Forklift rollover prevention control method based on zero moment point variable threshold

Abstract

The invention relates to a forklift anti-rollover control method based on a zero moment point variable threshold, and the method comprises the following steps: S1, building a whole forklift rollover kinetic model, and carrying out the optimization through a Kalman filtering algorithm, and obtaining the lateral acceleration, the roll angle and the second derivative of the forklift; s2, according to the load weight of the forklift, the combined center-of-mass coordinate of the whole forklift is determined; s3, according to the longitudinal position of the combined mass center, the maximum threshold value of the transverse component of the zero moment point when the forklift is in triangular supporting and the maximum threshold value of the transverse component of the zero moment point when the forklift is in trapezoidal supporting are determined; s4, calculating a transverse coordinate of a zero moment point through a formula; S5, respectively setting the forklift in three states of primary side inclination, intermediate side inclination and critical side inclination; and S6, designing an anti-rollover control strategy, and executing the strategy by using the controller. According to the method, Kalman filtering is used for optimizing the parameters of the whole forklift rollover kinetic model, the state of the forklift is accurately estimated, and different control methods are adopted for the two supporting oil cylinders in different stages.

Description

Technical Field

[0001] The present invention relates to the field of engineering vehicles, and in particular to a forklift anti-rollover control method based on a zero-moment point variable threshold. Background Art

[0002] Forklift rollover is an important direction in the field of industrial vehicle safety. The safety hazards caused by forklift rollover are very serious, not only causing serious casualties, but also causing property losses. Therefore, it is very important to be able to timely and accurately understand the driving status and body status of the forklift so that the controller can control the current status of the forklift in time.

[0003] At present, in the method of dividing the stability domain based on the zero moment point as the rollover evaluation index, on road vehicles and industrial vehicles, the distance from the center of mass of the vehicle to the boundary of the support area is taken as the threshold of the zero moment point, and it is generally assumed that the center of mass of the vehicle is constant. For forklifts among industrial vehicles, due to the special front-wheel drive and rear-wheel steering chassis structure of forklifts, the body is fixedly connected to the front drive axle and articulated to the rear steering axle. Therefore, the current research on forklift rollover indicators widely uses roll angle, lateral acceleration or lateral load transfer rate as rollover stability judgment indicators. When using vehicle roll angle and lateral acceleration as rollover indicators, the thresholds of both indicators need to be obtained through static rollover tests of vehicles, which is cumbersome and has certain limitations. In addition, the threshold of static measurement is not accurate enough for warning of moving vehicles, while dynamic measurement is dangerous and has high experimental costs, so it cannot fully reflect the roll state of the vehicle. The traditional vehicle load transfer rate is the ratio of the difference between the vertical loads on the left and right wheels to the sum of them. Due to the immaturity of related technologies, it is very difficult to measure the real-time load of tires through load sensors.

[0004] To this end, the present invention proposes a forklift anti-rollover control method based on a zero-moment point variable threshold. Summary of the invention

[0005] In view of the above problems, the present invention proposes a forklift anti-rollover control method based on zero-torque point variable threshold. By establishing a forklift rollover model, the model parameters are optimized using Kalman filtering, the vehicle state of the forklift is accurately estimated, and then the joint center of mass position is calculated according to the load size. The zero-torque point threshold of the two stages of the support area is determined, and different control methods are adopted for the two supporting cylinders in different stages to achieve the purpose of anti-rollover.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A forklift anti-rollover control method based on zero moment point variable threshold comprises the following steps:

[0008] S1. Establish a rollover dynamics model of the forklift, and optimize and obtain the lateral acceleration, roll angle and second-order derivative of the forklift through the Kalman filter algorithm;

[0009] S2. Determine the joint center of mass coordinates G0 (x0, y0) of the entire forklift according to the load weight of the forklift;

[0010] S3. Using formulas (1), (2) and (3), determine the maximum threshold Δl of the lateral component of the zero moment point of the forklift when it is triangularly supported according to the longitudinal position of the joint center of mass: a And the maximum threshold Δl of the lateral component at the zero moment point in the trapezoidal support b ;

[0011]

[0012] Among them, l f is the distance between the front tire and the center of mass of the forklift body, l r is the distance between the rear tire and the center of mass of the forklift body, d represents the distance between the rear tire and the center of the rear steering axle, and c represents the distance between the support cylinder and the center of the rear steering axle;

