US3810193A

US3810193A - Bitting card for data recording

Info

Publication number: US3810193A
Application number: US00862417A
Authority: US
Inventors: K Metcalfe; I Smith
Original assignee: SECRETARY SUPPLY AUSTRALIA
Current assignee: SECRETARY DEPARTMENT OF SUPPLY AU; SECRETARY SUPPLY AUSTRALIA
Priority date: 1968-09-30
Filing date: 1969-09-30
Publication date: 1974-05-07
Anticipated expiration: 1991-05-07
Also published as: GB1287463A; NL6914796A; AU4409368A; FR2019244A1; CA969229A; DE1949395A1; DE1949395C3; SE344514B; BE739612A; DE1949395B2; AU419759B2

Abstract

A method of data recording on bitting cards or sheets or other material which consists in traversing the material with a recording element on which is impressed an electrical signal which does not exceed 70 volts, the surface on which the recording takes place having a bulk resistivity not exceeding 1016 ohm cm.2 whereby to avoid holding of unwanted electrical characteristics on the sheet and whereby recording takes place without corona or gas effects present when high voltage is used, and then developing the resultant image to produce a permanent recoverable record of the impressed signal.

Description

Unite States Patent [191 Metcalfe et a1.

[ BITTINC CARD FOR DATA RECORDING [75] Inventors: Kenneth A. Metcalfe; Ian E. Smith,

both of Lockleys, Australia [73] Assignee: The Commonwealth of Australia, c/o

The Secretary, Department of Supply, Canberra, Australia [22] Filed: Sept. 30, 1969 [21] Appl. No.: 862,417

[30] Foreign Application Priority Data Sept. 30, 1968 Australia 44093/68 [52] US. Cl... 346/74 ES, 101/DIG. 13, 117/37 LE, 117/93.4 A, l18/DIG. 23

[4 1 May 7,1974

Primary Examiner-Howard W. Britton Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [57 ABSTRACT A method of data recording on hitting cards or sheets or other material which consists in traversing the material with a recording element on which is impressed an electrical signal dOeS not exceed volts, [58] Fie'ld 'f'g 346/74 ES 74 the surface on which the recording takes place having 1l8/DIG a bulk resistivity not exceeding 10 ohm cm. 101 whereby to avoid holding of unwanted electrical characteristics on the sheet and whereby recording takes 56] References Cited place without corona or gas effects present when high voltage is used, and then developing the resultant UNITED STATES PATENTS image to produce a permanent recoverable record of 2,053,494 9/1936 Plrie 117/37 LE h impressed i l 2,877,133 3/1959 Mayey ll8/DIG. 23 3,270,637 9/1966 Clark 1l8/D1G. 23 1 Claim, 11 Drawing Figures SIGNAL DEVELOPER GENERATOR 3 4- DEVELOPED STYLUS IMAGE POLARISABLE k SURFACE {3/ l l RECORDING SHEET SHEET TRAVEL PAIEIIIEIIIIII I I974 3810.193

SHEET 1 0f 4 DEVELOPER SUPPLY sIGNAL GENERATOR I DEVELOPING ROLLER 7 9 6 STYLUS POLARISABLE 5 4 ,4 5 IX SURFACE 13J l I! I a DEVELOPED S P D ING IMAGE 4 I SHEET TRAVEL ROLLER 17'15 1 l2 9 I /O sTYLus n I L I II i++ EjIB 4- I /6 u DEVELOPING\ \REGORDING ROLLER RsElgfiisED SHEET DEVELOPED g IMAGE 1* 1b ,3

DEVELOPER SUPPLY sIGNAL GENERATOR I DEVELOPING 22 ROLLER 4 E3 STYLUS POLARIsABLE ZR 1 SURFACE A as REGORDING SHEET 3 z SHEET TRAVEL I15 3 PATEMEU MM 7 mm 3,810.19

SHEET 2 [1F 4 SIGNAL DEvELoPED IMAGE POLARISABLE SURFACE r RQLLEEQ \RECORDING SHEET 36 SHEET I16 1 TRAVEL DEVELOPING SIGNAL ROLLER GENERATOR DEVELOPED 4/ IMAGE SIGNAL SPOgEIGHT LASER LIGHT BEAM 5 46 z x \RECORDING SHEET DEVELOPING ROLLER SIGNAL GENERATOR PATIiI-I'IEIIMAY 7 1974 3,810,193

