Boom Length Indicator

Abstract

The length of a telescoping boom on a crane is indicated to the crane operator by a reel of cable mounted on a fixed portion of the boom with a free end of the cable secured to the far end of the boom so that extension of the boom will pull cable from the reel. A measuring pulley is rotated by cable withdrawn from the reel or retracting into the reel, this measuring pulley operating an electrical potentiometer to provide an electrical signal proportional to the length of cable withdrawn. This signal operates a meter calibrated in units of length in the cab of the crane so that the operator is at all times advised of the length of the boom.

Description

This invention relates generally to indicators for use with cranes and more particularly to an indicator for displaying the length of a crane boom wherein the length of the boom is varied by changing the distance of the far end of the boom from the base of the crane.

BACKGROUND OF THE INVENTION

Many types of cranes utilize extensible boom structures either by articulated elements or nested telescoping tubes. If the angle of the boom is relatively small so that the boom is extending more in a horizontal direction than a vertical direction, heavy loads on the end of the boom structure can exert a substantial moment on the crane itself tending to topple the crane over. When a telescoping type crane carries such a load and even though the crane operator knows of the weight of the load, telescoping outwardly of the boom will increase the moment arm length and thus increase the tipping moment tending to topple the crane even though the load remains constant. To operate the crane safely, it is therefore necessary that the crane operator know at all times the length of the extended boom as well as the load at the end of the boom.

It will also be evident from the above that the angle of the boom is an important parameter in determining the lever are length through which any load is transmitted to the crane itself. Most crane manufacturers supply adequate information displayed in the cab of the crane relating to boom angles and load so that an operator can use the crane safely. In variable boom length types of cranes, however, it is also necessary, as noted above, that the operator be continuously apprised of the exact length of the boom, this information together with the boom angle information and load information then being sufficient so that the operator can be assured that the crane will not topple provided certain of the parameters are not exceeded.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

With the foregoing in mind, the present invention contemplates a simple, rugged, and extremely reliable boom length indicator for providing an indication at all times to a crane operator of the length of the boom structure as the far end of the boom varies in distance from the base of the crane.

More particularly, the invention comprises a reel of cable for attachment to a fixed portion of the boom, the free end of the cable being securable to the far end of the boom so that extension of the boom pulls cable from the reel. A biasing means exerts a retracting force on the cable to maintain the cable under tension. Means responsive to movement of the cable to indicate the amount of cable pulled from the reel are provided so that, in turn, an indication of the boom length is provided.

A first important feature of the invention is included in the biasing means wherein a substantially constant tension can be maintained in the cable over a longer length of withdrawn cable for a given sized biasing means than has been possible heretofore.

A second feature resides in the inclusion of means responsive to a sudden decrease in the tension in the cable as might result from a breaking or inadvertent release of the free end of the cable for preventing the continuous retraction of the cable onto the cable reel.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be had by now referring to a preferred embodiment thereof as illustrated in the accompanying drawings in which:

FIG. 1 is a rear elevational view of a typical crane with telescoping boom utilizing the boom length indicator of the present invention;

FIG. 2 is an enlarged perspective view of basic components making up the boom length indicator of this invention;

FIG. 3 is a schematic circuit diagram of electrical portions of the boom length indicator;

FIG. 4 is a side cross-section of a portion of the boom length indicator taken in the direction of the arrows 4--4 of FIG. 2; and,

FIG. 5 is a top cross-section of the same portion taken in the direction of the arrows 5--5 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1 there is shown a crane 10 having a rotational base portion 11 mounting a telescoping boom comprised of a fixed part 12 and telescoping tubes 13 and 14. The far end of the boom terminates in a boom head 15.

While the telescoping or extendable boom structure takes the form of nested tubes as shown in FIG. 1, it should be understood that the boom length indicator of the present invention can be utilized with any type of extensible boom structure wherein the distance of the far end from the base of the crane is varied.

Still referring to FIG. 1, the boom length indicator of this invention includes a housing 16 arranged to be rigidly mounted on the fixed portion 12 of the boom. As will be clear as the description proceeds, the housing 16 incorporates a reel of cable having a free end which may be pulled from the housing. The free end of the cable shown at 17 includes bracket means 18 for securing it to the far end of the boom or to the head 15. With this arrangement, extension of the boom will pull the cable 17 from the housing 16.

