Omni-directional moving multi-differential wheel set AGV trolley and control method thereof

Abstract

The invention relates to an omni-directional moving multi-differential-wheel-set AGV and a control method thereof.The omni-directional moving multi-differential-wheel-set AGV comprises a chassis, differential wheel sets and vertical rotating shafts, the vertical rotating shafts are installed on the chassis, gears are arranged on the vertical rotating shafts, the number of the vertical rotating shafts is the same as that of the differential wheel sets, and each vertical rotating shaft is connected with the corresponding differential wheel set; the differential wheel set comprises a pair of independently-controlled power wheels and a transversely-placed driving motor, and the driving motor is in driving connection with the power wheels on the two sides. Each vertical rotating shaft is connected with a corresponding offset encoder and is used for recording rotation of the vertical rotating shaft. Compared with the prior art, the device has the advantages of being high in automation degree, capable of reducing manual carrying requirements, stable in motion control and the like.

Description

Technical Field

[0001] The present invention relates to the field of AGV trolleys, and in particular to an omnidirectional mobile multi-differential wheel set AGV trolley and a control method thereof. Background Art

[0002] At present, in warehouse logistics and transportation scenarios, logistics AGV is a widely needed auxiliary handling tool. Traditional AGVs use power wheels, and the more common AGVs use steering wheels, differential wheels, and multi-wheel hybrid solutions. Pure power lacks flexibility and cannot meet the requirements of special scenarios for logistics AGVs. The steering wheel solution is the most commonly used, but it cannot adapt to high-load scenarios. The differential wheel solution lacks lateral movement capabilities and loses flexibility. Summary of the invention

[0003] The purpose of the present invention is to provide an omnidirectional mobile multi-differential wheel AGV and a control method thereof in order to overcome the defects of the above-mentioned prior art, such as lack of lateral movement capability and loss of flexibility.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] An omnidirectional mobile multi-differential wheel set AGV trolley, comprising a chassis, a differential wheel set and a vertical rotating shaft, wherein the vertical rotating shaft is mounted on the chassis, a gear is arranged on the vertical rotating shaft, the number of the vertical rotating shafts is the same as the number of the differential wheel sets, each vertical rotating shaft is respectively connected to a corresponding differential wheel set, the differential wheel set comprises a pair of independently controlled power wheels and a transversely placed drive motor, and the drive motor respectively drives the power wheels connected to both sides;

[0006] Each vertical rotating shaft is respectively connected to a corresponding encoder, and the encoder is connected to the gear for recording the rotation of the vertical rotating shaft.

[0007] Furthermore, when the number of the differential wheel sets is less than 3 or redundant passive support is required, the AGV trolley is also provided with universal wheels for auxiliary support.

[0008] Furthermore, the offset motor unit is provided with a transmission gear or a pulley matched with the gear.

[0009] Furthermore, the differential wheel set is connected to a differential wheel set side plate, the differential wheel set side plate is connected to a differential wheel set bottom plate, and the differential wheel set bottom plate is connected to the base of the encoder of the vertical rotating shaft.

[0010] The present invention also provides a control method for an omnidirectional mobile multi-differential wheel set AGV as described above, comprising the following steps:

[0011] According to the layout of the AGV, the position of each differential wheel set, the distance between two power wheels in each differential wheel set, and the power wheel radius parameters are set;

[0012] According to the layout and parameters of the AGV, establish the vehicle local coordinate system and determine the corresponding relationship between the vehicle local coordinate system and the space global coordinate system;

[0013] Manual control process: receiving the speed requirement, and using vector calculation according to the principle of dynamics to obtain the desired speed vector of each differential wheel set;

[0014] Automatic tracking process: According to the received standard trajectory, the tracking offset and posture deviation are calculated to obtain the center control rate, so as to calculate the expected speed of the power wheel in each differential wheel group and the expected speed direction of the vertical axis of the vertical rotation axis to control the AGV car.

[0015] Furthermore, PI feedback is used to perform speed control according to the desired speed direction of the vertical axis, and PD feedback is used to perform tracking control according to the desired speed of the power wheel.

[0016] Furthermore, the established vehicle local coordinate system includes the center of mass C(0,0), the center of the trajectory curvature O(x,y) and the coordinates of each differential wheel set:

[0017] Set vector P i , the corresponding calculation expression is:

[0018]

[0019] Where P is the position of each differential wheel set.

