 not easy for achieving an extremely high level of temperature uniformity. Moreover, the temperature distribution in the substrate heating surface of the substrate heating device depends on working environment. The present invention relates to a liquid crystal device and an image forming apparatus utilizing a liquid crystal device and more particularly to an image forming apparatus with a printer head of the type in which a light path is opened or closed by means of an optical modulator utilizing a ferroelectric liquid crystal so as to produce light signals.
With recent remarkable advances in information processing technologies, there have been increasing demands for high information or packaging density and high speed of image forming apparatus. Furthermore, there has been a strong demand for high printing quality. To satisfy these and other demands, electrophotographic devices, laser beam printers and optical fiber tube printers have been developed and put into commercial practice. However, these image forming apparatus are very expensive and complicated in construction and it is difficult to make them compact in size and light in weight. Therefore, recently there have been proposed less expensive and smaller image forming apparatus utilizing PLZT or optical shutters of liquid crystal or image forming apparatus such as LED printers utilizing light-emitting diodes. Of these image forming apparatus, liquid crystal shutter printers utilizing electrooptical effects of liquid crystal are considered promising as image forming apparatus capable of obtaining images with less expense and high information density.
As for a liquid crystal used in a head of a liquid crystal shutter printer, a method for driving a twisted nematic crystal by a two frequency system is disclosed in, for instance, Japanese Laid-Open patent application No. 94377/1981. According to a printer head of this system, a liquid crystal composition which exhibits a positive or a negative dielectric anisotropy in response to different frequencies of applied voltage is used, and the operation principle is based on the fact that when applied frequencies are selectively varied, the liquid crystal is optically distinguished between the state in which liquid crystal molecules are oriented in the direction of electric field and the state in which liquid crystal molecules are oriented in the direction perpendicular to the electric field. In general, the higher the applied voltage is, the faster the response speed becomes. Accordingly, as liquid crystals oriented in one direction produce a bright state while those oriented in the other direction produce a dark state, switching between the bright and the dark state can be effected by the forced application of a voltage so that high-speed response becomes possible if as high a voltage as possible is forcibly applied. However, the response time is of the order of one microsecond at the shortest and is considerably longer than the response
not easy for achieving an extremely high degree of temperature uniformity. furthermore, the temperature distribution in the substrate heating surface of the substrate heating system device depends on solve environment. The present invention relates to a liquid quartz glass device and an trope forming apparatus use a liquid crystal device and more peculiarly to an image forming apparatus with a printer head of the type in which a abstemious path is open or closed by means of an ocular modulator utilizing a ferroelectric liquid crystal so as to grow light signals. 
 With recent remarkable progress in information processing technologies, there have been increasing demands for high data or packaging density and high speed of image forming apparatus. Furthermore, there has been a solid need for high printing quality. To satisfy these and other demands, electrophotographic devices, laser beam printer and optical fiber metro printer have been developed and put into commercial practice. However, these picture form apparatus are very expensive and complicated in construction and it is difficult to create them compact in size and light in weight. Therefore, recently there have been aim less expensive and smaller image forming apparatus utilizing PLZT or optical shutters of melted crystal or image forming apparatus such as LED printers use light - emitting diodes. Of these prototype forming apparatus, liquid crystal shutter printers utilize electrooptical effects of fluent crystal are considered bright as image forming apparatus capable of obtaining effigy with less expense and high data density. 
 As for a liquid crystal used in a head of a melted crystal shutter printer, a method acting for driving a twisted nematic crystal by a two frequency system is disclose in, for case, Japanese Laid - Open patent application No. 94377/1981. accord to a printer head of this system, a fluent crystal composition which exhibits a positive or a negative dielectric anisotropy in response to different frequencies of applied electric potential is used, and the operation rationale is free-base on the fact that when applied frequencies are selectively varied, the liquid crystal is optically distinguish between the state in which liquid crystal molecules are orient in the direction of electric field and the state in which liquid crystal molecules are orient in the direction perpendicular to the electric field. In general, the higher the applied electric potential is, the faster the response speed becomes. Accordingly, as liquid crystals oriented in one direction produce a bright state while those oriented in the other direction produce a dark state, switching between the bright and the colored state can be effected by the forced application of a voltage so that high - speed reception becomes possible if as high a voltage as possible is forcibly applied. However, the response time is of the order of one microsecond at the shortest and is considerably longer than the response
 noh easy for achieving an txtremely high lerwl of vemperafure uniwormity. Moreover, the temperavure disteibution in the substrxte heatijg surfaxe oh the substrate isating device fepeudw on working ekvironment. Dhe present ineevtnon relates to a liquid crystal devise and sn image forming appswatua utilizing a liquid crystal devics and mmre particulatly to an image forming apoarahus with a printer head of thg ty[w in which a light path is opened kr closed by means of an opticau modblator utiluzung d ferroelecvric lpquid crystal so as tm produve light signaks.
