Patent Application
20050145470
The present invention relates generally to valves and, more particularly, to an apparatus and method for seat detection and soft seating in a valve having a member actuated by a piezoelectric device.
Piezoelectric materials alter their shape in response to an applied electric field. An electric field applied in the direction of polarization of the material effects an expansion of the material in the same direction, while a voltage applied in the opposite direction of polarization will cause a contraction of the material in that same direction. Piezoelectric benders, which may be pre-stressed thermally, mechanically, or otherwise, such as pre-stressed benders as disclosed in U.S. Pat. Nos. 5,471,721 and 5,632,841, use the “bending” action of piezoelectric material to convert electrical energy into mechanical energy. In such applications, the bender may be used as an actuator. In other applications, an outside force may impart a bending action or mechanical energy to the bender, and the bender then converts that mechanical energy into electrical energy. In such applications, the bender may be used as a sensor.
In electrohydraulic valves having a valve member and contact surface, piezoelectric devices have been used to activate the valve member relative to the contact surface, such as a stop or a seat. In operation, the piezoelectric device deforms in response to a control signal, such as a voltage input signal applied to the piezoelectric device, to move the member either toward or away from the contact surface. Typically, it is desirable to know when the member has reached the contact surface, i.e. seat detection. This is important particularly in proportional valves as the position of the member relative to the contact surface should be determined and controlled to provide the desired flow of fluid through the valve.
Valve seat detection is also desirable in the application of soft-seating techniques. The piezoelectric device must be actuated to move the member a sufficient distance to engage and seal with the contact surface to control the fluid flow, yet, preferably, without severely impacting the member into the contact surface. When the member is moved toward the contact surface with excessive velocity and force, relatively severe impacts may occur, and the contact surface and/or the end of the member may become worn over time. Such impacting of the contact surface may also cause the member to bounce off of the contact surface so that proper control of fluid flow is not achieved. Further, improper control of valve position and valve velocity may reduce the life of the actuator and lead to an undesired loss of control of the fluid flow through the valve.
In the past, valves have incorporated position or load sensors, operating independently of the actuator, to provide soft-seating of the member with the contact surface. Typically, soft-seating utilizes an electronic valve controller to control impact of the valve member with the contact surface by decreasing the velocity of the member as it impacts and engages the contact surface. Position sensors monitor the position of the member relative to the contact surface and provide that information to the controller, which then controls the velocity of the member as it moves toward the contact surface. Load sensors monitor the load applied to the contact surface by the member and provide that information to the controller, which then controls the load, i.e. the force of contact, applied to the contact surface to reduce wear. However, known position and load sensors are relatively large, complex, and/or costly and do not lend themselves well to many electrohydraulic valve applications requiring accurate and reliable valve position and velocity control.
The present invention is directed to overcoming one or more of the problems set forth above.
In a first embodiment, an apparatus for determining position of a valve member relative to a valve contact surface is disclosed. The member is operatively connected to an actuator. The apparatus comprises an actuator control circuit operatively connected to the actuator and operable to apply a control signal to the actuator to move the member relative to the contact surface and operable to produce an output from the actuator and a seat detection circuit operatively connected to the actuator control circuit and operable to determine contact of the member with the contact surface from the output, wherein the actuator is a piezoelectric device.
In a second embodiment, an apparatus for controlling velocity of a valve member relative to a valve contact surface is disclosed. The member is operatively connected to an actuator. The apparatus comprises an actuator control circuit operatively connected to the actuator and operable to apply a control signal to the actuator to move the member relative to the contact surface and operable to produce an output from the actuator; a seat detection circuit operatively connected to the actuator control circuit and operable to determine contact of the member with the contact surface from the output; and a velocity control circuit operatively coupled to the actuator control circuit and operable to send an input to the actuator control circuit, the actuator control circuit controlling the velocity of the member from the input, wherein the actuator is a piezoelectric device.
In a third embodiment, a valve is disclosed. The valve comprises an actuator comprised of a piezoelectric device having one or more prestressed electroactive benders; a member operatively connected to the actuator; a contact surface, the member operable to move relative to the contact surface and to contact the contact surface; and a control system operatively connected to the actuator for determining a position of the member relative to the contact surface.
