A variable-speed dynamotor has a stator having a first set of windings that provide a number of poles for rotating a rotor and a second set of windings that provide a number of poles different from the number of poles provided by the first set of windings. Voltages or currents supplied to the second set of windings are controlled to generate radial forces acting on the rotor for thereby controlling a radial position of the rotor, suppressing vibrations of the rotor, adjusting rotational balancing of the rotor, and controlling radial damping of the rotor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a variable-speed dynamotor-for use as a 
motor-generator in an electrical power system, and more particularly to a 
variable-speed dynamotor including a stator which has a first set of 
windings that provide a number of poles for rotating a rotor and a second 
set of windings that provide a number of poles different from the number 
of poles provided by the first set of windings, for generating radial 
forces acting on the rotor to control the radial position of the rotor, 
suppress vibrations of the rotor, adjust rotational balancing of the 
rotor, or control the radial damping of the rotor. 
2. Description of the Related Art 
Variable-speed dynamotors or motor-generators for use in electric power 
systems have a rotor which can be rotated at a variable speed. The 
variable-speed dynamotor has already been put to use, and can increase the 
stability of the electrical power system in which it is incorporated, with 
the inertial energy of the rotor by varying the rotational speed of the 
rotor. The variable-speed dynamotor has been reported in various documents 
including (1) "395MVA variable-speed system for pumped power generation by 
Keiji Saito, IEEJ (Institute of Electrical Engineers of Japan) Transaction 
D. Vol. 113, No. 2, p. 267, 1993, and (2) "Variable-speed pumped 
generation system"by Shaku Fujimoto, Power Electronics Research Society 
Journal Vol. 16, pp. 16-26. 
FIG. 1 of the accompanying drawings shows a conventional variable-speed 
dynamotor of general configuration. The variable-speed dynamotor shown in 
FIG. 1 has a stator 11 and a rotor 12 which are of the same structure as 
those of a wound-rotor induction machine. Specifically, the stator 11 has 
three-phase windings connected to power system terminals 10, and the rotor 
12 has three-phase windings connected through slip rings to a 
semiconductor power converter 15. The semiconductor power converter 15 
supplies variable-frequency currents to the rotor 12 depending on the 
rotational speed of the rotor 12, the frequency of the bus terminals of 
the power system, and so on. The semiconductor power converter 15 is 
connected to the power system terminals 10 for exchanging electrical 
energy with the power system terminals 10. 
The rotational speed of the variable-speed dynamotor shown in FIG. 1 is 
variable in a very small range of about 10%. The variable-speed range 
cannot easily be expanded because of the limited mechanical strength of 
the rotor 12 and also the mechanical resonance of the rotor 12. 
The mechanical resonance of the rotor 12 may be removed by improving the 
mechanical design of the rotor 12. However, it is a simpler approach to 
actively vary the damping capability and stiffness of the rotor 12 with 
magnetic bearings. 
Magnetic bearings are disclosed in detail in a document (3) "Magnetic 
bearing and its related technology I. Controlled magnetic bearing and its 
applications" by Fumio Matsumura, IEEJ (Institute of Electrical Engineers 
of Japan) Transaction D. Vol. 114, pp. 1200-1207, 1994, for example. 
If magnetic bearings are incorporated in a variable-speed dynamotor, then 
the axial length of the rotor is increased, making the mechanical system 
of the variable-speed dynamotor complex, and lowering the critical speed 
of the variable-speed dynamotor. Therefore, the controllability of the 
variable-speed dynamotor is reduced by the use of the magnetic bearings. 
It is desirable to generate radial forces on the rotor supplementally or 
actively without modifying the mechanical system, e.g., the length of the 
rotor, of the variable-speed dynamotor. 
