Pre-lab 5 - UBC Mechanical Engineering

MECH 421: Mechatronics System Instrumentation
Pre-lab 5: Conveyer Belt Controller Design
Objectives
(1) Mechanical system identification from frequency response measurement.
(2) Understand the physics of non-collocation and its effect on system dynamics.
(3) Loop-shaping motion controller design.
(4) xPC Target control system prototyping.
Note : Individual prelab and the lab write-ups are required for lab5.
Lab Description
Figure 1 shows the conveyor belt system layout in our part sorting machine. The moving
belt wraps around both the drive shaft and the idle shaft. The drive shaft is connected to a
brushless motor via a helical coupling. On the other end of the drive shaft, an optical
encoder is mounted. Figure 2 shows the mechanical system.
Detailed information about the motor can be found at:
http://www.specamotor.com/pdf/datasheet_DA34HBB-11_en.pdf
The encoder datasheet can be accessed at
http://web4.automationdirect.com/static/specs/encoderld.pdf
In this lab, a switching power amplifier will be used to drive the brushless motor. This
amplifier has a built-in current control loop to regulate the output current such that it is
proportional to the amplifier input command voltage. Information regarding this
amplifier is at:
http://www.logosolinc.com/download/ls-5y-bl.pdf
An xPC Target computer will be used as the conveyor belt controller. A DAC block and
an encoder counter block have been developed. The DAC block has a gain of one, which
means that the DAC output voltage is equal to the driver block input value. The output of
the encoder counter block has units of encoder counts. As shown in Figure 3, the DAC
output will connect to the power amplifier input command, and the encoder output signal
will go to the encoder counter.
1

MECH 421: Mechatronics System Instrumentation
Figure 1: Conveyor belt system setup
Figure 2: Conveyor belt system layout
Figure 3: Simplified system diagram
2

MECH 421: Mechatronics System Instrumentation
The system parameters are listed in Table 1.
Pre-Lab Assignment
1. Initial Model:
Parameter
Value
J1 – Idle Shaft Inertia
0.001069 Kg-m^2
J2 – Drive Shaft Inertia
0.001089 Kg-m^2
J3 – Gearbox Inertia (Output Side) 0.0007142 Kg-m^2
J4 – Motor Inertia
0.0001363 Kg-m^2
M1 – Total Mass of Belts
3.861 Kg
R1 – Pulley Pitch Radius
0.03183 m
Amplifier Gain
0.6195 A/V
Motor Torque Constant
0.193 Nm/A
Gearbox Reduction Ratio 10:1
Encoder Resolution (After
Quadrature Decoding)
1440 Counts/Rev
Table 1 – Conveyor System Parameters
Based on the information in the lab description and the parameters supplied, draw
a block diagram for the whole system assuming an infinitely stiff shaft coupling,
with input Vc in unit [V] and output drive shaft position in unit [revolution].
Establish a model for the whole system, and derive the transfer function from Vc
to . Draw Bodes plots of your transfer function.
2. Refined model:
Figure 4 shows the system frequency response experimentally measured by Darya
from Vc[V] to [rev]. Compare the Bode plot of your first model in part 1 with
Darya’s measurement result. Discuss and explain the differences. Based on this
measurement result, establish a new refined physical model which fits the
experiment result as much as possible. Draw Bode plots of your refined model.
Try to give an intuitive physical interpretation of the dynamics exhibited from the
frequency response, and relate the measurement results to design parameters of
the system. (HINT: remember the two mass coupled system. Is the shaft coupling
really infinitely stiff? )
3

MECH 421: Mechatronics System Instrumentation
Figure 4. Experimentally measured frequency response by Darya.
3. Loop shaping controller design.
Based on Darya’s measurement in Figure 4, design a controller satisfy ASAP 3
requirements:
a. at least 60 degrees of phase margin;
b. as high a motion bandwidth as possible;
c. zero steady-state error for step input conveyer belt position command and
static friction force on the motion stage.
4. Design a Simulink model to implement your controller.
In order to evaluate your controller performance, use your controller to control a
Simulink block representing the refined model that you established in Part 2.
Simulate the whole system (your controller controls your modeled plant) in realtime
with xPC Target. Use xPCDSA to measure the closed-loop bandwidth and
step response. Include the measured bode plot of the closed loop and the step
response in your prelab report.
NOTE: You may find that the x86 target computers will fail when trying to
evaluate higher order transfer functions with certain ODE solvers (e.g. ODE4 or
ODE5) with high sampling frequency. If this occurs, try reducing the sampling
frequency and rerun the simulation.
4