Abstract:
An ultrasonic surgery apparatus enabling smooth surgery. The ultrasonic apparatus is provided with an ultrasonic chip, a vibration inducing unit which induces ultrasonic vibration to the ultrasonic chip, an aspiration unit which aspirates tissue emulsified by vibration of the ultrasonic chip, a detection unit which detects a clogging condition of the ultrasonic chip, a footswitch, having a pedal, for emitting an output signal which is based on a depression amount or a depression position of the pedal, and a control unit which controls at least one of ultrasonic power and a pulse-duty ratio of the ultrasonic vibration based on the output signal from the footswitch and a detection result obtained by the detection unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ultrasonic surgery apparatus for use in cataract surgery in which an opaque crystalline lens caused by a cataract is subjected to ultrasonic vibrations and emulsified, and then is aspirated and discharged outside a body. 
     2. Description of Related Art 
     In cataract surgery, an ultrasonic surgery apparatus is generally widespread which gives ultrasonic vibrations to nucleus of a crystalline lens using a tubular ultrasonic chip (referred to as an US chip, hereinafter) attached to a handpiece for surgery for performing fragmentation and emulsification, and aspirates and removes emulsified tissue of the nucleus of the crystalline lens through an aspiration hole at the tip of the US chip for discharging outside a body. In this kind of apparatus, a surgeon controls operations of irrigation liquid supply to an eye, aspiration, and phacoemulsification (induction of ultrasonic vibrations) using a footswitch having a pedal (see Japanese Patent Application Unexamined Publication No. Hei11-206803). 
     Besides, an ultrasonic oscillation mode in this kind of apparatus generally includes a pulse oscillation mode in which ultrasonic oscillation and intermission alternate (see WO95/20374 (Japanese Patent Application Unexamined Publication No. Hei9-508298)) in addition to a continuous oscillation mode in which ultrasonic oscillation is successively performed. In the pulse oscillation mode, nucleus followability of the US chip is improved and an amount of ultrasonic wave used is decreased, so that heat production may be suppressed to lower tissue invasion as compared with the continuous oscillation mode. Further, for the apparatus of WO95/20374, ultrasonic power and a pulse-duty ratio at the time of pulse oscillation (the ratio of oscillation to intermission) are changed in accordance with a vacuum (aspiration pressure) level which corresponds to a clogging condition of the US chip. 
     Incidentally, the ultrasonic power and the pulse-duty ratio are preferably low in view of the tissue invasion because fragmentation power relatively sufficient for soft nucleus of the crystalline lens may thereby be obtained. However, when great fragmentation power is required in such a case where hard nucleus of the crystalline lens is encountered, the conventional apparatus can increase (raise) the ultrasonic power only to a maximum value previously set through an operation panel even if the pedal is depressed. In this occasion, the surgeon instructs an operator of the apparatus (an assistant) to reset and raise the ultrasonic power and the pulse-duty ratio through the operation panel. However, this is troublesome and smooth surgery is difficult to perform. 
     Additionally, the apparatus of WO95/20374 has a constitution where the ultrasonic power and the pulse-duty ratio are automatically changed according only to the aspiration pressure level. Therefore, the ultrasonic power and the pulse-duty ratio happen to change contrary to the surgeon&#39;s intention. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to overcome the problems described above and to provide an ultrasonic surgery apparatus which enables a surgeon to increase fragmentation power intentionally in such a case where hard nucleus of a crystalline lens is encountered, and enables smooth surgery. 
     To achieve the objects and in accordance with the purpose of the present invention, an ultrasonic surgery apparatus includes an ultrasonic chip, a vibration inducing unit which induces ultrasonic vibration to the ultrasonic chip, an aspiration unit which aspirates tissue emulsified by vibration of the ultrasonic chip, a detection unit which detects a clogging condition of the ultrasonic chip, a footswitch, having a pedal, for emitting an output signal which is based on a depression amount or a depression position of the pedal, and a control unit which controls at least one of ultrasonic power and a pulse-duty ratio of the ultrasonic vibration based on the output signal from the footswitch and a detection result obtained by the detection unit. 