[0020] Furthermore, during the manual control process, the calculation expression of the desired velocity vector of each differential wheel set is:

[0021]

[0022] In the formula, × is the matrix cross product, v is the cross product of each vector, c is the vehicle speed control quantity, ω=[0,0,ω] T , that is, the rotation is upward, which is the angular velocity control value of the whole vehicle; is the desired velocity vector of differential wheelset i.

[0023] Furthermore, the expression of the center control rate is:

[0024] V c =v d +k 1 ·|d c |

[0025] ω=k 2 ·δ c

[0026] Where V c is the expected linear velocity scalar of the vehicle, d c is the tracking offset, ω is the expected angular velocity scalar of the vehicle, and δ c is the posture deviation, k 1 and k 2 is a hyperparameter, v d It is the preset basic speed of the vehicle.

[0027] Furthermore, the calculation expression of the expected speed of the power wheel in each differential wheel set is:

[0028]

[0029] v iL (t)=|v i (t)|-ω i (t)·d w

[0030] v iR (t)=|v i (t)|+ω i (t)·d w

[0031] In the formula, v c is the desired linear velocity vector, (t x ,t y ) is the path target point, P i0 P i The first element, P i1 P i The second element, v iy v c The first element, v ix v c The second element of is the desired wheel orientation angle, is the desired wheel group heading angle at time t+1, θ i (t) is the desired wheel group heading angle at time t, ω i (t) is the angular velocity of the i-th differential wheel set, d w is the wheel spacing between the two wheels in the differential wheel set, v i (t) is the desired linear velocity vector of the ith differential wheel set, is the left power wheel speed of the i-th differential wheel set, is the speed of the right power wheel of the i-th differential wheel set.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) High degree of automation, reducing the need for manual handling:

[0034] The present invention is suitable for high-load scenarios, and solves the huge defect that the steering wheel structure is difficult to apply to high-load scenarios.

[0035] It has the characteristics of omnidirectional movement and flexible rotation, which solves the bottleneck of the differential wheel solution that cannot move horizontally or diagonally and lacks flexibility. It works well in crowded, complex and narrow warehouse working environments.

[0036] The vertical encoder is used to implement feedback control, ensuring that the decomposed desired velocity vector can be accurately tracked, ensuring the flexibility and accuracy of vehicle trajectory tracking control.

[0037] (2) The present invention can calculate the speed of the left and right differential wheels in each differential wheel set according to the yaw angle, lateral and longitudinal speed instructions, and track them according to the PD speed control. This method can ensure the accuracy of the overall motion parameters and maintain good performance even under complex motion constraints. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the bottom structure of an omnidirectional mobile multi-differential wheel set AGV vehicle with four differential wheel sets provided in an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the bottom structure of an omnidirectional mobile multi-differential wheel set AGV vehicle with eight differential wheel sets provided in an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the bottom structure of an omnidirectional mobile multi-differential wheel AGV vehicle provided in an embodiment of the present invention;

[0041] Figure 4 A schematic diagram of a vehicle local coordinate system provided in an embodiment of the present invention;

[0042] Figure 5 The figure is a schematic diagram of the direction of each wheel speed provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0046] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0047] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0048] In addition, the terms "horizontal", "vertical" and the like do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0049] Example 1

[0050] like Figure 1-Figure 3 As shown, this embodiment provides an omnidirectional mobile multi-differential wheel set AGV trolley, including a chassis, a differential wheel set and a vertical rotating shaft, the vertical rotating shaft is installed on the chassis, a gear 2 is provided on the vertical rotating shaft, the number of the vertical rotating shaft is the same as the number of the differential wheel sets, each vertical rotating shaft is respectively connected to a corresponding differential wheel set, the differential wheel set includes a pair of independently controlled power wheels 3 and a horizontally placed drive motor 5, the drive motor 5 respectively drives the power wheels 3 connected to both sides;

[0051] Each vertical rotation axis is connected to a corresponding encoder, which is connected to gear 2 and is used to record the rotation of the vertical rotation axis.

[0052] When the number of differential wheel sets is less than 3 or redundant passive support is required, universal wheels can be arranged at any position for auxiliary support.

[0053] The number of differential wheel sets is preferably four or eight, and the structure is as follows: Figure 1 and Figure 2 shown.

[0054] The vertical rotating axis has no power drive requirement, and the chassis does not need to be provided with a vertical drive motor 5 , and the lowest height of the chassis is not subject to the vertical constraint.

