13. Program Support Functions
13.15 High-accuracy Control ; G61.1, G08
412
(2) Arc speed clamp
During circular interpolation, even when moving at a constant speed, acceleration is
generated as the advance direction constantly changes. When the arc radius is large
compared to the commanded speed, control is carried out at the commanded speed. However,
when the arc radius is relatively small, the speed is clamped so that the generated
acceleration does not exceed the tolerable acceleration/deceleration speed before
interpolation, calculated with the parameters.
This allows arc cutting to be carried out at an optimum speed for the arc radius.
F : Commanded speed (mm/min)
R : Commanded arc radius (mm)
Δ
θ
: Angle change per interpolation unit
Δ
V : Speed change per interpolation unit
The tool is fed with the arc clamp speed F so that
Δ
V does not exceed the tolerable
acceleration/deceleration speed before
interpolation
Δ
V.
θ
F
F
F
F
Δ
V
Δθ
F
≤
R ×
Δ
V × 60 × 1000 (mm/min)
Δ
V =
G1btL (ms)
G1bF (mm/min)
When the above F' expression is substituted in the expression expressing the maximum
logical arc radius reduction error amount
Δ
R explained in the section "a) Pre-interpolation
acceleration/deceleration", the commanded radius R is eliminated, and
Δ
R does not rely
on R.
Δ
R
≤
1
2R
{Tp
2
(1
−
Kf
2
) } ( )
2
F
60
≤
1
2
{Tp
2
(1
−
Kf
2
) } ( )
Δ
V' × 1000
60
Δ
R : Arc radius reduction error amount
Tp : Position loop gain time constant of
servo system
Kf : Feed forward coefficient
F :
Cutting
feedrate
In other words, with the arc command in the high-accuracy control mode, in logical terms
regardless of the commanded speed F or commanded radius R, machining can be carried
out with a radius reduction error amount within a constant value.
To further lower the arc clamp speed (to further improve the roundness), the arc clamp
speed can be lowered with the machining parameter "#8019 R COMPEN". In this case,
speed control is carried out to improve the maximum arc radius reduction error amount
Δ
R by the set percentage.
Δ
R'
≤
Δ
R × (100 - Ks)
100
(mm)
Δ
R' : Maximum arc radius reduction error amount
Ks : R COMPEN (%)
After setting the "R COMPEN", the above
Δ
R' will appear on the parameter screen.
Accuracy coefficient
setting value
#8019 R COMPEN (0.078) 50
Δ
R'
(Note 1)
The maximum arc radius reduction error amount
Δ
R can be increased by setting a
negative value for the "accuracy coefficient".
(Note 2)
When the "R COMPEN" is set with positive value, the arc clamp speed will drop, so in a
machining program with many arc commands, the machining time will take longer.