Note: Descriptions are shown in the official language in which they were submitted.
SOLENOID ASSEMBLY ACTUATION USING RESONANT
FREQUENCY CURRENT CONTROLLER CIRCUIT
TECHNICAL FIELD
The present invention relates to a current controller for an inductive load
such as
a solenoid driver used to actuate a mechanism such as an electric door latch
or strike.
Specifically, the invention relates to a current controller circuitry and
method configured
to selectively and efficiently overcome a preload condition imposed on the
latch or a
keeper of the strike through actuation of the solenoid driver using a system
resonant
frequency current.
BACKGROUND OF THE INVENTION
Solenoids are often used as the driver to operate many types of
electromechanical devices, such as for example electromechanical door latches
or
strikes. In the use of solenoids as drivers in electromechanical door latches
or strikes,
when power is applied to the solenoid, the solenoid is powered away from the
default
state to bias a return spring. The solenoid will maintain the bias as long as
power is
supplied to the solenoid. Once power has been intentionally removed, or
otherwise,
such as through a power outage from the grid or as a result of a fire, the
solenoid
returns to its default position. Depending on the type latch or strike (fail-
safe or fail-
secure), the default position may place the latch or strike in a locked (fail-
secure) or
unlocked (fail-safe) state. In a "fail-safe" system, as long as the latch or
strike remains
locked, power has to be supplied to the solenoid to maintain stored energy in
the return
spring. In a "fail-secure" system, the opposite is true.
The current to pull in the plunger of the solenoid against the return spring
is
referred to as the "pick" current and the current to hold the plunger against
the return
spring is referred to as the "hold" current. Typically, the pick current is
much greater
than the hold current regardless of whether the solenoid is used in a "fail-
safe" or "fail-
secure" system. Power provided to the solenoid of an electric latch or strike
is most
efficiently maintained if a constant current is provided to the inductive
load.
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In U.S. Patent No. 10,378,242, assigned to Hanchett Entry Systems, Inc. ("the
'242 Patent"), a constant-current controller circuitry operable to supply a
constant
current to an inductive load such as a solenoid driver of an electromechanical
device is
disclosed. The circuitry includes a switching circuit comprising a primary
switch and a
secondary switch. The switches are sequentially opened and closed as timed
events
whereby a periodic current to the solenoid becomes constant when a
sufficiently large
switching frequency is implemented. The controller may be operated as a pulse-
width
modulated controller. In one aspect of the circuit disclosed, the primary
switch is a
MOSFET.
In U.S. Patent Application No. 16/406,464, assigned to Hanchett Entry Systems,
Inc. ("the '464 Application"), the constant-current controller circuit
includes a much more
compact GaNFET transistor as the primary switch, wherein a resulting, smaller
PCB
containing the GaNFET and its associated electronic components may be
integrated
with and made part of a solenoid assembly to simplify conversion of an
electromechanical device to one having constant current circuitry.
Overcoming a preload placed on a latch of an electric latch or a keeper of an
electric strike is recognized as a major problem in the field. In a solenoid
actuated, fail-
secure electric latch or keeper, the pull-in strength of the solenoid is
designed to retract
the plunger and, in turn, the latch or strike to allow the door to be released
from the door
frame. However, a pre-load placed on the latch or keeper when the solenoid is
attempting to pull in the plunger may cause the latch/keeper to act sluggish
or not to
move at all. Pre-load may be caused, for example, by a mis-aligned latch to
strike, a
sagging door or wind blowing against the door. It may also be caused if the
exiting
person tries to open the door before the latch or keeper of a strike has time
to retract.
This problem may sometimes be solved by utilizing a bigger solenoid than is
needed
under normal operations. However, this increases cost while reducing energy
efficiency.
While the aforementioned '242 Patent and '464 Application describe a constant-
current controller circuits that might be used with an electromechanical
device such as
an electric lock or strike to improve operation efficiency, neither address
preload
conditions that may be imposed on the electric lock or keeper.
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Date recue/date received 2021-10-22
Therefore, there exists a need for a controller circuit that selectively
supplies a
pick current at the latch system's resonant frequency so as to alleviate a
preload
condition on the latch or keeper (hereinafter referred to collectively as a
"latch").
