LIFTING APPARATUS

Abstract: A lifting apparatus comprising a chassis (1), a platform (13), a stretchable boom assembly (A, B) comprising lower (6), middle (10), upper (11) and cover member (18') respectively axially aligned with each other, a sliding member (141) mounted on the upper boom (11) including a hydraulic cylinder (149), and other three hydraulic cylinders (124,160,9,19) respectively mounted in the lower boom (6), between the lower boom (6) and the chassis (1) and between the upper boom (11) and the platform (13), a hydraulic control system for operating said three hydraulic cylinders (9,19,124,160) in synchronism to move the platform (13) toward and away from the chassis (1) in a substantially perpendicular relation to the chassis (1). Load on the platform (13) is imposed via the cover member (18'), on the stretachable member (A, B) so that the load on the platform (13) is stably movable horizontally and vertically irrespective of the level difference provided between each of the stretchable boom assembly (A, B).

Description: The present invention relates to a lifting apparatus capable of conveying persons and/or goods from or to different levels by raising a platform from a vehicle and, more particularly, to a lifting apparatus capable of raising a platform vertically and moving horizontally. Lifting apparatus capable of conveying persons and goods from or to different levels by raising or lowering a platform are used widely for assembling work, painting work or repairing work at a high level on expressways and building construction sites. A lifting apparatus has been disclosed in Japanese Patent Application No. 59-95797. (Equivalent to EP-A-0163430). This document discloses a lifting apparatus having a platform supported on a vehicle by a telescopically extensible boom assembly. The apparatus has a 'Z' shaped configuration when seen in profile. United States Patent No. 3809180, discloses a lifting apparatus comprising a chassis; a telescopically extensible boom assembly including a lower boom pivotally mounted to rotate about a first horizontal axis located at a rear end of the chassis, at least one intermediate boom received into the lower boom and an upper boom received into the intermediate boom; a first hydraulic cylinder disposed within the boom assembly to effect extension and retraction thereof; a second hydraulic cylinder coupled between the lower boom and a front portion of the chassis to rotate the boom assembly about the first horizontal axis; a platform pivotally mounted at the uppermost end of the upper boom to rotate about a second horizontal axis, a third hydraulic cylinder arranged to pivot the platform about the second horizontal axis and an hydraulic control system to control the operation of the hydraulic control cylinders and, an overlying cover fixedly mounted to an upper end of the upper boom. The lifting apparatus disclosed by US Patent No. 3809180 has a construction which results in all the weight of the platform being applied to the boom assembly through the second horizontal pivot. In consequence the forces applied to the boom assembly are highly concentrated. As will readily be appreciated by those persons skilled in the art this is mechanically disadvantageous leading to rapid wear of the load bearing components. It is an object of the present invention to provide a lifting apparatus of a construction to alleviate the aforesaid disadvantage of the prior-art. Accordingly the present invention provides a lifting apparatus characterised in that the second horizontal axis is located at a forward end of the platform, the cover is provided with a level correction mechanism which supports the cover against the boom assembly at a constant distance from the longitudinal axis of the boom assembly, the level correction mechanism being engageable with the lower boom to support the cover when the boom assembly is contracted and engageable with one of the booms other than the lower boom to support the cover when the boom assembly is extended, the third hydraulic cylinder being coupled between a rear portion of the platform and the cover and the control system being adapted to be capable of synchronising the operation of the hydraulic cylinders to raise and lower the platform vertically above the chassis. It will readily be appreciated that in a lifting apparatus constructed according to the present invention the weight of the platform will be applied to the boom assembly at a position remote from the second horizontal pivot axis, in addition to being applied at the second horizontal pivot axis, because the weight of the platform is carried by the third hydraulic cylinders, the cover and the level correction mechanism. In consequence the forces are dispersed and the load on the second horizontal pivot alleviated. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. Figure 1 is a perspective view of a first embodiment of a lifting apparatus; Figure 2 is a side elevational view of the lifting apparatus of Figure 1 as it is collapsed; Figure 3 is a front elevational view of the lifting apparatus shown in Figure 2. Figure 4 is a side elevational view of the lifting apparatus with its platform elevated to a highest position; Figure 5 is a fragmentary side elevational view of a stretchable assembly of the lifting apparatus shown in Figure 4; Figure 6 is a perspective view of a lifting apparatus according to second embodiment of a lifting apparatus according to the present invention; Fig. 7 is a side elevational view of the lifting apparatus of Fig. 6 as it is collapsed; Fig. 8 is a front elevational view of the lifting apparatus shown in Fig. 7; Fig. 9 is a side elevational view of the lifting apparatus with its platform elevated to a highest position; Fig. 10 is a fragmentary side elevational view of a stretchable boom assembly of the lifiting apparatus shown in Fig. 9; Fig. 11 is an enlarged cross-sectional view taken along line 11 - 11 of Fig. 10; Fig. 12 is an enlarged cross-sectional view taken along