User guide

➄ Basic 6250 Features 49
Enabling backup to home (HOMBAC) allows you to use two other homing features, HOMEDG
and HOMDF. The HOMEDG command allows you to specify the side of the home switch on
which to stop. The HOMDF command allows you to specify the final approach direction. If
HOMBAC is not enabled, HOMEDG and HOMDF will have no effect on the homing algorithm
(see Figures A and B).
Figures A and B show the homing operation when HOMBAC is not enabled. If a limit is
encountered during the homing operation, the motion will be reversed and the home switch will
be sought in the opposite direction. If a second limit is encountered, the homing operation
will be terminated, stopping motion at the second limit.
As soon as the homing operation is successfully completed, the absolute position register is
reset to zero.
CCW Edge
of Home
Home Active
Region
CW Edge
of Home
Velocity
CCW
Limit
Initial
Position
CW
Limit
Position
Figure A. Homing in a CW Direction (HOMØ) with backup to home
disabled (HOMBACØ)
CCW Edge
of Home
Home Active
Region
CW Edge
of Home
Velocity
CCW
Limit
Initial
Position
CW
Limit
Position
Figure B. Homing in a CCW Direction (HOM1) with backup to home
disabled (HOMBACØ)
CW Homing
with Backup
to Home
Enabled
The seven steps below describe a sample homing operation when HOMBAC is enabled (see
Figure C). The final approach direction (HOMDF) is CW and the home edge (HOMEDG) is the
CW edge.
NOTE
To better illustrate the direction changes in the backup-to-home operation, the illustrations in
the remainder of this section show the backup-to-home movements with varied velocities. In
reality, the backup-to-home movements are performed at the same velocity (defined with the
HOMVF command).
➀ A CW home move is started with the HOMØ command at the
HOMA acceleration. Default HOMA is 2,500,000 steps/sec
2
.
➁ The HOMV velocity is reached (move continues at that
velocity until home input goes active).
➂ The CCW edge of the home input is detected, this means the
home input is active. At this time the move is decelerated at
the HOMADA and/or HOMAD command values. It does not matter
if the home input becomes inactive during this deceleration.
➃ After stopping, the direction is reversed and a second move
with a peak velocity specified by the HOMVF value is started.
➄ This move continues until the CCW edge of the home input is
reached.
➅ Upon reaching the CCW edge, the move is decelerated at the
HOMAD command value, the direction is reversed, and
another move is started in the CW direction at the HOMVF
velocity.
➆ As soon as the home input CW edge is reached, this last
move is killed. The load is at home and the absolute position
register is reset to zero.
CCW Edge
of Home
Home Active
Region
CW Edge
of Home
Velocity
CCW
Limit
Initial
Position
CW
Limit
Position
Figure C. Homing in a CW Direction (HOMØ) with HOMBAC1,
HOMEDGØ, HOMDFØ