A control method and device for a forklift linear control drum brake system based on robust H∞

Abstract

A kind of robust H∞ control strategy suitable for forklift linear control drum brake system, specifically includes the following implementation steps: 1) the mechanical structure and its dynamics characteristics of forklift linear control drum brake system are analyzed, and then the dynamics model is constructed;2) according to the model established in step 1, an adaptive robust H∞ control gain K is designed to ensure that the system state can quickly tend to be stable;3) based on the control gain K designed in step 2, a robust H∞ control algorithm for forklift linear control drum brake system is designed;4) based on Lyapunov stability theory, it is proved that the control algorithm designed in step 3 can make the system state stable convergence, and numerical simulation is carried out in MATLAB / Simulink environment to verify the actual control effect of the control algorithm in the brake system. The control accuracy and robustness of forklift linear control drum brake system can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of industrial vehicle brake-by-wire control technology, specifically proposing a control method and corresponding device for a forklift brake-by-wire drum brake system based on a robust H∞ strategy. This solution aims to improve the control accuracy, response speed, and robustness of the forklift brake-by-wire drum brake system under complex and changing operating conditions. Background Technology

[0002] With the development of intelligent and unmanned logistics systems, forklifts, as important industrial transportation equipment, have seen their control systems' precision and robustness become key factors affecting operational efficiency and safety. Traditional hydraulic or mechanical braking systems have limitations in control precision, response speed, and system integration, making it difficult to meet the demands of modern intelligent warehousing and handling environments for high-performance, safe, and reliable braking systems. Therefore, brake-by-wire (BBW) technology based on electronic signal transmission has been researched and applied. Especially in the field of new energy forklifts, the use of brake-by-wire drum braking systems can effectively simplify the structure, improve control precision, and integrate multiple braking strategies, becoming an important direction for the technological evolution of forklift braking systems. However, in practical applications, forklifts face complex and variable operating conditions, such as load fluctuations, changes in road friction coefficients, inconsistent brake drum clearances, and unstable coupling between the motor and mechanical brakes. These factors lead to uncertainties in the system's dynamic model. Furthermore, brake-by-wire systems themselves suffer from actuator lag, nonlinear friction characteristics, and sensor noise, making the control system highly susceptible to external disturbances, resulting in performance degradation and even safety hazards.

[0003] To address these challenges, the accuracy and robustness of the control strategy become key indicators in system design. Among numerous control theories, robust H∞ control has become a widely adopted high-performance control strategy in industry due to its superior performance in suppressing system uncertainties and external disturbances. Robust H∞ control is essentially an optimization method; its core idea is to transform the system's disturbance rejection performance into an H∞ norm optimization problem, thereby maximally suppressing the impact of external disturbances or model uncertainties on the system. Compared to traditional PID control or LQR control, H∞ control can still guarantee the stability and performance constraints of the system even when there are structural uncertainties or parameter disturbances in the system model, making it particularly suitable for control scenarios with complex conditions such as time delays, nonlinearity, and strong coupling. In a forklift drive-by-wire drum brake system, factors such as changes in the friction coefficient, motor brake fade, load disturbances, and electronic control signal transmission delays directly affect the stability and accuracy of braking force output. By introducing a robust H∞ controller, the system can maintain accurate control of braking behavior even under modeling errors and environmental disturbances, improving the overall braking quality and safety of the vehicle.

[0004] Furthermore, robust H∞ control possesses excellent frequency domain performance adjustment capabilities. It can design weighting functions and perform performance weighting based on the system's sensitivity to high-frequency or low-frequency disturbances, thereby achieving superior interference suppression across the entire system frequency band. For forklift drum braking systems, low-frequency disturbances are often related to load inertia fluctuations and brake line response delays, while high-frequency disturbances are often related to signal noise, friction vibration, and other issues. Robust H∞ control can address different frequency disturbances specifically during the system design phase through frequency domain design techniques. Simultaneously, robust H∞ control can be effectively integrated with fault detection and fault-tolerant control to achieve fault-tolerant control under fault conditions. For example, when the braking actuator experiences performance degradation or malfunction, the H∞ control method adjusts the control gain and feedback structure in real time to ensure the system still meets the desired braking distance and response speed, providing a guarantee for the safe operation of new energy forklifts.

