Research on Self-Stiffness Adjustment of Growth-Controllable Continuum Robot (GCCR) Based on Elastic Force Transmission
Abstract
:1. Introduction
1.1. Background and Previous Work
- Active stiffness adjustment: It requires an additional structure or mechanism to lock the robot actively, which can be understood as active stiffness adjustment;
- Passive stiffness adjustment: Based on the motion characteristics of the robot, stiffness adjustment is achieved without introducing additional actuation components;
- Lightweight design: The use of lightweight materials can effectively reduce the impact of robot weight on motion accuracy in gravity; continuum robots with gradually changing diameters can effectively shorten the distance between the center of mass and fixed end;
- Kinematics compensation: To fit the target by changing the actuation displacement initiative by kinematics algorithms.
Reference | Stiffness Adjustment Method | Robot Length (m) | End Load (N) | Deflection (m) | Stiffness (N/mm) | Increase Percent (%) | Actuation for Stiffness Adjustment |
---|---|---|---|---|---|---|---|
Yang et al. [29] | Locking mechanism | 0.88 | 3 | 0.135 | 0.037 | 187 | Independent |
Kang et al. [31] | - | - | - | - | - | Independent | |
Ours | 0.2–0.75 | 5 | 0.018 | 0.032 | 80 | Coupled | |
Kim et al. [15] | Layer jamming | 0.44 | 3.8 | 0.02 | 0.198 | 90 | Independent |
Li et al. [32] | 0.063 | 1.1 | 0.024 | 0.046 | 540 | Independent | |
Wei et al. [33] | Particle jamming | 0.15 | 3.5 | 0.014 | 0.259 | 900 | Independent |
Cianchetti et al. [14] | 0.050 | 4.1 | 0.016 | 0.256 | 36 | Independent | |
Kim et al. [34] | Antagonistic actuation | 0.087 | 5 | 0.01 | 0.484 | 198 | Independent |
Zhao et al. [9] | Inserting rigid rod | 0.315 | - | - | 2.71 | 983 | Independent |
1.2. Contribution
- A stiffness adjustment mechanism (SAM) is proposed and built in a growth-controllable continuum robot (GCCR) to improve the motion accuracy in variable scale motion.
- A statistics model that considers the weight of the robot and the end load is constructed and the shape of the robot can be predicted.
- Experimental testing is carried out to investigate the effect of the proposed SAM, modeling errors, and stiffness enhancement. The results provide efficacious insights to improve the design of the stiffness adjustment mechanism.
1.3. Outline
2. Generalized Growth-Controllable Continuum Robot
2.1. Configuration
2.2. Kinematics
2.3. Workspace
3. Stiffness Adjustment Mechanism (SAM)
3.1. Working Principle
3.2. Force Transmission
4. Static Modeling and Analysis
- The continuum robot has a slender structure, and the mass distribution is assumed uniform;
- Each curve of the drive rod is parallel to each other, including the virtual bone;
- Due to the compression springs being utilized to keep an equidistant sate of the constraint disks, the elastic potential energy is negligible.
4.1. Elastic Potential Energy and Bending Stiffness
4.2. Static Modeling
4.3. Predicted Robot Shape
5. Experiments and Results
5.1. Robot Prototype and Test Platform Setup
5.2. Predicted Robot Shape in Different Actuation Displacement
- Both absolute and relative errors increase with the elongation of the robot.
- In general, the average error is greater than the robot end error.
- The average error almost shows a linear trend after the robot length is greater than 0.3 m, while the trend of end error change is not as significant as the average error.
