TMC223 DATASHEET (V. 1.05 / March 7, 2011)
39
SetPosition
This command will cause the stepper motor to move to the desired target position. See 6.8.12
SetPosition on page 37. After the motion has been finished, the situation is as depicted in the figure
below.
Stop
Actual Position
= Target Position
= 3000
X [µsteps]
Figure 24: Positioning Example: Motion finished
Afterwards the actual status and position can be verified by GetFullStatus1 and GetFullStatus2
commands. The master can check if a problem, caused by electrical or temperature problems,
occurred. Furthermore the actual position is read.
7 Sensorless Stall Detection
The sensorless stall detection of the TMC223 bases on the measurement of the Back EMF (electro
magnetic force) voltage (UBEMF) induced by the motion of the rotor. The amplitude of the Back EMF
voltage is proportional to the speed of the rotor. The Back EMF constant of a stepper motor can
determined by turning the axis of a non-connected motor measuring the amplitude and frequency of
generated voltage at one phase of the motor.
If a motor stalls, the velocity of its rotor varies and the amplitude of the BEMF varies. The TMC223
detects a stall or disturbances of the motion measuring the variations of the Back EMF.
From physical point of view, a stepper motor is an anharmonic oscillator causing disturbances of the
rotors motion. Although micro stepping cause low resonances - the measurement of the BEMF has to
be masked to separate signals caused by resonance effects from those caused by stall.
7.1 Stall Detection Flags
A Stall is signalised by dedicated stall detection flags (Table 16: Stall Detection Flags). The stall
detection flag named "Stall" is the logical function DelStallLo OR DelStallHi OR AbsStall.
The DelStallLo flag is set to one if the measured and averaged UBEMF_AVARAGE becomes below the
threshold UBEMF < ( UBEMF_AVARAGE - DelThr). This occurs when breaking the motor axis in a way that
tries to decelerate the rotor - when the stepper acts a motor. The DelStallHi is set to one if the
averaged UBEMF_AVARAGE becomes above the threshold (UBEMF_AVARAGE - DelThr) where UBEMF_AVARAGE
.
This occurs when a pulling torque is applied to the motor axis that tries to accelerate the rotor - when
the stepper acts as a generator.
The AbsStall flag becomes one if the UBEMF comes below the limit defined by AbsThr. This occurs
when a motor come at rest at a limit. A stepper motor might jump back a multiple of for full steps when
reaching a limit. This generates BEMF signals that might trigger the DelStallHi flag - depending on the
parameterizing.
Hint: If the sensorless stall detection stops the motor, the StepLoss status bit be set in addition.
DelStallLo
DelStallHi
AbsStall
Stall
Condition
1
0
0
0
1
0
0
0
1
1
1
1
UBEMF < ( UBEMF_AVARAGE - DelThr )
UBEMF > ( UBEMF_AVARAGE + DelThr )
UBEMF < AbsThr
Table 16: Stall Detection Flags
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