Faster Prototyping, Simulation

New systems allow prototype electronics components to be tested in real time using a simulated environment, reducing the need for expensive or destructive tests. Early prototype systems enabled engineers to test new designs to prove algorithms and test integration of the hardware and software earlier in the design process.

06/01/2005


Sidebars:
Rapid prototyping defined


New systems allow prototype electronics components to be tested in real time using a simulated environment, reducing the need for expensive or destructive tests.

Early prototype systems enabled engineers to test new designs to prove algorithms and test integration of the hardware and software earlier in the design process. These one-of-a-kind, proprietary systems—typically special-purpose, breadboard units—were developed in the automotive and aerospace industries.

More recently, commercial models of software and hardware systems have been introduced and enhanced to provide rapid prototyping and hardware-in-the-loop (HIL) simulation capabilities. Vendors have offered standard system configurations, usually based on DSP chips or advanced microprocessors, such as the Digital Alpha or PowerPC.

Industry application

The automotive industry in particular has welcomed these commercial rapid prototyping and HIL systems. Input and output capabilities used in automotive design were provided on standard interface boards for such functions as spark advance and crankshaft angle position. At the same time that these systems were introduced, system-modeling tools that could define algorithms and interfaces graphically and simulate behavior of the control models on a workstation or PC became available. After initial modeling and simulation, modeling tools were interfaced to rapid prototyping and HIL systems through automatically generated prototyping code. Because system-modeling tools could be used with rapid prototyping systems, these tools became an integral part of the automotive control design process. Rapid prototyping systems ranged from rugged, in-car units to large rack-mount systems supporting numerous I/O channels. The standard processor for the prototyping systems was the DSP or Digital Alpha processor.

The controller in the "Block diagram control system" graphic interfaces to the plant or engine through actuators and reads values or signals from sensors on the plant to form a closed-loop control system typical of that found in automotive and aerospace design. Using model-based design, the graphical model can be simulated and tested to prove the control design and integrity of the plant model.

Software

Using model-based design, this graphical model can be simulated and tested to prove control design and the integrity of the plant model.

"Automatic code generation" graphic shows the use of automatically generated software code from the control side of the model to run a rapid prototyping system, which tests the control algorithms in real time on commercial rapid prototyping equipment. In the same way, automatically generated software code from the plant side of the model can be used to simulate the responses and operation of the plant to test prototype controllers in real time on commercial HIL equipment.

While the automotive industry accepted rapid prototyping systems, the aerospace industry found significant value in the use of HIL systems. Aerospace companies found that they could simulate the flight and environmental characteristics of their planes, missiles, and satellites. They developed sophisticated Fortran models of systems and ran them on real-time hardware similar in concept to the hardware used by the automotive companies for rapid prototyping work. More sophisticated model-based designs were used to simulate models and generate code that could replace the older Fortran models on COTS (commercial off-the-shelf) hardware testing systems.

Early rapid prototyping and HIL systems were developed either by the automotive or aerospace companies, or by suppliers of proprietary systems. These systems were often one-of-a-kind, in-house systems that demanded internal support and maintenance staff. The proprietary suppliers offered a range of standard configurations and provided annual maintenance contracts and custom support as necessary. Both were fairly expensive systems, which limited use to companies that had suitable budgets.

PC-based prototyping

About five years ago, the first rapid prototyping and HIL systems based on x86 PCs became available. Although they cost much less, these systems were assumed to lack the level of sophistication or the power of the DSP-based systems. These systems supported standard PC processors and PC data acquisition boards, which had become widely available. Because these products could use any type or size of x86 processor, the resulting system offered a range of price/performance points, depending on the type of PC used for the customer application. This scalability offered the benefits of increasing performance of PC processors and reducing memory prices, with all components available off the shelf. But the initial industry reaction was skeptical, expressing concerns about the ability of an Intel 486 or Pentium computer (or equivalent) to perform at real-time speeds with complex models. The PC generally was thought incapable of such an advanced, processor-dependent task as rapid prototyping or HIL.

Software

Automatic code generation is used for rapid prototyping, hardware-in-the-loop simulation, and embedded system deployment.

Companies like Eaton and Caterpillar, however, attracted by the price and scalability of PC-based systems, began testing and found PCs could handle a significant amount of their rapid prototyping and HIL tasks. They began to apply PC-based rapid prototyping and HIL systems to supplement existing facilities, at much lower cost per system. Early experiments from each led to broader commitment to these tools within the embedded control development process.

Eaton, a producer of powertrain components for trucks, designed a flexible, medium-duty, prototype hybrid truck, containing a control unit designed with tools for model-based design. Because the hybrid powertrain was a prototype, Eaton tested the entire system on real-time PC-controlled dynamometer. Engineers at Eaton generated and executed various standard test scenarios and tested all components safely in the lab before road testing. Eaton tested the control unit as part of this system, in a combined rapid prototyping and HIL set-up.

To reduce time, expense, and safety hazards associated with road testing, Eaton also needed to develop a hardware-in-the-loop simulator. The simulator had to simulate the entire powertrain of medium- and heavy-duty trucks (including the engine dynamics, master clutch, transmission, driveshaft, tires, and road) in real time. It also had to communicate electrically with the shift console, the transmission controller, and other vehicle systems; provide for signal injection and acquisition; and allow for automated testing using field data.

After evaluating various options for cost, development time, risk, availability of I/O hardware, maintainability, flexibility, special driver requirements, and connectivity, Eaton's engineers concluded that the use of PC-based systems would provide the best solution. It would enable them to use standard ISA, PCI, and PC/104 I/O hardware, significantly reducing overall development costs and time. This standard equipment also would offer the most flexibility, provide for special driver requirements and connectivity, and be easy to maintain.