     Additional objects and advantages of the invention are set forth in the description which follows, are obvious from the description, or may be learned by practicing the invention. The objects and advantages of the invention may be realized and attained by the ultrasonic surgery apparatus in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the description, serve to explain the objects, advantages and principles of the invention. In the drawings, 
         FIG. 1  is a schematic external view of an ultrasonic surgery apparatus; 
         FIG. 2  is a view showing a schematic configuration of the ultrasonic surgery apparatus; 
         FIG. 3  is a view illustrating a depression mechanism in a footswitch; 
         FIG. 4  is a view illustrating operational control of irrigation, aspiration, and phacoemulsification on the basis of a depression amount (depression position) of the footswitch; 
         FIG. 5  is a view illustrating a control method of ultrasonic vibrations; 
         FIG. 6  is a view illustrating another control method of ultrasonic vibrations; 
         FIG. 7  is a view illustrating still another control method of ultrasonic vibrations; 
         FIG. 8  is a view illustrating still another control method of ultrasonic vibrations; 
         FIG. 9  is a view illustrating still another control method of ultrasonic vibrations; 
         FIGS. 10A and 10B  are views illustrating still other control methods of ultrasonic vibrations; and 
         FIG. 11  is a view illustrating still another control method of ultrasonic vibrations. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed description of one preferred embodiment of an ultrasonic surgery apparatus embodied by the present invention is provided below with reference to the accompanying drawings.  FIG. 1  is a schematic external view of an ultrasonic surgery apparatus.  FIG. 2  is a view showing a schematic configuration of the apparatus. 
     A main body  1  of the apparatus stores a control unit  5  which controls to drive the entire apparatus. An ultrasonic handpiece  2  for surgery (referred to as an US handpiece  2 , hereinafter) is held by a surgeon, and a tubular US chip  2   a  having an aspiration hole is attached to a tip of the US handpiece  2 . Ultrasonic vibrations generated by an integrated vibrator in the US handpiece  2  is amplified and conveyed to the US chip  2   a . The US chip  2   a  thereby becomes capable of giving ultrasonic vibrations to nucleus of a crystalline lens for performing fragmentation and emulsification thereon. The vibrator in the US handpiece  2  is provided with driving energy from the control unit  5  in the main body  1  via a cable  4 . For the ultrasonic vibrations conveyed to the US chip  2   a , a continuous oscillation or a pulse oscillation may be selected, and a switch in an input unit  3  may be used to switch to a mode for either oscillation. 
     The input part  3  is provided with a switch for altering a combination of irrigation, aspiration, and phacoemulsification in accordance with a depression degree of a pedal of a footswitch  6 , and with a group of switches for performing various settings for irrigation pressure, an amount of aspiration flow, aspiration pressure, ultrasonic power, a pulse-duty ratio and the like. Set values inputted through the input unit  3  are stored in a memory  7 . 
     An irrigation bottle  10 , filled with an irrigation liquid such as a saline which is supplied to a patient&#39;s eye E, is, hanged on a pole  12 . The pole  12  is vertically moved by a vertically moving device  13  (or manually moved) so that a height of the bottle  10  may be changed. The height of the bottle  10  is set so as to maintain pressure inside the eye E properly. A control valve  14  is provided midway along an irrigation tube  11  for leading the irrigation liquid to the eye E, and is opened and closed for flow control of the irrigation liquid. One end of the irrigation tube  11  is connected to the bottle  10  and the other end is connected to the US handpiece  2 . 
     An aspiration tube  16  is used to discharge a waste liquid containing the irrigation liquid and the nucleus of the crystalline lens subjected to fragmentation and emulsification aspirated through the aspiration hole of the US chip  2   a  into a drainage bag  17 . Provided midway along the aspiration tube  16  are a connecting part  32  connected to a pressure sensor  30  and a peristaltic aspiration pump  18 . Further, the aspiration tube  16  communicates with the irrigation tube  11  via a bypass tube  19 , and a control valve  15  is opened and closed for flow control through the bypass tube  19 . The aspiration pressure inside the aspiration tube  16  is always detected by the pressure sensor  30 . When the aspiration pressure reaches a predetermined (preset) upper limit, the control unit  5  controls to stop the aspiration pump  18 . Additionally, in a case where the aspiration pressure should be lowered, the control valve  15  is opened by the control unit  5 , and the irrigation liquid is permitted to flow from the irrigation tube  11  via the bypass tube  19  into the aspiration tube  16  for decreasing the aspiration pressure. The upper limit of the aspiration pressure (maximum aspiration pressure) is set with a switch in the input unit  3 . 
