Optical element driving circuit

An optical element driving circuit flexibly configures energy sources to cause illumination with an optical output element, such as a flash lamp. The energy sources include an illumination capacitor and a capacitive voltage divider circuit coupled with the optical output element. The illumination capacitor may be charged to a first voltage and a boost capacitor of the capacitive voltage divider circuit may be charged to a second voltage that is a fraction of the first voltage. The optical element driving circuit also includes a triggering circuit coupled with the capacitive voltage divider circuit. The triggering circuit is configured to place a sum of the first voltage and the second voltage across the optical output element.

BACKGROUND OF THE INVENTION

1. Technical Field

This application relates to optical element driving circuits and, more particularly, to setting a voltage level across an optical output element.

2. Related Art

Emergency warning systems often include visual alarms, such as strobe lights or flash lamps. Many strobe alarms include driving circuits which rely on a step-up transformer to prime a flash lamp for illumination and one or more capacitors to store energy to cause the illumination using the flash lamp. Flash lamps are designed to operate within a specified voltage range which must be met to ensure reliable flash lamp operation. Prior driving circuits sometimes employed voltage doubling circuits to drive the flash lamp and cause the illumination. However, the voltage must be carefully controlled not only to correctly generate the desired amount of illumination, but also to prevent component damaging arcing and other undesirable effects. Therefore, a need exists for an optical element driving circuit that provides reliable flash lamp operation at appropriate voltages.

SUMMARY

An optical element driving circuit flexibly configures energy sources to cause illumination with an optical output element, such as a flash lamp. In one implementation, the energy sources include an illumination capacitor and a capacitive voltage divider circuit coupled with the optical output element. The illumination capacitor may be charged to a first voltage and a boost capacitor of the capacitive voltage divider circuit may be charged to a second voltage that is a fraction (e.g., one half or one third) of the first voltage. The optical element driving circuit also includes a triggering circuit coupled with the capacitive voltage divider circuit. The triggering circuit is configured to place a sum of the first voltage and the second voltage across the optical output element.

In another implementation, an optical element driving circuit includes an illumination capacitor and a capacitive voltage divider circuit comprising multiple capacitors. The illumination capacitor and the capacitive voltage divider circuit are coupled with an optical output element. The illumination capacitor may be charged to a first voltage and the multiple capacitors of the capacitive voltage divider circuit may each be charged to the same or a different fraction of the first voltage. The optical element driving circuit also includes a controller coupled with the capacitive voltage divider circuit. The controller is configured to select zero or more capacitors from the capacitive voltage divider circuit for use to drive the optical output element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows an optical element driving circuit102for an optical output element104. In one implementation, the optical element driving circuit102may be a flash lamp driving circuit and the optical output element104may be a flash lamp, such as a xenon flash lamp. The optical element driving circuit102includes energy sources to drive the illumination phase of the optical output element104. In one implementation, the energy sources include an illumination source106and a capacitive voltage divider circuit108.

The voltage across the capacitive voltage divider circuit108as a whole is split between multiple divider capacitors within the capacitive voltage divider circuit108. In one implementation, the multiple capacitors are connected in series. The sum of the voltages of the individual capacitors approximately equals the voltage across the capacitive voltage divider circuit108as a whole. In one implementation, the capacitive voltage divider circuit108includes two capacitors. When the two capacitors have approximately the same capacitance, then the voltages across each of the two capacitors are approximately equal, namely half of the voltage across the capacitive voltage divider circuit108as a whole. However, the voltage divider circuit108may include capacitors with different capacitances, which then charge to different voltages in relation to their capacitances. For example, if the first capacitor has twice the capacitance as the second capacitor, then the voltage across the first capacitor will be half the voltage across the second capacitor. Therefore, one-third of the total voltage will be across the first capacitor and two-thirds of the total voltage will be across the second capacitor. The amount of voltage boost for the optical output element104may be adjusted by changing the relative capacitances of the divider capacitors.

