WO1996017194A1

WO1996017194A1 - Floating plate gas valve

Info

Publication number: WO1996017194A1
Application number: PCT/AU1995/000798
Authority: WO
Inventors: John Billingsley
Original assignee: The University Of Southern Queensland
Priority date: 1994-11-29
Filing date: 1995-11-29
Publication date: 1996-06-06
Also published as: AUPM971894A0

Abstract

A floating plate gas valve comprising a core of magnetically susceptible material. A wire coil (3) is wound about the core to form an electromagnet when current is passed through the wire. A sleeve (4) of magnetically susceptible material forms part of the magnetic circuit. A shaped pole-piece (5) on the core serves to increase the area over which attractive magnetic force is generated, increasing the force resulting from a given number of ampere-turns. Air or gas is supplied through a passage in the core. The air-flow through the valve is regulated by its passage through an annular region between the pole-piece and the floating plate (8) made of ferromagnetic material using the Coanda effect. A housing (9) serves to contain the emerging air or gas and permits its connection to an output device. Also disclosed is a dual floating plate gas valve useful for effecting pressure and force control of a pneumatic cylinder.

Description

TITLE "FLOATING PLATE GAS VALVE" FIELD OF THE INVENTION THIS INVENTION relates to a proportional air-flow control valve incorporating a floating plate. The valve is useful for effecting position control in pneumatic cylinders.

BACKGROUND OF THE INVENTION

For many applications in which position control is sought from a pneumatic cylinder, there is a need for a proportional air-flow control valve. Pneumatic valves commonly regulate the flow of compressed air or other gas in response to a magnetic field resulting from an electric current in a solenoid winding Typically the valve is designed to switch the flow from zero to a maximum value or vice versa with the application of a rated current or the cessation of current. Some valves are designed to have several ports allowing the flow to be switched between outputs

Existing air flow control valves are either of the spool or poppet variety. In spool valves, a machined spool moves in a cylindrical cavity to cover or reveal input and output ports. In poppet valves, a small plug is pressed onto an orifice to seal it by the action of a spring. An electromagnetic field can apply a force to counter the spring and open the orifice. Alternatively, the electromagnetic field can be arranged to close the orifice.

These valves operate as on/off valves and therefore most pneumatic cylinders act on a fixed displacement The cylinders are either retracted or extended depending on whether the valve regulating gas flow is open or closed To achieve an intermediate mean flow rate it is typically necessary to pulse such valves in a mark-space pattern. The result is a limit cycle with wastage of air and resulting noisy operation.

Other approaches to proportional air flow control have been disclosed such as described by Ross Operating Valve Co in United

Kingdom Patent Application number GB2153049 The Ross valve has a plug movable between a shut, intermediate and fully-open position. The Ross valve is not continuously variable

OBJECT OF THE INVENTION It is an object of the present invention to provide a floating plate gas valve able to effect proportional flow control

It is a further object of the invention to provide a pneumatic cylinder control system incorporating one or more floating plate gas valves Further objects will be clear from the following disclosure

DISCLOSURE OF THE INVENTION

In one form of the invention, although it need not be the only or indeed the broadest form, the invention resides in a floating plate gas valve comprising a magnetically susceptible core material having a gas inlet passage therethrough, a plate of ferromagnetic material located close to said passage such that gas flowing from the passage flows over and around said plate to produce a Coanda effect thereby causing the plate to float at a distance from the core, and a wire wound around said core material such that current flowing in the wire produces an electromagnetic effect in the core material to attract the floating plate, wherein increase of the current from zero amps produces a proportional decrease in the distance between the floating plate and the core The floating plate gas valve allows gas to flow from a supply pressure region, through the passage in the core, out of an inlet hole, radially outwards under and around the floating plate and towards a downstream back pressure region

In preference the floating plate gas valve further comprises a housing of non-ferromagnetic material adapted to contain the core and plate and including gas inlet means and gas outlet means

The upper surface of the core material is preferably a pole-piece 3 which is flat and polished The underside of the floating plate is also preferably flat and polished Close contact of the flat and polished surfaces provides an effective seal to stop flow of gas through the passage in the core material The floating plate preferably includes a plurality of holes or notches that increase the maximum volume flow rate

A spring may be positioned between the core material and the plate to further increase the maximum flow rate

