Prescott, Arizona Campus
Department of Electrical and Computer Engineering
EE 402 Control Systems Laboratory
Spring Semester 2016
Lab Section 51PC
Thursday 1:25 – 4:05 pm
King Eng. Bldg. Rm 122
Lab Instructor:
Dr. Stephen Bruder
Lab 02
Introduction to the Quanser QUBE Servo
Date Experiment Performed:
Thursday, Jan 28, 2016
Instructor’s Comments:

Comment #1

Comment #2
Lab Report Due:
Monday, Feb 1
Group Members:
Student # 1 Name & Email
Student # 2 Name & Email
Grade:
?? / 100
EE 402 Control Systems Lab
TABLE OF CONTENTS
Spring 2016
PAGE
1.
Lab Overview........................................................................................................................................ 3
2.
Background and Introduction................................................................................................................ 3
2.i.
The QUARC Real-Time Control Software ................................................................................... 3
2.ii.
The Hardware................................................................................................................................ 3
3.
Theory and Experimental Methods ....................................................................................................... 5
4.
Equipment and Procedures.................................................................................................................... 6
4.i.
Initializing the Simulink Model .................................................................................................... 6
4.ii.
Reading the Motor Shaft Angle .................................................................................................... 6
4.iii.
Driving the DC Motor ............................................................................................................... 7
4.iv.
Adding Stall Detection .............................................................................................................. 8
5.
Results and Discussion ......................................................................................................................... 8
6.
Conclusion ............................................................................................................................................ 9
7.
References ............................................................................................................................................. 9
LIST OF TABLES
PAGE
Table 1 Encoder angle vs physical angle (in deg)........................................................................................ 7
LIST OF F IGURES
PAGE
Figure 1 An optical incremental quadrature encoder. ................................................................................... 4
Figure 2 Inside the Quanser QUBE. ............................................................................................................. 5
Figure 3 A real-time Simulink-QUARC model ............................................................................................ 5
Figure 4 A Screen capture of your finalized Simulink model ...................................................................... 9
LIST OF SYMBOLS
Names of Students in the Group
PAGE
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EE 402 Control Systems Lab
Spring 2016
1. LAB OVERVIEW
In this lab, we will realize the following learning objectives:

Initial exposure to the Quanser QUBE-Servo hardware.

Develop familiarity with the QUARC® Real-Time Control Software that will be used to interface
with the QUBE-Servo.

Interface to a DC motor: Read the motor’s shaft angle from the quadrature encoder and drive the
motor with a fixed voltage.
2. BACKGROUND AND INTRODUCTION
2.i. The QUARC Real-Time Control Software
The QUARC real-time control software will be used to interact with the hardware of the QUBE-Servo
system. In particular, the QUARC software will allow us to run Simulink models in real-time in order to
read sensors (e.g., encoder) and generate PWM signals to realize desired motor drive voltages.
This process generally proceeds in three steps:
1. First, develop a Simulink model that contains QUARC blocks to interact with your QUBEServo and other optional blocks, which typically perform user defined signal conditioning or
implement a control algorithm.
2. Build your model and resolve any compile-time errors to produce real-time code.
3. Link this code to your real-time target, and then execute the code.
In MATLAB, type “doc quarc” at the command prompt to see QUARC documentation. Also, in
the Simulink Library Browser (type “simulink” in the MATLAB command window) expand
“QUARC Targets” to see a list of the supported blocksets.
2.ii. The Hardware
The Quanser QUBE contains a quadrature encoder, a pwm motor driver, and a brushed DC motor
(user manual).
2.ii.a.
The Quadrature Encoder
The quadrature encoder in the QUBE is a US Digital E8P OEM Optical Kit Encoder. Similar to rotary
potentiometers, optical encoders can also be used to measure angular position. There are many types of
encoders, but one of the most common is the rotary incremental optical encoder, as shown in Figure 1.
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EE 402 Control Systems Lab
Spring 2016
Figure 1 An optical incremental quadrature encoder.
Despite having a 1-pulse per revolution index signal (Channel I – see Figure 1), the relative encoder
does not measure an absolute angle, hence, when first powered up it resets its angle to zero. Absolute
optical encoders do exist, however, they are typically more sophisticated.
The encoder has a coded disk that is marked with a radial pattern (see Figure 1). As the disk rotates
(with the shaft), the light from an LED shines through the pattern and is picked up by a photo sensor. This
effectively generates the A and B signals shown in Figure 1 (left). An index pulse is generated once
every full rotation of the disk, which can be used for calibration or as a homing system.
The A and B signals that are generated as the shaft rotates are used in a quadrature decoder algorithm
to generate a count. The resolution of the encoder depends on the coding of the disk and the decoder. For
example, our encoder with 512 lines on the disk can generate a total of 512 pulses for every rotation of
the encoder shaft. However, in a quadrature decoder as depicted in Figure 1, the number of counts (and
thus its resolution) quadruples for the same line patterns and generates 2048 (= 4512) counts per
revolution. This can be explained by the 90 phase shift between the A and B channels. Instead of
Channel A (or B) being either high (=1) or low (=0), now there are now four patterns (AB = 00, 01, 10, or
11). This A/B phase shift changes from +90 (clockwise) to -90 (counter-clockwise), which allows the
encoder to also detect the direction of the rotation.
2.ii.b.
The DC Motor
The QUBE also contains an 18 volt, 7 watt Allied Motion CL40 Series Coreless DC Motor (model
9904 120). This motor is driven by a pulse width modulation (pwm) amplifier.
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EE 402 Control Systems Lab
Motor
driver
Spring 2016
DC motor
encoder
Figure 2 Inside the Quanser QUBE.
3. THEORY AND EXPERIMENTAL METHODS
In this lab, we will develop a Simulink model using QUARC blocks to drive the DC motor and
measure its corresponding relative shaft angle as shown in Figure 3.
Figure 3 A real-time Simulink-QUARC model
The QUARC block that reads the encoder outputs the motor’s shaft angle as the number of quadrature
counts.
Question 1.
What is the constant conversion factor to convert from counts to degrees?
K  ??? (deg/count)
Question 2.
What is the maximum voltage that should be applied to the DC motor (via the QUARC
write Analog block)?
Vmax  ???
Volts
Question 3.
For this motor, what is the starting current at nominal voltage (also known as the stall
current – see motor datasheet in Section 2.ii.b)?
istall  ???
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amps
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EE 402 Control Systems Lab
Spring 2016
4. EQUIPMENT AND PROCEDURES
In this section, we will create a Simulink model to read and display the motor’s shaft angle and drive
the motor with a constant voltage.
4.i. Initializing the Simulink Model

