Patent Publication Number: US-2015075557-A1

Title: Cleaning Mechanisms for Optical Elements

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates generally to optics and, more particularly, to cleaning mechanisms for optical elements. 
     BACKGROUND 
     In many oilfield environments, such as deepwater and subterranean drilling environments, remote measurement and logging tools can provide useful information concerning the characteristics of geological formations, fluid flows in the geological formations, objects present in a formation and/or a borehole, etc. Also, remotely controlled equipment operating in oilfield and/or other remote exploration environments, such as manipulators, robotic vehicles, etc., may utilize one or more tools to gather information concerning the environment in which the equipment is operating. Some such tools may include one or more optical elements to enable viewing of the remote environment, gathering of image data for processing by one or more suitable algorithms, etc. In some scenarios, the optical element(s) included in a tool may become dirty due to contact with fluids and/or other material in the remote environment, thereby degrading the imaging information collected via the optical element(s). 
     SUMMARY 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     Example methods and systems disclosed herein relate generally to optics and, more particularly, to cleaning mechanisms for optical elements. Disclosed example apparatus to clean an optical element can include a cover positionable over a first side of the optical element. In some examples, the cover is controllable to transition between a first position and a second position. For example, the cover can form a gap between a first side of the optical element and the cover when the cover is in the first position, and the cover can provide the optical element with access to a field-of-view when the cover is in the second position. Such example apparatus can also include a flushing assembly controllable to inject cleaning fluid into the gap when the cover is in the first position. In some examples, the flushing assembly also includes a valve that is controllable to permit the cleaning fluid to exit the gap after having been injected into the gap. 
     Disclosed example methods to clean an optical element can include electronically controlling a cover positioned over a first side of the optical element to cause the cover to transition from a second position providing the optical element with access to a field-of-view to a first position forming a gap between a first side of the optical element and the cover. Such example methods can also include electronically controlling a flushing assembly to cause the flushing assembly to (1) inject cleaning fluid into the gap when the cover is in the first position, and (2) permit the cleaning fluid to exit the gap via a valve after the cleaning fluid has been injected into the gap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example cleaning mechanisms for optical elements are described with reference to the following figures. Where possible, the same numbers are used throughout the figures to reference like features and components. 
         FIG. 1  is a block diagram illustrating an example wellsite system in which an example optical element cleaning mechanism as disclosed herein may be used. 
         FIG. 2  is a block diagram illustrating an example sampling-while-drilling logging device in which an example optical element cleaning mechanism as disclosed herein may be used. 
         FIG. 3  is a block diagram illustrating an example imaging-based remote control system including an example remotely operated vehicle in which an example optical element cleaning mechanism as disclosed herein may be used. 
         FIG. 4  is a block diagram illustrating a first example optical element cleaning mechanism that may be used in the example systems of  FIGS. 1  and/or  3 , and/or in the example device of  FIG. 2 . 
         FIG. 5  is a block diagram illustrating a first example optical element cleaning mechanism that may be used in the example systems of  FIGS. 1  and/or  3 , and/or in the example device of  FIG. 2 . 
         FIG. 6  is a block diagram illustrating an example operation of the optical element cleaning mechanisms of  FIGS. 4  and/or  5 . 
         FIG. 7  illustrates an example cover that may be used to implement the optical element cleaning mechanisms of  FIGS. 4  and/or  5 . 
         FIGS. 8-10  are flowcharts representative of example processes that may be performed to control the optical element cleaning mechanisms of  FIGS. 4  and/or  5 . 
         FIG. 11  is a block diagram of an example processing system that may execute example machine readable instructions used to implement one or more of the processes of  FIGS. 8-10  to control the optical element cleaning mechanisms of  FIGS. 4  and/or  5 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the disclosure. 
     As noted above, many tools used in oilfield and/or other remote exploration environments contain optical elements. Such optical elements can include, for example, lenses, windows, fiber optics, minors, etc. As further noted above, in some scenarios, such as when the optical element(s) of such tools come into contact with downhole fluid(s), the optical element(s) can become dirty. Prior techniques for maintaining the cleanliness of an optical element in such environments include coating the optical element with a special surfactant composition to repel oil or other downhole fluids. However, these prior techniques generally protect the optical element for a limited amount of time and for a particular type of downhole fluid. For example, if the optical element comes into contact with a different type of downhole fluid than what the surfactant composition is designed to repel, the optical element can become dirty in a relatively short time and reduce the visibility achievable by the optical element. In that case, cleaning of the optical element may then involve pulling the tool out of the remote environment and performing manual cleaning of the optical element, which may cause operational delays in the field. 
     The example optical element cleaning mechanisms disclosed herein can overcome at least some of the limitations associated with the foregoing prior techniques. For example, such disclosed optical element cleaning mechanisms can provide effective cleaning of optical elements for any amount of time and without being limited to a particular type of contaminating fluid. Furthermore, such disclosed optical element cleaning mechanisms can improve upon prior ultrasonic cleaning techniques that have been developed for cleaning optical windows and for clean marine fouling material from submerged surfaces. 
     Example apparatus disclosed herein to clean an optical element can include a cover positionable over a first side of the optical element. For example, the optical element can be a lens, a window, a mirror, a fiber optic cable, etc., or any combination thereof. In some examples, the cover is controllable to transition between a first position and a second position. For example, the cover can form a gap between a first side (e.g., a first surface) of the optical element and the cover when the cover is in the first position, and the cover can provide the optical element with access to a field-of-view when the cover is in the second position. Such example apparatus can also include a flushing assembly controllable to inject cleaning fluid into the gap when the cover is in the first position. For example, the cleaning fluid can be water, air, a noncombustible gas, a solvent, etc., or any combination thereof, and may include particles that are mixed with the cleaning fluid prior to the cleaning fluid being injected into the gap. In some examples, the flushing assembly also includes a valve that is controllable to permit the cleaning fluid to exit the gap after having been injected into the gap. In some examples, the optical element, the cover and the flushing assembly are included in a tool that is positionable downhole in a formation. 
