Two-colour printer

Abstract: The printer is mounted on a desk-top computer and can print both numeric characters and graphic and calculation symbols in two different colours. The characters and the symbols are provided in a relief configuration in accordance with a matrix of rows and columns (circumferential tracks) on a rubber sheet wrapped around a rotatable drum (12). The characters in adjacent tracks are inked by an inking roller (32) formed by adjacent porous discs (38) which are alternately impreganted with red and black ink. The drum (12) can perform a translatory movement in the axial direction selectively to present to the printing hammers the tracks of characters which are inked with black and tracks of characters which are inked with red. The drum (12) is translated with respect to the inking roller (32) by means of a cam (93) which rotates at a speed half the speed of the drum (12) and engages with one or the other of two cam follower pins (98, 99) which can be selected by means of a solenoid (102).

Description: The present invention relates to a two-colour printer of the type defined in the preamble of the main claim. From U.S. Patent No. 4430935, a two-colour printer is known, comprising two character wheels, two inking rollers of different colours and two hammers for printing the characters on each of the two wheels on a strip of paper interposed between the hammers and the character wheels. The character wheels, the rollers and the hammers can move synchronously to print one character at a time along a line of printing over the entire width of the paper. By selectively activating one or other of the hammers, it is possible to print with one or other of two different colours. That printer is very slow since the selected character wheel has to pass successively through all the printing positions in order to print a complete row of characters. A serial printer is also known from U.S. Patent No. 4683819 in which the characters are disposed in a relief configuration on a rubber mat or sheet which is wrapped around a rotatable drum. A single inking roller rolls against the drum to ink in a single colour all the characters which are printed in a serial mode by a line of hammers disposed within the drum. The inking roller cannot be easily replaced by a roller of another colour, so that that printer cannot print in two colours. Another two colour printer is disclosed is French Patent Application No. 2184358. In one embodiment the character drum carries a plurality of characters divided into two angular sections, each extending over about 180° around the circumference of the drum. An inking roller in contact with the drum has two corresponding angular sections each impregnated with ink of a different colour. Thus printing with different colours can be achieved by rotating the drum and the inking roller together to select a character in one of two colours. In another embodiment described in this French Patent Application different inking rollers are used for each colour. The inking rollers are selectively brought into contact with the character drum. A drying roller has to be rolled against the drum after each colour printing operation to remove the residual ink. Another printer is described in German Patent Application DE-OS-2808322 which corresponds to U.S. Patent No. 4655130. In this the character drum is divided into two portions on which there are respectively provided the characters to be printed in odd and even columns. A single inking roller is provided to ink all the characters of the drum with a single colour. Character selection is performed by rotating the drum and energising the appropriate hammers. A further printer is described in Japanese Patent Application No.60-141579. In this two inking rollers are provided in contact with the character drum. Each inking roller comprises alternating wide diameter inking portions and small diameter connecting portions. Each wide diameter portion is in contact with a circumferential track of characters on the character drum. The arrangement is such that adjacent tracks on the character drum are inked by wide diameter portions from different inking rollers. Each inking roller is impregnated with ink of a different colour. The inking rollers and character drum may be axially shifted together such that each character position may be printed with each colour. Axial shifting is effected by a cam which moves in a direction perpendicular to the axis of the character drum. The object of the present invention is to provide a fast, compact two-colour printer which is of a simple construction and which is of limited cost. This object is met by the two-colour printer according to the invention which is characterised in the manner defined in the characterising portion of claim 1. These and other features will be more clearly apparent from the following description of the preferred embodiment which is given by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 is a plan view of the printer according to the invention; Figure 2 is a view in cross-section taken along line II-II in Figure 1; Figure 3 is a view in cross-section taken along line III-III in Figure 1; Figure 4 is a view in section taken along line IV-IV in Figure 1; Figure 5 is a diagrammatic representation of the characters with