The housing 16 also incorporates means responsive to the length of cable pulled from the housing for providing an electrical signal constituting a function of the length of the cable and thereby a function of the length of the boom. An electrical conduit 19 for this purpose extends from the housing 16 to an indicating device or meter 20 which is preferably disposed in the cab 21 for easy observance by the crane operator. The face dial of the meter is calibrated in units of length.

Referring to FIG. 2 further details of the housing 16 and indicator 20 will be evident. As shown, the housing 16 includes flange means 22 enabling rigid securement of the housing to the fixed portion of the boom structure. In mounting the housing, the top surface thereof as well as the edge of the flange should be disposed in alignment with the direction of extension and retraction of the boom sections. This direction is also parallel to the exit direction of the cable 17 from the housing 16. In addition, it is desirable although not essential that the housing 16 be mounted as close as possible to the first movable or telescoping portion of the boom. By so mounting the housing, less cable is required for providing accurate length indications over the entire range of telescoping movement than would be the case were the housing mounted further from the first movable section.

The housing 16 itself includes a removable cover 23 to provide ease access to the interior thereof for maintenance purposes without the necessity of actually removing the housing from the boom. The outlet portion for the cable 17 is provided on the upper front portion of the housing as indicated at 24. The means for securing the free end of the cable 17 may take the form of a ring 25. This ring may thus simply be coupled to the bracket structure 18 on the far end of the boom as described in FIG. 1.

As will become clearer as the description proceeds, there is incorporated in the housing 16 means for applying a constant retraction force on the cable 17 so that it is at all times under tension. Under these circumstances, it will then be evident that the length of cable withdrawn from the housing 16 will be a function of the overall length of the boom.

Still referring to FIG. 2, the electrical signal provided in response to the length of cable withdrawn appears at an outlet socket 26 on the housing 16 for cooperation with a suitable plug on the cable 19 passing to the indicating meter 20. As shown, the meter itself may include a front glass 27 covering the dial for easy reading directly in units of length. Electrical power for the system is provided through a power plug line 28 which may be connected to the crane battery.

Essentially, movement of the cable 17 from the housing 16 operates an electrical potentiometer within the housing 16. The circuit is schematically illustrated in FIG. 3 wherein the potentiometer is shown at 29 and includes a slider movable up and down a resistance. The potentiometer resistance itself is connected across the battery B of the crane and the slider simply selects a voltage from this resistance which can vary between the maximum battery voltage and zero. The signal indicative of the length of cable withdrawn therefor is derived from the slider and passed through the electrical conduit leads 19 to an amplifier 30 and suitable meter M all housed within the indicator device 20 shown in FIG. 2. Withdrawal of the cable moves the potentiometer slider upwardly thereby providing an increased voltage and thus an increased meter reading. Retraction of the cable which will occur since the cable is under tension when the boom is retracted results in the potentiometer slider moving downwardly to decrease the voltage signal thereby reducing the reading on the meter.

The manner in which the foregoing takes place will now become clear by referring to FIGS. 4 and 5 which illustrate details of the mechanism within housing 16.

Referring first to the side cross-section of FIG. 4, the cable 17 is shown wound on a cable reel 31 rotatably mounted within the housing 16. In the particular embodiment illustrated, the cable passes over idler rollers 32 and 33 and thence passes out of alignment with its initial path to circle around a tension roller 34, the purpose for which will become clearer as the description proceeds. The cable then passes up over an idler roller 35 and thence around a measuring pulley 36. From the measuring pulley 36, the cable passes over a last idler roller and thence between friction means in the form of opposing pads 38 and 39 spring biased together to exert a slight drag on the cable as it is withdrawn from the outlet 24.

The measuring pulley 36 rotates a worm gear 40 coaxial with its rotative shaft. Gear 40 in turn is coupled to a ring gear 41 connected to the electrical potentiometer 29 to move the slider described in conjunction with FIG. 3. Electrical leads from the potentiometer 29 are housed in a conduit 42 passing to the socket portions 26 described in conjunction with FIG. 2. The foregoing described elements are also clearly visible in the top view of FIG. 5.

