The present invention relates to an arrangement with a raisable and lowerable working platform, wherein the arrangement includes an elongated, load bearing construction which is intended to be supported in a generally upstanding position, normally while defining an angle with the vertical line, and at least one working platform that is movable along the construction.

There are many types of workers who perform a substantial part of their tasks standing on a ladder, such as painters, electricians, etc. This means that the worker must constantly climb up and down the ladder as work progresses, and also to collect and replace tools and material. This can be extremely tiring and will also result in wear and tear on the body in time. Furthermore, it is difficult to find the correct and precise working height for a particular task when using a conventional ladder, due to the fixed positions of the ladder rungs.

It has earlier been proposed to provide conventional ladders with working platforms that can be moved along the ladders; cf. for instance US Patent Specifications 3 115 211, 3 428 145 and 4 183 423. Such arrangements become particularly heavy, bulky and complicated, especially when built together with a ladder, as in the case of the last mentioned patent specification. Ladders of conventional design that include two side supports and ladder rungs or surfaces mounted therebetween require the ladder to have a certain width in order to afford sufficient lateral support.

When working platforms of this kind are powered with the aid of electric motors, they become extremely heavy due to the power required.

The US Patent Specification 5 143 181 describes an arrangement having a raisable and lowerable working platform which is less space demanding than earlier known arrangements and which is also constructed so as to enable it to be used in relatively confined spaces. The electric motor used, however, must support the full weight of the platform, therewith requiring a high power output and a large and heavy motor.

The primary object of the present invention is to provide an arrangement of the general kind taught by US 5 143 181 but which can be powered by means of a small, light and inexpensive electric motor.

The invention is based on the realization that this object can be achieved by storing a part of the kinetic energy of the platform and its load as the platform moves downwards, and supplementing the lifting force with the stored energy as the platform is raised. There can be used to this end a spring that is tensioned during downward movement of the platform such as to store energy in the spring. The spring thus obtains the nature of a counterweight which partially balances the load on the platform without requiring the presence of a true, heavy counterweight in the construction.

An arrangement of the kind defined in the first paragraph is characterized in accordance with the invention by a spring device which is coupled to the platform and which is so adapted as to store energy therein as the platform moves downwards, this energy being used as a lifting force during upward movement of the platform, and by a transmission means which is coupled between the spring device and the platform and which functions to shorten the requisite length of movement of the spring device.

This arrangement thus utilizes the gravitational force that acts on the platform and a workman standing thereon as the platform moves downwards, so as to at least partially balance-

out the force that is later required to renew upward movement of the platform. The stored energy is thus utilized in the same way as a counter¬ balance for balancing-out at least a part of the weight of the workman and the platform.

Other characteristic features of the invention will be evident from the following claims.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.

Figure l is a schematic perspective view of an inventive arrangement.

Figure 2 is a sectional view taken on the line II-II in Figure

1, although with the contents of the beam excluded.

Figure 3 illustrates a part of the beam with platform and associated locking means. Figure 4 is a schematic perspective view of the beam with associated platform drive system.

Figure 5 is a schematic view of a line system according to

Figure 4 and shows the platform in an upper position.

Figure 1 illustrates a box beam 1 that has a U-shaped channel 2 along its front surface; see also Figures 2 and 3. A working platform 3 is movable along the beam and is guided therewith by two wheel pairs 4, 5 each of which runs in its respective guide rail 6, 7 that extend along respective opposite sides of the beam. Only the upper wheel of each wheel pair is shown in Figure 2.

Mounted on that part of the platform 1 which projects into the U-shaped channel 2 is a box 8 which contains a locking device that includes a locking pin 9 (Figure 3) . A spring 10 strives to press the locking pin 9 into one of a plurality of holes 11 disposed in the beam 1. The holes 11 may be disposed relatively

close together, so as to enable the working platform 3 to be locked in desired precise working positions. When wishing to move the platform 3, the pin 9 is withdrawn from its hole with the aid of a handle 12 that is connected to the pin 9 through the medium of wires 13. The pin 9 may, of course, be maneuvered electrically if so desired.

In the illustrated embodiment, the beam 1 is supported at a desired angle with the aid of a telescopically adjustable support leg 14, said leg being adjusted with the aid of a telescopic brace 15 connected to the beam l. The support leg 14 is intended to prevent rotation of the beam about its longitudinal axis and includes a telescopically adjustable tubular foot 16 for adapting the support to different ground surfaces. The foot 16 will also suitably be rotatable relative to the support leg 14. An adjustable support foot 17 is provided on the bottom end of the beam. To facilitate movement of the beam, the support foot 17 is conveniently provided with two spring-loaded wheels which support the beam when no load acts thereon.

Naturally, these support feet and braces may be modified in several respects. There may also be used two support legs that define a given adjustable angle therebetween. The leg attach- rtient points are suitably adjustable in a vertical direction along the beam. The beam 1 may be provided at its upper end with a support device 32 that prevents the beam from twisting when leaning against a wall or like structure. A ball joint may be provided between the bottom end of the beam and the support foot 17, such as to enable the beam to be orientated vertically irrespective of any sloping of the ground.

The beam 1 may optionally include hinge means 33 which enable the beam to be folded together and therewith facilitate transportation of the arrangement.

The platform 3 is powered by an electric motor 18 which, in the

illustrated embodiment, is operated by means of a foot pedal 19. The foot pedal 19 may, for instance, be replaced with a switch means mounted on the handle 12.

