12. Home Position Sensor
LEFT
RIGHT B
C
A
CARRIAGE HOLDER
The home position of carriage is detected as a result of change of output of photointurrupter A which is caused due to
While the photointerrupter is shut off by the slit B, the output (pin 1 of CN3) of photointerrupter gets H level (+5V). If it is not shut off, the output gets L level (0V).
In the home position the output is L. In case of L direction movement the output is H during passing through the slit, and after passing the output gets again L level.
The operation logic is as follows. Insignificant movement in L direction
(1) If in this case the output is L:
It is judged that the carriage exists in the L direction as compared to the slit B . The carriage is moved in the R direc- tion, so that the output changes from L to H (during passing through the slit B ). Further the carriage is moved in the R direction. The position where H changes to L again is regarded as a home position.
(2) If in this case the output is H:
It is judged that the carriage exists near the home position, the carriage is moved in the R direction. The position where the output is changed from H to L is regarded as a home position.
Operation in case of malfunction of photointerrupter A .
Case 1: When the output of photointerrupter remains H.
As is evident from the operation logic, the H output does not continue for a long time in case of normal operation. Hence, this state is judged to be abnormal. The carriage stops soon after it moves insignificantly.
Case 2: When the output of photointerrupter remains L.
The carriage is going to move according to the operation logic. Since the output remains L even when the sensor passes through the slit B , the home position cannot be found, and the carriage moves continuously in the R direction. Finally, it contacts the frame C , emitting an abnormal sound. The abnormal state is detected, and the motor stops.
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