Synchro-to-digital conversion method and apparatus

Claim 3

The method of synchro-to-digital conversion as specified in claim 1 wherein each of said two steps of subtracting the trigonometric equivalent of a known first angle omega from an unknown second angle theta comprises the steps of, multiplying a signal representing - cos theta by a signal representing tan omega to obtain a product signal representing - cos theta tan omega , adding said product signal to a signal representing sin theta to obtain a signal representing sin theta - cos theta tan omega , multiplying a signal representing sin theta by a signal representing tan omega to obtain a second product signal representing sin theta tan omega , and adding said second product signal to a signal representing cos theta to obtain a signal representing cos theta + sin theta tan omega , where sin theta - cos theta tan omega K sin ( theta - omega ), cos theta + sin theta tan omega K cos ( theta - omega ), and K is a constant 1/cos omega .

Claim 4

The method specified in claim 1 wherein the step of converting said remaining approximate angle X into a group of binary digital code output bits comprises the steps of, generating a pair of voltage signals proportional respectively to sin phi and A cos phi + B sin phi , applying the voltage signal proportional to A cos phi + B sin phi as a reference voltage signal to circuitry capable of successively comparing different fractions of said reference voltage signal against a second voltage signal applied thereto and generating a group of binary digital code output bits representing an approximation of the ratio of said second voltage signal divided by said reference voltage signal, and applying the signal proportional to sin phi to said circuitry as said second voltage signal, whereby the binary digital code produced by said circuitry is indicative of the quantity (sin phi /A cos phi + B sin phi ).

Claim 5

The conversion method specified in claim 1 and further comprising the additional steps of, registering in binary storage the binary digital code output bits produced by said successive approximation analog-to-digital conversion technique, detecting the octant in which said unknown input synchro angle exists, and controlling the stored binary digital code output bits to complement said stored binary digital code when said unknown input synchro angle is detected as occurring in an even-numbered octant.

Claim 6

Synchro-to-digital conversion apparatus for converting synchro data received in the form of a first pair of signals representing the sine and cosine respectively of an unknown input angle equal to or less than 45*, comprising in combination, first angle subtraction circuit means responsive to said first pair of signals for manipulating said signals to subtract the trigonometric equivalent of an angle of 22.5* from said unknown input angle, first signal producing circuit means operably connected to first angle subtraction circuit means and responsive to the result of the angle subtraction performed by said first angle subtraction circuit means for producing a second pair of signals representing the sine and cosine respectively of a first resultant aNgle equal to or less than 22.5* , said first resultant angle corresponding respectively to said unknown input angle if said unknown input angle is less than 22.5* and to said unknown input angle less 22.5* if said unknown input angle is greater than 22.5* , second angle subtraction circuit means responsive to said second pair of signals for manipulating said second pair of signals to subtract the trigonometric equivalent of an angle of 11.25* from said first resultant angle, second signal producing circuit means operably connected to said second angle subtraction circuit means and responsive to the result of the angle subtraction performed by said second angle subtraction circuit means for producing a third pair of signals representing respectively the sine and cosine of a second resultant angle equal to or less than 11.25* , said second resultant angle corresponding respectively to said first resultant angle if said first resultant angle is less than 11.25* and to said first resultant angle less 11.25* if said first resultant angle is greater than 11.25* , linear approximation circuit means for manipulating said third pair of signals to perform a linear approximation of said second resultant angle according to the equation Angle X (in degrees) 11.25 (sin phi /A cos phi + B sin phi ) where angle X is the remaining approximate angle to be converted to binary bit form, phi is said second resultant angle between 0* and 11.25*, and A and B are constants of predetermined value selected in accordance with desired accuracy, and means for converting said remaining angle X into a group of binary digital code output bits by a successive approximation analog-to-digital conversion technique.

Claim 7

Synchro-to-digital conversion apparatus for converting synchro data received in the form of a first pair of signals representing the sine and cosine respectively of an unknown input angle equal to or less than 45*, comprising in combination, first angle subtraction circuit means responsive to said first pair of signals for manipulating said signals to subtract the trigonometric equivalent of an angle of 22.5* from said unknown input angle, first signal producing circuit means operably connected to first angle subtraction circuit means and responsive to the result of the angle subtraction performed by said first angle subtraction circuit means for producing a second pair of signals representing the sine and cosine respectively of a first resultant aNgle equal to or less than 22.5* , said first resultant angle corresponding respectively to said unknown input angle if said unknown input angle is less than 22.5* and to said unknown input angle less 22.5* if said unknown input angle is greater than 22.5* , second angle subtraction circuit means responsive to said second pair of signals for manipulating said second pair of signals to subtract the trigonometric equivalent of an angle of 11.25* from said first resultant angle, second signal producing circuit means operably connected to said second angle subtraction circuit means and responsive to the result of the angle subtraction performed by said second angle subtraction circuit means for producing a third pair of signals representing respectively the sine and cosine of a second resultant angle equal to or less than 11.25* , said second resultant angle corresponding respectively to said first resultant angle if said first resultant angle is less than 11.25* and to said first resultant angle less 11.25* if said first resultant angle is greater than 11.25* , linear approximation circuit means for manipulating said third pair of signals to perform a linear approximation of said second resultant angle according to the equation Angle X (in degrees) 11.25 (sin phi /A cos phi + B sin phi ) where angle X is the remaining approximate angle to be converted to binary bit form, phi is said second resultant angle between 0* and 11.25*, and A and B are constants of predetermined value selected in accordance with desired accuracy, and means for converting said remaining angle X into a group of binary digital code output bits by a successive approximation analog-to-digital conversion technique.