       FIG. 3  is a view illustrating a depression mechanism in the pedal of the footswitch  6 . A rear part of the pedal  21  (a left side of  FIG. 3 ) is coupled to a base part  20  via a shaft  22 , and the pedal  21  is rotatable in a direction of the arrow A shown in  FIG. 3  about the shaft  22 . A spring  23  is interposed between the pedal  21  and the base part  20 , and is retained in a state as shown in  FIG. 3  when no power is applied to the pedal  21 . A conveying element  24  of a depression amount, having a gear part  24   a , is fixed inside the pedal  21 . A rotational potentiometer  25  is fixed to the base part  20  and a gear  26  in engagement with the gear part  24   a  of the conveying element  24  is attached to a rotation shaft of the potentiometer  25 . When power is applied to the pedal  21 , the conveying element  24  is rotated about the shaft  22 . This rotation is conveyed via the gear part  24   a  and the gear  26  to the potentiometer  25 , and a depression amount (depression position) of the pedal  21  is detected by the potentiometer  25 . And, each operational control of irrigation, aspiration and phacoemulsification (ultrasonic vibrations) is performed in accordance with a signal of the depression amount (depression position) of the pedal  21 , of the footswitch  6  (see  FIG. 4 ). 
     For the apparatus as above, the operation of emulsification and aspiration of the nucleus of the crystalline lens will be described. Incidentally, it is assumed that the upper limit of the aspiration pressure set in the input part  3  is 40 kPa (about 300 mmHg) and the ultrasonic oscillation is set in the pulse oscillation mode. 
     When a surgeon inserts the US chip  2   a  of the US handpiece  2  in the eye E and depresses the pedal  21  to a position  1 , the control valve  14  is opened under control of the control unit  5  and the irrigation liquid is supplied to the eye E. Next, when the pedal  21  is depressed to a position  2 , the aspiration pump  18  is driven under control of the control unit  5 , and the waste liquid is aspirated along with the irrigation liquid supply. Further, when the pedal  21  is depressed to a position  3 , ultrasonic vibrations are induced to the US chip  2   a  along with the irrigation and aspiration. 
       FIG. 5  is a view illustrating a control method of ultrasonic vibrations. Assuming that a depression amount F is 0% when no power is applied to the pedal  21  and the depression amount F is 100% when the pedal  21  is depressed at the maximum, a range of the depression amount F from 66% inclusive to 100% inclusive is set as the position  3  for inducing ultrasonic vibrations. Further, ultrasonic power Up is set so as to increase linearly to an upper limit predetermined in the input unit  3  in accordance with the depression amount F of the pedal  21 . 
     A pulse-duty ratio Q is determined based on the depression amount F of the pedal  21  and aspiration pressure Pc detected by the pressure sensor  30 . In a case where the depression amount F is below 90% being a value of predetermined (preset) level, the pulse-duty ratio Q is kept constant at an initial set value Q 0  (for example, 35%). In a case where the depression amount F is in a range from 90% being the value of predetermined level inclusive to 100% inclusive, the pulse-duty ratio Q is kept constant at 35% being the initial set value Q 0  when the aspiration pressure Pc detected by the pressure sensor  30  is below a value of predetermined (preset) level (for example, 33 kPa (about 250 mmHg)) which is lower than 40 kPa being the upper limit, and the pulse-duty ratio Q is changed to increase linearly in accordance with the depression amount F of the pedal  21  when the aspiration pressured Pc is greater than or equal to 33 kPa being the value of predetermined level. That is to say, the control method of ultrasonic vibrations is changed according to information on whether or not the aspiration pressure Pc is greater than or equal to the value of predetermined level (33 kPa) and information on the depression amount (depression position) of the pedal  21 . For instance, when the depression amount F is 90%, the pulse-duty ratio Q is set at 45%, and when the depression amount F is 100%, the pulse-duty ratio F is increased to 70%. In  FIG. 5 , diagonally shaded areas in a bar graph show an increased amount of the pulse-duty ratio Q from 35% being the initial set value Q 0 . 
