Abstract:
Demand is growing for affordable advanced sensor systems for use in counter-terrorism, criminal forensic analysis, and medical diagnosis. Next generation, million RPM class laser interferometry and spectrometry scanning systems are the ideal solution for this need due to their inherent ability to detect and identify microscopic quantities of evidence and resolve microscopic detail however a means to produce these systems with sufficient precision efficiently and inexpensively has been elusive. The scanning head is the heart of the system and in order for scanning heads of million RPM rotational speed class to be precisely aligned and balanced at operational speed they must be assembled while rotating. To facilitate this, a fully integrated feed-back based assembly system that measures and corrects optical alignment and balance of the scanning head during final assembly has been devised that subsequently enables economical high-precision, high production rate assembly.

Description:
FIELD 
       [0001]    This invention relates to the field of ultra-high definition laser interferometry and spectrometry. Specifically, a method and means for the manufacturing, produce-ability and assembly of scanning heads in the rotational speed class of over one million rotations per minute, including subcomponents that simultaneously satisfies the technical requirements for ultra-high speed scanning along with cost and assembly rate characteristics sufficient to enable economic viability. 
       BACKGROUND 
       [0002]    Potential customers of new ultra-high speed scanning systems have communicated a clear need for low unit cost given the anticipated quantity of devices needed for world-wide counter-terrorism efforts. A limiting factor in the practical and economical implementation of prior art ultra high speed (million RPM class) scanning systems is an assembly method for the most sensitive components that provides the necessary tolerance and precision required for high speed, high fidelity measurements, and production rates and efficiencies needed for low cost. This invention presents a viable method for efficient and economical manufacture of prior art ultra high speed scanning heads, which are the critical component of the prior art ultra high speed scanning system. 
         [0003]    While the magnitude of scanning and therefore assembly precision is established by the highest speed scanning heads, this method and means is readily adaptable to lower speed scanning heads. 
       SUMMARY 
       [0004]    In accordance with an embodiment of the present invention, a scanning head includes a crystal, crystal housing, and drive system components. An assembled and fully balanced scanning head is the product of the process. 
         [0005]    A feedback based autonomous process is employed to assemble the crystal and crystal housing. The primary components and key aspects of the assembly process are summarized as follows. The crystal housing, drive shaft and motor are assumed to be pre-assembled and dynamically balanced up to the design speed of the system including factors of safety at this stage of the process. 
         [0006]    A specialized, computer controlled adhesive applicator applies a spatially calibrated quantity of adhesive into the crystal housing. The adhesive applicator tip is of modular configuration, so that crystal housing recesses of differing geometries. Preferred adhesives for this method include slow-cure high tensile strength adhesives to support the demands of ultra-high rotational speed; and new advanced adhesives whose cure process can be controlled by external stimuli such as ultraviolet light. A high precision robotic device is used to transport the crystal from the supply source and insert it into the recess in the crystal housing without depressing force once the crystal housing recess is impregnated with adhesive. 
         [0007]    A crystal alignment and leveling system consisting of a plurality of pressure instrumented and feedback controlled probes is positioned above the inserted crystal and then lowered to a calibrated contact position. The tips of the positioning probes can have different configurations. For lower rotational speeds, softer crystal materials, or low production applications where infrequent service is required the preferred probe tip configuration assumes a low friction compound such as Teflon. For applications where crystal wear and damage could be a concern due to higher rotational speeds, choice of crystal material, or where long and continuous production is required the preferred probe configuration contains high-pressure gas jets which impart force on the crystal via pneumatic pressure to correct the displacement and laser beam trajectory. 
         [0008]    The balancing process is initiated by rotating the crystal housing at high speed. The preferred rotational curing speed avoids adhesive centrifuging and system mechanical resonances. While under rotation a laser or plurality of laser sources projects a beam or beams into the center of the crystal. A plurality of laser receptors is positioned in the path of the reflected laser beams. The receptors provide multi-dimensional beam trajectory data to a computer which compares actual trajectory to a perfectly aligned trajectory. The computer then calculates corrective displacements to the positioning probes which exert force on the crystal to correct the laser trajectory. Once a fully corrected trajectory is achieved the system maintains rotational speed and crystal position until the glue is fully cured. 