     In some such example apparatus, the flushing assembly further includes a first nozzle through which the cleaning fluid is to be injected into the gap, and a second nozzle through which the cleaning fluid is to exit the gap. In some examples, the flushing assembly is controllable to (1) inject the cleaning fluid into the gap for a first time period beginning after the cover has transitioned to the first position, (2) stop injection of the fluid into the gap for a second time period beginning after the first time period ends, and (3) open the valve to permit the cleaning fluid to exit the gap after the second time period ends. In other examples, the flushing assembly is controllable to inject the cleaning fluid into the gap and to permit the cleaning fluid to exit the gap via the valve continuously after the cover has transitioned to the first position. 
     In some such example apparatus, the cover includes a diaphragm controllable to change an aperture over the first side of the optical element. For example, the diaphragm can increase a size of the aperture when the cover is controlled to transition from the first position to the second position, and the diaphragm can decrease the size of the aperture when the cover is controlled to transition from the second position to the first position. 
     Some such example apparatus further include an ultrasonic transducer positionable to focus an ultrasonic beam on the first side of the optical element. In some such examples, the ultrasonic transducer is positioned on the cover and is arranged to focus the ultrasonic beam on the first side of the optical element when the cover is in the first position. In other such examples, the optical element is included in a housing, and the ultrasonic transducer is positioned on a wall of the housing. Furthermore, in some such examples, the flushing assembly is controllable to (1) inject the cleaning fluid into the gap for a first time period beginning after the cover has transitioned to the first position, (2) stop injection of the fluid into the gap for a second time period beginning after the first time period ends, and (3) open the valve to permit the cleaning fluid to exit the gap after the second time period ends, and the ultrasonic transducer is controllable to (4) emit the ultrasonic beam during the second time period. Furthermore, in other such examples, the flushing assembly is controllable to inject the cleaning fluid into the gap and to permit the cleaning fluid to exit the gap via the valve continuously after the cover has transitioned to the first position, and the ultrasonic transducer is controllable to emit the ultrasonic beam after the cover has transitioned to the first position. 
     Some such example apparatus also include a heating element to heat the cleaning fluid prior to the cleaning fluid being injected into the gap. 
     Example methods disclosed herein to clean an optical element can include electronically controlling a cover positioned over a first side of the optical element to cause the cover to transition from a second position providing the optical element with access to a field-of-view to a first position forming a gap between a first side of the optical element and the cover. Such example methods can also include electronically controlling a flushing assembly to cause the flushing assembly to (1) inject cleaning fluid into the gap when the cover is in the first position, and (2) permit the cleaning fluid to exit the gap via a valve after the cleaning fluid has been injected into the gap. 
     In some such example methods, controlling the cover includes controlling a diaphragm included in the cover to cause the diaphragm to decrease a size of an aperture over the first side of the optical element. 
     In some such example methods, controlling the flushing assembly includes causing the flushing assembly to perform operations including (1) injecting the cleaning fluid into the gap for a first time period beginning after the cover has transitioned to the first position, (2) stopping injection of the fluid into the gap for a second time period beginning after the first time period ends, and (3) opening the valve to permit the cleaning fluid to exit the gap after the second time period ends. 
     In some such example methods, controlling the flushing assembly includes causing the flushing assembly to perform operations including injecting the cleaning fluid into the gap and permitting the cleaning fluid to exit the gap via the valve continuously after the cover has transitioned to the first position. 
     Some such example methods further include controlling an ultrasonic transducer to cause the ultrasonic transducer to emit an ultrasonic beam focused on the first side of the optical element. In some such example methods, controlling the flushing assembly includes causing the flushing assembly to perform first operations including (1) injecting the cleaning fluid into the gap for a first time period beginning after the cover has transitioned to the first position, (2) stopping injection of the fluid into the gap for a second time period beginning after the first time period ends, and (3) opening the valve to permit the cleaning fluid to exit the gap after the second time period ends, and controlling the ultrasonic transducer comprises causing the ultrasonic transducer to perform second operations including (4) emitting the ultrasonic beam during the second time period. In other such example methods, controlling the flushing assembly includes causing the flushing assembly to perform first operations including injecting the cleaning fluid into the gap and permitting the cleaning fluid to exit the gap via the valve continuously after the cover has transitioned to the first position, and controlling the ultrasonic transducer comprises causing the ultrasonic transducer to perform second operations including emitting the ultrasonic beam after the cover has transitioned to the first position. 
     These and other example methods, apparatus, systems and articles of manufacture (e.g., storage media) to implement cleaning mechanisms for optical elements are disclosed in greater detail below. 
     Turning to the figures,  FIG. 1  illustrates an example wellsite system  1  in which the example optical element cleaning mechanisms disclosed herein can be employed. The wellsite can be onshore or offshore. In this example system, a borehole  11  is formed in subsurface formations by rotary drilling, whereas other example systems can use directional drilling. 
