Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PATENT - 9D-MA-16819 - Payne
BACKEROU~ID OF THE INYENTION
This invention relates generally to glass-ceramic cooktop
appliances and particularly to electronic power control systems for
such apptiances.
Use of glass-ceramic plates as cooktops is well known.
Advantages of the smooth surface include pleasing appearance and easy
cleanability. Glass-ceramic cooktop appliances using heating units
which radiate substantially in the infrared region in combination with
a glass-ceramic material which is transparent to such radiation
provides the appearance and convenience advantages of conventional
thermal conduction type glass-ceramic cooktops plus the additional
advantage of greater energy efficiency and improved cooking performance
due to a faster response to changes in user selected power settings.
- Infrared heating units employ resistance wire elements
designed to radiate primarily in the 1-3 micron region of the
electromagnetic spectrum. The total output power and watts density
parameters for the heating elements in such units is dictated by
cooking performance requirements. For domestic app7iances the power
supply available in the home is aenerally the line voltage from the
local power company. In the United States this is typically 120 and
240 volts. Resistance wire heating elements designed to provide the
desired power and watts density at these voltages are constructed of
relatively small diameter delicate expensive wire. Significant cost
advantages could be enjoyed if the wire diameter could be increased
thereby increasing the structural integrity of the wire and making it
possible to use a less costly wire material. However, with the power
and watts density constrained by cooking performance requirements, any
increase in wire diameter must be compensated for by a decrease in
voltage. In view of the high current required to provide the des1red
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PATE~T - 9D-MA-16819 - Payne
power, a step-down transformer would be impractical from both a size
and cost standpoint.
Thus, to enjoy the benefits of a less costly, ~ore reliable
infrared heating unit there is a need for a cost effective practical
energy efficient means of reducina the effective voltage apptied to the
heating units to an effective voltage level less than a domestic line
voltage.
Another consequence of increasing wire diameter is that the
time required for the wire to reach its radiant temperature is
increased. Infrared heating units, at least when operating at or near
the maximum user selected power setting, glow brightly. ~his glow is
perceivable by the user through the glass-ceramic cooktop. This glow
can be advantageously used to provide prompt visual feedback to the
user that the selected unit is operating properly. One such
arrangement for rapidly bringing a heating element to its radiatina
temperature to provide this feedback using commercially available
heating elements made of molybdenum disilicide (~loSi2) or tungsten
heating elements is disclosed in commonly assigned U.S. Patent
4,223,4g8. In that arrangement the unit is driven at the power level
associated with the maximum user selectable power setting for a brief
period when first turned on, reoar~ ess of the actual user selected
setting to quickly heat the unit to its radiating temperature
Since the heating element with the increased wire diameter was
designed for operation at a lower effective or RMS voltaae, the heat up
time can be reduced to an acceptable time by briefly over-driving the
heating element at full line voltage. However, the overdrive time must
be carefully limited to avoid over-stressing the wire. For example, if
the unit is turned off and then on again before it has cooled
sufficiently, applying the full line voltage for a time period ~hich
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PATENT - ~D-M~-1681g - Payne
has no adverse affect on the wire when heating up from room temperature
may damage the pre-heated wire. Use of wire temperature feedback
information is impractically costly and complex. Thus, in a system in
which the heating elements are designed primarily for operation at
voltage levels less than the full line voltage, there is a need for a
power control arrangement which can provide an overdrive capability for
the elements when turned on but which can adjust the overdrive time to
compensate for the past temperature history of the element.
In a multiple element cooktop appliance featuring heating
units with elements designed for operation at a voltage stepped down
from the normal line voltage, overdriving the elements at`full line
voltaoe for short periods of time may draw excessive total current.
Household electrical service generally employs a SO amp breaker in the
powe~ circuit for the main kitchen cooking appliances. In a four-unit
cooktop appliance for example, the total current is limited by
conventional design practice to a maximum level of 35 amps leaving 15
amps for the oven. Since this limit could be exceeded if one or more
of the heating units is overdriven depending on the power levels being
applied to the remaining units, there is a need for a power control
arrangement which can adjust the overdrive power levels to maintain the
totàl current drawn by the heating units within design limits, while
still heating the units to radiating temperature relatively quickly to
provide the desired visual feedback to the user.
It is therefore an object of the present invention to provide
an electric cooking appliance comprising at least one electric heating
unit and a power control system which applies an effective voltage
level to the heating unit at the maximum user selectable power setting
for the unit which is less than the ~lS voltage of the domestic power
supply so as to accommodate in the appliance heating units designed for
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~ PATE~JT - 9D-MA-16819 - Payne
maximum steady state operation at a voltage level less than the
domestic supply voltage~
It is a further object of the present invention to provide a
cooking appliance of the aforementioned type in ~hich the power control
system is operative to overdrive the heating units when initially
turned on by applying a voltage level higher than the maximum user
selectable level for a brief transient heat up period, the duration of
which is limited as a function of the elapsed time stnce the last
occurring use of the particular heating unit to avoid overheating a
heating unit which is not yet cooled down from its previous use.
It is yet another object of the present invention to provide a
cooktop appliance of the aforementioned type in which the power control
system is operative to reduce the power level applied to the surface
units during operation in the transient heat up period as necessary to
maintain the total current drawn by the appliance within predetermined
limits.
SUMMARY OF THE INVENTIO~I
The present invention provides a cool~ina appliance adapted for
energization by a standard domestic household power supply
characterized by an output power signal with a predetermined RMS output
voltage, the appliance comprising at least one electric resistive
Heating unit designed for steady state energization at a maximum RMS
voltage level less than the RMS voltage level of the output power
signal of the external power supply. User actuable input selection
means enables tne user to select one of a plurality of power settings
including an Off setting for the heating unit. Power control means
responsive to the input selection means is operative to couple power
pulses from the external power supply to the heating unit at one of a
plurality of available pulse repetition rates, each user selectable
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PATENT - 9D-M~-16819 - Payne
power setting having associated with it a corresponding power pulse
repetition rate, each repetition rate establishing a corresponding RMS
voltage level for application of power to the heating unit. The
repetition rate associated with the maximum user selectable power
setting is effective to apply an R~S voltage level to the heating unit
which corresponds to ~le voltage level for which the heating unit was
designed. By this arrangement the appliance can be equipped with
heating units designed for operation at a voltage levet less than the
normal supply voltage, yet which prov;de the output power and watt
density normally associated with heating units designed to operate at
the normal domestic supply voltages.
