Abstract:
In an insect lure and trap, a system for generating a carbon dioxide attractant has a combustion chamber in which carbon dioxide is generated by means of an exothermic reaction from a gaseous fuel rich in carbon. A container contains a pressurized supply of said fuel and a supply line connects said container to said combustion chamber. A normally closed valve is included in said supply line. The system includes means for sensing the temperature in said combustion chamber and for generating a control signal representative of said temperature. A controller responsive to said control signal compares said temperature to a reference temperature and opens said valve during selected segments of successive equal time intervals.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to the field of devices for trapping insects, and in particular to an insect lure and trap system that uses a carbon dioxide (CO2) attractant.  
         [0003]     2. Description of the Prior Art  
         [0004]     Generating carbon dioxide to attract mosquitos and other blood seeking insects by combusting a hydrocarbon fuel is well known. For example, U.S. Pat. No. 6,145,243 entitled “Method and Device Producing CO2 Gas for Trapping Insects” discloses a device for attracting and trapping bothersome flying insects.  
         [0005]     A problem with this system is that it requires a fixed orifice in the fuel line to control the volume of gas needed to maintain a desired exothermic reaction. Propane and other petroleum fuels, as commercially available, generally are contaminated with foreign particles and also with oil, some of which is applied during the manufacture of the tank to prevent rust on the tank&#39;s internal surfaces. The oil and foreign particles pass along with the gas through the system&#39;s valve and into the fixed orifice where they result in clogging or serve to alter the size of the orifice. This causes the exothermic reaction to lose efficiency or cease to operate entirely causing system failure. Filters placed in the gas line ahead of the valve and orifice likewise clog or become contaminated with oil and restrict the flow of gas or block it entirely. Frequent cleaning or replacement of the filter is a necessity. Purging the gas flow system, including the valve and restrictive orifice, requires an external source of gas, such as a CO2 cartridge, and is costly, only marginally successful, and requires frequent application.  
       SUMMARY OF THE INVENTION  
       [0006]     An objective of the present invention is to incorporate an adaptive control system to an insect lure and trap system that does not rely on a fixed orifice to meter the volume of gas needed to maintain an exothermic reaction. The use of an adaptive control system prevents losses in efficiency and possible total failure of the CO2 generating system due to contaminates in the fuel supply.  
         [0007]     Accordingly, in one aspect of the present invention, in an insect lure and trap, a system for generating a carbon dioxide attractant has a reactor in which carbon dioxide is generated by means of an exothermic reaction from a gaseous hydrocarbon fuel. A container contains a pressurized supply of said fuel. A supply line connects the container to said reactor. The system includes a normally closed valve in said supply line. The system further includes means for sensing the temperature in said reactor and for generating a control signal representative of said temperature. A controller responds to said control signal for comparing said temperature to a reference temperature and opens said valve during selected segments of successive equal time intervals.  
         [0008]     In another aspect of the present invention, a method of luring and trapping insects includes generating carbon dioxide by combusting a gaseous fuel provided by a normally closed valve that is open during selected segments of successive equal time intervals. A temperature of the generator is sensed and compared to a reference value. Selected segments during which the valve is open is increased if the temperature is below the reference value. Selected segments during which the valve is open is decreased if the temperature is above the reference value.  
         [0009]     Some advantages of the system according with the present invention are that the system continuously adjusts the volume of gas delivered to the reactor, allowing for maximum efficiency during startup when the gas/air mixture needs to be richer than at operating temperatures. The valve of the system is contantly pulsed, preventing particulates from building up on the valve surfaces, which avoids poor seating of the valve. The system of the present invention readily adapts to variations in materials used to produce the exothermic reaction. For example, variations in the thickness or quality of the catalyst plating are offset by the system adjusting the volume of gas flowing to the catalyst to maintain the optimum catalyst temperature for maximum CO2 conversion. The system according to the present invention is not dependent upon a restrictive orifice to meter the gas and so is not subject to malfunctions due to particulates and petroleum residues in the gas. Consequently, the system does not require purging or other cleaning actions.  
