A　proximate　time-optimal　control　(PTOC)　scheme　with　mode　switching　is　proposed　for　typical　servo　systems　characterized　by　the　double-integrator　model,　aiming　to　achieve　fast　and　accurate　position　regulation　under　speed　constraint.　The　PTOC　law　exerts　the　maximum　control　authority　for　acceleration　and　deceleration　when　the　initial　position　error　is　large,　and　ensures　a　smooth　transition　to　linear　control　when　the　error　goes　down　to　some　specified　value.　To　satisfy　the　speed　constraint,　a　stage　for　speed　regulation　is　inserted　between　the　acceleration　stage　and　the　deceleration　stage　of　the　servo　system,　and　a　mode-switching　logic　is　designed.　A　linear　extended　state　observer　is　adopted　to　estimate　the　un-measured　speed　and　the　unknown　disturbance,　to　be　used　for　feedback　and　compensation,　so　as　to　remove　the　steady-state　error.　The　control　scheme　is　then　applied　to　a　permanent　magnet　synchronous　motor　(PMSM)　position　servo　system.　Experimental　tests　have　been　carried　out　using　the　TMS320F2812DSP　and　the　results　verify　that　the　controlled　system　is　capable　of　tracking　a　wide　range　of　target　positions　with　desirable　performance　in　the　presence　of　load　disturbance　and　speed　constraint.　©,　2014,　Science　Press.　All　right　reserved.