Abstract:
An apparatus and method for controlling the operation of a solenoid includes a control circuit configured to receive an activation signal in response to a predetermined condition. The control circuit, in response to said activation signal, provides a first energizing signal to the solenoid for a first predetermined period, and cuts off the first energizing signal for a second predetermined period. The control circuit further provides a second energizing signal to the solenoid for a third predetermined period.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a solenoid control systems, and more specifically to an apparatus and method for controlling the operation of a solenoid. 
         [0003]    2. Description of the Prior Art 
         [0004]    Electromechanical solenoids provide a mechanical action in response to an electrical signal. Such electromechanical solenoids typically consist of an electromagnetically inductive coil wound around a movable ferromagnetic core or armature. The coil is configured to allow linear motion of the armature in response to an applied energizing signal in order to apply a mechanical force to some external mechanism or electromechanical device. A spring is typically provided to reset the armature to its original position when an energizing signal is removed. In a typical application, an electrical energizing signal is provided to the solenoid coil in response to a manual operation such as the operation of a pushbutton switch. In other applications, a logic device is used to provide an energizing signal to the solenoid in response to a predetermined condition. In many applications, a sensor is utilized to sense a condition of an external mechanism acted upon by the solenoid, and switches are then used to then deenergize the solenoid. 
         [0005]    In some cases, the energizing signal to the solenoid is inadvertently maintained for an extended period, often due to a delay in the operation of the desired external mechanical operation. In other examples, a manual switch is held in the closed position and continues to provide an energizing signal after solenoid operates, or, there is an unexpected mechanical delay in the solenoid operation after the signal is provided. In such cases of maintained energizing signals, the solenoid can fail from overheating due to extended current flow. 
         [0006]    One way to avoid failure of a solenoid due to such overheating would be to use a larger more robust solenoid device. However, this adds additional cost and requires more physical space than may be available. 
         [0007]    Another way the problem of solenoid overheating has been addressed has been to employ a control circuit for the solenoid that is configured to shut off the energizing signal to the solenoid after a predetermined time. For example, a monostable multivibrator is used to supply an electrical signal to a solenoid upon receipt of a switching initiation signal. The duration of the output pulse is controlled to be sufficiently long enough to properly operate the solenoid without overheating in most instances. Such methods protect the solenoid but are not capable of overcoming a delay in the operation of the solenoid or the desired external mechanical operation because the solenoid energizing signal is cut off after a predetermined time period. 
         [0008]    In view of the foregoing considerations, there is a need to provide a solenoid control circuit that protects a solenoid from overheating, and is capable of overcoming a delay in operation by automatically re-energizing the solenoid for one or more predetermined periods until the desired operation is effected. 
         [0009]    The present invention will be apparent to those skilled in this art from the following detailed description of a preferred embodiment of the invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In one aspect of the present invention, an apparatus and method for controlling the operation of a solenoid includes a control circuit configured to receive an activation signal in response to a predetermined condition. The control circuit, in response to said activation signal, provides a first energizing signal to the solenoid for a first predetermined period, and cuts off the first energizing signal for a second predetermined period. The control circuit further provides a second energizing signal to the solenoid for a third predetermined period. 
         [0011]    In another embodiment, a method for controlling the operation of a solenoid includes sensing an activation signal indicative of a predetermined condition; providing a first energizing signal to the solenoid; cutting off the first solenoid energizing signal after a first predetermined period, for a second predetermined period; providing a second solenoid activation signal to said solenoid after said second predetermined period; and maintaining the second solenoid activation signal for a third predetermined period. 
         [0012]    In another embodiment, a solenoid control system includes an activation signal control path in signal communication with a solenoid control unit; a solenoid circuit path in signal communication with the solenoid control unit; a power source configured to provide power to the activation signal control path and the solenoid circuit path; the solenoid control unit configured to receive an activation signal from the activation signal control path in response to a predetermined condition; wherein the solenoid control unit, in response to the activation signal, provides a first energizing signal to a solenoid included within the solenoid circuit path for a first predetermined period, and thereafter cuts off the first energizing signal for a second predetermined period; and thereafter provides a second energizing signal to the solenoid for a third predetermined period. 
