Pivoting load-bearing assembly with force sensor

Abstract

A load-bearing assembly including a clamping-force sensor in a pivoting support assembly that is adjustable to vary a radial spacing between a pivot pin and a clamp pad supported on the support assembly. A plurality of clamping-force sensors may be included in a plurality of pivoting clamp pad support assemblies to support a clamp pad and may be arranged to sense the magnitude of a clamping force exerted by a particular adjustable pivoting clamp pad support assembly and send signals indicative of the magnitude of the force to a controller. Force values sensed and transmitted to the controller may be used to evaluate and adjust the clamp arm assembly to grasp a load with a desired clamping force or distribution of clamping forces.

Claims

1. A load grasping assembly for a lift truck, comprising: (a) a clamp arm assembly, included in a lift truck attachment adapted to be mounted on a lift truck; (b) a clamp pad; (c) a pivoting clamp pad support assembly, carried by said clamp arm assembly and connected to and supporting said clamp pad, said pivoting clamp pad support assembly including a bearing block, mounted on a pivot pin so as to pivot through a limited angle with respect to the clamp arm assembly, and said pivoting clamp pad support assembly including a force sensor, the force sensor being mounted with respect to said bearing block and said pivot pin in such a way as to sense in isolation and measure a magnitude of a force exerted by said pivoting clamp pad support assembly through said bearing block and acting on said clamp pad in a predetermined direction while said load grasping assembly grasps a load, and wherein said force sensor is electrically connected so as to provide an electrical signal representative of the magnitude of said force exerted in said predetermined direction as measured by said force sensor at a particular time.

2. The load grasping assembly of claim 1, wherein said predetermined direction in which said force is exerted is a radial, clamping-force, direction relative to said pivot pin.

3. The load grasping assembly of claim 1 including a plurality of said pivoting clamp pad support assemblies, each one of said plurality being carried on said clamp arm assembly and being connected to and supporting said clamp pad, and each one of said plurality being mounted on a respective pivot pin so as to be free to pivot through a respective limited angle.

4. The load grasping assembly of claim 3, wherein each one of said plurality of said clamp pad support assemblies includes a respective force sensor mounted so as to sense a force exerted in said predetermined direction.

5. The load grasping assembly of claim 3, wherein said clamp pad is a carton clamp pad carried by said plurality of said pivoting clamp pad support assemblies, at least one of said pivoting clamp pad support assemblies being adjustable to establish a selected distance in said predetermined direction between a related part of the carton clamp pad and said pivot pin.

6. The load grasping assembly of claim 3 wherein the respective pivot pin of each one of said plurality of pivoting clamp pad support assemblies carried on said clamp arm assembly is vertical and coaxially aligned with the respective pivot pin of each other one of said plurality of pivoting clamp pad support assemblies carried on said clamp arm assembly.

7. The load-grasping assembly of claim 6 wherein said clamp arm assembly includes a load stabilizer including a plurality of elongate horizontal members and wherein respective ones of said plurality of said pivoting clamp pad support assemblies are carried on a plurality of respective ones of said plurality of elongate horizontal members and wherein each one of said plurality of pivoting clamp pad support assemblies is moveable about a respective pivot axis relative to a respective one of said plurality of elongate horizontal members on which it is carried.

8. The load grasping assembly of claim 7 wherein one of said elongate horizontal members defines a receptacle and a respective one of said plurality of pivoting clamp pad support assemblies is carried within said receptacle.

9. The load grasping assembly of claim 8 wherein said receptacle defined by said one of said elongate horizontal members includes an opening, and wherein the bearing block included in said respective one of said pivoting clamp pad support assemblies extends through the opening, and wherein said pivot axis of said pivoting clamp pad support assembly is defined by a respective pivot pin extending into said receptacle and on which the bearing block is mounted in said one of said elongate horizontal members.

