TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
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3.5.4 Measurement of Rotor Angle
Determination of the rotor angle is either done by sensors (digital encoder, analog encoder, digital Hall
sensors, analog Hall sensors) or sensorless by a reconstruction of the rotor angle. Currently, there are no
sensorless methods available for FOC that work in a general purpose way as a sensor down to velocity
zero.
The TMC4671 does not support sensorless FOC.
3.5.5 Measured Rotor Angle vs. Magnetic Axis of Rotor vs. Magnetic Axis of Stator
The rotor angle, measured by an encoder, needs to be adjusted to the magnetic axis of the rotor. This is
because an incremental encoder has an arbitrary orientation relative to the magnetic axis of the rotor, and
the rotor has an arbitrary orientation to magnetic axis of the stator.
The direction of counting depends on the encoder, its mounting, and wiring and polarities of encoder
signals and motor type. So, the direction of encoder counting is programmable for comfortable definition
for a given combination of motor and encoder.
3.5.5.1 Direction of Motion - Magnetic Field vs. Position Sensor
For FOC it is essential, that the direction of revolution of the magnetic field is compatible with the direction
of motion of the rotor position reconstructed from encoder signals: For revolution of magnetic field with
positive direction, the decoder position needs to turn into the same positive direction. For revolution of
magnetic field with negative direction, the decoder position needs to turn into the same negative direction.
With an absolute encoder, once adjusted to the relative orientation of the rotor and to the relative
orientation of the stator, one could start the FOC without initialization of the relative orientations.
3.5.5.2 Bang-Bang Initialization of the Encoder
A Bang-Bang initialization is an initialization where the motor is forced with high current into a specific
position. For Bang-Bang initialization, the user sets a current into direction D that is strong enough to
move the rotor into the desired direction. Other initialization methods ramp up the current smoothly and
adjust the current vector to rotor movement detected by the encoder.
3.5.5.3 Encoder Initialization using Hall Sensors
The encoder can be initialized using digital Hall sensor signals. Digital Hall sensor signals give absolute
positions within each electrical period with a resolution of sixty degrees. If the Hall sensor signals are used
to initialize the encoder position on the first change of a Hall sensor signal, an absolute reference within
the electrical period for commutation is given.
3.5.5.4 Minimum Movement Initialization of the Encoder
For minimal movement initialization of the encoder, the user slowly increases a current into direction D
and adjusts an offset of the measured angle in a way that the rotor of the motor does not move during
initialization while the offset of the measured angle is determined.
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