Patent Document

[0001]    This application claims priority from Provisional Application No. 60/324,545 filed Sep. 26, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the field of fiber optic component assembly and more specifically to the area of a fast actuator for use in the alignment of fiber optic components.  
         BACKGROUND OF THE INVENTION  
         [0003]    The basic building blocks behind the fiber optic internet are optical network components, many of which internally use simple components such as lenses, filters, optomechanical parts and waveguide structures.  
           [0004]    For a fiber optical component (FOC) to be useable in an optical communication system at some point at least one fiber, usually an input fiber, must be attached to the FOC. During the assembly of FOCs at some point the light needs to be at least one of coupled into and out of the FOC in order for the FOC to be useable in a fiber optic communication network. Coupling of light into the FOC is accomplished via an optical fiber, which is aligned to a port on the FOC in order to deliver a predetermined amount of optical intensity into the FOC; and the light coming out of the FOC is aligned to an output fiber, or in the case of a multi-port device, output fibers.  
           [0005]    Coupling of an optical fiber to the FOC require a positioning mechanism for actively aligning of the fiber relative to the FOC. Typically this type of mechanism allows for translational motion of optical fiber in three orthogonal directions. For each axis, translating that axis results in the optical power changing as the coupling of light changes between the fiber and the FOC in response to the movement of the fiber.  
           [0006]    Typically during the process of aligning a FOC in three axis the Z-axis determines the focusing of the optical system and the X and Y directions ensure capturing of the light as the fiber is brought physically closer to the FOC during active alignment.  
           [0007]    During active alignment an axis becomes optimally aligned when translation in either direction from this optimum point results in the detected optical power coupling into, or out of the FOC to decrease.  
           [0008]    Upon optimizing of a single axis in this manner the procedure is repeated for all the other axes, until such a point is reached where all axes are optimally aligned. This operation is typically performed by a human operator actuating knobs to move the fibers.  
           [0009]    Conventional means of coupling fibers to FOCs utilize expensive high precision mechanical 3 axis positioning stages. Typically, these positioning stages offer high precision, high repeatability, high rigidity. The majority of these positioning stages utilize high precision roller bearings on precision ground hardened steel rails. Moving of the axes within the positioning stage is accomplished by actuating sub micron resolution micrometers for each of the axes. Coupling springs in a variety of orientations tightly hold the positioning stage together to take up any form of mechanical tolerance within the positioning stage mechanics so that the inaccuracies in the mechanics does not aversely affect performance during optical alignment. These stages are very precise and any orthogonal error to in an axis during movement is unnoticed. In order to provide sub micron accuracy, each of the stages is built in a very robust manner. This helps to reduce low frequency vibration. Unfortunately, this also results in very heavy assembly units that support arrays of stages.  
           [0010]    For these precision stages to be useful in an optical alignment setup, it is required that optical alignment setup be somehow dampened from external vibrations. Typically the FOC and positioning stages are rigidly fixed to an optical table. Optical tables are large rectangular structures made from steel plates with holes drilled on the upper surface for mounting of positioning stages as well as FOCs. These drilled surfaces are made to be very flat. In some cases these optical tables are mounted to floating leg assemblies to further dampen any vibrations that may be present in the floor so that these vibrations do not adversely affect the alignment process. Because of the sheer weight of these tables they offer good vibration compensation for the optical alignment setup, however have an added expense of weight, sized and cost.  
           [0011]    Not to mention that if a table needs to be moved from one lab space to another, heavy lifting equipment is often required. Therefore in times of expansion or cut back in a company, when equipment needs to be moved, these tables pose a large inconvenience. Additionally, when tables like this are moved the positioning stages are typically removed, relocated and reassembled. Optical breadboards are an alternate solution to optical tables, however typically they also require some form of vibration isolation during an optical alignment procedure.  
           [0012]    In some cases, assembly of FOCs is accomplished by using non-human means. In this case motorized actuators take the place of fingers moving knobs. A feedback signal indicative of the optical alignment of the fibers in relation to the FOC is generated in response to the motorized movement of external inputs on the positioning stages.  
           [0013]    Motors utilized for these stages may either take the form of rotary actuators or linear actuators. Rotary actuators typically have rotary encoders on armature ends to count pulses in order to provide a feedback signal indicative of how many rotations were made. Rotary actuators are typically either DC motor based or stepper motor based. With a stepper motoer a rotary encoder is not necessary since the rotation angle the stepper motor is proportional to the applied pulses. Stepper motors however are more expensive than DC motors coupled to shaft encoders. Of course, in order to achieve any form of precision with either rotary actuator, the rotor must be coupled to a gear box for speed reduction and to some form of a lead screw and thread mechanism. All of which lead to quite expensive, heavy and bulky positioning stage actuator mechanics.  
