AC drive provides fine height control

Each Industrial Devices 25kN-rated ACME thread actuator is driven by a 0.55kW braked motor, with encoder feedback and controlled by a 0.75kW Control Techniques Unidrive SP AC drive.

Delta International has developed a climbing platform which uses Control Techniques servo-drives to control long-reach actuators When Delta could not find a proprietary modular climbing platform that met the standards of iits on-site engineers strengthening the 94m refinery chimney at BP Coryton, the company chose to design its own.

The result was a fast climbing, ultra-safe modular system that can be adapted to suit most chimney contracts.

The specification included a three-tonne uniformly distributed service load, ease of operator use, anti-skewing features, automatic expansion and contracting to adapt to different structures and compliance with all UK and European codes of practice.

Delta's Senior Engineer, Nigel Matthews, spent six months planning, designing and fabricating the electronic climbing platform.

"We realised that the success of this depended on the accuracy and reliability of the drive/actuator combination, so we took a lot of care in researching the market" Matthews said.

"We chose linear actuators from Industrial Devices of Shrewsbury and they recommended Control Techniques drives as being the best to provide the level of control, communications and onboard programming that we needed".

The climber comprises a lower scaffolding ring supported on a manually clamped steel ring.

An upper boarded section is also supported on a clamped steel ring.

Between the two layers are electrically-driven lead screw actuators, locked to the upper and lower structures.

Depending on the diameter of the chimney, there can be up to 20 actuators.

The refinery chimney at BP Coryton needed 15.

To climb, the upper clamping band is released and is pushed up 1.2m by the actuators working in unison, re-clamped and the lower ring is released.

The actuators then contract, smoothly pulling up the lower platform, which is re-clamped.

The process is reversed for the descent.

This means that the whole platform is raised and lowered in one piece, rather than in sections, like conventional climbing platforms, creating a far safer working environment.

Each Industrial Devices 25kN-rated ACME thread actuator is driven by a 0.55kW braked motor, with encoder feedback and controlled by a 0.75kW Control Techniques Unidrive SP AC drive, working in servo mode and fitted with an applications module to provide powerful on-board programming.

Each actuator has a maximum reach of 2m and maximum speed of 60m/min.

One Unidrive SP acts as master and 14 act as slaves, with all drives communicating using Control Techniques' own high speed drive-to-drive network, CT Net.

The Unidrive SP AC variable speed drive range spans 0.75kW right up to 1.9MW.

The Unidrive SP is configurable into five operating modes, including open and closed loop, vector, servo and regenerating modes.

It provides connectivity to most industry standard networks and accepts 14 position feedback protocols.

With a range of plug-in module options, its on-board PLC can be supplemented with programmable modules.

The purpose of the software for the climbing platform, written by Control Techniques software engineers, is to provide anti-skew control to ensure that when the master linear actuator's position is changed in auto-mode, all the other actuators on the system follow its position.

It is also possible to change the position of any actuator in manual mode, without affecting the others.

When changed back to auto-mode, the actuator continues to mimic the master from its new position.

The master constantly monitors the status of the slaves and if any actuator is prevented from operating, perhaps because of an obstruction, this error is reported and the whole operation is stopped.

The software is identical in each applications module and automatically configures itself to the correct settings based on CT Net node number.

Other system features include fully adjustable and independent speed of raising or lowering and the option of an Ethernet link for remote diagnostic purposes.

The climbing platform is run off a generator supply since its use is intermittent, keeping on site costs to a minimum.

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