Light amplification device and laser processing device

A light amplifier according to an aspect of the present invention includes: a seed light source configured to generate a pulsing seed light; an excitation light source configured to generate excitation light; a light amplifying fiber configured to amplify the seed light by the excitation light and output the amplified light; and a control unit configured to control the seed light source and the excitation light source. The control unit has a mode to control the excitation light's power such that as a set value of a pulse width of the amplified light increases, the amplified light's peak energy increases within a threshold value at a minimum set value of the pulse width.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a light amplification device and a laser processing device. In particular, the present invention relates to a technique for emitting a laser pulse stably from a fiber amplifier of a MOPA (Master Oscillator and Power Amplifier) system.

Description of the Background Art

A laser processing device which adopts a MOPA (Master Oscillator and Power Amplifier) system using a light amplifying fiber and uses light from a laser diode (LD) as seed light, allows emitted light's repetition frequency, peak power, pulse width, etc. to be varied independently of each other, and thus characteristically allows an optimal parameter to be easily selected depending on a target to be processed. For example, Japanese Patent Laying-Open No. 2011-181761 discloses a configuration in which a driver is controlled to vary a condition of excitation light in a non emission period so that energy of pulsed light output from a laser processing device can be stabilized regardless of the non emission period's length.

Japanese Patent Laying-Open No. 2012-248615 discloses a light amplification device which operates in response to a value detected by a peak value detector to control power of excitation light (a driver's bias current) in a non light emission period so that the first output light pulse and the last output pulse generated during a light emission period are equal in power.

SUMMARY OF INVENTION

It has been difficult in a conventional laser processing device having a fiber laser oscillator to increase average power in a low frequency region of an oscillation period. This is because such a problem occurs as follows: When a frequency is decreased while excitation light's power is fixed, peak power increases. When peak power increases, the fiber may be damaged. Furthermore, when a nonlinear optical phenomenon exemplified by stimulated Raman scattering (SRS) is caused by the increased peak power, a transmission mode with a mismatched phase is enhanced.

In order to avoid the above described problem, when using the fiber laser oscillator at low frequency, it must be used in a state where average power is decreased by decreasing excitation light's power.

On the other hand, for example, when a processing, such as deep metal penetration or black marking, is done using laser light, the laser light is required to have large power of some extent. Accordingly, when processing a metal by laser light, a laser oscillator having a large average power has been used at a low frequency. A conventional fiber laser oscillator has been unable to increase its output's average power, and processing, such as deep metal penetration or black marking, has been difficult. Accordingly, a fiber laser oscillator capable of outputting light of high power for processing is required.

A light amplifier according to an aspect of the present invention comprises: a seed light source configured to generate a pulsing seed light; an excitation light source configured to generate excitation light; a light amplifying fiber configured to amplify the seed light by the excitation light and output the amplified light; and a control unit configured to control the seed light source and the excitation light source, the control unit having a mode to control the excitation light's power such that as a set value of a pulse width of the amplified light increases, the amplified light's peak energy increases within a threshold value at a minimum set value of the pulse width.

The above “mode” is a mode in which the excitation light has power increased when the pulse width is increased.

Preferably, when the mode is set, the control unit decreases an upper limit of a repetition frequency of the amplified light to be smaller than an upper limit of the repetition frequency in another mode different from the mode, and also sets the pulse width to be larger than the minimum set value. The control unit increases the power of the excitation light generated by the excitation light source to be larger than the power of the excitation light in the other mode.

“Another mode” is a mode in which the excitation light has power fixed while a parameter such as pulse width, repetition frequency, etc. is adjusted.

Preferably, the control unit increases an average power of the amplified light in the mode to be higher than the average power in the other mode.

Preferably, a maximum value of the pulse width in the mode is larger than that of the pulse width in the other mode.

Preferably, when the control unit increases the pulse width, the control unit controls the seed light source to emit the seed light as a pulse train including a plurality of light pulses.

Preferably, the control unit performs a process to cause a user to select a pattern for setting each of the mode and the other mode from a plurality of set patterns for determining a number of the light pulses configuring the pulse train.

Preferably, the control unit performs a process to cause a user to select a pattern for setting each of the mode and the other mode from a plurality of set patterns for determining the repetition frequency.

