The mechanical transfer elements between the motor and the working machine for textile, packaging, printing, paper, rubber, plastic, and other, processing industries, and the machines themselves' exhibit inevitably some kind of mechanical imperfections. On the other hand, the dynamic performance demands 'are more and more raised because of the increasing requirements on productivity and thus machine utilisation. In these conditions, the effects of the mechanical imperfections are no more negligible and, in some cases, dramatically deteriorate the machine operation indeed. The structure modelling and the adequate controller design in presence of these imperfections is an involved and very complex task.
To facilitate the commissioning of the electrical drives, installed in the most of the aforementioned processing machines, a computer-aided drive commissioning (CADC) approach is the logical solution, which becomes almost inevitable if advanced control methods have to be implemented.
The development of software tools for supporting the commissioning of speed and position control of electrical drives loaded by unknown mechanical systems (belonging to the class of the stiff or elastic two-mass systems (TMS)), with unknown mechanical imperfections (presence and degree of friction and/or backlash) and with varying inertia, was the main objective of a two-year collaboration between the Universities of Padova (Italy) and Paderborn (Germany) and some Companies in the frame of an European CRAFT project. The task of the project was twofold: (i) development of algorithms for the mechanical structure recognition and parameter identification, which was undertaken by the University of Paderborn, and (ii) development of speed and position control algorithms and a CADC tool, that, by a friendly Graphical Interface guides also non expert personnel through the identification procedure and the selection and tuning of the controllers, undertaken by the University of Padova. Both identification procedure and control loops uses motor speed and position feedback only, since neither speed nor position transducers are assumed on the load side.
CADC has been designed to be implemented in a portable computer which can be connected to the drive under commissioning. The drive is equipped with a DSP controller able to run each of the control algorithms. The latter can be stored in the memory of the drive control system or downloaded from the computer, when selected. Acquisition capabilities are also foreseen for.the commissioning tool in order to evaluate the system response after a control algorithm has been activated.
The steps of a typical commissioning process are:
i) identification of the mechanical structure and parameters - to this purpose the drive is commanded by appropriate
exciting signals and the drive responses are elaborated by the identification algorithm implemented into the PC.
ii) selection of the speed controller - on the basis of the identified mechanical parameters and the control performance specified by the user, the different speed controller are self tuned at the best and their responses simulated and compared
by an evaluation index.
iii) commissioning of the speed controller - for the selected controller a fine tuning of its gains and a test of its performance on the plant are recursively executed. A parameter sensitivity can also performed to investigate on its robustness.
iv) commissioning of the position controller - a simple P controller is available for the position control combined with a state space speed controller. Backlash and friction compensation techniques can be incorporated and tuned.
The final product of the Project is a software tool which permits the identification of the mechanical structure and the selection commissioning of several speed and position controllers for TMS with mechanical imperfections such as friction and backlash. The tool is thought to be of easy use for the industry commissioning personnel, and thus is supported by a friendly Graphical Interface that guides also non expert personnel through the identification procedure and the selection and tuning of the controllers.