Development of a robotic weed control system for greenhouses

In this study, a robot prototype that moves on a monorail was designed and developed using analytical and experimental methods. It’s purpose was weed elimination between cucumber plants inside the greenhouse plants since there is not much research done for a robotic weed control in a cucumber greenhouse. The plants are cultivated in one row and the distance between two plants is about 40 cm. The distance between two rows is almost 1 meter. The soil type of the cucumber greenhouse was sandy loam soil. The robot benefits from 3 arrays of ultrasonic sensors for weed detection and a PIC18 F4550-E/P microcontroller board for processing. The feedback from the sensors activates a robotic arm which moves inside the rows of the cucumber plants for cutting the weeds using rotating blades. Fifty four experiments were carried out inside a greenhouse to find the best combination of arm motor (AM) speed, blade rotation (BR) speed, and blade design. Three BR speeds of 3500, 2500 and 1500 rpm were assigned. The selection of the BR speeds was based on the previously published results on rotary movers, and two AM speed of 10 and 30 rpm to three blade designs of S-shaped, triangular-shaped, and circular-shaped. These blades were selected due to their availability, low cost, and their performance during the initial test experiments. The results of analysis of variance indicated that different types of blades, different BR speed, and different AM speed had significant effects (P < 0.05) on the percentage of weeds cut (PWC). However, no significant interaction effects were observed. The comparison between the interaction effect of the factors (three blade designs, three BR speeds, and two AM speeds) showed that maximum mean PWC was equal to 89% with standard deviation of 3.9% and was achieved with the S-shaped blade when the BR speed was 3500 rpm, and the AM speed was 10 rpm. Using this setting, the maximum PWC that the robot achieved in a random experiment was 95%. The lowest as observed with the circular-shaped blade (mean of 45.66% and SD=1.86) which resulted from BR speed of 1500 rpm and AM speed of 30 rpm. This study can contribute to the commercialization of a reliable and affordable robot for automated weed control in greenhouse cultivation of cucumbers.

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