AU4852997A - Self-levelling, self propelled elevating work platform - Google Patents

Description

AUSTRALIA

Patents Act 1990 PATENT REQUEST STANDARD PATENT SELF-LEVELLING, SELF PROPELLED ELEVATING WORK

PLATFORM

The following statement is a full description of this invention, including the best method of performing it known to me The invention is described in the following statement.

SELF-LEVELLING, SELF PROPELLED ELEVATING WORK

PLATFORM

1. This invention relates in general to self propelled elevating work platforms (see figure 1) commonly known as cherry pickers or power ladders. These machines are used in the horticultural industry to gain access to the upper portions of fruit trees for the purpose of harvesting and pruning. Typically these machines are of a three wheeled configuration having two hydraulically driven wheels on a common line of axis and a third castor wheel at the rear The drive wheels can be controlled independently from the operators platform thus providing a high degree of manoeuvrability. Elevation is provided by Hydraulic ram (d) connected to a boom to which the work platform is attached.

2. The single rear wheel of the machine is mounted from an inclined arm and swivel hub attached to a vertical stub axle thus allowing the wheel to freely rotate in either direction about a vertical axis The incline arm allows the ground contact point of the wheel to be outside the vertical axis line of the swivel hub and in the same plane as the centre of the wheel thus providing an effective castor action. This allows the rear wheel to support the machine without adding to or detracting from the movements of the drive wheels.

3. This type of machine is very effective on flat ground or gentle slopes of up to degrees approximately. However where steeper slopes are involved there is an increased risk of rollover as well as a severe reduction of manoeuvrability due to loss of loss of traction on the uphill drive wheel. This problem is exacerbated as the boom is raised and the centre of gravity of the machine shifts downhill.

Another problem occurs on sloping ground. As the machine tilts the stub axle holding the inclined arm is no longer vertical. This causes the castor wheel to try to run downhill thus adding to the traction problems of the uphill drive wheel.

4. The object of this invention is to provide a machine that will automatically detect changes in attitude and adjust itself to maintain a level base. This ensures that the boom is always moving in a vertical plane thus maintaining an even weight distribution on the drive wheels. Also, the work platform remains level at all times thus increasing the operator's comfort and safety. In addition the castor wheel and its swivel axle remain vertical allowing it to function correctly.

To provide the self levelling feature described above it is necessary to be able to move both drive wheels in a vertical plane relative to the base of the machine (see figure This is achieved by the use of hinged joints along the support legs of the frame. Hydraulic rams are located above the hinges to control the vertical movement of the legs. These rams are of the displacement type. This is, they can extend but not retract by hydraulic means. Retraction is effected by the weight of the machine itself. Thus the wheels can be independently raised or lowered by the addition or subtraction of hydraulic fluid to the rams.

6. Because the castor wheel cannot move up or down it becomes the level datum point that determines the attitude of the drive wheels. As the machine moves onto a transverse slope it is necessary that one drive wheel move up and the other down to keep the base level. This action requires that hydraulic fluid be fed to the downhill side ram and simultaneously drained from the uphill side. If the machine confronts rising ground then hydraulic fluid needs to drain from both rams simultaneously until the machine is level. Conversely on falling ground both rams need to be filled together.

7. The device to control this oil flow is the subject of another patent but here is a brief description of its use in this application.

8. The self-levelling hydraulic control device consists of a pendulum attached to two pairs of three-way control valves. A three-way valve consists of a valve body and a sliding spool. The body contains three ports opening into the spool gallery. The centre port is connected to the hydraulic rams and the other two are connected to the pressurised fluid supply and to the fluid reservoir. When the spool is in the central position all ports are closed and fluid is locked in the ram.

As the spool moves in one direction it exposes the pressurised port and allows oil to flow into the ram. In the opposite direction it exposes the reservoir port and allows oil to drain from the ram.

9. The pendulum is suspended from a universal joint allowing it to swing in any direction. The pairs of control valves are attached to the stem of the pendulum and are mounted at 90 degrees to each other in the horizontal plane. One pair is mounted along the centre axis of the machine and controls pitch and the other pair controls roll.

As the machine moves onto a transverse slope the machine tilts to one side but the pendulum continues to hang vertically thus activating the valves simultaneously. One valve drains oil from the ram on the uphill side while the other fills the downhill side. This flow continues until the machine becomes level and the pendulum closes the valves.

11. If the machine encounters rising ground the pendulum swings back in relation to the machine and opens the other pair of valves which drain oil simultaneously from both rams allowing the machine to again become level. It is possible for both pairs of control valves to be activated at the same. time. This means the controlling device can constantly monitor and correct the attitude of the machine irrespective of the terrain below it.