A PWM control method for preventing jitter and slow start-stop of a forklift mast

Abstract

The application belongs to the technical field of fork trucks, and specifically discloses a PWM control method for preventing fork truck gantry from shaking and slowly starting and stopping, which comprises the following steps: detecting operation button signals in real time through an I / O port of a single-chip microcomputer; when it is determined that the process is starting, controlling the PWM duty cycle to gradually increase from 0% according to a preset ladder sequence; when it is determined that the process is stopping, controlling the PWM duty cycle to gradually decrease from 100% according to a preset ladder sequence; and amplifying the PWM signal through a power drive circuit to control the opening degree of a hydraulic electromagnetic valve core. The application can realize smooth control of the starting and stopping actions of the gantry, and only needs a low-cost general-purpose single-chip microcomputer, without the need to replace expensive special proportional valves or configure load sensors. The application can adapt to different tonnage fork trucks and various actions such as lifting, tilting and side shifting through software parameter adjustment, while ensuring smooth gantry action, eliminating shaking and improving work safety, and greatly reducing hardware cost and system complexity.

Description

Technical Field

[0001] This invention relates to the field of forklift technology, and in particular to a PWM control method for anti-shake soft start-stop of forklift mast. Background Technology

[0002] Forklifts are indispensable cargo handling equipment in modern logistics warehousing and industrial production. The smoothness of their mast movements directly affects operational safety, cargo integrity, and driver comfort. The lifting, tilting / reversing, and lateral movement of the forklift mast all rely on a hydraulic system, and the response characteristics of this system are primarily determined by the control method of the solenoid valves.

[0003] Currently, the industry mainly adopts two types of technical solutions for controlling the hydraulic system of forklift masts: one is the traditional on / off solenoid valve control scheme, which is also the solution commonly used in mainstream entry-level forklifts in China. CN102259809A discloses a control system for a forklift mast. This scheme directly controls the on / off of the solenoid valve through a relay or mechanical contact switch: when the operator moves the operating lever or presses the button, the solenoid valve coil is instantly energized to the rated voltage, and the valve core is fully opened; when the operation stops, the solenoid valve is instantly de-energized and closed. Although this binary control logic is simple in structure and low in cost, it has serious physical defects: the hydraulic system will generate huge hydraulic shocks at the moment of on / off, which will cause obvious jerking and shaking when the mast is raised or lowered. Especially when the mast is in a high-lifted state, the inertial swing amplitude of the goods is extremely large, which can easily cause the goods to fall. At the same time, frequent mechanical shocks will also accelerate the fatigue wear of the hydraulic pipeline and mast structure. Another type is the high-end proportional valve control solution. Some high-end forklifts or precision stacking equipment use proportional hydraulic valves in conjunction with dedicated motion controllers or PLCs (Programmable Logic Controllers). Although this solution can continuously adjust the valve opening through analog signals to achieve smooth transitions in motion, its inherent limitations are also quite obvious: First, the cost is high. The unit price of a dedicated proportional valve and its matching controller is usually several thousand to tens of thousands of yuan, which significantly increases the overall manufacturing cost and makes it difficult to promote in the low-to-mid-range economy forklift market; second, proportional valves have extremely high requirements for the cleanliness of hydraulic oil and require complex closed-loop control algorithms for debugging, resulting in a high maintenance threshold; moreover, traditional dedicated controllers are bulky and difficult to directly embed into the compact electrical control boxes of existing forklifts, leading to high retrofit costs.

[0004] In summary, the industry urgently needs a control method that can effectively suppress mast vibration, achieve smooth start-stop, and is low in cost. It should be compatible with existing forklifts that use ordinary switching solenoid valves and adaptable to different load and working height conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome at least one of the shortcomings of the prior art and provide a PWM control method for anti-shaking soft start-stop of forklift masts.

