Development of a prototype of weeding robot

Weeds, or wild grasses, are naturally occurring grasses that grow in the wild without human cultivation. Weeds have detrimental effects on soil and crops, including competing with crops for space, nutrients, light, and moisture in the soil, which ultimately reduces crop productivity. Typically, herbicides are used to eliminate weeds, but all of these chemicals carry a potential threat to human well-being. This article presents a detailed plan for building a DELTA robot that is specifically engineered to eliminate weeds in agricultural environments. This article presents a systematic approach encompassing research, kinematics calculation, robot control, and the fabrication of a weed-killing robot prototype. The article proposes a prototype of a weed-killing robot with simple operation suitable for Vietnam’s economic conditions. The experiments show that the robot can effectively remove different types of weeds from lettuce fields. The results show that the proposed prototype is completely capable of replacing humans, helping to improve productivity as well as protect health and help farmers avoid unwanted effects from herbicide chemicals.


Introduction
The current advancements in science and technology are rapidly progressing, resulting in major transformations in the area of industry.The implementation of automation across all industries involves the substitution of human labor with machines, resulting in enhanced labor productivity, output, and product quality [1][2][3][4].Hence, the utilization of manipulators, commonly referred to as robots, in manufacturing is highly prevalent due to their ability to fulfill the aforementioned criteria [5][6][7][8][9].Robots possess numerous benefits, particularly in terms of their superior quality and precision [10][11][12][13][14][15].Additionally, they offer significant economic efficiency and are capable of operating in hazardous environments that are inaccessible to humans [16][17][18].The jobs necessitate meticulousness, precision, and dexterity, demanding exceptional worker proficiency.Crucially, robots, unlike humans, are not susceptible to stress, enabling them to work continuously throughout the day [19][20][21].
Weeds, or wild grasses, are naturally occurring grasses that grow in the wild without human cultivation, as shown in the figure 1.They typically exhibit rapid growth and have the ability to thrive in various soil conditions, including those that are infertile or polluted.Weeds have detrimental effects on soil and crops, including competing with crops for space, nutrients, light, and moisture in the soil, which ultimately reduces crop productivity.Additionally, weeds negatively impact the quality of agricultural products and pose risks to human and livestock health.Contaminating and impeding water sources; Certain weed species serve as habitats or hosts for pests and microorganisms that are responsible for causing plant diseases [22][23][24][25][26][27][28].
Of the methods commonly employed thus far, manual methods (hand weeding) are frequently cited, but their applicability is limited to small areas with low grass density [29][30][31][32][33]. Presently, the utilization of chemicals for weed eradication is widely regarded as the most efficient approach due to its labor-saving nature, rapid applicability on a large magnitude, and flexibility in timing [34][35][36][37][38].It is less fatiguing and demanding compared to other methods of weeding.
However, it is important to note that all herbicides in Vietnam consist of highly toxic active components, including Dichlorophenoxyacetic acid (2,4-D), Propanil, Atrazine, Butachlor, Glyphosate [39].These substances not only emit an unpleasant odor, but they are also potent drugs that can cause significant harm if mishandled.Both humans and animals are being subjected to toxic substances.Presently, herbicides mentioned above are the most prevalent choice among farmers.However, these drugs have a significant propensity to induce blood, lung, and prostate cancers [40][41][42].
Therefore, the utilization of robots for weed eradication holds great significance, as it not only enhances agricultural output but also safeguards the well-being of farmers.The utilization of robots for weed killing has become commonplace worldwide [43][44][45][46][47][48][49][50][51][52].Nevertheless, the utilization of these robots remains uncommon in Vietnam due to the relatively high cost of these machines, which is not affordable for the majority of Vietnamese farmers given the prevailing economic circumstances.
Vietnamese scientists have conducted many studies on the development of robots to serve with various activities in daily life [53][54][55][56].However, there has been limited research on the creation of weed killing robots specifically for agricultural purposes..This article presents a detailed plan for building a DELTA Robot that is specifically engineered to eliminate weeds in agricultural environments.This article presents a systematic approach encompassing research, kinematics calculation, robot control, and the fabrication of a weed-killing robot prototype.Robots possess the capacity to autonomously perform tasks in expansive areas, harness solar power, and operate in challenging environments that are arduous for humans to endure over extended durations (such as exposure to sunlight, rain, etc).Optimal productivity and efficiency in agricultural production.