     In this setting, when the surgeon depresses the pedal  21  to the position  3 , ultrasonic vibrations are induced to the US chip  2   a  to perform fragmentation and emulsification on the nucleus of the crystalline lens. The aspiration pressure Pc detected by the pressures sensor  30  increases if the aspiration hole at the tip of the US chip  2   a  is clogged with the nucleus of the crystalline lens. In other words, a clogging condition (or a trapping condition of the nucleus of the crystalline lens) at the tip of the US chip  2   a  is detected from the aspiration pressure Pc. When the nucleus of the crystalline lens is relatively soft, it is easy to emulsify; therefore, the aspiration pressure Pc is not so significantly increased and the nucleus of the crystalline lens trapped at the tip of the US chip  2   a  is emulsified and aspirated. When the nucleus of the crystalline lens is relatively hard, the depression amount F of the pedal  21  is increased to raise the ultrasonic power Up so that emulsifying efficiency is enhanced. The surgeon increases the depression amount F of the pedal  21  at the time when he/she intends to expand capacity for fragmentation and emulsification. 
     Here, in a case where the relatively hard nucleus of the crystalline lens is encountered and the nucleus of the crystalline lens trapped at the tip of the US chip  2   a  is not easily emulsified and aspirated, the aspiration pressure Pc is increased. When the aspiration pressure Pc does not reach 40 kPa being the upper limit but is greater than or equal to 33 kPa being the value of predetermined level as well as when the depression amount F of the pedal  21  is greater than or equal to 90% being the value of predetermined level, the control unit  5  controls to increase the pulse-duty ratio Q from 35% being the initial set value Q 0  in accordance with the increase in the depression amount F. The pulse-duty ratio Q is increased, and energy of ultrasonic vibrations given to the nucleus of the crystalline lens in a predetermined period of time is increased. Therefore, the nucleus of the crystalline lens may be efficiently subjected to fragmentation and emulsification. 
     As the nucleus of the crystalline lens, which has clogged the aspiration hole at the tip of the US chip  2   a , is subjected to fragmentation and starts to be aspirated, the aspiration pressure Pc is also decreased. When the aspiration pressure Pc becomes less than or equal to 33 kPa being the value of predetermined level, the pulse-duty ratio Q is restored to 35% being the initial set value Q 0 . In the case of the relatively soft nucleus of the crystalline lens and the like for which high fragmentation power is not required, decrease in the pulse-duty ratio Q suppresses an amount of ultrasonic wave used as well as heat production to the tissue. 
     As mentioned above, when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level, i.e. when the nucleus of the crystalline lens is sufficiently trapped by the US chip  2   a , the surgeon may increase the fragmentation and emulsification power by regulating the depression degree of the pedal  21 , and the intention of the surgeon may be reflected with ease. On the other hand, when the aspiration pressure Pc is below 33 kPa being the value of predetermined level, the fragmentation and emulsification power is sufficient, and the amount of ultrasonic wave used need not be excessively increased. 
       FIG. 6  is a view showing another control method of ultrasonic vibrations. In this control, when the aspiration pressure Pc in the position  3  is below 33 kPa being the value of predetermined level, the ultrasonic power Up is kept constant at an initial set value U 0  (for example, 50%), and the pulse-duty ratio Q is increased in stages (or linearly) to 70% in accordance with the depression amount F of the pedal  21 . Further, in the range of the depression amount F from 90% being the value of predetermined level inclusive to 100% inclusive, when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level, the ultrasonic power Up is linearly increased from 50% being the initial set value U 0  in accordance with the depression amount F. In addition, when the depression amount F is 100%, the ultrasonic power Up is set at 100% being the upper limit. 