[0013] S4. Calculate the horizontal coordinate y of the zero moment point by formula (4) zmp ,

[0014]

[0015] in, is the roll angle, a y is the lateral acceleration, is the second-order derivative of the roll angle, g is the gravitational acceleration, I x is the moment of inertia of the vehicle body around the x-axis, h u is the distance from the center of mass of the chassis to the ground, h r is the distance from the hinge point to the ground, h s is the distance from the sprung mass center to the hinge point, m s is the mass of the vehicle body and cargo, m u is the mass of the chassis, M is the total mass of the vehicle;

[0016] S5. According to |yzmp| and Δl a The relationship between |yzmp| and Δl b The relationship between the forklift and the primary roll, intermediate roll and critical roll are divided into three states;

[0017] S6. Design an anti-rollover control strategy and use a controller to execute the strategy.

[0018] Furthermore, in S2, the joint center of mass coordinates G0(x0,y0) of the entire forklift are determined by formula (5);

[0019]

[0020] Among them, H is the height of the forklift body center of mass from the ground, h is the height of the cargo center of mass from the ground, m is the weight of the forklift body and chassis, q is the cargo load weight, x1 represents the ordinate of the forklift body center of mass, and x2 represents the ordinate of the cargo center of mass;

[0021] Where x1 is determined by formula (6),

[0022]

[0023] Where x2 is determined by formula (7),

[0024]

[0025] Among them, l1 is the distance between the center of mass of the cargo and the forklift mast, and l2 is the distance between the center of mass of the forklift body and the forklift mast.

[0026] Furthermore, in S5, when |yzmp|<Δl a The forklift is in the primary tilt state when Δl a <|yzmp|<Δl b When the forklift is in the middle level of roll, when |yzmp|>Δl b The forklift is in critical tilt.

[0027] Furthermore, in S6, the rollover warning time is calculated based on the forklift vehicle rollover dynamics model, and the upper limit threshold is set to 3 seconds; if the time is less than the upper limit threshold, the anti-rollover control strategy is triggered in advance.

[0028] Furthermore, in S6, the anti-rollover control strategy uses the positional relationship between the zero moment point and the support area as a control target, the support cylinder in the rollover direction is feedforward controlled, and the support cylinder on the other side is feedback controlled.

[0029] Furthermore, when the forklift is in the middle roll state, |yzmp| and Δl b The difference between |yzmp| and Δl is used as the input of the feedforward control cylinder. The closer the difference is to 0, the greater the strength of the feedforward control cylinder. After the feedforward action, |yzmp| and Δl b The difference and the force of the feedforward control cylinder are used as feedback control to perform feedback control on the input of the other supporting cylinder.

[0030] Furthermore, when the forklift is in a critical roll, the supporting cylinder in the rollover direction provides the maximum supporting force, and the cylinder on the other side provides the maximum pulling force, until the forklift is in a medium roll and executes the medium roll adjustment strategy.

[0031] The beneficial effects of the present invention are:

[0032] 1. The Kalman filter algorithm is used to optimize the rollover dynamics model of the forklift to obtain the optimized parameters. The joint center of mass position is calculated according to the current load size, and the threshold of the zero moment point corresponding to the current joint center of mass position is obtained. During the driving process of the forklift, the value of the zero moment point is calculated in real time and compared with the current threshold value, so that different control methods can be adopted at different stages.

[0033] 2. Design an anti-rollover strategy, which is executed by two supporting cylinders, which are respectively located on the left and right sides of the articulated shaft at the midpoint of the rear steering axle of the forklift. The forklift is divided into three rollover stages according to the zero torque point. The first stage is primary rollover, when the two control cylinders are free to move and do not provide force, playing a buffering role; the second stage is intermediate rollover, and the two supporting cylinders provide support force or tension force according to the distance from the zero torque point threshold and the rollover direction of the forklift, and the left and right supporting cylinders are divided into the joint action of feedforward control and feedback control; the third stage is critical rollover, when the forklift zero torque point has been exceeded and the rollover trend is very serious, the supporting cylinder on one side of the rollover direction extends to reversely support the forklift body, providing maximum support force to prevent the rollover from worsening, and the cylinder on the other side provides maximum pulling force to move the zero torque point in the opposite direction of the rollover until it enters the intermediate rollover, and then gradually reduce the force of the two cylinders so that the forklift can smoothly reach a balanced state. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0035] Figure 1 is a schematic diagram of the combined mass center of the forklift truck of the present invention;

