➃
Servo Tuning
41
Target Zone Mode
To prevent premature command execution before the actual position settles into the
commanded position, use the Target Zone Mode. In this mode, enabled with the
STRGTE
command, the move cannot be considered complete until the motor's actual position and actual
velocity are within the target zone (that is, within the distance zone defined by
STRGTD
and
less than or equal to the velocity defined by
STRGTV
). If the motor does not settle into the
target zone before the timeout period set with the
STRGTT
command, the 6250 detects a
timeout error (see illustration below).
Refer to Chapter 7
for error program
examples
If the timeout error occurs, you can prevent subsequent command/move execution only if you
enable the
ERROR
command to continually check for this error condition, and when it occurs
to branch to a programmed response you can define in the
ERRORP
program.
As an example, setting the distance zone to
±
5 steps (
STRGTD5
), the velocity zone to
≤
0.5 rps
(
STRGTVØ.5
), and the timeout period to 1/2 second (
STRGTT5ØØ
), a move with a distance of
8,000 steps (
D8ØØØ
) must end up between position 7,995 and 8,005 and settle down to
≤
0.5
rps within 500 ms (1/2 second) after the commanded profile is complete.
Damping is critical.
To ensure that a move settles within the distance zone, it must be damped to the point that it
will not move out of the zone in an oscillatory manner. This helps ensure the actual velocity
falls within the target velocity zone set with the
STRGTV
command (see illustration below).
Actual
STRGTD
(Distance Zone)
STRGTV
(Velocity Zone)
STRGTT
(Timeout Period)
Position
Velocity
Commanded
Fa ile d Move Comp le tio n
Timeout Occurs,
Error Bit Set
Commanded
Actual
S ucce ssful Move Comp le tio n
Time
Time
STRGTT
(Timeout Period)
Position
Velocity
Commanded
Actual
Commanded
Time
Time
STRGTD
(Distance Zone)
STRGTV
(Velocity Zone)
Actual
Move
Completed
Move
Completed
TSTLT
(Actual Settling Time)
Checking the
Actual Settling
Time
Using the
TSTLT
command, you can display the actual time it took the last move to settle
into the target zone (that is, within the distance zone defined by
STRGTD
and less than or
equal to the velocity defined by
STRGTV
). The reported value represents milliseconds. This
command is usable whether or not the Target Zone Settling Mode is enabled with the
STRGTE
command.
