Based on the structural shortage of an agricultural labor force and the continuous increase in tomato planting scale in China, as well as the limitation of a greenhouse working environment on the development of tomato picking productivity, a motor-driven end-effector for a tomato picking robot based on a hybrid force/position control strategy was designed. First, a hybrid force/position control strategy was applied to control the picking process. Consistent with this strategy, the mechanical structure design of the end-effector was determined. The maximum torque of the finger joint motor was verified by applying a load to the end-effector fingertip under a parabolic linear angular velocity. Second, the D-H method was used to establish the end-effector single-finger and whole-hand coordinate systems and to perform forward and inverse kinematic analysis. The Monte Carlo method was used to analyze the workspace of the end-effector, and an isochronous interpolation algorithm was used to analyze the angular displacement of the motor. A basic algorithm for starting, stopping and accelerating the finger joints was designed to achieve the smooth movement of the end-effector. The control system for the end-effector was designed based on STM32F103ZET6, and the end-effector remote wireless debugging system was designed based on Tiny6410. Finally, a test prototype of the tomato picking end-effector was manufactured and picking tests were conducted, which showed that our tomato picking end-effector moved smoothly. The proposed control algorithm reduced the impact force and recorded the contact force between the end-effector and the tomato in real time, and the end-effector essentially achieved nondestructive picking. Therefore, our tomato picking end-effector demonstrated good utility in practice.

The tomato picking lifting platform is the carrier for the installation of the picking manipulator, which directly affects the operating range, speed, and picking effect of the picking manipulator. Based on the six degree of freedom motion platform, this paper designs a tomato lifting platform with automatic lifting and automatic leveling functions, which can accurately dock at the designated height to complete the picking operation, and verifies the validity of its parameters and the rationality of the operation movement. First, we analyzed the tomato planting mode and growth characteristics of greenhouse; determined the predetermined trajectory, mechanism travel, and motion form of the lifting platform to complete the lifting process during tomato picking; and determined the basic design parameters of the platform; Secondly, we used SolidWorks to build the three-dimensional model of the lifting platform, and imported it into ADAMS. We used the driving function to complete the dynamic simulation of the virtual prototype of the lifting platform, and obtained the force curve of the electric cylinder and hinge. We analyzed the force on the electric cylinder and hinge of the lifting platform to determine the rationality of the device design. Finally, according to the design requirements and simulation data, we made the prototype of the lifting platform, constructed the motion control system, and carried out relevant experiments. The experimental results show that the maximum rotation angle around the x, y, and z axis is ±10°, the maximum lifting distance is 15 cm, and the maximum load is 50 kg; meanwhile, the average time for the system to reach steady state is 0.309 s, the in-tilt error increases with the increase in biaxial tilt angle, with the maximum error of 1.09°, and the maximum mean square root error of 0.119°, which can meet the automatic operation requirements of the tomato picking manipulator.