National Instruments. The boards control six stepper motors independently. T wo National Instruments UMI motion inter-face modules provide the interconnection point between the motor control boards and the stepper motors.We use a stepper motor to depress the switch from its off position to full-on position while current readings are made at both loca-tions. Initially, we program the stepper motor to slowly release the trigger, in 0.003-inch steps, from its full-on position to the position where the software detects breakthrough current. At this breakthrough (or tease)point, full current is flowing through the tips of the switch contacts, which causes arcing.T o simulate the user’s finger vibrating under fatigue on the trigger switch, the stepper motor toggles forward and back around the tease point at a user-specified distance and frequency. The minimum tease distance of the system is 0.001 in.Data Acquisition HardwareOne of the advantages of a PC-based system is the availability of plug-in data acquisition (DAQ) boards. We chose the National Instruments AT-MIO-64E-3 multipurposeby Jacquelyn Batson, MicroCraft CorporationThe Challenge: Rigorous,flexi-ble,automated life-cycle batch testing of AC and DC switches with varying voltage and current capacities.The Solution: Developing a PC-based system using National Instruments ValueMotion Stepper and DAQ boards controlled by LabWindows/CVI.IntroductionThe primary reason for testing consumer products is customer satisfaction. Early fail-ures on consumer products not only can damage product reputation with customers,but also can result in costly field returns for the manufacturer. These were two of the factors that led Black & Decker, Inc. to install a system to perform life-cycle testing on the trigger switches used in their power tools and other consumer products. They contracted with MicroCraft Corporation to develop a flexible PC-based system that uses National Instruments DAQ boards controlled by LabWindows/CVI.Specifically, Black & Decker was interest-ed in the analysis of switches undergoing a process called “teasing.” Rick Sharpe at Black & Decker reported, “We have found that a major contributor to switch failures on power tools is a user practice we call ‘teasing.’T easing results when the operator relaxes the pressure on the trigger switch to the point where the switch contacts are barely making contact, forcing the full tool current throughthe edge of the switch contact. T rying to duplicate this failure mode using operators would require an excessive expenditure of technician time and, most importantly,would not provide the consistent data we require.”Life-cycle testing of any type requires a robust test system. With a single test often taking several days, Black & Decker invests a lot of machine hours as well as man-hours testing each product. As a result, our chal-lenge at MicroCraft was to develop a system that could withstand the rigors of continuous use and smoothly handle catastrophic events such as power outages with no loss of data and minimal interference with the test in progress. The system also needed to run sev-eral test stations independently to simultane-ously test AC and DC switches with varying voltage and current characteristics.Motion ControlThe primary component of the Black &Decker switch test system is motion control.T o test six switches simultaneously, we decid-ed to use six Oriental Motor stepper motors controlled by two multiaxis ValueMotion PC-Step motor control boards fromAutomated Life-Cycle Testings DAQs LabWindows ™/CVI s ValueMotion™Life-Cycle Testing of Spring-Loaded Switches Using Motion, DAQ, and LabWindows/CVIT he primary component of theBlack & Decker switch test system is motion control.To test six switches simultaneously,we decided to use six Oriental Motor stepper motors con-trolled by two multiaxis ValueMotion PC-Step motor control boards from National Instruments.Main Panel of Automated Switch Test System Showing All Six StationsSC-2070 termination breadboard to provide connections to the analog signals because it provides a cold-junction reference signal for the thermocouple input.System SoftwareWe chose National Instruments LabWindows/CVI as our software environment. With its special features, we could satisfy the requirements for a graphical user interface and yet main-tain the speed necessary to test six switches simultaneously. The flexible LabWindows environment also made it easy to incorporate on-line help and a manual control ing the manual control mode, Black &Decker engineers can use the system as a laboratory tool for characterizing newDAQ board and AT-AO-6 analog output board; these DAQ boards easily handle the high-speed measurements and control signals. For each switch under test, the system acquires load, no-load, and locked-rotor current measurements; temperature measurements; and voltage measurements.The system also uses analog outputs to drive hysteresis brakes (or dynamometers) that apply load. We used the National Instrumentsswitches, in addition to its customary use as a test system. The system stores all test data points and test setup information to file in standard spreadsheet or SPC-compatible format. T o simplify backups and data analysis,all files are accessible over Black & Decker’s network via a plug-in Ethernet board.SummaryWith the automated switch test system, Black & Decker can perform consistent, reliable testing on the large variety of switch-es used in their consumer products and can maintain standardized test data. Black &Decker has saved thousands of man-hours thanks to the speed, accuracy, and data stor-age capabilities of the National Instruments-based system. In addition, because of the inherent flexibility of the system, we easily added the manual mode –as a result, Black & Decker received a laboratory analysis tool as well as an automated life-cycle test system.1For more information, contact Jacquelyn Batson,MicroCraft Corporation,3209-154 Gresham Lake Road, Raleigh, NC 27615tel (919) 872-2272, fax (919) 872-5822 **********************W e chose the National InstrumentsA T-MIO-64E-3 multipurpose DAQ board and A T-AO-6 analog output board; these DAQ boards easily handle the high-speed measurements and control signals.B lack & Decker has saved thousandsof man-hours thanks to the speed,accuracy,and data storage capabili-ties of the National Instruments-based system.In addition,because of the inherent flexibility of the system,we easily added the manual mode –as a result,Black & Decker received a laboratory analysis tool as well as an automated life-cycle test system.Control Panel for T est StationU.S.Corporate Headquarters • Tel:(512) 794-0100 • Fax:(512)683-9300•****************•Branch Offices:Australia 03 9879 5166 • Austria ***********•Belgium 02 757 00 20 • Brazil 000 811 781 0559 • Canada 905 785 0085 • China ***********• Denmark 45 76 26 00Finland 09 725 725 11 • France 01 48 14 24 24 • Germany 089 741 31 30 • Greece 30 1 42 96 562 • Hong Kong 2645 3186 • India 91805275406 • Israel 03 6120092 • Italy 02 413091Japan 03 5472 2970 • Korea 02 596 7456 • Mexico 001 800 010 0793 • Netherlands 0348 433466 • New Zealand 09 914 0488 • Norway 32 27 73 00 • Singapore 2265886 • Spain 91 640 0085Sweden 08 587 895 00 • Switzerland 056 200 51 51 • Taiwan 02 2377 1200 • U.K.01635 523545© Copyright 1999 National Instruments Corporation.All rights reserved.Product and company names listed are trademarks or trade names of their respective companies.361589A-01 051099。