10. The load grasping assembly of claim 1 including an opposite second clamp arm assembly, one of said clamp arm assembly and said second clamp arm assembly being mounted on a transversely-oriented horizontal member for movement toward and away from the other one of said clamp arm assembly and said second clamp arm assembly along said transversely-oriented horizontal member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side elevational view of a clamp arm assembly for a lift truck, including clamp pads mounted on the clamp arm assembly with the use of adjustable pivoting clamp pad support assemblies.

(2) FIG. 2 is a sectional view of one of the adjustable pivot assemblies included in the clamp arm assembly, taken along line 2-2 in FIG. 1, at an enlarged scale.

(3) FIG. 3 is a sectional view of the adjustable pivot assembly shown in FIG. 2, taken along line 3-3 in FIG. 1, at an enlarged scale.

(4) FIG. 4 is an exploded isometric view of the clamp arm and clamp pad assembly shown in FIG. 1, taken from the upper left front.

(5) FIG. 5 is an exploded isometric view of a portion of FIG. 4 including one of the adjustable pivoting clamp pad support assemblies, at an enlarged scale.

(6) FIG. 6 is an exploded isometric view of a bearing block and associated parts of an adjustable pivoting clamp pad support assembly such as the ones shown in FIGS. 1, 3, and 5.

(7) FIG. 7 is a diagrammatical view of a system incorporating the adjustable pivoting clamp pad support assemblies.

(8) FIG. 8 is an isometric view of a clamp assembly and a test body useful for checking the adjustment of the pivoting clamp pad support assemblies.

(9) FIG. 9 is an isometric view of a carton clamp assembly together with a set of cams equipped with force sensors, used to calibrate the force sensors in the adjustable pivoting clamp pad support assemblies.

(10) FIG. 10 is a perspective view of a layer picker clamp fork lift attachment incorporating the adjustable clamp pad support assemblies, shown grasping a selected number of layers of a stack of cartons of canned goods.

(11) FIG. 11 is a perspective view of one clamp arm assembly for a layer picker such as that shown in FIG. 10.

(12) FIG. 12 is an elevational view of the clamp arm assembly shown in FIG. 11.

(13) FIG. 13 is a sectional view taken along line 13-13 of FIG. 12, showing the locations of adjustable pivoting clamp pad support assemblies.

DETAILED DESCRIPTION OF EMBODIMENTS

(14) Referring first to FIG. 1 of the drawings, in a load clamp assembly that includes one embodiment of the subject matter disclosed herein a carton clamp arm assembly 10 for a lift truck includes transversely oriented horizontal members 12 adapted to be attached to a front of a lift truck (not shown), to permit the clamp arm assembly 10 to move transversely with respect to the lift truck, so that an opposed pair of such clamp arm assemblies 10 can move toward or away from each other to grip or release a load. Carried on the transverse members 12 is a clamp arm 14 that extends forward from the lift truck on which the clamp arm assembly 10 is mounted for use. A load stabilizer 16 is mounted on the outer ends 18 of the clamp arm 14, attached to the outer ends 18 by coaxial pins 20 defining a substantially vertical pivot axis of a hinge-like connection. The stabilizer 16 thus can pivot about the coaxial pins 20, to allow for deflection of the clamp arm 14 or misalignment of a package to be gripped. The stabilizer 16 may be a substantial steel member with a generally vertical central trunk portion and respective sets of multiple horizontal finger-like members 24 extending forwardly and rearwardly from the trunk. While three finger-like members 24 are shown in each direction here, there may be two to five finger-like members in various applications.

(15) A load-contact pad, such as a carton clamp pad, may be a unitary member (not shown) or may, as shown, have the form of two large generally rectangular and substantially flat load-contact pad members 28 and 30 of a split load-contact pad. The load-contact pad members 28 and 30 are carried respectively on the rearwardly-extending and forwardly-extending finger-like horizontal members 24 of the load stabilizer 16. Each of the load-contact or carton clamp pad members 28 and 30 is attached to the load stabilizer 16 by three adjustable pivoting clamp pad support assemblies 32, also called adjustable pivot assemblies, each of which is mounted within a receptacle 34 defined by a respective one of the finger-like horizontal members 24. Each of the receptacles 34 may be an opening extending through the respective finger-like portion 24 of the stabilizer 16.

