Oven regulator for a skin packaging machine

In a skin packaging machine, a method and apparatus for maintaining a film heating oven at a low temperature wherein during a very short repeating duty cycle, e.g., less than a minute, the power to the oven heaters is applied for a short period and is shut down for the remainder of the period through solid state relay switching.

This invention relates to a skin packaging machine, and more particularly, 
the invention is directed to the control system for the oven of such a 
machine which heats the film which is applied to the product. 
A skin pack package consists of a product mounted on corrugated board or 
paperboard and enclosed by a film of thermoplastic material. 
The apparatus for making a skin pack package includes a horizontal base 
including a horizontal perforate plate and a source of vacuum pulling 
downward through the plate, a supply roll of film, a frame through which 
the film passes, the frame normally overlying the perforate plate and an 
oven overlying the frame. In operation, the film is disposed in the frame 
and a product positioned on the paperboard is placed on the perforate 
plate over the source of vacuum. Heat is applied to the film within the 
frame to raise its temperature to 130.degree. to 200.degree. F. causing it 
to become soft and to begin to droop. The frame is then lowered onto the 
product and the paperboard substrate while vacuum is applied beneath the 
substrate. The vacuum pulls the film tightly down upon the substrate to 
which it adheres and snugly draws the product down onto the substrate and 
encloses it within the film. 
This apparatus generally has been known for many years. The problem, to 
which the present invention is addressed, is that during the portion of 
the operating cycle wherein the completed package is removed, a new 
substrate is placed on the plate and a fresh supply of film is drawn into 
the frame and it is desired to keep heat away from the film so that the 
fresh film does not become overheated and degrade. It is normally desired 
to keep the film unheated for 15 to 30 seconds while other operations are 
taking place. 
One solution to the problem has been to provide shutters in the oven, the 
shutters closing off the direct application of heat to the film. While the 
shuttered oven has performed reasonably well, it suffers from two 
disadvantages. First, there is a tendency of the radiant heat through the 
shutters to degrade the film prior to its application to the product and 
substrate and second, the apparatus is somewhat inefficient in that there 
is, during that portion of the cycle, an unnecessary dissipation of heat 
to atmosphere. 
Another approach to the problem has been to deenergize the oven during the 
no-heat required portion of the cycle. The drawback with that system is 
that there is a finite time, at least five to ten seconds, required to 
heat the oven to the temperature necessary to soften the film. That finite 
time reduces the cycle time for the operation thereby slowing down 
production. 
Therefore, an objective in the art of skin packing has been to reduce 
substantially the energy applied to the oven during the no-heat required 
portion of the cycle while maintaining a certain amount of residual or low 
heat in the oven so as to minimize or substantially eliminate that portion 
of the cycle required to raise the temperature of the oven to the 
temperature necessary to soften the film. 
One approach to maintaining a residual heat has been to reduce the voltage 
applied to the oven to a low voltage sufficient only to maintain the oven 
at a high enough temperature that there is no significant loss of cycle 
time to bring the oven up to the desired temperature for softening the 
film. 
There are some disadvantages with this approach. If a transformer is 
employed to reduce the applied voltage to the oven heaters, then there is 
no flexibility as to the level of energy applied. On the other hand, if a 
variable transformer such as a variac is employed, then the expense of 
providing a reduced but adjustable low voltage is prohibitive. 
An objective of the present invention has been to provide skin pack 
packaging apparatus wherein a variable control is employed to reduce the 
heat during the no-heat required period in order to avoid degrading the 
film, the control system being inexpensive compared to other comparable 
methods of achieving generally the same result. 
The objective of the invention is attained by two forms of the invention. 
One form of the invention, which is quite inexpensive, is suitable for low 
power requirements as, for example, those requiring an input of 
approximately nine killowatts. Such a system is suitable for applying film 
to a board of approximately 18.times.24 inches. 
A larger board to which the product is applied as, for example, 30.times.36 
inches, requires a higher power input as, for example, twenty-five 
killowatts, and requires a somewhat different but nevertheless effective 
system for applying a low heat during one portion of the cycle and a high 
heat during the other portion of the cycle. 
