The theory-practice gap has existed for decades and each of us needs to bridge this gap in all we do. As control is an essential element in all multidisciplinary systems, let's start there, and begin to bridge the gap that exists between the theory of control and its digital implementation. Top 10 lists are always popular, so here is one for classical control.
Control theory for the practitioner:
Feedback control is a pervasive, powerful, enabling technology that, at first sight, looks simple and straightforward, but is amazingly subtle and intricate in both theory and practice.
In a dynamic system, changes cannot be effected instantaneously, and so an otherwise correct control decision applied at the wrong time could result in catastrophe.
Nonlinearities are always present, e.g., backlash, Coulomb fricton, saturation, hysteresis, quantization, dead band, and kinematic nonlinearities. A linearized model can be used to approximate a nonlinear system near an operating point.
Stability of a dynamic system must be guaranteed. Closed-loop systems go unstable because of an imbalance between strength of corrective action and system dynamic lags. Stable systems must have adequate stability margins to work once built.
Stable systems have a frequency response. If a stable linear system has a sinusoidal input applied, then the steady-state output will be a sinusoid of the same frequency, however, the amplitude ratio and phase difference of the two sinusoids are frequency-dependent.
The open-loop transfer function is the product of all the transfer functions in the loop, e.g., controller, actuator, plant, and sensor. Compared to the closed-loop system transfer function, the open-loop transfer function is much less complex. The Nyquist criterion and the Root Locus procedure allow one to use the open-loop transfer function to predict closed-loop system performance.
After stability, performance is everything. Command following, disturbance rejection, insensitivity to modeling errors, and insensitivity to unmodeled high-frequency dynamics and noise are the main reasons for using feedback control, once a system is guaranteed to be closed-loop stable.
Time delays can be deadly. Always conserve phase, the equivalent of time delay. Integral control adds 90 degrees of phase lag at every frequency and digital control adds time delay primarily due to D/A conversion. Imagine trying to make decisions using old information.
High control gain has lots of benefits, e.g., good command tracking and good disturbance rejection. However, there are three areas of concern: roll-off, saturation, and noise.
People's lives may be at stake. There are no "details" in control engineering, as even the most insignificant detail may prove to be important. Real control systems must be extremely reliable, especially if people's lives depend on them.
Iterative design — the cycle of prototyping, testing, analyzing, and refining a product — existed long before additive manufacturing, but it has never been as efficient and approachable as it is today with 3D printing.
People usually think of a time constant as the time it takes a first order system to change 63% of the way to the steady state value in response to a step change in the input -- it’s basically a measure of the responsiveness of the system. This is true, but in reality, time constants are often not constant. They can change just like system gains change as the environment or the geometry of the system changes.
At its core, sound is a relatively simple natural phenomenon caused by pressure pulsations or vibrations propagating through various mediums in the world around us. Studies have shown that the complete absence of sound can drive a person insane, causing them to experience hallucinations. Likewise, loud and overwhelming sound can have the same effect. This especially holds true in manufacturing and plant environments where loud noises are the norm.
The tech industry is no stranger to crowdsourcing funding for new projects, and the team at element14 are no strangers to crowdsourcing ideas for new projects through its design competitions. But what about crowdsourcing new components?
It has been common wisdom of late that anything you needed to manufacture could be made more cost-effectively on foreign shores. Following World War II, the label “Made in Japan” was as ubiquitous as is the “Made in China” version today and often had very similar -- not always positive -- connotations. Along the way, Korea, Indonesia, Malaysia, and other Pacific-rim nations have each had their turn at being the preferred low-cost alternative to manufacturing here in the US.
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