US3145866A

US3145866A - Flexible load clamping arms with adjustable fulcrum means

Info

Publication number: US3145866A
Application number: US144940A
Authority: US
Inventors: Stanley E Farmer; Donald M Faust; Harry F Weinert
Original assignee: Cascade Corp
Current assignee: Cascade Corp
Priority date: 1961-10-13
Filing date: 1961-10-13
Publication date: 1964-08-25
Anticipated expiration: 1981-08-25

Description

Aug. 25, 1964 3,145,865

S. E. FARMER ETAL FLEXIBLE LOAD CLAMPING ARMS WITH ADJUSTABLE FULCRUM MEANS Filed Oct. 15, 1961 2 Sheets-Sheet l SianJeyEFarmer Donald M Fa us i Harry/ Weinerf' INVENTORS BY Waxy/W AH fys.

A g- 1964 s. E. FARMER ETAL 3,145,866

FLEXIBLE LOAD CLAMPING ARMS WITH ADJUSTABLE FULCRUM MEANS 2 Sheets-Shee 1 2 Filed Oct. 1.35, 1961 Sianley EFarmer Donald M F0 115? Harry Wein er INVENTORS United States Patent 3,145,866 FLEXIBLE LOAD CLAMPING ARMS WITH ADJUSTABLE FULCRUM MEANS Stanley E. Farmer, Portland, Donald M. Faust, Estacada, and Harry F. Weinert, Portland, reg., assignors, by mesne assignments, to Cascade Corporation, a corporation of Oregon Filed Oct. 13, 1961, Ser. No. 144,940

7 Claims. (Cl. 214-653) This invention relates to material handling apparatus, and more particularly to clamping apparatus, such as is found in lift truck attachments, that includes a pair of oppositely disposed load-clamping arms that are brought together against opposite sides of a load to enable such load then to be picked up and transported.

In the construction of such apparatus, there are a number'of factors that must be considered. Ideally the arms should be as thin as possible, to enable them, for instance, easily to slip between adjacent vertical stacks of articles, such as cartons and the like. Excessive mass should be avoided in the arms, since with relatively light arms a lift truck is more stable and can handle larger loads. Preferably the arms should be devoid of any clamping parts mounted closely thereon, that could shift in position with the arms empty and hinder positioning of the arms on either side of a load. Perhaps most important, some means should be provided for distributing in a clamping arm the clamping force the arms exerts on a load, so that over areas distributed on the side of a load pressures are substantially uniform.

In this connection, it should be remembered that a common type of load handled comprises stacked articles such as cartons. When such a load has nonuniform pressures exerted over a side, those cartons in areas where the highest pressures exist may be damaged, as by crushing, and those cartons in areas of light pressure may become dislodged and fall out of the load. Proper distribution of clamping force is important, not only when full loads are handled, but also in handling partial loads, such as those loads that only partially fill the length of the arms, i.e., only partially fill the space between forward and rear extremities of a pair of arms, and shallow loads that only fill the space between a pair of arms at the bottom of the arms.

Various types of constructions for load-clamping arms have been proposed in the past. A simple arm that is canted inwardy, and that flexes outwardly to reach parallelism with the side of a load when the same is clamped by the arm, is satisfactory when full loads only of a known type of carton or article is handled. However, any change in the size of the load or type of article handled, requiring a change in the clamping force exerted by the arms, cannot be accommodated, as such results in unequal force distribution. A load-clamping arm having one or more load-engaging face plates pivotally mounted on an outer support arm performs satisfactorily with full loads, but with partial loads pivotal action in the face plate or plates produces a nonuniform distribution of clamping force. Further, many of such arms have tended to be bulky, and problems are introduced in maintaining the face plate or plates properly positioned in the absence of a load.

Generally, it is an object of the invention to provide a novel load-clamping arm, constructed in such a manner whereby the above outlined difliculties are taken care of in a highly practical and satisfactory manner.

