position / speed mode - Harmonic Drive LLC

Chapter 2Functions
2-2-4 Absolute encoder signals
u
General descriptions and functions of absolute encoders
The absolute encoder housed in a FHA-C series actuator provides an absolute sensor to generate an
absolute pulse train for a resolvable position (the sensor is herein after referred to as “single-turn
encoder”.), and an electronic counter to generate an absolute pulse train for a revolution of the motor
(the counter is hereinafter referred to as “multi-turn counter”.).
An absolute position of the encoder is kept in the memory, which is always energized by a combination
of the built-in condenser in the actuator and the backup battery housed in the HA-655 driver.
Please interpret that “single-turn” and “multi-turn” in the manual mean one and plural revolutions of the
encoder (the motor) in an actuator, respectively. Therefore, the actual actuator resolvable position of
either “single-turn” or “multi-turn” can be obtained by multiplying an absolute pulse train of the single-turn
encoder and the multi-turn counter by a reduction ratio of the actuator.
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Single-turn absolute encoder
The single-turn encoder is composed of an encoder disk, an LED light source, and a photo-detector. The
single-turn absolute encoder system outputs a current absolute pulse train combined with an absolute
pulse train of the multi-turn counter in response to the [ABS data request] signal. The resolution of the
encoder is 8192 positions per turn (13 bits). To obtain actual resolvable position of the actuator, the
absolute pulse train should be multiplied by the reduction ratio of the actuator.
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Multi-turn counter
The multi-turn counter outputs a current absolute pulse train combined with an absolute pulse train of
the single-turn absolute encoder system in response to the [ABS data request] signal. The allowed
range of the counter is from +4095 to –4096. To obtain an actual resolvable position of the actuator, the
absolute pulse train should be multiplied by the reduction ratio of the actuator.
u Energy-saving mode
In the energy-saving mode, even during no power supply for the HA-655 driver, the multi-turn counter
keeps a count in its memory only by the power of a built-in condenser and a built-in battery.
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Allowable encoder (motor) speed in energy-saving mode
The limit of an encoder (a motor) speed is 5,000r/min. The [alarm 55: ABS multi-turn data error] occurs if
the encoder rotates at more than the limited speed, and a correct absolute pulse train of the multi-turn
counter may not obtained. Moreover, there are additional limits during motor acceleration duration as
shown the figure below.
Error undetectable range
(abnormal data)
Error detectable range (abnormal data)
Encoder speed(r/min)
Allowable speed range
16000rad/s 2
5000rad/s 2
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Response
(ms)
time