       FIG. 7  is a view illustrating an example of a control method where both the ultrasonic power Up and the pulse-duty ratio Q are changed in accordance with the depression amount F of the pedal  21  in the position  3  when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level. For example, when the depression amount F is in a range from 70% inclusive and 80% exclusive, the pulse-duty ratio Q is 30% and the ultrasonic power Up is 30%. When the depression amount F is in a range from 80% inclusive to 90% exclusive, the pulse-duty ratio Q is 40% and the ultrasonic power Up is 60%. In addition, in the range, of the depression amount F from 90% being the value of predetermined level inclusive to 100% inclusive, when the aspiration pressure Pc is below 33 kPa being the value of predetermined level, the ultrasonic power Up and the pulse-duty ratio Q are the same as in a case where the depression amount F is in the range from 80% inclusive to 90% exclusive. However, when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level, as shown by diagonally shaded areas in  FIG. 7 , the ultrasonic power Up is increased to 100% as well as the pulse-duty ratio Q is linearly increased in a range from 40% inclusive to 70% inclusive (or exclusive) in accordance with the depression amount F of the pedal  21 . 
     Also in the control methods shown in  FIGS. 6 and 7 , when the hard nucleus of the crystalline lens is encountered and the aspiration pressure Pc becomes greater than or equal to 33 kPa being the value of predetermined level, the surgeon may intentionally depress the pedal  21  to increase the fragmentation and emulsification power. 
     Besides, the value of predetermined level of the aspiration pressure Pc when the ultrasonic power Up and the pulse-duty ratio Q are changed is mentioned above, but this is only an illustration, and the surgeon may set a desired value as the value of predetermined level of the aspiration pressure Pc in relation to the value for the upper limit using the input unit  3 . The value of predetermined level of the aspiration pressure Pc may also be set in association with the value for the upper limit, such as 80% of the upper value. Further, the maximum value of the ultrasonic power Up may be arbitrarily changed by the input unit  3  so as to be, for example, 50% when the depression amount F of the pedal  21  is 100%. Furthermore, while the value of predetermined level of the depression amount F when the ultrasonic power Up and the pulse-duty ratio Q are changed is set at 90%, it may be arbitrarily changed by the input unit  3 . 
     Additionally, the aforementioned control methods may be variously modified. For example, in the control method shown in  FIG. 5 , when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level, it is conceivable that the pulse-duty ratio Q is uniformly set at 70% in the range of the depression amount F of the pedal  21  from 90% being the value of predetermined level inclusive to 100% inclusive. Further, an inducing condition of ultrasonic vibrations may be controlled more finely such that a plurality of the aspiration pressure Pc, when the ultrasonic power Up and the pulse-duty ratio Q are increased, is previously set, and the ultrasonic power Up and the pulse-duty ratio Q are increased for each set aspiration pressure Pc. In addition, this kind of control is not limited to the pulse oscillation mode, and may be applied to control of only the ultrasonic power Up in the continuous oscillation mode. 
     Further, in the above description, the aspiration pressure Pc obtained by the pressure sensor  30  is utilized as means for detecting the clogging condition at the tip of the US chip  2   a . However, a constitution may be employed such that an image-pickup camera for observing the eye E is attached to a surgical microscope, and the clogging condition at the tip of the US chip  2   a  is detected from an image obtained by the camera. 
     In the above description, a condition is made that the control method of ultrasonic vibrations through the ultrasonic power Up and the pulse-duty ratio Q is changed when the aspiration pressure Pc is greater than or equal to the value of predetermined level (a lower value than the value for the upper limit) and the depression amount (depression position) of the pedal  21  is greater than or equal to the value of predetermined level. However, another changing condition may be made on whether the depression amount (depression position) of the pedal  21  is kept constant longer than period of time of predetermined (preset) level. Hereinafter, the control method of ultrasonic vibrations under this changing condition will be described. 
