Abstract:
A radiation generating system for treating a coating on a substrate. A high voltage circuit provides power to a microwave generator that, in turn, supplies microwave radiation to drive a lamp. A current limiting device is connected between the high voltage circuit and the microwave generator, and a fault detector is connected to the high voltage circuit for providing an error signal in response to excess current being supplied to the microwave generator. A control is operative to interrupt a supply of AC power to the high voltage circuit in response to the error signal.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to power supplies and, more particularly, to a microwave generator power supply having a failure tolerant high voltage circuit.  
       BACKGROUND OF THE INVENTION  
       [0002]     In lamp heating and curing of adhesives, sealants or coatings in industrial applications, one or more microwave generators, for example, magnetrons, are used to provide microwave radiation to a lamp source, such as an electrodeless ultraviolet (UV) lamp. When the plasma of the lamp is sufficiently excited by the microwave radiation from each magnetron, the lamp illuminates to provide the necessary light wavelength and intensity for the particular heating or curing process.  
         [0003]     Microwave-excited lamp power supply systems often have one or more high voltage power supplies that provide higher voltages to one or more magnetrons and low voltage power supplies that provide a lower voltage to a blower, a magnetron filament and other devices. The power supply system is often electrically coupled to sensors positioned within the system and the lamp head. It has been observed that as a magnetron ages and approaches the end of its useful life, there is a higher probability of the magnetron experiencing short circuits that result in high voltage arcing. Further, on occasion, the high voltage circuit components associated with the magnetron can experience a short circuit. In either event, any such short circuits can cause components associated with the high voltage power supply to experience either a life shortening stress or destruction.  
         [0004]     Therefore, there is a need to provide apparatus and methods of detecting short circuit conditions in an output circuit of a high voltage power supply driving a microwave generator and minimizing or eliminating any harmful effects and damage.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides an improved high voltage power supply circuit for a microwave generator that minimizes and in most applications, eliminates, damage to power supply components that would otherwise occur from short circuits in an output circuit of the high voltage power supply.  
         [0006]     According to the principles of the present invention and in accordance with the described embodiments, the invention provides a radiation generating system for treating a coating on a substrate. A high voltage circuit provides power to a microwave generator that, in turn, generates microwave radiation to drive a lamp. A current limiting device is connected between the high voltage circuit and the microwave generator, and a fault detector is connected to the high voltage circuit for providing an error signal in response to excessive current being supplied to the microwave generator. A control is operative to interrupt a supply of AC power to the high voltage circuit in response to the error signal.  
         [0007]     These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0009]      FIG. 1  is a schematic block diagram of a power supply system that has fault detection in a high voltage power supply supplying power to a microwave generator in accordance with the principles of the present invention.  
         [0010]      FIG. 2  is a schematic diagram of one embodiment of a current fault detector in the high voltage power supply of  FIG. 1 .  
         [0011]      FIG. 3  is a schematic diagram of another embodiment of a current fault detector in the high voltage power supply of  FIG. 1 .  
         [0012]      FIG. 4  is a flow chart illustrating an operating cycle of the power supply system of  FIG. 1 .  
         [0013]      FIG. 5  is a flow chart illustrating an interrupt cycle of the power supply system of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     Referring to  FIG. 1 , a power supply system  20  is operative to supply a high voltage to a microwave generator, for example, a magnetron,  22  mounted within a lamp head  24 . Microwave radiation from the magnetron  22  is coupled to a lamp  26 , for example, an electrodeless ultraviolet (UV) light source, mounted within a processing space  27  of the lamp head  24 . When the plasma of the lamp  26  is sufficiently excited by microwave radiation from the magnetron  22 , the lamp  26  illuminates and provides a light wavelength and intensity within a processing space  27  of the lamp head  24 . Thus, the lamp head  24  may be used in industrial applications to heat and/or cure adhesives, sealants, coatings, etc., on a substrate  29  located in the processing space  27  in a known manner. The power supply system  20  and lamp head  24  may be used for other heating or curing processes that requires light of a particular wavelength and intensity to achieve the desired heating and/or curing result.  
         [0015]     The power supply system  20  has power control circuitry  28  that is connected to a source of AC power  30 . The power control circuitry  28  includes power switch contacts, a line filter, one or more phase controllers, transformers, etc., to provide desired voltages to a microcontroller  32  and other machine devices  33  in a known manner. A phase-controllable voltage is provided from the power control circuitry  28  to a high voltage power supply  34  comprised of a high voltage transformer  35  and a full wave voltage doubler  36 . The high voltage transformer  35  has a primary side connectable to the AC power  30  via the power control circuitry  28  and a secondary side connected to the voltage doubler  36  that provides a desired high voltage to the magnetron  22 . An operator panel  38  is also connected to the microcontroller  32  and contains input/output devices, for example, pushbuttons, switches, lights, and/or a display, etc., that allow an operator to initiate and/or determine various operating states of the power supply system  20 . Further, machine I/O  40  is connected to the controller  32  and is operative to receive input signals from, and provide output signals to, the lamp head  24  and machine devices  22  in a known manner. For example, input signals may be received from switches, light detectors, pressure sensors, etc.; and output signals may be provided to cooling fans, a starter bulb, lights, etc., located remote from the operator panel  28 .  