Both the low power and high power ovens employ the same generic concept for 
energizing the oven with a low heat during the no-heat required portion of 
the cycle. In both systems, within a very small increment of time, 
preferably less than a second which will be referred to as the "duty 
cycle," the power to the heaters is turned on and off. The amount of heat 
applied to the heaters is determined by the ratio of "ON time" to "OFF 
time." 
Through the use of solid state relays (SSR's) to switch the current to the 
oven heater elements on and off within very short intervals of time, and 
through the use of a control system which can vary the ratio of "ON time" 
to "OFF time," the power to system during the no-heat required portion of 
the cycle can be kept quite low, but also can be varied through a manual 
or operator control so as to adjust the system to varying types and 
thicknesses of films, ambient temperatures and the like for maximum 
efficiency and high production. 
In one system, the objective of the invention is attained by providing an 
electronic timer providing a three-quarter second duty cycle and within 
that duty cycle providing a variable time during which power is not 
applied to the heaters, power being applied during the remainder of the 
cycle. 
In the alternative system, the power is controlled in terms of units of 
alternating current cycles. Preferably, one complete alternating current 
cycle is the smallest unit of time employed by the system. If during each 
duty cycle the power applied to the heaters remains on for one complete ac 
cycle, then the ratio of ON to OFF time can be varied by programming the 
systems to deenergize the power to the heaters for one or more ac cycles. 
For example, if the power is to be reduced to fifty percent of full power, 
the ON time would be one cycle and the OFF time would be one cycle. A 
reduction to twenty-five percent would require an ON time of one cycle and 
an OFF time of three cycles. A reduction to thirty percent would require, 
in one hundred cycles, an "ON" time of one cycle with an "OFF" time of two 
cycles until thirty "ON" cycles had been operated. This control can be 
attained by employing solid state relays and a microcomputer for turning 
the relays on and off. The microcomputer is partially controlled by a 
manually-operable potentiometer which determines the ratio of cycles of 
"ON" to cycles of "OFF" time. 
Another feature of the invention is to provide for switching to an "idle" 
mode which deenergizes the heaters after the system has been on a low heat 
mode for a predetermined period of time as, for example, approximately one 
minute. 
Still another feature of the invention is to employ, with the circuits for 
the oven heaters, an instant "ON" heater wherein each heater consists of a 
quartz tube surrounded by a helical wound ribbon of nichrome wire as 
disclosed, for example, in U.S. Pat. No. 3,621,200. 
Another feature of the invention is to provide a fan blowing air under the 
film during the noheat required period so that the temperature of the oven 
can be maintained as high as possible for fast cycling time but without 
degrading the film by too great an exposure of heat to the film during the 
no-heat required period.

As shown in FIG. 1, the packaging apparatus indicated at 10 includes a base 
11 presenting a horizontal surface 12 to which vacuum is applied through a 
perforated surface 13. An oven 15 overlies the perforated surface 13, the 
oven containing heaters of the type disclosed in U.S. Pat. No. 3,621,200. 
A rectangular frame 17 is disposed between the vacuum surface 12 and the 
oven 15 and is provided with a mechanism, not shown but located within the 
base, for raising and lowering the frame between an upper position 
adjacent the oven and a lower position adjacent the surface 12. 
A supply roll 20 of film 21 is mounted adjacent the oven. The film is 
adapted to pass between upper jaw 23 and lower jaw 24 of the frame 7. The 
jaws are hinged at 25 so that they may be opened in order to pull a new 
supply of film into the frame. 
A cutter 27 is provided adjacent the end of the frame remote from the hinge 
25 for shearing the film between a finished skin pack package and the 
fresh film from the supply roll. 
Preferably, a fan 30 is provided to blow cooling air across the film during 
the no-heat required period to permit the oven temperature to remain as 
hot as possible so as to minimize the time required to raise the 
temperature to the level required to plasticize the film. 
In the operation of the apparatus, as thus far described, a substrate of 
corrugated board or paperboard is placed upon the perforated plate 13. A 
frame 17 with fresh film in it is positioned in its upper position between 
the oven 15 and the perforated plate 13. 
The heat of the oven is applied to the film until it is "ready." In the 
"ready" state it has become soft and tends to physically droop below the 
frame. Thereupon, the frame is lowered to its lowermost position in which 
the film drapes around the object and the substrate which supports the 
object. A vacuum applied to the substrate pulls the soft film down upon 
the substrate whose surface may be treated to adhesively secure the film 
to the substrate while snugly drawing the product down upon the substrate. 
