The automotive industry is on a steady march toward building vehicles with improved “sound quality,” one of the many important indicators of perceived product quality. The instrument panel, with its myriad of installed components and close proximity to the occupants, always is a target of both careful design and subsequent test refinement.
A basic tool of refinement is the squeak-and-rattle test. In this test, the assembled panel is excited in various directions at frequencies up to 200 Hz. Resulting sound sources emanating at frequencies of 500 to 3,000 Hz are detected, identified, and corrected.
It is important to hear only the product responses. Testing is conducted in a sound-absorbing quiet room using a silenced shaker with protective thermal monitoring that operates without a cooling fan. No fan-cooled instrumentation is permitted within the test room.
Preliminary audit runs may be made by exciting the panel with random profiles derived from road recording. During such audits, the Zwicker loudness is commonly recorded as an index of performance. Product refinement runs are made using dwell and swept sine excitation under manual control. Refinement runs help identify and correct design and assembly problems that lead to squeaks and rattles.
These sound-producing mechanisms invariably are nonlinear, such as the stick-slip “itch” noise of two plastic parts rubbing together. As a result, a certain degree of manual detective work is required to locate offensive mechanisms. Iterative experiments optimize a solution as clearances, pre-loads, and tie-downs are adjusted. During prototype evaluation, design modifications, including component isolation, material changes, and revised fastening strategies, may be introduced.
While electronic loudness recordings are an aid in such testing, nothing surpasses the human observer in locating faults. Manual control of the sinusoidal shaker excitation is essential, and that control must be at the test object. Figure 1 shows the control panel for a squeak-and-rattle test.
Modem shaker-control systems function under Windows 95 and NT. Recent advances in these operating systems permit a new form of inter-program connectivity termed ActiveX® transfer. Vibration controllers, such as the Data Physics SignalCalc® 550 Win and 350 Win, can take advantage of this standard, using ActiveX to provide remote control of the excitation process.
A hand-held computer is linked to the shaker-control computer via a standard local area network (LAN), as illustrated in Figure 2. This small PC executes a simple program that emulates the control group of the shaker-control program that runs concurrently on a PC in the control room.
ActiveX automation, a subset of Microsoft’s ActiveX products, passes control commands and display data between these computers, establishing a remote control/readout loop using standard LAN cards that may include those of RF or IR wireless technology. Loading and executing the remote-control program automatically initiate the shaker-control program in the other computer.
The vibration controller runs just as if it were initiated locally, controlling the shaker to excite the specimen against a pre-established amplitude/frequency profile and providing alarm and shutdown protection. The screen supplies a graphic of the moment-to-moment operation of the shaker (Figure 3). However, the operation and control of the test are entirely in the hands of the at-specimen operator.
Connectivity is the Key
The root of ActiveX automation is a distributed component object model (DCOM). The DCOM is a stand-alone piece of executable code. It may be called by multiple programs written in diverse programming languages and be resident on a machine that is linked to another executing the DCOM via a network rather than on the same computer.
The software is written to be a DCOM server, capable of providing analytic services to an external client program that can ask the product to perform specific measurement or control functions and return specified results to the client program. As a result, the client can become the human interface for specific applications. Or, the client may receive measurements made by the product and passed along for specialized post-processing, such as passing fast Fourier transform analyzer measurements to a modal analysis program.
The client controls and queries the server through an industry-standard interface format and protocol termed a dispatch interface. The dispatch interface standard allows the server to be called by programs written in a variety of languages including C++, Visual BASIC, and Java (Visual J++). All of these languages include specific function calls for dispatch interface communications.
The server exposes its methods and properties to the client. Each method is simply something the server can be called upon to do, such as increasing shaker frequency or amplitude. Invoking a method amounts to making a software call with the appropriate parameter passing. Each property is a variable or group of variables that the server can pass back to the client upon command.
The methods and properties are summarized with their appropriate parameters in a type library (.tlb file) that accompanies the server-executable module. The type library may be browsed from the compiler used to write a client, providing on-line guidance to the programmer.
Conclusions
ActiveX makes it simple to use a sophisticated instrument with other PCs and programs to solve a broad range of testing requirements using only inexpensive, general-purpose hardware. Now controllers may be integrated quickly into complex systems by writing a client program in Visual BASIC, LabVIEW, or a host of other languages. Such a program can employ multiple servers from multiple manufacturers running concurrently in a single computer or distributed across several computers in a network.
About the Author
George Fox Lang is a senior scientist at Data Physics. He earned a B.S.M.E. degree from the University of New Haven and did graduate studies in engineering mechanics. Mr. Lang is the former president of Fox Technology and a former vice president of Nicolet Scientific. His 30-year work history includes the General Motors Proving Ground and Sikorsky Aircraft. Data Physics, 2085 Hamilton Ave., #200, San Jose, CA 95125, (408) 371-7100.
Copyright 1998 Nelson Publishing Inc.
January 1998
|
|