Abstract:
A system for verifying the location of physical features on complex magnetic elements, such as magnetic rotors, for driving an electrostatic shutter. A magnetic rotor of the type measured by the magnetic measuring apparatus of the invention has a plurality of magnetic poles and physical features arranged thereon. Each one of both the magnetic poles and physical features has a spatial and magnetic field relative to one another which is rapidly measured by the magnetic measuring apparatus using a dual probe Gaussmeter and encoder means operably connected to a data comptroller.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to U.S. Application Ser. No. 09/420,825, filed Oct. 19, 1999, by Svetlana Reznik and Gary R. Kenny, and entitled, “Method Of Inspecting A Complex Magnetic Element;” and U.S. Application Ser. No. 09/420,828, filed Oct. 19, 1999, by Svetlana Reznik and Gary R. Kenny, and entitled, “Apparatus For Testing Complex Magnetic Elements.” 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of magnetic field measuring systems. More particularly, the invention concerns a system capable of verifying the location of physical features on a complex magnetic element such as miniature multi-pole, high energy, magnetic rotors that drives electromagnetic camera shutter actuators. 
     BACKGROUND OF THE INVENTION 
     Miniature bipolar cylindrical magnets are used as the drive element (rotor) in electromagnetic components such as electromagnetic camera shutter actuators. To ensure proper and reliable shutter performance, the polarization (operating point) and orientation of the magnets need to be controlled to a high degree of accuracy. However, during the mass production of these magnets significant variations occur in both of these characteristics. These variations are due to non-uniformity&#39;s of the bulk materials from which the magnets are cut and from variations in the magnetizing field strength over the group of magnets that are bulk magnetized. Moreover, experience indicates that it is difficult, if not impossible, to eliminate both of these causes. 
     There have been several attempts to provide an apparatus and method for rapidly determining de magnetization and orientation for purposes of selecting only those magnets that have acceptable values. 
     Referring to FIG. 1, one such existing apparatus  1 , disclosed in Research Disclosure No. 37841, dated October 1995, comprises a rectangular ferromagnetic core  11  with two gap regions  2  and  3 . A field sensor  4  is positioned in gap region  3  that is connected to a Gaussmeter  5 , and a first angular meter device  6 . First angular meter device  6  further comprises a first needle pointer  7  connected to a first support member  8  that is mounted for rotation about a pivot axis  9 , and a marked scale  10  for determining the angular deflection of the first needle pointer  7  from the vertical straight up position (illustrated in FIG.  1 ). The ferromagnetic core  11  and the first angular meter device  6  are mounted on a frame  12  that is constructed from a non-magnetic material such as aluminum. The core  11  is fixed to the frame  12  whereas the first angular meter device  6  is mounted for translation along the frame  12  as indicated by the solid arrow in FIG.  1 . 
     Referring to FIG. 2, a second prior art apparatus  14  (also disclosed in the above referenced Research Disclosure) for rapidly determining the orientation of miniature bipolar magnets for purposes of selection for assembly is illustrated. According to FIG. 2, the apparatus  14  comprises a second angular meter device  16  that is mounted for linear translation relative to a stationary member  18 . The second angular meter device  16 , made from non-magnetic material, comprises a second needle pointer  20  connected to a second support member  22  that is mounted for rotation about a pivot axis  24 . As shown in FIG. 2, second angular metering device  16  further includes a marked scale  26  for determining the angular deflection of the second needle pointer  20  from its detent position. The second support member  22  which is mounted for rotation has a top portion (not shown) that is designed to hold a miniature bipolar magnet that is to be tested. The stationary member  18  is made from non-magnetic steel and comprises a base  28 , and support structure  30  which supports two ferromagnetic pole pieces  32   a  and  32   b  that are in a spaced-apart relation. The second angular meter device  16  is mounted for translation as indicated by the dotted arrow in FIG.  2 . 
