The problem with this method is that the value of the D term substantially affects the optimal value of the P term, but much less so vice versa. The zone-based method resolved this by tuning D first. If you tune the P terms first, plan on going through a few iterations of P and D until you have a combination that you are happy with.

When in doubt, back off! Aggressive gain values may look good on the test bench, but don't forget they must work in the field day in and day out. For most applications oscillation and instability are much more serious problems than missing the target by a few encoder counts. It's best to explore different PID values on a variety of hardware if possible, including worn and used mechanisms. And of course, whenever exercising a system with new servo values, make sure you and your equipment will both be safe should the motor enter oscillation or undergo uncontrolled motion.

The tuning of feedforward systems starts with the velocity feedforward term, adjusting it to make servo lag as small as possible, and focuses on a portion of the profile where the velocity is flat. Next to be adjusted is the acceleration feedforward value, set to minimize the servo lag during periods of profile acceleration and deceleration.

Feedforward refers to the addition of open-loop information that is available to the profile generator. Typical feedforward terms are desired velocity and desired acceleration. By adding these values to the PID filter with a gain factor, it is possible to further improve the performance of the servosystem. Basically the additional terms let the servo better anticipate changes that are being commanded. Understanding when and how to use feedforward terms will maximize the performance of your system.

Feedforward will help when there are elements in your motion system that add a lag proportional to the feedforward term. For example, use velocity feedforward if there are velocity-proportional lags in the system. These most often come from use of voltage or velocity-mode amplifiers, and from frictional elements. The most common source of acceleration-proportional servo lag (or overshoot) is inertia of the motor system.

Start tuning velocity feedforward and focus on a portion of your profile where the velocity is flat, so acceleration effects do not come in to play. Adjust the velocity feedforward so that the servo lag is zero or small.

Leaving this value for velocity feedforward in place, adjust the acceleration feedforward value, and try to minimize the servo lag during periods of profile acceleration and deceleration.

There is one important thing to be aware of: Feedforward terms are by definition open-loop contributions to the final motor command. Thus if the conditions that caused the proportional lag change, such as a change in oil viscosity or increase in inertial load, then the optimum gain values will change as well. Because many of these factors cannot be controlled, you should select conservative average values for feedforward terms over the operating range and loads your system will encounter.

No tuning procedure can fully guarantee that a system will operate as desired under all conditions. However, as you gain experience in servo tuning you will develop an intuitive feel for the contribution of each of the PID terms. And using feedforward terms, you should be able to maximize system performance throughout the entire motion profile, during the acceleration, coast and deceleration phase.