Abstract:
A control circuit for a cooking oven. The control circuit includes a contactor. The contactor has at least one contact and at least one coil. A relay (such as a solid-state relay) is in series connection with the contactor. A heating element is controlled by the relay and is in series connection with the relay and the contactor. The controller also includes a controller. The controller is configured to bypass the relay and to control power to the at least one coil.

Description:
BACKGROUND 
       [0001]    The present invention relates to heating circuits and, more particularly, to heating circuits in conveyor ovens. 
         [0002]    Electric heating elements are used in infrared cooking ovens, including infrared conveyor ovens used to cook pizzas and other foods. Electric heating elements can be controlled by solid-state, zero-cross relays. In particular, the supply of electrical power to the heating elements is controlled by the relays. Electrical noise is generated when relay contacts open and close and zero-cross relays generate less noise than other types of relays. As with most components, solid-state relays are subject to failure and if a relay fails in the on position, a constant supply of power is provided to the heating element. This could lead to over-heating and other hazards. A coil-activated or triggered contactor can be used in the circuit prior to (or in series with) the solid-state relays to provide a safety (or circuit break) in case a solid-state relay fails in the on position. A high-temperature-limit-control switch operates the contactor coil and, if the high limit is tripped, the coil to the contactor is de-energized and the contactor opens. When the contactor opens, the supply of power to the heating element is interrupted. 
       SUMMARY 
       [0003]    Recently, the materials used in contactors have changed. In particular, the metal used for contacts in contactors has been changed to silver. Silver replaced other metal for environmental reasons. It is believed that silver contactors oxidize during normal use of the conveyor oven. Once a contactor is contaminated, such as by oxidation, the contamination creates a resistance high enough to prevent power from flowing through the contactor; even if the contacts of the contactors are in a closed position. Thus, the electric heating elements do not receive power, and cannot cook food. 
         [0004]    In one embodiment, the invention provides a control circuit for a cooking oven. The control circuit includes a contactor that has at least one contact and at least one coil; a solid-state relay in series connection with the contactor; and a heating element controlled by the solid-state relay. The heating element is in series connection with the solid-state relay and the contactor. The controller is configured to bypass the solid-state relay, and control power to the at least one coil. 
         [0005]    In another embodiment, the invention provides a method for controlling a cooking oven, the cooking oven including a housing and a heating element. The method comprising placing in a series-type configuration, a relay, a contactor including at least one contact and at least one coil, and the heating element. The method further comprising controlling a bypass of the relay; and controlling power to the at least one coil; wherein the heating element is controlled by the relay. 
         [0006]    In another embodiment, the invention provides a method of controlling a cooking oven having at least one heating element and at least one contactor, the at least one contactor having an associated coil. The method comprising receiving, at a controller, a signal from a user power switch; generating, with the controller, a signal to activate one or more first relays; shorting one or more second relays subsequent to activating the one or more first relays; connecting the at least one contactor directly in series with the at least one heating element; energizing the coil of the at least one contactor; and de-activating the one or more first relays. 
         [0007]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of an infrared conveyor oven. 
           [0009]      FIG. 2  is a circuit diagram of an infrared conveyor oven having a plurality of heating elements, solid-state control relays, and two contactors. 
           [0010]      FIG. 3  is a block diagram of a controller of an infrared oven. 
           [0011]      FIG. 4  is a flow diagram of a process for controlling the temperature of an infrared oven. 
           [0012]      FIG. 5  is a circuit diagram of an infrared conveyor oven having a plurality of heating elements, two contactors, and a high-amp bypass circuit. 
           [0013]      FIG. 6  is a block diagram of the high-amp bypass circuit. 
           [0014]      FIG. 7  is a flow diagram of a process for controlling power to a plurality of heating elements. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0016]      FIG. 1  is a perspective view of an infrared conveyor oven  1 . The conveyor oven  1  includes a housing  5  and conveyor  7 . The housing  5  encloses the electrical components  10  (shown in  FIGS. 2 and 5 ) of the conveyor oven  1 . The conveyor  7  is made of a metal woven wire mesh and is used to transport food through the conveyor oven  1 . The conveyor  7  is coupled to a motor  11  (shown in  FIGS. 2 and 5 ), which moves the conveyor  7  through the conveyor oven  1 . 
         [0017]      FIG. 2  is a circuit diagram illustrating the electrical components  10  of the conveyor oven  1 . The conveyor oven  1  generally includes heating elements  15 , solid-state control relays  20 , temperature sensors  25 , contactors  30 A and  30 B, a temperature switch  35 , and a controller  40 . In the embodiment shown, a power supply  45  provides 230V AC voltage to the electrical components  10 . It is possible that the conveyor oven  1  and electrical components  10  could be designed to operate using a different power supply voltage (and current). The heating elements  15 , solid-state control relays  20 , and contactors  30 A and  30 B are connected in a series-type configuration. In the embodiment shown, there are two controllers  40 , one controlling the upper set of heating elements, and one controlling the lower set of heating elements. In the embodiment illustrated, the controllers are substantially identical. 
