Method for path planning of a mobile robot and program product

Abstract

The application provides a path planning method for a mobile robot, wherein the path planning method comprises the following steps: an information acquisition step S11, wherein position information of a starting point, an ending point and a predetermined set of passing points of a first path to be planned is acquired, the set of passing points being a set composed of at least one passing point; a curve determination step S12, wherein a smooth curve starting from the starting point, passing through the at least one passing point and ending at the ending point is determined according to the position information of the starting point, the ending point and the set of passing points, the curve having a continuous second derivative; a path determination step S13, wherein the smooth curve is taken as the first path of the mobile robot. A global path planning method for a mobile robot, a motion control method for a mobile robot and a corresponding computer program product are also provided. By means of the application, it can be ensured that the mobile robot can move along a smooth path and accurately pass through the passing points.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of mobile robots, in particular the field of motion control of mobile robots, and specifically to a path planning method for a mobile robot, a global path planning method for a mobile robot, a motion control method for a mobile robot, and a corresponding computer program product. BACKGROUND

[0002] With the rapid economic growth and the gradual increase of labor costs, mobile robots are increasingly widely used in various industrial and home environments. For example, mobile robots such as automatic guided vehicles (AGVs), autonomous mobile robots (AMRs), and forklifts are one of the key equipment in modern logistics systems. Mobile robots can move and stop at target locations according to path planning and job requirements to complete tasks such as material handling and transportation. Path planning is a key in the motion control of mobile robots.

[0003] In some scenarios, a mobile robot needs to pass through a specific location accurately. For example, a two-dimensional code is placed at a specific location, and the mobile robot needs to read the two-dimensional code when passing through the specific location. However, when planning a path for a mobile robot, it often happens that the planned path does not pass through the passing point accurately.

[0004] For example, when planning a path, the exact location of the passing point may not be considered, so that the passing point is not accurately located on the planned path, but only near the planned path. For example, although the commonly used TEB algorithm can make the local planning trajectory pass through the passing point as much as possible by increasing the weight of the passing point, since the TEB algorithm is essentially a multi-objective optimization algorithm, it still cannot guarantee to pass through the passing point accurately. Or, although the exact location of the passing point is considered when planning a global path, the location of the passing point deviates from the location of the corresponding passing point considered in the global path planning process or changes afterwards. For example, the placement position of the two-dimensional code may have a certain deviation.

[0005] The prior art still has many deficiencies in the trajectory planning and motion control of mobile robots. SUMMARY

[0006] The purpose of the present application is to provide an improved path planning method, global path planning method, and motion control method for a mobile robot to ensure that the mobile robot can move along a smooth path and accurately pass through a passing point.

[0007] According to a first aspect of the present application, there is provided a path planning method for a mobile robot, wherein the path planning method comprises the following steps: an information obtaining step S11, wherein position information of a start point, an end point and a predetermined set of passing points of a first path to be planned is obtained, the set of passing points being a set consisting of at least one passing point; a curve determining step S12, wherein a smooth curve starting from the start point, passing through the at least one passing point and ending at the end point is determined according to the position information of the start point, the end point and the set of passing points, the curve having a continuous second derivative; and a path determining step S13, wherein the smooth curve is determined as the first path of the mobile robot.

[0008] In one example embodiment, the information obtaining step S11 further comprises obtaining additional constraint information of the first path to be planned, the additional constraint information comprising at least one of the following: a predetermined start point velocity direction representing a velocity direction of the mobile robot at the start point; a predetermined path start point curvature representing a curvature of the first path to be planned at the start point; a predetermined end point velocity direction representing a velocity direction of the mobile robot at the end point; a predetermined path end point curvature representing a curvature of the first path to be planned at the end point; and a predetermined passing point velocity direction representing a velocity direction of the mobile robot at the at least one passing point. In the curve determining step S12, the curve is additionally determined according to the additional constraint information.

[0009] In one example embodiment, the curve is a Bezier curve or a B-spline curve.

[0010] In one example embodiment, the number of the at least one passing point is m, where m is an arbitrary positive integer, the curve is a m+3 order Bezier curve, and the first control point and the m+4th control point of the Bezier curve are the start point and the end point respectively.

[0011] In one example embodiment, the curve is represented by the following equation:

[0012]

[0013] where i = 0, 1, …, m+3, denote the coordinates of the control points of the Bezier curve and where the coordinates of the control points are determined in the following way:

[0014] is the coordinate of the start point, is the coordinate of the end point;

[0015] (x1-x0), (y1-y0) respectively and wherein the signs of the positive and negative are the same, wherein is a unit vector representing a predetermined start point speed direction;

[0016] (x m+3 -x m+2 ), (y m+3 -y m+2 ) respectively and wherein the signs of the positive and negative are the same, wherein is a unit vector representing a predetermined end point speed direction;

[0017] wherein, represents the coordinates of the jthway point in the at least one way point, j = 1, 2, …, m, represents the value of s corresponding to the jthway point;

[0018] in the same direction as wherein, is a unit vector representing a predetermined way point speed direction at the jthway point, P'(s) represents the coordinates of the first derivative of represents the coordinates of the first derivative of at ;

[0019] Substitute s = 0 and K(0) = K0into , wherein K0represents a predetermined path start point curvature, P x '(s), P y '(s), P x "(s), P y "(s) are the first derivative horizontal, vertical coordinates and the second derivative horizontal, vertical coordinates of respectively;

[0020] Substitute s = 1 and K(1) = K1into , wherein K1represents a predetermined path end point curvature.

[0021] In one exemplary embodiment, the way point set contains exactly one way point, and the curve determined in the curve determining step S12 is represented by the following formula:

[0022]

[0023] wherein, represents the coordinates of the control points of the Bezier curve and i = 0, 1, …, 4, wherein the coordinates of the control point are determined in the following manner: ​

[0024] coordinates of the start point, coordinates of the end point;

[0025] (x1-x0), (y1-y0) respectively have the same sign as wherein, is a unit vector representing a predetermined start point velocity direction;

[0026] (x4-x3), (y4-y3) respectively have the same sign as wherein, is a unit vector representing a predetermined end point velocity direction;

[0027] wherein, (x v ,y v ) represents coordinates of the passing point, s v represents a value of s corresponding to the passing point;

[0028] wherein, the first component and the second component of have the same sign as and is a unit vector representing a predetermined passing point velocity direction at the passing point;

[0029] wherein, K0 represents a predetermined path start point curvature,

[0030] wherein, K1 represents a predetermined path end point curvature.

