A PINCH POINT SAFETY DEVICE
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|Soft Touch Flyer|
|Soft Touch Overview|
|Soft Touch Article|
|OSHA Spot Welding Compliance Research|
|Welding Journal Article Reprint|
|Soft Touch Selection Chart|
|Canadian Standards in Relation to Soft Touch|
|Soft Touch Trouble Shooting Instructions|
A NEW FUNCTION FOR
FORCE BETWEEN ELECTRODES UNTIL SAFE
announces a new safety function
that is now available
on all Unitrol
resistance welding controls.
This patent pending function keeps the electrode force very low
until it is safe to apply full welding force. Existing SOLUTION controls
can also be upgraded for this SOFT TOUCH function. The SOFT TOUCH system
cannot be installed on any other brand welding control.
After initiation, electrodes start to close under LOW FORCE.
A Unitrol TOUCH
SENSOR system decides
when the electrodes have closed on or near the metal being welded.
If an obstruction is detected prior to closing, the electrodes
will go back to the fully opened position.
No adjustment of SOFT TOUCH is needed when changing welding
force or electrode spacing.
The system is field
adjusted with lockable settings (to meet OSHA compliance) so that force between electrodes for the
advance portion of the stroke remains low enough to avoid major injury
to the operator’s fingers. For
press welders, this will even reduce force between electrodes to
considerably less than the dead weight of the ram.
the sensor switch is already closed when the welder is being initiated,
the electrode will not even start to move, and the display will show
which sensor input is closed at that time.
the sensor wires from the SOFT TOUCH system have become disconnected or
are making poor contact, the electrodes will close under low force and
then return after a short field-settable delay (1-999 cycles).
HARDWARE IS NEEDED:
To make this system operate, you will have to add a 5-way
externally piloted solenoid valve, a shuttle valve, and a precision
pressure regulator system to an existing 4-way externally piloted (or
direct acting) solenoid valve. Unitrol
offers three kits for easy installation:
WEIGHT RAMS: This
is used on:
that have dead weight (with air disconnected from welder) of over 50
pounds. The kit is factory pre-plumbed for fast installation and
includes all necessary components and interconnecting tubing.
WEIGHT RAMS: This #9181-34Y
kit is used on:
WEIGHT GRAVITY-DROP RAMS: This
is used on:
that have dead weight (with air disconnected from welder) of less than
50 pounds and drops smoothly by gravity. The kit is factory pre-plumbed
for fast installation and includes all necessary components and
SENSOR: You can also add your own proximity switch or LVD
system adjusted to close a switch when the electrodes are less than ¼”
apart to the system. The
SOLUTION will not turn on the high-pressure valve until both
metal is detected and the proximity switch has been closed.
This is often useful for applications where the parts being
welded are not flat prior to the welding process.
SOFT TOUCH ARTICLE
KEEPING SPOT WELDER OPERATORS SAFE
|By Roger Hirsch, President, Unitrol Electronics Inc.|
WHO KNEW THAT PEOPLE WERE GETTING INJURED ON SPOT WELDERS!
I never thought spot welder safety was such a big deal until recently. Here is the story:
He explained that a safety system had to be installed that did not depend on any operator settings or adjustments. And when electrodes were changed or holders were adjusted to alter the electrode spacing, the safety system had to continue to operate without the need to make adjustments
FIRST IDEA: The first attempt at finding a solution was to use a light curtain to protect the area between the electrodes. However this idea was quickly abandoned when they realized that the operator had to hold and move parts near the electrode and would be in the light curtain zone. Also when jobs were changed and the electrodes adjusted, very fine tuning of the light curtain system would have been required.
SECOND IDEA: They then decided to install a ring guard system. With this type of guard, a wire loop on the end of a rod is set around the top welding electrode. The loop is sent downward at the beginning of each weld before the electrode starts to move. The electrode will not close if the loop stops short of a set distance (as would happen if the loop contacted a finger).
