GB2160487A - Air cushion pressure regulation - Google Patents

Abstract

Equipment for automatic pressure control of an air cushion support unit (3) in an air cushion supported transport dolly. Said equipment comprises a main valve (1), connected to a compressed air network and an adjustable throttle valve (2) for each air cushion unit (3), the valve being connected between the main valve (1) and the air cushion unit (3). The control system in the present invention comprises a pressure regulator (8) with gain, connected between a main valve (1) and a throttle valve (2), and a feedback loop (5, 10), comprising a pressure line (5) from the air cushion unit (3) to the control port of the pressure regulator (8). The present invention facilitates, among other things, an automatic control of air pressure (flow) for an air cushion unit, independently of the load. <IMAGE>

Description

SPECIFICATION Air cushion pressure regulation The present invention relates to equipment in accordance with the preamble of claim 1 for the automatic pressure control of air cushions.

Such a system may be used with air cushion supported equipment for automatic feed air pressure control for each air cushion unit, according to the load on the unit.

The equipment is also applicable in existing air cushion support systems as a replacement for manually operated control systems to ease the use of the equipment, optimize the air consumption and minimize wear in the air cushion units.

Prior-art solutions, e.g., the following; - A ball valve type adjustable main valve (1) with fixed throttling settings for each air cushion unit (3) for balancing and limiting the airflow (Figure 1).

-A common pressure regulating valve (1) mounted on a control panel in combination with adjustable or fixed throttling settings (2) for each air cushion (3) with symmetrical load (Figure 2).

- A pressure regulating valve for each air cushion unit with asymmetrical load (Figure 3).

A common feature of these solutions is that the pressure of the inlet air for each air cushion unit must be set manually for each load condition and changed if the load changes. With asymmetrical load conditions, the pressure must additionally be controlled individually for each air cushion unit. The control operation is in addition difficult since the inlet pressures for the air cushion units must be controlled rather exactly. Too low pressure causes the air bag skirts to drag on the floor and too high pressure causes load vibrations (jumping).

Moreover, reference is made to the following papers that describe automatic pressure control systems: GB Patent Publication 1,174,938, US Patent Publications 3,332,508, 3,340,943, and 3,835,952 (DE) Published Prints 2,001,831 and 2,048,069 These prior-art automatic control systems are based on mechanical moving components and they are both complicated and expensive to manufacture.

The objective of the present invention is to eliminate the difficulties associated with the prior-art technology described above and to provide a fully new type of control system for automatic pressure control of air cushion units.

The invention is based on the fact that, utilizing the physical properties of the air cushion unit, the detaching of the air cushion unit from the floor is registered, and the air cushion inlet air pressure is fixed at the moment.

More specifically, the equipment in accordance with the invention is characterized by what is stated in the characterizing part of claim 1.

By means of the invention, considerable advantages are obtained. Thus, the invention enables, e.g.

the automatic control of air pressure (flow) of an air cushion unit, independently of the load. Hence, the operator only needs to cater to starting and stopping the air cushion system operation.

Since the pressure is controlled automatically in correct relationship with the load, the air consumption is optimized, the air cushion unit wear is minimized and its vibration tendency is eliminated.

Generally, the invention helps to automate air cushion supported systems and facilitates, e.g. remote controlled operation of air cushion supported dollies by remote radio or optical control equipment.

The invention will be examined in more detail in the following with the aid of the exemplifying embodiments in accordance with the attached drawings.

Figures 1 to 3 are a schematical presentation of the three prior-art control systems.

Figures 4 to 6 show in sectional views how the air cushion unit reacts at the inlet flow of compressed air.

Figure 7shows in graphical form the pressure (P2) in the air cushion unit as a function of the inlet air pressure (P1)forvarying loads.

Figure 8 is a schematical presentation of one embodiment of the equipment in accordance with the invention.

The following description refers to Figures 4 to 7.

When the compressed air is connected to the air cushion unit, the system behaves as follows: - the torus-shaped air bag 7 is filled with air (Figure 4), filling the gap between the air bag and the floor.

The external look and shape of the air bag may vary, depending on the manufacturer, - when air bag 7 sits tightly against the floor, the pressure inside air bag 7 rises (Figure 5). The inlet air pressure increases correspondingly and the pressure inside the air cushion unit 3 rises linearly, with unit 3 rising simultaneously.This is based on the fact that the lift force can be expressed as the product of pressure and area, F = p x a, - when the pressure increases, the lift force rises and when this lift force exceeds the load G, the air bag cannot any more stay tightly against the floor and air begins to leak out, forming an air flow sheet between the air cushion unit and the base surface; F = p x a > G (Figure 6), - if the inlet air pressure is further increased, the pressure inside the air cushion stays constant and only the air consumption is increased (Figure 7).