[0031] In one exemplary embodiment, the mobile robot is a differential drive robot.

[0032] According to a second aspect of the present application, a global path planning method for a mobile robot is provided, wherein the global path planning method comprises the following steps: an initial planning step S21, in which an initial global path for the mobile robot is obtained; a via point determination step S22, in which a via point set is determined, a via point representing a point that the mobile robot needs to pass through, the via point set being a set consisting of at least one via point and containing at least one missed via point that is not passed through by the global path; a local path determination step, in which an initial local path segment of the via points contained in a neighboring via point set in the global path is determined; a re-planning step S24, in which a first path for the mobile robot is determined based on the start point, the end point and the via point set according to the path planning method of the present application, with the start point and the end point of the initial local path segment as the start point and the end point respectively; and a path replacement step S25, in which the initial local path segment in the global path is replaced by the first path.

[0033] In one exemplary embodiment, in the re-planning step S24, at least one of the following is performed: the start point velocity direction of the first path is equal to the start point velocity direction of the initial local path segment; the path start point curvature of the first path is equal to the path start point curvature of the initial local path segment; the end point velocity direction of the first path is equal to the end point velocity direction of the initial local path segment; the path end point curvature of the first path is equal to the path end point curvature of the initial local path segment.

[0034] In one exemplary embodiment, in the re-planning step S24, the first path is determined such that the velocity direction at the at least one via point satisfies one of the following conditions: the velocity direction of the point closest to the via point corresponding to the distance on the initial local path segment is the same; the direction from the start point to the end point of the initial local path segment is the same; the task requirement of the mobile robot at the corresponding via point is met.

[0035] In one exemplary embodiment, in the via point determination step S22, the via points that the mobile robot should pass through are determined, starting from a first via point closest to the start point of the global path among the missed via points that are not passed through by the global path, the first via point and the via points that satisfy the following condition are taken as one of the via points in the via point set: the path length between each two adjacent points on the global path corresponding to the points closest to each via point in the via point set is less than a predetermined threshold.

[0036] In one exemplary embodiment, in the local path determining step, the start point and the end point of the initial local path segment are determined such that: in the direction along the global path, the start point of the initial local path segment is located before all points on the global path that are respectively closest to each of the set of way points; in the direction along the global path, the end point of the initial local path segment is located after all points on the global path that are respectively closest to each of the set of way points.

[0037] In one exemplary embodiment, the global path planning method further comprises: repeatedly performing the way point determining step S22, the local path determining step S23, the re-planning step S24 and the path replacing step S25 until there is no missed way point that the mobile robot should pass through but the global path does not pass through.

[0038] According to a third aspect of the present application, there is provided a motion control method for a mobile robot, the motion control method comprising the following steps: a real-time way point detecting step S31, in which at least one missed way point that is not passed through by a planned path is detected within a predetermined distance range relative to a current position point of the mobile robot during motion of the mobile robot along the planned path, the way point representing a point that the mobile robot needs to pass through; a real-time way point determining step S32, in which a set of way points is determined, the set of way points being a set consisting of at least one way point and containing the at least one missed way point; a real-time local path determining step S33, in which an original local path segment of way points contained by the set of adjacent way points in the planned path is determined; a real-time re-planning step S34, in which a first path for the mobile robot is determined based on a start point, an end point and the set of way points according to the path planning method of the present application, with the start point and the end point of the original local path segment as the start point and the end point respectively; and a real-time path replacing step S35, in which the original local path segment in the planned path is replaced by the first path, and the mobile robot is controlled to move along the replaced planned path.

[0039] In one exemplary embodiment, in the real-time local path determining step S33, the current position point of the mobile robot is taken as the start point of the original local path segment.

[0040] In one exemplary embodiment, in the real-time re-planning step S34, at least one of the following is performed: the start point speed direction of the first path is made equal to the start point speed direction of the original local path segment; the path start point curvature of the first path is made equal to the path start point curvature of the original local path segment; the end point speed direction of the first path is made equal to the end point speed direction of the original local path segment; the path end point curvature of the first path is made equal to the path end point curvature of the original local path segment.

[0041] In one example embodiment, in the real-time re-planning step S34, the first path is determined such that the velocity direction at the at least one passing point satisfies one of the following conditions: the same as the velocity direction of the point closest to the passing point corresponding to the distance on the original local path segment; the same as the direction from the start point to the end point of the original local path segment; satisfying the task requirement of the mobile robot at the corresponding passing point.

[0042] In one example embodiment, in the real-time passing point determination step S32, the at least one missed passing point and a passing point satisfying the following condition are taken as one of the passing points in the passing point set: the path length between each two adjacent points on the planning path closest to the respective passing points in the passing point set is less than a predetermined threshold.

[0043] In one example embodiment, in the real-time local path determination step S33, the start point and the end point of the original local path segment are determined such that: in the direction along the planning path, the start point of the original local path segment is located before all the points on the planning path closest to the respective passing points in the passing point set; in the direction along the planning path, the end point of the original local path segment is located after all the points on the planning path closest to the respective passing points in the passing point set.

[0044] In one example embodiment, the motion control method further comprises: repeatedly performing the real-time passing point determination step S32, the real-time local path determination step S33, the real-time re-planning step S34 and the real-time path replacement step S35 until there is no missed passing point that the mobile robot should pass through but the planning path does not pass through.

[0045] According to a fourth aspect of the present application, there is provided a computer program product comprising computer program instructions, wherein the computer program instructions, when executed by one or more processors, enable the processors to perform the path planning method according to the present application or the global path planning method according to the present application or the motion control method according to the present application.

