User's Manual

Turbo PMAC User Manual
Writing and Executing Motion Programs 293
Vel
Time
V
t
∆
P=1/2 Vt
Vel
Time
V
t
∆
P=1/3 Vt
Vel
Time
V
t
∆
P=2/3 Vt
Vel
Time
V
t
∆
P=Vt
Vel
Time
V
t
∆
P=1/2(V +V ) t
Vel
Time
V
t
∆
P =5/6 Vt
1
2
V/2
∆
P =1/6 Vt
1
2
2t
PVT
Segme
nt
Shapes
2
V
Use of PVT in Contouring
PVT mode provides excellent contouring capability, because it takes the interpolated commanded path
exactly through the programmed points. It creates a path known as a Hermite Spline. LINEAR and
SPLINE modes are 2nd and 3rd-order B-splines, respectively, which pass to the inside of programmed
points.
Compared to Turbo PMAC’s SPLINE mode, PVT produces a more accurate profile. Its worst-case error
can be estimated as:
384
4
R
3
R384
4
T
4
V
E
θ
==
where V is the vector velocity, T is the segment time, R is the local radius of curvature, and
θ is the
subtended angle.