FIG. 2 of the accompanying drawings illustrates an ultra-high-speed rotary 
machine system which comprises an electromagnetic rotary machine with 
windings for controlling the radial position of rotors, which has been 
proposed by the inventors of the present application. The electromagnetic 
rotary machine shown in FIG. 2 is disclosed in various documents including 
(4) "Principles of radial force generation of bearingless motors with a 
cylindrical rotor operating under no loads" by Akira Chiba, Kouichi Ikeda, 
Fukuzo Nakamura, Tazumi Deido, Tadashi Fukao, and M. A. Rahman, Electric 
Society Journal D. Vol. 113, No. 4, pp. 539-547, 1993, and (5) Japanese 
laid-open patent publication No. 2-193547. As shown in FIG. 2, the 
electromagnetic rotary machine has two units 16 each connected to a 
three-phase inverter 17 for controlling currents supplied to the windings 
for controlling the radial position of rotors, and also to a three-phase 
inverter 18 for generating a motor torque. Each of the units 16 has 
four-pole windings for generating a motor torque and two-pole windings for 
generating radial forces on the rotor. Since each of the units 16 is 
capable of generating a motor torque and radial forces, the 
electromagnetic rotary machine has a shorter shaft than general 
ultra-high-speed motors with magnetic bearings, and can produce a higher 
output power if its shaft length is the same as those of the general 
ultra-high-speed motors with magnetic bearings. 
The electromagnetic rotary machine proposed by the inventors of the present 
application has the following features: 
(1) The electromagnetic rotary machine, if it has three-phase windings, 
requires only six wire cables and two three-phase inverters for generating 
radial forces along two orthogonal axes and a motor torque. 
(2) Because the windings for generating the radial forces and the windings 
for generating the motor torque are separate from each other, the inverter 
or power amplifier for controlling the radial forces may be of a 
relatively small power requirement. 
(3) Inasmuch as the electromagnetic rotary machine employs the four-pole 
windings and the two-pole windings, if the rotors are positioned centrally 
within the stators, there is no mutual coupling, and no induced voltage is 
developed in the windings for controlling radial forces. 
(4) The electromagnetic rotary machine can be used in a wide variety of 
high-output-power rotary machines which assume a sine-wave distribution of 
electromotive forces and a sine-wave distribution of magnetic fluxes, 
including an induction machine, a permanent-magnet synchronous machine, a 
synchronous reluctance motor, etc. 
FIG. 3 of the accompanying drawings illustrates the principles of 
generation of forces acting radially on a rotor in the electromagnetic 
rotary machine. As shown in FIG. 3, a stator has four-pole windings 
N.sub.4 for producing four-pole magnetic fluxes .PSI..sub.4 and two-pole 
windings N.sub.2 for producing two-pole magnetic fluxes .PSI..sub.2. The 
four-pole windings N.sub.4 of the stator serve to generate a motor torque 
on the rotor. If the rotor is positioned centrally in the stator, then 
when a current flows through the four-pole windings N.sub.4 in a positive 
direction, the four-pole windings N.sub.4 generate four-pole symmetric 
magnetic fluxes .PSI..sub.4. 
When a two-phase alternating current is supplied to the four-pole windings 
N.sub.4 and four-pole windings perpendicular thereto, a four-pole 
revolving magnetic field is generated. The stator may alternatively have 
three-phase windings. If the rotor has a squirrel-cage type winding, then 
it generates a torque due to the revolving magnetic field, with the 
assembly operating as an ordinary squirrel-cage type induction machine. If 
the rotor has four-pole permanent magnets, then it generates a torque due 
to the revolving magnetic field, with the assembly operating as an 
ordinary permanent-magnet motor. 
The two-pole windings N.sub.2 of the stator serve to produce forces acting 
radially on the rotor. When a current flows through the two-pole windings 
N.sub.2 in a positive direction, they generate two-pole magnetic fluxes 
.PSI..sub.2 as shown in FIG. 3. Across a gap below the rotor as shown in 
FIG. 3, the four-pole magnetic fluxes .PSI..sub.4 and the two-pole 
magnetic fluxes .PSI..sub.2 flow in opposite directions. Therefore, the 
flux density is relatively high across the gap below the rotor. Across a 
gap above the rotor as shown in FIG. 3, the four-pole magnetic fluxes 
.PSI..sub.4 and the two-pole magnetic fluxes 2 flow in the same direction. 
Consequently, the flux density is relatively high across the gap above the 
rotor. 
When the magnetic fluxes are brought out of equilibrium as shown, the rotor 
is subjected to radial forces F which are directly upwardly in FIG. 3. The 
magnitude of the radial forces F can be adjusted by controlling the 
magnitude of the current flowing through the two-pole windings N.sub.2. To 
reverse the direction of the radial forces F, the direction of the current 
flowing through the two-pole windings N.sub.2 may be reversed. 