Preferably, the control unit switches the mode to the other mode and vice versa by a reboot process.

Preferably, when the mode is set from another mode different from the mode, the control unit operates in response to an input received from a user for decreasing an upper limit of the repetition frequency of the amplified light to increase the pulse width to be larger than that in the other mode and also increase the excitation light's power to be larger than that in the other mode.

Preferably, when the mode is set from another mode different from the mode, the control unit operates in response to an input received from a user for increasing the pulse width to increase the excitation light's power to be larger than the excitation light's power in the other mode and also decrease the repetition frequency's upper limit to be smaller than that in the other mode.

Preferably, when the mode is set from another mode different from the mode, the control unit operates in response to an input received from a user for increasing the excitation light's power to increase the pulse width to be larger than that in the other mode and also decrease the repetition frequency's upper limit to be smaller than that in the other mode.

A laser processing device according to another aspect of the present invention is a laser processing device comprising the light amplification device according to any of the above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in embodiments hereinafter in detail with reference to the drawings. Note that in the figures, identical or corresponding components are identically denoted, and accordingly, will not be described repeatedly.

Initially, a device configuration of a light amplification device according to an embodiment of the present invention and a laser processing device including the light amplification device will be described.FIG. 1shows a configuration example of the laser processing device according to the present embodiment.

With reference toFIG. 1, a laser processing device100according to an embodiment of the present invention is implemented for example as a laser marker. Laser processing device100includes a controller101and a marker head102. Controller101configures a main part of the light amplification device according to the embodiment of the present invention.

In this embodiment, the light amplification device emits laser light having an intensity periodically varying in a pulsing manner. Hereinafter, emitted light will also be referred to as a “laser pulse.” In the following description, unless otherwise indicated, the “laser pulse” means laser light composed of one or more pulses. A maximum value in intensity (or power) of each pulse included in the “laser pulse” is generally referred to as “peak power.” Typically, an envelope of a power that the “laser pulse” has corresponds to “peak power.”

Typically, laser processing device100includes a fiber amplifier of a MOPA (Master Oscillator and Power Amplifier) system. In this embodiment, laser processing device100includes a fiber amplifier of two stages. More specifically, controller101includes a light amplifying fiber1, a seed laser diode (LD)2, exciting laser diodes3and7, isolators4and6, combiners5and8, drive circuits21and22, and a control unit20. Marker head102includes a light amplifying fiber9, an optical coupler10, an isolator11, a beam expander12, a z axis scanning lens13, and galvanoscanners14and15. In the following description, a laser diode may simply be represented as an “LD.”

Light amplifying fiber1, seed LD2, and exciting LD3are basic elements of the fiber amplifier of the MOPA system. Light amplifying fiber1includes a core with a rare-earth element added as a light amplifying component, and a clad provided around the core. Light amplifying fiber9, as well as light amplifying fiber1, includes a core with a rare-earth element added as a light amplifying component, and a clad provided around the core.

The type of rare-earth element added to the core of light amplifying fiber1,9is not particularly limited and can be Yb (ytterbium), Er (erbium), and Nd (neodymium), for example. In the present embodiment, a case will be indicated as an example in which a light amplifying fiber with Yb added as a rare-earth element is used. Light amplifying fiber1,9may be a single clad fiber with a single layer of clad provided around the core or a double clad fiber with two layers of clad provided around the core.

Light amplifying fiber1amplifies seed light that is received from seed LD2by excitation light that is received from exciting LD3. In other words, in the fiber amplifier of the MOPA system, excitation light from exciting LD3and pulsing seed light from seed LD2are provided to light amplifying fiber1. The excitation light having entered light amplifying fiber1is absorbed by the atoms of the rare-earth element contained in the core and the atoms are excited. When the seed light is propagated through the core of light amplifying fiber1with the atoms excited, the seed light causes stimulated emission of the excited atoms, and therefore, the seed light is amplified. That is, light amplifying fiber1amplifies the seed light by the excitation light.

Seed LD2is a laser light source and is a seed light source generating seed light. The seed light's wavelength is selected from a range from 1000 nm to 1100 nm, for example. Drive circuit21operates in response to a command received from control unit20to repeatedly apply a pulsed current to seed LD2to drive seed LD2in a pulsing manner. That is, seed LD2emits pulsed seed light.

