Examples and tips
PROGRAMMING MANUAL
262
R
e
vi
si
o
n
1
.0
With these values, the command
MOVE(28)
rotates the table 28 degrees in
positive direction.
Absolute encoder setting
The absolute encoder keeps the current motor position, even if there is no
power supplied. The absolute encoder gives the position within one turn
(that is, a fraction from 0 to and excluding 1), and it has a multiturn counter.
You can set the multiturn behaviour of the absolute encoder with the
parameter Pn205 of the Sigma-II Servo Driver. This parameter adjusts the
maximum number of turns that the counter counts before it has an overflow.
For more information on Servo Driver parameter Pn205, see the Sigma-II
Servo Driver manual. Taking this parameter value into account, the
maximum position value the encoder can signal is:
which makes it Pn205 complete turns, plus the position within one turn (the
fraction from 0 to and excluding 1). When the MECHATROLINK-II
connection is established with the drive, the absolute encoder position is
read from the drive and the value is written in
MPOS
(after the conversion:
UNITS
× Pn202/Pn203). When the mechanical system has a limited travel
distance to move, like in a ball screw, the value of the parameter Pn205
should be set large enough to have an overflow of the counter out of the
effective position. This is called limited axis or finite axis. A typical example
of a limited axis is a ball screw, as shown in fig. 24. When the mechanical
system always moves in the same direction, it reaches the overflow of the
multiturn counter. In this case, the value of Pn205 must guarantee that the
overflow always occurs in the same position with respect to the machine.
This is called unlimited axis and a typical example of it is a turntable shown
in fig. 20. It can be achieved with the following equation: the smallest value
of
m
such that:
Pn202 = 32
Pn203 = 36
UNITS = 2
=256
8
max_encoder_count_value = (Pn205 + 1) encoder_counts - 1
.
