PACKAGING MACHINE

A packaging machine including a supply of film for wrapping a package and a hot plate for heat fusing the film of a wrapped package. Power to the heating element is only delivered to the element during a heating cycle, thus conserving electrical power. A photo eye senses the package and a control circuit energizes the heating element the element reaches a desired heating temperature in 2 to 4 seconds. The frame of the machine includes a lower base member to which an upper base plate, preferably formed from a continuous sheet, is rigidly attached. The upper plate includes a support surface for the hot plate, a vertical wall to which the photo eye is attached that is interconnected with the support surface by a curved transition surface. The upper base plate also includes a lateral, rearwardly extending plate portion which defines at least a portion of a hardware enclosure.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1A,1B illustrate a wrapping machine constructed in accordance with a preferred embodiment of the invention. As is known, this type of machine is used to wrap packages with a stretchable, heat-sensitive film. Once the package is wrapped, heat is used to fuse the wrapping in order to seal the package. This type of machine is often used in supermarkets to package produce, meats, etc.

The illustrated wrapping machine is considered a tabletop machine. It should be understood, however, that the principles of this invention, to be described, are equally applicable to floor and self-standing wrapping machines.

As seen best inFIG. 1B, the machine includes a frame indicated generally by the reference character10that comprises a pair of side plates14,16and base18. In the preferred embodiment, the frame is made from aluminum and is formed from a single sheet of material formed into the U-shape shown inFIG. 1B.

A roll of stretchable packaging film20is supported for rotation by a pair of supports indicated generally by the reference characters21,22(seeFIG. 1A). In the illustrated embodiment, each support comprises a pair of support blocks24,26that are clamped together by a pair of threaded studs or screws28and associated wing fasteners30. The roll20itself is mounted to a reusable roll support that comprises end pieces or flanges34and an axle36. The ends of the axle36are removably captured between the support blocks24,26. When the supply of wrapping material is exhausted, the roll support is removed from the machine by removing the wing nuts30to enable the upper support block24to be removed. This releases the ends of the axle36and allows the operator to install a fresh supply of wrapping material or film.

A pivotally mounted plate or bridge40defines a wrapping surface40aupon which a package is wrapped with film from the supply20. The bridge40includes a pair of downwardly depending end flanges40bwhich overlie the outer, upper edge surfaces of the side plates14,16and a rigidizing back flange40c. Gaps41dprovide clearance for the upper edge of the side plates14,16. This construction provides support for the bridge when rotated into its horizontal position shown inFIG. 1A. The bridge40can be pivoted upwardly about a pivot42to expose the inside of the machine including its electrical box46. As seen best inFIG. 2, a cover plate46aencloses the electrical components housed within the box46. The cover46acovers a compartment48which houses circuitry and other components necessary for the operation of the machine.

The wrapping material is dispensed from the roll20along the path P. The material is guided by the cover46aand emerges through an opening defined between the front edge41of the bridge40and a retainer rod50. In the preferred and illustrated embodiment, the retainer rod50is covered with a coating, i.e., vinyl, to which the wrapping material releasably adheres so that the end of the material is maintained and positioned for easy grasping by the operator. The cover40is pivoted upwardly (as viewed inFIG. 2) to expose the feed path and facilitate feeding of the wrapping material.

The package to be wrapped is placed on the bridge40and a suitable length of film material is pulled from the supply by the operator. The operator then hand wraps the material around the package.

When the wrapping material fully encompasses the package, the portion of the wrapping surrounding the package is severed from the rest of the web by preferably contacting a heated rod58. Since the material is heat sensitive, contact with the heated rod causes severance of the material.

In general, once the wrapped package is severed from the rest of the web, the wrapping is gathered, tucked or folded underneath the package. According to the invention, the side of the package with the gathered/folded material is placed upon a hot plate subassembly indicated generally by the reference character60which includes a heated hot plate64. The heat from the hot plate64causes fusion of the material and, hence, seals the package.

