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HARSFEN0602
A PVT motion is initiated by stating
PV=N with
64N1 , and BG.
The command PV=N sets the read pointer of the table to N and specifies that the next BG will start a PVT
motion. BG starts the motion.
The PVT table may be written on-line while PVT motion is on. An infinite-time non-periodic motion can be
generated in the cyclical mode (MP[3]=1), by programming the PVT table on the fly.
The host must know how much free place there is in the PVT table, in order to keep programming an
executing PVT motion. The best way is to keep tracking the table read and write pointers. The host knows
the write table, since it control the writing to the table. If the host is in doubt, it can inquire MP[6]. To
inquire the read pointer use the command PV.
The read pointer and the write pointer can be mapped to a synchronous PDO, so a CAN master can
efficiently and continuously get informed about the status of many amplifiers running PVT in parallel in a
network.
If the host doesn't want to poll the status of the PVT motion continuously, it can use the queue underflow
CAN emergency object as a request to refill the PVT table – see details in the sequel.
The unused part of the PVT table may be programmed for the next motion while the present motion is
executing.
An attempt to modify the data of an executing motion segment is an error.
12.1.6.4 Mode Termination
The PVT motion terminates upon one of the following cases:
The motor is shut down, either by programming MO=0 or by an exception
Another mode of motion is set active, e.g. by programming PA=xxx;BG. In this case, the new
motion command executes immediately, without having to explicitly terminate the PVT mode.
The PVT motion manager runs out of data. This happens when the read pointer reaches MP[2] and
MP[3] is zero. This may also occur in the auto increment mode (CAN communications only, see
below) if the read pointer reaches the write pointer. In that case, the PVT motion is stopped
immediately, using the SD deceleration. Note that if the last programmed PVT speed is zero, then
the PVT motion terminates neatly, and the stopping at the end of the motion does nothing.
12.1.6.5 PVT Motion Using CAN
The PVT table allows the performance of pre-designed motion plans, as well as the on-line design of motion
plan. For on-line motion design, you can write new entries to the PVT table while PVT motion is executing.
The on-line motion design ability is limited by the speed of the communication interface.
Consider an RS-232 ASCII communication interface.
Programming of a single PVT table row has the format
QP[xx]=xxxxxxxxx;QV[xx]=xxxxxxx;QT[xx]=xxx;
Up to 40 characters may be required to program a single PVT table row.
At the communication rate of 19200 baud, this may take 20msec. At the communication rate of 115200baud,
this may take 4msec.
The CAN communication option allows much faster PVT table programming, by packing an entire PVT
table row into one PDO communication packet. For easy synchronization with the host, the Amplifier may
be programmed to send the PVT read and write pointers continuously to the host as a synchronous PDO, or
to send an emergency object whenever the number of yet unexecuted motion segments falls below a given
threshold.