Electric proportional control device and method for electric fork lift truck

Abstract

The application relates to an electric proportional control device and method for an electric forklift, and belongs to the technical field of electric forklift control, which comprises a microprocessor, a proportional amplifier, a feedback circuit, an electro-hydraulic proportional valve and a hydraulic system; the proportional amplifier is used for proportional amplification of a control signal; the feedback circuit is used for PID adjustment of a PWM signal; and the hydraulic system is used for control of forklift fork work. After the microprocessor is started, the microprocessor receives a control signal, sends a corresponding PWM control signal, then carries out operation and power amplification through the proportional amplifier, then carries out current sampling, and then drives the electro-hydraulic proportional valve to control the hydraulic system; the feedback circuit converts the sampled current into a voltage signal through a current signal, carries out DC amplification, and then feeds back to the microprocessor to carry out PID adjustment on the PWM signal, thereby forming a closed-loop control system. The electric proportional control method and device for the electric forklift have the advantages of high reliability, strong anti-interference ability, high control precision, easy operation and maintenance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to an electric proportional control device for electric forklift and device method, belongs to electric forforklift control technical field. BACKGROUND

[0002] Electric forklift refers to the forklift that works by electricity, most of which is battery operated, and the battery is one of the batteries, which can store limited electrical energy for use in appropriate places. The electric forklift is powered by a battery, which drives the travel motor and the oil pressure system motor, thereby realizing travel and loading operation. Electric forklift is a loading and carrying vehicle powered by a DC power source (battery). In terms of new materials and new technologies, the most important manifestation is the application of transistor controllers (SCR and MOS tubes). Its appearance greatly improves the performance of electric forklifts. Overall, the durability, reliability and applicability of electric forklifts have been significantly improved, and they can fully compete with internal combustion engine forklifts.

[0003] At present, the proportional operation system adopted by the forklift is a multi-way valve control system device. When the forklift is working, the forklift action is generally controlled by the on-off electromagnetic reversing valve, but this control mode of forklift action does not have adjustability, and cannot adjust the amplitude and speed of forklift action according to the actual working condition. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned deficiencies in the prior art, and to provide an electric proportional control device for electric forklift and device method, which adjusts the hydraulic system and outputs signals by using digital or analog as input electrical signals, so that the pressure of hydraulic oil or the flow of hydraulic oil changes continuously with the dynamic change of input signals in a certain proportion.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] An electric proportional control device for electric forklift, the electric proportional control device for electric forklift comprises a microprocessor, a proportional amplifier, a feedback circuit, an electro-hydraulic proportional valve and a hydraulic system;

[0007] The proportional amplifier is used to amplify the control signal proportionally;

[0008] The feedback circuit is used to adjust the PWM signal output by the microprocessor PID;

[0009] The hydraulic system is used to control the lifting, lowering, tilting and stopping of the forklift forks according to the control signal of the microprocessor.

[0010] Further, the proportional amplifier comprises three parts of digital buffer, pre-power amplifier drive and power amplifier.

[0011] Further, the feedback circuit mainly consists of a sampling circuit, an I / V conversion circuit and a DC amplification circuit.

[0012] Further, the feedback circuit mainly includes a current sampling resistor 1R13, a current detection chip IN170, an I / V conversion resistor R302 and a high-precision low-noise operational amplifier OPA227.

[0013] Further, the hydraulic system comprises a hydraulic lock (1), a lifting hydraulic cylinder (2), an electro-hydraulic proportional valve (7) and a pressure compensation valve (8); the pressure compensation valve (8) is connected with the electro-hydraulic proportional valve (7), and the electro-hydraulic proportional valve (7) is connected with a rodless cavity and a rod cavity of the lifting hydraulic cylinder (2) through the hydraulic lock (1).

[0014] Further, the hydraulic system is provided with a one-way valve (5) on a rod cavity pipeline of the lifting hydraulic cylinder (2).

[0015] Further, the hydraulic system is provided with an overflow valve (4) on a rodless cavity pipeline of the lifting hydraulic cylinder (2).

[0016] Further, the hydraulic system is provided with a throttling orifice (6) on a hydraulic pipeline.

[0017] Further, the control method of the electric proportional control device for the electric forklift comprises the following steps: after the microprocessor is started, the microprocessor receives a control signal, sends a corresponding PWM control signal after internal processing, and then performs operation and power amplification on the electric control signal through a proportional amplifier, then samples the current, and then drives an electro-hydraulic proportional valve to control a hydraulic system.