line 12 - 12 of Fig. 10; Fig. 13 is an enlarged cross-sectional view showing operation of a slidable mechanism; Fig. 14 is a circuit diagram of a hydraulic control system of the lifting apparatus shown in Fig. 6; Fig. 15 is a an enlarged cross-sectional view showing operation of a slidable mechanism; Fig. 16 (a), (b) and (c) are side elevational views showing operation of the stretchable boom assembly of Fig. 6; Fig. 17 is a side elevational view of the lifting apparatus according to third embodiment of a lifting apparatus according to the present invention; Fig. 18 is a fragmentary side elevational view of a stretchable assembly of the lifiting apparatus shown in Fig. 17; Fig. 19 is an enlarged cross-sectional view taken along line 19 - 19 of Fig. 18; Fig. 20 is an enlarged cross-sectional view taken along line 20 - 20 of Fig. 10; Fig. 21 is an enlarged fragmentary cross-sectional view of the stretchable boom assembly of Fig. 17; Fig. 22 (a), (b) and (c) are side elevational views showing operation of the stretchable assembly of Fig. 17; Fig. 23 is a perspective view of a lifting apparatus according to fourth embodiment of a lifting apparatus according to the present invention; Fig. 24 is a side elevational view of the lifting apparatus of Fig. 23 as it is collapsed; Fig. 25 is a front elevational view of the lifting apparatus shown in Fig. 24; Fig. 26 is a side elevational view of the lifting apparatus with its platform elevated to a highest position; Fig. 27 is a fragmentary side elevational view of a stretchable boom assembly of the lifiting apparatus shown in Fig. 23; Fig. 28 is an enlarged cross-sectional view taken along line 28 - 28 of Fig. 10; Fig. 29 is an enlarged cross-sectional view taken along line 29 - 29 of Fig. 10; Fig. 30 is an enlaged fragmentary cross-sectional view of the stretchable boom assembly of Fig. 23; Figs. 31 (a), (b) and (c) are side elevational views showing operation of the stretchable boom assembly of Fig. 23. DESCRIPTION OF THE PREFERRED EMBODIMENTS Lifting apparatus will be described hereinafter with reference to preferred embodiments thereof in conjunction with the accompanying drawings in which identical or corresponding components are designated by identical or corresponding reference characters throughout the views. Figs. 1 through 5 show a lifting apparatus according to the first embodiment. As shown in Figs. 1 through 5, the lifting apparatus comprises a mobile chassis or base 1 on which front and rear wheels 2, 3 are rotatably supported, a power box 4 attached to the lower surface of the chassis 1 and accommodating therein an engine, a hydraulic pump and other parts. A pair of pedestals 5 are fixed to one longitudinal end of the topside of the chassis 1 at a spaced apart. A hollow lower boom 6 having a rectangular cross section is joined pivotally to the pedestals 5 with a pin 7. A pair of clevises 8 are fixed to the other longitudinal end of the topside of the chassis 1. A pair of hydraulic cylinders 9 for controlling the inclination of a stretchable boom assembly A are joined pivotally at the respective opposite ends thereof to the clevises 8 and the lower boom 6, respectively. A hollow middle boom 10 having the same rectangular cross section is slidabey fitted in the hollow lower boom 6, while a hollow upper boom 11 having the same rectangular cross section is fitted slidably in the middle boom 10. A stretchable boom assembly A comprises the lower boom 6, the middle boom 10 and the upper boom 11. When the stretchable boom assembly A is fully contracted, the length from the lower end of the lower boom 6 to the tip end of the upper boom 11 is substantially same length as the chassis 1. The lower boom 6 and the middle boom 10 have length about two-thirds of the length of the chassis. When the stretchable boom assembly A is fully contracted (as shown in Fig. 2), the upper boom is exposed at the upper portion thereof to the length of one third of the stretchable boom asembly A, namely the upper boom 11 is not accomodated in the lower boom 6 with the upper portion thereof being exposed from the tip end of the lower boom 6 when the stretachable boom is fully contracted. Designated at 13 is a flat platform having a floor which is substantially same area as the chassis 1. Pedestals 14 fixed to the underside of the platform at the opposite end of the stretchable boom assembly A fixing the pedestals. The upper boom 11 is pivotally inserted between the pedestals 14. The pedestals 14 and attachements 15 fixedly mounted at both tip end side of the upper boom 11 are pivotally supported by a pin 16. A pair of clevises 17 have been fixed to the underside of the platform at the opposite side of the pedestals 14. Pedestals 18 have been fixed at both side of the upper boom spaced apart from the tip end of the upper boom 18. Hydraulic cyliders 19 have been interposed between the clevises 17 and the pedestals 18. A handrail 20 is provided over the circumferential of the upper surface of the platform. Fig. 5 shows an internal structure of the stretachable boom A composed of the lower boom 6, the middle boom 10 and the upper boom 11 being telescopically inserted. Pedestals 21 are fixed at both side of the lower end 6 at the upper portion threeof at the position of one third from the left end of the lower boom as shown in Fig. 5. The pedestals have holes 22 for connecting the hydraulic cylinders 9 and the pedestals 18 also have holes 23 for connecting the hydraulic cylinders 19. Hydraulic cylinders 124 are fixedly inserted in the center of the inside of the lower boom 6 and a cylinder rod 125 of the hydraulic cylinder 124 is directed toward the upper boom 11. The middle boom 10 and the upper boom 11 may be synchronously stretchable and contractible by the cylinder rod 125 actuated by a conventional structure. Figs. 2 and 3 show a lifting apparatus with the platform 13 being lowered to the lowerst position by collapsing the stretchable boom assembly A. At this stage, workers and/or materials are put on the platform