In order to generate radial forces horizontally across the rotor in FIG. 3, 
two-pole windings may be provided on the stator which are directed 
perpendicularly to the two-pole windings N.sub.2, and a current flowing 
through the two-pole windings may be adjusted in magnitude and direction. 
By thus adjusting the magnitude and direction of the currents flowing 
through these two-pole windings, it is possible to generate radial forces 
of desired magnitudes and directions. 
In FIG. 3, the four-pole windings N.sub.4 are used to rotate the rotor and 
the two-pole windings N.sub.2 are used to control the radial position of 
the rotor. However, it is possible to use the four-pole windings N.sub.4 
to control the radial position of the rotor and the two-pole windings 
N.sub.2 to rotate the rotor. 
As far as the inventors know, there has been no report whatsoever on a 
system for applying such an electromagnetic rotary machine to a 
large-power-rating variable-speed dynamotor. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a 
variable-speed dynamotor which is free from various conventional problems 
including mechanical resonance and which can operate in a wide range of 
rotational speeds. 
According to the present invention, there is provided a variable-speed 
dynamotor comprising a rotor, a stator having a first set of windings that 
provide a number of poles for rotating the rotor and a second set of 
windings that provide a number of poles different from the number of poles 
provided by the first set of windings, and control means for controlling 
voltages or currents supplied to the second set of windings to generate 
radial forces acting on the rotor for thereby controlling a radial 
position of the rotor, suppressing vibrations of the rotor, adjusting 
rotational balancing of the rotor, and controlling radial damping of the 
rotor. 
The first set of windings may comprise two-pole windings, and the second 
set of winding may comprise four-pole windings. Alternatively, the first 
set of windings may comprise four-pole windings, and the second set of 
windings may comprise two-pole windings. 
The variable-speed dynamotor may further comprise a sensor for detecting 
the radial position of the rotor, the control means comprising a 
controller responsive to an output signal from the sensor for generating a 
current command to produce the radial forces, and means responsive to the 
current command from the controller for supplying currents corresponding 
to the current command to the second set of windings. 
Alternatively, the variable-speed dynamotor may further comprise a rotor 
position detector for detecting voltages and currents of the second set of 
windings and estimating the radial position of the rotor from the detected 
voltages and currents, the control means comprising a controller 
responsive to an output signal from the rotor position detector for 
generating a current command to produce the radial forces, and means 
responsive to the current command from the controller for supplying 
currents corresponding to the current command to the second set of 
windings. 
The current command can be substituted by voltage command. In this case, 
the current supply can be replaced by voltage supply. It is also possible 
that voltage and current are combined together with a certain 
relationship. Physically, variable impedance circuits with passive or 
active components can be connected at the terminals of second set of 
windings. 
The variable-speed dynamotor according to the present invention does not 
require the machine to be structurally modified, but only needs an 
additional set of windings, which provides a different number of poles 
from the number of poles provided by the existing set of windings for 
rotating the rotor, for producing radial forces acting on the rotor. The 
radial forces are controlled to control the radial position of the rotor, 
suppress vibrations of the rotor, adjust rotational balancing of the 
rotor, or control the radial damping of the rotor. The rotor is free from 
resonance, and the variable-speed dynamotor is allowed to operate stably 
in a wide range of rotational speeds from ultra-high speed to low speed, 
which is much wider than the speed range of conventional variable-speed 
dynamotors. 
Since the rotor of the variable-speed dynamotor is of a winding structure 
which is the same as that of a wound-rotor induction machine, any 
rotational loss of the variable-speed dynamotor is not increased by 
currents flowing through the additional second set of windings. 
Furthermore, inasmuch as the transfer function with respect to the radial 
forces and the currents flowing through the additional second set of 
windings does not suffer any phase delay, any power loss of the 
variable-speed dynamotor is reduced, and the variable-speed dynamotor has 
improved characteristics. 
The above and other objects, features, and advantages of the present 
invention will become apparent from the following description when taken 
in conjunction with the accompanying drawings which illustrate preferred 
embodiments of the present invention by way of example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 4, a variable-speed dynamotor for use in a power station 
according to an embodiment of the present invention includes a stator 11 
having a set of main windings 13 for supplying generated electric energy 
or being supplied with electric energy for energizing a motor, the main 
windings 13 being connected to power system terminals 10 The main windings 
13 will hereinafter referred to as "generator windings". The 
variable-speed dynamotor also includes a rotor 12 whose windings are 
connected to a semiconductor power converter 15a which is connected to the 
power system terminals 10. 
