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CROSS REFERENCE TO RELATED APPLICATIONS
The inventions taught herein are related to concurrently filed commonly
assigned copending applications as follows:
Application Ser. No. 016,425 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH ENERGY BALANCED CLOSING SYSTEM" by J. A.
Bauer.
Application Ser. No. 016,419 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH CONTROL CIRCUIT FOR PROVIDING
ACCELERATION, COAST AND GRAB FUNCTIONS" by J. A. Bauer.
Application Ser. No. 016,412 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH ALGORITHM CONTROLLED CLOSING SYSTEM" by J.
A. Bauer, D. A. Mueller, R. T. Basnett and J. C. Engel.
Application Ser. No. 016,426 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH DISCRIMINATOR FOR DETERMINING WHEN AN
INPUT CONTROL SIGNAL IS TRUE OR FALSE AND METHOD" by J. C. Engel.
Application Ser. No. 016,422 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH LIGHTWEIGHT WIDE RANGE CURRENT TRANSDUCER"
by J. A. Bauer.
Application Ser. No. 016,420 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH LIGHTWEIGHT WIDE RANGE CURRENT TRANSDUCER
WITH SINTERED POWDERED METAL CORE" by J. C. Engel.
Application Ser. No. 016,424 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH UNIVERSAL CONTROL" by J. C. Engel.
Applicaton Ser. No. 016,421 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH WIDE RANGE OVERLOAD CURRENT RELAY BOARD
UTILIZING LEFT SHIFTING AND METHOD" by G. F. Saletta et al.
Application Ser. No. 016,417 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH CIRCUIT BOARD SUPPORT SYSTEM" by D. W.
Cole and G. E. Pruitt II.
Application Ser. No. 016,415 filed concurrently herewith entitled
"ELECTROMAGNETIC CONTACTOR WITH REDUCED NOISE MAGNETIC ARMATURE" by R. A.
Hurley and B. L. DeVault.
Application Ser. No. 725,179 entitled "ANALOG SIGNAL PROCESSING CIRCUIT,"
filed Apr. 19, 1985 by J. C. Engel.
Application Ser. No. 725,050 entitled "A SUPERVISORY CIRCUIT FOR A
PROGRAMMED PROCESSING UNIT," filed Apr. 19, 1985 by J. C. Engel.
Application Ser. No. 868,834 entitled "MASTER METERING MODULE WITH VOLTAGE
SELECTOR" by D. P. Orange, J. C. Engel, G. F. Saletta, D. A. Mueller and
R. T. Elms.
Application Ser. No. 868,833 entitled "MASTER METERING MODULE WITH DIGITAL
SATURATION ADJUSTER AND METHOD FOR USE THEREOF" by D. P. Orange, J. C.
Engel, G. F. Saletta and D. A. Mueller.
Application Ser. No. 016,420 entitled "PROCESS FOR MANUFACTURING ELECTRICAL
EQUIPMENT UTILIZING PRINTED CIRCUIT BOARDS" by S. L. Glover.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject matter of this invention is related generally to
electromagnetic contactors and more specifically to apparatus for
maintaining the contacts of the contactor closed.
