Yaskawa MP920 User's Manual Design - Manual (Page 464)

10.3 Using an Absolute Encoder
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10.3.2 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.
As the number of rotations from the encoder zero point is controlled in the range shown
below, the number of rotations will be reset to 0 when it exceed the range.
• For Σ series SERVOPACKs: ±99,999 rotations
• For Σ-II series SERVOPACKs: 0 to 65,534 rotations
When the system power is turned ON therefore, the position data that the MP920 manages
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 MP920 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.
Pulse position = pulse position at power OFF
+ (encoder position - encoder position at power OFF)*
* Indicates the distance traveled while power is OFF (relative encoder posi-
tion).
„ 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: MP920 position data converted to pulses.
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