The seed light emitted from seed LD2passes through isolator4and then enters light amplifying fiber1. Isolator4has a function to pass light only in one direction and block light incident in the opposite direction. Isolator4passes the seed light from seed LD2while blocking return light returned from light amplifying fiber1. This can prevent the return light from light amplifying fiber1from entering seed LD2. This is done because if the return light from the light amplifying fiber1enters seed LD2, it may damage seed LD2.

Exciting LD3is a laser light source and it is an excitation light source generating excitation light for exciting atoms of the rare-earth element added to the core of light amplifying fiber1. If Yb is added to the core of light amplifying fiber1as a rare earth element, the excitation light's wavelength is set for example to 915±10 nm, for example. Exciting LD3is driven by drive circuit22.

The seed light from seed LD2and the excitation light from exciting LD3are combined together by combiner5and thus enter light amplifying fiber1. When light amplifying fiber1is a single clad fiber, the seed light and the excitation light both enter the core. In contrast, when light amplifying fiber1is a double clad fiber, the seed light enters the core and the excitation light enters a first clad. The first clad of the double clad fiber functions as a waveguide for the excitation light. When the excitation light having entered the first clad is propagating through the first clad, the rare-earth element in the core is excited according to the mode in which the excitation light passes through the core.

Light amplifying fiber1amplifies laser light which in turn passes through isolator6and is then combined in combiner8with excitation light received from exciting LD7. Exciting LD7generates excitation light for exciting atoms of the rare earth element added to the core of light amplifying fiber9. Exciting LD7is driven by drive circuit22.

Light amplifying fiber9is optically coupled with the fiber from controller101by optical coupler10. The laser light amplified by light amplifying fiber1is further amplified inside light amplifying fiber9by excitation light received from exciting LD7.

Light amplifying fiber9outputs laser light which in turn passes through isolator11. Isolator11passes the laser light which has been amplified by light amplifying fiber9and is also emitted from light amplifying fiber9, and isolator11also blocks laser light which returns to light amplifying fiber9.

The laser light having passed through isolator11has its beam diameter expanded by beam expander12. Z axis scanning lens13scans the laser light in a direction along the z axis (in other words, a vertical direction). Galvanoscanners14and15scan the laser light in a direction along the x axis and a direction along the y axis, respectively. Thus, the laser light is scanned in a two dimensional direction on a surface of a workpiece250. Note that although not shown, other optical components, such as a fθ lens for condensing the laser light, may be included in marker head102.

By scanning laser light, that is, a laser pulse received from the light amplification device, on a surface of workpiece250in a two dimensional direction, the surface of workpiece250, which is formed of resin, metal, etc., is processed. For example, on the surface of workpiece250, information which is composed of characters, graphics, etc. is printed (or marked).

In the present embodiment, the light amplification device is configured so that excitation light is enhanced in a first stage of amplification (light amplification in controller101). However, it is not necessarily essential that marker head102perform light amplification. That is, marker head102may dispense with light amplifying fiber9.

Control unit20mainly controls the generation of the light by seed LD2(a seed light source) and exciting LD3(an excitation light source). More specifically, control unit20receives from an upper device300a command required for scanning laser light. Furthermore, control unit20receives a setting from the user via a setting device301. Control unit20operates in response to a user operation from setting device301to control drive circuits21and22and also control galvanoscanners14and15.

Control unit20may be any hardware configured to provide a control command. For example, control unit20may be implemented using a computer which executes a prescribed program. As setting device301, a personal computer can be used, for example. The personal computer can include a mouse, a keyboard, a touch panel, etc. as an input unit.

Optical elements, such as seed LD2, exciting LDs3and7, and isolators4,6, and11have characteristics which may vary depending on temperature. Accordingly, it is more preferable to provide laser processing device100with a temperature controller for maintaining these optical elements' temperature constantly.

Laser processing device100according to the present embodiment allows its average power, the laser pulse's repetition frequency, and the laser pulse's pulse width to be controlled independently of each other. The user can set an average power, a repetition frequency of the laser pulse, and a pulse width of the laser pulse independently of each other. As shown inFIG. 1, in the present embodiment, the light amplification device has a multi-stage amplification configuration, and accordingly, by increasing excitation light at each amplifying stage, laser light's average power can be increased within a range in which a nonlinear optical phenomenon does not occur.

