Background
Adjustment of the flexural rigidity with slits
Equivalent moment of inertia of area
Slit pattern
Boundary condition of the ends
Procedure to optimally adjust the flexural rigidity
Step 1
Step 2
Step 3
Step 4
Step 4.1
Step 4.2
Simple stress confirmation
Error
Final stress confirmation
Step 5
Simulation and experiment
Simulation of 8 mm forceps
Candidate No. |
\(f_H\) (N) |
\(\phi \) (°) |
\(\varepsilon \) (mm) |
---|---|---|---|
1st candidate | 0.03 | 7.60 | 0.59 |
2nd candidate | 0.05 | 5.48 | 0.39 |
3rd candidate | 0.08 | 5.31 | 1.42 |
4th candidate | 0.10 | 4.46 | 2.25 |
5th candidate | 0.13 | 4.30 | 1.25 |
6th candidate | 0.15 | 4.33 | 0.61 |
\(\mathrm{O B_1}\) (mm) | 38 |
a (mm) | 1.6 |
e (mm) | 1.8 |
c (mm) | 0.3 |
\(\mathrm{B_1 B_2}\) (mm) | 31 |
a (mm) | 2.0 |
e (mm) | 1.0 |
c (mm) | 0.4 |
\(\mathrm{B_2 B_3}\) (mm) | 57 |
a (mm) | 2.0 |
e (mm) | 1.4 |
c (mm) | 0.5 |
\(\varepsilon \) (mm) | 1.25 |
Simulation of 5 mm forceps
Candidate No. |
\(f_H\) (N) |
\(\phi \) (°) |
\(\varepsilon \) (mm) |
---|---|---|---|
1st candidate | 0.10 | 4.41 | 1.08 |
2nd candidate | 0.15 | 3.48 | 3.94 |
3rd candidate | 0.20 | 3.25 | 0.85 |
4th candidate | 0.25 | 2.99 | 1.63 |
5th candidate | 0.30 | 2.93 | 1.45 |
\(\mathrm{O B_1}\) (mm) | 102 |
a (mm) | 1.6 |
e (mm) | 1.4 |
c (mm) | 0.3 |
\(\mathrm{B_1 B_2}\) (mm) | 81 |
a (mm) | 1.6 |
e (mm) | 1.4 |
c (mm) | 0.4 |
\(\varepsilon \) (mm) | 1.50 |
Material | SUS630 | Ti-6Al-4V | SUS304 |
---|---|---|---|
E (GPa) | 205 | 113 | 192 |
\(\sigma _\mathrm{proof}\) (MPa) | 1175 | 828 | 205 |
\(\sigma _s\) (MPa) | 1144 | 631 | 1071 |
\(\tau _s\) (MPa) | 157 | 139 | 155 |
\(\sigma _\mathrm{net}\) (MPa) | 1166 | 709 | 1131 |
\(\phi \) (°) | 2.93 | 4.93 | 3.12 |
Development of 5 mm arc-shaped forceps and measurement of rotation torque and twist angle
Ex vivo experiment
Discussion
Ex vivo experiment
Other methods to reduce friction
Sterilization
Conclusion
-
Different slit intervals and width change the flexural rigidity of the inner pipe. First, the database of the equivalent flexural rigidity is developed. Repeat the following by changing the contact force between the inner and outer pipes.
-
The desired distribution of the flexural rigidity of the inner pipe is calculated from the outer pipe curve.
-
It is discretized by applying the database.
-
The candidate is excluded if the stress and error are larger than the allowable values.
-
Slit pattern of the minimum twist angle is selected among the candidates.
-
In the 8 mm forceps (Ti-6Al-4V) simulation, the twist angle was 4.30°.
-
In the 5 mm forceps (SUS630) simulation, the twist angle was 2.93°, whereas the twist angle of the PEEK inner pipe was 24.3°.
-
In the 5 mm forceps experiments, SUS304 was selected, which has a similar Young’s modulus to SUS630. The twist angle of 2.8° was consistent with the simulation result.
-
In the ex vivo experiments, the forceps were inserted into the chicken liver, minced pork meat, and porcine blood the rotation torque was measured. It changed from 5.1 to 5.3, 5.4, and 3.8 Nmm respectively. Moreover, it was 5.3 Nmm when blood was poured in the outer pipe and coagulated. These increase are small.