More specifically, it is an object of this invention to provide a novel load-clamping arm, that includes face plate means adapted to engage the side of a load, and a novel mounting for such face plate means, whereby it is effective to apply a substantially evenly distributed force against the side of a load, over a wide range of clamping forces.

Another object is to provide a load-clamping arm capable of handling full and partial loads, with substantially uniform distribution of clamping force over the side of the load in each instance.

As contemplated by an embodiment of this invention, the load-clamping arm comprises arm structure including an outer, primary arm member that extends forwardly from the usual load carriage of a lift truck, and an inner, secondary arm member joined to a forward portion of the primary arm member and extending forwardly and rearwardly from its location of joinder therewith. A face plate is mounted on the arm structure, through connections with forward and rear portions of the secondary arm member. The primary and secondary arm members flex a certain amount when clamping onto a load, and this is utilized to produce proper distribution of clamping force. The load-clamping arm is devoid of a fully pivotable face plate or plates, such as has characterized some 'prior known constructions.

A further object of the invention, therefore, is to provide a load-clamping arm, where force distribution therein results from members in the clamping arm yieldably and resiliently flexing during the clamping of a load.

Another object is to provide a load-clamping arm, constructed so as to enable a degree of selection in the manner in which a force applied by the arm against the side of a load is distributed.

Yet another object is to provide an improved loadclamping arm having a face plate and a mounting therefor devoid of freely swinging pivot connections.

Other objects include the provision of an improved loadclamping arm that is relatively thin, and preferably tapered progressing from the rear to forward extremities of the arm, and to provide such a load-clamping arm that is relatively strong in relation to its mass and bulk.

These and other objects and advantages are attained by the invention, as will become apparent from the follow ing description, which is to be read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a plan view of a load-clamping arm attachment for a lift truck, with such including a pair of opposed load-clamping arms asconstructed according to one embodiment of the invention;

FIG. 2 is a side elevational view of the attachment illustrated in FIG. 1;

FIG. 3 is a plan View, partially in section, and on a slightly enlarged scale, of one of the load-clamping arms illustrated in FIG. 1;

FIG. 4 is a somewhat simplified view, illustrating diagrammatically the operation of a load-clamping arm, and how flexing of parts therein is operable to produce a distribution of clamping force when the arm is brought against the side of a load;

FIGS. 5 and 6 are similar views, illustrating diagrammatically other features of the operation of a load-clamping arm;

FIG. 7 illustrates a modification of the invention; and

FIGS. 8 and 9 are plan and elevational views, respectively, of still another modification of the invention.

Referring now to the drawings, first of all in particular to FIGS. 1 and 2, the attachment illustrated comprises base structure 5 of conventional construction. The structure includes a series of tubular guides 7 stacked one on top of the other and connected together by mounting plates 9. Slidably mounted in the guides for movement to and fro therein are slides 11. In FIG. 2, the bottommost slide 11 and the slide third up from the bottom can be seen to be attached through portions 13 to a loadclamping arm 15a. Arm 15a projects forwardly from one end of base structure 5. A similar load-clamping arm 1512 projects forwardly from the other end of base structure 5, such being secured through portions 13 to the uppermost slide and the slide third down from the top in FIG. 2.

Base structure 5 is similar to the expansion-contraction mechanism disclosed in Farmer et al., 2,844,403. As can be seen with reference to that patent, the structure includes a double-acting hydraulic motor or ram for each load-clamping arm, utilized in moving the arm to and fro as guided by the slides 11 connected thereto. Conventionally, means may be provided for actuating the rams, whereby both load-clamping arms may be shifted in unison toward one side or the other of the attachment, to effect side shifting, or the load-clamping arms moved toward and away from each other, for the purposes of clamping onto and releasing a load, respectively.

