GB1572548A

GB1572548A - Printing devices

Info

Publication number: GB1572548A
Application number: GB4847277A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-11-22
Filing date: 1977-11-22
Publication date: 1980-07-30

Description

(54) IMPROVEMENTS IN PRINTING DEVICES (71) I, HUGH-PETER GRANVILLE KELLY, a British subject, of 15, Leigh Hall Road, Leigh-on-Sea, Essex, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a stationery detecting device for printers.

A large and rapidly expanding use of computers and computing techniques is in the field of the preparation and printing of all forms of documents. A specific use is that known as Word Processing. This term is applied to equipment and software programs run within such equipment to increase the productivity of typists and to render less onerous the chores associated with typing.

Such equipment may, for example, comprise the following five elements: an electronic keyboard (to take the place of the customary typewriter keyboard), a visual display unit (for displayinging on an electroluminescent screen the text typed), a central processor unit (for running the software programs necessary for the manipulation and retrieval of text to be displayed), a disc storage unit (for storing standard texts and documents to be printed) and a high quality electromechanical printing device for the actual printing of the typed text.

To facilitate an understanding of the present invention, a brief explanation follows of the various main functions available with current Word Processing systems, especially with reference to a system of the type described.

Characters corresponding to those typed on the electronic keyboard are displayed on the visual display unit (hereinafter referred to as V.D.U.). If the typist makes a mistake, special control keys on the keyboard enable individual characters, words, sentences, paragraphs, orven-a whole page of text, to be erased instantly. The typist is also able to have access from the disc storage unit of the system 'standard paragraphs' which can instantly be interposed within the original text. It is also possible to widen or contract the left hand and/or right hand margins of a completed text for aesthetic reasons, or for accommodating the text within stationery of a particular width.The software programs which are run within the central processor unit, automatically reorganize all the words, spaces and punctuation marks, so ensuring that the text is presented in a logical fashion as wide or as narrow as is desired. As soon as a letter or text has been completed (the typed text being held temporarily within a memory associated with the typist's V.D.U, or, alternatively, on the disc storage unit) it is possible to activate an output program which will automatically cause selected portions of the typed text to be printed on the printing device.

Such printing devices are usually of high quality and precision and make use of very accurately constructed printing heads.

The authors of letters typed on such equipment may occasionally require the use of pre-printed stationery, for instance forms or letters already bearing such captions as 'Extension No.,', 'Your ref: Our ref: ' and the like. Displacement parameters within the output program controlling the printer will be pre-set and adjusted before hand to ensure that the correct text appears in exactly the correct spaces. It will be appreciated that it is essential to position the stationery on which the text is to be printed such that its displacements in the horizontal and vertical senses register exactly with the pre-set displacement parameters, otherwise for example the pre-printed captions could be overprinted. In typing pools where speed is of the essence, such careful positioning of paper is time consuming and tedious.

According to the present invention, there is provided a printing device comprising a printing mechanism for printing on stationery and means for ensuring registration of the stationery and print applied thereto by the printing mechanism, said means comprising a transducer arrangement arranged to scan stationery within the printing device to detect a leading edge of each item of stationery and control circuitry responsive to the output of the transducer arrangement for providing a signal indicating the detected leading edge of each item of stationery for positioning the text to be printed.

By "leading edge" there is meant that one of two opposite edges of the sheet which is encountered first during scanning.

The following description will be given with reference to the application of the present printing device to a Word Processor.

Such a transducer arrangement can be used for establishing the horizontal and/or vertical displacements of the stationery and thus ensure the corresponding activation of the printing mechanism according to one or both of these displacements. In general, however, the typist or operator responsible for mounting the stationery is able to position it accurately with relative ease in the vertical sense. [This is on account of the fact that platens of printers used in Word Processing systems usually resemble in operation those of ordinary typewriters, having a handle for feeding the stationery into the printer in discrete steps, for example, half or one line at a time.It will also be appreciated that use of the present device enables a typist to insert paper anywhere across the possible range of movement of the printing mechanism as the position of the stationery is automatically established obviating the necessity to position it accurately initially, according to preset parameters.