[0018] After the current is sampled, the feedback circuit converts the sampled current into a voltage signal, then performs DC amplification, and then feeds back to the microprocessor to perform PID adjustment on the PWM signal output by the microprocessor, thereby forming a closed-loop control system.

[0019] Further, the open-loop transfer function of the PID system is as follows:

[0020]

[0021] K c =K a K q K m / A

[0022] Wherein, K a is the gain of the amplifier, K c is the open-loop gain of the system, K m is the pressure feedback coefficient, K q is the flow gain of the proportional valve, and δ his the damping ratio of the hydraulic cylinder, ω v is the proportional valve frequency, ω h is the frequency of the hydraulic cylinder.

[0023] The electric proportional control method and device for electric forklifts provided by the application have the advantages of high reliability, strong anti-interference ability, high control precision, easy operation and maintenance, etc. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the architecture diagram of the electric proportional control device for electric forklifts of the application;

[0025] Figure 2 is the valve control circuit diagram of the application;

[0026] Figure 3 is the feedback circuit diagram of the application;

[0027] Figure 4 is the basic component block diagram of the electro-hydraulic proportional pressure control valve control system of the application;

[0028] Figure 5 is the control block diagram of the electro-hydraulic proportional pressure control valve control system of the application;

[0029] Figure 6 is the hydraulic system structure diagram of the application;

[0030] In the figure: 1. Hydraulic lock 2. Lifting hydraulic cylinder 3. External load 4. Overflow valve 5. Check valve 6. Orifice 7. Electro-hydraulic proportional valve 8. Pressure compensation valve. DETAILED DESCRIPTION

[0031] The technical solutions of the application will be described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific features in the embodiments and the specific embodiments of the application are detailed descriptions of the technical solutions of the application, and not limitations of the technical solutions of the application. In the case of no conflict, the technical features in the embodiments and the specific embodiments of the application can be combined with each other.

[0032] The term "and / or" in this paper is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the associated objects before and after are in an "or" relationship.

[0033] As Figure 1 , Figure 2 , Figure 3 An electric proportional control device for electric forklifts, the electric proportional control device for electric forklifts comprises a microprocessor, a proportional amplifier, a feedback circuit, an electro-hydraulic proportional valve and a hydraulic system;

[0034] After the microprocessor is started, the microprocessor receives a control signal, processes it internally, and then sends a corresponding PWM control signal. The proportional amplifier then processes, calculates, and power amplifies the electrical control signal, samples the current, and then drives the electro-hydraulic proportional valve. The electro-hydraulic proportional valve controls the hydraulic system, and the electro-hydraulic proportional pressure control valve can be selected.

[0035] The microprocessor can use the VMC40 controller, which is divided into two parts: one part is the execution unit (EU), which executes instructions; the other part is the bus interface unit (BIU), which performs the operation of fetching instructions from the memory. The EU part has a register stack consisting of 8 16-bit registers, which can be used to store data, index, and stack pointer. The arithmetic logic unit (ALU) performs arithmetic operations and logical operations, and the flag register stores the conditions of these operation results. The bus interface unit also has a register stack, in which CS, DS, SS, and ES are segment registers for storage space segmentation. The internal communication register is also a temporary data storage register. The instruction queue stores the pre-fetched instruction stream. The bus interface unit also has an address adder that adds the segment register value and the offset value to obtain a 20-bit physical address. Data and addresses are connected to the external system bus through bus control logic. It can realize the overlap of on-chip operation and off-chip operation.

[0036] The feedback circuit converts the sampled current into a voltage signal after current sampling, then amplifies it with a DC amplifier, and then feeds it back to the microprocessor. The microprocessor internally adjusts the output PWM signal based on the feedback, thus forming a closed-loop control system for the entire system.

[0037] Hydraulic system: used to control the lifting, lowering, tilting, and stopping of the forklift forks according to the control signal of the microprocessor.

[0038] PWM (Pulse Width Modulation) is a technique that uses the switching characteristics of transistors to modulate a constant DC power supply (5V in this document). The transistor turns on and off at a fixed frequency, and the time of turning on and off in a period can be changed, so that a single-pulse-width-adjustable rectangular wave with a fixed period can be obtained. This voltage signal applied to the proportional electromagnet can make the valve core of the proportional valve vibrate slightly, which avoids the heating phenomenon of the electromagnet coil. Since the response period of the valve core is much longer than the pulse period, the valve core movement only responds to the average value of the PWM signal. Applying this technology to the valve control circuit can simplify the circuit and save a large number of components, and the anti-interference ability of the system is also significantly enhanced.

