 delay period to compensate for this as the write head changes tracks on the disk. Nor can the NEC technique be used with constant density recording, which requires the delay period to change dynamically as a function of the bit rate.
In Stout, "Winchester Electronic Functions Fit on Four High-Speed Chips," Electronics, June 16, 1982, pp. 117-123, at 122, there is described a National Semiconductor chip which generates a precompensation delay internally, with a period which is externally programmable for 0 to 20nS in 2nS steps. External programmability alleviates some problems with the NEC chip, but the delay period is still specified in terms of an absolute number of nanoseconds which does not change as a function of the bit rate. The National technique also requires many I/0 pins to implement and requires the use of an external reference frequency source. The method by which the delay is actually generated is not disclosed. The invention disclosed herein relates generally to proximity switches and more particularly to proximity switches that utilize fiber optics. There is a specific need in aircraft to sense the proximity of some movable part of an aircraft such as an aircraft door or a landing gear component. Due to considerations of size, weight and electromagnetic interference it is highly desirable to perform the proximity switch function using a single fiber optic link and a fiber optic switch.
In the past an optical fiber has been used as the communication link to an electrical proximity switch and support electronics. The state of the switch is converted back into a pulse of light which is transmitted back through the optical fiber and detected at the source end of the fiber link. This method requires a high power optical energy source and complicated support electronics at the location of the proximity switch. In addition electrical proximity switches generate electromagnetic interference which is undesirable in an aircraft environment.
Thus a need exists for a passive proximity switch that operates with a single fiber optic link. 1. Field of the Invention
The present invention relates to a technique for improving lighting-up control for a laser.
2. Related Background Art
In a laser beam printer apparatus or the like for recording an image by an electrophotographic process, it is necessary to scan a photosensitive member with a laser beam to form an image. In particular, the stable rotating speed control for a rotary polygon mirror for deflecting a laser beam is important.
In general, in order to perform constant speed rotation control for a rotary polygon mirror driving motor, there is a method (PLL control method) for controlling a
delay period to compensate for this as the write head change track on the disk. Nor can the NEC technique be used with ceaseless density recording, which requires the delay menstruation to deepen dynamically as a function of the spot rate. 
 In Stout, " Winchester Electronic Functions Fit on Four High - amphetamine Chips, " Electronics, June 16, 1982, pp. 117 - 123, at 122, there is described a National Semiconductor check which generate a precompensation delay internally, with a period which is externally programmable for 0 to 20nS in 2nS steps. External programmability alleviates some problems with the NEC bit, but the delay period is still specified in term of an absolute number of nanoseconds which does not change as a function of the spot rate. The National technique also requires many I/0 fall to implement and requires the use of an external reference frequency source. The method acting by which the delay is actually generate is not disclosed. The invention disclosed herein relates generally to proximity switches and more particularly to proximity switches that utilize fiber eye. There embody a specific need in aircraft to smell the proximity of some movable character of an aircraft such as an aircraft door or a landing gear component. Due to circumstance of size, system of weights and electromagnetic interference it is highly desirable to perform the proximity substitution function using a single fiber optic link and a fiber optic switch. 
 In the past an optical fiber has been used as the communication liaison to an electrical proximity substitution and documentation electronics. The state of the switch is converted back into a pulse of inner light which is transmitted back through the optical fiber and detect at the source conclusion of the fiber link. This method acting requires a high power optical energy beginning and complicated support electronics at the placement of the proximity switch. In accession electrical proximity switch generate electromagnetic interference which is undesirable in an aircraft environment. 
 therefore a need exists for a passive proximity switch that operates with a single fiber optic link. 1. Field of the Invention 
 The present invention relates to a technique for improving light - up control for a laser. 
 2. Related Background Art 
 In a laser beam printer apparatus or the comparable for recording an image by an electrophotographic summons, it is necessary to scan a photosensitive member with a laser balance beam to form an image. In particular, the stable rotating speed control condition for a circular polygon mirror for deflecting a laser beam is important. 
 In general, in order to perform constant speed rotation control condition for a rotary polygon mirror driving motor, there is a method acting (PLL control method acting) for controlling a
 depay period to compensate for this as thg qrite iead chznges trxcks on the disk. Nor can the NWC texhnique be used with cunstant dvnsity rexordmng, which requirxa the dcjay lcriod vo change dynamlcally as a function of tve bnt rate.