respect to the print positions; Figure 6 is a block circuit diagram of a control circuit of the printer of Figure 1; and Figure 7 is a flat development of a cam. Referring to Figure 1, the printer 10 comprises a hollow cylindrical drum 12 which on its outside surface carries characters 14 to be printed, which comprises a series of digits 0 to 9 and a group of graphic signs which are normally used in numerical calculation operations. The characters 14 are provided in a relief configuration on a rubber mat or sheet 16 which is wrapped around the outside surface of the drum 12. The characters 14 are arranged on the sheet 16 around for example twenty-two juxtaposed circumferential tracks C1-C22 (Fig. 5). The characters on any one track are angularly spaced by a constant angle 2α. In fact each track includes ten characters so that α = 18°. The adjacent tracks are axially spaced from each other by a printing pitch p and are angularly phase-displaced relative to each other by half the angular pitch of the characters, that is to say by α (see Figure 2) so that the characters occur successively in alternate positions along a printing row. The drum 12 is rotatable about its own axis and is supported at its ends 18 and 19 respectively by two cylindrical coaxial elements 20 and 22 which are rotatable on corresponding support bushes 24 and 25 which are fixed with respect to the base portion 11. Disposed within the drum 12 are printing solenoids 15, each provided with a hammer M which are shaped in such a way as to cover two contiguous printing pitches p. The solenoids 15 are fixed on a frame 21 which extends within the drum 12 parallel to the axis thereof and which is fixed at its ends 21a and 21b to the base portion 11. Each hammer hits a striker pin 26 (see Figure 4) which is fixed at the rear to each character and which passes through openings 27 provided in the drum 12. In that way the characters 14 are pressed against a strip of paper 28 which passes on the outside of the drum 12 and which is advanced by means of a roller 30, as will be described hereinafter. Since, as already indicated hereinbefore, the characters on the drum 12 appear in alternate printing positions, both on each row of characters and along each character circumference, to be able to print the characters 14 on the strip of paper 28 in all the printing positions of a row, it is necessary in each printing cycle axially to move the drum by a step p so that each hammer M prints in the first printing position S1 (Figure 5) a character of a first track C1 and in a second adjacent printing position another character on an adjacent third track C3, as will be described in detail hereinafter. The characters 14 are inked by an inking roller 32 (Figure 1) which is parallel to the axis of the drum 12 and which is rotatable on a support 34 slidable parallel to the axis of the drum 12 and moved axially by the drum itself by means of a tooth 35 (Figure 1) engaged with a groove 37 in the drum 12. The roller 32 is formed by a number of inked rings 38 (Figure 1), equal to the number of character tracks 14. The rings 38 of absorbent material are saturated alternately with ink of different colours, for example black and red, whereby the characters 14 of adjacent tracks C1, C2, C3 (see Figure 5) are inked in different colours. The rings 38 are separated by impermeable circular walls 38a mounted on a shaft 38b which is rotatable on the support 34. The roller 32 is supported by elastic arms 39 (see Figure 4) connected to the support 34 in such a way as suitably to press the roller 32 against the drum 12. The drum 12 is rotated by means of a tooth 40 (see Figure 1) which projects radially from the cylindrical element 20 and which is received in a recess 42 in the drum 12 in such a way as to permit the axial sliding movement of the drum 12 with respect to the element 20. On its outside the cylindrical element 20 carries a ring of teeth 44 and a single tooth 46 which is disposed adjacent to the ring of teeth 44. The teeth 44 have an angular pitch equal to the angle 2α, so that each tooth 44 corresponds to a respective one of the rows L1-L20 (Fig. 5) of characters on the drum 12. The teeth 44 and the single tooth 46 alternately engage with a ratchet assembly 48 (see Figure 2) which is pivoted at 49 on the base portion 11 and controlled by a solenoid 50. The ratchet mechanism 48 comprises two latch portions 52 and 53 capable of respectively engaging the teeth 44 and the single tooth 46. Normally the ratchet mechanism 48 is rotated in an anti-clockwise direction by a spring 54 to hold the latch portion 53 in engagement with the single tooth 46. The cylindrical element 20 is rotated by a gear 51 by way of a friction clutch 55 provided between a projection 56 on the element 20 and a hub 57 on the gear 50. The gear 50 is in turn driven by a DC motor 58 by way of two reducing gears 59. Therefore when one or other of the latch portions 52 and 53 holds the cylindrical element 20 stationary, the motor can continue to rotate by virtue of the friction clutch 55. The cylindrical element 22 which supports the end 19 of the drum 12 (at the right in Figure 1) is fixed with respect to a ring 60 which is concentric with the axis of the drum 12. The ring 60 is connected by means of resilient latch portions 62 to a