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Market-leading micro-PLC adds motion control

01 November, 2005

Leading micro-PLC adds motion control

Mitsubishi has unveiled the third generation of its market-leading FX family of micro-PLCs - the first all-new version since 1990. As well as boasting many improvements - including speeds up to 4.5 times faster, a memory eight times larger, 75 new instructions, and a wide range of serial communications - the new FX3U can also control simple motion applications, and offers "the first motion control network for micro-PLCs".

To maintain compatibility with the six million FX PLCs sold since the family was launched 25 years ago, the FX3U (shown above) can be expanded in two directions. On its right-hand side, it accepts existing FX expansion modules; on its left-hand side, it provides a new, faster analogue expansion system called ADP (shown in close-up below), which can support up to 80 analogue inputs and 48 analogue outputs. The analogue modules can be addressed directly, halving the amount of control code needed, says Mitsubishi. Up to 384 inputs and outputs are supported between local and networked I/O.

John Sumner, Mitsubishi`s business development manager for motion control systems in the UK, hails the new PLC as "an exciting proposition for motion customers". He points out that it can be integrated directly with servo and stepper systems, and will provide three-axis control for simple positioning applications, without needing any extra hardware.

There are six 100kHz counters and three 100kHz pulse train outputs built in, as well as absolute position detection which means that you do not need to re-home servo motors each time a system is powered up. In addition, there are high-speed counter and pulse-train ADP expansion modules that can process signals at up to 200kHz. These can be used with any compatible servo or stepper motor.

The FX3U`s motion capabilities do not end there. It supports a servo controller bus called SSCNet III which Sumner describes as "the first dedicated motion control network for compact PLCs". This network, which runs at up to 50Mbps, can be used for two-axis interpolation control, with one CPU supporting up to 16 axes.

The FX3U also provides instructions for controlling up to eight Mitsubishi inverters. These instructions include commands for reading blocks of data from the inverter and are claimed to reduce programming times by up to 75%.

The FX3U processes instructions in about 65ns, resulting in much faster scan times and responses than earlier PLCs. With its 64k step memory, the PLC can handle more sophisticated applications, and allows all five IEC 61311-3 programming languages to be implemented fully. "You will never need to worry about capacity again," says Hugh Tasker, Mitsubishi`s UK PLC systems development manager.

The new PLC provides 40,000 data registers - five times more than before - which could be exploited in applications such as data-logging and energy monitoring. There are new instructions for manipulating data.

On the communications front, the FX3U supports 10/100Mbit Ethernet, Profibus, DeviceNet, AS-i, and CCLink, and is thought to be the first micro-PLC to offer the option of a USB port. It is also, "the only compact PLC with a Profibus master," according to Tasker.

As well as accepting expansion modules from earlier PLCs, the new CPU can also run their programs - much faster - after a simple conversion process. Its programming software incorporates a simulation tool, and "virtual training" facilities. A basic version of the software, supporting up to 1k steps, is available free of charge.

Despite the extra power offered by the new generation of micro-PLCs, Mitsubishi is keeping prices similar to the previous generation, with the new ADP analogue modules being cheaper than their predecessors.

Tasker acknowledges that the FX3U will take sales away from the Mitsubishi`s larger Q Series modular PLCs. But, he argues, there are some applications - such as those needing more than 384 I/O - where the modular systems will be more attractive. The Q Series motion modules are also more powerful than those in the FX3U family.

The FX3U PLCs will eventually supersede the earlier FX2N models, but these will continue to be available in the UK for at least 18 months.

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