2. Description of the Prior Art
Electromagnetic contactors are well known in the art. A typical example may
be found in U.S. Pat. No. 3,339,161 issued Aug. 29, 1967 to J. P. Connor
et al., entitled "Electromagnetic Contactor" and assigned to the assignee
of the present invention. Electromagnetic contactors are switch devices
which are especially useful in motor-starting, lighting, switching and
similar applications. A motor-starting contactor with an overload relay
system is called a motor controller. A contactor usually has a magnetic
circuit which includes a fixed magnet and a movable magnet or armature
with an air gap therebetween when the contactor is opened. An
electromagnetic coil is controllable upon command to interact with the
source of voltage which may be interconnected with the main contacts of
the contactor for electromagnetically accelerating the armature towards
the fixed magnet thus reducing the air gap and closing the contacts. As
the contactor closes, it works against the resistance of a kickout spring
which operates to cause the contactor to open once again at an appropriate
time. In order to maintain the contacts in the closed state in the prior
art, reduced voltage is usually placed upon the electromagnet thus
maintaining a small amount of electromagnetism which keeps the armature
abutted against the permanent magnet and thus keeps the contacts closed. A
disadvantage associated with this lies in the fact that such an
arrangement is not always energy efficient. For example, over time the
current flow through the windings may heat the windings of the
electromagnet thus increasing the resistance thereof thus reducing the
current therethrough. When this happens, the force on the magnet is
reduced. Alternatively the voltage which supplies the holding current may
vary within limits thus changing the current through the holding coil or
winding. It would be advantageous if an efficient system could be found
for maintaining the current through the holding coil at a relatively fixed
value thus guaranteeing sufficient magnetomotive force in the magnetic
circuit to keep the contacts closed during normal operating conditions and
to furthermore provide an energy efficient way of doing that.
SUMMARY OF THE INVENTION
In accordance with the invention, the control circuit for a contactor
includes a microprocessor which receives as an input the value of the
current flowing through the coil on a one-half cycle by one-half cycle
basis. This information is then converted to digital information and
compared against a stored standard. If the compared value is larger or
smaller than the stored standard the conduction angle on a triac which
controls the coil current is decremented or incremented respectively in
relatively small increments for the next succeeding half cycle. Eventually
regardless of what changes may take place in the applied voltage or in the
circuit which maintains the contacts in a closed state, a stabilized
current value will be reached which is equivalent to the stored value.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference may be had to the
preferred embodiments thereof, shown in the accompanying drawings in
which:
FIG. 1 shows an isometric view of an electromagnetic contactor embodying
teachings of the present invention;
FIG. 2 shows a cutaway elevation of the contactor of FIG. 1 at section
II--II thereof;
FIG. 3 shows force and armature velocity curves for a prior art contactor
with electromagnetic armature accelerating coil, kickout spring and
contact spring;
FIG. 4 shows a set of curves similar to those shown in FIG. 3 but for one
embodiment of the present invention;
FIG. 5 shows a set of curves similar to those shown in FIG. 3 and FIG. 4
but for another embodiment of the invention;
FIG. 6 shows still another set of curves for the apparatus of FIGS. 4 and 5
for voltage and current waveshapes;
FIGS. 7A through 7D show a schematic circuit diagram partially in block
diagram form for an electrical control system for the contactor of FIGS. 1
and 2;
FIG. 8 shows a plan view of a printed circuit board which includes the
circuit elements of FIG. 7 as well as the contactor coil, current
transducers and voltage transformers of FIG. 2;
FIG. 9 shows an elevation of the circuit board of FIG. 8;
FIG. 10 shows the circuit board of FIGS. 8 and 9 in isometric view in a
disposition for mounting in the contactor of FIG. 2;
FIG. 11 shows a circuit diagram and wiring schematic partially in block
diagram form for the contactor of FIGS. 2 and 7 as utilized in conjunction
with a motor controlled thereby;
FIG. 12 shows a schematic arrangement of a current-to-voltage transducer
for utilization in an embodiment of the present invention;
FIG. 13 shows a schematic arrangement of the transformer of FIG. 12 with an
integrator circuit;
FIG. 14 shows a plot of air gap length versus the voltage-to-current ratio
for the transducer arrangements of FIGS. 12 and 13;
FIG. 15 shows an embodiment of a current-to-voltage transducer utilizing a
magnetic shim;
FIG. 16 shows an embodiment of a current-to-voltage transducer using an
adjustable protrusion member;
FIG. 17 shows an embodiment of a current-to-voltage transducer utilizing a
movable core portion;
FIG. 18 shows an embodiment of a current-to-voltage transducer utilizing a
powdered metal core;
FIG. 19 shows an algorithm, READSWITCHES, in block diagram form for
utilization by a microprocessor for reading switches and discharging
capacitors for the input circuitry of the coil control board of FIG. 7;
FIG. 20 shows an algorithm, READVOLTS, in block diagram form for reading
line voltage for the coil control board of FIG. 7;
FIG. 21 shows an algorithm, CHOLD, in block diagram form for reading the
coil current for the coil control circuit of FIG. 7;
FIG. 22 shows an algorithm, RANGE, in block diagram form for reading line
current as determined by the overload relay board of FIG. 7;
FIG. 23 shows a schematic representation of an A-to-D converter and storage
locations associated with determining line current as found in the
microprocessor of the coil control board of the present invention;
FIG. 24 shows an algorithm, FIRE TRIAC, in block diagram form for
utilization by a microprocessor for firing the coil controlling triac for
the coil control board of FIG. 7;
FIG. 25A shows a plot of the derivatives of the line current shown in FIG.
