Yaskawa MotionWorks+ Windows Software - Manual (Page 223)

MotionWorks+™ Appendix C MW+ Camming 101
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What applications benefit from CAM SHIFT?
• A process that must accurately track randomly spaced products on a conveyor belt.
• A process where slippage, stretch, or shrinkage requires realignment of the master and
slave to continue working properly.
By using the external latch, MW+ can calculate the distance between products, and con-
tinually adjust so the slave motion is always synchronized to the product, not simply the
master position.
The following table demonstrates an effective way to understand what happens when the
product stretches or products are coming at random. This was created as an Excel sheet to
understand the formulas before entering them in a MW+ program.
After the second product has been latched, it is determined that the product has stretched
0.1 inches. A CAM SHIFT of an equal and opposite amount is given to negate the stretch.
This amount can be added over time, such that the adjustment is subtle, and causes little if
any negative effects due to the slight de-synchronization that occurs during the shift.
• Assume the external encoder machine cycle (default product length) is 5.5 inches.
This is the nominal product length.
• MaxShift is something that can be used mainly for random product infeed, where you
need to determine which way is better to shift, to the previous machine cycle, or the
next. This will cause the slave to either slow down or speed up.
A B C D E F
5.5 Modulus (Machine Cycle)
2.75 MaxShift (Mid Cycle)
Product
Number Current
Shift
Hypothetical
Latch
Relative Shift
Amount
Resulting Abs
Shift
Shifted
Master
1 0.00 0.00 0.00 0.00 0.00
2 0.00 5.60 -0.10 -0.10 5.50
3 -0.10 11.20 -0.10 -0.20 11.00
4 -0.20 16.80 -0.10 -0.30 16.50
5 -0.30 22.40 -0.10 -0.40 22.00
6 -0.40 28.46 -0.56 -0.96 27.50
7 -0.96 35.00 -1.04 -2.00 33.00
8 -2.00 42.11 -1.61 -3.61 38.50
9 -3.61 48.00 -0.39 -4.00 44.00
10 -4.00 54.00 -0.50 -4.50 49.50