Variable Stiffness Technologies for Soft Robotics: A Comparative Approach for the STIFF-FLOP Manipulator
Abstract
:1. Introduction
2. Materials and Methods
2.1. Manipulator Structure and Design Considerations
- The total length and the external diameter remain constant to maintain compliance with the standard laparoscopic trocars (diameter mm) and have comparable results in terms of the bending angle covered by the module;
- The module has a free central channel for the passage of tools to the tip;
- The module preserves three MPs to guarantee flexibility and dexterity;
- The module embeds a variable stiffness mechanism.
2.2. New Design
2.3. Variable Stiffness Mechanism
2.3.1. Jamming Transition
- Shape: fibers should have a cross-section shape able to fill the inner part of the chambers as efficiently as possible.
- Flexibility: fibers should be highly bendable, either thanks to a low Young’s modulus or their geometrical features.
- Elasticity: the material should not undergo plastic deformation during loading and its elastic return should be taken into consideration to restore the initial state and position when the vacuum is removed.
2.3.2. LMPA
2.4. Fabrication
- (a)
- Firstly, cotton thread was wrapped around the cylindrical mold of the fluidic chamber. The cylinder consists of three parts, one central and two sides (Figure 4a), so that the demolding steps are made easier.
- (b)
- Six molds were placed inside the manipulator mold together with a central core and three trapezoidal prisms (stiffening chambers). To guarantee a precise mold alignment, which is essential for avoiding any asymmetries in the module, both fluidic and stiffening chamber molds were held in place by a Plexiglas plate which is located on the top of the module. The Plexiglas component (thickness = 4 mm) was produced with a laser cutting machine (Universal Laser XLS10MWH, Universal Laser System Inc., South Carolina, USA). Then, uncured silicone (Ecoflex 0050, Smooth On Inc., Macungie, PA, USA) was poured into the mold and left to cure at room temperature. After the silicone had completely cured, all molds were removed (Figure 4b).
- (c)
- After obtaining the main silicone body of the manipulator, the next phase comprises the integration of the variable stiffness mechanism. For the FJ module version, a total of 36 fibers (i.e., 12 per chamber) were inserted in CT configuration in each stiffening chamber. In each module, the fibers were arranged as two tooth-interlocking combs: half were placed more than 3 mm from the bottom face of the module and the remaining amount was placed at the same length from the other side.For the LMPA module version, the LMPA core and heater were inserted in each stiffening chamber (Figure 4c). More details on this step are discussed in Appendix A.2.
- (d)
- The modules were sealed on the bottom side using a dedicated cup mold filled with harder silicone (Smooth Sil 950, Smooth On Inc., Macungie, PA, USA). At this stage, the pipes for the fluidic actuation (i.e., three for both modules) were incorporated into the soft structure. For the FJ module version, one pipe for the vacuum was also inserted (Figure 4d).
- (e)
2.5. Experimental Setup and Protocols
2.5.1. Variable Stiffness at Rest Position
2.5.2. Variable Stiffness in Bent Configuration
2.5.3. Workspace
2.5.4. Shape Locking
- The module in the soft state is bent, supplying a pressure of 1.2 bar to a pair of chambers;
- The angle is recorded ();
- The transition from the soft to the stiff condition is triggered;
- The pressure is removed from the fluidic chambers;
- The angle is recorded again ().
2.5.5. Transition Time Evaluation
3. Results and Discussion
3.1. Variable Stiffness in the Rest Position
3.2. Variable Stiffness in the Bent Condition
3.3. Workspace
3.4. Shape-Locking
3.5. Transition Time Evaluation
3.6. Performance Improvement in the STIFF-FLOP Manipulator
4. Conclusions and Future Perspectives
Author Contributions
Funding
Conflicts of Interest
Appendix A
Appendix A.1. Selection of the Heating System
Appendix A.2. Manufacturing of the LMPA Core
Appendix A.3. Thermal Analysis
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Melting Point | Specific Heat | Specific Latent Heat | Density | E | Ultimate Stress |
---|---|---|---|---|---|
62 °C | 172 | 38,980 | 33,800 | 3 GPa | 25 MPa |
(SOFT) (N) | (STIFF) (N) | Force Variation (%) | Stiffness Variation (%) | |
---|---|---|---|---|
FJ | 0.59 ± 0.01 | 1.06 ± 0.03 | 180 ± 8 | 151 ± 28 |
LMPA | 0.63 ± 0.02 | 4.51 ± 0.07 | 716 ± 50 | 550 ± 52 |
(SOFT) (N) | (STIFF) (N) | Force Variation (%) | Stiffness Variation (%) | |
---|---|---|---|---|
FJ | 0.56 ± 0.01 | 1.01 ± 0.03 | 178 ± 10 | 165 ± 27 |
LMPA | 0.51 ± 0.02 | 3.48 ± 0.10 | 682 ± 46 | 493 ± 55 |
and SOFT (°) | and STIFF (°) | (%) | |
---|---|---|---|
FJ | 55.2 ± 1.7 | 45.4 ± 2.6 | 82.2 ± 5.3 |
LMPA | 62.6 ± 1.1 | 57.4 ± 4.1 | 91.5 ± 6.7 |
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Pagliarani, N.; Arleo, L.; Albini, S.; Cianchetti, M. Variable Stiffness Technologies for Soft Robotics: A Comparative Approach for the STIFF-FLOP Manipulator. Actuators 2023, 12, 96. https://doi.org/10.3390/act12030096
Pagliarani N, Arleo L, Albini S, Cianchetti M. Variable Stiffness Technologies for Soft Robotics: A Comparative Approach for the STIFF-FLOP Manipulator. Actuators. 2023; 12(3):96. https://doi.org/10.3390/act12030096
Chicago/Turabian StylePagliarani, Niccolò, Luca Arleo, Stefano Albini, and Matteo Cianchetti. 2023. "Variable Stiffness Technologies for Soft Robotics: A Comparative Approach for the STIFF-FLOP Manipulator" Actuators 12, no. 3: 96. https://doi.org/10.3390/act12030096
APA StylePagliarani, N., Arleo, L., Albini, S., & Cianchetti, M. (2023). Variable Stiffness Technologies for Soft Robotics: A Comparative Approach for the STIFF-FLOP Manipulator. Actuators, 12(3), 96. https://doi.org/10.3390/act12030096