Self-regulated pressure control valve

A self-regulating pressure control valve, such as, for example, a self-regulated pressure reducing valve, including as the principal components, a pressure control valve, a pressure regulating unit, a driving unit for driving the pressure regulating unit, a control unit for controlling the operation of the driving unit, and a pressure setting unit for establishing a set pressure. The pressure regulating position of the pressure regulating element of the pressure regulating unit is regulated on the basis of the predetermined functional relationship between the pressure regulating position of the pressure regulating element and the controlled pressure so that the pressure regulating element is positioned properly to regulate the controlled pressure to the set pressure. The self-regulated pressure control valve is capable of controlling the controlled pressure at a high response speed.

The present invention relates to a self-regulated pressure control valve 
capable of controlling a secondary pressure, namely, the pressure of an 
associated controlled system, at a predetermined set level through 
self-regulation of the pressure setting condition thereof on the basis of 
a control signal corresponding to the current pressure of the controlled 
system detected by pressure detecting means. 
The present invention also relates to a valve for regulating the pressure o 
a fluid. More particularly, it relates to a pressure reducing valve for 
reducing the pressure of a fluid on the primary side thereof to maintain a 
constant fluid pressure on the secondary side thereof. 
Pressure reducing valves are generally of the type in which a main valve is 
directly controlled by the displacement of a diaphragm, or in which a main 
valve, such as a piston valve, is indirectly controlled by a pilot valve. 
The secondary pressure of a fluid acts on one side of the diaphragm and 
the resilient force of a pressure setting spring acts on the other side 
thereof. If there is any imbalance between the two forces, the diaphragm 
is displaced to cause a valve member to control the amount of a fluid 
flowing through the valve to maintain a secondary fluid pressure 
corresponding to the resilient force of the spring. 
An adjusting screw which is threadedly connected to a valve casing is used 
for setting a desired secondary fluid pressure. The screw is manually 
turned to adjust the resilient force of the pressure setting spring until 
a pressure gauge indicates the desired pressure. This arrangement is very 
inconvenient when the set pressure is frequently changed. It does not 
permit remote operation or automatic control. 
Thus, there is known in the prior art an automatic control valve operating 
in accordance with a working principle whereby the value to be controlled 
is detected and compared with a target value and the judgment or 
instruction based on any difference therebetween is processed into a 
signal for controlling a valve member actuator, such as an electric motor 
or fluid actuator. 
In case it is a pressure reducing valve, the secondary pressure is detected 
by a pressure sensor and compared with the target value which is applied 
through a setting mechanism and the result of the comparison is processed 
into a signal for bringing an actuator, such as an electric motor, into 
proportional or differential/integral control action. This valve, 
therefore, facilitates any change in target value and permits remote 
operation or automatic control. 
The automatic control valve is, however, expensive. This is due to the fact 
that an actuator having a high output and a controller for the complicated 
processing of signals are required for actuating the valve member 
directly, minutely and quickly. 
It is slower in response than a pressure reducing valve including a 
diaphragm. This is due to the fact that the actuator is not directly 
connected to the signal processor. 
SUMMARY OF THE INVENTION 
The applicant of the present invention has proposed an automatic pressure 
reducing diaphragm valve in the parent application, Ser. No. 770,845, 
identified above (Japanese Patent Application No. 59-207779). This 
automatic pressure reducing diaphragm valve comprises a pressure reducing 
diaphragm valve unit, a pressure setting unit including a pressure setting 
spring, an actuator for operating the pressure setting unit and a control 
unit which provides a control signal to actuate the actuator when the 
pressure deviation of a detected secondary pressure, namely, the 
controlled pressure, from a target pressure exceeds a predetermined 
reference deviation so that the pressure deviation is reduced to zero. 
This automatic pressure reducing diaphragm valve is capable of stable 
pressure reducing operation to stabilize the through mechanical action 
while the pressure deviation of the secondary pressure is below the 
reference pressure deviation. 
Accordingly, it is an object of the present invention to provide a pressure 
reducing valve which includes an actuator having a small output and, yet, 
which facilitates any change in pressure setting and permits remote 
operation and automatic control. 