         [0009]    The process for UV or other adhesive curing through light radiation is comparable with the exception that the curing light application process is integrated with the laser light trajectory correction system. Specifically, the integration includes sequencing logic both to prevent interference between the UV curing light and the laser radiation, and also to tailor the curing characteristics of the adhesive for optimal balancing. The curing light also has strategic focusing capability so that critical adhesive regions can be cured, thereby maximizing balance precision. Once cured, the completed crystal housing and crystal assembly is ready for distribution and incorporation into the scanning system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0011]      FIG. 1  is a top view depiction of several prior art crystal housing recess shapes along with isometric views of the crystal housings with their corresponding preferred modular adhesive applicator; 
           [0012]      FIG. 2  is a schematic diagram of the comprehensive crystal alignment system including the laser light source, alternate light curing source, crystal housing transport system, crystal transport and insertion system, crystal drive system, integrated laser trajectory measurement system, adhesive applicator transport system, adhesive applicator, crystal displacement system, CPU, and a prior art crystal and crystal housing assembly; 
           [0013]      FIG. 3  is a 2-D cross-section of the crystal positioning probes. 
           [0014]      FIG. 4  is a 2-D cross-section of a prior art crystal and crystal housing assembly connected to a high speed crystal housing drive system with multi-axes imbalance sensor. 
           [0015]      FIG. 5  is a 2-D cross-section of a prior art crystal housing with misaligned prior art crystal, laser trajectory sensors, and crystal displacement probes; 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0017]    The key systems of this invention are the integrated adhesive applicator assembly  56 ,  58 ,  60 ,  62   FIG. 1 , and the comprehensive integrated high-precision crystal displacement alignment system  FIG. 2  and crystal displacement systems  78   FIG. 3 . The final product  FIG. 4  includes a crystal  48 , attached to a crystal housing  50  with a thin layer of adhesive  54  that is operatively attached to a drive system  52  of preferred angular resolution capability of less than 0.1 degree, a multi-axes vibration sensor  108 , and drive system  52  program logic within CPU  74  that has fully variable speed control with reverse capability and high speed rotation during final cure. 
         [0018]    The adhesive applicator  56  system of  FIG. 1  utilizes a plurality of modular applicator tips  58 ,  60 ,  62  that are tailored to enable even adhesive  54  application to crystal recesses of arbitrary shape  64 ,  66 ,  68 , and also to enable convenient replacement in the event the tip  70  becomes clogged. The preferred width of the applicator tip  70  is two percent less than the minimum characteristic dimension of the crystal housing recess  72  to allow for insertion clearance and reduced overall process time. 
         [0019]    The principle elements of the comprehensive integrated crystal positioning apparatus of  FIG. 2  are the crystal housing  50 , crystal housing drive system  52 , CPU  74 , adhesive application system transport carriage  104  with adhesive applicator  56  and modular tips  58 ,  60 ,  62 , crystal positioning system transport carriage  76  with crystal displacement system  78 , a plurality of positioning laser(s)  80 , a plurality of laser receptors  82 , an optional adhesive curing light  84 , robotic crystal housing transport arm  103 , and the robotic crystal transport and insertion system  105 . 
         [0020]    The preferred quantity of crystal displacement systems  78  is equal to the quantity of laser receptors  82 . The preferred orientation of the crystal displacement systems  78  is such that each individual displacement system is equidistant angularly relative to the center of the crystal  48  between the laser receptors  82 . All of these elements are operatively connected to and controlled by the CPU  74 . The CPU  74  is programmed with algorithms that perform the integrated functions of precisely dispensing metered quantities of adhesive  54 , controlling the crystal housing drive motor  52 , and aligning and balancing the crystal  46 . 