which is raised upwardly. To raise upwardly the platform, the engine in the power box 4 is actuated to produce the oil under pressure which is supplied to the hydraulic cylinders 9 and the 124 inside the lower boom 6. The cylinder rod 125 is stretched with the hydraulic cylinder 124 being supplied with oil under pressure so that the middle boom 10 is stretched from the lower boom 6 and at the same time the upper boom 11 is stretched from the middle boom 10 so that the stretchable boom assembly A is gradually stretchable. With the extension of the hydraulic cylinders 9, the lower boom is inclined upwardly about the pin 7 so that the stretchable boom assembly A is raised to be inclined with respect to the chassis 1. An extension of the hydraulic cylinders allows an angle between the upper boom 11 and the platform 13 to be increased with the extenstion rate of the hydraulic cylinders 9, 19 being synchrounous with each other so that the platform 13 is at all times parallel to the chassis 1 to thereby allow the chassis 1, the stretchable boom assembly A and the platform 13 to be formed in a Z, when seen in side elevation. Controlling the extension rate of the hydraulic cylinders 9, 19, 124 to a predetermined value, the platform 13 is raised upwadly with respect to the chassis 1 and the upper surface thereof is kept horizontal at all times for thereby preventing the workers and/or materials to be dropped. With the platform being lifted at the desired height, the hydraulic cyliners are stopped to be actuated by the workers for thereby allowing the workers to carry out an assembling work, repairing work, or painting work, etc. To lower the platfrom 13 the oil under pressure from the hydraulic cylinder 9, 19, 124 is decreased to contract the length thereof so that the platform 13 is lowered in perpendicular direction with respect to the chassis 1 with the upper surface thereof being kept horizontal to thereby allow the platform to be in the first state as collapsed. With the simple structure according to the first embodiment, the platform is raised with being kept horizontally and the number of stretchable boom assembly is single for thereby it makes possible to maintain and insepct the lifting apparatus with ease and the parts to be used in the reparing is greatly reduced to thereby allow the maintenance fee to be also reduced. Figs. 6 through 16 (a), (b) and (c) show the second embodiment of the lifting apparatus. The lifting apparatus illustrated in Figs. 8 and 9 includes an stretchable boom B connected between the chassis 1 and the platform 13 substantially in the form of a Z, when seen in side elevation. The stretchable boom assembly B is composed of a hollow lower boom 6, a hollow middle boom 10, and a hollow upper boom 11, each of a rectangular crosse section. The lower boom 6 is of a largest cross sectional shape and has an upper open end. The middle boom 10 is slightly smaller in cross-sectional size than the lower boom 6 and slidably inserted in the lower boom 6 through the upper open end thereof. The upper boom 11 is slightly smaller in cross-sectional size than the middle boom 10 and slidably inserted in the middle boom 10 through its upper open end. The lower boom 6 has a lower end pivotally coupled by the pin 7 to the spaced pedestals 5. The hydraulic cylinders 9 have rod ends pivotally couled to the lower boom 6. A cover member 18' of a channel-shaped cross section opening downwardly is secured to the upper end of the upper boom 11. The cover member 18' has an upper wall or panel having an inner surface spaced in parallel relation from the outer surface of the lower boom 6, there being a clearance defined between the upper boom 11 and the cover member 18' for insertion therein of the lower boom 6. Each of the lower, middle, and upper booms 6, 10, 11 is of a length substantially eqaul to the length of the chassis 1. The cover member 18' is disposed between the spaced pedestals 14 on the platform 13 and pivotally coupled thereto by means of a pin 16. The hydraulic cyliners 19 have rod ends pivotally coupled to the cover member 18'. Fig. 5 shows a structure of the stretchable boom assembly B composed of the lower boom 6, middle boom 10 and the upper boom 11 being telescopically inserted. The cover member 18' has a length of two thirds at the upper side thereof of the lower boom 6 and one third of the lower side thereof of the lower boom 6. Pedestals 21 are fixed at both side of the lower end 6 at the upper portion thereof at the position of one third from the left end of the lower boom as shown in Fig. 5. The pedestals have holes 22 for connecting the hydraulic cyliners 9 and the pedestals 18 also have holes 23 for connecting the hydraulic cylinders 19. Pedestals 24 are fixed on the cover member 18' and at the position of left side in Fig. 10. Rollers 25 are pivotally mounted on the pedestals 24 and are slidably kept contact with the upper surface of the lower boom 6. A sliding member 41 as a level difference correction mechanism is provided on the surface of the member 18' and at the position close to the pededstals 24. Fig. 11 is a cross-sectional view taken along line 11 - 11 of Fig. 10, in which an auxiliary plates 26 is fixed mounted on the tip end of the middle boom 10 (at right side in Fig. 10) and has a support shaft 28 fixedly mounted under portion thereof. Two rollers 29 are rotatably mounted on the support shaft 28 in axially movably spaced relation between the auxiliary plates 26, the rollers 29 being rollingly engageable with the lower surface of the lower panel of the upper boom 11. A pulley 30 is mounted centrally on the support shaft 28 for rotating a chain (not shown) by which the lower and upper booms 6, 11 are interconnected. The auxiliary plates support thereon sliders 31 held in slidable contact with the outer side surfaces of the upper boom 11 and sliders 32 held in slidable contact with the inner side surfaces of the cover member 18'. Fig. 12 is a cross-sectional view taken along line 12 - 12 of Fig. 