Patent Publication Number: US-2012026569-A1

Title: System and method for illumination attenuation

Description:
This application is a continuation of U.S. application Ser. No. 12/787,811 filed on May 26, 2010, which is a divisional of U.S. application Ser. No. 11/561,718 filed on Nov. 20, 2006. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     Embodiments of the present invention relate to systems and methods for attenuating the brightness of a light beam. More particularly, embodiments of the present invention relate to systems and methods for time domain attenuators. 
     BACKGROUND OF THE INVENTION 
     Surgical instrumentation often uses fiber optics to direct light from a light source, such as a laser, LED or other light source, to a surgical hand piece. The tip of the surgical hand piece is then used to direct the light to the eye. In some cases, it is desirable to attenuate the brightness of the light received at the eye. Currently, position domain attenuators that proportionally interrupt part, or all, of a light beam are used. In these systems, a non-optically transmissive element is positioned to prevent a part of the light beam from reaching the target fiber, resulting in some attenuation. Position domain attenuators include rotating louvers, variable slot width obstructions, varying aperture size obstructions and varying neutral density filters. By obstructing just a portion of the light beam, the quality of the illuminated spot projected from the end of the fiber can be affected. For example, the projected spot on the eye may have a bright center from the light that is not obstructed as well as shadow and color rings from the light that was obstructed. Indeed, the center of the spot may exhibit no attenuation, while the edges of the spot are highly attenuated. This result can be undesirable as it provides an uneven energy distribution to the eye. 
     Another current attenuation approach includes adjusting the voltage or current of the light source, thereby changing the intensity of the produced light. While this approach can evenly attenuate the brightness of the light spot received at the eye, it suffers the shortcoming that the color temperature of the light is typically changed. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide systems and methods for attenuating the brightness of a light beam. Broadly speaking, an interrupter is moved completely into and fully out of the path of the light beam. This chopping of the light beam attenuates the beam. If the movement of the interrupter is quick enough and the repetition rate of the interrupter cycle high enough, the interruption of the light beam is not perceived by the human eye and the light beam simply appears attenuated. 
     Embodiments of the present invention include a light attenuation system comprising a light source to project a light beam, an interrupter operable to move into and out of a path of the light beam, a motor (actuator) coupled to the interrupter to move the interrupter from a position in which the light beam is unhindered by the interrupter to a position in which the light beam is incident on the interrupter, and a controller operable to control the motor and cause the motor to move the interrupter with a repetition rate so that the light beam is unhindered for a first portion of a cycle and the light beam is incident on the interrupter for a second portion of the cycle. When the light beam is incident on the interrupter, it can be fully incident on the interrupter. Attenuation can thus be achieved without affecting the color temperature of the light. 
     Another embodiment of the present invention can include a set of computer instructions comprising instructions executable to receive one or more attenuation control parameters. The attenuation control parameters can include any variables that can be user specified. In accordance with the implementation, these can include duty cycle, cycle time, repetition rate, attenuation level or other parameters. Based on the received control parameters and/or predefined control parameters, the instructions are executable to determine a control scheme. For example, the controller can determine the amount of time that a light beam should be fully interrupted and unhindered. Accordingly, the control scheme is configured to cause an interrupter to move into and out of a path of a light beam for a plurality of cycles with a repetition rate to attenuate the light beam&#39;s brightness. 
     Yet another embodiment of the present invention includes a method for attenuating light comprising projecting a light beam along a path and moving an interrupter into and out of the path of the light beam for a plurality of cycles with a repetition rate to attenuate the light beam&#39;s brightness without affecting the color temperature of the light beam. The light beam is unhindered by the interrupter for a first portion of each cycle and is incident (e.g., fully incident) on the interrupter for the second portion of the cycle. 
     Another embodiment of the present invention includes a method for attenuating light comprising projecting a light beam along a path and moving an interrupter into and out of the path of the light beam for a plurality of cycles with a repetition rate to create attenuated light that appears attenuated and continuous to the human eye. According to one embodiment light beam is unhindered by the interrupter for a first portion of each cycle and is incident (e.g., fully incident) on the interrupter for the second portion of the cycle. 