Referring both to FIGS. 4 and 5, a biasing means for exerting a rotative force on the cable reel 31 in a direction tending to retract the cable 17 is provided by a Negator spring means including reel 43 and coiled Negator spring 44. As shown, the Negator spring 44 is back-wound on a drum 45 also rotatably mounted in the housing 16. Gear means 46 and 47 couple the Negator spring means to the cable reel 31 through shaft 48 for the cable reel. This gear means is such that for each complete rotation of the cable reel 31, the drum 45 only executes a partial rotation so that a constant tension is applied over a greater length of withdrawn cable than would be the case in the absence of the gear means 46 and 47 for a similar sized Negator spring means, cable reel and housing. It will be understood that the rotative force biasing the cable reel in a direction tending to retract the cable is a result of such turning torque being applied to the drum 45 by the Negator spring 44, this spring having a tendency to return to its initial coiled configuration. In FIG. 4, the small arrows on the gears 46 and 47 indicate the direction of the turning torque applied by the Negator spring and it will be clear that when this force is transmitted to the cable reel 31 through the shaft 48, the cable 17 is biased to wind up on the cable reel.

In addition to the Negator spring biasing means and cooperating gear means described, another feature of this invention resides in a means for preventing the continuous retraction of the cable by the reel and cooperating Negator spring means in the event tension in the cable is suddenly lost as by breaking of the cable or inadvertent release of the free end of the cable. This means can best be seen in FIG. 4 and in the embodiment illustrated includes a bell crank means 49 pivoted about a shaft 50 secured to the housing 16. The shaft 50 may also serve to rotatably mount the idler roller 32. This mounting for the bell crank 49 permits swinging movement of the bell crank in the plane of the cable reel 31. It will be clear from the view in FIG. 5 that there are actually provided two arms for the bell crank structure on either side of the reel 31 so that downward swinging can take place without interference with the reel.

Referring particularly to FIG. 4, one end of the bell crank includes a pressure bar 51 cooperating with a friction pad 52 mounted on the housing to oppose a peripheral portion of the cable reel 31. The cable 17 passes between the one end comprising the pressure bar 51 and the friction pad 52 as shown such that the pressure bar 51 is movable into and out of engagement with the friction pad 52 upon swinging movement of the bell crank means 49.

The other end of the bell crank means 49 terminates in the tension roller 34 which, as described heretofore, is out of alignment with the initial path of the cable 16 between the idler rollers 32 and 33 such that tension on the cable tends to move the tension roller 34 in a direction towards the initial cable path; that is, upwardly as viewed in FIG. 4. Movement of the bell crank 49 in this manner will move the pressure bar 51 our of engagement with the pressure pad 52 so that the cable is free to move from the reel 31.

Attached to the far end of the bell crank 49 adjacent to the tension roller 34 as at 53 is a bias means in the form of a coiled spring 54. The other end of the bias means is secured to the housing as at 55. This bias means exerts a force on the bell crank 49 tending to swing it in the opposite direction from the force applied by the tension roller 34. Since the distance of the tension roller from the pivot point of the bell crank is substantially greater than the distance of the one end at which the pressure bar is disposed from the pivot point, the bias means need not exert a strong force and only a light tension, force is necessary to release the cable. However, such given light tension as a minimum must always be applied to the cable 17 in order that it can be pulled from the reel 31 and any removal or sudden diminution in this tension will permit the bell crank means 49 to swing and thus clamp the cable between the bar 51 and pressure pad 52.

OPERATION

The operation of the boom length indicator will be evident from the foregoing description. With the housing 16 and indicating meter 20 mounted on a fixed portion of the boom and in the crane cab respectively as described heretofore in conjunction with FIG. 1, the free end of the cable 17 from the housing 16 may be secured by the crane operator to the far end of the boom as by means of the ring attachment 25. This attaching of the cable is best done with the boom rully retracted.

After the free end of the cable has been properly attached to the end of the boom, and with the boom fully retracted, small set screws (not shown) on the potentiometer 29 within the housing 16 may be adjusted to provide a reading on the meter 20 in the cab of the minimum boom length. This small adjustment of the potentiometer is schematically illustrated in FIG. 3 and designated Dmin. Thereafter, the boom may be extended to its maximum extended position thereby pulling the cable 17 from the housing 16 and resulting in movement of the potentiometer tap through the gear means described in FIGS. 4 and 5 in an upward direction. A Dmax adjustment shown in FIG. 3 is then made in the potentiometer to provide a reading corresponding to the actual length of the boom when it is fully extended.

Thereafter, any intermediate position of the cable 17 will provide an indication on the meter 20 of the correct length of boom intermediate its minimum and maximum extension.

