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1. HCMC NATIONAL UNIVERSITY
HCMC UNIVERSITY OF TECHNOLOGY
DESIGN OF LINKED ROBOT JOINTS WITH CLOSED-LOOP
CONTROL IN A NEW ROBOTIC SYSTEM
SCIENCTIFIC RESEARCH
Ho Chi Minh City, 2025

2. Team information
Team member:
Name: Nguyen Vu Nguyen (Leader)
Major: Mechatronic Engineering
Name: Vu Ngoc Dinh
Major: Mechatronic Engineering
Name: Nguyen Hoang Danh
Major: Mechatronic Engineering
Name: Tu Phan Tuan Khang
Major: Mechatronic Engineering
Name: Dr. Pham Phuong Tung
Major: Mechatronic Engineering
Instructor:
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3. CONTENT
01
02
05
Introduction
Mechanical Design
03
Electrical Design
04
Control System Design
Verification and
Assessment
06
Conclusion and Future
work
3

4. 1. Introduction
Current Challenges in Robotics
Limitations of Traditional Robots:
• Mainly used in industry.
• Lack flexibility and adaptability.
• Fixed structure, high cost, difficult maintenance.
Current Status in Vietnam:
• Limited research and application of modular robots.
• Mostly use fixed-structure, imported robots.
• High investment cost, low adaptability.
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Fig 2. Co-bot
Fig 1. Industrial robots

5. 1. Introduction
1 DOF - Modular Robot
• Versatility & Reconfigurability: easily assemble various robot configurations.
• Scalability: add/remove modules to adjust degrees of freedom.
• Low cost: mass production, easy maintenance and repair.
• Ease - repair: faulty modules can be replaced for continued operation.
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Application
Fig 4. Compact Robot
Fig 3. T and I Joint Robot Module Fig 5. 4-Dof serial robot

6. 2. Mechanical Design
Principle diagram
Fig 6. I- Joint schematic diagram
Fig 8. T- Joint
schematic diagram
Fig 7. Base- Joint schematic diagram
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7. 2. Mechanical Design
Modular Design – Base module:
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Fig 9. Base module robot Fig 10. Base module prototype

8. 2. Mechanical Design
Modular Design – I module:
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Fig 12. Flange and motor holder
Fig 11. I - Joint module robot

9. 2. Mechanical Design
Modular Design – T module:
Fig 13. T - Joint module robot
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Fig 14. T - Joint module prototype

10. 3. Electrical System
Fig 15. Electrical
schematic diagram
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Electrical schematic diagram

11. 3. Electrical System
Fig 16. Electrical components diagram
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Components in electric system

12. 3. Electrical System
Requirements:
• Two separate power sources (for MCUs,
sensors and motors).
• Two sources have common ground.
• Using Circuit Breaker (CB) for safety.
Power source
24V Converter
12V Converter
12 - 5V Converter
Fig 17. Power source
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13. 4. Control system
Block Diagram of a Joint
Block Diagram of Control System
Design PID Controller:
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14. Based on the MATLAB Toolbox, we determine the
highest fit transfer function:
The total time: 120 s. Sampling time: 0.1 s.
The transfer function:
System modeling
4. Control system
10
11
12
13
14
15
16
17
18
y1
10 20 30 40 50 60 70 80 90 100 110 120
0.4
0.45
0.5
0.55
0.6
u1
System Identification Data: Input (Duty Cycle) vs Output (RPM)
Time (s) (seconds)
Value
10
11
12
13
14
15
16
17
18
y1
10 20 30 40 50 60 70 80 90 100 110 120
0.4
0.45
0.5
0.55
0.6
u1
System Identification Data: Input (Duty Cycle) vs Output (RPM)
Time (s) (seconds)
Value
Fig 18. 120 seconds Step run random between 40% to 60% duty Fig 19. 120 seconds Sine sweep from 0.001hz to 0.1hz
Fig 20. MATLAB System Identification Toolbox 14

15. 4. Control system
Control system designer:
Design controller target:
• Settling time (​
) ≤ 2 seconds.
• Overshoot (​
) ≤ 1%.
PID controller: , , .
Fig 21. Design PID using Root Locus method
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16. 5. Verification and Assessment
Expected Performance Targets (According to ISO 9283)
- Accuracy: Relative error < 1%, aligned with industrial robotic standards.
- Repeatability: Deviation within ± 0.5 mm, meeting high-precision mechanical system requirements.
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Repeatability
test
Joint 1 Joint 2 Joint 3
Case 1: Move
back and
forward 90
20 times/ per
test
20 times/ per
test
20 times/ per
test
Case 2: Move
back and
forward 180
20 times/ per
test
20 times/ per
test
20 times/ per
test
Repeatability Experiment Scenarios:
Accuracy
test
Joint 1 Joint 2 Joint 3
Case 1:
reach 360
20 times/
per test
20 times/
per test
20 times/ per
test
Case 2:
reach 180
20 times/
per test
20 times/
per test
20 times/ per
test
Accuracy Experiment Scenarios:

17. 5. Verification and Assessment
Fig 22. Testing setup for Accuracy testing
Step 1: Mount the encoder on the fixture and
align it concentrically with the joint shaft.
Step 2: Securely couple the encoder and joint.
Step 3: Command the joint to rotate back and
forth over a fixed angle for 30 cycles.
Step 4: Record encoder feedback and calculate
accuracy using the defined formula.
Accuracy testing:
Procedure:
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18. 5. Verification and Assessment
Step 1: Install the dial indicator and align it with
the joint’s motion.
Step 2: Adjust the joint to make contact with the
dial indicator.
Step 3: Perform repeated rotations and record
displacement to assess repeatability.
Repeatability testing:
Procedure:
Fig 23. Testing setup for Repeatability testing
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19. 5. Verification and Assessment
Accuracy test:
Joint 1 & 2: 0.28% – 0.39% error.
Joint 3: 0.76% – 1.31% error.
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Repeatability:
Joint 1: ~ 10 mm
Joint 2: ~ 5.5 mm
Obtain Performance Results
Fig 24. Accuracy test result
Fig 25.Repeatability test result

20. 6 Conclusion and Future work
Conclusion:
- Built a 1-DOF modular robotic joint.
- The system includes I-type, T-type, and Base joints.
- Each equipped with Hall sensors and optical encoders for precise feedback.
- A distributed control architecture with real-time PID control and UART communication.
Future work:
- Replacing the outside with aluminum.
- Upgrading the motor and gearbox.
- Adding an absolute encoder to provide precise position feedback.
- Develop a better homing algorithm, use an external memory to store the
home position.
- Develop a fine-tune filter — Kalman — to enhance signal accuracy.
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21. ANY QUESTIONS?
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