         [0016]     On occasion, a high voltage cable  42  connected to the magnetron  22  may experience a short circuit. It is also probable that during its life, the magnetron  22  will experience short circuiting arcing. All short circuits result in a charge and discharge of the capacitors  44  every half cycle and thus, very high current spikes in the voltage doubler  36 , which can either damage or destroy the capacitors  44  and diodes  46  within the high voltage bridge assembly  48 . Further, continued occurrences of such short circuit currents can cause further deterioration of the high voltage cable  42  as well as other components.  
         [0017]     The power supply system  20  includes elements to minimize and/or eliminate any harmful effects and damage caused by faults within the load circuit of the voltage doubler  36 , that is, the magnetron  22 , connecting cable  42 , etc. First, a fault current limiting resistor  50  is placed in series between the voltage doubler  36  and the magnetron  22 . The value of the resistor  50  is, for example, ten ohms, and is chosen to provide a desired current suppression without creating an undesirable heat source. In addition, a current sensor  52  is connected to the voltage doubler  36  and is implemented by a current sensing resistor  54 . The resistor  54  has a value of about five ohms and provides a feedback voltage on conductor  55 , which changes proportionally with current flow in the voltage doubler  36 . A current fault detector  56  senses the feedback voltage from the current sensor  52 ; and in response to an excessive feedback voltage, the current fault detector  56  provides a current error signal over conductor  58  to a microcontroller interrupt input  59 . Upon receiving the error signal from the current fault detector  56 , the microcontroller  32  causes the power control circuitry  28  to immediately disconnect the high voltage transformer  35  from the AC power  30 .  
         [0018]     There are many implementations of the current fault detector  56 . For example, as shown in  FIG. 2 , a voltage comparator  60  can be used, which has one input connected to the voltage feedback signal on conductor  55  and a second input connected to a reference voltage  62 . The reference voltage magnitude is chosen such that a fault is not detected unless a substantially large current, for example, a short circuit current, is detected in the voltage doubler  36 . Thus, when the magnitude of the feedback voltage on conductor  55  exceeds the reference voltage  62 , a current error signal is provided on the conductor  58  to the microcontroller interrupt input  59 .  
         [0019]     Referring to  FIG. 3 , in an alternative embodiment of the current fault detector  56 , a zener diode  64  is connected to the feedback voltage on the conductor  55 . When the feedback voltage exceeds a breakdown voltage of the zener diode  64 , current flows through the zener diode  54  and a resistor  66 . Thus, a voltage level is applied to a logic gate inverting buffer  68  that, in turn, is effective to change the state of the fault detector output  58  and the microcontroller interrupt input  59 .  
         [0020]     In use, referring to  FIG. 1 , in a known manner, a user operates a power switch (not shown) to connect the power supply system  20  to the AC power  30 , which initiates execution of an operating program of  FIG. 4  within the microcontroller  32 . The program first, at  402 , executes a power-on initialization routine. Thereafter, at  404 , the microprocessor  32  reads states of input signals from the operator panel  38  and machine I/O  40 ; and as determined by a logic program within the microprocessor  32 , the microprocessor  32  then switches the states of output signals to the lamp head  24  and machine I/O  40 . The microcontroller  32  then, at  406 , executes diagnostic and fault routines and, as a result thereof, updates, at  408 , operator displays within the operator panel  38 .  
         [0021]     Upon the occurrence of a short circuit, the state of the interrupt input  59  of the microcontroller  32  changes to initiate an interrupt subroutine shown in  FIG. 5 . In response to the interrupt, the microcontroller  32 , at  504 , provides appropriate signals to the power supply circuitry  28 , which results in the power supply system  20  immediately being disconnected from the AC power source  30 . Thereafter, the microcontroller  32  sets a default flag, at  506 , which initiates a current fault display or output on the operator panel  38 . The microcontroller  32  then, at  508 , exits the interrupt subroutine and returns to the main operating routine of  FIG. 4 .  
         [0022]     While the present invention has been illustrated by a description of an embodiment, and while such embodiment has been described in considerable detail, there is no intention to restrict, or in any way limit, the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, in the described embodiment, a single microwave generator  22  and high voltage power supply  34  are shown and described; however, as will be appreciated, in alternative embodiments, more than one microwave generator  22  and high voltage power supply  34  may be used.  
         [0023]     In the described embodiment, upon detecting a short circuit, the application of power to the high voltage power supply  34  is interrupted by the power control circuitry  28 , thereby turning the power supply off. As will be appreciated, in alternative embodiments, the short circuit signal can be used to open relay contacts between high voltage power supply and the microwave generator  22 . Alternatively, the relay contacts can be placed between the transformer  35  and the voltage doubler  48 . Thus, there are several alternative embodiments for removing the high voltage from the microwave generator  22 .  
         [0024]     Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.