TMCM-170 and TMCM-171 MODULE – Reference and Programming Manual
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Copyright © 2005, TRINAMIC Motion Control GmbH & Co. KG
1.5 Parameterizing the positioning algorithm
The module supports a positioning based on the encoder position. The user can either use the pure
positioning PID parameter set for positioning, or an integrated ramp generator with linear ramp control
(enable the “Velocity PID – Control setting”). Parameters for the ramp generator are the maximum
positioning speed as well as the acceleration value. It is recommended to use the ramp generator.
The ramp generator automatically calculates the slow down point, i.e. the point at which velocity is to
be reduced in order to stop at the programmed target position. This calculation is based on the
velocity setting and the acceleration setting. The PID parameter sets are used as follows:
•
Above min_pos_speed the motor speed is regulated by the Velocity PID
•
Below min_pos_speed a combination of Velocity and Position PID is used to get the best
performance
PID setting
stiffness
0
Velocity PID
Position PID
velocity
min
pos
speed
max
pos
speed
min
pos
speed
max
pos
speed
velocity difference for slow-down
velocity difference for slow-down
Reaching the target position is signaled by setting the POS_END flag. In order to minimize the time
until this flag becomes set, a positioning tolerance (MVP_target_reached_distance) can be chosen.
Since the motor typically is assumed not to signal target reached when the target was just passed in a
short moment of time at a high velocity, additionally a maximum target reached velocity
(MVP_target_reached_velocity) can be defined. A value of zero is the most universal, since it implies
that the motor stands still at the target. But when a fast raising of the POS_END flag is desired, a
higher value for MVP_target_reached_velocity will save a lot of time. The best value should be tried
out in the actual application. In hall sensor only mode (see SGP 250), this distance setting is used to
stop the regulation algorithm in order to avoid oscillations around the target position.
Depending upon the motor / mechanics, a bit of oscillation is normal, in the best case it can be
reduced to be at least +/-1 encoder step, because otherwise the regulation can not keep the position!
In order to dampen oscillations as much as possible, also try using the PWM hysteresis. Especially
with a friction in the mechanics, increasing this parameter might help to overcome it and to speed up
the regulation. Then, at the next step you should again try to optimize the P-part for the positioning P-
regulator, and after that add a bit of I and D, while always trying to keep the regulation loop stable /
stable to within your desired target range.
