Omron trajexia CJ1W-MCH72 Operation Manual page 299

How-to's
5-1-3-3 Absolute encoder setting
288
1 Pn202 and Pn203 are integers.
2 UNITS must not have an infinite number of decimal digits. This can create
rounding errors that result in small position errors that add up to large
accumulative position errors.
3 For reasons of stability, it is necessary to avoid situations where Pn202/
Pn203 is less than 0.01 or greater than 100. It is recommended that Pn202/
Pn203 is approximately 1.
We can now rewrite the last equation to:
One solution to this equation is:
When we consider the third recommendation from the above list (avoid
situations where Pn202/Pn203 is less than 0.01 or greater than 100), we can
rewrite the last equation to:
UNITS·
This gives us the solution:
With these values, the command MOVE(28) rotates the table 28 degrees in
positive direction.
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:
max_encoder_count_value = (Pn205 + 1) encoder_counts - 1
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
Pn202
10
13
.
UNITS
= 2
Pn203 360
13
UNITS = 2 = 8192
Pn202 = 10
Pn203 = 360
5
Pn202
10 2
13 8
= 2 = 2
Pn203 360 36
8
UNITS = 2 =256
Pn202 = 32
Pn203 = 36
.
Section 5-1
32
8
= 2
36