# Development of a Combined Orchard Harvesting Robot Navigation System
## 3 Results
### Navigation Experiments  
Based on the results of several orchard experiments in the early stage [44; 45], the robot walking speed was set to 0.5 m/s in this experiment. According to references [38; 57], an experimental scheme of an autonomous navigation system for a combined orchard harvesting robot was designed as shown in Figure 16. The transport (master) and picking (slave) robot of this navigation system starts from the starting point, stops repeatedly between inter-rows of the apple trees, drives out of the rows, turns at the head of the ground, enters the next row of apple trees for operation, and finally stops at the endpoint. The temporary stopping point is the point where the autonomous navigation system of the joint orchard harvesting robot stops in the row of apple trees, and the safety distance threshold between the two robots at this point is 0.35 m. When the combined orchard harvesting robot stops driving, the GNSS coordinate values and heading values provided by the robot are recorded in real-time, the current row spacing values of the apple trees, the distance between the center points of the two robots, the apple trees on the side where the robotic arm is located, and the following distance between the two robots are measured. This stop-drive experiment was repeated three times in the test area. The experimental scenarios are shown in Figure 17.  
The distance from the center of the transport robot to the left apple tree (the robot arm is closer to the left apple tree), and the distance from the center of the picking robot to the left apple tree, are measured, respectively, when the master-slave robot is stopped. Then, the spacing between the rows of apple trees on both sides is measured and, finally, the position deviation of the center point of the transport robot from the center point of the apple tree row (cited as the master's position deviation) and the position deviation of the center of the picking robot from the center point of the apple tree row (cited as the slave's position deviation) is calculated based on the measured values. The position deviation here is taken as the absolute value of the calculated value, as shown in Tables S2, S3 and S5 in the Supplementary Materials. The master-slave robot stopped 40 times in total. The first 20 times were for the master-slave robot to go from the start point to the turning point within the first row, and the last 20 times for the master-slave robot to go from the turning point to the endpoint within the next row. In the first row, there were apple trees on only one side of the apple tree row at stops 3, 5, 10, 12, 15, and 17, and at stops 2, 4, 6, 9, 11, 13, 15, and 19 in the next row. This shows that relying on the detection of apple tree trunks to achieve stops within the orchard rows is reliable, even for the case of missing apple trees on one side. The master's position deviation decreased gradually with the increase in the number of trials, as shown by the decrease in the mean value of the deviation from 0.027 m to 0.02 m. The standard deviation of the deviation decreased from 0.01 m to 0.006 m, indicating a smooth change in position deviation. For example, the position deviation was 0.027 m for the third (missing apple tree) stop in the first trial in row 1, 0.039 m for the fourth stop, and 0.021 m for the fifth (missing apple tree) stop. The same situation occurred successively in the first row and the other unilateral stops in the next row. The maximum value of the position deviation was 0.053 m at the thirteenth stop in the first row and the minimum value is 0.009 m at the ninth stop in the next row. The deviation of the main robot position at both ends of the stop was mostly smaller than the average value. For example, at the first stop in the second row, the position deviation was as low as 0.012 m.  
The slave's position deviation also decreased gradually with increasing number of trials, but the change was not obvious.