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Embedded Systems December 2000 Vol13_13

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• SPECTRA sampling analog-to-digital converter (ADC), 1 can take these values, per- form an arctangent, and again have my angle, n14: !!... = tan - I(0.785) 4 0.785 0.785 = sin(!) 0.785 = co{!) Now, depending on the resolution of my ADC and the integrity of my e lectronics, I can get whatever reso- lution I wish in the angle. Pretty nice, huh? But unless you choose to perform the calculations each time you get samples, you will need simul- taneously sampling ADCs and some lookup tables. Resolver The second technique also uses the sine/ cosine relationship and quadra- ture, but not in the same way. A resolver is basically a transformer with a rotating primary and two secondalies placed in quadrature on one another. See Figure 3. There, one secondary is rotated n/2 (90 degrees) relative to the other. In operation, the p.-imary is located on the rotor as shown in the illusu-ation. A constant sinusoidal frequency (called the reference frequency) is impressed upon this pl-imary and is allowed to rotate along with the shaft passing the two secondaries, as shown in Figure 2. Unlike the technique we discussed in the previous section, the output of each secondary is not out of phase (or in quadrature) with the others. Rather, the anlplill.lde of the output from each secondary is a function of the primary's relative angular position. When the primary and one of the secondaries are on the same plane, we get a null output on that winding and a full amplitude output on the other secondary winding. At any other point in the rotation , we will get outputs-at the reference frequency-whose amplitudes are scaled by the sine and cosinusoidal relationships each wind- ing bears to the rotor. As shown in the figure, when the primary is at a nl4 (45 degree) angle to both secondaries, the amplitude is equal on both secondaries. As with the previous example, if we were sampling these two windings with an A/ D, we could perform an arctan- gent on the two values and again have nl4 as our resulting angle. Calculating the result A great deal of noise is often present in a motion control environment, especially UnhoI ............ ..,.,.... Statement of OWl\ership. Management, and Circulation "-_~ Mout.h.ly witll a11 adds.t1aual 1 .. 1.1. 1n bUlU59 15, "'_I>I'_~AMIAb' "IWIIllfljGvlt~~~ .. 13 ;'B.OO "i.~~~~~ ... ~IiIw~QIIIo."'~PIoI~ CHI' W.d:lA be. 600 COIIIII'IU nlt.,. Did .. .,.: y.-n ..... c. If_ '!oTk 110)0 "'''!!~'''~MdI!tI~_~''''''''-:CIId''''''''' &!r!ItItI-....... Z;tic: I~rl. ClCP MlIcU.. IDe. 515 Kaz:ket Streat Suit" oa.rpu",.Md;;;:;..,;......,~ .~S~~~~~.~n~"~'~~~.~~~1~U~O;=d~'~'="~O~5~~~~~~~.-______ ~_~u.'._'6 2_7?q_7 __ __ ,~/II'''''''''''''''''''''-OIWOj'''''''''''''''''''''''''~~~'''''''''-J OIl" Xad1.a IDe. S2S H&rU1: s u •• t 8uiu ,00 ~I:I'- x..:u Sa.'II't\· '''fi~'-bllon'ndc E.."btuld.4 iy_tGCU! hOlCulIIl'I .. b. I. b.~~ C'iQ (31 == ", 500 8an l1: .. ncUc.o . CA , 4. l0~ '- - :c"_ ~I OII.-C:-M"'~_"'I"S o.~~OoIbIdr.v.""-II ~ - tI).O""'jQIottOf'-- ..... ~ .. ~ • ......,~--"".,..fW -- ~=s.b:!5:a~0.S=; .. =~:"=~,..::r.t-==~~:-.~ 600~~1~'yDJ:Lv" , l'tI\J!Ib." ... c ~(!'-' York 1 __ ...... A ~olly otorad Su'od.d.i.ery of tro1.tad Meyo it Medb pIc l.u4Sll.ta ~ ••. 145 'Sl a c.1c.tr:ia'u ke.1'I" __ _ Loudoc., SSl gUT UK. fn5tructions to Publ1sl'1an1 ~~~"one~clll\b'-nWltl'l,.au"~./8I'I1UIlIJClfterbdol'eOUDblr'. ICt.t.!It"IC6CI'I Itf .... .....,.T'""'l!,."""oIm fw~t~. . ~~~~S:::~~~~~!ncs~~;~::!'.=~~:';';~~'~'.!' lH_dlh .. tI:GI .. lYD.JtItolbonlk.~or ~toc:u~fII(OIe;out;IiotI"~D" ln '\ofn ·.1.if ,~"'.''; "c..tJ IIGII. Uul bI.'*~It_OI'IIUi"~ OIl'If\/ItIfJ)~aldnMat!Ol'lIn!otm1!lSonc.l!.d """"kefYl'6,,,,,,a~"""_.~'"itJlrrN,'''o6,.,'''~f ,t.'fU. __ ""~.~~"""""~ID=--.,""""_f)~" ThI>........,...~ . .... ~~R .. '_OOU ......... """'_......,....c.-.n .. r~ OH .. w.I~I'lIIIIrw~ ' ;,~~ ~ .• ~,~~>~s,~.~.~~-~~~~.--~--------~~~~ o ...... ___ .... ...-oIIf'~MMM"NtI .. """,- \,ISI"IO c.=~t~~~~~Ol\ jl)0I.Its~11 .. ~OftFor"llU41 ~ .. __ ...,A>trII.»t1 • .. .. .. 56 · L9'2 1 777 " ...... U~ . S9,6S7 '".19 18 .." I .1 l !..'Oa ..l----IW2L. 1 , :tOO - 6; ,1198 2,2.9' ~ 7fl ,:U& B) .US)) 56 490 ___ 70 . 218 __ Embedded Systems Programming DECEMBER 2000 167

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