Base structure 5 may be attached in a conventional manner to the usual vertically shiftable load carriage of a lift truck. Thus, when the load carriage is raised, arms 15a, 15b are raised to producing lifting of any load held therebetween, and similarly, lowering of the carriage is effective to lower the arms and any load held thereby. Although the lift truck is not shown, a vertical plane paralleling its longitudinal center line is indicated at Z.

Load-clamping arms 15a, 15b are similar in construction, and only one of them is described in detail. FIG. 3 illustrates load-clamping arm 15a on a somewhat enlarged scale, and reference is now made also to this figure during the more detailed description of a loadclamping arm that follows.

In the embodiment of the invention illustrated, loadclamping arm 150 comprises arm structure, generally indicated at 20, extending forwardly from base structure 5, the latter constituting the means whereby the arm structure is mounted on the load carriage of a lift truck. Positioned on the inner side of arm structure 20, and mounted thereon, is a face plate means, indicated generally at 22.

Arm structure includes an outer portion or primary arm member 26, and an inner portion or secondary arm member 28. The two members are interconnected or joined by a series of nut and bolt assemblies 30 aligned in a vertical row and adjacent the forward extremity or end of the primary arm (see FIG. 2). The nut and bolt assemblies provide a fixed connection or fastening at the location of joinder between the two arm members.

As already indicated, it is preferable that the loadclamping arm be relatively thin, with a minimum of mass in relation to its strength. A suitable construction is the one shown for the arm member, comprising a pair of

plates

31, 32 joined in a suitable manner along their rear set of edges or ends to a vertical bar 33. The forward set of edges or ends of the plates are secured in a suitable manner to a vertical bar 35.

Plates

31, 32 give a thin, slightly tapered profile to the primary arm member.

In the load-clamping arm, the primary arm member is toed in, so that progressing from rear to forward portions of the arm member it inclines inwardly at an angle X (see FIG. 1) relative to plane Z paralleling the longitudinal center line of the lift truck. The primary arm member ordinarily is constructed of metal, and as would be expected the arm member is not completely rigid, but somewhat flexible, so that forward portions of the arm member deflect outwardly when a load is clamped. To be noted is the fact that plate 31 of the arm member extends forwardly some distance beyond the forward end or edge of plate 32 and the location of joinder of arm member 26 with arm member 28. Because of the single plate thickness existing along forward portions of arm member 26, the arm member along these forward portions is somewhat more flexible than rear or butt portions of the arm member.

Secondary arm member 28 in the embodiment illustrated comprises a plate 36 that mounted in operative position is slightly bowed and has its concave side facing inwardly. The plate extends forwardly and rearwardly of nut and bolt assemblies 30 (or the location of joinder of arm member 28 with arm member 26). The midline of plate 36 is indicated at 37 (See FIG. 3), and this midline, it should be noted, is located somewhat rearwardly of nut and bolt assemblies 30.

Arm member 28 is also usually made of metal, and somewhat flexible, and on clamping onto a load, the arm member undergoes a flexing approximating a flattening action.

Face plate means 22, in the embodiment of the invention shown in FIGS. 1, 2, and 3, comprises a single clamping pad and includes an expansive plate 38 extending substantially the full length of the load-supporting arm. Secured in a suitable manner to the inner face or side of plate 38 is a backing plate 39 having a layer 40 of rubber or the like bonded thereto.

The face plate means is mounted on the arm structure through connections with secondary arm member 28. Thus, a series of nut and bolt assemblies 42 arranged in a vertical row connect the forward edge of the secondary arm member with the forward edge of face plate means 22, and a similar series of nut and bolt assemblies 44 connect the rear edge of the secondary arm member with the rear edge of the faec plate means. The bolts of the various assemblies pass through grommets 46 of elasto meric material, which function to prevent looseness in the connections, but accommodate a degree of tilting of the face plate means relative to portions of the secondary arm directly adjacent the nut and bolt assemblies.

A feature of the invention is that flexibility present in the primary and secondary arm members is relied upon to produce proper distribution of clamping force. Important in this connection is the extent of deflection that is allowed that portion of the inner or secondary arm member that extends rearwardly of nut and bolt connections 30 (or the location of joinder of the two arm members). Means is provided for restricting the deflection of this rearwardly extending portion of the secondary arm member, and such means takes the form of fulcrum bolts or studs 50 mounted on the primary arm member with inner ends engaging the secondary arm member 28 in the vicinity of its midline. The bolts are screwed into internally threaded bores 52 provided in plate 31 of the primary arm member, and jam nuts 54 are screwed onto the bolts to secure them tightly in place. When the loadsupporting arm clamps onto a load, the fulcrum bolts restrict flexing of the secondary arm member, in the sense that if deflection occurs, such is concentrated in portions of the arm member disposed rearwardly of the bolts.

It should be noted (see FIG. 2) that plural rows of vertically aligned bores 52 are provided in arm member 26. The rows are spaced a short distance apart. This enables the position of bolts 50 on the primary arm member to be changed. The bolts, of course, can also be adjusted to vary the extent they project inwardly of plate 31. These adjustments, as will be described, are important in setting up the arm for a desired type of force distribution.

Secured to face plate means 22, by screws 56, is a deflector plate 58. Plate 58 extends rearwardly and on the outside of the load-clamping arm over forward end or edge portions of secondary and

primary arm members

26, 28. The deflector plate covers projections in forward portions of the load-clamping arm, thus to give it a smooth outer contour. Face plate means 22 ordinarily is approximately parallel to the longitudinal center line of the lift truck, and as previously mentioned the primary arm member inclines inwardly. Thus, the deflector plate, primary arm member, and face plate means 22 together give a substantially tapered outline to the loadclamping arm as a whole. With the arm not engaging a load, the various parts are held without looseness, and the profile mentioned is maintained. This facilitates proper positioning of the clamping arm on the side of a load. The tapered profile and smooth outer contour facilitate picking up articles that are stacked in side-byside rows, when the arm must be thrust between closely adjacent rows.

Reference is now made to FIG. 4, which illustrates diagrammatically the load-clamping arm just described, and the functioning of various parts in the load-clamping arm when the same is used to pick up a load 60 that fully fills the arm. The arm as it appears in solid outline is in the condition it normally has when not exerting a clamping force, i.e., its relaxed state. In this relaxed state, the face plate means is approximately parallel to the midline of the lift truck, the secondary arm member bowed, and engaged along one side by fulcrum bolts 50, and the primary arm member defines an acute angle relative to the plane of the face plate means. For reasons of clarity, some exaggeration has been made in the figure of the incline of the outer or primary arm member and the extent that the inner arm member is bowed.

The dashed outline of the load-clamping arm in FIG. 4 illustrates the arm when the same is applying a clamping force. When such a clamping force is applied by the arm, the forward end of the primary arm member deflects outwardly, to assume a position more closely paralleling the plane of the face plate means. This deflection alone results in an inward force being exerted on rear portions of the face plate means. Movement of the face plate means is resisted by the load the plate means is engaging. Deflection of the primary arm member is also accom panied with deflection of the inner or secondary ann member, and more particularly that portion of the secondary arm member that extends rearwardly of nut and bolt assemblies 30. The secondary arm member tends to bend, with the rearwardly extending portion thereof bending about the fulcrum location established by bolts 50. Instead, therefore, of having a force applied substantially entirely on a forward portion of the load, as would be the case if there were no fiexure present, a distribution of force occurs, and rear portions of the load are clamped by a force related to the dimensions and flexibility of the various parts present in the arm.

For a given setting of bolts 50, a distribution of force may be produced, wherein the force exerted by the rear of the face plate means is substantially equal to the force exerted by the front of the face plate means, i.e., a 50-50 force distribution occurs. This ratio has been found to stay approximately the same, regardless of whether the total clamping force exerted by the arm is large or small.