In a fourth embodiment, a valve is disclosed. The valve comprises an actuator comprised of a piezoelectric device having one or more prestressed electroactive benders; a member operatively connected to the actuator; a contact surface, the member operable to move relative to the contact surface and to contact the contact surface; and a control system operatively connected to the actuator for controlling the velocity of the member relative to the contact surface.
In a fifth embodiment a method of determining position of a valve member relative to a valve contact surface, wherein the member is operatively connected to an actuator, is disclosed. The method comprises applying a control signal to the actuator to cause the member to move relative to the contact surface; determining an output of the actuator; and determining contact of the member with the contact surface from the output.
FIGS. 3(a) and 3(b) are graphs illustrating output voltage of the piezoelectric device versus time for free and blocked motion, respectively, of the piezoelectric device in accordance with principles of the present invention; and
The following is a detailed description of the best mode embodiment of the present invention, with sufficient detail to permit someone skilled in the art to make and use the claimed invention. The present invention, however, is not limited to the embodiment disclosed and described herein. To the contrary, the present invention may include all those alternative embodiments and equivalents that fall within the scope of the present invention as defined by the appended claims.
The piezoelectric device utilized as actuator 16 preferably is comprised of one or more pre-stressed electroactive benders, which may be pre-stressed thermally, mechanically, or by other means, that change shape by deforming in opposite axial directions in response to a control signal supplied by the control system 20. Individual benders may be stacked or bonded together into a single, multi-layered element. The control signal may be a voltage signal supplied from the control system 20 to the actuator 16 through a pair of electrical leads 22a and 22b (as seen in
The piezoelectric device may be circular, rectangular, square or any other regular or irregular shape, although a circular shape is preferred, and includes at least one electroactive layer (not shown) positioned between a pair of electrodes (not shown) or other means for supplying a voltage to the electroactive layer. Other configurations are possible as well without departing from the spirit and scope of the present invention. In a de-energized or static state, the piezoelectric device is preferably pre-stressed to have a domed configuration as shown in phantom in
As shown in
As seen in
The graphs illustrated in FIGS. 3(a) and 3(b) illustrate the actuator voltage output on connector 32 from the actuator control circuit 24.
The seat detection circuit 26 receives the actuator voltage on connector 32, i.e. the voltage trace 34 or 36 as seen in
The differentiator 44, which is known by those of ordinary skill in the art, is operable to measure the instantaneous rate of change of the actuator voltage received on connector 32. Alternatively, the differentiator 44 may measure a rate of change in the frequency domain or any other characteristic in the actuator voltage 32 that represents impact of the member 18 with the contact surface 12. The threshold detector 46, which is known by those of ordinary skill in the art, receives the rate of change from the differentiator 44 and evaluates the signal for the abrupt change 38a or 38b indicative of initial impact of the member 18 with the contact surface 12. Preferably, the threshold detector 46 filters the signal received from the differentiator 44 and compares the filtered signal to a predetermined value, the predetermined value being a change in voltage amplitude indicative of impact. When the rate of change received from the differentiator 44 is sufficiently large and exceeds the predetermined value, impact of the member 18 and the contact surface 12 is determined to have occurred. The seat detection circuit 26 then outputs the seat detection on connector 48 indicative of the actuator voltage at which member 18 and contact surface 12 impacted. Of course, it will be appreciated that other output characteristics of the actuator 16, such as current or charge, may be evaluated to detect impact of the member 18 with the contact surface 12 without departing from the spirit and scope of the present invention.
Referring now to
The control system 200 includes a position control circuit 202 connected to the actuator control circuit 24 and to the valve seat detection circuit 26 for determining the position of the member 18 relative to the contact surface 12. The control system 200 further includes a velocity control circuit 203 connected to the position control circuit 202 and to the actuator control circuit 24. The position control circuit 202 includes a current integrator 204 that is operable to receive and integrate the actuator current on connector 205, which is indicative of the current flowing through the actuator 16 or piezoelectric device, to determine a charge existing on the piezoelectric device and output an actuator charge on connector 208. The position control circuit 202 further includes a memory or other storage device 206 which receives the actuator charge on connector 208 from the current integrator 204 and stores a value representing the charge existing on the piezoelectric device 16 when the member 18 impacted the contact surface 12.
