| 摘要 |
A blade moves backward/forward to enter four different states, namely a first state in which the tip thereof is in sliding contact with the internal peripheral surface of an external side cylinder part, a second state in which the tip is positioned in the cutaway portion of a ring-shaped piston to thereby place only an external side cylinder chamber at rest, a third state in which the tip is positioned in the cutaway portion of an internal side cylinder part to thereby place only the external side cylinder chamber and an intermediate cylinder chamber at rest, and a whole rest state in which the tip is positioned in a blade groove to thereby place all of the cylinder chambers at rest.
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