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HARSFEN0602
The elements to be programmed are specified by a “write pointer”.
The value of the write pointer may be set by the parameter MP[6].
12.2.4 Initializing the external reference parameters.
This section details what happens when the external reference generator is initialized.
The external reference generator is initialized at MO=1, and each time a relevant parameter
(FR[3], AG[3], EM[1]) is changed. Note that changing EM[2],EM[3],EM[4],and EM[5]
does nothing immediately. Setting EM[1] activates the entire set of ECAM parameters.
12.2.4.1 Jump-Free Motor Starting Policy
Upon starting a motor by the MO=1 command, the motor should never jump.
The first and most important reason is safety. The other reason is to avoid an excessive
position error fault immediately after the motor is started.
In order that the motor will not jump, the initial software reference is automatically set to the
present position of the motor, and the software command remains stationary until a motion
instruction is accepted. After setting MO=1, the motion mode is Idle, so that commanding
BG without the prior specification of another motion mode will not launch any motion.
Example:
Suppose that MO=0, RM=0, and PX=1000 (Motor is off, no external reference, present position is
1000 counts). Entering MO=1 will automatically set the software position reference to 1000 counts,
in the Idle mode. The command sequence PA=0;BG will launch a PTP motion from the position of
1000 counts to the zero position.
Example:
Suppose that MO=0, RM=1, FR[3]=1, AG[3]=0, PY=3000, and PX=1000 (Motor is off, external
reference is generated by the auxiliary encoder input only with a unit follower ratio, the auxiliary
position is 3000 and the present position is 1000 counts). Entering MO=1 will automatically set the
software position reference so that the total position reference will equal PX. Therefore the initial,
automatic, software command will be PX – FR[3]*PY= 1000 - 1*3000 = -2000.
If the auxiliary encoder input is stable, the command sequence PA=0;BG will launch a PTP motion
from the position of 1000 counts to the position of 3000.
12.2.4.2 Switching the parameters of the external reference on the fly
The parameters of the external reference generator can be changed on the fly only if the software
reference generator is idle. This can be verified by the motion status – MS should return 0 or 1.
When the parameters of the external reference generator are changed, the software reference is set so
that the motor will not jump at the instance the new parameters are set. The setting of the software
reference is similar to the setting described in the section "Jump-Free Motor Starting Policy" above.
The external reference parameters that can be changed on the fly are:
Parameter Description
AG[N] Analog gain
FR[N] Follower ratio
EM[N] Ecam parameters
AS[1] Offset for analog input
HY[N] Reading of auxiliary encoder
Example:
Consider a manipulator that works a conveyer. Whenever a box arrives, the roller prints a label on
the box. When a new box arrives, it first homes the auxiliary encoder to read zero. The auxiliary encoder
references the roller in the follower mode, with FR[3]=CA[18]/(Conveyer encoder counts/mm*2*
*r(mm)).