The optical element driving circuit102may also include a controller110, a triggering circuit112, and an ionization circuit114. The controller110may determine5when to initialize and illuminate the optical output element104. For example, the controller110may send a signal to the triggering circuit112and/or the ionization circuit114to ready the optical output element104for illumination. The signals to the triggering circuit112and the ionization circuit114may be sent simultaneously or sequentially. Upon receipt of the signal from the controller110, the ionization circuit114causes an initial ionization of the gases inside the optical output element104. The optical output element104is then primed for current flow through the optical output element104to generate illumination. To illuminate the optical output element104, the triggering circuit112couples a boost node of the capacitive voltage divider circuit108to a ground potential which places zero or more capacitors of the capacitive voltage divider circuit108in series with the illumination source106across the optical output element104to drive the optical output element104.

FIG. 2shows a driving circuit202that is one implementation of the optical element driving circuit102presented inFIG. 1. The driving circuit202ofFIG. 2produces illumination from an optical output element104. The optical element driving circuit102also includes an illumination capacitor Cl and the capacitive voltage divider circuit108to drive the illumination phase of the optical output element104. As described in more detail below, the capacitive voltage divider circuit108includes a boost node204which separates a capacitor C4used to drive the optical output element104from a capacitor C3that is not used to drive the optical output element104.

The driving circuit202may additionally include a high frequency filter capacitor C6connected in parallel with the illumination capacitor C1. The filter capacitor C6may help to reduce noise in the optical element driving circuit202. More specifically, the filter capacitor C6may absorb high frequency transients in the charging pulses that charge the trigger capacitor C5, the illumination capacitor C1, and the capacitors C3and C4of the capacitive voltage divider circuit108.

The capacitors C1, C3, C4, and C6of the driving circuit202may be charged to specific voltage levels. The voltage levels may be set based on a desired output intensity for the optical output element104. The trigger capacitor C5may also be charged to a specific voltage level. In one implementation, two series connected 91-volt zener diodes D3and D15control the voltage on the trigger capacitor C5so that it does not charge above 182 volts. Other zener values may be used to charge the trigger capacitor C5to other voltage levels. The capacitors C1and C6may charge to the full voltage determined by a power source and capacitors C3and C4charge according to the configuration of the capacitive voltage divider circuit108. For example, the capacitive voltage divider circuit108as a whole is charged to a voltage level determined by the power source, and the capacitors C3and C4are each charged to a portion of the total voltage across the capacitive voltage divider circuit108.

In one implementation, C1and C6are charged to substantially the same voltage as the +HV voltage source. For example, if +HV is equal to 200 volts, then the potential difference across C1and C6is substantially equal to 200 volts minus any losses seen through the charging path. Also, the capacitive voltage divider circuit108is charged to substantially the same voltage as the +HV voltage source. For example, if +HV is equal to 200 volts, then the potential difference across the capacitive voltage divider circuit108is substantially equal to 200 volts minus any losses (e.g., the diode drop across D2) seen through the charging path. Charging current flows through a charging path to charge the capacitive voltage divider circuit108. The charging path includes the resistor R46, capacitors C3and C4, the diode D2, and the resistor R49.

In the implementation ofFIG. 2, the capacitive voltage divider circuit108includes two capacitors C3and C4. By splitting the voltage across the capacitive voltage divider circuit108between two or more capacitors, the driving circuit202implements a fractional voltage doubler circuit. The fractional voltage doubler provides the flexibility to achieve a wide range of values of electrode anode voltage across the optical output element104prior to ionization, without requiring full doubling of a particular source voltage.

Capacitors C3and C4charge from the +HV source through resistor R46. In one implementation, the +HV source provides the same charging voltage to the capacitor C1and the capacitive voltage divider circuit108. Thus, the total voltage across C3and C4combined substantially equals the voltage across C1. The voltage across C4can be determined approximately according to equation 1 below:
VC4=VCVD[CC3/(CC4+CC3)]  (equation 1),
where VCVDis the voltage across the capacitive voltage divider circuit108as a whole, and where CC3and CC4are the capacitances of capacitors C3and C4, respectively. If the capacitors C3and C4are chosen to have the same capacitance, then the voltage across C4is approximately half of the voltage across the capacitive voltage divider circuit108as a whole. If the capacitor C4is chosen to have a capacitance that is greater than the capacitance of the capacitor C3, then the voltage across C4will be less than half of the voltage across the capacitive voltage divider circuit108as a whole. In one implementation, the capacitor C3may have a capacitance that remains constant while the capacitance of the capacitor C4is adjusted to achieve a desired voltage level across the capacitor C3. Alternatively, the capacitance of the capacitor C3may be adjusted relative to the capacitance of the capacitor C4.

