Abstract:
A portable electric appliance includes a housing, an electrically operable element positioned within the housing, a transmitter adapted to transmit a beam of radiation, and a receiver responsive to the beam of radiation. The transmitter is positioned external to the housing, and the receiver is positioned to receive the beam of radiation. The electrically operable element is de-energized in response to the beam of radiation being blocked or interrupted. A method adapted to disable a portable electric appliance includes transmitting a beam of radiation from a transmitter on the portable electric appliance, receiving the beam of radiation by a receiver on the portable electric appliance, and de-energizing an electrically operable element associated with the portable electric appliance in response to the beam of radiation being blocked or interrupted.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/712,238 filed Aug. 29, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The field of the invention relates to portable electrical appliances such as heaters having sensors for detecting objects that may interfere with their operation.  
         [0004]     2. Description of the Related Art  
         [0005]     Portable appliances, such as heaters, have been provided with various sensors for determining whether an object is too close to them. Such sensors may be in the form of mechanical detectors as disclosed in U.S. Pat. No. 4,906,818. Electronic sensors have also been used to shut off a heater in the event an object is too close to the heater outlet. U.S. Pat. No. 5,805,767 discloses the use of motion sensors for this purpose. U.S. Pat. No. 6,091,888 discloses the use of infrared or ultrasonic proximity detectors for detecting a stationary or moving object within a predetermined distance of the heater inlet or outlet.  
       SUMMARY OF THE INVENTION  
       [0006]     A portable electric appliance is provided that includes a housing having electrically operable elements and an outlet. A transmitter is mounted to the housing near the outlet and is capable of transmitting a beam of radiation. A receiver is mounted to the housing in opposing relation to the transmitter. The receiver is positioned to receive the beam of radiation from the transmitter. A control circuit is provided for deactuating the appliance in response to interruption of the beam between the transmitter and the receiver.  
         [0007]     In one embodiment of the invention, the transmitter is an infrared transmitter and the receiver is an infrared receiver, both of which are positioned above the outlet as shown in  FIG. 1 . The appliance preferably includes an encoder for encoding the beam from the transmitter. A decoder is preferably provided for determining whether a correct signal has been received by the receiver from the transmitter. If a correct signal has not been received within a preselected period of time, the appliance and/or electrically operable elements are disabled and/or de-energized.  
         [0008]     A transmitter, receiver, and control circuit as described above can be employed in association with various electrical appliances. For example, a portable humidifier can be equipped with a radiation transmitter and a detector near an inlet and/or outlet. A control circuit will shut down the humidifier if an object covers the inlet or outlet, thereby interrupting the beam from the transmitter to the detector. The appliance can alternatively be an electric heater.  
         [0009]     A cover detector circuit is provided by the invention that checks for the presence of the infrared signal or other radiation signal sent by the transmitter. If a fault is detected, a control circuit, such as a microprocessor, microcontroller, or application specific integrated circuit (ASIC), stops the operation of the appliance. In the case of automatic heaters, the ASIC disables triac pulses. In the case of manual heaters, the 110 VAC supply is interrupted. The ASIC further may cause an LED or other indicator to be actuated when the path between the transmitter and detector is blocked. In a preferred embodiment, the ASIC must not receive a correct signal for a selected period of time (e.g. approximately 2.8 seconds) before it will disable the appliance. Short interruptions are ignored. Once a fault is detected and the appliance is disabled, the transmit signal needs to be detected correctly for a predetermined period before the ASIC will reset itself, turn off the LED and re-enable the appliance.  
         [0010]     A portable electric appliance is provided in accordance with a preferred embodiment of the invention, which includes a housing, an electrically operable element positioned within the housing, a transmitter adapted to transmit a beam of radiation, and a receiver responsive to the beam of radiation. The transmitter is positioned external to the housing, and the receiver is positioned to receive the beam of radiation. The electrically operable element is de-energized in response to the beam of radiation being blocked or interrupted.  
         [0011]     The transmitter may include an infrared or laser transmitter, and the receiver may include an infrared or laser receiver. The portable electrical appliance may include a heater, and the electrically operable element may include a heating element. The beam of radiation may be transmitted as pulses, and the electrically operable element may be de-energized in response to the beam of radiation being at least one of blocked or interrupted for a predetermined period of time.  