         [0010]     These and other features and objectives of the present invention will now be described in greater detail with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a functional block diagram of an insect lure and trap system;  
         [0012]      FIG. 2  is a simplified illustration of an arrangement of an exothermic fuel reactor, the fuel tank and valve;  
         [0013]      FIG. 3  is a functional block diagram of a method for controlling a valve;  
         [0014]      FIG. 4  is an illustration of a valve control signal;  
         [0015]      FIG. 5  is a schematic illustration of the controller;  
         [0016]      FIG. 6  is a flow chart illustration of the system operation; 
     
    
     DETAILED DESCRIPTION  
       [0017]     Referring to  FIG. 1 , insect lure and trap system  10  includes a controller  12  that receives a plurality of input signals and controls a plurality of output devices to control the operation of the system. The controller  12  comprises a controller/microprocessor (not shown) that executes program instructions to read the various input signals and control the output devices.  
         [0018]     The system includes an ambient temperature sensor  14  that provides a signal on a line  16  to the controller  12 , and an ambient light sensor  22  (e.g., a photocell) that provides a signal on a line  24  indicative of the amount of ambient light. A mode select signal on a line  26  is received from a mode select panel  28  that allows a user to select the operating mode of the system. Details of the various modes are discussed below.  
         [0019]     The system  10  also includes an exothermic reactor  30  that generates carbon dioxide (CO2) gas that is used as an attractant. A tank  31  provides a gas fuel via a flow line  32  to a normally closed valve  34 , which receives a valve command signal to open on a line  38  from the controller. When the valve  34  is open, fuel is released to the exothermic reactor  30 . In some examples, tank  31  is removable and/or disposable and the fuel is propane, butane, methanol, or any low molecular weight paraffin gas.  
         [0020]     Referring to  FIG. 2 , the fuel flows from the valve  34  through a catalyst  36 , which could include a ceramic honeycomb material that is coated with an element such as platinum or palladium. The heater  37  is mounted preferably directly below the catalyst  36 . In one embodiment the heater  37  may be a resistive heating element that receives a pre-heater control signal on a line  40 . The heater  37  heats the catalyst  36  to a point the catalyst can begin the self-sustaining exothermic reaction that generates the CO2 as the fuel passes through the catalyst. The control signal on the line  40  commands the heater on and off. A temperature sensor  41  (e.g., a thermocouple) is preferably located above the catalyst  36  to sense the temperature of the CO2 gas passing through the catalyst, and the temperature sensor  41  provides a temperature signal indicative thereof to an amplifier  39  and then out through line  43 .  
         [0021]     Referring to  FIG. 1 , the trap system  10  also includes a motor  42  that drives a fan  44 , which provides air flow through a screen  46  causing insects to be trapped on an interior side of the screen  46 . The controller  12  provides a motor command signal on a line  48  to the motor  42 . This command signal commands the motor on and off. The motor also drives an impeller  50  located in a flow path of the CO2 gas, to facilitate exhausting the CO2. In one example, the system  10  may also include an attractant supply  51 , such as a removable and replaceable time release cartridge containing Octenol, which releases attractant to create a CO2 and attractant mix.  
         [0022]     The operation of the catalyst  36  and specifically the generation of the CO2 is substantially the same as disclosed in U.S. Pat. No. 4,519,776 entitled “Apparatus for Attracting Insects”, assigned to Armatron International, Incorporated, the assignee of the present invention, and incorporated herein by reference. However, unlike the device disclosed in U.S. Pat. No. 4,519,776, the insect lure and trap system of the present invention includes an adaptive control system that monitors the temperature of reactor  30  and automatically controls the flow of fuel to ensure the system operates efficiently.  
         [0023]     Referring to  FIGS. 3 and 4 , system  10  produces the maximum amount of carbon dioxide when the temperature in reactor  30  is closest to a temperature set point, such as 1000° F., for example. To automatically adjust the temperature, system  10  uses a so-called “proportional-integral-derivative” (hereinafter “PID”) feedback control loop. The input of the PID is the temperature of reactor  30 . The output is the width of pulse  100  which is returned to valve  34  over line  38  to control the time during which valve  34  is open. By controlling the width of pulse  100 , the volume of fuel flowing to reactor  30  and therefore the temperature of reactor  30  are controlled. The pulse period  102  is constant and, in one example, is about 333 milliseconds.  
         [0024]     The pulse width (PW) is calculated according to the following formula:  
             PW   =       K   *     e   ⁡     (   t   )         +       Δ     T   i       ⁢       ∫   0   t     ⁢       e   ⁡     (   t   )       ⁢     ⅆ   t           +     Td   ⁢       ⅆ     e   ⁡     (   t   )           ⅆ   t                   (   1   )             
 
 where e is the control error determined by the difference between the temperature set point for maximum CO2 output (T setpoint ) and the temperature of the reactor (T reactor ). The pulse width is the sum of three terms. The proportional term (“P” term) is proportional to the control error. The integral term (“I” term) provides a control action that is proportional to the time integral of the control error and ensures that the steady state error becomes zero. The derivative term (“D” term) is proportional to the time derivative of the control error and improves closed loop stability. 