[0005] In summary, the proposed control method for a forklift drive-by-wire drum brake system based on robust H∞ effectively enhances the system's adaptability to model uncertainties and external disturbances, significantly improving the braking stability and safety of the forklift in complex operating environments. This control method and device not only possess high-precision and robust control performance but also lay a solid technical foundation for the development of drive-by-wire braking systems towards intelligence and adaptability, demonstrating broad engineering application prospects and promotional value. Summary of the Invention

[0006] To address the issues of slow response, low control accuracy, and weak robustness in current forklift drive-by-wire drum braking systems under complex operating conditions, this invention proposes a robust H∞-based forklift drive-by-wire drum braking method and corresponding device. Compared to traditional control technologies, this invention, by introducing a robust H∞ control algorithm, addresses system uncertainties and external disturbances, maintaining good control performance under multiple operating conditions, thereby further ensuring the operational safety and handling efficiency of new energy forklifts.

[0007] To address the aforementioned technical challenges, the first aspect of this invention relates to a robust H∞ control method applied to a forklift drive-by-wire drum brake system, comprising the following steps:

[0008] Step 1: Conduct a mechanism analysis on the mechanical structure and dynamic characteristics of the forklift's drive-by-wire drum braking system, and then construct its dynamic model;

[0009] Step 2: Based on the model established in Step 1, design an adaptive robust H∞ control gain K to ensure that the system state can quickly reach stability;

[0010] Step 3: Based on the control gain K designed in Step 2, design a robust H∞ control algorithm for the forklift drive-by-wire drum brake system;

[0011] Step 4: Based on Lyapunov stability theory, prove that the control algorithm designed in Step 3 can make the system state converge stably, and conduct numerical simulation in MATLAB / Simulink environment to verify the actual control effect of the control algorithm in the braking system.

[0012] The second technical solution of the present invention relates to a robust H∞ control device suitable for a forklift drive-by-wire drum brake system. This device integrates an electronic hydraulic brake (EHB) system, an electronic control unit (ECU), a data communication module, etc., to construct a collaborative control platform for achieving high-precision real-time control of the forklift drive-by-wire brake system.

[0013] This invention addresses the braking and control problems of forklifts in complex operating scenarios, proposing a novel control strategy to effectively solve the robustness deficiencies of traditional control schemes caused by inaccurate system models, nonlinear characteristics, and external disturbances. Compared to existing technologies, this solution has the following characteristics: by designing a robust H∞ control algorithm, the stability and anti-interference capability of the forklift's brake-by-wire system are significantly enhanced when faced with changes in system parameters and external disturbances. The system can maintain reliable operation under complex and variable operating conditions (such as heavy load, no load, or frequent start-stop), thereby significantly improving the forklift's operating efficiency and safety. Attached Figure Description

[0014] To more intuitively illustrate the technical solution of the present invention, the accompanying drawings referenced in the technical description of the present invention are now briefly introduced. It should be noted that the following drawings are only schematic diagrams of some embodiments of the present invention. For those skilled in the art, other similar illustrations can be drawn based on these drawings without any creative effort.

[0015] Figure 1 This is a schematic diagram illustrating the dynamic modeling principle of the forklift drive-by-wire drum braking system proposed in this invention.

[0016] Figure 2 The structure diagram of the simulation program built on the MATLAB / Simulink platform is shown;

[0017] Figure 3 Figure 1 shows the MATLAB / Simulink simulation results of the master cylinder piston position tracking performance under smooth braking conditions.

[0018] Figure 4 The MATLAB / Simulink simulation results for the master cylinder piston position tracking error under smooth braking conditions are shown in the figure.

[0019] Figure 5 The MATLAB / Simulink simulation results of the servo motor output torque under smooth braking conditions are shown in the figure.

[0020] Figure 6 The figure shows the MATLAB / Simulink simulation results of the master cylinder piston position tracking performance under emergency braking conditions.

[0021] Figure 7 The figure shows the MATLAB / Simulink simulation results of the master cylinder piston position tracking error under emergency braking conditions.

[0022] Figure 8 The figure shows the MATLAB / Simulink simulation results of the servo motor output torque under emergency braking conditions.