This concludes the heating portion of the cycle. At this point, energy to 
the oven is greatly reduced to a level which will not degrade a fresh film 
drawn into the frame even though the fresh film will underly the oven for 
a long period of time--for example, thirty seconds. The vacuum turbine is 
switched off. The jaws of the frame open up. The substrate with the object 
encased in the plastic film is slid toward the right as viewed in FIG. 1. 
In moving the substrate toward the right, a fresh supply of film 21 is 
pulled between the jaws 23 and 24 of the frame 17. When the substrate is 
moved completely from beneath the frame, jaws 23 and 24 close and the 
knife 27 is reciprocated to sever the film from the skin pack package and 
the fresh film supply. 
The frame 17 is then raised to a point underneath the oven and a new 
substrate with product mounted on it is positioned on the perforated 
plate. When these operations have taken place, the oven then begins to 
heat the plastic film to soften it for the next skin pack package. 
One circuit for operating the oven is diagrammatically illustrated in FIG. 
2. 
There, the oven heaters 35 are connected in delta configuration to the 
power supply which in the preferred embodiment is a three-phase 200 to 240 
volts 60 hertz supply. The power supply is connected to the heaters 35 
through three series solid state relays 36. 
The function of the remainder of the circuit is to switch the solid state 
relays 36 on and off during a very short duty cycle as, for example, 
three-quarters of a second, and to be able to vary the ratio of "ON" time 
to "OFF" time so as to vary the level of energy which is put into the oven 
heaters. To that end, the circuit employs an A timer which is a 
free-running oscillator oscillating at approximately 1.3 hertz. The timer 
A is connected to a timer B which produces a pulse which may be from 0 to 
3/4 second. The length of the pulse is varied by a manually operable 
potentiometer circuit 37. 
A timer C is connected to the main machine logic indicated at 38 and has an 
output connected to timer B. Timer C is set for about one or two minutes 
and is designed to prevent timer B from applying power to the oven after 
the oven has been on a low energy input for a predetermined period of time 
as, for example, a minute and a half. That length of time is substantially 
longer than would normally be required for the time required before 
another package cycle. The expiration of that length of time would 
indicate that there is no more packaging activity and that the oven should 
be shut completely down. 
The operation of the timers is indicated in FIG. 3. It can be seen that 
timer A provides the main duty cycle which controls and resets timer B 
during the interval t.sub.RB. Timer B controls the oven through the 
OR-gate 40. 
t.sub.H is the time left in the duty cycle after timer B has timed out. 
During the time t.sub.H, in each duty cycle, the oven is on. As the length 
of time for the timer B to time out is increased, through the manipulation 
of the potentiometer 37, the energy to the ovens is decreased. The energy 
to the oven will stay low until either the machine logic turns the oven 
onto full power through the OR-gate 40 or, alternatively, until the timer 
C times out at the end of t.sub.LH. At that point, timer C will shut down 
timer B so that no more signal from timer B can be applied to the OR-gate 
40 and hence the power to the oven will be completely turned off until the 
machine is recycled. 
Alternative Embodiment 
In the alternative embodiment of the invention, the duty cycle for the 
lower power input to the oven heaters will be effected generally as 
follows: the power to the heaters will be turned on, through solid state 
relays, for one full alternating current cycle of the three-phase power 
supply. The solid state relays will be controlled to turn off the power to 
the heaters for one or more full alternating current cycles. A number of 
cycles during which no power is applied to the heaters determines the 
level of energy applied to the heaters. If the ratio of ON to OFF is 
one-to-one, then the energy to the heaters is fifty percent of full power. 
If the heaters are turned off for two cycles, then the power has been 
reduced to one-third as compared to full power, etc. 
The circuit for effecting the variable power input to the oven is 
diagrammatically illustrated in FIG. 4 in block diagram form. The circuit 
includes a process control 50 which is a microcomputer which runs on a 
fixed clock by itself and thus has its own timing functions built in. 
The process control reads power sense inputs indicated at 51. The power 
sense inputs monitor the status of the solid state relays every cycle. All 
three of the two hundred to two hundred forty volt inputs are monitored by 
the power sense inputs. These straight parallel inputs to the process 
control are read by the process control as required by the process 
control. 