To prime the lamp104to provide a light output, the driving circuit202provides a trigger signal on a trigger input206to commence ionization and illumination of the optical output element104. The trigger input206may be coupled with an ionization triggering circuit and an illumination triggering circuit. In one implementation, the trigger input206is coupled with switches Q7and Q8. The driving circuit202includes a resistor R38between the trigger input206and the switch Q7. The driving circuit also includes a resistor R7between the trigger input206and the switch Q8. The values of the resistors R7and R38may be selected to ensure a desired order of switching (e.g., a staggered order). For example, the driving circuit202may be configured to ensure that the switch Q7closes before the switch Q8so that the voltage of the capacitors C1and C4is applied across the optical output element104before ionization occurs.

In one implementation, the resistance of the resistor R38is selected to be lower than the resistance of the resistor R7. Therefore, a greater amount of current will flow to the switch Q7than will flow to the switch Q8. Thus, the switch Q7will begin conducting well before the switch Q8. Accordingly, the driving circuit202ensures that the illumination phase occurs without substantial delay after ionization. In the implementation shown inFIG. 2, R38is523Ohms and R7is 1.69 kOhms. However, other values may be selected for the resistors R7and R38to select the drive level applied to the switches that control triggering and illumination, and the order in which the switches are activated. Furthermore, switches Q7and Q8may be thyristors, triacs, silicon controlled rectifiers (“SCRs”), or other types of switching devices.

The trigger signal on the trigger input206causes the switch Q8to conduct, thereby completing a circuit for the trigger capacitor C5to energize the primary coil of the step-up transformer T1of the ionization circuit114. The secondary winding of the transformer T1includes a first lead L3connected to ground and a second lead L4coupled with the optical output element104. Specifically, the lead L4may be wrapped around the optical output element104. The secondary winding of the transformer generates a damped multi-KV oscillation applied to the outside of the lamp104. In one implementation, the voltage developed across the pair of leads in the secondary winding of the transformer has a nominal output of approximately 5,800 volts at 185 candela output. The high voltage output of the transformer secondary winding causes an initial ionization of the gases inside the lamp104. The lamp104is then primed for high current discharge flow to generate illumination.

The capacitor C1may be considered an illumination capacitor as it provides a source of illumination energy to the optical output element104. Capacitor C4may be considered a boost capacitor (e.g., a fractional doubling capacitor) as it adds to or boosts the voltage provided by the illumination capacitor C1for driving the illumination phase of the optical output element104. Capacitor C3may be considered a divider capacitor as it splits the total voltage of the capacitive voltage divider circuit108with the capacitor C4. Illumination occurs when the illumination capacitor C1and the boost capacitor C4drive the optical output element104after the trigger signal causes switch Q7to conduct. One terminal of the switch Q7is coupled with a ground potential. A second terminal of the switch Q7is coupled with the boost node204between the capacitors C3and C4. The trigger signal on the trigger input206causes the switch Q7to conduct, thereby bringing the boost node204between the capacitors C3and C4substantially near a ground potential.

A first side of capacitor C4is coupled with the boost node204between the capacitors C3and C4. A second side of the capacitor C4is coupled with the cathode (K) side of the optical output element104. When the first side of the capacitor C4at the boost node204is brought down to near ground potential, the second side of the capacitor C4at the node between the boost capacitor C4and the optical output element104is level shifted down to a negative voltage level. The voltage at the anode (A) of the optical output element104is held at a positive voltage by the illumination capacitor C1, and the voltage at the cathode (K) of the optical output element104is held at a negative voltage by the boost capacitor C4. Therefore, the potential difference across the optical output element104is approximately equal to the sum of the voltage across C1and the voltage across C4.

When the switch Q7is conducting, the boost capacitor C4is placed in series with the illumination capacitor C1to drive the optical output element104. The boost capacitor C4may still be considered in “series” with the illumination capacitor C1even though some current may be flowing through the capacitor C6. Specifically, switch Q7may place the boost capacitor C4in series with the set of capacitors (e.g., capacitors C1and C6) that drive the optical output element104. By connecting the boost node204between the capacitors C3and C4with the ground potential, the switch Q7specifically selects the voltage across capacitor C4to add in series across the lamp, and prevents the voltage across the capacitor C3from being placed in series with the illumination capacitor C1.

