PURPOSE: To stop a robot by a method wherein signals of both phases A and B outputted from an encoder are sampled at a sufficiently short cycle and abnormality of the encoder is detected when both pulses change simultaneously at the subsequent sampling time.
CONSTITUTION: When the phase relationship between signals SA and SB is normal, the logical level of the signals SA and SB is "1" and "0", for example, at the sampling time ti and hence, a latch circuit 10 latches OA=1 and OB=0. But at the subsequent sampling time ti+1, OA=1 and OB=0 as the latch content of the circuit 10 and the logical states NA=1 and NB=1 are latched. When abnormality is caused in the encoder (when the phase difference between SA and SB changes to 0° and 180°), the logical states of SA and SB at the time t1' are "0" and "0" respectively but change to "1" and "1" at the subsequent time ti+1. Thus, any abnormality of an incremental encoder can be detected accurately thereby automatically stopping a robot.
ASADA KAZUHIDE
SHIRAE TAKASHI
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