SUMMARY OF THE INVENTION
What is presented is a latch assembly or system that includes a releasably
secured latch and/or a keeper. A solenoid assembly is used to drive an
associated
electromechanical device. The solenoid assembly has a solenoid driver coupled
to a
power supply, a switching circuit connected with the solenoid driver, and a
function
generator to selectively adjust a frequency of a pick current output from the
power
supply and provided to the solenoid driver. The frequency is adjusted by the
function
generator until the pick current induces a resulting vibration of the latch
system, and
wherein upon inducing the resulting vibration of the latch system the latch or
keeper is
released from a preloaded condition.
In accordance with an aspect of the present invention, the function generator
may be a waveform generator and the switching circuit may include a metal-
oxide-
semiconductor field effect transistor (MOSFET) or a gallium nitride field
effect transistor
(GaN FET).
In accordance with another aspect of the invention, a method for releasing a
preloaded latch or a keeper of an electromechanical latch system is provided.
At a first
step, when the latch of a fail-secure electromechanical latch system is in its
default,
locked condition, the solenoid driver of the latch is not energized. At a next
step,
access credentials are presented to and verified by an authentication device
wherein
the authentication device communicates with a provided waveform generator to
supply
a baseline (or base) pick current to the solenoid driver at a sufficient level
to pull back
the latch or keeper under normal operating conditions (i.e., when the latch or
keeper is
not preloaded). At a next step, latch a preload sensor interrogates whether a
latch or
keeper preload condition exists. If the preload sensor determines that a latch
or keeper
preload does not exist, a communication is provided to the waveform generator
to
reduce the baseline pick current to a hold current to the solenoid driver at a
sufficient
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Date recue/date received 2021-10-22
level to hold the latch or keeper in a released, unlocked condition. Upon
receipt of the
communication from the preload sensor by the waveform generator, the hold
current
may be supplied by the waveform generator after a predetermined period of time
elapses since application of the base pick current to assure retraction of the
latch or
.. keeper is complete or after retraction of the latch or keeper is confirmed
by the preload
sensor. If the preload sensor determines that a latch or keeper preload does
exist in a
further step, a communication is provided to the waveform generator to supply
a pick
current at a predetermined target frequency or predetermined range of
frequencies
sufficient to free the latch or keeper from its preload condition to a
released, unlocked
condition. Thereafter, a hold current is provided to the solenoid driver. In
yet another
step, if a latch or keeper preload condition continues to be sensed by the
preload
sensor, the target frequency or the range of frequencies may be reapplied, or
an
enlarged range of frequencies may be applied as a pick current and an optional
alert
signal may be provided indicating that repairs to the latch system are needed.
In accordance with another aspect of the invention, a method is disclosed
wherein, a target frequency or a range of frequencies sufficient to free a
preloaded latch
or keeper has not been predetermined. In a first step, after the latch or
keeper preload
sensor has sensed that a latch or keeper preload exists, waveform generator
may
supply current at a varying frequency, sweeping the frequency between the base
pick
current frequency and a pre-designated, outer limit of pick current
frequencies so as to
force the latch system to vibrate and to release the preloaded latch or
keeper. Once the
current frequency sweep is completed sufficient to free the latch or keeper,
the method
proceeds to provide a hold current to the solenoid driver.
In yet another embodiment, a method is provided wherein each time access
credentials are presented to and verified by the authentication device, the
baseline pick
current is provided to the solenoid driver followed by a sweep through the a
predetermined range of frequencies needed to free a latch or a keeper from a
preload
condition in the event the latch or keeper is preloaded to assure that the
latch becomes
fully retracted. A preload sensor may be added to confirm full latch or keeper
retraction
in this embodiment.
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Date recue/date received 2021-10-22
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example, with reference
to the accompanying drawings, in which:
FIG. 1 is a functional schematic of a switching circuit, as disclosed in the
'242
Patent;
FIG. 2 is a schematic of an embodiment of a constant current PWM controller
circuit, as disclosed in the '242 Patent;
FIGS. 3A and 3B is a schematic of another embodiment of a constant current
PWM controller circuit configured for pick and hold states, as disclosed in
the '242
Patent;
FIG. 4 is a generalized schematic of a PCB containing a GaFNET and its
supporting electronic components as disclosed in the '464 Application;
FIG. 5 and 5A are views of an electric strike assembly;
FIGS. 6A and 6B are views of a solenoid assembly with integrated constant-
current controller circuit as disclosed in the '464 Application;
FIGS. 7A and 7B are views of another solenoid assembly with integrated
constant-current controller circuit as disclosed in the '464 Application;
FIG. 8 is a functional schematic of a preload circuit, in accordance with an
aspect
of the present invention; and
FIG. 9 is a schematic flow chart of a method of releasing a latch under a
preload
condition.