         [0021]    The crystal displacement systems  78  of  FIG. 3  are of two preferred configurations. The primary type of displacement system exerts direct pressure on the crystal  48  via physical contact. Friction and abrasion between the displacement probe  85  and the crystal  48  is minimized by use of a low friction material on the tip  86  such as Teflon. This probe is also equipped with a displacement measuring probe  88  that is operatively connected to the CPU  74 . The displacement measuring probe  88  utilizes non-interfering signal and signal detection systems such as ultrasound, as a laser based system could interfere with the crystal positioning lasers  80 . The preferred displacement precision for the mechanical contact probes  86  is micrometer precision. The second type of positioning probe is a pneumatic probe  90  that uses gas pressure to displace the crystal  46 . The preferred gas is a heavy inert gas in order to exert maximum displacement force and avoid any unnecessary introduction of Oxygen or other reactants into the system. Preferred gasses include Argon or Krypton however Nitrogen can be considered to reduce cost if it is inert relative to other components. 
         [0022]    Gas pressure is controlled or throttled via valves  94  and controlled throat  96  area capability. The pneumatic probe also utilizes the same type of displacement measurement probe  88  as the direct contact displacement probe. Linear Variable Differential Transformer systems  89  are shown both for actuation of the contact probe  108  and the throat  96  plug however other displacement technologies can be used if greater performance, control and precision are possible. 
         [0023]    When use of light cured adhesives is preferred either of the previously discussed positioning systems can be used, with the exception that they are augmented with a integrated curing light source  98  that is operatively connected to the CPU  74 . For crystal displacement with direct physical contact a shorter displacement probe  85  is used to accommodate an embedded curing light source  98 . The Teflon tip  86  is replaced with a transparent material such as highly-polished diamond  100 . Natural or synthetic diamond is acceptable. The second option attaches an adhesive curing light source to the side of pneumatic nozzle  90 . The curing light source  98  is focused at the point of contact. 
         [0024]    The crystal alignment process follows. At the very beginning of the process an integrated robotic crystal housing transport arm  103  operatively connected to the CPU  74  acquires a pre-assembled empty crystal housing  50  and drive assembly  52  from their supply source and transports them into position. The adhesive applicator control arm  104  positions the applicator assembly  56  with pre-selected applicator tip  58 ,  60 ,  62  at its pre-defined reference point within the crystal housing  50  recess. For polygon crystal housing  50  recesses  64 ,  68  the reference position point for the adhesive applicator is identified as the position where the applicator tip is against one side of the crystal housing  50  recess  64 ,  68 . For circular recesses  66  the center of the crystal housing  50  is the reference position. For all types of crystal housings  50  the vertical component of reference point is one millimeter above the bottom, or floor of the crystal housing  50  recess  64 ,  66 ,  68 . 
         [0025]    Two primary adhesive application programs are employed and administered by the CPU  74 . The Polygon program can be generally described as a sequence of inwardly directed adhesive strokes that number in the same quantity as the number of polygon faces. Specifically, once positive adhesive flow is indicated the adhesive applicator control arm pulls the applicator toward the center of the crystal housing  50  recess  64 ,  66 ,  68 . The quantity of adhesive is decreased as the applicator approaches the center of the crystal housing  50  recess  64 ,  66 ,  68  to ensure even application and prevent adhesive buildup in the center of the housing. When the center of the crystal housing  50  recess  64 ,  66 ,  68  is reached a slight vacuum is applied to the applicator assembly  56 ,  58 ,  60 ,  62  to eliminate dripping and then the repositioning sequence commences. During this repositioning sequence the applicator assembly  56 ,  58 ,  60 ,  62  is raised and the crystal housing drive motor  52  rotates the crystal housing  50  until the next face of the polygon within the recess  64 ,  68  is aligned. When the adhesive application is totally complete a slight vacuum is applied again to the applicator assembly  56 ,  58 ,  60 ,  62  and the adhesive applicator control arm  104  retracts the applicator assembly  56 ,  58 ,  60 ,  62  and positions the applicator assembly  56 ,  58 ,  60 ,  62  in an inerting chamber charged with inerting gas specific to the preferred adhesive  54  that prevents curing while the crystal  48  is being positioned. The inerting gas can be temperature controlled if this further assists cure prevention. 