     Embodiments of the present invention provide an advantage over the prior art by attenuating the brightness of a light beam while minimizing deleterious effects such as shadow and color rings caused by position domain attenuators. 
     Embodiments of the present invention provide another advantage by allowing for attenuation of a light beam without changing the color temperature of the light, as occurs with attenuation schemes in which the intensity of the light source is varied by reducing the power delivered to the light source. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       A more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description, taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein: 
         FIGS. 1A and 1B  are diagrammatic representations of one embodiment of a system for attenuating a light beam in a surgical system utilizing fiber optics. 
         FIGS. 2A-2B  are diagrammatic representations of another embodiment of a system for attenuating a light beam; 
         FIGS. 3A-3B  are diagrammatic representations of yet another embodiment of a system for attenuating a light beam; and 
         FIG. 4  illustrates example duty cycles for various levels of attenuation. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments of the invention are illustrated in the FIGURES, like numerals being used to refer to like and corresponding parts of the various drawings. 
     Embodiments of the present invention provide systems and methods for attenuating light in a manner that reduces or eliminates the shadow and color ring effects of position domain attenuators without affecting the color temperature of the light. In other words, embodiments provide for even attenuation of the light beam without affecting the quality of the intensity distribution or color of the light. 
     Generally speaking, the output brightness of an illuminator is varied by alternately chopping the light beam such that the beam is both fully interrupted and fully unhindered. An interrupter can be rapidly moved into and out of the transmission path of a light beam. The brightness of the light beam received at a site will be attenuated based on the amount of time per cycle the light beam remains obstructed and unhindered because less light will be received at the site per unit of time. 
     For purposes of explanation, the term “cycle time” of the interrupter is the sum of the unhindered and interrupted time for a cycle, the “repetition rate” is the number of cycles in a given time period, and the “duty cycle” is the ratio of unhindered time to the cycle time. The repetition rate is essentially the frequency of the interrupter, but preferably with a square profile rather than a sinusoidal profile. The duty cycle can range from 0% (no light passes) to 100% (no attenuation). 
     Preferably, the interrupter is moved into and out of the path of the light beam at a repetition rate such that the interruption of the beam is not perceived as flashing light by the human eye. To achieve this, the repetition rate should be greater than 30 cycles and preferably greater than 60 cycles per second. Although usable, certain repetition rates may not be preferred. For example, background lights in the surgical theater can flicker at certain frequencies (e.g., 60 cycles per second in the United States and 50 cycles per second in other areas). Such lights may produce interference with an attenuator running at 60 or 50 cycles a second, depending on location. The brightness of a light beam compared to its un-attenuated state is approximately proportional to the duty cycle of the interrupter. Using the example of a repetition rate of 75 cycles per second, the cycle time is approximately 13.3 milliseconds. If the duty cycle is 40%, meaning that the light is unhindered for 5.32 milliseconds of the cycle, the attenuated light beam will appear to be approximately 40% as bright as the un-attenuated light beam. Brightness adjustment can be achieved by changing the duty cycle of the interrupter and by changing the repetition rate as necessary to maintain the experience of non-flashing (i.e., continuous) light. According to various embodiments, the interrupter can be linearly placed into and removed from the light beam or rotated into and out of the light beam. 
       FIGS. 1A and 1B  are diagrammatic representations of one embodiment of a system  100  for attenuating a light beam in a surgical system utilizing fiber optics. In system  100 , a light source projects a light beam  104  to an optical fiber  106 . Light source  102  can comprise light sources such as a xenon light source, a laser, an LED or other light source used to illuminate or ablate tissue. Optical fiber  106  can be a plastic, glass or other material fiber that guides light from light beam  104  to a surgical handset or otherwise guides light to a surgical site. Linear actuator (linear motor, solenoid, pneumatic cylinder, hydraulic cylinder, etc.)  108  moves an interrupter  110  into and out of the path of light beam  104  between the light source and optical fiber  106 . Interrupter  110  moves from a position in which light beam  104  is unhindered by interrupter  110  (shown in  FIG. 1A ) to a position in which light beam  104  is fully incident on interrupter  110  (shown in  FIG. 1B ). It should be noted that system  100  can include other optical components located between optical fiber  106  and light source  102 . Additionally, the path of light beam  104  may not be straight. 
