Panasonic MINAS-A4P Technical Reference page 109

[1] Setting of external scale ratio
Set up the external scale ratio using the numerator of external scale ratio (Servo parameter
No.78), the multiplier of numerator of external scale ratio (Servo parameter No.79) and the
denominator of external scale ratio (Servo parameter No.7A).
- Check the number of encoder pulses per motor rotation and the number of external scale pulses
per motor rotation, set up the numerator of external scale ratio (Servo parameter No.78), multiplier
of numerator of external scale ratio (Servo parameter No.79) and denominator of external scale
ratio (Servo parameter No.7A) so that the following formula is fulfilled.
- If the ratio is incorrect, the difference between the position calculated from the encoder pulse and
the position calculated from the external scale pulse is increased. Particularly, when it is driven a
long distance, a hybrid deviation error (Err.25) occurs.
- When Servo parameter No.78 is set to 0, the encoder resolution is automatically set to a numerator.
[2] Hybrid deviation error setup
Set the hybrid deviation error level (Servo parameter No.7B) to the minimum value within the range
where the difference of a position between a motor (encoder) and a load (external scale) can be
considered excessive.
- As for the hybrid deviation error (Err.25), make sure to check its reason carefully as it also occurs due to
a reason other than that stated in the above item (1), such as the reverse connection of an external scale,
the loosened connection between a motor and a load, etc.
Precautions
(1) Input position command on the basis of an external scale.
In the full-closed control mode, the encoder is used for the speed control and the external
scale is used for the position control.
(2) External scales, which can be used for the full-closed control, are as listed below.
- AT500 series made by Mitutoyo Corporation
- ST771 series made by Mitutoyo Corporation
(3) To prevent the breakage of a machine due to excursion based on the setting of the above external
scales, set the hybrid deviation error level (Servo parameter No.7B) to a proper value in units of
external scale resolution.
(4) For an external scale, the value of 1/20 ≤ External scale ratio ≤20 is recommended.
If the external scale ratio is set to a value less than 50 / Position loop gain (Servo parameter
No.10, 18), its control per pulse may become impossible.
The larger the external scale ratio is, the bigger the operation noises may be.
A4P
Pr.79
17
Pr.78 1 x 2
＝
Pr.7A 5000
MOTOR COMPANY, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD
Number of encoder pulses per motor rotation
Number of external scale pulses per motor rotation
- 105 -
No. SR-DSV09485