[0046] By the present application, a smooth path that accurately passes through specific passing points from the start point and ends at the end point can be obtained. Thus, the mobile robot can accurately pass through the specific passing points along the smooth path, and thus can complete the task at the passing points. BRIEF DESCRIPTION OF DRAWINGS

[0047] The principles, features and advantages of the present application will be better understood by referring to the following detailed description of the application, in conjunction with the accompanying drawings. The drawings include:

[0048] Figure 1 a flowchart schematically showing a path planning method according to one example embodiment of the present application;

[0049] Figure 2 A first path obtained by a path planning method according to an example embodiment of the present application is schematically shown;

[0050] Figure 3 A flowchart of a global path planning method for a mobile robot according to an example embodiment of the present application is schematically shown;

[0051] Figure 4A 、 Figure 4B and Figure 4C A process of global path planning by a global path planning method according to an example embodiment of the present application is schematically shown; and

[0052] Figure 5 A motion control method for a mobile robot according to an example embodiment of the present application is schematically shown. DETAILED DESCRIPTION

[0053] In order to make the technical problems to be solved by the present application, the technical solutions and beneficial technical effects more clearly understood, the present application will be further described in detail below in conjunction with the accompanying drawings and multiple example embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the protection scope of the present application.

[0054] The present application is applicable to a mobile robot 1, which can be any robot capable of autonomously moving in space, such as an AGV, an AMR, etc. The mobile robot 1 can be used to perform various tasks, such as used as a warehouse robot, a cleaning robot, a home companion robot, a welcome robot, etc.

[0055] It should be understood that, in this document, the expressions "first", "second", etc. are only used for descriptive purposes and should not be understood as indicating or implying relative importance, nor should they be understood as implicitly indicating the number of the technical features indicated. The features defined with "first", "second" can explicitly or implicitly indicate that they include at least one such feature.

[0056] Figure 1 A flowchart of a path planning method for a mobile robot 1 according to an example embodiment of the present application is schematically shown. The path planning method comprises the following steps:

[0057] An information acquisition step S11, in which the position information of the start point, the end point and the predetermined set of passing points of the first path 2 to be planned is acquired, the set of passing points being a set composed of at least one passing point;

[0058] a curve determination step S12 in which a smooth curve starting at the start point, passing through the at least one via point and ending at the end point is determined on the basis of the position information of the start point, the end point and the set of via points, the curve having a continuous second derivative; and

[0059] a path determination step S13 in which the smooth curve is determined as the first path 2 of the mobile robot 1.

[0060] The mobile robot 1 needs to pass through a specific position accurately in some scenarios to complete a task. For example, the mobile robot 1 can include a code scanner and has a task of scanning a two-dimensional code at a specific position. By means of this path planning method, a smooth first path 2 starting at the start point and passing through the specific via point accurately and ending at the end point can be obtained. Thus, the mobile robot 1 can pass through the specific via point accurately along the smooth path, and thus can complete the task at the via point.

[0061] Figure 2 The first path 2 obtained by means of the path planning method according to one exemplary embodiment of the application is schematically shown.

[0062] In Figure 2 In the embodiment shown, the mobile robot 1 is, for example, a differential robot, i.e. the mobile robot 1 comprises a differential wheel movement system. For a differential robot, the first path 2 planned to have a continuous second derivative can particularly advantageously adapt to the movement characteristics of the differential robot. In particular, the first path 2 can have a continuous curvature. This makes the changes in the speed and acceleration of the mobile robot more gentle. Alternatively, the mobile robot 1 can also be another type of robot, such as a single-steering wheel robot or a double-steering wheel robot, etc. Correspondingly, the mobile robot 1 can comprise, for example, a double-steering wheel movement system.

[0063] The mobile robot 1 further comprises, for example, a sensor. In the information acquisition step S11, the required information, such as the position information, can be acquired by means of the detection result of the sensor. The mobile robot 1 further comprises, for example, a communication device for communicating with other devices, such as a dispatch control system. In the information acquisition step S11, the required information can be acquired by means of the signals received by the communication device.

[0064] The mobile robot 1 further comprises, for example, a controller. The controller is used for the components of the mobile robot 1, which components include, for example, the differential wheel movement system, the sensor, the communication device, etc. The controller can also receive the working state or detection data of the corresponding components, such as the sensor, by means of a communication line, in order to monitor or control the operation of the mobile robot 1. The path planning method can be performed, for example, by means of the controller, or by means of another device, such as a dispatch control system, which can exchange data with the controller.

[0065] InFigure 2 In the illustrated embodiment, the curve determined in the curve determining step S12 is a Bezier curve. Alternatively, the curve can also be another type of smooth curve, such as a polynomial curve or a B-spline curve, in particular a clamped-B-spline curve, such as a NURBS curve.

[0066] The information obtaining step S11 further comprises, for example, obtaining additional constraint information of the first path 2 to be planned, the additional constraint information comprising at least one of: a predetermined start point velocity direction representing a velocity direction of the mobile robot 1 at the start point; a predetermined path start point curvature representing a curvature of the first path 2 to be planned at the start point; a predetermined end point velocity direction representing a velocity direction of the mobile robot 1 at the end point; a predetermined path end point curvature representing a curvature of the first path 2 to be planned at the end point; a predetermined via point velocity direction representing a velocity direction of the mobile robot 1 at the at least one via point. Accordingly, in the curve determining step S12, the curve is additionally determined in accordance with the additional constraint information. By means of the additional constraint information, a more demand- conforming first path 2 can be obtained.

[0067] Figure 2 The case where the set of via points contains exactly one via point is shown in the middle. Here, the curve determined in the curve determining step S12 can be represented by the following equation:

[0068]

[0069] wherein, denote the coordinates of the control points of the Bezier curve and i = 0, 1,..., 4. The above equation (1) can be represented in matrix form as follows:

[0070]

[0071] The coordinates of the first control point may be set to the coordinates of the start point, the coordinates of the fifth control point are the coordinates of the end point.

[0072] The process of determining the other control points will be described exemplarily in the following.

[0073] Taking the derivative of equation (2) with respect to s yields:

[0074]

[0075] When s = 0, When s = 1, It can be seen that the tangent direction at the start point and the end point is parallel to the direction of the line connecting the two adjacent control points at the start and the end.

[0076] In other words, the direction of the line connecting the first control point and the second control point is the trajectory direction at the starting point. The predetermined starting velocity direction is expressed as a unit vector. If this is true, then the first control point and the second control point have the following relationship:

[0077]

[0078] in And (x1-x0) and (y1-y0) are respectively with Both positive and negative values ​​are considered. This allows the planned first path 2 to have a predetermined starting velocity direction. This is particularly advantageous for differential robots, as their velocity direction can only be along their forward direction. Given a given starting pose for the differential robot at the starting point, the planned first path 2 thus has a starting velocity direction that matches the given pose.