The light amplification device (laser processing device100) according to the present embodiment has two modes. In other words, control unit20has two control modes. A first mode is a mode in which excitation light has power fixed while a parameter such as pulse width, repetition frequency, etc. is adjusted. A second mode is a mode in which excitation light has power increased when a pulse width is increased. Note that the second mode corresponds to “a mode” in the present invention and its embodiment(s), and the first mode corresponds to “another mode” in the present invention and its embodiment(s).

In the first mode, the laser pulse's repetition frequency and the laser pulse's pulse width can be set in a wide range.

FIG. 2is a waveform diagram for illustrating a laser pulse emitted by laser processing device100according to the present embodiment, that has a minimum pulse width. With reference toFIG. 2, f represents the laser pulse's repetition frequency. w represents the laser pulse's pulse width. Average power can be defined as a sum of energy of laser pulses output per unit time (e.g., 1 second) from the light amplification device.

Pp represents the laser pulse's peak power. Peak power Pp is controlled not to exceed a threshold value power Pth. Threshold power Pth is previously determined to be the power of an upper limit which does not damage the light amplifying fiber for example.

FIG. 3is a waveform diagram for illustrating a laser pulse emitted by laser processing device100according to the present embodiment, that has a larger pulse width than the minimum pulse width. With reference toFIG. 3, in the present embodiment, when pulse width w is increased, a single pulse's width is not increased; rather, a pulse train including a plurality of pulses is output. The single pulse's width is the same as the minimum pulse width. Accordingly, pulse width w is proportional to the number of pulses.

In the first mode, pulse width w has a minimum value of 15 ns, for example, and is variable between 15 ns and 300 ns. Furthermore, repetition frequency f is variable, for example within a range of 10 kHz to 1000 kHz.

FIG. 4is a waveform diagram for illustrating variation of peak power Pp when laser processing device100according to the present embodiment increases a pulse width in the first mode. With reference toFIG. 4, when pulse width w is increased with the laser pulse's energy fixed, peak power Pp decreases.

For example, in metal processing (for example, deep metal penetration or black marking), it is necessary to make the laser pulse's energy higher. The laser processing device having the fiber laser oscillator must have an average power increased (for example to 50 W) and a repetition frequency decreased. By decreasing the repetition frequency, a time interval at which the laser pulse is output from the light amplifying fiber becomes long. As a period of time for which excitation light's power is accumulated in the light amplifying fiber becomes long, peak power Pp increases by decreasing repetition frequency f.

As the laser processing device having the fiber laser oscillator allows a repetition frequency, a peak power, a pulse width, etc. to be varied independently of each other, it is not easy to set a condition for generating a laser pulse required for a processing which requires high average power. Accordingly, in the present embodiment, laser processing device100has the second mode. The second mode is a mode allowing the laser pulse to be output with a higher average energy than the first mode.

In the second mode, a setting range of the repetition frequency and a setting range of the pulse width are determined so that the average power can be higher than in the first mode.

FIG. 5is a waveform diagram for illustrating variation of peak power Pp when laser processing device100according to the present embodiment increases a pulse width in the second mode. With reference toFIG. 5, a waveform indicated by a solid line represents the power of a laser pulse output from laser processing device100in the second mode. A waveform indicated by a dotted line represents the power of a laser pulse output from laser processing device100in the first mode. In the second mode, the laser pulse's pulse width w is increased to be larger than a minimum pulse width, and peak power Pp is increased within threshold value power Pth. This can increase the average power, and processing such as deep metal penetration or black marking can be done for example.

In the second mode, repetition frequency f has a setting range narrower than that of the repetition frequency in the first mode, and pulse width w also has a setting range narrower than that of the pulse width in the first mode. Specifically, in the second mode, the setting range of repetition frequency f has an upper limit value smaller than that of the setting range of the repetition frequency in the first mode. In other words, in the second mode, the repetition frequency can be set within a low frequency region. This allows peak power to be increased. Furthermore, in the second mode, pulse width w has a lower limit value larger than a minimum value of the pulse width. This can reduce a possibility that peak power Pp exceeds threshold value power Pth.

Furthermore, pulse width w has a maximum value larger than that of the pulse width in the first mode. Thus, a laser pulse of high power suitable for processing, such as deep metal penetration or black marking, can be output.

