ISA Certified Automation Professional (CAP) program

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Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.

CAP question

In tuning an axis for point-to-point moves, what would the automation professional look for?

A. Axis that has no following error
B. Axis with a lot of feedforward to adjust for velocity changes
C. Axis that quickly makes the move but with minimal or no overshoot
D. Extremely hot axis with very little following error

CAP Answer

The answer is C: "Axis that quickly makes the move but with minimal or no overshoot".

There are many types of moves that can be configured for a motion control application, including single axis point –to-point, coordinated multi-axis, blended mult-axis, and contoured motion.

For single axis point-to-point moves, tuning involves adjusting the velocity of motion and the acceleration along the axis. Taking the derivative of the classic (positional) PID equation, the resulting velocity form of the PID equation yields Velocity, Position, and Acceleration as the three controller terms. Adjusting the Velocity and Acceleration terms of this equation is as easy as setting the gain and derivative of the classic PID equation.

When moving along an axis, “good” tuning implies moving as quickly as possible without overshoot moving from the original position to the new, final position.

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, 2nd Ed., 2006