Ring guard systems were installed on six welders and then shown to the OSHA advocate. He said this application of a ring guard would not pass an OSHA inspection. The problem was that a ring guard could be easily defeated by the operator. Also he pointed out that the actual safety value of a ring guard was completely dependent on the mechanical adjustment of the wire ring by the setup person. In other words, the only time it was safe was when the ring was set at the proper height and the operator did not bend or rotate it out of place.
The OSHA advocate told them that they had to find a FULLY PASSIVE SYSTEM.
He explained that a safety system had to be installed that did not depend on any operator settings or adjustments. And when electrodes were changed or holders were adjusted to alter the electrode location, the safety system had to continue to operate without the need to make adjustments.
THE SOLUTION: Unitrol took up the challenge and developed SOFT TOUCH, a fully passive patent-pending system that provides very low electrode force when the area between the electrodes is not safe, and only applies full electrode force when it is safe to do so. This new development was done using electronic sensing rather than mechanical switches or moving parts.
HOW SOFT TOUCH WORKS: SOFT TOUCH is a fully passive fail-safe system that is controlled by the Unitrol SOLUTION welding control. Because SOFT TOUCH is part of the control and not just an add-on system, it is fully integrated into the welding sequence. This means that the system works “right out of the box” without the need to wire together and program multiple components.
REDUNDENT SYSTEM: If desired, a limit switch can be added to the welder and adjusted to close when the space between the electrodes is less than 1/4”. In this case, the SOLUTION control has to see both that there is metal between the electrodes and that the limit switch has been closed. This is useful where the weld surfaces on parts, such as C-shaped loops, are not touching at the start of a weld sequence and use the electrodes to push them together..
FULLY PASSIVE: There are no operator adjustments. Even if electrode height is changed or welding pressure is adjusted, the SOFT TOUCH system operates without any setting changes. In fact, there is nothing for the operator to adjust. All settings are locked in the cabinet.
OSHA RESEARCH FOR SOFT TOUCH CONCEPT
Unitrol contacted an OSHA representative and discussed the requirements for pinch point
guarding for resistance welders. The operation of the SOFT TOUCH system was also
discussed. The OSHA representative recommended the following regulations to cover
requirements for this device:
Types of guarding. One or more methods of machine guarding shall be provided to
protect the operator and other employees in the machine area from hazards such as
those created bypoint of operation, ingoing nip points, rotating parts, flying chips and
sparks. Examples of guarding methods are-barrier guards, two-hand tripping devices,
electronic safety devices, etc.
Unitrol note: The SOFT TOUCH sensor board is an "electronic safety device" in that it
closes an electro-mechanical relay when it electronically senses that the electrodes are
closed on the metal part in the work area prior to application of high force.
1910.255(b)(4)(resistance welding machines)
Guarding. All press welding machine operations, where there is a possibility of the operator's
fingers being under the point of operation, shall be effectively guarded by the use of a device
such as an electronic eye safety circuit, two hand controls or protection similar to that prescribed
for punch press operation, 1910.217.
Unitrol note: The following sections are all that were recommended for this application:
A presence sensing point of operation device shall protect the operator as provided in
paragraph (c)(3)(i)(a) of this section, and shall be interlocked into the control circuit to
prevent or stop slide motion if the operator's hand or other part of his body is within the
sensing field of the device during the downstroke of the press slide.
Unitrol note: The electrode on the low-force ram becomes the "sensor" in this system.
The "downstroke" of the welder, with the Soft Touch system installed, starts when high
pressure is applied to the welder ram.
The device may not be used as a tripping means to initiate slide motion.
Unitrol note: This Soft Touch circuitry does not initiate any valves. It is only an input into
the weld control to indicate that the part being welded has been sensed in between the
The device shall be constructed so that a failure within the system does not prevent the
normal stopping action from being applied to the press when required, but does prevent
the initiation of a successive stroke until the failure is corrected. The failure shall be
indicated by the system.
Unitrol note: At the start of each stroke, we check to see if the sensing system is closed.
If it is, the sensor stroke is never started, and the control’s display shows the fault. The
sensor must be opened before any other action is possible on the welder.
For a downloadable printable PDF version of this document click hereFor a downloadable VIDEO of Soft Touch in action click here this is a 14 MB file in Windows Media Player Format