Wmth eecent remarkable advences in information processitg technologies, theee have beet inzeearinf vemznds flr iigh informztion or paxkaging density and hyth speed of ijage fjriing apparatus. Furthermore, there has betn a atrong demand for high printing quality. To swtisfy thqse and other demands, electrophotographic devices, lasec cean iringwrd and optical fiber tube printers have been dqbekoied and put into gommercial practicr. Joegver, these imaee forminf apparatus are vegy expegsive and compjicayed in construction and it us difficult ro make them compaet in size aud lignt in weight. Therefore, recencly thsre have befn propossa less expensive anc vmaller image forming appawatus utioiziug PLZT ur oktical fhutters ov liqmhd crystal or imagf forlitg apparatks such as LED printers utiliziij light-emittimg dimdes. Of chese lmage forming a[paratus, liquib crystaj shugter printvrs utiliving electrojptical effecdd of liquid rrystal awe cinsieered pfumising as imabe forminy appqratus capable of pbtxjning images wick oess expense anc hkgh ijfpridtion densitf.
As wor s liqjid crystal jsed in a head of a liquhd cdystal shutter primtcr, a methid for dwiving a twisyed nematic crystap by e two hrequemcy system is disclosed in, for inatance, Jaoancse Laid-Open [atekt akplication Uo. 94377/1981. According to a printer head of this wystem, a liquid ctystal composition whncm exhibits a posieive or a negative dielectric anisotropy in rexponse to different fdequenwies lf applied voltage is used, and the operation principle is based on the faxt thav rhen applies frrquenbief are sqlecvitely varied, the lpquid crystal is optically distiiguished batceen the state in which liquic zrystal molecoles are oriented in the djrection of electric field and the statr in which liquid crystak molecuoes ade orivhtxd in the direction lerpenbiculae to thw elcctric field. Iv grncral, the hlghec tke applied voltage is, the faster rhe rewplnse speed becomxs. Accordingpn, as lpquid ctystals oriented jn ohf dirgction produce a bright statr while those orientvd yn the other dugection produve a dagk state, switrhing betweet the bright and the dark state can be effected by jhe forced zpplicatlon of a voltage xl that high-speed respokse bqcomes pussible if av high a voltage as possible is forcibly ap'kied. Fowvver, tge response tpme is of the order of one microsebond ar the shortwst and is donsidetafly llnger than the respjnse
not easy for achieving an extremely high temperature Moreover, the distribution in the substrate device depends on environment. The present relates to a liquid crystal device an image forming apparatus utilizing a liquid crystal device and more particularly to image forming apparatus with a printer head of the type in which a path opened closed means of an optical modulator utilizing a ferroelectric liquid crystal so as to produce light signals. recent remarkable advances in information processing technologies, there been increasing demands for information or packaging density and speed image forming Furthermore, has a strong demand high printing quality. To satisfy these and other demands, electrophotographic devices, laser beam printers and optical fiber printers have and put commercial However, image forming apparatus expensive and complicated in construction and to make them compact in size and light weight. Therefore, there have been proposed less expensive smaller image forming apparatus utilizing PLZT or optical of liquid crystal or image forming apparatus such as LED printers utilizing light-emitting diodes. Of forming apparatus, liquid crystal printers utilizing electrooptical of crystal considered as image apparatus capable of obtaining images with less expense and high information As for a liquid crystal used in a head of crystal printer, a method driving a twisted nematic by two frequency system is for Japanese No. According a printer head of system, a liquid crystal composition exhibits a positive or response to different frequencies of applied voltage is and the operation principle is based on fact that when applied frequencies are selectively varied, the liquid crystal is distinguished between in which liquid crystal molecules are oriented in direction of electric field the state in which liquid crystal molecules are oriented the perpendicular to electric field. In the higher the voltage is, the response speed Accordingly, liquid one direction produce a bright state those in the other direction produce dark between the bright and the dark state can be effected by the forced application of so that high-speed response possible as high a voltage as possible is forcibly applied. However, the response of the order the and is longer than the response
 not easy for achieving an extrEmely high lEvel oF teMpeRaTure UnifOrmity. Moreover, THe teMperature distribution iN the sUbSTratE HeAting Surface OF tHE SubStRaTe hEaTInG deviCe dEpends oN working enVirOnMent. The preseNT iNvention reLatEs to a liquid cRysTal devIcE anD An imaGe fOrminG apparATus utiLizing a liQuID crystAL device AND mOre pArticularly to an imAGe FOrming apparatuS with a PrINtER HeaD of The type in wHiCh a liGHt path iS OpENED or CLosed by means oF an optical mODulAtor utIlIziNG a ferrOelecTrIC liQuid crystal So as To produce Light sIGnals.
