Abstract:
An apparatus for positioning an object in a remote location with a high degree of precision, insuring stability and repeatability for discrete sampling to be taken at intervals between each sampling on the order of years. A preferred embodiment of the present invention positions an optical probe in a propellant bore hole. The present invention measures and records the exact position of an optical probe within the bore hole, so that exact position may be repeated for future measurements to be taken over the lifetime of the system.

Description:
DEVELOPMENT 
     The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     MICROFICHE APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a machine for positioning an analytical device. More specifically, the present invention may be used to make propellant surface optical measurements. The measurements are used to determine the aging characteristics of rocket motor propellant. 
     2. Background 
     After missiles have been in the field or storage for long periods of time, it may be necessary to determine the dynamic properties of the propellant. There is currently a need for support devices capable of sensing the dynamic properties of rocket motor propellant over long periods of time without disturbing the integrity of the propellant itself. Any change in the dynamic properties of the rocket motor propellant may affect the performance of the rocket motor. As a result, rocket motor propellant is periodically inspected to ensure that the propellant is able to effectively perform its required function. 
     One common problem of storing various propellants is the migration of nitroglycerin around the liner of a rocket motor casing. The periodic measuring for nitroglycerine and stabilizers at various points in close proximity to the liner is used to determine the rate and concentration of the transfer. This information is used to determine the long term effects of storage in different conditions, such as temperature and relative humidity. 
     Optical probes are highly useful in determining the characteristics of propellant and the relative concentration of nitroglycerine and other compounds. An optical probe uses light to determine relative concentrations of propellant stabilizer. A precisely positioned light beam is emitted from a hepta plex fiber optic probe onto the propellant surface to be examined. The incident light is reradiated from the propellant surface, captured by a single optical fiber and conveyed to a device, which compares transmitted and received light over a given spectral range. The relative level of stabilizer present is determined from the spectral deltas at the stabilizer characteristic absorption wavelength. 
     SUMMARY OF THE INVENTION 
     Broadly, the present invention is an apparatus for positioning an object in a remote location with a high degree of precision and stability. More specifically, the present invention is an apparatus for positioning an optical probe in a propellant bore hole. Also, the present invention is equipped to measure the exact position of an optical probe, so that exact position may be repeated for future measurements to accurately determine the aging characteristics of the propellant. A preferred embodiment of the present invention is positioned using an outer bar and an inner bar connected by parallel rails, an upper bar, and a pressure foot. A base is slidably attached to the rails and a probe positioning rod is attached to the base. A vernier assembly is used to precisely position the base. An analytical device holder is rotatably mounted on a support on the base to analyze the characteristics of a test subject at various points without adjusting the base or vernier assembly. 
     One object of the present invention is to provide a mechanism for positioning an object with a high degree of specificity and repeating the position for future use. 
     Another object of the present invention is to provide an apparatus that may position an analytical device in a wide variety of areas with a high degree of precision. 
     Another object of the present invention is to provide an apparatus that may be positioned in various locations within a propellant bore hole for the purpose of measuring various characteristics of the propellant. 
     Another object of the present invention is to provide an apparatus that creates stability, while minimizing the potential damage to an object being measured. 
     Yet another object of the present invention is to provide a mechanism for positioning an optical probe. 
