Abstract:
A rotary position transducer with a cosine and sine attenuating voltage wave output has the substantially linear portions segmented and pieced together from a predetermined set of conditions to form a continuously linearly varying voltage output.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to providing a continuously variable electrical signal from a transducer indicating the relative position of an object with respect to a stationary reference. In particular, the invention relates to providing an electrical signal indicative of the angular position of a magnet disposed on the object with respect to the stationary reference. Devices of this type are particularly desirable for indicating the relative position of the magnet and the object and find application in linear and rotary position sensing devices. 
     It is known to provide a magneto resistive sensor for indicating the position of a magnet moving with an object; and, such a sensor is that produced by the Honeywell Corporation and bearing manufacturer designation HMC1512. 
     Referring to FIG. 4, the electrical output of a known sensor is shown wherein the voltage wave is plotted as a function of the rotary position {circle around (−)} in degrees and indicates the phase difference of 45° for the functions SIN 2{circle around (−)} and COS 2{circle around (−)} with a period of 180° (Π radians) for the voltage wave output of the transducer. 
     However, it has been desired to provide a rotary position transducer having a linear voltage output with respect to the rotary position of the magnet with respect to the stationary sensor. A linear output has the advantage that the output voltage may be used to drive directly an indicator such as a volt meter to give an easy-to-read indication to the user of the rotary position of the object. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method for linearizing the output of a motion detecting transducer having a dual wave form output in the form of a sine and cosine wave voltage. The linearization is accomplished by piecing together and inverting where necessary the substantially linear portion of the sine and cosine waves of the transducer output voltage. An amplifier and comparator function are utilized to provide an analog output of substantially linearly varying voltage as the transducer detects motion of an object moving with respect to the stationary transducer. The moving object has a magnet associated therewith; and, the change in angular bearing of the object is measured by a transducer and the transducer voltage wave form segmented and pieced together in accordance with a predetermined set of conditions for each segment as the angle of bearing changes from zero to 90°. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an embodiment of the present invention with a magnet mounted for rotation at a radius R about an axis fixed with respect to a sensor; 
     FIG. 2 is an alternate embodiment of the invention with the magnet rotating about an axis fixed with respect to the sensor and passing through the center of the magnet; 
     FIG. 3 is another embodiment of the invention having a magnet mounted on a trolley moving along a linear path displaced from the sensor; 
     FIG. 4 is a plot of voltage versus angle of rotation for a dual wave form output transducer; 
     FIG. 5 is a schematic of the processing circuitry for the present invention; and 
     FIG. 6 is a plot of voltage versus angle of rotation for the output voltage of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a sensor arrangement employing the present invention is indicated generally at  10  and includes a magnet  12  disposed on an object  14  rotated by shaft  16  disposed in a bearing block  18  for rotation about fixed axis  20 . The magnet is positioned to revolve about the axis  20  at a distance “r”. A transducer or sensor  22  is mounted adjacent the object  14  on a suitable base  24  and is adapted for connection to input to appropriate signal processing circuitry, which will hereinafter be described, by means of the electrical terminals  26  provided on the sensor  22 . Sensor  22  measures the angle {circle around (−)} with respect to the fixed reference  28 . 
     In the present practice of the invention, a rotary position sensor manufactured by the Honeywell Corporation bearing manufacturer designation HMC1512 has been found satisfactory for the sensor  22 . However, any suitable transducer having a dual sine and cosine wave form voltage output may be employed. 
     Referring to FIG. 2, an alternate embodiment of a system employing the invention is illustrated generally at  30  and has an object  32  with a magnet  34  disposed thereon for rotation on shaft  36  journalled in fixed support  38  for rotation about fixed axis  40 . A sensor  42  which may be similar to the sensor  22  of the FIG. 1 embodiment is mounted adjacent the rotating magnet  34  on a suitable base  44 . The magnet is denoted as subtending a central angle {circle around (−)} with a fixed reference  46  for purposes of correlation with the wave form signal output of sensor  42 . 
     Referring to FIG. 3, another embodiment of the invention is indicated generally at  50  and includes a magnet  52  disposed on a moving object  54  in the form of a trolley moving in the direction indicated by the black arrow along a surface or track  56  and subtending a central angle {circle around (−)} with respect to a fixed reference  58 . A rotary position sensor  60  is disposed on base  62 ; and, in the present practice of the invention the sensor  60  is similar to the sensor  22  of FIG. 1 or the sensor  42  of FIG.  2 . 
     Referring to FIG. 5, the circuit schematic of the present invention is indicated generally at  64 . A positive COS 2{circle around (−)} voltage wave form from any of the sensors  22 ,  42 ,  60 , which are excited by a constant D. C. voltage Vcc is applied through a resistor R 1  to the negative input of a differential amplifier  68 , with preferably a gain of 2, with the positive terminal of the amplifier also receiving a negative voltage for COS 2{circle around (−)} through a resistor R 2 . The output of amplifier  68  at terminal  72  is fed back to the negative input through resistor R 3  thus giving the amplifier output a value of 2A COS 2{circle around (−)}+K 2  which is applied to junction  74  and through R 5  to the negative input of a comparator  76  which outputs a signal to a switch  80  when COS 2{circle around (−)} is greater than K 2 . The output of comparator  76  is fed back through R 8  to the positive input. 
     The positive voltage wave form comprising SIN 2{circle around (−)} is applied through R 9  to the positive input of a differential amplifier  78 , which is connected through a resistance R 13  to the feed or common input of switch  80 ; and, the positive input of amplifier  78  also receives a reference voltage K 3  through resistor R 9 . The negative input of amplifier  78  receives the negative voltage SIN 2{circle around (−)} through resistor R 8 . The output of amplifier  78  is 2B SIN 2{circle around (−)}+1 and is connected to junction  82  and is fed back through resistance R 21  to the negative input of the amplifier  78 . Junction  82  is also connected through R 13  to one side the of switch  80  and provides a positive SIN 2{circle around (−)} input thereto. 
     The wave form voltage COS 2{circle around (−)} from junction  74  is also applied through R 7  to the negative input terminal of a differential amplifier  84  which has its positive input receiving a positive or negative SIN 2{circle around (−)} signal from switch  80 . 
     The switch  80  is thus operative to provide switched positive and negative values of SIN 2{circle around (−)} the amplifier  84  at the positive input of amplifier  84 , which is biased with about 1.5 volts applied through a resistor R 23 . The output of amplifier  84  is set forth in Table I below. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Θ 
                 V 
               