     Referring again to FIG. 1, an existing method for evaluating the polarization and orientation of miniature bipolar magnets  40  include the step of initially providing first angular meter device  6  in position A, separated from core  11 . A miniature bipolar cylindrical magnet  40  is mounted on first support member  8  of first angular meter device  6  with its “anticipated” north pole  40   a  vertically up. In this initial position, first needle pointer  7  is straight up indicating 0 degrees of deflection on the marked scale  10 . The first angular meter device  6  is then moved to position B as illustrated until the magnet  40  is symmetrically positioned in gap region  2  of core  11 . The magnet  40  will then align itself in the gap  2  so that its “true” north pole  40   a  is symmetrically positioned with respect to tapered pole tip  2   a.  If the “true” north pole  40   a  is offset in an angular sense from the “anticipated” north pole, the magnet  40  will rotate and first needle pointer  7  will deflect indicating the angular offset on the marked scale  10 . In this way, the orientation of the magnet  40  is determined. Once the magnet  40  has oriented itself, it comes to rest. In its rest position, the flux from the magnet  40  passes through the core  11  and is directed through gap region  3  where the field sensor  4  is located. The field through the sensor  4  is registered on Gaussmeter  5 . This registered field value is compared to a calibration field value from a known magnet. In this way, the magnetization of the magnet  40  is determined. Depending on the results of the test, the magnet  40  is either accepted or rejected. 
     A shortcoming of the aforementioned existing apparatus and method for screening bipolar magnets  40  is that they do not have the ability to verify manufacturing variability and magnetization in complex magnetic rotors. More importantly, existing apparatus and methods, as described above, do not have the ability to compare magnetic flux density of a magnet with angular position or angular position of certain post features with reference to magnetic poles. Moreover, existing models do not have the ability to display acquired data and then compare such data with predetermined calibrated complex magnetic elements, such as magnetic rotors. 
     Therefore, a need persists in the art for a measurement apparatus and method that can generate specific magnetic flux and angular position data of bipolar miniature magnets for determining their acceptability for use in electromagnetic components, such as high speed shutter applications. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the invention to provide a system capable of verifying manufacturing variability and magnetization in complex magnetic elements, such as magnetic rotors for driving electromagnetic components. 
     It is another object of the invention to provide a system that correlates physical features to angular positions of magnetic poles arranged on a complex magnetic element, such as a magnetic rotor. 
     Still another object of the invention is to provide a system that produces and displays multiple data arrays including relative angular positions of each point, magnetic pole flux density and post magnetic flux density. 
     Yet another object of the invention is to provide a system that simultaneously measures the radial components of a magnetic field even when spatial separation between magnetic poles is less than 1 mm, and the magnetic element has a complicated 3-dimensional shape. 
     Yet another object of the invention is to provide a system that can produce measurement results in a relatively short time. 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a system measures magnetic properties of each one of a plurality of magnetic poles and each one of a plurality of physical features arranged on a complex magnetic element having a fixed reference feature thereon. The system includes means for rotating the magnetic element so as to continuously expose each one of the plurality of magnetic poles and each one of the plurality of physical features to a measurement of magnetic flux. An encoder means, operably connected to the means for rotating, generates a first signal corresponding to an angular position of each one of the plurality of magnetic poles relative to a predetermined one of the plurality of physical features. In this application of the system, angular position defines the location of the predetermined physical feature. Means for measuring magnetic flux is positioned proximate to the magnetic element. Important to the present invention, the means for measuring has a first and second magnetic flux measuring probe. The first magnetic flux probe, when in contact with the rotating magnetic element, as described, generates a plurality of second signals each one of which corresponds to a first magnetic flux value associated with each one of the magnetic poles. Similarly, the second magnetic flux measuring probe generates a plurality of third signals each one of which corresponds to a second magnetic flux value associated with each one of the plurality of physical features. Finally, a data controller, in operable connection with both the encoder means and means for measuring magnetic flux, acquires and then analyzes the first, second and third signals. 
