US3048367A - Load handling apparatus having optimum efficiency - Google Patents

Description

L. A. M CARTY Aug. 7, 1962 LOAD HANDLING APPARATUS HAVING OPTIMUM EFFICIENCY 3 Sheets-Sheet 1 Filed Aug. 26, 1959 mm M mM y A A 7' TOPNE I S A. MOCARTY 3,048,367

LOAD HANDLING APPARATUS HAVING OPTIMUM EFFICIENCY Aug. 7, 1962 3 Sheets-Sheet 2 Filed Aug. 26, 1959 m m m m LEE A. M CAR7Y A 7' TOPNEVS 1962 L. A. MCCARTY 3,048,367

LOAD HANDLING APPARATUS HAVING OPTIMUM EFFICIENCY Filed Aug. 26, 1959 3 Sheets-Sheet 3 INVENTOR. LEE A. M-CARTV United States Patent Ofiice 3,48,357 Patented Aug. 7, 1932 3,048,367 LOAD HANDLING APPARATUS HAVING OPTllVIUM EFFICIENCY Lee A. McCarty, Pleasant Hill, Calif., assignor to H. S. Watson Company, Emeryville, Califl, a corporation of California Filed Aug. 26, 1959, Ser. No. 836,237 Claims. (Cl. 254-124) This invention relates to load handling apparatus in which a constant unidirectional load is moved by a rigid pivotally mounted arm which is in turn moved by a pivotally mounted extendible arm. In most applications, the load is a mass in the earths gravitation field, and the extendible arm is a piston cylinder combination to the interior of which a pressurized fluid is delivered. More particularly, the invention relates to such apparatus in which the respective arms are so assembled that maximum efiiciency of the apparatus is obtained.

Load handling apparatus of the above identified type finds extensive application in various equipment such as cranes, lift mechanisms for truck tail gates, etc. because this type of load handling apparatus is very compact and can be mounted in confined spaces without substantially limiting the path through which it can move a load. From the standpoint of the manufacture of the load handling apparatus, the efliciency of the apparatus is a direct function of the extent to which the force exerted by the extendible arm fluctuates during a lifting cycle in the operation of the apparatus. Thus where the apparatus is to employ a hydraulic cylinder as the extendible arm to lift a weight, the manufacturer desires to use a fluid pressure pump for operation of the cylinder which will have a minimum pressure requirement in order for the system to lift the given weight through a given distance with the given cylinder. From this point of view a load handling system has 100% efficiency when the pressure in the cylinder, and hence the force exerted by the cylinder piston combination, is constant throughout the lifting cycle, since only then can a pressure pump lifting a maximum rated load be Working at full pressure capacity throughout the cycle.

Furthermore, from the standpoint of the user of the load handling apparatus, the apparatus is most eflicient and safest when force variation on the extendible arm is reduced to a minimum because failure of the equipment due to excessive loading occurs when the load is first applied rather than at some intermediate position in the path of movement of the load.

Accordingly, it is an object of this invention to provide a rigid arm-extendible arm load handling apparatus in which the fluctuation of the force on the extendible arm during a lifting cycle is reduced to a minim-um.

It is a further object of this invention to provide such an apparatus in which the force on the extendible arm is substantially constant throughout a lifting cycle.

Other objects and advantages of the invention will become apparent from the following description read in conjunction with the attached drawings in which:

FIGURE 1 is a side elevational view of one form of the load handling apparatus employing the principles of this invention;

FIGURE 2 is a geometric representation of the apparatus of FIGURE 1;

FIGURE 3 is a plot of the approximate variation of force on the extendible arm, expressed in units of percent variation from ideal force, versus the angle the rigid arm makes with a horizontal plane as such angle varies between 85 below the horizontal to 85 above the horizontal;

FIGURE 4 is a side elevational view of load handling apparatus employing an additional feature of the invention by which substantially constant force on the extendible arm is obtained;

FIGURE 5 is a geometrical representation of the apparatus of FIGURE 4;

FIGURE 6 is a side elevational view of another form of load handling apparatus employing the principles of this invention and in which the rigid arm is one support for a horizontal load carrying platform; and

FIGURE 7 is a cross-sectional view partially broken away of the apparatus of FIGURE 6 taken along the plane and in the direction indicated by the lines and the arrows at 77 in FIGURE 6.