         [0018]    The phrase “series-type configuration” as used herein refers to a circuit arrangement where the described elements are arranged, in general, in a sequential fashion such that the output of one element is coupled to the input of another, but the same current may not pass through each element. For example, in a “series-type configuration,” it is possible for additional circuit elements to be connected in parallel with one or more of the elements in the “series-type configuration.” Furthermore, additional circuit elements can be connected at nodes in the series-type configuration such that branches in the circuit are present. Therefore, elements in a series-type configuration do not necessarily form a true “series circuit.” 
         [0019]    The heating elements  15  are electrical loads that produce infrared light to produce heat. The heating elements  15  receive power from the power supply  45  and, in the embodiment illustrated, produce long-wave, infrared light to cook food. 
         [0020]    The solid-state control relays  20  control the supplied power to the heating elements  15  (and, thus, can be considered power control relays). The solid-state control relays  20  are electronic switching devices that switch the power to the heating elements  15  on or off. In some embodiments, the solid-state control relays  20  do not contain moving parts, thus minimizing any electrical noise when switching the supplied power on or off. In other embodiments, the solid-state relays  20  contain moving parts. 
         [0021]    The contactors  30 A and  30 B further control the supplied power to the heating elements  15 . The contactors  30 A and  30 B act as a safety, in case a solid-state control relay  20  fails. The contactors  30 A and  30 B are electronic switching devices that control the power to the heating elements  15 , through the solid-state control relays  20 . The contactors  30 A and  30 B include contacts and coils. When the coil is energized or powered, the contacts close together, allowing current to flow to the heating elements. If the coil is de-energized, the contacts are open, and current is not supplied to the heating elements  15 . 
         [0022]    The temperature switch  35  senses the temperature of the oven and controls the power to the coils. The temperature switch  35  provides power to the coils if the sensed temperature of the oven is under a safety shutoff temperature (approximately 975° Fahrenheit). If the safety shutoff temperature is met, the temperature switch  35  disconnects the power to the coils of the contactors  30 A and  30 B opening the contacts, thereby cutting off power to the solid-state relays  20  and heating elements  15 . 
         [0023]      FIG. 3  is a block diagram illustrating one of the controllers  40 . Each controller  40  includes a microcontroller  48  and a user interface  50 . The microcontroller  48  includes a processor  55  and memory  60 . The processor  55  receives inputs from the user interface  50  and temperature sensors  25 . The processor  55  then executes software stored in the memory  60 . The processor  55  (using the software) analyzes the received inputs and generates one or more control signals that control the solid-state relays  20  and motor  11 . 
         [0024]    At least one controller  40  controls the speed of the motor  11 , and thus the speed of the conveyor  7 . The controller  40  receives a user set cook time input from the user interface  60  and controls the speed of the motor  11  based on the set cook time. 
         [0025]    Each controller  40  further controls the temperature of the conveyor oven  1 . The temperature is based on a user set temperature entered into the user interface  50 . The controller  40  controls the temperature by turning the solid-state relays  40  on or off which, in turn, controls power (on or off) being supplied to the heating elements  15 . The controller  40  controls the solid-state relays  40  depending on the current temperature sensed by the temperature sensors  25  as compared to the user set temperature. 
         [0026]      FIG. 4  is a process  70  for controlling the temperature of the conveyor oven  1 , or more specifically, one set of the heating elements  15  (either upper or lower). The process  70  is performed when the controller  40  receives a user set temperature from the user interface  50  (Step  71 ). The controller  40  then receives the temperature of the conveyor oven  1  from the temperature sensors  25  (Step  72 ). The controller  45  then determines if the temperature of the conveyor oven  1  is above the user set temperature (Step  73 ). If the temperature of the conveyor oven  1  is above the user set temperature, the controller  40  turns the solid-state relays  20  off, thus cutting off power to the heating elements  15  (Step  74 ). If the temperature of the conveyor oven  1  is not above the user set temperature, the controller  40  turns the solid-state relays  20  on, thus providing power to the heating elements  15  (Step  75 ). The controller  40  then cycles back to Step  71 . 
         [0027]      FIG. 5  is a circuit diagram illustrating the electrical components  10  of a conveyor oven  1  with a bypass controller  100 . The bypass controller  100  is a controller used at startup of the conveyor oven  1  to create a burning arc across the contacts of the contactors  30 A and  30 B. The arc burns away oxidation on the contacts of the contactors  30 A and  30 B. Burning away contamination, such as oxidation, is sometime referred to as “wiping” the contacts or “cleaning” the contacts. 
