Pg 42 S22A / S23A mits 2001
PROBLEM # 2, for automatic models with a shuttle.
Inaccurate lengths in AUTO mode.
POSSIBLE CAUSES;
i) Encoder - pinion not engaging rack all the way from front to back; mechanical interference,
pinion loose on encoder shaft.
ii) Encoder Cable - bad connection at encoder or at PLC
- intermittent open in one or more signal wires
iii) Improper programmed information
- existing parameter(s) incorrect
- incorrect blade kerf
iv) PLC - faulty PLC unit (not repairable in the field)
GENERAL RULES - Normally, three types of length inaccuracies may occur.
1) Inconsistent - lengths cut are not consistent, error changes. It doesn't matter how long the part
required is the error is never the same.
Cause: - most likely a defective electrical, hydraulic or mechanical component.
2) Consistent - lengths cut are consistent and the error is also consistent. The error always stays the
same regardless of part length.
Cause: - Kerf value
3) Linear - lengths cut are consistent but the error increases as the part length increases. The
longer the part the greater the error.
Cause: - when self-calibration is executed, incorrect "Act Lth" value entered
DIAGNOSIS;
i) Check and record existing parameters. Also check for proper blade kerf.
By making a cut part way into a piece of material and measuring the width of the cut, the operator
can check blade kerf.
INCONSISTENT INACCURACY
i) - with the machine in MANUAL mode, move the shuttle all the way forward and clear (zero) the length
display. Move the shuttle in reverse, in slow speed, all the way to the end of it's travel. Return the shuttle
forward to the home position, also in slow. The display should read 0.000" +/- .005". Do this test several times to
be sure the read-out is repeatable.
DIAGNOSIS;
i) Following the same procedure, run the shuttle alternating between fast and slow speed going back and
coming forward. Again the display should be able to read 0.000" +/-.005" when returning to the home position.
If the display does not read as specified:
- check the encoder pinion gear to be sure it can run smoothly down the rack and that the gear and rack
teeth engage over the entire travel of the shuttle.
- check that the pinion gear is tight on the encoder shaft.
- check the encoder cable connections, a loose connection could easily cause this concern.
- remove the encoder from the machine and check that the shaft can rotate freely. There should be no
binding or rough spots felt when spinning the shaft. Plug the encoder cable into the encoder, clear the
length display, and rotate the shaft exactly (or as close as possible) one revolution. The display should read
approximately 3.142" (positive or negative). Repeat this 3 or 4 times, spinning the shaft several times
between tries.
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