EP0084215A2

EP0084215A2 - Improvements in or relating to control of pneumatic motors

Info

Publication number: EP0084215A2
Application number: EP82305235A
Authority: EP
Inventors: John Edward Garrard
Original assignee: JH Fenner and Co Ltd
Current assignee: JH Fenner and Co Ltd
Priority date: 1981-10-02
Filing date: 1982-10-01
Publication date: 1983-07-27
Also published as: EP0084215A3; JPS5878991A

Abstract

A control unit for the remote control of a pneumatic motor main valve, the unit having a spool which controls the connection of an output connection to a main supply connection or to exhaust. ln order to provide an improved response over the entire movement range of the valve a fixed orifice is provided between the main supply connection (21) and the output connection (23) and a variable orifice is provided between the output connection (23) and exhaust. The fixed and variable orifices are formed by parallel (15) and tapered (13) portions respectively on the spool.

Description

The present invention relates to the control of pneumatic motors and in particular to a pendant control unit for operating remotely a main control valve of a pneumatic motor. The pendant control unit is particularly suitable for use with a main control valve.
In a known control unit a main air supply passes by way of a variable restrictor through to an output port and continues by way of another variable restrictor to an exhaust port. Both variable restrictors are ganged together and in the neutral off position the first restrictor,that is the mains restrictor,is closed and the second restrictor, that is the exhaust restrictor, is wide open, hence zero output signal. Typically the restrictors are formed by respective tapered portions on a plunger and when this plunger is moved then the mains restriction is gradually opened and at the same time the exhaust restriction is gradually closed. Because the unit throughout its cycle exhausts a small degree of air then the unit is live throughout its operational life and a finite pressure can be achieved. With this arrangement it is possible to achieve a varying pressure signal with valve movement and it has been found that by varying the diameters and tapers of the restrictions the response curve can be arranged to give a larger travel for less pressure increase at the initial onset of the valve opening and as the motor gradually speeds up the reverse applies where the controllability is not so critical. That is to say, the pressure rises more sharply for less travel of the valve. Whilst this effect is acceptable to a large degree it is desirable to have a control curve which produces superior control over the entire movement range of the valve, producing a more even response but this has not been possible with the known valve unit using ganged variable restrictors.
Thus the invention sets out to provide a control unit having superior control over the entire movement range of the valve.
According to one aspect of the invention there is provided a control unit for the remote control of a pneumatic motor main valve, the control unit having a fixed control orifice disposed between a main supply connection and an output connection and a variable orifice disposed between the output connection and an exhaust point.
Preferably the fixed control orifice and the variable orifice are formed by respective parallel and tapered portions of a spool. The spool may be tapered up to five degrees but preferably has a one degree taper. The spool is axially slidable either directly or by way of a lever pivotally connected to a housing of the control unit and abutting one end of the plunger which emerges from the housing. By virtue of the fixed control orifice, pressure is allowed through to the output of the valve immediately the lever.is operated and this has the advantage that the operator does not feel the initial compression or the sealing gland on the main valve.
In the preferred embodiment the plunger is balanced so that the unit does not jump open upon initial movement. The plunger is returned to the neutral position under the action of a spring, in which position the main supply is sealed off from the output connection and the exhaust taper is wide open venting the exhaust connection.
The invention will now be described further, by way of example only, with reference to the accompanying drawings, in which:-

Fig.l illustrates the response curve for a known remote control unit having a taper inlet and taper exhaust,
Fig.2 illustrates a section through a control unit in accordance with the present invention, and
Fig.3 is a response curve for a remote control unit in accordance with the invention.

