International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 05 | May 2022
p-ISSN: 2395-0072
www.irjet.net
Structural Design, Analysis and Optimisation of Robotic Arm Er. Sandeep Chowdhry1 1Engineering
Consultant & Trainer, Chandigarh, India
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Abstract – The structural elasticity and the vibrations in
FEA data for a new high-performance robot arm; 2) to Maximise the Robotic Arm’s natural vibration frequencies; 3) to Minimise the mass of the Robotic Arm. This study aims to contribute to the literature on the Robotic Arm's design, analysis, and optimisation.
the links are two leading causes that significantly affect the performance of the Robotic Arm. This study aims to design a structurally stable Robotic arm with higher natural frequencies and low mass. Finite Element Analysis (FEA) is used to find the modal frequencies. Response Surface Method (RSM) is used to optimise the process variables. The result findings show that link 1 thickness has a more significant effect on the natural frequencies and the mass of the Robotic Arm than the thickness of link 2. Second, to increase the structural strength of the Robotic Arm, link 2 may be designed lighter in weight than link 1.
2. KINEMATIC MECHANISM The band-drive mechanism is chosen for the Robotic Arm. This design provides excellent vibrational characteristics at all joint positions. Moreover, it can be optimised to exhibit fundamental modes that are nearly identical at all joint positions. Second, the design is mechanically simple and easy to fabricate. Third, an optimised band drive design will be significantly lighter than the alternative designs [10]. In this design, both motors are mounted directly on the base to reduce their gravitational and inertial coupling. Link1, the proximal link is directly operated by motor 1 and link 2, the distal link is actuated by motor 2 through 1:1 pre tensioned steel band and pulley arrangement.
Key Words: Robotic Arm, RSM, FEA, Structural Design, Modal Analysis
1. INTRODUCTION In this study, a Robotic Arm is designed for tracking and force control for education purposes. The design objectives for the complete arm include three degrees of freedom, a large (0.98 m to 1.8 m) workspace, 4 kg payload capacity, electrical actuation and mechanical simplicity. Specific design objectives arising from the proposed application include the following 1) Precise joint level torque control; 2) High structural vibration frequencies; 3) High stiffness; 4) Low weight; 5) High static strength. The inclusion of the robot structural strength constraint in the optimisation helps in reducing mass effectively. It also addresses the fatigue limit, a significant concern in robot systems, by conducting fatigue simulation in FEA module [1]. The robotic arm’s structural elasticity and the torque ripple of permanent magnet motors degrade the fidelity of joint level torque control and cause oscillations in the position and force control loops [2]-[6]. [6] suggested that careful motor design and structural design optimisation [7][8] can lead to arm design exhibiting superior force and position tracking performance. When the operating frequency of the system is near the natural frequency is one of the reasons for the system's vibration [9]. Therefore, designing the robtic arm with a high natural frequency is essential. Arm design possessing high structural vibration frequencies while carrying a gripper payload also satisfies the objectives of low mass, high stiffness and high strength [10]. However, it is not clear whether high structural vibration frequencies will automatically optimise the mass of both links. As a result, in this study, high structural vibration frequencies and mass are selected as the response variables. This research aims 1) To present the mechanical design and supporting structural
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3. MECHANICAL DESIGN 3.1 MOTOR DESIGN The electric motor design task is simplified by selecting NEMA 23S stepper motors to drive both the links. It has 2500 rpm, holding torque at peak current of 1.3 Nm, step angle of 1.8° and weighs 0.80 kg.
3.2 LINK DESIGN The length of the two links is selected as 0.49m. The crosssections of both the links are chosen to be square tubular. The outer cross-sectional dimensions of link1 and link 2 are chosen to be 0.13m and 0.94m, respectively. The pulley diameter is 0.16m. The materials used for the links and the pulleys is aluminium-6061 and steel, respectively. Fig. 1 shows the Robotic Arm assembly without a gripper. The finite element method (FEM) based design optimisation procedure described in the next section dictates the local wall thickness of both links.
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