Since the automatic pressure reducing diaphragm valve regulates the 
secondary pressure on the basis of the result of comparison between the 
detected pressure deviation and the reference pressure deviation, it does 
take a long time to stabilize the secondary pressure at the predetermined 
set pressure, however. 
Accordingly, it is another object of the present invention to provide a 
self-regulated pressure control valve capable of rapidly adjusting the 
secondary pressure to a predetermined set value. 
The present invention also utilizes the functional relation between the 
position of pressure regulating means and the secondary pressure of a 
self-regulated pressure reducing valve including the pressure regulating 
means and driving means for driving the pressure regulating means. 
To achieve the object of the invention, the invention provides a 
self-regulated pressure control valve comprising: a pressure control valve 
unit, a detecting unit for detecting the secondary pressure, a pressure 
regulating unit for regulating the secondary pressure of the pressure 
control valve unit, a driving unit for operating the pressure regulating 
unit, a control unit for controlling the driving unit, and a pressure 
setting unit for establishing a set pressure. 
The control unit controls the driving unit on the basis of the functional 
relation between the position of the pressure regulating unit and the 
secondary pressure corresponding to the controlled pressure to adjust the 
secondary pressure to a desired pressure, namely, to the set pressure. 
In one mode for carrying out the present invention, the control unit 
comprises a computer including arithmetic means, correcting means and 
memory means. 
According to the present invention, when an optional set pressure is 
established by means of the pressure setting unit, the operating means of 
the control unit calculates an appropriate position of the pressure 
regulating member of the pressure regulating unit on the basis of the 
functional relationship between the secondary pressure and the position of 
the pressure regulating member and then the control unit provides a 
control signal to the driving unit to adjust the position of the pressure 
regulating member to a calculated appropriate position so that the 
secondary pressure is regulated to the set pressure. 
After the secondary pressure has been thus regulated to the set pressure, 
the self-regulated valve unit starts mechanical pressure control operation 
in the conventional manner. 
When further fine control of the secondary pressure is necessary, it is 
desirable to provide a secondary pressure detecting means to detect the 
secondary pressure continuously or periodically and to control the driving 
unit by a correction signal calculated by the operating means of the 
control unit on the basis of the difference between the set pressure and 
the detected secondary pressure to control the second pressure 
continuously or periodically. 
Thus, the self-regulated pressure control valve is capable of rapid 
response to the variation of the secondary pressure and of instantly 
regulating the secondary pressure, namely, the controlled pressure, to a 
set pressure, namely, a target pressure. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the drawings and descriptive matter in which there is 
illustrated and described a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The first embodiment of the present invention depicted in FIG. 1 depicts 
the application of the invention to a pressure reducing valve 1. Referring 
to FIG. 1, the pressure reducing valve 1 has a pressure setting spring 2 
having one end seated on a spring seat 3 and the other end seated on a 
spring seat 6. The spring seats 3 and 6 are pressed against the diaphragm 
4 and against the lower end, as viewed in FIG. 1, of a pressure regulating 
screw rod 8 through a ball 7, respectively. The secondary pressure of the 
pressure reducing valve 1 prevails in a pressure chamber 5 covered with 
the diaphragm 4. The position of the diaphragm 4 is dependent on the 
pressure balance between the pressure applied thereto by the pressure 
setting spring 2 and the secondary pressure prevailing within the pressure 
chamber 5. Since the secondary pressure control function of the diaphragm 
4 is well known, the description thereof will be omitted. 
An external thread 9 is formed in the lower portion of the pressure 
regulating screw rod 8. A threaded lower end of the pressure regulating 
rod 8 is screwed in a fixed member provided with an internal thread 10 in 
the central portion thereof. An axial bore is formed in the upper portion, 
as viewed in FIG. 1, of the pressure regulating screw rod 8. A retainer 11 
retaining balls 12 is inserted in the axial bore of the pressure 
regulating screw rod 8. A spline shaft 13 is fitted in the axial bore of 
the pressure regulating screw rod 8 so as to engage with the balls 12. The 
spline shaft 13 is connected through a reduction gear 14 to the output 
shaft of a motor 15. 