SHEET 3 OF 4 GENERATOR STY LU S RECORDING SHEET SHEET TRAVEL PE RFORAT E D POLARISABLE SURFACE 67 ROLLER SIGNAL GENERATOR DEVELOPED 73' SIGNAL ROLLER I EVELOPING D W ROLLER RECORDING SHEET DEVELOPED LAYER STYLUS SHEET TRAVEL SIGNAL GENERATOR 82 DEVELOPER CONTAINING 8! SHEET x DEVELOPED STYLUS SIGNAL (1:: SHEET TRAVEL ROLLER PATENTEDIIAY H914 3310.193

SHtEI L; (If 4 SIGNAL GENERATOR 1 MULTIPLE HEAD RECORDER DEVELOPER APPLICATOR RECORDED SIGNAL TRACKS -DEVELOPED K TRACKS sENsER PRINTER /54 /o'5 SENSING DEVELOPED L k f #4 l 3:: I ma /0/ SHEET RECORDING n TRAVEL SHEET I'll: 11

. 1 BITTING CARD FOR DATA RECORDING This invention relates to a bitting card for data recording and the method of recording.

Many forms of data recording are already in use, these consisting usually of a medium on which the information is recorded either directly or in coded form and is retrievable by suitable mechanisms.

Certain difficulties exist in the storage and retrieval of information particularly where space is at a premium and where the recording must be of a permanent nature.

Other problems exist where large quantities of data are contained on a bitting card such as on a card containing say 90 by 12 bits which must be recorded in their relatively small standardised space and the information of which must be readily retrievable yet of a permanent nature and easily read without destruction of the image through constant use.

The object of the present invention is to provide an improved bitting card for data recording in which the recorded data is applied on a card or other medium by modulating an electrical field and effecting a deposition of a developer in proportion to the field intensity or characteristic.

With this type of recording however certain difficulties exist chief of which is the avoidance of artefacts such as are caused for instance where relatively'high voltages are used to produce the modulated field, which voltages can result in lateral distortion over the "surface such as by the formation of lichtenberg figures or the like.

It will be realised that as electrostatic recording as practiced heretofore involves charge transfer from the recording stylus to the recording member, i.e.,-from a metal electrode to a semiconductor or insulating sheet, there are at least two possible ways to transfer the charge.

According to the first method the stylus is not in contact with the recording member or is in contact only intermittently due to surface roughness. A relatively high stylus voltage is required (greater than SOQ Volts) which causes a gas discharge between the stylus and recording sheet resulting in charge transfer and storage due to collection of the ionised gas. This method has the following disadvantages:-

a. The recorded line trace is broader than the diameter of the stylus due to mutual repulsion of the ions within the discharge,

b. The stylus to recording sheet distance is critical and must be maintained to within close limits as this effects the discharge onset,

c. Apart from' the recording signal voltage, a bias voltage must be applied to the stylus to maintain the stylus at a point just below that voltage required to initiate discharge this voltage is dependent on the gap.

Generally the above method of signal recording provides low resolution which has little practical use. The positive voltage signal produces a different pattern to the negative voltage.

One of the objects of this invention is to provide a method of and means for producing data on bitting cards in which there will be a minimum of artefacts and thus a relatively true signal.

A further object of the invention is to provide a surface which can readily accept the bits as they are produced and will be free of artefacts caused through high voltage fields.

A still further object is to provide a method whereby the signal will be immediately developed into a permanent form which is readily translated when required.

A yet further object is to provide a method in which recovery of the recorded data can be readily effected by the superimposing of retrieval information on the bitting cards.

Other objects of the invention will be apparent from the following description which is made in some detail but it is to be clear that the invention need not necessarily be limited to this.

According to our invention the signal is recorded by means of a relatively low voltage on a surface which consists of a base of a relatively conductive material such as cellulosic film on which base is supported a readily polarisable thin film or layer of a substance such as polyvinylidene chloride, the data bits being preferably produced by stylus medium which operates preferably in the presence of a developer of the electrophotographic type which is capable of depositing on the relatively thin polarisable film in proportion to the signal strength.

We have found that materials classified as medium to poor insulators produce acceptable developed traces at a much lower voltage than good insulators.

