Laminator with heating control system

An improved laminator with a novel heating control system is disclosed for particular employment with laminating packets formed of an article to be laminated positioned between top and bottom leaves. When the packet is aligned in a ready position within the laminating machine, heating elements in a heating zone of the laminating machine are activated while the packet is stationary. When the heating zone attains a first temperature, movement of the packet is initiated in the heating zone. During passage through the heating zone, when the heating zone attains a second temperature, power to the heating elements is cycled so as to maintain the second temperature substantially constant. Also, to further minimize temperature overshoot, power to the heating elements is temporarily removed when the first temperature is attained. With the system of the invention, the dual problems of temperature overshoot and insufficient lamination of lead ends of the packet is avoided.

BACKGROUND OF THE INVENTION 
In reissue patent application Ser. No. 965,097, "POWER ACTUATED LAMINATING 
MACHINE", filed Nov. 30, l978, incorporated herein by reference, a 
laminating system is disclosed for use with laminating packets. Each 
packet preferably comprises upper and lower laminating leaves such as 
polyethylene film with a heat reactivatible adhesive layer thereon and a 
cardboard tab attached at one end of the packet which is releasable such 
as by adhesive tape. After the packet is run through the laminating 
machine, the tab is then removed. 
In this system, the lamination machine provided has upper and lower heating 
plates forming a heating zone and rearwardly of the heating zone upper and 
lower drive rollers are provided which form a nip for engaging the 
cardboard tab. Initially, an operator inserts the packet into the machine 
into a "ready" position. Thereafter, the operator may activate a handle on 
the machine which causes the heating plates to approach one another and 
also causes the drive rollers to engage the cardboard tab. 
When the handle is engaged, the heaters come up to proper operating 
temperature and a thermistor is provided through a zero crossing switch 
which causes the heaters to turn off and on to maintain desired 
temperature. A drive motor is activated which causes the packet to begin 
moving through the machine. As the trailing edge of the packet passes a 
sensor, a time delay is actuated and the motor continues to operate for a 
sufficient length of time for the packet to completely clear the machine. 
The tab is then torn off the packet and the lamination operation is 
completed. 
With this system, temperature overshoot problems occur since the heating 
zone temperature continues to rise despite disconnection of power after 
achieving an operating temperature. This temperature overshoot causes 
excessive heating of the packet and particularly the connection tape 
between the tab and the packet. Also, since the packet remains stationary 
while the temperature increases to operating temperature, the packet does 
not act as a "load" in the heating zone since typically only the lead end 
of the packet is present in the heating zone. Since this lead end is 
stationary in the heating zone, the amount of heat transfer is less than 
it is when the packet is moving and consequently excessive temperature 
rises occur. 
SUMMARY OF THE INVENTION 
It is an object of the invention to laminate an object positioned within a 
laminating packet such that the entire object is laminated in a uniform 
manner without initial portions of the packet experiencing low heat 
laminating conditions while other portions of the packet exhibit higher 
heat laminating conditions. 
It is a further object of the invention to prevent temperature overshoot 
which results in excessive heating during laminating operation which can 
result in damage to the laminating film and/or adhesive tape connecting a 
tear off cardboard tab to the packet film leaves. 
It is an additional object of the invention to provide temperature control 
during laminating so as to provide a superior product which has uniform 
laminating characteristics. 
In accordance with the method and apparatus for laminating of the 
invention, the lead edge of the packet is initially placed in a ready 
position in the heating zone prior to applying electrical power to the 
heating member. Electrical power is then applied to the heating member 
without initiating movement of the packet through the heating zone. When 
the heating zone attains a first temperature, movement of the packet is 
initiated through the heating zone. While the packet is moving, power is 
controlled to the heating member to maintain the heating zone at a 
subsequent second temperature which is substantially higher than the first 
temperature and which is suitable for continuous laminating of product. 
Preferably to reduce temperature overshoot, when the first temperature is 
reached the power to the heating member is temporarily interrupted. 
