Danaher Motion
06/2005
Appendix B
M-SS-005-03 Rev
E
191
You can classify objects in the working frame and only track certain types of objects. Each
moving frame can have several master sources (external sources of moving position). The
number of sources is the number of degrees of freedom of the moving frame. You can use
several robots to track the same operating region, but the region must be presented as a
different moving frame object. Robots must be of the same type as the world frame of the
object in the tracking process (dimension and robot type). The process is completed in one
of two ways: disable tracking or send no new triggers.
There are two different concepts of NDOF’s: one for the robot which means the number of
motors driving it and one for the moving frame, which means the number of external
position sources assigned to it. These two numbers can be different. Only the object type
(dimension and type) of the moving frame must match the robot's world frame.
Window Declaration
Limit the region by one or more pairs of points, depending on the number of degrees of
freedom of the element to be tracked. For every degree of freedom a pair of points defines its
region limits. The boundaries are the
upstream
(lower limit) and the
downstream
(the upper
limit). The lower and upper limits are referred to the trigger point. The lower limit is closer to
the trigger point than the upper limit. Moving direction is from upper to lower. While the object
is inside the working frame, every change of conveyor movement direction is tracked. The
only limitation is that region limits must be relative to the trigger position so the upstream is
closest to the trigger. An object might enter from the downstream limit. To correct this error,
add a direction flag to the trigger to indicate if the region limits are inverse.
The moving frame is divided into components. For example, an XY table tracks as two axes:
X and Y. The coordinate translation is done automatically when using the robot coordinate
system as a base for the position calculation. The moving frame coordinate system is the
same as the tracking robot. The master source is independent in the moving frame type. The
group master is used as an input position to follow.
Tracking
Tracking starts when the tracking process flag is enabled, which assumes that the object has
passed the sensor. Tracking actually starts when the relevant object enters the operation
region and ends when it leaves the frame. During its motion in the frame, the moving frame
position is re-calculated every sample. The position is based on the frame boundary limits
and the scaling ratio in moving frame units. To this basic formula, a correction term is added
to correct a delay of 1-2 samples between the trigger from the sensor to the start of the
operation. Due to the discretization of the SERCOS samples, this delay causes a gap in the
position.
Moving Frame
The input position is the current moving fame position. The input position (master source) is
usually taken as an external source (external encoder), simulated axis or even another
moving frame position.
If the master source is another moving frame (e.g., TCP-coordinates of any other kinematics
with more than 2 axes), the offset/transformation between the tracking kinematics and the
tracked kinematics is considered. In the implementation state of group as a master source
(phase 3), the offset must be taken into consideration in
TRIGGER
or other alternative.
The tracking element and the moving frame must have the same kinematics system. It is
impossible to track a different kinematics system.