In a further form the invention resides in a dual floating plate gas valve comprising a lower floating plate gas valve comprising a magnetically susceptible core material having a gas inlet passage therethrough, a plate of ferromagnetic material located close to said passage such that gas flowing from the passage flows over and around said plate to produce a Coanda effect thereby causing the plate to float at a distance from the core, and a wire wound around said core material such that current flowing in the wire produces an electromagnetic effect in the core material to attract the floating plate an upper floating plate gas valve comprising a magnetically susceptible core material having a gas inlet passage therethrough, a plate of ferromagnetic material located close to said passage such that gas flowing from the passage flows over and around said plate to produce a Coanda effect thereby causing the plate to float at a distance from the core, and a wire wound around said core material such that current flowing in the wire produces an electromagnetic effect in the core material to attract the floating plate a housing of non-ferromagnetic material containing the upper and lower floating plate gas valves, a gas inlet passage in the housing associated with the lower floating plate gas valve, a gas outlet passage in the housing associated with a region intermediate the upper and lower floating plate gas valves, and a vent in the housing associated with the upper floating plate gas valve, wherein variation of the current flowing in the wire of the upper and lower floating plate gas valves effects control of the gas flow pressure at the gas outlet passage between a supply pressure at the gas inlet passage and a vent pressure at the vent

BRIEF DETAILS OF THE DRAWINGS To assist in understanding the invention preferred embodiments will now be described with reference to the following figures in which . FIG 1 is a cross-sectional side view of a floating plate gas valve, FIG 2 is a sketch of the floating palte gas valave of FIG 1 ;

FIG 3 shows sketches of four types of floating plates for the valve of FIG 1 , FIG 4 is a schematic of a pneumatic cylinder control system incorporating a second embodiment of a floating plate gas valve, and

FIG 5 is a schematic of a dual floating plate gas valve for the control system of FIG 4.

DETAILED DESCRIPTION OF THE DRAWINGS In the drawings, like reference numerals refer to like parts

Referring to FIG 1 , there is shown a schematic of a floating plate gas valve, generally indicated as 1 The valve 1 comprises a core 2 of magnetically susceptible material A wire coil 3 is wound about the core 2 to form an electromagnet when current is passed through the wire A sleeve 4 of magnetically susceptible material forms part of the magnetic circuit A shaped pole-piece 5 on the core 2 serves to increase the area over which attractive magnetic force is generated, increasing the force resulting from a given number of ampere-turns

Air or gas is supplied through passage 6 in the core 2 The air-flow through the valve is regulated by its passage through the annular region 7 between the pole-piece 5 and a floating plate 8 made of ferromagnetic material A housing 9 serves to contain the emerging air or gas and permit its connection to an output device (not shown).

A strong suction force exists when the plate 8 is held within a small range of distances from the pole-piece 5. This force is known as the Coanda effect. The suction force decreases as the plate 8 approaches the pole-piece 5. If the plate 8 is constrained laterally above the pole- piece 5 and is then released, it will float at a steady maximum gap height, regulating the flow of air or gas at a constant maximum rate where all forces acting on the plate 8 are in balance. The term steady refers to the stationery or constant floating height of the plate 8. An increasing repulsion force is felt and flowrate decreases as the plate 8 is pushed further below the maximum gap height.

The undersurface of the plate 8 and the top surface of the pole- piece 5 are highly polished. When the highly polished undersurface of the plate is in contact with the flat, highly polished surface of the pole-piece around the inlet hole, the flow ceases. In practice, this metal to metal contact provides a seal just as effective as a rubber to metal seal provided that no solid particles or rust is present between the contact faces.

The valve 1 is unconventional in that it is closed when the coil 3 is fully energised This can be altered by the addition of a permanent magnet to the magnetic circuit Either the core material may be a permanent magnet or the floating plate may be a permanent magnet. In either case the valve will be normally closed and will open with the application of current through the wire coil Inlet air is supplied through passage 6 to the centre of the pole- piece 5, above which floats the plate 8. When the coil 3 is energised, the plate 8 is pulled towards the pole-piece 5, thus restricting the flow of air or gas from the passage 6.

When the coil 3 is not energised, the plate 8 is attracted to the pole-piece 5 by the Coanda effect of the airflow, until it floats at a separation of only two or three hundred microns from the pole-piece 5. A spring can be added to force the plate away from the pole-piece if larger flowrates are required. The magnetic flux then serves first to counter the Coanda effect, and then to seal the plate 8 against the pole-piece 5.

The core 2 and sleeve 4 are used as an electromagnet to attract the plate 8 from the maximum flow condition at the maximum gap height down towards full shut off at zero gap. Flowrate of the gas is therefore inversely proportional to solenoid current flowing in coil 3. The Coanda effect serves the purpose of stabilising the plate much like a spring working to push the plate towards its steady state gap height, without the need for obstructions to hinder the flow behind the plate The steady maximum gap height is dependent on supply pressure, supply temperature, inlet hole radius, plate radius and back pressure when the solenoid current is zero When the floating plate gas valve allows gas to flow into a fixed volume downstream reservoir, increasing back pressure acting on the top surface of the plate acts to push the plate below its steady maximum height so that the flowrate is reduced. Thus, for this application, the flowrate for the floating plate gas valve is naturally damped.