Claim 8

The synchro-to-digital conversion apparatus specified in claim 5 wherein each of said first and second angle subtraction circuit means generate a pair of output signals representing respectively the sine and cosine of the difference angle resulting from the associated angle subtraction of a known angle from an unknown input angle and wherein each of said first and second signal producing means comprises, detecting circuit means operably connected to receive the output signal representing the sine of the difference angle resulting from the angle subtraction performed by the connected angle subtraction circuit means for detecting whether the sine of said difference angle is positive or negative, and circuit means operably connected to said sine detecting circuit means for selectively causing said signal producing means to produce a pair of signals representing the sine and cosine of said difference angle if the sine of said difference angle is positive or a pair of signals representing the sine and cosine of the unknown input angle applied to said connected angle subtraction circuit means if the sine of said difference angle is negative.

Claim 9

The synchro-to-digital conversion apparatus specified in claim 5 wherein each of said first and second angle subtraction circuit means for subtracting a known angle omega from an unknown angle theta comprises, a first operational amplifier having an output connection and an input connection connected to an input summing junction, a feedback resistor of first predetermined value connected between said output connection and said input summing junction, a first input resistor of said predetermined value having one end connected to said input summing junction and having its other end connected to receive a signal representing sin theta , a second input resistor of a value 1/tan omega multiplied by said predetermined value and having one end connected to said input summing junction and having its other end connected to receive a signal representing - cos theta , a second operational amplifier havIng an output connection and a pair of opposite polarity input connections, each of said opposite polarity input connections having an associated input summing junction connected thereto, a feedback resistor of second predetermined value having one end connected to the output connection of said second operational amplifier and its other end connected to one of said input summing junctions for said second operational amplifier, a resistor of said second predetermined value having one end connected to said one input summing junction for said second operational amplifier and having its other end connected to receive said signal representing - cos theta , a second resistor of said second predetermined value having one end connected to the other input summing junction for said second operational amplifier and having its other end connected to receive said signal representing sin theta , and a resistor having a value (tan omega /2 - tan omega ) multiplied by said second predetermined value and having one end connected to said other summing junction for said second operational amplifier and having its other end connected to ground.

Claim 10

The synchro-to-digital conversion apparatus specified in claim 7 wherein each of said first and second angle subtraction circuit means further includes switch means responsive to the result of the angle subtraction performed by the associated angle subtraction circuit means for disconnecting said first operational amplifier from said - cos theta signal and said operational amplifier from said sin theta signal if said known angle omega is greater than said unknown angle theta , whereby the output from said first operational amplifier is a signal representing either sin ( theta - omega ) or sin theta and the output from said second operational amplifier is a signal representing either cos (- omega ) or cos theta depending respectively upon whether said known angle omega is less than or greater than said unknown angle theta .

Claim 11

The synchro-to-digital conversion apparatus specified in claim 8 further including circuit means responsive to the output signal produced by said first operational amplifier of each of said first and second angle subtraction circuit means for detecting whether the polarity of the output signal from said first operational amplifier is negative, and said switch means being operated to disconnect said first and second operational amplifiers in the associated angle subtraction circuit means if said detecting circuit means determines that the output signal from said first operational amplifier is negative in polarity.

Claim 12

The synchro-to-digital conversion apparatus specified in claim 5 further including means responsive to input synchro data for detecting the octant in which the input synchro angle exists, and means responsive to said octant detecting means for generating a digital binary code representing the octant of said input synchro angle.

Claim 13

The synchro-to-digital converter apparatus specified in claim 10 further including register means comprising a plurality of digital binary storage stages for storing the digital binary output code bits representing the successive approximation of said remaining angle X.

Claim 14

The synchro-to-digital converter apparatus as specified in claim 11 further including means responsive to the octant code produced by said octant code generating means for controlling said binary digital register means to store the complement of the output of said successive approximation means when said octant code indicates that said synchro angle lies in an even-numbered octant.

Claim 15

The conversion apparatus specified in claim 7 wherein each of said first and second angle subtraction circuit means includes, switch means for disconnecting said second input resistor of the value 1/tan omega multiplied by said predetermined value from the signal representing - cos theta and for disconneCting said second resistor of said second predetermined value from the signal representing sin theta , whereby said conversion apparatus can be utilized as a scalar-to-binary digital converter when said signals representing sin theta and - cos theta are replaced by signals representing respectively an unknown scalar quantity and an associated reference quantity.