     Therefore, the measurement system of the present invention has several important advantages over current development. In the first instance, the system of the invention is a unique spatial non-predictive magnetic field measurement device unlike existing apparatus. Further, it correlates physical rotor features relative to the magnetic pole position. Also, it provides an isometric visual display of magnetic field. Moreover, it simultaneously measures the radial components of a magnetic field even when distance between poles are less than 1 mm, and magnetized rotor has a complicated 3-D shape. Still further, it provides easy data storage and retrieval in color hardcopy printout. The present invention provides rapid measurement results in just a few minutes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
     FIG. 1 is a prior art apparatus for evaluating the polarization and orientation of miniature bipolar magnets; 
     FIG. 2 is another prior art apparatus of the type shown in FIG. 1; 
     FIG. 3 is a perspective view of a magnetic rotor and partial electromagnetic shutter actuator; 
     FIG. 4 is a perspective view of the magnetic rotor having a plurality of magnetic poles and a plurality of physical features; 
     FIG. 5 is a schematic diagram of a preferred embodiment of the measurement apparatus of the invention; 
     FIG. 6 is a schematic diagram of the operational sequence of the apparatus of the invention used for testing complex magnetic elements; 
     FIG. 7 is an output display graph of results produced by the apparatus of the invention for an “acceptable” magnetic element; and 
     FIG. 8 is another output display of results produced by the apparatus of the invention for a “rejectable” magnetic element. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and in particular to FIGS. 3-4, magnetic properties of a complex magnetic element, such as magnetic rotor  50  for driving an electromagnetic shutter  70 , may be measured with magnetic test apparatus  100  (described fully below) of the invention. Magnetic rotor  50 , having a generally cylindrically shape, has a plurality of outwardly extending physical features or posts  52  spatially separated and arranged along a first peripheral edge  54 . According to FIG. 4, a plurality of magnetic poles  56  is arranged about the circumference of magnetic rotor  50 . Further, an outwardly extending stop tab  58  is arranged on a second peripheral edge  60  of the magnetic rotor  50  preferably opposite the plurality of outwardly extending physical features  52 . 
     Generally cylindrical magnetic rotors  50  magnetized with a plurality of magnetic poles  56 , for instance  36  or more, are used in applications such as magnetic zoom/shutters  70 , as shown in FIG.  3 . 
     Referring again to FIG. 3, what makes applications of magnetic rotor  50  so complex is that in addition to the multiple closely spaced magnetic poles  56 , these magnetic rotors  50  require additional physical features  52  (such as posts) and a tab  58  that must maintain proximity to the magnetic poles  56 . For example, the magnetic rotor  50  depicted in FIG. 3 has four (4) posts or physical features  52  located 90 degrees apart on the top peripheral edge  54  of the cylinder and one tab  58  located on the bottom peripheral edge  60  of the cylinder. 
     Referring to FIG. 5, to achieve optimum system performance, a unique and unobvious magnetic test apparatus  100  was designed to verify the manufacture and magnetization of complex magnetic rotors  50 , as described above. Importantly, magnetic test apparatus  100  simultaneously yields a host of desirable and some unexpected results as described below. 
     According to FIGS. 7 and 8, magnetic test apparatus  100  verifies the manufacture and magnetization of the magnetic poles  56  on magnetic rotor  50  by measuring spatial separation (d) between a predetermined one of a plurality of spaced apart physical features  52  and one of a plurality of magnetic poles  56 . As indicated, physical features  52  and magnetic poles  56  are each arranged on a multi-pole magnetic rotor  50  (as described above). As depicted in FIG. 4, each one of the magnetic poles  56  has a fixed angular position relative to a predetermined one of the physical features  52 . 
     Referring again to FIG. 5, magnetic test apparatus  100 , broadly defined, includes motor/encoder means  104  for rotating the magnetic rotor  50  so as to continuously expose each one of the plurality of magnetic poles  56  and each one of the physical features  52  to a measurement of magnetic flux. A rotatable fixture (not shown) is provided to mount magnetic rotor  50  for rotation. In the preferred embodiment, means  104  for rotating magnetic rotor  50  is a DC motor drive coupled with a  5000  line graduated encoder means (described below). 
     The motor/encoder is preferably a Model H3007 made by Electro-Craft located in Eden Prairie, Minn. is used to determine the angular position of each one of the magnetic poles  56  relative to a predetermined one of the plurality of physical features  52 . The angular position defines the location of a predetermined physical feature  52  relative to the predetermined magnetization pattern of the magnetic element as defined by the pairs of magnetic poles  56 . 
