WO1993004973A1

WO1993004973A1 - Balancing device for raising a boom assembly and a method of retrofitting a balancing device

Info

Publication number: WO1993004973A1
Application number: PCT/US1992/007428
Authority: WO
Inventors: Kishi Mitsuhiro
Original assignee: Americ Corporation
Priority date: 1991-08-30
Filing date: 1992-08-31
Publication date: 1993-03-18
Also published as: AU2570292A; JPH0558596A; JPH0825717B2

Abstract

The present invention generally relates to a balancing device used in conjunction with a boom assembly (6) and a method of retrofitting a balancing device to cooperate with a given boom assembly (6). The present invention enables the boom assembly (6) to move in a prescribed path of movement. The balancing device adjusts the amount lower (15, 16, 17, 18) and upper (19, 20, 21, 22) telescopic boom sections extend out of a middle boom section (10, 11, 12, 13), and thereby enables the boom assembly (6) to raise a work table (7) along a linear or vertical path, without horizontal eccentricity (5).

Description

BALANCING DEVICE FOR RAISING A BOOM ASSEMBLY AND A METHOD OF RETROFITTING A BALANCING DEVICE

DESCRIPTION

Technical Field

The present invention relates to a balancing device for raising a boom assembly and work platform and a method of retrofitting the balancing device for a boom assembly. Background of the invention

Boom assemblies for lifting work platforms to high positions are well-known. These boom assemblies are commonly used in elevator work vehicles for working on high positions such as elevated freeways and high-rise buildings. Elevator work vehicles are capable of loading operators and materials on work tables and elevating them to high positions. This enables workers to perform their work efficiently and safely. Figure 1 shows a typical boom assembly. Hollow middle booms A and B are connected in the center by pivot axle C to make a figure X when extended. Upper booms D and E and lower booms F and G are telescopically connected to middle booms A and B respectively. Work table I is connected to a top of upper booms D and E. Lower booms F and G are connected to chassis H. A pair of hydraulic cylinders J and K are installed between chassis H and axle C to resemble an isosceles triangle when extended. Extending hydraulic cylinders J and K causes pivot axle C, and middle boom sections A and B to rise up on lower boom sections F and G. This causes upper booms E and D to simultaneously raise out of middle booms A and B, thereby raising work table I. For work table I to rise exactly vertical , upper and lower booms D, E, F and G should be extended equally by a balancing device connected to the boom assembly.

Several types of balancing or^' adjusting device designs have been developed. One type of balancing device utilizes sprockets and drive chains as shown in Figures 2 and 3. pair of sprockets a and b are rotatably supported by bearing c on axle C. When sprockets a and b are elevated, they force drive chains f and g to rotate smaller sprockets e and d. When sprockets e and d turn, they rotate pinions that travel along pinion racks (not shown) attached to lower booms F and G shown in Figure 2. This type of adjusting device is typically installed inside of the boom assembly. The adjusting device starts operating when hydraulic cylinders J and K elevate pivot bearing C. Boom sections D and E should extend at the same rate from middle boom sections A and B, because sprockets a and b should rotate at the same rate. Unfortunately, work table I often rises along an arcuate path W as shown in Figure 2. When hydraulic cylinders J and K are fully extended, work table I is horizontally off by a distance or eccentricity S with respect to chassis H. Ideally, axle C should rise along a vertical path (as shown in Figure 1) , because the same amount of hydraulic oil should be provided to each hydraulic cylinder J and K. Unfortunately, exact unison of cylinders J and K is difficult to achieve, and they fall out of unison once put into operation with a given boom assembly. Manufacturing tolerance in the boom assembly and balancing device can also cause work platform I to rise in an arcuate path W having eccentricity S. As shown in Figure 7, cylinder J has extended a greater distance than cylinder K. As shown in Figure 3, small sprockets d and e are driven by sprockets a and b and drive chains f and g respectively. Hydraulic cylinders J and K raise axle C and middle booms A and B. This causes sprockets a and b to rotate about bearing c. When middle booms A and B turn a given degree of angle from horizontal, sprockets a and b turn that same degree of angle plus an extra degrees of angle. When the boom assembly moves from its horizontal position to its fully extended position, sprockets a and b should each rotate a total of φ degrees of angle.