     A drillstring  12  is suspended within the borehole  11  and has a bottom hole assembly  100  that includes a drill bit  105  at its lower end. The surface system includes platform and derrick assembly  10  positioned over the borehole  11 , the assembly  10  including a rotary table  16 , kelly  17 , hook  18  and rotary swivel  19 . In an example, the drill string  12  is suspended from a lifting gear (not shown) via the hook  18 , with the lifting gear being coupled to a mast (not shown) rising above the surface. An example lifting gear includes a crown block whose axis is affixed to the top of the mast, a vertically traveling block to which the hook  18  is attached, and a cable passing through the crown block and the vertically traveling block. In such an example, one end of the cable is affixed to an anchor point, whereas the other end is affixed to a winch to raise and lower the hook  18  and the drillstring  12  coupled thereto. The drillstring  12  is formed of drill pipes screwed one to another. 
     The drillstring  12  may be raised and lowered by turning the lifting gear with the winch. In some scenarios, drill pipe raising and lowering operations involve the drillstring  12  being unhooked temporarily from the lifting gear. In such scenarios, the drillstring  12  can be supported by blocking it with wedges in a conical recess of the rotary table  16 , which is mounted on a platform  21  through which the drillstring  12  passes. 
     In the illustrated example, the drillstring  12  is rotated by the rotary table  16 , energized by means not shown, which engages the kelly  17  at the upper end of the drillstring  12 . The drillstring  12  is suspended from the hook  18 , attached to a traveling block (also not shown), through the kelly  17  and the rotary swivel  19 , which permits rotation of the drillstring  12  relative to the hook  18 . In some examples, a top drive system could be used. 
     In the illustrated example, the surface system further includes drilling fluid or mud  26  stored in a pit  27  formed at the well site. A pump  29  delivers the drilling fluid  26  to the interior of the drillstring  12  via a hose  20  coupled to a port in the swivel  19 , causing the drilling fluid to flow downwardly through the drillstring  12  as indicated by the directional arrow  8 . The drilling fluid exits the drillstring  12  via ports in the drill bit  105 , and then circulates upwardly through the annulus region between the outside of the drillstring and the wall of the borehole, as indicated by the directional arrows  9 . In this manner, the drilling fluid lubricates the drill bit  105  and carries formation cuttings up to the surface as it is returned to the pit  27  for recirculation. 
     The bottom hole assembly  100  includes one or more specially-made drill collars near the drill bit  105 . Each such drill collar has one or more logging devices mounted on or in it, thereby allowing downhole drilling conditions and/or various characteristic properties of the geological formation (e.g., such as layers of rock or other material) intersected by the borehole  11  to be measured as the borehole  11  is deepened. In particular, the bottom hole assembly  100  of the illustrated example system  1  includes a logging-while-drilling (LWD) module  120 , a measuring-while-drilling (MWD) module  130 , a roto-steerable system and motor  150 , and the drill bit  105 . 
     The LWD module  120  is housed in a drill collar and can contain one or a plurality of logging tools. It will also be understood that more than one LWD and/or MWD module can be employed, e.g. as represented at  120 A. (References, throughout, to a module at the position of  120  can mean a module at the position of  120 A as well.) The LWD module  120  includes capabilities for measuring, processing, and storing information, as well as for communicating with the surface equipment. 
     The MWD module  130  is also housed in a drill collar and can contain one or more devices for measuring characteristics of the drillstring  12  and drill bit  105 . The MWD module  130  further includes an apparatus (not shown) for generating electrical power to the downhole system. This may include a mud turbine generator powered by the flow of the drilling fluid, it being understood that other power and/or battery systems may be employed. In the illustrated example, the MWD module  130  includes one or more of the following types of measuring devices: a weight-on-bit measuring device, a torque measuring device, a vibration measuring device, a shock measuring device, a stick slip measuring device, a direction measuring device, and an inclination measuring device. 
     The wellsite system  1  also includes an example surface monitoring tool  135  to monitor operation of one or more surface portions of the example wellsite system  1 . For example, the surface monitoring tool  135  can be arranged to monitor the operation of and/or condition of the platform and derrick assembly  10 , the rotary table  16 , the kelly  17 , the hook  18 , the rotary swivel  19 , the platform  21 , the hose  20 , the pump  29 , the pit  27 , etc., and/or any combination thereof. The wellsite system  1  further includes a logging and control unit  140  communicably coupled in any appropriate manner to the LWD module  120 / 120 A, the MWD module  130  and/or the surface monitoring tool  135 . In the illustrated example, the LWD module  120 / 120 A, the MWD module  130  and/or the surface monitoring tool  135 , possibly in conjunction with the logging and control unit  140 , implement optical element cleaning mechanisms in accordance with the examples disclosed herein. 
     For example, the LWD module  120 / 120 A and/or the MWD module  130  may include one or more optical elements to permit imaging information to be obtained from the downhole environment. Similarly, the surface monitoring tool  135  may include one or more optical elements to permit imaging information to be obtained from the surface environment. The LWD module  120 / 120 A, the MWD module  130  and/or the surface monitoring tool  135  may also report such imaging information to the logging and control unit  140  for viewing, analysis, processing, etc. In some examples, one or more of the LWD module  120 / 120 A, the MWD module  130  and/or the surface monitoring tool  135  may include example optical element cleaning mechanisms to clean their respective optical element(s) in accordance with one or more of the example optical element cleaning methods disclosed herein. Examples of such optical element cleaning mechanisms and methods for use in the example wellsite system  1  and/or in other remote environments are described in greater detail below. Also, although some of the example optical element cleaning techniques disclosed herein are described in the context of LWD and MWD applications and other remote sensing applications, the example optical element cleaning techniques are not limited thereto. Instead, optical element cleaning techniques as disclosed herein can also be used in other applications, such as wireline logging, production logging, permanent logging, fluid analysis, formation evaluation, sampling-while-drilling, etc. 
