GB2267695A

GB2267695A - Scissor lift convertor mechanism

Info

Publication number: GB2267695A
Application number: GB9212534A
Authority: GB
Inventors: John Martin Fiske
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-06-12
Filing date: 1992-06-12
Publication date: 1993-12-15
Also published as: GB9212534D0

Abstract

Scissor lift with a crank mechanism, consisting of a crank 11 and link 13, pivotally connected to each other, to each of the scissor arms 10, 12 at predetermined positions, and to the free end of an actuator 14 whose base is connected to the captive arm, near its fixed pivot. The purpose of the crank and link is to convert, or divide, the actuator movement into two movements which separate the scissor arms, creating a fixed-ratio movement between actuator and arms, and hence a constant force for a given load. Preferably the scissor arms are shorter at the top than bottom. Preferably the links operate in parallel. <IMAGE>

Description

SCISSOR LIFT CONVERTOR MECHANISM This invention relates to the controlled application of power to scissortype lift constructions, by means of a crank convertor mechanism.

Scissor lift constructions are widely used for lift platforms, providing a parallel motion, and usually power-actuated by hydraulic ram or rams.

Where used in a restricted-height situation, the near-horizontal ram has a geometric disadvantage against the scissor arms, which only move sideways to its line of action. By tilting the ram as far as possible, and creating a lot of thrust, movement can be obtained; however, it is basically inefficient in concept and the control of positioning is guess-work.

Hydraulics are used because they can provide the great forces needed to start lifting at minimum height, but they also severely limit the range of applications for scissor construction in general. Devices such as ramps, or short vertical hydraulic rams, have been added by makers to overcome the problem, but are of limited help, cumbersome, and still inefficient.

According to the present invention, with a pair of scissor arms, a crank and link are pivotally connected to each other and to both arms, in a prescribed manner. A push-pull actuator is connected to the free end ot the crank, and to the captive arm near the fixed pivot. Proportioned correctly, the arrangement will give a constant ratio between movement ot the actuator and lift ot the scissor, to a maximum position, and thus ensure a constant force for a given load throughout.

The need for excessive hydraulic force is thus obviated; mechanical actuators can be used instead, with high efficiency, thus greatly widening the scope or applications. Where two scissor assemblies are required in parallel, to support a lift platform for instance, a mechanical interconnection can be made which leaves the intervening space clear, if needed.

Typical construction of the scissor lift convertor mechanism is best described with reference to the accompanying drawings.

Fig. 1 shows two scissor arms 10 and 12 of indeterminate length, pivoted at their centres and arm 10 captive to a fixed pivot. Arm 10 has the crank Ii pivoted upon it, while arm 12 has link 13 pivoted upon it, the common ends of crank and link being pivoted together. To the free end of crank 11 is connected a push-pull actuator 14, the base of which is connected to arm 10 near the fixed pivot. Contraction of the actuator, by any power source, will cause displacement of the crank and link, in turn causing the scissor arms to lift. The centre distances used are critical for each application Fig. 2 shows an alternative arrangement, having the same description as above, but of reversed orientation for certain types ot application.

Claims

1. A crank convertor for scissor lift construction, which connects the motion of a push-pull actuator, differentially, to each scissor arm in a prescribed manner.

2. A crank convertor as claimed in Claim 1, wherein a crank and link are pivotally connected together and to both scissor arms, while the crank is also connected to the push-pull actuator.

3. A crank convertor as in the preceding Claims which is arranged to allow alternative actuator size or position, at base or top ot construction.

4. A pair of scissor lift constructions incorporating the crank convertor and actuator as in the preceding Claims, for fitting to each side of a lift platform and interconnected mechanically to operate in parallel.

5. Scissor lift convertor mechanisms as in the preceding Claims and constructed, arranged or adapted, to operate as hereinbefore described, with reference to the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS l. A crank convertor for scissor lift construction, which connects the motion of a push-pull actuator, differentially, to each scissor arm in a prescribed manner.

2. A crank convertor as claimed in Claim 1, wherein a crank and link are pivotally connected together and to both scissor arms, while the crank is also connected to a push-pull actuator in a prescribed manner, to obtain a defined ratio of relative movement.

3. A crank convertor as in the preceding Claims which is arranged to allow alternative actuator size or position, and at base or top of construction.

5. A crank convertor as in Claims 1,2 & 3, wherein one or both scissor arms are foreshortened beyond the mutual pivot point, for non-parallel movement operations and a defined ratio of relative movement.

6. A crank convertor as in Claims 1,2 & 3, wherein both arms are foreshortened beyond the mutual pivot point, one arm becoming a fixed member with pivot point for the other and a defined ratio of relative movement.

7. Scissor arms or control arms, with convertor mechanism and actuator as in the preceding Claims, constructed, arranged or adapted to operate as hereinbefore described, with reference to the accompanying drawings.