‘Control’ is a term for the use of binary calculation methods to execute a process or task. I suspect it is as ambiguous a term as ‘mechatronics’. I suspect that we cannot even agree on what control is, without getting into some depth on the all the possible definitions of the subject.
This is rather ironic considering the billions of dollars that are spent on control systems across all fields. Is control fundamentally any different if it is inside a car, automating lighting and HVAC in a large building, on an automotive manufacturing plant floor, in a biological resesearch laboratory, or in a giant refinery where chemical products are made. It’s all control. And the more we try to define it, the more inclusive we make the definition, the more vague and ambiguous the term becomes.
Efforts continue to increase the power of the PLC (programmable logic controller) across many vendors. By increasing processor speed, memory and capability PLC’s are becoming the universal platform of control as a discrete controller, process controller and motion controller.
Simultaneously, motion control specialty companies continue to increase speed, processing power and I/O structures in an effort to expand the dedicated motion controller as a competitive platform to the PLC. This is a necessary migration to address control applications where an external PLC could be eliminated.
Is there an ideal mix of motion axes and I/O that will help resolve which hardware solution is best? Not really. The fact is that the majority of the market is made up of motion control using stand-alone axes that are triggered by logical conditions in the system. Coordinated axes require the sharing of pulse to pulse position feedback information. Stand-alone axes do not share data at that low a level in time. Most PLC controllers are well able to handle stand-alone axes, especially if an intelligent indexer is used. This off-loads the motion to the servoamplifier and only I/O handshakes are used.
Part of the ambiguity here is that control is the result of hardware and software together. ‘Control’ seeks to generate complex behaviors using digital methods. The digital methods, processors, depend on programming techniques in order to implement the desired behavior. So when we talk about Control, we are talking about hardware and software simultaneously.
What matters most to users of automation technology is both logic control and motion control programming exist in a single environment. It doesn’t matter if the programming environment is a PLC with motion blocks inside it, or a motion controller with logic blocks inside it. What matters is that all aspects of a control system can be programmed using a single editor. Controllers from the major electrical companies like Rockwell Automation and others have opted for the logic-centric programming environment with motion blocks in the ladder diagram.
This approach eliminates the complexity of multi-processor solutions, each with their own programming language, that were commonplace a few years ago. Multiprocessors have their own unique programming environments and a significant amount of programming to create proper interaction between the various platforms.
Missing from this description is the hard wired control that is part of system start up, power management and safety. More on this in the next installment.