A self-locking expansion mechanism

There are many types of mechanisms. In this article, we introduce a self-locking expansion mechanism, and it is a two-position locking mechanism too. It can be used to expand pipes or other cylindrical parts.

Figure 1.
1.Cylinder body, 2. Piston, 3. Cylinder ring, 4. Driving plate, 5. Pin, 6. Spring, 7. Support block, 8. Bottom cover, 9. Bolts

This expanding mechanism comprises a cylinder body, a cylinder ring, a driving plate, a bottom cover, 6 pins, 6 pistons, 6 springs and 6 support blocks.

There are 6 pistons, and 6 springs are arranged between the pistons and the cylinder ring. When assembling, the pistons need to be insert into the holes firstly, then assembly the springs and the cylinder ring. After that, the pin can be insert into the hole of the piston. Three bolts are used to assemble the driving plate and the bottom cover together.

Figure 2

Due to the force of springs, the pistons won’t move automatically when they are at the original position (position A in Figure 2) — the outer diameter is the smallest.

When rotating the driving plate, the pistons move along the axis holes, and the diameter of support blocks (outer diameter) becomes larger. After the diameter becomes the largest (position B in Figure 2), continue to rotate the driving plate 2~3 degrees, and the diameter becomes a little smaller. Then the expansion mechanism will be locked at that position (position C in Figure 2).

The parts’ stiffness is assumed to be large enough and won’t be deformed under a big force, so the outer diameter (the red circle’s diameter in position B) won’t become smaller again even though there is a big force along the axis direction of the pistons. When rotating the driving plate in reverse, the pistons will retract to the original position under the force of springs.

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