In accordance with another aspect of the invention, the power
control means includes timing reans for measuring the elapsed time
since the unit was last turned off by the user, and means for detecting
the transition from an Off power setting to one of the non-Off power
settings. Upon detection of such a transition the power ccntrol means
is operative to implement a power pulse repetition rate ~)ich
establishes an RMS voltage level for the heating unit which is higher
than the maximum user selectable level, and preferably equal to the RtlS
voltage level of the external power supply output signal, for a
transient heat up period. The duration of this transient heat up
period is controlled as a function of the elapsed time since the unit
was last turned off as determined by the timing means whereby the
heating unit is protected against damage from overheating in the event
sufficient time has not elapsed for it to cool since its last occurring
use.
In accordance with yet another aspect of the invention,
particularly applicable to a cooking appliance comprising multiple
heating units designed for steady state energization at a maximum ~MS
PATENT - 9D-MA-16819 - Payne
voltage level less than the RMS voltage level of the power signal from
the external supply, the power control means further comprises means
for determining when the total current drawn by the heating units
exceeds a predetermined reference limit and means for reducing the
effective voltage level applied to each of the heating units to reduce
the total current to less than this limit. In a preferred form of the
invention, each of the power pulse repetition rates implementable by
the control means is assigned numerical designator. The means for
determining when the total current exceeds the reference limit
compri`ses means for computing the sum of the numerical designators
corresponding to the power pulse repetition rates then being applied to
each heating unit and comparing this sum to a predetermined reference
value corresponding to the maximum acceptable total currenè for the
heating units. The control means is operative to lower the repetition
rate being applied to each of the heating units until this sum is less
than the reference value. The control means is further operative to
extend the duration of the transient heat up period for heating units
operating in the transient heat up mode when the repetition rate being
applied to such units is lowered, so as to compensate for the reduction
in the effective voltage level applied to the overdriven units so that
the heating units are still heated to radiating temperature relatively
quickly to provide the desired visual feedback to the user.
While the novel features of the invention are set forth with
particularity in the appended claims, the invention both as to
organi~ation and content will be better understood and appreciated from
the following detailed description taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a portion of a cooktop
illustratively embodying the power control system of the present
PATENT - 9D-M~-16819 - Payne
invention;
FIG. 2 is a sectional side view of a portion of the cooktop of
Fig. 1 showing details of one of the heating units;
FIG. -~ is an enlarged top vie~l of a portion of the cooktop of
Fig. 1 showing details of the heating unit;
FIG. 4 is a functional block diagram of the power control
circuitry for the cooktop of Fig. l;
FIG. S illustrates power signals corresponding to various
operator selectable power settings and a timing signal for sychroni2ing
control system operat;on with the power signal;
FIG. 6 is a simplified schemat;c diagram of a control circuit
illustratively embodying the power control system of the present
invention as embodied in the cooktop of Fig. l;
; FIG. 7 is a flow diagram of the Scan routine incorporated in
the control program for the microprocessor in the circuit of Fig. j~,
. ,.~ . .
FIGS. 8A and 8B are flow diagrams of the Keyboard Cecode
routine incorporated in the control program for the microprocessor in
the circuit of Fig. 6;
FIG. 9 is a flow diagram of the Off Timer rDutine incorporated
in the control program of the microprocessor in the circuit of Fig. 6;
FIGS. lOA and lOB are flow diagrams for the Instant Cn routine
;ncorporated in the control program of the microprocessor in the
circuit of Fig. 6;
FIG. 11 is a flow diagram of the PSET routine incorporated in
the control program of the microprocessor in the circuit of Fig. 6;
FIG. 12 is a flow diagram of the Power Out routfne
incorporated in the control program of the microprocessor in the
circuit of Fig. 6; and
FIG. 13 is a flQw diagram of the PWRSUM routine incorporated
in the control program of the microprocessor in the circuit of Fig. 6,
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PATENT - 9D-MA-16819- Payne
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
Overview
Fig. 1 illustrates a glass-ceramic cooktop appliance
designated generally 10. Cooktop appliance 10 has a generally planar
glass-ceramic cooking surface 12. Circular patterns 13(a)-13(d)
ident;fy the relative lateral positions of each of four heatfng un;ts
~not shown) located directty underneath surface 12. A control and
display panel generally designated 15 includes a complete set of touch
control keys 17 and a seven-segment digital LE~ display element 19 for
ea`ch heating unit.
The term glass-ceramic with reference to the material
comprising cooktop surface 12 refers to a boron silicate m~terial in
the Ceran family of materials. In particular in the illustrative
en~odiment the glass-ceramic material is an infrared transmissive
7~)
glass-ceramic material designated Ceran-85'manufactured by Schott,
Incorporated.
In the discussion to follow the designators 14(a) - 14(d)
shall be understood to refer to the heating units disposed under
patterns 13(a) - 13(d) respectively. Surface unit 14(a) is shown in
greater detall in Figs. 2 and 3. For purposes of illustration only one
of the heating units is shown. It will be understood that heating
units 14(b) - 14(d) are similar in structure to that shown in Figs~ 2
and 3. Heating units 14~a) and 14~c) are 8 inches in diameter. Units
14~b) and 14~d) are 6 inches in diameter.
Referring again to Figs. 2 and 3, heating unit 14~a) comprises
an open coii electrical resistance element 16 of spiral configurat;on,
which is designed when fully energized to radiate primarily in the
infrared ~1-3 micron) region of the electromagnetic energy spectrum.
Element 16 is arranged in a concentric coil pattern and staked or
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PATENT - 9D-MA-16819 - Payne
otherwise secured to a support disk 18 formed of Micropore material
such as is available from Ceramaspeed under the name Microtherm' Disk
18 is supported in a sheet metal support pan 20, by an insulating liner
22 formed of a conventional aluminum oxide, silicon oxide composition.
This insulating liner 22 includes an annular upwardly extending portion
22(a) which serves as an insulating spacer between disk 18 and the
underside of glass-ceramic cooktop 12. ~hen fully assembled, pan 2~ is
spring loaded upwardly forcing the annular portion 22(a) of insulating
liner 22 into abutting engagement with the underside of cooktop 12 by
support means not shown. Heating units 14(a) - 14(d) are manufactured
and sold commercially by Ceramaspeed under the part name. Fast Start
Radiant Heater with Concentric Coil Pattern.
Fig. 4 illustrates in simplified schematic form, an embodiment
of-a heating system to be controlled in accordance with the present
invention. Each of four heating units 14(a) - 14(d) is coupled to a
standard 240 volt, 60 Hz AC power source via power lines Ll and L2
through one of four triacs 24(a) - 24(d) respectively, the heating
circuits being connected in parallel arrangement with each other.