FIG. 6is a waveform diagram showing an example of a waveform of a laser pulse when laser processing device100according to the present embodiment is operated in the first mode and the second mode. With reference toFIG. 6, the two graphs have equal scales for an axis of ordinate representing power and equal scales for an axis of abscissa representing time. In the second mode, peak energy can be made higher than in the first mode. In the example shown inFIG. 6, in the second mode, a pulse train is shown which has an initial pulse with particularly high peak power. Such a pulse waveform allows large contribution to deep metal penetration.

FIG. 7shows an example of a set pattern for operating laser processing device100according to the present embodiment in each of the first mode and the second mode. With reference toFIG. 7, for example in the first mode, the user can select a pattern suitable for a condition for processing from 15 set patterns which laser processing device100stores. In contrast, in the second mode, the user can select a pattern suitable for a condition for processing from 3 set patterns which laser processing device100stores. In the set patterns in the second mode, the number of pulses settable, i.e., the setting range of the pulse width is limited more than in the set patterns in the first mode.

A maximum value of the pulse width in the second mode is larger than that of the pulse width in the first mode. In other words, in the second mode, a maximum value of the number of pulses settable is 30, whereas in the first mode, a maximum value of the number of pulses settable is 20.

<D. Setting a Mode>

FIG. 8is a flowchart for illustrating a setting process of laser processing device100according to the present embodiment. The process indicated in this flowchart is mainly performed by control unit20. With reference toFIG. 8, in step S1, control unit20determines whether a process for rebooting laser processing device100has been performed. When the reboot process is not performed (NO in step S1), the current mode (the first mode or the second mode) is held (step S2). In contrast, when the reboot process is performed (YES in step S1), control unit20switches the mode (step S3).

Following step S2or step S3, in step S4, control unit20prepares a set pattern corresponding to the current mode (seeFIG. 7). For example, control unit20reads a set pattern stored therein.

In step S5, control unit20performs a process to cause the user to select a pattern for setting each of the first mode and the second mode from a plurality of set patterns. For example, setting device301operates in response to an instruction received from control unit20to prepare an input screen for the user to input a pulse width etc. The user can select a pulse width (a number of pulses) via the input screen. A parameter input to setting device301is sent from setting device301to control unit20. An example of the input screen will specifically be described hereinafter.

In step S6, control unit20receives the input (a setting parameter) from the user via setting device301. The setting parameter is a repetition frequency, an average power, etc., for example. For the sake of illustration, while inFIG. 8the process in which control unit20receives a setting done by the user is described as being divided into step S5and step S6, the process in which control unit20receives the setting done by the user may be performed in one step. Furthermore, the plurality of set patterns is not limited to the pulse width's patterns, and may be the repetition frequency's set patterns or set patterns of the pulse width and the repetition frequency combined together.

In step S7, control unit20determines whether the user's setting has been completed. For example, when the user indicates to setting device301that a setting has been completed, the indication is sent from setting device301to control unit20.

Thus control unit20determines that the user's setting has been completed. In that case (YES in step S7) control unit20stores a parameter set by the user. The stored parameter is used when laser processing device100operates. In contrast, when control unit20determines that the user's setting has not yet been completed (NO in step S7), the process returns to step S5and the user's setting process is continued.

In the following description of a user interface, the first mode and the second mode will be referred to as a “standard mode” and an “EE mode”, respectively. It should be noted that these names are not intended to limit the present embodiment.

FIG. 9is a schematic diagram showing an example of a user interface screen for setting a mode of the laser processing device according to the present embodiment. With reference toFIG. 9, when setting a mode of laser processing device100, the user selects an “environment setting” menu (reference numeral:210) from a menu list. This allows “EE mode setting (option)” to be selectable, and the user selects “EE mode setting (option)” for example by clicking the mouse. This displays a dialog for selecting a mode from the standard mode and the EE mode.

FIG. 10is a schematic diagram showing an example of a dialog for selecting a mode. With reference toFIG. 10, the user selects the EE mode or the standard mode via a dialog211and presses an OK button212. This reboots laser processing device100and switches a mode. In other words, step S1and step S3shown inFIG. 8are performed.

