Programmable Limit Switch Basics - - A Beginners' Guide to Programmable Cam Switches

Programmable Limit Switch Basics
Jim Finnerty
Product Manager
Wintriss Controls Group
www.wintriss.com
4/17/2019©2019 Wintriss Controls Group– All rights reservedSlide 1

What is it?
• A programmable limit switch (PLS)
is a programmable timing device for
metal stamping presses
• A PLS is the modern replacement for
the rotating mechanical cam limit
switches that used to be installed on
stamping presses
• This gives rise to the Programmable
Limit Switch’s other name: The
Programmable Cam Switch (or
simply Programmable Cam).
4/17/2019©2019 Wintriss Controls Group LLC - All rights reservedSlide 2
Rotating Cam Limit Switch of the type that
used to be common on stamping presses

The Press Cycle
• A “cycle” or stroke” for a metal
stamping press is when the ram (also
known as the “slide”) of the press goes
from the top of its travel to the bottom
and back
• The ram is driven down and up by
Pitman arms connected to a rotating
crankshaft
• As the crankshaft rotates, the ram
moves down and up

What Kind of Timing?
• During each cycle, the press crank-
shaft makes one complete revolution
• One revolution = 360⁰ of rotation
• All press timing signals are set with
respect to the crankshaft position in
degrees
• A Programmable Limit Switch is able
to measure the press’s crankshaft
position and activate various electrical
outputs at the appropriate angles
Top Dead Center (0⁰)
Bottom Dead Center (180⁰)
Direction
of Rotation 90⁰270⁰

PLS Components - The Resolver
• At the heart of a modern
Programmable Limit Switch is a
rugged sensor called a “resolver”
• A resolver measures angular position
• The resolver is driven 1:1 with the
press crankshaft through a chain and
sprocket or timing belt and gears
• The PLS controller reads electrical
signals from the resolver to
determine crankshaft position

Programmable Cam Outputs
• Ancillary equipment such as the feeder, and functions like top
stop require precise timing during the press cycle
• Programmable cam limit switches are able to provide timing
signals accurate to within 1/3⁰ to control these items
• An advanced Programmable Limit Switch such as the one in the
Wintriss SmartPAC PRO can deliver different types of timing
signals to suit many diverse applications

On/Off Output
• The simplest type of PLS output
is a single On/Off output
• The user simply specifies the
angle where the output should
turn on and when it should turn
off
• The output actuates once per
press cycle
• This output type replicates the
signals provided by mechanical
rotary limit switches

On/Off Output
• There’s a possible drawback:
• If the press stops between the On
and Off angles, the output stays
activated even though the press is
stopped
• If the output is for an air blow-off
or lubricant delivery, you have a
problem
• When this is the case, a different
output type is required

Timed Output
• For a Timed PLS output, you
specify the ON angle and dwell
time (in milliseconds)
• The output turns On at the on
angle, and turns Off when the
dwell time elapses, whether the
press is running or not
• Timed outputs are ideal when
the PLS is controlling the
delivery of air or lubricant

The Timed output type enables the
programmable limit switch to turn off a device
after a preset time regardless of crankshaft
position.
This prevents wasteful instances of part blow-
offs or lube systems unnecessarily running
after a press has stopped.
Remember: Air is free until you compress it
Timed Output Benefits

Timing for Variable Speed Presses
• Certain events initiated by the PLS take a constant (fixed)
amount of time to occur, regardless of press speed
• Examples include top stop, or an air cylinder-powered roll lift on a
servo feed (for pilot release)
• The timing for such items can only be optimized for one speed
• If the press runs slower, the event will occur earlier than desired
• If the press is sped up, the event will occur late
• A feature called “Auto Advance” enables the PLS to keep fixed-
time items in synch with the press – regardless of speed

Auto Advanced Outputs
• The Auto Advance function
automatically adjusts the timing
signal according to press speed
• As the press runs faster, the
SmartPAC PRO Programmable Limit
Switch will advance the timing to turn
the output on earlier
• If the press slows down, the output
turns on later in the stroke

Auto Advanced Outputs
• In addition to providing
accurate timing for variable
speed presses, auto advanced
outputs can keep ancillary
functions “in synch” with a
high speed press as it ramps
up to its operating speed at
start-up

Unlike “fixed” PLS outputs, Auto Advance
outputs do not experience timing inaccuracy
as a press ramps up to speed.
This enables higher press speeds without risk
of part quality issues or potential damage to
ancillary equipment that could occur, for
example, if the feeder’s pilot release timing
was off.
Auto Advance Output Benefits

“On-With-DSV” Outputs
• Some items - such as conveyors and scrap choppers -
should be running whenever the press is running, but
should shut off when the press stops
• Although they’re not timed with respect to crankshaft
position, these items can still be controlled by the PLS
using an output type called “On With DSV”
• An ON-with-DSV output turns on when the press starts -
i.e. when the Dual Safety Valve (DSV) energizes and
turns off either immediately when the press stops or a
preset number of seconds after the press stops
4/17/2019©2019 Wintriss Controls Group– All rights reservedSlide 15

On w/DSV Output Benefits
The ON w/DSV Output removes the need for
the press operator to turn off conveyors,
scrap choppers, or other devices that need
not run while the press is stopped.
These types of press controls save energy as
well as wear-and-tear on the equipment.

Multiple On/Off Output
• There are certain functions (such
as spray lube systems) that may
have to actuate several times
during the press cycle
• If the PLS has multiple On/Off
capability, these functions can be
controlled with a single output
from the Programmable Limit
Switch
• The SmartPAC PRO’s ProCamPAC
outputs can turn on and off up to
four times per cycle

Multi-On/Off Output Benefits
The ability to turn a single output on and off
several times per cycles simplifies wiring and
programming.
The Multi-On/Off output of these press
controls provides additional flexibility for
many types of automation.

Gagged Outputs
• Instead of actuating every cycle,
some jobs require an output to
actuate only on certain cycles
• An example would be the cut-off
for long part that takes multiple
feeds/cycles to produce
• This process is know as “gagging”
• Advanced PLS systems like the
SmartPAC PRO support this
function

Gagged Output Benefits
The ability to mask outputs from cycle-to-
cycle enables programmable cam limit
switches to run complex automation functions
without having to use additional electronics
such as programmable logic controllers
(PLCs).
This simplifies installation, programming, and
operation.

Global Cams
• There are often fixed timing signals that are required by the
press regardless of which tool is run
• Examples include timing signals used by automated clamping
systems, and timing for the hydraulic overload system
• Advance programmable limit switches such as the ProCamPAC
module for the SmartPAC PRO include “Global Cams” that are
automatically placed into every setup
• Because of their sensitive nature, Global Cams can be secured
with a password to prevent unauthorized modifications

Global Cam Benefits
The use of Global Cams ensures that
“mission-critical” timing signals are always
included automatically in every setup.
In addition to reducing programming time,
Global Cams provide a higher level of security
for important timing signals.

For more information, please visit
Wintriss.com

Programmable Limit Switch Basics - - A Beginners' Guide to Programmable Cam Switches

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Programmable Limit Switch Basics - - A Beginners' Guide to Programmable Cam Switches

Similar to Programmable Limit Switch Basics - - A Beginners' Guide to Programmable Cam Switches (20)

Recently uploaded

Recently uploaded (20)

Programmable Limit Switch Basics - - A Beginners' Guide to Programmable Cam Switches