Corresponding reference characters indicate corresponding parts throughout the
several views. The exemplifications set out herein illustrate currently
preferred
embodiments of the invention, and such exemplifications are not to be
construed as
limiting the scope of the invention in any manner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Date recue/date received 2021-10-22
As disclosed in the '242 Patent, a functional schematic of the switching
circuit 10
that produces constant current in an inductive load via switches controlled by
pulse-
width modulation (PWM) is shown in FIG. 1. There are two switches; a primary
switch
12 and a secondary switch 14. When primary switch 12 is closed, the secondary
switch
14 is open. When the primary switch 12 is open, the secondary switch 14 is
closed. The
series resistance (R), indicated in the circuit as resistor 18, is the sum of
the coil
resistance and the load resistance. Coil inductance and total circuit
resistance comprise
the inductive load.
When primary switch 12 is closed, source voltage (Vs) is applied across
inductor
.. ("coil") 16 and resistor 18. However since coil 16 opposes any change in
current flow
by producing a counter electromotive force (EMF) equal to the source voltage,
current
flow through coil 16 and resistor 18 is zero at the instant the primary switch
12 is closed,
i.e., (to). Once primary switch 12 is closed, the counter EMF begins to decay
until the
voltage across coil 16 and resistor 18 equals the source voltage Vs, thereby
allowing a
current to flow through coil 16 and resistor 18. The time interval in which
primary switch
12 is closed may be defined as ton.
At the beginning of the time interval when secondary switch 14 is closed and
primary switch 12 is opened (i.e. from ton until the end of the cycle (T)),
there is no
longer a source voltage Vs across coil 16. Once again, coil 16 opposes the
change in
current flow by producing a positive EMF equal to the source voltage Vs in the
direction
that was the source voltage's direction. Therefore, current continues to flow
through coil
16 and resistor 18 without source voltage Vs being applied. From ton to the
end of the
cycle T, current through and voltage across coil 16 and resistor 18 decays to
zero via
the EMF discharged by coil 16. As such, the current in the inductive load is
dependent
upon the circuit parameters and the rate at which the switches 12 and 14 are
opened
and closed with respect to each other. This rate is the PWM frequency (f).
From the above discussion, it can be understood that current flow may be held
constant by increasing the frequency in which the switches 12 and 14 are
opened and
closed. If the primary switch 12 is closed before the current decays to zero,
the initial
.. current becomes the boundary current. The load current is equal to the
boundary
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Date recue/date received 2021-10-22
current at the beginning and end of each period T. Non-zero boundary current
increases
the average value of the load current. As the period T is decreased
substantially less
than the L/R time constant, wherein L/R is the ratio of coil inductance to
circuit
resistance, the current may be held to any value between 0 and Vs/R by varying
the
duty ratio of primary switch 12, where the duty ratio is defined by ton IT.
This constant
current control is especially useful since, in the example of a magnetic lock
or solenoid
driver, power to the lock can be precisely controlled by varying the duty
ratio (i.e., power
can be increased to resist an instantaneous and unwanted attempt to open the
door yet
be reduced while the door is at idle). That is, for a sufficiently high
frequency, the
.. current is constant and can be maintained by a PWM controller so as to be
any value
between 0 and Vs/R.
Further in regard to the disclosure made in the '242 Patent, FIG. 2 depicts a
constant-current controller circuit that may be used in conjunction with an
electric latch
or strike. It has been found that power to an access control device having
inductive
load actuator, such as but not necessarily limited to either a magnetic lock
or a solenoid
driver, is most efficiently provided if a constant current is provided to the
inductive load
actuator. An exemplary circuit 20 for a constant-current PWM controller 22 is
shown in
FIG. 2. The circuit makes use of a PWM controller integrated circuit 22 with
current
sensing used as the feedback mechanism. The primary switch 24 is typically a
.. MOSFET (analogous to primary switch 12 described above) while the secondary
switch
26 (i.e. switch 14) is typically a free-wheeling diode (shown as "Dfw").
A current transformer 28 with two single-turn primary windings 30a and 30b and
one secondary winding 32 with N-turns is used to sense the two components of
the load
current 34a and 34b. Primary windings 30a and 30b are connected in series with
switches 24 and 26, respectively. Secondary winding 32 is connected to a
bridge
rectifier 36, burden resistor (RB) 38, and low-pass filter resistor (Rf) 40
and capacitor (Cf)
42. It should be noted that any component having an equivalent functionality
to the
current transformer 28 may be installed within circuit 20. For example, a
skilled artisan
will see that the current transformer 28 may be replaced with Hall-effect
sensors
.. specified to have similar functionality.