[0023] Figure 9 This is a flowchart illustrating the implementation of the control method of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0025] Example 1

[0026] This embodiment relates to a robust H∞ control method applied to a forklift drive-by-wire drum brake system. The specific implementation steps are as follows:

[0027] Step 1: Conduct a mechanism analysis on the mechanical structure and dynamic characteristics of the forklift's drive-by-wire drum braking system, and then construct its dynamic model;

[0028] 1. Let the actual displacement of the master cylinder piston in the system be x, and the actual speed be... acceleration is n represents the gear ratio, λ is the transmission efficiency, R is the gear radius, h is the internal hydraulic pressure of the system, c is the damping coefficient, k is the stiffness coefficient, and A sc The cross-sectional area of ​​the master cylinder piston, T m This represents the output torque of the motor. Based on the analysis of the relationships between various physical quantities within the forklift's drive-by-wire drum brake system, and combined with Newton's second law, the dynamic equations of this braking system can be derived as follows:

[0029]

[0030] Among them, F r For rack force, F h F is the internal hydraulic pressure of the system. s For the spring force, F f This is friction.

[0031] Based on the assumption that the movement of the master cylinder piston does not affect the fluid volume within the system, and assuming that the mechanical structure and physical principles are fundamental, the dynamic relationship of the hydraulic system can be expressed as follows:

[0032]

[0033] in, Defined as the first derivative of h with respect to time, Q represents the volumetric flow rate of the brake fluid within the system, β e This indicates the bulk modulus of the brake fluid.

[0034] The hydraulic pressurization model of the wheel cylinder of the system is given below:

[0035]

[0036] Among them, h sc This indicates the hydraulic pressure of the wheel cylinder. Considering... Substituting equation (4) into equation (3), we get:

[0037] (5)

[0038] Equation (5) yields the following mapping relationship between master cylinder pressure and piston position:

[0039]

[0040] Where h0 is the initial pressure inside the cylinder.

[0041] In practical applications, there is a nonlinear relationship between the master cylinder pressure *h* and the piston displacement *x*, which is affected by various factors such as dead zone effect, friction, temperature fluctuation, and brake pad wear. In dynamic modeling, these nonlinear effects can be considered as disturbance terms of the system. To facilitate modeling and control algorithm design, a second-order polynomial can be used to fit the relationship curve between the master cylinder pressure *h* and the piston displacement *x*. This method not only reflects the trend of pressure change with displacement but also simplifies the construction of subsequent control strategies. The fitted second-order relationship expression between pressure *h* and displacement *x* is shown below:

[0042] h = ηx 2 (7)

[0043] Among them, parameter η is an important characteristic variable describing the relationship between master cylinder pressure h and piston displacement x. Its physical meaning is closely related to the overall stiffness of the system and the properties of the hydraulic medium.

[0044] The core purpose of the above modeling method is to provide a dynamic model with reasonable accuracy and easy implementation for the design of control algorithms for forklift wire braking systems, rather than pursuing a completely accurate physical characterization of the system.

[0045] Based on the above analysis, the complete dynamic model of the controlled system can be derived as follows:

[0046]

[0047] Where w represents the lumped model parameter uncertainty. Based on the mechanical structure and dynamic properties of the forklift's wire-controlled braking system, it can be assumed that this lumped perturbation has an upper bound, i.e. in, Its upper limit.

[0048] Step 2: Design a robust H∞ control gain K to ensure that the system state can quickly stabilize;

[0049] The original dynamic model of the system, expressed in terms of differential equations, is as follows:

[0050]

[0051] In the above formula, let u = T m x1 = x, This can then be transformed into a state-space model as follows:

[0052]

[0053] Because the value of variable x is relatively small in actual working conditions, usually less than 0.08 meters, its quadratic term x 2 The impact on the overall result can be approximated as zero, so it is ignored during the modeling / analysis process, resulting in the simplified system state-space model as follows:

[0054]

[0055] The above equation can be rewritten as a standard state-space model as follows:

[0056]

[0057] in,

[0058] The master cylinder piston displacement tracking error is defined as follows:

[0059] e = x1 - x r (13)

[0060] Therefore, the design expectation error dynamics are as follows:

[0061]

[0062] Where a1 and a2 are the artificially designed error convergence rates; w eqIt represents all equivalent disturbances in the system, including model uncertainty, external disturbances, modeling errors, and nonlinear residuals.

