ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 264)

PT motion must begin with the initial programming of the PT arrays. To do so, set:
MP[1] = First valid line in PT table.
MP[2] = Last valid array in PT table.
MP[3] = 1 for cyclical mode.
MP[4] = The ratio between the length of the PT time interval and the sampling time of
the position controller.
MP[5] = Number of as yet unused QP[N] elements when a “PT queue low” emergency
object is sent. Set to zero if no “PT queue low” warning is desired.
MP[6] = Write pointer. This is the next position in the QP[N] vector to be written by the
CANopen object 0x2002.
Set QP[N] for at least the first two points in the PT motion. This is needed because the PT
algorithm requires at least two time points for interpolating the motion trajectory. Set at
least three points if the speed at the second point is to be continuous.
If not already set, set UM=4 or UM=5, and MO=1.
Set PT=N, where QP[N] and QP[N+1] — and preferably QP[N+2] — are all programmed
to valid values.
Use the CAN PT auto-increment command for the rest of the PT motion.
When object 0x2002 is used to feed PT reference points to the drive while a PT motion is
executing, the drive automatically enters Online Feed mode, in which the drive is aware
of the position written and takes the following precautions:
If the feed is too slow, so that the drive must fetch unprogrammed points, the
motion will abort with a “Queue underflow” emergency.
If the feed is too fast, so that points not yet used by the drive are overstruck, the
drive will reject the feed attempt with a “Queue overflow” emergency.
The Online Feed mode will continue until the end of the current PT motion and will not
be applied to the next motion.
To stay informed about how the PT motion is advancing, the read and write PT table
pointers can be received continuously, mapped to a synchronous PDO, or the “Queue
low” emergency signal can be used to indicate the need for more data. The “Queue low”
emergency message includes the present location of the read pointer and the write
pointer. It is safe to send more PT data PDOs until the write pointer is one location before
the read pointer specified by the “Queue low” emergency message.
The host is well aware of the location of the write pointer, because it can count its own
messages. However, a data message may be rejected because the queue is full, or because
a message has been lost. In such a case, the drive issues an emergency object to the host.
After receiving the object, the true location of the write pointer may be unclear. The host
may then set MP[6] to the possibly-rejected table row and continue writing from there.
SimplIQ for Steppers Application Note The Position Reference Generator
MAN-STECR (Ver. 1.1)
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