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Date recue/date received 2021-10-22
When primary switch 12 is on (MOSFET 24 in FIG. 2), the first current
component flows through the primary winding at Terminals 3 and 4. This
component is
transformed to the secondary winding 32 as:
DVs
= s _____________________________________ 0<t<t
- - OIL NR'
When primary switch 24 turns off, the coil current continues to flow, due to
the
stored energy, but is now diverted into the free-wheeling diode 26 (i.e.
secondary switch
14). This second current component now flows through the primary winding at
Terminals 1 and 2. Due to the arranged phasing of the current transformer 28,
the
second current component is transformed to the secondary winding 32 as:
DVs
1=- ______________________________________ to <t
s NR' n
The secondary currents are rectified through bridge rectifier 36 to produce a
constant
current through the burden resistor 38:
DVs
i = ______________________________________ ,0<tT
NR
The value of the burden resistor is calculated to produce a voltage that is
equal to the
internal voltage reference, Vr, of the integrated circuit:
NRVr
RB= ___________________________________________
D Vs
Thus, the value of burden resistance 38 establishes the feedback voltage to
the
PWM controller 22 at Vr. At this voltage, PWM controller 22 regulates the
current
through the inductive load to maintain the feedback voltage at this operating
point.
Thus, the value of RB establishes the value of the constant current through
the inductive
load.
Still further in regard to the disclosure made in the '242 Patent, FIG. 3
shows
another exemplary circuit schematic 50 that may be suitable for use in
conjunction with
an electric latch or strike which employs a solenoid. As is recognized in the
art,
solenoid-driven actuators have long been known for their power inefficiencies.
Since
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Date recue/date received 2021-10-22
their pull-in current (pick current) is higher than the current needed to hold
the solenoid
plunger in place (hold current), to save energy, it is desirable for the
controller to step
down the current after the fixed duration of time during which the pick
current has been
applied.
To improve energy efficiencies, circuit 50 may use a combination of individual
resistors in parallel to produce a collective burden resistor that may be used
to change
the operating current in the solenoid. In the case of a solenoid, two
operating points are
required, with the first being the pull-in or pick current. This relatively
large current is
sourced into the solenoid coil for a short time interval to engage the
solenoid. Once the
solenoid has been actuated, the pick current is followed by a much smaller
holding or
hold current to maintain the position of the solenoid plunger. In accordance
with an
aspect of the present invention, this pick and hold operation may be
accomplished using
a constant current controller by changing the value of the burden resistor
once the
solenoid has engaged, as will be discussed in greater detail below.
In reference to FIG. 3, circuit 50 makes use of a timer integrated circuit 52
to
establish the time interval of the pull-in operation. The timer receives a
signal through
input 54 that initiates the pull-in interval. With no signal applied,
transistor 56 (Q7) is on,
Pin 1 (58a) of PWM controller 58 (U14) is pulled to ground such that PWM
controller 58
is disabled. As a result, no current flows through the solenoid coil connected
at
terminals 34a (+24VDC) and 34h (OUT#2).
When input 54 is switched to logic-level HIGH, PWM controller 58 is enabled
and
the pick interval starts with a logic-level HIGH at the OUT pin (52a) of timer
integrated
circuit 52. This output turns on transistor 60 (Q8) and connects resistor 62
(R71) and
resistor 64 (R72) in parallel. This combined resistance value establishes the
value of the
pull-in current. Once the pull-in interval has expired, OUT pin 52a returns to
a logic-
level LOW, transistor 60 (Q8) turns off, and resistor 62 (R71) is disconnected
from the
circuit. Resistor 64 (R72) remains as the burden resistance and establishes
the hold
current of the solenoid. By way of example, if resistor 62 has a resistance of
100 ohms
and resistor 64 has a resistance of 10,000 ohms and 24 V is being supplied,
the pick
current will be about 0.24 A (24 V/99 ohms = 0.24 A) while the hold current
will be about
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Date recue/date received 2021-10-22
2.4 mA (24 V/10,000 ohms = 0.0024 A). In this manner, power efficiencies may
be
realized as high current is applied only for a set, limited period of time
before the circuit
switches to provide the less-demanding hold current.
The above discussion with
reference to FIGS. 1-3 was disclosed in the co-pending '242 Patent.