Because of the action of the Negator spring applying a retraction force on the cable, the cable will always be under tension and thus will remain substantially straight so that an accurate reading proportional to the length of cable withdrawn and thus proportional to the boom length is provided. As mentioned heretofore, the gear means coupling the Negator spring to the cable reel is such that a greater overall length of cable with uniform tension therein can be withdrawn than would be possible in the absence of the gear means.

Finally, in the event the cable itself should break or in the event that an operator should inadvertently release the far end of the cable when attempting to attach the same to the far end of the boom, the bell crank arrangement described in FIGS. 4 and 5 will effectively clamp the cable to thereby prevent continuous retraction into the housing 16. Dangerous whiplashing of the cable under such circumstances of inadvertent loss of tension is thus avoided.

The small opposed friction pads 38 and 39 exerting a slight drag on the portion of the cable 17 passing from the housing prevents slack from forming in the portion of the cable between the friction pad 52 and pressure bar 51 and the cable portion passing over the last idler roller 37 in the event of sudden loss of tension wherein the cable is clamped by the friction pad. Such slack could result in the cable possibly becoming disengaged from one or more of the idler rollers as well as possible slippage relative to the measuring pulley 36. The drag provided by the friction pads 38 and 39 prevent this slack from occuring.

From the foregoing description, it will be evident that the present invention has provided a greatly improved boom length indicator which is simple, compact, rugged in construction, and accurate in view of the direct proportion of boom length with length of withdrawn cable.

Claims

What is claimed is:

1. For use in a crane having a cab for housing a crane operator and an extensible boom under control of the operator, a boom length indicator including in combination:

a. a housing having flange means for securing the housing in a fixed position to a fixed portion of the boom;

b. a cable reel rotatable mounted in said housing;

c. a cable wound on said reel with its free end passing through an opening in the housing;

d. means for securing said free end to the far end of the boom so that extension of the boom will pull the free end of the cable from the housing;

e. a Negator spring coil back-wound on a drum mounted in said housing so that a substantially constant turning torque is applied to the drum as the Negator spring rewinds itself back to a coil, the drum being coupled to the reel to apply a rotative force on the reel in a direction to retract the cable so that tension is maintained in the cable, the coupling of the drum to the reel including gear means such that for each complete rotation of the reel, the drum executes only a partial rotation as determined by the gear ratio of the gear means, whereby a substantially constant tension can be maintained in the cable over a longer length of withdrawn cable for a given sized Negator spring, cable reel and housing therefor than is possible in the absence of gear means;

f. a measuring pulley in said housing, the cable passing around a peripheral portion of the measuring pulley to rotate the measuring pulley in one direction or the other as the cable is extended or retracted, respectively, and a potentiometer resistance having a movable slider geared to the measuring pulley for movement in one direction or the other depending on the direction of rotation of the measuring pulley so that an electrical signal may be derived from said slider having a value that is a function of the length of cable pulled from the reel and thereby a function of the length of the boom;

g. an indicator means for mounting in said cab of the crane electrically connected to said potentiometer for converting said electrical signal into a visual display of the length of the boom; and

h. means in the housing for preventing the continuous retraction of the cable in the event tension in the cable is suddenly lost as by the breaking of the cable or inadvertent release of the free end of the cable, said means including: a bell crank means pivoted for swinging movement in a plane parallel to the plane of the cable reel; a friction pad fixed in the housing in a position facing peripheral portion of the reel, one end of the bell crank means being movable into and out of engagement with the friction pad upon swinging movement about its pivot, the cable from the reel passing between the pad and said one end, the other end of the bell crank means terminating in a tension roller; idler roller means mounted in said housing guiding the cable along a path wherein the cable passes about the tension roller out of alignment with its initial path in such a manner that tension in the cable tends to move the tension roller towards the cable path to swing the bell crank means in a direction to move its said one end out of engagement with the pad so that the cable can move freely from the reel; and bias means urging the bell crank means in an opposite direction so that a given tension must be maintained to overcome the bias means, sudden loss of tension in the cable permitting the bell crank means to swing in said opposite direction so that its one end clamps the the cable against the friction pad.

2. A boom length indicator according to claim 1, including friction means adjacent to the idler roller means for engaging the portion of the cable passing from the last of the idler roller means towards the far end of the boom for exerting a slight drag on the cable to prevent slack from forming in the cable portion between the friction means and said friction pad in the event of sudden loss of tension in the cable.