Coarse/fine digital pattern combiner for high accuracy
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorElzie H. Freeman
Life of this patent
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Abstract
A rotary shaft position measurement system using digital position detectors roviding coarse and fine binary word readouts having four overlapping bits all of which are having subtractively compared to provide command signals that are used to correct the non-overlapping portion of the coarse word prior to combining with the fine word. The comparator utilizes a binary four bit full adder in combination with coarse word input inversion, and direct and inverted application of the carryout and .SIGMA.4 outputs to first and second AND gates to generate coarse word correction commands.
Claims6
A measurement system comprising in combination:
- first means for generating a first binary number of more than four bits representative of a coarse measurement of a predetermined parameter;
- second means, coupled to said first means, for generating a second binary number of four or more bits representative of a fine measurement of a portion of said predetermined parameter;
- coarse/fine comparator means, responsive to the lower four bits of said first binary number and to the upper four bits of said second binary number, for generating first, second, and third command signal conditions;
- means, responsive to said command signal conditions, for respectively adding one count to, subtracting one count from, or leaving unchanged the upper bit portion of said first binary word to provide a corrected or unchanged first binary word, and;
- means for combining said corrected or unchanged first binary word with said second binary word to provide a combined binary word representative of said predetermined parameter;
- said coarse/fine comparator means comprising a four bit binary full adder having four first bit inputs, four second bit inputs, a carry-out output and a .SIGMA.4 output, first inverter means for inserting inputs to said four first inputs, a first AND gate having first and second input connections, a second AND gate having first and second input connections, second inverter means for inverting inputs to said first and second input connections of said second AND gate, said carry out output being connected to one of said input connections to said first AND gate and by said second inverter means to one of said first AND gate and by said second inverter means to one of said inputs connections to said second AND gate, and said .SIGMA.4 output being connected to the other of said input connections to said first AND gate and by said second inverter means to the other of said input connections of said second AND gate, whereby said first AND gate provides a true output only when said carry out and said .SIGMA.4 outputs are both true, and said second AND gate provides a true output only when said carry out and said .SIGMA.4 outputs are both not true, said first output signal condition existing when only one of said AND gates has a true output, said second output signal condition existing when only the other of said AND gates has a true output, and said third output signal condition existing when neither of said AND gates has a true output.
A coarse/fine comparator for use in an angular displacement readout system of the type comprising first and second discs encoded with repeating coarse and fine binary patterns and means for converting the positions of said discs to first and second binary words, each having a plurality of digits, N of which overlap, said comparator comprising:
- an N bit adder;
- N first inverter means connected to invert and apply the N overlapping bits of said first binary word as a first input to said adder;
- means connected to directly apply the N overlapping bits of said second binary word as a second input to said adder, whereby said adder effects a subtraction process of said overlapping bits of said second word from said overlapping bits of said first word by a 2's compliment add, so as to provide a carry out bit as a first binary level signal and .SIGMA.N as a second binary level signal;
- first AND means, responsive to coincidence of a predetermined condition of both of said first and second binary level signals to provide a first binary level comparator output;
- second inverter means responsive to said first and second binary level signals to provide inverted first and second binary level signals;
- and
- second AND means, responsive to coincidence of a predetermined condition of both of said inverted first and second binary level signals to provide a second binary level comparator output.
A rotary shaft position measuring system of the type including rotation detecting means for generating a plural bit coarse count binary word and a plural bit fine count binary word, coarse/fine count comparator means, responsive to a predetermined number of overlapping bits of the coarse and fine count words, for providing command signals for correcting the non-overlapping portion of the coarse count word prior to combining with the fine count word to provide a combined binary word representing shaft position, said system being characterized by the improvement wherein said comparator means comprises:
- a plurality of first inverter means, corresponding in number to said predetermined number, for inverting said overlapping bits of said coarse count binary word;
- a plural bit binary full adder means for subtracting said overlapping bits of said coarse count binary word from said overlapping bits of said fine count binary word to provide a .SIGMA.N output, where N is said predetermined number, and a carry out output;
- first AND gate means, responsive to said .SIGMA.N and said carry out outputs, for providing as one of said command signals a first true output only when both of said .SIGMA.N and said carry out outputs are true;
- second inverter means for inverting said .SIGMA.N and said carry out outputs;
- and
- second AND gate means, responsive to outputs of said second inverter means, for providing as another of said command signals a true output only when both of said .SIGMA.N and carry out outputs are not true.
Dependencies are inferred from the claim text.