TMC246/A ETC2 [List of Unclassifed Manufacturers], TMC246/A Datasheet - Page 10

• Manufacturer Part Number: TMC246/A
• Description: High Current Microstep Stepper Motor Driver with sensorless stall detection, protection / diagnosis and SPI Interface
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

TMC246 DATA SHEET (V2.01 / Sep. 14th, 2005)
Stall Detection
Using the sensorless load measurement
The TMC246 provides a patented sensorless load measurement, which allows a digital read out of the
mechanical load on the motor via the serial interface. To get a readout value, just drive the motor
using sine commutation and mixed decay switched off. The load measurement then is available as a
three bit load indicator during normal motion of the motor. A higher mechanical load on the motor
results in a lower readout value. The value is updated once per fullstep.
Since the load detection is based on the motor’s back EMF, the readout results depend on several
factors:
Implementing sensorless stall detection
The sensorless stall detection typically is used, to detect the reference point without the usage of a
switch or photo interrupter. Therefore the actuator is driven to a mechanical stop, e.g. one end point in
a spindle type actuator. As soon as the stop is hit, the motor stalls. Without stall detection, this would
give an audible humming noise and vibrations, which could damage mechanics.
To get a reliable stall detection, follow these steps:
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG
stall threshold
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1. Choose a motor velocity for reference movement. Use a medium velocity which is far enough
2. Use a sine stepping pattern and switch off mixed decay (at least 1 to 3 microsteps before zero
3. Choose a threshold value L
4. Monitor the load indicator during each reference search movement, as soon as the desired
5. If the motor stops during normal movement without hitting the mechanical stop, decrease
Motor velocity: A higher velocity leads to a higher readout value
Motor resonance: Motor resonances cause a high dynamic load on the motor, and thus
measurement may give unsatisfactory results.
Motor acceleration: Acceleration phases also produce dynamic load on the motor.
Mixed decay setting: For load measurement mixed decay has to be off for some time before
the zero crossing of the coil current. If mixed decay is used, and the mixed decay period is
extended towards the zero crossing, the load indicator value decreases.
away from mechanical resonance frequencies. In some applications even motor start / stop
frequency may be used. With this the motor can stop within one fullstep if a stall is detected.
crossing of the wave). Monitor the load indicator during movement. It should show a stable
readout value in the range 3 to 7 (L
may be increased, if desired.
velocity is reached. Readout is required at least once per fullstep. If the readout value at one
fullstep is below or equal to L
L
STALL
max
v_max
min
indicator
. If the stall condition is not detected at once, when the motor stalls, increase L
load
v(t)
acceleration
acceleration
jerk
STALL
STALL
constant velocity
between 0 and L
, stop the motor.
L
L
STALL
MOVE
MOVE
stall detected!
vibration
). If the readout is high (>5), the mixed decay portion
stall
MOVE
- 1.
t
t
STALL
.
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