Abstract:
Control system and apparatus for controlling power consumption of a heat chamber such as a shrink tunnel. The system and apparatus of the present invention is modification to conventional systems, and takes advantage of the inherent equipment usage model in a packaging process. When the shrink wrap sealer has been idle for a predetermined duration, control circuitry in the shrink tunnel forces the tunnel to enter an energy savings mode.

Description:
[0001]    This application is a divisional of co-pending Ser. No. 10/286,243 filed Nov. 1, 2002, the disclosure of which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Packaging systems typically utilize two distinct machines to perform seal and shrink functions. The first is a shrink wrap sealer, which is employed to wrap and seal plastic film about an article. These machines conventionally utilize a heated wire to seal film layers to one another and to melt through the layers in order to separate one article from another as the articles pass through the machine. When the sealer jaw is lowered, current is supplied to the wire to heat the wire to a high temperature in order to affect the seal and cutting operation. The appearance of the resulting seal is fine and neat as the film shrinks tightly around the package, especially where polypropylene films are involved. Such hot wires are typically used to form both end seals and side seals.  
           [0003]    After the plastic has been wrapped and sealed around the article, the article is transferred into the second machine, a shrink tunnel. The shrink tunnel is a heated chamber through which the article is passed, typically on a conveyor belt. The heat within the chamber causes the plastic wrap to shrink, tightening it around the article. Tunnel temperature and dwell time are typically variable in order to achieve the desired result for a particular plastic.  
           [0004]    The shrink tunnel uses a large amount of energy to maintain the tunnel at the desired temperature, even in the absence of articles passing through it, as it runs independently of the sealer. Moreover, heat is lost to the surroundings through both the inlet and the outlet of the shrink tunnel, and to the conveyor itself which is often made of a thermally conductive material.  
           [0005]    In a typical packaging process, articles are passed into the shrink tunnel immediately after they are sealed. It would be desirable to implement an energy saving mode for the shrink tunnel that responds to inactivity of the shrink wrap sealer in order to reduce the overall power consumption of the shrink tunnel.  
         SUMMARY OF THE INVENTION  
         [0006]    The energy consumption problems of the prior art have been overcome by the present invention, which provides a control system and apparatus for adjusting the energy usage of a heat tunnel, such as a shrink tunnel. The system and apparatus of the present invention is a modification to conventional systems, and takes advantage of the inherent machine usage model of the shrink wrap process. When the shrink wrap sealer machine, which typically carries out the preceding operation in a packaging process and is generally physically separate from the heat tunnel, has been idle for a predetermined amount of time, the power consumption of the shrink tunnel is automatically reduces by entering an energy efficient mode. In this energy efficient mode, the energy used by certain high power components of the tunnel, such as the heaters and blower, is reduced, and conveyor speed can be reduced.  
           [0007]    The control system of the present invention thus directly monitors the activity at the shrink wrap sealer. If the control system of the shrink tunnel does not detect any sealer activity within a predetermined time period, it forces the shrink tunnel to enter an energy efficient state, where the temperature, blower speed and/or conveyor speed are reduced to a predetermined percentage of the operating levels. The aforementioned predetermined time period and predetermined percentage are preferably user-selectable variables.  
           [0008]    In a preferred embodiment, a wireless signal is generated by the shrink wrap sealer each time the sealer jaw is depressed. Wireless receptors at the shrink tunnel receive these signals and pass this information to the control circuitry of the shrink tunnel. This control circuitry monitors the elapsed time between these received signals. If the elapsed time between received signals exceeds a duration specified by the operator, the control circuitry then enters a power savings mode. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]    [0009]FIG. 1 is a perspective view of a shrink wrap sealer in accordance with the present invention;  
         [0010]    [0010]FIG. 2 is a side view of a shrink wrap sealer in accordance with the present invention;  
         [0011]    [0011]FIG. 3 is a side view of a shrink tunnel in accordance with the present invention;  
         [0012]    [0012]FIG. 3A is a perspective view of the tunnel of FIG. 3;  
         [0013]    [0013]FIG. 4 is a front view of the shrink tunnel user interface; and  
         [0014]    [0014]FIG. 5 is a flow chart of the shrink tunnel control electronics in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The typical packaging process includes wrapping a plastic film around an article and sealing this film so that it completely envelops the article. The film is then made to contract about the article, typically upon the application of heat. This contraction draws the film toward the article, causing the article to be tightly wrapped in the plastic film. A shrink wrap sealer performs the wrapping and sealing function, while a shrink tunnel heats the plastic to create the tight fit, known as “shrink wrap”.  
         [0016]    Turning now to the figures, there is partially shown the equipment used in a typical packaging process. It should be understood that the sealer and tunnel are shown by way of illustration, as the present invention is not limited to any particular embodiment of the sealer or the tunnel.  