The difference in extension of hydraulic cylinders J and K is believed to produce eccentricity S. The degree of rotation φ of sprockets a and b is also believed to differ. When fully extended, cylinders J and K generate a force having a horizontal component Y that puts an eccentric load on axle C. In addition, because work table I does not rise along a linear path V, it is impossible to control its position as it rises. The equation for calculating the eccentricity x of chains f and g, and thus sprockets d and e is as follows:

Ta = Number of teeth in sprocket a Tb = Number of teeth in sprocket b

Td - Number of teeth in sprocket d Te = Number of teeth in sprocket e x = eccentricity of the drive chains S = eccentricity of the work table φ - total degrees of rotation of a sprocket when fully extended R = total revolutions undergone by a sprocket when fully extended r = turn ratio; eg., Ra / Rb or Rd /Re

When Td = Te and hydraulic cylinders J and K extend axle C to its highest position as shown in Figure 1, drive^"-chain f moves a different amount than drive chain g. This difference is eccentricity x.

x = φ (Ta + Tb) / 360

To eliminate eccentricity S of work table I as shown in Figure 2, eccentricity x has to be eliminated. Provided sprockets a and b have Ta and Tb teeth respectively, and sprockets d and e have a turn ratio r when hydraulic cylinders J and K are extended, the following equation applies:

Te = Td (Tb / Ta) + (x / r)

This means that eccentricity S of work table I can be eliminated if sprockets d and e turn different amounts of angle φ, so that their turn ratio r is altered. The turn ratio r of sprockets d and e can be changed by designing sprocket e to have a greater or fewer number of teeth than sprocket d. The greater the value of eccentricity x to be eliminated, the greater the turn ratio r of sprockets d and e should be changed. When the amount of eccentricity x is relatively small, the number of teeth Te in sprocket e may be increased by one (Te = Td + 1) . When eccentricity x is large, the number of teeth Te in sprocket e should be increased further (Te = Td + 2, or Te = Td + 3, etc.) .

If eccentricity x remains uncorrected, an excessive load will be put on sprockets a, b, d and e and drive chains f and g. This excessive load is believed to be due to the upper and lower booms D, E, F and G being extended different amounts. This extra load becomes a source of trouble because it leads to torn-out gear teeth and drive chains which can cause the boom assembly to fall down.

fiiiwimwry of the Invention

The present invention generally relates to a balancing device used in conjunction with a boom assembly and a method of retrofitting a balancing device to cooperate with a given boom assembly. The present invention enables the boom assembly to move in a prescribed path of movement. The balancing device adjusts the amount lower and upper telescopic boom sections extend out of a middle boom section, and thereby enables the boom assembly to raise a work table along a linear or vertical path, without horizontal eccentricity.

The balancing device includes a first pair of sprockets connected in the center of the middle boom sections. A second pair of sprockets is connected at the lower ends of the lower boom sections. Drive chains connect the first and second pairs of sprockets. The amount of extension of lower and upper booms is adjusted by providing a sprocket with one or more teeth than its companion sprocket. The balancing device may also include a pair of rack and pinion assemblies secured to the lower and upper telescoping boom sections.

One advantage of the present balancing device invention is that it provides a means for adjusting the extension of the lower and upper telescopic boom assemblies so that the work table rises vertically. This enables the location of the work table to be precisely controlled. Another advantage of the present invention is that it reduces the load put on the drive chains, sprockets and pinions. This reduces the stress and wear on these components and helps prevent the drive chains from being 5 torn and the sprockets and pinion teeth from being stripped, thereby producing a safer and more reliable work platform.

Brief Description of the Drawinσs 10 Figure 1 is a plan view of a conventional boom assembly extended to form a figure X.

Figure 2 is a plan view of a conventional boom assembly showing eccentricity S of a raised work table. Figure 3 is a perspective view of a conventional 15 balancing device used in combination with the conventional boom assembly of Figure 2.

