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66 SMT007 MAGAZINE I MARCH 2021 Proportional Proportional control is the most common kind of control loop. It is inherently stable when properly tuned. A proportional control- ler is just the error signal multiplied by a con- stant and fed out to the drive, but it experi- ences offset at steady state. Figure 5 shows what happens when one adds proportional feedback to the motor and gear system. e motor goes to the correct target for small gains (kp = 1), but it does this quite slowly. Increasing the gain (kp = 2) speeds up the response to a point. Beyond that point (kp = 5 or 10), the motor starts out faster, but it overshoots the target. In the end, the system does not settle any quicker than it would have with low gain, but there is more overshoot. If gain continues to be increased, it most will eventually reach a point where the system just oscillates around the target and never settles. e system would be unstable. Integral Integral control is used to add long-term precision to a control loop. It is almost always used in conjunction with proportional control, which provides better dynamics responses than integral alone. Again, there is the possi- bility for instability. Figure 6 shows the temperature control sys- tem with pure integral control. is system takes a lot longer to settle than the same plant with proportional control (Figure 52). How- ever, notice that when it does settle, it settles out to the target value even with the added dis- turbance. If a problem does not require fast settling, this might be a workable system. Meanwhile, Figure 7 shows the motor and gear with proportional-integral (PI) control. Compare this with Figures 5 and 6. e posi- tion takes longer to settle than the system with pure proportional control, but it will not settle to the wrong spot. Figure 5: Temperature controller with proportional feedback. The kink at time = 2 is from the external disturbance [1] .