Pneumatic cylinder device with locking mechanism

Claim 1

A pneumatic cylinder device with a locking mechanism comprising a pneumatic cylinder having a cylinder, a piston slidably received in said cylinder and a piston rod extending from said piston outwardly of said cylinder; and a locking mechanism adapted to selectively lock said piston rod against movement; said locking mechanism comprising: a housing disposed adjacent said cylinder and through which said piston rod is slidably extended; a flexible tubular member disposed in said housing so as to surround said piston rod, said flexible tubular member being contractable and expandable in a radial direction for locking and unlocking of said piston rod; an annular variable-volume chamber means formed around said flexible tubular member and having a variable volume; a volume changing means for causing a change in the volume of said variable-volume chamber means; and a pressure transmission means accommodated in said variable-volume chamber means and adapted to transmit to said flexible tubular member a pressure change produced in said variable-volume chamber means as a result of a volume change; and said variable-volume chamber means including a first pressure chamber formed between the outer peripheral surface of said flexible tubular member and the inner peripheral surface of an annular partition wall means extending in said housing in the axial direction, said partition wall means having a large-diameter portion and a small-diameter portion; and a second pressure chamber defined by a stepped outer peripheral surface of said annular partition wall means and a recess formed in the inner peripheral surface of a control piston slidably fitted over said stepped outer peripheral surface, said second pressure chamber communicating with said first pressure chamber through communication passage means formed in said annular partition wall means, said second pressure chamber extending over at least said small-diameter portion of said annular partition wall means, the volume of said second pressure chamber being variable as a result of axial sliding movement of said control piston with respect to said annular partition wall means.