Page 290 - Programmable Logic Controllers, Fifth Edition - Mobile version

16 15 14 13 12 11 10 9 Station 7 6 5 4 3 2 1
8
O:4/15 O:4/14 O:4/13 O:4/12 O:4/11 O:4/10 O:4/9 O:4/8 O:4/7 O:4/6 O:4/5 O:4/4 O:4/3 O:4/2 O:4/1 O:4/0 O:4
Rework Inspection

Inputs Ladder logic program Outputs
O:4 L2
L1
Prox #1 I:1/1 0
(Carrier detection) BSL 1
BIT SHIFT LEFT EN 2
Prox #1 File #O:4
I:1/1 Control R6:0 DN 3
Bit address I:1/2 4
Prox #2 Length 16 5
(Part detection) 6
7
I:1/2 I:1/3 O:4/4 8
U 9
10
PB1 PB1 PL4
(Failed part) 11
12
I:1/4 O:4/6 O:4/6
I:1/3 13
L 14
PB2 PB2 PL6 15
(Reworked part)

I:1/4
Figure 12-30 Program for tracking of carriers flowing through a 16-station machine.
Source: Photos courtesy Omron Industrial Automation, www.ia.omron.com.

• Station 5 is an inspection station where parts are Control—A tag of data type Control that stores the sta-
examined. tus bits and the size (number of bits) of the bit array.
• If the part fails, the inspectors push PB1 as they Source Bit—A tag of type BOOL, the status of
remove the part from the system, which turns output which the instruction inserts into the first bit position
O:4/4 off. of the bit array on every false-to-true rung transition.
• Rework parts can be added back into the system at Length—The size (number of bits) of the bit array.
station 7. Figure 12-32 illustrates an application for the Control-
• When the operator puts a part on an empty carrier, Logix Bit Shift Left (BSL) instruction. A pass/fail inspec-
he or she pushes PB2, turning output O:4/6 on to tion station is used in a conveyor system to keep track of
resume tracking. defective products as they move down the conveyor at an
equal distance. A partially completed product is moved
Allen Bradley ControlLogix has two shift register down a conveyor to an inspector before proceeding to the
instructions: Bit Shift Left (BSL) and Bit Shift Right final stages of manufacture. If a product is deemed defec-
(BSR). The BSL instruction is shown in Figure 12-31. tive, it is pointless to continue building it, so the part is iden-
Data are loaded into, shifted through, and unloaded from tified as a reject. Before the part arrives at the reject bin, it
a bit array, one bit at a time when the instruction transi- must pass through three more zones of manufacture. The
tions from false to true. Bit shift instructions contain the operation of the program can be summarized as follows:
following parameters.
• At the zone 1 pass/fail station an inspector examines
Array—A one-dimensional array of type DINT with the product before it proceeds to the final 3 stages of
enough bits to accommodate the length. manufacture.

Sequencer and Shift Register Instructions Chapter 12 271

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