For purposes of explanation, let it be assumed that loads are to be handled that do not fill the length of the load-clamping arms, i.e., the loads fill the space between the arms only along forward portions of the arms, such as load 70 illustrated in FIGS. 5 and 6. In this situation a 50-50 distribution of clamping force may not be desirable, as such may result in the crushing of rear portions of the load, if it is at all fragile. This is because of the fact that with such partial loads, a substantial part of the face plate means at the rear thereof does not engage any portion of the load, and thus while the clamping force of the face plate means at the forward end thereof is exerted on a large expanse of the side of a load, at the rear of the face plate means the clamping force is exerted upon a relatively small area of the side of the load. As a result, the load is clamped with greater pressure along the rear than at the front thereof.

In such a circumstance, it may be desirable to shift bolts 50 to a series of vertically aligned bores 52 located more forwardly on the load-clamping arm than was their setting when full loads were handled. Thus, with reference to FIG. 5 (which shows the clamping arm in a relaxed state) it will be noted that bolts 50 are nearer nut and bolt assemblies 30 than they are in the arm of FIG. 4. With such a setting, for a given clamping force,

a greater amount of deflection is permitted rear portions of the secondary arm member, and if the load-clamping arm were to engage the side of a full load a larger percentage of the total force of the load-clamping arm would be exerted on the load by a forward portion of the face plate means than was the case with the bolts 50 in their original setting. For instance, the ratio of force distribution might be in the range of 60-40. With the loadclamping arm engaging a partial load, and with a smaller amount of force distributed to the rear of the face plate means, over that area of the face plate means that actually engages the load, the clamping force of the arm tends to be substantially evenly distributed. From this it will be seen that a means is provided for adjusting the type of force distribution that occurs in the load-clamping arm, to take care of special load handling conditions.

In FIG. 7 there is illustrated a modified form of the invention where, instead of a face plate means comprising a single unitary plate, such as plate 38 of the first embodiment, an assembly of double plates indicated at 76, 78 is provided. Such a construction may be desirable, for instance, where loads handled are for the most part full loads, and force distribution in general is to be maintained approximately at a 5050 ratio. As in the case of the earlier embodiment discussed, flexibility in the primary arm member and secondary arm member is relied upon to produce the force distribution desired.

In FIGS. 8 and 9 a still further embodiment of the invention is illustrated. In this instance, an arm structure 80 is shown that comprises a single unitary plate, with fingers 80a reversely turned and projecting rearwardly thereof, and fingers 8% extending forwardly at the forward edge of the plate. Thus, instead of separate primary and secondary arm members joined together with nut and bolt assemblies, an integral type of construction is contemplated. The construction of FIGS. 8 and 9 is similar to the construction of FIGS. 1, 2, and 3, in that in both arm structures are present, having an outer portion that extends forwardly from the means mounting the arm structure on a load carriage, and a defiectable inner portion joined to said outer portion at a location spaced forwardly of such means with the inner portion extending rearwardly from its location of joinder with the outer portion. As in the case of the first embodiment described, a face plate means 22 may be provided, secured to the ends of fingers 80a, 80b in a suitable manner.

A number of embodiments of the invention have been discussed for the purpose of fully illustrating the same. It is not intended by the discussion of these embodiments to limit the invention only to those constructions disclosed. It is appreciated that various changes may be made in the selection of the parts and/or their organization, without departing from the invention and it is therefore intended to cover all modifications and variations that would be apparent to one skilled in the art, and that come within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a load-clamping arm, said arm having an outer side and an inner side opposite said outer side that faces a load, the improvement comprising a flexible primary arm member adjacent the outer side of the arm, means for mounting the rear end of said primary arm member on a truck, a flexible secondary arm member disposed on the inner side of said primary arm member and joined to the latter at a location spaced forwardly of the rear end of the primary arm member, said secondary arm member including a portion extending rearwardly from the location of joinder of the secondary arm member with the primary arm member, fulcrum means mounted on the primary arm member and engaging the rearwardly extending portion of the secondary arm member at a point disposed intermediate the location of joinder of the secondary arm member with the primary arm member and the rear margin of the secondary arm member, face plate means mounted at least in part on said rearwardly extending deflectable portion of said secondary arm member, and means accommodating a change in the position of said fulcrum means, such a change in a position of said fulcrum means being effective to change the amount of deflection occurring in the secondary arm member under load conditions.

