Revolution counter using a magnetic bubble device for multi-turn absolute encoder

In a multi-turn absolute encoder comprising a turn detector for detecting number of turns of a rotary shaft and a shaft angle encoder for measuring turning angle of said rotary shaft, said shaft angle encoder comprising a code plate;

• the improvement comprising
• a magnetic bubble element for sequentially transferring magnetic bubbles on a transfer pattern in accordance with a turn of a driving magnetic field;
• and
• a permanent magnet turning together with said code plate and for generating said driving magnetic field, so that said turn detector detects the number of turns of said rotary shaft from positions of said magnetic bubbles on said transfer pattern in said magnetic bubble element;
• wherein said turn detector further comprises two magnetic bubble detectors disposed corresponding to transfer elements adjacent to each other in a transfer loop comprising N transfer elements as said transfer pattern of said magnetic bubbles;
• a magnetic bubble transfer means for transferring said magnetic bubbles on said transfer loop independently of said permanent magnet;
• and a differential amplifier for obtaining a difference in output signals from said two magnetic bubble detectors;
• wherein a bit pattern obtained by interposing zeroes into a pattern of an n-th memory wheel which satisfies the relation N>2.sup.n.gtoreq. N/2 is written into said transfer loop depending on the presence or non-presence of said magnetic bubbles;
• and wherein positions of said magnetic bubbles are detected from a pattern of strains of signals generated in output signals from said differential amplifier when said magnetic bubble transfer means transfers said magnetic bubbles 2n times.

In a multi-turn encoder comprising a turn detector for detecting number of turns of a rotary shaft and a shaft angle encoder for measuring turning angle of said rotary shaft, said shaft angle encoder comprising a code plate;

• the improvement comprising
• a magnetic bubble element for sequentially transferring magnetic bubbles on a transfer pattern in accordance with a turn of a driving magnetic field;
• and
• a permanent magnet turning together with said code plate and for generating said driving magnetic field, so that said turn detector detects the number of turns of said rotary shaft from positions of said magnetic bubbles on said transfer pattern in said magnetic bubble element;
• wherein said turn detector further comprises two magnetic bubble detectors disposed corresponding to transfer elements adjacent to each other in a plurality of transfer loops in which the number of transfer elements are two or more integers N.sub.1, N.sub.2 . . . , which have no common divisor, said transfer loops being formed as said transfer pattern of said magnetic bubbles;
• a magnetic bubble transfer means for transferring said magnetic bubbles on said respective transfer loops independently of said permanent magnet;
• and a differential amplifier for obtaining a difference in output from said two magnetic bubble detectors;
• wherein a bit pattern obtained by interposing zeroes into a pattern of an ni-th memory wheel which satisfies the relation Ni>2.sup.n.gtoreq. Ni/2, wherein i=1,2, . . , is written into each of said transfer loops depending on presence or non-presence of said magnetic bubbles;
• and wherein the number of turns of said rotary shaft is obtained from a combination of patterns of series of signals generated in outputs from said differential amplifier when said magnetic bubble transfer means transfers said magnetic bubbles 2nm times when the maximum value of n, n.sub.2 . . . , is nm.