| Spraying for fruit trees is the main link in fruit production chain.Automatic pesticide application can effectively improve the efficiency of spraying for fruit trees.As an important part of plant protection machinery,orchard automatic dispensing device has a wide development prospect.At present,most of spraying for fruit trees in China is done by manual operation with low efficiency and poor application quality.A few orchards use a fixed boom sprayer for spraying to improve the work efficiency,but pesticide deposition rate is low and pesticide residues in the soil are large,which will damage the ecological environment of the orchard seriously.In order to realize the precision spraying in hilly and mountainous citrus orchards,principle of combining agricultural machinery and agronomy was applied to solve problems such as poor quality in orchard spray,low efficiency in application,strong labor intensity,environmental pollution.On the basis of consulting the relevant documents and information at home and abroad,this paper compared and analyzed the performance characteristics of all kinds of sprayers from four aspects:the structure design,the target scheme,the air delivery mode and the spraying quality.A bidirectional automatic spraying system with adaptive ability for the hilly and mountainous citrus orchards was designed in this paper.The main work is as follows:(1)An injection mode and automatic target capture scheme of the bidirectional automatic spraying system for citrus orchard was formulated.This paper designed three different spraying models for different citrus orchards and different growth condition of fruit tree,namely,vertical spraying mode,45 degrees spraying mode and the mode of ground spraying,which could meet the requirements of different orchards.A scanning automatic target was used to realize the location of the canopy position.When signal of the canopy was detected,the system would shoot at the target,according to the height of the fruit tree and the distance between the spraying rod and the canopy of the fruit tree,the spraying rod could move up and down,left and right.(2)Creo 2.0 was used to draw the three-dimensional mode of bidirectional automatic spraying system for citrus orchards.To optimize parameters of the system and meet the demands of design,switching mechanism of the system modes,combined distance measurement module and high pressure atomization system were analyzed and calculated.The interference of ultrasonic wave velocity angle to the detection signal was reduced furthest and the problems of flow resistance and pressure compensation were solved.(3)This paper designed the automatic control hardware circuit,wrote the automatic control program,and realized the communication between modules through the IIC bus.A combined ranging module composed of ultrasonic sensors and laser diode array were proposed in our work,which could detect spatial position signal of fruit tree canopy structure and improved the data rate and target accuracy.In order to coordinate the three aspects of combined ranging module,automatic control system and structure subject,to solve the problem of motor response ahead or lag,the paper adopted a speed synchronization module to carry out real-time detection of crawler tractor speed and control the program processing time and the motor response time.(4)By means of spraying test,data of the horizontal range,spraying swath and flow level was tested.The experimental results showed that under the condition of4.168MPa pressure provided by liquid power unit and 4000r/min of centrifugal fan,the single side effective injection distance of the system could reach up to 3.5m,the single side spraying range was up to 2.5m,and the average flow rate was 343L/h.(5)Taking the average droplet coverage as the main evaluation index,and the deposition density as an auxiliary index,a field test was held in citrus orchard when speed of the crawler-type walking tractor was 3m/s,air-feed strength reached 5m/s,and distance from the high-pressure atomizing nozzle to the canopy was 0.5m.Experimental optimization design method was used to analyze the spraying effects and obtain the optimal engineering parameters.The test results shows:1)When the average height of fruit trees is more than 2.5m,the bidirectional automatic spraying system is selected as the vertical spraying mode.The crawler walking tractor has a running speed of 5m/s,wind strength is 5m/s,the high pressure atomizing nozzle component to the canopy distance is 0.5m,the average coverage rate of the positive surface of the fruit tree can reach 84.9%,the droplet deposition density is117drops/cm~2,the average coverage rate of the negative surface of the fruit tree canopy is 38.6%,the droplet deposition density is 53drops/cm~2.In the distance of the canopy surface at depth of 0.625m,the average canopy coverage rate of the positive sides is49.1%,the droplet deposition density is 72drops/cm~2,and the average canopy coverage rate of the negative sides is 12.9%,the droplet deposition density is 33drops/cm~2,the average coverage rate of the positive spraying on the axial plane of the tree trunk is13.3%and the deposition density is 28drop/cm~2.2)When the average height of fruit trees is from 1.5m to 2.5m,the bidirectional automatic spraying system is selected as the 45 degrees spraying mode.The crawler walking tractor has a running speed of 5m/s,wind strength is 5m/s,the high pressure atomizing nozzle component to the canopy distance is 0.5m,the average coverage rate of the positive surface of the fruit tree canopy can reach 85.5%,the droplet deposition density is 126drops/cm~2,the average coverage rate of the negative surface of the fruit tree canopy is 35.3%,the droplet deposition density is 61drops/cm~2.In the distance of the canopy surface at the depth of 0.375m,the average canopy coverage rate of the positive sides is 52.6%,the droplet deposition density is 89drops/cm~2,and the average canopy coverage rate of the negative sides is 18.1%,the droplet deposition density is40drops/cm~2.The average coverage rate of the positive spray on the axial plane of the tree trunk is 30.5%and the deposition density is 53drop/cm~2.3)When the average height of fruit trees is less than 1.5m,the bidirectional automatic spraying system is selected as the mode of ground spraying,and the spraying span of the ground spraying mode is about 2.3m.The average coverage of fog droplets in all layers met the requirements for pesticide spraying in orchard,and the deposition density of each layer was also consistent with the requirement of not less than 20drops/cm~2 in the prevention and treatment of fruit tree diseases and pests. |
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