Page 224 - Flexible Robotics in Medicine

Compliant bending tubular mechanisms with variable groove patterns 211

8.5 Other trials and errors

8.5.1 Compression and tension springs

The inspiration for using springs as the manipulator comes from “compressible steerable
spring mechanism [17].” In this study, two coil springs are used, innerspring and an outer
one. The smaller diameter spring, which is placed inside the larger spring (in the diagram
below), can be used to guide the flexible drill for our prototype. The space in between the
two springs is filled with cables.

The idea for using springs is to use two springs of differing diameter, with wires in between
them for steering, as shown in Fig. 8.18. The beginning position would be that the springs
were compressed. Releasing one of the wires, while the other two are tied down, results in
the spring pushing itself outward with a bending. The test of concepts was done using
springs with the dimensions in Table 8.5.

Figure 8.18
Spring-cable idea: innerspring, outer spring, and three wires (inside the outer spring).

Table 8.5: Dimensions of compression and tension spring.
Outer diameter Inner diameter Free length Spring rate
(mm) (mm) (mm) (N/mm)
Compression 4.00 0.3 17.00 0.193
spring (outer)
Compression 1.45 0.15 15.88 0.105
spring (inner)
Tension spring (outer) 4.00 0.3 15.80 0.0567
Tension spring (inner) 1.59 0.20 15.88 0.1928