary circle 1 and an arc BC on the auxiliary circle 2 are intercepted; the forklift can be inserted into the pallet after reversing along the curve ABC and then driving straight forward.

2. The self-adaptive posture calibration method of the unmanned forklift according to claim 1, characterized in that: A world coordinate system is obtained through laser SLAM or multi-sensor fusion SLAM, and all coordinates are converted to the world coordinate system.

3. The self-adaptive posture calibration method of the unmanned forklift according to claim 1, characterized in that: A forklift model is constructed according to the size of the forklift, the body of the forklift is constructed by a rounded rectangle, and the fork tooth of the forklift is constructed by two rounded rectangles.

4. The self-adaptive posture calibration method of the unmanned forklift according to claim 1, characterized in that: R1 and R2 are equal to the minimum turning radius of the forklift.

5. The self-adaptive posture calibration method of the unmanned forklift according to claim 1, characterized in that The method for acquiring the midpoint A of the line connecting the two steering wheels of the forklift comprises the following steps: acquiring the coordinates of a center point P of the forklift and a wheelbase; 6. The self-adaptive posture calibration method of the unmanned forklift according to claim 5, characterized in that the midpoint A is calculated by using a trigonometric function according to the coordinates of the center point P of the forklift and the wheelbase. The method for calculating the midpoint A by using the trigonometric function comprises the following steps: the coordinates of the center point P of the forklift are (x, y, R), the distance between the center point P and the midpoint A is L / 2, the coordinates of the center point P are (x1, y1, R1), and the formula is: x1 = x-cosR*(L / 2) 7. The self-adaptive posture calibration method of the unmanned forklift according to claim 1, characterized in that: y1 = y-sinR*(L / 2) 8. An autonomous forklift truck self-adapting posture calibration system, characterized by R1 = R. The arc AB and the arc BC are shorter arcs on the auxiliary circle 1 and the auxiliary circle 2, respectively. The method comprises the following steps: a target pallet end point acquisition module is configured to acquire the coordinates of two end points of a target pallet facing a forklift in a world coordinate system, and calculate a perpendicular bisector L1 of the two end points according to the coordinates of the two end points; a forklift steering wheel midpoint acquisition module is configured to acquire the coordinates of a midpoint A of a line connecting two steering wheels of the forklift and a perpendicular bisector L2; an auxiliary circle 1 acquisition module is configured to draw a perpendicular line L3 of the perpendicular bisector L2 with the midpoint A as a foot, the perpendicular line L3 is located on a side to which a fork tooth of the forklift deviates when the perpendicular bisector L1 is used as a reference, acquire a point O1 on the perpendicular line L3 so that the distance between the point O1 and the perpendicular bisector L2 is R1, and draw an auxiliary circle 1 with the point O1 as a center and R1 as a radius, and R1 is not less than a minimum turning radius of the forklift. An auxiliary circle 2 obtaining module is configured to obtain an auxiliary circle 2, a center O2 of the auxiliary circle 2 is located on a side of a perpendicular bisector L1 of the auxiliary circle 1 and is located behind the midpoint A, and a radius of the auxiliary circle 2 is R2, the auxiliary circle 2 is tangent to the auxiliary circle 1 and the perpendicular bisector L1, and R2 is not less than a minimum turning radius of the forklift truck; A route generating module is configured to obtain coordinates of a point B at which the auxiliary circle 1 and the auxiliary circle 2 are tangent and coordinates of a point C at which the auxiliary circle 2 and the perpendicular bisector L1 are tangent, intercept an arc AB on the auxiliary circle 1 and an arc BC on the auxiliary circle 2, and generate a forklift truck reversing path curve ABC.

9. The self-adapting pose calibration system for unmanned fork truck of claim 8, wherein Further comprising: A world coordinate system constructing module is configured to obtain a world coordinate system through laser SLAM or multi-sensor fusion SLAM and convert all coordinates to the world coordinate system.

10. The self-adapting pose calibration system for unmanned fork truck of claim 8, wherein Further comprising: A forklift truck model constructing module is configured to construct a forklift truck model according to a size of the forklift truck, the forklift truck body is constructed by a rounded rectangle, and the forklift truck tines are constructed by two rounded rectangles.

Images