Yaskawa MP940 - Manual (Page 332)

Absolute Position Detection
7.3.2 Infinite Length Mode Axis
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7.3.2 Infinite Length Mode Axis
„ Description
Infinite Length Positioning is a function that automatically updates machine position, pro-
gram position (absolute values in a program coordinate system), and current values at regu-
lar intervals according to fixed parameter settings. The function can be used for repeated
positioning in one direction.
Unfortunately, if the number of rotations from the encoder zero point goes out of the range
from 0 to the number set in parameter Pn 205: Multi-turn Limit Setting, it is reset to 0. When
system power is turned ON, therefore, the MP940 position may not be the same before and
after power is turned ON.
This problem can be resolved using the following method.
„ Position Control for an Infinite Length Mode Axis
Determine the MP940 position when power is turned ON and use the following equation to
determine the pulse unit position from the relative encoder position.
Always save the pulse position and encoder position as paired data in memory backed up by
battery power. This data is used as pulse position and encoder position at power OFF set-
tings the next time power is turned ON in order to determine number of pulses from the rel-
ative encoder position using the following equation.
∗ Indicates the distance traveled while power is OFF (relative encoder
position).
The following explains the terminology used here.
• Encoder position: Position data for an absolute encoder
(Multi-turn data the number of encoder pulses + initial increment)
• Pulse position: MP940 position data converted to pulses.
POSMAX
0
Pulse position = pulse position at power OFF +
(encoder position - encoder position at power OFF)
∗
INFO
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