According to the invention, the hot plate64is not energized or heated until a package is placed on its sealing surface64a. According to the preferred embodiment and, as best seen inFIGS. 2 and 3, the hot plate or heated platform64is pivotally attached to the base18by a lever arm assembly66which includes a lever arm66aand a sub-base66b. The lever arm66ais best shown inFIG. 4and includes a pair of side plates67a, a rear plate67b, a top plate67cand a support plate67dto which the hot plate64is attached by a plurality of fasteners69. The lever arm66amounts an axle68which, as seen inFIG. 3, includes ends that extend beyond the side plates67a. The sub-base66bincludes a plurality of mounting holes65by which the sub-base66bis rigidly attached to the base18. The sub-base66bincludes a pair of parallel, upturned flanges71, which include apertures71a, by which fasteners71bare used to secure ends of the axle68to the flanges71and which thus pivotally support the lever arm66a. The axle68is preferably supported by flanged bushings73.

In a preferred and illustrated embodiment, and as best seen inFIGS. 1A and 2, an indicator light75(i.e., LED) is mounted to the top plate67cof the lever arm66a. In the preferred embodiment, the LED is energized to indicate to an operator that the machine is in a heating/sealing cycle.

As seen inFIGS. 2 and 3, the hot plate subassembly60includes a micro-switch70that is secured to the back plate67bof the lever arm66aand which includes an actuating plunger72. In the illustrated embodiment, when the hot plate subassembly60is in its upper position as viewed inFIG. 2, the plunger72is depressed by contact with the sub-base66b. When a package is placed on the hot plate surface64a, either the pressure of the operator or the weight of the package or both causes the hot plate to move downwardly as viewed inFIG. 2, thereby causing upward movement in the opposite end of the lever arm66awhich, in turn, causes the micro-switch plunger72to be released allowing it to move outwardly (downwardly as viewed inFIG. 2). In the preferred embodiment, the hot plate subassembly is biased towards its upper position shown inFIG. 2by a tension spring76that is captured by a lug78forming part of the lever arm66aand a lug79secured to the sub-base66b(shown best inFIGS. 3 and 4).

As is known, the plunger72is coupled to normally closed (N/C) and normally opened (N/O) contacts within the micro-switch70which open and close, depending on the position of the plunger72. As will be explained, the micro-switch70is used to control the energization of the indicator light75and a heating element forming part of the hot pate64. It should be noted here, that the location of the micro-switch can be varied and, may in fact, be positioned further upstream from the hot plate64should earlier energization of the hot plate be desired.

Referring toFIG. 4, the details of the hot plate construction are illustrated. In addition to what has already been described, the hot plate64includes a base plate80which may be fiberglass, a sheet of insulation82and a heating element84, all of which are sandwiched together by a pair of longitudinal frame rails86and a pair transverse frame rails88. In the preferred embodiment, a temperature monitoring thermistor89having connection wiring89ais attached (as by taping) to the insulation sheet82. In the preferred embodiment, a heat sink pad91is provided to buffer the heat generated by the heating element84. The heat sink pad91allows the use of a thinner heating element layer. In the preferred embodiment, the heat sink pad is graphite and this type of material is available from EGC Enterprises, Inc., of Chardon, Ohio. Fasteners, including a plurality of nuts and washers, are used to maintain the assemblage.

As seen best inFIG. 4, the base plate80is rigidly fixed to one side of the lever arm66by suitable fasteners. The base plate80and insulation sheet82include respective access holes80a,82athrough which wiring W (shown inFIG. 3) for the heating element84are fed.

According to the invention, the heating element84is capable of reaching a desired operating temperature sufficient to provide sealing of the package in less than 10 seconds. This is achieved by utilizing a graphite-based heater and a suitable control circuit. According to the invention, the micro-switch70is used to sense the presence of a package on the hot plate64i.e. when a package is placed on the hot plate, the resulting downward movement of the lever arm66causes the micro-switch to change state. The micro-switch forms part of a power circuit for providing power to the heating element84sufficient for it to reach a desired operating temperature within a very short period of time, i.e., 2 to 10 seconds. In the preferred and illustrated embodiment, the heating element84is of a rapid, response flexible graphite foil heater, an example of which is available from EGC Enterprises, Inc., of Chardon, Ohio.

