Piezoelectric/fluid pressure transducer apparatus

A flat, elongate, laminated plate of ceramic piezoelectric material is fixedly mounted on one end to permit movement of the other end responsive to the application of a variable electronic control signal to electrodes on the outer surfaces of the laminated plate. The movement and force applied by the movable end of the plate controls the release of air pressure from the pressure chamber so that the pressure in the chamber varies in response to the variations of the electronic control signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention. 
This invention has relation to apparatus for utilizing the changes in shape 
of piezoelectric material due to changing electrical signals applied to 
the material to develop a fluid pressure in a fluid flow conduit which 
varies with the variations in the electrical signal applied to the 
piezoelectric material. 
This invention has initially found its greatest utility where the fluid 
pressure is a pneumatic pressure, and where the fluid involved is air. 
2. Description of the Prior Art. 
It is known to develop a variable air pressure for operating a pneumatic 
linear motor by supplying air from a constant pressure source through a 
restrictor to a pressure chamber open to the linear motor, and varying the 
pressure in the chamber by mechanically controlling a pressure relief 
valve to bleed off air in the chamber. Mechanical means for operating such 
valving have heretofore proved unduly slow, imprecise, unresponsive to 
minute changes and/or unacceptably expensive for use in certain 
applications. 
It is a known that certain crystals such as quartz, Rochelle salt, 
tourmaline, and barium titanate, have piezoelectric properties such that 
when an electrical field is applied to them, the crystal changes shape. 
Piezoelectric materials in common use as electromechanical transducers 
include barium titanate and four variations of lead zirconate-lead 
titanate ceramics. These ceramics are polycrystalline in nature. 
Piezoelectric behavior is induced in these ceramic materials by a 
polarizing treatment. 
It is known to join two transverse-expander plates of piezoelectric ceramic 
material together face-to-face in such a manner that a voltage applied to 
two electrodes each in contact with an outer face of a different one of 
the plates will cause the plates to deform in opposite directions, 
resulting in a bending action. Such piezoelectric elements were developed 
by Vernitron and are available under the trade name BIMORPH. Such BIMORPH 
brand plates can be used in series operation by being positioned between 
silver foil electrodes. 
What was lacking before the present invention was a transducer apparatus 
which could control the operating pressure in a pressure chamber so that 
it would vary substantially instantaneously with variation in an 
electrical control signal, and which was responsive to even the minutest 
variations in the magnitude of that signal. 
SUMMARY OF THE INVENTION 
A transducer apparatus utilizing a varying electronic signal for developing 
a varying fluid pressure in a chamber for actuating a pressure actuated 
work device is disclosed herein as an apparatus for developing a varying 
pneumatic pressure for actuating a pneumatic linear motor such as a rotary 
actuator. However, by utilizing a hydraulic accumulator open to the 
chamber supplying the pressure to the pressure actuated work device, 
liquids can be utilized in the transducer apparatus of the invention. 
A transducer apparatus for developing a varying fluid pressure for 
actuating a pressure actuated work device responsive to the magnitude of a 
varying electronic signal includes a piezoelectric/fluid pressure control 
unit having a base, a plate of piezoelectric material fixedly mounted at a 
first portion thereof with respect to the base, a second portion of the 
piezoelectric plate being free to vary its position responsive to 
application of a variable electronic signal applied to opposed faces of 
the plate, and means for transmitting such a variable electric control 
signal to such opposed faces of the plate. A fluid flow conduit providing 
a fluid flow cavity or chamber has a first flow input portion, a second 
working portion open to a pressure actuated work device, and a third 
pressure relief and flow output portion which is open to the fluid flow 
chamber between the first and second portions. A source of fluid under 
pressure is connected to the first flow input portion through a fluid flow 
restrictor. A pressure relief valve means is open to the third portion of 
the fluid flow conduit and includes a valve seat fixedly mounted with 
respect to the base, the valve seat being provided with a pressure relief 
and flow orifice open to the fluid flow chamber through the third output 
portion of the conduit. 
A valve including the second portion of the piezoelectric material is 
situated in operational alignment with the valve seat in position whereby 
fluid under pressure in the fluid flow chamber tends to flow through the 
pressure relief and flow orifice and the valve seat to tend to force the 
valve away from the valve seat and whereby a change of position of the 
second portion of the piezoelectric material responsive to the varying of 
the magnitude of the electronic signal transmitted to that material 
changes the force with which the valve resists the flow of fluid from the 
chamber through the valve seat to the end that the pressure within the 
chamber varies with the variations of the signal transmitted to the 
piezoelectrical material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A transducer apparatus 10 includes a piezoelectric/fluid pressure control 
unit 11 having a main frame or base 12, an elongate plate of ceramic 
piezoelectric material 14. This plate 14 has a first end portion 15 
fixedly or rigidly mounted to the base 12 as at 16 and a second free end 
portion 17 in clearing relation to the base 12. 