In one implementation where the capacitive voltage divider circuit108includes two capacitors of equal capacitance (e.g., 0.047 uF capacitors C3and C4), the boost voltage provided by the boost capacitor C4is determined approximately according to equation 2 below:
VBoost=(V+HV−VR)/2  (equation 2),
where V+HVis the voltage level of the fully charged illumination capacitor C1, and where VRis the residual (terminal) voltage across the illumination capacitor C1after the illumination phase of the optical output element104. If V+HVequals 225 volts and VRequals 35 volts, the boost voltage provided by the boost capacitor C4equals approximately 95 volts. Therefore, with the boost voltage from the boost capacitor C4, the total voltage developed across the optical output element104prior triggering is 225 volts−(−95 volts)=320 volts. For high candela applications, where the optical output element104may be specified to operate with a potential difference in the range of 250 to 390 volts, the boost voltage from the capacitor C4raises the total voltage from 225 (which is below the specified operation range) to 320 (which is within the specified operation range). Therefore, the boost capacitor C4may help ensure reliable flash lamp operation.

In another implementation where the capacitive voltage divider circuit108includes more than two capacitors of equal capacitance, the boost voltage provided by the boost capacitor is determined approximately according to equation 3 below:
VBoost=(V+HV−VR)/n(equation 3),
where V+HVis the voltage level of the fully charged illumination capacitor C1, where VRis the residual voltage across the illumination capacitor C1after the illumination phase of the optical output element104, and where n is the number of capacitors of equal capacitance included in the capacitive voltage divider circuit108. If V+HVequals 225 volts, VRequals 35 volts, and one of three capacitors in the capacitive voltage divider circuit108is used as a boost capacitor, then the boost voltage provided by the boost capacitor equals approximately 63.33 volts. Therefore, with the boost voltage from the boost capacitor, the total voltage developed across the optical output element104prior triggering is 225 volts−(−63.33 volts)=288.33 volts.

When the capacitor C4is used to drive the optical output element104, at least a portion (e.g., most) of the energy stored in capacitor C4is discharged to initiate illumination. However, the capacitor C3has no discharge path through the optical output element104during illumination. Therefore, the driving circuit202may provide an alternative path for the capacitor C3to discharge prior to commencing the boost cycle to make sure the capacitor C3conducts current to the capacitor C4for the next charging cycle. In one implementation, the driving circuit202includes a diode D13to provide a discharge path for the capacitor C3. Before capacitor C4is recharged, the driving circuit202may discharge the energy from capacitor C3through diode D13into the illumination capacitor C1.

Before illumination occurs, a charge pump (or other power supply) may charge the illumination capacitor C1, capacitive voltage divider circuit108as a whole, and the boost capacitor to voltages selected according to the desired output intensity of the optical output element104according to any manufacturer specifications for the optical output element104. For example, the capacitor C1and the capacitive voltage divider circuit108as a whole may be charged to approximately 140 volts for a 15 candela output and approximately 185 volts for a 30 candela output. Similarly, the capacitor C1and the capacitive voltage divider circuit108as a whole may be charged to approximately 250 volts for a 75 candela output and approximately 286 volts for a 110 candela output. Any of the voltages, capacitances, or types of energy sources may be modified, adjusted, or substituted to provide any desired set of output intensities.

In one implementation, the optical output element104operates with an anode voltage in the range of 250 to 390 volts. The triggering voltage may be approximately 200 volts or more. In the example of the optical element driving circuit102described above, the +HV voltage level is approximately 190 to 225 volts. To ensure that the optical output element104is driven with sufficient voltage for illumination, the capacitive voltage divider circuit108is configured to boost or add to the voltage provided by the capacitor C1to achieve a larger total potential difference across the optical output element104.

FIG. 3shows an alternative optical element driving circuit302for an optical output element104. The optical element driving circuit302includes one or more trigger selection connections305between the controller303and the triggering circuit304. The trigger selection connections305may couple multiple trigger inputs with the triggering circuit304. The optical element driving circuit302also includes one or more boost node selection connections306between the triggering circuit304and the capacitive voltage divider circuit108. The boost node selection connections306may couple selected nodes in the capacitive voltage divider circuit108with the triggering circuit304.