     For example,  FIG. 2  is a simplified diagram of an example sampling-while-drilling logging device of a type described in U.S. Pat. No. 7,114,562, incorporated herein by reference, utilized as the LWD tool  120  or part of an LWD tool suite  120 A, in which optical element cleaning techniques as disclosed herein can be used. The LWD tool  120  is provided with a probe  6  for establishing fluid communication with the formation and drawing the fluid  22  into the tool, as indicated by the arrows. The probe may be positioned in a stabilizer blade  23  of the LWD tool and extended therefrom to engage the borehole wall. The stabilizer blade  23  comprises one or more blades that are in contact with the borehole wall. Fluid drawn into the downhole tool using the probe  6  may be measured to determine, for example, pretest and/or pressure parameters. Additionally, the LWD tool  120  may be provided with devices, such as sample chambers, for collecting fluid samples for retrieval at the surface. Backup pistons  81  may also be provided to assist in applying force to push the drilling tool and/or probe against the borehole wall. 
     An example remote exploration system  300  including an example remotely operated vehicle (ROV)  305  having an example remotely controlled imaging tool  310  that may employ one or more of the example optical element cleaning techniques disclosed herein is illustrated in  FIG. 3 . In the illustrated example, the ROV  305  can be used for oilfield equipment maintenance, construction and/or observation in a deep sea environment, etc. The system  300  of  FIG. 3  includes an example telemetry communication link  315  between the ROV  305  and an example drilling ship  320  at the surface. In the illustrated example, the imaging tool  310  includes one or more optical elements to obtain imaging information from the remote environment. As described in greater detail below, the imaging tool  310  can also include a disclosed example optical element cleaning mechanism to clean the optical element(s) of the imaging tool  310  in accordance with the optical element cleaning methods disclosed herein. Also, as described in greater detail below, such optical element cleaning methods may be performed autonomously at the imaging tool  310 , or controlled via commands issued at the drilling ship  320  and conveyed to tool  310  via the telemetry communication link  315 . 
     A block diagram of a first example optical element cleaning mechanism  400  that can be used to clean optical element(s) of, for example, one or more of the LWD module  120 / 120 A, the MWD module  130 , the surface monitoring tool  135 , and/or the imaging tool  310  is illustrated in  FIG. 4 . In the illustrated example of  FIG. 4 , the optical element cleaning mechanism  400  is configured to clean an example optical element  405  of an example tool  410 . For example, the optical element  405  can correspond to one or more of a camera lens, a window, a minor, a fiber optic cable, etc., or any combination thereof. The example tool  410  can correspond to, for example, the LWD module  120 / 120 A, the MWD module  130 , the surface monitoring tool  135 , the imaging tool  310 , etc. In the illustrated example of  FIG. 4 , the optical element  405  can come into contact with downhole fluid and/other sources of contamination. 
     The optical element cleaning mechanism  400  of the illustrated example uses example flushing fluid  415 , possibly in combination with ultrasonic emissions from one or more example ultrasonic transducers  420 , to clean the optical element  405 . Moreover, the optical element cleaning mechanism  400  operates to form a cleaning region around the optical element  405  to thereby increase the effectiveness of the cleaning achievable by flowing the flushing fluid  415  over the optical element  405  and/or by directing ultrasonic emissions at the optical element  405 . 
     For example, to form a cleaning region around the optical element  405 , the optical element cleaning mechanism  400  includes an example cover  425  that is positionable over a first side (e.g., a first surface) of the optical element  405 . The cover  425  of the illustrated example can be implemented by any type of cover or similar device that is controllable such that the cover  425  can transition between a first (e.g., closed) position and a second (e.g., open) position. For example, the cover  425  includes or is otherwise controllable via one or more actuators (not shown) to enable the cover  425  to transition between the first (e.g., closed) position and the second (e.g., open) position. Such actuator(s) may include, but are not limited to, one or more electromechanical actuators, one or more pneumatic actuators, one or more hydraulic actuators, etc., or any combination thereof. 
     In the illustrated example of  FIG. 4 , the cover  425  is affixed or otherwise coupled to an example housing  430  such that, when the cover  425  is in the first (e.g., closed) position, the cover  425  and housing  430  form a substantially confined cleaning area  435  around at least the first side of the optical element  405 . In such examples, the housing  430  can be implemented by a housing of the tool  410 , tubing extended down into the borehole in which the tool  410  is positioned, the formation wall of the borehole, etc., or any combination thereof. During operation of the tool  410  to obtain imaging information, the cover  425  is controlled to transition to the second (e.g., open) position to provide the optical element  405  with access to a field-of-view that allows the optical element  405  to view the environment outside the housing  430 . 
     In some examples, when the cover  425  is in the second (e.g., open) position, the optical element  405  may come into contact with drilling fluid and/or other opaque fluid and/or other contaminants in the outside environment. Accordingly, the optical element cleaning mechanism  400  may include flushing jets (not shown) to propel flushing fluid into the field-of-view of the optical element  405  while the cover  425  is in the second (e.g., open) position to improve visibility while the optical element  405  is gathering imaging information. Examples of flushing techniques that may be used while cover  425  is in the second (e.g., open) position are disclosed in U.S. application Ser. No. 13/439,824, entitled “IMAGING METHODS AND SYSTEMS FOR CONTROLLING EQUIPMENT IN REMOTE ENVIRONMENTS” and filed on Apr. 4, 2013, which is incorporated by reference herein in its entirety. 