10 in which a support member 33 is fixedly mounted inside the pedestals 24 and extending parallel to the side surface thereof, a pin 34 is provided between the pedestals 24 and the support member and the rollers 25 are supported on each pin 33. Liners 35 are fixed on the side surface of the cover member 18' eagageable with the side surface of the lower boom 6 and liners 36 are fixed on the lower boom 6 engageable with the outer surface of the middle boom 10. The sliding member is shown in detail in Fig. 8 in which opening 142 is defined at the lower end (at left side in Fig. 8) and center of the cover member 18', pedestal 143 are fixedly mounted at both ends of the opening 142. A lever 144 is pivotally swigably mounted by a pin 145 on the pedestal 143. One end of the lever 144 is exposed over the upper surface of the cover member 18' and other end of the lever 144 is opposetely directed to the lower boom 6. A roller 146 is rotatably mounted on the lower end of the lever 144 by a pin 147. An end presser 148 is fixed on the upper portion of the cover member 18'. An end of the hydraulic cylinder 149 is connected and an tip end of an cylinder rod 150 is connected to the upper end of the lever 144 by pin 151. A contact lever 152 is mounted on the piston rod 150 and directed to the cover member 18' and a pair of limit switches 152, 154 are provided on the surface of the cover member 18' in the manner of sandwiching the contact lever 153. A detector 155 to detect the upper end of the lower boom 6 is provided between the rollers 146 and 124 in the opening 142. A hydraulic circuit according to the present invention is shown in Fig. 9 in which a hydrulic pump 156 is connected to an engine 157. The hydraulic pump have a suction side communicated with an oil tank 158 and discharge side connected to a directional control valve 159. The control valve 159 is connected to the hydraulic cylinder 9 which has a discharge side connected to the hydraulic cylinder 19. The hydraulic cylinder 19 has a discharge side connected to the direction control valve 159 to which a hydraulic cylinder 160 and a solenoid valve 161 are connected in parallel. The solenoid valve 161 is connected to a hydraulic cylinder 149. The detector 155 detects as to whether the lower boom 6 is present or not and issues different signals in dependece on the state thereof. That is, detected that there is no lower boom 6 a signal is produced and applied to one end of the solenoid valve 161 through the switch 162, and detected that the lower boom 6 is present a signal is produced and applied to the other end of the solenoid 161 through the switch 163. There are provided limit switches 154 and 153 respectively at the side of switches 162 and 163. Operation according to the second embodiment of the present invention is described hereinafter. Figs. 7 and 8 show the lifting apparatus lowered at the lowest position with the stretchable boom assembly B being contracted. At this stage, workers and/or materials are put on the platform which is raised upwardly. To raise upwardly the platform, the engine in the power box 4 is actuated to produce the oil under pressure which is supplied to the hydraulic cylinders 9, 19 and 160 inside the upper boom 11. With the hydaulic cylinder 160 being supplied with oil under pressure, the middle boom 10 is stretched from the lower boom 6 and at the same time the upper boom 11 is stretched from the middle boom 10 so that the distance between pins 7 and 15 is extended so that the stretachable boom assembly A is gradually stretchable. With the estension of the hydraulic cylinders 9, the lower boom 6 is inclined upwardly above the pin 7 so that the stretachable boom assembly B is raised to be inclined with respect to the chassis 1. Provided the rate of extension of the hydralic cylider 60 accomodated in the upper boom 11 is synchornized with the rate of extension of the stretchable boom assembly, the pin 16 of the cover member 18' is raised upwadly with respect to the chassis 1. The hydraulic cylinders 19 actuates with extenstion thereof to enlage the angle between the cover member 18' and the platform 13 with the plaform 13 being moved about the pin 16. With the rate of extension of the hydraulic cylinders 19, 9 is synchronous with that of the hydraulic cylinders 19, the platform 16 becomes parallel to the chassis 1, the chassis 1, the stretchable boom B and the platform 13 is formed in Z when seen in side elevation. With the platform raised at the desired height, operation of the hydraulic cylinders 9, 19 and 160 are stopped by the workers to thereby keep the lifting apparatus in the same height so that the assembling work, reparing work, painting work, etc. are carried out at that height. Rollers 25 are rotatably brought contact with the upper surface of the lower boom 6 and moved with the stretchable boom assembly B being streched and contracted. There are clearances on level difference between the cover member member18' and the upper boom 11, the upper boom 11 and the middle boom 10, and the middle boom 10 and the lower boom 6, which cause the lifting appraratus to be rickety or unstable. Further, the lifting apparatus is likely deformed by the load of the platform 13. The load of the platform 13 is delivered to the pin 22 through the hydraulic cylinders 19, and the cover member 18' is applied to the stress to be bent downwardly by the stress of the pin 23. However, as mentioned above, the rollers 25 are rolling over the surface of the lower boom 6, the load is applied to the rollers 25 and delivered to the lower boom 6 so that the cover member 18' is not deformed and extends upwardly with the upper boom 11 with the platform 16 being kept at the same height. With this state, provided that the lower boom 6 is moved against the cover member 18', the upper end of the lower boom 6 passes through the lower surface of the rollers 146. However, the upper end of the lower boom 6 is detected by the detector 155 to thereby produce a signal which is applied via the switch 