25A;
FIG. 25B shows a plot of a one-half per unit, a one per unit and a two per
unit sinusoidal representation of a line current for the apparatus
controlled by the present invention;
FIG. 25C shows a plot of resultant analog-to-digital converter input
voltage versus half-cycle sampling intervals (time) for three examples of
line current magnitude of FIG. 25A;
FIG. 26 shows a representation of the binary numbers stored in storage
locations in the microprocessor of FIG. 23 for Example 1 of an
analog-to-digital conversion for six sampling times in the RANGE sampling
routine of FIG. 22 for the one-half per unit line cycle;
FIG. 27 shows a representation of the binary numbers stored in storage
locations in the microprocessor of FIG. 23 for Example 2 of an
analog-to-digital conversion for six sampling times in the RANGE sampling
routine of FIG. 22 for the one per unit line cycle;
FIG. 28 shows a representation of the binary numbers stored in storage
locations in the microprocessor of FIG. 23 for Example 3 of an
analog-to-digital conversion for six sampling times in the RANGE sampling
routine of FIG. 22 for the two per unit line cycle;
FIG. 29 shows plots of VLINE, VRUN(T), and VRUN(F) at the input of the
microprocessor;
FIG. 30 shows a plan view of a printed circuit board similar to that shown
in FIGS. 8 and 9 for utilization in another embodiment of the invention;
FIG. 31 shows a cutaway elevation of a contactor similar to that shown in
FIGS. 1 and 2 for another embodiment of the invention; and
FIG. 32 shows a sectional view of the contactor of FIG. 31 along the
section lines XXXII--XXXII.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, a three phase electrical contactor or
controller 10 is shown. For the purpose of simplicity of illustration the
construction features of only one of the three poles will be described it
being understood that the other two poles are the same. Contactor 10
comprises a housing 12 made of suitable electrical insulating materials
such as glass/nylon composition upon which are disposed electrical load
terminals 14 and 16 for interconnection with an electrical apparatus, a
circuit or a system to be serviced or controlled by the contactor 10. Such
a system is shown schematically in FIG. 11, for example. Terminals 14 and
16 may each form part of a set of three phase electrical terminals as
mentioned previously. Terminals 14 and 16 are spaced apart and
interconnected internally with conductors 20 and 24, respectively, which
extend into the central region of the housing 12. There, conductors 20 and
24 are terminated by appropriate fixed contacts 22 and 26, respectively.
Interconnection of contacts 22 and 26 will establish circuit continuity
between terminals 14 and 16 and render the contactor 10 effective for
conducting electrical current therethrough. A separately manufactured coil
control board 28 (as shown hereinafter in FIGS. 8, 9 and 10) may be
securely disposed with housing 12 in a manner to be described hereinafter.