Figure 4 is a perspective view showing a boom assembly installed on a chassis of a truck.

Figure 5 is a side view showing the boom assembly in 20 a retracted position.

Figure 6 is a side view showing the boom assembly fully extended.

Figure 7 is a rear view showing the boom assembly fully extended. 25 Figure 8 is a sectional view of the boo assembly and balancing device in their retracted positions.

Figure 9 is a sectional view showing of Figure 8 taken along line 9-9.

Figure 10 is a sectional view showing two sets of 30. upper, middle and lower booms connected at their mid- section by a connect assembly.

Figure 11 is a perspective view showing the balancing device attached to the telescopic boom assembly. 5 Figure 12 is a perspective view showing the balancing device separate from telescopic boom assembly. Figure 13 is a perspective view showing the balancing device with additional sprockets and chains for extending the upper boom sections. Figure 14 is a plan view showing the vertical path of movement of the end of the upper telescopic boom assembly and work platform.

Detailed Description of the Preferred Embodiment

While this invention is susceptible of embodiments in many different forms, there is shown in the drawings 5 and will herein be described in detail, a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention 10 to the embodiment illustrated.

As shown in Figures 4-7, the present invention is generally installed on a chassis 1 of a truck having front 2 and rear 3 wheels, and a cabin 4. Outriggers 5 are attached to both sides of chassis 1 at the center and 15 rear end. A boom assembly 6 is mounted on chassis 1, and a work table 7 is connected to an upper part of boom assembly 6.

Boom assembly 6 is telescopic and preferably constructed of four sets of three booms: middle boom 20 sections 10, 11, 12 and 13; lower boom sections 15, 16, 17 and 18; and upper boom sections 19, 20, 21 and 22. Middle boom section 10, lower boom section 15, and upper boom section 19 construct one set. Similarly, a second set is constructed from boom sections 11, 16, and 20, a 25 third set from boom sections 12, 17 and 21, and a fourth set from boom sections 13, 18 and 22. Middle boom sections 10 and 11 are preferably pivotally connected at their centers and resemble a figure X when extended. Middle boom sections 12 and 13 are connected in the same 30. way. Middle boom sections 11 and 13 are connected in parallel at their centers by a bearing 43.

Lower booms 15, 16, 17 and 18 are connected with brackets 23, 24, 25 and 26 to chassis mounts 31, 32, 33 and 34. Each bracket 23, 24, 25 and 26 is preferably 35 connected to its respective mount 31, 32, 33 and 34 by a pin. Brackets 27, 28, 29 and 30 are attached to upper ends of upper boom sections 19, 20, 21 and 22. Mounts 35, 36, 37 and 38 are attached to a bottom side of work table 7. Again, each bracket 27, 28, 29 and 30 is connected to its respective mount 35, 36, 37 and 38 by a pin. Boom assembly 6 is preferably constructed to resemble a figure X from side when extended.

Hydraulic cylinders 41 and 42 extend telescopically and are connected to front and rear sides of chassis 1. Cylinder rods from hydraulic cylinders 41 and 42 are connected to bearing 43. Hydraulic cylinders 41 and 42 should resemble a reverse figure V when extended, and control bearing 43 to rise vertically against chassis 1. The distance between mounts 31 and 32 is the same as mounts 35 and 36. The distance between mounts 33 and 34 is the same as mounts 37 and 38. Lower boom section 15- 18 and upper boom sections 19-22 preferably extend from middle boom sections 10-13 at the same rate. All boom sections, chassis 1 and work table 7 resemble a figure X with two isosceles triangles in upper and lower directions.

Figures 8, 9 and 10 show the inside of boom assembly 6 which is constructed of four sets of boom sections. Each of the middle boom sections 10, 11, 12 and 13 have similar inside constructions.

Middle boom 10 is hollow and preferably made of thin steel plates. Lower boom 15 and upper boom 19 are telescopically connected to middle boom 10 and are also preferably made of thin steel plates. Bearings 44 and 45 are connection to both ends of middle boom 10. A pair of guide rollers 46 and 47 are connected to bearings 44 and 45. Lower boom 15 fits between guide roller 46 and smoothly extends from middle boom 10. In the same way, upper boom 19 fits between guide rollers 47 and extends from middle boom 10. Rack 52 is attached to a bottom of lower boom 15, and pinion 53 is connected to bearing 44.