toothed wheel 64 which is coaxial with the ring 60 and which is rotatable on the support bush 25 fixed to the base portion 11. The toothed wheel 64 is rotated by the cylindrical element 20 by way of the gears 67, 68 and 69 of which the gear 67 is fixed with respect to the cylindrical element 20 while the gears 68 and 69 are mounted on a shaft 70 parallel to the axis of the drum 12 and respectively engage with the gear 67 and the wheel 64. The transmission ratio between the element 22 and the wheel 64 is 2:1 whereby, while the drum 12 rotates through one revolution, the toothed wheel 64 rotates through 180°. Fixed to the base portion 11 in front of the toothed wheel 64 is a printed circuit board 72 carrying a plurality of electrical contacts (not shown in the drawings) which are angularly spaced by half the angle α and against which rubs a resilient conducting tongue 74 mounted on the wheel 64 to generate on a line 76 strobe signals corresponding to the angular positions of the characters on the drum 12. Mounted over the ring 60 is a cylindrical barrel portion 80 which is entrained in rotation by the ring 60 by means of an axial key 82. The barrel portion 80 is also connected to the drum 12 by means of a radial pin 84, engaging with a circular groove 86 in the drum 12. Provided on the outside surface of the barrel portion 80 is a channel 93 comprising two portions 95 and 96 which are connected by inclined portions 97′ and 97″ (see Figure 7). The two portions 95 and 96 are straight and parallel and are displaced relative to each other by the pitch p. One or other of two cam follower pins 98 and 99 which are mounted at 180° from each other on an arcuate support 100 can engage selectively into the channel 93 (see Figure 3). The support 100 is fixed in the axial direction and is moved radially by a solenoid 102 from a first position in which it is held by a spring 101 and in which the pin 98 is in engagement with the portion 95 of the channel 93, to a second position in which the pin 99 is engaged with the portion 96 of the channel 93. The drum 12 is held in an angular rest position by the latch portion 53 (see Figure 2) engaged with the single tooth 46. In that position the barrel portion 80 is oriented in such a way that the pins 98 and 99 (see Figure 7) are in positions corresponding to the beginnings of the respective portions 95 and 96 with respect to the direction of movement E. By leaving for example the pin 99 engaged (see Figure 1), at the end of each revolution of the drum 12, the cam 93 displaces the drum 12 axially by a step p, first towards the right and then in the opposite direction. On the other hand, by leaving the pin 98 engaged, the drum is moved axially first towards the left and at the end of the second revolution towards the right. The rotary movement of the drum 12 and selection of the characters to be printed is produced under the control of a circuit (see Figure 6) in response to the strobe signals produced on the line 76 by the rubbing contact 74. When the machine is started up by means of the switch 110, the motor 58 is set in continuous rotation but, by virtue of the friction clutch 55 (see Figure 1) the drum 12 remains stationary since the latch portion 53 holds the tooth 46 (see Figure 2). The printing operations take place during two complete revolutions of the drum 12. When a colour, for example black, is selected, in the first revolution characters are printed in the odd-numbered printing positions while in the second revolution, characters are printed in the even-numbered positions of the same printing row. When the other colour, red, is selected, in the first revolution characters are printed in the even-numbered printing positions while in the second revolution of the drum characters are printed in the odd-numbered printing positions. The control circuit (Fig. 6) comprises a logic control unit LCU adapted to control an arithmetic logic unit (ALU) 122 and a keyboard unit 126, which includes the conventional keyboard encoder and control circuitry. The control unit LCU under the control of a permanently stored program causes the keyboard 126 to transfer to the arithmetic unit 122 the binary informations corresponding to each one of the keys of the keyboard 126. The arithmetic unit 122 under the control of the unit LCU performs the arithmetical operations to give the numerical results of calculations and the positive or negative sign of the results. The control unit LCU is also controlled by the arithmetic unit 122 to select the printing colour of characters to be printed. For example the positive number and the mathematical symbols, except the minus sign (-), are to be printed in black, while the negative numbers preceded by the (-) sign are to be printed in red. The ALU 122 includes a transcoder which is adapted to transcode the code of each character to a code formed by four bits and representative of the angular position of the character on the drum 12. The ALU 122 under the control of the unit LCU transfers the characters so translated to a character register 124 including 11 locations, each one associated with a corresponding printing position, whereby in each printing cycle each location of the register 124 stores the angular position of the character to be printed. Since the entire line of characters