Over the past few years, support provided by PC-based prototyping systems for I/O devices has grown significantly. Simple analog and digital I/O, and counter/timer support have been augmented by more advanced pulse-width modulation support, encoders, linear/ rotational variable differential transformers, synchro-resolvers, and other advanced I/O capabilities. Availability of PC-based hardware components, coupled with software driver support, plus the rapid advancement of PC processor performance, have raised PC-based prototyping systems to a performance level that rivals that of proprietary systems, at far less cost and with COTS components. As performance and I/O capability have increased, numerous automotive and aerospace companies have put PC-based rapid prototyping and HIL systems to work within their development processes.

On the high end of the HIL simulation area, a major aerospace supplier developed an impressive, high I/O count system based on a standard Dell 3 GHz Intel Pentium 4 desktop computer system, extended with two PCI bus expansion chassis. By separating the CPU unit from the I/O units, this configuration allows for convenient future CPU replacement as more powerful processors become available. This system has the expansion space for 28 PCI I/O boards, which provide 288 16-bit D/A channels and 128 16-bit A/D channels in the first expansion chassis.

The second chassis provides special I/O capabilities, offering 384 digital I/O lines using 16 threshold programmable DIO modules on four IP-carrier boards. Three linear variable differential transformer (LVDT) boards provide 24 LVDT inputs and 18 LVDT outputs, which are used for linear motion control. This HIL system now simulates the environmental aspects of a new, large commercial aircraft design.

Beyond automotive, aerospace

Cost effectiveness of PC-based rapid prototyping and HIL systems means that they can now be applied to more cost-sensitive applications. Engineers from automotive and aerospace companies have brought the concepts of model-based design, together with rapid prototyping and HIL, to other industries including medical, industrial equipment, and computer equipment.

In 2003 and 2004, one-third of PC-based rapid prototyping and HIL systems were delivered to industries other than automotive and aerospace, most prominently the medical, industrial equipment, and computer equipment industries.

In the medical equipment area, companies use this equipment to emulate various body functions in an HIL modeling application. Prototype devices under development simulate the heart. Various types of medical device hardware use rapid prototyping of control algorithms. Some devices use robotics and haptic systems that can be quickly designed and tested using rapid prototyping hardware. Another medical application simulates medical conditions to assist in doctor training.

Vascular injection pumps developed by Medrad lets physicians detect arterial blockages, illuminate single blood vessels, and gauge the health of a beating heart using radiological or magnetic resonance imaging. Using PC-based prototyping tools, Medrad created a hardware-in-the-loop simulation of vascular injection pump fluid dynamics and the human vascular system. This real-time simulation enables Medrad to reduce the number of tests using real fluids, which are typically required to validate pump controller designs.

Gulf Coastal Group, Micro Systems Engineering Inc. uses model-based design to accelerate research to develop implantable medical devices such as pacemakers. The company uses model-based design for initial modeling and simulation before moving to rapid prototyping of its algorithms. Using cost-effective prototyping capabilities, the company can perform data analysis and simulation functions, as well as implement a flexible real-time system to test research hardware and new analysis algorithms.

Several computer equipment companies now use rapid prototyping to develop systems to control large printers and copiers. Applications include rapid prototyping and HIL simulation of printer and copier mechatronics, such as paper movement through extremely large printers.

Whirlpool is rapid prototyping new ideas in a near-production format for testing with customers. Operation of washers, dryers, and ovens are prototyped in test units under consumer conditions, with modifications to test new designs and ideas. These PC-based prototyping systems give Whirlpool a simple testbed for new system development and testing of control algorithms and user interfaces.

Additional applications of rapid prototyping and HIL

Aircraft systems

Aircraft braking, including anti-skid, deceleration control, and automatic braking

Climate control

Full car climate HIL simulator with extensive I/O, sensors, and actuators

Consumer audio systems

Rapid prototyping of algorithms for multi-dimensional audio sound systems

Fuel cells

Rapid prototyping of fuel cell systems

Gaiting robot

Control of a 4-leg robot with distributed control systems

Hearing aids

Rapid prototyping of new digital signal processing algorithms for hearing aids

Heavy-duty truck simulator

HIL system for engine, transmission, dashboard, ABS/braking, cruise control

HVAC controls

Rapid prototyping and HIL of HVAC systems for large buildings

Injection molding controls

Rapid prototyping of controllers for injection molding machines

Jet engine controls

Rapid prototyping of controls for jet engine propulsion systems

Material handling systems

Control of automated handling systems

Satellite dynamics

HIL simulation of actuators, satellite dynamics, and kinematics

Spacecraft docking

HIL simulation of spacecraft docking in space

Structural test systems

Rapid prototyping of a control system to control shake tables

Steering systems for ships

Rapid prototyping of a distributed steering control system for ships

Turbines and generators

HIL and rapid prototyping for power generation machinery

Vehicle controls

Prototype algorithms for ECUs across powertrain, chassis, and hydraulics


Author Information

Mike Dickens is technical marketing manager at The MathWorks;


Rapid prototyping defined

The term rapid prototyping can be used to mean different things for different applications. It can be used to generate 3-D solid objects, to study parts before they are fabricated in volume, or to test custom ASIC designs using a programmable FPGA approach.

This article focuses on using rapid prototyping to test software control algorithms in a real-time environment before implementing code on an embedded processor—a common application for engineers who model and simulate control systems.



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