Triacs 24(a) - 24(d) are conventional thyristors capable of conducting
current in either direction irrespective of the voltage polarity across
their main terminals when triggered by either a positive or negative
voltage applied to the gate terminals.
The power control system 26 controls the power applied to the
heating units by controlling the rate at which gate pulses are applied
to the triac gate terminals in accordance with power setting selections
for each heating unit entered by user actuation of tartile touch
membrane switch keyboard 28 comprising touch keys 17 (Fig. 1). The
columns of keys designated SU0 through SU3 provide the control inputs
for heating units 14(a) - 14(d) respectively.
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PATENT - D-MA-16819 - Payne
In the illustrative embodiment gate signals are applied to
triacs 24(a) - 24(d) to couple power pulses to the heating units. Each
pulse is a full cycle of the 240 ~olt, 60 Hz AC power si~nal; howe~er,
power signals of different frequencies and voltaae levels such as 120
volts, 60 Hz or 220 ~olts, 50 H~ could be similarly used.
A plurality o~ discrete power levels are pro~ided, each having
uniquely associated with it a particular power pulse repetition rate.
In the illustrati~e embodiment fifteen non-Off power levels are
implementable by the control system. ~ine power settings correspond;ng
to power levels 1-9, plus Off and Cn are selectable for each heating
unit by user actuation of the keys in keyboard 2~. The six hiahest
power levels designated A-F are not user selectable. These levels are
used to overdrive the heating units when operating in a transient heat
up mcde to rapidly heat the units to radiant temperature as will be
hereinafter described. Table I shows the pulse repetition rate
associated with each power level.
TABLE I
Look Up Table
Power Pulse
Power Power Repetition
5ettings Level Rate Address Power Pulse Code Watts
OFF O - TBLADDR 0000 0000 0000 0000 0
0~l 0 - TBLADDR 0000 0000 0000 0000 0
1 1 1/64 TBLADDR +8 8000 0000 0000 0000 60/40
2 2 1/32 TBLADDR +10 8000 0000 8000 0000 120/75
3 3 ~f~ TBL~DDR +18 8000 8000 8000 8000 230/150
4 4 :kf4 l/~ TBLADDR +20 8080 8080 8080 8080 400/275
10/64 TBLADDR +28 8088 8QaO 8088 8080 65Q/425
6 6 15/64 TBLADDR t30 8888 8888 8888 8880 875/fiOO
7 7 21/64 TBLADDR +38 AA88 A888 A888 A888 1225/800
8 8 28/64 TBLADDR +40 AA8A M 8A M 8A AA8A 1650/1100
9 9 36/64 TBLADDR +48 E M A E M A EAAA E M A 2100/14QO
A 41/64 TBLADDR +50 EEEA EAEA EAEA EAEA 2400/1600
B 45/64 TBLADDR +58 EEEE AEEE EAEE EEAE 2650/1750
C 51/64 TBLADDR +60 FEEE EEEE FEEE FEEE 2900/1900
D 55/64 TBLADDR +68 FEFE FEFE FEFE FEEE 3150/2100
E 59/64 TBLADDR +70 FFEF FEFF EFFE FFEF 3400/2250
F 64/64 TBLADDR +78 FFFF FFFF FFFF FFFF 3700/2450
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PATE~T - 9D-MA-16819 - Payne
The power pulse code in Table I represents 64-bit control
words in hexadecimal format. These control words are used to implement
the corresponding pulse repetition rates. The basic control period
comprises 64 full cycles of the 60 Hz power signal. The distribution
of ON power pulses over this 64 cycle control period for each power
setting is defined by the bit pattern of the associated control word.
0~ pulses or cycles are represented by logical one bits and Off cycles
by logical zero bits respectively. Thé repetition rates for the user
selectable power settings have been empirically established to provide
a range of power settings for good cooking performance in the appliance
of the illustrative embodiment. The bit patterns have been selected to
minimize the duration of idle or OFF cycles for each power level.
As shown in Table I, the pulse repetition rate for the first .
four power settings range from 1 ON pulse per 64 power cycles for power
setting 1, the 1 ~lest non-Off power setting, to 1 0~1 power pulse for
every 8 cycles for power level 4. In Fig. 5 waveforms A-D represent
the voltage applied to heating element for each of power settings 1
through 4 respectively. Wave form E represents the power signal
appearing across lines Ll and L2. P wer pulses or ON cycles are
represented by full lines. Those cycles of the power signal during
which the triac is non-conductive are shown in phantom lines.
One aspect of the present invention involves a novel
application of the repetition rate power control concept disclosed in
commonly assigned U.S. Patent 4,256,951. As mentioned briefly in the
Background discussion, significant cost and reliability beneff ts can be
enjoyed if the appliance can accommodate heating units designed for
operation at an effective or RMS voltage level less than the 240 volt
supply leYel. As used hereinafter the phrase "designed for operation
at a particular voltage" with reference to a heating unit shall be
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PATFNr - CD-MA-16819 - Payne
understood to mean that the unit is designed to provide the maximum
output power and watts density desired for good cooking performance
when that particular effective or RMS voltage is applied to the unit.
A reduction of the effective Yoltage for which the unit is designed
permits an increase in heating element wire diameter to provide better
structural integrity without compromising on the power and watts
density specifications essential to good cooking performance.
Heating element wire manufacturers have determined that a less
costly, structurally stronger, heating unit which provides the output
power and watts density normally associated with the heating element
designed to operate at line voltages can be designed for operation at
about 75~ of line voltage. h r example, a unit can be designed for
operation at 180 volts RMS which provides the output power and watts
density normally associated with a unit designed to operate at 240
volts RMS. Similarly, a unit can be designed to operate at 90 volts
RM5 and provide the output power and watts density ~ormally associated
with a unit designed to operate at 120 volts PMS.
In accordance with the present invention the RMS voltage
applied to the heating unit is effectively stepped down from the
typical supply line voltage of 240 volts to the voltage level for which
the unit is designed by determining the repetition rate which provides
in RMS voltage equal to the design voltase and assigning this rate to
the maximum user selectable power setting.
Repetition rate control can be used to step down the effective
or RMS voltage applied to the heating unit, provided the time base is
properly selected, because when power switching is conducted at a
switching rate which provides On and Off times which do not exceed the
same order of magnitude as the thermal time constant of the wire
heating material, the voltage in terms of heating effect or output
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PATENT - 9D-~A-16819 - Payne
power is approximately equal to the RM5 value of the supply voltage
reduced by a factor equal to the square root of the ratio of the number
of On cycles to the total number of cycles in the control period. This
relationship is expressed in the equation listed below.