         [0013]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and benefits obtained by its uses, reference is made to the accompanying drawings and descriptive matter. The accompanying drawings are intended to show examples of the many forms of the invention. The drawings are not intended as showing the limits of all of the ways the invention can be made and used. Changes to and substitutions of the various components of the invention can of course be made. The invention resides as well in sub-combinations and sub-systems of the elements described, and in methods of using them. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Referring to the exemplary drawings wherein like elements are numbered alike in the accompanying Figures: 
           [0015]      FIG. 1  depicts a schematic representation of an exemplary circuit for controlling the operation of a solenoid in accordance with an embodiment of the invention; 
           [0016]      FIG. 2  depicts a schematic representation of an exemplary circuit of a timer as used in controlling the operation of a solenoid in accordance with an embodiment of the invention; 
           [0017]      FIG. 3  depicts a schematic representation of an alternative exemplary circuit for controlling the operation of a solenoid in accordance with an embodiment of the invention using a microcontroller to perform the timing and logic functions; 
           [0018]      FIG. 4  depicts a logic flow for a microcontroller to perform the timing and logic functions; 
           [0019]      FIG. 5  depicts an alternative logic flow for a microcontroller to perform the timing and logic functions; 
           [0020]      FIG. 6  depicts an alternative logic flow for a microcontroller to perform the timing and logic functions; 
           [0021]      FIG. 7  depicts various waveforms associated with the circuit embodiments of  FIGS. 1 ,  2 , and  3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    A schematic of the solenoid control circuit in accordance with the present invention is generally illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 3 . As these embodiments of the present invention are described, reference should also be made to  FIG. 7  as necessary, as a depiction of various waveforms associated with the described circuits is provided. 
         [0023]    Referring initially to  FIG. 1 , an exemplary solenoid control system  1  is depicted. As shown, an external AC source  2  provides power to an activation signal control path  3  and a solenoid circuit path  4 . Both the activation signal control path  3  and the solenoid circuit path  4  are in signal communication with a solenoid control unit  5 . As is further depicted, the solenoid control unit  5  includes a full wave bridge rectifier  17 , a filtering diode D 5 , a current limiting resistor R 2 , a smoothing capacitor C 2 , a timer  15 , and a silicon controlled rectifier (SCR) or other suitable solid state switching device  18  (e.g., MOSFET (metal oxide semiconductor field effect transistor), TRIAC (triode for alternating current) or other transistor device). 
         [0024]    In operation of the control system  1 , an AC electrical signal is provided from the external AC source  2  at terminals  11  and  12 . For the first half of the cycle, the AC signal at terminal  11  is passed through a solenoid  22  (included within the solenoid circuit path  4 ), through diode D 1  of bridge rectifier  17 , and to an output terminal  16  of the full wave bridge rectifier  17 . For the second half of the cycle, the AC signal at terminal  12  is passed through diode D 2  of rectifier  17  to output terminal  16  of full wave bridge rectifier  17 . The rectified signal at output terminal  16  is then provided to a filtering circuit comprising diode D 5 , series current limiting resistor R 2 , and smoothing capacitor C 2 . The signal from the filtering circuit is passed to the timer  15  in order to provide input power V cc  thereto. The resistance value of series resistor R 2  is selected to provided sufficient impedance to limit the current through solenoid  22  below its actuation current level until the timer  15  provides a solenoid energization signal, as described in more detail below. 
         [0025]    A switch  10 , such as a pushbutton, included within the activation signal control path  3  is disposed between terminal  11  and a current limiting resistor R 1  (also within the activation signal control path  3 ). When the switch  10  is closed, an electrical signal from the AC source  2  is sent through current limiting resistor R 1 , and across the primary windings of a current transformer  13  included within the activation signal control path  3 . An activation signal  14  is thereby induced on the secondary windings of current transformer  13 , and provided to start the timer  15 . It will be understood that an activation signal  14 ′ from an external circuit  23 , such as from a programmable logic controller (PLC) for example, may also be provided in lieu of, or in addition to, the timer  15 . 