[0006] To solve the above-mentioned technical problems, the present invention adopts a PWM control method for anti-shake soft start-stop of forklift mast, which is applied to the solenoid valve control of the forklift hydraulic system, and includes the following steps: S1, Signal Acquisition; The button signals of the operating handle or screen are detected in real time through the I / O port of the microcontroller. S2, Status judgment; When the microcontroller detects that a button signal changes from non-triggered to triggered, it determines that the process is started and enters S3-1; When the microcontroller detects that the signal of a button has changed from triggered to not triggered, it determines that the process has stopped and enters S3-2; When the microcontroller detects that a button signal is continuously triggered, it enters S3-3; S3, Signal output control; S3-1, Soft start control; The microcontroller outputs a PWM signal to control the PWM duty cycle to gradually increase from 0% to 100% according to a preset step sequence; S3-2, Stop Control; The microcontroller outputs a PWM signal to control the PWM duty cycle to gradually decrease from 100% to 0% according to a preset step sequence; S3-3, Maintain control; The microcontroller outputs a PWM signal to maintain a constant PWM duty cycle. S4, Action Execution; The PWM signal is output to the hydraulic solenoid valve through the power drive circuit. The hydraulic solenoid valve adjusts the opening of the hydraulic valve core according to the PWM signal to achieve smooth control of the gantry movement.

[0007] Furthermore, in S3-1, the total soft-start duration is set to T_start, which is then divided into N time steps Δt1. Within each time step Δt1, the PWM duty cycle changes sequentially in an increasing sequence until the duty cycle reaches 100%. Preferably, the increasing sequence is: 0%→5%→15%→30%→50%→70%→85%→95%→100%.

[0008] Furthermore, in S3-2, a total pausing time T_stop is set, and T_stop is divided into M time steps Δt2; within each time step Δt2, the PWM duty cycle changes sequentially according to a decreasing sequence until it drops to 0%. Preferably, the decreasing sequence is: 100%→95%→85%→70%→50%→30%→15%→5%→0%.

[0009] Furthermore, in S3-1, the first time step at the beginning of startup and the penultimate time step at the end of startup are set with longer dwell times, while the intermediate steps are set with shorter dwell times, so that the duty cycle change rate follows an S-shaped curve to reduce startup shock.

[0010] Furthermore, in S3-2, the first time step at the beginning of the stop and the penultimate time step at the end of the stop are set with longer dwell times, while the intermediate steps are set with shorter dwell times, so that the duty cycle change rate follows an S-shaped curve to reduce the stop impact.

[0011] Furthermore, the method operates on a microcontroller system, which includes: A microcontroller is used to perform the logic operations and signal output of the PWM control method. The signal input interface connects to the microcontroller's I / O port to receive button signals; it can be an operating handle or a screen. The power drive circuit is connected to the PWM output port of the microcontroller and is used to amplify the PWM signal to drive the hydraulic solenoid valve coil. The power module is used to convert the forklift power supply voltage into the microcontroller's operating voltage.

[0012] Furthermore, the power drive circuit includes a two-stage transistor isolation circuit and a MOSFET switch. The MOSFET switch is connected in series in the power supply circuit of the hydraulic solenoid valve, and its gate is controlled by the PWM signal of the microcontroller.

[0013] Furthermore, the microcontroller is an STM32F407 series microcontroller; the signal input interface uses an optocoupler isolated input circuit to improve anti-interference capability.

[0014] The beneficial effects of this invention are: 1. This invention replaces the traditional "on / off" binary control with stepped PWM duty cycle control, enabling the hydraulic solenoid valve core to open and close slowly. This mechanism effectively eliminates the "water hammer effect" in the hydraulic system, completely solves the jerking and shaking problems during gantry start / stop, avoids the risk of goods falling due to severe inertial shaking during high-level operations, and reduces mechanical wear. In some specific embodiments, an S-curve optimization strategy can be used to make acceleration changes more ergonomic, further improving the smoothness of operation; 2. This invention adopts a "general-purpose microcontroller + ordinary solenoid valve" architecture. It eliminates the need to replace expensive dedicated proportional valves, achieving the same soft start / stop effect that would otherwise require a dedicated controller costing thousands of yuan using only a low-cost general-purpose microcontroller (such as STM32). The incremental hardware cost is extremely low. Furthermore, the entire system requires no load sensor; it can adapt to different tonnage forklifts and various actions such as lifting, tilting, and lateral movement simply by adjusting parameters (soft start / stop time, step sequence) through software. In other words, this solution not only simplifies system complexity but also, due to its small size and strong compatibility, facilitates low-cost upgrades and modifications to existing forklifts, possessing extremely high commercial promotion value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the control system in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the driving circuit in Embodiment 1 of the present invention; Figure 3 This is a control principle diagram of the method in Embodiment 1 of the present invention; Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the accompanying drawings. Example 1

