Published at : 10 Jul 2024
Volume : IJtech
Vol 15, No 4 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i4.6559
Louie Villaverde | Department of Mechatronics Engineering, Rajamangala University of Technology Thanyaburi 39 Moo 1, Khlong 6, Khlong Luang Pathum Thani 12110 Thailand |
Dechrit Maneetham | Department of Mechatronics Engineering, Rajamangala University of Technology Thanyaburi 39 Moo 1, Khlong 6, Khlong Luang Pathum Thani 12110 Thailand |
The increasing
demand for automated equipment for precision and versatility requires innovative methods in manufacturing. Despite the high demand, the design and development of industrial robot systems are costly, showing the
importance of improving design
conceptualization phase. Therefore, this study aimed to address the need by developing an industrial welding robot using a
parametric and kinematic modeling method. The
investigation focused on the design of six degree of
freedom (6DOF) industrial robotic arm for arc welding, exploring kinematic
model and dimensional parameters of robotic structure. Computer-aided design
(CAD) was
applied for modeling and analysis, using Denavit-Hartenberg (DH) convention
for mathematical analysis of link and frame movements. This study introduced forward kinematic simulation, which
included exploring the position and orientation of the end effector regarding the joint angular values and link
parameters. Furthermore, the development of kinematic model of robotic
mechanism was proposed to describe the behavior of
the physical system compared to an actual robot assembly. Due a reduction ratio of 80 from a rated
torque of 22 Nm at a 2000r/min
input harmonic drive, the system
mechanism was fabricated and assembled. The results showed
that robot successfully performed welding process, as indicated by tests carried out using a four-point movement. Moreover, further separate studies should be conducted to assess the quality of welds.
Industrial robot design; Kinematic model; Parametric modelling; Robotic simulation
Industrial robot applications are improving product quality due to their reliability and precision in motion
Consistency in
achieving high quality makes robotic welding advantageous to
manual operation, thereby
conferring a competitive edge
to industrial
applications, particularly
automating the process (Wu et al., 2015).
Examples of the demand for robotic arc welding are the automotive industry and
electronics manufacturing assembly lines(Kah et al., 2015). This robot
executes the programmed commands to perform welding operations with minimal
human intervention (Dinham and Fang, 2013), although there is a challenge in designing and fabrication. Recently, standard commercial robot has been
available for deployment in the industrial setup (Bilancia et al., 2023), leading to the development of
the mechanical design of robot in this study. Building
an industrial robot requires a significant
amount of initial financial investment,
as conceptualization
plays an essential role
in minimizing
developmental costs(Wang et al., 2024). Therefore, this study aimed to contribute to the
cost-effective and optimal development of custom industrial robot.
Based on
the background above, this
study focused on designing and assembling robot system for
welding applications,
considering standard methods (Vasilev et al., 2021).
The design of robot for industrial applications starts with the mechanical
structure (Zeng, Liu, and You, 2019), which includes the
configuration of robot mechanism using kinematic modeling. In this context, the configuration of six degree of
freedom (6DOF) robotic manipulator is suitable for industrial processes such as
welding. Therefore, the
analysis of the movement of end effector position and orientation is based on
the rigid component’s measurements and joint angle (Nektarios and Aspragathos, 2010).
The custom
mechanical design of robot also contributes to the concept of industrial
modularity and ease of fabrication. The
development process is carried out to construct a parametric model of
the industrial welding robot including the parameters’ topology (Zhang et al., 2022). To optimize the movement or
rigidity characteristics, adjustment was
made to these parameters, and selection was based on
the dimensions conceived from the developed kinematic model(Russo et al., 2024).
This study also applied a paradigm shift in the
optimization of robot characteristics through the derivation of parameters
using the developed kinematic model and simulation.
Several studies have been conducted on design of
industrial robot. For
example, (Li
and Wang, 2019) used genetic algorithm for optimization,
while (Jiang et al., 2020) focused on accuracy improvement using
artificial networks by algorithm with differential evolution. Furthermore,
there is a study on selecting industrial robot used for arc welding (Chodha et al., 2021) through the implementation and presentation
of simulated and actual experimental results. According to
This
study is significantly different from previous
investigations by including
comprehensive kinematic and parametric modeling in the development of industrial robot. Conceptualization
of new hardware components for industrial robot application is simplified using simulated
models. The use of computer system can
help save
the cost associated with the
building process. Moreover, modeling kinematic before developing robot control is significant, as these models are
categorized as forward and inverse kinematic (Farzan
and Desouza, 2013). The pose is described using a
set matrix or vectors in Cartesian coordinate system, with kinematic model having
constraints such as joint angle, link length, inertia, etc(Andersen, 2020). The joint variables measured in
angles for each link directly reflect end effector pose (Pham et al., 2018).