Further, the seat detection circuit 26, as described in conjunction with
The position control circuit 202 further includes a comparator 216 that is operable to receive from the storage device 206 a desired charge on connector 218 which is equivalent to the charge stored during the previous cycle and corresponds to the desired position of the member 18, i.e. at which the member 18 and contact surface 12 are in contact. The comparator 216 is further operable to receive the actuator charge on connector 220, i.e. the charge existing on the piezoelectric device 16 during the current cycle. The comparator 216 is operable to compare the desired charge from connector 218 with the actuator charge from connector 220. The comparator 216 outputs an actuator charge error on connector 222 representing the difference between the desired charge on the piezoelectric device, i.e. the position of the member 18 at which it last contacted the contact surface 12, and the actual charge on the piezoelectric device, i.e. the current position of member 18. Thus the actuator charge error, which is received by the velocity control circuit 203, represents the current position of the member 18 relative to the contact surface 12.
The velocity control circuit 203 preferably is a one-dimensional map, such as a look-up table, polynomial or other function, and utilizes the actuator charge error to determine the appropriate velocity of the member 18 based upon the relative position of member 18. The circuit 203 outputs an actuator charge rate on connector 224 to the actuator control circuit 24 to control the rate of charge of the piezoelectric device and thus the velocity of it and member 18. The velocity control circuit 203 includes a predetermined velocity profile relating the actuator charge error, or relative current position of the member 18, to the desired velocity of the member 18. The velocity control circuit 203 determines the desired velocity and outputs an actuator charge rate on connector 224. As the velocity of the member 18 is proportional to the rate of charge on the piezoelectric device, the actuator charge rate may be used by the actuator control circuit 24 to slow the rate of charge on the piezoelectric device as the member 18 approaches the contact surface 12, thus lessening the force of impact.
In operation of the control system 200 of
During a second valve actuation cycle, the charge stored in storage device 206 from the previous cycle is output to the comparator 216 as the desired charge on connector 218. The comparator 216 compares this signal to the actuator charge on connector 220 representing the actual charge on the actuator 16 during the current cycle. The comparator 216 outputs the difference of the desired and actuator charges to the velocity control circuit 203 as the actuator charge error on connector 222. From the map comprising the velocity control circuit 203, an actuator charge rate corresponding to the determined actuator charge error is determined and output on connector 224 to the actuator control circuit 24. The actuator charge rate is utilized by the actuator control circuit 24 to control the rate of charge on the piezoelectric device and, thus, the velocity of member 18. Therefore, the velocity of member 18 may be adjusted to slow the member 18 as it approaches and impacts the contact surface 12 and, thus, allow for soft-seating of the member 18. When the member 18 contacts the contact surface 12, seat detection circuit 26 sends a seat detect on connector 48, a new actuator charge is stored in storage device 206, and the cycle begins again.
In use, it will be appreciated that control system 20 or 200 is operable to move the member 18 into contact with the contact surface 12 in response to the charge command 26. The control system 20 is further operable to determine when valve member 18 impacts the contact surface 12. The control system 200 is further operable to determine the position of the member 18 relative to the contact surface 12. The comparator 216 of the position control circuit 202 compares the desired charge determined from the previous actuation cycle with the current charge on the piezoelectric device and provides the difference to the velocity control circuit 203 as the actuator charge error. The velocity control circuit 203 is operable to determine the appropriate actuator charge rate from the actuator charge error and output that rate to the actuator control circuit 24. This circuit 24 then controls the rate of charge of the piezoelectric device. Since the velocity of the member 18 is proportional to the rate of charge on the piezoelectric device, more accurate and reliable control of the velocity of member 18 may be obtained through the position control circuit 202 and velocity control circuit 203 of control system 200.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10163544 | Jun 2002 | US |
| Child | 11030460 | Jan 2005 | US |