The ability for the hot plate to quickly reach the desired temperature is further achieved by reducing the thermal mass of the hot plate64, thus reducing the thermal time constant for the apparatus. As noted above, the base plate80is preferably constructed of fiberglass which has a relatively low mass. In addition, the insulation sheet82is also of a low mass material. One such material is sold under the “AEROGELS” brand and is sold by Aspen Aerogels, Inc. of Northborough, Mass. In addition, the heating element84is selected to have a low mass as well. In the preferred construction, the relatively low mass of the overall hot plate64, coupled with the rapid response time of the preferred heating element84, provides a hot plate with a very rapid response time. In the preferred embodiment, the heater reaches the desired operating temperature from ambient in 2 to 4 seconds.

FIG. 5illustrates a block diagram of the control system for energizing the hot plate64. The block100represents a source of power, in this case, AC power. AC power is fed to the micro-switch or cycle start switch70(the details of which will be described later) and to a pair of interval timers106a,106b. In the preferred and illustrated embodiment, the interval timer106ais a relatively low powered timer, (i.e., 1 amp) and is used to control the energization of the light indicator75and/or a signaling buzzer75a. The interval timer106bhas the capability of controlling significant power, (i.e., 30 amps) and is used to control the energization of the heating element84.

As seen inFIG. 5, both timers106a,106bare initiated by a change of state in the cycle start switch70(which is mounted to the lever arm66a). The length of time that the timers106a,106bapply power to their respective devices is determined by external resistors. In the preferred embodiment, a multi-position, rotary or slide switch114is used to connect suitable resistances to the timers106a,106b. The resistance selected determines, in part, how long a given timer will apply power to its associated device. In the preferred embodiment, the timer106aenergizes the light indicator75(and/or the buzzer75a) for a length of time totally determined by the resistance selected. The interval timer106b, however, applies power to the hot plate heater84as a function of both the resistor selected and the thermistor89that monitors the temperature of the heating element. In particular, the resistance selected and connected to the interval timer106bdetermines the maximum time that power will be applied to the heating element. However, if the thermistor senses that the desired temperature is reached prior to the time determined by the resistor, the timer106bwill time-out and interrupt power to the heater84. During periods of heavy usage, the actual time that power is applied to the hot plate heater84is substantially shorter than the heating cycle time determined by a given resistor. It should be noted, that because the indicator light75is controlled by an independent timer, the sealing time, as observed by the operator by virtue of the indicator light, remains unchanged, even though power to the hot plate heater may be terminated. As a result, consistent sealing of packages is assured, as compared to a circuit in which an indicator light is only illuminated when power to the hot plate84is applied.

FIG. 6is a schematic for a control circuit for the hot plate heater. In the illustrated embodiment, the circuit is powered from a 115 volt AC receptacle. The circuit includes a power switch200which, when closed, provides power to the heated rod cutter element58(shown inFIG. 1A), and the micro-switch70(also termed cycle start switch). As seen inFIG. 6, the temperature of the cutter element58is controlled by a conventional circuit carried on a circuit board58a, which is supplied by TUTCO Inc. of Cookeville, Tenn. The switched leg of the AC power is connected to the cycle switch70, the hot rod cutter circuit58a, and one side of a heat indicating light75. The micro-switch70forming part of the hot plate platform and seen best inFIG. 3is represented in the schematic by the double pole switch70termed a cycle start switch inFIG. 6. It is shown with the normally open (N/O) contacts closed because when the platform is in the upper position, the plunger72is depressed which opens the normally closed (N/C) contacts and closes the normally open contacts. When the platform is moved downwardly by placement of the package on the heating surface64a, the state of the switch70changes so that the normally open contacts open and the normally closed contacts close. The closure of the normally closed contacts causes power to be fed to pins21(+pins) of the interval timers106a,106b. This change in switch position causes activation of the timers106a,106band causes these timers to apply power to their associated devices, depending on the external resistance connected to a given timer. In the case of the interval timer106a(which controls the activation of the indicator light75), a selected external resistance is applied to its terminals34,33, the value of the resistance being determined by the position of the switch114.

