WO2016007754A1

WO2016007754A1 - Method and system for controlling actuators

Info

Publication number: WO2016007754A1
Application number: PCT/US2015/039759
Authority: WO
Inventors: Edward G. Holtgraver
Original assignee: Qtrco, Inc.
Priority date: 2014-07-10
Filing date: 2015-07-09
Publication date: 2016-01-14

Abstract

A method and system for controlling output torque of a fluid-actuated actuator connected to an input shaft of a movable device so as to control output force or torque of the actuator. The system and method involve determining first and second allowed pressures at all positions of travel of the actuator shaft when pressure is increasing and decreasing, respectively. In the method, the position of the actuator shaft is sensed and under the control of a PLC or similar controller, the pressure applied and/or exhausted from the actuator is controlled.

Description

Method and System for Controlling Actuators

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Application No. 62/022,830 filed on July 10, 2014, the disclosure of which is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to actuators and, more particularly, a method and system for controlling actuators used to operate valves.

BACKGROUND OF THE INVENTION

An actuator is an apparatus that converts energy into motion. Actuators typically are used in manufacturing or industrial applications and are used extensively in devices such as motors, pumps, switches and valves. One of the most common types of actuators is a pneumatic actuator but actuators can also be electric or hydraulic.

Actuators can create a linear motion, rotary motion or oscillatory motion. Hydraulic and pneumatic actuators can be single acting meaning that the media energy source causes movement in one direction and a spring causes movement in the opposite direction. Alternatively, the actuator can be double acting meaning that the media pressure causes movement in both directions.

One of the most common uses of actuators is with rotary shaft style valves such as ball valves or butterfly valves. One of the concerns of valve companies in connection with their choice of actuators is choosing an actuator that does not apply so much torque output it could break the valve shaft should the valve element become stuck for some reason. To this end, valve companies generally supply actuator manufacturers with a so called MAST value (maximum allowed shaft torque) but for functional purposes request a substantial safety factor of actuator torque over the expected operating valve torque requirement. Thus actuators sized for the desired operational output plus safety factors, and considering their output characteristics, may be inherently capable of providing an output greater than the MAST value. Accordingly, there exists a need for a method and system to automatically control actuator output at all travel positions and in both directions of travel as applied to the shaft of the valve to ensure that the MAST value is not exceeded.

SUMMARY OF THE INVENTION

In one aspect the present invention provides a system operatively connected to an actuator to control the actuator output.

In another aspect the present invention provides a method and system for controlling actuator output applied to a linearly or rotatably movable shaft.

In still a further aspect, the present invention provides a method and system for controlling actuator output to a rotatable valve shaft.

These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of one embodiment of the system of the present invention used with a Scotch yoke single acting actuator.

Fig. 2 is a schematic view similar to Fig. 1 showing another embodiment of the system of the present invention as used with a double acting Scotch yoke type actuator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While in the description which follows reference will be made to the use of the method and system of the present invention with respect to rotatable shafts and, more particularly, to valves with rotatable shafts, it will be understood that it is not so limited. Thus, the method and system of the present invention could be used with a movable shaft in any device wherein travel of the shaft must be controlled, albeit its use is more susceptible to use with rotatable shafts such as those in quarter turn valves.

Further, while in the description that follows, there is described the use of the method and system of the present invention both with single acting, spring return and double acting actuators, it is particularly adaptable to spring return actuators since in that case there is only a single pressure to control as opposed to double acting actuators where pressure measurements need to be made on both sides of a piston.

Referring first to Fig. 1 , the system of the present invention according to one embodiment of the present invention is shown generally as 10. System 10 comprises a spring return Scotch yoke actuator, shown generally as 12. As is well known to those skilled in the art, there is an actuator coupler (not shown) by which the actuator 12 can be attached to the shaft of a rotatable valve which by way of example and in the case described in Fig. 1 can be a quarter turn valve such as a butterfly valve (not shown).

It will be understood that in the systems described in Figs. 1 and 2 as well as any other apparatus to which the present method is applied, the coupler or adapter between the actuator shaft and the shaft to be controlled will actually reflect the position of the latter and hence, for example, the position of the valve element attached to that shaft. It will also be understood by those in the art that the actuator and device being controlled, e.g., the valve, are connected together in such a fashion that their relative position to one another remains fixed or constant, barring which valve element positioning would not be controllable. In other words, it is important to compare actuator output to the MAST value in the case of a valve such that actuator output torque, subject to any override discussed hereafter, does not exceed the MAST value without effecting valve shaft orientation.

The system 10 further includes a position sensor/transmitter shown schematically as 14 which is connected to a PLC 16, or other device having programmable memory e.g., an EPROM, connected to electrical supply E. Actuator 12 comprises pistons 12A and 12B which are in modules disposed on either side of the valve shaft coupler and can be pressurized with a suitable fluid media e.g., gas or liquid, via lines 15 and 17, respectively, which are in open communication with a pressure transducer 18, there being a conduit connecting pressure transducer 18 to a two way solenoid operated valve (SOV) 20.