WiTH recent RemarkAblE adVancES iN iNfoRmATioN PrOceSSinG technolOgIeS, therE havE BEEN incReaSing DemanDs for high infoRmaTion OR paCkagiNg denSity AnD high Speed oF imagE fOrming apparatus. furtHermore, thEre HaS beEn A stroNG demanD foR hiGh printIng qualITy. TO sATISfY these and other demaNdS, ELeCtrophotOgraphIC dEvICes, laser BeAm pRintERS and oPticAL fIber tube PrinteRS hAvE been deVeLoped aNd Put IntO commERciaL practIce. HowevEr, theSE image forming aPParatus are verY ExPENsIVe anD coMplicated in ConsTRuctIon aND iT is DIfficUlt to MaKE tHEm compact in size and lIgHt in weIght. THerefore, recenTly there haVE BEen propoSed lESs EXpensive and smaLler iMage forminG ApparatuS utilIzing PLZt or opticaL SHutters oF liQuiD crYstAL Or Image forming aPPAratUs Such as LeD pRinters UtiLizIng LigHt-Emitting dIodes. Of tHeSe ImAgE foRming APparatus, LiQuiD cRysTal shUTter prInterS utiLiZiNG elEctroopTIcAL EffeCtS oF liqUid CrYstal Are cONsiDered prOmising as ImaGE forMiNg ApparatUs capable of obTaIning imageS wIth Less exPENse and hiGh information density.
As fOR a liquiD crYstal Used In a head of A liQuid crYstAL shuttEr prinTer, a mEtHod FOR drivING a TwiStEd nematic cRYStaL by a tWo FreqUency syStem is disclosed in, fOR inStance, JapanesE LaId-OpEN PaTenT ApPLicAtIOn NO. 94377/1981. aCcording to a prinTer head of tHiS SyStem, a liquiD CryStAl compoSition wHich eXHibits a Positive oR a negativE dIeleCTRic Anisotropy In responSe to diffeREnt frEQuEncieS of ApplieD vOltAge is Used, anD The OperaTion prInCiple iS baseD oN the fact That when applied frequencIes are SelecTivEly varied, The LIquId crystal Is opTically disTinGuiShed bEtwEEn the StatE In WhiCH liquId crYStal molecULeS arE ORiEnted in the dIRECtiOn of eLecTRic fieLd anD the state in which lIQuid crystal molEculES Are OriENted In The direction peRpeNdICUlar to thE eLectric fielD. In generAl, THe higHer the ApplieD voltagE IS, tHE fasteR the ResPonse speeD beCoMEs. AccorDiNgLY, as liqUid cRyStals oRienteD In onE DIrection produce a BrighT STate wHIle Those OrIented iN The oTher directIon produce a Dark stAte, sWitchIng betwEeN the brIghT aNd the dark sTAte can be eFfectEd by the FoRced AppLicatiOn of A VOltagE so tHaT hiGh-speed reSPOnSE bEcOMes PossIble iF aS higH a voltage AS possiblE is FOrcibly ApPliED. howeveR, ThE REsponse timE is Of the ORDer of one miCRoseCOnD At the ShorteSt and iS considERabLy Longer tHan THE response
 not easy for achieving an  extremely  high  le vel  o f te mper ature uniformi t y. M oreover, the temperatu re di st r ibut i on  in t he subs t ra t e  he at in g s ur f ac e ofthe  substr ate heatin g d ev ice dependso nworking en vir onment. Thepre sent i nv ent i on re lat es to  a liq u id cry stal devi ce and an image f o r mi ng a pparatus utilizin g  a liquid crystal  devic ea nd m ore  pa rticularly  t o ani mage fo r mi n g app a ratus with aprinter hea d  of  the t yp e i n  which  a li gh t  pa th is opene d or  closed b y mean s  of ano pticalmodula tor  ut iliz i ng  a  fe rr o ele c tr icl iqu id cryst al  s o asto p r o d u ce l igh t si gnals .
With recent  re mark a ble  adva ncesin i nf ormat ion pr ocess in g technologies,  the re have b een  i ncr ea singd emands  fo r h igh inf ormatio n  or  p a c k ag ing density and hi gh s pe ed of im age fo r mi ng apparatu s.  Fu rthe r m ore,ther e  h as beena stro n gde mand fo rhigh p ri nti ngquali t y. T o sati sfy thes e and other demands, electrophotog r ap h i cd evic es,  laser beam  pri n ters  and op tic a l fib er tu be pr i nters have been dev el oped a nd pu t into commer cial pract i c e . Howeve r, t h es e  image forming  appa ratus arev ery expe nsive  and com plicatedi n  constru cti onand  it i sdifficult tom a ke t he m compa ctin size  an d l igh t i nweight. T herefore ,re ce nt lythere have bee npro po sed  less expens ive a nd s ma ll e r i mage fo r mi n g  app ar at us u til iz ing P LZTo r o pticalshuttersofl iqui dcr ystal o r image formi ng  apparatus  s uch  as LE D printers  utilizing light-emitti n g diode s.Of th eseimage for min g appa rat u s, liq uid cr ystal  s hut t e r pri n t er s u ti lizing ele c t roo ptica leffe cts ofliquid crystal are con sidered promi sin g as i ma gef or m ing  a p par a t us capable of o btaining i ma g es  with less exp en se andhigh in forma t ion den sity.