The response curve of Fig.l illustrates the relationship between valve travel (Vt) and output pressure (Po) for a known remote control unit having a tapered inlet restriction and a tapered exhaust restriction which are ganged together. It will be seen that initially the pressure rises only slowly for relatively long travel and subsequently the pressure rises more rapidly. The valve is not effective over the full travel. It has an effective section Es and a dead section Ds. The control unit in accordance with the invention provides a more smooth response curve in which the pressure rises more gradually over the full valve travel (Vtf) thus giving an improved feel to the unit (see Figure 3, which shows output pressure P plotted against valve travel Vt for the control unit according to the invention).
Referring now to Fig.2 there is shown a pendant control valve unit having a housing 1 provided with a body portion 3 and a handle 5. The illustrated pendant valve illustrates a six station unit particularly suitable for use with overhead travelling cranes where six movements have to be controlled, namely raise, lower, traverse left, traverse right, up and down stop, thus the unit is provided with six valve units, only three of which are shown in the sectional drawing, the other three being positioned by the side of these three. All the valves are constructed in an identical manner although it will be noted that the upper two pairs are button operated whilst the lower pair are lever operated. The lower pair control the raise and lower of the hoist and as such the levers accentuate the degree of control available at the valve.
For convenience the operation of the valve will be described with reference to the uppermost valve 7. A stepped bore 9 is machined into the body 3 and a main spool 11 is received in the smaller diameter of the stepped bore 9. The spool 11 is axially slidable in the bore 9 and is provided with a tapered portion 13 which co-operates with the smaller diameter portion of the bore 9 to form a variable orifice. The spool has a parallel portion 15 which together with the small bore 9 forms a fixed orifice 51. The spool has a reduced diameter 11 between the parallel and tapered portions. A shoulder 17 formed between the larger and smaller diameter portions of the bore 9 constitutes a valve seat with which a valve member 19 in the form of an 0-ring seal carried by the spool co-operates. A mains air supply inlet port 21 opens into the larger diameter portion of the bore 9 and an output connection -23 opens into the smaller diameter portion of the bore 9. With the spool in the position illustrated air pressure acts on the closure member 19 to urge the spool to the right so as to cause the valve closure member to abut the valve seat 17 closing off the mains air supply inlet from the output connection and in this position the variable orifice is fully open, so venting the output connection to exhaust.
An end 25 of the spool 11 projects from the valve body 3 and carries a button by means of which the spool can be axially displaced. The end of the spool remote from the button is received sealingly in a bore 26 of a plug 27 and is acted on by a return spring 29. The bore 26 in which the return spring 29 is received is vented to atmosphere by way of a vent passage 31.
When the spool 11 is moved to the left, the closure member 19 opens the valve seat 17 and air is permitted to flow through inlet restriction 51 from the mains air inlet through to the output connection 23. The output connection leads to a main valve which is changed over so as to direct air to the motor.
The air passing to the output connection is also permitted to exhaust by way of the variable orifice and the amount of air which is exhausted is dependent upon the position of the valve spool 11. Thus, as the valve spool is pushed more to the left less air is exhausted and consequently the output pressure rises and the speed of the motor is increased. It will be seen that the valve spool carries an 0-ring seal 33 by means of which the exhaust may be sealed off completely so permitting mains pressure on the output and full speed operation of the motor.
The valve spool areas are balanced so that upon opening of the valve member the spool does not jump open but gives smooth finger tip operation.

Claims

1. A control unit for the remote control of a pneumatic motor main valve, comprising a variable orifice disposed between the output connection and an exhaust point and characterised by a fixed control orifice (51) disposed between a main supply connection (21) and an output connection (23).

2. A control unit as claimed in claim 1, characterised in that the variable orifice and the fixed orifice (51) are formed by a tapered portion (13) and a parallel portion (15) respectively of a spool (11) which is axially slidable in a housing of the control unit.

3. A control unit as claimed in claim 2, characterised in that the tapered portion has up to a 5° taper.

4. A control unit as claimed in claim 3, characterised in that one end of the spool projects from the housing and the spool is actuable for sliding movement either directly or by way of a lever abutting said one end and pivotally connected to the control unit housing.

5. A control unit as claimed in claim 4, -characterised in that the spool (11) is received in a stepped bore (9) formed in the housing, and in that the spool carries a valve member 19 which is co-operable with a shoulder 17 of the stepped bore 9 to close off the connection from the main supply connection (21) to the fixed orifice (51).

6. A control unit as claimed in claim 5, characterised in that the valve member (19) is biased into contact with the shoulder (17) by a spring (29) which is disposed in the stepped bore and which acts on the spool (11).

7. A pendant control valve comprising a plurality of control valves, as claimed in any of claims 1 to 6.