to be printed is printed in two successive printing cycles, the LCU during a first rotation of the drum 12, causes the arithmetic unit 122 to transfer to the register 124 the transcoded characters to be printed in the odd printing positions and during a second revolution of the drum 12, to transfer to the register 124 the transcoded characters to be printed in the even printing positions, as it will be explained hereinbelow. The angular positions of the drum 12 are detected by a counter 142, by counting the pulses generated by the sliding contact 74. A coincidence circuit 132, formed of 11 sections associated with the locations of the register 124, compares each time the contents of the counter 142 with the transcoded characters to be printed, stored in the register 124. Whenever the angular position of the drum 12 equals the character code, the corresponding section of the circuit 132 generates a character selection signal which is transferred to a buffer 130. The buffer 130 is a latching register of capacity of 11 bits for storing the character selecting signals of the 11 characters to be printed. A drive circuit 140 is activated by the register 130 under the control of a strobe supplied by LCU on the connection 143 to cause the hammers 15 to print the selected characters. The printing colour may be manually selected by means of a key, not shown, of the keyboard 126, or, as previously described, the colour selection may be performed through the control unit LCU according to the calculation results of the arithmetic unit 122. In greater detail, the printing operations take place in the following manner. PRINTING IN BLACK Under the control of an operator key (not shown) of the keyboard 126, the LCU activates a character selection circuit 144 which, with a 10 msec pulse energises the solenoid 50 (Figure 2) to free the single tooth 46 from the latch portion 53. The drum 12 begins to rotate in the anti-clockwise direction, entrained by the friction clutch 55 (see Figure 1), while the pin 99 engages into the portion 96 (see Figure 7) of the cam 93. During the first revolution of the drum 12 it is possible to print in black, as already stated hereinbefore, the characters on the odd-numbered tracks C1, ...C21 (see Figure 5) in the odd-numbered printing positions S1...S21. Therefore the coincidence circuit 132 (see Figure 6) activates the solenoid 50 at successive intervals by way of circuit 144 to lock the drum 12 by means of the latch portion 52 (see Figure 2) in the angular positions corresponding to the odd-numbered lines of characters L1, L3, L5,... (see Figure 5). At the same time the buffer 130 is enabled to activate, each time that the drum stops, the circuit 140 for actuation of the hammers M for printing the selected characters. Before being stopped at the end of the first revolution, the drum 12 is axially translated by a step p towards the right in Figure 6 into the position 12a (at the left in Figure 5) by the inclined portion 97' of the cam 93 (Figure 7), since the latter has only performed half a revolution. Therefore the tracks C3,...C21 (see Figure 5) of the characters which are inked black are moved into positions corresponding to the printing positions S2, ...S20 in which the remaining black characters are printed during the second revolution of the drum 12, in the manner already referred to above. At the end of the second revolution, the drum is returned by the portion 97'' of the cam 93 (Figure 7) into the initial axial position and is stopped by the latch portion 53 bearing against the single tooth 46 (see Figure 2). Shortly before the drum 12 stops, after two revolutions equivalent to a revolution of the cam 93 and the cylindrical element 22 (see Figure 1), the roller 30 for feeding the paper 28 (Figure 4) is rotated by a line spacing by means of a gear 31 (Figure 1) which engages with three teeth 33 carried by the cylindrical element 22. PRINTING IN RED The LCU enables a colour selection circuit 145 (see Figure 6) to energise the solenoid 102 (see Figure 3) in such a way as to engage the pin 98 into the portion 95 (see Figure 7) of the cam 93. During the first revolution of the drum 12, the characters in red of the even-numbered tracks C2,...C22 are printed in the above-described manner, at the corresponding even printing positions S2, S4...etc. The coincidence circuit 132 now stops the drum 12 at a position corresponding to the even-numbered lines L2, L4... etc. (see Figure 5) which contain the red-inked characters. At the end of the first revolution of the drum 12, the pin 98 engages into the portion 97'' of the cam 93 (see Figure 7) which has rotated through 180°, and moves the drum towards the left (see Figure 6) into the position 12b (at the right in Figure 5) whereby the characters on the even tracks C2, C4...C22 are in positions corresponding to the odd-numbered printing positions, S1, S3,...S21 (see Figure 5). Thus during the second revolution of the drum 12, the red-coloured characters can be printed, in the odd-numbered printing positions S1,...S21, completing a row of printing in red. At the end of the second revolution, the paper 28 is advanced by a line spacing while the drum 12 is returned by a step p to the right (see Figure 6) and thus locked by the tooth 46 and the latch portion 53 (see Figure 2).

