| China is the largest apple producer in the world and the apple industry is an important part of the fruit industry.Apple is still mainly hand-picked and the picking work is labor-intensive.It needs to be picked in time,which requires lots of picking workers.In order to enhance the level of automation of apple picking in our country,supported by the National Natural Science Foundation of China,under the project of “ Research on picking method of high efficiency for apple picking robot based on fast vision servo control in multiple-illumination environment “(Project No.31571571),the research integrated image processing,motion control,data communication,sensor technology and other technologies to the design and building of the apple picking robot.The main research contents and results are summarized as follows:(1)A PRRRP five-DOF manipulator and an end effector were designed for the apple picking robot.The first degree of freedom was the degree of freedom for lifting and lowering,and the height of the robot base had to be manually raised.The middle three degrees of freedom were rotational degrees of freedom.The last one was the pneumatic push rod controlled by the Festo pneumatic servo control system,which was the biggest unique innovation of this apple picking robot.In order to increase the mobility of the apple picking robot,the traveler No.4 mobile car produced by Beijing upteck harmony Technology Co.,Ltd.was purchased and the manipulator was mounted on it.An end effector was designed for apple grasping,and installed at the end of the pneumatic push rod.Advantech IPC-611 IPC was purchased to run the control software.(2)The installation of various types of sensors on the end effector was finished.In order to amplify the sensor signals,signal conditioning circuit was designed by the Altium Designer 13 software,and the circuit board was welded by hand.KPCI-847 H data acquisition card was used to transfer signals.(3)Parameters of Delta A2 servo driver were configured,and serial communication program was written in Visual Studio 2013 to establish the communication between the IPC and the A2 servo driver.Hardware assembly of Festo pneumatic servo motion control system and establishment of a stable pressure source of 0.8MPa were completed,and OPC communication program was written in Visual Studio 2013 to establish the communication between the IPC and the axis controller CMAX.The speed response curve of the pneumatic push rod was optimized by Festo configuration tool FCT to ensure the rapid and stable operation of the push rod.(4)An image processing algorithm for apple recognition and localization was proposed,and the algorithm was programmed by using Open CV2.4.10 in Visual Studio 2013 to obtain the pixel difference between the center point of the apple and the center point of the image,which was the input variable of the Delta A2 servo motion control system.(5)The control software was written in VC++ programming language.Positioning accuracy of the control system of the apple picking robot was evaluated through laboratory experiments.Experimental results showed that the apple picking robot can automatically and accurately target apple center point and the positioning accuracy was less than 10 pixels,and the Festo axis controller CMAX can control the position of the pneumatic push rod precisely,with the control error within 1mm.Through experiments,it was verified that the apple picking robot's control strategy was in line with its mechanical selection and can meet the requirements of actual apple picking. |
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