Design And Experiment Of Grape-picking Device With A Grasping And Rotary-cut Type Of Underactuated Double-fingered Hand

Grape is a kind of clustered growth berry fruit.The fruit has thin skin,large grain,less juice,more water and it is easy to be damaged,which mainly relied on manual picking,and high labor intensity.With the transfer of agricultural labor force to other industries,and the aging of the population,the shortage of labor is becoming more and more prominent.Therefore,it is of great research value and practical significance for grape production to develop the key technology of grape picking robot.According to the growth characteristics of grape vertical suspension and flexible non-damage grape-picking,a kind of grape-picking device with a grasping and rotary-cut type of underactuated double fingered hand was developed based on the underactuated principle and cooperative working mode of grasping and rotary-cut.The device mainly comprises an underactuated finger mechanism,a rotary telescopic mechanism,a rotary cutting mechanism,a wrist connecting disk,a Intel RealSense solid sensing camera.The RealSense camera is used to locate the fruit and fruit stalk accurately,and the picking device is guided by the manipulator to the fruit,an electric motor drives a double fingered hand with four knuckles by a linkage mechanism,and the hand approaches from the middle of the grape and envelopes it.To realize the separation of the fruit from the stalk,its rotary-cut device installed on the hand drives the cutting disc to cut off the stalk by the rotating and telescopic motion.Based on this design idea,the research on the equipment of under actuated double fingered hand grape picking was carried out:1)According to the requirements of flexible and nondestructive grape-picking,and considering the factors such as the growth characteristics of grape vertical suspension,biological characteristics and agronomic traits,put forward the overall design scheme of grape-picking device with a grasping and rotary-cut type of underactuated double fingered hand.the three-dimensional model is established by Solidworks software,and the mechanism of the picking device is integrated.Based on the design and calculationof the motor of the rotary cutting device,the suitable motor is selected according to the material of the step motor,and the possibility of the motion control of the device is verified.2)The dimensions and rotation angle range of two knuckles of underactuated finger mechanism are firstly determined by analyzing equatorial diameter of grape.Then,the static model of the underactuated finger mechanism was established,and the driven linkage size was determined according to the requirements of optimal force transfer and well-distributed contact force.Combining with the contact force analysis and squeezing-bursting test of the grapes,maximum contact force of grasping 2 kilogram grape without damage was obtained and equal to 20 Newton.Thrust force of the electric motor was obtained by solving the static model of the underactuated finger mechanism,and type choice of the electric motor was directed according to the thrust force.And the simulation analysis of the motion posture and grasping action is carried out by using Adams,the accuracy of the static force model is validated preliminarily.3)Firstly,the hardware composition of the control system of underactuated double finger hand grape picking device is introduced.Then the circuit main controller module,USB USART module and power module based on STM32F103ZET6 MCU are designed.Based on the Keil uVision5 software,the software programming of the maximum contact force control,the motion limit control and the step motor acceleration and deceleration motion control is carried out.4)The physical model machine of the underactuated double fingered hand device is manufactured and it is installed the end of mechanical arm.The accuracy of the static force model was further verified by the experiment of grasping the grapes with the underactuated two fingered hand device.By picking 50 bunches of grapes with the equatorial diameter range of 95 mm to 200 mm,the results of grape-picking tests showed that the picking success rate of the device is 100%,the crush rate is 5.2%,and average cost time of the device is 12 seconds without including time consuming of vision localization of grape and its stalk to complete a grasping and rotary-cut motion.The motion of the rotary-cut device was realized by adopting the control mode ofacceleration and deceleration,cutting disc can effectively cut off the stalk with the speed of 1000 to 1300 rotations per minute.