Page 725 - Mechatronics with Experiments

PROGRAMMABLE LOGIC CONTROLLERS 711
to the first one. The second conveyor is controlled in slave mode. The speed of the
first conveyor may be programmed or determined based on a sensor (i.e., speed of
another station in the line).
3. Master-slave speed control with position phase adjustment: in addition to making
one conveyor follow the speed of the other conveyor (master-slave relationship), the
position of one slave conveyor relative to the master conveyor can be adjusted based
on position sensor information. This is very common in packaging applications where
material is transferred from one conveyor to another. In steady-state, two conveyors
run in a certain gear ratio (i.e., 1:1 master-slave relationship). Due to the variation
in material location on each conveyor (product on one and container on the other),
in order to place the product on the container properly, the position phasing must be
adjusted to correct for the placement variations.

9.4.3 Closed Loop Servo Position Control System
Servo positioning using a lead-screw (or ball-screw) drive is a very common high precision
motion control application (Figure 9.12). The ball-screw positioning system is used in
all CNC machine tools, XYZ positioning tables, gantry-type robots, printed circuit board

Position control
module

I/O
I/O
CPU
Control panel
Inputs Start Stop
Outputs
Mechanical
System

CCW limit switch

Home sensor
Motor Driver CCW limit
switch

Electric power source Encoder
Motor

CCW

CW

FIGURE 9.12: Example servo positioning control with a PLC and servo control module.