[0063] The augmented state is defined as follows:

[0064]

[0065] Based on this, the final expression for the error dynamics is obtained as follows:

[0066]

[0067] in, u a It is the auxiliary control quantity to be designed.

[0068] The performance specifications for H∞ are designed as follows:

[0069]

[0070] Where Q is a weighted matrix set by the user, and ξ is the disturbance suppression performance index.

[0071] Furthermore, the control gain K of the robust H∞ control algorithm is designed as follows:

[0072]

[0073] Where P is a symmetric positive definite matrix, it must satisfy the following Licati matrix inequality conditions:

[0074]

[0075] Step 3: Based on the above control gain K, design a robust H∞ control algorithm for the forklift drive-by-wire drum brake system;

[0076] Based on the obtained adaptive control gain K, the robust H∞ control algorithm is designed as follows:

[0077]

[0078] Step 4: Based on Lyapunov stability theory, prove that the designed control algorithm can make the system state stable and converge, and conduct simulation in MATLAB / Simulink environment to verify the actual control effect of the control algorithm in the braking system.

[0079] The Lyapunov function is defined as follows:

[0080] V(t) = z T (t)Pz(t) (21)

[0081] Taking the first derivative of the Lyapunov function, we get:

[0082]

[0083] Substituting the control algorithm (20) into the above equation and simplifying, we get:

[0084]

[0085] Based on the following standard quadratic inequality:

[0086]

[0087] Where ∈ is any positive number, and for ease of calculation, let ∈ = ξ. 2 We can obtain:

[0088]

[0089] Further analysis revealed the following:

[0090]

[0091] The design goal of robust H∞ control is to make the z-correlation term of this inequality non-positive. In order to suppress the system state energy as much as possible, the natural energy change of the system can be reduced. Set to -Q, and because Equation (26) can be simplified to:

[0092]

[0093] Integrating both sides of equation (27) yields:

[0094]

[0095] Therefore, the system satisfies:

[0096]

[0097] This indicates that the energy amplification factor (H∞ norm) of the system state with respect to the equivalent disturbance satisfies ||G||. ∞ Therefore, this robust H∞ control system can guarantee that the closed-loop feedback tracking error is bounded under bounded energy disturbances, and possesses the specified stability.

[0098] The dynamic model parameters and values ​​of the forklift drive-by-wire drum brake system are given below:

[0099]

[0100]

[0101] Two verification conditions were designed in the simulation. The first is smooth braking, with the expected master cylinder piston position x.r The expression is as follows:

[0102]

[0103] The second scenario is emergency braking, where the forklift's brake-by-wire system has the expected master cylinder piston position x. r It is its limiting position, i.e., x r =0.06m.

[0104] Simulation programs built on the MATLAB / Simulink software platform, such as Figure 2 As shown, the simulation results are as follows: Figures 3 to 8 As shown.

[0105] Simulation results show that the designed robust H∞ control algorithm can achieve stable tracking of the master cylinder piston to the reference position, exhibiting good control stability and robustness. This further demonstrates that the robust H∞ control algorithm has excellent tracking performance when facing different types of master cylinder piston target trajectories, effectively verifying the applicability and reliability of this control method in forklift brake-by-wire systems.

[0106] Example 2

[0107] This embodiment relates to a robust H∞ device applied to a forklift drive-by-wire drum brake system. It achieves precise closed-loop tracking control of the expected master cylinder piston position by incorporating a pedal displacement sensor, a data acquisition module, a servo motor encoder, a CAN data bus, a host computer with a built-in robust H∞ control algorithm, a slave electronic control unit (ECU), a master cylinder servo motor, brake fluid lines, an in-cylinder pressure sensor, and a data communication unit. The specific implementation steps are as follows:

[0108] Step 1: Receive the braking demand input signal from the forklift;

[0109] When the driver presses the brake pedal, the pedal displacement sensor converts the displacement change into a corresponding electrical signal output.

[0110] Step 2: Calculate the target braking response signal based on the input information;

[0111] After receiving the electrical signal from the pedal displacement sensor, the host computer calculates the desired piston displacement value based on the mapping relationship between the forklift pedal travel and the target master cylinder piston displacement, and uses this value as the reference signal for the robust H∞ control system. The host computer then runs the robust H∞ control algorithm, based on the current braking demand and the real-time system state (i.e., the actual piston position x and velocity in the master cylinder). This generates a control signal, which is the target output torque of the servo motor. The actual displacement x of the master cylinder piston is indirectly calculated by measuring the angular displacement signal obtained from the servo motor encoder and based on the mapping relationship between the angular displacement and the piston displacement.