 
         [0025]     Referring to  FIG. 5 , temperature in the reactor  30  is measured by thermocouple  41 , which produces a voltage that is amplified by operational amplifier  39  and enters microcontroller  12  on line  43 . Microcontroller  12  generates a pulse width signal according to the PID equation and outputs the pulse width signal on line  40 . The pulse width signal opens or closes transistor  110  whereby the collector current thereof opens or closes valve  34  accordingly.  
         [0026]     At the same time, the microcontroller controls the motor  42  which drives fan  44  used to draw insects into trap  49  and also drives impeller  50  to propel CO2 out of the trap. Microcontroller  12  also controls heater  37  to preheat the catalyst to facilitate combustion of the fuel. Motor  42  and heater  37  are controlled in response to information received from ambient light sensor  20  and ambient temperature sensor  14 , as well as signals from the mode selector switch located on control panel  28 . Motor control and heater control are performed through triac  112  and triac  114  respectively.  
         [0027]      FIG. 6  is a flow chart illustration  200  of the system operation. Following a system reset/power-up, initialization  202  is performed to clear all outputs and set the stand-by mode 0. Test  204  is performed to determine if any mode has been set by an operator. If a mode has been set, the mode is memorized and indicated on the device panel  28 .  
         [0028]     Mode 0 is a stand-by mode. Mode 1 is a manual mode. Mode 2 is an automatic mode in which the system comes on at dusk and operates (i.e., dispenses attractant) for three hours. Mode 3 is an automatic mode in which the system comes on at dusk and operates for three hours and comes on again at dawn for two hours. Mode 4 is also an automatic mode in which the system operates starting at dusk for a period of four hours, and again starting at dawn for a period of three hours.  
         [0029]     Test  206  determines the day status which could be Dawn, Daytime, Dusk, or Night according to the photo sensor  20  reading and predetermined time duration of each state.  
         [0030]     Test  208  checks the ambient temperature and if the temperature is below a threshold value (e.g., 55° F.), the system is commanded not to run in the automatic mode.  
         [0031]     Step  210  analyses information from steps  204 ,  206 , and  208  to determine the system work status: either stop all operations; stop valve  34  and heater  37  but leave motor  42  running; or run all output devices. Step  212  checks the reactor  30  temperature and if the temperature is above the pre-determined upper threshold level of normal reactor  30  operation (e.g., 1370° F.), the system shuts down and can be activated only by the operator. If the temperature is below the pre-determined lower threshold level of normal reactor  30  operation (e.g., 800° F.), step  214  initiates the preheat function. If the temperature is within the range of normal reactor  30  operation, the pulse width applied to valve  34 , which regulates the amount of gas supplied to reactor  30 , will be controlled in accordance with the standard PID algorithm to keep the reactor  30  temperature at the level of normal reactor  30  operation.  
         [0032]     One of ordinary skill in the art will recognize that the present invention is of course not limited to the specific valve timing and threshold values discussed herein as way example. For example, the specific valve timing and threshold values will be a function of the overall system design. In addition, although the embodiments illustrated herein employ a normally OFF valve, the system may be modified to use a modulating valve that receives a command signal to control the flow of gas from the tank, rather than opening and closing the valve. It is further contemplated that various types of sensors may be employed. For example, it is contemplated that sensors other than thermocouples, thermistors and photocells may be used to sense the associated parameters. Also, the present invention is not limited to placing the temperature sensor that senses the exhaust gas temperature in close proximity to the catalyst. Other locations in the CO2 flow path may provide sensing locations that allow fuel flow to be controlled as a function of temperature, while maintaining the exothermic reaction. Furthermore, although the control technique of the present invention has been discussed in the context of incorporating a PID feedback loop on temperature, it is contemplated that the loop may be controlled by sensing other parameter(s) indicative of the exothermic reaction (e.g., the amount of CO2 gas).  
         [0033]     It should be further understood that although the system employs a controller that receives the sensed analog signal values, digitizes the values and processes the resultant digitized values to perform the control functions of the present invention, a less complex controller may be used that, for example, receives Boolean inputs. It suffices, that a number of different embodiments can be provided to enjoy the benefits of controlling the flow of fuel as a function of the exhaust gas/catalyst temperature.  
         [0034]     Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.