Linear actuators overcome limitations of pneumatics As the food industry focuses increasingly on batch processes, so the limitations of pneumatic control are being highlighted. The new linear motor-based technology looks set to overcome these limitatons. Manufacturing processes are advancing all the time and this is especially the case in fast-moving consumer goods (FMCG) industries such as food and beverages. In food packaging, for example, one of the latest trends is towards custom labelling and packaging of products. Another trend is smaller batch sizes, which means that production changeovers occur once or twice a day rather than weekly. At the same time, however, manufacturers are also demanding higher throughput. In order to achieve these seemingly conflicting requirements, the cutting, coating and positioning processes must be fast and cost effective. This, in turn, relies on the use of pneumatics. Nevertheless, one of the biggest challenges traditionally posed by pneumatics is that they are difficult to control smoothly and so only suited to point-topoint manoeuvres. So, for example, if a different product is to be manufactured, the production line may need to be rebuilt with new, or manually-adjusted pneumatics. One way to address this controllability issue is by using ballscrewbased actuation. Up to now, ballscrews have suffered from slow speeds typically in the 800-2000 mm/s range. All that has now changed with the launch of new tubular linear motor based technology. A new type of linear actuator, called the ServoTube actuator, delivers the controllability of a ballscrew together with the ease of use associated with high-speed pneumatic actuators. With its rugged IP67 housing it can be used in the frequent wash-down environments found in the food industry and meets FDA regulations concerned with both direct contact with food and spillage prevention. A new breed of linear actuator In order to meet the rigorous requirements of the food industry, when designing its new actuator Copley focused on four issues: how to match the speed and form factor of the pneumatic cylinder; delivering the controllability of a ballscrew; the need for a rugged wash-down design; and maintenance and lubricant-free operation. Achieving the first two was simple, as high speed – up to 8.7m/s – and precise electronic control are inherent features of linear motors. The next step was to provide a rugged, direct mounting forcer (body) so that the thrust rod can be extended, making Servo- Tube behave like a faster, quieter ballscrew actuator rather than a linear motor. Similarly, taking the position encoder inside the body of the actuator reduced cabling, cost per unit and crucially made the design very rugged. In fact, the actuator is fully submersible for intermittent periods and meets IP67 requirements. At the heart of ServoTube’s design is patented arrangement of magnets with opposing poles and spacers, hermetically sealed within the thrust rod. This arrangement induces a smooth sinusoid field in the forcer coils. Unlike linear motors that require a special triangular or trapezoidal servo amplifier, Servo- Tube is controlled using a standard servo amplifier, which accepts sine / cosine feedback. In addition, errors that normally occur because of misalignment are reduced with patent-pending, low-cost signal conditioning electronics, resulting in an actuator repeatability that exceeds 12 microns. An accessible replacement In order to succeed in replacing pneumatics, ServoTube has the same DIN/ISO 6431 mountings as pneumatic actuators and accepts standard pneumatic accessories. It even looks and operates like a double-acting pneumatic actuator. This was a deliberate and essential step in making the design accessible to both machinery OEMs and system integrators. Unlike a ballscrew actuator, no gearbox and coupling is required. The lack of such mechanical limitations gives the actuator its high-speed, high repeatability features. Importantly for the batch manufacturing operations becoming so popular in the food industry, ServoTube also reduces downtime. Actuation is adjusted by simply changing the commands sent to the servo drive. If a digital drive such is used, this can be achieved using a PC or PLC. The CANOpen facility can be used to synchronise actuation across multiple axes. On replacing pneumatics, further cost reductions are made by reducing the associated compressed air costs and by improving reliability. For example, the dramatic noise reduction in changing to near-silent linear motors benefits employee and employer alike in the face of increasingly stringent environmental regulations. Food grade, no lubricants Unlike a mechanical ballscrew or lead screw assembly, tubular linear motors are completely non-contact. However, this comes at a price, requiring careful installation to ensure that the thrust rod is aligned centrally. Alternatively, a factory assembled module can be used, with the linear guide and chassis provided positioning the thrust rod the correct distance from the coils for optimal, frictionless movement. The new ServoTube linear actuator was designed for use independent of a module or machine chassis, so the thrust rod would need to be supported with a bearing. The actuator coils also needed to be electrically insulated from the magnetic thrust rod. Copley decided that if they could combine the insulation layer inside the motor coil with a polymer bearing sleeve to control alignment, they could simplify the design and keep the cost of the actuator low. Bearing manufacturer igus already supplied bushes and cable management systems to Copley. Their product director considered Copley’s problem and thought igus might be able to solve the problem using a polymer they had developed called iglidur. The state-of-the-art plastic bearing eliminates the need for any lubricant in applications where the actuator can be used – a big plus for food and drink manufacturers. The finished product By keeping the bearing integral to the actuator, Copley has managed to produce a linear actuator that is directly compatible with pneumatic actuators. Suitable for mid accuracy applications, the new design can be easily integrated in the place of pneumatics. The food industry is already making use of this technology in applications such as cutting, stacking, pick-and-place, and bottle filling. In addition, as uptake increases, unit cost will reduce further, opening up new design possibilities for machine and plant builders, apart from the increase in flexibility and accuracy. 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