[0036] Figure 2 is a schematic diagram of the forklift support area of ​​the present invention;

[0037] Figure 3 is a schematic diagram of the state of the primary roll according to the present invention;

[0038] Figure 4 is a schematic diagram of the state of the intermediate roll according to the present invention;

[0039] Figure 5 is a schematic diagram of the critical roll state of the present invention;

[0040] Figure 6 1 is a calculation diagram of the lateral coordinates of the zero moment point in the embodiment.

[0041] In the figure: 1. Support cylinder. DETAILED DESCRIPTION

[0042] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0043] It should be noted that the present invention provides the following specific implementation scheme:

[0044] like Figure 1-3 As shown, the present invention provides a forklift anti-rollover control method based on zero moment point variable threshold, comprising the following steps:

[0045] S1. Establish a forklift vehicle rollover dynamics model, process the rollover warning model through the Kalman filter algorithm, optimize the relevant parameters, and accurately estimate the rollover state of the forklift.

[0046] S2. Determine the joint center of mass coordinates G0 (x0, y0) of the entire forklift according to the load weight of the forklift;

[0047] Specifically, Figure 1 As shown in the figure, the forklift coordinate system is established with the forklift rear wheel grounding point as the origin, and the forklift body center of mass, cargo center of mass and joint center of mass are obtained. f , l r are the distances from the front and rear tires to the center of mass of the forklift body, l1 is the distance from the center of mass of the cargo to the forklift mast, l2 is the distance from the center of mass of the forklift body to the forklift mast, H is the height from the center of mass of the forklift body to the ground, h is the height from the center of mass of the cargo to the ground, the weight of the forklift body and chassis is m, and the weight of the cargo load is q.

[0048] The center of mass of the forklift body is G1(x1,y1):

[0049]

[0050] The dotted part in the figure shows the situation when the forklift mast is vertical and loaded with goods. At this time, the centroid of the goods is G2(x2,y2):

[0051]

[0052] Then the joint centroid coordinates G0(x0,y0) can be expressed as:

[0053]

[0054] Assuming that the forklift is unloaded, the joint center of mass position coincides with the center of mass position of the vehicle body. Depending on the weight of the cargo, the position of the joint center of mass in the x-axis direction is also different.

[0055] S3, such as Figure 2 As shown, using formulas (1), (2) and (3), according to the longitudinal position of the joint center of mass, the maximum threshold Δl of the component of the zero moment point of the forklift on the transverse coordinate axis when the triangle is supported is determined a And the maximum threshold Δl of the zero moment point component on the transverse axis when the trapezoidal support is b ;

[0056]

[0057] Among them, l f is the distance between the front tire and the center of mass of the forklift body, l r is the distance between the rear tire and the center of mass of the forklift body, d represents the distance between the rear tire and the center of the rear steering axle, and c represents the distance between the support cylinder and the center of the rear steering axle.

[0058] S4. Calculate the lateral coordinate y of the vehicle's zero moment point zmp , the definition formula of the vehicle zero moment point is:

[0059]

[0060] In formula (8), m i 、r i and M i Respectively represent the mass of each part of the system, the vector position in the corresponding coordinate system, and the inertia moment, i = 1 represents the body, i = 2 represents the chassis; M z is the net moment at the zero moment point; g is the gravitational acceleration. The center of mass position of the vehicle body represents the joint center of mass position of the forklift body and cargo. When calculating the zero moment point of the forklift, the vehicle body is replaced by the mass point at the joint center of mass position. Figure 6 As shown, according to the joint center of mass position and the center of mass position of the chassis, the resultant moment of the two points about the zero moment point is projected onto the coordinate axis to obtain formula (9),

[0061]

[0062] In the study of forklift rollover prevention, we only need to consider the relationship between the component of the zero moment point on the transverse coordinate axis, i.e., the Y axis, and the forklift support plane. Substituting the forklift chassis and body parameters into equation (9), we can get