SOV 20 is connected to PLC 16 as is pressure transducer 18. A conduit 22 connects SOV 20 to a three-way SOV 24 which has a media pressure supply line 26 and an exhaust line 28. As was noted above, one goal of the present invention is to control the actuator output force and accordingly the force (torque) applied to the valve shaft such that to MAST value for the valve is not exceeded.

The operation of the embodiment shown in Fig. 1 will now be described. At the outset, the MAST value supplied by the valve manufacturer would be programmed into PLC 16. As is known to those in the art, the actuator manufacturer knows the output torque of the actuator for all media pressures which will vary as related to travel direction and all positions of travel. For example in the case of spring return actuators, the torque is the result of the net difference between spring force and media force and in this regard in the media force direction it is media force less spring force while in the spring movement direction it is spring force less media force. The position sensor/transmitter 14 provides real time data to PLC 16 such that at any given time that the valve shaft is moving, its position and hence the position of the valve element is known. Using appropriate software, and since PLC 16 has been programmed to know the actuator output torque for all media pressure values and at all travel positions, PLC 16 via SOV 20 can ensure that when pistons 12A, 12B are being moved by the media pressure, there is no more pressure applied than that which would cause the output of actuator 12 to exceed the MAST value. Conversely, in the spring movement direction of travel, PLC 16 again via the SOV 20 prevents exhaustion of media pressure beyond the value that is less than that which would allow the spring to apply more than the MAST value. In the system of Fig. 1 employing Scotch yoke actuator 12 and as is well known to those skilled in the art, more torque is applied at the ends of travel of the pistons than in any intermediate position. However in determining actuator sizing, it is the lesser value of the spring and media produced output torque on which the actuator is sized to meet the operational requirements of the valve. The net result is that in the ordinary case, at the ends of travel, be it in the media applied force direction or the spring applied force direction, the actuator output torque may exceed the MAST valve. This is important given the user's desires for high safety factors of actuator output versus valve required input. The present invention overcomes this problem as follows. The known parameters are 1 ) torque output versus pressure, 2) known valve position (actuator travel rotation) via position sensor/transmitter 14 3) the pressure via transducer 18 and 4) the MAST value. With these parameters, PLC 16 is programmed to calculate a maximum pressure when pressure is rising and a minimum pressure when pressure is decreasing at every travel position of the actuator. Since PLC 16 is connected to solenoid valve 20, when pressure to the actuator is being decreased, SOV 20 is designed to prevent further release of media so that the spring force does not result in torque in excess of the MAST value. When pressure is being increased to the actuator, SOV 20 is designed to prevent further inflow of media so that the pressure force does not result in torque in excess of the MAST value.

Due to spring compression and internal mechanisms, actuator output forces and torques are not constant throughout the full range of travel. Therefore it is impractical to simply establish and to limit the maximum allowed operating pressure as this pressure would cause differing outputs as the actuator travel changes. Also, setting a maximum applied pressure value would not limit the output caused by the spring when pressure is exhausted.

Thus, given that the actuator manufacturer knows the actuator output at all travel positions and all pressure values, the output at any travel position can be controlled by limiting the applied pressure. Likewise the output caused by the spring can be controlled by limiting the exhaust of pressure to prevent full spring force.

With control of both increasing and decreasing pressures (pneumatic or hydraulic) it is practical to prevent any pneumatic or hydraulic actuator from producing more output than the valve MAST with no negative effect on normal operation.

The simplicity of the concept is highlighted by the fact that once the PLC is properly programmed with suitable software it requires only the opening or closing of a valve (SOV 20) to ensure that the, MAST value is never exceeded.

Referring now to Fig. 2, there is shown another embodiment of the method and system of the present invention involving a double acting actuator. In Fig. 2, components that were used in the embodiment of Fig. 1 are given the same reference characters. As can be seen with reference to Fig. 2, basically the only difference between the embodiment shown in Fig. 1 and the embodiment shown in Fig. 2 is that since in the embodiment shown in Fig. 2 media pressure has to be applied and monitored on both sides of the pistons, there is a second pressure transducer 18A, a second two way solenoid operated valve 20A and a four way SOV 40. Those components along with associated plumbing to accommodate pressure to both sides of the piston in each of the modules are the only substantial differences between the embodiments shown in Fig. 1 and Fig. 2. Thus, instead of having to take into account spring force as in the case of the embodiment of Fig. 1 , in the embodiment of Fig. 2, media pressure must be monitored on both sides of the piston in each of the force modules but again controlling output torque by the actuator to the valve is conducted simply by opening and closing two SOV's, 20, 20A as necessary. In this regard, the differential between the two pressures can be monitored and SOV 20 and 20A locked off by the PLC when the difference reaches a value that would cause excessive torque.

