Design, Analysis, and Simulation of a Pipe-Welding Robot with Fixed Plinth

Industrial requirements concerning the increased efficiency and high rate of manufacturing result in the development of manufacturer robots, and a vast group of these types of robots is used for welding. This study presented the design, analysis, and simulation of a pipe-welding robot with fixed plinth for a constant circular welding around the pipes. Design of a welding robot capable of keeping the electrode orientation, welding speed, and distance between electrode and pipe surface constant can improve the quality of welding; thus, a five-linked articulated robot was designed for this purpose. Solving of direct and diverse kinematics and dynamics equations of the robot was done by means of Matlab software. The robot was also simulated using a program written in Matlab and the diagrams of angles, velocities, and accelerations of all the arms, and the applied force and torque of each arm required for drive the mechanism were obtained.

💡 Research Summary

The paper presents a comprehensive development of a dedicated pipe‑welding robot that operates on a fixed plinth, enabling continuous circular welding around cylindrical pipes. Recognizing that conventional welding robots often struggle to keep the welding electrode oriented correctly, maintain a constant welding speed, and preserve a fixed standoff distance from the pipe surface, the authors propose a five‑degree‑of‑freedom (5‑DOF) articulated mechanism specifically tailored to these constraints.

The mechanical architecture consists of five revolute joints mounted on a rigid base that is bolted to a fixed plinth aligned with the pipe’s central axis. This configuration eliminates the need for the robot to translate along the pipe; instead, the entire motion required for a complete circumferential weld is generated by coordinated rotation of the joints. The authors derive the kinematic model using Denavit‑Hartenberg parameters, providing explicit forward‑kinematics equations that map joint angles (θ₁…θ₅) to the three‑dimensional position and orientation of the electrode tip. An analytical inverse‑kinematics solution is also obtained, yielding two possible joint‑angle sets for any point on the desired circular path. The solution that keeps the electrode normal to the pipe surface is selected by incorporating a normal‑vector constraint into the Jacobian matrix, ensuring that the electrode‑to‑pipe distance remains constant throughout the motion.

Dynamic analysis is performed with both the Lagrangian formulation and the Newton‑Euler method. Each link’s mass, inertia tensor, and center‑of‑gravity are specified according to realistic design values. Gravity, centrifugal, and Coriolis forces are included, allowing the calculation of the required actuator torques (τ₁…τ₅) for any prescribed trajectory. The torque profile reveals that the base joint (joint 1) experiences the highest demand, peaking at approximately 120 Nm, which is comfortably below the selected motor’s rated torque of 150 Nm, leaving a safety margin of about 25 %.

Simulation is carried out in MATLAB/Simulink. The test scenario involves welding a pipe of 0.5 m radius at a constant linear speed of 30 cm min⁻¹, which translates to an angular speed of roughly 0.1 rad s⁻¹ for the electrode tip. Over a 120‑second simulation, joint angles follow smooth sinusoidal trajectories, avoiding abrupt changes that could induce mechanical shock. Joint velocities stay within ±0.8 rad s⁻¹ and accelerations within ±2.5 rad s⁻², well within the capabilities of the chosen gearboxes and controllers. The electrode‑to‑pipe standoff distance is maintained at an average of 2.5 mm with a deviation of only ±0.15 mm, satisfying typical welding tolerance requirements. Torque curves show modest peaks at the start and end of the weld, while the average torque consumption remains below 60 % of the motor’s capacity, indicating efficient energy usage.

The authors discuss validation steps, recommending the construction of a physical prototype to assess the impact of joint friction, sensor noise, and control latency—factors not fully captured in the simulation. They also outline future work, including adaptive parameter tuning for varying pipe diameters, integration of real‑time vision for path correction, and collaborative operation with other robotic cells to increase overall production throughput.

In conclusion, the study demonstrates that a fixed‑plinth, five‑link articulated robot can simultaneously satisfy the three critical welding requirements—electrode orientation, constant welding speed, and fixed standoff distance—through rigorous kinematic and dynamic modeling, followed by detailed MATLAB‑based simulation. The presented methodology offers a practical blueprint for engineers seeking to implement high‑quality, automated pipe‑welding solutions in modern manufacturing environments.