Printer with interchangeable print heads

Abstract: The printer has a thermal printing head 20 which is interchangeable with an ink-jet printing head. Each of the heads can be mounted on a carriage on the printer and has terminals 23a for engagement with terminals on the carriage. The head 20 has an arm 27 which is detected by a photo-sensor on the carriage to identify the presence of a thermal printing head. The ink-jet printing head does not have such an arm. The photo-sensor determines the appropriate set of pulse currents to be supplied by the electronic circuit of the printer through the terminals 23a to operate the printing head which is in use. Alternatively the nature of the printing head which is in use can be sensed electronically in dependence on the resistance of the resistors in the two heads.

Description: Background of the Invention The present invention relates to a printer of the type that prints characters and the like by means of a printing head successively on a paper sheet fed on a platen roller, and more particularly to such a printer having the printing head devised so as to be changeable with another type printing head. Conventional printers whose printing mechanism consists essentially of a platen roller and a printing head for printing characters on a paper sheet fed on the platen roller can be classified tentatively into three types by the type of printing head used: an ink-jet type, a thermal type and a printing ribbon type. Of these three types, the last printing ribbon type printer is outside the present invention. The ink-jet type printer, in which the printing head is made up of a set of ink-jet nozzles combined with an ink fountain into a unit, has an advantage that the print face is clear and durable, and therefore, suitable for printing a formal document, definitive scientific data and others to be kept clear for a long term. However, the printer of this type has a disadvantage that the ink stored in the printing head may happen to be exhausted midway of printing continuously for a long time, for instance, in the case of printing a long series of data outputted from a scientific instrument automatically operating continuously. On the contrary, the thermal type printer, in which the printing head made up of a plurality of dot resistors thermally print characters on a thermosensible paper sheet, is free from such a disadvantage, but has a drawback that the printed characters are undurable and apt to fade away because the thermosensible paper is made to change color by heat and infrared radiations contained in the day light and ordinary lighting. Accordingly, the thermal type printer is unsuitable for printing a document or data to be kept clear for a long period of time. Such being the case, in many science laboratories, these two types of printers have conventionally been used properly in accordance with different printing purposes. Objects and Summary of the Invention The present invention aims at eliminating the above inconvenience involved in using printers, and makes it an object to provide a printer improved so as to serve both as an ink-jet type printer and as a thermal type printer. Another object of the present invention is to construct such an improved printer in a simple form by making the printing head of the printer changeable between an ink-jet type printing head and a thermal type printing head. European Patent Specification No. EP 0 352 698 A2 published on 31st January 1990, after the filing date of the present application (prior art under Art. 54(3) EPC), describes a printer having several printing stations each fitted with a removable and interchangeable printing head. The printing heads can be of different types and are mechanically and electrically coupled to the printing stations. A circuit is described which produces information as to which type of printing head is present at a printing station. The present invention is defined in the accompanying claims 1 and 2. A preferred embodiment of a printer in accordance with the invention comprises an ink-jet type printing head cartridge, a thermal type printing head cartridge, a cartridge holder devised so as to accept any optionally selected one of the above two types of printing head cartridges, a sensor for detecting which type of the cartridges is mounted on the cartridge holder, and an electronic circuit for supplying pulse currents to heating resistors installed in the respective printing head cartridges. Instructed by a signal outputted from the sensor, the pulse currents supplied by the electronic circuit have their pulse width varied in accordance with the type of the printing head cartridge mounted on the cartridge holder. Brief Description of the Drawings In the following the present invention is described in further detail with reference to the accompanying drawings, in which: Fig. 1 shows a disassembled view of the cartridge holder for holding in an embodiment of the present invention any one of the printing head cartridges shown in Figs. 2 and 3; Fig. 2 shows a perspective view of the thermal type printing head cartridge used in the above embodiment; Fig. 3 shows a perspective view of the ink-jet type printing head cartridge used in the above embodiment; Fig. 4 shows a side view illustrating the state that the thermal type printing head cartridge shown in Fig. 2 is mounted on the cartridge holder shown in Fig. 1; Fig. 5 shows a side view illustrating the state that the ink-jet type printing head cartridge shown in Fig. 3 is mounted on the cartridge holder shown in Fig. 1; Fig. 6 shows an electronic circuit for supplying, in the above embodiment, pulse currents to the printing head cartridges shown in Figs. 2 and 3; and Fig. 7 shows an electronic circuit for supplying, in another embodiment of the present invention, pulse currents to printing head cartridges substantially the same as those shown in Figs. 2 and 3. Detailed Description of the Invention In an embodiment of the present invention, one of two printing head cartridges as shown in Figs. 2 and 3 is optionally mounted on a common cartridge holder whose disassembled view is shown in Fig. 1. Referring to Fig. 1 the cartridge holder 10 is constituted essentially of a box-shaped main frame 11, a terminal plate 12, a latch member 13 and a cover plate 14. The main frame 11 consists of a frontal wall 11a, two side walls 11b and a bottom plate 11c. The cartridge holder 10 is positioned so that the frontal wall 11a of the main frame 11 may be directed toward a platen roller (not shown) to be coupled with this cartridge holder. The terminal plate 12, which