PLANT MANAGEMENT
DRIVING FORCE W
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Mark Checkley states the top five factors to consider when selecting a drive controller for highly automated, safety-oriented process machines
hen choosing a drive controller for highly automated process plant and machines, a number of factors should be considered, including:
functional safety; real time communications; ease of integration; feedback control; and stability of the operating environment. In applications such as materials handling, textiles, woodworking, plastics, food and beverage processing, packaging, robotics and machine tools, processes are typically high speed with production plant, equipment and machines operating at high speeds, high reliability and in a stable operating environment. Minimising production downtime is critical, as well as ensuring the safety and energy efficiency of machines and processes.
When selecting drive controllers for high- speed, highly automated, safety-oriented applications, a number of important factors should be considered.
FUNCTIONAL SAFETY Machine and process safety is a major consideration. If you are designing a new production process or machine, it is important to consider the cost of safety.
For example, could you purchase drive controllers with integrated functional safety? If so, this is likely to reduce the cost of installing separate protective devices, as well as their associated cabling and installation costs. With drive-based safety, the safety functions are shifted into the drive platform. Some suppliers only provide drives with basic safety functions such as safe torque off (STO). Other suppliers go much further, providing modular, scalable functional safety from the basic STO to higher-level encoder- based safety functions such as safe limited speed, safe maximum speed, safe speed range, safe operating stop, safe direction and safe emergency limit. It is also extremely helpful and cost effective if the supplier provides its own software that enables faster parameter set up, configuration, analysis and parameterisation of key safety indicators and functions. In safety-oriented drive applications, it
is important to adhere to the relevant safety standards. Some key questions may need to be asked here, including whether the safety functions of the drive can be used up to IEC 62061-SIL3 levels in accordance with IEC 61508. Or whether the functional safety
is controlled via fail safe over EtherCAT (FSoE). FSoE will help to ensure interaction of the drive controllers with safety PLCs and safety I/Os. It may be possible to download encrypted data packets through machine controllers. FSoE allows all available safety functions to be controlled and secure measurement values (speed, position, etc.) and the switching state of the secure I/Os to be transmitted serially to the safety PLC. Limit values of all safety functions relevant to machine safety can be adapted to the application at any time via FSoE. Te result is tremendous flexibility and a significant saving in controls and wiring.
REAL-TIME COMMUNICATIONS If machines or production processes are high speed, choosing drive controllers that provide real-time Ethernet-based communications interfaces is critical. Tese Ethernet-based interfaces typically include Ethercat, Varan, Profinet, Powerlink and Ethernet IP, allowing optimal motor control and communication with higher level controllers. It is important that these real-time Ethernet-based interfaces are built-in (i.e. fully integrated) to the drives and not simply provided as an add- on module, as these add-ons can create unwanted latency in networks. It is also worth checking whether other diagnostic and/or display interfaces are provided as standard with the drive, such as RS 232, RS 485 and CAN interfaces. What motor types will the drive need
Several factors must be considered when choosing drive controllers 26
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to control? Does the drive support specific motor types, just some, or all of the major technologies? Motors are available in a wide variety of designs, including synchronous, asynchronous, permanent magnet, synchronous reluctance, linear, high-torque and high speed motors. It is therefore important to consider which motor types your drive will need to support,
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