Methodology Delta parallel robot structure
The Delta parallel robot has three degrees of freedom.Figure 2 illustrates the constituent parts of the Delta robot, which comprises three closed-loop kinematic linkages.The parallelogram configuration provides a consistent alignment between the fixed plate and the movable plate.The ultimate operational phase of the robot is positioned on the mobile platform.Delta robots are capable of manipulating objects within a 3-dimensional Cartesian coordinate system.
The upper section of the robot is directly connected to the motor to ensure optimal stability.The three motors are securely affixed to the base plate, positioned 120°apart.The lower link of the robot is comprised of two parallel bars that connect the upper link to the movable plate using ball joints.

Kinematic analysis
The purpose of performing inverse kinematics is to precisely determine the angles formed at each joint when the final operation is in a particular position.
The comprehensive system parameters are already identified to encompass: The required angles corresponding to each arm of the robot θ 1 , θ 2 , θ 3 , the total length of each upper link L a , the total length of each lower link L b , and the position are specified.The desired position of the final operation step is indicated by the x-axis, y-axis, and z-axis coordinates, as depicted in figures 3 and 4. Additionally, the distance between the two motor axes is also shown.
The inverse kinematics problem involves determining the values of angles θ 1 , θ 2 , θ 3 given the known position (x, y, z) of the final step in the operation.The reference coordinate systems are established according to the illustrations provided below.It is important to understand that the parallelogram structure is regarded as a connection.Table 1 displays the primary parameters of the Delta robot, including the size of the linkage and the available working area.

Dynamic analysis
The Delta robot is a mechanism with three degrees of freedom, consisting of three rotating links.Each link is connected to both the fixed platform and the moving platform through a ball joint.Modeling the dynamics of parallel robot manipulators is crucial for controlling the motion of the machine.There exist four primary approaches to  simulate the movement patterns of delta robots: The Newton-Euler method, The Lagrangian method, Kane's method, and virtual work.This article uses the virtual work method to calculate the dynamics of the delta robot.
, , ] are the motor torque vector and virtual angle displacement vector, , , ]respectively.represents the virtual linear displacement of the movable plate.The following equations are written by applying the virtual work principle to describe the dynamics of the structure: In which: M m m gl I cos cos cos ) is the gravitational moment vector of the above link.And m a and m b are the mass of the upper link and each connecting bar of the lower link, respectively.I is a 3 × 3 unit matrix.

M
F J M F And then 0 Differentiating the equation over time, the dynamic model of the structure is described as follows: ) is the Coriolis force matrix and centrifugal force, G q ( ) is gravitational force vector.

Designing the motion trajectory of delta robot
Due to their closed-loop structure, parallel robots present a complex forward kinematics problem with multiple solutions.Essentially, to ensure the robot functions as intended, our primary focus is typically on designing the path it follows within its operational environment.
The nth degree polynomial approximation method or the coordinate form are commonly employed in designing a robot's trajectory.This study utilizes a 3rd degree polynomial to determine the robot's trajectory.This selection is made due to the simplicity of the design and its ability to meet requirements, such as maintaining velocity continuity for a smooth trajectory.However, it is important to note that this applies specifically to robots' operation.Figure 5 displays the trajectory of the robot's velocity and acceleration in a cycle time of 1 s.q q ; 3 2 p p -

