Making an electric motor operate correctly is as varied and complex as the millions of ways we use electric motors. Most of the time it’s just a matter of turning the motor on with a switch and letting nature take its course. Nature in this case as defined by Maxwell and Faraday.
But when the application requires some level of precision it can be more complex. And that’s where tuning comes in. The difficulty with tuning is that there are almost as many different descriptions of what servo tuning is, as there are suppliers of servo motors and drive amplifiers.
One of the most significant aspects of electric motors is understanding the performance requirement in terms of time. How quickly must the motor and control system respond to changes in the load? This property of motion is called dynamic response.
As an example, if a conveyor is running unloaded using a gearmotor to control belt speed, whenever a product is added to the conveyor, the belt speed will momentarily decrease. The specification for how much time will be allowed for the motor to recover its speed is the dynamic response. The inverse of the time period of the load is the frequency response in Hertz is the value of dynamic response required for stable control.
Dynamic response is also important in defining what technology of motor and control is required for an application. Variable frequency drives have a basic frequency response of 10 Hertz. So that sets the bar for a range of performance.
Variable frequency drives are also capable of greatly improved performance as the technology has migrated over the last 30 years. By adding a feedback device, the close loop performance of a frequency drive can be as high as 200 Hertz. Which is 50 milliseconds.
The time domain of frequency response can be translated to the position domain as following error. When a closed loop system uses an encoder to measure motor or load position, time and position can be interchangeable measures of performance.
In this way, defining a certain number of encoder counts as an allowable error becomes a significant way to define when the system is properly tuned. And since no system is “perfect” defining the following error as zero or one is likely going to lead to constant control system faults for exceeding the following error limit.
When it comes to “tuning” the performance of the motor and control, the motor and the load must be controlled together because the motor and control are required to convert electricity to torque. So the “tuning” of the system is much more complicated.
One of the best descriptions is by George Ellis of Kollmorgen corporation. His paper on tuning and autotuning is the most coherent explanation of all the unique elements of tuning a servomotor. I highly recommend a thorough study of this paper in order to become familiar with tuning and its application.