162 to the solenoid 161 to actuate the hydraulic cylinder 149 which allows to push the cylinder rod 150. By the movement of the cylinder rod 150, the lever 44 is anticlockwisely moved to cause the rollers 146 to contact with the upper surface of the middle boom 10. The contact lever 152 contats with the limit switch 162 to thereby close the solenoid switch 161 so that the switch 162 is opened. The hydraulic cylinder 149 is kept in the state as shown in Fig. 15. Therefore, if the lower boom 6 is further caused to be stretched, the interval betwen the cover member 18' and the middle boom 10 is kept parallel since the load of the platform 13 is delivered to the middle boom 10 via the cover member 18' and the roller 146. Fig. 16 (a) shows a first state of the extension of the stretchable boom assembly B in which hole 23 is applied to the load from the platform 13 and the load is also applied to the rollers 124. With further extension operation, the lower boom 6 is stretchable from the cover member 18' for thereby allowing the rollers 124 to be moved away from the upper surface of the lower boom 6 (as shown Fig. 16 (b)). The roller 146 is contacting with the upper surface of the middle boom 10 and the load applied to the hole 23 is delivered to the cover member 12 through the roller 146 so that the interval between the cover membe 18' and upper boom 11 is kept in parallel. With further extension of the middle boom 10, the interval between the upper member 11 and the middle boom 10 is greater to cause the roller 146 to be rollingly moved over the middle boom 10 and further moving to the tip end of the middle boom 10, and stop to the state as shown in Fig. 16 (c). This state is the maximum extension of the stretchable assembly B. Thus the rolling movement of the rollers 125 is transfered to the roller 146 to cause the stretchable boom assembly B to be moved slidably and smoothly. When the stretchable assembly boom is contracted the roller 146 is in contact with middle boom 10. With the lower boom 6 being brought contact with the rollers 25 and moving, the tip end of lower boom 6 reaches to the position of the detector 155 which produces a signal and same signal is delivered to the switch 163 so that the solenoid valve 161 is actuated in the opposite direction. With this operation, the hydraulic cylinder 149 allows to contract with the cylinder rod 150 to be contracted for thererby to allowing level 144 rotate clockwise about the pin 145 so that the roller 146 is moved away from the middle boom 10 as shown in Fig. 13. With further insertion of the lower boom 6 into the cover member 18', the lower boom 6 passes through the lower part of the roller 146 and further moves. With the structure according to the second embodiment as mentioned above, the load of the platform having same area of that of chassis is applied to the cover memeber, and the load applied to the cover member is successively delivered to the stretchable boom assembly. When the clearances on level difference between each of the plural booms composing of the stretchable boom assembly have been produced on opereation thereof the two rollers are actuated to decrease the clearances so that the load of the platform is safely supported by the stretchable boom assembly. Figs 17 through 22 (a), (b), and (c) show a third embodiment of the lifting apparatus in accordance with the present invention. The lifting apratus includes a stretchable boom assembly B connected between the chassis 1 and the platform 6 substantialy in the form of a Z, when seen in side elevation. The stretchable assembly B is composed of a hollow lower boom 6, a hollow middle boom 10, and a hollow upper boom 11, each of a rectangular cross section. The lower boom 6 is of a largest cross-sectional shape and has an upper open end. The middle boom 10 is slightly smaller in cross-sectional size than the middle boom 10 and slidably inserted in the middle boom 10 through its upper open end. The lower boom 6 has lower end pivotally coupled by the pin 58 to the spaced support legs 5. The hydraulic cylinders 9 have rod ends pivotally coupled to the lower boom 6 by means of a pin. A cover member 18 of a channel-shaped cross section opening downwardly is secured to the upper end of the upper boom 11. The cover member 18' has an upper wall or panel having an inner surface spaced in parallel relation from the outer surface of the lower boom 6, there being a clearance defined between the upper boom 11 and the cover member 18' for insertion therein of the lower boom 6. Each of the lower, middle, and upper booms 6, 10, 11 is of a length substantially equal to the length of the chassis 1. The cover member 18' is disposed between the spaced support legs 14 on the platfrom 6 and pivotally coupled thereto by means of a pin 16. The hydraulic cylinders 19 have rod ends pivotally coupled to the cover member 18'. As shown in Fig. 18, the cover member 18' has an upper edge of a length wich is about 2/3 of the entire length of the lower boom 6 and a lower edge of a length which is about 1/3 of the entire length of the lower boom 6. The lower boom 6 has pedestals 21 positioned on its upper panel at a distance of about 1/3 of the entire length of the lower boom 6 from the left end thereof, the pedestals 21 having holes 22 for insertion of the pin therein. The cover member 18' has lower pedestal positioned on its lower edges at a distance of about 1/2 of the entire length of the cover member 18' from either end thereof, the lower pedestal having holes 23 for insertion of the pin 24 therein. The cover member 18' also has an upper pedestal 24 on its upper panel at the left end. Rollers 25 are rotatably mounted on the upper pedestal 24 for rolling contact with the upper surface of the lower boom 6. Sprockt wheels 41 are rotatably supported in the upper boom 11 by shafts 45 secured to the upper boom 11, the sprocket wheels 41 being positioned at the upper (right in Fig. 18) end of the upper boom 11. Companion sprocket wheels 42 are also rotatably