Application Example Programs
E–37
Spray Booth Operation Overview
An overhead conveyor with part carriers (hooks) carries parts from a previous
operation to the spray booth. Before the part enters the spray booth, 2 items are
checked on the conveyor. The first check is for part presence and the second check
is for the needed color. This information is stored and accessed later when the part
carrier is in the paint spraying area. A proximity switch is used to check for the
presence of a part on the carrier and a barcode reader is used to determine color
choice. When the part carrier reaches the spraying area, the previously stored
information is accessed. If there is a part on the carrier, it is painted according to its
bar code and if the carrier is free, paint is not dispensed.
The bit shift and FIFO instructions store the part presence and color information
before each carrier enters the spray booth. Both of these instructions place data into
their data structures every time a part carrier actuates the shift limit switch.
If the proximity switch senses a part on the carrier, a 1 is shifted into the shift
register. If the carrier is free as it passes the shift limit switch, a 0 is shifted into the
shift register. The shift register tracks the part carriers approaching the spraying
area.
The FIFO does the same type of shifting, except rather than shifting one bit at a
time, the FIFO shifts an entire word at a time. Just before the part carrier actuates
the SHIFT limit switch, the barcode reader reads the barcode on the part to
determine what color the part should be painted. The barcode reader has three
outputs that it sets according to what color the part should be. These outputs are:
•
wired to the controller as inputs I:0/2, I:0/3, and I:0/4
•
combined together to form an integer which is decoded later in the program
This integer is then shifted into the FIFO when the carrier actuates the SHIFT limit
switch.
Reference
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive
