Gemini GV6K and Gemini GT6K Programmer's Guide

Scenario #2: OTF change of distance, where
new commanded distance (D 2 ) is less than the
original distance (D 1 ) that was pre-empted [D 2 <
D 1 ]. In this example, the position where the OTF
change was entered is already beyond D 2 (or D 2
can not be reached with the commanded
deceleration). The result is an error and motion is
killed (decel at the LHAD value) and TAS bit #30
and TER bit #10 are set.
Scenario #3: OTF change of velocity. Note that
motion must continue for a longer time at the
reduced velocity to reach the original
commanded distance than if it had continued at
the original velocity (t 2 > t 1 ).
On-The-Fly Motion — Sample Application
A manufacturer of three products wishes to produce a “sampler-pak” package which will
contain a few of each of his products. The products all have the same width and length, but
are 3, 4, and 5 inches high respectively. The 3 products are fed from individual lines into a
common conveyor, and arrive at a stacking and wrapping station. At this station, a tray
accepts a product and must have moved down by that product’s height by the time the next
product arrives. This means that each time a new product arrives, the velocity of the tray must
be changed to match the height of that product. Although product spacing will be regular, the
ordering of product type on the common conveyor will be random, due to variations in the
input lines. Also, a finished sampler-pak should contain 5 products or be at least 18 inches
high, whichever occurs first. This means that the total move distance of the tray will be
unknown until the last product arrives. When the last product is stacked, an output is asserted
which will pause the conveyor and start the wrapping process. When wrapping is complete,
the sampler-pak is removed from the tray, and the tray returns to the starting position.
The basic problems in this application are that the move distance is not known until near the
end, and the velocity must change on the fly. As the products approach the tray, they are
detected with a near vertical arrangement of three sensors. Products of heights 3, 4, and 5
inches are detected by 1, 2, or all 3 sensors respectively. Input 1 always detects a product, and
switches last, so that the others will be stable. When each product is identified, the motion
profile is modified accordingly.
Chapter 6. Following 157