As indicated at 52, the process control also reads external control inputs 
from the machine logic. These inputs are basically two, namely, the full 
power to the heaters and the low power reset input. The full input is the 
machine logic input command to put the oven at full power continuously. 
The reset low power input is that function whereby the operator presses 
the reset button on the machine and restarts the low power after it has 
been stopped in an idling mode. Block 53 is a standard low-voltage dc 
power supply for the process controller. 
Block 55 is an operator adjustment input which determines what percentage 
of full power will be applied to the heaters during the lower power 
portion of the cycle of operations. It includes a potentiometer operable 
by the operator of the machine and an analog-to-digital converter to 
provide a digital input to the process control. 
Block 56 represents status indicators. These are strictly outputs which 
indicate the mode of operation that the apparatus is in. They indicate 
whether the oven is in a low heat or full heat mode; they indicate any 
necessary fault conditions; and they indicate whether there is any problem 
with any one of the six banks of heaters in the oven. 
Block 57 represents the group of six solid state relays which control the 
six heaters which are connected in two parallel delta configurations, as 
indicated at block 60 (FIGS. 4 and 5). 
In the operation of the system of FIG. 4, when power is applied to the 
oven, the power supply 53 will supply power to the process control 50. 
Power to the oven heaters, block 60, is supplied through the solid state 
relays, block 57, associated with the heaters, the solid state relays 
being under the control of the process control 50. 
The operator sets the level of energy applied to the heaters during the 
no-heat required portion of the cycle of operations by manipulating the 
potentiometer at 55. 
Referring to FIG. 1, a substrate is placed on the perforate support forming 
part of the base 11 with the articles to be skin packed to that substrate 
placed upon it. The frame, indicated at 17, has been raised to a position 
adjacent the oven and carries the fresh film to be applied to the 
substrate. The external controls, at 52, cause the solid state relays to 
apply full heat to the oven heaters at 60. When the film becomes "droopy" 
or ready, the frame is lowered to a position overlying the substrate and 
vacuum is applied to draw the film down tightly against the substrate and 
the article on the substrate. Vacuum is applied to the perforate sheet 
upon which the substrate rests to pull the film down upon the substrate. 
Thereafter, the turbine applying the vacuum is turned off and the oven is 
switched to the no-power required mode. 
During the no-power required mode of operation, the microcomputer or 
process control 50 applies full power to the heaters for one cycle only, 
through the operation of the solid state relays, and thereafter applies no 
power to the heaters for one or more cycles, as determined by the setting 
on the input 55. 
This duty cycle of power applied for one cycle and power removed for a 
plurality of cycles is repeated during the period of time that the oven is 
in the no-heat required mode. During this period, on the machine, air is 
blown through the perforate plate supporting the substrate to loosen the 
substrate from the plate. The film clamp or frame 17 opens. The package is 
ejected toward the right as viewed in FIG. 1, pulling with it a new supply 
of film into the frame 17. The frame then closes upon the new supply of 
film and a cut-off knife slits the film between the freshly made package 
and the frame. 
The frame then rises and pauses for a short period of time to let all 
automatic circuits return to their initial or OFF state. At this time, a 
new substrate is placed on the perforate plate 13 and the oven shifts to a 
full On power mode. 
If for some reason it was not possible to have the elements of the machine 
in a position ready for the full power mode, and the machine had been in a 
low power mode for a substantial period of time as, for example, a minute 
and eight seconds, the control circuit would automatically shift the oven 
heaters to "idle" during which the power is turned completely off the 
heaters. 
The circuit and control system for operating the apparatus in the manner 
just described is more completely disclosed in FIGS. 5-8. 
Referring to FIG. 5, the drawing can be blocked out in a simple manner. In 
the upper left-hand corner of FIG. 5 are the actual oven-heating elements 
60 which are under control by this device. In the more or less center top 
of the drawing is a section 51 where the external three-phase power is 
brought into the system. All the devices located to the left center, 
indicated at 51, are high voltage power sensors that bring information 
into the central processor. There are two external inputs 52 shown between 
the center and the left of the drawing, one of which, 52A, is an operator 
input, namely, the residual or low heat input, and the other, 52B, which 
is a machine control input, namely, the full ON input. The center section 
50 is the processor controller itself where all of the data that is input 
is manipulated and modified to control the outputs which in turn control 
the heating elements. The section 55 at the top right center of the 
drawing which is dominated by integrated circuit I4 is the operator set 
point input conversion system for the process controller. All of the 
devices 56, 57 to the right are output control devices, and the section at 
the bottom center 53 is the controller's own power supply showing the 
external control power connection. 