The greatest performance advantage of the floating plate gas valve over the majority of variable flow solenoid valve designs is its ability to handle significantly larger flowrates for a given valve size and the same number of valve parts Infinite flow resolution is also possible by simply adjusting the gap height of the plate. Also, there are no tight fitting sliding parts causing mechanical friction which would tend to hinder the movement of the plate and cause significant wear The floating point gas valve also works upside down, sideways or in any orientation

The inventor speculates that the reason why the Coanda vacuum effect works in the floating plate gas valve is due to the presence of the extremely low pressure regions caused by a supersonic flow regime beneath the floating plate As the exit or back pressure increases towards supply pressure, the flow approaches subsonic conditions where the pressure distribution curves tend to flatten out towards the maximum supply pressure lines Thus even if the floating plate gas valve is 7 servicing a fixed volume downstream reservoir and back pressure increases to reduce the floating height of the plate along with flowrate, the plate will not be forced to shut off the flow without magnetic force since the pressures on the bottom and top of the plate approach each other Notch hole sizes and disk design also affect flow properties of the floating plate gas valve Several different floating plate designs are shown in FIG 3, along with their typical air flow characteristics The air flow characteristics are shown as plots of flow rate in litres per minute against coil current in milliamps The plate design of FIG 3a is also shown in FIG 2 This floating plate consists of a 1 5 mm thick disk 10 with four equispaced 2 mm diameter holes 1 1 The flow of air or gas through the valve varies smoothly from 8 litres per minute to zero with applied current

The plate of FIG 3b has the holes expanded to 4mm diameter notches 12 The maximum flow rate is increased to 9 litres per minute

The plate of FIG 3c has deep notches 13-provιdιng two modes of flowrate an extremely high maximum flowrate in the lower portion of the current range, and a proportional range identical to the flows of the plates of FIG 3a and 3b above this region The plate of FIG 3c has the highest maximum flowrate of all the designs tested because the gas doesn't have to travel far around the deep notches to complete the transition from the high pressure to the low pressure region A control program may utilise the "turbo" mode of this plate in high speed pneumatic piston movements and then utilise the "slow" mode when approaching the stopping position One interesting phenomenon encountered in experiments was that the flowrate increases significantly when the gap height between the plate and the pole-piece is increased above the steady maximum floating height This indicates that using a spring to repel the plate away from the pole-piece, hence overcoming some of the Coanda attraction force, is beneficial for increasing the proportional flow range as long as the magnetic force is capable of overcoming the extra spring force

A spring loaded floating plate is shown in FIG 3d It comprises a 1.5mm thick rod 14 with a steel spring 15 spot welded on top The plate of FIG 3d is able to provide a much higher maximum flowrate than the standard flat round plate designs of FIG's 3a and 3b, while maintaining smooth proportional flow control over the entire range of flows The reason for this is because the spring 15 mechanically pushes the plate into the positive Coanda suction force region for a much larger gap

It has been found that larger and 'smoother' proportional flow regions can be obtained from spiralling or circular springs which allow circular sliding of the spring steel lugs in a tangential direction to the top surface of the sleeve 4 This results in overall lower sliding friction than in the case of lugs being pushed radially outwards as the spring is deflected

FIG 4 shows a mechanical layout for a position and force controlled pneumatic cylinder 16 which uses two dual floating plate gas valves 21 and 22 The pneumatic cylinder 16 contains a moving piston 17 and rod 18 which separates two variable-volume reservoirs, namely, the blind side 19 and the rod side 20 chambers In fluid connection with the chambers 19 and 20 of the cylinder 16 are dual valve units 21 and 22 respectively which independently act as pressure control devices for the blind and rod side chambers Pressure is provided by supply means 30

Pressure sensors 27 and 28 measure the blind side chamber 19 and rod side chamber 20 pressures respectively The sensor signals are provided to a control means (not shown) to calculate currents to be applied to the valves 21 and 22 to effect changes in the position of the piston 17 and hence move the rod 18 The position of the rod 18 is monitored by position sensor 29 and fed back to the processor

Valves 23 and 24 control the inlet and outlet flows for the blind side chamber 19, respectively, and valves 25 and 26 control the inlet and outlet flows for the rod side chamber 20 Valves 24 and 26 serve as vent valves as well as pressure relief outlets For example, a severe unexpected movement of the piston 17 may force the blind side chamber force to exceed the maximum holding force of valve 24 In this case, the outlet plate of 24 will break free and release air in order not to damage any mechanical hardware When the blind side pressure approaches the supply pressure, 24 may exhaust air so that the plate of 23 may lift to permit inlet flow For pressure energy efficiency and quiet operation, both inlet valve and outlet valve should not pass air at the same time If an increase in pressure is required, the inlet valve must allow air to flow into the chamber If a decrease in pressure is needed, the outlet valve must vent air to atmosphere, hence, both valves in the dual housing take turns in flow control so that no air is wasted in the pressure control process Such air wastage is a disadvantage of many commercially available, servo-pneumatic systems which employ on-off spool valves

