Linear encoders aid consistent placement

Renishaw linear encoders are key to the performance of a new generation of large-board pick and place machines from Mydata.

Mydata is one of the world's leading developers and suppliers of pick and place machines for the electronics industry, set apart from other manufacturers by the flexibility and fast changeover its machines offer.

Its new generation of large-board machines has broken new ground, with recently integrated Renishaw linear encoders being key to the performance.

The electronics industry experiences extremely rapid advances in technology, placing constantly increasing demands on production machinery.

Mydata machines must be capable of placing components with a very high level of accuracy to cope with an ever-increasing variety and complexity of components, for example smaller BGAs (ball grid array) and tiny "flip-chips" (where the electrical connections are made directly to the chip's silicon).

These components have the added need for far higher positional and rotational alignment to ensure the extremely high levels of quality, now considered standard.

Renishaw encoders have been key to design changes on the y-axis of certain Mydata machines where, instead of the ballscrew and rotary encoder drive system, linear motors and linear feedback have now been employed.

Olle Tullstedt, Mydata R and D Manager, explains: "The linear motor and Renishaw encoder give us a big advantage, particularly when handling large boards with the T5 and T6 board handling conveyors - a capability unique to Mydata".

While the machine's acceleration and top speed are comparable to the ballscrew/rotary encoder drive, stiffness is much greater, meaning that the time taken to stabilise position after a move is much shorter and overall speed of operation is greater.

Positioning accuracy is also far better and consistent along the whole y-axis travel.

On the ballscrew system, the rotary encoder is remote from the head such that the positioning uncertainty varies along the axis travel.

This is not a problem with the machines that handle smaller boards, but has a considerable effect on machines with large-board conveyors.

Mydata has found other key advantages in using Renishaw linear encoders, including ease of installation.

Robert Pettersson, Mydata Servo Engineer, comments: "We tried several linear encoder systems and found Renishaw read heads very user-friendly".

"They were much more forgiving when we were aligning them on the axis, saving us time when setting up".

"Alignment is also extremely easy, probably the biggest factor being the bicolour LED on the read head, which gives us a very clear visual alignment indicator at all times".

Continues Pettersson: "The end clamps Renishaw supplies are vital to ensure that the scale expansion is linear and tracks the overall expansion of the system".

"Linear motors have a localised heating effect - the Renishaw scale distributes the expansion evenly".

He has no issues whatsoever with accuracy and resolution, and has had no experience of any inconsistencies or quality concerns.

Mydata machines are extremely flexible and versatile in their operation.

Whereas other manufacturers' high-volume electronic production machines can achieve raw speeds of up to 60,000 components per hour, this can be largely irrelevant if a process takes hours to change over.

After all, how fast is a machine that is standing still?.

Mydata machines are ideal for short batch jobs, allowing many customers to free up their "chip-shooters" for the long batch production.

The key to this flexibility is the combination of smart magazines, flexible software and feeder equipment.

The feeder magazines and trays come in a wide variety and can be changed while the machine is running.

They can be configured in many different ways because Mydata provides software that calculates how to optimise the configuration for each job, offline and extremely rapidly.

Advanced vision systems are employed to control multiple aspects of the process, recognising, aligning and inspecting components prior to placement.

The pick and place tools themselves offer intelligent functions, holding components in the optimal way, and also performing electrical tests on the components as they travel to their place on the board.

This allows the software to make the decision whether to reject the component if necessary, before it is placed on a board.

In an industry showing tentative signs of improvement, Mydata is continuing to innovate and develop its systems to cope with all the latest components and variety of tasks.

Renishaw linear encoder systems have already contributed to significant advances and are likely to contribute further in the future.

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