电容触摸屏控制设计外文文献及中文翻译

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A Low－Cost, Smａrt Capaｃitｉvｅ Posｉｔｉon Seｎsｏ

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Absｔract

A new hｉgｈ-perforｍａnce, ｌow-cosｔ， capaciｔｉｖe pｏｓitiｏn－measuring ｓystem is ｄｅscriｂed. Bｙ usinｇ a higｈly lｉnear oｓcilｌａｔor， shielding ａｎｄ a threｅ-ｓiｇｎaｌ appｒoacｈ, ｍost of ｔhe errｏrs ａre elimｉｎatｅd. The accurａcｙ amｏuntｓ to １ μm over a 1 ｍm raｎgｅ. Sinｃe ｔhe ｏｕｔpｕt of the ｏｓcｉllａtｏr ｃaｎ dirｅcｔly be coｎnecｔed ｔo a microcontｒｏｌlｅｒ, ａn A／D ｃoｎvertｅr is ｎot ｎeeded.

Ｉ． INTRODＵCＴIOＮ

Ｔhis ｐaper describes a ｎｏvel higｈ-performance, loｗ－cosｔ, cａpacｉtive ｄiｓｐlaceｍent measｕｒiｎg ｓysteｍ feａturiｎg: 1 mｍ ｍeaｓuｒing ｒangｅ, 1 μm accｕracy,

０．1 s tｏtａｌ mｅaｓuring tiｍe.

Ｔraｎslated to tｈｅ capａciｔive domaiｎ, the sｐeｃｉficaｔｉoｎs ｃorrespond ｔo：

a possｉbｌｅ ｒaｎge of １ pF;

oｎｌy 50 fF of this range is ｕsed for the displａｃeｍent transｄucer; ５0 aF aｂsolｕte caｐａcitance-measurinｇ ｉnａccｕracy.

Meｉjer and Schrier [l］ anｄ ｍore recenｔｌy Ｖan Ｄreｃhｔ,Meijer, and Ｄｅ Jｏｎg [2］ have pｒｏposed a dｉsplaｃeｍｅｎt-meａsurinｇ system， usｉnｇ a ＰＳD (Ｐosition Ｓｅnｓitive Detectoｒ） as sensing elｅment. Some disa

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ｄvaｎｔagｅs of ｕｓiｎg a PSＤ arｅ the higheｒ cｏsｔs and ｔｈe ｈigher ｐoweｒ consuｍptiｏn oｆ thｅ PＳD and LＥＤ (Light-Eｍitｔing Dｉode) as cｏmpared to ｔhe ｃaｐacｉtive senｓｏr eｌemｅnｔs desｃｒｉｂed ｉn this ｐaｐeｒ.

Tｈe ｓignal processｏｒ uses the conceptｓ presｅnteｄ in [2］,but is aｄｏｐｔｅｄ for ｔhe use ｏf caｐａｃitｉve eｌementｓ. Bｙ ｔhｅ eｘtensive use oｆ ｓｈiｅｌding, guarding and sｍart A／D conｖeｒｓiｏｎ,the ｓysteｍ iｓ able to ｃｏmbinｅ a ｈigh aｃcｕracy ｗith a vｅｒｙ loｗ cost-prｉｃe． The transｄucer ｐroｄuｃes ｔhｒee－perｉｏd－moduｌated sｉgnals wｈiｃh can be seｌecｔed ａnd ｄirectｌy reaｄ ｏut ｂｙ a ｍｉcrocｏｎtｒｏｌｌeｒ. Ｔhe mｉcｒocontrolleｒ,ｉn rｅtｕrn, ｃalcｕｌatｅs tｈe ｄisｐｌacement aｎｄ ｃan seｎｄ thｉs vaｌuｅ to a ｈoｓt ｃomputer (Fig. 1) or a display or ｄｒive aｎ aｃtuatｏr.

Personal ComputerElectronic CxCircuit ?C Display Actuator CrefＦｉｇ. 1． Ｂlock dｉagram ｏf ｔｈe systｅm

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Fig． ２. Ｐｅrspeｃtｉve and dｉmenｓｉons ｏf tｈe eｌectrｏde strｕctuｒe

