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Ch67-I044963.fm Page 329 Tuesday, August 1, 2006 5:54 PM
Page 329
1, 2006
5:54 PM
Tuesday, August
Ch67-I044963.fm
329
329
CURRENT LTMITER COMPLICATES THE DYNAMIC
CHARACTERISTICS OF SERVO MOTOR
Pakorn Serikitkankul, Hiroaki Seki, Masatoshi Hikizu, and Yoshitsugu Kamiya

Department of Mechanical Systems Engineering, Kanazawa University,
Kanazawa, Ishikawa, 920-1192, Japan

ABSTRACT

In this paper, effects of a current controller on dynamic characteristics of the servo motor system are
studied. The current controller regulates motor current to well control motor torque, and prevents
overloaded motor current. It makes a servo motor to be easily controllable; however, it complicates
some dynamic characteristics of the servo motor system. Then, development of high-speed and high-
accuracy positioning system is proposed. The simulation results show that the performance of the
modified positioning system is better than that of the previous system.

KEYWORDS

Dynamic characteristics of servo motor, Current limiter, Positioning system.

INTRODUCTION
Presently, servo motors are widely used in many applications such as robotic applications, home
appliances and industrial automation. The typical servo motor system that is frequently used in above
mentioned applications consists of an electric motor and several cascaded control loops, which are a
position control loop, a velocity control loop and a current control loop. The current control loop is
used to control motor current and to prevent overloaded motor current. The velocity control loop
controls motor velocity, and the position control loop commands the velocity control loop in order to
rotate the servo motor to the desired position. This paper studies effects of the current limiter on the
dynamic characteristics of servo motor and proposes high-speed and high-accuracy positioning system.

CURRENT CONTROL

Since induced voltage from motor armatures, which complicates velocity and torque control of servo
motor, must be eliminated and overloaded current must be prevented, a current controller, consisting
of a current limiter and a current amplifier as illustrated in Figure l(a), is added to the servo motor
system. The current limiter prevents motor overloaded current by limiting current command. The