         [0012]     The beam of radiation may be transmitted having a first value of an electrical characteristic, the beam of radiation may be received having a second value of the electrical characteristic, and the electrically operable element may be de-energized in response to the second value being unequal to the first value for a predetermined period of time. The electrical characteristic may include at least one of duty cycle, on-time, off-time, intensity, amplitude, and frequency.  
         [0013]     The electrically operable element may be energized in response to the beam of radiation being unblocked or uninterrupted for a predetermined period of time. The beam of radiation may be transmitted having a first value of an electrical characteristic, the beam of radiation may be received having a second value of the electrical characteristic, and the electrically operable element may be energized in response to the second value being equal to the first value for a predetermined period of time.  
         [0014]     A method adapted to disable a portable electric appliance is provided in accordance with a preferred embodiment of the invention, which includes transmitting a beam of radiation from a transmitter on the portable electric appliance, receiving the beam of radiation by a receiver on the portable electric appliance, and de-energizing an electrically operable element associated with the portable electric appliance in response to the beam of radiation being blocked or interrupted.  
         [0015]     These and other objects, features, and advantages of this invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a top perspective view of a heater including an object sensing assembly in accordance with the invention.  
         [0017]      FIG. 2  is a schematic diagram of a first embodiment of a circuit to perform the object sensing function in accordance with the present invention.  
         [0018]      FIG. 3  is a schematic diagram of a second embodiment of a circuit to perform the object sensing function in accordance with the present invention.  
         [0019]      FIG. 4  is a schematic diagram of a third embodiment of a circuit to perform the object sensing function in accordance with the present invention.  
         [0020]      FIG. 5  is a schematic diagram of a heater in which the object sensing circuit of  FIG. 2, 3 , or  4  can be incorporated.  
         [0021]      FIG. 6  is a top perspective view of a second embodiment of the object sensing assembly in accordance with the invention.  
         [0022]      FIG. 7  is a schematic diagram of a fourth embodiment of a circuit to perform the object sensing function in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     A portable appliance in the form of a heater  10  is provided with an object sensing assembly that causes power to be interrupted or shut off if an object near the heater outlet is sensed. Referring to  FIG. 1 , the heater  10  includes a housing  12  having a front wall  14  that includes an outlet  16 . A grill  18  having vanes is provided in the outlet  16 . The vanes can be fixed or movable. Other types of heater grills are well known. Some, for example, include metal panels having rows of circular openings to allow the passage of heated air.  
         [0024]     The top wall of the heater includes a control panel  20 . The control panel may include a power button  21  for turning the heater on and off, a timer button (not shown) for setting the time of operation, and controls for adjusting a thermostat and/or controlling the amount of heat to be generated. These and other controls are known to the art.  
         [0025]     The heater  10  shown in  FIG. 1  includes one or more heating elements (not shown) that can be selectively operated. A fan (not shown) is present within the housing for moving air over the heating elements and through the outlet  16 . Air can be drawn into the housing through one or more air inlets (not shown) in the rear wall of the housing or other suitable location. The heating elements can be resistance heating elements. Other types of portable heaters are known to the art, including radiant heaters that do not require the use of a fan. Such heaters may lack a grill.  
         [0026]     The heater  10  includes an object sensing assembly that includes at least one radiation transmitter assembly  22  and at least one radiation receiver assembly  24  for receiving signals from the transmitter. As shown on  FIG. 1 , both the transmitter and receiver are mounted above the outlet  16 . If the radiation path between the transmitter and receiver is interrupted, the heater is shut off. As discussed below, the radiation path must preferably be interrupted for a preselected time duration before the heater shuts off. While the heater could be shut off following a momentary interruption, such an arrangement is not preferred.  
         [0027]     The locations of the transmitter  22  and receiver  24  assemblies are shown as being above the outlet. Obstructions, such as drapes or clothing items that may extend over the heater, will be readily detected. The transmitter and receiver assemblies preferably extend only a short distance from the front wall and are unobtrusive. Each is positioned near a side wall of the heater. The distance between the transmitter and receiver assemblies preferably at least generally corresponds to the maximum width of the outlet.  
