OE-5.4 Digital Computers as Controllers & Actuators
You can describe how a digital computer is placed in a control loop and what interface electronics it needs, and select among solenoids and DC, AC and stepper motors.
Putting a computer in the loop turns a continuous problem into a sampled one, and the information the computer needs from the process - and the process from the computer - is the interface design question this unit poses. Stepper motors are the ones worth understanding well, because they give open-loop position control, which is why 3D printers and older disk drives could be cheap. Match actuator to load and duty cycle rather than to headline torque.
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Digital computers as process controllers: introduction
Replacing dedicated hardware with a general machine, which is what actually happened in industry. The rest of this topic is the consequences of that change.
Information required by the computer and by the process
What has to cross the boundary in each direction, which is the interface specification in plain terms. Getting this list right is most of the design.
Computer interface electronics; digital computer input-output
The circuits that let a computer talk to a plant, in both directions. Isolation is the detail that separates a laboratory build from an industrial one.
Computer processing of data
What the machine does with the numbers once it has them: filtering, scaling and the control law itself. It is where the theory from earlier topics becomes code.
Digital process control computer design and programming
Designing and programming the whole thing, taken as a process rather than a device. Reliability requirements here are unlike ordinary software, which is worth noticing.
Electromechanical actuators: linear and rotary motion solenoids
The devices that turn a signal into motion, starting with the simplest. Solenoids are on-off devices, which constrains what control law can be used with them.
DC motors, AC motors and stepper motors
The three motor families, and the reason there are three. Stepper motors give you position without feedback, which is why they are everywhere in cheap equipment.
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