In one embodiment of the invention where horizontal displacement of the stationery is detected, the tranducer arrangement can be mounted on a carriage movable horizontally across the printer and comprises a transducer sensitive to electromagnetic radiation and positioned to detect changes in reflected radiation effected by the presence of the stationery. The change in characteristics of the transducer corresponding with the detection of stationery is interpreted by control means which, in turn, ensure the registration of the printing mechanism with the stationery..

A disadvantage of using a word processing system is the ease with which a typist can start a printing program without mounting stationery within the printer of the system. Damage to both the printing mechanism and the platen of the printer can occur if this is not done. A feature of the above described embodiment of the invention provides for the transducer to be caused to move from a given datum point each time it searches to detect stationery, and if the time taken by the movement of the apparatus from the datum point equals our exceeds a predetermined reference value, activation of the printing mechanism is prevented.The reference value can be set to la period during which stationery would normally be detected (stationery might as mentioner earlier be positioned anywhere across the width of the printer). 'Thus, if the typist neglects to mount stationery within the printer, which will not then be detected, activation of the printing mechanism, with consequent damage, will be prevented.

For those applications of word processing systems which require continuous or repetitive printing, but on separate pieces of paper, a system often used is one in which, for example, the actual sheets of paper on which text is to be printed are affixed lightly to a continuous backing sheet, known as continuous feed stationery. The continuous feed stationery passes through the printer and is perforated along each edge by regularly spaced holes receiving spokes of drive wheels controlled by the printer. Rotation of the drive wheels causes movement through the printer of the continuous feed stationery - and thus the actual sheets to be printed.To ensure that each sheet to be printed is precisely presented-in the vertical sense-to the printing mechanism, the sheets are mounted very accurately at regular intervals on the continuous feed stationery, and the rotation of the drive wheels of the printer is controlled very carefully.

However, minute variations in both of these parameters can accumulate each time a new sheet passes through the printer, until at some point, the printing mechanism is no longer activated in register with the stationery. Where as mentioned earlier, the stationery is pre-printed with captions, the printing mechanism, when this happens, may print text out of line with such captions.

The present invention may be applied to the handling of continuous feed stationery.

Using the present method to control the motion of continuous feed stationery through the printer obviates the need for accurate location thereon of the paper to be printed, and also precise control of the dvancement motion of the paper drive wheels of the printer. Accumulative error is avoided.

The transducer arrangement may, as mentioned earlier, include a transducer sensitive to electromagnetic radiation. When used to sense, for example the horizontal position of stationery, a preferred type of such a transducer is a photo-electric cell.

When, for example, this is moved across the platen of the printing device, sensing of stationery occurs when the general light received by the cell and reflected by the surface of the platen (which is usually of a dark matt nature) increases as the cell approaches the more reflective stationery.

The control circuitry is used to interpret the change in value of characteristics of the cell corresponding to these two conditions.

It will be appreciated that in this arrangement, ambient light reflected by the platen may falsely indicate in very bright lighting conditions the presence of stationery or, alternatively, in dull conditions light reflected by stationery into the cell may be inadequate for detection of the stationery.

In a preferred form, the transducer arrangement comprises an array of two or more transducers placed substantially one after another in the scanning direction, and are interconnected in such manner that when a current is passed therethrough and one part of the array receives radiation of different intensity to another, a change occurs in the potential with respect to either end of the array of at least one of the interconnections. Suitably two photo-resistors connected in series and placed side by side may be used. A small light source may advantageously be positioned adjacent to the resistors for increasing the level of ambient light. A potential is applied to the free ends of the resistors. When one resistor is positioned over stationery mounted in the printer and the other is positioned over the platen, the potential of the interconnection changes.This change can be appropriately interpreted by the control circuitry. Within the tolerance imposed by slight dissimilarities in characteristics of the two resistors, this arrangement is unaffected by variations in the general level of ambient light, as such variations will affect the resistance of both photo-resistors equally. An advantage of this arrangement is that on being moved across the platen of a printer, both the left-hand and right-hand edges of stationery mounted therein can be identified, as the potential of the interconnection between the two resistors will rise and then fall from a quiescent value with such motion. Such detection of both edges can be used to convey to the printing mechanism of the printing device the width of the stationery.

