Multi-Axis Coordinated Motion Instructions
Rockwell Automation Publication MOTION-RM002H-EN-P-February 2018 513
Lock Position
Data Type Description Valid Default
Values
IMMEDIATE
REAL or
TAG
Lock Position in Master Driven Mode
The position on the Master Axis where a Slave Coordinate System should start after the move has been initiated on
the Slave Coordinate System when executing in Master Driven Mode. This is an absolute position (plus or minus) on
the Master Axis in Master Axis units. You can specify a Lock Position to delay the start of motion of a Slave
Coordinate System after the motion instruction has been initiated on the Slave Coordinate System.
If an axis in the Slave Coordinate System is already moving and a coordinated move instruction (MCLM, or MCCM)
with a Lock Position is activated on the Coordinate system, then you will receive an MDSC_LOCK_WHILE_MOVING
error for the MCLM or MCCM instruction.
Because Merge is always performed immediately when an instruction is enabled, a merge instruction that starts at
a nonzero velocity with both a Lock Position and a Merge enabled will receive an MDSC_LOCK_WHILE_MOVING
error.
The Lock Direction determines the direction in which the Master Axis must be moving when it crosses the Lock
Position before the Slave Coordinate System locks to the Master Axis.
Note that if there is an unwind value specified on the Master Axis, then the Lock Position must be between 0 and
the unwind value (that is, the Lock Position cannot be more than one unwind.)
This parameter is only used in Master Driven Mode.
Lock Position in Time Driven Mode
There is no Lock Position in Time Driven Mode for a coordinate system. An error will be generated if the Lock
Direction is not NONE and the system is in Time Driven Mode for an MCLM or MCCM.
This parameter is only used in Master Driven Mode.
Axis Lock Behavior
When the Master axis crosses the Master Lock position in the direction as specified by the motion instruction, the
Slave Coordinate System becomes locked to the Master axis. The LockStatus bit is set at this time.
The MCLM and MCCM instructions on the Slave Coordinate System in MDSC mode go IP as soon as they reach the
head of the motion queue. The head of the queue is defined as the move right before the active move.
For the Immediate Forward Only or Immediate Reverse Only Lock Directions, the Slave Coordinate System gets
locked to the Master Axis immediately when the MCLM or MCCM instruction is executed (goes IP). For the Position
Forward Only or Position Reverse Only Lock Directions, the slave gets locked to the Master Axis when the Master
Axis crosses the Master Lock Position in the direction as specified by the motion instruction. In either case, the
LockStatus bit is set when the lock occurs.
Because there is no bi-directional behavior defined, once locked, the Slave Coordinate System follows the Master
only in the specified direction. If the Master reverses direction, then the Slave stops following the Master. Note that
the LockStatus bit remains set until the Master decelerates to zero. It is cleared at the point of reversal of the Master
axis. The Slave does not follow the Master while the Master travels in the reverse direction.
If the Master axis changes directions again, then the axis LockStatus bit is set again when the Slave Coordinate
System crosses the original reversal point, at which time the slave resumes following the Master Axis.
On the Slave Coordinate System the following restrictions apply:
• If a new instruction succeeds the active motion instruction but it is in the opposite direction of its current
direction, then the error MDSC_LOCK_DIR_MASTER_DIR_MISMATCH is generated on the new motion
instruction when it goes IP. The same is true if the new instruction is started via a merge operation.
• A new instruction merged to an active instruction on the Slave Coordinate System must use the Immediate
Forward Only or Immediate Reverse Only Lock Direction. If the new instruction uses the Position Forward Only or
Position Reverse Only Lock Direction, the error MDSC_LOCKDIR_CONFLICT is generated on the new instruction.
• A Lock Position may be used on an instruction that is merging a paused or dwelling motion instruction.
On the Master Axis, no special restrictions apply.
Note that if an instruction with the merge enabled is enqueued, then the whole queue is flushed and the active
move is terminated.
Note that if Master Axis filtering is enabled on the master axis, then the lock position for the Slave Coordinate
System is delayed by the filter; the amount of delay is dependent on the filter bandwidth.
Default = 0.0
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