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)

Mechatronics Notes Part I Page 1 Perceive the environment Sensors

Controlle Make Decisions r

Actuator Take Action s Figure 2:

2. Diagram of a Mechatronic System:

Mechanical System Sensors

Measurement Signal Interface -filters -ATD -amplifiers, etc. Or “plant”

Actuators

Controller: MCU (or other PC, PLC, etc)

Output Signal Interface - Contains control - amplify power of signals algorithm, decision - condition making, control theory, etc.

Output Display - leds, crt, buzzer Data Storage/ Retrieval Figure 3: Diagram of a Mechatronic System

Mechatronics Notes Part I Page 2 Mechanical System

Plant Sensors

Or “plant” Measurement Signal Interface

Actuators

Output Signal Interface MCU

Human/Machine Interface

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

Mechatronics Notes Part I Page 3 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 block- diagram form. 1) Open loop system:

Input Output controller actuator Plant

Figure 4: Open loop block diagram

2) Closed-loop system: Controller Desired Desired behavior Operational, output Control compare Actuators Plant logic controller alg.

Actual output Measure Sensors

Feedback Output behavior 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:

Mechatronics Notes Part I Page 4 Controller + PID ctrl Driver 1 Motor 1 Joint 1 - Desired  1 output Encoder 1  2 Desired PID ctrl Driver 2 Motor 2 Joint 2 Forward / Inverse behavior - Kinematics, Path Tool pose Planning, velocity kins. Encoder 2  3 PID ctrl Driver 3 Motor 3 Joint 3 - Encoder 3  4 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?

Mechatronics Notes Part I Page 5 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 + PID ctrl Driver 1 Motor 1 Joint 1 - Desired  1 output Encoder 1

Desired Forward / Inverse behavior 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.

Mechatronics Notes Part I Page 6 Controlcontroller MHC12 + PID ctrl Driver 1: Motor 1 Gear train 50:1 3- - AMC 50A8t Maxon DC Desired  1 2260.885- stage output 73.216 planetary

Desired Forward / Inverse Interface 500 PPR behavior Kinematics, Path HPCTL Optical Inc. Joint 1 Planning, velocity kins. 2020 16 encoder Revolute, counter HEDS 500 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 + PID ctrl Driver 1: Motor 1 Gear train 50:1 3- - AMC 50A8t Maxon DC Desired  1 2260.885- stage output 73.216 planetary

Desired Forward / Inverse Interface 500 PPR behavior Kinematics, Path HPCTL Optical Inc. Joint 1 Planning, velocity kins. 2020 16 encoder Revolute, counter HEDS 500 brg type

Tool pose

Figure 9: Block diagram for a SCARA robot showing component interaction

Mechatronics Notes Part I Page 7 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:

V dot Controller V pow  ref i T e + 1 Tool + * k Gain k 1 1 Ls+R t (J +GR2J )s+C pose - * k s - a g s d * k /s i K b

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 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.

Mechatronics Notes Part I Page 8