FIG. 11is a schematic diagram showing an example of a setting screen for the standard mode (the first mode). With reference toFIG. 11, “Basic Setting” (reference numeral:221) and “Detail Settings” (reference numeral:222) are fields for setting parameters. The laser pulse's power, repetition frequency (inFIG. 11, it is indicated as “frequency”), the pulse's shape (corresponding to the pulse width), and processing speed are basic setting parameters. In the standard mode, the repetition frequency can be set for example within a range of 10.0 kHz to 1000.0 kHz. The pulse's shape can be selected from pattern1to pattern15.

FIG. 12is a schematic diagram showing an example of a setting screen for the EE mode (the second mode). With reference toFIG. 12, in the EE mode, the repetition frequency can be set within a range of 10.0 kHz to 100.0 kHz. The pulse's shape can be selected from pattern1to pattern3.

In each of the standard mode and the EE mode, patterns and numbers of pulses are associated as shown inFIG. 7and stored in control unit20. When the user inputs a parameter via the setting screen shown inFIG. 11orFIG. 12, steps S5and S6shown inFIG. 7are performed.

An example of laser characteristics when laser processing device100according to the present embodiment is operated is shown inFIG. 13toFIG. 16.FIG. 13is a graph representing an average power of an output when laser processing device100according to the present embodiment is operated in each of the first mode and the second mode.FIG. 14is a graph representing pulse energy when laser processing device100according to the present embodiment is operated in each of the first mode and the second mode.FIG. 15is a graph representing peak power when laser processing device100according to the present embodiment is operated in each of the first mode and the second mode.

InFIG. 13toFIG. 15, each graph's axis of ordinate represents a numerical value when a characteristic value in the second mode is standardized as 1. Furthermore, inFIG. 13andFIG. 14, for both the first mode and the second mode, a laser characteristic when the number of pulses (seeFIG. 7) is 20 is indicated. InFIG. 15, for both the first mode and the second mode, a peak power when the number of pulses (seeFIG. 7) is 20 and in addition, a peak power in the second mode when the number of pulses (seeFIG. 7) is 10 are indicated.

As shown inFIG. 13toFIG. 15, for a repetition frequency of 100 kHz or less, laser processing device100has an average output, a pulse energy, and a peak power all higher in the second mode than in the first mode. Furthermore, in the second mode, the peak power for 10 pulses is higher than that for 20 pulses. That is, the smaller the pulse width is, the larger the peak power is.

Thus laser processing device100according to the present embodiment has a mode (the second mode) in which excitation light's power is controlled so that as a set value of the pulse width of amplified light (or the number of pulses) increases, the amplified light's peak energy increases within a threshold value at a minimum set value of the pulse width. This allows the fiber laser oscillator to output a laser pulse of higher average power.

FIG. 16is a figure for illustrating an effect of deep metal penetration in the second mode. A metal of aluminum is used. As shown inFIG. 16, when the second mode is compared with the first mode, the former allows a larger processing depth from a surface of the metal relative to how many times the processing is done. Accordingly, a processing ratio (a processing depth in the second mode/a processing depth in the first mode) is larger than one and increases as the processing is done more times.FIG. 16shows that deep metal penetration can be implemented in the second mode.

In the embodiment disclosed above, switching between the two modes of the first mode and the second mode is described. In another embodiment, when the second mode is set from the first mode, control unit20may operate in response to an input (a user input) received from a user interface for varying an upper limit of repetition frequency f of amplified light stepwise or smoothly to increase a pulse width to be larger than that in the first mode and also increase excitation light's power to be larger than that in the first mode. Control unit20may increase the pulse width and the excitation light's power stepwise or smoothly.

Furthermore, in another embodiment, when the second mode is set from the first mode, control unit20may operate in response to an input received from the user interface for varying a pulse width stepwise or smoothly to increase excitation light's power to be larger than that in the first mode stepwise or smoothly and also decrease the repetition frequency's upper limit to be smaller than that in the first mode stepwise or smoothly.

In still another embodiment, when the second mode is set from the first mode, control unit20may operate in response to an input received from the user interface for varying amplified light's power stepwise or smoothly to increase a pulse width to be larger than that in the first mode stepwise or smoothly and also decrease the repetition frequency's upper limit to be smaller than that in another mode stepwise or smoothly.

While the present invention has been described in embodiments, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.