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Digitax ST User Guide

171

Issue Number: 5

This parameter enables sequencer latching. When sequencer latching is
used, a digital input must be used as a run permit or not stop input. The
digital input should write to Pr

6.39

. The run permit or not stop input must

be made active to allow the drive to run. Making the run permit or not
stop input inactive resets the latch and stops the drive.

12.22.8 Catch a spinning motor

When the drive is enabled with this bit at zero, the post ramp reference
(Pr

2.01

) starts at zero and ramps to the required reference. When the

drive is enabled with this bit at one, the post ramp reference is set to the
motor speed.
When closed-loop vector mode is used without position feedback, and
catch a spinning motor is not required, this parameter should be set to
zero as this avoids unwanted movement of the motor shaft when zero
speed is required. When closed-loop vector mode without position
feedback is used with larger motors it may be necessary to increase
Pr

5.40

Spin start boost

from its default value of 1.0 for the drive to

successfully detect the motor speed.

12.22.9 Position modes

This parameter is used to set the position controller mode as shown in
the table below.

Rigid position control

In rigid position control the position error is always accumulated. This
means that, if for example, the slave shaft is slowed down due to
excessive load, the target position will eventually be recovered by
running at a higher speed when the load is removed.

Non-rigid position control

In non-rigid position control the position loop is only active when the 'At
Speed' condition is met (see Pr

3.06

). This allows slippage to occur while

the speed error is high.

Velocity feed forward

The position controller can generate a velocity feed forward value from
the speed of the reference encoder. The feed-forward value is passed to
menu 1, and so ramps may be included if required. Because the position
controller only has a proportional gain, it is necessary to use velocity
feed-forward to prevent a constant position error that would be
proportional to the speed of the reference position.
If for any reason the user wishes to provide the velocity feed forward
from a source other than the reference position, the feed forward system
can be made inactive, i.e. Pr

13.10

= 2 or 4. The external feed forward

can be provided via Menu 1 from any of the speed references. However,
if the feed forward level is not correct a constant position error will exist.

Relative jogging

If relative jogging is enabled the feedback position can be made to move
relative the reference position at the speed defined by Pr

13.17

Orientation

If Pr

13.10

is 5 the drive orientates the motor following a stop command.

If hold zero speed is enabled (Pr

6.08

= 1) the drive remains in position

control when orientation is complete and hold the orientation position. If
hold zero speed is not enabled the drive is disabled when orientation is
complete.
If Pr

13.10

is 6 the drive orientates the motor following a stop command

and whenever the drive is enabled provided that hold zero speed is
enabled (Pr

6.08

= 1). This ensures that the spindle is always in the

same position following the drive being enabled.
When orientating from a stop command the drive goes through the
following sequence:
1. The motor is decelerated or accelerated to the speed limit

programmed in Pr

13.12

, using ramps if these are enabled, in the

direction the motor was previously running.

2. When the ramp output reaches the speed set in Pr

13.12

, ramps are

disabled and the motor continues to rotate until the position is found
to be close to the target position (i.e. within 1/32 of a revolution). At
this point the speed demand is set to 0 and the position loop is
closed.

3. When the position is within the window defined by Pr

13.14

, the

orientation complete indication is given in Pr

13.15

The stop mode selected by Pr

6.01

has no effect if orientation is

enabled.

6.09

Catch a spinning motor

Uni