[0039] The proportional amplifier includes three parts: digital buffer, pre-power amplifier driver, and power amplifier.

[0040] The proportional amplifier is open-loop controlled, which is PWM pulse voltage control, so it works in the switch state, it is a digital proportional amplifier. The digital buffer module is prepared for the pre-power amplifier driving module. Since the processing speed of the microprocessor is faster than that of the subsequent circuit, the control signal is buffered after it comes out of the microprocessor. The pre-power amplifier driving module receives the buffered data to preprocess the subsequent power amplifier module, and finally performs power amplification. In this way, the control signal can have enough power to drive the system load after passing through the proportional amplifier. The whole process is actually to convert the voltage signal into a current signal, and to provide a control current proportional to the input voltage and with sufficient power, and to provide a valve control pressure proportional to the voltage signal. Since the movement of the proportional valve spool is mainly controlled by the output force of the proportional electromagnet, and the output force of the electromagnet is proportional to the input current of the proportional electromagnet, the main task of the proportional amplifier is to obtain a current proportional to the control signal.

[0041] The main control chip in the system has 8 PWM channels, and each channel cooperates with one of the two ports to control the operation of two electro-hydraulic proportional pressure control valves. The simplified circuit principle diagram of the lifting and lowering valve control is as follows.

[0042] The feedback circuit mainly consists of a sampling circuit, an I / V conversion circuit and a DC amplification circuit. The resistance 1R13 in the figure is a current sampling resistance. The sampling current passes through the current detection chip IN170, then passes through a resistance R302 for I / V conversion, and then passes through a high-precision low-noise operational amplifier OPA227 for voltage amplification. Finally, the AD conversion pin of the main control chip is used to calculate the AD value of the feedback current.

[0043] As shown in Figure 4 , Figure 5 , the open-loop transfer function of the PID system is:

[0044]

[0045] K c =K a K q K m / A

[0046] (1) When the step input is input, the steady-state error is 0. The main factors affecting the dynamic performance of the system are the frequencies ω v and ω h of the proportional valve and the hydraulic cylinder. The damping ratio δ h of the hydraulic cylinder, according to experience, the value of δ h is 0.1-0.2 when it is empty, and the value of δ h increases slightly when it is loaded.

[0047] (2) Stability, accuracy and rapidity are mutually restricted. The control performance of the control system is related to the open loop gain K c , the greater K c is, the higher the accuracy of the system is. The rapidity of the control system is related to the frequency ω c of the system, the greater ω c is, the wider the frequency bandwidth of the system is. When the open loop gain of the system is increased, the accuracy and the frequency bandwidth of the control system are improved, but the amplitude stability domain will be reduced.

[0048] (3) After the preliminary design of the system is completed, the dynamic performance of the system is basically determined. The main factors affecting the stability and rapidity of the control system are the open loop gain K c , the damping ratio δ h and the inherent frequency ω h of the hydraulic cylinder. In the open loop gain, the effective area A h of the hydraulic cylinder and the flow gain K q of the proportional valve cannot be adjusted after the preliminary design is completed. But the amplifier gain K a can be adjusted, which is mainly to adjust the input current of the control proportional valve. The pressure feedback coefficient K m is related to the cylinder cavity pressure of the hydraulic cylinder, and the adjustment range is limited.

[0049] For example Figure 6As shown, the hydraulic system comprises a hydraulic lock 1, a lifting hydraulic cylinder 2, an electro-hydraulic proportional valve 7, and a pressure compensation valve 8. The pressure compensation valve 8 is connected with the electro-hydraulic proportional valve 7, and the electro-hydraulic proportional valve 7 is connected with the rodless cavity and the rod cavity of the lifting hydraulic cylinder 2 through the hydraulic lock 1. When the lifting device works, the hydraulic oil reaches the lifting hydraulic cylinder 2 through the pressure compensation valve 8, the electro-hydraulic proportional valve 7 and the hydraulic lock 1. When the piston rod of the lifting hydraulic cylinder 2 is lifted to the required height, the valve core of the electro-hydraulic proportional valve 7 is switched to the middle position, the oil supply port oil way is cut off, the pressure of the rodless cavity of the lifting hydraulic cylinder 2 will increase and be kept at a certain value, at this time the goods will stay in the air. At the same time, the electro-hydraulic proportional valve 7 and the pressure compensation valve 8 form the speed regulating valve of the system, and the working principle of the pressure compensation valve 8 is similar to that of the constant-difference pressure reducing valve, which can keep the pressure difference of the electro-hydraulic proportional valve 7 at a certain value, so that the output of the electro-hydraulic proportional valve 7 only keeps a certain relationship with the opening degree of the valve, and will not change due to the change of the external load 3. In order to ensure the stability and safety of the working performance of the electric forklift, the following improvements are made in the hydraulic system: a one-way valve 5 is added to the rod cavity pipeline of the lifting hydraulic cylinder 2 to prevent the hydraulic cylinder from appearing air pocket due to insufficient pump oil supply when the piston rod of the lifting hydraulic cylinder 2 is retracted; a hydraulic lock 1 is added between the electro-hydraulic proportional valve 7 and the lifting hydraulic cylinder 2, which can prevent the goods from falling due to sudden conditions of the hydraulic system when lifting heavy objects; when the piston rod of the lifting hydraulic cylinder 2 suddenly encounters an emergency, an overflow valve 4 is added to the rodless cavity pipeline of the lifting hydraulic cylinder 2 as a safety valve. At the same time, a throttle 6 is arranged on the hydraulic pipeline.