[0079] Similarly, the direction of the line connecting the fourth and fifth control points is the trajectory direction at the endpoint. The predetermined endpoint velocity direction is represented by a unit vector. Therefore, the fourth control point and the fifth control point have the following relationship:

[0080]

[0081] in And (x4-x3) and (y4-y3) are respectively with Both positive and negative values ​​are considered. This allows the planned first path 2 to have a predetermined endpoint velocity direction. This is particularly advantageous for differential robots. Given an endpoint pose for the differential robot at the endpoint, the planned first path 2 thus has an endpoint velocity direction that matches the given pose.

[0082] To ensure that path 2 passes through the waypoints accurately, the waypoints should lie on the curve. Use P... v (x v ,y v ) represents the coordinates of the points passed through, and s is used to represent the coordinates of the points passed through. v This represents the value of s corresponding to the waypoint, where s v If ∈(0,1), then the points along the path satisfy the following equation:

[0083]

[0084] Additionally, the velocity direction of the mobile robot 1 at the waypoints can be set (i.e., the predetermined velocity direction at the waypoints). The predetermined velocity direction at the waypoints is expressed as a unit vector. If the predetermined path point velocity direction satisfies the following equation:

[0085]

[0086] in, The first and second components are respectively with and Both positive and negative.

[0087] To obtain a more optimized first path 2, the curvature of the first path 2 at its start and end points can also be considered. The curvature formula for a fourth-order Bézier curve is as follows:

[0088]

[0089] Where P x ′(s), P y ′(s), P x "(s), P y "(s) are respectively in equation (1) The first-order x-coordinate and the second-order x-coordinate. When s = 0, P can be obtained according to equation (3). x ′(0)=-4x0+4x1,P y ′(0)=-4y0+4y1. Taking the derivative of s in equation (3) again, we get:

[0090]

[0091] From equation (9), we can see that P x "(0) = 12x0 - 24x1 + 12x2, P" y "(0) = 12y0 - 24y1 + 12y2. Let K0 represent the curvature of the predetermined starting point of the path, then the curvature of the first path 2 at the starting point satisfies the following equation:

[0092]

[0093] For differential robots, the curvature of the motion trajectory can be derived from the ratio of the magnitude of the angular velocity to the magnitude of the linear velocity. By setting the magnitude of the linear velocity at the starting point P0 as V0 and the magnitude of the angular velocity as ω0, the predetermined curvature of the starting point of the path can be set. Similarly, the predetermined path endpoint curvature can be obtained at the endpoint.

[0094] From equations (3) and (8), we can also obtain: P x ′(1)=4(x4-x3), P y ′(1)=4(y4-y3), P x "(1) = 12(x² - 2x³ + x⁴), P" y "(1) = 12(y2-2y3+y4). Let K1 represent the curvature of the predetermined path endpoint, then the curvature of the first path 2 at the endpoint satisfies the following equation:

[0095]

[0096] By the above equations (4), (5), (6), (7), (10) and (11), the coordinates of the control points P1, P2 and P3 can be obtained. In other words, in the case that the first path 2 satisfies the condition that it goes from the start point to the end point via the via points, by taking the predetermined start point velocity direction, the predetermined path start point curvature, the predetermined end point velocity direction, the predetermined path end point curvature, and the predetermined via point velocity direction as additional constraint conditions, the coordinates of the second, third and fourth control points can be obtained. The coordinates of the first control point and the fifth control point have been determined by the start point and the end point of the first path 2. Thus, the five control points of the quartic Bezier curve represented by equation (1) can be determined, and further the whole curve can be determined. By the additional constraint conditions set as above, the first path 2 can be obtained which is particularly adapted to the motion characteristics of the differential robot. It should be understood that other constraint conditions can also be considered to determine the curve, such as the total length of the curve, etc.

[0097] Obviously, in further embodiments according to the application, the set of via points can also comprise more than one via point. In the case that the set of via points comprises m (m being any positive integer) via points, the curve can for example be a Bezier curve of order m+3, the first control point and the m+4th control point of the Bezier curve being respectively the start point and the end point of the first path 2.

[0098] In this case, in the curve determining step S12, the curve can be represented by the following equation:

[0099]

[0100] where i = 0, 1,..., m+3, denotes the coordinates of the control points of the Bezier curve and

[0101] the coordinates of the control points can be determined by:

[0102] is the coordinate of the start point, is the coordinate of the end point;

[0103] (x1-x0), (y1-y0) respectively have the same sign, wherein is a unit vector representing the predetermined start point velocity direction;

[0104] (x m+3 -x m+2 ), (ym+3 -y m+2 ) respectively with Both positive and negative, among which, It is a unit vector representing the direction of the predetermined endpoint velocity; in, This represents the coordinates of the j-th waypoint among the at least one waypoints, where j = 1, 2, ..., m. This represents the value of s corresponding to the j-th waypoint;

[0105] and The directions are the same, among which, It represents the unit vector of the velocity direction at the predetermined path point at the j-th path point, P′(s) represents The coordinates of the first derivative, express exist The coordinates of the first derivative at that point;

[0106] Substitute s = 0 and K(0) = K0 into In the context of the path, K0 represents the curvature of the predetermined starting point; and

[0107] Substituting s = 1 and K(1) = K1 into In the denominator, K1 represents the curvature of the predetermined path endpoint.

[0108] When m>1, the method for determining each control point is the same as described above. Figure 2 The method described for the case where m=1 is similar. The main difference is that when the number of waypoints is greater than 1, for each additional waypoint, two additional constraints are added based on the coordinates of the waypoint and the velocity direction at that waypoint. Correspondingly, the order of the Bézier curve increases by one, requiring the determination of the coordinates of an additional control point, which can be achieved by adding two additional constraints.

[0109] Figure 3 A flowchart illustrating a global path planning method for a mobile robot 1 according to an exemplary embodiment of the present invention is shown schematically. Figure 3 As shown, the global path planning method includes the following steps:

[0110] Initial planning step S21, wherein the initial global path 3 for mobile robot 1 is obtained;

[0111] Step S22, which involves determining a set of waypoints, where a waypoint represents a point that the mobile robot 1 needs to pass through. The set of waypoints is a set consisting of at least one waypoint and includes at least one missed waypoint that the global path 3 has not yet passed.

