Consideration of Hardware Constraints in Designing Servo Drive Control Systems

Abstract

In designing a servo drive operating in a high-precision tracking mode, its motion trajectory should be shaped so that none of the specified drive state variables exceeded the preset constraints. This is one of the most important factors essential for securing the required accuracy and stability of system operation. On the other hand, if the drive operation parameters are kept far from the constraints, the drive equipment is underused; it will have excessive capacity and overall dimensions and, hence, excessive capital cost. Therefore, from the economic point of view it is important to set up the drive operation close to the constraints imposed on it. The article considers the constraints imposed on a direct servo drive equipped with a permanent-magnet synchronous machine (either a linear or rotary one). A constraint consideration concept is presented, according to which the constraints are conditionally subdivided into internal (constraints relating to the servo drive components) and external ones (constraints connected with the technological process and environment). Dedicated software for analyzing the constraints is presented, and its underlying principles are described. By using this software, it is possible to determine the permissible coordinates of a servo drive composed of the preset components (electrical machine, servo amplifier, position sensor, etc.) subject to the specified external constraints. Proceeding from the servo drive components (a synchronous machine, control unit, position sensor) selected from an editable library and the process installation parameters specified by the user as the input data, the software produces the domain of static mechanical characteristics individually for the electrical machine, for the machine together with the control unit and position sensor, and for the servo drive with taking into account the constraints specified by the user. As a result, the following positive aspects become available. First, the compatibility of the selected components is checked, and the possibility of using the selected equipment for implementing the required motion law is determined. Second, the components limiting the servo drive performance indicators are revealed. And third, the possibility of improving the servo drive performance characteristics in the case of using sophisticated control algorithms is analyzed. In particular, it has been shown that weakening of the field does not always make it possible to broaden the servo drive speed range. By using the proposed constraint consideration concept, a direct drive and its control systems can be designed and optimized much more rapidly, so that the newly developed drive can become commercially available within a shorter period of time.