[0050] The electric proportional control device and method for the electric forklift provided by the embodiment of the present application can adjust the hydraulic system and output signals by taking digital or analog signals as input electric signals, so that the pressure of the hydraulic oil or the flow of the hydraulic oil continuously changes with the dynamic change of the input signals in a certain proportion. The electric proportional control method and device for the electric forklift provided by the present application have the advantages of high reliability, strong anti-interference ability, high control precision, easy operation and maintenance, etc.

[0051] The above description is only the preferred embodiment of the present application, and it should be pointed out that those skilled in the art can make some improvements and modifications without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. An electric proportional control device for an electric forklift, characterized in that, The electric proportional control device for electric fork truck comprises a microprocessor, a proportional amplifier, a feedback circuit, an electro-hydraulic proportional valve and a hydraulic system. The proportional amplifier is used for proportional amplification of the control signal. The feedback circuit is used for PID adjustment of the PWM signal output by the microprocessor. The hydraulic system is used for control of the lifting, lowering, tilting and stopping of the fork truck forks according to the control signal of the microprocessor. The control method of the electric proportional control device: After the microprocessor is started, the microprocessor receives the control signal, sends the corresponding PWM control signal after internal processing, then the electric control signal is operated and power amplified by the proportional amplifier, then the current is sampled, and then the electro-hydraulic proportional valve is driven to control the hydraulic system. After the current is sampled, the feedback circuit converts the sampled current into a voltage signal, then the voltage signal is amplified by DC, and then the voltage signal is fed back to the microprocessor to adjust the PWM signal output by the microprocessor, thereby forming a closed-loop control system. The open-loop transfer function of the PID is: ， ， where K a is the amplifier gain, K c is the system open loop gain, K m is the pressure feedback coefficient, K q is the proportional valve flow gain, is the proportional valve damping ratio, is the hydraulic cylinder damping ratio, is the proportional valve frequency, is the hydraulic cylinder frequency, s is the complex frequency variable.

2. The electrically powered proportional control device for a forklift truck as set forth in claim 1, wherein The proportional amplifier comprises a digital buffer, a pre-power amplifier driver and a power amplifier.

3. The electrically powered proportional control device for a forklift truck as set forth in claim 1, wherein The feedback circuit mainly comprises a sampling circuit, an I / V conversion circuit and a DC amplification circuit.

4. The electrically powered proportional control device for a forklift truck as set forth in claim 3, wherein The feedback circuit mainly comprises a current sampling resistor 1R13, a current detection chip IN170, an I / V conversion resistor R302 and a high-precision low-noise operational amplifier OPA227.

5. The electrically powered proportional control device for a fork truck as set forth in claim 1, wherein The hydraulic system comprises a hydraulic lock, a lifting hydraulic cylinder, an electro-hydraulic proportional valve one and a pressure compensation valve one; the pressure compensation valve one is connected with the electro-hydraulic proportional valve one, and the electro-hydraulic proportional valve one is connected with the rodless cavity and the rod cavity of the lifting hydraulic cylinder through the hydraulic lock.

6. The electrically powered proportional control device for a forklift truck as set forth in claim 5, wherein The hydraulic system is provided with a one-way valve on the rod cavity pipeline of the lifting hydraulic cylinder.

7. The electrically powered electrically proportional control device for a fork truck as set forth in claim 5, wherein, The hydraulic system is provided with an overflow valve on the rodless cavity pipeline of the lifting hydraulic cylinder.

8. The electrically powered proportional control device for a forklift truck as set forth in claim 5, wherein The hydraulic system is provided with a throttling opening on the hydraulic pipeline.

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