A printed circuit board (PCB), as known in the art, is a modular platform of
electronic components that are interconnected to form a circuit. The
structural base or
substrate of the PCB is formed of an insulating material. The circuit itself
is formed by a
thin layer of conducting material deposited in a pattern on the insulating
base. The
necessary electronic components making up the desired circuitry may be then
placed
on the surface of the insulating material and soldered to the deposited
conducting
material. Thus the overall size of the PCB is substantially dependent upon the
types of
electronic components needed to form the circuitry and the physical sizes of
the
electronic components. Further, while the PCB substrate may be approximately
1.5mm
thick and itself flexible, depending on the number of electronic components
soldered to
the substrate and their physical sizes, the resulting PCB may be rendered
relatively rigid
and inflexible.
As disclosed in the '464 Application, the footprint of MOSFET 24 as disclosed
in
the '242 Patent measures approximately 4.0mm x 5.0mm and therefore requires a
relatively large PCB to contain it and its supporting components. The
thickness of
MOSFET 24 is approximately 1.75mm. As a result of these physical attributes of
MOSFET 24, and the layout and construction of the necessary supporting
electronic
components, the size of its PCB becomes relatively large, measuring
approximately
30.0mm x 40.0mm, and is also rendered rigid and inflexible. Consequently, a
dedicated
space must be provided remote from the electromechanical device for mounting
such a
large PCB, making a retrofit of the constant-current controller circuit as
disclosed in the
'242 Patent difficult and impractical.
The use of a Gallium Nitride FET (GaNFET) manufactured by Efficient Power
Conversion Co. of El Segundo, CA 90245 (part no. EPC2039) as a primary switch
in
place of MOSFET 24 solves the problem. The physical size of a GaNFET is much
smaller than a MOSFET. Therefore, the size of the PCB needed to support the
Date recue/date received 2021-10-22
GaNFET is much smaller. Thus, the smaller physical size of a GaNFET/PCB will
enable the PCB to be mounted directly on an associated solenoid driver.
Referring to FIG. 4, a magnified view of much smaller PCB 120 of a constant-
current control circuit sized to contain GaNFET 124 and its supporting
electronic
components is shown. The footprint of GaNFET 124 measures approximately 1.35mm
x 1.35mm and is much less than the footprint of MOSFET 24. Its thickness is
also less
than the thickness of MOSFET 24, measuring approximately 0.625mm. The result
is
that a much smaller PCB 120 may be utilized, having a length (L) of
approximately
24.1mm and a width (W) of approximately 17.5mm. Moreover, PCB 120 is rendered
flexible via the use of GaNFET 124.
The use of GaNFET 124 as the primary switch in the circuit enables PCB 120 to
be located within the framework of the associated electromechanical device and
integrated with the associated solenoid driver itself, making the circuit of a
prior art
electromechanical devise easily upgraded to a constant-current controller
circuit. The
upgrade may be accomplished for the most part by a simple replacement of the
solenoid driver.
FIGS. 5 and 5A show an example of a prior art electric strike assembly 210 as
disclosed in U.S. Patent No. 8,454,063. Electric strike assembly 210 utilizes
two
solenoid assemblies 215 and two solenoid drivers 216a to control release of
keeper(s)
270 to their unlocked state. Each solenoid assembly includes solenoid driver
216a and
solenoid bracket 217.
With reference to FIG. 5A depicting only one side of electric strike assembly
210,
when solenoid driver 216a is energized and solenoid plunger 272 extends,
actuating
components 274 interact with each other to permit keeper 270 to move to its
unlocked
state. In the example of an electric strike assembly shown, upon extension of
plunger
272, release lever 276 rotates, allowing transmission lever 278 to rotate
about pivot 280
which in turn releases keeper 270 for movement to its unlocked state. Solenoid
assembly 215, solenoid driver 216a and actuating components 274 are located
within
housing 282 of electric strike assembly 210.
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Date recue/date received 2021-10-22
Power for energizing solenoid driver 216a is provided by a switch (not shown)
located remote from the strike assembly 210; a feed wire (not shown) connects
the
switch to solenoid driver 216a. In the example shown, the switch may be a
button
switch, a keypad, a swipe card, or the like. If strike assembly 210 were to be
configured
with constant-current circuits 20 or 50, because of its size, the PCB (with
included
MOSFET 24) would have to be mounted somewhere remote from electric strike
assembly 210 making conversion of strike assembly 210 to constant-current
circuit
configuration difficult.
