At present, the main reason for restricting the development of cotton topping machines is that the automatic height detection of cotton plants is difficult and the topping accuracy is not high. Therefore, it is urgent to develop a cotton topping machine with high topping precision and good overall performance. The automatic height control system of the cotton topping machine cutter is an important part of the cotton topping machine. Its working performance will directly affect the precision and efficiency of the whole machine work, and ultimately affect the total cotton output. If the cutter is too high, there will be leakage topping, which will not remove the top advantage of the cotton plant, so that the number of bolls in the whole plant will decrease; if the cutter is too low, the topping will be too high, which will not only increase the loss rate of the flower bud, but also make the whole machine easy. The workload is increased.
The grounding height of the 3MDZK-12 group-controlled single-row profile cotton topping machine cutter is manually adjusted by the operator through the lifting pedal to drive the unequal arm parallel four-bar mechanism; while the surface of the field is undulating, the height of the cotton plant All are randomly changed, the operator can only operate according to real-time observation and work experience, resulting in difficult operation and difficult to meet the work requirements. Therefore, according to the working requirements of 3MDZK-12 group-controlled single-row profiling cotton topping machine cutter, the AT89C52 single-chip microcomputer is taken as the core to design the automatic height detection and cutter height automatic control system to improve the automation level of the machine. in accordance with.
1 cutter hydraulic control system analysis 1.1 cutter height of the hydraulic system control principle: 2010-03-23 ​​Foundation item: Xinjiang Corps science and technology support project (2009Z14) Corresponding author: Hu Bin (1968-), male, Hubei British Hermit, Professor, master's tutor, (E- 3MDZK-12 type control single-row profile cotton topping machine cutter hydraulic lifting mechanism schematic, as shown. It can be seen that the upper end of the hydraulic cylinder is fixedly hinged to the frame, the lower end It is hinged on the connecting rod bracket of the drum cutter, and controls the height of the cutter by the change of the length of the hydraulic cylinder. The operation is carried out by the single chip microcomputer and the command is issued to drive the multi-way reversing solenoid valve, and the pressure oil from the oil pump is multi-channel. The reversing valve enters the cylinder to raise or lower the cutter to a suitable position; when the cotton topping machine does not work, the hydraulic oil flows back to the tank through the multi-way reversing valve.
This system selects the electro-hydraulic proportional directional valve as the control valve. The electro-hydraulic proportional directional valve continuously controls the load flow or pressure in different directions. In actual use, it is only necessary to change the control current of the valve to control the output pressure or flow of the valve. In the hydraulic system with high control of the cotton topping machine cutter, the electro-hydraulic proportional directional valve is added, and the controller composed of the single chip microcomputer and its peripheral circuits is used to construct the electro-hydraulic proportional control system by using the PID control algorithm. A schematic diagram of the hydraulic control system, such as the relationship between the height of the cutter and the height of the cotton plant, is based on the agronomic requirements of the cotton topping, and the relationship between the height H of the drum cutter and the height h of the cotton plant is calculated. The diameter of the drum cutter is D=400mm11, and the average top height is 40mm. Calculate H=h+(D/2-40), H=(h+160)mm, as shown in the center of the drum cutter. The relationship with the height of the cotton plant is required to achieve the effect shown in the control system, but it is difficult for the actuator to accurately track the height change of the cotton plant, and it is adjusted too frequently. The cutter height also increases wear on the entire control system and mechanism. Therefore, the control system sub-samples the height of the plant at intervals, calculates the average height of the output of the cutter, and ensures that the control accuracy is within ±20 mm.
2 Automatic detection of the height of the cotton plant and the height of the cutter from the ground 2.1 Automatic detection of the height of the cotton plant If the contact sensor is used to detect the height of the cotton plant, the loss rate of the cotton harvest will be increased. Since the cotton topping machine automatically adjusts the height of the cutter off the ground during the operation, and the cotton topping machine works in a vibrating, dusty environment, the sensor should have the ability to adapt to this environment.
Ultrasonic ranging, image processing detection technology and infrared ranging are widely used non-contact detection methods. Although the ultrasonic ranging is not complicated, its economic cost is high. Although the image processing detection technology can better detect the shape of the target, due to its complexity, poor stability, large data processing capacity, slow response speed and high cost, most of this technology is still in existence. It is not difficult to find the positional relationship of the motion by analyzing it, as shown in (b).