Since the pressure regulating screw rod is engaged with the internal thread 
10 of the fixed member, the pressure regulating screw rod 8 is rotated 
through the spline shaft 13 so as to shift downward when the output shaft 
of the motor 15 rotates in one direction and, thereby, the pressure 
setting spring 2 is compressed through the spring seat 6 by the pressure 
regulating screw rod 8 to increase the set pressure. On the other hand, 
when the output shaft of the motor 15 rotates in the opposite direction so 
as to shift upwardly and, thereby, compression of the pressure setting 
spring 2 is reduced to reduce the set pressure. 
The distance of shift of the lower end of the pressure regulating screw rod 
8 from a predetermined reference position (a position where the lower end 
of the pressure regulating screw rod 8 is in contact with the spring seat 
6 through the ball 7 without compressing the pressure regulating spring), 
which will be referred to as the "screw rod position", is proportional to 
the magnitude of compression of the pressure setting spring 2 and, hence, 
to the set pressure as shown in FIG. 2. The present invention effectively 
utilizes such a relationship between the distance of shift of the lower 
end of the pressure regulating screw rod 8 and the set pressure. 
Referring to FIG. 3 showing the first embodiment of the present invention, 
the self-regulated pressure control valve comprises a pressure reducing 
valve 1, a pressure regulating unit 50 including the pressure regulating 
screw rod 8, a driving unit 52 including the motor 15, a pressure 
detecting unit 54, a signal conversion unit 55, a control unit 56 
including a computer storing screw rod position data representing the 
functional relationship between the screw rod position and the controlled 
pressure, and a pressure setting unit 58. In the first embodiment, the 
motor 15 is a stepping motor. 
The pressure sensor of the pressure detecting unit 54 detects the secondary 
pressure of the pressure reducing valve 1 and gives a pressure signal 
representing the secondary pressure to the signal conversion unit 55. 
Then, the signal conversion unit 55 converts the pressure signal into a 
corresponding digital pressure signal and then gives the same to the 
computer of the control unit 56. 
Upon the reception of a set pressure signal representing a set pressure 
from the pressure setting unit 58, the computer calculates a screw rod 
position corresponding to the set pressure for the pressure regulating 
screw rod 8 on the basis of the screw rod position data previously stored 
therein, and then gives a pulse signal corresponding to the calculated 
screw rod position to the driving unit 52 to drive the pressure regulating 
unit 50 so that the pressure regulating screw rod 8 is shifted to the 
calculated screw rod position. Consequently, the secondary pressure of the 
pressure reducing valve 1 is adjusted instantly to the set pressure. The 
angle of rotation of the output shaft of the stepping motor 15 is 
proportional to the number of pulses of the pulse signal and, hence, the 
position of the pressure regulating screw rod 8 corresponds to the number 
of pulses of the pulse signal. 
The pressure detecting unit 54 detects the secondary pressure continuously 
or periodically and the signal conversion unit 55 gives digital signals 
accordingly to the control unit 56. The computer of the control unit 56 
compares the detected secondary pressure with the set pressure. When the 
deviation in the detected secondary pressure from the set pressure is 
within a predetermined range of deviation, the control unit does not 
provide any signal to actuate the driving unit 52. When the deviation in 
the detected secondary pressure from the set pressure is greater than the 
limit value of the predetermined range of deviation, the computer 
calculates a distance correction by which the pressure regulating screw 
rod 8 needs to be shifted to correct the deviation on the basis of the 
difference between the detected secondary pressure and the set pressure 
and the screw rod position data stored therein, and then provides a 
control signal representing the calculated distance correction for 
secondary pressure correction to actuate the driving unit for shifting the 
pressure regulating screw rod 8 for fine adjustment of the secondary 
pressure. 
For example, when the set pressure is 5 kg/cm.sup.2, the reference range of 
deviation is .+-.0.1 kg/cm.sup.2 and the detected secondary pressure is 
4.5 kg/cm.sup.2. The computer calculates a distance correction 
corresponding to the pressure deviation of 0.5 kg/cm.sup.2 on the basis of 
the screw rod position data to shift the pressure regulating screw rod 8 
accordingly. 
For further advanced pressure control, digital data representing the 
functional relation between the set pressure and the screw rod position, 
for example, a predetermined correlation between the set pressure and the 
screw rod position represented by set pressures of 1 kg/cm.sup.2 intervals 
and the corresponding screw rod positions is stored in the table of the 
memory means of the computer and the control operation and correcting 
operation are executed on the basis of the digital data according to the 
predetermined correlation. When a correction is made, the digital data 
representing the previous screw rod position is replaced with the 
corrected data representing the new screw rod position to update the table 
of the memory means. 