[0017] like Figure 1-3 As shown, this embodiment provides a PWM control method for anti-shake soft start / stop of a forklift mast, applied to the solenoid valve control of the forklift hydraulic system, including the following steps: S1, Signal Acquisition; The microcontroller's I / O ports are used to detect button signals from the operating handle or screen in real time; each button corresponds to an action (e.g., up, down, tilt forward, tilt backward, move left, move right), and the signal is a digital quantity (0 = no action, 1 = in action); S2, Status judgment; When the microcontroller detects that a button signal changes from non-triggered to triggered (button signal changes from 0→1), it determines that the process has started and enters S3-1; When the microcontroller detects that a button signal changes from triggered to not triggered (button signal changes from 1→0), it determines that the process has stopped and enters S3-2; When the microcontroller detects that a button signal is continuously triggered (button signal is continuously 1), it enters S3-3; S3, Signal output control; S3-1, Soft start control; The microcontroller outputs a PWM signal to control the PWM duty cycle to gradually increase from 0% to 100% according to a preset step sequence. Specifically, the total soft-start time T_start is set to 0.8 seconds and divided into 8 time steps, each step lasting Δt1 = 0.1 seconds. The duty cycle increment sequence is: 5% → 15% → 30% → 50% → 70% → 85% → 95% → 100%. That is, every 0.1 seconds, the duty cycle jumps to the next value according to the above sequence; after 8 time steps, the PWM reaches 100% full operation. S3-2, Stop Control; The microcontroller outputs a PWM signal to control the PWM duty cycle to gradually decrease from 100% to 0% according to a preset step sequence. Specifically, the total stop time T_stop is set to 0.8 seconds and divided into 8 time steps, each with a duration Δt2 = 0.1 seconds. The duty cycle decrease sequence is: 100% → 95% → 85% → 70% → 50% → 30% → 15% → 5% → 0%. After 8 time steps, the PWM is completely turned off. S3-3, Maintain control; The microcontroller outputs a PWM signal to maintain a constant PWM duty cycle. S4, Action Execution; The PWM signal is output to the hydraulic solenoid valve through the power drive circuit. The hydraulic solenoid valve adjusts the opening of the hydraulic valve core according to the PWM signal to achieve smooth control of the gantry movement.

[0018] The method in this embodiment runs on a microcontroller system, which includes: The microcontroller is used to perform the logic operations and signal output of the PWM control method. The microcontroller is an STM32F407 series microcontroller. The handle signal input interface is connected to the microcontroller's I / O port to receive button signals. It uses an optocoupler-isolated input circuit to improve anti-interference capability. The power drive circuit is connected to the PWM output port of the microcontroller and is used to amplify the PWM signal to drive the hydraulic solenoid valve coil. The power drive circuit includes a two-stage transistor isolation circuit and a MOSFET switch. The MOSFET switch is connected in series in the power supply circuit of the hydraulic solenoid valve, and its gate is controlled by the PWM signal of the microcontroller. The power module is used to convert the forklift power supply voltage into the microcontroller's operating voltage.

[0019] The PWM control method for anti-shake soft start-stop of the forklift mast in this embodiment can use the microcontroller to output a stepped increasing / decreasing PWM duty cycle to realize the soft switching of the hydraulic valve. Unlike the traditional on-off control, the relevant parameters can be adjusted by software, and it can be adapted to forklifts of different tonnages without modifying the hardware. Example 2

[0020] The main difference between this embodiment and Embodiment 1 is that in S3-1, the first time step at the initial stage of startup and the penultimate time step at the end of startup are set with longer dwell times, while the intermediate steps are set with shorter dwell times, so that the duty cycle change rate presents an S-shaped curve, thereby further reducing startup impact. Specifically, it can be: 0.15 seconds (5%) → 0.1 seconds (15%) → 0.1 seconds (30%) → 0.1 seconds (50%) → 0.1 seconds (70%) → 0.1 seconds (85%) → 0.15 seconds (95%) → 0.1 seconds (100%).