The telescopic rod of the hydraulic cylinder rod drives the center of the drum cutter with a point as the center of the circle and a circular oscillation motion with the radius of oe. The movement track is as shown by the dotted line in (b). The initial length of the hydraulic cylinder rod is m, the expansion and contraction amount is x, and the length of the ad rod is m +x. Among them, the lengths of the ab rod, the ob rod, the od rod and the oe rod are known, and are represented by 11, 12, 3, 4 respectively. The height of the frame c is indicated by B. Then there is a point as the origin, b, c is the x-axis, and the axis establishes a Cartesian coordinate system. Then the coordinates of the d point are (os sing), and the motion trajectory function is based on the positional relationship, and the following equation H-cutter center is obtained. Off-site height; h-frame ab length; h-frame b-segment length; h-cutter linkage bracket d-segment length; h-cutter linkage bracket e-segment length; l5-frame beam off-ground Height; m - the initial length of the hydraulic cylinder.
Therefore, the current height of the cutter can be determined by measuring the current position of the lift hydraulic cylinder. Considering that the hydraulic cylinder is a piston type hydraulic cylinder, the potentiometer circuit is used to detect the current position of the hydraulic cylinder, as shown in the figure 2. The current position of the hydraulic cylinder is converted into a voltage output with a certain relationship through the potentiometer circuit. The output voltage U is obtained by dividing the potentiometer. When no oil pressure enters, that is, the piston rod zero scale=0; when the hydraulic cylinder reaches full scale U=U; when the piston rod is in any position, U0 3 hardware design of automatic control system 3.1 The current position of the hardware structure of the automatic control system is measured, the measured value is processed according to the PID control algorithm, the corresponding control signal is generated, and the electro-hydraulic proportional valve is actuated, so that the cutter follows the cotton plant. The height of the rise and fall. In the control system, the main control unit adopts 8-bit AT89C52 single-chip microcomputer, and the peripheral circuit includes input and output signal processing circuits.
3.2 single-chip system AT89C52 single-chip system with 8K flash ROM inside, so no external program memory; expand 8K data memory as needed, select 6264 chip.
3.3 Position measurement and A/D conversion circuit The position of the hydraulic cylinder is measured by a potentiometer circuit. The output signal of the potentiometer circuit is large, generally does not need to be amplified, but the load capacity is not strong, and an operational amplifier is connected for impedance matching and amplification. This circuit uses the OP07 operational amplifier to match and amplify its signal. The amplified signal is input to the A/D converter and converted into digital quantities for processing into the microcontroller.
The A/D converter uses the A/D serial chip TLC1543, which is a CMOS, switched-capacitor successive approximation analog-to-digital converter with 11 10-bit resolutions. An on-chip automatic sample-and-hold circuit is provided. At the end of the conversion, the "end of conversion" signal (EOC) output goes high to indicate the completion of the conversion. 4. 3.4D/A conversion circuit The actuator of the control system is electro-hydraulic. Proportional directional valve, the control voltage is 0~10V. The output signal of the single-chip microcomputer is converted by the 8-bit D/A conversion chip DAC0832, and after proportional amplification, the control of the electro-hydraulic proportional directional valve is realized. 5.4 Software design of the automatic control system According to the control requirements of the automatic control system, the entire software system is composed of a main program module, an infrared detection module, an external interrupt module and a communication module, and is programmed in the C51 language. The design idea is as follows: firstly, the system is initialized when starting up, the infrared detection system is started and the current cotton plant height value is measured, the collected data is sent to the single-chip microcomputer for processing, and the position sensor detects the hydraulic cylinder position information, and sends the single-chip RAM memory. Finally, the single-chip microcomputer compares the measured cotton plant height value and the hydraulic cylinder position information, controls the proportional amplifier according to the PID control algorithm strategy, and amplifies the hydraulic directional valve oil and oil by the proportional amplifier, thereby controlling the cutter The lifting amount makes the cutter highly stable within the set control range. The design main program flow chart is as shown in Figure 6.5. The conclusion is based on the 12-group group-controlled single-line profiling cotton topping machine. With the AT89C52 single-chip microcomputer as the core, the cotton plant height automatic detection and the cutter height automatic control system are designed to solve The manual manual control of the height of the topping height enables the system to automatically control the height of the cutter off the ground according to the height of the cotton plant detected by the infrared sensor. The system has a simple structure and is easy to implement. Applying the control system on the 3MDZK-12 group-controlled single-row profile cotton topping machine can automatically adjust the cutter according to the change of cotton plant height, improve the automation level of cotton production and reduce the labor intensity of agricultural workers.
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