Starting with the power input sensors 51 at the far left, these sensors are 
optical isolators which can sense the power waveform in either direction 
by transferring the information of the power waveform by optoelectrics 
into the logic circuit. That is what is being done by OP-1, OP-4, OP-5, 
OP-6, etc. These devices are protected from overcurrent by the 150,000 ohm 
resistors at the head end which are R-1, R-4, R-5, etc. the diode CR-1 
which is used on OP-1 limits it to strictly being able to read only 
one-half of the waveform, and in this manner the controller can always key 
in at the beginning of a waveform instead of accidentally keying in 
halfway through a waveform. 
The AB-phase opto-input which is OP-1 will always only be able to read at 
one point in the ac waveform. The ac forms which are being read by these 
input devices are either the A-phase to B-phase, A-phase to C-phase, 
B-phase to C-phase power voltages or the voltages across any one of the 
six solid state relays (SSR). Consequently, there are nine power input 
points. They read the voltage across the solid state relays in a reverse 
mode; that is to say, when they sense there is a signal, it means that the 
solid state relay is not conducting. When there is no signal the solid 
state relay is essentially a short which means that it is turned on. So 
these devices, by looking at the opposite state, can determine whether or 
not the solid state relays are actually performing their function when 
required. Moving into the logic section of the inputs, the optical 
isolators (OP-1-9) are only able to give a logical zero by pulling their 
output into ground and there being fed into Schmitt triggers which are 
CMOS devices which must have either a logical 1 or logical 0 to have 
significant results displayed in their outputs. 
To attain the logical 1 condition when the optoisolator is not signalling, 
the 10,000 ohm resistors provide that logical 1 condition, and these 
resistors are such as R-10, R-13, R-14, etc. The Schmitt triggers which 
are all located in I-1 and I-2 are a logic gate that will turn on upon the 
input to that gate reaching a specified voltage and will not turn off 
until it drops significantly below that specified voltage. This voltage is 
specified by the manufacturer of the device. The idea of the Schmitt 
trigger is that it has what we call a defined hysteresis for turning on 
and turning off. It has a greater input level switching span than the 
standard logic gate. These are inverters in addition, which means that 
when you have a logical zero applied at the input, you have a logical 1 on 
the output. This is really inconsequential except that that has to be 
taken into account when the inputs are tested by the process controller. 
Moving over to the external inputs 52, the residual or low heat reset input 
52A has a circuit design on it that will not only prevent misfires from 
external noise, but also forces the process controller to reset itself 
when the power is turned on. The machine that this controller is located 
in also has one of the contacts of its own master reset button tied across 
this input so that anytime anyone presses the reset button on the machine, 
they will cause the controller to restart in its reset mode. The full ON 
input 52B only has filtering to prevent miscellaneous electrical noise 
from misfiring the input. The process controller 50 is a single chip 
microcomputer. It is running at 3.58 megahertz, which is dictated by the 
X-1 crystal in the upper left corner of it; it is an Intel 8747-8 and it 
is preferably programmed with a program that is defined on the 
accompanying flow charts in order for this whole system to operate. 
Up in the top center right is the conversion area which is operator 
controlled to determine the energy input to the heaters during the period 
of low heat. This conversion system is a Motorola analog-to-digital 
conversion subsystem. It cannot do an entire analog-to-digital conversion 
on its own. The timing and counting functions must be provided from the 
central processor to accommodate this function. The potentiometer R-1 is 
the operator's set point adjustment where he can select from 0 to 50% of 
maximum heat for the low heat to the heaters. That potentiometer is 
located on the front of the controller where an operator can usually get 
to it. The capacitor C-6 is only used to maintain a relatively steady 
voltage across P-1 while the conversion is taking place. 