     In between times when the tool  410  is operated to obtain imaging information, there may be times at which the tool  410  may configured to be nonoperational to permit the tool  410  to be moved to another position, depth, etc. During such times, or whenever cleaning of the optical element  405  is to be performed, the cover  425  is controlled to transition to the first (e.g., closed) position to form the cleaning region  435  around the optical element  405 . For example, the cleaning region  435  can be a substantially confined cavity characterized by a gap having distance, d, formed between a first side of the optical element  405  and the cover  425  when the cover  425  is in the first (e.g., closed) position. Accordingly, during time periods when the tool  410  is not being used to obtain imaging information, the cover  425  can be closed to avoid further contamination of the optical element  405 . 
     Furthermore, the optical element cleaning mechanism  400  of the illustrated example includes an example flushing assembly having an example injector nozzle  440 , an example exit nozzle  445  and an example exit valve  450 . In the illustrated example of  FIG. 4 , the injector nozzle  440  can be implemented by any type of nozzle or similar device that permits the flushing (e.g., cleaning) fluid  415  to be injected or otherwise projected into the cleaning area  435  and into the gap that is formed after the cover  425  transitions into the first (e.g., closed) position. The exit nozzle  445  can be implemented by any type of nozzle or similar device that permits the injected flushing fluid  415 , which may contain any contaminants removed from the optical element  405 , to exit the gap and the cleaning area  435 . The exit valve  450  can be implemented by any type of valve or similar device that permits the used flushing fluid  415  to be removed from the optical element cleaning mechanism  400 . In some examples, any type of packing material  455  can be used to prevent the flushing (e.g., cleaning) fluid  415  from exiting the cleaning area  435 , or to at least reduce the amount of flushing fluid  415  that can exit the cleaning area  435 , except through the exit nozzle  445  while the cover  425  is in the first (e.g., closed) position. 
     In the illustrated example of  FIG. 4 , to clean the optical element  405 , the cover  425  is controlled to transition into the first (e.g., closed) position to form a narrow gap (d) between at least a first side (e.g., a first surface) of the optical element  405  and the cover  425 . The injector nozzle  440  then injects the flushing fluid  415  into the cleaning area  435  and, thus, the gap (d) formed after the cover  425  is closed. The narrow gap formed between the optical element  405  and the cover  425  when the cover  425  is closed causes the flow rate of the flushing fluid  415  across the optical element  405  to increase relative to when the cover  425  is opened. This increase in fluid flow rate can increase the effectiveness of the flushing fluid  415  for removing fluids (e.g., such as oil) and/or other contaminants from the surface of the optical element  405 . In some examples, the valve  450  of the flushing assembly is controllable such that the valve  450  can be opened or closed to maintain a desired flow rate of flushing fluid  415  across the surface of the optical element  405 . In other examples, the valve  450  is implemented by a port that, for example, permits fluid flow in one direction (e.g., out of the optical element cleaning mechanism  400 ) but not in another direction (e.g., into the optical element cleaning mechanism  400 ). 
     As mentioned above, the optical element cleaning mechanism  400  may include one or more ultrasonic transducers  420  to emit ultrasonic waves focused at the optical element  405 . In the illustrated example, the ultrasonic transducers  420  are positioned on a wall of the housing  430  such that they are able to focus an ultrasonic beam on a first side (e.g., surface) of the optical element  405 . The ultrasonic transducers  420  of the illustrated example generate ultrasonic waves in the flushing fluid  415  to clean the optical element  405 . The narrow gap formed between the optical element  405  and the cover  425  when the cover  425  is closed can increase the effectiveness of the ultrasonic waves for cleaning the optical element  405  relative to when the cover  425  is opened. 
     For example, in a first example cleaning operation, after the cover  425  is controlled to transition into the first (e.g., closed) position to form the narrow gap (d), the injector nozzle  440  is controlled to cause the flushing fluid  415  to be injected into the cleaning area  435  and, thus, the gap (d), which may cause contaminants on the optical part  405  to be dislodged. The injector nozzle  440  continues to inject the flushing fluid  415  into the cleaning area  435  for a first time period. After the first time period ends, the injector nozzle  440  is controlled to stop further flushing fluid  415  from being injected into the cleaning area  435  for a second period of time. In some examples, if the ultrasonic transducer(s)  420  are present in the optical element cleaning mechanism  400 , then the ultrasonic transducer(s)  420  are controlled to emit an ultrasonic beam (e.g., focused on the optical element  405 ) during this second time period to further cause any remaining contaminants on the optical part  405  to be dislodged. Then, after the second time period ends, the valve  450  is controlled to cause the valve  450  to open to permit the flushing fluid  415 , which contains any contaminants dislodged from the optical part  405 , to exit the gap and the cleaning area  435 . If the ultrasonic transducer(s)  420  are present and were controlled to emit an ultrasonic beam during the second time period, then at the end of the second time period, the ultrasonic transducer(s)  420  is controlled to halt emission of the ultrasonic beam. Afterwards, the cover  425  may be controlled to transition into the second (e.g., open) position to permit the tool  410  to resume normal imaging operation. 
     As another example, in a second example cleaning operation, after the cover  425  is controlled to transition into the first (e.g., closed) position to form the narrow gap (d), the nozzles  440 / 445  and the valve  450  are controlled to cause the flushing fluid  415  to flow into the cleaning area  435  and, thus, into the gap and across the optical element  405  at a desired flow rate continuously (or almost continuously) while the cover  425  is closed, thereby causing contaminants on the optical part  405  to be dislodged. Also, if the ultrasonic transducer(s)  420  are present in the optical element cleaning mechanism  400 , then the ultrasonic transducer(s)  420  can be controlled to emit an ultrasonic beam (e.g., focused on the optical element  405 ) while the cover  425  is closed, thereby further causing contaminants on the optical part  405  to be dislodged. After cleaning is complete, the cover  425  may be controlled to transition into the second (e.g., open) position to permit the tool  410  to resume normal imaging operation. 
