A control method and device for omnidirectional counterbalanced forklift

Abstract

The application discloses a kind of omnidirectional counterbalance fork truck control methods, and the method specifically includes the following steps: S1, the instantaneous center O of current pose to next time target pose is determined;S2, the linear velocity of omnidirectional counterbalance fork truck is calculated based on instantaneous center O;S3, omnidirectional counterbalance fork truck is controlled to travel to the target position of next time with the linear velocity, and the attitude of omnidirectional counterbalance fork truck when in target position is target attitude.The application uses omnidirectional structure to replace single rudder wheel structure in counterbalance fork truck, and realizes the synchronization of angle control and position control of counterbalance fork truck, improves the working efficiency and control precision of omnidirectional counterbalance fork truck.

Description

Technical Field

[0001] This invention belongs to the field of path tracking technology, and more specifically, this invention relates to an omnidirectional counterbalanced forklift control method and device. Background Technology

[0002] Counterbalance forklifts are widely used in the logistics field, and their models are relatively fixed, generally adopting a single-steering wheel structure (steering wheel + differential driven wheel). They are non-holonomic constraint mobile robots, and therefore do not have an advantage in precision control compared to omnidirectional mobile robots. While omnidirectional mobile robots are widely used, the motion control of most of them is still equivalent to differential model motion control. Omnidirectional functionality is manifested and applied by rotating, translating, and lateralizing the robot after it has stopped. This type of control method involves switching control modes, which cannot achieve smooth control. Therefore, when switching control algorithms, the robot must first be stopped, and during this process, the robot needs to accelerate and decelerate, which can significantly impact performance. This reduces the robot's working efficiency. In addition, common counterbalance forklifts use a single-steering wheel structure. Generally, the control center of this type of robot is located at the center of the differential driven wheel. Since the fork teeth of the counterbalance forklift are in front of the differential wheel, and the length of the fork teeth is generally about 1.2 meters, plus the thickness of the power mechanism of the fork teeth, the distance between the end of the fork teeth and the control center of the differential wheel is about 1.5 meters. Therefore, when the angle control accuracy of the differential wheel control center is ±1°, the error at the end of the fork teeth has already reached 26mm. And this error is only caused by the angle control error. If positioning error, calibration error, position error, and assembly error (mechanical clearance) are also taken into account, the error will be even greater. Summary of the Invention

[0003] This invention provides an omnidirectional counterbalanced forklift control method, which aims to improve the above-mentioned problems.

[0004] This invention is implemented as follows: an omnidirectional counterbalance forklift control method, the method specifically including the following steps:

[0005] S1. Determine the instantaneous center O from the current pose to the target pose at the next moment;

[0006] S2. Calculate the linear velocity of the omnidirectional counterbalanced forklift based on the instantaneous center of gravity O;

[0007] S3. Control the omnidirectional counterbalance forklift to travel at the linear speed to the target position at the next moment. The attitude of the omnidirectional counterbalance forklift at the target position is the target attitude.

[0008] Furthermore, the method for determining the instantaneous center O is as follows:

[0009] S11. Connect the current position point C with the target position point C′ at the next moment using a straight line segment to form the perpendicular bisector of the straight line segment on the direction of the instantaneous center.

[0010] S12. Determine the angle difference θ between the current attitude angle and the target attitude angle at the next moment;

[0011] S13. Find the point on the perpendicular bisector that satisfies ∠COC′=θ. This point is the instantaneous center O.

[0012] Furthermore, the method for determining the direction of linear velocity is as follows:

[0013] With the instantaneous center O as the center and line segment OC or line segment OC′ as the radius R, an arc segment CC′ is formed. The tangent direction of the arc segment CC′ is the direction of the linear velocity of the omnidirectional counterbalanced forklift.

[0014] Furthermore, the method for determining the linear velocity value is as follows:

[0015] Calculate the arc length θ*R of the circular arc segment CC′. The ratio of the arc length θ*R to the time difference Δt is the linear velocity of the forklift. Δt is the time difference between the current moment and the next moment.

[0016] Furthermore, the angular velocity w is the ratio of the linear velocity value to the radius R.

[0017] This invention is implemented as follows: an omnidirectional counterbalance forklift control device, the device comprising:

[0018] The instantaneous center determination unit is used to determine the instantaneous center O from the current pose to the target pose at the next moment, and output it to the velocity determination unit;

[0019] The linear velocity determination unit calculates the forklift's line of travel based on the instantaneous center of gravity O and outputs the result to the speed control unit.

