A hoist pivotally connecting mast 1 to lifting arm 2, by a mechanism comprising a link 5 pivoting about a fixed pivot 8 on the mast 1 and a moving pivot 6 on the lifting arm 2. A restraining link 9 between a pivot 10 on the mast 1 and actuator attachment point 11 on the lifting arm 2 restricts the movement of link 5. The second link 9 acts as a stabilizer allowing the pivot 11 on the lifting arm 2 to move only through a set arc, determined by the length of the link 9 and the position of the pivot 10 on the mast 1. With the moving pivot according to the invention, the spreader bar attachment point 7 has a greater traveling distance than if it were simply pivoted about pivot 8 as with conventional hoists.
1. A hoist comprising a chassis, a mast upstanding from the chassis, a lifting arm, and an actuator moving the lifting arm with respect to the mast, wherein:
(1) the mast has a moving pivot pivotally supporting the lifting arm at one end wherein the position of the moving pivot varies with movement of the lifting arm,
(2) the moving pivot comprises an intermediate link pivotally connected to the mast about a fixed point and pivotally connected to the lifting arm about a moving pivot point, and
(3) a stabilizing link attached to the mast and actuator restricts the movement of the moving pivot.
2. The hoist of claim 1 wherein the fixed point about which the intermediate link pivots is spaced from the longitudinal axis of the mast.
3. The hoist of claim 2 wherein the stabilizing link is pivotally connected to the mast at a point located closer to the longitudinal axis of the mast than the fixed point at which the intermediate link is pivotally connected to the mast.
4. The hoist of claim 1 wherein the stabilizing link is pivotally attached between the mast and actuator.
5. The hoist of claim 4 wherein the stabilizing link has opposing ends, one end being pivotally affixed to the mast and the other end being pivotally affixed to the actuator.
6. The hoist of claim 5 wherein the end of the stabilizing link pivotally affixed to the actuator is also pivotally affixed to the lifting arm.
7. The hoist of claim 1 wherein a four-link loop is defined by:
a. the mast, the mast bearing spaced pivot points affixed to the stabilizing link and to the intermediate link;
b. the intermediate link, the intermediate link bearing spaced pivot points affixed to the mast and to the lifting arm;
c. the lifting arm, the lifting arm bearing spaced pivot points affixed to the intermediate link and the stabilizing link;
d. the stabilizing link, the stabilizing link bearing spaced pivot points affixed to the lifting arm and to the mast.
8. The hoist of claim 7 wherein the distance between the spaced pivot points on the intermediate link is less than the distance between the spaced pivot points on both:
a. the lifting arm, and
b. the stabilizing link.
9. The hoist of claim 8 wherein the distance between the spaced pivot points on the mast is less than the distance between the spaced pivot points on both:
a. the lifting arm, and
b. the stabilizing link.
10. The hoist of claim 1 wherein the distance between the spaced pivot points on the mast is at least substantially equal to the distance between the spaced pivot points on the intermediate link.
11. A hoist comprising:
a. a mast;
b. a lifting arm;
c. an intermediate link pivotally connecting the mast and the lifting arm;
d. an actuator for moving the lifting arm relative to the mast; and
e. a stabilizing link attached to the mast and the actuator, the stabilizing link restricting movement of the link pivotally connecting the mast and the lifting arm.
12. The hoist of claim 11 wherein the intermediate link is pivotally connected to the mast at a point spaced from the longitudinal axis of the mast.
13. The hoist of claim 12 wherein the stabilizing link is pivotally connected to the mast at a point located closer to the longitudinal axis of the mast than the point at which the intermediate link is pivotally connected to the mast.
14. The hoist of claim 11 wherein the stabilizing link is pivotally attached between the mast and actuator.
15. The hoist of claim 14 wherein the stabilizing link has opposing ends, one end being pivotally attached to the mast and the other end being pivotally attached to the actuator.
16. The hoist of claim 15 wherein the end of the stabilizing link pivotally affixed to the actuator is also pivotally affixed to the lifting arm.
17. The hoist of claim 11 wherein a four-link loop is defined by:
a. the mast, the mast bearing spaced pivot points affixed to the stabilizing link and to the intermediate link;
b. the intermediate link, the intermediate link bearing spaced pivot points affixed to the mast and to the lifting arm;
c. the lifting arm, the lifting arm bearing spaced pivot points affixed to the intermediate link and the stabilizing link;
d. the stabilizing link, the stabilizing link bearing spaced pivot points affixed to the lifting arm and to the mast.
18. The hoist of claim 17 wherein the distance between the spaced pivot points on the intermediate link is less than the distance between the spaced pivot points on both:
a. the lifting arm, and
b. the stabilizing link.
19. The hoist of claim 18 wherein the distance between the spaced pivot points on the mast is less than the distance between the spaced pivot points on both:
a. the lifting arm, and
b. the stabilizing link.
20. The hoist of claim 19 wherein the distance between the spaced pivot points on the mast is at least substantially equal to the distance between the spaced pivot points on the intermediate link.