The Mechatronics Design Process System.

The traditional electrome chanical-system design approach attempted to inject more reliability and performance into the mechanical part of the system during the development stage. The control part of the system was then designed and added to provide additional performance or reliability and also to correct undetected errors in the design. Because the design steps occur sequentially, the traditional approach is a sequential engineering approach. A Standish Group survey of software dependent projects found.

• 31.1% cancellation rate for software development projects.
• 222% time overrun for completed projects.
• 16.2% of all software projects were completed on time and within budget.
• Maintenance costs exceeded 200% of initial development costs for delivered software.

The Boston-based technology think tank, Aberdeen Group, provided key information on the importance of incorporating the right design process for a mechatronic system design. Aberdeen researchers used five key product development performance criteria to distinguish “best-in-class” companies, as related to mechatronic design. The key criteria were revenue, product cost, product launch dates, quality, and development costs. Best-in-class companies proved to be twice as likely as “laggards ” (worst-in-class companies) to achieve revenue targets, twice as likely to hit product cost targets, three times as likely to hit product launch dates, twice as likely to attain quality objectives, and twice as likely to control their development costs. Aberdeen’s research also revealed that best-in-class companies were.

• 2.8 times more likely than laggards to carefully communicate design changes across disciplines.
• 3.2 times more likely than laggards to allocate design requirements to specific systems, subsystems, and components.
• 7.2 times more likely than laggards to digitally validate system behavior with the simulation of integrated mechanical, electrical, and software components.

A major factor in this sequential approach is the inherently complex nature of designing a multidisciplinary system. Essentially, mechatronics is an improvement upon existing lengthy and expensive design processes. Engineers of various disciplines work on a project simultaneously and cooperatively. This eliminates problems caused by design incompatibilities and reduces design time because of fewer returns. Design time is also reduced through extensive use of powerful computer simulations, reducing dependency upon prototypes. This contrasts the more traditional design process of keeping engineering disciplines separate, having limited ability to adapt to mid-design changes, and being dependent upon multiple physical prototypes.

The mechatronic design methodology is not only concerned with producing high-quality products but with maintaining them as well—an area referred to as life cycle design. Several important life cycle factors are indicated.

• Delivery: Time, cost, and medium.
• Reliability: Failure rate, materials, and tolerances.
• Maintainability: Modular design.
• Serviceability: On board diagnostics, prognostics, and modular design.
• Upgradeability: Future compatibility with current designs.
• Disposability: Recycling and disposal of hazardous materials.

We will not dwell on life cycle factors except to point out that the conventional design for life cycle approach begins with a product after it has been designed and manufactured. In the mechatronic design approach, life cycle factors are included during the product design stages, resulting in products which are designed from conception to retirement. The mechatronic design process is presented in Figure 1-4.

FIGURE 1-4 MECHATRONIC DESIGN PROCESS

 The mechatronic design process consists of three phases: modeling and simulation, prototyping, and deployment. All modeling, whether based on first principles (basic equations) or the more detailed physics, should be modular in structure. A first principle model is a simple model which captures some of the fundamental behavior of a subsystem. A detailed model is an extension of the first principle model providing more function and accuracy than the first level model. Connecting the modules (or blocks) together may create complex models. Each block represents a subsystem, which corresponds to some physically or functionally realizable operations, and can be encapsulated into a block with input/output limited to input signals, parameters, and output signals. Of course, this limitation may not always be possible or desirable; however, its use will produce modular subsystem blocks which easily can be maintained, exercised independently, substituted for one another (first principle blocks substituted for detailed blocks and vice versa), and reused in other applications.

Because of their modularity, mechatronics systems are well suited for applications that require reconfiguration. Such products can be reconfigured either during the design stage by substituting various subsystem modules or during the life span of the product. Since many of the steps in the mechatronics design process rely on computer-based tasks (such as information fusion, management, and design testing), an efficient computer-aided prototyping environment is essential.

Important Features

• Modeling: Block diagram or visual interface for creating intuitively understandable behavioral models of physical or abstract phenomenon. The ability to encapsulate complexity and maintain several levels of subsystem complexity is useful.
• Simulation: Numerical methods for solving models containing differential, discrete, hybrid, partial, and implicit nonlinear (as well as linear) equations. Must have a lock for real-time operation and be capable of executing faster than real time.
• Project Management: Database for maintaining project information and subsystem models for eventual reuse.
• Design: Numerical methods for constrained optimization of performance functions based
on model parameters and signals. Monte Carlo type of computation is also desirable.
• Analysis: Numerical methods for frequency-domain, time-domain, and complex-domain design.
• Real-Time Interface: A plug-in card is used to replace part of the model with actual hardware by interfacing to it with actuators and sensors. This is called hardware in the loop simulation or rapid prototyping and must be executed in real time.
• Code Generator: Produces efficient high-level source code from the block diagram or visual modeling interface. The control code will be compiled and used on the embedded processor. The language is usually C.
• Embedded Processor Interface: The embedded processor resides in the final product. This feature provides communication between the process and the computer-aided prototyping environment. This is called a full system prototype.

