GB2293574A - Scaling for an unformatted non-volatile visible display - Google Patents

Abstract

A machine readable, coded pattern of indicia 2 fixed in relationship to the carrier of an unformatted non-volatile re-writeable display medium 1 with the purpose of defining via a read head 3 the spatial disposition of contrasting areas comprising the displayed character or graphic 10 and of sensing the direction of scanning such as to facilitate formatting the display via a write head 4 to properly replicate the intended characters or graphical pattern in predetermined positions. The pattern of indicia 2 comprises two identical patterns displaced by one quarter pitch. <IMAGE>

Description

Scaling for an Unformatted Non-volatile Visible Display This invention relates to visible display materials requiring no power source for image maintenance and iu particular to apparatus and methods for clearing and writing to such displays under control from a fonnatting scale spatially fixed in relation to the body or carrier on which the display is mounted.

The requirement to provide an alterable display of data or graphical representation in locations where no power is available, or is only intermittently available, has existed for some time. For example in cashless payment systerns such as are used for vending and payphones, where magnetic or optical cards are used to store value, the credit remaining on the card can only be read during the time it remains inserted in a terminal device with display capability. At all other times the value and any other data on the card is invisible. Users of such cards would find it advantageous to be able to see at any time what the remaining value of the card is.

Developments of smart (integrated circuit) card technology for cashless payment and other applications requiring enhanced data storage capacity and security capability has highlighted the need to be able to display some ofthe variable data stored electronically on the types of card cornmonly used in such applications or data from an external source.Requirements include; the need to write data in alignment with fixed characters printed on the card, for example a currency symbol; writing multiple fields of data accurately in relation to descriptors printed on the card, for example 'remaining credit', 'last transaction', 'appointment date', 'service due date'; to be able to modify the display to reflect changes in the value of the data recorded on the card and to provide the display function on thin cards similar to the common credit card which typically carry no energy source. Sucli developments are taking place as to extend the use of these cards from credit and debit to stored value functions and the electronic purse concept where the user may need to refer to the remaining 'value or values and other data on the card plus data from some other source in the absence of a terminal device with display capability. Othel- applications ofnon-volatile displays exist where costly permanent printing is periodically discarded and a new display installed.For example, product, price and bar code displays mounted on supermarket shelving units are from time to time required to be changed. Non-volatile re-writeable display devices offer a low cost, re-usable altemative.

Display materials exist responsive to magnetic fields or heat to reversibly produce contrasting light and dark areas such that with proper formatting any alpha or numeric character can be written or any graphical shape may be drawl with a suitable write mechanism However, unlike electrically driven displays such as are typically found incorporated in battery operated calculators, remote controllers and similar devices, in which the display formatting framework is predetermined in manufacture, the magnetic field or heat sensitive display materials have no formatting framework and no integral means of self clearing and re-writing. A write mechanism must be provided, for convenience mounted in a card telminal or similar device, such that as the display is moved relative to the write mechanism appropriate magnetic or heat stimuli are generated using electrical signals derived from stored data together with electrical power from the terminal device which may be either battery or mains operated. The spatial formatting of characters to be written on the display'is determined in a first dimension by the pitch of individual writing elements of the writing mechanism and in a second dimension by a measuring scale. Such scales may be part of the terminal device driven by fictional contact with the display material or display carrier. However such an arrangement has the disadvantage that card or carrier thickness variations cause variable fictional contact resulting in variable character formatting and positioning.A further disadvantage is that wear in the terminal device'will also cause variable formatting and positioning of characters. Yet a further disadvantage is the requirement for the terminal device to incorporate a number of moving parts subject to wear and failure. Alternatively a measuring scale mounted integrally with the display material on its carrier with its longitudinal axis parallel to the direction of movement of the carrier relative to the terminal device may advantageously be employed with the effect that characters or graphics may be reliably and accurately positioned in spatial relationship to the carrier and the writing mechanism may be constructed with a minimum of moving parts.

According to the present invention there is provided an unformatted display medium, capable of accepting stimuli to create and maintain contrasting patterns of light and dark areas to form humanly recognisable characters or graphics, a writing means for stimulating said display medium, to erase old characters or graphics and write new and, integrated in the plane of said display medium, a coded pattern comprising a scale formed from materials resistant to damage, corruption and degradation to provide first dimensional spatial formatting and direction of travel information to said writing means for precise and repeatable positiolling of said contrasting areas.A second dimension orthogonal to the axis of said coded pattern and the plane of said display medium is formatted by the construction of said writing means in which the magnetic field or heat stimulating transducers are fixed in relation to mechanical guiding features constraining the lateral position of a datum edge of the display carrier as it moves relative to the writing means longitudinally parallel to said coded pattern.

A specific embodiment of the Invention will now be described by way of example with reference to tlle accompanying diagram fig. 1 which shows a strip of material 1 encapsulating liquid clystal in a matrix sensitive to magnetic fields fixed by adhesive to a plastic card 5. Next to the liquid crystal matrix material 1 are alternate reflective and non-reflective indicia 2 plinted ill two rows. The pitch ofthe indicia shown is arranged to be twice the pitch of contl asting light or dark areas required on the display 1 to generate characters 10. The two rows of indicia 2 are arranged to be displaced by one quarter of a pitch as illustrated in fig. 2.Two photo detectors 3 integral with the writing head 4 and fixed to tlle card guide datum 16 provide electrical signals indicative of either reflective or non-reflective surfaces. Springs 14 hold the datum edge ofthe card in contact with the datum guide face 16 ofthe write mechanism.