Referring to FIGS. 6A and 6B, in accordance with the invention disclosed in
the
'464 Application, solenoid assembly 315, including integrated constant-current
control
circuit is shown. Solenoid assembly 315 includes solenoid bracket 317,
solenoid driver
316 and generally planar PCB 120. Cavity 314 of bracket 317 is sized to
receive
solenoid driver 316. When solenoid driver 316 is energized, plunger 372 of
solenoid
driver 116 interacts with actuating components (not shown) of associated
electromechanical device 310 such as an electrical latch or strike, thereby
placing the
latch or strike in its locked or unlocked state as known in the art. Flange
330 may
extend outward from housing and includes mounting holes 322 for mounting
solenoid
assembly 315 to the associated electromechanical device 310 with appropriate
fasteners (not shown). With the reduced footprint of GaNFET 124, PCB 120 may
be
attached with fastener 332 to solenoid driver 316 and made part of solenoid
assembly
315. Feed wires 326 provide electrical connectivity to PCB 120 and to solenoid
driver
316, as needed.
Thus, in accordance with the invention disclosed in FIGS. 6A and 6B of the
'464
Application, an electromechanical device 210 without a constant-current
control circuit
may be readily converted to one with a constant-current control circuit by:
a) providing a first electromechanical device 210 without a constant-current
control circuit, wherein the first electromechanical device 210 includes a
first solenoid
assembly 215 comprising a solenoid driver 216a;
b) removing the first solenoid assembly 215;
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Date recue/date received 2021-10-22
C) providing a second solenoid assembly 315 comprising a solenoid driver 316
and PCB 120;
d) replacing the removed first solenoid assembly 215 with second solenoid
assembly 315; and
e) making the required feed wire connections to convert the first
electromechanical device 210 to a second electromechanical device 310 having
said
constant-current control circuit.
Referring to FIGS. 7A and 7B, an alternate embodiment of a solenoid assembly
415 with an integrated constant-current controller circuit in accordance with
the
invention disclosed in the '464 Application is shown. Solenoid assembly 415
includes
solenoid mounting bracket 417 and solenoid driver 416. When solenoid driver
416 is
energized, plunger 472 of solenoid driver 416 interacts with components (not
shown) of
the electromechanical device shown schematically as 410. In the case of an
electrical
latch or strike, such interaction places the associated latch or strike in its
locked or
unlocked state as known in the art. Tab 430 may extend from mounting bracket
417 for
mounting solenoid assembly 415 to the associated electromechanical device by
appropriate means as known in the art. With the reduction in size of GaNFET
124, PCB
420 may be flexed into an arcuate shape as shown, assuming the general contour
of
the outer cylindrical surface of solenoid driver 416. The length (L) and
circumference
(C) of solenoid driver 416 are sized to accommodate the width (17.53mm) and
length
(24.13mm) of PCB 420, when flexed. As shown in FIG. 7B, flexed PCB 420 may be
bonded to the cylindrical surface 440 of solenoid driver 416 as known in the
art. A wrap
444 may then by placed over flexed PCB 420 for protection. Feed wires (not
shown)
provide electrical connectivity to PCB 420 and to solenoid driver 416, as
needed.
With respect to the embodiment shown in FIGS. 7A and 7B of the '464
Application, an electromechanical device 210 without a constant-current
control circuit
may be readily converted to one with a constant-current controller circuit by:
a) providing a first electromechanical device 210 without a constant-current
controller circuit wherein the first electromechanical device 210 includes a
first solenoid
assembly 215 comprising a solenoid driver 216a;
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Date recue/date received 2021-10-22
b) removing the first solenoid assembly 215;
C) providing a second solenoid assembly 415 comprising a solenoid driver 416
and integrated PCB 420;
d) replacing the removed first solenoid assembly 215 with said second solenoid
assembly 415; and
e) making the required feed wire connections to convert the first
electromechanical device 210 to a second electromechanical device 410 having
the
constant-current controller circuit.
Thus, solenoid assemblies 315 and 415 may be built into an "as-manufactured"
electromechanical device with a self-contained constant current circuit or
serve as a
"drop-in" replacement for a standard solenoid used in an existing
electromechanical
device thereby converting the standard circuit to a constant-current control
circuit so as
to provide the increased efficiency and power savings enjoyed by the circuit
disclosed in
the '242 Patent.