The other devices R-24, R-25 and C-5 are used by the Motorola subsystem to 
make it operate. R-26, the 10,000 ohm resistor, is used in the same manner 
as R-10 is used over on I-2 on the left, and that is to pull up the input 
to the central processor from the Motorola system because the Motorola 
system can only switch to a logical 0. 
Moving over to the outputs 56 and 57, starting at the bottom and working 
up, there are six indicator lights labeled as 1-SSR error, 2-SSR error, 
3-SSR error, 4-SSr error, and so on to 6-SSR error. Those indicator lights 
are driven by pnp transistors. The pnp transistor base current is driven 
by the central processor, and it is limited by resistors R-33, R-35, R-37, 
R-39, R-41 and R-43. When the processor is outputting a logical 1, the 
10,000 ohm resistors shown there, R-34 to R-44, prevent the pnp 
transistors from turning on. When the processor outputs a logical 0, the 
transistors are turned on by the base current being sunk through the 2,000 
ohm resistors. A residual or low heat-on indicator, a fault indicator and 
the full-on indicators are also in the upper section 56. In the center of 
the drawing, in section 57, are the solid state relay control transistors 
Q-1-Q-3. The gating function is the same except instead of driving 
indicator lights, the transistors Q-1 to Q-3 are driving the input sides 
of the solid state relays 1-SSR to 6-SSR. Whenever those transistors 
conduct, the solid state relay power circuits will appear as a dead short 
in the power system indicated at 60 as 1-SSR to 6-SSR. 
The heater rods themselves are shown in the oven as two elements 66 and 67 
in series with two other series elements in parallel for each bank. The 
oven is made up of six banks, and if that is drawn out as a typical 
three-phase diagram, it would be found that there are two delta 
configurations of twelve rods per delta, four rods per bank, and in each 
case the solid state relay is in series with each bank of the rods. 
Because they are parallel delta configurations 1-SSR and 4-SSR are 
essentially operated at the same time along with 2-SSR and 5-SSR; and then 
3-SSR and 6-SSR. They are all the corresponding parts one delta versus 
another. 
The power supply 62 is simple 120 volt ac 50-60 hertz input supplying a 
high enough voltage rectified via CR-2 and CR-3 and filtered through C-1 
to allow the 5 volt 1 amp integrated circuit voltage regulator No. I5 to 
supply 5 volt power for the operation of the process controller. 
The flow chart of FIG. 6A to 6N describes in a general manner all of the 
functions of the operating program. 
In FIG. 6A, power-on and residual heat reset are both feeding reset. The 
characteristic of the reset is built into the processor by Intel. When the 
power comes on, if the reset input to the processor is at logical 0, then 
the controller will automatically start at location 0 and at location 0 in 
the program the reset routine is to be jumped to. The concept here is that 
if you turn either the power on or if you hit the reset button of the 
machine to provide the reset residual heat input with a signal, you will 
command that operation. 
The basic function of the reset routine is to establish the system timing 
and to initialize the error memories and to insure that the power is 
available on all three phases. There is some description here about 
monitor for fault on these. If it did not get the entire information 
within a certain period of time, then the machine goes into a fault mode. 
The maximum period of time can be, with 3.58 megahertz crystal on this 
unit, 34 milliseconds, which is what we call one entire count from 0 to 
256 of the internal timer of the microcomputer 50. 
In FIG. 6B through 6D is described the basic loop of the residual heat 
mode. The residual heat is the first of the three primary modes of 
operation. Residual or low heat counts the number of cycles that is 
performing through, and once it has counted up to 4096 cycles, which is 
approximately one minute, eight seconds, it will jump into the idling 
mode. If a full-heat request is made by the machine to the full-on input 
during the residual heat, then it will jump into the full-heat mode. The 
idling mode and the full-heat mode are the other two major modes of 
operation. 
The residual heat routines uses three counters to perform its task. The 
three counters are the rate counter, the state counter and the base 
counter. The information given by these three counters determines the 
switching characteristics for the whole collection of waveforms to achieve 
the desired residual heat percentage. The rate counter is the amount of 
cycles that will be allowed to go by before a change of state is commanded 
by the residual heat routine for the SSR's. At the last count of the rate 
counter, the SSR's will be, for one cycle, the other state. This residual 
heat routine switching system is designed to operate from 0 to 100%, but 
the calculation system routine is limited only to fifty percent. So 
essentially, the major ON mode program will never be operated--only the 
major OFF mode which is shown in the vertical column in FIG. 6-C to the 
left as opposed to the columns to the right. 