In the case of the interval timer106b(which provides power to the heating element84), its time-out is determined by the external resistance applied to its associated terminals25,24. As seen best inFIG. 6, the actual resistance applied to these terminals is determined by the position of the switch114, as well as the thermistor89. The time-out of the interval timer106bcan vary for a given position of the switch114. The timer interval is also determined by the temperature of the heating element84as measured by the thermistor89. As a result, and especially during heavy usage, the interval of time during which power is applied to the heating element84may be substantially shorter than the actual sealing cycle time as indicated by the interval timer106a.

With the preferred construction, when a package is placed on the hot plate64, the resulting downward movement of the hot plate causes the micro-switch70to deactivate which, in turn, causes the energization of the timers106a,106bfor a predetermined time determined by the external resistance selected by the switch114and the thermistor89. As indicated above, the indicator light75is energized for a predetermined time determined solely by the resistance selected by the switch114. For the interval timer106b, the resistance selected by switch114determines the maximum time that the heating element84will be energized. If a threshold temperature is exceeded during the heating cycle, this excess temperature sensed by the thermistor89will cause the timer106bto time out and interrupt power to the heating element84.

With the present invention, the heater is only energized when a package is to be sealed. Since the heater is only energized for a predetermined length of time as determined by the rotary or slide switch114and thermistor89, leaving the package on the platform will not cause continuous energization of the heater which could cause overheating. It should be noted here that the rotary or slide switch114which is used to connect selected external resistors to the interval timers106a,106b, can be replaced by one or more potentiometers.

It should also be noted that the present invention contemplates a sealing machine that does not have an adjustable sealing time. For this type of machine, fixed resistors may be connected to the suitable terminals of the interval timers106a,106bor, alternately, timers having a fixed time interval may be used and, thus, eliminate the need for external resistors. It should also be noted that, in the preferred embodiment, the switch114may comprise a three position slide switch available from Switchcraft Inc., of Chicago, Ill., under part number 502-46313LDRX. The thermistor89in the preferred embodiment has a resistance of 500 K ohms at 25° C.

FIG. 7Aillustrates a block diagram of an alternate control system for energizing the hot plate64. The block100′ represents a source of power, in this case, AC power. AC power is fed to the micro-switch or cycle start switch70and to an off delay timer106′ which is arranged to energize the hot plate heating element84for a predetermined interval upon actuation. The communication of power to the hot plate heater is actually controlled by a solid-state switch114′. In order for the solid state switch to close and provide power to the hot plate heating element84, it must receive an ON signal from both the off delay timer106′ and from a thermostat118(which is also connected to the incoming AC power). In the preferred embodiment the thermostat118is attached and forms an integral part of the heating element84. The thermostat118senses an overheat condition and opens to interrupt the signal or power to the solid state switch114′ coming from the power block100′. As indicated above, if either the signal from the thermostat118or from the off delay timer106′ is terminated, the solid-state switch114′ opens to interrupt power to the hot plate heating element84.

