Manual

11
ATA6830
4575B–BCD–01/03
Reference Run In normal operation, new position commands are transmitted as absolute values. To
drive the stepping motor to these absolute positions, the circuit has to know the motor’s
zero position. Therefore, the stepping motor has to perform a reference run after each
power-up in which it is extended or retracted to its limit stop. Before the execution of the
reference run, the motor is supplied with hold current.
As the actual position is not known at the beginning of the reference run the whole posi-
tion range has to be passed. To optimize performance for smaller actuators, the
reference run has been reduced to 698 steps. Therefore, it is prohibited to access posi-
tions higher than 698, because in a following reference run the stepping motor would not
reach its zero position.
If it is necessary that the entire range up to position 1024 can be used, the reference run
has to be executed twice. Since any command during reference run is ignored, the sec-
ond reference command has to be sent about 2.4 s after the first command.
To avoid any possible mistake, e.g., the loss of a step during the reference run or the
bouncing at the limit stop, there is a special run to be executed.
This is shown in Table 2.
Cruise Control The travel operation control independently moves the stepping motor into its new posi-
tion. To reach the new position as fast as possible but without abrupt velocity changes,
the stepping motor is accelerated or slowed down depending on the difference between
actual and nominal position. If this difference is huge the stepping frequency will
increase (acceleration). When the new position is nearly reached, the frequency will
decrease again (deceleration). In the case of a new nominal position opposite to the
direction of the motion being from the microcontroller, the stepping frequency will
decrease to its starting value (300 Hz) before the direction can turn. The cruise control is
shown in Figure 11.
The possible stepping frequencies for velocity control are shown in Table 3.
Table 2. Reference Run Course
Phase Action Int. Counter
Steptime
I Ramp up to 446 Hz step frequency Drive
through
the
whole
range
(698
steps)
704 3300 µs
703 2895 µs
702 2540 µs
701 2240 µs
Drive at constant speed 700 to 11 2240 µs
Ramp down to minimum step
frequency (303 Hz)
10 2240 µs
92549 µs
II 8 2895 µs
III 7 to 6 3300 µs
IV Wait for 6 ´ 3300 µs with the last coil current 6 3300 µs
V Perform another 6 steps with 3300 µs 5 to 0 3300 µs
VI Wait for 5 ´ 3300 µs with the last coil current 0 3300 µs
VII Set current to hold current; normal operation varied varied