     The flushing fluid  415  may correspond to any type of fluid, such as water, air, one or more solvents, etc., or any combination thereof. Furthermore, in some environments, such as when the optical element cleaning mechanism  400  is used in flammable environments, such as in the surface monitoring tool  135  of  FIG. 1 , the flushing fluid  415  may correspond to a noncombustible gas, such as carbon dioxide, nitrogen, etc., or any combination thereof. In some examples, particles may be mixed with the flushing fluid  415  (e.g., prior to injection into the cleaning area  435  and, thus, into the gap) to increase the cleaning effectiveness of the flushing fluid  415 . Also, in some examples, the optical element cleaning mechanism  400  may include an example heating element (not shown) to heat the flushing fluid  415  (e.g., prior to injection into the cleaning area  435  and, thus, into the gap) to increase the cleaning effectiveness of the flushing fluid  415 . 
     The example optical element cleaning mechanism  400  of  FIG. 4  further includes an example controller  460  to control operation of one or more of the ultrasonic transducer(s)  420 , the cover  425 , the ports  440  and/or  445 , and/or the valve  450 . In some examples, the controller  460  can be implemented by any type of processor platform, such as the example processor platform  1100  of  FIG. 11 , which is described in greater detail below. In some examples, the controller  460  can be co-located with the optical element cleaning mechanism  400  and the tool  410  such that controller  460  performs autonomous control of the optical element cleaning mechanism  400  in accordance with one or more of the optical cleaning methods disclosed herein. In other examples, the controller  460  can be located remotely from the optical element cleaning mechanism  400  and the tool  410 , such as at the logging and control unit  140  or in the  320 , to permit remote control of the optical element cleaning mechanism  400  (e.g., via a telemetry link) in accordance with one or more of the optical cleaning methods disclosed herein. 
     A block diagram of a second example optical element cleaning mechanism  500  that can be used to clean optical element(s) of, for example, one or more of the LWD module  120 / 120 A, the MWD module  130 , the surface monitoring tool  135 , and/or the imaging tool  310  is illustrated in  FIG. 5 . The second example optical element cleaning mechanism  500  includes many elements in common with the first example optical element cleaning mechanism  400  of  FIG. 4 . As such, like elements in  FIGS. 4 and 5  are labeled with the same reference numerals. The detailed descriptions of these like elements are provided above in connection with the discussion of  FIG. 4  and, in the interest of brevity, are not repeated in the discussion of  FIG. 5 . 
     For example, the second example optical element cleaning mechanism  500  includes the example ultrasonic transducer(s)  420 , the example cover  425 , the example housing  430 , the example injector nozzle  440 , the example exit nozzle  445 , the example valve  450 , the example packing material  455  and the example controller  460 , which are described above in connection with the first example optical element cleaning mechanism  400 .  FIG. 5  also illustrates the transitioning of the cover  425  from the first (e.g., closed) position, which is represented by solid lines, and the second (e.g., open) position, which is represented by dashed lines. Furthermore, in the second example optical element cleaning mechanism  500  of  FIG. 5 , the ultrasonic transducer(s)  420  are positioned on the cover  425 , rather than on the housing  430  as in the first example optical element cleaning mechanism  400 . For example, the ultrasonic transducer(s)  420  are positioned on the cover  425  of the optical element cleaning mechanism  500  such that the ultrasonic transducer(s)  420  are brought into close proximity to and become focused on the optical element  405  when the cover  425  is brought into the first (e.g., closed) position. In at least some examples, by positioning the ultrasonic transducer(s)  420  on the cover  425 , the ultrasonic transducer(s)  420  can be positioned over and brought to within the distance, d, or less, from the optical element  405 , which may improve the effectiveness of cleaning with the ultrasonic transducer(s)  420  relative to the positioning shown in the example of  FIG. 4 . 
       FIG. 6  depicts an example operation of the optical element cleaning mechanisms  400  and/or  500  during which the flushing fluid  415  is injected into the gap (d) formed between the optical element  405  and the cover  425  when the cover  425  is in the first (e.g., closed) position. As illustrated in the example of  FIG. 6 , when the cover  425  is in the first (e.g., closed) position, the flushing fluid  415  is caused to flow in a confined region across a surface  605  of the optical element  405 . As noted above, injecting the flushing fluid  415  into such a confined region causes the flow rate of the fluid to increase, thereby enhancing the effectiveness of the fluid  415  for cleaning the surface  605  of the optical element  405 . 
     An example cover  700  that may be used to implement the cover  425  of the optical element cleaning mechanisms  400  and/or  500  is illustrated in  FIG. 7 . The cover  700  implements a movable diaphragm having multiple elements  705  arranged to form an aperture  710 . The elements  705  can be implemented by one or more blades, plates, etc., and/or any other type(s) and/or combination of elements that are interleaved, interlocked and/or otherwise arranged to form the aperture  710 . In the illustrated example, the aperture  710  is an opening whose size may be decreased and increased by one or more actuators (not shown) such that the size of the aperture  710  ranges, respectively, between a first (e.g., closed) position and a second (e.g., open) position. 
     Other types of cover technologies may be used to implement the cover  425  of the optical element cleaning mechanisms  400  and/or  500 . For example, the cover  425  may be implemented using one or more hinged doors, plates, etc., and/or one or more sliding doors, plates, etc., and/or any other types of cover mechanisms or combination thereof. 
