Teaching & Learning in Undergraduate Lab Experimentation in Engineering
Introduction (LabVIEW Based Identification
of a DC Motor Transfer Function and Simulink-based Triangle Response)
Objectives: Students will learn (1) how to use
dataflow programming to model a DC motor to achieve various design
specifications and (2) simulate the unit step response using Simulink
Prelab: DC motor is one of the most commonly used
actuating devices for control systems. Visit the 258 web site at
http://eecs.vanderbilt.edu/courses/eecs258/ and investigate the
characteristics of the DC motor.
INLAB: Students will use the National Instruments
LabVIEW to model the Quanser QNET DC Motor and to experiment with PID
(Proportional Integral Derivative) controller parameter tuning using Simulink.
REQUIREMENTS: You will be required to learn the
virtual instrumentation approach using LabView and dataflow programming and
another control system analysis tool Simulink to run the experiment and achieve
the following design specifications:
1. Getting the transfer function of a DC motor
2. Marginal Stability (Square wave)
3. Best tracking of a triangle wave (~0 steady-state error, <4% overshoot, and
<.4sec. settling time). Also, observe the effect of a disturbance (load) on the
motor when Ki has a very low value.
Introduction to Instruments
Personal Computer (PC)
Computer receives the input signal
from the terminal board and output the control signal according to the
Requirement. System identification and PID control system is designed using
LabVIEW on the computer which
is related to the hardware, specifically the PCI card inside the computer.
Read about the MATLAB guideline
National Instruments ELVIS II
NI ELVIS is a LabVIEW-based platform
designed to provide an integrated and flexible environment that enhances
measurement, design, and prototyping in an educational laboratory. NI ELVIS
integrates LabVIEW software, a multifunction data acquisition board, and the NI
ELVIS Workstation to build a suite of virtual instruments. visit
The NI ELVIS II platform incorporates a DC motor. This is a high efficiency, low inductance motor with a small
The figure below shows an electrical
diagram of a simple DC motor. Notice that the DC voltage is
applied directly to the field winding and the brushes. The
armature and the field are both shown as a coil of wire. In
later diagrams, a field resistor will be added in series with
the field to control the motor speed.
When voltage is applied to the motor, current begins to flow
through the field coil from the negative terminal to the
positive terminal. This sets up a strong magnetic field in the
field winding. Current also begins to flow through the brushes
into a commutator segment and then through an armature coil. The
current continues to flow through the coil back to the brush
that is attached to other end of the coil and returns to the DC
power source. The current flowing in the armature coil sets up a
strong magnetic field in the armature.
The magnetic field in the
armature and field coil causes the armature to begin to rotate.
This occurs by the unlike magnetic poles attracting each other
and the like magnetic poles repelling each other. As the
armature begins to rotate, the commutator segments will also
begin to move under the brushes. As an individual commutator
segment moves under the brush connected to positive voltage, it
will become positive, and when it moves under a brush connected
to negative voltage it will become negative. In this way, the
commutator segments continually change polarity from positive to
negative. Since the commutator segments are connected to the
ends of the wires that make up the field winding in the
armature, it causes the magnetic field in the armature to change
polarity continually from north pole to south pole. The
commutator segments and brushes are aligned in such a way that
the switch in polarity of the armature coincides with the
location of the armature's magnetic field and the field
winding's magnetic field. The switching action is timed so that
the armature will not lock up magnetically with the field.
Instead the magnetic fields tend to build on each other and
provide additional torque to keep the motor shaft rotating.
When the voltage is de-energized to the motor, the magnetic
fields in the armature and the field winding will quickly
diminish and the armature shaft's speed will begin to drop to
zero. If voltage is applied to the motor again, the magnetic
fields will strengthen and the armature will begin to rotate
The DC motor has an optical encoder
installed that measures the angular position of the load shaft. The encoder in
the system has a resolution of 8192 counts per revolution in quadrature
mode(2042 lines per revolution). Remark that incremental encoders measure the
relative angle of the shaft.
The position signal generated by the
encoder can be directly connected to the data-acquisition device using a
standard 5-pin DIN cable.
In this lab, you will be required to
implement LabVIEW based system to get the transfer function model of a DC motor
and control a DC motor using PID control
law in simulation
After you have completed the
Perspective and Resources, you may proceed to "Research and Revise" stage.