         [0028]      FIG. 6  is a block diagram illustrating the bypass controller  100  of the conveyor oven  1 . The bypass controller  100  includes a microcontroller  105 . The controller  100  has an input  110  which is connected to a user power switch  115 . The controller  100  is also connected to solid-state shorting relays  120 , and provides commands and similar signal on an output  125  connected to the controller  40 . In one embodiment, the microcontroller is a Microchip model number PIC12F508 integrated circuit. The microcontroller  105  generally includes a processor  130  and a memory  135 . The processor  130  receives various inputs and executes a software program, stored in the memory  135 , for analyzing the received inputs, and generates one or more control signals, or outputs. The user power switch  115  is the main power switch of the conveyor oven  1  and is located on the user interface  50 . The bypass controller  100  receives a signal from the user power switch  115  (through input  110 ) when the conveyor oven  1  is turned on or off. The bypass controller  100  is electrically coupled to the coils of the contactors  30 A and  30 B. 
         [0029]    The solid-state shorting relays  120 , when activated, short out the solid-state relays  20 . In other words, when the shorting relays  120  are turned on, a circuit path is created that bypasses the relays  20 . Thus, the controller  100  can be considered or viewed as bypassing or shorting the relays  20 . As discussed in greater detail below, shorting the relays is a first step in a process where contactors  30 A and  30 B are “wiped” or cleaned. Upon completion of the “wipe” process, the bypass controller  100  sends a signal to the controller  40  through output  125  to continue operation of the oven, as is further discussed below. 
         [0030]    At startup or shutdown the bypass controller  100  receives a signal from the user power switch  115  at input  110 . Upon receiving either signal, the bypass controller  100  activates the solid-state shorting relays  120 . Activation of the shorting relays  120 , shorts out the solid-state relays  20 . Once the solid-state relays  20  are shorted out, the contactors  30 A and  30 B are connected directly in series with the heating elements  15 . The bypass controller  100  then energizes the coils of the contactors  30 A and  30 B. Once the coils are energized, the contacts of the contactors  30 A and  30 B close. The heating elements  15  then draw a relatively large current (approximately ten amps) through the contacts of the contactors  30 A and  30 B. The ten amps of current create a burning arc across the contacts. The arc “wipes” the contacts clean (or removes or reduces the contamination, such as oxidation). The bypass controller  100  then de-activates the solid-state shorting relays  120 , releasing the short across the solid-state relays  20 . The bypass controller  100  then sends a signal to the controller  40  through the output  125 . In the case of startup, the controller  40  receives the signal and begins normal operation of the conveyor oven  1 . In the case of shutdown, the controller  40  receives the signal and powers down the conveyor oven  1 . In another embodiment the bypass controller  100  performs the “wiping” process upon user activation or other preprogrammed events. In such an embodiment, the conveyor oven  1  further includes a user bypass switch. Upon activation by a user, the user bypass switch sends a signal to the bypass controller  100 . Upon receiving the signal, the bypass controller  100  performs the “wiping” process. 
         [0031]      FIG. 7  illustrates a process  200  for controlling the power to the heating elements  15  upon startup. The process  200  is performed when the conveyor oven  1  is powered on (Step  205 ). Once the conveyor oven  1  is powered on and the bypass controller  100  receives the signal, the bypass controller  100  activates the solid-state shorting relays  120  to short out the solid-state relays  20  (Step  210 ). The bypass controller  100  then powers the coils of the contactors  30 A and  30 B, thus closing the contacts of the contactors  30 A and  30 B (Step  215 ). The heating elements  15  draw approximately ten amps of current through the contacts of the contactors  30 A and  30 B, creating a burning arc across the contacts (Step  220 ). The bypass controller  100  then releases the short across the solid-state relays  20  (Step  225 ). The bypass controller  100  then sends a signal to the controller  40  to begin normal operation of the conveyor oven  1 , as discussed in process  70  (Step  230 ). 
         [0032]      FIG. 8  illustrates a process  300  for controlling the power to the heating elements  15  upon shutdown. The process  300  is performed when the conveyor oven  1  is turned off (by the user or otherwise), and a signal is sent to the bypass controller  100  (Step  305 ). Before powering down, the bypass controller  100  activates the solid-state shorting relays  120  to short out the solid-state relays  20  (Step  310 ). The heating elements  15  draw approximately ten amps of current through the contacts of the contactors  30 A and  30 B, creating a burning arc across the contacts (Step  315 ). After a predetermined period of time, the bypass controller  100  de-energizes the coils of the contactors  30 A and  30 B (Step  320 ). The bypass controller  100  then de-activates the solid-state shorting relays  120  (Step  325 ). The bypass controller  100  then sends a signal to the controller  40  to power down the conveyor oven  1  (Step  330 ). 
         [0033]    Thus, the invention provides, among other things, a bypass circuit and wipe technique for contactors used to operate solid state relays that control heating elements of a conveyor oven. Various features and advantages of the invention are set forth in the following claims.