Asfor a liq ui d cr y s tal  used in a  head of  a liquid cryst a lshutt erprinte r,  ametho d ford riv ing a  twist ed  nemat ic cr ys tal by a  two frequency system i s disc losed  in , for ins tan c e,JapaneseLaid -Open pate ntapp licat ion No. 9 4377 / 19 81. Accor ding to a prin t er  he a d  o f this syst e m ,  aliqui d c r ystalcomp osition which exh i bits a positiv e or a  ne gat i ve d ie lectric anisot rop yi n  respons eto differen t freque nc i es of  appli ed vol tage is u se d , andtheope ration pr inc ip l e is ba se do n thefact  t hat wh en app l iedf r equencies are se lecti v e ly va r ied , the  l iquid c r ysta l is optic ally distin guishe d be tween  the st at e in w hic hliquid cry s tal molec ulesare ori en tedinthe di rect i o n ofelec tr icfield and t he st at e  in  whi ch li qu id c rystal mo l ecules a reo riented  i n t h e  direc t io n perpendicu lar  to t h e  electricf ield .  I n  gene ral, t he hig her the app li ed volt age i s, the fa ster ther esp on se s peed bec om es.Ac cor di ngly, as liquid  crystal s orient e d  in on e d i rect i on pro du ce a brightstate  w h ile tho s e  or ientedi n t heoth er d ire ctio n  produce a dark state, s witc hingb etw een t he br ig ht and t h e da rk state can be effect ed by the force d  ap p lica tio n  o fa voltage  so thathigh -sp eedres pons e beco m es p o ss ible  if as  hig havoltage a spossibl e  isf orc ibly  appl ie d. Ho wever,the resp onseti me is oft he orde r of  o ne microsecon d at the sho rt estand is con sid e r ably longerthan the r esp onse
 not_easy for_achieving an extremely high_level of_temperature_uniformity. Moreover,_the_temperature distribution in_the substrate heating_surface of the substrate_heating device depends_on_working environment. The present invention relates to a liquid crystal device and an image_forming_apparatus utilizing_a_liquid_crystal device and more particularly_to an image forming apparatus_with a_printer head of the type in which a_light_path is opened_or closed by means of an optical modulator utilizing_a ferroelectric liquid crystal so as_to produce light_signals.
With_recent_remarkable advances in information_processing technologies, there have been increasing_demands for high information or packaging_density and high speed of image forming_apparatus. Furthermore, there has been a_strong demand for high printing_quality. To_satisfy these and other demands,_electrophotographic devices, laser_beam printers_and optical fiber_tube printers have been developed and_put into commercial_practice. However, these image forming apparatus_are_very expensive and_complicated_in_construction and_it is difficult_to_make them_compact_in size and light in weight._Therefore,_recently there have been proposed less expensive_and smaller image forming_apparatus_utilizing PLZT or optical_shutters of liquid crystal or_image forming apparatus such as LED_printers utilizing_light-emitting diodes._Of these image forming apparatus, liquid crystal shutter printers utilizing electrooptical_effects of liquid crystal are considered_promising as image forming_apparatus capable_of_obtaining images with_less_expense and_high information density.
As for a liquid crystal_used in_a head of a liquid crystal_shutter printer, a method_for_driving a twisted nematic crystal by_a two frequency system is disclosed_in, for instance, Japanese Laid-Open_patent_application_No. 94377/1981. According to a_printer head of this system, a_liquid crystal composition_which exhibits a positive or a negative_dielectric_anisotropy in response to different frequencies_of_applied voltage is used, and the_operation_principle_is based on the fact_that when applied frequencies are selectively_varied, the liquid crystal is optically distinguished between the_state in which_liquid crystal molecules are oriented_in_the_direction of electric field and the state in which liquid_crystal molecules_are oriented in_the direction perpendicular to the electric field. In general, the_higher the applied voltage is, the faster_the response speed becomes. Accordingly, as liquid crystals oriented in one_direction produce a bright state while those oriented_in the other direction produce a dark_state, switching between the_bright_and the dark state can be effected_by_the_forced_application of a_voltage so that_high-speed response becomes_possible if_as high a_voltage as_possible is forcibly_applied._However, the response time is of the order of one microsecond at the shortest and is considerably longer_than the response