[0112] locally determining an initial local path segment 31 of a passing point contained in the set of adjacent passing points in the global path 3;

[0113] replanning step S24, in which a first path 2 for the mobile robot 1 is determined based on the start point, the end point and the set of passing points according to the path planning method of the present application, with the start point and the end point of the initial local path segment 31 as the start point and the end point, respectively; and

[0114] path replacing step S25, in which the initial local path segment 31 in the global path 3 is replaced by the first path 2.

[0115] Currently, when planning a global path for a mobile robot 1, it often happens that the planned global path 3 does not pass all passing points that need to be passed. For example, when planning the global path, the exact position of a passing point can not be considered, so that the passing point is not accurately located on the planned global path 3, but only near the global path 3. Or, although the exact position of a passing point is considered when planning the global path, the position of the (part of) passing point deviates from the position of the corresponding passing point considered in the global path planning process or has changed afterwards, for example, the position of a two-dimensional code to be scanned by the mobile robot 1 can deviate from the position of the passing point considered in the global path planning process. Or, for example, after completing the global path planning, new passing points that need to be passed by the mobile robot 1 are added due to task setting or environmental changes, etc.

[0116] By means of the above global path planning method, even if the initial global path 3 does not pass all passing points that need to be passed, it is not necessary to perform a complete global path planning process again. Instead, optimization can be performed on the basis of the initial global path 3 to obtain a new global path 3 that is more optimized, so that the new global path 3 accurately passes the passing points and can deviate from the initial global path 3 less.

[0117] The global path planning method can be performed by means of a controller of the mobile robot, for example, or by means of another device capable of data exchange with the controller, such as a dispatch control system.

[0118] The initial global path 3 can be acquired by any applicable known method. For example, the initial global path 3 can be planned by an A* algorithm. Generally, the initial global path 3 has already considered a relatively optimal path for the constraints and optimization objectives of the mobile robot 1. For example, the initial global path 3 can be the shortest path from the start point to the end point. The global path planning method according to the present application performs local optimization based on less deviation from the initial global path 3, and can maintain the advantages of the initial global path 3, such as a short path length. In addition, the planning process can be simplified, and the amount of calculation can be reduced.

[0119] Figure 4A 、 Figure 4B and Figure 4C The process of global path planning by the global path planning method according to one exemplary embodiment of the present application is schematically shown in FIG. 1. The process of global path planning by the global path planning method according to one exemplary embodiment of the present application is schematically shown in FIG. 2. Figure 4B and Figure 4C are Figure 4A are enlarged views of the parts framed by blocks B and C in FIG. 1. The execution process of the global path planning method according to one exemplary embodiment of the present application is exemplarily described below in connection with Figure 4A , Figure 4B and Figure 4C .

[0120] First, in an initial planning step S21, an initial global path 3 for the mobile robot 1 is acquired. As shown in FIG. 3, the initial global path 3 does not accurately pass through all the waypoints. Figure 4A

[0121] Then, in a waypoint determination step S22, a set of waypoints is determined. For example, in the waypoint determination step S22, the waypoints that the mobile robot 1 should pass through are determined, and the missed waypoints that the global path 3 does not pass through are determined, such as the waypoints P v1 and P v2 . Starting from the first waypoint (for example, the waypoint P v1 ) closest to the start point of the global path 3 among the missed waypoints that the global path 3 does not pass through, the first waypoint and the waypoints (which can or can not be located on the current global path 3) that satisfy the following condition are taken as one of the waypoints in the set of waypoints: the path length between each two adjacent points in the corresponding points on the global path 3 closest to each of the waypoints in the set of waypoints is less than a predetermined threshold value.

[0122] Figure 4B An enlarged view at the missed waypoint P v1 is schematically shown in FIG. 4. The following is described by way of example with the waypoint P v1 . For the purpose of simplifying the description, the set of waypoints in this example only contains one waypoint P v1 ​However, as mentioned above, the set of waypoints can also contain more than one waypoint. For example, if waypoint P is shown in this enlarged view... v If there are other waypoints nearby, these other waypoints can also be included in the waypoint set so that the first path 2 obtained in the replanning step S24 additionally passes through these other waypoints.

[0123] In the local path determination step S23, an initial local path segment 31 containing the path points of the neighboring path point set in the global path 3 is determined. For example, the start and end points of the initial local path segment 31 are determined such that: along the direction of the global path 3, the start point of the initial local path segment 31 is located before all points on the global path 3 that are respectively closest to each path point in the path point set, for example, at a predetermined first path length (e.g., 2m) at a previous interval; and along the direction of the global path 3, the end point of the initial local path segment 31 is located after all points on the global path 3 that are respectively closest to each path point in the path point set, for example, at a predetermined second path length (e.g., 2m) at a subsequent interval. The second path length may, for example, be set to be less than or equal to a predetermined threshold.

[0124] In the replanning step S24, the starting point and ending point of the initial local path segment 31 are respectively taken as the starting point and ending point, and a first path 2 for the mobile robot 1 is determined based on the path planning method according to the present invention, using the set of starting points, ending points, and waypoints. In the replanning step S24, at least one of the following can be performed: making the starting velocity direction of the first path 2 equal to the starting velocity direction of the initial local path segment 31; making the starting curvature of the first path 2 equal to the starting curvature of the initial local path segment 31; making the ending velocity direction of the first path 2 equal to the ending velocity direction of the initial local path segment 31; making the ending curvature of the first path 2 equal to the ending curvature of the initial local path segment 31. Thus, additional constraints can be set for the first path 2, such that the first path 2 has the same starting velocity direction, starting curvature, ending velocity direction, and ending curvature as the initial local path segment 31. Therefore, when the initial local path segment 31 is replaced by the first path 2, a seamless connection can be achieved. In other words, a smooth connection can be achieved without abrupt changes in velocity or curvature.

[0125] exist Figure 4B In the embodiment shown, the first path 2 is determined such that the path point P is passed through. v1 The velocity direction at point P and the distance along the initial local path segment 31 are related to the path point P. v1 The nearest points have the same velocity direction. Therefore, the deviation of the first path 2 from the initial local path segment 31 can be reduced.