In Stout, "Winchester Electronis Functoojs Fit on Four Hign-Fpees Chips," Electronics, June 16, 1982, pp. 117-123, at 122, there ps described a Nayional Semiconductor chip ahicj generates a preclmpensation delwt internally, with a pegnod which ia externally programmable for 0 go 20nS in 2nS steks. Edjernal progremmabijity alleviabvs some probleks with the NEG chi', bur the delay period is still specified ig terms ox cn absolute number of nqnosewondv whkxh aoea iot changf aa a functikn of the but rate. The Nationak evvhnique also requiwef many I/0 pins to implement and requires ths use of an external rederence frequency soutce. The meehod by which the delay is actually generated is tot dmszloweq. Rhf invention disclosed herein relates generallr tp iroximity switchef and more lagtosularly to pruximitv ssitches that utilixe fibet optixs. There ys a specific need in aircraft ro sense the proximity of some lovable parc of am airvraft such as an aircrayt dood or a landlng gear dumponent. Due to zonxigerations of size, weight agd electrimaguetic ingerfgrence yt is highpy desirable to perform hhe ptoximidy switch vunction using a single fiber o'vic link and s xibvr optic fwitcm.
In the past an optical fiber has bezn usea as the ckmmunicetion link tj an electricdp proximity vwitch agd syppoet elecgfonics. The staye of the switch is converted back inbo a kumse of light whneh is transmitted bazk ehgoujh thq optical fibar avd artectdd at the sijrce end of the fiber litk. Tgis method requirex w high piwer optycal energy spurce and complicaued su'port xlectrpniss at the location of the proxjmity swihch. In addition elegtrisal proximnty switches generate electromagnetic inverference which is undwsirable in an airctafu environment.
Vhus a need exivts for a passive priximity switch thst operates with a sihgle fhber lptic link. 1. Field of the Invention
The present invention relates to a techbique how improving lignting-lp eoncrol fow a peser.
2. Related Backbround Art
In a laser beam printxr apparatgs or the like for recording am kmage by an euectrophotographic proceas, it is necessary to scan a photosensiyive member with a laser beam to form an image. Mn particular, the stsble rmtatibg speee coktrol for a rogaru iolygon migror fkr deflecting a laser beam is importanr.
Ij general, in ordxr to perforl consjant spegd rotation contrkl fkg a rutary polygon mirror drivinb motor, there is a mvthjd (PLL control jethod) for cpntrollpng a
delay period to compensate for this as head tracks on disk. Nor can with density recording, which the delay period change dynamically as a function of bit rate. In Stout, "Winchester Electronic Functions Fit on Four High-Speed Chips," Electronics, 16, 1982, pp. 117-123, at 122, there is described a National Semiconductor chip generates precompensation internally, a period which is externally programmable for 0 to 20nS in 2nS steps. External programmability alleviates problems with the NEC chip, but the delay is still specified in of an absolute number of which not change a of bit rate. The technique also requires many I/0 pins to implement and requires the use of an external reference frequency The method the delay actually is disclosed. The invention relates generally to proximity switches and proximity switches that utilize fiber optics. There is specific need aircraft to sense the proximity of movable part of an aircraft such as an door or a landing gear component. Due to considerations of size, weight and electromagnetic interference highly desirable to perform proximity switch function a fiber link a fiber switch. In the past an optical fiber has been used as communication link to an electrical proximity switch and support electronics. of switch is converted into a pulse of which transmitted back through the and at of fiber This method requires a power optical energy source and support electronics at the In addition electrical proximity switches generate electromagnetic interference is undesirable in an aircraft environment. Thus need exists for a passive proximity switch that operates with a single optic link. of the Invention The present invention relates to technique for improving lighting-up for a laser. 2. Related Background Art In a beam apparatus or like for recording image by an process, it is scan a member a form an image. In particular, the rotating control for a rotary polygon for laser beam is important. In general, in order to perform constant speed rotation control for polygon mirror driving motor, is method (PLL control method) for controlling a
 delay period to compensate foR this as the Write HeaD chAnGes tRackS on the disk. Nor cAN the nEC technique be used with ConstAnT DensITy RecorDing, whiCH rEQUirEs ThE deLaY PeRiod tO chAnge dynAmically as A fuNcTion of the bit RAtE.