The stator 11 also has another set of control windings 20 for controlling 
the radial position of the rotor 12. The control windings 20 provide a 
number of poles different from the number of poles provided by the 
generator windings 13. When currents are supplied to the control windings 
20, the stator 11 generates radial forces acting on the rotor 12 to 
control the radial position of the rotor 12 within the stator 11, adjust 
the transfer function of a system for damping the rotor 12, and correct 
the rotor 12 out of an unbalanced condition. 
If the generator windings 13 provide four poles, then the control windings 
20 provide two poles. Conversely, if the generating windings 13 provide 
two poles, then the control windings 20 provide four poles. The 
combination of the poles provided by the generator windings 13 and the 
poles provided by the control windings 20 allows the generator windings 13 
to generate three-phase alternating-current electric energy, and also 
allows the stator 11 to generate radial forces which provide magnetic 
bearings for supporting the rotor 12 out of contact with the stator 11. 
The control windings 20 may comprise three-phase windings or two-phase 
windings. 
To permit a variable-speed dynamotor to have a wide variable-speed range, 
it has heretofore been practiced to connect the dynamotor to power system 
terminals 10 through an inverter for converting the frequency of electric 
energy supplied from the power system terminals 10. With such a 
conventional arrangement, if the variable-speed dynamotor has a very large 
power rating, then the semiconductor power converter used also of has a 
very large power rating. According to the embodiment shown in FIG. 4, the 
generator windings 13 are connected directly to the power system terminals 
10, not through any semiconductor power converter. 
The variable-speed dynamotor shown in FIG. 4 has another semiconductor 
power converter 15b for supplying currents to the control windings 20, and 
a controller 21 for issuing a current command to control the currents 
supplied to the control windings 20 depending on the frequency of the 
power system terminals 10, the rotational speed of the rotor 12, or the 
currents flowing through the windings of the rotor 12. 
The controller 21 detects a radial displacement of the rotor 12 with a 
radial displacement sensor, and applies a current command depending on the 
detected radial displacement to the semiconductor power converter 15b to 
supply currents to the control windings 20 for generating radial forces to 
radially displace the rotor 12 to a radial position corresponding to the 
current command. In this manner, the radial position of the rotor 12 is 
controlled. 
The damping capability of the rotor 12 can be adjusted to prevent 
mechanical resonance thereof by adjusting the frequency characteristics of 
the controller 21 as with conventional magnetic bearings. 
If only the rotor 12 is to be corrected out of an unbalanced condition 
which has occurred when the rotor 12 has been manufactured, then the 
controller 21 estimates the magnitude and direction of the unbalanced 
condition from the output signal from the radial displacement sensor, 
generates a current command to produce radial forces to cancel out the 
unbalanced condition, and applies the current command in a feed-forward 
control configuration for eliminating periodic fluctuations of the rotor 
12 without varying the damping capability of the rotor 12. 
FIG. 5 shows an arrangement capable of adjusting the balance of the rotor 
12 with a disturbance (unbalanced condition) observer 22 for estimating an 
unbalanced condition of the rotor 12. The disturbance observer 22 analyzes 
the displacement of the rotor 12 detected by the radial displacement 
sensor and information indicative of an angular frequency .omega. of the 
rotor 12 or the like, and detects an unbalanced condition of the angular 
frequency .omega.. Based on the detected unbalanced condition, the 
controller 21 controls currents flowing through the control windings 20 to 
generate radial forces to compensate for the unbalanced condition of the 
rotor 12. The rotor 12 is now adjusted out of the unbalanced condition, 
and can rotate about its own axis without any eccentric motion. 
FIG. 6 shows an arrangement capable of radially damping the rotor 12. The 
controller 21 has a sensor amplifier which amplifies a radial position 
signal detected by the radial displacement sensor, and a compensating 
circuit which effects phase compensation on the amplified signal from the 
sensor amplifier. Based on the compensated signal, the controller 21 
adjusts currents supplied to the control windings 20 to apply radial 
forces on the rotor 12 to keep the rotor 12 in a desired target position. 