         [0017]    Referring to FIG. 1, shrink wrap sealer  10  positions the plastic film with which the article is to be wrapped. The film is placed around the article, and then sealed. The sealing operation is performed by sandwiching the film between top sealer jaw  11  and bottom sealing jaw  11 A, the top sealing jaw  11  being pivotally connected to the top surface of the shrink wrap sealer  10 . The sealer jaw  11  contains a wire or other electrical resistance heating element (such as a blade, not shown) that is heated each time that the jaw is depressed. The heating of this heat sealing element melts together layers of the plastic film to create an envelope of plastic film around the article.  
         [0018]    In a preferred embodiment, activity of the sealer is indicated by a signal generated when the top seal jaw contacts the bottom seal jaw. For example, mounted on sealer jaw  11  is a jaw magnet  12  (FIG. 2). Upon closure of the sealer jaw, jaw magnet  12  contacts opposite base magnet switch  13  on the bottom jaw. This contact generates a signal, which is then sent to the control circuitry contained in the sealer. The control circuitry receives this signal from the magnetic switch, and generates another electrical signal that is sent to transmitters as discussed below. Other means for generating a signal based upon contact between the top and bottom jaws, such as a momentary switch, could be used and are within the scope of the present invention.  
         [0019]    Referring to FIG. 2, one or more transmitters  13   a  and  13   b  are mounted on the sealer  10 , such as along the side of the sealer leg  14 . These transmitters generate a signal each time the sealer jaw  12  is depressed. In the preferred embodiment, this signal is generated wirelessly using infrared light. However, those skilled in the art will appreciate that other methods of communication could be used as well. These methods could include other types of optical signals, radio waves, or more traditional cabled connections. Preferably multiple transmitters are used to maximize the field which is covered by the generated signals. In the case of infrared light, which is an optical medium, there must be a clear line of sight from the transmitter to the receiver. This combination of multiple transmitters allows flexibility in placing the shrink wrap sealer  10  in a variety of positions relative to the shrink tunnel.  
         [0020]    Referring to FIGS. 3 and 3A, a detector  15  such as an infrared detector is located on the side of the shrink tunnel  20 . This detector  15  receives the infrared signal (or other type of signal) sent by the transmitters  13  mounted on the sealer.  
         [0021]    The shrink tunnel  20  includes a conveyor belt  16  onto which the sealed article is placed. The conveyor belt  16  draws the article being sealed into the heated compartment  17 . Inside the heated compartment  17 , there are one or more conventional heating elements (not shown) that are used to raise the temperature of the compartment to a predetermined level. The operator, using the keypad, can select the desired temperature of the chamber. Higher temperatures are typically needed for thicker films. The hot air is circulated inside the compartment by a blower fan (not shown). This blower fan insures that the air throughout the entire chamber is at a uniform temperature. Articles are transferred into the tunnel on conveyor belt  16 . The speed of the conveyor belt determines the amount of time that the article is subjected to the tunnel temperature and is selectable by the operator of the tunnel using the keypad.  
         [0022]    The detector  15  is in electrical communication with the shrink tunnel control circuitry via a cable or the like. Each time a signal is detected by the detector  15 , a signal is generated by the detector and sent to the control circuitry. The control circuitry then uses this signal to determine the proper operation of the shrink tunnel. There are two parameters that can be set, such as manually, by the operator to control the power savings mode operation. The first parameter is “Inactivity Time”. This is the amount of time, in minutes, which the sealer jaw must be inactive before the shrink tunnel can enter its power savings mode. The second parameter is “Power Savings Percentage”. This value represents the reduction in power, as measured by percentage in blower speed, conveyor belt speed and oven temperature, to be implemented in the power savings mode.  
         [0023]    [0023]FIG. 4 shows the user interface for the shrink tunnel control circuitry. It should be understood that the user interface is shown by way of illustration, as the present invention is not limited to any particular embodiment of a user interface. This interface allows the operator to set the two aforementioned parameters. The user interacts with the interface using panel  100 . Panel  100  has several buttons, as well as a display. Power Save button  110  is used to manually initiate the power savings mode for the shrink tunnel. In other scenarios, it is used to input various power savings parameters. Up button  111  and Down button  112  are used to increase and decrease, respectively, the values shown on output display  113 . This output display is used to inform the user of various settings, such as oven temperature.  
         [0024]    To set the Inactivity Time, the following steps are taken. The operator actuates and holds the Power Save button  110  for a predetermined duration, such as 3 seconds. After this duration, the output display  113  will show the current Inactivity Time. This value can be adjusted, in specific intervals (such as 1-minute intervals), using Up button  111  and Down button  112 . An exemplary minimum value is 5 minutes, while an exemplary maximum Inactivity Time value is 255 minutes. In this embodiment, an Inactivity Time value of 0 will completely disable the power savings mode and neither the Power Save button  110  nor the lack of sealer activity will allow the tunnel to enter Power Savings mode. An Inactivity Time value of 255 has the effect of setting an infinite Inactivity Time. In this case, lack of sealer activity will never cause the shrink tunnel to enter Power Savings mode. However, Power Savings mode can still be invoked, such as by actuating Power Save button  110 . Because of the special operations associated with values of 0 and 255, the useful range of the Inactivity Time is from 5 minutes up to 250 minutes. Those skilled in the art will appreciate that the upper value of 255 is chosen by way of illustration; other values can be chosen to achieve the same objective.  