As shown in Figure 8, gear box 48 is attached to a lower end of middle boom 10 next to bearing 45. Two sprockets 49 and 50 are supported by bearings and located inside gear box 48. Drive chain 51 is attached to an upper end of lower boom 15 and a lower end of upper boom 19. Drive chain 51 is secured around sprockets 49 and 50 to make a figure S and control the extension of lower boom 15 and upper boom 19.

As shown in Figure 9, shaft 54 is connected to bearing 44, and pinion 53 is attached to a center of shaft 54. Gear teeth of pinion 53 fit in rack 52.

Sprocket 55 is connected to a side of shaft 54, but outside of bearing 44.

As shown in Figure 10, a support 59 is attached to middle boom section 10. Cylindrical collar 58 is attached to a side of middle boom section 10 facing middle boom section 11. Similarly, a support 60 is attached to middle boom section 11, and cylindrical bearing 14 is connected to a side of support 60 facing middle boom section 10. Bearing-14 fits inside of collar 58 and pivotally connects middle boom sections 10 and 11. A connect groove 62 is formed on an outside surface of bearing 14. A connect flange 63 is attached to collar 58 with screws 64 and fits into connect groove 62. Middle boom sections 10 and 11 are preferably pivotally connected. Cylindrical collar 65 is connected to bearing 14. A first pair of sprockets 66 and 67 are attached to and extend outwardly from cylindrical collar 65.

A cylindrical support bearing 61 is attached to a second side of support 60 opposite connect bearing 14, and faces middle boom section 12 through lift bearing 43. Therefore, two pairs of middle boom sections (10 and 11) and (12 and 13) rotate in opposite directions about the center of bearings 14 and 43 to resemble a figure X when fully extended.

Figures 11 and 12 show a preferred embodiment of the balancing device installed between middle boom sections

10 and 11. This balancing device adjusts or controls the extension of lower boom sections 15 and 16 from middle boom sections 10 and 11.

As mentioned above, sprockets 66 and 67 are attached to collar 65. Sprocket 55 is attached to shaft 54, which is connected to the end of middle boom section 10. Drive chain 76 is installed on sprockets 66 and 55. Rack 52 and pinion 53 are located at an end of lower boom section 15 and are attached to shaft 54. Rack 70 and pinion 71 are located at an end of lower boom section 16. Pinions 71 and 73 are connected to an end of shaft 72. Pinion 74 fits into pinion 73, and sprocket 75 is connected to pinion 74. Drive chain 77 is installed on sprocket 75 and sprocket 67. Preferably, sprockets 66 and 67 have same number of teeth, as do pinions 53 and 71, and pinions 73 and 74, but sprocket 75 has one or more teeth than sprocket 55.

When collar 65 starts turning, sprockets 66 and 67 should turn at the same rate, and drive chains 76 and 77 move at the same speed. Drive chains 76 and 77 turn sprockets 55 and 75. Sprocket 55 drives pinion 53, shaft 54 and rack 52, so that lower boom 15 is pulled out from middle boom 10 at a first predetermined rate. Sprocket 75 drives pinion 74 which turns pinion 73 in the opposite direction. Pinion 73 drives shaft 72, pinion 71 and rack 70, so that lower boom 16 is pulled out from middle boom 11 at a second predetermined rate. Because sprocket 75 has one or more teeth than sprocket 55, boom 16 is extended from middle boom 11 a smaller amount than lower boom 15 is from middle boom 10. The difference in the amount of extension of lower booms 15 and 16 eliminates eccentricity S as shown in Figure 2.