Thereafter, as the packet is moving through the heating zone power is 
reapplied until the second temperature is reached at which point the power 
is cycled on and off so as to maintain the second temperature. When a 
trailing edge of the packet has approximately cleared the heating zone, 
power is disconnected to the heating member to permit cooling thereof. 
With the invention, insufficient laminating at leading edges of the packet 
is prevented by allowing the heaters to warm up prior to movement of the 
laminating packet. Movement of the packet is initiated, however, before a 
desired operating temperature for continuous laminating is achieved so as 
to present a moving "load" and thus prevent temperature overshoot. Also, 
power to the heating elements is interrupted when the first temperature is 
reached to further prevent temperature overshoot. Finally, when the second 
temperature is achieved, the temperature is stabilized. The overall result 
is the elimination of excessive heating at the leading edge of the packet 
caused by temperature overshoots and the overall lamination quality is 
greatly improved by providing a uniform laminating characteristic over the 
entire packet yet without harming the packet itself or particularly 
connecting tape which retains the tear-off cardboard tab to the packet 
laminating leaves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1A, a laminator machine 10 of the invention has a front 
panel 11 with an entrance aperture 12 therein into which a laminating 
package such as shown in FIG. 1B can be inserted. An operator start 
command lever 13 is provided which initiates lamination after insertion of 
the packet into a "ready" position. A main power on-off switch 14 is 
preferably provided on the front panel together with a main power light 
15. A "ready" light 16 is similarly positioned on the front panel for 
indicating positioning of a compatible packet in the machine. 
The laminating packet 17 as shown in FIG. 1B contains an article 18 to be 
laminated. Article 18 is positioned between lower and upper laminating 
leaves 19 and 20 such as of polyethylene and having a heat reactivatible 
adhesive layer thereon in well-known fashion. A cardboard tab 21 connects 
at a leading end of the packet to the leaves 19 and 20 by use of a strip 
of tape 22. In place of the above-described packet, with the laminating 
machine of the invention it is also possible to employ a cardboard carrier 
within which the laminating leaves and product are positioned in sandwich 
fashion. 
As shown in FIG. 2A, the laminating machine contains an upper and lower 
heater plate 23 and 24 which form a heating zone through which the 
laminating packet passes. A thermistor 9 may be placed on the lower heater 
plate 24, for example, to measure a temperature at a surface thereof which 
approximates a temperature within the heating zone between the plates. 
Upper and lower drive rollers 25 and 26 are provided rearwardly of the 
heating zone for engagement with a leading end of the packet and 
preferably the cardboard tab 21. Initially the heating plates may be 
spaced such as by providing the upper heating plate 23 movable, and as 
described in the aforementioned reissue application. Also, the upper drive 
roller 25 may be movable so that in a down position it forms a nip which 
engages the cardboard tab 21 as the operating lever 13 is pulled, again as 
described in the reissue application. 
A drive motor 27 is linked to the drive rollers to permit selective drive 
thereof. 
A photocell preferably of a reflection type is positioned at 28 so as to 
sense presense of the packet in the machine. 
Operation of the laminating machine system will now be described by 
reference to FIG. 3. When the power switch is activated, the power light 
illuminates. Thereafter, a pouch is inserted in the machine into a "ready" 
position which is sensed by the photocell 28 and the "ready" light 
illuminates. Thereafter, the operator lowers the handle 13 which provides 
the operator start command. This operator start command results in heater 
power being applied to the heater elements until a first temperature is 
attained such as 230.degree.-240.degree. F. At this first temperature 
termed in the graph as a "set temperature-lower", power to the motor for 
the drive rollers is applied and the laminating packet begins moving 
through the machine. At the same time, power to the heaters is cut 
temporarily and then reapplied until a second higher temperature such as 
approximately 275.degree. F. is attained. This temperature is chosen as 
the most desirable continuous laminating temperature after steady state 
conditions for laminating have been attained. Heater power is then cycled 
on and off so as to approximately maintain the second temperature termed 
in the graph as a "set temperature-upper". Finally, when the laminating 
packet clears the photocell, power to the heaters is disconnected, the 
ready light extinguishes, and a timer is activated which allows the drive 
motor to continue operating until the packet clears the machine for a 
given time interval. The temperature of the heating zone is shown at the 
bottom of the graph in FIG. 3. 