         [0028]      FIG. 2  is a schematic diagram of a first embodiment of a circuit  26  to perform the object sensing function in accordance with the present invention. The object sensing circuit  26  preferably includes a cover detector application specific integrated circuit (ASIC)  28 , which is connected at pin  1  to a 5 VDC power source provided by operation of Zener diode  30  and capacitor  32 . Capacitor  32  and Zener diode  30  are connected in parallel across ground and a 110 VAC power supply, which is coupled to connector  34 . Specifically, the anode of zener diode  30  is connected to ground and the cathode of zener diode  30  is coupled to connector  34 . The 5 VDC power source is thus available at the cathode of zener diode  30 .  
         [0029]     The frequency of a clock signal internal to the cover detector ASIC  28  is controlled by resistor  36  and capacitor  38 . Specifically, resistor  36  is preferably connected in series between pins  1  and  2  of a cover detector ASIC  28 . Capacitor  38  is preferably connected in series between pin  2  of the cover detector ASIC  28  and ground.  
         [0030]     The neutral or ground connection associated with the 110 VAC power source is preferably coupled to connector  40  and provided through resistor  42  to pin  3  of the cover detector ASIC  28 . Capacitor  44  is connected in series between the cover detector ASIC  28  and ground, thus providing a direct connection to the 110 VAC line voltage and the cover detector ASIC  28  at pin  3  to enable it to operate whenever the heater is plugged in.  
         [0031]     The output of an infrared (IR) receiver  46 , incorporated as part of the receiver assembly  24  shown in  FIG. 1 , is preferably connected to pin  4  of the cover detector ASIC  28 . The receiver  46  is connected to the 5 VDC power source (VCC) through a filter, which includes resistor  48  and capacitor  50 . Specifically, capacitor  50  is connected in series between the IR receiver  46  and ground, and resistor  48  is connected in series between the IR receiver  46  and the 5 VDC power source. The IR receiver  46  is also connected to ground.  
         [0032]     A switch  52  is preferably connected in series between pin  12  of the cover detector ASIC  28  and ground, and a switch  54  is preferably connected in series between pin  5  of the cover detector ASIC  28  and ground. Switch  52  is preferably used to manually turn the heater on and off, and switch  54  is preferably used to enable or disable a timer mode. The power button  21  on the heater controls the on/off status by means of the switch  52 . The power is off by default (at power-on), and each push of the button will change the on/off status. While a power LED is not provided in the embodiment of  FIG. 2 , such an LED or other indicator could be used to indicate whether power is on or off.  
         [0033]     The timer mode enables the heater to remain on for a predetermined period of time and to thereafter automatically turn off. In a preferred embodiment, the timer turns the heater off after about four hours. The power needs to be on before the timer can be used. The timer LED is turned on when the timer is activated. It provides steady illumination during the four-hour period, then flashes at a given rate (e.g. 400 ms on, 400 ms off, etc.) to indicate that the heater is off because the time has expired. If the timer button (not shown) is pushed while the timer is active, the timer function will be cancelled and the timer LED will turn off. If the heater is off because time has expired, only the power button (not shown) can be used to turn the heater back on.  
         [0034]     The cathode of diode  58  is preferably connected to the neutral or return of the 110 VAC supply at connector  40  and half-wave rectifies the AC supply. Resistors  60  and  62  are preferably connected in series between the anode of diode  58  and ground to limit the current through diode  58 . Current flows from the hot side of the AC line at connector  34  through Zener diode  58 , resistor  62 , resistor  60 , and back to the neutral side of the AC line at connector  34  producing voltage across Zener diode  58 . Since Zener diode  30  is connected from VCC to ground, a regulated voltage is created.  
         [0035]     Light emitting diode  64  preferably provides an indication of when the heater is covered and diode  66  indicates when the heater is in the timer mode. The anode of diode  64  is preferably connected to the 5 VDC supply and its cathode is connected to pin  11  of the cover detector ASIC  28 . Resistor  68  is connected in series between pin  11  of the cover detector  28  and the cathode of diode  64 . Similarly, the anode of diode  66  is preferably connected to the 5 VDC supply and its cathode is connected to pin  10  of the cover detector ASIC  28 .  