[0126] Alternatively or additionally, the first path 2 can also be determined such that the velocity direction at at least one waypoint is the same as the direction from the start point to the end point of the initial local path segment 31. This can facilitate obtaining a smoother first path 2.

[0127] Alternatively or additionally, the first path 2 can also be determined such that the velocity direction at at least one waypoint satisfies the task requirements of the mobile robot 1 at the corresponding waypoint. This facilitates the mobile robot 1 in completing its task conveniently as it passes through waypoints along the first path 2. For example, if the mobile robot 1 needs to complete its task at waypoint P... v1 If the task of scanning the QR code placed here is completed at point P, then the first path 2 can be determined as such that at the point P along the way... v1 The velocity direction at point P is advantageous for mobile robot 1 when passing through path point P. v1 The scanner is positioned directly in front of the QR code placed there.

[0128] In path replacement step S25, the initial local path segment 31 in global path 3 is replaced with the first path 2 (in Figure 4A (Illustrated schematically by a dashed curve). From this, a new global path 3 can be obtained.

[0129] See Figure 4A After obtaining the new global path 3, the new global path 3 can be used as the current global path 3. Then, the waypoint determination step S22, the local path determination step S23, the replanning step S24, and the path replacement step S25 are repeated until there are no missed waypoints that the mobile robot 1 should have passed through but the global path 3 has not passed through (see...). Figure 3 (As shown by the dashed line in the diagram). For example, at point P along the way. v1 After the nearby initial local path segment 31 is replaced, the via point P can be... v2 As the first waypoint closest to the starting point of global path 3 among the missed waypoints not visited in global path 3, and starting from waypoint P... v2 Begin to re-determine the set of waypoints.

[0130] Figure 5 A motion control method for a mobile robot 1 according to an exemplary embodiment of the present invention is illustrated schematically. The motion control method includes the following steps:

[0131] Real-time waypoint detection step S31, wherein, during the movement of the mobile robot 1 along the planned path, at least one missed waypoint located within a predetermined distance range relative to the current position of the mobile robot 1 is detected that has not been passed by the planned path, the waypoint representing a point that the mobile robot 1 needs to pass through;

[0132] a real-time via point determination step S32, in which a set of via points is determined, the set of via points being a set consisting of at least one via point and containing the at least one missing via point;

[0133] a real-time local path determination step S33, in which a local original path segment of a via point contained in the set of adjacent via points in the planned path is determined;

[0134] a real-time replanning step S34, in which a first path 2 for the mobile robot 1 is determined based on the start point, the end point and the set of via points according to the path planning method of the present application, with the start point and the end point of the local original path segment as the start point and the end point, respectively; and

[0135] a real-time path replacement step S35, in which the local original path segment in the planned path is replaced by the first path 2, and the mobile robot 1 is controlled to move according to the replaced planned path.

[0136] As mentioned above, for the mobile robot 1, it often happens that its planned path does not pass through all the via points that need to be passed through. Taking the commonly used TEB algorithm as an example, although the TEB algorithm can make the local planning trajectory pass through the via points as much as possible by increasing the weight of the via points, since the TEB algorithm is essentially a multi-objective optimization algorithm, it cannot guarantee to pass through the via points accurately.

[0137] By means of the above motion control method, even if the original planned path of the mobile robot 1 does not pass through all the via points that need to be passed through, the planned path of the mobile robot 1 can be optimized during its movement to ensure that the planned path passes through the via points accurately near the via points and deviates from the original planned path as little as possible.

[0138] The original planned path can be obtained by any applicable known method. For example, the original planned path can be planned by the A-star algorithm. The motion control method according to the present application performs local optimization based on deviating from the original planned path as little as possible, which can maintain the advantages of the original planned path, such as short path length. In addition, the planning process can be simplified and the amount of calculation can be reduced.

[0139] The motion control method may, for example, be executed by means of a controller of the mobile robot.

[0140] In the real-time local path determination step S33, the current position point of the mobile robot 1 can be taken as the start point of the local original path segment.

[0141] Optionally, in the real-time replanning step S34, at least one of the following is performed: the start point speed direction of the first path 2 is made equal to the start point speed direction of the original local path segment; the path start point curvature of the first path 2 is made equal to the path start point curvature of the original local path segment; the end point speed direction of the first path 2 is made equal to the end point speed direction of the original local path segment; the path end point curvature of the first path 2 is made equal to the path end point curvature of the original local path segment.

[0142] Optionally, in the real-time replanning step S34, the first path 2 is determined such that the speed direction at the at least one passing point satisfies one of the following conditions: the same as the speed direction of the point closest to the passing point on the original local path segment; the same as the direction from the start point to the end point of the original local path segment; the task requirement of the mobile robot 1 at the corresponding passing point is satisfied.

[0143] Optionally, in the real-time passing point determination step S32, the at least one missed passing point and a passing point satisfying the following condition are taken as one of the passing points in the passing point set: the path length between each two adjacent points on the planning path closest to the respective passing points in the passing point set is less than a predetermined threshold.

[0144] Optionally, in the local path determination step, the start point and the end point of the original local path segment are determined such that: in the direction along the planning path, the start point of the original local path segment is located before all the points on the planning path closest to the respective passing points in the passing point set; in the direction along the planning path, the end point of the original local path segment is located after all the points on the planning path closest to the respective passing points in the passing point set.

[0145] After the real-time path replacement step S35, the original local path segment in the planning path is replaced by the first path 2, and a new planning path is formed. After obtaining the new planning path, the new planning path can be taken as the current planning path, and then the real-time passing point determination step S32, the real-time local path determination step S33, the real-time replanning step S34 and the real-time path replacement step S35 are repeatedly performed until there is no missed passing point that the mobile robot 1 should pass through but the planning path does not pass through.

[0146] The motion control method according to the present application has corresponding characteristics and similar principles to the path planning method and the global planning method according to the present application. The features and advantages described above for the path planning method and the global planning method can also be correspondingly applied to the motion control method.

[0147] In addition, the present application also relates to a computer program product comprising computer program instructions which, when executed by one or more processors, enable the processors to perform the path planning method, the global planning method or the motion control method according to the present application.