     A very specific object of the invention is to precisely measure the position of an optical probe in a propellant bore hole, so that the position may be duplicated for future measurements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial representation of a preferred embodiment of the slidable fixture positioner of a preferred embodiment of the present invention; 
     FIG. 2 is a pictorial representation of the outer support assembly of the slidable fixture positioner of a preferred embodiment of the present invention; 
     FIG. 3 is a pictorial representation of the vernier assembly of the preferred embodiment of the slidable fixture positioner of a preferred embodiment of the present invention; 
     FIG. 4 is a pictorial representation of the device holder assembly of the slidable fixture positioner of a preferred embodiment of the present invention; 
     FIG. 5 is a pictorial representation of the slidable fixture positioner assembly of a preferred embodiment of the present invention secured in a propellant bore hole; and 
     FIG. 6 is a pictorial representation of the inner support assembly of the present invention, which details a preferred alignment of a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     Referring more specifically to the drawings, for illustrative purposes, a preferred embodiment of the present invention is embodied in the apparatus as shown in FIG.  1  through FIG.  6 . Referring to FIG. 1, the present invention consists of a device holder assembly  123  rotatably attached to a vertical support  101  by a wing nut and bolt  108 . The vertical support  101  is secured to a base  102 , which is slidably attached to a pair of parallel rails  106   a  and  106   b . In a preferred embodiment, the base  102  is slidably attached to the rails  106   a  and  106   b  through linear bearings and a scale  124  is located on the vertical support  101 , so that the position of the device holder assembly  123  relative to the base  102  may be repeated. The rails  106   a  and  106   b  are affixed to a lower inner bar  113  and slidably attached to the lower outer bar  107 . The lower outer bar  107  may be fixed in a position on the rails by locking screws  125   a  and  125   b . One end of a position measurement rod  112  is longitudinally attached to the lower inner bar  113  and slidably supported by the measurement sensing unit  115 , which is fixed to the base  102 . The measurement sensing unit  115  detects minor changes in the position of the base  102  along the rails  106   a  and  106   b . A data cable  117  connects the measurement sensing unit  115  to the position readout box  103 , which is secured to the upper bar  104 . The upper bar  104  is slidably attached to two parallel threaded rods  118   a  and  118   b  and supported by tension nuts  111   a  and  111   b , which are threadably attached to the rods  118   a  and  118   b . The parallel threaded rods  118   a  and  118   b  are threadably attached to the lower outer bar  107  and are held in place by jam nuts  119   a  and  119   b . The positioning rod  121  is longitudinally attached to the base  102  and slidably supported in the probe positioning vernier  120 . A pressure foot  109  is slidably attached to a foot rod  110  and supported by a tensioning nut  105 , which is threadably attached to the foot rod  110 . The foot rod  110  is threadably attached to the lower inner bar  113 . 
     The slidable fixture outer support hardware, FIG. 2, consists of at least two lower feet  201   a  and  201   b  attached to the lower outer bar  107  with lower foot screws  205   a  and  205   b  and at least one upper foot  204  attached to the upper bar  104  with an upper foot screw  202 . The lower feet  201   a  and  201   b  and upper foot  204  are used in positioning the slidable fixture positioner  126  in a desired area by setting the lower feet  201   a  and  201   b  and upper foot  204  in contact with the desired area, as depicted in FIG.  5 . This type of positioning creates stability while minimizing the contact area and limiting and any damage to a contact surface. Also, the lower feet  201   a  and  201   b  and upper foot  204  may be shaped to fit flush with the contact area to maximize stability and minimize damage to the contact surface. The locking screws  125   a  and  125   b  lock the rails  106   a  and  106   b  in place in the lower outer bar  107 . 
     Referring to FIG. 3, the vernier assembly  120  consists of a slotted and bored bolt  307  upon which an engagement cylinder  305  is slidably affixed. At one end, the slotted and bored bolt  307  is affixed to the lower outer bar  107 . A vernier hand wheel  302  is threadably attached to the bored and slotted bolt  307  and bears against one side of the engagement cylinder  305 . The vernier hand wheel  302  is threadably attached at the end of the slotted and bored bolt  307  opposite the lower outer bar  107 , as illustrated in FIG. 3. A first end of a first spring  304  bears against the lower outer bar  107  and a second end of the first spring  304  bears against the engagement cylinder  305 . This causes the engagement cylinder  305  to remain in a stable position along the slotted and bored bolt  307  bearing against the vernier hand wheel  302 . The positioning rod  121  is slidably attached through the bore of the slotted and bored bolt  307 . Friction pads  306   a  and  306   b  are attached to the engagement cylinder  305  such that the friction pads  306   a  and  306   b  are free to slide radially, but restrained longitudinally. The positioning rod  121  runs between the friction pads  306   a  and  306   b . A thumb screw  301  and a set screw  303  are threadably attached to the engagement cylinder  305  and each screw  301  and  303  controls the position of one of the friction pads  306   a  and  306   b . 
     Referring to FIG. 4, the device holder assembly  123  consists of a shoe  401  to which a device  410  is slidably attached and locked in place with a retaining screw  402 . The shoe  401  is attached to a support rod  406 . The support rod  406  is slidably attached to the bored section  409  of a support arm  405  and set in place in the support arm  405  by a locking nut  404 . A second spring  403  is contained within the bored section  409  of the support arm  405  such that the bored section  409  restrains one end of the second spring  403  and the other end is restrained by the support rod  406 , as illustrated in FIG.  4 . The tension of the second spring  403  is carefully selected to minimize the possible damage to the surface of any object being analyzed, such as rocket propellant, which is described below in greater detail. 