For example, suppose that screw rod positions S4 and S5 stored in the 
memory means of the computer correspond to set pressures, more 
specifically, to set secondary pressures, 4 and 5 kg/cm.sup.2, 
respectively, when the valve is set for the set pressure 5 kg/cm.sup.2 by 
means of the pressure setting means, the motor drives the pressure 
regulating screw rod to the corresponding screw rod position S5. When a 
reference deviation range is .+-.0.1 kg/cm.sup.2, the motor remains 
stopped while the deviation of the actual secondary pressure from the set 
pressure is within the reference deviation range. 
Suppose that the set pressure is 5 kg/cm.sup.2, the reference deviation 
range is .+-.0.1 kg/cm.sup.2 and the current secondary pressure is 4.5 
kg/cm.sup.2. The computer then calculates a screw deviation: 5.0-4.5=0.5 
kg/cm.sup.2 by using the following equation: 
EQU .DELTA.S=(S5-S4).times.0.5/(5-4). 
The motor then drives the pressure regulating screw rod by the calculated 
screw rod position correcting displacement .DELTA.S to increase the 
secondary pressure from 4.5 kg/cm.sup.2 to 5.0 kg/cm.sup.2. The initial 
screw rod position S5 stored in the memory means is then replaced with 
S5+.DELTA.S. 
When the same set pressure is given to the control unit to regulate the 
controlled pressure to the same target pressure after the pressure 
regulating screw rod 8 has been shifted from the previous screw rod 
position to change the set pressure, the computer calculates the true 
screw rod position to instantly regulate the secondary pressure to the 
target pressure. 
When the pressure control system of the self-regulated pressure control 
valve is thus constituted, the pressure control system generates an ideal 
control data even when the operating condition of the pressure reducing 
valve is varied so that the self-regulated pressure control valve is able 
to operate at a high response speed. 
A second embodiment of the invention is shown in FIG. 4 and incorporates 
the mechanism shown in FIG. 1. Basically, the second embodiment is the 
same as the first embodiment in constitution and function. The second 
embodiment employs a rotary potentiometer for detecting the position of 
the pressure regulating screw rod 8 and a reversible motor instead of the 
stepping motor for driving the pressure regulating screw rod 8. 
Referring to FIG. 4, the second embodiment comprises a pressure reducing 
valve 1, a pressure regulating unit 50, a driving unit 52, a pressure 
detector 54, a signal converter 55, a control unit 66, a pressure setting 
unit 58, a reduction gear 14, and a rotary potentiometer 20. 
Referring to FIG. 1, the rotary potentiometer 20 is operatively interlocked 
with one of the gears (not shown) of the reduction gear 14. The output 
voltage of the potentiometer 20 is proportional to the distance of shift 
of the pressure regulating screw rod 8 from the reference position (a 
position where the pressure regulating screw rod is in engagement with the 
pressure setting spring 2 without compressing the latter), namely, the 
screw rod position. Accordingly, the output voltage of the rotary 
potentiometer 20 represents the screw rod position, hence, the secondary 
pressure, namely, the controlled pressure. In the second embodiment, the 
screw rod position data representing the functional relationship between 
the screw rod position represented by the output voltage of the rotary 
potentiometer 20 and the secondary pressure is stored in the computer. 
The rotary potentiometer 20 may be substituted by a linear potentiometer or 
a differential transformer. When a linear potentiometer is employed, the 
arm of the linear potentiometer is arranged so as to move linearly 
together with the pressure regulating screw rod 8. When a differential 
transformer is employed, the core of the differential transformer is 
arranged so as to move linearly together with the pressure regulating 
screw rod 8. 
The control unit 56 gives a signal continuously to the driving unit 52 
until the output signal of the rotary potentiometer 20, namely, the screw 
rod position signal, coincides with a signal given to the control unit 56 
by means of the pressure setting unit 58. Since the rest of the functions 
are the same as those of the first embodiment, the description thereof 
will be omitted to avoid duplication. 
A third embodiment of the invention is shown in FIG. 5. Referring to FIG. 