The triggering circuit304may couple selected boost nodes in the capacitive voltage divider circuit108with a ground potential. Depending on which boost node of the capacitive voltage divider circuit108is coupled with the ground potential, zero or more of the capacitors of the capacitive voltage divider circuit108will be placed in series with the illumination source106across the optical output element104to drive the optical output element104. In the implementation described above, the capacitive voltage divider circuit108included two capacitors, one of which was placed in series across the lamp104with the illumination source106.

In other implementations, the capacitive voltage divider circuit108includes more than two capacitors. Similarly, the triggering circuit112may drive the optical output element104with the voltage from zero, one, two, or more of the capacitors by selecting the appropriate node to couple with the ground potential. The amount of boost voltage applied across the optical output element104may be adjusted by changing the appropriate node of the capacitive voltage divider circuit108to couple with the ground potential so that a selected number of the divider capacitors are used to drive the optical output element104.

In one implementation, the triggering circuit304includes a switch, such as a thyristor, for each of the trigger selection connections305and that may connect a specific boost node in the capacitive voltage divider circuit108to ground. For example, the optical element driving circuit302may include a first trigger selection connection308and a second trigger selection connection310between the controller303and the triggering circuit304. The optical element driving circuit302may also include a first boost node selection connection312and a second boost node selection connection314between the triggering circuit304and the capacitive voltage divider circuit108. The triggering circuit may include a first switch that couples the trigger selection connection308with the boost node selection connection312, and a second switch that couples the trigger selection connection310with the boost node selection connection314. The trigger selection connections308and310provide gate control signals to the switches of the triggering circuit304. The trigger selection connections312and314provide a path from a selected boost node of the capacitive voltage divider circuit108through the switches of the triggering circuit304to ground when the corresponding gate control signals are asserted.

The controller303may then assert a trigger signal on the trigger selection connection308to the first switch to connect one node of the capacitive voltage divider circuit108(i.e., the node connected with the boost node selection connection312) to the ground potential. Alternatively, the controller303may send a trigger signal on the trigger selection connection310to the second switch to connect a different node of the capacitive voltage divider circuit108(i.e., the node connected with boost node selection connection314) to the ground potential. In other words, the controller303and the triggering circuit304may use multiple trigger paths to select the number of capacitors from the capacitive voltage divider circuit108to use to drive the optical output element104.

FIG. 4shows a capacitive voltage divider circuit108with multiple capacitors402,404,406, and408, and multiple connection nodes410,412,414,416, and418. Terminal420of the capacitive voltage divider circuit108is coupled with the cathode (K) of the optical output element104(FIG. 2), while terminal422is connected to a charging source (e.g., one side of resistor R46inFIG. 2). The capacitors402-408may each be charged to a voltage level that is a fraction of the total voltage across the capacitive voltage divider circuit108. The sum of the voltages of each of the capacitors402-408may substantially equal the total voltage across the capacitive voltage divider circuit108. Similarly, the capacitors402-408may each be charged to a voltage level that is a fraction of the total voltage across the illumination capacitor C1(FIG. 2) and the sum of the voltages of each of the capacitors402-408may substantially equal the total voltage across the illumination capacitor C1.

In one implementation, a triggering circuit424may receive an input signal426indicating which of the capacitors402-408should be used to drive the optical output element. The input signal426may be implemented as individual gate control signals for individual switches that are operable to couple any specific node410-418to ground. In another implementation, the triggering circuit424may receive an input signal426indicating which of the capacitors402-408should be prevented from driving the optical output element. In yet another implementation, the triggering circuit424may receive an input signal426indicating a desired voltage level to be applied across the optical output element104(FIG. 2). In response to the input signal426, the triggering circuit424will couple one of the nodes410-418to a ground potential to set the appropriate voltage level across the optical output element104. Additionally, the triggering circuit424may choose to select any of the nodes410-418to commute to ground potential to change the voltage level across the optical output element104. For example, the triggering circuit424may receive an input426indicating that a different voltage is needed across the optical output element. In response, the triggering circuit424may move the ground potential from a currently selected node to a different node so that the boost voltage provided by the capacitive voltage divider circuit108may be adjusted to the desired level for driving the optical output element.

