ADLINK Technology PCI-8254, User Manual

Page: 155 / 226

Motion Control Theory 141
PCI-8254 / PCI-8258
Coordinates of end point may have certain error caused by
computing accuracy of your computer. To get precise end point
position, you may use method 2 to enter exact end position
accurately (as described in next section)
¾ method 2: given center of circle and end point
This method requires center of circle and position of end point
only. Benefit of this method lies in that it does not need a normal
vector and that it can have accurate ending position to meet
demands from contour or applications that need accurate
positioning. This method has two restrictions:
1. It cannot execute half circle (angle of 180 degree)
2. It cannot execute full circle (angle of 360 degree)
Figure 4-43: Three dimension arc interpolation (method 2)
• How to determine direction of arc
Use the right-hand grip rule as shown in figure below, where the
your thumb indicates normal vector direction and the other four
fingers the positive rotating direction.
Use parameter “I16 Dir” to determine direction, if Dir>= 0 then
rotate in positive direction and negative direction if DIR <= -1
• Path of multiple laps (arcs of angle greater than 360 degree)
Use parameter “I16 Dir” to determine rotating angle with formula
described below:
Angle =
θ
+ Dir * 2PI
S