5, the third embodiment comprises a pressure reducing valve 1, a reduction 
gear 14, a rotary potentiometer 20, a pressure regulating unit 50, a 
driving unit 52, a control unit 70 and a pressure setting unit 72 
including a potentiometer. 
The control unit 72 does not include any computer. The third embodiment is 
capable of most simply controlling the secondary pressure on the basis of 
the relationship between the screw rod position and the secondary 
pressure, namely, the controlled pressure. The rotary potentiometer 20 
operatively connected to the reduction gear 14 gives a voltage signal 
representing a screw rod position corresponding to the secondary pressure 
to the control unit 70, while the potentiometer of the pressure setting 
unit 72 gives a voltage signal representing a set pressure to the control 
unit 72. The control unit 72 compares the voltage signal representing the 
screw rod position and the voltage signal representing the set pressure, 
and then gives a control signal to the driving unit 52 to shift the 
pressure regulating screw rod until the voltage signal provided by the 
rotary potentiometer 20 coincides with the voltage signal representing the 
set pressure. 
The rotary potentiometer 20 may be substituted for by a linear 
potentiometer or a differential transformer as mentioned in the 
description of the second embodiment. 
Referring now to FIG. 6, the automatically set pressure reducing valve of 
this embodiment is shown as comprising a mechanical pressure reducing 
valve portion 101, an electric motor portion and a control portion. 
The valve portion 101 is similar in construction to a known pressure 
reducing valve. It has a fluid inlet 102 and a fluid outlet 103 which are 
connected to a primary passage 104 and a secondary passage 105, 
respectively. It has a main valve port 107 which can be opened or closed 
by a main valve member 106. The valve member 106 is urged by a spring into 
its port closing position and connected by a valve rod to a piston 108. 
The pressure of the fluid flowing through the main valve port 107 to the 
fluid outlet 103 acts on the lower surface of the piston 108, while the 
pressure of the fluid acting on the upper surface of the piston 108 
through passages 109 and 111 is controlled by a pilot valve member 112. 
The pilot valve member 112 is urged by a spring into its closing position 
and is connected to a valve rod contacting the lower surface of a 
diaphragm 113 so that its downward displacement may force the pilot valve 
member 112 into its open position. 
If the diaphragm 113 is displaced downwardly, the pilot valve member 112 is 
forced down to allow the fluid to flow from the fluid inlet 102 into the 
area above the piston 108 through the passages 109 and 111 and lower the 
piston 108 and thereby the main valve member 106, whereby the main valve 
port 107 is opened to allow the fluid to flow from the fluid inlet 102 to 
the fluid outlet 103. If the diaphragm 113 is displaced upwardly, the 
pilot valve member 112 is forced up by the spring to break the fluid 
communication between the passages 109 and 111 and the fluid in the area 
above the piston 108 flows to the fluid outlet 103 through the passage 
111, a clearance surrounding the valve rod for the pilot valve member 122 
and a passage 110, whereby the main valve member 106 and the piston 108 
are forced up to close the main valve port 107. 
The area above the diaphragm 113 is connected with the open atmosphere by a 
passage 114 of small diameter and kept at a substantially uniform 
atmospheric pressure. A pressure setting spring 116 has a lower end 
contacting the upper surface of the diaphragm 113 and exerts a resilient 
force thereon. The upper end of the spring 116 is carried on a spring 
support and an adjust screw 117 has a lower end contacting the spring 
support so that the rotation of the adjust screw 117 in either direction 
may adjust the compression of the spring 116 and thereby its resilient 
force acting on the diaphragm 113. The adjust screw 117 is threadedly 
engaged with an internally threaded member fitted in a spring housing 115 
forming a part of a valve housing. 
The motor portion is connected to the valve portion 101 by a yoke 118 
secured to the spring housing 115. An output shaft 120 is coaxial with the 
adjust screw 117 and has a lower end connected to the hexagonal head 142 
of the screw 117 by a connecting member 119. 
The output shaft 120 defines a shaft for a ball spline 121. A gear 122 is 
secured to the outer periphery of the spline 121 and held between upper 
and lower bearing members 123 and 124 against vertical and radial 
displacement. The bearing members 123 and 124 are held between a mounting 
plate 125 and a bottom plate 126. An electric motor 129 and a speed 
reducer 128 are secured on the mounting plate 125 and its output shaft 127 
is threadedly engaged with the gear 122. 