         [0036]     Resistor  70  is preferably connected in series between pin  10  of the cover detector ASIC  28  and the cathode of diode  66 . Thus, in response to pin  11  of the cover detector ASIC  28  being substantially grounded, diode  64  is illuminated, and in response to pin  11  being at or near 5 VDC, the diode  64  is turned off. Diode  66  operates in a similar manner in response to control by voltage levels output on pin  10  of the cover detector ASIC  28 .  
         [0037]     The cathode of infrared (IR) LED or transmitter  72  is preferably connected to ground and a resistor  74  is connected in series between pin  6  of the cover detector ASIC  28  and the anode of IR LED  72 . The IR LED  72  is incorporated in the transmitter assembly  22  shown in  FIG. 1  and provides the infrared signal to be received by the IR receiver  46 , as described above.  
         [0038]     Pin  8  of the cover detector ASIC  28  is preferably connected through resistor  75  to pin  1  of an optoisolated triac driver MOC3010, which is commercially available from Fairchild Semiconductor Corporation (www.fairchildsemi.com). Further details concerning the triac driver MOC3010  84  are provided in the “Random-Phase Optoisolators Triac Driver Datasheet”, pp. 1-10 (2005), which is incorporated herein by reference. Capacitor  76  is connected in series between pin  8  of the cover detector ASIC  28  and ground, and operates to filter spikes that may occur on the AC supply to the heater.  
         [0039]     A triac  78  selectively switches the 110 VAC supply coupled to connector  80  to the heater, which is coupled to connector  82 . Pin  4  of a triac driver MOC3010  84  is preferably connected to a gate of the triac  78  and operates to control switching of the 110 VAC supply to the heater. Resistor  85  is preferably connected in series between connector  82  and pin  6  of the triac driver MOC 3010  84  to limit the gate current provided to the triac  78 .  
         [0040]      FIG. 3  is a schematic diagram of a second embodiment of an object sensing circuit  29  to perform the object sensing function in accordance with the present invention. The second embodiment is essentially the same as the first embodiment described in connection with  FIG. 2 , except that the on/off switch and timer mode have not been implemented in the second embodiment, and thus switches  52 ,  54 , diode  66 , and the circuitry associated therewith have been omitted. In addition, indication of the cover detector function is provided through pin  7  of the cover detector ASIC  28 , which is connected to pin  6  of a safety check ASIC  86  for this purpose.  
         [0041]     The safety check ASIC  86  preferably indicates whether the object sensing assembly and/or other features of the heater are indeed operational when the heater is turned on. It may cause various indicators, such as LEDs associated with pins  7 - 10  thereof to illuminate if certain elements are inoperable.  
         [0042]     In addition to the cover detector ASIC  28 , other elements that can be tested for operability include a PTC breaker, a thermal fuse, and a tilt switch. As such an ASIC is not a necessary part of the invention described herein, further discussion of the ASIC is not provided. Additional LEDs  88 - 94  are provided for indicating when the tilt switch, thermal fuse, PTC breaker, and cover detector ASIC, respectively, have detected an abnormal condition.  
         [0043]     A further distinction between the embodiments is that the cover detector ASIC  28  in  FIG. 3  preferably controls whether the heater is turned off or not through action of the output at pin  9  of the cover detector ASIC  28  rather than pin  8  of the cover detector ASIC  28  shown in  FIG. 1 . Thus, the circuitry, which includes the triac  78 , optoiosolated triac driver MOC3010  84 , resistor  75 , and capacitor  76  shown in  FIG. 2  have been omitted in  FIG. 3 . The cover detector ASIC  28  shown in  FIG. 3  preferably controls whether or not the heater is turned off by means located in a position remote to the circuit shown in  FIG. 3 .  
         [0044]      FIG. 4  is a schematic diagram of a third embodiment of a circuit  50  to perform the object sensing function. The circuit  50  is substantially similar to that shown in  FIG. 3 , except that the IR diode  72  has been replaced with a laser diode or transmitter  86  and the IR receiver  46  has been replaced with a photo-sensitive transistor  88 . In addition, the value of resistor  98  has been modified and capacitor  50  has been eliminated to accommodate different electrical characteristics of the photo-sensitive transistor  88 .  