(16) Referring also to FIGS. 2, 3, and 4, a spring 22 is mounted on one of the finger-like portions 24 of the load stabilizer 16 and presses against an inner face of the clamp arm 14, tending to rotate the load stabilizer 16 about the coaxial pins 20, while a pair of stop members 26 mounted on the clamp arm 14 limit angular movement of the load stabilizer 16 to a slightly toed-out attitude.

(17) For each of the separate carton clamp pad members 28 and 30 a pivot axis is defined by respective pivot pins 36 extending vertically through coaxially aligned bores 38 in the respective finger-like members 24 supporting the clamp pad 28 or 30 and securing the respective adjustable pivoting clamp pad support assemblies 32 in the receptacles 34.

(18) As shown best in FIG. 5, each receptacle 34 may include a pair of opposed upper and lower horizontal bearing faces 40 between which a respective adjustable pivot assembly 32 is located, and the bores 38 for the pivot pins 36 extend through the bearing faces 40.

(19) Referring also to FIG. 6, each adjustable pivoting clamp pad support assembly 32 includes a bearing block 42 defining a pivot pin bore 44 to receive a pivot pin 36. A pair of threaded bores 46 extends through a flat base or inner face 48 of the bearing block 42 in a direction perpendicular to the axis of the pin bore 44. An adjustment collar 50, which has external threads and which may have a portion shaped to be engaged by a wrench, is threaded into each of the bores 46 as may be seen in FIG. 2 and acts as a positioning member, as is described below.

(20) The pressing, or grasping pressure forces exerted inwardly by the pivoting support assemblies 32 urging the clamp pads 28 and 30 toward each other are carried from each finger-like horizontal member 24 of the clamp arm 14 and transmitted by the bores 38 and the respective pivot pin 36. The pressing, or clamping, force is transmitted from each pivot pin 36 to a load tube 52 fitted in the pin bore 44 of the bearing block 42. The load tube 52 fits snugly but rotatably about the pivot pin 36. A central portion 56 of the load tube 52 fits within the pin bore 44 of the bearing block 42 and nearly in contact with an interior surface of the pin bore 44, and is located and oriented so as to receive a fastener such as the screw 54 in a small hole 58 that may be provided in the outer surface of the central portion 56 to keep the load tube 52 in its intended location and orientation in the bearing block 42. The load tube is still free, however, to move radially a small distance within the bore 44 as will be explained presently. Outer end portions 60 of the load tube 52, extending from the central portion 56 toward the upper and lower faces 62 of the bearing block 42, are slightly smaller in exterior diameter 64 than the interior diameter 66 of the pin bore 44, to provide a radial space between the end portions 60 and the interior of the pin bore 44, where the pivot pin 36 and the load tube 52 may flex under load without bearing on the interior surface of the pin bore 44. It will be understood that the load tube 52 might instead be of a constant size along its end portions 60 and central portion 56, in which case the interior diameter of the pin bore 44 surrounding the end portions 60 could be larger to provide radial clearance around the load tube 52.

(21) A cavity 70, which may be cylindrical, extends into the bearing block 42 from the outer face 48 and intersects with the pin bore 44. A central axis of the cavity 70 is oriented in the direction of forces that it is desired to measure, and the cavity 70 needs to extend deeply enough so that all the forces exerted in the direction of interest are carried through the central portion 56 of the load tube 52 to the plunger 72. At the same time, the cavity 70 needs to be shallow enough to leave the central section 56 of the load tube 52 able to receive forces in directions other than along the central axis of the cavity 70, so that those forces can be carried from the bearing block 42 to the finger 24 of the load stabilizer 16 or an equivalent member of a load clamp assembly of another type.