[0148] In the present application, the computer program product can be stored in a computer readable storage medium. The computer readable storage medium can include, for example, a high-speed random access memory, and can also include a non-volatile memory such as a hard disk, a memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, at least one disk storage device, a flash storage device, or other volatile solid-state storage device. The processor 10 can be a central processing unit (CPU), and can also be another general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0149] Although specific embodiments of the present application are described in detail herein, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, changes in material selection and combinations, changes in the arrangement of elements, methods, and computer program instructions), without materially departing from the scope and nature of the subject application. Some elements can be left out or eliminated entirely in other embodiments. The order or sequence of any process, or method can be different, and the use or Although specific embodiments of the present application are described in detail herein, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, changes in material selection and combinations, changes in the arrangement of elements, methods, and computer program instructions), without materially departing from the scope and nature of the subject application. Some elements can be left out or eliminated entirely in other embodiments. The order or sequence of any process, or method can be different, and the use or

Claims

1. A path planning method for a mobile robot, wherein, The path planning method comprises the following steps: an information obtaining step S11, wherein position information of a start point, an end point and a predetermined set of passing points of a first path (2) to be planned is obtained, the set of passing points being a set consisting of at least one passing point; a curve determining step S12, wherein a smooth curve starting from the start point, passing through the at least one passing point and ending at the end point is determined according to the position information of the start point, the end point and the set of passing points, the curve having a continuous second derivative; and a path determining step S13, wherein the smooth curve is determined as the first path (2) of the mobile robot (1), wherein the number of the at least one passing point is m, wherein m is an arbitrary positive integer, the curve is a Bezier curve of order m+3, a first control point and an m+4th control point of the Bezier curve are the start point and the end point respectively, the curve is represented by the following formula: where i = 0, 1,..., m + 4 ， denote the coordinates of the control points of the Bezier curve and where the coordinates of the control points are determined by coordinates of the start point, coordinates of the end point; respectively with same positive, wherein is a unit vector representing a predetermined start speed direction; respectively with same positive and negative, wherein, is a unit vector representing a predetermined terminal speed direction; wherein, represents a coordinate of the jth waypoint in the at least one waypoint, j = 1, 2, …, m, represents a value of s corresponding to the jth waypoint; and The directions are the same, among which, It represents the unit vector of the velocity direction at the predetermined path point at the j-th path point, P′(s) represents The coordinates of the first derivative, express exist The coordinates of the first derivative at that point; Substitute s = 0 and K(0) = K0 into where K0 denotes a predetermined path start curvature, P x ′(s), P y ′(s), P x ″(s), P y ″(s) are first and second order derivatives of the lateral and longitudinal coordinates, respectively; Substituting s = 1 and K(1) = K1 into the defined path end curvature. wherein K1 represents a predetermined 2. The path planning method according to claim 1, wherein the information obtaining step S11 further comprises obtaining additional constraint information of the first path (2) to be planned, the additional constraint information comprising at least one of the following: a predetermined start point velocity direction representing a velocity direction of the mobile robot (1) at the start point; a predetermined path start point curvature representing a curvature of the first path (2) to be planned at the start point; a predetermined end point velocity direction representing a velocity direction of the mobile robot (1) at the end point; a predetermined path end point curvature representing a curvature of the first path (2) to be planned at the end point; a predetermined passing point velocity direction representing a velocity direction of the mobile robot (1) at the at least one passing point, wherein in the curve determining step S12, the curve is additionally determined according to the additional constraint information.

3. The path planning method according to claim 1 or 2, wherein the curve is a Bezier curve or a B-spline curve.

4. The path planning method according to claim 1 or 2, wherein the set of passing points contains exactly one passing point, and the curve determined in the curve determining step S12 is represented by the following formula: wherein, denote the coordinates of the control points of the Bezier curve and wherein the coordinates of the control points are determined by coordinates of a starting point, coordinates of an end point; respectively with same positive, wherein is a unit vector representing a predetermined start speed direction; respectively with same positive, wherein is a unit vector representing the direction of the predetermined terminal velocity. where (x v ,y v ) represents the coordinates of the passing point, s v represents the value of s corresponding to the passing point; wherein, the first component and the second component of and have the same sign, is a unit vector representing a predetermined passing point speed direction at the passing point; wherein K0represents a predetermined path start curvature, wherein K1 represents a predetermined path end curvature.

5. The path planning method according to claim 1 or 2, wherein the mobile robot (1) is a differential robot.

6. A global path planning method for a mobile robot, wherein, The global path planning method comprises the following steps: an initial planning step S21, wherein an initial global path (3) for the mobile robot (1) is obtained; a passing point determining step S22, wherein a set of passing points is determined, a passing point representing a point that the mobile robot (1) needs to pass through, the set of passing points being a set consisting of at least one passing point and containing at least one missed passing point that is not passed through by the global path (3); a local path determining step, wherein an initial local path segment (31) of the passing points contained in a set of adjacent passing points in the global path (3) is determined; a re-planning step S24, wherein a start point and an end point of the initial local path segment (31) are respectively taken as a start point and an end point, a first path (2) for the mobile robot (1) is determined according to the path planning method of any one of claims 1-3, 5 based on the start point, the end point and the set of passing points; and a path determining step S13, wherein the smooth curve is determined as the first path (2) of the mobile robot (1), wherein the number of the at least one passing point is m, wherein m is an arbitrary positive integer, the curve is a Bezier curve of order m+3, a first control point and an m+4th control point of the Bezier curve are the start point and the end point respectively, the curve is represented by the following formula:

2. The path planning method according to claim 1, wherein the information obtaining step S11 further comprises obtaining additional constraint information of the first path (2) to be planned, the additional constraint information comprising at least one of the following: a predetermined start point velocity direction representing a velocity direction of the mobile robot (1) at the start point; a predetermined path start point curvature representing a curvature of the first path (2) to be planned at the start point; a predetermined end point velocity direction representing a velocity direction of the mobile robot (1) at the end point; a predetermined path end point curvature representing a curvature of the first path (2) to be planned at the end point; a predetermined passing point velocity direction representing a velocity direction of the mobile robot (1) at the at least one passing point, wherein in the curve determining step S12, the curve is additionally determined according to the additional constraint information.