In accordance with this invention, the load handling apparatus comprises a rigid arm and an extendible arm each pivotally connected to a frame about first and second parallel axes respectively, and the arms are pivotally connected together about a third axis; the fluctuation of force on the extendible arm is maintained at the theoretical minimum for this simple system by locating the first axis in a plane normal to the direction of action of the unidirectional load to be moved, said plane also being equidistant between the two positions between which the load is to be moved, and by locating the first and second axes on a cylinder, the axis of which lies along the line of intersection of said normal plane and the plane perpendicular to and bisecting the plane surface bounded by the first axis and the third axis in its position furthest removed from the normal plane. Thus, minimum force fluctuation on the extendible arm is achieved by locating the pivot axes for 'both arms in such positions that both arms will swing through equal angles during a given load lifting cycle, and by locating the point of pivotal mounting of the rigid arm in such a position that during the lifting cycle the rigid arm will describe equal arcs on either side of the normal plane from said axis of pivotal connection to the direction of action of the unidirectional load to be lifted.

Referring now in detail to the drawings, and particularly to FIGURE 1, a rigid arm 10 is pivotally connected to a frame 11 about an axis 12. The free end of arm 10 is pivotally connected to a load 13 at a pivot pin 14. The load is a weight hanging from arm 10 under the influence of the earths gravitational field. A piston cylin der combination 15 is pivotally connected to frame 11 about an axis 16 and pivotally connected at its free end to arm 10 about an axis 17 which divides arm 10 into portions 18 and 19. A fluid conduit 20 leads into cylinder 15 and supplies fluid under pressure thereto from any suitable source thereby contracting the piston cylinder combination and moving the various parts to the elevated position indicated by the broken lines and primed reference characters in FIGURE 1; The location of axis 16 and the difference between the extended and contracted lengths of the cylinder piston combination 15 are selected so that during the desired maximum lifting arc the rigid arm 10 moves through equal sectors above and below the horizontal plane through axis 12 and sothat the axes 12 and 16 and the axis 17 in its positions most remote from said horizontal plane all lie on a cylinder 21.

In FIGURE 2, similar reference characters are used to denote lines and points as Where used to denote arms and axes respectively in FIGURE 1. In addition to the structure of FIGURE 1, FIGURE 2 illustrates the radius 22 of piston cylinder combination 15 from axis 12 and the horizontal distance 23 of axis 17 from the axis 12 when arm 18 makes a given angle 0 with a horizontal plane through axis 12. Angle 0 is measured as positive above the horizontal plane. It should first be noted in FIGURES l and 2 that the relative magnitude of the fluctuation of pressure in cylinder 15 as axis 17 moves from 17 to 17 is independent of the length of segment 19 of rigid arm since segment 19 merely determines the effective weight at axis 17 which weight 13 will cause. Accordingly the structure of load handling apparatus of FIGURE 1 is represented geometrically in FIGURE 2 where it is considered that an adjusted weight W is suspended at 17, which adjusted weight is the weight 13 multiplied by the ratio of the length of arm 10 to the length of portion 18.

It will be noted in FIGURE 2 that the force F acting along piston cylinder combination may be calculated by equating the clockwise and counter-clockwise torques tending to move arm 18 around axis 12 so that the force F when arm 18 makes an angle 0 with the horizontal equals the weight W times the horizontal distance 23 divided by the radius 22, which in turn equals the weight W times the length of arm 18 times the cosine of angle 0 divided by the length of radius 22.