         [0026]    An output energizing signal  19  from timer  15  is provided to the gate of SCR  18 , thereby biasing it closed and in the conduction state. During the first half of the AC cycle, the current at the cathode of SCR  18  then flows through diode D 4  of full wave bridge rectifier  17 , and through the windings of solenoid  22 , thus increasing current flow through the solenoid  22  sufficiently to energize the windings and to actuate a plunger (not shown) associated with the solenoid  22 . For the second half of the AC cycle, the current at the cathode of SCR  18  flows through diode D 3  of full wave bridge rectifier  17  and to the terminal  12 . During the period the SCR  18  is in the conduction state allowing current to flow from the output terminal  16  of the rectifier  17  through the SCR  18 , the capacitor C 2  discharges, providing continued input signal to timer  15  for a duration depending on the chosen value of the capacitor C 2 . 
         [0027]    It will be understood by those of skill in the art that various signal processing techniques (e.g., such as level conversion and filtering of the activation signal to enhance the overall circuit performance) may optionally be utilized in conjunction with the timer circuit, without departing from the scope of the invention. For example, the activation signal to timer  15  may be latched or maintained until the SCR  18  has been placed in the conduction state allowing current to flow from the output terminal  16  of the rectifier  17  through the SCR  18 , diode D 4  of full wave bridge rectifier  17 , and through the windings of solenoid  22 , thus increasing current flow through the solenoid  22  sufficiently to energize the windings and to actuate the solenoid  22  plunger. This ensures if the activation signal is noisy or not maintained for a sufficient period to enable the timer  15  to output an energization signal to the solenoid, the initial activation signal will be latched “ON” to the timer to ensure operation. This can be accomplished by using a simple flip-flop type circuit (not shown) to function as a latch. The latch (not shown) will reset when the capacitor C 2  discharges. 
         [0028]    Referring again to  FIG. 1 , during normal operation, the SCR  18  will remain in a conducting state until the energization signal  19  to SCR  18  gate is shut off by the timer  15 . When the switch  10  is released or placed in the “open” state, the activation signal  14  to the timer  15  is shut off, resetting the timer and cutting off the energization signal  19  from the timer  15  to the gate of SCR  18  and thereby cutting current to flow from the output terminal  16  of the rectifier  17  through SCR  18 , thus decreasing current flow through the windings of solenoid  22  sufficiently to deactivate or reset the solenoid  22  plunger. 
         [0029]    However, if the activation signal  14  is maintained beyond a predetermined period, the timer  15  will cut off the energization signal  19  to the gate of SCR  18 . The timer  15  will then hold the gate of SCR  18  in an “open” or non-conducting state for a predetermined period by continuing to cut off the energization signal  19  for that predetermined period. 
         [0030]    At the end of the predetermined non-energization or delay period, if an activation signal  14  remains provided to the timer  15 , the timer  15  will reset and an output energizing signal  19  from timer  15  is provided to the gate of SCR  18 , thereby biasing it closed and in the conduction state allowing current to again flow from the output terminal  16  of the rectifier  17 , through the SCR  18 , and diode D 4  of full wave bridge rectifier  17  thus increasing current flow sufficiently to energize the windings of solenoid  22  to actuate the solenoid  22  plunger. 
         [0031]    The timer  15  circuit may be implemented using various circuit components and configurations. Having described the timer operation in a general way, a description of a particular implementation thereof will be described by way of example in  FIG. 2 . 
         [0032]    Referring now to  FIG. 2 , a schematic of an exemplary timer circuit  15  is shown. To provide a clean input to the timer  15 , the input activation signal  14  is provided to a comparator  26 , with input resistors R 3  and R 4  values chosen to set the threshold for the output signal from comparator  26 . 
         [0033]    Under normal conditions, when no activation signal is present, and timer  27  is not triggered or in the OFF state, there is no output signal from comparator  26  to resistors R 8 , R 16  and capacitor C 4 , and therefore transistor Q 3  remains in a non-conducting, or OFF state. With Q 3  OFF, the input voltage, V cc  to timer  15  allows current to flow through resistors R 9  and R 10  such that the voltage on the base of Q 1  is greater than at the emitter thereof so the PNP transistor Q 1  remains in a non-conducting, or OFF state. 