Disposed on the coil control board 28 is a coil or solenoid assembly 30
which may include an electrical coil or solenoid 31 disposed as part
thereof. Spaced away from the coil control board 28 and forming one end of
the coil assembly 30 is a spring seat 32 upon which is securely disposed
one end of a kickout spring 34. The other end of the kickout spring 32
resides against portion 12A of base 12 until movement of carrier 42 in a
manner to be described causes bottom portion 42A thereof to pick up spring
34 and compress it against seat 32. This occurs in a plane outside of the
plane of FIG. 2. Spring 34 encircles armature 40. It is picked up by
bottom portion 42A where they intersect. The dimension of member 42 into
the plane of FIG. 2 is larger than the diameter of the spring 34. A fixed
magnet or slug of magnetizable material 36 is strategically disposed
within a channel 38 radially aligned with the solenoid or coil 31 of the
coil assembly 30. Axially displaced from the fixed magnet 36 and disposed
in the same channel 38 is a magnetic armature or magnetic flux conductive
member 40 which is longitudinally (axially) movable in the channel 38
relative to the fixed magnet 36. At the end of the armature 40 and spaced
away from the fixed magnet 36 is the longitudinally extending electrically
insulating contact carrier 42 upon which is disposed an electrically
conducting contact bridge 44. On one radial arm of contact bridge 44 is
disposed a contact 46, and on another radial arm of contact bridge 44 is
disposed a contact 48. Of course, it is to be remembered that the contacts
are in triplicate for a 3 pole contactor. Contact 46 abuts contact 22
(22-46), and contact 48 abuts contact 26 (26-48) when a circuit is
internally completed between the terminal 14 and terminal 16 as the
contactor 10 closes. On the other hand, when the contact 22 is spaced
apart from the contact 46 and the contact 26 is spaced apart from contact
48, the internal circuit between the terminals 14 and 16 is open. The open
circuit position is shown in FIG. 2. There is provided an arc box 50 which
is disposed to enclose the contact bridge 44 and the terminals 22, 26, 46
and 48, to thus provide a partially enclosed volume in which electrical
current flowing internally between the terminals 14 and 16 may be
interrupted safely. There is provided centrally in the arc box 50 a recess
52 into which the crossbar 54 of the carrier 42 is disposed and
constrained from moving transversely (radially) as shown in FIG. 2, but is
free to move or slide longitudinally (axially) of the center line 38A of
the aforementioned channel 38. Contact bridge 44 is maintained in carrier
42 with the help of a contact spring 56. The contact spring 56 compresses
to allow continued movement of the carrier 42 towards slug 36 even after
the contacts 22-46 and 26-48 have abutted or "made". Further compression
of contact spring 56 greatly increases the pressure on the closed contacts
42-46 and 26-48 to increase the current-carrying capability of the
internal circuit between the terminals 14 and 16 and to provide an
automatic adjustment feature for allowing the contacts to attain an
abutted or "made" position even after significant contact wear has
occurred. The longitudinal region between the magnet 36 and the movable
armature 40 comprises an air gap 58 in which magnetic flux exists when the
coil 31 is electrically energized.
Externally accessible terminals on a terminal block J1 may be disposed upon
the coil control board 28 for interconnection with the coil or solenoid
31, among other things, by way of printed circuit paths or other
conductors on the control board 28. Another terminal block JX (shown in
FIG. 32) may also be disposed on printed circuit board 28 for other useful
purposes. Electrical energization of the coil or solenoid 31 by electrical
power provided at the externally accessible terminals on terminal block J1
and in response to a contact closing signal available at externally
accessible terminal block J1 for example, generates a magnetic flux path
through fixed magnet or slug 36, the air gap 58 and the armature 40. As is
well known, such a condition causes the armature 40 to longitudinally move
within the channel 38 in an attempt to shorten or eliminate the air gap 58
and to eventually abut magnet or slug 36. This movement is in opposition
to, or is resisted by, the force of compression of the kickout spring 34
in initial stages of movement and is further resisted by the force of
compression of the contact spring 56 after the contacts 22-46 and 26-48
have abutted at a later portion of the movement stroke of the armature 40.