Thus a signal may be recorded on a polyvinyl butyral at a stylus voltage of 10 volts whereas mylar, which is a better insulator, requires at least volts to produce a visible signal.

Another important consequence of the use of the me- .dium to poor insulators for a recording member is freedom from static charges. Good insulators such as mylar polystyrene and polyethylene when developed in a liquid developer produce pigmentation due to unwanted static charges.

This inherent static is relatively insignificant on the materials which we have found suitable for low voltage stylus recording.

We have found that signals produced on cellophane film are unaffected by the thickness and type of insulation interposed between the recording surface and the backing electrode. For instance if the cellophane film is placed on a mylar film on a metal backing, the developed signal produced with this arrangement is identical to that produced without the interposed mylar film. The practical importance of this phenomenon is that the thickness of the recording member is not materially important with a relatively low-value insulating material as the recording action appears to be the result of an action within the relatively low-insulating polarisable material itself, not dependent on a flow through the film itself, although dissipation of charge build up is sometimes necessary.

The apparatus for carrying out the invention can therefore be of a very simple nature in that it is only necessary to provide a thin polarisable film which is preferably wetted with a liquid developer comprising a carrier liquid of high electrical resistivity such as 10 ohm cm. and having a dielectric constant less than 3 in which is suspended a finely divided developer medium capable of depositing under the actual electrical field, or latent electrostatic field, produced by the stylus medium, the developer material being formed according to any of the already known formulations but preferably being of the type in which the developer medium is itself of a magnetisable medium or other medium which can be sensed by a field when retrieval of information is required.

During the placing of the bits on to the bitting card it is possible for instance to modulate the stylus or a series of styluses so that as well as the signal, retrieval information such as a regular frequency can be included on the card or medium.

As deposition is in accordance with the strength of the field it will be obvious that for instance a hill and dale signal can be produced and this could also at the same time be transversely modulated by an appropriate movement of the stylus or by deflection of the field by electrical means, and of course instead of simply using a stylus this can be used independently of a further recording medium which can be placed adjacent to the stylus position to record other data. By utilizing a compound developer in which the particles which are to be deposited are pre-treated with a control agent in a manner already outlined in earlier Patents of ours, it is possible to cause deposition of positive and negative particles quite independently by two stylus means or to deposit one under control of a stylus or series of styluses and to deposit the other which can be a retrieval data signal by means of an opposite polarity.

It will be realised that the reading back of such information can then be carried out by two different sensing or transducing devices because owing to the difference in the deposited medium on what could be termed two tracks or on two patterns, one such medium can supply the bits which have been recorded and the other can be used for instance by means of stepper motors or the like to immediately pick up any particular position on the bitting card for reading of the data at that location. lt will be realised that the deposition of material under an electrical field while the medium is wetted with the developer allows the thickness of deposit to be varied in accordance with the strength of the field and therefore mechanical retrieval means can also be used for recovery of the information from the bitting card. Retrieval can of course also be effected by producing a magnetic field which would polarise or energise the deposited developer so that a transducing head can readily read the signal, and as referred to earlier in this specification because the bits can be formed by the physical deposition of a developer medium which can be permanently fixed on the card or other medium it will be realised that a strong and durable bitting card can be produced which can stand a considerable amount of handling without appreciable deterioration. The device can be used to develop a single spiral on a disc or to develop a helix on the drum as well as producing information on cards or the like.

It has been found in practice that using the stylus on a surface of the type described a voltage of from say to 40 volts is sufficient to give an adequate developed deposition whereas with previously used devices it has been usual to use high voltages with a result that'these have produced lichtenberg figures and other electrical problems such as transverse creep which however is verymuch less likely to occur with the low voltage used in this invention, the low voltage of course being possible by using a thin film of a relatively readily polarisable material, preferably on a base which is relatively more conductive than the insulating but polarisable recording medium.

The low voltage also ensures that artefacts are not produced by voltage spread through air transfer which again is a-problem with higher voltages and as the recording in the present instance can be carried out beneath an insulating liquid in which the developer medium is itself carried it will be realised that a further protection at the recording locality again exists because the recording can be carried out under the protective liquid.

ln explanation it can be stated that a highly insulating material will hold static charges for long periods, and materials such for instance as mylar which have a bulk resistivity of about 10 ohm cm. squared are not suitable for this invention because of their inability, due to the high electrical resistance, to discharge unwanted artefacts and acquired charges.