YR~S Vpeak ~ 1/2 X (umber of on cycle
Total Cycles in Control Perio
The thermal time com tant of heating element wire is on the
order of 800 milliseconds, varying slightly with wire radius. ThuS, a
control period of 64 cycles is of the same order of nagnitude as the
thermal time constant for the heating unit of the illustrative
embodiment. U5ing the foregoing equation, a ratio of 36 Gn cycles to
64 total cycles provides an effecff ve PMS voltase of 180 volts for the
peak supply voltage of 339 volts associated with the standard 240 volt
PMS 60 Hz domestic supply. -
AS sh~m in Table I the maximum user selectable power settingin the illustrative e~bodiment is power setting 9. The corresponding
power level iS defined by a repetition rate of 36 On cycles per 64
total control period cycl es.
One undesirable consequence of heating units designed to
operate at lower voltage levels iS that the increased wire diameter
extends the time required to heat the wire to itS visually radiating
temperature when operated at the voltage level corresponding to the
maximum user selectable power setting. For example, in the
illustrative embodiment the time required for the unit designed for
operation at 180 volts to reach the visible radiating temperature at
power level 9 iS on the order of 30 seconds. For purposes of prompt
visual feedback to the user thiS iS undesirably slow. A heat Up time
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PATENT - 9D-MA-16819 - Payne
not significantly greater than 4-6 seconds is preferred. To this end,
in accordance with another aspect of the present invention, upon
detecting a change in power setting from Off to a non-Off power
setting, an overdrive power level higher than the power level
associated with the maximum user selectable setting is applied to the
unit for a relatively short transient heat up period of time, long
enough to bring the heating unit to its radiating temperature quickly
but not so long as to subject the unit to excessive thermal stress.
In the illustrative embodiment when the heating element wire
is at or near room temperature, the unit can be operated at full line
voltage for up to 5 seconds without undue stress on the wire. However,
if the unit is turned from Off to On without sufficient time to allow
the unit to cool adequately from a previous On period, operation of the
unit at full power for the normal 4-5 seconds could, if repeated over a
period of time, lead to a premature failure of the unit. To protect
against such damage, in accordance with the present invention timing
means is provided to measure the Off time, that is the elapsed time
since the last occurring OFF setting was selected by the user. The
power control system is operative in response to the timing means to
vary the duration of the next occurring transient heat up period as a
function of Off time so as to establish a shorter heat up period when
the elapsed time indicates that the wire has not had adequate time to
cool since a previous usage.
In the illustrative embodiment the timing means compares the
elapsed time to three successively increasing reference times. The
transient heat up period is selectively limited to one of four
corresponding predetermined heat up time periods, the selected one of
the time periods corresponding to the longest of the reference times to
be exceeded. The predetermined reference times are 3 seconds, 14
PATENT - 9D-MA-16819 - Payne
seconds, and 60 seconds. If the unit has been turned Off for less than
approximately 3 seconds, the overdrive power level is applied for
approximately 1 second; if the Off time is greater than 3 but less than
1~ seconds, the overdrive power level is applied for approximately 2
seconds; if the Off time is greater than 14 but not greater than 60
seconds, the overdrive power level is applied for approximately 3
seconds; and finally if the elapsed Off time is greater than 60
seconds, the overdrive power level is applied for approximately 4
seconds.
These specific reference times and heat up periods have been
found to provide satisfactory results for the heating units of the
illustrative embodiment. It will be appreciated, however, that these
values are provided for purposes of illustration and are not to be
considered as limitations on the invention.
Gverdriving the heating unit at an overdrive power level
corresponding to full line voltage or 100~ power brings the heating
unit to its radiating temperature quickly. However, in a multiple unit
cooktop such as that of the illustrative embodiment, the maximum
current which can be drawn by the appliance at a given time is limited,
thereby limiting the total output power available from the heating
units. This current limit may be exceeded by applying full line
voltage in the heat up mode depending on what power levels are set by
the user for the other heating units.
In view of the standard use of 50 amp circuit breakers for the
domestic kitchen range power circuit, it is good design practice to
limit the current to the cooktop to approximately 35 amps. Assuming
supply voltage variations of +10~ and +5~ variation in the resistance
of the heating units the extreme case current load is presented by a
llO~ voltage variation and a -5~ resistance variation. A maximum
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PATENT - 9D-MA-16819 - Payne
current limit of 35 amps at 264 volts ~240 votts ~lOX) defines a
maximum output power limit of 9240 watts for the four un;t cooktop.
In accordance with the present invention means are provided
for determining when the total current being drawn by the heating units
is greater than a predetermined limit, and for reducing the voltage
from full line voltage to a lower voltage level to bring the total
current load within acceptable limits.
In a preferred form of the invention the means for detecting
excess current computes a sum representing the maximum output power of
the appliance for the power levels then being applied to each of the
- heating units. When this sum exceeds a predetermined maximum value,
power levels are adJusted until the sum is less than the reference. In
the illustrative embodiment the implementable repetition rates are
represented by the corresponding numerical power level designators.
The power level designators are summed and compared to a reference
value representing the power level sum corresponding to the maximum
power limit. Output power data for each of the six inch and eight inch
units for the cooktop of the illustrative embodiment under both the
nominal and extreme tolerance conditions are listed in Table II for the
maximum user selectable power settings 8 and 9 and the top three power
levels available during operation in the transient heat up mode.
'
TABLE II
P~ler 6" Unit 8" Unit
Level N~minal Extreme Nominal Extre~e
8 1100 1380 1650 2065
9 1400 1780 2100 2670
D 2100 2730 3150 4090
E 2250 2910 3400 4370
F 2450 3170 3700 4750
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PATENT - 9D-MA-16819 - Payne
Using the data from Table II for extreme Yoltage and
resistance conditions, with all four units operating at the power level
corresponding to the maximum user selectable power level, power level
9, the total combined output power for the two 6" and two 8" units is
8900 watts. This is 340 watts less than the above defined maximum
power limit of 924Q watts. As can be seen in Table II, a one power
level change, particularly with respect to the top three power levels,
corresponds to approximately three to four hundred watts difference in
output power for a single heating unit. Thus this 340 watt difference
corresponds to a power level change of approximately one power level.
In the illustrative embodiment with all four heating units
operating at power level 9 the sum of the power levels is 36. This sum
represents the maximum output power value of 8900 watts. An increase
of one additional power level for one surface unit would place the
total output power at approximately the maximum desirable limit of 9240
watts. Thus a maximum power level sum of 37 would meet the maximum
power and corresponding current limit requirements under all possible
operating conditions. However, a power level sum of 38 satisfactorily
meets the maximum power conditions under all operating conditions
reasonably likely to occur. Thus, 38 is employed in the illustrative
embodiment as a reference value for the reference maximum sum of power
levels for the appliance. No adiustments to the power level applied to
any of the heating units is made to limit the current until the sum of
the power levels exceeds the total 38.