           [0014]    In order to reduce the number of mechanical components required within a positioning stage, manufacturers offer linear positioning stages. Within a linear positioning stage, such as that offered by Aerotech Inc., are a series of magnetic coils and fixed magnets forming a linear stepper motor. The linear stepper translates an axis of the actuator in response to a series of parallel pulses provided to the windings of the linear motor. Again, since a stepper motor is used, complicated control electronics are also employed in order to obtain precision alignment of light coupled into or out of the FOC.  
           [0015]    Piezoelectric actuators are also offered as actuators within linear positioning stage to precise provide motion. These actuators require high voltages, typically around 150V, and their controllable displacement is function of their mechanical length. For example if 150 V is applied to a 10 mm actuator about 0.1 mm of travel results. Position feedback is afforded by the change in capacitance as the actuator elongates. Again, using a feedback mechanism involves adding complicated control electronics to obtain precision alignment of light coupled into or out of the FOC.  
           [0016]    In fiber optic network component assembly it is preferable to have an actuator mechanism that is capable of precisely positioning the optical component at high speeds. It is also preferable to have a multi-axis actuator that is inexpensive such that the overall cost of purchasing and maintenance does not adversely affect profit margins. A system developed around electromagnetic coil actuators is ideal since these actuators are inexpensive to manufacture and require simpler control. Voice coil actuators have replaced stepper motors in hard drives because of the speed afforded by the voice coil as well as reduced manufacturing costs.  
           [0017]    To one skilled in the art at the time it is apparent that the current fiber optic component automation industry uses big, bulky, expensive, automated positioning stages to align FOCs. FOCs are small, precise, and low weight. Therefore using non-rigid electromagnetic actuators is ideal in aligning FOCs because of speed and precision, unfortunately the benefits gained from using such an actuator also result in an increased susceptibility to external forces. A trade off exists between quality of alignment, speed, and vibration. Such an actuator is susceptible to external forces, has a compact size, and is relatively inexpensive, all of which are quite contrary to that which is taught by the prior art.  
           [0018]    It is therefore an object of the present invention to provide a three axis actuator system for precision alignment of an optical fiber to a FOC that overcomes the deficiencies of the prior art.  
         SUMMARY OF THE INVENTION  
         [0019]    In accordance with the invention there is provided a three axis controllable component actuator comprising: a magnetic stator assembly having permanent magnets disposed therein and having a magnetic yoke assembly with a gap therebetween having magnetic flux therein; a carriage having electromagnetic coils wound around a first central and around a second central axis, the carriage flexibly mounted to the magnetic stator assembly with a portion of the electromagnetic coils disposed within the gap to permit controllable displacement of the carriage along at lease one of the first and the second axis in response to electric current flowing in the electromagnetic coils interacting with the magnetic flux within the gap; and, a linear actuator coupled to the magnetic stator assembly for moving the magnetic stator assembly in a substantially orthogonal direction in relation to the first and second axes.  
           [0020]    In accordance with an aspect of the invention there is provided a component actuator comprising:  
           [0021]    a first linear actuator having a first stator and a first actuatable shaft, the first actuatable shaft for being displaced in a direction along a first axis and with a distance in proportion to a first control signal having a polarity and a magnitude and applied to the first linear actuator; a first magnet coupled to the first actuatable shaft; and, a carriage magnetically coupled to the first magnet and other than fixedly coupled to the first linear actuator, for, in use, moving along an axis substantially parallel to the first axis in dependence upon the first control signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The invention will now be described with reference to the drawings in which:  
         [0023]    [0023]FIG. 1 is a perspective view of a prior art CD player lens focusing and tracking mechanism (FTM);  
         [0024]    [0024]FIG. 2 is a diagram of an electromagnetic controllable dual axis mechanism (ECM), similar to the FTM, coupled to a linear actuator;  
         [0025]    [0025]FIG. 3 is a perspective view showing the ECM coupled to a linear slide and a linear motor for use in a component alignment system;  
         [0026]    [0026]FIG. 4 is illustrates angular calibration of the ECM;  
         [0027]    [0027]FIG. 5 illustrates a reflective optical intensity positional calibration system for the carriage of the ECM;  
         [0028]    [0028]FIG. 6 shows a plurality of ECMs positioned with a common axis for aligning a plurality of components to each other; and,  
         [0029]    [0029]FIGS. 7 a  and  7   b  illustrate an alternative embodiment of a three axis component actuators actuated using linear actuators. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    In the below description directions are arbitrarily selected and are indicated as directions of travel parallel to an axis for linear axes and rotating about an axis for axes of rotation.  