The fluctuation of force F" as angle 0 changes is minimized when the load handling apparatus is constructed as described above, i.e., the fluctuation is less than it would be if arm 18 were employed to lift weight W from point 17 to point 17 with axis 16 either inside or outside of cylinder 21. However, as illustrated hereinafter, even when axis 16 lies on cylinder 21 the force F on cylinder 15 fluctuates a small amount as axis 17 moves from 17 to 17 and the magnitude of such fluctuation increases as the system is altered to lift the same weight W with the same arm 18 between points 17 and 17 which are increasingly separated. As the distance between points 17 and 17' increases, the angle subtended by the remote positions of arm 18 increases and accordingly cylinder 21 increases in diameter. However, even when the distance 17-17' is very large when compared to the length of arm 18 so that angle between the remote positions of arm 18 approaches 180, the magnitude of the fluctuation of the force on cylinder 15 is still smaller than such fluctuation would be if the arms were not asassembled with axis 16 on cylinder 21.

As illustrative of the fact that even when the maximum positions of arm 18 are widely separated, the force fluctuation on cylinder 15 is small, reference is had to FIG- URE 3 which illustrates the character of this force fluctuation where arm 18 moves from 85 below the horizontal to 85 above the horizotnal, a total angular movement of 170. The force fluctuation is plotted in FIG- URE 3 as the percent variation of actual force from ideal force where ideal force is the constant force which would be necessary to lift the adjusted weight W from 17 to 17 while force -F" acts through a distance equal to the distance between the expanded and contracted lengths of the cylinder piston combination 15. It will be noted from FIGURE 3 that as 0 varies between minus 85 and plus 85 the maximum relative fluctuation of force on cylinder 15 is limited to 13% above ideal force and 17% below ideal force. Variation in force is of course a linear function of the variation of pressure in cylinder 15 since the pressure always equals the force divided by constant piston area.

Though the principles of this invention may be employed in load handling apparatus where the arm 18 swings through unequal angles above and below the horizontal, the efficiency of the system so constructed is less than the efliciency of the system where both remote positions of axis 17 lie on cylinder 21; thus if in a given system the arm 18 swings through a smaller angle than the angle subtended by points 17 and 17 in 'FIGURE 2, the system could be redesigned, relocating axes 12 and 16 so that the diameter of cylinder 21, and accordingly the fluctuation of pressure over the lifting cycle, is reduced. However, in many cases the characteristics of the equipment on which the load handling apparatus is mounted preclude pivotally mounting the arm 18 in a position where it will swing through equal angles above and below the horizontal. In these cases, the system is constructed with axes 12 and 16 and the most remote position of axis 17 on a cylinder 21 thus giving the nearest practical approximation to the ideal construction for this simple system. This cylinder 21 is slightly larger than the most eflicient cylinder 21 which could be used to swing the arm 18 through the same angle, but the most eflicient cylinder can not be used because of other practical considerations.

Referring now to FIGURE 4, in which is illustrated geometrically an improved form of the load handling apparatus of this invention, FIGURES 4 and 5 illustrate apparatus similar to that illustrated in FIGURE 1, with the exception that axis 16 of the apparatus of FIGURE 1 has been replaced by a moving axis generally indicated by the arrow 16' in FIGURES 4 and 5. The moving axis 16 conveniently comprises a circular disc 25 pivotally connected at its center to frame 11 and having piston cylinder combination 15 pivotally connected to its periphery at axis 24. Disc 25 is connected to arm 18 by any suitable means so that disc 25 rotates through 360 as arm 18 swings from position 18 to 18. Conveniently, a spring biased rack 26 is pivotally connected to arm 18 and engages with a pinion 27 on disc 25 so that movement of disc 25 is in the rotary direction opposite the direction of rotation of arm 18, as illustrated by the arrows 28 and 29 in FIGURE 4.

