Apple harvesting is one of the most complex and least mechanized processes at present. A picking robot can greatly contribute to the advancement of the apple industry. Among them, the picking manipulator is one of the key components in the picking robot. However, the current apple picking manipulators are limited to the complex structures and low modularity, unsuitable for the multi-arm picking operations. It is necessary to develop an apple-picking manipulator with a larger range of motion, high modularity, and a lightweight structure. Efficient, stable, and flexible operation can often be required to optimize the configuration parameters of the manipulators. Particularly, the space constraints rather than motion performance have been focused primarily on optimization in recent years. In this study, a modular configuration of the apple-picking manipulator was designed to optimize the parameters of the motion performance. Firstly, an apple-picking manipulator was designed to fully meet the operational requirements, according to the distribution of the fruits in orchards. The manipulator consisted of three translational and three rotational joints. Specifically, the three translational joints were used to control the motion along the x, y, and z axes, while the three rotational joints were used to control the rotation along the roll, pitch, and yaw axes. The horizontal and telescoping joints were used to realize the different types of motion in the xoy plane using the joint drive motors 1 and 2 with the translational motion. Secondly, the multiple indices were combined with a single objective function in order to evaluate the operational accessibility, structural compactness, velocity, and load smoothness. The analytic hierarchy was employed to determine the weights of each index. The linear weighting was used to generate the objective function. As such, an optimization algorithm was then proposed using an improved hippopotamus optimization algorithm (IHOA). Among them, the hippopotamus optimization (HO) was employed for the global search in the initial stage, the particle swarm optimization (PSO) was to accelerate the convergence using collaboration and learning within the population, and the incorporated simulated annealing (SA) was to introduce the random perturbations. Finally, the simulation and field experiments were performed to validate the operational reachability, structural compactness, velocity, and load stability of the apple picking manipulator. The simulation results showed that the link lengths of the pitch joint, horizontal joint, telescoping joint, and end-effector revolute joint were 122.02, 138.00, 101.45, and 103.12 mm, respectively. The link offsets of the telescoping joint, end-effector revolute joint, end-effector prismatic joint, and twisting joint were 855.00, 166.67, 189.95, and 126.63 mm, respectively. The installation heights of the lower and the upper picking manipulator were 1344.59 and 2460.00 mm, respectively. The experimental results showed that operational accessibility index F₁, structural compactness index F₂, global velocity fluctuation performance index F₃, and global load fluctuation performance index F₄ were 97.05%, 2 882.74 mm, 0.20 m/s, and 0.15 N·m, respectively. Field experiments showed that the maximum absolute torque increments for the pitch joint, joint motor 1, and 2 with translational motion, and the end rotation joint were 0.51, 0.87, 0.80, and 0.79 N·m, respectively, during picking apples at the boundary points. The maximum absolute velocity increments were 0.03, 0.17, 0.17, and 0.01 m/s, respectively. Therefore, the manipulator demonstrated full accessibility to the boundary positions within an operational range of 890.25 to 1 035.47 mm from the tree trunk. This finding can also provide valuable insights to design the modular picking manipulators for apple harvesting.

Conservation tillage has been one of the most modern agricultural technologies in recent years. Stalk returning and no-tillage seeding have been combined to improve the soil's physical and chemical properties. The soil fertility can also be protected to reduce the soil disturbance for the stalk coverage and crop yield. At the same time, the long-term high-intensity tillage and stalk burning have caused serious erosion with the limited content of soil organic matter in Northeast China. It is highly required for the conservation tillage with the high level of agricultural mechanization. However, the existing anti-blocking device for no-tillage seeders cannot fully meet the high requirement of high-speed no-tillage seeding. In this study, a stalk cleaning device was designed to combine the seeding belts, particularly for high-speed no-tillage seeding. The double-row planting mode of large ridges was also selected in Northeast China. A pair of drive discs and stalk cleaning teeth were composed in the combined device. Among them, the profile of the disc blade was utilized as the normalized curve of variable parameter logarithmic spiral. The dynamic sliding cutting was then realized under the curve operation. The stable angle of the interception curve was achieved at 22.5° during dynamic sliding cutting. The curve number of the blade disc was further determined to be 18 using kinematic analysis. The two sides of each disc were equipped with the stalk cleaning teeth. The stalks were fully cleaned inside or outside the ridge. A systematic analysis was implemented to optimize the structural, spatial, and operation parameters of the stalk cleaning teeth. A series of simulation tests were also carried out to clarify the interaction between the device and the stalk under high-speed operation using the discrete element method. The ridge soil model was established using the Hertz-Mindlin and Bonding models. The flexible body of the maize stalk was designed with lengths of 130, 150, and 170 mm, respectively. The positioning and laying of the stalk were set at different angles. The stalk cleaning performance was evaluated under different declination angles of the device. The range of deflection angles was determined to be 30°-75°. An optimal model of ridge soil was constructed with a stalk covering amount of 1.66 kg/m². The quadratic rotation-regression-orthogonal experiment was carried out using Design-Expert software. The target variables were taken as the operation speed and inner and outer declination angle. The optimal parameters of the device were obtained: the inner and outer deflection angles of the stalk cleaning teeth were 45.3° and 75.0°, respectively. The average working power was 7.653 kW, and the stalk cleaning rate was 95.00%, where the relative errors were 3.06% and 1.35%, respectively. The performance of the device was also verified under different amounts of stalk covering. The stalk covering amounts of 2.06, 1.59, and 0.87 kg/m² were selected in the field experiments, corresponding to the small, medium, and large stalk covering. The field experiments showed that the ideal performance of the device was achieved in the stalk covering amount of 0.87 kg/m² at the operating speed of 3.0 m/s. Specifically, the stalk cleaning rate of the anti-blocking device was 96.1%, and the average operating power was 8.219 kW. Once the stalk covering amounts were 2.06 and 1.59 kg/m², respectively, the stalk cleaning rates of the anti-blocking device were 86.7% and 92.2%, while the average values of operating power were 10.460 and 9.024 kW, respectively. The optimal device has fully met the needs of no-tillage seeding under different stalk covering rates in Northeast China. The finding can also provide a theoretical and technical reference for the anti-blocking devices under high-speed seeding.