FEATURE ROBOTICS & MOTION CONTROL
MOTION CONTROL: MAKING AN INFORMED CHOICE
Phil Nicholas, channel and platform deployment manager, mechatronics at SKF, argues for a holistic approach towards system design
T
he debate between advocates of fluid power and electro-mechanics across all sectors of industry has been rumbling on for a number of years. In the food production and processing sector it’s often been a discussion about using one technology or the other, or about replacing pneumatics and, on occasion, hydraulics with electromechanical devices. One of the issues in the past has been that fluid power is an old and established technology that engineers knew and understood. Fluid power may not have been perfect, and it certainly had its limitations, but it has generally done the job. Indeed, advances in pneumatics technology in particular have kept pace with the changing needs of the food sector, in terms of performance, reliability and ability to comply with a host of energy, environmental and health and safety legislation. The quality of the debate was not
improved in the early days as suppliers of electromechanical systems sometimes made claims for their products that were often widely enthusiastic. It was not unknown for suppliers to over-sell and under-deliver, or to fail to match the performance of their products correctly to the needs of each application, with the result that new systems sometimes fell far short of expectations.
APPROPRIATE TECHNOLOGY Those days are now behind us. Today the discussion has moved on. Companies now recognise that it’s not a question of one technology or another, but of using the most appropriate technology, or more likely a combination of technologies, to achieve the task in hand. Developing a successful motion control system, whether that be a simple component upgrade or modification for a filling unit, or a complete packaging machine build, requires a holistic approach that firstly considers the fundamental system requirements and then looks at the most appropriate methods of motion technology.
28 OCTOBER 2015 | AUTOMATION
The questions that need to be asked
will vary considerably from project to project, but will generally start with a definition of what needs to be achieved. This might be a description of the number of packs or products that have to be processed per hour, or be more specific such as the speed or precision with which a filling head or sealing unit has to be moved and positioned. Cost will, inevitably, be a key factor in
Made of high-grade material, the CASM is a linear unit designed to withstand even the hardest conditions
any project, as will the availability of power sources. For example, if a machine being modified is already set up with a compressed air feed then it may be more cost effective to add further pneumatic devices, even though these may not offer the same level of control or energy efficiency offered by a comparable electromechanical system. Conversely, the air losses and difficulty of positioning pneumatic actuators repeatedly and precisely to within a few microns at multiple stop-start positions along the stroke length can make an electromechanical actuator and controller a better choice. This is especially true if actuation systems have to move through different temperature zones, as the compressibility of air is temperature dependent. Similarly, for larger or higher load applications, it may be possible to
CASM electric cylinders from SKF
replace a number of pneumatic actuators with a single electromechanical device; although the unit cost of the latter will be higher, the total system cost may well be lower.
PERFORMANCE FIGURES An important point is to consider the headline performance figures quoted by suppliers of motion control equipment with a degree of caution and to look instead at factors such as required speed, load and cycle rates. For example, a device that has a particularly high maximum cycle speed or duty load may not necessarily provide the best long term solution, in terms of functionality, reliability, operating life and total cost of ownership. The risk of contamination is clearly a
major factor to consider in areas where food products are being processed. Depending on requirements, oil-free compressed air systems can be successfully used; alternatively, electromechanical devices are available with high levels of sealing to enable them to be easily cleaned. This last point illustrates the fact that
engineers now have a far wider choice of solutions than ever before for food production and processing applications. Based on different, but not necessarily competing technologies, these solutions create the opportunity to develop new and exciting methods of machine automation and control.
SKF (UK) T: 01582 490049
www.skf.co.uk
/AUTOMATION
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