The piezoelectric plate 14 can be of the type sold by Vernitron under the 
trademark BIMORPH. It can consist of upper and lower laminates of ceramic 
piezoelectric material secured in face-to-face electrical contact with 
each other. An upper electrode 18 of silver foil, for example, can be 
bonded to the top surface of the upper laminate and a similar lower 
electrode 19 can be bonded to the bottom surface of the lower laminate. 
In the form of the invention as shown, the apparatus also includes a source 
20 of air under pressure, a pressure actuated work device 21 in the form 
of a pneumatic linear motor 22 serving as a rotary actuator 23, and fluid 
or air flow conduit 24 providing a fluid or air flow chamber 25 open 
between the air pressure source 20 and the linear motor 22. 
Air flow conduit 24 has a first fluid or air flow input portion 26, a 
second working portion 27 and a third pressure relief and fluid or flow 
output portion 28. This third portion of conduit 24 is provided with a 
pressure relief and air flow orifice 29 open between air flow chamber 25 
and the atmosphere. This third portion 28 of the conduit 24 is fixedly 
positioned with respect to the main frame or base 12 so that the orifice 
29 is directly below the free end portion 17 of the piezoelectric ceramic 
plate 14 as seen in FIGS. 2 through 5. The third portion 28 of air flow 
conduit 24 effectively terminates in a valve means 30. In the first form 
of the invention, as seen in FIGS. 2 and 3, this valve means includes an 
upwardly facing conical valve seat 31 and a spherical ball 32 nominally 
resting in closing relation to the valve seat. 
A fluid or air flow restriction means 34 is situated between input portion 
26 of the air flow conduit 24 and the air pressure source 20. This 
restriction means limits the flow of air into the air flow chamber 25 from 
the pressure air source 20 sufficiently so that the pressure in the air 
flow chamber 25 at any particular point in time can be varied by varying 
the amount of outward flow through the air flow orifice 29. The more flow 
permitted through the orifice 29, the lower is the pressure in the air 
flow chamber 25. This air flow restriction means 34 can be in the form of 
a permanent restriction, or can be, as shown here, in the form of a 
coupling 36 encompassing a replaceable air restrictor disk 38 having an 
air passage 39 therethrough. By using several different air restrictor 
disks 38 with air flow passages 39 of different areas, the operating 
parameters of the transducer apparatus 10 can be modified as may prove 
necessary or desirable. 
Any pressure responsive device or pressure actuated work device open to the 
air flow chamber 25 will be operable responsive to the changes of pressure 
in that chamber. The uses of such devices are many. For example, such 
devices can control and operate valve operators, damper operators, 
receiver controllers and the like. 
In the form of the invention as shown, the pressure actuated work device is 
the pneumatic linear motor 22 which includes a casing 40, a piston 42 and 
a piston rod 43 slidably mounted within the casing. A diaphragm 44 
separates the casing into a pressure compartment 46 and a open compartment 
48 open to the atmosphere. A spring 50 tends to hold the piston 42 and 
piston rod 43 in the position as seen in FIG. 6, and pressure in the air 
flow chamber 25 operates to tend to move the piston rod to the right as 
seen in that figure to rotate a gear segment 52 of a rotary actuator lever 
54 to the end that a rotary actuator shaft 56 causes an actuator arm 58 to 
control a damper operator arm 60. This will allow the damper itself (not 
shown) to be positioned in an infinitely different number of positions 
responsive entirely, substantially instantly and precisely to changes in 
the pressure in the air flow chamber 25. 
This control of the air pressure in air flow chamber 25 by some kind of a 
valve means to control the rate of flow of air out of the chamber 25 by 
some kind of a valve means is known in the prior art. However, such valve 
means have, in the past, been cumbersome in their operations due to the 
mass of the valve parts and the mechanical and/or electronic means used to 
control the valve parts. Therefore, before the present invention, it was 
not possible to effectively control a valve means for developing a 
pressure within an air flow chamber which would follow precisely and 
substantially instantaneously variations in the magnitude of an electronic 
signal developed to control the pressure in the chamber and hence the 
operation of a pressure responsive device such as a pneumatic linear motor 
forming part of a rotary actuator. 
OPERATION 
In describing the operation of the transducer apparatus of the invention, 
it is assumed, by way of example, that the object is to position a damper 
(not shown) of a heating, ventilating and air conditioning system by 
control of its damper operating arm 60 through rotation of rotary actuator 
arm 58 all in accordance with the magnitude of an electronic signal 
provided through input lines 62 and 63 to the control unit 11. This 
control signal to electrical input lines 62 and 63 will vary in magnitude 
in accordance with the desired positioning of the damper, the damper 
operator arm 60 and, consequently, the actuator arm 58. The damper can be 
completely closed or completely open or constantly fluctuating between 
opened and closed condition as it precisely responds to the magnitude of 
the electronic signal being imposed on electrical input signal lines 62 
and 63. 