     To better describe the operation of the slidable fixture positioner, the utility as it pertains to a propellant bore hole will be detailed. The following description is not intended to limit the possible utilities of the present invention. Referring to FIG. 5, the present invention may be used to examine the sidewalls of a cylindrical hole bored through the rocket motor outer case  502  and into the propellant  503 . The operation is performed with the bore hole  508  longitudinal axis in a horizontal position. The slidable fixture positioner is installed in the propellant bore hole. The slidable fixture may also be used to examine the “as cast” exposed surfaces of the motor central bore. Of particular concern is the area in close proximity to the liner  501 . 
     Referring to FIG. 5, a preferred embodiment of the present invention is positioned in a bore hole with the inner support assembly  505  set in the bottom of the bore hole  508 . The outer support subassembly  504  is then slid along the rails  106   a  and  106   b  to a desired position. The locking screws  125   a  and  125   b  are tightened to secure the lower outer bar  107  to the rails  106   a  and  106   b . Adjusting the tension nut  105  of the pressure foot  109  presses the pressure foot  109  and the position adapters  122   a  and  122   b  on the lower inner bar  113  firmly against contact points on the bore wall, securing the inner support subassembly  505  of the slidable fixture positioner  126 . In a preferred embodiment, position adapters  122   a  and  122   b  are placed on the lower inner bar  113  at the contact points to ensure the stability of the slidable fixture positioner  126  and minimize the damage to propellant  503  or any other surface at the contact points. The position adapters  122   a  and  122   b  may be rounded or shaped to fit other surface contours, so that the invention sits flush against the contact points. Also, a single position adapter (not separately shown) that covers the entire lower inner bar  113  may be incorporated. Tightening the tension nuts  111   a  and  111   b  of the parallel rods  106   a  and  106   b  raises the upper bar  104 , which presses the lower feet  201   a  and  201   b  and upper foot  204  against the case  502  and propellant bore. This secures the outer support subassembly  504  of a preferred embodiment of the present invention. 
     The preferred material of construction for the base  102 , lower inner bar  113 , lower outer bar  107 , upper bar  104 , rails  106   a  and  106   b , positioning rod  121 , upper foot  204 , lower feet  201   a  and  201   b , parallel rods  118   a  and  118   b  and pressure foot  109  is a metal such as steel, aluminum or stainless steel. Metal provides a durable material at a relatively low cost. In a preferred embodiment, a bumper  506  is affixed to the lower inner bar  113  to cushion contact with the base  102 . Two or more bumpers may be utilized in place of a single bumper as illustrated in FIG.  5 . The bumper(s)  506  may be constructed of a non-metallic material, such as plastic or fabric, as a safety precaution. A metal-to-metal contact may cause a spark that could ignite propellant or other combustible material. In another preferred embodiment, the parallel rods  118   a  and  118   b  are constructed of metal, such as steel, and the tension nuts  111   a  and  111   b  are constructed of a non-metallic material, such as plastic, as a safety precaution. A metal-to-metal contact may cause a spark that could ignite propellant or other combustible material. Additionally, propellant could get squeezed in several areas as the apparatus is set or adjusted. Also as a safety precaution when using the present invention in area exposed to propellant or other combustible material, the slidable fixture positioner  126  may be grounded through a ground wire (not separately shown) to drain any static charge buildup away from the potentially hazardous area. 