         [0034]    With no activation signal  14  present, and no output signal from comparator  26 , the voltage at the base of Q 2  is less than V be , and Q 2  remains in a non-conducting, or OFF state and therefore no current flows through R 13 , Ra, Rb, or C 3  and the timer  27  does not operate. 
         [0035]    However, the normal operation of the timer  27  is such that an output signal at Pin  3  of timer  27  will be provided to transistor Q 4  until the timer  27  turns ON. The voltage divider resistors R 11  and R 12  provide greater than base-emitter voltage (V be ) on the base of transistor Q 4 , putting transistor Q 4  in a conducting, or ON condition. Transistor Q 4  conducts current through resistor R 7 , holding the voltage at R 7  and diode D to V ce , hence no current flows through diode D and the voltage signal output of timer  15 , remains low, or essentially at zero volts. 
         [0036]    When an activation signal is provided on pin  3  of the comparator  26  that is higher than the voltage on pin  2  of the comparator  26  across dividing resistors R 3  and R 4 , an output signal from the comparator  26  is provided to R 8 , C 4 , and R 16 , putting Q 3  in a conducting, or ON state, thus enabling current through resistor R 9 . This pulls the base voltage of transistor Q 1  down to the V ce  of transistor Q 3  (low) and puts transistor Q 1  in a conducting, or ON condition. Transistor Q 1  on current flows through resistor R 6  to the output of timer  15  (V gate ) providing an output energization signal from the timer  15 . 
         [0037]    Additionally, when an activation signal  14  is provided on pin  3  of the comparator  26  that is higher than the voltage on pin  2  of the comparator  26  across dividing resistors R 3  and R 4 , an output signal from the comparator  26  is provided to resistor R 14 , putting transistor Q 2  in a conducting, or ON condition, enabling current flow through resistors R 13 , Ra, Rb, capacitor C 3  and triggers the timer  27  to begin the timing cycle through an input signal to Pin  2  of timer  27 . 
         [0038]    The integrated circuit timer  27  is configured as an a stable multivibrator which provides an output as a series of pulses, with an adjustable duration between the pulses. The timer  27  output “ON” and “OFF” times are adjusted by selection of the values of Resistors Ra and Rb and capacitor C 3 . The duration of the timer  27  “ON” time is given by: 
         [0000]        T   on =0.693( Ra+Rb )× C 3. 
         [0039]    The duration of the timer  27  “OFF” time is given by: 
         [0000]        T   off =0.693( Rb )× C 3. 
         [0040]    When timer  27  turns on, the output signal at pin  3  of timer  27  is cut off. 
         [0041]    This effectively grounds resistor R 11  and drops the voltage on the base of transistor Q 4  below V be , putting transistor Q 4  in a non-conducting, or OFF state. With transistor Q 4  effectively OFF, current flows from timer  15  input V cc  through resistor R 7  and diode D to continue to provide an output energization signal (V gate ) from timer  15 . 
         [0042]    During the period of timer  27  “ON” time (T on ) as calculated above based on the values of resistors Ra and Rb and capacitor C 3 , the voltage on the base of transistor Q 3  will drop below V be  due to the C 4 , R 16  time constant and place transistor Q 3  in a non-conducting, or OFF state. With transistor Q 3  non-conducting, the voltage divider of resistors R 9 , R 10  also places transistor Q 1  in a non-conducting, or OFF state. At the end of timer  27  “ON” time (T on ), the timer  27  again provides an output signal at pin  3  of timer  27  putting transistor Q 4  in a conducting, or ON condition, enabling current flow through resistor R 7  to ground cutting off the output signal (V gate ) from timer  15  for a duration of “OFF” time (T off ) as calculated above based on the values of resistors Ra and Rb and capacitor C 3 . 