         [0045]      FIG. 5  is a schematic diagram of the heater, which may incorporate any of the object sensing circuits described above. The heater includes a heater assembly  100  including a pair of resistance heating elements  102 ,  104 . The heating elements can be selectively operated to vary the heat output of the heater. Triacs  106  and  108  are connected in series between the respective heating elements  102 ,  104 , and signals provided at terminals TRIAC 1   110  and TRIAC 2   112  of a printed circuit board (PCB) control the TRIACS  106 ,  108 , respectively. A fan motor  114  is provided for causing a fan to blow air by the heating elements, thereby heating the air prior to its exiting the outlet  16  shown in  FIG. 1 .  
         [0046]     The fan is selectively energized by a signal from the PCB at connector  116 . An oscillating motor  118  is provided for oscillating the fan, thereby directing heated air in various directions as the fan oscillates back and forth. The oscillating motor is selectively energized by a signal from the PCB at connector  120 . The heater can be operated with or without fan oscillation. The heater can also function as a fan when neither heating element is operated. The oscillating motor can alternatively cause the heater housing to oscillate back and forth about a vertical axis.  
         [0047]     The heater includes various safety features in addition to the sensing assembly described above and shown in  FIG. 2, 3 , or  4 . A tilt switch  132  shown in  FIG. 3  is provided for cutting power to the heater assembly  100  and fans  114  and  118  if the heater is tilted beyond a predetermined amount. The tilt switch is connected to connector  124  of the printed circuit board. A thermal fuse  126  and a positive temperature coefficient breaker  128  are connected in series between the source of AC current and the PCB at connector  130 . They are also connected to the triacs  106  and  108 . Power to the heater assembly  100  is disconnected in the event of an overheating and/or over-current condition by operation if the fuse  126  and/or breaker  128 .  
         [0048]      FIG. 6  shows a second embodiment  132  of the heater formed in accordance with the present invention, which is substantially similar to that shown in  FIG. 1 , except that there are preferably three sets of radiation transmitter and receiver assemblies  22 ,  24 . The assemblies  22 ,  24  are preferably located along the left and right sides of the grill  18 . In addition, air inlets  19 , a power button  134 , and a power indicator  136  are provided along the lower front side of the heater  132 . The heater  10  shown in  FIG. 1  includes one or more heating elements (not shown) that can be selectively operated. A fan (not shown) is present within the housing for moving air over the heating elements and through the outlet  16 . Air can be drawn into the housing through one or more air inlets (not shown) in the rear wall of the housing or other suitable location. The heating elements can be resistance heating elements. Other types of portable heaters are known to the art, including radiant heaters that do not require the use of a fan. Such heaters may lack a grill.  
         [0049]     As in the embodiment shown in  FIG. 1 , if any one of the radiation paths between the transmitter and receiver assemblies is interrupted, the heater is preferably shut off and/or the heating elements de-energized. The radiation path must preferably be interrupted for a preselected time duration before the heater shuts off. While the heater could be shut off following a momentary interruption, such an arrangement is not preferred.  
         [0050]      FIG. 7  is a schematic diagram of a fourth embodiment  135  of a circuit to perform the object sensing function. The circuit  135  includes a power control portion, which is connected to AC input power pads  136 ,  138 . Pad  136  is connected in series with a fuse  140 , a resistor  142 , and a capacitor  144 . The capacitor  144  is connected to an input of a bridge rectifier, which includes diodes  146 ,  148 ,  150 ,  152  which rectifies the input AC power supply to a DC power supply. A Zener diode  154  is connected from the fuse  140  to pad  138  and a resistor  156  is connected in parallel across the capacitor  144 . The capacitor  144  and resistor  156  preferably operate to filter spikes and noise from the input power signal. The Zener diodes  158 ,  160  are preferably connected in series from an input of the bridge rectifier to pad  138  and provide a 24 VDC power source. A capacitor  162  is preferably connected in parallel with the Zener diodes  158 ,  162 . A 5-volt regulator  164  is connected to the output of the bridge rectifier and supplies a 5 VDC power supply at its output.  