         [0026]    At the same time the adhesive  54  application begins the integrated high-precision robotic crystal transport and insertion system  105  obtains a crystal  46  and positions it at a holding position close to the adhesive application system  56 ,  58 ,  60 ,  62 . Once the adhesive application process is complete the crystal  46  is immediately inserted into the recess  64 ,  66 ,  68  and the crystal transport arm  105  is retracted. The preferred insertion orientation is parallel with the floor of the crystal housing  50  recess  64 ,  66 ,  68  and the preferred insertion orientation depth is sufficient for the adhesive  54  just to make initial contact with the under-side of the crystal  48 . 
         [0027]    At this time the positioning probe transport carriage  76  transports the crystal displacement systems  78  to the reference point directly above the surface of the crystal  46 . The probes  78  are lowered to a point of initial contact and the laser  80  is activated as represented in  FIG. 5 . Once laser signals are detected at all of the laser receptors  82  the alignment/balancing program is initiated and the crystal housing  50  begins to turn. Once the rotational speed is stable the system evaluates imbalance via sensors  108  located on the crystal drive system  52  and misalignment via laser receptors  82 . If imbalance modes are sufficient to be observed in the laser receptors  82  the program is terminated and the items being assembled are discarded. If the imbalance stays within acceptable ranges the program in the CPU  74  records error alignment displacements  106  and calculates corrective crystal  48  displacements and applies via the crystal displacement systems  78 . The corrective crystal  48  displacements are all triggered at the same time to prevent adhesive elastic  54  crystal  48  counter-displacement reaction. While the corrective displacement signal given to the crystal displacement probe  78  is calculated to offset the measured alignment displacement  106 , the adhesive  54  may exhibit some slight elastic reaction behavior before it cures. The continued application of corrective displacements ensures a fully corrected position when the adhesive  54  is set. Success criteria is achieved once all of the laser detectors  82  are indicating measured displacement error  106  is preferably less than one-tenth of desired measurement resolution and the multi-axis vibration detector  108  on the crystal housing drive system  52  reflects out-of-balance force magnitudes preferably less than 0.00001 of the standard g-force for the maximum design rotational speed. Greater imbalance can be accepted as the crystal  48  rotational design speed is decreased however minimum imbalance is always preferred. If the crystal  48  is fully aligned yet the assembled system remains to be out of balance the product is rejected. 
         [0028]    A novel provision of this invention is the option for use of light-cure adhesives. In this provision, the adhesive  54  is applied using the exact same process as conventional adhesives. The main difference comes in the design of the crystal displacement systems  78 . To take advantage of light-cure adhesive, curing must occur at the precise time that optimal alignment and balance is achieved. To facilitate this, two designs are employed. 
         [0029]    For contact-based crystal displacement probes  78  using light cure adhesive a shorter displacement probe  85  is fitted with an integrated curing light source  98  operatively connected to the CPU  74  for the light cure adhesive  54 . The Teflon tip  85  is replaced with a non-abrasive round clear cap  100 . The cap  100  is preferably made of polished diamond however alternative materials can be considered provided the general requirements for light transmission and surface smoothness are met. 
         [0030]    For pneumatic displacement probes  78  utilizing light cure adhesive, each nozzle  90  is fitted with an integrated curing light source  98  that is focused at the center of the point of where the gas-jet impacts the crystal  48 . For both contact and pneumatic applications an additional array of curing flood-lights  84  is positioned for final adhesive  54  cure once the localized cure is accomplished by the positioning probe lights  98 . 
         [0031]    The adhesive curing light sources  84 ,  98  are operatively connected to the CPU  74 . Specifically, once the CPU  74  has calculated that the crystal displacement probes  78  have properly aligned the crystal  48 , the adhesive curing lights  98  at the probe tips  100  are actuated to provide rapid localized adhesive curing light to fix the alignment of the assembly. Once alignment is verified the crystal is flooded with curing light  84  to solidify the adhesive layer. To ensure prevention of interference between the positioning lasers  80  and curing lights  84 ,  98  the controls of both have phasing logic that enables synchronized light application. Furthermore, for all crystal displacement systems  78 , CPU  74  has protection logic. Specifically, if for any reason the adhesive  54  cures prematurely or incorrectly the process will cease and the assembled parts are rejected. The CPU  74  can determine this for example if the crystal  48  displacements measured by the displacement sensors  88  cease to change and a misalignment  106  or imbalance via the multi-axes imbalance sensor  108  is still indicated.