In both the systems shown in Figs. 1 and 2, PLC 16 can be programmed to transmit a failure/fault message should the MAST be reached indicating that the valve resistance to motion has reached the valve's MAST value i.e., when the valve is perhaps stuck in a position. So that the user can recognize when the valve resistance is increasing towards the MAST value allowing the user to take appropriate action, according to the present invention, the PLC 16 could also be programmed to signal each and every time that the output torque of the actuator 12 exceeds some percent of the MAST value. This would allow the user to take the necessary preventative action to avoid either restricting flow or allowing flow through the valve. It will also be recognized that there could be multiple levels of warnings for different percentages of output i.e., valve resistance. In short, using the system of the present invention actuator 12 will not apply more torque than the MAST but it may also serve to provide the user a real time awareness of changes in the valve / actuator assembly to enable corrective action before a MAST failure will occur.

Additionally, should the system recognize that the MAST value has been exceeded, it may, in addition to preventing excessive output torque, permit the user in an emergency to override the system fully or at a percentage in excess of MAST that may be chosen such that while the valve shaft is stressed beyond normal design limits, it is not stressed to the point of expected failure.

The system of the present invention can be used on any quarter turn, linear or multi-turn actuator which uses media pressure as at least one source to provide output torque.

In summary, according to one embodiment of the method of the present invention, the maximum allowed pressure at all degrees of travel of the actuator shaft coupler when pressure is increasing and a minimum allowed pressure at all degrees of actuator coupler travel when pressure is decreasing is determined. The position of the actuator at all degrees of travel is sensed and this information is sent to the PLC. Since the MAST values are known and the valve position is being determined in real time by the position sensor/transmitter, the software in the PLC then controls pressure applied to the actuator via a solenoid operated valve to ensure that the maximum allowed pressure is not exceeded at any degree of travel of the actuator shaft coupler when media pressure is increasing and, as well, when pressure is falling and again via the SOV, the PLC controls, the pressure to ensure that it does not fall below a minimum allowed pressure at any degree of travel of the actuator shaft coupler e.g., so the force of the spring does not exceed the MAST value.

It will also be understood that the method of the system of the present invention can be used in conjunction with a positioner when it is desired to move the valve to a certain position e.g., to act as a throttle. Essentially, the positioner would essentially replace the three-way solenoid valve in this event. A suitable media pressure source would be used in conjunction with the pressure transducer which could be built into the positioner and the SOV which also could be built into the positioner. Again with the PLC and proper software, the valve could be moved to a certain position without exceeding the MAST value and moved in the opposite direction again without the spring or media force exerting a torque exceeding the MAST value.

As noted above, the method can include real time monitoring. Thus, in a case where it is desired to know what the operating parameters of the valve or other device over one or a multiplicity of operations, real time torque values for all travel positions during those operation(s) can be transmitted by the PLC to a monitoring station or the like. Accordingly, the PLC could override media pressure control in an emergency that could lead to shaft failure. Such an override could be a full override in the sense that the actuator would cease operation. Alternatively, the override could be such as to allow, for example, the MAST value and therefore the desired stress on the shaft to be exceeded, but not to the extent to result in shaft failure. Such an override could be manual or the PLC could be programmed to allow such override subject to preprogrammed parameters being met.

Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.

Claims

WHAT IS CLAIMED IS:

1 . In a system comprising an actuator having an actuator output shaft, a pressure source connected to said actuator, an actuator coupler operatively interconnecting said actuator shaft and the input shaft of a movable device, a method of controlling actuator output applied to said input shaft, comprising: determining a first allowed pressure at all position of travel of said actuator coupler when pressure to said actuator is increasing and a second allowed pressure at all positions of actuator coupler travel when pressure to said actuator is decreasing;

sensing the position of said actuator coupler at all positions of travel of said actuator coupler; and

controlling pressure applied to said actuator so said first allowed pressure is not exceeded at any given position of travel of said actuator coupler, and pressure supplied to said actuator does not fall below said second allowed pressure at any given position of travel of said actuator coupler.

2. The method of claim 1 , wherein said actuator comprises a single- acting actuator.

3. The method of claim 1 , wherein said actuator comprises a double- acting actuator.

4. The method of claim 1 , further comprising: calculating actuator-applied torque values for all travel positions of said shaft in a given operation and transmitting said torque values to a monitoring station.

5. The method of claim 4, further comprising:

at least partially overriding actuator operation in response to data from said monitoring station.

6. The method of claim 1 , wherein said input shaft is a rotatable shaft.

7. The method of claim 6, wherein said rotatable shaft comprises a quarter turn valve.