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6250 Servo Controller User Guide
End-of-Travel Limits
The 6250 can respond to both hardware and software end-of-travel limits. The 6250 is shipped
from the factory with the hardware limits enabled. If you are not using end-of-travel limits in
your application, you must disable these limits either through software or hardware before
motion will occur.
Refer to Chapter 3,
Installation
, for instructions
to wire hardware end-of-
travel limit switches.
End-of-travel limits prevent the motor's load from traveling past defined
limits. Once a hardware or software limit is reached, the 6250 will decelerate that axis at a
rate specified with the
LHAD
or
LSAD
command. Typically, software and hardware limits are
positioned in such a way that when the software limit is reached the motor will start to
decelerate towards the hardware limit. This will allow for a much smoother stop at the
hardware limit. Software limits can be used regardless of incremental or absolute positioning.
Refer to the
LH
,
LS
,
LHAD
,
LHADA
,
LSAD
, and
LSADA
commands in the 6000 Series
Software Reference Guide for more information.
The example below uses the Distance Scaling (
SCLD
) command to define software limits in
revolutions (assuming a 4000 step/rev resolution). Software limits are defined by the
LSCW
and
LSCCW
commands. They are enabled with the
LS
command. The software limits are referenced
from a position of absolute zero. Both software limits may be defined with positive values
(Axis #2 in example below) or negative values. Care must be taken when performing
incremental moves because the software limits are always defined in absolute terms. They must
be large enough to accommodate the moves, or a new zero point must be defined (using the
PSET
command) before each move.
NOTE
To ensure proper motion when using soft end-of-travel limits, be sure to set the
LSCW
value to
a greater absolute value than the
LSCCW
value.
Example
In this example, the hardware limits are enabled on axes #1 and #2. Deceleration rates are
specified for both software and hardware limits. If a limit is encountered, the motors will
decelerate to a stop.
Command
Description
>
SCALE1
Enable scaling
>
@SCLD4ØØØ
Distance scale factor
>
@SCLA4ØØØ
Acceleration scale factor
>
@SCLV4ØØØ
Velocity scale factor
>
LH3,3
Enable limits 1 and 2
>
LHAD1Ø,1Ø
Hard limit deceleration
>
LSAD5,1Ø
Soft limit deceleration
>
LSCCWØ,2
Establish CCW soft limit
>
LSCW1Ø,2Ø
Establish CW soft limit
>
LS3,3
Enable soft limits 1 and 2
Homing
(Using the Home Inputs)
Refer to Chapter 3,
Installation
, for instructions
to wire hardware home limit
switches.
The
HOM
command initiates a sequence of moves that position an axis using the Home and/or
the Z channel inputs. The result of any homing operation is a repeatable initial starting
location. The home inputs to be used, the edge of those inputs, and the final approach
direction may all be defined by the user. If the Z channel input is to be used, the
HOMZ
command must be enabled. The input polarity (normally-open or normally-closed) of the
home input or switch is defined with the
HOMLVL
command.
The velocity for a move to the home position is specified with the
HOMV
command. The
acceleration and deceleration rates are specified with the
HOMA
and
HOMAD
commands,
respectively. (
HOMAA
and
HOMADA
are also used if you are using S-curve Profiling—see
Chapter 6 for more details.) If backup to home (
HOMBAC
) is enabled, the velocity of the final
approach toward the home position is specified with the
HOMVF
command.