2. In a load-clamping arm, said load-clamping arm including a. flexible primary arm adapted to be mounted at the rear end thereof on a lift truck with the arm extending forwardly from the truck, and face plate means disposed inwardly of said primary arm adapted to engage the side of a load, the improvement comprising a flexible secondary arm between said face plate means and primary arm joined to a forward portion of the latter and extending both forwardly and rearwardly from its point of joinder with said primary arm, first mounting means mounting said face plate means on a portion of said secondary arm which is located rearwardly of said point of joinder of said secondary arm with said primary arm, second mounting means mounting said face plate means on a portion of said secondary arm which is located forwardly of said point of joinder of said secondary arm with said primary arm, said first and second mounting means accommodating canting of said portions of said secondary arm relative to said face plate means, and fulcrum means mounted on said primary arm, engageable with said secondary arm at a point on the secondary arm located forwardly of said rear portion of said secondary arm and rearwardly of said point of joinder of said secondary arm with said primary arm, said fulcrum means producing bending of said rear portion of said secondary arm outwardly about said fulcrum means upon said loadclamping arm picking up a load, with such bending producing a force distribution in the load-clamping arm.

3. In a load-clamping arrn, said load-clamping arm including a flexible primary arm adapted to be mounted at the rear end thereof on a lift truck, with the arm extending forwardly from the truck, and face plate means comprising a clamping pad disposed inwardly of said primary arm adapted to engage the side of a load, the improvement comprising a flexible secondary arm mounted between said pad and primary arm joined to a forward portion of the latter and extending forwardly and rearwardly from its point of joinder with said primary arm, means mounting said pad on a portion of said secondary arm which is located rearwardly of the point of joinder of said secondary arm with said primary arm and on a portion of said secondary arm which is located forwardly of the point of joinder of said secondary arm with said primary arm, and fulcrum means mounted on said primary arm engageable with said secondary arm at a point on the secondary arm located forwardly of said rear portion of the arm and rearwardly of said point of joinder of the secondary arm with said primary arm, said fulcrum means producing bending of said rear portion of said secondary arm outwardly about said fulcrum means on said load-clamping arm picking up a load with such bending producing a force distribution in the load-clamping arm.

4. The load-clamping arm of claim 3, wherein the point of joinder of said secondary arm with sail primary arm is disposed substantially forwardly of the center of said secondary arm, and the means engaging said secondary arm is adjustable thus to accommodate change in the extent that the secondary arm bends upon said loadclamping arm picking up a load.

5. In a load-clamping arm, said load-clamping arm including a flexible primary arm adapted to be mounted at the rear end thereof on a lift truck, with the arm extending forwardly from the truck, and face plate means comprising a clamping pad disposed inwardly of said primary arm adapted to engage the side of a load, the improvement comprising a flexible secondary arm between said pad and primary arm joined to a forward portion of the latter and extending both forwardly and rearwardly from its point of joinder with said primary arm, first mounting means mounting said pad on a portion of said secondary arm which is located rearwardly of said point of joinder of said secondary arm with said primary arm, second mounting means mounting said pad on a portion of said secondary arm which is located forwardly of said point of joinder of said secondary arm with said primary arm, said first and second mounting means accommodating canting of said portions of said secondary arm relative to said pad, and fulcrum means mounted on said primary arm engageable with said secondary arm at a point on the secondary arm located forwardly of said first mounting means and rearwardly of said point of joinder of said secondary arm with said primary arm, said fulcrum means producing bending of said rear portion of said secondary arm outwardly about said fulcrum means on said load-clamping arm picking up a load with such bending producing a force distribution in the load-clamping arm.

