Lift truck parts & components
Firmly in control
Electric Lift trucks have been getting steadily more reliable over the years and one of
the companies behind the scenes that is responsible for making that happen, is Curtis
Instruments. Simon Duddy talks to Curtis about the secrets of that reliability.
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any of you will remember how lift trucks typically used
to struggle with gradients. Rather than stopping dead,
forklifts would creep down the slope. Modern lift
trucks have got a great deal more precise and this has boosted
health and safety as well as efficiency. One of the companies
responsible for this development is Curtis Instruments, which
manufactures motor controllers and instrumentation.
The company believes it is at the forefront of controller
technology, with greater reliability the key benefit delivered.
David Wilkes, sales director at Curtis Instruments explains:
“The product reliability of the AC range has been phenomenal,
better than we’d hoped. We were not the first company to
develop AC induction motor controllers, and we learned from
the mistakes of others. Most controller problems are caused by
overheating, so our aim has been to eliminate overheating.”
Curtis claims the excellent heat management of its controllers
sets the company apart. While some competitors are said to need
heat sinks and cooling fans to help the motor controller work
optimally, the Curtis system is self-regulating. So how has this
been achieved?
Kerry Green, European support manager at Curtis Instruments
puts the success of the controllers down to two key developments
– Auto Characterisation and Vehicle Control Language (VCL).
“With a Vector Controller, if you don’t have a very accurate
motor model your efficiencies are down. That means you waste a
lot of energy resulting in excess heat. If you start to heat things up
you get early failures,” Green explains.
“So we spent a lot of time on Auto Characterisation. We were
the first company in the world that could auto characterise a
motor successfully with a motor controller on a vehicle. Before
that, if you wanted to use a new motor type, you had to model it
on a dynamometer rig and it could take weeks.”
Auto characterisation allows a manufacturer to evaluate a
number of motors very quickly, critical when developing a
forklift. It is not unusual for a forklift manufacturer to test and
evaluate a number of motors in search of the optimised part for
their truck.
“If a motor doesn’t give the desired performance, within an
hour we’ll have another motor and a fully characterised system,
so the guys can be out testing again. We can build such an
accurate motor model using auto-characterisation, the efficiency
of our system is very high, it runs cool, and the batteries last
longer. This was the first major achievement on the controllers.”
The second development was Vehicle Control Language,
which is somewhat analogous to a PC’s operating system and
application software. The operating system in the controller takes
care of the motor control and safety functions. On top of that
Curtis loads application software that customises the controller to
the vehicle.
“Previous to this, you basically took motor controllers out of
the box, and it performed the way it performed,” says Green.
“With our system, if a truck has special functions, we or the
customer can write the VCL code, and download it to the
controller using flash memory. For example, with
multidirectional trucks there is a lot of hydraulic control, where
you can rotate all of the wheels by 90 degrees, and then drive in
another direction. This has to be managed and the customisable
logic on the controller allows this be achieved to an optimal
Also with the logic on the controller, the truck manufacturer
can remove un-needed components, such as PLCs, and banks of
relays, so there are fewer things to go wrong, which again adds to
reliability. Enhancing reliability further are IP65-rated controller
housings to eliminate moisture issues, and ESD protection.
Green continues: “The next step on the AC was to incorporate
software to control dual drive motor applications, which is quite
common in forklifts. This allows two controllers to operate sideby-side, connected via CANBUS, which is also a standard feature
in our controllers. With the dual drive function , the controllers
will read the steer angle and drive the front motors differentially
allowing enhanced performance and safety within confined
turning spaces.”
Curtis also takes a full system approach and supplies traction
controllers, pump controllers, and steering controllers. In fact, the
company supplies the whole electronic system outside of motors
and batteries, although it tests and recommends motors for
particular applications.
The firm also provides dashboard instrumentation within
IP67-rated enclosures, and allows the customer to design their
own screen design, which Curtis will download into the product
before despatch.
“Like the controllers,” says Wilkes. “We can mass produce
standard hardware and the customisation is enabled with the
software. This approach and the innovation and reliability of the
products are helping us gain market share, which we want to
continue, with the Asian market
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a particular focus.”
Handling & Storage Solutions – October 2011
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