The Mechatronics Design Process System.

Integrated Design Issues in Mechatronics System

The inherent concurrency or simultaneous engineering of the mechatronics approach relies heavily on the use of system modeling and simulation throughout the design and prototyping stages. Because the model will be used and altered by engineers from multiple disciplines, it is especially important that it be programmed in a visually intuitive environment. Such environments include block diagrams, flow charts, state transition diagrams, and bond graphs. In contrast to the more conventional programming languages such as Fortran, Visual Basic, C , and Pascal, the visual modeling environment requires little training due to its inherent intuitiveness. Today, the most widely used visual programming environment is the block diagram. This environment is extremely versatile, low in cost, and often includes a code generator option, which translates the block diagram into a C (or similar) high-level language suitable for target system implementation. Block diagrambased modeling and simulation packages are offered by many vendors, including MATRIXxTM, Easy5TM, SimulinkTM, Agilent VEETM, DASYLabTM, VisSimTM, and LabVIEWTM.

Mechatronics is a design philosophy: an integrating approach to engineering design. The primary factor in mechatronics is the involvement of these areas throughout the design process. Through a mechanism of simulating interdisciplinary ideas and techniques, mechatronics provides ideal conditions to raise the synergy, thereby providing a catalytic effect for the new solutions to technically complex situations. An important characteristic of mechatronic devices and systems is their built-in intelligence that results through a combination of precision in mechanical and electrical engineering, and real-time programming integrated into the design process. Mechatronics makes the combination of actuators, sensors, control systems, and computers in the design process possible.

Starting with basic design and progressing through the manufacturing phase, mechatronic design optimizes the parameters at each phase to produce a quality product in a short-cycle time. Mechatronics uses the control systems to provide a coherent framework of component interactions for system analysis. The integration within a mechatronic system is performed through the combination of hardware (components) and software (information processing).

• Hardware integration results from designing the mechatronic system as an overall system and bringing together the sensors, actuators, and microcomputers into the mechanical system.
• Software integration is primarily based on advanced control functions.

Figure 1-3 illustrates how the hardware and software integration takes place. It also shows how an additional contribution of the process knowledge and information processing is involved besides the feedback process.

FIGURE 1-3 GENERAL SCHEME OF HARDWARE AND SOFTWARE INTEGRATION

 

The first step in the focused development of mechatronic systems is to analyze the customer needs and the technical environment in which the system is integrated. Complex systems designed to solve problems tend to be a combination of mecahanical, electric, fluid power, and thermodynamic parts, with hardware in the digital and analog form, coordinated by complex software. Mechatronic systems gather data from their technical environment using sensors. The next step is to use elaborate modeling and description methods to cover all subtasks of this system in an integrated manner. This includes an effective description of the necessary interfaces between subsystems at an early stage. The data is processed and interpreted, thus leading to actions carried out by actuators. The advantages of mechatronic systems are shorter developmental cycles,
lower costs, and higher quality.

Mechatronic design supports the concepts of concurrent engineering.

In the designing of a mechatronic product, it is necessary that the knowledge and necessary information be coordinated amongst different expert groups. Concurrent engineering is a design approach in which the design and manufacture of a product are merged in a special way. It is the idea that people can do a better job if they cooperate to achieve a common goal. It has been influenced partly by the recognition that many of the high costs in manufacturing are decided at the product design stage itself. The characteristics of concurrent engineering are

• Better definition of the product without late changes.
• Design for manufacturing and assembly undertaken in the early design stage.
• Process on how the product development is well defined.
• Better cost estimates.
• Decrease in the barriers between design and manufacturing.