FIG. 7Bis a schematic for the alternate control circuit for the hot plate heater. In the illustrated embodiment, the circuit is powered from a 115 volt AC receptacle. The circuit includes a power switch200′ which, when closed, provides power to the heated rod cutter element58(shown inFIG. 1A), the solid switch relay114′ and one leg of the off delay timer106′. The switched leg of the AC power is connected to the off delay timer106′, the hot rod cutter58, one side of a heat indicating light206, one side of the thermostat118and one side of the heating element84. The micro-switch70forming part of the hot plate platform and seen best inFIG. 3is represented in the schematic by the double pole switch70. It is shown with the normally open (N/O) contacts closed because when the platform is in the upper position, the plunger72is depressed which opens the normally closed (N/C) contacts and closes the normally open contacts. When the platform is moved downwardly by placement of the package on the heating surface64a, the state of the switch70changes so that the normally open contacts open and the normally closed contacts close. The closure of the normally closed contacts causes power to be fed to pin9of the off delay timer106′ and interrupts power to pin7. This change in switch position causes the off delay timer106′ to send a signal to pin3of the solid state relay114′ for a predetermined length of time as determined by the adjustable potentiometer210′ that is connected across pins5and6of the off delay timer106′. If the thermostat118that forms part of the heating element84is closed, the application of the power signal to pin4of the solid state relay114′ causes power to be applied to the hot plate heater from pin1of the solid state relay114. When the off delay timer106′ times out, the interruption of signal to pin3of the solid state relay114′ causes the de-energization of the hot plate heater64.

It has been found, that with the disclosed construction and the use of the thin film graphite-based heater, continuous heating of the hot plate is not required. It has been found that the application of power to the heating element results in the heater reaching a desired temperature within 2 to 10 seconds, preferably less than 4 seconds. In short, during machine operation power is applied to the heater for only short intervals of time and, as a result, significant power savings can be realized as compared to a package-wrapping machine in which the hot plate is continuously energized.

FIGS. 8 and 9illustrate another preferred embodiment of the invention. To facilitate the explanation, components and structures of the alternate embodiment that are the same or similar to the components and structures shown inFIGS. 1A,1B and2will be given like reference characters, followed by an apostrophe.

The packaging machine shown inFIG. 8includes a frame indicated generally by the reference character10′. Referring also toFIG. 9, the frame10′ comprises a lower base member220to which an upper base plate224is rigidly attached. As seen best inFIG. 8, the upper base plate224spans the entire width of the lower base member220and includes downturn flanges224a,224bwhich are secured to associated upturned flanges220a,220b(seeFIG. 9) integrally formed in the lower base member220. As seen best inFIG. 9, the upper base plate224is a continuous plate that includes a horizontal support surface230and a vertical wall232joined together by a continuous, arcuate transition236. From the vertical wall236, another horizontally extending plate portion238is formed and joins an L-shaped vertical plate240(seeFIG. 9) which joins and rigidly attaches a rear downwardly depending flange238aof the upper base plate to the lower base member220. With the disclosed construction, an extremely rigid and cost effective frame is defined by two formed, sheet metal components. The upper horizontal plate section238, as seen inFIG. 9in cooperation with the L-shaped vertical plate240defines an electrical box46′ which houses circuitry and other components necessary for the operation of the machine (not shown). With the disclosed arrangement, the construction of the packaging machine is greatly simplified and many individual frame components used in theFIG. 1embodiment are eliminated.

Like the embodiment shown inFIG. 1, theFIG. 8embodiment includes a pivotally mounted plate or bridge40′ that defines a wrapping surface40a′, upon which a package is wrapped with film from a supply20′. Side plates14′ integrally formed in the lower base member220include integrally formed flanges242that mount a heated rod cutter element58′ and a retainer rod50′. The bridge plate40′is pivotable about an axle or pivot42′ to expose the inside of the machine and to facilitate feeding of the film from the supply roll20′. The feed path for the film is indicated by the reference character P′. As seen best inFIG. 9, the forward end of the bridge plate40′ defines a curved rigidizing edge40c′. As seen best inFIG. 8, the bridge40′ includes a pair of downwardly depending end flanges40b′ which overlie the outer, upper edge surfaces of the side plates14′. This construction provides support for the bridge40′ when rotated into its horizontal position. The illustrated arrangement is substantially similar to the arrangement shown in connection with the bridge40shown inFIG. 1A. It should also be noted that the curved forward edge40c′ of the alternate bridge plate40′ provides a construction by which the bridge plate40′ can be pivotally mounted so that it opens about a pivot defined by the curved edge40c′ and an associated pivot rod (not shown). The engagement of the upper edges of the side plates14′ with the end flanges40b′ maintains a bridge plate40′ in the horizontal position shown inFIG. 9.