Figure 13 shows a preferred construction of boom assembly 6. As mentioned above with respect to•Figure 8, the ends of lower boom 15 and upper boom 19 are connected by drive chain 51. When middle boom 15 is pulled out from middle boom 10, upper boom 19 is pulled by drive chain 51. As a result, lower boom 15 and upper boom 19 are extended from middle boom 10 the same amount. Similarly, ends of lower boom 16 and upper boom 20 are connected by drive chain 80. When lower boom 16 is pulled out from middle boom 11, upper boom 20 is pulled by drive chain 80. As a result, lower boom 16 and upper boom 20 are extended the same amount. In this way, drive chains 51, 76, 77 and 80 extend booms 15 and 19 the same amount and booms 16 and 20 the same amount. While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the broader aspects of the invention. Also, it is intended that broad claims not specifying details of a particular embodiment disclosed herein as the best mode contemplated for carrying out the invention should not be limited to such details.

Claims

CLAIMSI claim:

1. In combination with a boom assembly having first and second base boom sections and first and second telescopic boom sections telescopically secured to the first and second base boom sections respectively, a balancing device comprising: means for extending the first telescopic boom section at a first predetermined rate; and means for extending the second telescopic boom section at a second predetermined rate, said first and second predetermined rates differing by a predetermined amount to enable the boom assembly to rise vertically without horizontal eccentricity.

2. The combination of Claim 1, wherein said first extending means includes a first drive sprocket connected to said first base boom section, a first companion sprocket connected to said first telescopic boom section and a first drive member joining said first drive and companion sprockets, and wherein said second extending means includes a second drive sprocket connected to said second base boom section, a second companion sprocket connected to said second telescopic boom section and a second drive member joining said second drive and companion sprockets.

3. The combination of Claim 2, wherein said sprockets have teeth and said first drive sprocket has a different number of teeth than said second drive sprocket.

4. The combination of Claim 3, wherein said first drive sprocket has one more tooth than said second drive sprocket.

5. The combination of Claim 2, wherein said first companion sprocket has a different number of teeth than said second companion sprocket.

6. The combination of Claim 5, wherein said first companion sprocket has one more tooth than said second companion sprocket.

7. The combination of Claim 2, wherein said first and second drive sprockets are pivotally attached to and between the base boom sections, and said first and second companion sprockets are attached to an end of the telescopic sections.

8. The combination of Claim 7, further comprising first and second rack and pinion sets, said first rack being secured to the first telescopic boom section and said first pinion cooperating with said first companion sprocket, and said second rack being secured to the second telescopic boom section and said second pinion being cooperating with said second companion sprocket.

9. The combination of Claim 7, wherein said first pinion has a different number of teeth than said second pinion.

10. The combination of Claim 9, wherein said first pinion has one more tooth than said second pinion.

11. In combination with a boom assembly having first and second base boom sections joined at their centers by a shaft, the first and second telescopic boom sections being telescopically connected to one of the base boom section, and the middle and lower boom sections having lower ends, a balancing device comprising: first and second sprockets pivotally connected to the shaft, the shaft being located at the center of the base boom sections; third and fourth sprockets connected to the lower ends of the base boom sections, said third sprocket having a different number of teeth than said fourth sprocket; and first and second drive chains, said first drive chain being installed on said first and third sprockets and said second drive chain being installed on said second and fourth sprockets, said sprockets and drive chains controlling the amount of extension of the lower boom sections.

12. The combination of Claim 11, wherein said first and second sprockets are located between the middle boom sections.

13. The combination of Claim 11, further comprising first and second rack and pinion sets, said first rack being secured to the end of the first telescopic boom section and said first pinion being secured to said third sprocket, and said second rack being secured to the end of the second telescopic boom section and said second pinion being secured to said fourth sprocket.

14. The combination of Claim 11, wherein said first and second sprockets are located between the base booms and have a greater number of teeth than said third and fourth sprockets.

15. A balancing device for a boom assembly having first and second middle boom sections joined at their centers, first and second lower boom sections, each being telescopically connected to a lower end of the middle boom sections, and first and second upper boom sections, each being telescopically connected to an upper end of the middle boom sections, the lower boom sections having lower ends attached to a chassis, and the upper boom sections having top ends supporting a work table, said balancing device comprising: first and second sprockets pivotally attached between the middle boom sections; third and fourth sprockets located at the lower ends of the middle boom sections, one of said sprockets having a different- number of teeth to ensure the work table rises vertically without horizontal eccentricity; and first and second drive chains joining said first sprockets to said third sprocket and said second sprocket to said fourth sprocket respectively.