If the motor 129 is driven, the output shaft 127 of the speed reducer 128 
is rotated to rotate the outer periphery of the spline 121 via the gear 
122. Depending on the direction of its rotation, the output shaft 120 is 
rotated for upward or downward movement, causing the rotation of the 
adjust screw 117 in either direction via the connecting member 119. 
The output shaft 120 is provided with a disk 135 which enables the 
detection of the adjust screw 117 when it is brought to its uppermost or 
lowermost position. A pair of position sensors 133 and 134 are located on 
one side of the disk 135 for detecting it in the uppermost and lowermost 
positions, respectively, of the screw 117. The sensors 133 and 134 are 
secured on the sidewalls of the motor 129 and the speed reducer 128, 
respectively. 
The sensors 133 and 134 are preferably photosensors of the reflective type, 
though it is, of course, possible to use any other type of sensor, such as 
potentiometers, limit switches or magnetic sensors. 
A driver 130 is located beside the motor 129. The motor portion is enclosed 
in a cover 136 which protects it against dust and moisture. The motor 
portion further includes the necessary wiring and terminals (not shown). 
The control portion comprises the position sensors 133 and 134, a 
comparative controller 131, a target pressure setter 132 and a pressure 
sensor 140 disposed in the secondary fluid passage. Signal lines 137 and 
138 extend from the position sensors 133 and 134, respectively, to the 
comparative controller 131. A signal line 139 extends from the pressure 
sensor 140 to the comparative controller 131. A signal line also extends 
from the comparative controller 131 to the driver 130. The comparative 
controller 131 may alternatively be located at the driver 130. 
A target pressure is set by the setter 132 and inputted to the comparative 
controller 131. The pressure of the fluid in the secondary passage 105 is 
detected by the pressure sensor 140 and inputted to the comparative 
controller 131 continuously or at relatively short intervals. The 
comparative controller 131 calculates the difference between the pressure 
of the fluid in the secondary passage 105 as detected by the sensor 140 
and the target pressure and compares it with a standard difference. 
If the comparison indicates a deviation of the detected difference from the 
standard difference, the comparative controller 131 transmits a control 
signal to the driver 130 in order to bring the detected difference t 
virtually zero, i.e., bring the pressure of the fluid in the secondary 
passage 105 to substantially the target pressure. The motor 129 is driven 
by the driver 130 to adjust the flow o the fluid through the valve. The 
comparative controller 131 transmits a control signal to the driver 130 to 
stop the operation of the motor 129 if the detected difference has become 
virtually zero, i.e., fallen within a range of fine standard differences 
which are sufficiently smaller than the standard difference hereinabove 
stated. 
The position sensors 133 and 134 cooperate with the disk 135 to detect the 
adjust screw 117 in its uppermost and lowermost positions, respectively, 
and transmit the corresponding signals to the comparative controller 131. 
The comparative controller 131 responds to both of those signals more 
quickly than to any other control signal and transmits a signal to the 
driver 130 to stop the operation of the motor 129. This makes it possible 
to prevent the application of any undue force to the system for 
controlling the adjust screw 117. 
As will be noted from the description set forth above, the invention 
produces a number of special advantages. The actuator functions only when 
the detected difference has deviated from the standard difference, and 
ceases to function when the detected difference has been brought to 
virtually zero. It follows that the actuator is not placed in operation 
often or for any long time continuously, and that the valve has by far a 
longer life than any automatic control valve. 
If the pressure reducing valve is of the type including a pilot valve, the 
pilot valve is actuated by a small force to operate a main valve which 
requires a large force for operation. As the pressure setting spring has a 
small resilient force, it is sufficient to employ an actuator having a 
small output. 
The actuator is easily applicable to any existing pressure reducing valve, 
insofar as it is provided for axially moving the adjust screw for the 
spring. 
If the difference between the secondary fluid pressure and the set pressure 
exceeds the standard difference, the actuator functions to alter the set 
pressure to enable a greater amount of fluid to flow. Therefore, the valve 
of this invention enables quicker control in the case of any variation in 
secondary fluid pressure than any pressure reducing valve relying solely 
on mechanical control. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.