Articulation for tower crane boom that has a parking position

A crane comprising an upright tower (5) that has a top and front (13) and rear (14) sides, a boom (6) that has an outer end from which a load hoisting cable (7) can depend and an inner end, and articulation means (8) providing a connection between said top of said tower (5) and said inner end of said boom (6) whereby said boom (6) can swing through a range of upwardly projecting positions above horizontal about a horizontal rear fixed axis (F-1) that is located at said top of said tower (5) between said front (13) and rear (14) sides of said tower (5) and whereby said boom (6) can swing through a range of downwardly projecting positions below horizontal about a horizontal forward fixed axis (F-2) that is located at said top of said tower (5) and spaced forwardly from and parallel to said rear fixed axis (F-1), said downwardly projecting positions including an inoperative position wherein said boom (6) extends substantially vertically downward along said front side (13) of said tower (5), said articulation means (8) comprising:

• A. at least one rear pair of engageable and disengageable joint elements (35,37),
• (1) said rear pair comprising
• (a) a rear tower joint element (35) fixed on the top of said tower (5) on said rear fixed axis (F-1) and
• (b) an associated rear boom joint element (37) fixed on said inner end of said boom (6),
• B. at least one forward pair of engageable and disengageable joint elements (36,38),
• (1) said forward pair comprising
• (a) a forward tower joint element (36) fixed on the top of said tower (5) on said forward fixed axis (F-2) and
• (b) an associated forward boom joint element (38) fixed on said boom (6) at a location outwardly of said rear boom joint element (37) at a distance equal to that between said rear and forward axes (F-1,F-2),
• (2I) one joint element (37,38) of said pair comprising a trunnion and
• (3) the other joint element (35,36) of each forward pair comprising a slot (41,42)
• (a) with a closed end that defines a seat on which the trunnion of an associated element can rotate when engaged therewith and
• (b) with an opposite open end to enable engagement and disengagement of the trunnion of an associated element in the ocurse of substantially vertical relative motion of the boom joint elements;
• (4) said boom (6) being swingable through said downwardly projecting positons about said forward fixed (F-2) when said forward pair of joint elements (36,38) are engaged and said rear pair of joint elements (35,37) are disengaged;
• (5) said boom (6) being swingable through said upwardly projecting positions about said rear fixed axis (F-1) when said rear pair or joint elements (35,37) are engaged and said forward pair of joint elements (36,38) are disengaged;
• C. at least one elongated first link (47) having
• (1) one end pivotally conntected (51,52) to the top of said tower (5) on said rear fixed axis (F-1) and
• (2) an opposte end pivotally connected (53) to said boom (6) on the same axis (B-2) as said forward boom join element (38);
• D. at least one elongated second link (49) having
• (1) one end fixedly connected (55) to said boom (6) the same axis (B-1) as said rear boom joint element (37) and
• (2) an opposite end pivotally connected (56) to the top of said tower (5) on said forward fixed axis (F-2);
• (3) said first and second links (47,49) being operable to prevent said boom (6) from moving relative to said tower (5) to a position in which neither of said rear or forward pairs of joint elements is engaged;
• and
• E. means (17, 18, 19, 24) connected to said boom (6) to effect swinging movement of said boom (6) about either one of said rear fixed axis (F-1) or said forward fixed axis (F-2).