There may also be provided within the housing 12 of the contactor 10 an
overload relay printed circuit board or card 60 (also shown in FIGS. 8, 9
and 10) upon which are disposed current-to-voltage transducers or
transformers 62 (only one of which 62B is shown in FIG. 2). In those
embodiments of the invention in which the overload relay board 60 is
utilized, the conductor 24 may extend through the toroidal opening 62T of
the current-to-voltage transformer or transducer 62B so that current
flowing in the conductor 24 is sensed by the current-to-voltage
transformer or transducer 62B. The information thus sensed is utilized
advantageously in a manner to be described hereinafter for providing
useful circuit information for the contactor 10.
There may be also provided at one end of the overload relay board 60,
selector switches 64, which may be accessible from a region external of
the housing 12. Another embodiment of the invention is depicted on FIG. 30
and FIG. 31 the description of which and operation of which will be
provided hereinafter.
Referring now to FIG. 2 and FIG. 3, four superimposed curves are shown for
the purpose of depicting the state or the art prior to the present
invention. In particular, plots of force versus distance for a magnetic
solenoid such as 31 in FIG. 2, a kickout spring such as 34 shown in FIG.
2, and a contact spring such as 56 shown in FIG. 2, are depicted. In
addition, a superimposed plot 92 of instantaneous velocity versus distance
is depicted for an armature such as 40 shown in FIG. 2. Although the
independent variable in each case is distance, it could just as well be
time as the two variables are closely related for the curves shown in FIG.
3. It is to be understood that the reference to component parts of the
contactor 10 of FIG. 2 is made for the purpose of simplifying the
illustration; it is not to be presumed that the elements shown in FIG. 2,
when taken together as a whole, are covered by the prior art. There is
shown a first curve 70 which depicts force versus distance (time could be
utilized) for a kickout spring (such as 34) as the spring is compressed
starting at point 72. The spring 34 offers initial force 74. The spring 34
gradually resists compression with greater and greater force until point
78 is reached on the distance axis. The area enclosed by the lines
interconnecting point 72, point 74, the curve 70, point 76, point 78 and
point 72 once again represents the total amount of energy that is
necessary to compress a kickout spring by the movement of the armature 40
as it is accelerated to close the air gap 58 between it and the fixed
magnet 36. This force resists the movement of the armature 40. At point 80
on the distance axis, the contacts 22-42 and 26-48, for example of FIG. 2,
abut, and continued movement of the armature 40 causes compression of the
contact spring 56 which operates to place increasing force on the now
abutted contacts for reasons described previously. Curve 79 represents the
total force which the moving armature 40 works against as it is
accelerated to close the air gap 58. A step function increase in force
between point 81 and point 82 occurs as the contacts 22-42 and 26-48
touch. This force grows increasingly larger until at point 78 the moving
armature 40 experiences the maximum force applied by the combination of
the kickout spring 34 and contact spring 56. That amount of additional
energy which the moving armature must supply to overcome the resistance of
the contact spring 56 is represented by the area enclosed by the lines
which interconnect the points 81 and 82, curve 79, points 84 and 76, curve
76A and point 81 once again. Consequently, as the armature 40 is
accelerated from its position of rest at 72 to its position of abutment
against the magnet 36 at 78 the coil or solenoid 31 must supply at least
the amount of energy represented by the line which connect the points 72,
74, 81, 82, 84, 78 and 72 once again. The positive slope of curve 70 is
purposely kept as small as possible consistent with allowing the armature
40 to be driven in the reverse direction when the coil energy is removed
so that the contactor may reopen. The initial force required to be
overcome by the armature 40 in its first instant of movement is the
threshold value of force represented by the difference between the points
72 and 74. Consequently, the armature must supply at least that much force
at that instant of time. For purpose of simplicity of illustration,
therefore, in an illustrative sense, it will be presumed that the
electromagnetic coil 31 provides the force represented at point 88 in FIG.