[0112] Step 3: Transmit the calculated control commands to the execution unit;

[0113] The host computer sends relevant signals to the electronic control unit (ECU) via the CAN bus, including the desired position signal of the master cylinder piston and the torque command signal for controlling the servo motor.

[0114] Step 4: Drive the actuator to complete the braking operation;

[0115] After receiving the control command transmitted from the host computer, the electronic control unit (ECU) starts the servo motor inside the EHB system. The servo motor drives the master cylinder piston to achieve the feed motion through the internal reduction gear transmission mechanism.

[0116] Step 5: Generate the corresponding braking force;

[0117] The feed motion of the master cylinder piston compresses the brake fluid in the cylinder, which is then delivered to the brake lines and further acts on the wheel cylinders, thereby generating the braking force required to brake the forklift wheels.

[0118] Step 6: Adjust the control precision through a closed-loop feedback mechanism;

[0119] The in-cylinder pressure sensor and the servo motor angular displacement sensor work together to monitor the system status in real time, primarily to obtain the current position of the master cylinder piston. The electronic control unit (ECU) feeds back the signals collected by these sensors to the host computer via the CAN bus. Based on this feedback information and combined with the robust H∞ control algorithm, the data communication module adjusts the control quantity (i.e., the servo motor output torque) in real time and sends the updated control signal back to the lower-level ECU to dynamically correct the braking execution process, constructing a closed-loop feedback control structure to ensure that the master cylinder piston can accurately follow the set target position and maintain the required hydraulic pressure inside the master cylinder, thereby effectively meeting the braking requirements of the forklift.

[0120] The above description is merely one embodiment of the present invention, intended to illustrate the technical solution of the present invention, and does not constitute a limitation on its application scope. For those skilled in the art, various modifications, substitutions, or optimizations can be made without departing from the core ideas and basic principles of the present invention, and all equivalent variations of these technical solutions should be covered within the protection scope of the present invention.

