Heidenhain CNC for Xaar's customised machinery

For a machine that Loadpoint developed for Xaar, designers made use of the Heidenhain TNC 426 control due to its precise positioning capability while enabling the machine to operate at very high speed

An ink jet printing machine capable of printing a full A4 page in full colour in under one-third of a second needs a very special print head.

One of the world's leading developers of this technology, and the specialist inks that they require, is Cambridge based Xaar plc.

Xaar manufactures its own range of heads up to 70 mm wide and has also developed a full page width printing head.

To achieve a resolution of 360 dpi across a 70 mm head width requires the head to have 1,000 individual but closely spaced nozzles.

These are partially formed by a high precision series of slots machined into a piece of lead zirconate titanate, or PZT.

For this, Xaar utilises a customised development of the NanoAce high precision wafer dicing system developed by Loadpoint, based at Swindon, Wiltshire.

The NanoAce was originally created as a sub-micron precision dicing and grinding platform for the electronics and semiconductor industry.

In this application however, the machine uses a Heidenhain TNC 426 CNC contouring control system to provide full three-axis control of the spindle position, thereby allowing Xaar to machine a profiled slot within the required repeatability and accuracy.

Loadpoint director John Sweet comments: "We have a long standing relationship and a considerable experience of Heidenhain controls and measuring systems and have used their gratings and scales for linear measurement since the early 1970s.

Over that time, we've found them an ideal supplier of standard packages that will meet our needs 'out of the box', which has led us to use Heidenhain components in most of our machines.

For the machine that we developed for Xaar, it was logical to make use of the TNC 426 control due to its precise positioning capability, while enabling the machine to operate at very high speed." NanoAce is the latest in a line of machines developed by Loadpoint since 1966 mainly used for dicing, cutting or scribing semiconductor wafers into individual integrated circuits.

The latest machine is capable of handling wafers up to 300 mm diameter, with a linear resolution of 0.0001 mm and angular resolution of 0.0001 degrees.

When the company originally began to manufacture the machines, the absence of a suitable proprietary spindle unit led it to develop its own air bearing spindles.

Subsequently, this area of the company's activities became significant in its growth with Loadpoint now supplying spindles capable of operating at speeds up to 60,000 revs/min for use with diamond cutting wheels.

The company has also developed optical grinding and polishing techniques for fibre-optic applications and this technology has spread to many other precision engineering areas.

The machining of PZT can be traced back to early body scanner development when Loadpoint produced a machining process for the scanning heads which have characteristics very similar to the current print heads.

John Sweet describes how NanoAce essentially offers a high precision three-axis positioning system which can be developed for any application that will fit within its work envelope.

On a dicing application, for instance, it would supply its own dedicated PC-based dicing control.

"However, the slot profile demanded by the Xaar application, needed a machine tool oriented approach and we had no hesitation in adopting the Heidenhain system," he says.

A basic NanoAce is constructed as a three-axis, moving-bridge type linear positioning system, with the option of a rotary table.

Twin matched brushless DC servo-driven ballscrews on each leg of the X-axis eliminates crabbing and the latest Heidenhain encoder technology ensures positioning to 0.1 micron resolution.

Furthermore, the system can position itself at high speeds of 750 mm/sec in dicing applications, and 100 mm/sec for high precision applications such as that at Xaar.

Says John Sweet: "The machine lends itself to dicing, slotting, grinding or drilling depending on the control, linear feedback system and spindle that is fitted." He goes on to describe for Xaar: "Repeatability was hugely important so the thermal compensation capability within the Heidenhain TNC 426 was critical - even though the machine operates in a temperature controlled and clean room environment." The NanoAce has now been installed at Xaar's factory for some time, where its capabilities have become central to print head production.

"It's a relatively small volume production process but it has proved very reliable and repeatable," John Sweet concluded.

"This is certainly due in part to the high performance capability of the Heidenhain control and feedback package," he says.

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