User Manual
Chapter 15
GFK-1742F
Jan 2020
Using the Electronic CAM Feature
330
15.3.2
Interpolation and Smoothing
One key CAM feature is the interpolation scheme used to define the CAM profiles. The
following is a reprint of a section from the CAM Editor help system. It is included in this
section to not only introduce these important concepts, but also to encourage you to
explore the CAM Editor on-line help for additional information.
The CAM editor employs spline polynomial interpolation to define regions of a profile that
fall between user-defined points. This approach reduces the memory required for profile
storage on the target motion module while providing accurate and smooth motion
trajectories. Without this interpolation scheme, a large number of data points, thus a large
amount of memory, would be needed to define each profile.
A CAM profile is defined with a minimum number of actual data points. After these points
are defined they are grouped into sectors; a profile is composed of one or more sectors. For
each sector, you specify the curve-fit order (1, 2 or 3). The higher the order, the smoother
the curve-fit. The curve-fit order is the order of the polynomial curves used to define the
regions of the sector not specified by user-defined points. Unique curve-fit polynomial
coefficients are generated for each segment of a sector (that is, between each pair of user-
defined points). The coefficients of the polynomials are calculated to include the user-
defined points and to match the slope of the profile on either side of a user- defined point
(except for 1st order sectors).
Figure 152: Windowing Strobes Example
The polynomial curves for a position profile are described by the following function:
Y(X) = A
n-1
(X
n
-X
n-1
)
3
+ B
n-1
(X
n
-X
n-1
)
2
+ C
n-1
(X
n
-X
n-1
) + Y
n-1
Where:
Y = slave position value for a master position X.
X
n-1
= master position value at point n-1.
A
n-1
, B
n-1
, C
n-1
= curve-fit coefficients at point n-1.