For example assume one 8" heating unit is operating in the
transient heat up mode with the maximum overdrive power level, power
level F, being applied and the remaining three heating units are
operating at the maximum user selectable power level, power level 9.
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PATENT - 9D-MA-16819 - Payne
The sum of the power levels in this case is 42 and the total output
power is 10980 watts~ Reducing the power level of each heating unit by
one level lowers the sum to 38 and lowers the total output power to
9195 watts which is slightly less than the allo~able maximum of 9240
watts.
In order to limit the effect on any one heating unit, the
power level for each of the heating units may be lowered to bring the
total current within limits. In the illustrative embodiment, in order
to further limit the adverse affect on cooking performance for those
units not operating in the transient heat up mode, the power level for
such units is never reduced by more than one level to comply with the
current limits. If reducing the power level for all units by one level
is not sufficient, the power level applied to those units operating in
the transient heat up mode will be successively reduced one level at a
time until the total current as signified by the power level sum is
within acceptable limits. The power control system is operative in
response to this lowering of the power level being applied during
trinsient heat up mode to correspondingly increase the duration of the
transient heat up period to compensate for the lower power levels being
applied.
Microprocessor Embodiment
Fig. 6 schematically illustrates an embodiment of a power
control circuit for the cooktop of Fig. 1 which performs power control
functions in accordance with the present invention. In this control
system power control is provided electronically by microprocessor 40.
Microprocessor 40 is a M68000 series microprocessor of the type
commercially available from Motorola/. Microprocessor 40 has been
customized by permanently configuring its read only memory to implement
the control scheme of the present invention.
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PATENT - 9D-MA-16819 - Payne
As previously described with reference to Fig. 4, keyboard 28
is a conventional tactile touch type entry system. The keyboard array
comprises four columns of 11 keys each. Columns for controlling
heating elements are designated SUO through SU8 respectively. The keys
enable a user to select power levels 1 through 9 in addition to ~n and
Off for each of the four heating units. Keyboard 2~ has one input line
for each column commonly shared by all keys in that column and 11
output lines, one for each row of keys. Each particular column of
keyboard 28 is scanned by periodically generating scan pulses
sequentially at outputs P400 through P403 of microprocessor 40. These
pulses are transmitted as they appear to the corresponding column input
lines of keyboard 28. This voltage is transmitted essentially
unchanged to the output lines of all the untouched keys. The output of
an actuated key will differ, signifying actuation of the key in that
row and column.
In this manner each column of keyboard 28 is scanned for a new
input periodically at a rate determined by the control program stored
in the ROM of microprocessor 40. As will become apparent from the
description of the control routines which follow, each column is
scanned once every four complete power cycles of the power signal
appearing on lines Ll and N. The output from keyboard 28 is coupled to
input ports PlIO-PlIA of microprocessor 40 via a 410 parallel port
interface circuit.
A zero crossing signal marking zero crossings of the power
signal appearing on lines Ll and N from the power supply is input to
microprocessor 40 at input port P8IO from a conventional zero crossing
detector circuit 44. The zero crossing signal from circuit 44 is
illustrated as wave form F of Fig. 5. The pulses mark the position
going zero crossings of the power signal across lines Ll and N of the
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PATENT - 9D-MA-l68l9 - Payne
AC power supply. The zero crossing signals are used to synchronize thetriggering of the triacs with zero crossings of the power signal and
for timing purposes in the control program executed by microprocessor
40.
Microprocessor 40 transmits triac trigger signals from I/O
ports P500 through P~03 to the gate terminals of triacs 241a) ^ 2 (d)
respectively via a conventional 615 triac driver circuit. Triac driver
circuit 64 amplifies the outputs from ports P500-P503 of microprocessor
40 and isolates the chip from the power line. Display data is
transmitted from I/C ports P200-P20F. Display 58 is a conventional
four digit display, each digit comprising a 7-segment LED display.
Display information is coupled from I/O ports P200-P20F to the display
segments via a conventional 410 parallet port interface circuit 60 and
a conventional segment display decoder driver circuit 62 in a manner
well known ln the art.
Control Program
It will be recalled that microprocessor 40 is customized to
perform the controt functions of this invention by permanently
configuring the ROM to i~plement a predetermined set of instructions.
Figs. 7-13 are flow diagrams which illustrate the control routines
implemented in microprocessor 40 to obtain, store and process the input
data from the keyboard and generate control signals for triggering the
triacs in a manner which provides the power pulse repetition rate
required to apply appropriate power levels to each of the heating
un;ts. From these diagrams one of ordinary skill in the programming
art could prepare a set of instructions for permanent storage in the
ROM of microprocessor 40 which would enable the microprocessor to
perform the control functions in accordance with this invention.
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PATENT - g~-MA-16819 - Payne
The control program comprises a set of predetermined control
instructions stored in the read only memory (RoM) of microprocessor
40. A separate file in the random access memory (RAM) of the
microprocessor is associated with each of heating units l~a) - 14(d).
Each file stores the control inforration for its associated heating
unit ~ich is acted upon by the instructions in the ROM. Execution of
the control program is synchronized with the 60 Hz power signal such
that the set of control instructions in the ROM is cycled through once
during each cycle of the power signal. A file register common to all
four files functioning as a four count ring counter is incremented once
during each pass through the control program. The count of this file
reaieter identifies the RAM file to be operated on by the contrDl
instructions during the ensuing pass through the control program. By
this arrangement the control program is executed for any one particular
heating unit once every four cycles of the 60 Hz power signal.
The control program is logicall~ divided into a set of
sub-routines which includes the Scan routine, the Keyboard Decode
routine, the Off Timer routine, the Instant On routine, the PSET
routine, the Power Out routine, and the PwrSum routine. It will be
appreciated that other sub-routines may also be included to perform
control functions unrelated to the present invention.
The Scan routine lFig. 7), which contains the file register
identifying the RAM file to be acted upon during the ensuing pass
through the control program, sets the scan line for the keyboard column
associated with the heating unit which is the subject of the current
pass through the routine, reads the input from the keyboard for that
heating unit, and stores the user selected power setting selection
information in temporary memory. The Keyboard Cecode routine lFigs. 8A
and 8B) validates keyboard entries and updates the control variable
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PATENT - 9D-MA-16819 - Payne
representing the po~er level selected by the user as appropriate to
reflect the most recent valid user input for that heating unit. The
Off Timer routine (Fig. 9) determines the time elapsed since that
heating unit was last turned Off. This information is used in the
Instant On routine (Figs. lOA and 10~) to vary the duratSon of the
transient heat up period during which the unit is overdriven as a
function of how long the unit has been Off in accordance with the
present invention.