Start MATLAB and then create a new Simulink model. Save the model as
LastName_FirstName_Lab02.slx (use your LastName and FirstName and save on
your P-drive).

Enter >> simulink in the MATLAB Command Window to display the Simulink Library
Browser.

In the Library Browser, expand QUARC Targets  Data
Acquisition  Generic and select Configuration.

Drag a copy of the HIL Initialize icon into your new
Simulink model.

In your model-double click on the HIL Initialize icon,
and from the pull-down list under “Board type”, select
“qube_servo_usb”.

Be sure to save your Simulink model. From the pull-down
menu, select “External.” Then, click on the Build icon (wait a few secs), next connect to
target, and then Run.

This process should complete without generating any errors (look at the MATLAB command
window). You will need to resolve any errors before
proceeding.

Click on the stop button (icon to the right of the Run icon)
Connect
to target
Build
Run
before continuing.
4.ii. Reading the Motor Shaft Angle
In this section, you will add the necessary blocks to your Simulink model to read the motor’s shaft
angle and display the angle in degrees.

Return to the Simulink Library Browser, expand QUARC Targets  Data
Acquisition  Generic, and select Timebases.
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EE 402 Control Systems Lab
Spring 2016

Add a copy of the HIL Read Encoder Timebase icon to your Simulink model.

Add a gain block (Simulink  Commonly Used Blocks) to the output of your HIL
Read Encoder icon, and then enter the constant conversion factor you calculated in
Question 1 therein.

Add a display (Simulink  Sinks) to the output of the gain block.

Physically adjust the Red disk on the QUBE-Servo to point to 0, and then Build, Connect to
Target, and Run the model.

Manually, rotate the disk counterclockwise (positive angle) to align with the 45 mark and
record the value Displayed in your Simulink model.
o

If you found any issues/problems resolve them.
Record the values displayed for the physical angles selected in the table below.
Table 1 Encoder angle vs physical angle (in deg)
Physical Angle
+90
+45
0
-45
-90

Displayed Angle
Stop your Simulink model before continuing. Manually, rotate the disk to physical angle other
than 0.
What was the physical angle you chose? ___???____ deg

Now, Connect to Target and then Run the model. Move the disk around and stop with the disk
pointing to an angle of 0 deg (see image below).
Record the final angle displayed in your Simulink model: ___???____ deg
Question 4.
What can you conclude from this test?
-90
+90
4.iii. Driving the DC Motor
Now, we will apply a voltage (actually PWM) to the DC motor to drive it.
-45

+45
Return to the Simulink Library Browser, expand QUARC
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EE 402 Control Systems Lab
Spring 2016
Targets  Data Acquisition  Generic, and select Immediate I/O.

Add a copy of the HIL Write Analog icon to your Simulink model.

Drive this block with a constant voltage (Simulink  Sources then add Constant
icon).

Enter a value of +0.5 in the Constant Block and then Build, Connect, and Run the model.
The motor should rotate in a positive (i.e., counterclockwise) direction.
o
Question 5.
If you found any issues/problems resolve them.
What is the minimum voltage required to cause the disk to begin rotating? ________V
HINT: Start from 0 Volts and incrementally increase the value slowly while running!!!
Question 6.
Why does the motor not begin rotating at a much lower voltage?
4.iv. Adding Stall Detection
As a safeguard against damaging the DC motor, we will add “stall detection” to our model. This block
will monitor the applied voltage and speed of the DC motor to ensure that if the motor is motionless for
more than 2 seconds with an applied voltage of over 5V, the model execution is halted to prevent damage
to the motor.

Open the provided Simulink model stall_detect.slx and copy the “Stall
Detection” block to your model. Be sure to connect it as shown in Figure 3.

Test your stall detection. Apply 5.5 V and hold the disk stationary with your hand for more
than 2 seconds (first you must: Save, Build, Connect, and Run the model).

Demonstrate this functionality to the instructor or lab TA.
5. RESULTS AND DISCUSSION
Include a screen capture of your final Simulink model in Figure 4. Be sure to add text with your
name(s) and date to the Simulink diagram.
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EE 402 Control Systems Lab
Spring 2016
Figure 4 A Screen capture of your finalized Simulink model
6. CONCLUSION
What can you say (qualitatively) about the main difference(s) that you have observed between this
physical DC motor and an idealistic theoretical model of a DC motor?
7. REFERENCES
[1] www.quanser.com
Names of Students in the Group
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