6. The load clamping arm of claim 2, which further comprises means for changing the position of the fulcrum means whereby the bending occurring in the secondary arm under load conditions may be adjusted.

7. In a load-clamping arm, said load-clamping arm including a flexible primary arm adapted to be mounted at the rear end thereof on a lift truck, with the arm extending forwardly from the lift truck, and face plate means comprising a clamping pad disposed inwardly of the primary arm adapted to engage the side of a load, the improvement comprising a flexible secondary arm between said pad and primary arm joined to a forward portion of the latter and extending both forwardly and rearwardly from its point of joinder with the primary arm, first mounting means mounting the pad on a portion of the secondary arm which is located reawardly of the point of joinder of the secondary arm with the primary arm, second mounting means mounting the pad on a portion of said secondary arm which is located forwardly of the point of joinder of the secondary arm with said primary arm, said first and second mounting means including yieldable devices accommodating canting of the portions of said secondary arm relative to said pad, fulcrum means mounted on the primary arm engageable with the secondary arm at a point on the secondary arm located forwardly of the first mounting means and rearwardly of the point of joinder of the secondary arm with the primary arm, and means for adjusting the position of the fulcrum means, said fulcrum means producing bending of said rear portion of the secondary arm outwardly about the fulcrum means on the load-clamping arm picking up the load with such bending producing a force distribution in the load-clamping arm.

References Cited in the file of this patent UNITED STATES PATENTS 2,120,945 Sprankle June 14, 1938 2,528,979 Smulski Nov. 7, 1950 2,674,387 Ehmann Apr. 6, 1954 2,707,394 Lewis May 3, 1955 2,782,066 Lord Feb.19, 1957 2,819,113 Phillips Jan. 7, 1958 2,822,209 Cichaczewski Feb. 4, 1958 2,844,403 Farmer et al July 22, 1958 2,956,700 Quayle Oct. 18, 1960

Claims

1. IN A LOAD-CLAMPING ARM, SAID ARM HAVING AN OUTER SIDE AND AN INNER SIDE OPPOSITE SAID OUTER SIDE THAT FACES A LOAD, THE IMPROVEMENT COMPRISING A FLEXIBLE PRIMARY ARM MEMBER ADJACENT THE OUTER SIDE OF THE ARM, MEANS FOR MOUNTING THE REAR END OF SAID PRIMARY ARM MEMBER ON A TRUCK, A FLEXIBLE SECONDARY ARM MEMBER DISPOSED ON THE INNER SIDE OF SAID PRIMARY ARM MEMBER AND JOINED TO THE LATTER AT A LOCATION SPACED FORWARDLY OF THE REAR END OF THE PRIMARY ARM MEMBER, SAID SECONDARY ARM MEMBER INCLUDING A PORTION EXTENDING REARWARDLY FROM THE LOCATION OF JOINDER OF THE SECONDARY ARM MEMBER WITH THE PRIMARY ARM MEMBER, FULCRUM MEANS MOUNTED ON THE PRIMARY ARM MEMBER AND ENGAGING THE REARWARDLY EXTENDING PORTION OF THE SECONDARY ARM MEMBER AT A POINT DISPOSED INTERMEDIATE THE LOCATION OF JOINDER OF THE SECONDARY ARM MEMBER WITH THE PRIMARY ARM MEMBER AND THE REAR MARGIN OF THE SECONDARY ARM MEMBER, FACE PLATE MEANS MOUNTED AT LEAST IN PART ON SAID REARWARDLY EXTENDING DEFLECTABLE PORTION OF SAID SECONDARY ARM MEMBER, AND MEANS ACCOMMODATING A CHANGE IN THE POSITION OF SAID FULCRUM MEANS, SUCH A CHANGE IN A POSITION OF SAID FULCRUM MEANS BEING EFFECTIVE TO CHANGE THE AMOUNT