Lenze PLC Designer PLC Designer (R3-1) - Manual (Page 578)

L-force | PLC Designer
General Editors
576 DMS 4.1 EN 03/2011 TD29

absolute: At the start of the new CAM cycle the CAM is evaluated independently
from the current slave position. This results in a jump, if the slave position related
to the start master position differs from the one related to the end master position.
relative: The new CAM will be shifted according to the current slave position; that
is the position the slave holds at the end of the former CAM cycle will be added as
'slave offset' to the values evaluated by the CAM. Nevertheless this results in a
jump if the slave position related to the start master position differs from 0 in the
CAM definition.
ramp_in: Starting the CAM potentially occurring jumps will be prevented by a
compensating movement (according to the limitations VelocityDiff, Acceleration,
Deceleration). Thereby, as far as the slave is rotatory, the option ramp_in_pos will
compensate in positive direction only, whereas ramp_in_neg will compensate in
negative direction. For linear slaves the direction of the compensation will result
automatically, that is ramp_in_pos and ramp_in_neg are interpreted like ramp_in.
Switching between CAMs
Basically a switch between two CAMs is possible at any time. However, there are some
items to be thought about:
Within the CAM editor the position of the slave has been defined as output of the CAM
function evaluated at a master position that is contained in the master range, what
can be expressed by the simple formula:
SlavePosition = CAM( MasterPosition )
As the actual period of the master drive generally is differing from the master range in
the definition of the CAM, the master position has to be scaled to the function domain
to serve as adequate input of the CAM function:
SlavePosition = CAM( MasterScale*MasterPosition + MasterOffset )
In analogical manner the output of the function (that is the virtual slave position) has
to been scaled, if the start of a CAM in absolute mode gave rise to a jump:
SlavePosition = SlaveScale*CAM( MasterPosition ) + SlaveOffset
In the worst case both scalings have to be adopted, so that the SlavePosition in fact
results in the more complex formula
Slaveposition = SlaveScale*CAM( MasterScale*Masterposition + MasterOffset ) +
SlaveOffset
The appropriate scales and offsets may change at the end of each CAM cycle.
Unfortunately, a restart of CAM module MC_CamIn will delete its memory and
therefore also the scaling and offset values. Hence, the CAM function as defined will
be used yielding different slave values in general. For this reason it is recommended to
restart MC_CamIn-FB only in case that a different CAM shall be processed.