     While example manners of implementing the optical element cleaning mechanisms  400  and  500  have been illustrated in  FIGS. 1-7 , one or more of the elements, processes and/or devices illustrated in  FIGS. 1-7  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. Further, the example controller  460  and/or, more generally, the example optical element cleaning mechanisms  400  and/or  500  may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware. Thus, for example, the controller  460  and/or, more generally, the example optical element cleaning mechanisms  400  and/or  500  could be implemented by one or more analog or digital circuit(s), logic circuits, programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example optical element cleaning mechanisms  400  and/or  500 , and/or the controller  460  is/are hereby expressly defined to include a tangible computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. storing the software and/or firmware. Further still, the example optical element cleaning mechanisms  400  and  500  may include one or more elements, processes and/or devices in addition to, or instead of, those illustrated in  FIGS. 1-7 , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
     Flowcharts representative of example processes for implementing the example optical element cleaning mechanisms  400 / 500  and/or the example controller  460 , and/or for controlling one or more of the example ultrasonic transducer(s)  420 , the example cover  425 , the example injector nozzle  440 , the example exit nozzle  445  and/or the example valve  450 , are shown in  FIGS. 8-10 . In these examples, the processes may be implemented by one or more programs comprising machine readable instructions for execution by a processor, such as the processor  1112  shown in the example processor platform  1100  discussed below in connection with  FIG. 11 . The one or more programs, or portion(s) thereof, may be embodied in software stored on a tangible computer readable storage medium such as a CD-ROM, a floppy disk, a hard drive, a digital versatile disk (DVD), a Blu-ray Disk™, or a memory associated with the processor  1112 , but the entire program or programs and/or portions thereof could alternatively be executed by a device other than the processor  1112  and/or embodied in firmware or dedicated hardware (e.g., implemented by an ASIC, a PLD, an FPLD, discrete logic, etc.). Also, one or more of the processes represented by the flowcharts of  FIGS. 8-10 , or one or more portion(s) thereof, may be implemented manually. Further, although the example processes are described with reference to the flowcharts illustrated in  FIGS. 8-10 , many other methods of implementing the example optical element cleaning mechanisms  400 / 500  and/or the example controller  460 , and/or for controlling one or more of the example ultrasonic transducer(s)  420 , the example cover  425 , the example injector nozzle  440 , the example exit nozzle  445  and/or the example valve  450 , may alternatively be used. For example, with reference to the flowcharts illustrated in  FIGS. 8-10 , the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, combined and/or subdivided into multiple blocks. 
     As mentioned above, the example processes of  FIGS. 8-10  may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a tangible computer readable storage medium such as a hard disk drive, a flash memory, a read-only memory (ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, a random-access memory (RAM) and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term tangible computer readable storage medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, “tangible computer readable storage medium” and “tangible machine readable storage medium” are used interchangeably. Additionally or alternatively, the example processes of  FIGS. 8-10  may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a non-transitory computer and/or machine readable medium such as a hard disk drive, a flash memory, a ROM, a CD, a DVD, a cache, a RAM and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term non-transitory computer readable medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, when the phrase “at least” is used as the transition term in a preamble of a claim, it is open-ended in the same manner as the term “comprising” is open ended. Also, as used herein, the terms “computer readable” and “machine readable” are considered equivalent unless indicated otherwise. 
     A first example process  800  that may be executed to implement the example controller  460  to control the example optical element cleaning mechanisms  400  and/or  500  of  FIGS. 4-5  is illustrated in  FIG. 8 . For convenience and without loss of generality, operation of the example process  800  is described from the context of being performed to control the optical element cleaning mechanism  400  of  FIG. 4 . With reference to the preceding figures and associated written descriptions, the example process  800  of  FIG. 8  begins execution at block  805  at which the controller  460  issues one or more commands to cause the cover  425  of the optical element cleaning mechanism  400 , which is positioned over the optical element  405 , to transition to a first (e.g., closed) position to form a cavity (e.g., the cleaning area  435 ) having a gap (d) between the cover  425  and the optical element  405 , as described above. At block  810 , the controller  460  issues one or more commands to cause the injector nozzle  440  included in the flushing assembly of the optical element cleaning mechanism  400  to inject the flushing fluid  415  into the gap formed at block  805 , as described above. At block  815 , the controller  460  issues one or more commands to cause the exit nozzle  445  and/or the valve  450  of the flushing assembly of the optical element cleaning mechanism  400  to permit the flushing fluid, which was injected at block  810 , to exit the gap formed at block  805 , as described above. 
     A second example process  900  that may be executed to implement the example controller  460  to control the example optical element cleaning mechanisms  400  and/or  500  of  FIGS. 4-5  is illustrated in  FIG. 9 . For convenience and without loss of generality, operation of the example process  900  is described from the context of being performed to control the optical element cleaning mechanism  400  of  FIG. 4 . With reference to the preceding figures and associated written descriptions, the example process  900  of  FIG. 9  begins execution at block  905  at which the controller  460  issues one or more commands to cause the cover  425  of the optical element cleaning mechanism  400 , which is positioned over the optical element  405 , to transition to a first (e.g., closed) position to form a cavity (e.g., the cleaning area  435 ) having a gap (d) between the cover  425  and the optical element  405 , as described above. 
     Next, at block  910 , the controller  460  issues one or more commands to cause the injector nozzle  440  included in the flushing assembly of the optical element cleaning mechanism  400  to inject the flushing fluid  415  into the gap formed at block  905 . At block  910 , the controller  460  causes the injector nozzle  440  to continue injecting the flushing fluid  415  into the gap for a first time period after the cover  425  transitions to the first (e.g., closed) position, as described above. At block  915 , the controller  460  issues one or more commands to cause the injector nozzle  440  to stop injecting the flushing fluid  415  into the gap for a second time period after the first time period ends, as described above. At block  920 , if one or more ultrasonic transducer(s)  420  are included in the optical element cleaning mechanism  400 , the controller  460  issues one or more commands to cause the ultrasonic transducer(s)  420  to emit ultrasonic beam(s) focused on the optical element  405  during the second time interval, as described above. 