When the load handling apparatus is constructed in accordance with FIGURES 4 and 5, the disc 16 is pivotally connected to frame 11 at axis 30 inside cylinder 21 in such a position that diametrically opposed positions of axis 24 (24 and 24b) on the disc 25 lie, respectively, one on cylinder 21 and one on cylinder 31, the circumference of which passes through axis 12 and is internally tangent to the are described by arm 18. The positions 24 and 24b of axis 24 are equidistant from axis 12. It will be noted from a comparison of FIGURES 2 and 5 that the moving pivot point 16 changes the radius of cylinder piston combination 15 from axis 12 in order to flatten the pressure variation curve of FIGURE 3. More particularly, when arm 18 is in position 18a in FIGURE 5, disc 25 has moved axis 24 to a position 24a whereby the radius of piston cylinder combination 15 from axis 12 is increased, and hence the pressure increase indicated in FIGURE 3 is reduced; when the arm 18 has moved to position 1811, disc 25 has moved axis 24 to position 24b, at which position the force along cylinder 15 is equal to the force along cylinder 15 when arm 18 lies at positions 18 and 18'; when arm 18 has moved to position 180, disc 25 has moved axis 24 to position 240 whereby the radius of piston cylinder combination 15 from axis 12 is reduced and accordingly causes the pressure reduction indicated in FIGURE 3 to be eliminated. While the improvement of my invention, as illustrated in FIGURE 4, may not completely eliminate the pressure variation indicated in FIGURE 3, the apparatus of FIGURE 4 reduces such pressure variation to a point where it is substantially undetectable.

Referring now in detail to FIGURE 6, a load handling apparatus similar to that illustrated in FIGURE 1 is illustrated with the exceptions that in FIGURE 6 the axis of pivotal connection 16 of cylinder 15 to frame 11 has been moved to a line below the horizontal but a line still on cylinder 21. Accordingly, cylinder 15 in FIGURE 6 is employed to push up on arm 10 instead of pull arm 10 as did cylinder 15 in FIGURE 1. Furthermore, the load 13 in FIGURE 1 has been replaced by a horizontal load handling platform 32 in FIGURE 6. The platform 32 is pivotally connected to arm 10 at axis 14. A rigid arm 33 of the same length as arm 10 is provided parallel to arm 10 and pivotally connected at its opposite ends to axes 34 and 35 on platform 32 and frame 11, respectively. As hydraulic fluid is supplied to piston cylinder combination 15 to lift arm 10 to position 10, the parallelogram formed between axes 12, 14, 34 and 35 maintains platform 32 in a horizontal position.

As illustrated in FIGURE 7, lateral stability of the apparatus of FIGURE 6 is obtained by providin'gtW0 laterally spaced sets of arms 10 and 33, each one pivotally connected to platform 32 and frame 11. Piston cylinder combination is pivotally connected to extended axle 16 connected to frame 11 and is pivotally connected to axle 1'7 extending between the two ri'gid arms 10. p

While preferred embodiments of the invention have been shown and described, it is to be understood that all substantial equivalents thereof are considered to be within the spirit of the invention and the scope of the appended claims.

What is claimed is:

'1. In a load handling apparatus for lifting a load from a first position to a second position which is in vertica alignment with said first position, said apparatus comprising a frame, a rigid arm adapted to be connected to said load and pivoted about a first axis connected to said frame, an extendible arm pivoted about a second axis connected to said frame and having an extendible portion pivotally connected about a linking axis on said rigid arm whereby said linking axis describes a circular are When said load is moved from said first position to said second position, and means for applying force to said extendible portion of said extendible arm to change the length of said extendible arm, the improvement comprising said load handling apparatus, as herein structurally and operationally defined, in which said first axis lies on the horizontal plane bisecting said circular arc, and said first and second axes lie on a cylinder whose axis lies at the intersection of said horizontal plane and the perpendicular bisector of the plane surface connecting said first axis and a position of said linking axis of maximum remoteness from said horizontal plane.

2. The improved load handling apparatus of claim 1 characterized further in that said extendible arm comprises a piston cylinder combination, and said means for applying a force to said extendible portion of said extendible arm comprises means adapted to deliver fluid under pressure to the interior of the cylinder of said combination.