While the determination of what power level to be applied to a
heating unit is determined only during execution of the control program
for that particular heating unit, a power control decision must be made
for the ensuing power cycle for each of the units during each pass
through the program. The PSET routine (Fig. 11) obtains power level
information from each file during each pass through the routine,
- performs a table look-up for each heating unit to check the appropriate
bit for the power level control word for each heating unit, and
generates a four bit trigger control word which identifies which
heating units are to be triggered on and which are to be off during the
next power cycle. This four bit control word is then used by the Power
Out routine (Fig. 12) which monitors the input from the zero crossing
circuit and triggers those triacs associated with heating units to be
energized during the next power cycle into conduction upon detection of
the next occurring positive going zero crossing of the power signal.
The PWRSUM routine (Fig. 13) monitors the power level being
applied to each of the four heat;ng units and reduces power ievels as
necessary to limit the total current drawn by the appliance to within
acceptable limits. Each of these control r w tines will now be
described in greater detail with reference to its flow diagram in the
discussion to follow.
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PATENT - 9D-MA-16819 - Payne
SCAN Routine - FiG. 7
The function of this routine is to address the appropriate RAM
file for the current pass through the program, set the appropriate scan
line for the keyboard, and read in the input information from the
keyboard for the heating unit associated with the designated R~M file.
RAM file register SU functions as a four count ring counter which
counts from O to 3. Counts O through 3 of the SU counter identify R~l
files for surface units 14(a)-14(d) respectively.
Upon entering the Scan routine the register SU is incremented
(Block 102) and Inquiry 104 determines if SU is greater than 3. If so,
the counter is reset to O (Block 106). Next the address of the R~l
file to be acted upon during this pass through the control program is
set equal to SU (Block 108). The scan iine set during the previous
pass through the control program designated R(SU-l) is reset IBlock
110). The scan line associated with the surface unit for the current
pass through the program designated R(S O is set (Block 112). The data
of input lines PlIA through 9 are read in, conveying the current input
information for this RAM file from keyboard 28 (Block 114) and this
information is stored as variable KB (Btock 116). The program then
branches (Block 118) to the Keyboard Decode routine oi Fig. 8A.
KEYBOARD DECQDE Routine - FIGS. 8A and 8B
The Keyboard Decode routine validates inputs from keyboard 28
and updates the user selected power setting variable PWD accordingly.
The routine ff rst determines if the new keyboard entry is a blank
signifying no input, an Off entry, an On entry, or one of the power
levels 1 through 9. To be valid when switching the heating unit from
Off to another power setting, the Qn key must be actuated first
followed by the desired power setting. The power setting must be
entered within 8 seconds of actuation of the On key. If not, the On
key must be re-actuated.
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PA~ENT- 9D-MA-16819 - Payne
The varia~le P~D represents the user selected power setting.
P~D is only changed in response to user inputs. However, in accordance
with the present invention the power level actually applied to the
heating unit may be less than the level corresponding to the user
selected power setting. The variable PLYL is introduced in this
routine to represent the power level to be actually applied to the
heating unit. PLYL is assigned the value of PWD in this sub-routine.
However, PLVL is subiect to be changed in the temperature limiting
routines hereinafter described.
In the Keyboard Decode routine the eight second period for
entering a valid power setting after actuition of the Qn key is
established using a flag designated the On flag and a timer or counter
designated the ONTIMER. The Gn flag is set when the On key is actuated
and is only reset in response to actuation of the Off key or timing out
of ON~IMER.
Referring to the flow diagram of Figs. 8A and 8B, Inquiry 120
first determines if the K8 represents a blank signifying that no key is
presently actuated. If KB is blank, the system branches to the Decode
2 sub-routine (Fig. gB). In the Decode 2 sub-routine Inquiry 122
determines if the On flag is set. If the On flag is not set, the power
level stored in PWD is assigned to the variable PLVL (Block 124). If
the Qn flag is set, Inquiry 126 determines if the previously selected
power setting presently stored as PWD is the Qff settin~. If not, the
system is presently operating at one of power settings 1 through 9 and
the program proceeds to ass;gn the value of P~ID to PLYL (Block 124) and
branches (Block 128) to the Off Time routine (Fig. 9). If Inquiry 126
determines that PWD equals O representing an Off power le~lel, this
indicates that the user has switched from Off to Qn and the On timer is
decremented (Block 130). When On timer equals O as determined at
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PATENT - 9D-MA-16819 - Payne
Inquiry 132 signifying that the time to enter a valid power level has
expired, the On flag is cleared (Block 134) and program proceeds to
Block 124 as before.
Referring again to Fig. 8A, if KB is not a blank, Inquiry l35
determines if the new entry is the Off setting. If so, the On flag is
cleared (Block 136) and the ~ariable PWD is assigned the Yalue O
representing the Off power setting (Block 138). The variable PLYL is
assigned the value of PWD (Slock 140) and the program branches (Block
142) to the Off Timer routine of Fig. 9. If KB is not Off, Inquiry 144
determines if the new entry is the On setting. If it is, the On timer
is re-initialized (Block 146). Inquiry 148 checks the state of the Cn
flag. If set, the program proceeds to Block 140. If not set, the flag
is set (Block 150) and the PWD is assicned the value O which
corresponds also to the On setting (Block 152). The program then
proceeds to Block 140 as before.
If the answer to Inquiry 144 is No, signifying that the new
entry is one of power levels 1 through 9, Inquiry 154 checks the state
of the On flag. If it is not set, signifying the user has attempted to
go from Off to a power level without first actuating the On key, the
new entry is ignored and the program proceeds to Block 140 wlth PWD
unchanged. If the On flag is set, the power setting input is valid,
and variable PWD is assigned the new value corresponding to the new
entry KB (Block 156).
Having assigned the value of PWD representing the most recent
valid user selected power setting to the variable PLVL the system
proceeds to the Off Timer routine (Fig. 9).
OFF TnMER Routine - FIG. 9
The function of this routine is to measure the time elapsed
since the particular unit was last turned off to establish the
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PATENT - 9~-MA-16819 - Payne
appropriate duration of the next occurring transient heat up period for
that heating unit. A timer designated OFFTMR is provided for each
heating unit. The timer is incremented by one each pass through the
rouff ne for that particular heating unit. The duration of the
transient heat up period for the next occurring transient heat up
period is defined by the value of the variable INSTIME. This variable
is successively set equal to values of 1.07 seconds, 2.13 seconds, 3.07
seconds and 4.26 seconds as the count of the Off timer goes from less
than 3 seconds to greater than 3 seconds, from greater than 3 to
greater than 14 seconds, and from greater than 14 seconds to greater
than 60 secondsj respectively.