[0055] Specifically, the differential wheel set includes a pair of independently controlled power wheels 3, a transversely placed drive motor 5, and an encoder for recording motor operation information.

[0056] The differential wheel set is fixed to the differential wheel set side plate 4, and the motor is placed transversely in the differential wheel, and can be placed with staggered axes. The offset motor set includes a transmission gear or a pulley.

[0057] The differential wheel set side plate 4 is connected to the bottom plate, and the differential wheel set bottom plate is connected to the vertical rotary shaft encoder base 1.

[0058] The vertical rotation axis position determines the relative position of the differential wheel set and the center of the chassis base, which is a key parameter affecting the vehicle dynamics settlement;

[0059] The vertical rotating shaft is fixed on the chassis and includes an unpowered encoder and gear 2. The position of the vertical rotating shaft can be arranged arbitrarily, and the chassis does not need to be arranged with a vertical drive motor 5. The minimum height of the chassis is not subject to the vertical constraint. The vertical encoder is fixed to the encoder base 1;

[0060] This embodiment also provides a control method for an omnidirectional mobile multi-differential wheel set AGV as above, comprising the following steps:

[0061] S1: According to the layout of the AGV, set the position of each differential wheel set, the distance between the two power wheels 3 in each differential wheel set, and the radius parameters of the power wheel 3;

[0062] S2: According to the layout and parameters of the AGV, establish the vehicle local coordinate system and determine the corresponding relationship between the vehicle local coordinate system and the space global coordinate system;

[0063] Manual control process S3: receiving the command speed requirement, and using vector calculation according to the principle of dynamics to obtain the desired speed vector of each differential wheel set;

[0064] Automatic tracking process S4: According to the received standard trajectory, the tracking offset and posture deviation are calculated to obtain the center control rate, so as to calculate the expected speed of the power wheel 3 in each differential wheel group and the expected speed direction of the vertical axis of the vertical rotation axis to control the AGV car.

[0065] The direction of the wheel's rotation axis is set to the left, with forward rotation defined as the positive direction.

[0066] The desired speed direction of the vertical axis is controlled using PI feedback, and the speed of the power wheel 3 motor is tracked using PD control.

[0067] Specifically, in step S1, in the AGV vehicle control system, accurate positioning and navigation are very important links. In order to realize the autonomous driving of the vehicle, it is necessary to establish an accurate vehicle local coordinate system to facilitate the accurate positioning and navigation of the vehicle during driving.

[0068] like Figure 4 As shown, first, establish the center of mass C(0,0) and the center of the trajectory curvature O(x,y). Then, define the wheel As the four wheels of the vehicle.

[0069] In step S2, set the vector P i , the initial position is as follows:

[0070]

[0071] The manual control process of step S3 is specifically as follows:

[0072] The matrix cross product is agreed to be the cross product of each vector, and the speed expression of wheel i is obtained as shown in the following formula:

[0073]

[0074] Where ω=[0,0,ω] T (i.e. the rotation is upward, which can also be understood as counterclockwise rotation is positive), calculate the speed of each wheel set respectively, such as Figure 5 shown.

[0075]

[0076] In the automatic tracking process in step S4, the tracking offset and the attitude deviation are calculated according to the received standard trajectory, and the control process thus performed includes:

[0077] In order to eliminate the tracking offset d c , attitude deviation δ c , the center control rate is set. Specifically, the center control rate is:

[0078] V c =v d +k 1 ·|d c |

[0079] ω=k 2 ·δc

[0080] Among them, k1 and k2 are hyperparameters used to adjust the ratio of centerline speed and angular speed. After obtaining the desired centerline speed and angular speed through the center control rate, the desired speed vector can be calculated by the following formula:

[0081]

[0082] In which, let the next target point of the local path be t(t x ,t y ).

[0083] The desired wheel heading angle is:

[0084]

[0085] Assume that time 0 is the initial state, and the wheels are all facing forward, even if θ i (0) = 0. At other times, the encoder feedback is θ i (t). Where d w It is the distance between the two wheels in a differential wheel set.

[0086]

[0087] v iL (t)=|v i (t)|-ω i (t)·d w

[0088] v iR (t)=|v i (t)|+ω i (t)·d w

[0089] Finally, the left and right differential wheel speeds of each differential wheel set are solved and tracked according to the PD speed control. This method can ensure the accuracy of the overall motion parameters and maintain good performance even under complex motion constraints.