     A controller  112  can control the motion of linear actuator  110 . Controller  112  can include any suitable controller that can receive data from various components of system  100 . Controller  112  can include a processor  114  (such as an ASIC, CPU, DSP or other processor) and computer instructions  116  executable by processor  114  (e.g., software or other instructions stored on a computer readable medium). Instructions  116  can be stored on a computer readable memory  118  (e.g., hard drive, Flash memory, optical memory, RAM, ROM, processor memory or other computer readable medium known in the art). Controller  112  can include any number of additional computer components. For example, controller  112  can include an analog to digital converter  120  to convert signals from linear actuator  108  to digital signals, and a digital to analog converter  122  to convert signals from processor  114  to analog control signals. While shown as communicating electrical analog signals to a linear actuator  108 , controller  112  can send electrical digital or analog, or pneumatic, control signals to actuator  108  or to other controllers to cause actuator  108  to operate according to a particular control scheme. Additionally, while controller  112  is shown as a single block in  FIG. 1  for the sake of simplicity, the control functionality of system  100  can be distributed among multiple processors. 
     In operation, linear actuator  108  is controlled to move interrupter  110  into and out of light beam  104 . In the embodiment of  FIG. 1  in which a linear motor is used, interrupter  110  reciprocates from a position in which light beam  104  is unhindered (e.g., as shown in  FIG. 1A ) and a position in which light beam is fully incident on interrupter  110  (e.g., as shown in  FIG. 1B ). In other words, the stroke of linear actuator  108  is sufficient to linearly position the interrupter fully into the light beam. Preferably, interrupter  110  is made of a non-transmissive material to fully block light beam  104  when light beam  104  is fully incident on interrupter  110 . As one example, interrupter  110  can be formed of aluminum. 
     According to various embodiments, controller  112  can receive attenuation control parameters that affect the control scheme according to which controller  112  controls actuator  108 . These parameters can include, for example, duty cycle and repetition rate or other parameters. In other embodiments, one or more of the attenuation control parameters can be predefined at controller  112 . 
     Controller  112  can, for example, control linear actuator  108  to have a particular repetition rate and duty cycle. The duty cycle can range from 0 to 100% of the cycle time. Preferably, the repetition rate is selected so that if the duty cycle is greater than 0% and less than 100% of the cycle time, the human eye will not perceive flickering of the light (at 0% duty cycle, the interrupter is continuously in the path of light beam  104  and, at 100% duty cycle, the interrupter does not interrupt the light beam  104 ). Generally, repetition rates of greater than 60 cycles per second will not be visible to the human eye so that the resulting light appears continuous and attenuated. 
     Actuator  108  can be selected to have sufficient energy to move interrupter  110  between states in which light beam  104  is unhindered to a state where light beam  104  is fully incident on interrupter  110  in as short a time as possible to minimize the transition period in which light beam  104  is only partially incident on interrupter  110 . Furthermore, controller  112  can account for the fact that actuator  108  is moving a mass that must accelerate and decelerate to reciprocate. Consequently, interrupter  110  may be moving in the time in which light beam  104  is fully unhindered and the time in which light beam  104  is fully incident on interrupter  110 . For example, if the cycle time is 13.3 milliseconds and the time that light beam  104  is fully incident on interrupter  110  is 8 milliseconds, interrupter  110  can be moving during the 8 milliseconds it is blocking light beam  104 . 
     In the above example, a linear actuator is used to selectively interrupt light beam  104 .  FIGS. 2A and 2B  are diagrammatic representations of another embodiment of the present invention in which a rotary actuator  124  rotates interrupter  126  into and out of the path of beam  104 . Actuator  124  can be a rotary motor, a rotary action hydraulic or pneumatic device to impart rotary motion or other rotary actuator. According to one embodiment, rotary actuator  124  can rotate back and forth to move interrupter  126  into and out of the path of light beam  104 . According to one embodiment, rotary actuator  124  alternately rotates 90 degrees. Again, the repetition rate can be selected so that interruption of the light beam is not perceived by a human eye to which light is directed by optical fiber  106 . 