     Operably connected to the motor/encoder means  104  is a Gaussmeter  106  that provides the means for measuring magnetic flux. Gaussmeter  106 , preferably one made by F. W. Bell Co., located in Orlando, Fla., has dual Hall effect probes  108 ,  110 . In the preferred embodiment, first Hall effect probe  108  is used for measuring a first magnetic flux value associated with each one of the magnetic poles  56 . Second Hall effect probe  110 , in the preferred embodiment, is used for measuring a second magnetic flux value associated with each one of the plurality of physical features  52 . For analytical purposes, the first magnetic flux value, second magnetic flux value and angular position collectively define a data array. 
     Further, a data controller  102  for acquiring and then analyzing the data array connects with all of the components of the magnetic test apparatus  100 , as shown in FIG.  5 . We prefer for convenience using an IBM PC  300  PL as the data controller means. A DAQ card installed in PC  102  is used to capture the various data. LabView™ software with proprietary algorithm linked to the PC  102  provides the angular position of each point, magnetic flux values of the magnetic poles  56  and the physical features  52  of the complex magnetic part  40 , and is drawn graphically. A personal computer interface (PCE) compatible DAQ (data acquisition) card is used to acquire and capture data. 
     A quadrature decoder  114  connected to motor/encoder means  104  (shown in FIG. 5) that produces 20,000 pulses per revolution is used to trigger the data controller  102 . We prefer a quadrature decoder  114  model no. LS 7083 made by LSI Computer System, Incorporated of Melville, N.Y. This chip is preferred because of its compatibility with the other components of the invention. The quadrature decoder is connected to the data controller  102  via a connector box  112 , preferably a Nations Instruments CA-100 connection box. 
     The measurement process begins with placing the magnetic rotor  50  on a rotatable fixture or spindle (not shown). As shown in FIG. 4, The tab  58  of the magnetic rotor  50  is used to establish and approximate the rotational position of magnetic rotor  50 . The motor/encoder means  104  is instructed to begin rotation. The data controller  102  is initiated with the quadrature index pulses. Each time a pulse is generated data is collected and stored. The magnetic rotor  50  is over-sampled, i.e., repeat sampled for verification, through one and a quarter revolution. The data array is searched for the first positive going zero cross-over, i.e., first change in polarity between adjacent magnetic poles, after one of the plurality of physical features or post  52  location has been determined by the second Hall probe  110 . Twenty thousand data points representing one full revolution of magnetic rotor  50  is stored beginning from the first zero cross-over. 
     A commercial software package, BRU Master  64  made by Electro-Craft is used for motor parameter control. BRU Master was selected because of its convenience and it has a complete set of easy to understand windows available from its pull down menus. Moreover, the BRU Master package provides indexing functionality that is important to our magnetic test apparatus  100 . Importantly, the BRU Master  64  package enables the magnetic rotor so to be mounted on the spindle without requiring precision alignment, thus avoiding costly tooling and additional labor to do the initial alignment. The magnetic field measurements are relative to the positions of the magnetic poles  56 . Since data is triggered by the motor/encoder means  104 , the angular position of each magnetic pole  56  is easily determined. The data array contains three data sets (relative angular position of each point, magnetic pole flux density, and post flux density). The array is processed for each measurement requirement. The program displays a pass/fail screen, as well as detailed graphs and data parameters. The program is also required to accept calibration parameters. By using this simple, inexpensive, and easily manufacturable magnetic test apparatus  100 , all measurement requirements are done in a few minutes, moreover, it is ideal for the large-scale selection of multipole complex shape magnets  50  for mass production. requiring precision alignment, thus avoiding costly tooling and additional labor to do the initial alignment. The magnetic field measurements are relative to the positions of the magnetic poles  56 . Since data is triggered by the encoder means  112 , the angular position of each magnetic pole  56  is easily determined. The data array contains three data sets (relative angular position of each point, magnetic pole flux density, and post flux density). The array is processed for each measurement requirement. The program displays a pass/fail screen, as well as detailed graphs and data parameters. The program is also required to accept calibration parameters. By using this simple, inexpensive, and easily manufacturable magnetic test apparatus  100 , all measurement requirements are done in a few minutes, moreover, it is ideal for the large-scale selection of multipole complex shape magnets  50  for mass production. 