               
                   
                   
               
             
             
               
                   
                  0 
                 SIN2⊖-COS2⊖ + K 1   
               
               
                   
                 45°- 
                 ————————— 
               
               
                   
                   
                 -SIN2⊖-COS2⊖ + K 2   
               
               
                   
                 90° 
               
               
                   
                   
               
             
          
         
       
     
     The values and description of the individual circuit components are set in Table II. 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Resistors 
                 Capactors 
                 Other Devices 
               
             
          
           
               
                 R 
                 Ohms 
                 C 
                 Farads 
                 Ref. No. 
                 Type 
               
               
                   
               
             
          
           
               
                 1,2,8,9 
                 1 
                 Meg, 
                 1,3, 
                 56 
                 pf 
                 22,42,60 
                 HMC 
               
               
                   
                 1% 
                   
                 4,5 
                   
                   
                   
                 1512 
               
               
                 3,4.12, 
                 2 
                 Meg, 
                 2 
                 .1 
                 μf, 200 V 
                 68,76,78, 
                 1/4 
               
               
                 21 
                 1% 
                   
                   
                   
                   
                 84 
                 LMC 
               
               
                   
                   
                   
                   
                   
                   
                   
                 6484 
               
               
                 7,13,14 
                 130K, 
                 1% 
                   
                   
                   
                 80 
                 PISA 
               
               
                   
                   
                   
                   
                   
                   
                   
                 383AP 
               
               
                 5,6 
                 10K 
                   
               
               
                 10 
                 4.02K, 
                 1% 
               
               
                 11 
                 1K, 
                 1% 
               
               
                 8 
                 5.1M 
                   
               
               
                 15,18 
                 3.6K 
                   
               
               
                 16,19 
                 1.0K 
                 Var. 
               
               
                 17 
                 500 
                   
               
               
                 20 
                 1K 
                   
               
               
                 22 
                 100, 
                 1/4 W 
               
               
                 23 
                 1 
                 Meg. 
               
               
                   
               
             
          
         
       
     
     It will be understood that A and B shall be chosen to provide the desired output voltage span over the range of the operating angle {circle around (−)}. In the present practice of the invention, A and B have been chosen such that the linear output spans from 0 to 5 volts over the angle range 0 to 90°. It will be apparent that other values may be used. 
     It will be further understood that the constants K 1  to K 2  shall be chosen such that when the substantially linear segments are pieced together, there is a smooth and continuous linear output voltage without steps at each connecting segment. 
     The present invention thus provides a simple and relatively low cost method of converting the sine and cosine voltage wave forms of a rotary position sensor to an analog signal varying linearly with respect to the position angle of an object moving with respect to the sensor. 
     Although the invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.