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 θ in degrees and indicates the phase difference of 45° for the functions SIN 2θ and COS 2θ, 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 multiplexer 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 180°. 
    
    
     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 one embodiment of the present invention; 
     FIG. 6 is a plot of voltage versus angle of rotation for the output voltage of the present invention and, 
     FIG. 7 is a schematic of the processing circuitry for another embodiment of the 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 θ 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 θ 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 θ 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 COS 2θ voltage wave form from any of the sensors  22 ,  42 ,  60 , is applied at terminal  66  and  70  through a resistor R to the input of an amplifier  68  with the positive terminal of the amplifier also receiving a reference voltage K 2  through a resistor B*R at terminal  70   a . The output of amplifier  68  at terminal  72  is fed back to the negative input through resistor B*R thus giving the amplifier output a value of −B COS 2θ+K 2  which is applied to junction  74  and to input  75  of multiplexer  76 . 
     The voltage wave form comprising SIN 2θ is applied to input terminal  78  and  78   a  which is connected through a resistance R to the input of an amplifier  80 ; and, the positive input of amplifier  80  also receives a reference voltage K 3  through input terminal  78   b  and resistance A*R. The output of amplifier  80  is connected to junction  82  and is fed back through resistance A*R to the negative input of the amplifier  80 . Junction  82  is also connected to the negative input of amplifier  84  which has a positive input thereof receiving a reference voltage K 1 -K 3 . The output of amplifier  84  is fed back to the negative input thereof and is connected to an additional input  73  of the multiplexer  76  and provides an output signal in the form of A SIN 2θ+K 1 . 
     Junction  82  is also connected to a separate input  77  of the multiplexer  76  and provides the inverted signal −A SIN 2θ+K 3  to input  77 . Junction  74  is also connected to the negative input of an amplifier  88  which has the positive input thereof connected to receive input reference voltage K 4 -K 2  and the output thereof fed back to the negative input with the output in the form of B COS 2θ+K 4  applied to input  79  of the multiplexer  76 . 
     The wave form voltage COS 2θ is applied to the positive input terminal  86  of amplifier  90  which has its negative input  87  grounded and thus provides output only when the input wave is positive to a select input S 3  of the multiplexer  76 . 
     Similarly, the SIN 2θ is applied through input terminal  92  to the positive input of an amplifier  94  which has its negative input  93  grounded with the output only when the input sine wave form is positive and which is applied through select input S 2  of the multiplexer  76 . It will be understood that the reference voltage at the negative input terminal  86  of amplifier  90  and at the negative terminal  93  of amplifier  94  can also be established at a valve other than ground, depending on the supply voltage used. In the present practice of the invention, a supply of 5 VDC is used and the reference voltage is 2.5 V. 
     The sensor wave form COS 2θ is also applied to terminal  96  which is the positive input of an amplifier  98  which has the negative input thereof connected through terminal  100  to receive the sensor wave form SIN 2θ; and, amplifier  98  provides an output only when the magnitude of the cosine wave form is greater than that of the sine wave form and provides the input to select terminal S 1  of multiplexer  76 . 
     The voltage wave form for COS 2θ from the sensor is also applied to input terminal  102  which is connected to the positive input of amplifier  104  which receives through terminal  106  at its negative input a voltage wave form for −SIN 2θ from the sensor; and, the amplifier  104  provides an output only when the magnitude of the cosine wave form is greater than that of the negative sine wave form and the output is applied to select input S 0  of multiplexer  76 . 
     The multiplexer  76  is programmed to provide an output signal in the form of a linearly increasing analog voltage such as shown in FIG. 6 with the voltage as a function of the angle θ formed by the magnet with the fixed reference. The multiplexer  76  provides the voltage output of FIG. 6 by selecting the linear portion of the sine and cosine voltage waves of the sensor in accordance with the schedule of Table I. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Θ 
                 V 
               
               
                   
                   
               
             
             
               
                   
                        0-22.5°  
                   A SIN2Θ + K 1   
               
               
                   
                  22.5°-67.5°  
                 −B COS2Θ + K 2   
               
               
                   
                  67.5°-112.5° 
                  −A SIN2Θ + K 3   
               
               
                   
                 112.5°-157.5° 
                  B COS2Θ + K 4   
               
               
                   
                 157.5°-180°   
                   A SIN2Θ + K 1   
               
               
                   
                   
               
             
          
         
       
     
     The multiplexer  76  segments and provides the output voltage according to FIG. 6 by combining the voltage wave forms of Table I in accordance with the logic of Table II. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                 V = 
                 S 3   
                 S 2   
                 S 1   
                 S 0   
                 FIG. 5 Input Pin 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   A SIN2Θ + K 1    
                 1 
                 — 
                 1 
                 1 
                 73 
               
               
                   
                 −B COS2Θ + K 2   
                 — 
                 1 
                 0 
                 1 
                 75 
               
               
                   
                  −A SIN2Θ + K 3    
                 0 
                 — 
                 0 
                 0 
                 77 
               
               
                   
                  B COS2Θ + K 4   
                 — 
                 0 
                 1 
                 0 
                 79 
               
               
                   
                   
               
             
          
         
       
     
     Where S 3 , S 2 , S 1  and S 0  are designated select inputs of the multiplexer  76  as follows: S 3 =COS 2θ positive, S 2 =SIN 2θ positive, S 1 =COS 2θ&gt;SIN 2θ and S 0 =COS 2θ&gt;−SIN 2θ. 
     Referring to FIG. 7, an alternate embodiment of the circuit schematic of the present invention is indicated generally at  108  for a simplified sensor arrangement intended for sensing movement of an object relative to the sensor having an angular bearing from zero to 90°. 
     A sine 2θ voltage wave form from any of the sensors  22 ,  42 ,  60  is applied at terminals  110 ,  112  through resistor R to the inputs of an amplifier  114  with the positive terminal of the amplifier also receiving a reference voltage K 5  through a resistor A*R. The output of amplifier  114  is fed back to the negative input through a resistor A*R and is applied to one side terminal  116  of a switch indicated generally at  118 . 
     The voltage wave form comprising CO2θ is applied to the input terminals  120 ,  122  of which are each connected through a resistor R to an input of amplifier  124 . The positive terminal of amplifier  124  also receives the voltage K 6  through resistor B*R. The output of the amplifier  124  is fed back through a resistor B*R to the negative input terminal by the amplifier. The output of amplifier  124  is applied to a second side terminal  126  of the switch  118 . The moveable or common terminal of the switch  118  is the output and is controlled by the output of amplifier  128  which has its positive input receiving the wave form CO2θ and its negative input receiving the wave form −SIN 2θ. 
     The strategy for the measurements of the embodiment of FIG. 7 is shown in Table III hereinbelow. 
     
       
         
               
               
               
             
           
               
                 TABLE III 
               
               
                   
               
               
                   
                   
                 Waveform 
               
               
                 Condition 
                 Angle 
                 Segment 
               
               
                   
               
             
             
               
                 COS2Θ ≧ −SIN2Θ 
                 22.5° to 67.5°  
                 −B COS2Θ + K 6   
               
               
                 COS2Θ ≦ −SIN2Θ 
                 67.5° to 112.5° 
                 −A SIN2Θ + K 5   
               
               
                   
               
             
          
         
       
     
     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 θ. 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 O to 180°. It will be apparent that other values may be used. 
     It will be further understood that the constants K 1  to K 6  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.