Backstop

A backstop that is to be attached to a crane including a machine body, a boom tiltably supported on the machine body, and a strut, the boom including:

• a boom proximal end rotatably attached to the machine body;
• and a boom distal end located opposite the boom proximal end and having a strut supporting part and a backstop supporting part located in the rear of the strut supporting part, the strut including:
• a strut proximal end supported rotatably in a tilting direction about a reference rotation central axis extending horizontally by the strut supporting part at the boom distal end;
• a strut distal end located opposite the strut proximal end;
• and a backstop connection part located between the strut proximal end and the strut distal end, the backstop being located between the boom and the strut for supporting the strut, the backstop comprising:
• an outer cylinder including an outer cylinder proximal end to be connected to the backstop connection part of the strut rotatably about a first rotation central axis being parallel to the reference rotation central axis, and an outer cylinder distal end located opposite the outer cylinder proximal end;
• an inner cylinder including an inner cylinder proximal end to be supported by the backstop supporting part at the boom distal end rotatably about a second rotation central axis being parallel to the reference rotation central axis, and an inner cylinder distal end located opposite the inner cylinder proximal end to extend in the outer cylinder through the outer cylinder proximal end, the inner cylinder being movable relative to the outer cylinder in an axial direction to permit a change in a distance between the backstop supporting part and the backstop connection part in accordance with a rotation of the strut about the reference rotation central axis to the boom;
• a spacer having a predetermined dimension in the axial direction and a semi-cylindrical inner surface fittable on an outer surface of the inner cylinder in a direction perpendicularly intersecting the axial direction, the spacer having opposite ends in the axial direction respectively coming into contact with the outer cylinder distal end and the inner cylinder proximal end to keep the backstop from contracting in such a manner that the outer cylinder distal end comes closer to the inner cylinder proximal end than a distance corresponding to the dimension;
• a spacer holder attached to the outer cylinder of the backstop for supporting the spacer swingably about a swing central axis perpendicularly intersecting the axial direction, the spacer holder supporting the spacer in such a manner that the spacer swings about the swing central axis under the weight of the spacer to fit on the inner cylinder when the boom rises with respect to the machine body while supporting the strut;
• and
• a lock mechanism that is shiftable between a locking state of locking the spacer to keep the spacer from swinging about the swing central axis in a state where the spacer is located away from the outer surface of the inner cylinder and an unlocking state of permitting the spacer to swing about the swing central axis.