JVL MAC050 User Manual page 67

2.12 Absolute Multiturn Encoder
2.12.3 How to stay within the encoder working range (detailed guide)
The motor is equipped with a offset register that holds an encoder position offset.
When 24V power has been applied the motor will read the position from the encoder
and set the actual shaft position according to this calculation:
Absolute (motor) position (P_IST) = Absolute_Encoder_Position + Encoder_Offset
So if the motor shaft is placed in position 1000 and the offset is set to -1000 the motor
will set the actual position register (P_IST) to 0.
The encoder has a limitation in the dynamic working range to be +/- 16.777.216 counts
which corresponds to +/- 2048 shaft revolutions. Within this range the offset can be
placed at any point but considerations regarding the wrap around of the position value
must be made. Cycling 24V power for the motor, when the shaft is placed in a wrapped
position, may result in an unexpected position.
Example 1: The motor position has been reset when the Absolute_Encoder_Position
was 16.000.000. This limits the positive working range to approx. 94 motor shaft revo-
lutions which may cause an overflow and failure situation if the motor moves more than
94 revolutions during operation.
Example 2: Let's assume the motor has moved 100 revs. Placing the motor (MAC400)
in the actual position = 819.200 counts.
Now the motor is reset (24V control power is cycled) the motor wakes up and reads the
Absolute_Encoder_Position which in the mean time has been wrapped around to the
position -16.735.232. Now the offset is used to calculate the actual shaft position of the
motor:
Actual (motor) position (P_IST) = -16.735.232 + (-16.000.000)
Actual (motor) position (P_IST) = -32.735.232!
Which is not exactly what was expected, because the encoder passed its working range.
JVL A/S - User Manual - Integrated Servo Motors MAC050 - 4500
F
Only MACxxx-yy- zzz
63