[0020] The speed control unit controls the forklift to travel at the specified linear speed to the target position at the next moment. The forklift's posture at the target position is the target posture.

[0021] Furthermore, the instantaneous center determination unit includes:

[0022] The perpendicular bisector forming module connects the current position point C with the target position point C′ at the next moment using a straight line segment, forming the perpendicular bisector of the straight line segment on the instantaneous center direction.

[0023] The change in attitude angle is synchronized with the change in velocity direction angle. The deflection angle determination module is used to determine the angle difference θ between the current attitude angle and the target attitude angle at the next moment.

[0024] The instantaneous center determination module is used to find the point on the perpendicular bisector that satisfies ∠COC′=θ, and this point is the instantaneous center O.

[0025] Furthermore, the linear velocity determination unit includes:

[0026] The linear velocity direction determination module uses the instantaneous center O as the center and line segment OC or line segment OC′ as the radius R to form an arc segment CC′. The tangent direction of the arc segment CC′ is the linear velocity direction of the forklift.

[0027] Furthermore, the linear velocity determination unit also includes:

[0028] The linear velocity value determination module is used to calculate the arc length θ*R of the circular arc segment CC′. The ratio of the arc length θ*R to the time difference Δt is the linear velocity value of the omnidirectional counterbalance forklift. Δt is the time difference between the current moment and the next moment.

[0029] This invention replaces the single steering wheel structure in the counterbalanced logistics forklift with an omnidirectional structure, and realizes the synchronization of angle control and position control of the counterbalanced forklift, thereby improving the working efficiency and control accuracy of the omnidirectional counterbalanced forklift. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the kinematic model of an omnidirectional forklift provided in an embodiment of the present invention;

[0031] Figure 2 This is a control diagram of an omnidirectional forklift provided in an embodiment of the present invention;

[0032] Figure 3 This is a comparison diagram of the effects of a traditional single-steering wheel counterbalance forklift and an omnidirectional counterbalance forklift provided in an embodiment of the present invention, wherein A is the traditional single-steering wheel counterbalance forklift and B is the omnidirectional counterbalance forklift.

[0033] Figure 4 This is a flowchart of an omnidirectional counterbalance forklift control method provided in an embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of the omnidirectional counterbalance forklift control device provided in an embodiment of the present invention. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0036] Omnidirectional structures include: four-Mecana wheel structure, dual-steering wheel structure (diagonally mounted / axisymmetric centerline mounted), and four-steering wheel structure. Mecana wheel structures have high requirements for the ground surface, resulting in higher unit and maintenance costs, and are generally used in well-maintained indoor environments. Dual-steering wheel structures typically require additional casters to maintain vehicle stability, thus having poor obstacle-crossing ability and are also commonly used in well-flat indoor environments. Four-wheel structures, on the other hand, offer excellent obstacle-crossing performance and can adapt to both indoor and outdoor environments. Regardless of the type of omnidirectional structure, all meet the requirements for synchronized angle and position control.

[0037] The control model of the omnidirectional counterbalance forklift is as follows: Figure 1 As shown, the robot's instantaneous velocity is V, and the angle between V and the positive direction of the robot's coordinate system is θ. (Not coinciding with the robot's heading angle), the robot's velocity after a movement time Δt is V′, and the angle between velocities V and V′ is θ. In addition, when position C moves to position C′, and from x0 to x′0, the angle between vector C-x0 and vector C′-x′0 is the change in the robot's attitude angle, and its magnitude is also θ. Therefore, the robot's heading angle can be controlled by controlling the robot's velocity (vector).