3. The improved load handling apparatus of claim 1 characterized further by the inclusion of a second rigid arm pivotally connected about a third axis connected to said frame and pivotally connected at a remote point thereon to a fourth axis on said load, said first rigid arm being pivotally mounted about a fifth axis on said load, said first, third, fourth and fifth axis forming a parallelepiped.

4. The improved load handling apparatus in claim 1 characterized further by the inclusion of means for moving said second axis relative to said frame along a closed path responsive to pivotal rotation of said rig-id arm as said rigid arrn moves said load from said first to said second position.

5. The improved load handling apparatus of claim 4 in which said means for moving said second axis comprises a disc pivotally connected at its center to said frame and pivotally connected adjacent its periphery to said extendible arm at said second axis, said disc being so positioned that first and second diametrically opposed positions thereon of said second axis lie one on said cylinder and the other on a second cylinder the circumference of which passes through said first axis and is internally tangent to said are, said first and second positions of said second axis being equidistant from said first axis whereby the force applied to said extendible arm is substantially constant as said load is lifted from said first position to said second position.

6. In a load handling apparatus for moving a load essentially vertically in opposition to the force of gravity from a first position to a second position with respect to a frame, said apparatus having a rigid arm adapted to be connected to said load and pivotally mounted about a first axis on said frame, an extendible arm pivotally mounted about a second axis on said frame and having an extendible portion pivotally connected about a linking axis on said rigid arm whereby said linking axis describes a cylindrical are when said load is moved from said first position to said second position, and means for applyin a force to said extendible portion of said extendible arm to change the length of said extendible arm, the improvement comprising said load handling apparatus, as herein structually and operationally defined, in which said first axis lies in a plane perpendicular to the direction of movement of said load, and in which said first and second axes and a point on said cylindrical arc of maximum remoteness from said plane all lie on a cylinder, the center of which lies in said plane.

7. The improved load handling apparatus of claim 6 characterized further iby the inclusion of a second rigid arm pivotally connected about a third axis connected to said frame and pivotally connected at a remote point thereon to a fourth axis on said load, said first rigid arm being pivotally mounted about a fifth axis on said load, said first, third, fourth and fi-fth axis forming a parallelepiped.

8. The improved load handling apparatus of claim 6 characterized further by the inclusion of means for moving said second axis relative to said frame along a closed path responsive to pivotal rotation of said rigid arm as said rigid arm moves said load from said first to said second position.

9. The improved load handling apparatus of claim 8 in which said means for moving said second axis comprises a disc pivotally connected at its center to said [frame and pivotally connected adjacent its periphery to said extendible arm at said second axis, said disc being so positioned that first and second diametrically opposed positions thereon of said second axis lie one on said cylinder and the other on a second cylinder the circumference of which passes through said first axis and is internally tangent to said arc, said first and second positions of said second axis being equidistant from said first axis whereby the force applied to said extendible arm is substantially constant as said load is lifted from said first position to said second position.

10. In a load handling apparatus for moving a load essentially vertically in opposition to the force of gravity from a first position to a second position with respect to a frame, said apparatus having a rigid arm adapted to be connected to said load and pivotally mounted about a first axis on said frame, an extendible arm pivotally mounted about a second axis on said frame and having an extendible portion pivotally connected about a linking axis on said rigid arm whereby said linking axis moves along a cylindrical are from a first position closer to said second axis to a second position more remote from said second axis as said extendible arm is lengthened to move said load from said first position to said second position, and means [for applying a force to said extendible portion of said extendible arm to change the length of said extendible arm, the improvement comprising said load handling apparatus as herein structurally and operationally defined in which said first axis lies in a horizontally disposed plane which is perpendicular to the vertical direction of movement of said load, and in which said first and second axes and said first position of said linking axis all lie on a cylinder, the center of which cylinder lies in said horizontally disposed plane.

References Cited in the file of this patent UNITED STATES PATENTS 2,464,224 Gratbert Mar. 15, 1949 2,675,209 Freed Apr. 13, 1954 2,841,299 Gildner July 1, 1958 FOREIGN PATENTS 1,133.110 France Nov. 12 1956

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