Mechatronics 1
Week 9 & 10
Learning Outcomes
• By the end of week 9-10 session, students
will understand the control system of
industrial robots.
Course Outline
•
•
•
•
•
Overview.
Gear Box.
DC Motor.
Closed loop model.
Stability analysis on : damping ratio, moment
inertia & controller gain.
• Robot control system as a multi input multi
output system (brief introduction).
• Latest development of robot control system.
HOW DOES A ROBOT MOVE
?
θ
t
Torque
o/p (movement)
dynamics
i/p
o/p
Controller
Board
Torque
DC Motor
Control System (1)
• Based on its dynamic behaviour, a control
system can then be developed.
• Different dynamic behaviour requires different
control system.
• Most industrial robots comes with conventional
PID (Proportional, Derivative, Integral) control
system.
Sequence Controlled/ Playback PTP
Trajectory Operated/ Continuous Path Playback
Adaptive
Teleoperated
Not Classified
Total
Denmark
18.2%
79.4%
2.4%
0.0%
0.0%
100.0%
Finland
0.0%
75.6%
24.2%
0.2%
0.0%
100.0%
Italy
16.6%
83.4%
0.0%
0.0%
0.0%
100.0%
Japan
7.3%
78.8%
13.9%
0.0%
0.0%
100.0%
Norway
0.0%
100.0%
0.0%
0.0%
0.0%
100.0%
Poland
28.6%
57.1%
14.3%
100.0%
Source : World Robot Statistics, 2000, United Nations & IFR.
Spain
8.9%
79.7%
11.4%
0.0%
0.0%
100.0%
Korea
82.8%
17.2%
0.0%
0.0%
0.0%
100.0%
Total
8.5%
79.4%
12.1%
0.0%
0.0%
100.0%
Control System (2)
DC Motor
Computer
 d (s ) +
-
K
+
-
1
Ls  R
Mechanical Links
1
s
1
J eff s  B
KI
KB
 s ( s ) nK K I

 d ( s)
RJ eff
s
2

RB

eff
1
 K I K b s
RJ eff

KI KB
   RBeff 
2 nK K I RJ eff





nK K I
RJ eff
n
 s (s)
Problems
• How to obtain a desired system by
maintaining the characteristic equation.
• Maintaining characteristic equation means
keeping the damping ratio larger than 1*).
• By observing the equations, one can
adjust the robot parameters in such away
so that the required damping ratio value
can be obtained.
*) For the sake of safety, in a robot control system, the value of
damping ratio should be bigger than 1.
Robot System
Robot Arm
Control Unit
(Controller)
Teach Pendant
(Teaching Box)
Host Computer
Operating
System
Programming Mode
• Teach Pendant
– On Line
• Host Computer
– On Line
– Off Line
– Simulation
Programming Types
• Textual Programming
– Sitting in front of a computer terminal (host
computer).
– Requires robot programming knowledge.
• Teaching by Showing
– Physically moving the robot arm through a
sequence of position.
– Requires no robot programming knowledge.
Programming Types (2)
• Teaching by Showing (cont’d) :
– Lead Through Programming (sometimes
referred to Lead by Nose).
• The robot may be equipped with a special
attachment.
• Ideally used for continuous path purposes, e.g.
paint spraying.
• Difficulties arise in an area close to the work
volume boundaries.
Programming Types (3)
• Teaching by Showing (cont’d)
– Walk Through Programming.
• It requires a teach pendant
(teaching box) to deliver commands
to a robot.
• Once a correct position and
orientation of end effector is
attained, this posture is then stored
in a control unit.
• The robot then accomplishes its job
according to the stored information
during a play back mode.
ON/OFF Switch
ON OFF
EMG.STOP
Emergency Stop Switch
RV-MI TEACHING BOX
LED (Seven Segment Display)
INC
DEC
PS
PC
NST ORG
TRN WRT
MOV STEP
PTP
XYZ
ENT TOOL
X+
X-
B+
BY+
YS+
SZ+
4 E+
P +
3
R +
2
Z9 EP 8
R 7
OPTION OPTION
1+
O
0
MITSUBISHI
6C
5
Control Key
Robot Programming Language
• Special/ Dedicated Programming Language
– Specifically developed for the purpose of robot
specific area.
– Poor structure.
– Interpreter type.
• Robot Library Via Common/ Popular Computer
Language.
– Specific subroutine is developed for the purpose of
manipulating object with robot arm.
– Utilizing a good structure of common computer
languages, e.g. Pascal.
Control Unit
• It provides capability to communicate with a
robot via the aforementioned programming
mode.
• It stores the required movement provided by the
host computer, and hence once programmed,
the robot can operate in the manufacturing floor
without the use of host computer (just the robot
alone with its control unit).
• It carries out the joint interpolation for
intermediate path during a play back session.
• Main job is controlling the robot movement.
Control Unit Implementation
Slow Movement
Fast Movement
Notice that basically velocity control can be carried out via position control.
Robot Programming Language
• Special/ Dedicated Programming Language
– Specifically developed for the purpose of robot
specific area.
– Poor structure.
– Interpreter type.
• Robot Library Via Common/ Popular Computer
Language.
– Specific subroutine is developed for the purpose of
manipulating object with robot arm.
– Utilizing a good structure of common computer
languages, e.g. Pascal.