The　instantaneous　rotational　speed　(IRS)　of　a　rotating　machine　is　key　information　to　understand　the　machine　operation　and　diagnose　the　potential　faults.　A　novel　nonprojection　fringe　vision-based　system　was　proposed　to　realize　the　measurement　of　IRS,　which　was　simply　composed　of　an　artificial　linearly　varying-density　fringe　pattern　(LVD-FP)　as　a　sensor　and　a　high-speed　camera　as　a　detector.　The　designed　LVD-FP,　printed　by　a　normal　printer,　was　pasted　around　the　surface　of　the　rotary　shaft　completely　along　the　fringe　density　change　direction.　Part　of　the　LVD-FP　was　captured　by　the　high-speed　camera.　The　fringe　period　density　of　each　imaged　LVD-FP　intensity　changed　due　to　the　rotation　of　the　shaft,　from　which　the　rotational　angle　could　be　obtained.　Subsequently,　both　the　instantaneous　angular　speed　(IAS)　between　two　adjacent　frames　and　the　IRS　could　be　accurately　and　efficiently　obtained.　The　influences　of　the　key　parameters　of　the　proposed　system　on　the　measurement　accuracy　were　investigated　by　simulations　and　experiments.　Both　the　simulation　and　experimental　results　demonstrated　that　the　proposed　system　can　accurately　measure　the　IAS　and　correctly　track　the　wide　range　IRS　with　the　advantage　of　noncontact　and　cost　effective.　In　addition,　the　rotation　direction　of　the　shaft　could　be　directly　obtained　from　the　sign　of　the　IRS　curves.　Therefore,　the　proposed　system　could　provide　a　novel　vision-based　approach　for　IRS　measurement,　especially　when　the　conventional　speed　sensor　cannot　be　installed　on　the　rotary　shaft.　The　good　performance　of　the　system　in　IRS　measurement　makes　it　attractive　for　fault　diagnosis　of　rotating　machinery.