On the other hand, materials such as cellophane, a regenerated cellulose, having a bulk resistivity of about 10 ohm cm. squared have a sufficiently high bleed rate to ensure removal of unwanted charges yet will accept a signal on quite a low voltage, say varying between 0 and 40 volts. Similarly cellulose acetate with a bulk resistivity of 10 to 10 ohm cm. squared is very suitable.

We have found that with materials having a bulk resistivity between 10 and 10 ohm cm. squared the recorded image can be held sufficiently long to allow the development to be carried outremotely from the recording locality, but with materials more conductive than this the recording should be carried out under the developer itself or in a position where the recording stylus or medium is wetted with the developer.

Thus relatively conductive bitting cards can be used under selected conditions with a stylus in contact provided that as the resistivity decreases there is an insulating liquid film at the stylus lcality which has the effect of spacing the stylus from the material sufficiently to ensure that effective recording at low voltage can take place. Thus a range is available under selected conditions varying from a conductive metal surface to a material having a bulk resistivity up to l0 ohm cm. squared. 1

In order however that the invention will be fully appreciated embodiments thereof willnow be described with reference to the accompanying drawings designated FIGS. 1 to 11, these being illustrative of the principles of the invention.

In the drawings:-

FIG. 1 illustrates one example of the invention in which the recording sheet 1 comprises a supporting web 2 of a relatively conductive material which in this case may be cellophane or the like, which web is coated with a thin layer of a polarisable material 3 having higher insulating properties, which materialcould for instance be polyvinylidene chloride, for example to a thickness of 0.000] inch to 0.001 inch.

Such a composite sheet generally forms the basis of this invention, because for highly effective recording it is desirable that a polarisable surface be supported on a relatively more conducting base although this is not always necessary. According to this invention the polarisable surface forms a very important feature as it allows the low voltage characteristic to be used to give highly satisfactory recording as explained earlier herein.

The recording sheet 1 is carried on a grounded supsupported on a grounded sheet along its length, the recording sheet 1 moving past the stylus 5 which forms the recording means whereby the signal is impressed on the polarisable surface.

The recording stylus 5 terminates in a conductive or semiconductive point or filament preferably in contact with the polarisable material 3 on the sheet 1 although it could be raised slightly therefrom. The sheet 1 is moved in relation to the stylus during recording.

A voltage is applied to the stylus in the order of 1 to 70 volts but this voltage is varied according to the signal and a varying surface charge is thus produced on the insulator surface which can then be developed to render it visible one make it suitable for recording, by means of a liquid developer which in the case shown is effected shortly after the signal has been impressed on the insulator surface as a latent electrostatic image.

A developing roller 6, is in contact with the polarisable surface, and this roller 6 can be fed from a developer supply tank 7 through a suitable feed tube 8 which can have metering means within it to ensure that the developer roller 6 is maintained at the correct degree of wetness.

As shown in the centre track of FIG. 2 the developer deposit 9 varies in width and in thickness according to the applied voltage, this being obtained from the recorded signal 10 which varies in amplitude and also frequency according to the data which is being impressed.

It will be realised of course that the polarisable surface 3 can take various forms and may for instance be formed of polyethylene, or ethyl hydroxy ethyl cellulose, or polyvinylbutyrate, or polyvinylalcohol, or cellulose acetate, or nylon or one of the phenolic resins, but instead of using a polarisable surface of this nature it could be composed of a semi-conductive material such as zinc oxide embedded in a base of insulating characteristic so that the zinc oxide surface still maintained the electrical isolation of particles necessary to prevent spread of the image carried on the polarisable surface.

It would also be possible to use a ferroelectric material such as barium titanate, or it could include conductive material such as graphite, metal powder, or treated pigments, or even magnetic materials such as magnetic iron oxide, but in these cases again, with the form shown in FIG. 1, it is essential that the material be embedded in a film of insulating material having a sufficiently high degree of insulation to prevent loss of the impressed latent image or by lateral transfer of the image over the surface which could take place if the conductive or semiconductive particles were not insusents a timing or retrieval sequence produced by spaced signals on the stylus 14 which can be used in association with a stepper motor for information retrieval. The track 13 shows how with a laterally movable stylus 15 an undulating track can be produced.