Claims

1. A robust method for use with a forklift drive-by-wire drum brake system The control method specifically includes the following implementation steps: Step 1: Conduct a mechanism analysis on the mechanical structure and dynamic characteristics of the forklift's drive-by-wire drum braking system, and then construct its dynamic model; Step 2: Based on the model established in Step 1, design an adaptive robust model. Control gain This is to ensure that the system state can quickly stabilize; Step 3: Based on the control gain designed in Step 2 Design a robust method for a forklift drive-by-wire drum brake system. Control algorithm; Step 4: Based on Lyapunov stability theory, prove that the control algorithm designed in Step 3 can make the system state converge stably, and conduct numerical simulation in MATLAB / Simulink environment to verify the actual control effect of the control algorithm in the braking system. Step 1 specifically includes the following: setting the mass of the master cylinder piston to be... Its actual displacement in the system is The actual speed is acceleration is , Indicates the gear ratio. For transmission efficiency, For the gear radius, For the internal hydraulic system, The damping coefficient is... This is the stiffness coefficient. The cross-sectional area of ​​the master cylinder piston. Based on the analysis of the relationships between various physical quantities within the forklift's drive-by-wire drum brake system, and combined with Newton's second law, the dynamic equation of the braking system can be derived as follows: (This is the motor output torque.) in, For rack force, For the internal hydraulic pressure of the system, For spring force, For friction, Based on mechanical structure and physical principles, assuming that the movement of the master cylinder piston does not affect the fluid volume within the system, the hydraulic relationship of the system can be expressed as follows: (3) in, Defined as The first derivative with respect to time Represents the internal brake fluid volume flow rate. This indicates the bulk modulus of brake fluid. Represents the volume of the master cylinder. The following is a hydraulic pressurization model of the wheel cylinder system: (4) in, The hydraulic pressure change rate of the wheel cylinder, This indicates the volume of the wheel cylinder, taking into account... Substituting equation (4) into equation (3), we get: (5) Equation (5) yields the mapping relationship between master cylinder pressure and piston position: (6) in, The initial pressure inside the main cylinder. To simplify the mapping relationship between master cylinder pressure and piston position shown in equation (6), a second-order polynomial is used to fit the relationship curve of equation (6). The fitted master cylinder pressure The second-order relationship between the piston displacement x and the piston displacement x is expressed as follows: (7) Among them, parameters It describes the master cylinder pressure. The important characteristic variable relating to piston displacement x has a physical meaning that is closely related to the overall stiffness of the system and the properties of the hydraulic medium. Based on the above analysis, the complete dynamic model of the controlled system can be derived: (8) in, To account for the uncertainties in the lumped model parameters and external disturbances to the system, based on the mechanical structure and dynamic properties of the forklift drive-by-wire braking system, it is assumed that the lumped perturbation has an upper bound, i.e. ,in, Its upper boundary; Step 2 specifically includes: System dynamics model expressed in terms of differential equations: (9) In the above formula, let , Then it is transformed into a state-space model: (10) Due to variables in actual working conditions The value of is relatively small, usually less than 0.08 meters, and its quadratic term The impact on the overall result can be approximated as zero, so it is ignored in the modeling process, thus obtaining a simplified system state-space model: (11) Rewriting the above equation in a standard state-space model: (12) in, , , , , Define the master cylinder piston displacement tracking error: (13) Design expected error dynamics: (14) in, It is a manually designed error convergence speed. This represents all equivalent disturbances in the system, including model uncertainties, external disturbances, modeling errors, and nonlinear residuals. Define augmented states: (15) Based on this, the final expression for the error dynamics is obtained: (16) in, , , It is an auxiliary control variable. design Performance metrics: (17) in, It is a weighted matrix. It is a disturbance suppression performance indicator. Furthermore, design robust Control gain of the control algorithm : (18) in, For a matrix to be symmetric and positive definite, it must satisfy the following Licati matrix inequality conditions: (19) Step 3 specifically includes: Based on the control gain obtained in step 2 Designed to be robust for forklift drive-by-wire drum braking systems The control algorithm is as follows: (20) Step 4 specifically includes: Define the Lyapunov function: (21) Taking the first derivative of the Lyapunov function, we get: (22) robust Substituting the control algorithm into the above formula and simplifying, we get: (23) Based on the following standard quadratic inequality: (24) in, Let be any positive number, take We can obtain: (25) Further analysis revealed the following: (26) Robust The design goal of the control is to make this inequality The related terms are not positive. In order to suppress the system's state energy as much as possible, the formula representing the change in the system's natural energy can be changed. Set as - And because Equation (26) can be simplified to: (27) Integrating both sides of equation (27) yields: (28) Therefore, the system satisfies: (29) This indicates that the energy amplification factor of the system state with respect to the equivalent disturbance satisfies... Therefore, the stability of the forklift's drive-by-wire drum brake control system is guaranteed; 2. A robust device for implementing the claim 1 The forklift drive-by-wire drum brake control system is characterized by the following: Includes pedal displacement sensor, data acquisition module, servo motor encoder, CAN data bus, and built-in robustness. The system comprises a host computer for the control algorithm, a slave computer for the electronic control unit, a master cylinder servo motor, an internal reduction gear transmission mechanism, brake fluid lines, an in-cylinder pressure sensor, and a data communication unit; wherein, the pedal displacement sensor receives braking demand input signals from the forklift driver, the servo motor encoder and the in-cylinder pressure sensor are used to collect system status information, and the host computer is configured to execute the robust control algorithm described in claim 1 based on the input information and the system status information. The control method generates a target position signal for the master cylinder piston and control commands for the servo motor. These commands are then transmitted to the lower-level electronic control unit (ECU) via a CAN bus. The lower-level ECU drives the master cylinder servo motor according to the control commands. The servo motor, through an internal reduction gear transmission mechanism, drives the master cylinder piston to feed and compress the brake fluid within the cylinder, which is then delivered to the brake lines and further acts on the wheel cylinders to generate braking force. The lower-level ECU also feeds back the system status information to the upper-level computer via the CAN bus. This allows the upper-level computer to adjust the control input in real time via a data communication module, resend the updated control signal to the ECU, and dynamically correct the braking process, thus achieving closed-loop feedback control.

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