       FIGS. 3A and 3B  are diagrammatic representations of yet another embodiment that utilizes a rotary actuator  128  to move interrupter  130  into and out of the path of light beam  104 . In the example of  FIGS. 3A and 3B , interrupter  130  is coupled to actuator  128  by an arm  132 . As actuator  128  moves arm  132 , interrupter  130  swings into and out of the path of light beam  104 . For example, rotary actuator  128  can alternately rotate a set number of degrees, say 30 degrees, to swing interrupter  130  into the path of light beam  104  to fully block light beam  104  and out of the path of light beam  104  to leave light beam  104  unhindered by interrupter  130 . According to other embodiments, interrupter  130  can swing through an arc such that for one cycle interrupter  130  is on one side of the beam path when light beam  104  is unhindered and for the next cycle is on the other side of the beam path when light beam  104  is unhindered. Controller  112  can control actuator  128  such that a particular repetition rate and duty cycle are achieved. 
       FIG. 4  is a set of graphs representing one embodiment of cycle states for various levels of attenuation of light beam  104 . In the example of  FIG. 4 , the cycle time is 16 milliseconds, corresponding to a repetition rate of 62.5 cycles per second. Line  140  represents a 25% duty cycle, line  142  represents a 50% duty cycle and line  144  represents a 75% duty cycle. As can be seen from line  140 , the interrupter  130  is in a position in which light beam  104  is fully unhindered for approximately 4 milliseconds and fully blocked for 12 milliseconds, resulting in 75% attenuation of light beam  104  (i.e., light beam  104  will only appear to be 25% as bright downstream of the interrupter  130  as it appears upstream of interrupter  130 ). During each state (e.g., the fully blocking and the fully non-blocking state) the interrupter  130  can still be moving, so the states of the interrupter  130  with respect to light beam  104  may, but do not necessarily, correspond to the actuator  128  states. In other words, a graph of the actuator  128  state may be different than the graph of the interrupter  130  state relative to light beam  104 . 
     The transitions (e.g., transition  146  and transition  148 ) between a fully blocking and fully non-blocking state shown in  FIG. 4  are shown as corresponding to a square wave. That is, they are shown as instantaneous transitions. In practice, there is some small transition zone in which light beam  104  is only partially blocked. If that transition zone is too long, some of the negative effects of position domain attenuators, such as shadow rings, may be seen briefly. Therefore, it is preferable to make the transition as close to ideal as possible to minimize the transition time. 
     Embodiments of the present invention thus provide a light attenuation system comprising a light source to project a light beam, an interrupter operable to be positioned into and out of a path of the light beam, an actuator coupled to the interrupter and operable to move the interrupter from a position in which the light beam is unhindered by the interrupter to a position in which the light beam is fully incident on the interrupter, and a controller operable to control the actuator and cause the actuator to move the interrupter with a repetition rate so that the light beam is unhindered for a first portion of a cycle and the light beam is fully incident on the interrupter for a second portion of the cycle to attenuate the light beam&#39;s brightness. Attenuation can thus be achieved without affecting the color temperature of the light. 
     Another embodiment of the present invention can include a set of computer instructions comprising instructions executable to receive one or more attenuation control parameters. The attenuation control parameters can include any variables that can be user specified. According to the particular implementation, these can include duty cycle, cycle time, repetition rate, attenuation level or other parameters. Based on the received control parameters and/or predefined control parameters, the instructions are executable to determine a control scheme. For example, if the system has a preprogrammed repetition rate, the instructions can be executable to receive a duty cycle or other parameters. Based on the received parameters and the predefined repetition rate, the amount of time that a light beam is fully interrupted versus unhindered can be determined. Accordingly, the control scheme is configured to cause an interrupter to move into and out of a path of a light beam for a plurality of cycles with a repetition rate to attenuate the light beam&#39;s brightness. In general, the light beam is unhindered by the interrupter for a first portion of each cycle and is fully incident on the interrupter for the second portion of the cycle. 
     The instructions can be further executable to generate one or more control signals to cause an actuator to move the interrupter into and out of the path of the light beam according to the control scheme. The control signals can be sent to the actuator, another control or other component that can cause the actuator to move according to the control scheme. 
     While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as detailed in the following claims.