(22) A plunger 72 is fitted slidably within the cavity 70 and may have a concave cylindrical inner end surface 74 that fits against and conforms to the shape of the exterior surface of the central part 56 of the load tube 52, so that inwardly-directed, load-grasping forces of the respective fingerlike member 24 are carried through the pivot pin 36 and the central part 56 of the load tube 52 and are applied to the plunger 72.

(23) A force-transmitting outer end 76 of the plunger 72 has a contact surface 78 which may have a concave, large-radius, spherical shape and which may be surrounded by a shallow rim 80.

(24) A button-like force-sensing or load cell 82 may have a centrally located contact portion including a contact face 84 that may have a large radius convex spherical contact surface that corresponds with the shape of the contact surface 78, and that rests against and may be centered on the contact surface 78 of the plunger 72, while the load cell 82 is held in a central location by the rim 80. An oppositely-located base surface 86 of the load cell 82 rests against an interior face of a retainer plate 88 that is fastened to the inner face 48 of the bearing block 42 by suitable fasteners such as screws 90 extending through corresponding holes in the retainer plate 88 into respective threaded bores in the inner face 48 of the bearing block 40. A shim 92 may be provided in an appropriate thickness to establish sufficient space for the load cell 82, yet assure that the retainer plate 88 has positive contact with and through the load cell 82, the plunger 72, and the central part 56 of the load tube 52 to the interior surface of the pin bore 44, so that forces directed inwardly, in a clamping direction, by the pivot pin 36 are carried in isolation to the bearing block 42 through the load tube 52, the plunger 72, the load cell 82, and the retainer plate 88, and can thus be sensed by the load cell 82. At the same time, however, the plunger 72 is intended to ensure that only the compressive load-clamping forces are transmitted to the load cell 82, while forces in other directions, such as load-lifting vertical forces, are carried to the bearing surfaces 40 through the upper and lower faces 62 of the bearing block 42. Thus, the load cell 82 will measure only forces in the direction in which the plunger 72 is free to move in the cavity 70.

(25) The load cell 82 may be a subminiature industrial compression load cell available from various sources, such as OMEGA Engineering, Inc., of Stamford, Conn. One acceptable load cell has a diameter 94 of about 19 mm and a thickness or height 96 of about 6.5 mm and may be obtained in an appropriate capacity, depending upon the clamping force desired to be applied. A load cell 82 having a capacity of 2230 N, for example, may be used, or a load cell which has a similar size and a capacity of, for example, 4450 N may also be used. A signal conductor 98, including a suitable wire or wires, extends from the load cell and passes through an opening 100 provided through the bearing block 42 to carry an electrical signal representative of the pressure exerted on the load cell 82 by the retainer plate 88 and the plunger 72 when the clamp arm assembly 10 is exerting inwardly directed clamping force upon a load. The signal conductor 98 for the type of load cell 82 described above, for example, includes a pair of excitation wires and a pair of signal conducting wires.

(26) A flat spacer plate 104, which may have a shape similar to that of the outer face 48 of the bearing block 42, defines a pair of bores 106 that are coaxially aligned with the bores 46 in the bearing block 42. Fasteners such as flat head screws 108 may be countersunk in and extend through a supporting plate portion 110 of the clamp pad 28 or 30, through the bores 106 in the spacer plate 104, and be engaged in threaded bores 112 defined by the collars 50, holding the spacer plate 104 tightly against the inner ends 120 of the collars 20. A lock-washer 114 and a self locking nut 116 may be provided on the flat head screw 108 and tightened against the collar 50 to retain the screw 108 with the clamp pad 28 or 30 held tightly against the spacer plate 104 as shown in FIG. 2 and to keep the spacer plate 104 from moving with respect to the collar 50. The spacer plate 104 defines an opening 118 somewhat larger than the retainer plate 88, so that the spacer plate 104 can be close to or rest flush against the face 48 of the bearing block 42, with the retainer plate 88 in the opening 118.