[0038] Knowing the robot's heading angle, control can be achieved by controlling the robot's velocity (vector). However, the magnitude of the velocity is still uncertain. The following discussion will explore this further. Figure 3 Using a simplified control diagram of an omnidirectional robot as an example, the robot's current instantaneous position is C, and the next instantaneous target position is C′. The robot's instantaneous pose at point C is known, and the robot's pose at the target position C′ is also determined. This pose can be allocated to each instant based on the attitude angle deviation between the initial and target positions. For example, if the attitude angle deviation is 10 degrees, and adjustments are made using five instantaneous position points, the angle between two adjacent positions is 2 degrees. Since the attitude angle difference between position C′ and position C is known, to control the forklift from position C to the target position C′, the instantaneous center O must lie on the perpendicular bisector of the line segment connecting C′ and CC′. The robot's attitude angle can be adjusted by changing the distance from the instantaneous center O to the line CC′. When the instantaneous centers change to O1 and O2, the corresponding changes in the forklift's attitude angles are ∠CO1C′ and ∠CO2C′, respectively. Assuming the attitude angle control quantity is θ, by adjusting the position of the instantaneous center (assuming it is O) so that ∠COC equals θ, the robot's angle control can be achieved. Once the position of the instantaneous center is determined, the instantaneous center radius R is known. The magnitude of the linear velocity V can be obtained from θ*R=V*Δt (Δt is determined by the control frequency). The direction of V is perpendicular to the line segment CO, so the direction can also be determined. Therefore, V (vector) can also be obtained. At this point, the synchronous control of the robot's angle and position is fully realized. The robot can achieve the control objective without switching to the control mode of stationary rotation and lateral movement through differential control, thereby improving control efficiency.

[0039] To improve the loading accuracy of the counterbalance forklift, the control center of the omnidirectional mobile robot was adjusted. In the aforementioned analysis diagrams, the robot's control center is located at the robot's geometric center, i.e., as shown... Figure 3 As shown in A, the centers of the driven wheels of forklifts 1 and 2 are adjusted by changing the control center of the forklift to... Figure 3 At point 8 (black dots) in B, even if the forklift control angle precision is consistent, i.e. Figure 3 The angular error shown is θ. However, the horizontal deviations e1 and e2 between the forklift in Figure A and the target straight line in Figure B clearly satisfy e1 > e2. This control method can effectively improve the control error.

[0040] Figure 4 The flowchart of the omnidirectional counterbalance forklift control method provided in the embodiment of the present invention includes the following steps:

[0041] S1. Determine the instantaneous center O from the current pose to the target pose at the next moment;

[0042] In this embodiment of the invention, the method for determining the instantaneous center O is as follows:

[0043] S11. Connect the current position point C with the target position point C′ at the next moment using a straight line segment to form the perpendicular bisector of the straight line segment on the direction of the instantaneous center.

[0044] S12. The change in attitude angle is synchronized with the change in velocity direction angle to determine the angle difference θ between the current attitude angle and the target attitude angle at the next moment.

[0045] S13. Find the point on the perpendicular bisector that satisfies ∠COC′=θ. This point is the instantaneous center O.

[0046] S2. Calculate the linear velocity of the omnidirectional counterbalanced forklift based on the instantaneous center of gravity O;

[0047] In this embodiment of the invention, the linear velocity consists of the linear velocity direction and the linear velocity value. The method for determining the linear velocity direction is as follows: with the instantaneous center O as the center and the line segment OC or the line segment OC′ as the radius R, an arc segment CC′ is formed. The tangent direction of the arc segment CC′ is the linear velocity direction of the forklift. Since the arc segment CC′ is the travel trajectory of the forklift, the tangent direction of the travel trajectory is the linear velocity direction.

[0048] In this embodiment of the invention, the method for determining the linear velocity value is as follows:

[0049] Calculate the arc length θ*R of the circular arc segment CC′. The ratio of the arc length θ*R to the time difference Δt is the linear velocity of the forklift. Δt is the time difference between the current moment and the next moment.

[0050] In this embodiment of the invention, the angular velocity w is the ratio of the linear velocity value to the radius R. As long as the linear velocity is determined, the angular velocity is a fixed value.

[0051] S3. Control the omnidirectional counterbalance forklift to travel at the linear speed to the target position at the next moment. The attitude of the omnidirectional counterbalance forklift at the target position is the target attitude.

[0052] Figure 5 This is a schematic diagram of the omnidirectional counterbalance forklift control device provided in an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown. The device includes:

[0053] The instantaneous center determination unit is used to determine the instantaneous center O from the current pose to the target pose at the next moment, and output it to the velocity determination unit;

[0054] In this embodiment of the invention, the instantaneous center determination unit includes: a perpendicular bisector forming module, an instantaneous center determination module, and an instantaneous center determination module connected in sequence, wherein...

