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Product category: Drives, motors and power transmission, couplings, clutches
News Release from: Control Techniques | Subject: Unidrive SP AC drives at Witter Towbars
Edited by the Manufacturingtalk Editorial Team on 27 March 2008

Automated jig control cuts welding time
by 50%

Automated jig control used on rotating manipulators provide up to 360 deg rotation, most often in 45 deg increments, between periods of MAG welding of towbar assemblies.

Using drives from Control Techniques, automated jig control has made a significant contribution to increased production at Deeside, UK-based Witter Towbars, cutting the welding time for each towbar assembly by up to 50% The rotating jigs were designed and produced by Telford, UK-based Automatic Technologies International (ATI) using Unidrive SP AC drives with UMD servomotors from Control Techniques Dynamics

Programming was provided by on-board EZMotion modules.

Used in conjunction with MAG-welding robots, the jigs or welding manipulators, provide up to 360 deg rotation, most often in 45 deg increments, between periods of welding.

Managing director of ATI, Alex Wilson, said: "The client was looking at different ways of automating what had been a manual task.

The solution required integration with the welding robot and special machine builders were offering solutions that required PLCs to provide the control and interface - a costly solution".

H continued: "We were able to provide a much simpler solution, with no PLC required, simply by using position numbers from the robot output card direct to an EZMotion module within the Unidrive SP.

And, as a bonus, we could guarantee complete safety whilst loading each job, using the secure disable feature on the drive, so that it wasn't necessary to power down the drive each time or use contactors to provide a category 4 safety stop".

Just three outputs are used from the robot, making up eight binary codes covering the jig rotation, as well as 'stop' and 'run'.

The programming for acceleration/deceleration and positioning is all carried out in the easy-to-program EZ-Motion card fitted inside each of the 2.2kW Unidrive SP AC drives.

To give the best dynamic response, matched to the drive, 115UMD Unimotors low cogging brushless AC servomotors are used, with Sin/Cos absolute encoder feedback to give precise position control.

* Welded assembly - the elements of each assembly including brackets, legs and side plates, are fitted into one of 80 different jigs and are clamped into place.

Jigs are up to 1.5m in width and up to 800mm in depth.

The job is set up on the robot controller and a press of the start button initiates the full sequence of welding, rotation to the required position and welding again.

There are around 850 variants in all and the launch of each new vehicle brings several new towbar designs.

Seven robots are engaged in the welding of the towbar assemblies, four of which are now fitted with two manipulators, considerably cutting the time required for welding each assembly.

"Previously, each job was completed in four separate stages," explained Witter's senior manufacturing engineer, Gary Nuttall.

He said: "Each stage requiring its own jig.

Then of course, partly welded assemblies had to be moved from one stage to another by hand, a manual handling issue we were keen to eliminate.

Now, as well as much less handling, we get improved weld quality.

It's consistent, there's much less chance of human error, and of course, there's up to 50% time saving on the whole of the welding procedure".

Unidrive SP is the world's most advanced 'solutions platform' AC drive, said Parker to manufacturingtalk, configurable into five operating modes.

These include the following.

* Open loop.

* Closed loop.

* Vector.

* Servo.

* Regenerating.

Connectivity is to most industry standard networks and accepting 14 position feedback protocols.

With a range of plug-in module options, its on-board PLC can be supplemented with high-end PLC processors, customer programmable application modules are also offered with a library of software.

EZMotion is an easy to program motion controller that clicks into one of the Unidrive SP's option slots, taking up no additional cubicle space.

It provides fast, precise motion control using its own internal processor, giving one and a half axis motion synchronized to a reference encoder for a wide range of applications.

* Drives - Unimotors are very smooth, low cogging brushless AC servo motors from Control Techniques.

They are three-phase, six- or eight-pole, permanent magnet motors exhibiting a sinusoidal back EMF characteristic.

The novel 'finned' motor housing is a high-strength aluminum alloy casting that improves heat dissipation by conduction, radiation and convection.

This medium inertia motor optimises torque output and reduces cogging torque and the compact design gives increased torsional stiffness.

* About Witter - the Witter name is synonymous with the highest standards of design, quality, safety and security for motorists and road users.

From its modern headquarters on Deeside, North Wales, UK, the company supplies a complete range of towbars and accessories through a nationwide network of specialist stockists and fitters.

Its towbars are manufactured from high strength structural steel plate, tube and section material and shaped into components using the very latest production techniques and processes. Request a free brochure from Control Techniques ...

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