# Servomotors

## Subject description

Mathematical tools for description of servomotors and electromechanical systems. Electric motor fundamentals. Electromechanical analogies, electrical and mechanical properties of some commonly used servomotor type. DC motors controlled by armature current and stator magnetic field: basic properties, implementations, calculation of losses, transfer functions. Heat losses, heat transfer function, temperature dependence of motor parameters. The impact of type of power supply on servomotor response. The resonance in a electromechanical system. Brushless DC motors. Asynchronous AC servomotors: physical principles of operation and main properties. Stepper motors: permanent magnet, variable reluctance and hybrid stepper motors; static moment and positioning error, torque-speed characteristic. Power supply and control of DC, asynchronous AC and stepper motors. Physics of hydraulic flow of fluid under pressure. Hydraulic servomotors of different types. Electrohydraulic controllers, different combinations and static characteristics of controllers and hydraulic-motors. Transfer function of hydraulic and electrohydraulic systems. Nonlinear properties of hydraulic elements, Coulomb friction, linearization of characteristics.

## Objectives and competences

To learn about physical principles and working properties of various servomotor types (electric and hydraulic). To get insight into mathematical modeling and estimation of servomotor transfer function estimation and into application of different servomotor types with respect to their characteristics.

## Teaching and learning methods

The next teaching methods will be used: lectures and practical lab work.

Lectures: Formal transfer of fundamental knowledge and data using theoretical and mathematical explanations and supported with graphical tools (images, movies) and computer simulations. Exercises in solving problems concerning servomotor analysis and performance.

Lab vork: practical assignments to support the material covered in lectures, on which the students work in pairs. Some of the lab work may be conducted in a form of larger mini-projects on topics not neccessarily covered in lectures. Practical work consists of measurement and determination of of static and dynamic properties of motors and of performance testing of electromechanical systems. The students are requested to self-study and to prepare for the assignment. Reports must be written for all practical assignments.

## Expected study results

After successful completion of the course, students shoud be able to:

– Describe physical background of operation of different selected types of motors (actuators) and relationships between the input electrical or hydraulic quantities and the output mechanical quantities.

– Explain the effect of different parameters on operation of motors.

– Apply transfer functions for mathematical description of relationship between the controlling and the controlled variable in open- and closed loop case.

– Use measurement instrumentation in a correct and safe manner.

– Apply the selected motor as actuator in a regulated servosystem.

– Apply mathematical modelling of electromechanical and electrohydraulic systems for description of operation of these systems.

## Basic sources and literature

1. P. Kramar, T. Jarm. Servomotorji : zbirka rešenih nalog. izd. Ljubljana: Založba FE in FRI, 2014.
2. Hughes, Electric motors and drives, 4th ed., Newnes/Elsevier, 2013.
3. R. Firoozian, Servo Motors and Industrial Control Theory. Springer, 2008
4. N.D. Manring, Hydraulic control systems, Wiley, 2005.
5. S. Reberšek, Servomotorji, Fakulteta za elektrotehniko, 2011 (interno gradivo).
6. S. Reberšek, Hidravlična krmilja in servosistemi, Založba FER, Ljubljana, 1995

## Stay up to date

University of Ljubljana, Faculty of Electrical Engineering Tržaška cesta 25, 1000 Ljubljana