5.3. Effect of Stiffness Adjustment Mechanism
5.4. Effect of Variable Stiffness Demonstration and Validation
5.5. Effect of Basic Motions on Cable Length Changing
6. Discussion and Conclusions
7. Patents
- Mingyuan Wang et al., A driving component for a continuum robot, Chinese patent, ZL202111404400.5, Shanghai University, 2022. 12. 27. (Granted)
- Mingyuan Wang et al., A Modular Continuum Robot with Multiple Operation Modes, Chinese patent, ZL202111403853.6, Shanghai University, 2023. 8. 11. (Granted)
Author Contributions
Funding
Institutional Review Board Statement
Data Availability Statement
Conflicts of Interest
Abbreviations
CR | Continuum Robot |
GCCR | Growth-controllable Continuum Robot |
SAM | Stiffness Adjustment Mechanism |
SMA | Shape Memory Alloy |
CM | Center of Mass |
Bending angle between the end plane and base plane | |
Rotation angle between and the projection of bending plane on the base plane | |
L | The length of the robot, i.e., virtual bone’s length |
The variable length of each drive rod () | |
The posture parameters of the robot | |
The guided end position of the robot | |
r | The distance between the drive rods and the virtual bone |
The diameter of the drive rods | |
The normal force between constraint disks and drive rods | |
The frictional force between constraint disks and drive rods | |
The tension force provided by the tension springs | |
The load on the guided end | |
The distance between the cable and the virtual bone () | |
Stiffness of the tension spring | |
Stiffness of the robot | |
Variable length of each spring | |
Length of the built in cable | |
Frictional coefficient of cable and constraint disks | |
Equivalent compensation torque provided by the frictional force | |
Elastic potential energy of each fiberglass rod (drive rod) () | |
Bending stiffness of the fiberglass rod () | |
Curvature of each point on the fiberglass rod () | |
Equivalent bending stiffness of the robot | |
Bending moment acting on the guided end of the robot | |
Equivalent mass on the guided end of the robot | |
K | Curvature of the virtual bone |
The load factor [44] | |
The equivalent density per unit length of the robot | |
g | Gravitational acceleration |
n | Number of the drive rods |
N | Number of the constraint disks |
The direction of force on the i-th constraint disk |
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Variable | Value | Unit | Description |
---|---|---|---|
n | 3 | — | The number of drive rods |
0.2 | m | The initial length of the GCCR (minimum length of the robot) | |
L | 0.2∼0.75 | m | The length range of the GCCR in this paper |
7.5 × 10 | Pa | Young’s modulus of fiberglass | |
2.029 × 10 | kgm | The moment of inertia of an area of fiberglass | |
0.17 | kg/m | The equivalent density of the GCCR | |
r | 0.05 | m | The distance between the fiberglass rods and the virtual bone |
0.0015 | m | Diameter of each fiberglass rod | |
g | 9.81 | m/s | Gravitational acceleration |
43.8 | N/m | The stiffness of the tension spring | |
0.128 | — | Frictional coefficient of cable and constraint disks |
Length (m) | State | (m) | (%) | (m) | (%) |
---|---|---|---|---|---|
0.20 | With SAM * | 0.013 | 1.44 | 0.011 | 1.53 |
0.35 | 0.010 | 1.17 | 0.009 | 1.22 | |
0.45 | 0.009 | 1.23 | 0.014 | 1.81 | |
0.60 | 0.017 | 2.29 | 0.029 | 3.87 | |
0.75 | 0.021 | 2.71 | 0.042 | 5.57 |
Length (m) | State | (m) | (%) | (m) | (%) | (m) [ (%)] | (m) [ (%)] |
---|---|---|---|---|---|---|---|
0.75 | With SAM * | 0.021 | 2.71 | 0.042 | 5.56 | 0.097 [12.91] | 0.069 [9.27] |
No SAM | 0.023 | 3.03 | 0.051 | 6.82 |
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Wang, M.; Yuan, J.; Bao, S.; Du, L.; Ma, S. Research on Self-Stiffness Adjustment of Growth-Controllable Continuum Robot (GCCR) Based on Elastic Force Transmission. Biomimetics 2023, 8, 433. https://doi.org/10.3390/biomimetics8050433
Wang M, Yuan J, Bao S, Du L, Ma S. Research on Self-Stiffness Adjustment of Growth-Controllable Continuum Robot (GCCR) Based on Elastic Force Transmission. Biomimetics. 2023; 8(5):433. https://doi.org/10.3390/biomimetics8050433
Chicago/Turabian StyleWang, Mingyuan, Jianjun Yuan, Sheng Bao, Liang Du, and Shugen Ma. 2023. "Research on Self-Stiffness Adjustment of Growth-Controllable Continuum Robot (GCCR) Based on Elastic Force Transmission" Biomimetics 8, no. 5: 433. https://doi.org/10.3390/biomimetics8050433
APA StyleWang, M., Yuan, J., Bao, S., Du, L., & Ma, S. (2023). Research on Self-Stiffness Adjustment of Growth-Controllable Continuum Robot (GCCR) Based on Elastic Force Transmission. Biomimetics, 8(5), 433. https://doi.org/10.3390/biomimetics8050433