The arrangement shown in FIG. 6 has a control loop comprising a notch 
filter 23, a gain adjuster 24, and a phase advancer 25, the control loop 
being connected to the controller 21. The control loop is effective to 
damp the rotor 12 against resonance thereof. In order for the 
variable-speed dynamotor to operate over a wide speed range, it is 
important to effect damping control on the rotor 12 because of the natural 
frequency of the rotor 12 or the entire mechanical system including the 
stator 11 and the rotor 12. 
In the arrangement shown in FIG. 6, the notch filter 23 has a central 
frequency fc set to the natural frequency of an object to be damped, e.g., 
the rotor 12. The notch filter 23 extracts a signal component of the 
frequency fc, and the gain adjuster 24 amplifies the signal component to 
adjust its gain. Then, the phase advancer 25 advances the phase of the 
amplified signal component. The advanced-phase signal component from the 
phase advancer 25 is added to the output signal from the radial 
displacement sensor by the controller 21. With the arrangement shown in 
FIG. 6, the controller 21 keeps the rotor 12 in the target position in the 
normal variable-speed range of the variable-speed dynamotor, and the 
control loop connected to the controller 21 enables the controller 21 to 
apply damping forces to attenuate undesirable vibrations of the rotor 12 
when it resonates at the frequency fc. 
FIG. 7 shows an arrangement capable of estimating a radial displacement of 
the rotor 12 by detecting currents flowing through the control windings 
20. A radial displacement of the rotor 12, i.e., a gap between the stator 
11 and the rotor 12, can be detected when a change in the inductance of 
the stator 11 is detected. Specifically, the shaft of the rotor 12 or the 
circumferential portion of the rotor 12 is generally made of a magnetic 
material. When the gap between the stator 11 and the rotor 12 varies, the 
inductance of the stator 11 as seen from the control windings 20 also 
varies as shown in FIG. 8. The mutual couplings between the motor windings 
and control windings are almost proportional to the rotor displacements. 
If the displacements in radial coordinates are represented by x and y, the 
mutual couplings can be transformed from three phase system to two phase 
coordinates by conventional three phase to two phase transform matrix. 
Then, the mutual couplings can be expressed by 2-by-2 matrix with linear 
expression of x and y. The inverse matrix can be used to calculate 
displacements x and y from the inductance values. The arrangement shown in 
FIG. 7 has a voltage/current detector 28 for detecting voltages and 
currents of the control windings 20, and a displacement estimator 29 for 
estimating a radial position of the rotor 12 based on an output signal 
from the voltage/current detector 28. Based on the estimated radial 
position, the controller 21 generates a current command for producing 
radial forces on the rotor 12. With the arrangement shown in FIG. 7, it is 
necessary to measure beforehand the relationship between the gap between 
the stator 11 and the rotor 12, i.e., the radial displacement of the rotor 
12, and the inductance of the stator 11 as seen from the control windings 
20, and store data representative of the measured relationship in the 
displacement estimator 29. 
FIG. 9 shows a variable-speed pumped dynamotor for use in a hydroelectric 
power station according to another embodiment of the present invention. As 
shown in FIG. 9, the variable-speed pumped dynamotor has a rotatable shaft 
35 supporting an impeller 31 on a lower portion thereof and a rotor 32 on 
an upper portion thereof. When the variable-speed pumped dynamotor 
operates as a generator, the impeller 31 is rotated by a water flow to 
rotate the rotor 32. When the variable-speed pumped dynamotor operates to 
pump water, the impeller 31 functions as a pump impeller to pump water. 
The rotor 32 has windings 14 connected through slip rings to a 
semiconductor power converter 26 which is connected to power system 
terminals 10. The variable-speed pumped dynamotor also includes a stator 
33 having two-pole main windings 13 connected to the power system 
terminals and four-pole control windings 20 connected to a controller 21. 
If the main windings 13 provide four poles, then the control windings 20 
provide two poles. 
When the variable-speed pumped dynamotor is to operate as a motor, the 
semiconductor power converter 26, which serves to control the output power 
and speed of the motor, generates electrical energy under a desired 
voltage at a desired frequency, and supplies the desired voltage and 
current through the slip rings to the windings 14 of the rotor 32 for 
rotating the rotor 32 at a desired speed. 