The challenge of this study is to design the dimensions and physical components
of each link based on analysis of kinematic model described using lengths and
Denavit-Hartenberg (DH) convention.
In this study, kinematic model leading to the physical structure is
presented using the software.
Establishing a conceptual kinematic model is important to design the desired
motion of robotic system
The contributions made in this
study included (1) the effect of kinematic on the
position of welding torch. (2) A new industrial welding robot design based on
revolute joint was fabricated and assembled along with essential parts
including links and servo motors, as a
custom-made welding robot developed first in Thailand. Changing the joint angles of each axis affected the position and orientation of
the end-effector, namely
welding torch. This was because the integration of robotic components
from a design in Thailand to fit an industrial application such as welding was
considered
more economical.
This study was organized as follows, Section 2 discussed methods of the mechanical structure, kinematic model, and forward
kinematic model. Section 3 presented
the results and discussion, while Section 4 concluded this study and presented
future endeavors.
2.1. Mechanical Structure
The
criteria for designing a custom-made robotic arm were established by considering a serial robot configuration and range of
motion to determine the dimensions of each link. Industrial robot joints could be prismatic or revolute, depending on the application. In
this study, the
configuration of joints is all revolute, which was in line with the common standard of industrial welding. The
anthropomorphic structure was
composed of the waist, shoulders, elbows, also wrists, which corresponded to the joints of the human arm
Figure 1 Anthropomorphic
Arm Configuration
Table 1 Robotic Arm Specification
Feature |
Description |
Range of Motion (ROM) |
Wrist - Pitch: 180°, Roll:180°, Yaw:180°,
Elbow: 130°, Shoulder: 110°, Waist: 180° |
Table 2 Link Lengths and Offsets
Joint |
Waist |
Shoulder |
Elbow |
Wrist |
Symbol |
L1 |
L2 |
L3 |
L4 |
Link Length (mm) |
635 |
650 |
455 |
421 |
2.2. Forward Kinematic (FK)
Forward
kinematic is the study
of describing the position and orientation of the end effector in terms of the
joint angular values and link parameters (Vacharakornrawut et al., 2016; Mehmood et al.,
2014). This can
be solved by determining the
homogeneous transformation matrix through
the combination of
the rotational matrix and the displacement vector. Moreover, the mathematical solution of forward
kinematic is based on DH parameters (Bian, Ye, and Mu, 2016). The
convention is a maturely recognized parameterization for industrial robot
modelling (Zhao et al., 2018), which is carried out by computing the product of the
homogeneous matrices resulting in the final transformation matrix (Ritboon
and Maneetham, 2019). The product is
used to identify
the pose of the end effector,
given the joint parameters,
in the form of Special Euclidean (SE) (3) or 4x4 homogeneous matrix
composed of the rotation matrix and displacement vector. The initial step in determining forward kinematic of the manipulator is categorizing each frame
using DH parameters (Bouzgou
and Ahmed-Foitih, 2014), which is called kinematic model as shown in Figure 3. The construction of kinematic model follows the right-hand rule and DH parameters can be found based
on the frame assignment, as
shown in Table 3. Each column is assigned for specified parameters, named joint angle angle of twist link offset (d), and link length (a). This is carried out to precisely determine the spatial
configuration of robotic arm by establishing kinematic model and applying
forward kinematic simulation, thereby
contributing to the prototyping
process of 6DOF robotic arm (Ekrem and Aksoy, 2023).
Figure 2 Robotic Arm Configuration showing major
mechanical components and direction of articulation
Figure 3 Kinematic
Model of the Robotic Arm with dimension
Table 3 DH Parameter
Equation 1 shows the general formula of the transformation matrix,
The general formula was applied to respective components from DH parameter
table. The substitution of the values corresponding to
respective joint and link parameters led to individual transformation matrix per coordinate
frame. Simulation and modeling were made to validate the equation and analyze
kinematic of robot arm using MATLAB software.