supported in the upper boom 11 by shafts secured to the upper boom 11, the sprocket wheels 42 being positioned at a distnace of about 1/3 of the entire length of the upper boom 11 from the lower (left in Fig. 18) end of the upper boom 11. Two chains 43 are trained around the sprocket wheels 41, 42, and have ends coupled to the middle boom 10 in the vicinity of its upper end (indicated by C in Fig.18). A plurality of rollers 44 (preferably ten rollers) made of a slippery material such as MC nylon and serving as spacers are coupled to each of the chains 43 at spaced intervals therealong. As illustrated in Fig. 19, two auxiliary plates 26 are attached to the opposite outer side surfaces of the middle boom 10 on the upper (right in Fig. 18D) end thereof. A support shaft 28 is fixed to and extends between the lower ends of the auxiliary plates 26, and two rollers 29 are rotatably mounted on the support shaft 28 in axially spaced relation between the auxiliary plates 26, the rollers 29 being rollingly engageable with the lower surface of the lower panel of the upper boom 11. A pulley 30 is mounted centrally on the support shaft 28 for rotating a chain (not shown) by which the lower and upper boom 6, 11 are interconnected. The auxiliary plates 26 support thereon sliders 31 held in slidable contact with the outer side surfaces of the upper boom 11 and sliders 32 held in slidable contact with the inner side surface of the cover member 18'. As shown in Fig. 21, two parallel support legs 41 are attached in depending relation to the bracket 24. The rollers 25 are rotatably supported on pins coupled between the support legs 33 and the side panels of the bracket 24. The cover member supports on its side panels liners 35 for abutment against the outer side surfaces of the lower boom 6. The lower boom 6 supports liners 36 for abutment against the outer side surfaces of the middle booms 10. As shown in Fig. 21, a rail 46 made as of MC nylon is fixed to an upper outer surface of the upper boom 11 in parallel relation to the upper boom 11, with the rollers of each of the chains 43 being held in rolling contact with the rail 46. L-shaped angles 47 are attached to both sides of each of the chains 43, and a support 48 is attached to and disposed between each pair of L-shaped angles 47. Each of the rollers 44 is rotatably supported on a shaft 49 mounted on the support 48. Operation of the stretchable boom assembly B shown in Fig. 18 through 21 will be described hereunder. When the stretchable boom assembly B is extened, the rollers 25 rollingly moved in contact with the upper surface of the lower boom 6. The load of the platform 6 is imposed through the fydraulic cylinders 19 on the pedestals, so that the cover member 18' is subject to a downward stress. Since the rollers 25 roll on the upper surface of the lower boom 6, the load on the cover member 18' is also borne by the rollers 25 to guard against undesired deformation of the cover memer 18' when the stretchable boom assembly B is being extended to raise the platform 13 while keeping the platform 13 in the horizontal position. As the upper boom 11 and hence the cover member 18' are continuously moved upwardly away from the lower boom 6, the upper end of the lower boom 6 is displaced past the rollers 25. Since the upper end of the middle boom 10 is also slidably moved in a direction away from the upper end of the upper boom 11 when the stretchable boom assembly B is extended, the chains 43 are also moved in a direction out of the upper boom 11 while rotating the sprocket wheels 41, 42. The chains 43 are smoothly moved on the rails 46, and the rollers 44 attached to the chains 43. The rollers 44 are therefore moved the middle boom 10 in the space or clearance between the upper boom 11 and the cover member 18'. At the same time, the rollers 44 are held in rolling contact with the inner wall surface of the cover member 18'. Therefore, the load on the cover member 18' is transmitted through the rollers 44, the chains 43, and the rails 46 to the upper surface of the upper boom 11. Accordingly, even after the rollers 25 have moved out of contact with the lower boom 6, the load on the cover member 18' is borne also by the upper boom 11, so that the cover memaber 18' will be prevented from being deformed under the load from the platform 6. Fig. 22 shows the stretchable boom assembly B which has just started to be extended. The load imposed by the platform 13 on the cover member 18' through the pedestals 150 is borne by the rollers 25. When the stretchable boom assembly B is continuously extended until the lower boom 6 is relatively displaced out of the cover member 18', the rollers 25 are brought out of contact with the upper surface of the lower boom 6. At this time, some rollers 44 have already been pulled by the middle boom 10 out of the upper boom 11 into the space between the upper booom 11 and cover member 18'. The load on the cover member 18' is now transmitted through the rollers 44, the chains 43, and the rails to the upper boom 11. The cover member 18' and the upper boom 11 are kept spaced from each other in parallel relation by the rollers 44 serving as spacers. As the middle boom 10 is further pulled out away from the upper end of the upper boom 11, the rollers 44 are rollingly disposed in equally spaced relation between the upper boom 11 and the cover member 18'. The upper boom 11 is drawn progressively out of the middle boom 10 until the stretchable boom assembly B is fully extended. The stretchable boom assembly B is therefore smoothly extended while the cover member 18' is supported securely by the rollers 25 and then the rollers 44. When the stretchable boom assembly B is contracted, the upper boom 11 is progressively inserted into the middle boom 10 which is in turn progressively pushed into the lower boom 6. The chains 43 are moved in the reverse direction to move the rollers 44 back into the upper boom 11. When the lower end of the cover member 18' approaches the upper end of the lower