     Turning to FIG. 6, the operational sequence for testing a complex magnet  50  with the magnetic test apparatus  100  of the invention is illustrated. As indicated, once the magnetic element or magnetic rotor  50  is mounted for testing and rotation, an arbor (not shown) is directed to rotate the magnetic rotor  50  vis-a-vis&#39; system start-up sequence  116 ,  118 ,  120 . Computer  102  initiates the test (via process  122 ,  124 ) by causing the rotation of the magnetic element and receives signals from Gaussmeter  106  indicating magnetic flux values from either of probes  108  and  110 . These magnetic flux values are then stored in computer  102  for later processing. Computer  102  is then programmed by making unput via keyboard  103  to retrieve and analyze data and display (via monitor  107  or printer  105 ) either a pass or fail decision for the magnetic element  50  under test. 
     Example of Magnetic Rotor Test 
     Referring to FIGS. 7 and 8, the magnetic test apparatus  100  of the invention was used to test several complex magnetic rotors  50 . Apparatus  100  simultaneously measures the magnetic flux of the magnetic poles  56  and physical features  52  of the multipole magnetic rotor  50 . An analysis of the signals generated, as discussed above, provides data for accepting or rejecting the magnetic rotor  50  being tested. According to FIGS. 7 and 8, the magnitude (denoted by the heights of the peaks) of the magnetic fields (in gauss) is displayed at any one of the positive and negative magnetic poles  56  and at physical features  52 . This data is then compared with a computer modeled prediction or a preferred magnetization pattern. According to FIG. 7, an acceptable tested magnetic rotor  50  tested with the apparatus  100  of the invention is illustrated. Based upon the magnitude and uniformity of the peaks and the calculated value of a predetermined physical feature  52 , the graph display confirms that the test results of the magnetic rotor  50  meets all the predetermined test specifications. 
     With respect to FIG. 8, a graph of a rejected magnetic rotor  50  is illustrated. According to the operations of our test apparatus  100 , the graph displays non-uniform magnitudes of the magnetic poles  56 . Moreover, the resulting post angle (denoted by A and determined from the graphical display) of the predetermined physical  52  does not meet the predetermined test specification. 
     The invention has, therefore, been described with reference to a preferred embodiment. It will be appreciated, however, that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     Parts List 
       1  prior art apparatus 
       2  gap region 
       2   a  tapered pole tip 
       3  gap region 
       4  field sensor 
       5  gaussmeter 
       6  first angular meter device 
       7  first needle pointer 
       8  first support member 
       9  pivot axis 
       10  marked scale 
       11  ferromagnetic core 
       12  frame 
       14  second prior art apparatus 
       16  second angular meter device 
       18  stationary member 
       20  second needle pointer 
       22  second support member 
       24  second pivot axis 
       26  marked scale 
       28  base 
       30  support structure 
       32   a  ferromagnetic pole 
       32   b  ferromagnetic pole 
       40  miniature bipolar magnet 
       40   a  north pole of magnet  40   
       50  magnetic rotor 
       52  outwardly extending physical features, or posts, on rotor  50   
       54  first peripheral edge of rotor  50   
       56  magnetic poles 
     Parts List—Continued 
       58  outwardly extending stop tab 
       60  second peripheral edge of rotor  50   
       64  BRU Master motor controller 
       70  shutter body 
       100  magnetic test apparatus 
       102  data controller (PC) 
       103  keyboard 
       104  (motor drive) means for rotating the magnetic rotor  50   
       105  printer 
       106  gaussmeter 
       107  monitor 
       108  first Hall effect probe of gaussmeter  106   
       110  second Hall effect probe of gaussmeter  106   
       112  encoder means 
       114  quadrature decoder 
       116  system startup 
       118  system startup 
       120  system startup 
       122  system test 
       124  system test