(27) As shown in FIG. 2 an inner end 120 of the adjustment collar 50 extends proud of the outer face 48 of the bearing block 42, and keeps the spacer plate 104 an adjustable distance 122 away from the inner face 48 of the bearing block 42. Thus, as shown in FIG. 2, a radial distance 124 between the axis of the pivot pin 36 and the support plate 110 of the clamp pad 30 is defined by the location of the spacer plate 104 against the inner end 120.

(28) As shown best in FIGS. 2, 3, and 5, and also in an enlarged, exploded view in FIG. 6, with the adjustable pivoting clamp pad support assemblies 32 all assembled as is the one shown in FIG. 2, both of the clamp pad members 28 and 30 are parallel with the central axes defined by the pivot pin bores 38 and pin bores 44 and thus are positioned so as to provide equal pressure along the entire height of the respective clamp pad 28 or 30 against a vertical side of a carton to be gripped by the carton clamp. The orientation of, and to some extent the shape of, each clamp pad 28 or 30 may be changed, however, by adjusting the clamp pad support assemblies 32 to vary the spacing, that is, the radial distance 124, between the clamp pad plate portion 110 and the central axis of the respective pivot pin 36 and pin bore 44, as shown in FIG. 2. The adjustable support assemblies 32 may be adjusted by loosening the lock nuts 116 and the screws 108, relieving pressure from the adjustment collars 50. The collars 50 may then be backed out from or screwed in farther through the threaded bores 46 in the bearing block 42 toward the spacer plate 104. The inner end 120 of each collar 50 bears against the spacer plate 104 and establishes a selected position of the adjacent part of a clamp pad support plate 110 by varying the gap distance 122 between the spacer plate 104 and the inner face 48 of the bearing block 42, within a range of available positions determined by the lengths of the collars 50 and the resulting distance 122 to which each can be made to protrude beyond the inner face 48 of the bearing block 42. With the screws 108 tightened, the lock nuts 116 may be tightened against the lock washers 114 and the depressed face 126 of the respective collar 50. This keeps the spacer plate 104 positioned tightly against the inner ends 120 of the collars 50, establishing and maintaining the gap 122 between the bearing block 42 and the spacer plate 104, and thus establishes the radial distance 124.

(29) The signal conductor 98 may be connected electrically to a system controller 128 of the lift truck equipped with a clamp arm assembly 10 incorporating the load-sensing adjustable pivoting support assembly 32, as shown in FIG. 7. In response to receiving signals from one or more pivoting clamp pad support assemblies 32 representing the force transmitted in a predetermined direction by each of those one or more pivoting clamp pad support assemblies 32, the controller 128 may adjust the amount of hydraulic or other mechanical force applied to the clamp arm assembly 10 on which the load-sensing adjustable pivoting clamp pad support assemblies 32 are mounted.

(30) In a more general sense, then, a pivoting support assembly 32, equipped with a load cell and a pivot pin 36 and a load tube 52 fitting against a plunger carried so as to be movable radially with respect to the pivot pin, in the direction in which an applied force is desired to be measured, and wherein the pivot pin has radial clearance to allow some flexure of its end portions adjacent to the central portion, permits accurate measurement of forces actually exerted in the direction of interest in pivoting force-applying mechanisms where the pivot pins are too small to incorporate a strain gauge arrangement safely or economically.

(31) The adjustable pivoting support assembly 32 has been described above with respect to its use in a load clamp assembly 10 in the form of a carton clamp arm assembly 10, as shown in FIG. 10. The adjustable pivoting support assembly 32 may also be used in other applications where it is desired to measure in isolation the forces exerted in a particular direction, such as a radial direction relative to a pivot shaft, as in other types of load grasping clamp equipment such as, for example, a layer picker clamp assembly.