With the invention, temperature overshoots resulting in excessive heating 
are avoided and also uneven laminating such as an initial cold laminating 
followed by initial excessive heating laminating is avoided. Also, the 
sensitive adhesive tape employed for connecting the cardboard tab to the 
packet is not damaged with the heating control system in accordance with 
this invention. 
FIG. 4 is one preferred electrical circuit for performing the functions 
described in FIG. 3 The on/off switch 14 supplies mains power 29 to a DC 
power supply 30 which supplies DC power for operating the various 
electronic circuits. AC power is also fed to AND gate 43 and also AND gate 
32. The operator start command 31 which comprises a multiple switch 
controlled by the lever arm 13 also provides an enabling signal to AND 
gate 43, AND gate 39, and AND gate 32. 
AND gate 32 when enabled supplies the AC power to the triac 34 which 
controls the heaters. The triac is also cycled by the temperature 
controller 35 preferably constructed as an integrated circuit RCA type 
3059. This integrated circuit receives an input from amplifier 33 
connected to the pouch sensor photo-cell 28. Ready light 16 also connects 
to amplifier 33. 
The temperature controller integrated circuit 35 further receives an input 
from a resistance type temperature sensor bridge 36. This bridge circuit 
has one leg which can be selectively shunted by a transistor switch 37 
when so directed by the inhibited pulse generator 40 which generates 
switching pulses for the transistor switch 37. A timer 41 preferably 
formed of an integrated circuit RCA type 555 controls the inhibit pulse 
generator for creating the switching pulses for the transistor switch 37. 
Timer 41 receives enabling signals from the AND gate 39 which in turn is 
enabled by signals from the temperature controller 35 through amplifier 38 
and also from the operator start command 31. The timer 41 controls the 
triac 42 which further receives AC power through the AND gate 43. Triac 42 
controls the motor 27. 
The circuit determines the lower and upper "set temperatures" (also termed 
the first and second temperatures) in the following manner. Upon receiving 
an operator start command and pouch signal from amplifier 33, the 
temperature controller 35 triggers the triac 34 on. The triac 34 remains 
on until the selected heater temperature is reached. At this point, the 
bridge temperature sensor 36 which monitors the heater temperature 
initiates a signal to the temperature controller 35 turning the triac 34 
off. This action of triac on and off maintains the heater temperature to a 
value in accordance with signals from the temperature sensor bridge. The 
temperature sensor bridge can be out of balance low, out of balance high, 
or in balance. In two of these conditions power to the heater is off. In 
the third condition power to the heater is on until the bridge changes as 
a result of increased heater temperature, to one of the other two 
conditions at which time heater power is switched off. The point at which 
power to the heater is turned off initiates a timer turning the motor 
triac to on and applying power to the motor. Power to the motor remains on 
until the timer times out. 
The value of the temperature sensor bridge which determines at what point 
the motor is turned on is a function of not only the bridge sensor but 
also of the bridge shunt. The bridge shunt alters the bridge balance on 
the initial machine turn on so as to turn the motor on at a lower heater 
temperature (first temperature). This point is referred to as the lower 
set temperature. When the bridge shunt is inhibited, the temperature 
sensor bridge is set to the upper set temperature. 
It will be appreciated by those skilled in the art that other electronic 
circuitry may be employed for performing the novel functions of FIG. 3. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that I wish to embody within the scope of 
the patent warranted hereon, all such embodiments as reasonably and 
properly come within the scope of my contribution to the art.