When the variable-speed pumped dynamotor is to operate as a generator, the 
semiconductor power converter 26 similarly generates electric energy under 
a desired voltage at a desired frequency, and supplies the desired voltage 
and current through the slip rings to the windings 14 of the rotor 32 for 
generating and supplying electric energy under a desired voltage at a 
desired frequency to the power system terminals 10 regardless of the 
rotational speed of the shaft 35. 
A lower end of the shaft 35 is supported by mechanical radial and thrust 
bearings, and an upper end of the shaft 35 is supported out of contact 
with other components by a radial magnetic bearing under radial 
electromagnetic forces acting between the stator 33 and the rotor 32. The 
radial electromagnetic forces are generated by currents flowing through 
the main windings 13 and the control windings 20 which provide different 
numbers of poles. The radial magnetic bearing provided by the radial 
electromagnetic forces thus generated perform various functions referred 
to above in the preceding embodiment under the control of the controller 
21. Since the upper end of the shaft 35 is supported out of contact with 
other components by the radial magnetic bearing and can be controlled for 
controlling the radial position, damping capability, balance, etc. of the 
rotor 32, the variable-speed dynamotor can operate stably as a motor or 
generator without an appreciable loss in a wide range of rotational 
speeds. 
FIG. 10 shows a horizontal dynamotor for use in a thermal, nuclear, or 
cogeneration power station according to still another embodiment of the 
present invention. As shown in FIG. 10, the variable-speed pumped 
dynamotor has a rotatable shaft 41 supporting a turbine 46 at its center 
and a rotor 47 mounted on a left-hand end of the shaft 41 and supported by 
a magnetic bearing provided by a stator 40 disposed around the rotor 47. 
The shaft 41 has a right-hand end which may be supported by a magnetic 
bearing or a mechanical bearing. 
The stator 40 has main windings 13 for supplying generated electrical 
energy or being supplied with electric energy for energizing a motor, the 
main windings 13 being connected to power system terminals 10. The rotor 
47 has windings 14 connected through slip rings to a semiconductor power 
converter 26 which is connected to the power system terminals 10. 
The stator 11 also has control windings 20 for controlling the radial 
position of the rotor 47 under the control of a controller 21. The control 
windings 20 provide a number of poles different from the number of poles 
provided by the main windings 13. If the main windings 13 provide four 
poles, then the control windings 20 provide two poles. Conversely, if the 
main windings 13 provide two poles, then the control windings 20 provide 
four poles. 
When currents are supplied from the controller 21 to the control windings 
20, they produce radial forces acting on the rotor 47 in the same manner 
as with the previous embodiments for controlling the radial position of 
the rotor 47, adjusting the transfer function of a system for damping the 
rotor 47, and correcting the rotor 47 out of an unbalanced condition. 
The controller 21 detects a radial displacement of the rotor 47 with a 
radial displacement sensor, and applies a current command to supply 
currents to the control windings 20 for generating radial forces to 
radially displace the rotor 47 to a radial position corresponding to the 
current command. In this manner, the rotor 47 is controlled by the 
magnetic bearing for its radial position, rotational balancing adjustment, 
and radial damping. 
When the variable-speed dynamotor shown in FIG. 10 operates as a generator, 
the turbine 46 rotates the shaft 41 at high speed, and the semiconductor 
power converter 26 converts electrical energy from the power system 
terminals 10 into electrical energy at a suitable voltage and frequency, 
and supplies the converted electrical power through the slip rings to the 
windings 14 of the rotor 47. When the rotor 47 is thus energized, it 
generates electrical energy across the main windings 13 of the stator 40 
at a frequency in synchronism with the power system terminals 10, and the 
generated electrical energy is supplied to the power system terminals 10. 
The variable-speed dynamotor operating as a generator can supply 
electrical energy under a desired voltage at a desired frequency in a wide 
range of rotational speeds. Since the rotor 47 is supported by the 
magnetic bearing, the variable-speed dynamotor can operate stably without 
any substantial loss in a wide range of rotational speeds. 
The variable-speed dynamotor shown in FIG. 10 can also operate as a motor. 
Although certain preferred embodiments of the present invention have been 
shown and described in detail, it should be understood that various 
changes and modifications may be made therein without departing from the 
scope of the appended claims.