It is endeavored, in accordance with the present invention, to use the smallest possible electric motor and therewith reduce the weight of the arrangement among other things, so as to enable the arrangement to be carried easily by one man. According to the invention, there is utilized to this end a spring which balances-out the major part of the combined weight of the platform and a workman standing thereon, wherein the electric motor need only give a small additional force when lifting the platform or when lowering the platform with a small load. Energy is therewith stored in the spring as the platform and the workman move downwards and is utilized when the platform and the workman shall move upwards.

The embodiment illustrated in Figures 4 and 5 utilizes a gas spring 20 that includes a piston rod 21. One advantage with a gas spring is that it exerts a constant force over the whole of its length of stroke. Furthermore, it is possible to adjust the speed at which the piston moves. It is preferred to use a pulling gas spring, since requirements with regard to guiding the piston rod are less demanding with such a spring, because the spring is less liable to buckle. However, a pressure spring may also be used.

The gas spring drives the working platform 3 via a line 22 which is attached to the platform and to the outer end of the piston rod 21 respectively. In order to enable the use of a gas spring whose length of stroke is much shorter than the desired extent of movement of the platform 3 while still enabling the platform to move along the full length of the beam 1 without the gas spring needing to extend beyond the beam, there is used a transmission means in the form of a plurality of wheels over which the line 22 runs.

The line thus runs from the platform 3 over an upper pulley wheel 23 and a lower pulley wheel 24 to an upper fixed wheel 25 in the transmission means. The line runs from the fixed wheel 25 over a lower wheel 26 mounted on the piston rod and up over a second fixed wheel 27 and from there down to the end of the piston rod and secured thereto. This line system provides a three-fold transmission, i.e. the platform is moved 3 m when the piston rod 21 is moved 1 m.

The electric motor 18 drives a toothed belt 28 which runs in a closed loop around two belt guide wheels 29 and 30 respec¬ tively. The motor may therewith be adapted to drive the wheel 30 directly via a transmission means. Mounted between the belt 28 and the upper end of the piston rod 21 is a fixed connection 31 which causes the piston rod 21 and the belt 28 to move up and down synchronously with one another as the platform 3 moves along the beam.

Figure 4 shows the platform 3 in its bottom position with the piston rod 21 fully extended from the cylinder, whereas Figure 5 shows the platform in its top position with the piston rod 21 fully retracted into the cylinder.

The gas spring 20 is suitably dimensioned so that when a workman stands on the platform 3 with the platform in the position shown in Figure 5, the combined weight of the workman and the platform - when the locking pin 9 is withdrawn - will cause the platform to move down along the beam under the force of gravity. The piston rod 21 will therewith be drawn out from the cylinder housing while storing energy therein. The speed of movement of the platform can be controlled with the aid of the motor 18 without requiring power to this end. The platform can be stopped in any desired position with the aid of the motor and locked in said position with the aid of the locking pin 9. The gas spring 20 may also be provided with mechanical latching means.

When the workman then wishes to raise the working platform, for instance from the position shown in Figure 4, he withdraws the locking pin 9 and starts the motor 18 in the opposite direction of rotation. The energy stored in the gas spring 20 then strives to retract the piston rod into the cylinder housing, therewith imparting a lifting force to the working platform. The motor 18 thus needs only contribute with a small force in order for the platform to move upwards. Accordingly, the motor need only generate a relatively small power, therefore enabling a very light motor to be used.

Alternatively, if the gas spring is dimensioned so that a workman standing on the platform does not cause the platform to be pressed down, sufficient additional power can be obtained from the motor via the connection 31 disposed between the belt 28 and the piston rod 21. When again raising the platform, the energy required herefor will be stored in the spring 20 and the platform can be raised while utilizing solely the spring force. This enables the motor 18 to be used to control the upward speed of the platform.

Since the belt 28 only reciprocates over a short distance, the motor 18 is provided with a reduction gear arrangement which further increases the torque. The speed is conveniently adjusted so that the time taken for the working platform to move between its end positions will be from 10-15 seconds.

In applications that require a large length of stroke of the spring, two or more gas spring may be connected in series. If required, several springs may be used in parallel when desiring to increase the force. Lubrication of the piston rod 21 of the gas spring can be improved by positioning the spring the other way round, i.e. with the piston rod facing downwards. In this case, the transmission means that includes the wheels 25-27 will suitably be mounted at the bottom end of the beam 1.

Another advantage with the use of gas springs is that they will

retard movement of the platform such that it will move downwards at a controlled speed, even should the motor malfunction or in the event of a power cut. However, it is also possible to use other types of spring devices, for instance coil springs, rubber bands or the like.

In the illustrated embodiment, the toothed belt driven by the motor 18 can be tensioned between the belt guide wheels 29, 30 so as to eliminate slipping tendencies. An alternative, however, is to allow the motor 18 to drive the guide wheel 24 that coacts with the line 22. In order to prevent slipping tendencies in this regard, that part of the line which passes the wheel 24 as a result of movement of the platform 3 can be replaced with a toothed belt, chain or like means.

In order to secure the platform in a given position when folding the arrangement for transportation purposes, a fastener device may be fitted to the beam for securely locking the line 22 and therewith prevent it from moving.

The beam may suitably be comprised of an extruded aluminium profile. This enables the weight of the beam to be minimized and manufacturing costs reduced.

The illustrated beam may alternatively have some other chosen configuration and the inventive drive system may also be applied with arrangements that include a step-like stand structure, if so desired. The transmission means may be varied as desired and, for instance, provided with more or fewer wheels than shown so as to obtain the desired transmission. Furthermore, a working table 34 for accommodating tools and the like, and a collapsible seat may be provided for movement along the beam synchronously with the platform.