Referring to the flow diagram of Fig. 9, on entering this
routine the state of the On flag is checked at Inquiry 160. It will be
recalled that the Qn flag is set in the Keyboard ~ecode routine
hereinbefore described during the first pass through that routine
following the user selection of the On key. It then remains set until
the next occurring user actuation of the Off key. Thus, if the On flag
is set, the system is already operating in the transient heat up mode
or has completed the transient heat up mode and the value for INSTIME
has already been established. Thus, when the On flag is set no
adjustment to INSTIME is needed and the program branches to the Instant
On routine (Block 162) of Fig. lOA. If the On flag is not set, the
count of the timer (OFFTMR) is compared to a maximum count of 61
seconds at Inquiry 164. If the count is greater than 61, the program
branches (Block 162) to the Instant On routine of Fig. lOA. If the
count represents a time that is not greater than 61 seconds, the
counter is incremented by one (Block 166).
The timer is then compared to maximum reference time of 60
seconds at Inquiry 168. If the count represents a time greater than 60
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PATENT - 9D-MA-16819 - P4yne
seconds, the variable INSTDME is set equal to 4.26 seconds ~Block 17C)
and the program branches to the Instant On routine. If OFFTMR is not
greater than 60 seconds, the count i5 compared to a reference of 14
seconds at Inquiry 172. If greater than 14 seconds, the Instant Gn
time variable INSTDME is set equal to 3.07 seconds (Block 174) and the
program branches to the Instant On routine. If the count is not
greater than 14 seconds, the count is compared to a reference of 3
seconds at Inquiry 176. If greater than 3 seconds, INSTIME is set
equal to 2.13 seconds. If the count is not greater than 3 seconds,
Instant On time variable INSTIME is set equal to t.O7 seconds (Block
180). Having established the correct reference value for the duration
of the transient heat up period as a function of the Off time, the
program branches to the Instant On routine of Figs. lOA and lOB.
INSTANT ON Routine - FIGS. lOA and lOB
The function of the Instant On routine is to establish the
appropriate overdrive power level when operating in the transient heat
up mode; to control the duration of this mode; and to make adjustments
to the power level when not operiting in this mode as required to limit
the total current drawn by the appliance.
It will be recalled that under certain conditions the sum of
the power levels may exceed the predetermined limits signifying that
the appliance is drawing too much current this determination is made in
the PWRSUM routine hereinafter described with reference to Flg. 13.
latch designated PWRSUML, is set in that routine when the sum of the
p~wer levels is greater than a reference value. When PWRSUML is set,
power level adJustments are made in this routine durjng each ensuing
pass through the control program for each heating unit until the sum of
the power levels is no longer greater than the reference.
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PATENT^ 9D-MA-16819 - Payne
Additionally, a variable designated OPR is used to make
adJustments in power level to be applied to heating units in the
transient heat Up mode and to vary the duration of this mode. More
specifically when the transient heat up power level i5 reduced in order
to meet the current limit requirements, the duration of the transient
heat up period is correspondingly extended. The value of OPR is
established in the PWRSI~ routine but it is used in this routine to
make the appropriate power level and time adiustments for units
operating in the Instant On routine.
Referring now to Figs. lOA and lOB, on entering this routine
the state of the Instant Cn flag is checked at inquiry 182. If it is
not set, signifying the unit for which the change is being executed is
not operating in the transient heat up mode, the state of the power sum
latch (PWRSlltL) is checked at inquiry 184. If PWRSU~L is set,
signifying a need to adjust the power level to meet current limitation
requirements the power level is reduced by one (Block 186) and the
program branches to the next routine. If PWP5UML is not set no
adjustments are made and the program continues on to the next routine.
Referring back to Inquiry 182, if Instant On flag is set
signifying operation in the Instant On mode, the power level variable
PLVL is set equal to the maximum power level F, reduced as required by
the value of the adjustment variable OPR (Block 190). Inquiry 192 and
Block 194 cooperate to prevent the applied power level during Instant
On from being less than 9 and Inquiry 196 and Block 198 cooperate to
keep PLYL not greater than F. The program then proceeds to inquiries
202-208 which operate in combination with 810cks 210-218 to vary the
duration of the transient heat up mode as a function of the value of
the OPR variable. A counter designated OVDRIMR is used to control the
duration of the transient heat up mode. When OPR is not greater than
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PATENT - 9D-MA-16819 - Payne
1, OYDRTMR is incremented by one, each pass through the routine (Block
210). If OPR is greater than one but not greater than three, Inquiries
204 and 206 and Blocks 212 and 214 cooperate to increment OVDRTMR on
alternate passes through the routine for a particular heating unit,
effectively reducing the increment rate by two thereby extending the
duration of the Instant Cn period by a factor of two. If OPR i5
greater than three, Inquiry 208 and Blocks 216 and 218 cooperate to
increment OVDRTMR by one on every fourth pass through this routine for
this particular heating unit effectively extending the transient heat
up mode by a factor of four.
Thus, the variable OPR serves as here before described to
reduce the power level applied during operation of the transient heat
up mode at block 190 and also is used to compensate for the lower power
level by extending the duration by causing the duration of operation in
the instant on mode to be extended to compensate for this lower power
setting.
At Inquiry 220 the value of OVDRTMR is compared to the
reference value INSTIME established in the hereinbefore described Off
Timer routine of Fig. 9. When Inquiry 220 determines that OVDRTMR has
timed out, the Instant Cn flag is cleared, OVDRTMR is reset to zero,
and the reference variable INSTIME is set to zero.
PSET Routine - FIE. 11
Having established the appropriate power level to be applied
to the heating unit, it remains to make the triac triggering decision
for the next occurring power signal cycle. This decision is made for
all four heating units during each pass through the control program.
Use is made in this routine of information from each of the four
heating unit RAM files each time through the routine.
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PATENT - 9D-MA-168t9 - Payne
It will be recalled that the power pulse repetition rate for
each power level is defined by the bit pattern of a 64 bit word with
the logical one bit representing an On cycle and logical zero
representing an Off cycle. The bits of the control word for each
heating unit representing the power level to be applied to it are
tested sequentially with one bit being tested each pass through this
routine. The state of that tested bit determines whether the triac for
the corresponding heating unit will be triggered on or not in the next
power signal cycle.