3 for the armature 40 at 72. It is also necessary that the amount of force
provided by the coil or solenoid 31 at the instant that the contacts 22-42
and 26-48 touch and the contact spring 56 is engaged at 80 be greater than
the amount of force represented by the distance between the points 80 and
82 in FIG. 3, otherwise, the accelerating armature 40 will stall in
midstroke, thus providing a very weak abutment of contacts 22-46 and
26-48. This is an undesirable situation as the tendency for the contacts
to weld shunt is greatly increased under this condition. Consequently, the
force supplied by the coil 31 in accelerating the armature 40 must be
greater at point 80 than the force represented at point 82. A magnetic
pull curve for solenoids and their associated movable armatures follows
relatively predictable configurations which are a function of many things
including the weight of the armature, the strength of the magnetic field,
the size of the air gap, etc. Such a curve is shown at 86 in FIG. 3. With
the relative shape of the curve 86 and the previous conditions of
constraint associated with the value of the force required of the coil 31
at points 72 and 80 on the distance axis of FIG. 3, the entire profile for
the magnet pull curve for the armature 40 and coil 31 of FIG. 2 is fixed.
It ends with a force value 90. It is to be understood that it is a
characteristic of magnetic pull curves that the magnetic force increases
appreciably as the air gap 58 narrows as the moving armature 40 approaches
the stationary magnet 36. Consequently, at point 78, the force 90 exists.
It is at this point that the armature 40 first abuts or touches the fixed
magnet 36. This unfortunately creates two undesirable situations: First,
it can be easily seen that the total energy supplied to the magnetic
system by way of the coil 31, as represented by the lines which
interconnect the points 72, 88, curve 86, points 90, 78 and point 72 once
again, is significantly greater than the amount of energy needed to
overcome the various spring resistances. The difference in energy is
represented by the area enclosed by the lines which connect the points 74,
88, curve 86, points 90, 84, 82, 81 and 74 once again. This energy is
wasted or unnecessary energy, and it would be very desirable not to have
to produce this energy. The second undesirable characteristic or situation
is the fact that the armature 80 is accelerating at its maximum and
producing its most force of kinetic energy at the instant immediately
before it makes abutting contact with the permanent magnet 36. A velocity
curve 92 which starts at point 72 and ends at point 94 as shown in FIG. 3,
represents the velocity of the armature 40 as it accelerates along its
axial motion path. Note the change in shape at 80 as the kickout spring 34
is engaged. At the time immediately before the armature 40 touches the
permanent magnet 36, the velocity V1 is maximum. This has the very
undesirable characteristic of transferring high kinetic energy due to high
velocity at the instant of impact or abutment between the armature 40 and
the permanent magnet 36. This energy must be instantaneously dissipated or
absorbed by other elements of the system. Typically, the reduction of the
armature velocity to zero instantaneously at 78 requires the energy to be
instantaneously reduced. This kinetic energy is converted to the sound of
abutment, to heat, to " bounce", to vibration, and mechanical wear, among
other things. If the armature 40 bounces, since it is loosely
interconnected with the contacts 46-48 on the contact bridge 44 by way of
the contact spring 56, there is a high likelihood that the mechanical
system represented thereby will oscillate or vibrate in such a manner that
the contact arrangements 22-42 and 26-48 will rapidly and repeatedly make
and break. This is a very undesirable characteristic in an electrical
circuit. It would therefore be desirable to utilize the contactor 10 of
FIG. 2 in such a manner that the energy which is supplied to the coil 31
is carefully monitored and chosen so that only the exact amount of energy
(or an energy value close to that amount) which is necessary to overcome
the resistance of the kickout spring 34 and the contact spring 56 is
provided. Furthermore, it would be desirable if the velocity of the moving
armature 40 is significantly reduced as the armature abuts against the
permanent magnet 36 so that the likelihood of "bounce" is correspondingly
reduced. The solution to the aforementioned problems is accomplished by
the present invention as shown graphically in FIGS. 4, 5 and 6, for
example.