Equations
2-7 are substitutions of the values each respective frame. The application of
the equation to 6DOF robotic arm manipulator includes the multiplication for respective
transformation matrix. The
result is reflected in matrix
2.3. Post Processor
The tasks of the system for
translating the joint angles to the specific tool location were designed in the
post processor stage. In this section, the mechanism of transformation was
discussed. Initially, the post processor of robotic arm was developed using
Programmable Logic Control (PLC), with servo motors executed through drivers as
the final actuating elements. The ladder logic design focused on transmitting
signal from GUI, which showed the joint angle of the axis, along with the tool
position. To ensure the program executed the intended position and orientation,
ROM was considered along with workspace requirements and coordinate system
relating to the physical world. Calibration of each axis joint angle with the
servo motor was carried out by checking the angle against the corresponding
feedback from drivers’ encoders. Simulating each corresponding angle by jogging
axis using robot pendant was performed to verify the response of the servo
motor driver and motors. Subsequently, data collection was carried out by
recording the angles versus input feedback from the servo motors’ absolute
encoder.
3.1. Forward Kinematic Simulation
Kinematic simulation model was
performed using MATLAB Robotics Toolbox. The numerical results, combined with a
visual plot of robot's pose in MATLAB software, provide a comprehensive
knowledge of the end
effector pose. The results have been plotted using various joint angles as
inputs to the forward kinematic
model and MATLAB Robotics Toolbox. Subsequently,
visual simulation is performed by feeding the four parameters
derived from the six links using the software.
The process is carried out with
several different joint configuration value scenarios. The first scenario, [0 0
0 0 0 0] results in the position of the xyz end effector at [421 0 1740] with a
yaw, pitch, and roll of
[0 90 180]. This is followed by
matrix value generated using the first scenario, while the results of robot arm
simulation plot are shown in
Figure 4 and Equation 9.
Figure 4 Visualization
from Plot function for [0 0 0 0 0 0] configuration
The second scenario with the value of the joint angle
configuration is set to [-15 -15 -15 0 0 0], followed by the xyz end effector position
[734 -196.8 1446.39] and the yaw pitch roll end effector value [28.2 56.8
155.9], as
shown in Figure 5 and Equation 10. Subsequently, matrix and simulation plots are
obtained from
scenario.
Figure 5 Visualization from Plot function for [-15 -15 -15 0 0 0] configuration
Figure 6 Visualization
from Plot function for [-30 -30 -30 0 0 0] configuration
Forward
kinematic is an essential requirement in building industrial robot to establish
the relationship between the joint angle and tool position. Furthermore,
it serves as a fundamental
theory during the development of
robotic arm, particularly when the application does not require autonomous
control. In this study, MATLAB was used for simulation and analysis
3.2. Parametric Modeling
This study is
divided into
two stages, namely design
and implementation. CAD software is used
during the design stage to create 3D models
One of the contributions of this study is a novel design of 6 DOF
industrial robotic arm,
presented in Figure 7, as
2D parametric model of (a) elbow
link (b) wrist link, and (c) shoulder link. Figures 8 (a), (c), (e), (g), (i), and
(k) are the results of 3D model design using CAD application, while (b), (d),
(f), (h), (j), and (l) are the actual robot implementation. The total weight of
the mechanism including the motors is
155 kilograms. There is an application of the harmonic gear concept in Figures
8 (i) and (j), while Figures 8 (k) and (l) are the
design of the end effector link model
to enable movement in
roll and pitch. Moreover, the system
has a reduction ratio of 80 from a rated torque of 22 Nm with a 2000r/min input.
Figure 7 2D
Parametric model. Components labeled as (a) Elbow link, (b) Wrist link, (c)
Shoulder link
Figure 8 3D model and Actual. These images
are components, which are labeled as (a)Base Model, (b) Actual Base,
(c)Shoulder Link Model, (d) Actual Shoulder Link, (e) Elbow Link Model, (f)
Actual Elbow Link, (g) Wrist Link, Model (h) Actual Wrist Link, (i) Servo Motor
and Harmonic Gear Model, (j) Actual Servo Motor and Harmonic Gear, (k) End Effector Link Model, (l) Actual
End-Effector Link
3.3. Implementation
Figure 9 shows the schematics and control box, which consists of six
servo motors connected to three servo drives, with robot's CPU being
a Beckhoff C5102-0040. Additionally,
the Ehave-CM350 serves as welding
machine that is connected to the IO Device through USB cable for
remote control. The arm is fully driven with each DOF achieved by a precision
servo motor equipped with a three-phase synchronous motor excited by a
permanent magnet. The specifications of
the servo motor used are shown
in Table 4.