The movement could be obtained from a piezo electric wafer 16.

In FIG. 1 a signal generator is designated 17.

FIG. 3 is a figure corresponding to FIG. 1 but in this case showing the stylus 20 positioned to record the signal in the presence of a developer fed from a developer supply tank 21 through a metering member 22 to a developer 23, the stylus being connected to a signal generator 24, the recording sheet being designated 25. In this case the roller 4 is replaced by an earthed electrode 26, but this earthing is not always necessary in any of the embodiments, depending on the conductivity of the polarisable material. With more conductive materials the film itself will receive the signal probably by rearrangement of the electron holesand allied factors due to the locally applied signal.

It will be realised that the developer roller 23, because it is in contact with the polarisable surface 27, will have a quantity of liquid along its forward nip 28 that the actual recording point of the stylus 20 will be disposed in this and will therefore be submerged in the developer liquid. The recorded track is designated 29.

FIG. 4 again relates generally to a similar system to that used in FIG. 1 but in this case the stylus 30 itself is hollow and contains the developer liquid 31 and developer flows through the duct 32 of the stylus to the polarisable surface.

In such a case the field can be used to control the flow of developer from the stylus 30 because obviously the developer 31 can be so selected that a greater feed takes place with a field which encourages flow through the duct, and therefore again in this case the developed image 33 which is produced simultaneously with the signal being applied to the stylus 30 is an exact copy of the signal impressed by the signal generator 34. The recording sheet is designated 35 and the backing roller 36. The polarisable surface is indicated by 37.

In FIG. 5 a modified system is.shown in which instead of utilising a stylus, a spot of light or a laser beam is generated in the unit 41 and is modulated by the signal generator 42 but in this case the polarisable surface 43 contains a photoconductor embedded within it as previously stated, so that while there is still an insulator surface there is present in the surface a photoconductor which is influenced by the light or laser beam 40 to change its characteristic so that the signal impressed on the polarisable surface 43 will result in a modulated latent image 44 being produced on the photoconductor surface which is then developed by the developer which in this case is shown as applied from a roller 45 of absorbant material which is pre-wetted with the developer liquid. A rest 46 is used. The developed image is designated 47.

Instead of using zinc oxide such materials as lead iodide, cadmium selenide or the like may be used, and in any of the aforesaid embodiments a biasing voltage could be applied to the rollers 4 or 30 or the backing

member

26 or 46. During development a conductive pigment, for example phthalocyanine blue or graphite could be used which would enable the image to be read out conductively.

FIG. 6 shows how a disc 50 can have a polarisable surface on it and in this case the stylus 51 produces the latent electrostatic image 52 on the disc 50 and this image is then developed by the developer roller 53, to produce the developed track 54 both the stylus 51 and the roller 53 being mounted on an arm 54 arranged to move across the disc as shown by the arrow 55 so that in this case the message is recorded by the track 54 in spiral form on the disc. The stylus is again fed from a suitable signal generator 56.

FIG. 7 is a view again showing the stylus 60 and signal generator 61 associated with a polarisable surface 62 but in this case the surface 62 contains a large number of pores 63 or holes through its thickness at regular intervals and fine spacing, for example 200 dots per inch.

In such a case the sheet 64 could carry developer 65 mainly in the pores or apertures and would give a patterned read-out modulated by the hole spacing as well as by the signal 65 generated by the stylus 60. Thus a grained or perforated member or an engraved plate can have the signal modified by the pattern of the holes or graining or the like where this is desirable for reproduction or other purposes such for instance where a particular frequency requires to be impressed on the recorded signal for play-back selection or the like. The developer roller is designated 66 and the backing roller 67.

FIG. 8 shows yet another embodiment of the invention in which the recording sheet 70 is wetted by means of a developer roller 71 prior to the recording locality, having a layer of developer 72, and the signal generator 73 which feeds the stylus 74 then modulates this developer layer 72 according to the impressed voltage changes and it will be obvious that the stylus 74, which operates in conjunction with the grounded backing roller 75, could be used either to displace or draw developer in accordance with the field changes but the result will be to modulate the developer layer 72 to give a developed signal 76.

FIG. 9 relates to a similar idea to that illustrated in FIG. 8 but in this case a sheet 80 itself can consist of a spongey polymer carrying the developer within it and development in this case takes place through the stylus 81 under influence of the signal generator 82 and the grounded roller 83 drawing the developer to the surface in accordance with the signal to produce the developed signal 84.

