| 摘要 |
PROBLEM TO BE SOLVED: To prevent the service life of a casing by inhibiting an accelerating increase in a grip force of the casing even when the outside diameter of a cylinder-shaped casing is subjected to a partial reduction due to wear out or deformation and so forth. SOLUTION: Both end of an axis 4 of a lever 3 pivoted radially with an axis 2 on a first rotary ring 1 of a rotatable lifting arm surrounding a casing 10 are engaged with long holes 5b of a second rotary ring 5 turnably held on a liftable holding ring 7 with a chuck cylinder 6 respectively. A friction shoe 9 is pivoted on each lever with an axis 8 so as to form a tossle joint mechanism which is joined with and separated from the casing 10, thereby equalizing an included angle between the central line which connects the axes 2 and 4 and the central line which connects the axes 2 and 8 to the sum of the friction angle of the fiction shoe 9 and aπ/2 radiant. A grip force on the casing to the friction show when the casing 10 is pressed into the ground is arranged to be constantly maintained definitely.
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