     After the second time period ends, at block  925  the controller  460  issues one or more commands to cause the exit nozzle  445  and/or the valve  450  of the flushing assembly of the optical element cleaning mechanism  400  to permit the flushing fluid, which was injected at block  910 , to exit the gap formed at block  905 , as described above. In some examples, at block  925  the controller  460  may also issue one or more commands to cause the injector nozzle  440  to inject further flushing fluid  415  to assist in removal of the contaminated flushing fluid from the gap. 
     A third example process  1000  that may be executed to implement the example controller  460  to control the example optical element cleaning mechanisms  400  and/or  500  of  FIGS. 4-5  is illustrated in  FIG. 10 . For convenience and without loss of generality, operation of the example process  1000  is described from the context of being performed to control the optical element cleaning mechanism  400  of  FIG. 4 . With reference to the preceding figures and associated written descriptions, the example process  1000  of  FIG. 10  begins execution at block  1005  at which the controller  460  issues one or more commands to cause the cover  425  of the optical element cleaning mechanism  400 , which is positioned over the optical element  405 , to transition to a first (e.g., closed) position to form a cavity (e.g., the cleaning area  435 ) having a gap (d) between the cover  425  and the optical element  405 , as described above. 
     Next, at block  1010 , the controller  460  issues one or more commands to cause the injector nozzle  440  included in the flushing assembly of the optical element cleaning mechanism  400  to inject the flushing fluid  415  into the gap formed at block  1005  continuously (or almost continuously) while the cover  425  is in the first (e.g., closed) position, as described above. At block  1015 , if one or more ultrasonic transducer(s)  420  are included in the optical element cleaning mechanism  400 , then the controller  460  issues one or more commands to cause the ultrasonic transducer(s)  420  to emit ultrasonic beam(s) focused on the optical element  405  while the cover  425  is in the first (e.g., closed) position, as described above. Then, at block  1020 , the controller  460  issues one or more commands to cause the exit nozzle  445  and/or the valve  450  of the flushing assembly of the optical element cleaning mechanism  400  to permit the flushing fluid, which was injected at block  1010 , to exit the gap formed at block  1005  continuously (or almost continuously), as described above. 
       FIG. 11  is a block diagram of an example processor platform  1100  capable of executing the processes of  FIGS. 8-10  to implement the example optical element cleaning mechanisms  400 / 500  and/or the example controller  460 , and/or to control one or more of the example ultrasonic transducer(s)  420 , the example cover  425 , the example injector nozzle  440 , the example exit nozzle  445  and/or the example valve  450  of  FIGS. 1-7 . The processor platform  1100  can be, for example, a server, a personal computer, a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance, or any other type of computing device. 
     The processor platform  1100  of the illustrated example includes a processor  1112 . The processor  1112  of the illustrated example is hardware. For example, the processor  1112  can be implemented by one or more integrated circuits, logic circuits, microprocessors or controllers from any desired family or manufacturer. 
     The processor  1112  of the illustrated example includes a local memory  1113  (e.g., a cache) (e.g., a cache). The processor  1112  of the illustrated example is in communication with a main memory including a volatile memory  1114  and a non-volatile memory  1116  via a link  1118 . The link  1518  may be implemented by a bus, one or more point-to-point connections, etc., or a combination thereof. The volatile memory  1114  may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or any other type of random access memory device. The non-volatile memory  1116  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1114 ,  1116  is controlled by a memory controller. 
     The processor platform  1100  of the illustrated example also includes an interface circuit  1120 . The interface circuit  1120  may be implemented by any type of interface standard, such as an Ethernet interface, a universal serial bus (USB), and/or a PCI express interface. 
     In the illustrated example, one or more input devices  1122  are connected to the interface circuit  1120 . The input device(s)  1122  permit(s) a user to enter data and commands into the processor  1112 . The input device(s) can be implemented by, for example, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, a trackbar (such as an isopoint), a voice recognition system and/or any other human-machine interface. 
     One or more output devices  1124  are also connected to the interface circuit  1120  of the illustrated example. The output devices  1124  can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display, a cathode ray tube display (CRT), a touchscreen, a tactile output device, a light emitting diode (LED), a printer and/or speakers). The interface circuit  1120  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip or a graphics driver processor. 
     The interface circuit  1120  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem and/or network interface card to facilitate exchange of data with external machines (e.g., computing devices of any kind) via a network  1126  (e.g., an Ethernet connection, a digital subscriber line (DSL), a telephone line, coaxial cable, a cellular telephone system, etc.). 
     The processor platform  1100  of the illustrated example also includes one or more mass storage devices  1128  for storing software and/or data. Examples of such mass storage devices  1128  include floppy disk drives, hard drive disks, compact disk drives, Blu-ray disk drives, RAID (redundant array of independent disks) systems, and digital versatile disk (DVD) drives. 
     Coded instructions  1132  corresponding to the instructions of  FIGS. 8-10  may be stored in the mass storage device  1128 , in the volatile memory  1114 , in the non-volatile memory  1116 , in the local memory  1113  and/or on a removable tangible computer readable storage medium, such as a CD or DVD  1136 . 
     As an alternative to implementing the methods and/or apparatus described herein in a system such as the processing system of  FIG. 11 , the methods and or apparatus described herein may be embedded in a structure such as a processor and/or an ASIC (application specific integrated circuit). 
     Although a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not just structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function. 
     Finally, although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.