This information could also be made available to the programme controlling the printing which could then automatically readapt the text to suit the width of the stationery. A further variation is the use of the signals from the control circuitry to only permit printing on lighter areas of a form where other areas are relatively darker.

It will be appreciated that the output signals of transducers of the type described above normally require the use of electronic amplification apparatus to enable the change of characteristics thereof to control the printing mechanism of the printing device.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagram of part of one embodiment of printing device according to the present invention, for use in a word processing system; Figure 2 is an illustration showing enlarged and in more detail, part of the printing mechanism and transducer arrangement of the embodiment of Figure 1; Figure 3 is a circuit diagram of the stationery detecting apparatus of Figure 2.

The embodiment of printing device shown in part in Figure 1 is intended to be incorporated in a word processor also incorporating an appropriately programmed central processing unit, mass storage unit for text to be printed, keyboard, display unit and the various items of interface circuitry required to interface the processing unit to the other components of the word processor.

The printing device is generally designated 10 and includes a platen 11 embraced circumferentially along part of its length by stationery 12. Two guide bars 13 and 14 are mounted on the printer and are positioned parallel to and in front of the platen 11. The guide bars are used to enable a trolley 15 to slide in a horizontal sense from left to right and vice-versa, as indicated by the arrow. The trolley is held in position on the guide bars 13 and 14 by four collars, one of which is shown at 16. Aflixed to the collars by brackets is a small stepping motor, 17. Protruding from the end of the motor nearest the platen is a spindle on which is mounted a printing wheel 18. (This wheel is known as a daisy wheel and com-prises a multiplicity of flexible radial arms ending in a printing head bearing a character.The principle of operation is that the wheel rapidly rotates and at a predetermined point, a hammer (not shown) strikes the printing head and causes a character to be imprinted-through an inked ribbon (also not shown)-onto the stationery. The trolley then moves along the guide bars and a further character is printed, and so on). A mounting bracket 19 is affixed to the two collars riding the guide bar 13 and acts as a base for stationery detecting apparatus indicated generally at 20 and incorporating a transducer arrangement for detecting the position of the stationery.

Referring to Figure 2, the stationery detecting apparatus 20 comprises two photoresistors 21 and 22 located side by side on the mounting bracket 19. Positioned between the two resistors is a tungsten filament bulb 23. The photo-resistors and bulb face the surface of the platen. Sufficient space between the combination and the platen is allowed to permit reflected light to enter the photo-resistors. The photo-resistors are connected in series and a potential is applied to their free ends. (This potential may also conveniently be used to supply the bulb 23).

The mode of operation of the apparatus is as follows: As soon as the whole assembly is moved on the trolley 15 from left to right, a change in value of the reflected light occurs as soon as the detecting apparatus approaches the stationery. (The platen of such printers is usually of a dark matt nature as opposed to the reflective nature of stationery). The photo-resistor 21 which reaches the stationery 12 first. drops in resistance, and therefore causes the potential of the interconnection between the resistors to change.

This change is interpreted by control means (to be hereinafter described in more detail) and activation of the printing mechanism is permitted.

Thus it will be appreciated that stationery bearing pre-printed captions can be inserted into the printer without careful positioning in the horizontal sense, and the printing mechanism, as directed by the output programme, will only print in the desired locations. The effects of ambient light and variations in temperature on the two photoresistors alter the characteristics of each equally. Thus, in this arrangement, the quiescent value of the potential of the interconnection remains unaltered during such variations and is only changed when one resistor receives a different amount of light to the other.

As mentioned before, the locations at which the characteristics of the transducer change as it traverses the left and right hand edges of the stationery can be conveyed to the programme of a word processing system in which this apparatus is used to enable it automatically to re-adjust text, before printing, to suit the width of the stationery.

A more detailed explanation of the stationery detecting apparatus shown in Figure 2 will now follow with reference to Figure 3. The two photo-resistors 21 and 22 of Figure 2 are indicated as two resistors connected to one input of a differential comparative operational amplifier 31. The other input of the amplifier is connected to a potential divider 32 to provide a reference voltage. The bulb used to augment the general level of light impinging on the platen and stationery is shown at 33. The amplifier used is of the type which gives a change in output voltage 34 when the potential of one input exceeds the other, with reference to a given datum potential. The action of the circuit is as follows: The potential of the reference voltage is first pre-set to be just above the quiescent value of the junction of the two resistors.

