Let’s break down some of the terms pertaining to motion control. I am suggesting a definition along the lines of “An independently functioning system capable of converting energy to perform work”, or something to that effect. The notion being that the most central elements are that it is a system, the system performs work, energy is converted from one form to another to accomplish the work, and the system is under some type of control.
“An independently functioning system” can be expanded slightly to incorporate the assemblage of a number of parts that make up the system. This requires intelligent design (yes, I like controversial phrases) and that there is design intent. What is the task that needs to be performed and how does the designer break that task down so that it can be accomplished by automatic means. An important aspect of the assemblage of parts also requires consideration of the mechanical envelope required to support the inputs to the task, the operation of the task and the output of the task.
The task itself may be a process or a discrete manufacturing step. This fact blurs the definitions of the control requirement. Most engineers consider the processing of material to be substantially different from discrete manufacturing because the traditional control tools were different. I think this aspect is simply a function of the history of the respective industries and in today’s extremely powerful and inexpensive controls environment, not as substantial of a distinction as in times past. If one is writing application software for converting crude oil to polyethylene pellets on an industrial computer, is this very different from using the same computer to make automobile transmissions? 20 years ago when Programmable Controllers were the dominant form of control in the auto industry, the distinction was clear. Today, not so much.
The performance of the work task under automatic control begs another series of questions. The machinery design is intended to operate “independently” or “automatically” by means of a control system, without the need for constant monitoring by an attendant. This is different from “autonomous” operation which is evident in a Roomba robotic vacuum or as in the Darpa challenge of a vehicle finding it’s way from one location to another by means of intelligent searching algorithms programmed into computers. The use of controls has migrated from banks of relays in the 1950’s to multicore processors with vast computing power. The boundaries between the various control disciplines, process, discrete and motion, have mostly evaporated. But in all cases of control, the system under consideration is operating based on programmed instructions, even if it is adapting to changing conditions, which it cannot exceed.
The conversion of energy is always taking place regardless of the motive power source. Hydraulics are charged by a pump, usually electric, to create pressure and flow. We convert rotary motion to linear with electric motors of various types. Even the pneumatics industry has adopted a variety of electronics to add to the capability of the basic system. In all cases the conversion of energy from one form to another is closely linked to the work required. As a result it is most important to pay close attention to the details of the task requirement, especially as regards the work over time. All energy conversion results in waste which generally takes the form of heat. The thermodynamic limit must be observed in all applications.