Self-actuating slack puller

Details Self-actuating slack puller Self-actuating slack puller

1998-10-09

2001-01-02

Matecki, Katherine A. (Department: 3653)

Advancing material of indeterminate length

By orbitally traveling material-engaging surface

With control or adjustment means

C226S187000, C226S188000, C212S089000, C254S287000, C254S291000, C254S333000

Utility Patent

active

06168062

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a slack puller for taking up the slack in a cable. The slack puller includes one or more rotating sheaves which may be brought into contact with the cable. The invention has particular application as a slack puller in a log skidding carriage for paying out and taking up slack in a mainline. In a preferred embodiment the puller is hydraulically operated.
BACKGROUND OF THE INVENTION
In typical skyline logging operations a skyline cable is strung over a logging area between a spar on a yarder and a support, such as a spar tree. A carriage is movable along the skyline. A mainline (or “skidder” cable or “drag” cable) extends from a winch on the yarder and over a sheave on the carriage. The main cable terminates at a choker or a number of chokers. The carriage has a skyline brake for arresting the motion of the carriage along the skyline and a mainline brake for arresting the motion of the mainline through the carriage. In operation, the carriage is moved to a location over a log and a chokerman connects the choker to the log. The winch is then operated to lift the log off of the ground and to draw the carriage and log together toward a landing near the yarder.
The main cable is heavy. A slack puller is generally provided in the carriage to draw the mainline through the carriage so that the chokerman can reach the choker and connect the choker to the log. Without a slack puller the end of the mainline would generally be pulled up to the carriage by the weight of the portion of the mainline between the carriage and the yarder which inevitably sags toward the ground. The chokerman would then have to manually pull enough of the mainline over the sheave on the carriage to permit the choker to be connected to the log. The weight of the portion of the mainline between the yarder and the carriage increases as the carriage moves away from the yarder. Pulling the mainline manually would be very arduous for the chokerman, especially if the skyline is high above the ground and the log is in an area of rugged terrain.
Existing slack pullers have two main problems. They are either undesirably slow or they cause excessive damage to the mainline when they are used. Some existing slack pullers are both slow and cause excessive cable damage. Kuehn, U.S. Pat. No. 4,454,951 discloses a log skidding carriage in which the drag line passes between a rotating sheave and a clutch sheave. The clutch sheave can be driven toward the rotating sheave by a hydraulic cylinder. When the hydraulic cylinder is actuated the drag line is pinched between the rotating sheave and the clutch sheave. Kuehn does not provide any means for modulating the force exerted by the hydraulic cylinder. The hydraulic cylinder could exert enough force to damage the drag line, especially if the rotating sheave slips or “chatters” on the drag line when all of the slack has been taken up from the drag line.
Maki, U.S. Pat. No. 4,515,281 shows a log skidding carriage which includes a slack puller comprising a pair of sheaves biased toward each other by a spring. The mainline passes between the sheaves. A hydraulically operated clutch permits the sheaves to rotate freely when the mainline is being pulled in.
Rennie et al. U.S. Pat. No. 3,531,000 and Davis, U.S. Pat. No. 4,687,109 each show a logging carriage in which a load line passes between a rotating sheave and a pair of smaller sheaves. The smaller sheaves are biased against the rotating sheave by a spring mechanism. There is no provision for releasing the spring during operation in either direction.
There is a need for a slack puller which operates more quickly than prior art slack pullers, has better pulling power than existing slack pullers and yet does not cause unnecessary cable damage. More particularly, what is needed is a slack puller that does not apply unnecessarily large compressive forces to a line being pulled and avoids slip or chatter when the line is under tension. There is a particular need for such a slack puller which is compact enough to use in a logging carriage.
SUMMARY OF THE INVENTION
This invention provides a slack puller which may be used to advantage in a logging carriage for taking up slack in a line. The slack puller may also be used to take up slack in lines in other contexts. The slack puller comprises: a first sheave having an axis of rotation, the first sheave coupled to a frame by a first sheave linkage such that the axis of rotation of the first sheave is constrained to travel in a first arcuate path between first and second positions; a second sheave coupled to the frame and rotatable about an axis of rotation; an actuator coupled between the frame and the first sheave to move the first sheave between its first and second positions; and, a motor for turning the first sheave about the first sheave axis of rotation. When the first sheave is in its first position, a line extending between the first and second sheaves is compressed between the first and second sheaves; when the first sheave is in its first position and the motor is operated to turn the first sheave, the line is pulled between the first and second sheaves and tension in the line tends to pull the first sheave along the arcuate path in a direction which moves the first sheave axis of rotation closer to the second sheave axis of rotation. When the first sheave is in its second position, the line is free to slip longitudinally between the first and second sheaves.
Preferably the second sheave is coupled to the frame by a second sheave linkage such that the second sheave axis of rotation is constrained to travel in a second arcuate path between first and second positions and the slack puller comprises a coupling linkage coupling the first and second sheave linkages. The coupling linkage moves the second sheave from its first position to its second position in response to motion of the first sheave from its first position to its second position. The coupling linkage may comprise first and second sectors bearing intermeshing teeth, the first and second sectors rigidly coupled to the first and second sheave linkages. Preferably the second sheave linkage comprises an arm pivotally mounted to the frame.
Most preferably the first and second sheaves are respectively turned by first and second motors respectively mounted on the first and second arms and the first and second motors are positive displacement hydraulic motors connected in series with a hydraulic pump. In a preferred embodiment the hydraulic pump is of the type where a rate of flow of fluid output by the pump approaches zero as an output pressure approaches a maximum pressure.
Another aspect of the invention provides a slack puller for pulling a cable. The slack puller comprises first and second sheave assemblies mounted to a frame on either side of a cable path. Each of the sheave assemblies comprises an arm pivotally mounted to the frame at a pivot point, a sheave mounted to the arm for rotation about an axis of rotation, and a motor for turning the sheave about its axis of rotation. The sheaves are both located on the same side of a reference line joining the pivot points of the first and second sheave assemblies. The slack puller also comprises a linkage connected between the first and second sheave assemblies, the linkage coupling the arms of the first and second sheave assemblies to move toward one another or apart from one another about the cable path; and an actuator coupled to the first sheave assembly for moving the arms between an engaged configuration in which the sheaves would bear against opposed sides of a cable extending along the cable path and a disengaged position wherein the sheaves would not contact a cable extending along the cable path. When the arms are in the engaged configuration, a line between the axis of rotation and the pivot point defines an angle with the reference line in the range of about 10 degrees to about 40 degrees.
In preferred embodiments of this second aspect of the invention, the sheaves of the first and second sheave assemblies are equal in diam

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