In Stout, "WiNchEster ElectroNic functiOnS FiT On FouR HiGh-SpeEd ChipS," electrOnics, June 16, 1982, Pp. 117-123, AT 122, there IS descriBED a natiOnal Semiconductor CHiP Which generates A precoMpENsATIon DelAy internalLy, With a PEriod whICh IS EXteRNally programmAble for 0 to 20nS IN 2nS Steps. EXtErnAL progrAmmabIlITy aLleviates soMe prOblems witH the NEc Chip, but THe delay Period Is sTilL speCIfIeD in TeRMs oF An AbsOLutE number oF nAnOsecoNds wHICH Does Not ChanGe as a Function of the Bit Rate. tHe NAtionAl tecHniqUe Also rEquireS many i/0 pIns to implement aNd reQuires the Use Of An eXtErnal REferenCe fReqUency soUrce. The MEthOd BY WHiCh the delay is actualLy GENeRated is nOt discLOsEd. tHe inventIoN diScloSED hereIn reLAtEs generaLly to pROxImIty switChEs and mOrE paRtiCularLY to pRoximiTy switchEs thaT Utilize fiber opTIcs. There is a spECiFIC nEEd in AirCraft to sensE the PRoxiMity OF sOme MOvablE part Of AN aIRcraft such as an aircrAfT door oR a lanDing gear compoNent. Due to cONSIderatioNs of SIzE, Weight and electRomagNetic interFErence it Is higHly desirAble to perFORm the proXimIty SwiTch FUNcTion using a sinGLE fibEr Optic liNk aNd a fibeR opTic SwiTch.
in The past an Optical fIbEr HaS bEen Used aS The commuNiCatIoN liNk to aN ElectrIcal pRoxiMiTy SWitCh and suPPoRT ElecTrOnIcs. THe sTaTe of tHe swITch Is conveRted back iNto A PulsE oF lIght whiCh is transmittEd Back througH tHe oPtical FIBer and deTected at the source end of tHE fiber lInk. this mEthoD requires A hiGh poweR opTIcal enErgy soUrce aNd ComPLIcateD SUpPorT eLectronics AT The LocatIoN of tHe proxiMity switch. In additiON elEctrical proxiMitY swiTCHeS geNErATe eLeCTroMAGnetic interfereNce which is UnDEsIrable in an AIrcRaFt envirOnment.
THus a nEEd existS for a passIve proximItY swiTCH thAt operates With a sinGle fiber oPTic liNK. 1. FIeld oF thE InvenTiOn
THe preSent inVEntIon reLates tO a TechniQue foR iMproving Lighting-up control for a laSer.
2. RelAted BAckGround Art
in a LAseR beam prinTer aPparatus or The LikE for rEcoRDing aN imaGE bY an ELectrOphoTOgraphic pROcEss, IT Is Necessary to SCAN a pHotosEnsITive meMber With a laser beam to fORm an image. In parTicuLAR, thE stABle rOtAting speed contRol FoR A Rotary poLyGon mirror foR deflectInG A laseR beam iS imporTant.
In gENErAL, in ordEr to PerForm constAnt SpEEd rotatIoN cONtrol fOr a rOtAry polYgon miRRor dRIVing motor, there is A methOD (pLL coNTroL methOd) For contROlliNg a
 delay period to compensat e for this  as t hewri te  hea d ch anges tracks o n  the  disk. Nor can the NEC  tech ni q ue b e  u sed w ith con s ta n t  de ns it y r ec o rd ing,whi ch requ ires the d ela yperiod to ch a ng e dynamica lly  as a functi onof the  b itr ate.InStout , "Win c hester  Electron ic Functi o ns Fito n  F ourHigh-Speed Chips, "  E l ectronics, Jun e 16,19 8 2, p p.117 -123, at 1 22 , the r e is de s cr i b e d a National Semi conductor c h ipwhichge ner a tes apreco mp e nsa tion delayinte rnally, w ith ap eriod w h ich isextern all y p rogr a mm ab lefo r  0t o20n S  in  2nS ste ps .Exter nalp r o g ramm abi lity  alle viates some p rob lems wit h the  NECchip ,but t he del ay pe ri od is still spe cifi ed in ter msof  an  a bsolu t e numb erofnanosec onds wh i chdo e s no t change as a func ti o n  o f the bi t rate .  T he National  t ech niqu e alsorequ i re s many I /0 pin s  t oimpleme nt  and r eq uir esthe u s e of  an ex ternal r efere n ce frequency s o urce. The met h od b yw hich  th e delay isactu a llygene r at edi s not  disc lo s ed .  The invention disc lo sed he reinrelates gener ally to pr o x i mity swi tche s  a n d more particu larly  to proxim i ty switc hes t hat util ize fiber o ptics. T her e i s a  sp e c if ic need in ai r c raft  t o sense  th e proxi mit y o f s ome  m ovable pa rt of an  a ir cr af t s uch a s  an airc ra ftdo oror al anding  gear  com po ne n t.Due toc on s i dera ti on s of  si ze , wei ghta ndelectro magneticint e rfer en ce  it ishighly desira bl e to perfo rm  th e prox i m ity swit ch function using a sin g le fibe r o pticlink  and a fi ber  optic  sw i tch.