Whether such input signal is digital, amplitude modulated or frequency 
modulated alternating current, or direct current, it will be converted 
into a direct current signal in a signal converter box 64 of the control 
unit 11 using any usual or preferred circuitry, forming no part of the 
present invention per se. This corrected output is transmitted on output 
signal lines 66 and 67 to silver foil electrodes 18 and 19 bonded to the 
top and bottom surfaces of the plate 14. 
In one form of operation, as the magnitude of the electrical signal applied 
to the electrodes 18 and 19 by the output signal lines 66 and 67 
increases, a BIMORPH plate 14 of ceramic piezoelectrical material will 
tend to deflect in downward direction as seen in FIGS. 2 and 3, increasing 
the force on the spherical ball 32 thus tending to inhibit flow from the 
air flow chamber 25. This will cause a buildup of pressure in chamber 25 
toward the maximum pressure available from pressure source 20. At some 
particular pressure, the force of plate 14 will be overcome, the ball will 
raise allowing pressure to escape and an equilibrium will be established 
at that particular pressure. 
By way of example, it will be assumed that the transducer apparatus is 
designed and adjusted to produce a pressure in pressure chamber 25 which 
varies between three and fifteen pounds per square inch (psi) with a 
variation of from zero volts to 200 volts of direct current excitation 
across the electrodes 18 and 19, using a constant source 20 of air under 
pressure of twenty psi. When no voltage is applied across output signal 
lines 66 and 67, the relationship of the parts will be such that only 
sufficient force will be applied by second free end portion 17 of BIMORPH 
plate 14 on spherical ball 32 such that an equilibrium is reached between 
the air-lifted ball 32 and the valve seat 31 sustaining a three psi 
pressure inside of the chamber 25. The piston 42 will then be deflected to 
the right as seen in FIG. 6 until an equilibrium is reached balancing the 
force of the three psi acting on the diaphragm 44 and piston 42 will 
balance with the force exerted by the spring 50. 
As the voltage on output terminals 66 and 67 is increased, an equilibrium 
will be substantially immediately reestablished between the physical 
positioning of the ball 32 and the valve seat 31 with the ball closer to 
the valve seat and with the pressure in the pressure chamber 25 
commensurately increased. When the output voltage across the signal lines 
66 and 67 reaches 200 volts of direct current excitation, the force 
exerted by the free end 17 of the plate 14 will be such that the ball is 
maintained in much closer relationship to the valve seat, and the pressure 
and the pressure chamber will be established at fifteen psi. 
Minute changes in the excitation voltage across the electrodes of the 
ceramic plate 14 substantially instantaneously result in establishing new 
equilibrium pressures within the chamber 25 exactly representative of the 
magnitude of those changes. This reduces or virtually eliminates any lag 
between the change in pressure applied to a pressure responsive device 
such as pneumatic linear motor 22 and the application of an electronic 
signal to the piezoelectrical material calling for such pressure change. 
It is not necessary that the ball 32 be a part of the valve means 30. A 
substantial number of different constructions can be used to cause the 
force exerted by the free end portion 17 of the BIMORPH plate 14 to 
control the pressure developed inside of pressure chamber or air flow 
chamber 25. For example, in FIG. 4, the second free end portion 17 of the 
plate 14 is seen to rest directly over the output end of the pressure 
relief and air flow orifice 29 provided in the third pressure relief and 
flow output portion 28 of the air flow conduit 24. Here the free end 
portion 17 will be forced into spaced relation with respect to the outer 
end of the air flow orifice 20 sufficiently so that an equilibrium is 
reached between the outer end of the plate 14 and the orifice 29, and the 
pressure in the air flow chamber will be a function of that spacing. 
Similarly, in FIG. 5, the outer end portion 17 of the plate 14 exerts 
pressure on the top outside surface of a diaphragm 68 held in a modified 
block 70 which can be fixedly mounted to the main frame or base 12 of the 
control unit 11. The less pressure exerted by the second free end portion 
17 of the plate, the more the diaphragm 68 will be lifted away from the 
air flow orifice 29 by the escape of air from chamber 25, and the lower 
will be the pressure inside of that chamber. As the pressure exerted by 
the ceramic plate 14 tending to seal the diaphragm against the orifice 29 
increases, the pressure inside of air flow chamber 25 will also increase. 
A BIMORPH brand of elongated piezoelectric ceramic plate material is 
illustrated herein because of the relatively large mechanical force which 
can be applied by it responsive to changes in magnitude of electronic 
signal applied to it. It is to be understood, however, that any valve 
means which is responsive to a change in position or size or shape due to 
piezoelectric effect can be utilized within the spirit of the invention 
and the scope of the claims which follow. For example, when signal lines 
such as output signal lines 66 and 67 are connected to piezoelectric 
crystals in such a manner that increase of the magnitude of the electric 
signal to those lines causes the piezoelectric crystal to grow or 
otherwise move in a first direction, valve means responsive to this 
movement can be placed in operable contact with these crystals. This valve 
means will exert more force tending to retard flow from the pressure 
chamber 25 and, when a signal of greater magnitude is applied, and will 
exert less force when a signal of lesser magnitude is applied. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.