     Referring to FIG. 3, the vernier assembly  120  is engaged by tightening the thumb screw  301 . The thumb screw  301  bears on a first friction pad  306   a , which grips the positioning rod  121  between the first friction pad  306   a  and a second friction pad  306   b . The second friction pad  306   b  is supported radially by a set screw  303 . The positioning rod  121  passes through the vernier assembly  120  and is attached to the base  102 . When the vernier assembly  120  is disengaged, i.e. the grip of the friction pads  306   a  and  306   b  is loosened by adjusting the thumb screw  301  or set screw  303 , the base  102  may be positioned with the positioning rod  121 . The set screw  303  is adjusted to center the positioning rod  121  so that it does not drag on the slotted and bored bolt bore  307 . The friction pads  306   a  and  306   b  are attached to the engagement cylinder  305  so that tightening the thumb screw  301  locks the positioning rod  121  to the engagement cylinder  305 . The engagement cylinder  305  is supported on the slotted and bored bolt  307  so that it may move along its length, but it is restrained by the vernier hand wheel  302  and a first spring  304 . Referring to FIG.  1  and FIG. 3, when the vernier hand wheel  302  is turned clockwise about the slotted and bored bolt  307 , the vernier hand wheel  302  is advanced on the slotted and bored bolt  307  causing the engagement cylinder  305  and positioning rod  121  to be moved along the slotted and bored bolt  307  in small increments. The small incremental changes in the position of the engagement cylinder  305  on the slotted and bored bolt  307  cause corresponding small changes in the position of the positioning rod  121  and base  102 . The small changes are detected by the measurement sensing unit  115  and relayed to the position readout box  103  via a data cable  117 . Movement of the positioning rod  121  toward the lower inner bar  113  moves the base  102  deeper into the bore hole  508 . When the vernier hand wheel  302  is retracted on the slotted and bored bolt  307 , the first spring  304  pushes the engagement cylinder  305  and positioning rod  121  away from the lower inner bar  113 . Movement of the positioning rod  121  away from the lower inner bar  113  moves the base  102  to out of the bore hole  508 . Since the optical probe  410  is attached to the base  102  through the device holder assembly  123 , movement of the base  102  results in a corresponding probe  410  movement. 
     A measurement sensing unit  115 , which is attached to the base  102 , has the measurement bar  112  sliding through it. The first end of the measurement bar  112  is attached to the lower inner bar  113 . The measurement sensing unit  115  senses relative movement of itself along the measurement bar  113 . In a preferred embodiment, the relative position information is transmitted over a data cable  117  to the position readout box  103 . The position readout box  103  contains a switch (not separately shown), which allows the relative position reading to be set to zero at any point along the measurement bar  112 . Once the zero is set, any new table position indicated along the rails  106   a  and  106   b  is set to zero at that point along the measurement bar  112 . Once the zero is set, any base  102  position along the rails  106   a  and  106   b  is measured as absolute, relative to the zero set point. A gage is used to position the probe  410  precisely at the bore hole motor case&#39;s  502  outer edge. The position readout box  103  is zeroed at this point to establish a longitudinal reference point. Following this, any probe  410  position is read directly on the position readout box  103  as distance from the motor case  502  outer edge to the optical probe  410  imaging center. 
     Loosening the wing nut  108  allows the device holder assembly  123  to be rotated through approximately  200  degrees about the bore hole&#39;s longitudinal axis. This allows the probe  410  to be positioned at various azimuth locations. The gage used to set the table position zero is also used to place a reference mark on the motor case  501  corresponding to the selected probe azimuth position. The azimuth reference mark and outer case zero reference allows the probe  410  to be repositioned at the desired location for future re-examination of a propellant surface  503 . 
     Referring to FIG. 4, the optical probe  410  is placed in the shoe  401  at the desired location and secured in place by tightening the retaining screw  402 . Before relocating the optical probe  410 , the shoe  401  is moved away from the bore wall compressing the second spring  403  and then, the locking nut  404  is tightened. This holds the shoe  401  away from the bore surface so that the probe  410  may be repositioned without dragging on the propellant  503 . When the optical probe  410  is in position, the locking nut  404  is loosened allowing the second spring  403  to lightly press the shoe  401  against the propellant surface  503 . In a preferred embodiment, the axis around which the device holder assembly  123  rotates acts as the geometric center of the cylinder created by the bore hole. This enables the relative position of the device holder assembly  123  to be measured and duplicated with a high degree of precision by limiting the relative adjustments of a preferred embodiment of the invention. 
     The probe  410  is positioned at the desired inspection location by means of the positioning rod  121  while noting this position on the position readout box  103 . Sliding the positioning rod  121  into the bore hole moves the optical probe  410  further in the bore hole  508  and retracting it moves the probe  410  out of the bore hole  508 . Fine probe position adjustments are made by tightening the thumb screw  301  and turning the vernier hand wheel  302 . As a result, the slidable fixture positioner  126  of the present invention may be adapted for use in many areas. 
     Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing an illustration of the presently preferred embodiment of the invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.