However, the lack of a common interface language has made the information exchange in concurrent engineering difficult. Successful implementation of concurrent engineering is possible by coordinating an adequate exchange of information and dealing with organizational barriers to crossfunctional cooperation. Using concurrent engineering principles as a guide, the designed product is likely to meet the basic requirements:

• High quality
• Robustness
• Low cost
• Time to market
• Customer satisfaction

The benefits that accrue due to the integration of concurrent engineering management strategy are greater productivity, higher quality, and reliability due to the introduction of an intelligent, selfcorrecting sensory and feedback system. The integration of sensors and control systems in a complex system reduces capital expenses, maintains a high degree of flexibility, and results in higher machine utilization.

What is Mechatronics System

Mechatronics is a methodology used for the optimal design of electromechanical products.

A methodology is a collection of practices, procedures, and rules used by those who work in a particular branch of knowledge or discipline. Familiar technological disciplines include thermodynamics, electrical engineering, computer science, and mechanical engineering, to name several. Instead of one, the mechatronic system is multidisciplinary, embodying four fundamental disciplines: electrical, mechanical, computer science, and information technology.

The F-35, a U.S. Department of defense joint strike fighter plane developed by Lockheed Martin Corporation, is an example of mechatronic technology in action. The design metric emphasizes reliability, maintainability, performance, and cost. Multidisciplinary functions, including the on-board prognostics for zero downtime and cockpit technology, are being designed into the aircraft starting at the preliminary design stage.

Multidisciplinary systems are not new. They have been successfully designed and used for many years. One of the most common is the electromechanical system, which often uses a computer algorithm to modify the behavior of a mechanical system. Electronics are used to transduce information between the computer science and mechanical disciplines.

The difference between a mechatronic system and a multidisciplinary system is not the constituents, but rather the order in which they are designed. Historically, multidisciplinary system design employed a sequential design-by-discipline approach. For example, the design of an electromechanical system is often accomplished in three steps, beginning with the mechanical design. When the mechanical design is complete, the power and microelectronics are designed, followed by the control algorithm design and implementation. The major drawback of the design-by-discipline approach is that, by fixing the design at various points in the sequence, new constraints are created and passed on to the next discipline. Many control system engineers
are familiar with the quip:

Design and build the mechanical system, then bring in the painters to paint it and the control system engineers to install the controls.

Control designs often are not efficient because of these additional constraints. For example, cost reduction is a major factor in most systems. Trade offs made during the mechanical and electrical design stages often involve sensors and actuators. Lowering the sensor–actuator count, using less accurate sensors, or using less powerful actuators, are some of the standard methods for achieving cost savings.

The mechatronic design methodology is based on a concurrent (instead of sequential) approach to discipline design, resulting in products with more synergy.

The branch of engineering called systems engineering uses a concurrent approach for preliminary design. In a way, mechatronics is an extension of the system engineering approach, but it is supplemented with information systems to guide the design and is applied at all stages of design—not just the preliminary design step—making it more comprehensive. There is a synergy in the integration of mechanical, electrical, and computer systems with information systems for the design and manufacture of products and processes. The synergy is generated by the right combination of parameters; the final product can be better than just the sum of its parts. Mechatronic products exhibit performance characteristics that were previously difficult to achieve without the synergistic combination. The key elements of the mechatronics approach are presented in Figure 1-1.

Even though the literature often adopts this concise representation, a clearer but more complex representation is shown in Figure 1-2. Mechatronics is the result of applying information systems to physical systems. The physical system (the rightmost dotted block of Figure 1-2) consists of mechanical, electrical, and computer systems as well as actuators, sensors, and real-time interfacing. In some of the literature, this block is called an electromechanical system.

FIGURE 1-1 MECHATRONICS CONSTITUENTS

FIGURE 1-2 MECHATRONICS KEY ELEMENTS

A mechatronic system is not an electromechanical system but is more than a control system.

Mechatronics is really nothing but good design practice. The basic idea is to apply new controls to extract new levels of performance from a mechanical device. Sensors and actuators are used to transduce energy from high power (usually the mechanical side) to low power (the electrical and computer side). The block labeled “Mechanical systems” frequently consists of more than just mechanical components and may include fluid, pneumatic, thermal, acoustic, chemical, and other disciplines as well. New developments in sensing technologies have emerged in response to the ever-increasing demand for solutions of specific monitoring applications. Microsensors are developed to sense the presence of physical, chemical, or biological quantities (such as temperature, pressure, sound, nuclear radiations, and chemical compositions). They are implemented in solid-state form so that several sensors can be integrated and their functions combined.

Control is a general term and can occur in living beings as well as machines. The term “Automatic control” describes the situation in which a machine is controlled by another machine. Irrespective of the application (such as industrial control, manufacturing, testing, or military), new developments in sensing technology are constantly emerging.

Mechatronics Systems