[0090] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. An omnidirectional mobile multi-differential wheel AGV, characterized in that: The invention comprises a chassis, a differential wheel set and a vertical rotating shaft, wherein the vertical rotating shaft is mounted on the chassis, a gear (2) is arranged on the vertical rotating shaft, the number of the vertical rotating shafts is the same as the number of the differential wheel sets, each vertical rotating shaft is respectively connected to a corresponding differential wheel set, the differential wheel set comprises a pair of independently controlled power wheels (3) and a drive motor (5) arranged horizontally, and the drive motor (5) respectively drives the power wheels (3) connected to both sides; Each vertical rotation axis is respectively connected to a corresponding offset encoder, and the offset encoder is connected to the gear (2) and is used to record the rotation of the vertical rotation axis.

2. The omnidirectional mobile multi-differential wheel AGV according to claim 1, characterized in that: When the number of the differential wheel sets is less than 3 or redundant passive support is required, the AGV trolley is also provided with universal wheels for auxiliary support.

3. The omnidirectional mobile multi-differential wheel AGV according to claim 1, characterized in that: The offset motor group is provided with a transmission gear or a pulley matched with the gear (2).

4. The omnidirectional mobile multi-differential wheel AGV according to claim 1, characterized in that: The differential wheel set is connected to a differential wheel set side plate (4), the differential wheel set side plate (4) is connected to a differential wheel set bottom plate, and the differential wheel set bottom plate is connected to the base (1) of the encoder of the vertical rotating shaft.

5. A control method for an omnidirectional mobile multi-differential wheel AGV as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: According to the layout of the AGV, the position of each differential wheel set, the distance between two power wheels in each differential wheel set, and the power wheel radius parameters are set; According to the layout and parameters of the AGV, establish the vehicle local coordinate system and determine the corresponding relationship between the vehicle local coordinate system and the space global coordinate system; Manual control process: receiving the speed requirement, and using vector calculation according to the principle of dynamics to obtain the desired speed vector of each differential wheel set; Automatic tracking process: According to the received standard trajectory, the tracking offset and posture deviation are calculated to obtain the center control rate, so as to calculate the expected speed of the power wheel in each differential wheel group and the expected speed direction of the vertical axis of the vertical rotation axis to control the AGV car.

6. The method according to claim 5, characterized in that PI feedback is used to perform speed control according to the desired speed direction of the vertical axis, and PD feedback is used to perform tracking control according to the desired speed of the power wheel.

7. The method according to claim 5, characterized in that The established vehicle local coordinate system includes the center of mass C (0, 0), the center of the trajectory curvature O (x, y) and the coordinates of each differential wheel set: Set vector P i , the corresponding calculation expression is: Where P is the position of each differential wheel set.

8. The method according to claim 7, characterized in that During manual control, the calculation expression of the desired velocity vector of each differential wheel set is: Where × is the matrix cross product, and v is the cross product of each vector; c is the vehicle speed control quantity, ω=[0,0,ω] T , that is, the rotation is upward, which is the angular velocity control value of the whole vehicle; is the desired velocity vector of differential wheelset i.

9. The method according to claim 7, characterized in that: The expression of the center control rate is: V c =v d +k1·|d c | ω=k2·δ c Where V c is the expected linear velocity scalar of the vehicle, d c is the tracking offset, ω is the expected angular velocity scalar of the vehicle, and δ c is the posture deviation, k1 and k2 are hyperparameters, v d It is the preset basic speed of the vehicle.

10. The method according to claim 9, characterized in that The calculation expression of the expected speed of the power wheel (3) in each differential wheel set is: v iL (t)=|v i (t)|-ω i (t)·d w v iR (t)=|v i (t)|+ω i (t)·d w In the formula, v c is the desired linear velocity vector, (t x ,t y ) is the next target point of the local path, P i0 P i The first element, P i1 P i The second element, v iy v c The first element, v ix v c The second element of is the desired wheel orientation angle, is the desired wheel group heading angle at time t+1, θ i (t) is the desired wheel group heading angle at time t, ω i (t) is the angular velocity of the ith differential wheel set, d w is the wheel spacing between the two wheels in the differential wheel set, v i (t) is the desired linear velocity vector of the ith differential wheel set, v iL (t) is the speed of the left power wheel of the ith differential wheel set, v iR (t) is the speed of the right power wheel of the i-th differential wheel set.

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