         [0031]    Referring to FIG. 1, a prior art CD player focus and tracking mechanism (FTM), is shown. The FTM comprises a magnetic stator assembly  10 , having a magnetic yoke and having two magnets  13  disposed thereon, a carriage  11 , mounting wires  12 . The mounting wires  12  for flexibly mounting the carriage to the stator assembly as well as for conducting current to the electromagnetic windings  16  as part of the carriage  11 . A gap  19  is formed between the magnets  13  and the magnetic yoke, the gap  19  having magnetic flux therein. With no current applied to the electromagnetic windings  16 , the carriage is supported within the gap  19  using mounting wires  12  in such a manner that it does not touch the magnetic stator assembly  10 . Furthermore, the carriage  11  is spatially oriented by the mounting wires  12  within the gap  19  in such a manner so as to be able to be displaced proportionately in two substantially orthogonal axes upon the application of a control signal having a polarity and magnitude. In response to the control signal, the carriage linearly displaces proportionately to the applied control signal as the current in the coils reacts with the magnetic flux within the gap  19 . Thus, controllable motion of the carriages  11  is obtainable in the two substantially orthogonal axes. Namely, controllable horizontal displacement along an X direction  15 , as well as controllable displacement in a vertical, Y direction  14 . Unfortunately, the FTM assembly has no provision for controllable motion along the Z direction. In use within a CD player the FTM is mounted to a third motorized axis, in such an orientation that this third axis is parallel to one of the controllable axes of the FTM. Meaning, that unfortunately the device is unsuitable for three axis alignment since it lacks controllable motion along a third controllable axis that is oriented orthogonal to the X direction axis and the Y direction axis.  
         [0032]    In FIG. 2, an electromagnetic controllable dual axis mechanism (ECM)  29 , similar to the FTM of prior art FIG. 1, is shown. The ECM  29  has two substantially orthogonal electromagnetically actuated axes of displacement that displace a carriage  28  relative to a stator portion  27  of the ECM  29 . The stator assembly having a magnetic yoke with the magnets coupled therewith to permit a magnetic flux to reside in a gap therebetween. Electromagnetic coils coupled to the carriage have a portion thereof located within this gap. The stator portion  27  of the ECM  29  is coupled to a sliding portion  21  of a linear actuator bearing slider assembly  20  and  21 . The stator portion  20  of the bearing slider assembly is fixedly mounted to a plate  33  (FIG. 3). A linear actuator  22  is coupled to the stator portion  20  of the bearing slider in such a manner that upon receiving a control signal the linear actuator  22  slides the sliding portion  21  on bearing provided within the bearing slider assembly  20  and  21  in response thereto, resulting in displacement of the ECM  29  along an axis substantially orthogonal to the electromagnetically actuated axes of displacement of the ECM  29 . In use, when a control signal is applied to the windings of each of the coils wound about the carriage, a magnetic field is generated that interacts with the magnetic flux in the gap, resulting in movement of the carriage in response thereto.  
         [0033]    A variation of the embodiment shown in FIG. 2 is shown in FIG. 3. In this case similarly to that shown in FIG. 2. The ECM  29  is coupled to a linear actuator  22  in an orientation such that the resultant two electromagnetically actuated axes of displacement are substantially orthogonal to the axis of the linear actuator  22 .  
         [0034]    In use, the linear actuator  22  moves the slider assembly  21  along a Z direction in response to a control signal applied to the linear actuator  22  by a control circuit. Two optical components  34  and  35  are held by component holders  32  and  31 , wherein component holder  32  is stationary with respect to all axes of travel of the component holder  31 . Component holder  31  is coupled to the carriage  28  of the ECM  29 . It is therefore preferable to orient the optical component  35  on the mounting plate  24  of the ECM  29  in such a manner that the axes of the optical component  35  which require precise travel are those which are mounted parallel to the electromagnetically controllable axes of the ECM  29 , the third axis thus being utilized for coarse positioning of optical component  35  with respect to optical component  34 .  
         [0035]    Optionally, component holder  31  is coupled to the mounting plate with a small magnet  26  embedded within the carriage  28  for magnetically attracting a metallic portion of the component holder  31 . The mounting plate allows for various component holders  31  to be removably mounted to the carriage  28 . Preferably, precision alignment marks on both the mounting plate and component holders allow for repeatable positioning of the component holders. The orientation of the magnet  26  within the carriage  28  is advantageously provided in such a manner as to oppose the magnetic flux generated by the stator assembly  27 , thereby reducing a portion of the weight imposed on the carriage  28  by the optical component  35  when in use.  