[0063]

[0064] Let τ x = 0, the lateral coordinates of the vehicle zero moment point are as follows:

[0065]

[0066] In formula (4), is the roll angle, a y is the lateral acceleration, is the second-order derivative of the roll angle, g is the gravitational acceleration, I x is the moment of inertia of the vehicle body around the x-axis, h u is the distance from the center of mass of the chassis to the ground, h r is the distance from the hinge point to the ground, h s is the distance from the sprung mass center to the hinge point, m s is the mass of the vehicle body and cargo, m u is the mass of the chassis, M is the total mass of the vehicle;

[0067] To obtain yzmp, we need to know the lateral acceleration, roll angle and second-order derivative of the forklift. These three parameters are estimated through Kalman filtering.

[0068] S5. According to |yzmp| and Δl a The relationship between |yzmp| and Δl b The relationship between the forklift and the primary roll, intermediate roll and critical roll is divided into three states; when |yzmp|<Δl a When Δl a <|yzmp|<Δl b When |yzmp|>Δl, the forklift is in the intermediate roll stage, the support plane expands to the CEGD isosceles trapezoidal area, and point E is the position of the hydraulic cylinder on the rear steering axle; when |yzmp|>Δl b When , the forklift reaches critical tilt.

[0069] S6. Design an anti-rollover control strategy and use a controller to execute the strategy, wherein the anti-rollover control strategy includes a primary rollover strategy, an intermediate rollover strategy, and a critical rollover strategy;

[0070] like Figure 3 As shown, the forklift is in primary roll: the two supporting cylinders on the left and right of the hinge point of the forklift steering axle play a buffering role;

[0071] like Figure 4As shown, the forklift is in the middle rollover state: the two supporting cylinders are dynamically coordinated and controlled according to the rollover direction of the forklift. a <|yzmp|<Δl b Change within this range until |yzmp|=Δl b When |yzmp| and Δl b The difference is set as index S, that is, the closer S is to 0, the greater the degree of forklift rollover and the greater the risk; the closer S is to Δl b -Δl a , which means that the smaller the forklift rolls over, the smaller the risk. The support cylinder in the rollover direction is feedforward controlled, and the index S is used as input to directly control the strength of the support cylinder. The closer the index S is to 0, the greater the strength. The support cylinder on the other side is feedback controlled. After the feedforward control is applied, the index S and the force ΔF1 of the feedforward control cylinder are used as the input of the feedback control to feedback control the force ΔF2 of the support cylinder on the other side, so as to timely adjust the force as a supplement to prevent the forklift from rolling over or becoming unbalanced again.

[0072] like Figure 5 As shown, the forklift's critical roll: the forklift's zero moment point has exceeded Δl b , one side of the wheel is lifted and the rollover is very serious. The supporting cylinder on one side of the rollover direction extends to support the forklift body in the opposite direction to provide maximum supporting force to prevent the rollover from worsening. The cylinder on the other side provides maximum pulling force until the forklift is in a medium roll and executes the medium roll strategy.

[0073] Based on the dynamic model of the forklift vehicle rollover, the Kalman filter algorithm is optimized to obtain the optimized parameters. The joint center of mass position is calculated according to the current load size, and the threshold of the zero torque point corresponding to the current joint center of mass position is obtained. During the driving process of the forklift, the value of the zero torque point is calculated in real time and compared with the current threshold value, so that different control methods can be adopted at different stages.

[0074] Design a body posture control mechanism, which consists of two supporting cylinders, one on each side of the articulated shaft at the midpoint of the rear steering axle of the forklift. According to the zero torque point, the forklift is divided into three rollover stages. The first stage is primary rollover, when the two control cylinders are free to move and provide no force, thus playing a buffering role. The second stage is intermediate rollover, and the two supporting cylinders provide support force or tensile force according to the distance from the zero torque point threshold and the rollover direction of the forklift, and the left and right supporting cylinders are divided into the combined effect of feedforward control and feedback control. The third stage is critical rollover, when the forklift has a very serious rollover tendency, the supporting cylinder on one side of the rollover direction extends to support the forklift body in the opposite direction, providing the maximum support force to prevent the rollover from being aggravated. The cylinder on the other side provides the maximum pulling force, so that the zero torque point moves in the opposite direction of the rollover until it enters the intermediate rollover, and then gradually reduces the force of the two cylinders so that the forklift reaches a balanced state smoothly.

