Encoder

Claim 1

An absolute-type encoder coupled to a drive shaft for detecting an amount of rotation of the drive shaft when said drive shaft is rotatively driven by a driving means, comprising: an encoder case, a drive shaft journaled for rotation within said case, rotary magnetic disk means for storing prevailing rotational position information of said drive shaft on a data storage track of said rotary magnetic disc means and being coupled to said drive shaft to be rotated in accordance with rotation of the drive shaft; reading means for reading serial phase signals recorded as said rotational positional information by said rotary magnetic disk means, counting output means including a counter for counting and holding said serial phase signals read by said reading means and outputting the read serial phase signals from said counting output means as parallel information signals; a reset signal means and a latch circuit means are provided for presetting said counter to a previously latched position information setting whenever a clock input signal is sensed by said latch circuit means and for resetting an output position information setting at any timing in response to an input from the reset signal means for correcting any error in count each time one revolution of the disk of said rotary magnetic disk means is made; data preservation means for preserving the data in said latch circuit means and the count recorded by said counter in the event drive power is cut off; and wherein signal detection means is provided for determining the direction of shaft rotation from stored information on a timing track on said rotary magnetic disk means, said counting output means being counted up or down in accordance with the direction in which the drive shaft rotates.