Overview of Mechatronic Systems
Contents:
1. Introduction to Mechatronics
2. Diagrammatic view of a Mechatronic system
3. Example of a Mechatronic system
4. General Design process
5. Summary
1. Introduction to Mechatronics:
Mechatronics is defined as the interdisciplinary field of engineering that deals
with the design of products whose function relies on the integration of
mechanical, electrical, and electronic components connected by a control
scheme.
Examples:
figure 1: Mechatronic devices?
What do these devices have in common?
A mechatronic device is one that is able to perceive the surrounding
environment, make appropriate decisions based on that information, and execute
those decisions (take action)
Perceive the
environment
Sensors
Controller
Make Decisions
Actuators
Take Action
Figure 2:
2. Diagram of a Mechatronic System:
Mechanical System
Sensors
Or “plant”
Measurement Signal
Interface
-filters
-ATD
-amplifiers, etc.
Actuators
Controller:
MCU (or other PC, PLC, etc)
Output Signal Interface
- amplify power of signals
- condition
Output Display
- leds, crt, buzzer
- Contains control
algorithm, decision
making, control
theory, etc.
Data Storage/
Retrieval
Figure 3: Diagram of a Mechatronic System
Figure 3 provides insight into the design process for a mechatronic (M) system:
1) Select elements in each of the areas
2) Model/Analyze/characterize behavior of the elements
3) Account for interactions between modules
One technique to represent and model an M system is as a block diagram. Block
diagrams range from symbolic to mathematic in representation. Block diagrams
serve as a starting point in the design of the system. They also serve as tools to
build mathematical models that can simulate the behavior of the system.
Simulink (Matlab) is a tool that was specifically created to simulate such systems
in block diagram form. First, consider a general M system in symbolic blockdiagram form.
1) Open loop system:
Input
controller
actuator
Figure 4: Open loop block diagram
Plant
Output
2) Closed-loop system:
Desired
behavior
Controller
Desired
output
Operational,
logic controller
compare
Actual
output
Control
alg.
Actuators
Measure
Plant
Sensors
Output
behavior
Feedback
Figure 5: closed-loop block diagram
This represents a general representation for the class of M systems. Now
consider a specific instance of this class: for example a four degree-of-freedom
SCARA robot:
3. Example of a Mechatronic System: The SCARA Manipulator
The SCARA manipulator can be represented in the following block diagram form:
Controller
+
Desired
output
Desired
behavior
θ1
PID ctrl
-
-
Planning, velocity kins.
Motor 1
Joint 1
Encoder 1
θ2
Forward / Inverse
Kinematics, Path
Driver 1
PID ctrl
Driver 2
Motor 2
Joint 2
Tool pose
Encoder 2
θ3
-
PID ctrl
Driver 3
Motor 3
Joint 3
Encoder 3
θ4
-
PID ctrl
Driver4
Motor 4
Joint 4
Encoder 4
Figure 6: Block diagram for a SCARA robot
This provides a representation of the SCARA at an early stage of the design
process. Discuss the information that exists in this block diagram. What
information is not here?
4. Design Process/ Evolution of a Mechatronic System:
The general steps in the design process of developing a Mechatronic system will
be demonstrated here. This process will start with a form of the system (a
SCARA robot).
1) Develop a high-level diagram of the necessary system components:
Much like figure 6 above, this will show actuators, sensors, controller, mechanical
system, and their relationship. Figure 7 gives an example for 1 dof of the
SCARA manipulator:
Controller
+
Desired
output
Desired
behavior
θ1
-
PID ctrl
Driver 1
Motor 1
Joint 1
Encoder 1
Forward / Inverse
Kinematics, Path
Tool pose
Planning, velocity kins.
Figure 7: Block diagram for a SCARA robot
2) Specify each of these elements in greater detail: Select specific components
for each. This stage requires:
1) knowledge of the necessary requirements for each block
2) knowledge of various Commercial-off-the-shelf (COTS) components that
are available
3) Input and output requirements for each
As these decisions are made, the mechatronic system can be represented in
greater detail in the block diagram. This is shown in Fig. 8 for the SCARA.
controller MHC12
Desired
output
Desired
behavior
+
-
θ1
PID ctrl
Forward / Inverse
Kinematics, Path
Driver 1:
AMC 50A8t
Motor 1
Maxon DC
2260.88573.216
Interface
HPCTL
2020 16
counter
Planning, velocity kins.
Gear train
50:1 3stage
planetary
500 PPR
Optical Inc.
encoder
HEDS 500
Joint 1
Revolute,
brg type
Tool pose
Figure 8: Block diagram for a SCARA robot showing component selection
3) At this stage in the design process, interaction of the various components
should be considered. This consideration should include:
1) input and output types
a. Analog/DC
b. Incremental, absolute
c. etc.
2) Power requirements
3) Impedence
4) Signal power
Figure 9 shows in a general form how the block elements communicate with
each other.
Contro MHC12
+
Desired
output
Desired
behavior
Forward / Inverse
Kinematics, Path
Planning, velocity kins.
θ1
-
PID ctrl
Driver 1:
AMC 50A8t
Motor 1
Maxon DC
2260.88573.216
Interface
HPCTL
2020 16
counter
Gear train
50:1 3stage
planetary
500 PPR
Optical Inc.
encoder
HEDS 500
Joint 1
Revolute,
brg type
Tool pose
Figure 9: Block diagram for a SCARA robot showing component interaction
4) As the design process progresses, the behavior of the system should be
modeled for analysis and simulation purposes. This can be used to:
1) Design controller
2) Determine motor requirements
3) Determine power requirements
4) Evaluate system performance
5) Determine driver requirements
6) etc.
A system model is developed based on inserting specific models for the various
block elements into the block diagram. This process is shown in Fig. 10 for one
axis of the SCARA manipulator:
Controller
e
+
-
Vpow
Vref
* k
* kds
* ki /s
Gain
+
1
-
Ls+R
i
T
kt
θ_dot
1
1
2
s
(Ja +GR Jg)s+C
θ
Kb
Figure 10: System model for one axis of the SCARA
In the block diagram, these are shown in Laplace (or “s”) space. Remember that
this is a handy technique to represent differential equations as algebraic
equations. More on this later.
5) Complete the design of the elements in the system (Mechanical, electrical,
controller code). Update the system framework as necessary
6) Develop system prototype for testing, evaluation purposes. This stage will
show how well you have prepared your system design. A good designer will
expect a few flaws to show up in the design during the testing process.
However, at this stage it is far more expensive to fix major design/analysis errors
than any other point. (That is not completely true, it is even more expensive to fix
an error after the product is sent to market).
5. Summary
This outline has provided a brief introduction to mechatronic systems and the
general design process. Every mechatronic product is unique in function and
form. Yet they all share a common structure when viewed in component function
form (Fig. 3). The design process then involves the selection, design and
integration of the elements that form these parts of the mechatronic system. The
Tool
pose
general design process is demonstrated for a SCARA manipulator. The block
diagram provides a useful tool to organize a mechatronic system and the overall
design process.