3. The path planning method according to claim 1 or 2, wherein the curve is a Bezier curve or a B-spline curve.

4. The path planning method according to claim 1 or 2, wherein the set of passing points contains exactly one passing point, and the curve determined in the curve determining step S12 is represented by the following formula:

5. The path planning method according to claim 1 or 2, wherein the mobile robot (1) is a differential robot. The global path planning method comprises the following steps: an initial planning step S21, wherein an initial global path (3) for the mobile robot (1) is obtained; a passing point determining step S22, wherein a set of passing points is determined, a passing point representing a point that the mobile robot (1) needs to pass through, the set of passing points being a set consisting of at least one passing point and containing at least one missed passing point that is not passed through by the global path (3); a local path determining step, wherein an initial local path segment (31) of the passing points contained in a set of adjacent passing points in the global path (3) is determined; a re-planning step S24, wherein a start point and an end point of the initial local path segment (31) are respectively taken as a start point and an end point, a first path (2) for the mobile robot (1) is determined according to the path planning method of any one of claims 1-3, 5 based on the start point, the end point and the set of passing points; and replacing the initial local path segment (31) in the global path (3) with the first path (2). 7.The global path planning method according to claim 6, wherein, in the re-planning step S24, at least one of the following is performed: the start point velocity direction of the first path (2) is made equal to the start point velocity direction of the initial local path segment (31) ; the path start point curvature of the first path (2) is made equal to the path start point curvature of the initial local path segment (31) ; the end point velocity direction of the first path (2) is made equal to the end point velocity direction of the initial local path segment (31) ; the path end point curvature of the first path (2) is made equal to the path end point curvature of the initial local path segment (31). 8.The global path planning method according to claim 6 or 7, wherein, in the re-planning step S24, the first path (2) is determined such that the velocity direction at at least one of the passing points satisfies one of the following conditions: the velocity direction of the point closest to the passing point corresponding to the distance on the initial local path segment (31) is the same; the direction from the start point to the end point of the initial local path segment (31) is the same; the task requirement of the mobile robot (1) at the corresponding passing point is satisfied. 9.The global path planning method according to claim 6 or 7, wherein, in the passing point determination step S22, the passing points through which the mobile robot (1) should pass are determined, starting from the first passing point closest to the start point of the global path (3) among the missed passing points not passed through by the global path (3), and the passing points in the passing point set are determined as one of the passing points in the passing point set, which satisfy the following condition: the path length between each two adjacent points among the points on the global path (3) closest to each passing point in the passing point set is less than a predetermined threshold. 10.The global path planning method according to claim 6 or 7, wherein, in the local path determination step, the start point and the end point of the initial local path segment (31) are determined such that: in the direction along the global path (3), the start point of the initial local path segment (31) is located before all the points on the global path (3) respectively closest to each passing point in the passing point set; in the direction along the global path (3), the end point of the initial local path segment (31) is located after all the points on the global path (3) respectively closest to each passing point in the passing point set. 11.The global path planning method according to claim 6 or 7, wherein, the global path planning method further comprises: repeatedly performing the passing point determination step S22, the local path determination step S23, the re-planning step S24 and the path replacing step S25 until there is no missed passing point not passed through by the global path (3) through which the mobile robot (1) should pass.

12. A motion control method for a mobile robot, wherein, the motion control method comprises the following steps: a real-time via point detecting step S31, in which at least one missed via point, which is a point on the planned path that the mobile robot (1) needs to pass through and is located within a predetermined distance range from a current position point of the mobile robot (1), is detected during the movement of the mobile robot (1) along the planned path; a real-time via point determining step S32, in which a via point set is determined, the via point set being a set composed of at least one via point and containing the at least one missed via point; a real-time local path determining step S33, in which a original local path segment of the planned path containing the via points comprised in the via point set is determined; a real-time replanning step S34, in which a first path (2) for the mobile robot (1) is determined based on the start point, the end point and the via point set according to the path planning method of any one of claims 1-3, 5, with the start point and the end point of the original local path segment as the start point and the end point respectively; and a real-time path replacing step S35, in which the original local path segment in the planned path is replaced by the first path (2), and the mobile robot (1) is controlled to move along the replaced planned path.

13. The motion control method of claim 12, wherein in the real-time local path determining step S33, the current position point of the mobile robot (1) is determined as the start point of the original local path segment.

14. The motion control method of claim 12 or 13, wherein in the real-time replanning step S34, at least one of the following is performed: the start point velocity direction of the first path (2) is equal to the start point velocity direction of the original local path segment; the path start point curvature of the first path (2) is equal to the path start point curvature of the original local path segment; the end point velocity direction of the first path (2) is equal to the end point velocity direction of the original local path segment; the path end point curvature of the first path (2) is equal to the path end point curvature of the original local path segment.

15. The motion control method of claim 12 or 13, wherein in the real-time replanning step S34, the first path (2) is determined such that the velocity direction at the at least one via point satisfies one of the following conditions: the velocity direction of the point on the first path (2) closest to the via point is the same as the velocity direction of the point on the original local path segment closest to the via point; the direction from the start point to the end point of the first path (2) is the same as the direction from the start point to the end point of the original local path segment; the velocity direction satisfies the task requirement of the mobile robot (1) at the via point.

16. The motion control method of claim 12 or 13, wherein in the real-time via point determining step S32, the at least one missed via point and a via point satisfying the following condition are determined as one of the via points in the via point set: the path length between each two adjacent points on the planned path closest to the respective via points in the via point set is less than a predetermined threshold.

17. The motion control method of claim 12 or 13, wherein in the real-time local path determining step S33, the start point and the end point of the original local path segment are determined such that: In the direction along the planned path, the start point of the original local path segment is located before all the points on the planned path closest to the respective passing point in the set of passing points respectively; In the direction along the planned path, the end point of the original local path segment is located after all the points on the planned path closest to the respective passing point in the set of passing points respectively.

18. The motion control method according to claim 12 or 13, wherein, The motion control method further comprises: repeatedly performing the real-time passing point determination step S32, the real-time local path determination step S33, the real-time replanning step S34 and the real-time path replacement step S35 until there is no missed passing point that the mobile robot (1) should pass through but the planned path does not pass through.

19. A computer program product comprising computer program instructions, wherein, When the computer program instructions are executed by one or more processors, the processors are capable of performing the path planning method according to any one of claims 1-5 or the global path planning method according to any one of claims 6-11 or the motion control method according to any one of claims 12-18.

Images