Harmonic Drive MMA Series, Manual, Page: 24 / 62

1-8 Detector specifications (Absolute encoder)
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1-8 Detector specifications (Absolute encoder)
Absolute encoders installed in the MMA series are multi-turn absolute encoders. The encoder consists
of a single-turn detector for detecting the motor shaft position, and a multi-turn detector for detecting
the number of revolutions.
The encoder constantly detects the absolute position of the machine and stores it by means of the
battery backup, regardless of whether the servo amplifier or external controller power is turned ON or
OFF. Accordingly, once the origin is detected when the machine is installed, originating is not required
for subsequent power ON operations. This facilitates the recovery operation after a power failure or
breakdown.
The single-turn absolute position detector and the accumulation counter that detects the number of
revolutions are both made dual-redundant, where data is constantly checked between two identical
devices while the power is ON to ensure a highly reliable design that allows self-detection of encoder
errors should they occur.
In addition, a backup capacitor is installed in the encoder to retain absolute positions even when the
servo amplifier-encoder extension cable is disconnected for initial startup of the device, etc. However,
the backup capacitor has a limited life and its performance deteriorates. Therefore, switch OFF
everything but the control circuit power when replacing the MELSERVO-J4 servo amplifier permanent
battery. If the battery is replaced with the control circuit power ON, the absolute position data is not lost.
Specifications
Type Magnetic sensor/electronic battery backup type
Resolution
Single-turn
detector
2
17
: 131072 pulses
Multi-turn
detector
2
16
: 65536 (-32768 to 32767)
Maximum allowable
rotational speed
7000 r/min
*1
Safety/redundancy
･
Check method in which two identical single-turn detectors are compared
･
Check method in which two identical cumulative revolution counters that detect
the number of revolutions are compared
Backup time by external
battery
Approx. 14000 hours
*2
(when power is not supplied, ambient temperature of 20
℃
)
Backup time by internal
battery
30 minutes (after 3 hours of charge, ambient temperature of 25
℃
, axis stopped)
(For backup while the servo amplifier and encoder are disconnected briefly)
*1: This is the rotational speed limit of the encoder and is different from the rotational speed that the motor can
drive.
*2: The value is obtained with the axis stopped. Frequent movement of the axis with no power supply would
cause the external battery to drain quickly.