Experimental Study Of Electrical Contact Behaviors For Au-plated Contact Materials At Super Low Speed Making And Breaking Contact

Electrical life and reliability of the miniature relay are dependent on electrical contactcharacteristics greatly, therefore the precise observation and measurement of electricaladhesion and metal bridge are the fundamental research during electrical apparatusmake and break. In order to determine the failure makes and failure mechanism ofelectrical contact in terms of this type relay, a novel test rig for simulating and recordingthe behaviors of electrical contact was designed, electrical contact of gold-plated contactmaterials were tested at super-low make and break speed, meanwhile the effect ofcontact motion condition and electrical load condition on electrical contactcharacteristics were investigated explicitly.Firstly, a novel electrical contact characteristics test and analyzing system wasproposed and designed in detail. Three linear translation stages and the opticalbreadboard were selected as3D adjustment structure, and the piezomotor, the gratingruler and the precision slider constitute the actuation unit. At the same time, the μNscale force transducer, the μA scale current supply and the nV scale voltmeter wereintegrated into the system as the measurement and data acquisition unit. So, theactuation position of the piezomotor, the contact force and the contact voltage can becollected simultaneously in real time. The motion control function and data read＆save ability were realized by using LabVIEW software.Secondly, the emerged electrical adhesion phenomena in terms of gold-platedcontacts were researched comprehensively for motion speed range of50~150nm/s, loadvoltage range of5~25V and load current range of0.2~1A. The effects of electrical loadconditions of contact close and open on electrical adhesion were analyzedexperimentally. Thus, the critical condition of the metal changed into molten status waspresented. Furthermore, the variation behaviors of contact force during make processwere discussed and the relationship between dynamic contact parameters and theadhesion force was also identified. In addition, a mathematic model for describing thecorrelation between the contact resistance and the adhesion force at the moment ofadhesion was build, with the help of the model, the ingredient of contact resistancecorresponding to the adhesion status is confirmed.Thirdly, the metal bridge phenomena emerged on gold-plated contacts were alsoresearched comprehensively for motion speed range of25~150nm/s, load voltage rangeof5~25V and load current range of0.2~1A. The change of contact voltage at metalbridge stage was analyzed, followed by a proposed physical model which can exhibitthe repetitive melting competition among multi ’a’ spots. The model was then proved by the analysis of contact force characteristics. Furthermore, the effects of open speed andload current on time and distance of metal bridge were also presented.Finally, the electrical contact establishing process of gold-plated contact materialswas studied for the load current of50mA and the motion speed of150nm/s. When theactual gap distance is smaller than the critical gap distance, the reason for periodicbounce which happened before electrical contact buildup was given, as well as thevariation pattern of bounce period and duty ratio. Moreover, the relationship betweenthe critical gap distance and strain coefficient, contact area were also confirmed.This novel test rig developed in this thesis can provide a experimental platform forthe characterization and evaluation of electrical contact materials, and the researchfindings are useful for analyzing the failure mechanisms of contact materials which usedin micro miniature relay.