Datasheet

TMC4671 Datasheet • IC Version V1.3 | Document Revision V2.00 • 2020-Apr-17
48 / 142
4.6.9.3 External Position Register
A register value written into the register bank via the application interface is available for commutation
as well. With this, the user can interface to any encoder by just writing positions extracted from external
encoder into this regulator. From the decoder engine point of view this is just one more selectable encoder
source.
4.6.10 Encoder Initialization Support
The TMC4671 needs proper feedback for correct and stable operation. One main parameter is the com-
mutation angle offset PHI_E_OFFSET. This offset must not be calculated when an absolute sensor system
like analog or digital Hall sensors is used. All other supported feedback systems need to be initialized -
their PHI_E_OFFSETs need to be identified. The user has several options to determine PHI_E_OFFSET with
support of the TMC4671.
4.6.10.1 Encoder Initialization in Open-Loop Mode
In the case of a free driving motor, the motor can be switched to Open-Loop Mode. In this mode, the
used commutation angle (PHI_OPEN_LOOP) can be used to match the measured PHI_E. This method is
supported by the TMCL-IDE.
4.6.10.2 Encoder Initialization by Hall sensors
The TMC4671 can calculate PHI_E_OFFSET very precisely at a Hall state change for a second encoder
system, when Hall sensors are correctly aligned. Therefore, the function needs to be enabled and calculate
a new offset at the next Hall state change. After disabling of the module, the process can be started again.
This function can also be used as a rough plausibility check during longer operation.
4.6.10.3 Encoder Initialization by N Pulse Detection
After determination of a correct offset, the value can be used again after power cycle. The encoder’s N
pulse can be used as reference for this. For starters the user can drive the motor in open-loop mode or by
using digital Hall sensor signals. After passing the encoder’s N pulse, the ABN encoder is initialized and
can be used for operation.
4.6.11 Velocity Measurement
Servo control comprises position, velocity and current control. The position and the current are measured
by separate sensors. The actual velocity has to be calculated by time discrete differentiation from the
position signal. the user can choose a calculated position from the various encoder interfaces for velocity
measurement by parameter VELOCITY_SELECTION.
The user can switch between two different velocity calculation algorithms with the parameter VELOC-
ITY_METER_SELECTION. Default setting (VELOCITY_METER_SELECTION = 0) is the standard velocity meter,
which calculates the velocity at a sampling rate of about 4369.067 Hz by differentiation. Output value is
displayed in rpm (revolutions per minute). This option is recommended for usage with the standard PI
controller structure.
By choosing the second option (VELOCITY_METER_SELECTION = 1), the sampling frequency is synchronized
to the PWM frequency. This option is recommended for usage with the advanced PI controller structure.
Otherwise, the controller structure might tend to be unstable due to non-matched sampling.
Velocity filters can be applied to reduce noise on velocity signals. Section 4.8 describes filtering opportuni-
ties in detail.
©2020 TRINAMIC Motion Control GmbH & Co. KG, Hamburg, Germany
Terms of delivery and rights to technical change reserved.
Download newest version at www.trinamic.com