Rockwell Automation GMLC Reference Manual - Manual (Page 287)

Publication GMLC-5.2 - November 1999
250 Motion Blocks
Configuring Position Lock Cams
Selecting Once in the Perform Profile field causes the selected cam
profile to execute only once, when initiated by a subsequent Position
Lock Cam block. This means that cam motion of the slave axis starts
when the master axis moves into the range defined by the start and end
points of the profile. When the master axis moves outside the range of the
profile, cam motion on the slave axis stops; it resumes when and if the
master moves back into the profile range specified by the start and end
points.
Selecting Continuously in the Perform Profile field causes the selected
cam profile to execute indefinitely, when initiated by a subsequent
Position Lock Cam block. With continuous operation, the profile master
and slave positions are unwound when the position of the master axis
moves outside the profile range, causing the cam profile to repeat
indefinitely. This feature is particularly useful in rotary applications
where it is necessary that the position-lock cam run continuously in a
rotary or reciprocating fashion. To generate smooth continuous motion
using this technique, however, take care to design the cam profile to
ensure that there are no position, velocity, or acceleration discontinuities
between the start and end points of the profile.
Configuring Pending Position Lock Cams
Use a Pending Position Lock Cam to seamlessly blend two position-lock
cam profiles together without stopping either axis. This is useful in such
applications as high-speed packaging, when a slave axis must lock onto a
moving master axis, and accelerate to the proper speed using a specific
profile. When this acceleration profile finishes, your program must
smoothly blend it into the operating profile, which typically executes
continuously. To stop the slave axis, your program must smoothly blend
the operating profile into a deceleration profile, so that the axis stops at a
known location, as shown below.