While the above Description of the Preferred Embodiments has disclosed novel
and/or improved constant-current control circuits, assemblies and methods of
using the
same, the Description has heretofore been silent as to a control circuit which
can
selectively supply a current at a latch system's vibrational resonant
frequency so as to
overcome a preload condition placed upon a latch or strike keeper (hereinafter
referred
to as a preloaded latch) of the associated latch system. As is known in the
art, a square
wave current is supplied to the actuating solenoid having a certain frequency
suitable to
provide the needed current to the solenoid (both the pick and hold currents)
to move the
latch to its retracted position. The frequency of the square wave current
supplied to the
solenoid also induces a sinusoidal vibration wave of the same frequency to the
latch
system employing the solenoid.
It has been found that, if a sinusoidal vibration wave can be imposed on the
latch
system by the controller at the natural (resonant) frequency of the latch
system, the
"resulting vibration" of the latch system imposed by the sinusoidal wave
causes the pre-
loaded latch to release. The natural frequency of the latch system that causes
the
resulting vibration is believed to be dependent, at least in part, on the mass
of the
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Date recue/date received 2021-10-22
components of the latch system involved in the unlatching event and other
forces
placed on these components. Accordingly, in the event of a preloaded latch
preventing
retraction of the latch, if the frequency of a pick current supplied to the
solenoid by the
constant circuitry disclosed in the '242 Patent and the '464 Application were
to be
selectively varied to sweep past the resonant frequency of the latch system to
induce
the resulting vibration, the disclosed circuitry could be used to selectively
induce the
resulting vibration upon the latch system to free the preloaded latch. Once
the latch is
released, the current frequency supplied to the solenoid may then be returned
to a
lower modulation needed to hold the solenoid in its energized state and to
keep the
.. latch retracted.
Turning now to FIG. 8, a schematic of an exemplary circuit 500 for inducing
resulting vibration upon a latch system having a preloaded latch includes a
power
supply 502, FET 504 which may be either MOSFET or GaNFET described above, a
function generator, such as but not limited to waveform generator 506, and
solenoid 508
which may generally represent a solenoid driver of an electromechanical
device, such
as electromechanical device 210 or 310. During operation, power supply 502 is
activated upon receipt of a valid instruction at a remote switch (e.g., a
credential device
such as a key pad or swipe card, etc.). Power supply 502 may then output the
pick
current to solenoid 508 so as to release the latch, then to return to a hold
current as
described above.
In accordance with an aspect of the present invention, the supplied voltage
from
power supply 502 may be conditioned by waveform generator 506 to induce a
resulting
vibration upon the latch. In one embodiment, upon installation of the latch
system, an
installer may utilize waveform generator 506 to sweep a range of frequencies
until
inducing a resulting vibration upon the latch system. For example, a resulting
vibration
upon the latch system may be identified by noting a frequency (i.e., a target
frequency)
in the swept frequency range where an audible vibration of the latch system
may be
heard, for example, 45Hz. The target frequency or a range of frequencies
surrounding
the noted target frequency of the generated waveform causing the vibration,
for
example, +/- 20 Hz of the noted target frequency, may then be recorded and
saved
Date recue/date received 2021-10-22
within a system memory located on the PCB, such as PCB 120. Solenoid 508 may
then
receive the pick current at the target frequency or the saved range of
frequencies each
time power is supplied to the solenoid to assure retraction of the latch. In
the
alternative, the target frequency or saved range of frequencies may be
provided to the
solenoid only when a latch preload condition is sensed, as described below.
In accordance with a further aspect of the present invention, the resonant
frequency of the latch system needed to induce the resulting vibration upon
the latch
system may change over time, such as due to wear and tear on the various
components of the latch system or as a result of environmental changes. As a
result,
the previously saved target frequency or range of frequencies may not cover
the
frequency needed to induce the resulting vibration upon the latch system to
release the
latch when the latch system is under preload. To remedy this, waveform
generator 506
may be configured to re-sweep the frequencies a preset intervals or preset
intervals
until an updated target frequency of updated range of frequencies of the latch
system is
determined to present a frequency that causes a resulting vibration of the
latch system.
This updated target frequency or updated range of frequencies may then be
recorded
and saved within the system memory. Solenoid 508 may then receive the pick
current
at the updated target frequency or updated range of frequencies each time
power is
supplied to the solenoid.
Further, the preload condition may vary wherein the latch experiences only a
periodic preload condition such as when an occasional wind blows against the
door or
when an exiting person pushes the door to open before the latch or keeper has
time to
retract. In that situation, instead of providing the target frequency or saved
range of
frequencies each time power is provided to the solenoid, the target frequency
or saved
range of frequencies may be provided to the solenoid as pick current only when
a latch
preload condition is sensed.