Since the valves are used in pairs, supplying pressure to the cylinder and allowing it to exhaust, small leakage flows are not important The resulting smooth push-pull control allows loops to be closed of pressure and of position error, giving the possibility of more sophisticated algorithms including programmable compliance

A dual floating plate gas valve 31 is shown in detail in FIG 5 The dual valve is essentially two of the valves of FIG 1 joined in tandem in a housing 32 Each valve 31a and 31 b comprises a core 33a and 33b of magnetically susceptible material A wire coil 34a and 34b is wound about the core 33a and 33b to form an electromagnet when current is passed through the wire A sleeve 35a and 35b of magnetically susceptible material forms part of the magnetic circuit A shaped pole-piece 36a and 36b on the core 33a and 33b serves to increase the area over which attractive magnetic force is generated increasing the force resulting from a given number of ampere-turns A plate 37a and 37b floats above the pole-piece 36a and 36b respectively

An inlet passage 38 is connected to a source of air or gas pressure Air may flow out of the valve 31 a and outlet passage 39 according to the position of plate 37a Back pressure at outlet passage 39 may be vented through valve 31b depending on the setting of plate 37b The pressure at the outlet passage 39 is monitored by pressure sensor 40.

The floating plate gas valve described herein is simple to manufacture, reliable, compact, fast in response, easy to control and delivers large flowrates. It is small enough to be integrated into the ends of high speed "intelligent" pneumatic cylinders which may be independently controlled by dedicated slave microcontrollers. Such actuators can be mass produced at low cost and may be used as 'building blocks' for quickly developing flexible automation systems.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features.

Claims

1 A floating plate gas valve comprising a magnetically susceptible core material having a gas inlet passage therethrough, a plate of ferromagnetic material located close to said passage such that gas flowing from the passage flows over and around said plate to produce a Coanda effect thereby causing the plate to float at a distance from the core, and a wire wound around said core material such that current flowing in the wire produces an electromagnetic effect in the core material to attract the floating plate, wherein increase of the current from zero amps produces a proportional decrease in the distance between the floating plate and the core material

2 The floating plate gas valve of claim 1 further comprising a housing of non-ferromagnetic material adapted to contain the core and plate and including gas inlet means and gas outlet means

3 The floating plate gas valve of claim 1 further comprising a pole- piece associated with a surface of the core adjacent the floating plate

4 The floating plate gas valve of claim 3 wherein the facing surfaces of the pole-piece and floating plate are highly polished and flat such that close contact of said surfaces provides an effective seal to stop flow of gas through the passage in the core material

5 The floating plate gas valve of claim 1 wherein either the core material or the plate is a permanent magnet such that increase of the current from zero amps produces a proportional increase in the distance between the floating plate and the core material

6 The floating plate gas valve of claim 1 wherein the plate includes a plurality of holes or notches

7 The floating plate gas valve of claim 1 further comprising a spring between the core material and the plate

8 The floating plate gas valve of claim 7 wherein the spring is associated with the plate 1 2

9 A dual floating plate gas valve comprising a lower floating plate gas valve comprising a magnetically susceptible core material having a gas inlet passage therethrough, a plate of ferromagnetic material located close to said passage such that gas flowing from the passage flows over and around said plate to produce a Coanda effect thereby causing the plate to float at a distance from the core, and a wire wound around said core material such that current flowing in the wire produces an electromagnetic effect in the core material to attract the floating plate, an upper floating plate gas valve comprising a magnetically susceptible core material having a gas inlet passage therethrough, a plate of ferromagnetic material located close to said passage such that gas flowing from the passage flows over and around said plate to produce a Coanda effect thereby causing the plate to float at a distance from the core, and a wire wound around said core material such that current flowing in the wire produces an electromagnetic effect in the core material to attract the floating plate a housing of non-ferromagnetic material containing the upper and lower floating plate gas valves, a gas inlet passage in the housing associated with the lower floating plate gas valve, a gas outlet passage in the housing associated with a region intermediate the upper and lower floating plate gas valves, and a vent in the housing associated with the upper floating plate gas valve, wherein variation of the current flowing in the wire of the upper and lower floating plate gas valves effects control of the gas flow pressure at the gas outlet passage between a supply pressure at the gas inlet passage and a vent pressure at the vent

10 The dual floating plate gas valve of claim 9 further comprising pressure sensing means associated with the region intermediate the upper and lower floating plate gas valves