[0055] The perpendicular bisector forming module connects the current position point C with the target position point C′ at the next moment using a straight line segment, forming the perpendicular bisector of the straight line segment on the instantaneous center direction.

[0056] The change in attitude angle is synchronized with the change in velocity direction angle. The deflection angle determination module is used to determine the angle difference θ between the current attitude angle and the target attitude angle at the next moment.

[0057] The instantaneous center determination module is used to find the point on the perpendicular bisector that satisfies ∠COC′=θ, and this point is the instantaneous center O.

[0058] The linear velocity determination unit calculates the forklift's line of travel based on the instantaneous center of gravity O and outputs the result to the speed control unit.

[0059] The linear velocity determination unit includes: a linear velocity direction determination module and a linear velocity value determination module.

[0060] The linear velocity direction determination module uses the instantaneous center O as the center and line segment OC or line segment OC′ as the radius R to form an arc segment CC′. The tangent direction of the arc segment CC′ is the linear velocity direction of the forklift. Since the arc segment CC′ is the forklift's travel trajectory, the tangent direction of the travel trajectory is the linear velocity direction.

[0061] The linear velocity value determination module is used to calculate the arc length θ*R of the circular arc segment CC′. The ratio of the arc length θ*R to the time difference Δt is the linear velocity value of the forklift, where Δt is the time difference between the current moment and the next moment.

[0062] The speed control unit controls the forklift to travel at the specified linear speed to the target position at the next moment, and the forklift's posture at the target position is the target posture.

[0063] The present invention has been described by way of example. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A control method for an omnidirectional counterbalanced forklift, characterized in that, The method specifically includes the following steps: S1. Determine the instantaneous center O from the current pose to the target pose at the next moment; S2. Calculate the linear velocity of the omnidirectional counterbalanced forklift based on the instantaneous center of gravity O; S3. Control the omnidirectional counterbalance forklift to travel at the linear speed to the target position at the next moment. The attitude of the omnidirectional counterbalance forklift at the target position is the target attitude. The method for determining the instantaneous center O is as follows: S11. Connect the current position point with a straight line segment. The target position at the next moment This forms the perpendicular bisector of the line segment on the side of the instantaneous center direction; S12. Determine the angle difference between the current attitude angle and the target attitude angle at the next moment. ; S13, Find the satisfactory value on the perpendicular bisector. The location point is the instantaneous center O; The method for determining the direction of linear velocity is as follows: With the instantaneous center O as the center, line segment or line segment radius Forming an arc segment Circular arc segment The tangent direction is the direction of the linear velocity of the omnidirectional counterbalance forklift. The method for determining the linear velocity value is as follows: Calculate the arc segment arc length arc length With time difference The ratio is the linear velocity of the forklift. This represents the time difference between the current moment and the next moment.

2. The omnidirectional counterbalance forklift control method as described in claim 1, characterized in that, angular velocity Linear velocity value and radius The ratio of .

3. A control device for an omnidirectional counterbalanced forklift, characterized in that, The device includes: The instantaneous center determination unit is used to determine the instantaneous center O from the current pose to the target pose at the next moment, and output it to the velocity determination unit; The linear velocity determination unit calculates the linear velocity of the forklift based on the instantaneous center of gravity O and outputs it to the speed control unit; The speed control unit controls the forklift to travel at the linear speed to the target position at the next moment, and the forklift's posture at the target position is the target posture. The instantaneous center determination unit includes: The perpendicular bisector formation module connects the current position point with a straight line segment. The target position at the next moment This forms the perpendicular bisector of the line segment on the side of the instantaneous center direction; The change in attitude angle is synchronized with the change in velocity direction angle. The deflection angle determination module is used to determine the angle difference between the current attitude angle and the target attitude angle at the next moment. ; The instantaneous center determination module is used to find the condition on the perpendicular bisector. The location point is the instantaneous center O; The linear velocity determination unit includes: The module for determining the direction of linear velocity uses the instantaneous center O as the center of a circle, and the line segment... or line segment radius Forming an arc segment Circular arc segment The direction of the tangent is the direction of the linear velocity of the forklift. The linear velocity determination unit further includes: The linear velocity value determination module is used to calculate the linear velocity segment. arc length arc length With time difference The ratio is the linear velocity of the omnidirectional counterbalance forklift. This represents the time difference between the current moment and the next moment.

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