boom 6, the rollers 25 begin to roll on the upper surface of the lower boom 6. The stretchable boom assembly B is thus contracted from the position of Fig. 22 (c), 22 (a). The load on the cover member 18' is thererfore transmitted first to the rollers 44 and then to the rollers 25. While the spacers between the cover member 18' and the upper boom 11 are shown as comprising the cylindrical rollers 44, the spacers may be rectangular or triangular in shape provided they fill the space between the cover member 18' and the upper boom 11. With the arrangement shown in Figs. 17 through 22, the load applied to the cover member 18' by the platform 13 can be transmitted to the stretchable boom assembly B first through the rollers 25 and then through the rollers or spacers 44 or vice versa while the stretchable boom assembly B is being extended or contracted. Therefore, the load from the platform 13 can reliably be borne by the stretchable boom assembly B without deforming the cover member 18' even if the stretchable boom assembly B is extended to and increased length with the lower and middle booms 6, 10 being successively pulled out of the cover member 18'. Fig. 23 through 31 (a), (b) and (c) show the fourth embodiment of a lifting apparatus. The stretchable boom assembly B is similar to the stretchable boom assembly B shown in Figs. 17 through 22, but differs therefrom in that a pair of chains 43 is disposed between the upper outer surface of the upper boom 11 and the lower inner surface of the cover member 18', each of the chains 43 having one end coupled to the upper end C of the middle boom 10. The chains 43 extend out of the upper end of the cover member 18' and are placed as two superimposed folds on the upper outer surface of the cover member 18'. The opposite ends of the chains 43 are coupled to the lower surface of the platform 13. A plurality of rollers 44 made as of a slippery material such as MC nylon and serving as spacers are coupled at spaced intervals to one side of each of the chains 43 for rolling contact with the upper inner surface of the cover member 18'. The cable assemblies 63 each composed of a plurality of bunched hydraulic rubber hoses extend along and are attached to the chains 43, respectively, for movement therewith. The cable assemblies 63 are coupled at lower ends to other cable assemblies 57 in the middle boom 10, and at upper ends to a control panel (not shown) on the platform 13. As illustrated in Fig. 30, the rollers 44 are coupled to the chain 43 by the angle, the support 47, and the shafts 49, and the chain 43 is rollingly movable on and along the rail 46 mounted on the upper boom 11 in the same manner as shown in Fig. 21. Each of the cable assemblies 63 has a pair of hydraulic hoses 51 supported by a substantially horizontal hose holder 50 joined to one of the angles 47. The chain 43, rollers 44 and cable assemblies 63 are placed loosely on the surface of the cover member 18'. The load applied to the hole 22 is supported by the rollers 25. Lower cable assemblies 55 foled twice is placed on the cable receiver 54. Operation of the stretchable boom assembly B is substantialy the same as the operation of the stretchable boom assembly B shown in Fig. 17 through 22. When the stretchable boom assembly B starts being extended as shown in Fig. 31 (a), the chains 43, the rollers 44, and the cable assemblies 63 are entirely placed as folded on the upper surface of the cover, member 18' and the load imposed on the cover member 18', and the load imposed on the cover member 18' from the platform 13 is borne by the rollers 25 held against the lower boom 6. As the stretchable boom assembly B is further extended, the lower boom 6 is srelatively drawn out of the cover member 18' to displace to rollers 25 out of contact with the upper surface of the lower boom 6 as shown in Fig. 31 (b). At this time, the chains 43 and hence the rollers 44 thereron are partly drawn into the space between the upper boom 11 and the cover member 18'. The load on the cover member 18' is now transmitted through the rollers 44 to the upper boom 11, while the cover member 18' and the upper boom 11 are kept parallel to each other. The lower cable assemblies 55 is pulled out upwardly at the same time with the middle boom being pullud out and the loosened cables are successively pulled out from the cable receiver 54. Upon continued extension of the stretchable boom assembly B, the middle boom 10 is drawn out of the cover member 18' away from the upper end thereof, during which time the rollers 44 rollingly move at equal intervals between the upper boom 11 and the cover member 18'. The upper boom 11 is relatively pulled progressively in the direction out of the middle boom 10 until the stretchable boom assembly B is fully extended as shown in Fig. 31 (c). Therefore, the load on the cover member 18' is first borne by the rollers 25 and then by the rollers 44, preventing the cover member 18' from being displaced or deformed. While the stretchable boom assembly B is being thus extended, the cable assemblies 63 are also drawn with the chains 43 into the cover member 18'. When the stretchable boom assembly B is contracted, the chains 43 and the cable assemblies 63 are progressively pushed out of the cover member 18' and placed in the folded configuration onto the upper surface of the cover member 18'. The load on the cover member 18' is first borne by the rollers 44 and then by the rollers 25, preventing the cover member 18' from being displaced or deformed during contraction of the stretchable boom assembly B. With the fourth embodiment of this invention, the weight of the platform and the load on the platform are imposed on the cover member, next to the stretchable boom asembly via roller and the spacer successively. Even if there occurs a level difference between each of the stretchable boom when operated, the spacer is actuated to correct the level difference so that the stretchable boom can ensure to support the platform when stretched at maximum.