[0021] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. For those skilled in the art, any obvious changes such as equivalent transformations or simple substitutions based on the technical solutions of the present invention, without departing from the spirit and scope of the present invention, are within the protection scope of the present invention.

Claims

1. A PWM control method for anti-shake soft start / stop of a forklift mast, applied to the solenoid valve control of a forklift hydraulic system, characterized in that, Includes the following steps: S1, Signal Acquisition; The button signals of the operating handle or screen are detected in real time through the I / O port of the microcontroller. S2, Status judgment; When the microcontroller detects that a button signal changes from non-triggered to triggered, it determines that the process is started and enters S3-1; When the microcontroller detects that the signal of a button has changed from triggered to not triggered, it determines that the process has stopped and enters S3-2; When the microcontroller detects that a button signal is continuously triggered, it enters S3-3; S3, Signal output control; S3-1, Soft start control; The microcontroller outputs a PWM signal to control the PWM duty cycle to gradually increase from 0% to 100% according to a preset step sequence; S3-2, Stop Control; The microcontroller outputs a PWM signal to control the PWM duty cycle to gradually decrease from 100% to 0% according to a preset step sequence; S3-3, Maintain control; The microcontroller outputs a PWM signal to maintain a constant PWM duty cycle. S4, Action Execution; The PWM signal is output to the hydraulic solenoid valve through the power drive circuit. The hydraulic solenoid valve adjusts the opening of the hydraulic valve core according to the PWM signal to achieve smooth control of the gantry movement.

2. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 1, characterized in that: In S3-1, the total soft start time is set to T_start, and then T_start is divided into N time steps Δt1. Within each time step Δt1, the PWM duty cycle jumps sequentially in an increasing sequence until the duty cycle reaches 100%.

3. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 2, characterized in that: The increasing sequence is: 0%→5%→15%→30%→50%→70%→85%→95%→100%.

4. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 1, characterized in that: In S3-2, the total pausing time T_stop is set, and T_stop is divided into M time steps Δt2. Within each time step Δt2, the PWM duty cycle changes sequentially in a decreasing sequence until it drops to 0%.

5. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 4, characterized in that: The preferred decreasing sequence is: 100%→95%→85%→70%→50%→30%→15%→5%→0%.

6. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 2, characterized in that: In S3-1, the first time step at the beginning of startup and the penultimate time step at the end of startup are set with longer dwell times, while the intermediate steps are set with shorter dwell times, so that the duty cycle change rate follows an S-shaped curve to reduce startup shock.

7. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 4, characterized in that: In S3-2, the first time step at the beginning of the stop and the penultimate time step at the end of the stop are set with longer dwell times, while the intermediate steps are set with shorter dwell times, so that the duty cycle change rate follows an S-shaped curve to reduce the stop impact.

8. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 2, characterized in that, The method operates on a microcontroller system, which includes: A microcontroller is used to perform the logic operations and signal output of the PWM control method. The signal input interface connects to the microcontroller's I / O port and is used to receive button signals. The power drive circuit is connected to the PWM output port of the microcontroller and is used to amplify the PWM signal to drive the hydraulic solenoid valve coil. The power module is used to convert the forklift power supply voltage into the microcontroller's operating voltage.

9. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 8, characterized in that: The power drive circuit includes a two-stage transistor isolation circuit and a MOSFET switch. The MOSFET switch is connected in series in the power supply circuit of the hydraulic solenoid valve, and its gate is controlled by the PWM signal of the microcontroller.

10. The PWM control method for anti-vibration soft start / stop of forklift mast according to claim 8, characterized in that: The microcontroller used is an STM32F407 series microcontroller; the signal input interface uses an optocoupler isolated input circuit.

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