In conjunction with this embodiment, a latch preload sensor 510 may be used to
sense a latch preload condition as shown schematically in FIG. 8. The latch
preload
sensor would sense when latch movement is sluggish or when the latch has not
moved
at all upon initiating a signal to open the latch. For example, latch preload
sensor 510
16
Date recue/date received 2021-10-22
may include a latch position sensor and a timer to sense a latch preload
condition. If a
predetermined amount of latch travel is not sensed by the position sensor
within a
predetermined period of time, the latch preload sensor could signal waveform
generator
506 to a provide a pick current to solenoid 508 at the target frequency or
saved range of
frequencies to overcome the preload forces and to retract the latch. The latch
position
sensor could then be used to confirm full retraction of the latch. If full
retraction is not
indicated, a further signal could be provided to again provide a pick current
at the target
frequency or saved ranges of frequencies, or at an enlarged range of
frequencies, and
an alert may be provided indicating that repairs to the latch system are
needed. As
further examples, the latch preload sensor may utilize any other mechanical,
electrical
or magnetic field strength sensing means for detecting a latch preload
condition.
Turning now to FIG. 9, shown is a flow chart illustrating an operating method
600
for releasing a preloaded latch of an electromechanical latch system in
accordance with
one aspect of the invention. At step 602, when the latch of an
electromechanical latch
system is in its default, locked condition, the solenoid driver of the latch
is not energized
(in this example, the electromechanical latch system is set to a fail-secure
mode). At
step 604, access credentials are presented to and verified by authentication
device
(e.g., keypad, biometric sensor, button, etc.) wherein the authentication
device
communicates with waveform generator 506 to supply a baseline pick current to
the
solenoid driver at a sufficient level to pull back the latch under normal
operating
conditions (i.e., when the latch is not preloaded). At step 606, latch preload
sensor 510
interrogates whether a latch preload condition exists. If the preload sensor
determines
that a latch preload does not exist, at step 608, a communication is provided
to
waveform generator 506 to reduce the baseline pick current to a hold current
610 to the
solenoid driver at a sufficient level to hold the latch in a released,
unlocked condition.
Upon receipt of the communication from the preload sensor by the waveform
generator
at step 608, the hold current may be supplied by the waveform generator after
a
predetermined period of time elapses since application of the baseline pick
current to
assure retraction of the latch is complete or after retraction of the
latch/keeper is
.. confirmed by preload sensor 510.
17
Date recue/date received 2021-10-22
If the preload sensor determines that a latch preload does exist at step 606,
a
communication is provided to waveform generator 506 at step 612 to supply a
pick
current at a predetermined target frequency or range of frequencies sufficient
to free the
latch from its preload condition to a released, unlocked condition.
Thereafter, the
method may proceed to step 610, applying a hold current to the solenoid driver
as
described above. If a latch preload condition continues to be sensed by the
preload
sensor, the target frequency or range of frequencies may be reapplied, or an
enlarged
range of frequencies may be applied as a pick current and an optional alert
signal may
be provided indicating that repairs to the latch system are needed.
In the above described method, at step 612, the range of frequencies
sufficient to
free the latch to a released, unlocked condition has been previously
determined. In
another aspect of the invention wherein the range of frequencies has not been
predetermined, after the latch preload sensor has sensed that a latch preload
exists,
waveform generator may supply current at a varying frequency, sweeping the
frequency
between the baseline pick current frequency and a pre-designated, outer limit
of pick
current frequencies so as to force the latch system to vibrate and to release
the
preloaded latch. Once the current frequency sweep is completed sufficient to
free the
latch, the method proceeds to steps 608 or 612 as discussed above.
In yet another embodiment, each time access credentials are presented to and
verified by the authentication device, the baseline pick current is provided
to the
solenoid driver as in step 604, followed by a sweep through the predetermined
range of
frequencies needed to free a latch from a preload condition in the event the
latch is
preloaded to assure that the latch becomes fully retracted. A preload sensor
may be
added to confirm full latch retraction.
While the invention has been described by reference to various specific
embodiments, it should be understood that numerous changes may be made within
the
spirit and scope of the inventive concepts described. Accordingly, it is
intended that the
invention not be limited to the described embodiments, but will have full
scope defined
by the language of the following claims.
18
Date recue/date received 2021-10-22