The rate counter will therefore, in the major OFF mode, run the first set 
of cycles as it is counting down OFF, and when it gets to 0 it will set 
one cycle ON. That means that the solid state relays will all be On for 
one cycle and then they will all be OFF again. At that time, the rate 
counter is reset and allowed to count down again. As soon as the total 
number of ON cycles has met the quantity of the state counter, then the 
cycles are no longer allowed to turn ON until the base counter has totally 
counted out. The base counter counts every single cycle. There is a 
diagram accompanying the flow chart (FIG. 7) which describes these 
features in greater detail. 
The idling routine in FIG. 6E is very self-explanatory. It just states the 
fact that residual heat light must not be ON. Your full-heat light must 
not be ON. You oven must not be ON. And then it just tests to see if the 
full-heat request is made. If it is not, it just keeps waiting. Full-heat 
in FIG. 6F of course is the opposite of the no-heat during idling. It 
makes sure that the residual-heat light is OFF, the full-heat light is ON 
and that the oven is full-ON, but it also counts the number of cycles that 
it has been running. And if it ever receives the count of 8192 which is 
approximately two minutes, sixteen seconds, then it reverts to the 
residual-heat mode. It is to try to keep the machine from overheating if 
something went wrong and for some reason an operator was not attending it 
at that moment. It will keep flopping between two minutes and sixteen 
seconds in full heat, and one minute, eight seconds in residual heat until 
someone stops it. 
All of these modes refer to a cycle routine. The cycle routine will be 
described later. 
The next item is the error check of FIG. 6G and FIG. 6H. The whole function 
of the error check is to: pick up information given by the cycle routine 
as to which solid state relays are to be checked; determine whether or not 
they are at the proper state; determine whether or not they have been at 
that proper state; determine whether they have missed that proper state 
three times. If they have not missed the proper state at all, the error 
memories which are being maintained on every one of the solid state relays 
for ON state and OFF state are set to 0 for the appropriate state. If they 
have missed three proper states, the information is given into a special 
error fault memory which is checked at the end of the error routine, and 
if the error fault memory does have an error fault in it, the error 
automatically jumps into the fault mode which stops everything. 
The fault mode of FIG. 6I of course insures all the indicator lights are 
off except the fault indicator. Then it lights the appropriate solid state 
relay error indicators if there are any. The fault routine is also the 
routine that is acted upon by what is referred to as the fault timer 
during monitor for fault. What it means is that when the controller is 
seeking one of the power inputs, the AB-phase opto or the BC-phase opto or 
the AC-phase opto, and it does not encounter them, it is not checking a 
solid state relay, which means that one would not get any error light for 
a solid state relay, but it did not find what it needed to in terms of the 
main power. So this fault routine is automatically called if the time has 
expired that it is allowed to look for it. 
Moving into the cycle routine in FIG. 6J and FIG. 6K, the cycle routine 
operates with the concept of checking the peaks of the waveforms at the 
appropriate times to determine whether or not the solid state relays are 
either ON or OFF at the appropriate times, and to set them for the next 
cycle when they must be set. They cannot all be set out at once because it 
would not be a smooth operation. They have to be set sequentially, that 
is, solid state relays number 1 and 3 must be set first because the system 
is keying off the A-phase, B-phase for the beginning of each cycle, and 
solid state relays 2, 3, 5 and 6 are set on at the end of the cycle 
routine. This is based on the concept that the solid state relays will 
change state if the input state is modified 5.degree. before the 0 
crossover line of the ac waveform. 
The timing of the cycle routine is best viewed on the waveform chart of 
FIG. 8. 
Moving on to the conversion function (FIG. 6L and FIG. 6M) which converts 
the operator set point potentiometer reading into digital information for 
the switching characteristic requirement of the residual-heat mode 
program, the flow chart describes the internal timing and counting 
functions of the processor, as was mentioned earlier, to do a radiometric 
conversion which is merely a relative conversion, "relative" being 
comparing the set point of the potentiometer against what its maximum 
reading could be. 
The calculation routine (FIG. 6N) determines the quantities required for 
the rate counter, the state counter and the base counter based on the 
maximum input and the set point inputs.