Referring now to FIG. 2, FIG. 3 and FIG. 4, a series of curves similar to
those shown in FIG. 3 is depicted in FIG. 4 for the present invention. In
this case, the spring force curves 70 and 79 for the kickout spring 34 and
contact spring 56 respectively are the same as those shown in FIG. 3.
However, the energy represented by the contact spring and kickout spring
are designated X and Y respectively. In this embodiment of the invention
the magnet pull curve 86' representing the force applied by the coil 31
starts at point or force level 95 in order to overcome the kickout spring
threshold force as described previously and continues on to point or force
level 97 which occurs at distance 96. It will be noted that the electrical
energy supplied to the armature 40 by the coil 31 ceases at distance 96
corresponding to force level 97. This occurs before the armature 40 has
completed its movement to the position of abutment with fixed magnet 36.
It will be noted at this time that the maximum velocity V.sub.m attained
by the armature 40 is indicated at point 98 on the velocity curve 92'.
This is the maximum velocity that the armature will attain during its
movement to the position of abutment with the magnet 36. Said in another
way, this means that once the electrical energy has been removed from the
coil 31, the armature will cease accelerating and begin to decelerate. The
deceleration curve is shown at 100 in FIG. 4 and it ranges from point 98
to point 78 with a slope change where the kickout spring is engaged. This
is accomplished by prematurely interrupting the flow of electrical energy
to the coil 31 at the time distance 96 is achieved. Prior to the armature
40 completing its movement to the position of abutment with fixed magnet
36, only that amount of energy necessary to overcome the spring forces
need be applied, thus providing for an energy-efficient system. At the
time the electrical energy is removed from the solenoid 31, the energy
necessary to complete the movement of the armature to its resting position
of abutment with magnet 26, is represented by the area enclosed by the
lines interconnecting the points 96, 99, curve 70, points 81, 82, curve
79, points 84, 78 and 96 once again. This energy is supplied during that
portion of time that electrical energy is being supplied to the armature
coil 31 which is represented by the area Z (not necessarily to scale)
enclosed by the lines interconnecting the points 74, 95, curve 86', points
97, 99 and point 74 once again. The latter-mentioned energy balance is
chosen in some convenient way which may include empirical analysis in
which the energy levels are determined experimentally. The energy
represented by area Z' is utilized to compress the kickout spring 34
during initial movement of the armature and is not available for
utilization later in the travel stroke. As will be described hereinafter,
a microprocessor may be utilized to determine the amount of energy to be
supplied. The continued motion of the armature 40 during the deceleration
phase depicted by curve 100 is a function of the kinetic energy level E
attained by the armature 40 at point 96 as the electrical energy is
removed from coil 31. This energy E is equal to one-half the mass (M) of
the armature times the velocity (V.sub.m) it achieves at point 98 squared.
In a perfectly energy-balanced system, the decelerating armature 40
strikes the permanent magnet 36 with zero velocity at 78, thus eliminating
bounce and the need to absorb excessive energy in the form of noise, wear,
heat, etc. It is to be understood, of course, that the attainment of the
ideal as shown in FIG. 4 is difficult and is, in fact, not necessary for a
highly efficient system to be nevertheless produced. Consequently, FIG. 4
should be viewed as depicting an ideal system which is provided to
illustrate the teachings of the present invention. It may become very
difficult to have the armature 40 impact the permanent magnet 36 with
exactly zero velocity at 78. A small residual velocity is tolerable,
especially when compared with the velocity 94 which is attained in the
prior system as shown in FIG. 3.
