Clamping apparatus

A clamping apparatus comprising:

• a first cylinder for clamping provided with a first piston and a first actuation chamber, said first piston being advanced from an unclamping position to a clamping position by adjusting a fluid pressure within said first actuation chamber through a fluid pressure introducing/removal means;
• a clamping member carried by said first piston so as to be moveable with said first piston between unclamping and clamping positions;
• a locking chamber communicated crosswise with said first actuation chamber;
• a wedge type locking member having a first pressure receiving surface and a second pressure receiving surface and inserted into said locking chamber so as to be movable between a locking position where said locking member has been advanced into said first actuation chamber and an unlocking position where said locking member has been retracted into said locking chamber;
• said first pressure receiving surface serving to move said locking member toward said unlocking position by means of the fluid pressure within said first actuation chamber;
• said second pressure receiving surface serving to move said locking member toward said locking position by means of the fluid pressure within said first actuation chamber;
• pressure receiving areas of those pressure receiving surfaces being defined substantially equal;
• a second cylinder for unlocking provided with a second piston and a second actuation chamber, said second piston shifting said locking member from said locking position to said unlocking position by adjusting a fluid pressure within said second actuation chamber through said fluid pressure introducing/removal means;
• and
• a pushing means biasing said locking member toward said locking position, a pushing force of said pushing means being set at a value smaller than an unlocking actuation force of said second cylinder.