16. The balancing device of Claim 15, further comprising first and second rack and pinion sets, one rack and pinion set being located on each lower boom section, said pinions being driven by said third and fourth sprockets.

17. The balancing device of Claim 15, further comprising fifth and sixth sprockets pivotally attached to the first upper boom section, seventh and eighth sprockets pivotally attached to the second upper boom section, and third and fourth chains connected to said fifth, sixth, seventh and eighth sprockets respectively for extending said first and second upper boom sections.

18. In combination with a boom assembly having middle boom sections connected at their centers to resemble a figure X when extended, lower and upper boom sections telescopically connected to each of said middle boom section, said lower boom sections having ends connected to a chassis by brackets, and said upper boom sections having ends connected to a work table by brackets, said lower and upper boom sections being extend from said middle booms when said middle boom sections are moved to raise said work table, a balancing device comprising: central sprockets having a specific number of teeth and being connected by bearings to the centers of the middle boom sections; lower sprockets having a specific number of teeth and being connected by bearings to the ends of the lower boom sections; drive chains installed on said central and lower sprockets for controlling the amount of extension of the upper and lower boom sections by rotation of said sprockets due to said sprockets having a different number of teeth.

19. The combination of Claim 1, wherein said central sprockets are located between the middle boom sections and said lower sprockets have a different number of teeth.

20. The combination of Claim 1, wherein two central sprockets are located between said middle boom sections and one lower sprocket and pinion are located at each end of the lower boom sections.

.

21. The combination of Claim 1, wherein said central sprockets consist of two sprockets located between the middle boom sections, and one of said lower sprockets and pinions are located at each of the ends of the lower boom sections, and wherein said central sprockets have a turn ratio less than said lower sprocket

SUBSTITUTESHEET turn ratio due to said sprockets having a different number of teeth and being connected by a drive chain.

22. In combination with a boom assembly having middle boom sections connected at their centers to resemble a figure X when extended, lower and upper boom sections telescopically connected to each of the middle boom section, said lower boom sections having ends connected by brackets to a chassis, and upper boom sections having ends connected by brackets to a work table, the lower and upper boom sections being extend from the middle booms to raise the work table by moving the middle boom sections, a balancing device comprising: two central sprockets and bearings located between the middle boom sections; two lower sprockets and pinions, one sprocket and pinion being located at each end of the lower boom sections; two drive chains, each drive chain connecting one of said central sprockets to one of said lower sprockets; two rack and pinion sets, one rack and pinion set being located at each end of the lower boom sections, and said sprockets having a different number of teeth to allow said drive chains and rack and pinion sets to adjust the amount of boom extension so that the boom assembly moves in a vertical path without horizontal eccentricity.

23. The combination of Claim 5, wherein one of said central sprockets has one more tooth than said other central sprocket.

SUBSTITUTESHEET

24. A method of retrofitting a balancing device installed in a boom assembly, said balancing device having sprockets and drive chains, said method comprising the steps of: assembling the boom assembly; attaching the balancing device to the boom assembly; determining the eccentricity of the drive chains selecting a sprocket to be replaced to reduce said eccentricity; determining a number of teeth needed in said selected sprocket to reduce said eccentricity; replacing said selected sprocket with a sprocket having said number of teeth needed to reduce said eccentricity so that the boom assembly moves along a desired path.

25. The method of Claim 1, wherein said sprockets form two drive sprockets Ta and Tb, and two companion sprockets Td and Te having turn ratio r, said sprocket to be replaced being Te and said step of determining said number of teeth in said sprocket to be replaced Te¹ is calculated as follows:

Te' = Td (Tb / Ta) + (x /r) .

26. The method of Claim 1, wherein the boom assembly has middle boom sections attached at their centers, and lower and upper boom sections that telescope out of the middle boom sections, and the boom assembly is raised by a pair of hydraulic cylinders.

SUBSTITUTE SHEET