Claims: A lifting apparatus comprising: a chassis (1); a telescopically extensible boom assembly (A,B) including a lower boom (6) pivotally mounted to rotate about a first horizontal axis (pin 7) located at a rear end of the chassis (1), at least one intermediate boom (10) received into the lower boom (6) and an upper boom (11) received into the intermediate boom (10); a first hydraulic cylinder (124) disposed within the boom assembly to effect extension and retraction thereof; a second hydraulic cylinder (9) coupled between the lower boom (6) and a front portion of the chassis (1) to rotate the boom assembly about the first horizontal axis; a platform (13) pivotally mounted at the uppermost end of the upper boom (11) to rotate about a second horizontal axis (pin 16), a third hydraulic cylinder (19) arranged to pivot the platform (13) about the second horizontal axis and an hydraulic control system to control the operation of the hydraulic cylinders (9, 19, 124), an overlying cover (18') fixedly mounted to an upper end of the upper boom (11), characterised in that the second horizontal axis (pin 16) is located at a forward end of the platform (13), the cover (18') is provided with a level correction mechanism which supports the cover (18') against the boom assembly (A,B) at a constant distance from the longitudinal axis of the boom assembly, the level correction mechanism being engageable with the lower boom (6) to support the cover (18') when the boom assembly is contracted and engageable with one of the booms (10, 11) other than the lower boom (6) to support the cover (18') when the boom assembly is extended, the third hydraulic cylinder (19) being coupled between a rear portion of the platform (13) and the cover (18') and the control system being adapted to be capable of synchronising the operation of the hydraulic cylinders (9, 19, 124) to raise and lower the platform (13) vertically above the chassis (1). Apparatus according to claim 1 wherein the level correction mechanism comprises a first support member (25) mounted to engage between the lower boom (6) and the cover (18') when the boom assembly is contracted and a second support member mounted to be displaced between a first position where the second support member does not foul the lower boom (6) when the boom assembly is contracted and a second position where the second support member engages one of the booms (10, 11) other than the lower boom (6) to support the cover (18') when the boom assembly is extended. Apparatus according to claim 1 or claim 2 wherein the second support member is mounted on an end of a lever (144), the lever (144) being mounted to rotate about a pivot axis (pin 145) mounted on the cover (18'), the other end of the lever (144) being engaged by an hydraulic ram (149, 150) so that the action of the hydraulic ram (149, 150) rotatably displaces the second support member between the first and second positions. Apparatus according to claim 3 wherein the pivot axis (pin 145) and the hydraulic ram (149, 150) are mounted on the outside of the cover (18'). Apparatus according to claim 3 or claim 4 wherein the hydraulic ram (149, 150) is actuated in response to a detector (155) sensitive to the proximity of the uppermost end of the lower boom (6). Apparatus according to any of claims 3 to 5 wherein the action of the hydraulic ram (149, 150) is limited by limit switches (152-154). Apparatus according to claim 1 or claim 2 wherein the second support member (44) is mounted by an elongate flexible member (43), the elongate flexible member (43) being arranged to be moved in accordance with the extension and contraction of the boom assembly to displace the second support member (44) into the second position where the second support member (44) engages in a gap between the cover (18') and the upper boom (11). Apparatus according to claim 7 wherein the elongate flexible member (43) is endlessly entrained around guide elements (41, 42) mounted in the upper boom (11) so that the second support member (44) is displaced between the first position within the upper boom (11) and the second position. Apparatus according to claim 7 wherein the elongate flexible member (43) is guided into the gap from a position outside the boom assembly. Apparatus according to claim 9 wherein cable assemblies (63) are attached to the elongate flexible member (43) to be accommodated in the gap. Apparatus according to any of the preceding claims wherein the support members (25, 44, 124, 126) are provided by rollers.

Inventors: KISHI, MITSUIHIRO
Applicants: KABUSHIKI KAISHA HIKOMA SEISAKUSHO
Application year: 1986
Main classification: B66F11
IPC codes: B66F11