This routine performs a Table Look-Up function to find the
appropriate control word for each of the four surface units and then
checks the state of the appropriate bit in that word. The triac
triggering information is then stored in a four-bit word designated
TMPON, which is used in the Power Cut routine (Fig. 12) to generate the
appropriate triac trigger signals.
The variable lBLADD represents the address in RA~ of the
starting location for the look-up table containing the 64 bit control
words. The address and associated bit pattern in Hex representation is
shown in Table I. Each of the 16 diaits in the code as shown for each
control word is the hexidecimal representation of four binary bits.
The variable designated BITADD represents the location within
the 64 bit control word of the bit to be tested with O and 63
corresponding to the location of the most significant bit and least
significant bit respectively.
An indexing variable n is used to iterate the table look-up
loop four times during each pass through the routine, once for each
heating unit. The variable PWDADD is the address of the control word
representing the power level to be applied to the nth heating unit.
As can be seen in Table I, the address for any particular power word is
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PATENT - 9D-MA-16819 - Payne
obtained by multiplying the value of PL~L for its associated power
level, which is a number O through 9, by a factor of 8 and adding this
to TBLADD.
Referring to Fig. 11. on entering this routine the control
word lMPON i5 cleared (810ck 226) and a ring counter which counts from
O to 63 is incremented (Block 228). Inquiry 230 determines if the
counter is greater than its maximum count of 63. If so, it is reset to
O (Block 232). Next BITADD is set equal to the count of the ring
counter thereby defining the location within the control word for the
bit to be tested for each heating unit (Block 234). The same bit
location is tested for each of the heating units.
The variable n is initialized to zero at Block 236. PWDPDD
for the power level to be applied to the nth heating unit is
deter0ined at Block 240. The state of the bit location defined by the
variable BITADD in the control word located at the address PWDADD is
then tested (Inquiry 242). If the tested bit is a logical 1, the nth
bit of the control word TMPON is set (Block 244). Othen~ise, the nth
bit of ~MPON will remain 0. After the index n is incremented (Block
246) the value of n is checked (Inquiry 248). If greater than 3,
signifying that the loop comprising Blocks 240, 244 and 246 and
Inquiries 242 and 248 has been iterated four times, n is reset (Block
250) and the program branches (Block 252) to the Power Qut routine
(Fig. 12). If n is not greater than 3, the program returns to Block
284 to test the bit for the power word for the next heating unit.
After the appropriate state for all four bits of the variable TMPON
have been established, the program branches (Block 252) to the Power
Out routine (Fig. 12).
POWER OUT Routine - FIG. 12
The function of this routine is to trigger triacs 24(a) -
24(d) to implement the triac triggering decision for the next power
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PATENT - 9D-MA-16819 - Payne
cycle for each of the four heating units. The triggering of the triacs
is synchronized with the positive going zero crossings of the power
signal.
Referring now to the routine in Fig. 12, on entering this
routine the output latches P500-P503, which control the triacs, are
reset (Block 260). Next the program reads in the input from the input
port P8IO representing the state of the zero cross detector (Block 262)
and Inquiry 264 checks the state of this input until it switches to a
logical 1 signifying the occurrence of a positive going zero cross;ng
of the power signal. When P8IO equals 1, the program proceeds to
Inquiry 266 to sequentially check the four bits of the power word TMPON
and set the appropriate one of output latches P500-P503. Index
variable n is again used to sequentially check bits O through 3. It
will be recalled that prior to branching from the PSET routine the n is
reset to 0. Inquiry 266 tests the nth bit for a 1. If it is a 1,
the output P50(n) is set (Block 268), n is incremented (Block 270) and
Inquiry 272 checks for an n greater than 3. If n is less than 3, the
program returns to Inquiry 266 to check the next bit and set the
corresponding output port as appropriate. Those ones of output latches
P500-P503 associated with bits in the variable TMPON which are in the
logical one state are set. Those ones with output latches associated
with zero bits in TMPON are not set. In the latter case these latches
remain in the reset state since each of the latches is reset upon
entering this routine.
In this fashion each bit of the control word lMPON is tested
each pass through the Power Out routine. In this way a decision to
trigger or not trigger each triac is carried out during each pass
through the control program. Once the loop comprising Inquiries 206
and 272 and Blocks 268 and 270 is iterated four times, once for each
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PATE~T - 9D-MA-16819 - Payne
heating unit, the power control decision for the next power cycle has
been implemented and the program branches (Block 274) to the PWRSUM
Routine of Fig 13.
PWRSUM Routine - FIG. 13
The function of this routine is to monitor the power levels
being applied to each of the heating units and set or reset the latch
designated the PWRSUML and update as appropriate the variable OPR It
will be recalled that the PWRSUML and the OPR variable are utilized in
the Instant Qn routine to modify the power level being applied to each
heating unit as appropriate to bring the total current drawn by the
appliance to within acceptible limits. The variable P~RSW~ is set
equal to the numerical sum of the power level designator for each of
the heating units. If this sum is greater than 38, the total current
drawn by the appliance will exceed the maximum 35 amp design limit.
Thus, if the sum exceeds the reference value of 38, the PWRSUML is set
and the variable OPR is ~ncreased by one. If the sum of the power
levels is not greater than this reference, the PWRSUML is reset and the
OPR variable is decremented by one.
Referring to the flow diagram of Fig. 13, on entering the
program the variable PWRSUM is set equal to the sum of the power levels
(Block 280). This variable is compared to the reference value which is
expressed in hexadecimal representation (In hexadecimal the hexadecimal
value 26 corresponds to a decimal value of 38.) at Inquiry 282. If
PWRSUM exceeds the reference value, PWRSUML is set (Block 284) and the
variable QPR is incremented by one (Block 286). If PWRS~l does not
exceed the reference, PWRSUML is reset (Block 290). If OPR is less
than or equal to O at Inquiry 292, the variable is set equal to O
(Block 296). If OPR is not less than 0, it is decremented by one
(Block 294). Having established the apprcpriate state for PWRS~lL and
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PATENT - gD-MA-16819 - Payne
the appropriate value for the variable OPR, the program then returns
(Block 288) to the Scan rout;ne of Fig. 7 to repeat the control program
for the next heat;ng unit.
~ hile in accordance with the Patent Statutes a specific
e~bodiment of the present invent;on has been illustrated and described
herein, it is realized that numerous modifications and changes will
occur to those skilled in the art. For example, the illustrative
embodiment employs infrared heating units. However, the invention
could also be used in conventional conduction cooktops as well. It is
therefore to be understood that the appended claims are intended to
cover all such modifications and changes as fall within the true spirit
and scope of the invention.
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