         [0025]    After the operator has input the desired Inactivity Time value, he may actuate the Power Save button  110  again in order to set the Power Savings Percentage. If the Power Save button  110  is actuated while the output display  113  is still showing the Inactivity Time value, the control circuitry will then display the current Power Savings Percentage. This value can be adjusted using the Up button  111  and the Down button  112  in a manner similar to that used for the Inactivity Time. The value of the Power Savings Percentage can be from 0 to 99. In the current implementation, any value above 95 will cause the shrink tunnel to shut down when Power Savings mode is entered. The Power Savings Percentage determines the extent of the operation of the shrink tunnel while in Power Savings mode.  
         [0026]    As an illustration of the power savings mode, a tunnel with a 300° operating temperature and a Power Savings Percentage of 40% would reduce its temperature to 120° and reduce the speed of the blowers and conveyor belts to 40% of their normal operating rates in Power Savings mode.  
         [0027]    [0027]FIG. 5 is a flowchart illustrating the process used to determine whether to enter Power Savings mode. Decision Box  200  checks whether the sealer jaw is closed. If the jaw is closed, as determined by the presence of a signal at the infrared detectors, the code progresses to Action Box  201 . In this Box, a flag, called Jaw Active, is set. The Jaw Active flag is used to denote that the jaw has been activated at least one time before Power Savings mode is invoked. Additionally, the jaw timer, which counts the minutes since the last sealer jaw operation, is reset. This path is followed each time the sealer jaw closes.  
         [0028]    If the jaw is not closed, the code progresses to Decision Box  202 . If the jaw timer has not been set, this means that either the sealer jaw has never closed, or it was closed the previous time that this code was executed. Decision Box  203  determines whether the sealer jaw has ever been closed by checking the Jaw Active flag that only gets set in Action Box  201 . If the Jaw Active flag is not set, the sealer jaw has not been used and the code terminates. This behavior guarantees that the shrink tunnel will never enter power savings mode unless the sealer jaw has closed at least once.  
         [0029]    Action Box  205  is executed if the sealer jaw has just opened. In this case, the Jaw Active flag will be set, but the Jaw timer has not been set to the Inactivity Time. Action Box  205  sets the Jaw timer to the Inactivity Time. This timer now begins counting down toward zero.  
         [0030]    Decision Box  204  is entered if the sealer jaw is currently open, but the Jaw timer has been already set. If the timer has not reached the Inactive Time, the code simply terminates. If the timer has expired, the sealer jaw has been inactive for at least the amount of time specified by the Inactivity Time. If all other conditions are met, the shrink tunnel should enter power savings mode.  
         [0031]    Decision Box  206  checks if automatic power saving mode has been enabled. If the Inactivity Time was set to 0 or 255, the shrink tunnel will not enter power savings mode and the code terminates. If the Inactivity Time is set to any value between 5 and 250, the code will move to Decision Box  207 .  
         [0032]    Decision Box  207  checks if the tunnel is already in a shutdown process. In this embodiment, there is a cool down mode wherein the tunnel is cooled to a lower temperature before being completely turned off. If the shrink tunnel is in cool down mode, the code simply terminates. If the tunnel is operating normally, the code moves to Decision Box  208 .  
         [0033]    Decision Box  208  checks if the blowers or conveyor are currently running. If they are operating normally, all of the conditions necessary to enter power savings mode have been met, and the control circuitry modifies the blower and conveyor belt speeds based on the Power Savings Percentage. The tunnel temperature is also reduced in accordance with the Power Savings Percentage. It is in this Decision Box that the oven, belt and blowers will all be turned off if the Power Savings Percentage exceeds 95%.  
         [0034]    In the current embodiment, once the shrink tunnel has entered power savings mode, it can only resume normal operation by actuation of the Power Save button  110 . Resumed sealer jaw activity will not automatically cause the shrink tunnel to resume normal operation. This is done to ensure that the operator is aware that the tunnel has entered a reduced power mode and allows the tunnel sufficient time to return to its normal operating temperature before placing more articles on the conveyor mode.  
         [0035]    In another embodiment, the conveyor speed is reduced to 0 when the tunnel enters power savings mode. Renewed sealer jaw activity automatically causes the shrink tunnel to return to normal operation. Since the tunnel needs significant time to return to normal operating temperature, the operator cannot place articles in the shrink tunnel immediately. To insure that articles are not presented to the tunnel until it is fully operational, the conveyor belt does not turn back on until the shrink tunnel has returned to its normal operating temperature. Once the conveyor belt resumes operation, it is safe to use the shrink tunnel.