(32) As shown schematically in FIG. 7, information such as an electrical signal from each of the load cells 82 is transmitted by the signal conductors 98 to the central controller 128 that can utilize or give an indication of the force exerted at a particular time by each pivoting clamp pad support assembly 32, and a closed loop feedback system can use the value of the clamping force as thus measured to provide the desired amount of clamping force to handle the load to be grasped. An operator input and display unit 130 may be associated with the controller 128. The controller 128 may control a hydraulic fluid pump and valving system 132 connected operatively to hydraulic rams 134 incorporated in the clamp arm assembly 10. Alternatively, other types of motors such as pneumatic cylinder and piston assemblies or electric motors and appropriate power sources may be used instead of a hydraulic system.

(33) As illustrated in FIG. 8, a clamp arm assembly 10 may be tested or checked routinely by having a test body 136 of known dimensions and rigid construction and clamping it with a predetermined total clamping force exerted by the clamp arm assembly 10. The force sensed by the load cell 82 of each of the several pivoting clamp pad support assemblies 32 is transmitted to the central controller 128. This allows the distribution of forces exerted by the several pivoting clamp pad support assemblies 32 to be evaluated. If it is observed that clamping forces are not distributed as desired, as when one of a related pair or group of the pivoting clamp pad support assemblies 32 is exerting too great a load, the collar members 50 may be backed out through the bearing block 42 of that one of the pivoting clamp pad support assemblies 32 after loosening the associated lock nut 116, allowing the related portion of the clamp pad 28 or 30 to move back or protrude less.

(34) Especially where a lift truck is to be used to clamp loads that are of a routinely consistent configuration, the adjustable pivoting support assemblies 32 described above provide force measurement during actual clamp assembly operation that can allow the load grasping mechanism to be adjusted to provide optimum pressures distributed as desired along the surface of the loads to be grasped and lifted.

(35) A set of hydraulic rams 140, each equipped with a force sensor (not shown) may be used between the clamp arms 14 of the clamp assembly 10, with each ram 140 aligned with one of the pivoting clamp pad support assemblies 32, as shown in FIG. 9, to calibrate the load cells 82.

(36) It may be important to have an actual force measurement available in other related mechanisms in order to prevent overloading a clamp arm of a forklift unit. The force measurement may be used to determine that forklift arms are not overloaded by their use to lift and move large, heavy loads.

(37) With some modifications, the pivoting support assembly 32 can be used to measure forces applied between a load and load engagement surface of many types of forklift attachments. It can be used to balance clamping forces applied to a load, to limit forces applied to a load, to selectively distribute forces applied to a load, to warn of excessive forces, to sum several forces applied to determine the total of applied forces, or even to sum forces on different load-engaging surfaces and applied in different directions.

(38) For example, in tire-handling lift truck attachments intended to lift and rotate large wheels and to mount such wheels on large machines such as earthmoving equipment, pivoting clamp pad support assemblies 32 including load cells 82 can be used to ensure that a tire handling clamp is not subjected to excessive forces by increasing the inflation pressure in a tire being held in such a tire handling attachment.

(39) As another example, it may be desirable to have an accurate representation of clamping forces applied by other load handling mechanisms such as a layer picker forklift attachment 144 as shown in FIG. 10, where it is important to have sufficient force to grasp the load and it is also important not to use too much force.

(40) As shown in FIGS. 11, 12, and 13, a clamp arm assembly 148 included in such a layer picker attachment 144 may have a pair of horizontal motors 150 such as hydraulic rams to move a pair of vertical legs 152, to which a clamp pad 154 is attached by a pair of pivoting clamp pad support assemblies 32 supported on and free to pivot about a horizontal pivot shaft 156 extending between the legs 152. Load cells 82 in the pivoting clamp pad support assemblies 32 can be used in a manner similar to that described above to ensure that sufficient but not excessive forces are applied to a load such as a layer of cases of soft drink cans as shown in FIG. 10.

(41) 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.