Claims: A two-colour printer for impact printing alpha-numeric symbols on a printing line in printing positions (S1-S22) which are equally spaced by a predeterminated pitch (p), comprising a rotatable character drum (12), said characters being disposed on the outside surface of said drum at a constant angular spacing (2α) over a plurality of pairs of adjacent circumferences C1-C22 which are axially spaced from each other by said pitch, an inking roller (32) rolling against the outside surface of said drum, and extending over the entire length of the drum, said inking roller comprising a plurality of juxtaposed inking discs (38) alternately impregnated with ink of different colours for inking with a first colour the characters of a first circumference (C1, C3,....) of said pair and the characters of a second circumference (C2, C4,....) of said pair with a second colour, the inking roller (32) being connected with the drum (12) for an axial displacement with the drum, characterised by a drum shifting means (80) rotated at a rotational speed half than the rotational speed of the drum (12), said shifting means (80) being connected with the drum for only an axial displacement thereof and comprising a continuous circular cam element (93) divided into a first and a second cam portions (95, 96) connected to each other and axially spaced therebetween by said pitch (p), and a cam follower member (100) selectively engageable with said first or said second cam portions to axially shift said drum by one pitch in a first direction or respectively in an opposite direction with respect to a central position, whereby the characters of a first colour are successively printed in odd positions and in even positions of said printing line during two subsequent revolutions of said drum when said cam follower member (100) engages said first cam portion (95), while the characters of a second colour are successively printed in even and in odd positions during two subsequent revolutions of the drum (12) when said cam follower (100) engages said second cam portion (96). A printer according to claim 1, characterized in that said shifting means (80) comprises a cylindrical member (80) coaxially mounted at one end of the drum (12) and connected to the drum by a pin (84) engaged within a circular groove (86) of the drum, the circular member (80) carrying on the outside surface thereof the continuos cam element (93), each of said cam portions (95, 96) extending through 180°. A printer according to anyone of claims 1 or 2, characterised in that said cam follower (100) comprises first and second pins (98, 99) which are angularly spaced relative to each other through 180°, said cam follower (100) being radially movable from a first position to a second position in which said first and second pins are selectively engaged with said cam for moving said drum in said first direction and in said opposite direction respectively. A printer according to claims 1 or 2, characterised in that said inking roller (32) is mounted on a slider (34), the slider (34), being connected with the drum (12) by a tooth (35) engaged with a circumferential groove (37) on the drum (12) to axially translate the inking roller together with the drum. A printer according to any of the preceding claims, characterised in that said drum (12) is stopped after each revolution by a stop member (48) which is normally engaged with a single tooth (46) on said drum (12), said stop member (48), being selectively activable to free the drum for rotation in response to a command from an actuator circuit (144). A printer according to claim 5 characterised in that said stop member (48) comprises a first ratchet means (53) co-operating with said single tooth (46) and a second ratchet means (52) co-operating with a plurally of teeth (44) on said drum (12) which are angularly spaced by half (d) said angular spacing, said stop member being selectively activable to lock said drum in an angular position corresponding to the characters of said pairs of circumferences.

Inventors: BERRUTI PIERANGELO, BERRUTI, PIERANGELO
Applicants: OLIVETTI & CO SPA, ING. C. OLIVETTI & C., S.P.A.
Application year: 1988
Main classification: B41J27
IPC codes: B41J1, B41J27