User Manual V 1-4.XX User guide

9-28 Applications
When the Trim Gain parameter is above a value of 2.0, the profile
control will decelerate as it approaches the target at approximately the
programmed Decel rate (P44).
If the shaft overshoots the target area it will back up. If this is
unacceptable, the Error Trim Gain parameter can be lowered to
eliminate this overtravel.
As the value of this parameter is lowered it will begin to “round off”
the end of the decel ramp (Fig. 9.13). The end of the target approach
can be made as “smooth” as desired using this method.
Figure 9.13
Example: Encoder Step Trim
Continuing to lower the trim gain value will cause this rounding to
begin earlier in the Decel ramp. This will also cause the time to target
position to extend longer.
Step Position Error
The control will position the motor within the tolerance on each step
before proceeding to the next step. The actual rotor position may be
slightly forward or behind the exact target and still be within range.
Increasing the tolerance parameter value will enlarge this range.
When the next step calculates a target, it uses the actual position the
new step begins at.
Repeating Profile Sequences
If a Goto End Action is selected the position error will continue to
accumulate over multiple sequences. Over time the accrued error
could be significant.
If a Home End Action is selected, the error of a single sequence will
Not accumulate over multiple sequences. The rotor will return to the
same position it was in when the Profile enable bit was first set. As
long as the enable bit is set, the control will retain this as its home
position. Additional sequences can be started by toggling the Run
Sequence bit.
Velocity Blend Mode
Encoder mode applications which don’t require great precision can
utilize the Velocity Blend mode to switch from one step velocity to
another. In this blend mode, control will not demand that the motor
rest at zero speed for eleven update intervals before continuing to the
next step as illustrated in Figure 9.14.
Time
Speed
Step 1
Speed
Accel Rate
P42
Rate P44
+/- Value Tolerance
P244
Target Position
100 Revs
Rounding
Approximate Decel