11

ATA6830

4575C–BCD–05/03

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

9

2549 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