       FIG. 8  is a view illustrating an example where the pulse-duty ratio Q is changed based on a time t during which the depression amount (depression position) F of the pedal  21  is kept constant. The control unit  5  controls to start measurement of the time t from a point when the depression amount F of the pedal  21  becomes constant based on an output of the potentiometer  25  and reset the time, t in a case where the depression amount F is changed. Besides, the ultrasonic power Up, as in the case of  FIG. 5 , is linearly changed in accordance with the depression amount F. When the nucleus of the crystalline lens trapped at the tip of the US chip  2   a  is not emulsified and aspirated, the aspiration pressure Pc is increased. When the aspiration pressure Pc becomes greater than or equal to 33 kPa being the value of predetermined level, the US chip  2   a  is judged to be in the clogging condition produced by attraction for the nucleus of the crystalline lens. Here, the pedal  21  is, for example, assumed to be retained by the surgeon in a position of the depression amount F of about 80% in which the ultrasonic power Up is 50%. The control unit  5  controls to increase the pulse-duty ratio Q from 35% to 70% when the time t, during which the depression amount F of the pedal  21  is kept constant, is greater than or equal to a value of predetermined (preset) level (for example, one and a half seconds). The pulse-duty ratio Q is increased to raise the fragmentation power and enable efficient fragmentation and emulsification of the nucleus of the crystalline lens. If the fragmentation and emulsification of the nucleus of the crystalline lens make the aspiration pressure Pc below 33 kPa being the value of predetermined level, the pulse-duty ratio Q is restored to 35% being the initial set value. That is, the initial control method is restored. In addition, when the surgeon changes the depression amount F of the pedal  21  as well, the control unit  5  controls to reset measurement of the time t and restore the pulse-duty ratio Q to 35% being the initial set value. 
       FIG. 9  shows a modification of the control method for changing the pulse-duty ratio Q. A control method may be made such that, when the time t is greater than or equal to one and a half seconds being the value of predetermined level, the pulse-duty ratio Q is increased in stages (or linearly) in accordance with an elapsed time thereafter. 
       FIGS. 10A and 10B  are views illustrating an example of control methods for changing the ultrasonic power up based on the time t during which the depression amount F is kept constant. In  FIG. 10A , when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level as well as when the time t is greater than or equal to one and a half seconds being the value of predetermined level, the ultrasonic power Up is increased by 10% from the ultrasonic power Up for the depression amount F. In  FIG. 10B , as in the case of  FIG. 10A , when the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level as well as when the time t is greater than or equal to one and a half seconds being the value of predetermined level, the ultrasonic power Up is linearly increased in accordance with an elapsed time thereafter. 
       FIG. 11  is a view illustrating an example of a control method for changing both the ultrasonic power Up and the pulse-duty ratio Q based on the time t during which the depression amount F is kept constant. When the aspiration pressure Pc is greater than or equal to 33 kPa being the value of predetermined level and the time t is greater than or equal to one and a half seconds being the value of predetermined level, the ultrasonic power Up is increased by 5% from the ultrasonic power Up for the depression amount F, and the pulse-duty ratio Q is increased from 35% to 50%. 
     In the control methods shown in  FIGS. 5 to 7 , if the hard nucleus is encountered, the pedal  21  must be depressed greater than or equal to an amount for the predetermined (preset) level in order to increase the fragmentation power. In contrast, in the control methods shown in  FIGS. 8 to 11 , the fragmentation power may be increased regardless of the depression amount (depression position) of the pedal  21 . Therefore, a same advantage may be obtained by only keeping the amount (position) for the predetermined level constant without depressing the pedal  21  greatly. 
     Incidentally, in the above description, the respective values for the depression amount (depression position) F, the aspiration pressure Pc, the ultrasonic power Up, the pulse-duty ratio Q, and the time t may be changed through the input unit  3 . Further, a switch provided to the input unit  3  may be used to select from a variety of control methods of ultrasonic vibrations as mentioned above. In this case, a mode is included where the aforementioned methods are not used. 
     As mentioned above, according to the present invention, when the hard nucleus of the crystalline lens is encountered and is sufficiently trapped by the ultrasonic chip, the surgeon may increase the power for the fragmentation and emulsification intentionally to enable smooth surgery. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in the light of the above teachings or may be acquired from practice of the invention. The embodiments chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.