1. Field of the Invention:
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 moving horizontally and raising a platform vertically.
2. Description of the Prior Art:
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 performed at high elevations on expressways and building construction sites. The typical conventional lifting apparatus employs a telescopic parallel mechanism, namely, a so-called scissors type linkage, comprising a plurality of pairs of arms with each pair of arms being pivotally joined at the middle. In order to increase the maximum lift of such a lifting apparatus, it is necessary to increase the length of the arms or to increase the number of the pairs of arms. Accordingly, such a lifting apparatus having a large lift needs a parallel mechanism consisting of many links. Therefore, the lifting platform of the lifting apparatus is located at a high level even when the parallel mechanism is collapsed, and hence it is difficult for persons to get on and off the platform and it is troublesome to load and unload the platform.
Lifting apparatus having a single extendable arm comprising a plurality of telescopically combined booms have been proposed in Japanese Patent Application Nos. 56-134487 and 56-191065.
All of the above-mentioned newly proposed lifting apparatus, however, inevitably need an increased number of booms, and hence so many components are necessary that troublesome manufacturing and assembling work is required and the lifting apparatus are expensive. Furthermore, the above-mentioned lifting apparatus have a large number of sliding parts for assembling the booms and arms. Since these sliding parts are provided with sliding members, such as MC nylon members, a large number of parts need to be replaced periodically requiring high inspection and maintenance costs and troublesome work.
Another lifting apparatus has been disclosed in Japanese Patent Application No. 59-95797. This lifting apparatus has a single extendable boom mounted on a vehicle, and the boom is telescopically moved in the manner of an expanding Z-shape as viewed from the side portion thereof. However, in this lifting apparatus it is difficult to support the platform horizontally when in a fixed elevated position since the single extendable boom is made up of a plurality of booms each of which is moved slidably in a telescopic manner and the surfaces of the booms are not even along the longitudinal axes thereof because of differences in cross section thereof. The differences in cross section between each boom thereby causes the expandable boom assembly to be unstable. Hence, it is difficult to mount a horizontal leveling mechanism on a telescopic boom to maintain the platform horizontal with respect to the chassis.