Accuracy

You wake at precisely 6:47 a.m., as you always do. You lift the bedclothes and fold them over at a precise 40 degree angle, as always, swing your feet to the floor, and stand with your weight balanced precisely along your central axis, stay in this position for 3 seconds, and step briskly—

No you don’t. As a human being, you don’t have that kind of accuracy at your disposal. Even in a factory setting, human beings don’t produce 10,000 precisely identical copies of the initial product. Most human beings wouldn’t want to even if they could. It would be unsatisfying and stressful.

That’s where automation comes in. With the power of automation, human beings can produce amazing precision without giving up our basic humanity.

Increasing accuracy is a continual goal for industrial motion control. If we’re within a millimeter today, we want to be within a tenth of a millimeter next time we check.

The factors that can improve accuracy

• Better sensors mean greater accuracy. Optical encoders and magnetic encoders which are unaffected by dirt and can be sealed for use in washdown environments, can reduce cumulative error.
• Better feedback can make a big difference, too. The more clearly the elements of the motion control system communicate with one another, the better. Adding external feedback to a system can ramp up positioning accuracy.
• Repeatability is part of accuracy in industrial motion control. Being able to position a device precisely once is not enough. It has to be possible to return the device to the same position repeatedly — and fast. Any strategy relating to accuracy has to take this into account.
• Heat, friction, and vibration are unavoidable factors than can affect accuracy. They may be generated by the machine itself, or by resonance from other machines in the system or external factors such as the HVAC system. Improvements in accuracy can rely either on better control of these elements, or on measuring and taking them into account.

When working toward increased accuracy, design and configuration are sensible starting points. But the need for precision has to be balanced by the cost of providing greater precision. There is a point for every project at which the need for greater accuracy is not great enough to justify the additional cost.

Recognizing that point is key.