When the triggering circuit424couples the node410with the ground potential, none of the capacitors402-408of the capacitive voltage divider circuit108will be used to drive the optical output element. When the triggering circuit424couples the node412with the ground potential, the capacitor402will be used as a boost to drive the optical output element together with the illumination capacitor, but the remaining capacitors404-408will be prevented from driving the optical output element. When the triggering circuit424couples the node414with the ground potential, the capacitors402and404will be used as a boost to drive the optical output element together with the illumination capacitor, but the remaining capacitors406and408will be prevented from driving the optical output element. When the triggering circuit424couples the node416with the ground potential, the capacitors402-406will be used as a boost to drive the optical output element together with the illumination capacitor, but the remaining capacitor408will be prevented from driving the optical output element. When the triggering circuit424couples the node418with the ground potential, all the capacitors402-408of the capacitive voltage divider circuit108will be used as a boost to drive the optical output element together with the illumination capacitor.

FIG. 5is a flow diagram of the operation of a warning system including an optical element driving circuit. In some implementations, discrete circuitry in the warning system coordinates illumination through the optical output element104. In other implementations, the warning system includes a controller that may execute an illumination control program, and the flow diagram may represent the logic implemented by the illumination control program. In such an implementation, the controller may include general purpose outputs that drive the trigger signal, boost node selection signal, or other signals under program control. The warning system determines whether multiple boost nodes in the capacitive voltage divider circuit108are available to select from, as described in connection withFIGS. 3 and 4(502).

When the warning system may select from multiple boost nodes to customize the voltage level applied to the optical output element, the warning notification appliance determines the supply or illumination capacitor voltage level (504). For example, the warning system may determine the voltage level +HV used to charge the illumination source106and the capacitive voltage divider circuit108. The warning system also determines the voltage level or range that would result in reliable optical output element operation (506). The warning system determines the boost voltage level (508). For example, the warning system may compare the voltage level +HV used to charge the illumination source106with the voltage level or range that would result in reliable flash lamp operation. The warning system selects the capacitors from the capacitive voltage divider circuit108to drive the optical output element (510). For example, the warning system may determine which capacitors would set (in sum with the voltage across the illumination capacitor) the voltage level across the optical output element within the reliable optical output element operation range. The warning system may then choose a specific boost node from among those available in the capacitive voltage divider circuit108to couple to ground so that the desired boost voltage will be used to drive the optical output element in sum with the voltage on the illumination capacitor.

Whether or not the warning system may select from multiple boost nodes, the warning system charges the illumination, boost, and trigger capacitors (512). The warning system then determines when to issue a trigger signal (514). The trigger signal initiates the ionization of the gas in the optical output element, and the illumination from the optical output element at the selected output intensity.

FIG. 6shows an alternative block diagram of an optical element driving circuit602. The optical element driving circuit602includes a power converter604, control logic606, and one or more triggering circuits608. The control logic606may transmit one or more signals that close the switches Q7and Q8. Some implementations may include a delay unit610to ensure that switch Q7closes before switch Q8. By closing the switches Q7and Q8, the control logic initiates a sequence that results in capacitors C1and C4producing illumination from the flash lamp104, as described above.

FIGS. 7-11show a warning system that includes an optical element driving circuit202.FIGS. 7-9show the driving circuit202in the context of surrounding warning system control circuitry.FIG. 10shows a trigger synchronization circuit, input connectors, and electromagnetic interference filtering.FIG. 11shows power supply generation for the warning system.

The disclosed driving circuits may be modified and still fall within the spirit of the disclosure. For example, the optical output element may be any source of illumination (or energy output in the visible or non-visible spectrum), including a xenon flash lamp, flash lamp with gas, or other light source. The zener diode voltages may vary to accommodate any particular design or application. The driving circuit may produce other output intensities. Other energy sources may be used in addition to or as alternative to the capacitors. Other types of switches may be used instead of the thyristors. Resistor and capacitor values may be adjusted to accommodate other designs or specifications. The charge pump may provide another voltage level. The charge pump may be replaced with another type of power supply. The control circuitry may be analog or digital control circuitry, including discrete circuits, processors operating under programmed control, or other circuitry. Jumpers, selector switches, or other configurable circuit elements may set the desired output level and may select, for example, which of multiple boost nodes to connect to ground in the capacitive voltage divider circuit. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this disclosure.