FIG. shows the invention applied to a multi-pin stylus member 90 which can carry signals on some of the styluses 91 and can carry other data such as timing data or identification data on other styluses, or the system can be used to provide a large number of tracks on the polarisable surface 92 of the recording sheet 93 which are then developed by the developer applicator 94 in association with the grounded backing roller 95 to produce the developed signal tracks 96 from the latent signal image 97 in parallel formation on the recording sheet 93, thus allowing a large number of tracks to be simultaneously recorded. The styluses 91 are modulated by the signal generator 98.

FIG. 11 shows one embodiment of how the signal can be read back in any of the foregoing embodiments by using a senser associated with a sensing head 100 and roller 100 which supports the sheet in relation to the sensing head 100, the senser being of course arranged to suit the particular type of recording'The sensing unit being arranged for instance for sensing dielectric differences in the developed image or the conductivity or capacitance or the magnetic difference depending on which system or recording and development was used, but it will be realisedthat the method of read-back will be within the scope of technicians versed in the art because once a developed image representing the signal is produced, it is relatively simple to either read difference in capacitance between the sensing head 100 and the backing 101 or second electrode or to impress a signal between-the sensing head 100 and the roller 101 which is then varied by the properties of the recorded signal. It is also obvious that piezo electric devices could be used for both recording and readback in which for instance stresses set up in the piezo electric member by the signal generator would cause modulation of the signal, or physical stresses set up could read the signal.

It would also be possible to use ball pointed contact reading means as the sensing member, variations of this nature being within the spirit of this invention which is generally directed to the recording of'signals on a polarisable surface modified by particulate materials if required but still of an insulating nature and the use of a relatively low voltage which can build up a sufficient signal on this insulating surface to enable it to be developed by the relatively sensitive liquid developers which are now available. In FIG. 10 the recording sheet is designated 102 and the recorded signal 103. The sensor supply unit is designated 104 and a printer is designated 105.

It will be obvious of coursethat the use of low voltage and medium insulating property surfaces ensures that a much greater definition is possible because of the absence of spread and the absence of corona effects and leakage effects which take place where the normally high sensing voltages are used according to present methods, the low voltage ensuring also that the recording flow can be from an extremely fine point with only small lateral flow from areas adjacent the point so that spread of the signal is avoided as would happen where higher voltages would cause flow from a greater area back from the tip of the stylus due to corona effects.

The following is a guide to the materials which are suitable with both latent images or direct development;

B. Materials suitable only for direct development simultaneously with production of the impressed signal voltages;

Polarisable materials such as thin metallic layers or films or materials generally below 10 ohm cm.

Tests carried out with materials such as polystyrene, polyethylene and Mylar, all well above 10 ohm cm. show no usefulsignal track at voltages below about 500 at which objectionable side effects such as signal spread, gas ionisation and the like occur, and also inherent artefacts or charges are maintained on these materials and mar the recordings.

. What we claim is:-

1. A method of recording data on hitting cards or materials comprising forming the material with a photoconductive polarizable surface having a bulk resistivity less than l0 ohm cm, and a backing for the polarizable surface having a relatively greater conductivity, transversing the material with a modulated signal the voltage of which does not exceed seventy volts, the voltage being applied to a stylus in contact with the surface whereby the stylus produces a latentsignal image on the surface, and developing the said image with a stylus when in contact with the said surface and in the liquid developer comprising an electrically insulating presence of the developer liquid which wets the surface carrier liquid in which is dispersed a medium attractat the point of stylus contact. able to the latent image, the signal being applied by the

Claims

1. A method of recording data on bitting cards or materials comprising forming the material with a photoconductive polarizable surface having a bulk resistivity less than 1013 ohm cm2, and a backing for the polarizable surface having a relatively greater conductivity, transversing the material with a modulated signal the voltage of which does not exceed seventy volts, the voltage being applied to a stylus in contact with the surface whereby the stylus produces a latent signal image on the surface, and developing the said image with a liquid developer comprising an electrically insulating carrier liquid in which is dispersed a medium attractable to the latent image, the signal being applied by the stylus when in contact with the said surface and in the presence of the developer liquid which wets the surface at the point of stylus contact.