         [0043]    At the end of timer  15  “OFF” time (T off ), the timer  27  automatically provides again the output signal at pin  3  of timer  2 . This again places transistor Q 4  in a non-conducting, or OFF state and current flows from timer  15  input V cc  through resistor R 7  and diode D to continue to provide an output energization signal (V gate ) from timer  15  as before. 
         [0044]    The cycle of providing an output energization signal  19  (V gate ) from timer  15  for a predetermined period in response to an activation signal, and cutting off the output signal  19  (V gate ) from timer  15  for a predetermined duration and will repeat as long as activation signal is above the threshold and V cc  is adequate to power the circuit. 
         [0045]    It will be understood by those skilled in the art that the duration of the output energization signals (V gate ) and the duration of the OFF time between output energization signals, may be made adjustable in the field through the use of variable resistors and capacitors in the above described circuit. 
         [0046]    Referring now to  FIG. 3 , an alternative embodiment of a solenoid control system  50  is shown that is identical to that of  FIG. 1 , except that the timer circuit  15  of  FIG. 1  is replaced by a programmable microcontroller  31  that includes internal timers and switches. The microcontroller  31  may additionally be provided with user adjustable input signals such as through adjustable resistors (varistors) R 10 , R 11 , and R 12  to enable adjustment of the duration of the initial and subsequent energizing signals and the “OFF” time between signals. It will be understood by those of skill in the art that as an alternative to varistors R 10 , R 11 , and R 12 , many other devices or circuits may also be used to enable a user to provide an adjustable input to the microcontroller  31  to enable adjustment of the duration of the initial and subsequent energizing signals and the “OFF” time between signals. The microcontroller  31  is programmed to respond to the received activation signal by providing an energizing signal  19  to switching device  18  (e.g., SCR) to energize the solenoid  22  for a predetermined period and cut off the energizing signal  19  to the solenoid  22  for a second predetermined period, and if the activation signal is maintained, reapply the energizing signal  19  to the solenoid for a third predetermined period. The microcontroller  31  is also programmed to cut off the energization signal  19  if the input activation signal  14  is shut off. 
         [0047]    It will be appreciated that the logic steps used to perform the timing and switching functions for the operation of the present invention embodiments are readily programmable for execution by a microcontroller. It will be further appreciated that each defined energizing signal-OFF or energizing signal-ON period need not be identical, but may instead be programmed or adjusted as desired by the user. 
         [0048]    Referring now to  FIG. 4 , a flow chart representation of an exemplary algorithm  400  as implemented by, for example, the programmable microcontroller  31  of  FIG. 3  is shown. The microcontroller starts the solenoid control algorithm at block  402  when the activation signal is provided to the microcontroller. The microcontroller initializes and starts an initial energizing signal timer at blocks  404  and  406 , respectively, and provides an energizing signal output to enable the solenoid as shown at block  408 . The output energization signal will be maintained until the initial energizing signal timer has timed out. As shown in decision block  410 , if the microcontroller initial energizing timer has timed out, the energization signal will be cut off to disable the solenoid at block  412 . 
         [0049]    The microcontroller will then initialize both an energizing signal-OFF timer at block  414  and a timer for subsequent energizing signals-ON at block  416 . Next, the energizing signal-OFF timer is started at block  418  and the output energization signal is cut off until the energizing signal-OFF timer has timed out. If the microcontroller  31  energizing signal-OFF timer has timed out, as determined in decision block  420 , the subsequent energizing signals-ON timer is started at block  422  and the microcontroller provides an energizing signal output to re-enable the solenoid at block  424 . If the microcontroller subsequent energizing signals-ON timer has timed out, as determined at decision block  426 , the energization signal will be cut off to disable the solenoid at block  428 . 
         [0050]    It will be appreciated that the microcontroller  31  may be programmed to repeat the subsequent energizing signals and signal-OFF cycles indefinitely, or until the activation signal to the microcontroller  31  is cut off. 
         [0051]    Referring now to  FIG. 5 , a flow chart representation of an exemplary algorithm  500  in which the duration of the initial and subsequent energization signals, as well as the duration of the OFF time between signals, is defined in the field at start-up (as implemented, for example, by the programmable microcontroller  31  of  FIG. 3 ) is shown. 