Signal processing circuits 6 detect the transition from reflective to non-reflective or non-reflective to reflective indicia to produce electrical pulses 19 as shown in fig. 3 being the combination of all transitions from both pulse trains 17 and 18 derived from detectors 3 indicating to drive circuits 7 the correct positions for the application of write stimuli to the display material 1. Additionally, signal processing circuits 6 are provided using well knowll techniques to create a further signal 12 comprising a high or low level 20 indicative of tlle direction of travel relative to the indicia 2 of the photo detectors 3. Such signal processing circuits 6 are well know to those trained in the art and therefore form no part of this invention.The display medium 1 and spatial definition indicia 2 are shown laminated to a plastic card 5 the pattern of indicia being precisely positioned such as to fix the disposition of written display characters 10 relative to the card outline.

Integral with the photo detectors 3 is a write head 4 comprising an array of9 electromagnets arranged to switcllably generate nine cylindrically shaped magnetic fields perpendicularly intersecting the plane of the display medium 1. For the purposes of this description the polarity of the fields generated by the nine electromagnets will be called positive. At the position where a positive cylindrically shaped magnetic field intersects the display medium I a circular dark area is generated which remains dark after the removal ofthe magnetic field. Control circuits 7 switch electrical current selectively to the electromagnets to either create a dark area on the display medium 1 when current flows or to leave the display medium 1 light when no current flows. In addition to and fixed to the write head, an erase head 13 comprising a switchable electromagnet producing a negative magnetic field perpendicular to and the same width as the write head 4, is switched on by direction of travel signal 12 during the write stroke the direction of which is indicated by arrow 21. Photo detector 15 senses the edge of a card producing a sigiial 22 to initiate writing at a predetermined position relative to the edge of the card 5.

As the card 5 is moved relative to the write head 4 photo sensors 3 detect the indicia 2 and signal to the write head 4 via signal processing circuitry 6 and write head drive circuitry 7 the positions where contrasting areas may be written according to a predetermined pattern representative of humanly readable characters stored in memory 8. In this way a representation of characters or graphical shapes demanded by an external source 9 may be generated within a predetermined area and with predetermined feature sizes on the substantially unformatted display medium 1. The source of data 9 may conveniently be the integrated circuit memory mounted on the card or any other suitably complected and controlled electronic memory incorporated in or external to the write mechanism.

The machine readable indicia 2 shown are alternate reflective and non-reflective square areas suitable for detection by photo sensors 3. Alternative techniques for providing machine readable features, knoll to those trained in the art, may bè used. By way of example alternate areas of high and low dielectric constant may be used in conjunction with capacitive sensors. Another possibility is alternate areas of high and low permeability in conjunction with magnetic sensors. Other techniques may be found to be suitable by those familiar with such techniques.

The machine readable indicia 2 are shown as alternate rectangular areas for convenience. Other shapes may be used to define alternative formats and sizes of contrasting areas on the display. Squares, circles, ellipses or complex shapes may be used without affecting the principle of operation.

Other types of non-volatile, re-writeable display 1 are known to be adaptable for application in the same way as described here. For example heat sensitive material wherein contrasting areas may be generated and a previous display pattern may be over-written by applying alternate heating and cooling cycles.

The write head is described comprising 9 electromagnets as display stimulating transducers being a convellient number for good character definition. Any number of transducers may be employed and activated in any combination without affecting the principles of the invention.

Indicia are shown and described for convenience mounted next to the display medium.

Indicia could be mounted parallel to the datum edge ofthe display canier and in any location without affecting the principle ofthe invention.

The erase head is described as being switchable in this embodiment. In other applications a suitably mounted llon-switchable erase head may be employed without affecting the principle of the iiiveiition.

Claims (11)

1. A coded pattern of indicia with machine readable qualities fixed in a pre-defined spatial relationship to a non-volatile, re-writeable visible display medium and its carrier with the purpose of longitudinally controlling the spatial disposition of contrasting areas on the display.

2. A coded pattern of indicia as claimed in claim I arranged longitudinally parallel to a datum edge of the display medium carrier.

3. A coded pattern of indicia as claimed in claim 1 arranged in precise longitudinal relationship to the edge of its carrier or fixed features on the canier.

4. A coded pattern of indicia as claimed in claim I formed from damage, corruption and degradation resistant materials.

5. A coded pattern of indicia as claimed in claim 1 comprising two identical patterns displaced by one qualter pitch with the purpose of indicating the direction oftravel relative to a display writing mechanism.

6. A read head comprising two sensors sensitive to the qualities of indicia as claimed in claim 4.

7. A read head as claimed in claim 6 arranged integrally with a display write head and erase head such that the read head scans indicia as claimed in claims 1 to 5.

8. A write head fixed in precise relationship to a datum face against which the display medium carrier is located.

9. Signal processing circuitry connected to the read head as in claims 6 and 7 arranged to provide signals for use by a controller in stimulating the write head at longitudinal positions defined by the coded pattern of indicia.

10. A write head responsive to signals from a read head and signal conditioning circuits as claimed in claims 6,7,8 and 9 together with input pattern coding signals providing write stimuli to the display medium.

11. A method of controlling the read and/or writing functions of a read/write head moving relative to a visible display recording medium at indeterminate speed which comprises providing the medium with a permanent fixed pattern of machine readable indicia, reading said indicia upon relative movement of the read/write head past the recording medium, interpretillg the pattern being read in terms of position and velocity of the head and controlling the write operation accordingly whereby to write by the head iii desired locations on the medium relative to the indicia.