As soon as the resistance of the photoresistor 21 drops on sensing stationery, the reference voltage is exceeded, and the output of the amplifier 31 changes. (Note, however, that once both resistors are situated over stationery, the quiescent value of the junction potential is restored as the resistances of each will be equal).

The actual time of change of the output of the amplifier can be adjusted by varying the discrepancy between the quiescent input voltage and the reference voltage. Thus the apparatus can be adjusted to detect the left hand edge of the stationery exactly.

It will be appreciated that this circuit can be employed to detect the right hand edge of the stationery. The reference potential is instead set initially below the quiescent value, the former value being crossed as the resistance of the photo-resistor 21 rises as it reaches the exposed platen. Thus two operational amplifiers can be used togetber to give outputs changing respectively as each edge of the stationery is traversed by the stationery detecting apparatus.

Numerous modifications of the printing device will be apparent to those skilled in the art. For example, the control circuitry can be arranged to turn on the bulb 23 only when the position of the stationery is being detected; illumination of the bulb can then be controlled by a suitable signal originating in the processing unit.

Furthermore the control circuitry can be arranged to produce its output signal indicating detection of the stationery in such a manner that there is delay of appropriate duration between the stationery being detected and the movement of the printing mechanism and transducer arrangement being stopped so that they stop a predetermined position beyond the edge or the marking being sought, for example to stop the printing mechanism one character width in from the edge so that printing can then start immediately. The delay may be generated by means of a monostable multivibrator.

WHAT I CLAIM IS: 1. A printing device comprising a printing mechanism for printing on stationery and means for ensuring registration of the stationery and print applied thereto by the printing mechanism, said means comprising a transducer arrangement arranged to scan stationery within the printing device to detect a leading edge of each item of stationery and control circuitry responsive to the output of the transducer arrangement for providing a signal indicating the detected leading edge of each item of stationery for

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 23. The photo-resistors and bulb face the surface of the platen. Sufficient space between the combination and the platen is allowed to permit reflected light to enter the photo-resistors. The photo-resistors are connected in series and a potential is applied to their free ends. (This potential may also conveniently be used to supply the bulb 23). The mode of operation of the apparatus is as follows: As soon as the whole assembly is moved on the trolley 15 from left to right, a change in value of the reflected light occurs as soon as the detecting apparatus approaches the stationery. (The platen of such printers is usually of a dark matt nature as opposed to the reflective nature of stationery). The photo-resistor 21 which reaches the stationery 12 first. drops in resistance, and therefore causes the potential of the interconnection between the resistors to change. This change is interpreted by control means (to be hereinafter described in more detail) and activation of the printing mechanism is permitted. Thus it will be appreciated that stationery bearing pre-printed captions can be inserted into the printer without careful positioning in the horizontal sense, and the printing mechanism, as directed by the output programme, will only print in the desired locations. The effects of ambient light and variations in temperature on the two photoresistors alter the characteristics of each equally. Thus, in this arrangement, the quiescent value of the potential of the interconnection remains unaltered during such variations and is only changed when one resistor receives a different amount of light to the other. As mentioned before, the locations at which the characteristics of the transducer change as it traverses the left and right hand edges of the stationery can be conveyed to the programme of a word processing system in which this apparatus is used to enable it automatically to re-adjust text, before printing, to suit the width of the stationery. A more detailed explanation of the stationery detecting apparatus shown in Figure 2 will now follow with reference to Figure 3. The two photo-resistors 21 and 22 of Figure 2 are indicated as two resistors connected to one input of a differential comparative operational amplifier 31. The other input of the amplifier is connected to a potential divider 32 to provide a reference voltage. The bulb used to augment the general level of light impinging on the platen and stationery is shown at 33. The amplifier used is of the type which gives a change in output voltage 34 when the potential of one input exceeds the other, with reference to a given datum potential. The action of the circuit is as follows: The potential of the reference voltage is first pre-set to be just above the quiescent value of the junction of the two resistors. As soon as the resistance of the photoresistor 21 drops on sensing stationery, the reference voltage is exceeded, and the output of the amplifier 31 changes. (Note, however, that once both resistors are situated over stationery, the quiescent value of the junction potential is restored as the resistances of each will be equal). The actual time of change of the output of the amplifier can be adjusted by varying the discrepancy between the quiescent input voltage and the reference voltage. Thus the apparatus can be adjusted to detect the left hand edge of the stationery exactly. It will be appreciated that this circuit can be employed to detect the right hand edge of the stationery. The reference potential is instead set initially below the quiescent value, the former value being crossed as the resistance of the photo-resistor 21 rises as it reaches the exposed platen. Thus two operational amplifiers can be used togetber to give outputs changing respectively as each edge of the stationery is traversed by the stationery detecting apparatus. Numerous modifications of the printing device will be apparent to those skilled in the art. For example, the control circuitry can be arranged to turn on the bulb 23 only when the position of the stationery is being detected; illumination of the bulb can then be controlled by a suitable signal originating in the processing unit. Furthermore the control circuitry can be arranged to produce its output signal indicating detection of the stationery in such a manner that there is delay of appropriate duration between the stationery being detected and the movement of the printing mechanism and transducer arrangement being stopped so that they stop a predetermined position beyond the edge or the marking being sought, for example to stop the printing mechanism one character width in from the edge so that printing can then start immediately. The delay may be generated by means of a monostable multivibrator. WHAT I CLAIM IS:

1. A printing device comprising a printing mechanism for printing on stationery and means for ensuring registration of the stationery and print applied thereto by the printing mechanism, said means comprising a transducer arrangement arranged to scan stationery within the printing device to detect a leading edge of each item of stationery and control circuitry responsive to the output of the transducer arrangement for providing a signal indicating the detected leading edge of each item of stationery for

positioning the text to be printed.

2. A printing device according to Claim 1 wherein the transducer arrangement and control circuitry are operative to detect the difference in reflectivity of the platen and stationery or of different areas of the stationery.

3. A printing device according to Claim 1 wherein the transducer arrangement and printing mechanism are mounted on a common support for movement together relative to stationery mounted within the device.

4. A printing device according to Claim 1 or 2, and including a cylindrical platen on which, in use, the stationery is mounted, at least the printing mechanism being movable relative to the platen longitudinally thereof to print across the width of the stationery and the platen being rotatable to effect a line feed of the stationery.

5. A printing device according to claim 4, wherein the transducer arrangement is arranged to scan longitudinally of the platen to detect an edge of the stationery.

6. A printing device according to any one of the preceding claims and adapted for use with continuous feed stationery.

7. A printing device according to any one of the preceding claims, wherein the transducer arrangement is arranged to detect the vertical position of the stationery so as to enable vertical registration to be achieved.

8. A printing device according to any one of the preceding claims, wherein the transducer arrangement comprises a sensor for sensing electro-magnetic radiation reflected from the stationery.

9. A printing device according to claim 8 wherein two such sensors are provided, spaced apart in the direction of said scanning, and the control circuitry is operative to produce said signal by detecting the difference in outputs of the sensors.

10. A printing device according to claim 8 or 9 and including an electro-magnetic radiation source disposed to cause said radiation to impinge on the stationery.

11. A printing device according to claims 9 and 10 wherein the two sensors share a common radiation source.

12. A printing device according to claim 10 or 11 wherein the control circuitry is arranged to energize said source only while the position of stationery is being detected.

13. A printing device according to any one of the preceding claims wherein the area of the stationery scanned by the transducer arrangement is coincident with, or directly adjacent to, the printing zone of the printing mechanism.

14. A word processor incorporating a printing device according to any one of the preceding claims.

15. A word processor according to claim 14 and having a central processing unit connected to interface with said control circuitry to control the operation of the printing device, the central processing unit being programmed to cause the transducer arrangement to scan a new item of stationery before printing thereon takes place to ensure registration of the stationery and the text to be printed thereon.

16. A word processor according to Claim 15 which is arranged to operate such that the transducer arrangement will measure the horizontal and/or vertical dimension of the stationery and the format of text to be printed is adjusted in accordance with the measured dimension(s).

17. A printing device constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figures 1, 2 and 3 of the accompanying drawings.

18. A word processor constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figures 1, 2 and 3 of the accompanying drawings.