The inlet air pressure at which air bag 7 drags against the floor varies with the air cushion unit 3 load as shown in Figure 7.

The air pressure is measured inside air cushion 3 and the pressure signal is used for controlling the inlet air pressure to the air cushion unit. The pressure signal can either be used for directly controlling a pneumatic regulator unit or, converted into an electrical signal, for driving an electrical pressure regulator device.

In the following, the control system function is described in detail, referring to Figure 8.

The inlet air from the compressed air network is taken to the main valve 1 that is used for switching the system on and off. The air goes from main valve 1 to the pressure regulating valve 8 with gain, referred to as the pressure regulator in further discussion, that regulates the inlet air pressure for air cushion unit 3. Between pressure regulator 8 and unit 3 is connected an adjustable control valve 2 with which the gain of pressure regulator 8 is set. The pressure signal from air cushion unit 3 is taken via pressure line 5 and the other adjustable throttle valve 10 to the control port of pressure regulator 8.

The pressure line 5 can be provided with an pulsation damper 9 to filter out fast pressure fluctuations in the pressure line when air cushion unit 3 passes, e.g., over uneven areas on the floor.

Pressure regulator 8 is mechanically preset for a pressure that corresponds to transfers with an empty air cushion supported dolly. When main valve 1 is opened, the inlet air is connected to pressure regulator 8 and air cushion unit 3 is fed with the preset pressure of air regulator 8. Simultaneously as air cushion unit 3 is filled, also the pressure in pressure line 5 increases and pressure regulator 8 begins to increase the inlet air pressure in the same proportion. The pressure in pressure line 5 increases linearly until air bag 7 is detaching from the floor. At this moment, the pressure in air cushion unit 3 is stabilized and pressure regulator 8 is set for the pressure that corresponds to the load of air cushion unit 3, resulting in optimized air consumption.

The setting of pressure regulator8 can next be locked in order to avoid being influenced by pressure fluctuations in air cushion unit 3 during the transport. The operating range of pressure regulator 8 is set so that the pressure for maximum load (regulator gain) is set by throttle valve 2. After this adjustment, regulator 8 is set for all load conditions from zero load up to maximum load.

For symmetrical loads, a common control system is sufficient for all air cushion units in the dolly and the pressure control signal is taken only from one of the air cushion units 3. If the load is asymmetrical, the air cushion units 3 can be controlled individually or in pairs.

Within the scope of the invention naturally also other embodiments are conceivable than those described above. Consequently, the system can, e.g., be configured so that the pressure signal from the air cushion unit is taken to a piezoresistive pressure transducer that converts the pressure signal into an electrical signal (mV or mA). The analog electrical signal can then be taken to a microprocessor based control unit that controls an electrical pressure regulator device in a corresponding way as described in the application example above.

Claims (7)

1. Equipment for automatic pressure regulation of air cushion units in air cushion supported transport dollies, comprising - a main valve connected to a compressed air network, and - an adjustable throttle valve for each air cushion unit connected between the main valve and the air cushion unit, characterized by - an air pressure regulator valve with gain, connected between the main valve and the throttle valve, and - a feedback loop, consisting of a pressure line from the air cushion unit to the control port of the pressure regulator.

2. Equipment as claimed in claim 1, characterized in that the feedback loop comprises a second adjustable throttle valve, connected in the pressure line.

3. Equipment as claimed in claim 1, characterized in that the pressure line is provided with a pulsation damper for filtering out pressure fluctuations in the pressure line.

4. Equipment as claimed in claim 1, characterized in that the pressure regulator is mechanically preset for an operating pressure corresponding to the pressure of an air cushion supported transport dolly in no-load condition transfers.

5. Equipment as claimed in claim 1, characterized in that the pressure regulator is provided with a lockable pressure setting.

6. Equipment for automatic pressure regulation of air cushion units in air cushion supported transport dollies, substantially as described herein with reference to Figures 4 to 8 of the accompanying drawings.

7. A transport dolly supported by air cushions connected to equipment according to any preceding claim for automatic regulation of the air pressure in the cushions.