The horizontal plate portion230of the upper base plate224includes a heated hot plate64′ which may be similar or substantially the same as the hot plate64shown inFIG. 1A. However, the hot plate64′ is rigidly attached to the fixed, upper base plate224and is not pivotally movable. In the embodiment shown inFIG. 9, a photo eye250is used to detect the presence or absence of a package and forms part of the heating circuit for the hot plate64′. When a package is detected by the photo eye,250,the heating cycle is initiated in order to heat the hot plate64′ and thereby fuse the package film.

It should be noted that the sealing functioning performed by the packaging machine embodiment shown inFIGS. 9 and 10is similar to sealing function performed by the packaging machine embodiment shown inFIG. 1A. However, the pivot assembly and associated plunger switch forming part of the packaging machine shown inFIG. 1Aare eliminated in the packaging machine shown inFIG. 8.

The film supply20′ is supported for rotation by a pair of supports indicated generally by the reference characters21′,22′, which may be the same or similar to the supports21,22shown inFIGS. 1A,1B.

The packaging machine embodiment shown inFIGS. 9 and 10requires less individual components than the packaging machine shown inFIG. 1A. Moreover, the frame comprises only two major components, i.e., lower base member220and upper base plate224. Each base member is formed from a single sheet metal and once assembled, form a rigid frame which as seen best inFIG. 9, can be easily cleaned and maintained. The elimination of the pivoting platform and the use of a continuous plate member that forms both the support surface for the hot plate and the cover for the electrical enclosure substantially reduces costs while providing surfaces that can be easily cleaned and maintained. The alternate embodiment substantially reduces the number of moving parts such as the platform assembly shown inFIG. 1A, thus reducing or eliminating a maintenance issue. In the preferred and illustrated embodiment, the lower base member and the upper base plate are formed from a continuous sheet of material, such as steel or aluminum sheet metal.

FIG. 10Aillustrates a block diagram of an alternate control system for energizing the hot plate64′ shown inFIGS. 8 and 9. The block100′ represents a source of power, in this case AC power. Those skilled in the art will recognize that entire circuits may be DC powered. AC power is fed to the cycle start switch250which in this alternate embodiment preferably comprises a photo eye assembly. A photo eye assembly suitable for this application is available from Banner Engineering of Minneapolis, Minn. under the Part No. QSI18VP6D.

When the cycle start switch250closes, power is communicated concurrently to an interval timer106″ and a thermostat118′. The interval timer106″ doses for a predetermined interval of time after energization, i.e., 5 seconds. As indicated above, power is also communicated to the thermostat118′ which, if closed, communicates power to a temperature controller260. In the preferred embodiment, the thermostat118′ is located within the hot plate assembly64′ and opens to interrupt power if the hot plate temperature exceeds a predetermined value.

If the thermostat118′ is closed, power is communicated to the temperature controller260, which in the preferred and illustrated embodiment is a proportional-integral-derivative (PID) controller. The controller260directs power to the hot plate64′ via the interval timer106′. The temperature of the hot plate64′ is monitored by a feedback component such as a thermistor or thermocouple266. At the start of the heat cycle, the temperature controller260communicates a substantial current to the hot plate64′ in order to quickly heat the hot plate64′ to a desired sealing temperature. When the preselected temperature is reached and communicated to the temperature controller260via the feedback component266, the temperature controller260modulates the power being fed to the hot plate in order to maintain the selected temperature.

In the preferred embodiment shown inFIG. 10A, when the photo eye250detects a package being placed on the hot plate64′, the temperature controller feeds sufficient power to the hot plate in order to heat it to a desired temperature within a few seconds, i.e., three. Once this temperature is reached, the temperature controller modulates power to the hot plate64′ to maintain it at the desired temperature until removal of the sealed package is detected by the photo eye250. If a package is inadvertently left on the hot plate platform64′ beyond a predetermined time, i.e., five seconds, the interval timer106″ opens to interrupt power to the hot plate64′. In the preferred embodiment, a heat cycle cannot be reinitiated until removal of the package from the hot plate64′ is detected by the photo eye assembly250.