( )
• Conduct an examination and simulate robot models using the MATLAB Simscape Tool.
The simulation results for the robot's end effector and joints' coordinates and velocities are displayed in figures 7 to 10.As can be seen in figure 7, the motion of the robot is considered in 3 cycles and the total time is 3 s.Coordinate of end effector varies from −100 to 150 mm and from −150 to 100 mm along X and Y axis, respectively.Along Z axis, it changes in a range of (−400; −250) mm.
The line charts of the velocities shown in figures 8 and 9 have shape of circular function with cycle time of 1 s. Figure 8 shows that the velocity of end effector varies from 0 to 0.7 m s −1 while velocity of joints change in a range of (−40; 40), (−32; 32) and (−18; 18) rad/s along the X, Y and Z axis, respectively.
Figure 10 shows that in order for the robot to achieve a velocity of 0.7 m s −1 , the motor must generate a torque exceeding 0.36Nm to drive the joints, while maintaining a speed greater than 40 rpm.The torque of joint T3 is almost 'zero' all the time in simulation.It cannot be definitively established that this is an essential prerequisite for the motor in relation to its torque and speed, it serves as a foundation for ascertaining the necessary parameters for the driving motor in the presence of an extra safety margin.
Examination of the working area of the Delta robot  Limits the range of motion of the joints: ; , -P P ( ) Utilize MATLAB software to simulate the robot's workspace using the results (x, y, z) acquired from the forward kinematics problem.The input parameters for this problem are as follows: f = 100 mm, L a = 165 mm, L b = 340 mm, and e = 50 mm.The working space of the Delta robot can be observed in figure 11.As can be seen that in geometry, the working space of the robot has a shape of 3D paraboloid, the radius of the working space decreases from the top to the bottom.Along Z axis, the end effector moves from the coordinate of −150 to about −500 mm.Along X and Y axis, the working space ranges from −250 to 250 mm.

Structure of Delta robot
The robot consists of 4 main parts described in figure 12: Machine frame system, Operating system, Powertrain system, Electrical and control systems.The operational trajectory of the grass killing location: X Axis: 250.274 mm, Y Axis: 250.274 mm, Z Axis: 250.275 mm.Robot DELTA's frame system design The machine frame system has design dimensions of: 640 × 580 × 645 mm.The machine frame system is made of 30 × 30 mm shaped aluminum.The parts are assembled using square frames and aluminum plates with M6 bolts for fixation, ensuring the perpendicularity of the machine frame system, as shown in figure 13.
Figure 14 illustrates the results of structural simulation analysis and strength testing carried out on the frame system.The results indicate that the maximum stress observed on the frame is 8.15 Mpa, which is significantly lower than the material's stress limit of 195 Mpa.The machine frame ensures both strength and stable operation.

Delta robot design
The Delta robot is responsible for the precise application of chemicals in the field.The Delta Robot employs lightweight materials to minimize its overall weight, thereby enabling smoother and easier movements.
Figure 15 provides an overview of the main parameters of the Delta Robot • The base radius, denoted by f, is 100 mm.It is the distance from the center of the base to the center of each motor shaft.• The length of the upper link, which is the distance from the motor shaft to the robot's elbow, is 165 mm.
• The lower suture length, which is the distance from the elbow to the wrist at the Robot's movable plate, is 340 mm.
• The radius of the fixed plate, denoted as e, is 50 mm, which represents the distance from the center of the plate to the robot's wrist.
• The distance from the base to the surface of the plant area is 500 mm.
• The working range of the robot: • The range of the X axis is from −250 mm to 250 mm.
• The Y axis ranges from −250 mm to 250 mm.
• The range of the Z axis is from −500 mm to −150 mm.

Conclusion
This research article introduces the process of developing a herbicide robot from design, simulation to manufacturing and testing.The article proposes a prototype of a weed-killing robot with low cost and simple operation suitable for Vietnam's economic conditions.The experiments show that the robot can effectively remove different types of weeds from lettuce fields.The results show that the proposed prototype is completely capable of replacing humans, helping to improve productivity as well as protect health and help farmers avoid unwanted effects from herbicide chemicals.

Figure 4 .
Figure 4.The Delta robot's kinematic is in the XZ plane.

Table 1 .
Delta robot parameter.Base radius (f) 100 mm Length of the upper arm (L a ) 165 mm Length of the lower arm (L b ) 340 mm Lower base radius (e) 50 mm Distance from fixed base to floor 500 mm Workspace-X axis From −250 mm to 250 mm Workspace-Y axis From −250 mm to 250 mm Workspace-Z axis From −500 mm to −150 mm Constrain the angles ,

Figure 8 .
Figure 8.Total velocity of end effector.

Figure 11 .
Figure 11.The working space of a delta robot.
Figure 17  shows the input image dataset consisting of 6000 training images (depicting grass and vegetables) with sizes of 640 × 480 pixels, as well as 2000 test images (also depicting grass and vegetables) with the same sizes of 640 × 480 pixels.

Figure 13 .
Figure 13.The machine frame is designed using SolidWorks software.

Figure 17 .
Figure 17.Object labeling for model training vegetable and grass.