         [0036]    In FIG. 4, the ECM  29  shown is adjustably mounted to a mounting plate  40 . The mounting plate  40  is coupled to the slider portion  21  of the linear slider assembly  21 ,  20  via a three point mounting system. A first mounting point is a pivot point (not shown) that enables pivoting of the ECM  29  about two and optionally three substantially orthogonal axes located at a center of the pivot point. The other three mounting points comprise of a calibration screw  41 ,  42 , and  43  and threaded portion. For calibration screws  41  and  42  a spring is disposed on or about the calibration screws  47  and  46  to bias the mounting plate  40  against the linear slider assembly  21 . Rotation of the calibration screws  41  and  42  results in angular movement of the ECM  29  about the first pivot point about at least an axis  45  that is preferably the X axis. Preferably the calibration screws  41  and  42  are adjusted in tandem to prevent rotation of the ECM  29  about the Z axis. Rotating the screw  43  results in angular movement of the ECM  29  about another axis  44 , preferably the Y axis. A biasing spring  48  is provided for biasing the mounting plate against calibration screw  43 .  
         [0037]    In the case in which the optical component is an optical fiber, angular degrees of freedom may need to be fine tuned using the calibration screws  41 ,  42  and  43 , in order to ensure that the optical fibers are substantially parallel with each other. Adding the optical component may cause angular misalignment of the carriage  39  due to the additional weight or due to the orientation the component. Thus, calibration screws are used to position the ECM  29  in such a manner that the controllable electromagnetic axes actuate as desired. In some cases additional flexible mounting is preferably added to aid in supporting the carriage  28  of the ECM  29  to provide additional biasing to the carriage.  
         [0038]    Preferably, in use, as the linear actuator  22  moves the ECM  29 , mechanical inaccuracies of the linear slide assembly  20  and  21  are actively compensated for by the active control of the ECM  29  in a feedback loop in combination with a control circuit.  
         [0039]    It would be also advantageous to provide an optical feedback assembly for determining the absolute position of the carriage  28  with respect to the stator portion  27 . An example of this is shown in FIG. 5. Effects such as vibration may offset the carriage  28  and the absolute position of the component  35 . Therefore, having an absolute position feedback mechanism for the carriage  28  would be advantageous. For the absolute position feedback mechanism for the carriage  28  a light source  55 , such as an inexpensive diode laser, is thus provided within the ECM  29  to emit light for reflecting off a reflective portion  57  of the carriage  28 . A detector  56  embedded within the stator  27  for use in receiving the reflected light from the carriage  28 . As the carriage  28  of the ECM  29  moves in relation to the stator  27  of the ECM  29 , the intensity of the light impacting the detector varies in an axis in a predetermined manner in dependence upon the position of the carriage  28  relative to the stator portion  27  of the ECM  29 . Thus with the use of a calibration table correlating reflected optical intensity to control signal magnitude, the position of the carriage  28  in relation to the optical intensity is determinable. Preferably, such an optical intensity position determining system is provided for sensing the position of the carriage in more than one axis of displacement.  
         [0040]    In FIG. 6, a plurality of ECMs  29  are shown, coupled to a same stator portion  20  of a linear actuator bearing slider assembly. Two ECMs are coupled to a same stator portion  20   a , and a single ECM is coupled to another same stator portion  20   b . Component holders  31  have V-grooves  51  aligned along a common Z axis, with each of the ECMs  29  optionally actuated with respect to the same stator portion  20  using linear motors  29 . Preferably, fine adjustment of angular position of the ECMs  29  is performed using the calibration screws prior to use in optical alignment of optical components.  
         [0041]    In FIG. 7, an alternate embodiment of the invention is shown using three linear motors  72  having an output shaft  70  of each fixedly coupled to a magnet  71 . The three linear motors are preferably oriented orthogonally to each other and mounted to a common mounting plate (not shown). The magnets  71  from all three axes are magnetically attracted to a carriage  73 . The carriage  73  is displaced in an axis substantially parallel to the orientation of the linear motor  72  upon the application of a control signal having a magnitude and polarity to the linear motor  72  oriented along that axis. Motion of the carriage  73  along a controlled axis causes the carriage  73  to slide past the magnets  71  of the other stationary axes. Due to the magnetic attraction between the carriage  73 , the magnet  71  and the output shaft  70 , the carriage  73  is maintained in a substantially parallel orientation to all three axes even during motion of any axis. This arrangement allows for controllable displacement in directions substantially parallel to the three actuated axes without the need for expensive linear slide mechanisms.  
         [0042]    The use of an actuator mechanism such as that described herein provides active alignment of components. Because of the dynamic nature of such a system, it allows for compensation of variations in alignment due to temperature changes, epoxy hardening, solder expansion, fusing processes, and other effects resulting during a process of affixing aligned components one to another. Advantageously, such an alignment system thus provides for improved alignment speed as well as significant cost reduction over conventional alignment system designs.  
         [0043]    Numerous other embodiments may be envisaged without departing from the spirit or scope of the invention.

Technology Category: 3