Installation manual
CNC 8035
5.
CONCEPTS
Spindle
(SOFT M: V15.3X)
(S
OFT T: V16.3X)
·232·
To use it, acc/dec must be active s.m.p. ACCTIME (P18).
It is defined with s.m.p. FFGAIN (P25).
Derivative gain or AC-forward gain.
The "derivative gain" sets the percentage of velocity command applied depending on the
fluctuations of following error.
The "AC-forward gain" sets the percentage of velocity command proportional to the feedrate
increments (acceleration and deceleration stages).
To use it, acc/dec must be active s.m.p. ACCTIME (P18).
It is defined with s.m.p. DERGAIN (P24) and ACFGAIN (P46).
Proportional gain setting
In a "pure" proportional position loop, the velocity command provided by the CNC to control the
spindle is, at all times, proportional to the following error (axis lag) which is the difference between
its theoretical and actual (real) position.
Velocity command = Proportional Gain x Following Error
a.m.p. PROGRAIN (P23) sets the value of the proportional gain. Expressed in millivolts/degree, it
takes any integer between 0 and 65535.
Its value indicates the velocity command corresponding to a feedrate resulting in 1º of following error.
This value is taken for the first spindle gear and the CNC calculates the values for the rest of the
gears.
Example
The maximum speed for the 1st gear is 500 rpm and we would like to obtain 1º of following error
at a speed of S = 1000 º/min. (2.778 rpm).
Command from the drive: 9.5V for 500 rpm
Velocity command corresponding to S = 1000 º/min. (2.778 rpm)
Analog velocity command = (S x 9,5 V) / "MAXGEAR1"
Analog command = (9.5 V / 500 rev/min) *2.778 rev/min =52.778 mV.
Therefore "PROGAIN" = 53
Bear in mind
When setting the proportional gain that:
• The maximum amount of following error allowed by the CNC for the spindle is the value indicated
by s.m.p. MAXFLWE1 (P21). When exceeded, the CNC issues the corresponding following error
message.
• The amount of following error decreases as the gain increases, but it tends to make the system
unstable.
Feed-forward gain setting
With the feed-forward gain, it is possible to reduce the following error without increasing the gain,
thus keeping the system stable.
It sets the percentage of velocity command due to the programmed feedrate; the rest depends on
the proportional and derivative/AC-forward gains.
If "ACFGAIN = No" it applies derivative gain
If "ACFGAIN = Yes" it applies AC-forward gain.
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