         [0052]    The microcontroller starts the solenoid control algorithm at block  502  when the activation signal is provided to the microcontroller. The microcontroller first reads the user input defining the initial energizing signal duration at block  504 . Next, the microcontroller initializes and starts an initial energizing signal timer at blocks  506  and  508 , respectively, and provides an energizing signal output to enable the solenoid at block  510 . The output energization signal will be maintained until the initial energizing signal timer has timed out. If the initial energizing timer has timed out as reflected in decision block  512 , the energization signal will be cut off to disable the solenoid at block  514 . 
         [0053]    The microcontroller will then read the user inputs defining both the duration signal-OFF periods, and the duration of the subsequent energizing signals at blocks  516  and  518 , respectively. The microcontroller then initializes both an energizing signal-OFF timer (block  520 ) and a timer for subsequent energizing signals-ON (block  522 ). 
         [0054]    Next, the energizing signal-OFF timer is started at block  524  and the output energization signal is cut off until the energizing signal-OFF timer has timed out. If the microcontroller energizing signal-OFF timer has timed out, as determined at decision block  526 , the subsequent energizing signals-ON is started at block  528  and the microcontroller provides an energizing signal output to re-enable the solenoid at block  530 . If the microcontroller  31  subsequent energizing signals-ON timer has timed out as reflected at decision block  532 , the energization signal will be cut off to disable the solenoid at block  534 . 
         [0055]    It will be appreciated that the microcontroller may be programmed to repeat the subsequent energizing signals and energizing signal-OFF cycles either for a specific number of cycles, or indefinitely (as shown), or until the activation signal to the microcontroller is cut off. 
         [0056]    Referring now to  FIG. 6 , a flow chart representation of an exemplary algorithm  600  in which the duration of the initial and subsequent energization signals as well as the duration of the OFF time between signals is defined at any time and is adjustable while operating in the field (as implemented, for example, by the programmable microcontroller  31  of  FIG. 3 ) is shown. 
         [0057]    The microcontroller starts the solenoid control algorithm  600  at block  602  when the activation signal is provided to the microcontroller. The microcontroller first reads the user input defining the initial energizing signal duration at block  604 . Next, the microcontroller initializes and starts an initial energizing signal timer at blocks  606  and  608 , respectively, and provides an energizing signal output to enable the solenoid at block  610 . The output energization signal will be maintained until the initial energizing signal timer has timed out. If the initial energizing timer has timed out as reflected at decision block  612 , the energization signal will be cut off to disable the solenoid at block  614 . 
         [0058]    The microcontroller will then read the user inputs defining both the duration of the energization signal-OFF periods, and the duration of the subsequent energizing signals at blocks  616  and  618 , respectively. The microcontroller then initializes both an energizing signal-OFF timer at block  620  and a timer for subsequent energizing signals-ON at block  622 . 
         [0059]    Next, the energizing signal-OFF timer is started at block  624  and the output energization signal is cut off until the energizing signal-OFF timer has timed out. If the microcontroller energizing signal-OFF timer has timed out as reflected at decision block  626 , the subsequent energizing signals-ON timer is started at block  628  and the microcontroller provides an energizing signal output to re-enable the solenoid at block  630 . If the microcontroller subsequent energizing signals-ON timer has timed out as reflected at block  632 , the energization signal will be cut off to disable the solenoid at block. 
         [0060]    Next, the microcontroller will return to block  616  and then re-read the user inputs defining both the duration of the energization signal-OFF periods, and the duration of the subsequent energizing signals (block  618 ). The microcontroller then re-initializes both an energizing signal-OFF timer and a timer for subsequent energizing signals-ON (blocks  620 ,  622 ). 
         [0061]    It will be appreciated that the microcontroller may be programmed to repeat the subsequent energizing signal-ON and energizing signal-OFF cycles as described above either for a specific number of cycles or indefinitely, or until the activation signal to the microcontroller is cut off. 
         [0062]    While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.