APPLICATION STORY
 

The increasing important role load pins play in the
integrated control systems of forklift trucks,
telescopic handlers and mobile cranes.


As competition increases, designers and manuacturers of mechanical
handling equipment such as forklift trucks are under increasing pressure
to bring new designs to the market place faster by reducing lead times.
In addition, vehicle manufacturers have to conform to increasingly rigorous quality and safety requirements.

The sheer amount of current legislation concerning health and safety provides
an insight into how important it is that manufacturers of mechanical handling
equipment include safety measures to guard against potentially hazardous
situations. This emphasis on vehicle safety and efficiency has resulted in
manufacturers becoming increasingly dependent on load pins to act as primary measuring sensors; providing data on a wide range of vehicle operating parameters
such as tension and compression forces, bending and shear movements, torsion,
torque, pressure and weight.

The performance of mechanical handling equipment is governed not only by
individual components or subassemblies, but also by the effectiveness of the
integration and interface between measurement sensors, the main control unit
and the operator. As a result, vehicle manufacturers are now looking for
complete solutions in a single package.

To meet this challenge, leading manufacturers of force sensors and transducers
are establishing closer working relationships with both vehicle manufacturers
and electronic control suppliers. By ensuring that products are not developed
in isolation they can be more easily integrated into vehicle control system.

Sensors such as load pins, for example, are now being designed to fit seamlessly
into the overall control system, guaranteeing optimum performance, minimising
testing procedures and reducing development time.

Ensure stability
The majority of load pins are designed for single axis measurement, but where
applicable multiple axis devices can be designed to provide independent force
data from a number of sources and components. In handling and storage
applications, load pins are used to ensure forklift truck stability, telescopic
handler stability and mobile crane stability.

Robust, compact and easily fitted, load pins feature strain gauge technology:
small, resistive elements bonded to heat-treated metal sensor elements using
special adhesives. Usually connected in a Wheatstone Bridge arrangement,
strain gauges work by applying a known voltage to the bridge. The resistance
changes caused by an applied force generate a change in voltage output that
is proportional to that force.

Strain gauges are bonded inside the load pin and then filled with a proprietary
potting compound and sealed using a metal plug, providing both sealing and
vibration protection for vital components.

With a relatively low electrical output and requiring a stable power supply, it
is worth noting that while standard strain gauges are useful for a number of
applications, they can cause problems for on-board sensors. One company
effectively addressing this problem is Tedea-Huntleigh.

Tedea-Huntleigh manufactures load pins that incorporate a highly effective
internal amplifier and are able to withstand typical power supply fluctuations,
providing a stable and noise-immune voltage or current output. It is a
testament to the company's commitment to safety that designers are
incorporating this type of sensor more frequently, though unfortunately
not as standard.


Overloads detected
A prime example of the important role load sensors play in ensuring the safe
operation of mechanical handling equipment is forklift trucks. By fitting load
pins to the rear axle assembly it is possible to measure the reaction between
the wheels and the ground to ensure that dangerous overload conditions are
detected well in advance. In addition, by comparing load distribution across
the axle, the control system can also prevent the vehicle from tipping
sideways if used on uneven or unstable ground.

Other vehicles, such as telescopic handlers, also benefit greatly from load pins.
Given the complex boom extension, boom angle and lifting load combinations,
a reliable and effective overload monitoring system is essential to ensure
safe operation. To address these needs, designers are increasingly fitting
load pins to the rear axle assembly of these vehicles as well.

New demands are now being placed on sensors that form part of the integrated monitoring system in mobile cranes. Incorporating load pin technology into
telescopic stabilisers means that load distribution can be measured, while
bending and twisting forces within the boom can also be calculated, providing
important safety information. By combining sensor outputs with data from
position transducers and inclinometers, the crane operation and stability
can be computed and integrated into the overall control system. Should the
crane become unstable the system will automatically prevent the operation
proceeding, allowing the operator to assume a more secure position.

Drive by wire
Advancements in position and force transducer technology means the systems
are also being increasingly used in off-road vehicle 'drive by wire' controls
where sensors are replacing complex cables, rod mechanisms and hydraulic
connections found in traditional steering, brake, clutch and throttle controls,
to provide total control integration.

As the versatility of industrial vehicles such as forklift trucks increases, so
does the need for safer and more integrated operating systems.Advances
made in load pin technology mean that vehicle designers are now in a far
better position to not only extend the boundaries of engineering, but to
also contribute to the safety of operators.
_________________________________________________________

For more information contact:-

John Goodson( General Sales Manager) at Tedea-Huntleigh
Tel: +44(0) 29 2046 0231 Fax: +44(0) 29 2046 2173

March 2002

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