Revolving paper roll clamp with short arm drift prevention

Abstract

A load-handling clamp mountable on a lift truck is capable of clamping a load between respective opposed clamp arms each capable of hydraulic movement selectively toward or away from each other. One of the clamp arms is preferably substantially incapable of movement toward the other clamp arm unless actuated independently of the other clamp arm. One of the clamp arms also preferably has a lesser maximum range of hydraulic movement than the other of the clamp arms and is hydraulically movable at a maximum hydraulic pressure greater than that of the other clamp arm.

Claims

1. A load handling clamp capable of clamping a load between respective opposed first and second clamp arms each of the first and second clamp arms is capable of hydraulic movement selectively toward or away from each other, the second clamp arm having a lesser maximum range of said hydraulic movement than the first clamp arm and being substantially incapable of movement toward the first clamp arm unless actuated independently of any actuation of the first clamp arm, wherein the second clamp arm is hydraulically movable only at a hydraulic pressure that is greater than hydraulic pressure used to move the first clamp arm, further comprising a counterbalance valve assembly that prevents hydraulic fluid flow to and from the second clamp arm unless the hydraulic fluid is at the hydraulic pressure that is greater than the hydraulic pressure used to move the first clamp arm, further comprising an adjustment screw to allow a user to set the hydraulic pressure for the counterbalance valve assembly to allow hydraulic flow to and from the second clamp arm.

2. A load handling clamp capable of clamping a load between respective opposed first and second clamp arms each of the first and second clamp arms is capable of hydraulic movement selectively toward or away from each other, the second clamp arm having a lesser maximum range of said hydraulic movement than the first clamp arm and being substantially incapable of movement toward the first clamp arm unless actuated independently of any actuation of the first clamp arm, wherein the second clamp arm is hydraulically movable only at a hydraulic pressure that is greater than hydraulic pressure used to move the first clamp arm, wherein the second clamp arm is shorter in length than the first clamp arm.

3. The load handling clamp of claim 2, further comprising a counterbalance valve assembly that prevents hydraulic fluid flow to and from the second clamp arm unless the hydraulic fluid is at the hydraulic pressure that is greater than the hydraulic pressure used to move the first clamp arm.

4. The load handling clamp of claim 3, further comprising an adjustment screw to allow a user to set the hydraulic pressure for the counterbalance valve assembly to allow hydraulic flow to and from the second clamp arm.

5. A load handling clamp capable of clamping a load between respective opposed first and second clamp arms each of the first and second clamp arms is capable of hydraulic movement selectively toward or away from each other, the second clamp arm having a lesser maximum range of said hydraulic movement than the first clamp arm and being substantially incapable of movement toward the first clamp arm unless actuated independently of any actuation of the first clamp arm, wherein the second clamp arm is hydraulically movable only at a hydraulic pressure that is greater than hydraulic pressure used to move the first clamp arm, further comprising a counterbalance valve assembly that prevents hydraulic fluid flow to and from the second clamp arm unless the hydraulic fluid is at the hydraulic pressure that is greater than the hydraulic pressure used to move the first clamp arm, further comprising an adjustment screw to allow a user to set the hydraulic pressure for the counterbalance valve assembly to allow hydraulic flow to and from the second clamp arm, wherein the second clamp arm is shorter in length than the first clamp arm.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The single drawing is a hydraulic circuit diagram incorporating exemplary embodiments of the foregoing invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiment 1

(2) With reference to the foregoing drawing, the present invention is intended to substantially prevent, or at least significantly limit, uncontrolled “short arm drift” which commonly results in unintended premature lift truck load clamp closures by one or more “short arm” clamping actuators such as 10 and 12, toward opposing “long arm” clamping actuators such as 13 and 14, during successive clampings of large paper rolls or other comparable loads.

(3) As shown in the foregoing drawing, a preferred embodiment of the invention has hydraulic flow paths 1 which can selectively extend short arm clamping actuators 10 and 12, and also opposing hydraulic flow paths 2 which can selectively retract the same short arm actuators 10 and 12. These flow paths can selectively clamp or unclamp a load hydraulically, pursuant to control of the short arm actuators 10 and 12, by controlling hydraulic flow which can potentially result in undesirable short arm leakage known as “short arm drift,” which is diverted from hydraulic lines 1 or 2 respectively through respective check valves such as 1a or 2a to intended leakage points 1b or 2b and, if desired, to additional leakage points.

Embodiment 2

(4) However, if “short arm drift” problems persist, a hydraulic system which would otherwise result in short arm drift can utilize an alternative hydraulic circuit element which ensures that a flow path, which introduces fluid into short arm actuators such as 10 and 12, is not a flow path of least resistance and therefore can avoid the foregoing “short arm drift” problem. This is exemplified as follows:

(5) (a) fluid which creates inward drift can be introduced into the “head side” of the short arm actuators and exhausted from the “rod side” of the short arm actuators. Inward drift is prevented by increasing the pressure necessary for exhausted fluid to be returned to the tank. The circuit element used to increase the pressure necessary to exhaust rod side fluid is counterbalance valve assembly 3. By default, the counterbalance valve assembly 3 is preferable set at 1000 psi but could be increased by an adjustment screw 3c. An exemplary component of valve assembly 3 which prevents fluid flow until driving pressure exceeds 1000 psi is labeled as item 3a. Fluid flow in the opposite direction is permitted by counterbalance valve 3b;

(6) (b) alternatively, fluid which creates outward drift can be introduced into the “rod side” of the short arm cylinders and exhausted from the “head side” of the short arm cylinders. Outward drift is prevented by increasing the pressure necessary for exhausted fluid to be returned to tank. An exemplary valve assembly 4 which could be used to increase the pressure necessary to exhaust head side fluid has a counterbalance valve, indicated as Item 4a. By default, the counterbalance valve 4a is preferably set at 1000 psi but can be increased by turning an adjustment screw 4c. An exemplary component of circuit 4 which prevents flow until driving pressure exceeds 1000 psi is labeled as item 4b.

(7) The foregoing circuit element as applied is adjustable in order to compensate for cases where other circuit realities impact the resistance inherent within the alternative flow path. The above-mentioned adjustment screw enables quick field adjustment capabilities. One such circuit element is necessary in cases where “inward” drift is experienced. Another equivalent circuit element could be employed in cases where “outward” drift is experienced.

(8) The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.