         [0051]     The circuit  135  also includes a sensor assembly, which incorporates three infrared (IR) LEDs  166 ,  168 ,  170 , each of which are connected through a resistor  172 ,  174 ,  176  to the 5 VDC power source, as well as being connected to pin  12  of a microcontroller  178 . The sensor assembly also includes 3 infrared receivers  180 ,  184 , each of which are connected to the 5-volt power supply and a resistor  186 ,  188 ,  190 , respectively. Each of the resistors  186 ,  188 ,  190  are then connected to separate inputs pins  1 - 3  of a microcontroller  178 .  
         [0052]     The microcontroller  178  preferably pulses the IR LEDs  166 ,  168 ,  170  at pin  12  and obtains an indication of whether the beam of radiation emitted by the IR LEDs  166 ,  168 ,  170  has been blocked and/or interrupted through receipt of a signal representing the received infrared light on pins  1 - 3 . The infrared LEDs  166 ,  168 ,  170  are preferably pulsed at a predetermined frequency (such as 38 KHZ) transmitted in a predetermined sequence (such as on for 2 seconds, off for 1 second, and on for 3 seconds), and/or transmitted with a predetermined electrical characteristic, such as but not limited to variations in duty cycle, on-time, off-time, intensity, amplitude, and frequency while remaining within the scope of the present invention including.  
         [0053]     The microcontroller  178  preferably determines when the received infrared signal substantially matches that transmitted and, if not, raises an error condition that represents blockage of the beam of radiation, which signals the heating elements to be turned off by the microcontroller  178 . Entry into the error condition may be delayed for a predetermined period of time such that blockage of the transmitted beam must be more than transitory before the heating elements are turned off. Similarly, if the microcontroller  178  determines that the received infrared signal substantially matches that transmitted, the error condition is either not entered or, if the error condition is already present, it may be exited such that the heating elements are turned on again following a predetermined period of time after blockage of the beam of light has been removed.  
         [0054]     Circuit  135  also includes a reset and 5 VDC monitoring circuit  192 , which detects the 5 VDC power supply and provides a reset signal to the microcontroller  178  in accordance with its electrical specifications. Circuit  192  includes a transistor  194  and a resistor  196  connected from the base to the emitter of the transistor  194 . The circuit  192  also includes resistor  198  connected from the base of the transistor  194  to ground, a resistor  200  connected from the collector of the transistor  194  to ground, and a capacitor  202  connected from the collector of the transistor  194  to ground. A resistor  204  is connected in series between the collector of the transistor  194  and pin  6  of the microcontroller  178 , a diode  206  is connected in parallel across the resistor  204 , and a capacitor  208  is connected from pin  6  of the microcontroller  178  to ground.  
         [0055]     The state of an on/off switch  210 , which is connected to the 5 VDC power supply through a resistor  212  is monitored at pin  8  of the microcontroller. An audio indicator  214  or buzzer is connected to pin  9  of the microcontroller  178  through a resistor  216 .  
         [0056]     The microcontroller  178  is preferably able to control energization of the heating elements by action of pin  13 , which is connected to the series combination of a resistor  218 , diode  220 , capacitor  222 , and resistor  224 . The diode  226  is connected across a point between the diode  220  and the capacitor  222  and ground. A capacitor  228  is connected between a point between the resistor  218  and the diode  220  and ground. The collector of transistor  230  is preferably connected to a relay  232  and the emitter of the transistor  230  is preferably connected to ground. Thus, the microcontroller  178  is able to control whether the transistor  230  is either conducting or not conducting, which selectively energizes the relay  232  that further selectively energizes the heating elements (not shown). Circuit  135  also includes a light emitting diode  232 , which is connected to pin  14  of the microcontroller  178  through a resistor  234  and is preferably used to indicate whether the heater is powered or not.  
         [0057]     It will be appreciated that more than one transmitter receiver pair may be incorporated on the heater. One such additional pair could extend from the front wall  14  near the bottom of the heater while another pair could extend from the rear wall near an air inlet. As discussed above, the present invention may be applicable to other portable consumer appliances where it may be desirable to turn the appliance off if an object is covering an inlet, an outlet, or other element thereof. Other modifications could be made without departing from the spirit of the invention.  
         [0058]     Although the illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.