Ⅱ. TＨＥ ＥLECTRODE STRUCＴURE

Tｈｅ ｂａｓiｃ ｓeｎｓing element ｃonsiｓts of tｗo simple ｅlectｒodｅs wｉth capａcitanｃe Cx, (Ｆig. 2）. The ｓmaｌleｒ one （E2） is surroｕndｅd by a guard elｅctｒode. Tｈanｋs ｔo the usｅ oｆ ｔｈe guaｒｄ ｅｌeｃtｒode, the capａｃitaｎｃｅ Cx ｂetwｅｅn the twｏ elｅctrodes ｉｓ indeｐendeｎt of ｍｏvemenｔｓ （lateral disｐｌaceｍｅntｓ as wｅll ａs rotaｔions) paralleｌ ｔo tｈe eｌｅcｔｒode surｆacｅ．The inｆlｕence of thｅ parａsｉｔic ｃapaｃｉtaｎces Cp ｗilｌ be elｉｍｉnatｅｄ ａs wｉｌｌ be discuｓsed in Sｅctｉoｎ Ⅲ．

Aｃcｏｒdiｎg to Hｅｅrens [3］， the reｌatｉve ｄeviation iｎ the caｐacitａnce Cx bｅtｗｅen thｅ ｔwｏ electrodｅs cauｓｅd ｂｙ the fiｎｉtｅ guard eｌｅctrode size is sｍalｌer thaｎ:

δ

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requｉｒe thaｔ δ is lｅss thaｎ 100 ｐpm.Aｌso the gａp bｅtwｅｅn tｈｅ small electrｏｄｅ and tｈe ｓｕrrouｎｄing guard caｕses ａ ｄｅviａtｉon：

δ

ｗitｈ s tｈe wｉdｔh of thｅ gaｐ. Thｉs dｅvｉａtioｎ ｉs ｎｅgｌigｉble compared tｏ （ｌ）， ｗhen ｔhe gaｐ wiｄtｈ is leｓs than １/3 of ｔｈe dｉsｔaｎｃe beｔweeｎ tｈe eｌectroｄｅs.

Anｏtｈeｒ ｃaｕse of ｅrｒors oｒigiｎａtｅs frｏm a poｓsiｂｌe fiｎｉｔe ｓkew angｌe α bｅtweｅn the two ｅlｅctrodes (Fiｇ. ３). Aｓsumｉnｇ the folloｗｉng conditｉonｓ：

ｔhe ｐｏｔentｉaｌｓ on tｈe small eｌectrode and the gｕarｄ eｌｅctrｏde are ｅｑual tｏ 0 V,

the potentiａｌ ｏｎ the ｌarge eｌectrode ｉs equａl to V ｖolt， thｅ ｇuard eleｃｔrode iｓ lａｒge enｏugh,

ｉt ｃａn be ｓｅen ｔhａt the ｅleｃtrｉc ｆieｌd will bｅ ｃｏncentric.

? d l/2 l/2

Fig. 3. Electｒodes wｉth ａngle α．

To keｅp the caｌｃulaｔions siｍple, wｅ will ａssｕmｅ the elｅctrodes ｔo

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be infinitelｙ large in one dｉｒｅcｔion． Now ｔhe ｐroblem is a two-dimensionａl onｅ that cａn be sｏlｖｅｄ ｂy usｉｎg polar-coordinates (r， φ）． In tｈis cａse tｈｅ electricaｌ ｆield caｎ be desｃrｉｂed by：

?Vsin???????r? （３) E??Vcos???????r?To calｃulａｔｅ thｅ ｃharｇe oｎ ｔhe ｓmａlｌ eleｃtrode， wｅ ｓet φ to 0 and integｒatｅ ｏveｒ r: Q??0?BrBlVdr （4) ?rwｉth Bl the leｆｔ borｄer oｆ thｅ sｍall electrode:

Bl?dl? (5） tan?2ａｎd Br the rｉght border:

Br?dl? (6) tan?2Ｓｏlvｉng (４) ｒesulｔｓ in:

Q?V?0?2dcos??lsin??ln?? (7) a?2dcos??lsin??Ｆor smaｌl α＇s this ｃan be approｘiｍated by:

4d2?l22??1? C???2? (8) d?12d???0l?Iｔ appｅaｒｓ to ｂe ｄｅｓiｒａblｅ to chｏose l ｓmaller ｔhａn d， sｏ tｈe ｅrror wｉll depend only oｎ the ａngle α. Ｉn our caｓe， a chａnge in ｔhｅ ａnｇle oｆ ０.6°ｗｉｌl cause an error leｓｓ tｈan 100 ｐpm. Ｗitｈ a pｒｏper ｄesign ｔhe parａｍｅteｒｓ εｏ and l arｅ ｃoｎｓtaｎt,ａnd then tｈe caｐacitancｅ betweeｎ the tｗo eleｃtrodeｓ ｗｉll depeｎd

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