Electro Cam 5000 Series - Manual (Page 5)

Basic Cam Switch Operation
Basic Cam Switch Operation
A PL
µ
S control’s main purpose is to operate outputs in a
manner that simulates cam switches. The drawing to the
right illustrates the operation of a cam switch. Its function is
to switch the load on and off at the same rotary positions of
the cam shaft during each revolution of that cam shaft. The
rotating cam shaft is driven by a machine at a 1:1 ratio, so
that the on / off positions of the cam switch always match
specific positions in the machine cycle. However, cam limit
switches have the following disadvantages: unreliable
(wear), hard to adjust (machine must be stopped during
adjustment), and they cannot run at high speeds because
of contact bounce and excessive mechanical wear.
PL
µ
S controls overcome these basic cam switch problems.
They have no moving wear parts, they are easy to adjust
from the keyboard with the machine running or stopped,
and they can operate at speeds up to 3000 RPM. They also
add many capabilities far beyond simple cam switch logic.
The limit switch will turn on and off at
the same cam degree positions every
cam revolution (every machine cycle)
Standard Product Features
Keyboard/Controller
The keyboard controller is the main component of the PL
µ
S
system. The front keypad and displays provide a complete
user interface from which every aspect of the control’s
operation can be monitored and programmed. When
properly mounted with the gasket provided, the keyboard
meets NEMA 4 standards. A clear silicon rubber boot
assembly is available to provide NEMA 4X protection for
installations where harsh washdown chemicals are used.
Ease of Setup
All output position setpoint values are simply entered
through the numeric keypad. These setpoints can be
adjusted while the machine is running or stopped by using
the increment, decrement, or numeric keys. The keyboard
is also used to synchronize the control’s position to the
machine, eliminating the need to mechanically adjust the
resolver’s shaft position.
Multiple Programs
Depending on the model ordered, up to 64 different
programs, or “job recipes” can be stored in the control’s
memory. This minimizes down time for job change over
because simply changing program numbers makes all of
the output setting changes required. Program numbers can
be changed by mechanical switches; PLC’s (using the
hardware program select inputs); the keypad; or serial
communication messages.
Output Speed Compensation
Speed compensation allows outputs to compensate for the
response time of the controlled devices by turning on earlier
as machine speeds increase. This eliminates the need to
adjust output settings whenever machine speeds are
changed. Using speed compensation often allows higher
production speeds and eliminates the need for output
adjustments.
Motion ANDing
A speed range can be programmed into the controller, and
outputs can then be ANDed with the speed range so that
they will be disabled unless the machine speed is within the
range. This can be used to turn off outputs if the machine
stops; disable outputs until the machine reaches a minimum
speed; or disable outputs if the machine goes above a
specified maximum speed. A common use for this feature
is disabling outputs to glue valves so the flow of glue turns
off if the machine stops.
Timed Outputs
Outputs can be programmed to turn on at the programmed
“on” position and turn off when the specified time elapses,
rather than staying on until an “off” position is reached. The
result is a constant output duration, regardless of machine
speed. The output will turn off when the “off” position is
reached if it hasn’t already timed out. Timed outputs are
used to drive devices which require a fixed time to perform
a task, regardless of machine speed.
1-1 Introduction
Introduction