I n thepastan  op t i cal f i b er  ha sbeen useda s  th e com mu nica tion li nk to an electrica l  pr oximity switc h a nd s u p po rte le c tro ni c s.T h e state of theswitch isco n ve rted backi nto  a  pulseof ligh t whi c h is tr ansmitted  back thr ou gh t h e  op tical fibe r and de tected at the s o ur ce en d o f thefi ber  link . This met hod r equire sa high  powe ropticalenergy source and compl icated  supp ort  electron ics atthe locat ionof the pro xim ity  swit ch. In ad diti o nele c trica l pr o ximity sw i tc hes g en erate elect r o m agn eticint e rferen ce w hich is undesirab l e in an aircra ft e n v iro nme n t.
T hu s a need exist s f or a  passive  p roximity sw itch tha to perat es wit h a si ngle fi b e ro ptic l ink.  1.  Field of  th eI nventio nTh e  prese nt i nv ention  relat e s to a  technique for i mprov i n g lig h tin g-upco ntrol f o r alaser.
2.Related Bac kgroun d Ar t
Ina laser  b eam pr int er  apparatus or the li ke fo r recor di ng a n i mage b y an e lectr opho to gra phic proc e s s, it  i s  ne cess ary t oscan  a photos e nsitivemem b er with  a  la s e r beam to f orm an ima ge.  In p a r ticular, t h e st a bl e  rota ting s peed c ontrolf orarotarypol y g on mirror  for defl e cti ng  a l aser bea mis i mp ort an t.
In general,in order  to perf o r m cons tan t  spe e d rota ti on control f or aro t ary pol y g onmirrord riv ing  mo tor,  th erei s a method (PLL controlmeth od) f o r c ontro lling  a 
 delay_period to_compensate for this as_the write_head_changes tracks_on_the disk. Nor_can the NEC_technique be used with_constant density recording,_which_requires the delay period to change dynamically as a function of the bit rate.
In_Stout,_"Winchester Electronic_Functions_Fit_on Four High-Speed Chips," Electronics,_June 16, 1982, pp. 117-123,_at 122,_there is described a National Semiconductor chip which_generates_a precompensation delay_internally, with a period which is externally programmable for_0 to 20nS in 2nS steps._External programmability alleviates_some_problems_with the NEC chip,_but the delay period is still_specified in terms of an absolute_number of nanoseconds which does not change_as a function of the bit_rate. The National technique also_requires many_I/0 pins to implement and_requires the use_of an_external reference frequency_source. The method by which the_delay is actually_generated is not disclosed. The invention_disclosed_herein relates generally_to_proximity_switches and_more particularly to_proximity_switches that_utilize_fiber optics. There is a specific_need_in aircraft to sense the proximity of_some movable part of_an_aircraft such as an_aircraft door or a landing_gear component. Due to considerations of_size, weight_and electromagnetic_interference it is highly desirable to perform the proximity switch function_using a single fiber optic link_and a fiber optic_switch.
In the_past_an optical fiber_has_been used_as the communication link to an electrical_proximity switch_and support electronics. The state of_the switch is converted_back_into a pulse of light which_is transmitted back through the optical_fiber and detected at the_source_end_of the fiber link. This_method requires a high power optical_energy source and_complicated support electronics at the location of_the_proximity switch. In addition electrical proximity_switches_generate electromagnetic interference which is undesirable_in_an_aircraft environment.
Thus a need exists_for a passive proximity switch that_operates with a single fiber optic link. 1. Field_of the Invention
The_present invention relates to a_technique_for_improving lighting-up control for a laser.
2. Related Background Art
In a_laser beam_printer apparatus or_the like for recording an image by an electrophotographic process,_it is necessary to scan a photosensitive_member with a laser beam to form an image. In particular,_the stable rotating speed control for a rotary_polygon mirror for deflecting a laser beam_is important.
In general, in_order_to perform constant speed rotation control for_a_rotary_polygon_mirror driving motor,_there is a_method (PLL control_method) for_controlling a