FIG. 10Bis a schematic of the alternate control system/circuit for the hot plate heater that is shown in block form inFIG. 10A. The circuit is powered from 115 volt AC receptacle264. The circuit includes a power switch200″ which, when closed, provides power to the heated rod cutter element58′ and a DC power supply270. The closure of the AC power switch200′ also communicates power to one leg or side of a solid state switch or relay268and one power leg of the temperature controller260. The photo eye assembly250is arranged such that when placement of a package on the hot plate64′ is detected, the photo eye assembly250causes power to be communicated to the other power leg or side of the solid state switch268causing its closure and the communication of DC power to the other leg of the temperature controller260and to a contact on the solid state switch268. Power is thus communicated to the hot plate64′ provided that the appropriate contacts of the interval timer106″ are closed and the thermostat118′ is closed.

In the illustrated embodiment, the hot rod cutter58′ is powered by the same circuit as that shown inFIG. 6and as used in the embodiment of the packaging machine shown inFIG. 1A.

As the hot plate approaches the set point temperature, the PID controller260begins to modulate power in an effort to reduce the rate of heating. As the set point is attained, the PID temperature controller260will modulate power to maintain this temperature until the system is deactivated. A potentiometer276forms part of the circuit and is used to modify the resistive feedback to the temperature controller260and provides a means by which different temperature set points can be set for the hot plate64′.

With the disclosed circuit and package detecting methodology, a robust control circuit is provided for providing an “instant on” function for the packaging machine. It is believed that the arrangement which uses a photo eye assembly250for package detection causes quicker energization of the hot plate when a package is to be sealed. With theFIG. 1Aembodiment, the package must be placed on the platform and the platform must pivot downwardly in order to actuate the plunger switch70. In this alternate embodiment, as the package is moved from the wrapping platform40′ to the hot plate64′, its movement is detected and the heating cycle is immediately initiated even before the package to be sealed reaches the hot plate64′. This causes the hot plate to reach its sealing temperature quicker as compared to theFIG. 1Aembodiment.

It is believed that the alternate control system/circuit, reduces costs while improving functionality. It is believed that the circuit can be further simplified by eliminating what some would consider to be redundant components. For example, the temperature controller260can be used without the interval timer106″. The feedback component266can be relied upon to control the temperature controller in order to cause it to terminate power to the hot plate when a temperature above a predetermined threshold is detected by the feedback component266. It is believed that the thermostat118′ may also be eliminated if the temperature controller is also used to detect an over temperature condition in the hot plate64′ as measured by the feedback component266.

In the disclosed embodiment, the photo eye assembly250works in conjunction with a DC power supply and controls the operation of the DC powered control components. The disclosed photo eye assembly operates on a supply voltage of from 10 to 30 volts DC. There are photo eye assemblies that operate with a supply voltage of 110 volts AC. If this type of photo eye assembly is employed, the DC power supply270could be eliminated. In fact, a photo assembly of the type that operates on a supply voltage of 110 AC can be directly substituted for the plunger switch70of the first embodiment (seeFIGS. 3 and 6).

A suitable temperature controller is available from Crydom Inc. under Part No. MCTC2425JLA-E. A suitable solid state switch/relay is available from Crydom Inc. of San Diego, Calif. under Part No. EL240A20-US. A suitable interval timer is available from Precision Timer, a division of Prime Technology of North Branford, Conn. under part No. 843E-150. A suitable DC power supply is available from CUI Inc. of Tualatin, Oreg. under Part No. VSK-S5-24UA-T.

The invention has been described as forming part of a hand-wrapping machine use in supermarkets. However, the invention has much wider applicability. For example, it can be used in other environments such as laundry wrapping environments. It also may be used as part of automated wrapping machines used in various industries. Accordingly, the present invention should not be limited to wrapping machines of the type found in supermarkets.

Although the invention has been described with a certain degree of particularity, those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.