[0075] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A forklift anti-rollover control method based on zero moment point variable threshold, characterized in that: The method comprises the following steps: S1, establishing a rollover dynamics model of a forklift, and optimizing and obtaining the lateral acceleration, roll angle and second-order derivative of the forklift by using a Kalman filter algorithm; S2. Determine the joint center of mass coordinates G0 (x0, y0) of the entire forklift according to the load weight of the forklift; S3. Using formulas (1), (2) and (3), determine the maximum threshold Δl of the lateral component of the zero moment point of the forklift when it is triangularly supported according to the longitudinal position of the joint center of mass: a And the maximum threshold Δl of the lateral component at the zero moment point in the trapezoidal support b ; Among them, l f is the distance between the front tire and the center of mass of the forklift body, l r is the distance between the rear tire and the center of mass of the forklift body, d represents the distance between the rear tire and the center of the rear steering axle, and c represents the distance between the support cylinder and the center of the rear steering axle; S4. Calculate the horizontal coordinate y of the zero moment point by formula (4) zmp , in, is the roll angle, a y is the lateral acceleration, is the second-order derivative of the roll angle, g is the gravitational acceleration, I x is the moment of inertia of the vehicle body around the x-axis, h u is the distance from the center of mass of the chassis to the ground, h r is the distance from the hinge point to the ground, h s is the distance from the sprung mass center to the hinge point, m s is the mass of the vehicle body and cargo, m u is the mass of the chassis, M is the total mass of the vehicle; S5. According to | yzmp | With Δl a relationship and | yzmp | and Δl b The relationship between the forklift and the primary roll, intermediate roll and critical roll are divided into three states; S6. Design an anti-rollover control strategy and use a controller to execute the strategy.

2. A forklift anti-rollover control method based on zero moment point variable threshold according to claim 1, characterized in that: In S2, the joint center of mass coordinates G0(x0,y0) of the entire forklift are determined by formula (5); Among them, H is the height of the forklift body center of mass from the ground, h is the height of the cargo center of mass from the ground, m is the weight of the forklift body and chassis, q is the cargo load weight, x1 represents the ordinate of the forklift body center of mass, and x2 represents the ordinate of the cargo center of mass; Where x1 is determined by formula (6), Where x2 is determined by formula (7), Among them, l1 is the distance between the center of mass of the cargo and the forklift mast, and l2 is the distance between the center of mass of the forklift body and the forklift mast.

3. The method for determining a rollover index based on a zero moment point threshold according to claim 1, characterized in that: In S5, when | yzmp | <Δl a The forklift is in the primary tilt state when Δl a < | yzmp | <Δl b The forklift is in the middle level of tilt. | yzmp | >Δl b The forklift is in critical tilt.

4. The method for determining a rollover index based on a zero moment point threshold according to claim 1, characterized in that: In S6, the rollover warning time is calculated based on the forklift vehicle rollover dynamics model, and the upper limit threshold is set to 3 seconds; if the time is less than the upper limit threshold, the anti-rollover control strategy is triggered in advance.

5. The method for determining a rollover index based on a zero moment point threshold according to claim 3, characterized in that: In S6, the anti-rollover control strategy takes the positional relationship between the zero moment point and the support area as the control target, the support cylinder in the rollover direction is feedforward controlled, and the support cylinder on the other side is feedback controlled.

6. The method for determining a rollover index based on a zero moment point threshold according to claim 5, characterized in that: When the forklift is in the middle tilt state, | yzmp | With Δl b The difference is used as the input of the feedforward control cylinder. The closer the difference is to 0, the greater the strength of the feedforward control cylinder. After the feedforward action, | yzmp | With Δl b The difference and the force of the feedforward control cylinder are used as feedback control to perform feedback control on the input of the other supporting cylinder.

7. The method for determining a rollover index based on a zero moment point threshold according to claim 6, characterized in that: When the forklift is in critical roll, the support cylinder in the rollover direction provides the maximum support force, and the cylinder on the other side provides the maximum pulling force until the forklift is in intermediate roll and executes the intermediate roll adjustment strategy.

Images