Referring now to FIG. 2, FIG. 4 and FIG. 5, a collection of curves similar
to that shown in FIG. 4, is depicted for a system in which the contact
spring 56 is stiffer and thus offers more force against which the moving
armature 40 must work. In addition to the foregoing, other illustrative
features are depicted; for example, the electrical power is applied to the
coil for a longer period of time, thus allowing the velocity of the moving
armature 40 to attain a higher value. The higher value of velocity is
necessary because increased kinetic energy is necessary to overcome the
increased spring force of the contact spring 56. With regard to the
comparison of FIGS. 4 and 5, like reference symbols represent like points
on the curves of the two figures. In the embodiment of the invention of
FIG. 5, the total energy necessary to compress the kickout and contact
springs 34 and 56, respectively, is increased by an amount U represented
by the area enclosed by the curves or lines connecting the points 82, 102,
curve 79', points 104, 84, curve 79 and point 82 once again. The remaining
area, i.e., the area enclosed by the lines interconnecting the points 72,
74, curve 70, points 81, 82, curve 79, points 84, 78, and 72 once again,
is the same as that shown in FIG. 4. In order to provide the increased
energy U, a different magnet pull curve 86" is generated. This magnetic
pull curve has a slightly higher average slope and continues for a time
period represented by the distance difference between point 96 and point
100 thus generating an incremental increase in energy U. The new magnetic
pull curve 86" starts at point 95, which may the same as that shown in
FIG. 4, and ends at point 97' at time represented by distance 100. This in
turn generates a steeper and longer velocity curve 92" for the moving
armature 40. The peak velocity V.sub.2 is attained at point 98' on
velocity curve 92". At this time, the kinetic energy (E.sub.2) of the
armature 40 is equal to one-half MV.sub.2 squared. The instantaneous
velocity then decreases, following curve 100' with a definite breakpoint
at velocity V.sub.1. This breakpoint represents the armature initially
abutting against the contact spring 56. A portion of the increased
velocity V.sub.2 and thus increased energy E.sub.2 is quickly absorbed by
the previously described increase in energy provided by the stiffened or
more resistive contact spring such that the curve 100' theoretically
reaches zero at the point 78 which corresponds to the moving armature 40
abutting the fixed magnet 36.
Referring now to FIGS. 2, 4 and 6, voltage and current curves for the coil
31 and their relationship to force curves of FIG. 4 are shown and
described. In a preferred embodiment of the invention, the coil current
and voltage are controlled in a manner described with respect to the
embodiment of FIG. 7 in a four-stage operation: (1) the ACCELERATION
stage, for accelerating the armature 40, (2) the COAST stage, for
adjusting the speed of the armature later in the armature movement
operation prior to abutment of the armature 40 with the fixed magnetic 36,
(3) the GRAB stage, for sealing of the armature 40 against the fixed
magnet 36 near or immediately after abutment to dampen oscillation or
bounce, if any, and (4) the HOLD stage, for armature hold-in. Reference
may be had to Table 1 to help understand the foregoing and that which
follows. Information from cable 1 is disposed as a menu in memory in a
microprocessor as will be described hereinafter. Electrical energy is
supplied to the coil or solenoid 31 at a time 72' which is related to
point 72 on the distance axis of FIG. 4 and ending at a time 96' which is
related to point 96 on the distance axis of FIG. 4 for the ACCELERATION
stage. The energy represented by areas Z and Z' in FIG. 4 is provided by
judicious choice of the electrical voltage across the terminals of coil 31
and the electrical current flowing therethrough.
TABLE 1
__________________________________________________________________________
Closing Profile
ACCELERATION COAST GRAB HOLD
Percent Percent Percent
Percent
Conduction Conduction Conduction
Conduction
of TRIAC Q1 of TRIAC Q1 of TRIAC
of TRIAC Q1
Control Voltage
Number of
FOR Number of Pulses
FOR Number of Pulses
FOR FOR
106 Pulses of Coil
.beta..sub.1, .beta..sub.2
of .beta..sub.3
of .beta..sub.4,
.beta..sub.5,
.beta..sub.6
.beta..sub.7,
.beta..sub.8 . . .
etc
(VOLTS) Current 108
(%) Coil Current 108
(%) Coil Current 108
(%) (%)
__________________________________________________________________________
Below 78VAC
None -- None -- None -- --
78.0-96.0
2 58 1 53 3 89 .beta..sub.7
Equal
22% Initial.
Then regulate
to 0.28A Peak
of coil current
108.
9 | | |