is pictured with both sides 12b bent at a right angle, is inserted into the main frame 11 from below with the bent side portions 12a through two slits 11d of the bottom plate 11c. Then, with the two bent sides 12a reopened flat, the terminal plate 12 is secured to the inner surface of the frontal wall 11a by means of two fixing pin sets 15 with the same engaged with holes 11e provided to the frontal wall 11a. Between the frontal wall 11a and the terminal plate 12 are inserted cushion elements 17. The terminal plate 12 carries a plurality of contact terminals 12a, from which parallel lead wires 16 are drawn out with thier outlet portion protected by the cover plate 14. The latch member 13 has an angled U-shape configuration consisting of two parallel leg plates 13b linked to each other by a handle plate 13a. The two parallel leg plates 13b are provided with their respective pivot tenons 13c on the lower rear portion and have their lower front corners cut off to form cartridge pressing edges 13d. The thus formed latch member 13 is incorporated into the main frame 11 with the pivot tenons 13c engaged in bearing holes 11f provided to the side walls 11b of the main frame 11. The thus assembled cartridge holder accepts a printing head cartridge according to the present invention such that the cartridge has its trunk portion kept between the leg plates 13b of the latch member 13. With the latch member 13 turned to a standing posture, the cartridge pressing edges 13d press lateral protrusions provided to the cartridge, causing it to be thrusted to the frontal wall 11a of the main frame 11 so that the contact terminals 12a on the terminal plate 12 may come in contact with corresponding contact terminals provided to the cartridge. A pair of holes 18 (only one of which is seen in Fig. 1) on the frontal wall 11a of the main frame 11 is to accept positioning tenons provided, as will be described later, to the cartridge to be mounted on this cartridge holder 10. The mechanism for making the cartridge holder 10 travel along a platen roller is not mentioned here, since it is out of the subject matter of the invention and may be any conventional one. Fig. 2 shows a thermal type printing head cartridge 20 to be mounted on the above described cartridge holder 10. This type of printing head cartridge consists essentially of a thermal printer chip 22 on which are formed dot resistors 22a and their leads 22b, a flexible circuit board 23 carrying thereon printed wirings 23b and contact terminals 23a, a block-shaped heat radiator (made of aluminum) 24, a radiator stopper 25 and aframework 26 holding the stopper 25. The radiator stopper 25 is provided, on its front surface, with a pair of positioning tenons 28 and a L-shaped arm 27 turning downward rectangularly. The positioning tenons 28 are engaged with the previously mentioned pair of holes 18 (Fig. 1) provided to the cartridge holder 10. The function of the L-shaped arm 27 is described later. The framework 26 not only holds the heat radiator 24 but also makes both its sides 26b pivotally (24a) support the lower portion of the heat radiator 24 at the rear of the heat radiator stopper 25 so that the heat radiator 24 may have its upper part exposed above the radiator stopper 25. The printer chip 22 is held from below by the flexible circuit board 23, with their corresponding leads 22b and wirings 23b electrically connected to each other. The flexible circuit board 23 has its lower end fixed to the front surface of the radiator stopper 25 so that the back of the printer chip 22 may get in touch with the upper part of the heat radiator 24. Further, the framework 26 pushes, by means of a spring 26a, the heat radiator 24 toward the radiator stopper 25 (in order to make the printer chip 22 touch a thermosensible paper sheet). In the above constitution of this thermal type printing cartridge, both protrusions of the radiator stopper 25 over both the sides 26b of the framework 26 have their rear faces made to be contrapositive to the cartridge pressing edges 13d of the latch member 13 (Fig. 1) of the cartridge holder 10. A side view of the cartridge holder 10 carrying thereon this thermal type printing head cartridge 20 is shown, in conjunction with a platen roller 40, in Fig. 4. A reference numeral 50 indicates a photosensor, which is shaded by the tip of the above-mentiond L-shaped arm 27. The photosensor 50 is to judge the thermal type printing head cartridge 20 to be mounted on the cartridge holder 10. Fig. 3 shows an ink-jet type printing head 30 to be mounted, as a substitution for the thermal type printing head cartridge 20, on the cartridge holder 10 shown in Fig. 1. This type of printing head cartridge consists essentially of an ink reservoir 31 and a front plate 32 carrying thereon ink-jet nozzles 33, contact terminals 34, electric leads 35 connecting the contact terminals 34 to resistors (not shown) built in the cartridge. The front plate 32 is further provided with a pair of positioning tenons 36. The resistors built in the cartridge are located near the not shown capillaries connecting the ink-jet nozzels 33 and the ink reservoir 31, and make ink jets by being electrically energized. Since the functional principle and detailed inner construction of the ink-jet type printing head are conventionally known and out of the subject matter of the invention, their further description is omitted here. In this ink-jet type printing head cartridge 30 the ink reservoir 31 constitutes the trunk portion of the cartridge, and the front plate 32 has its protrusions 37 made to be contrapositive to the cartridge pressing edges 13d of the latch member 13 (Fig. 1) of the cartridge holder 10. A side view of the cartridge holder 10 carrying this ink-jet type printing head cartridge 30 is shown in Fig. 5, in conjunction with the same platen roller 40 as shown in Fig. 4. Fig. 5 also shows thephotosensor 50. In this case the photosensor 50 is left exposed to ambient light. In the following is described an electronic circuit for energizing the resistors of the above two types of printing head cartridge. The pulse currents to be supplied to the dot resistors 22a of a the thermal type cartridge (Fig. 2) and those to be supplied to the above-mentioned not shown ink-jet making resistors of the ink-jet type cartridge 30 (Fig. 3) are, in general, necessarily different in pulse width in accordance with their respective different functions; the dot resistors 22a heat a thermosensible sheet itself inserted on the platen roller 40 (Fig. 4), while the ink-jet making resistors heat, to make ink-jets, the capillaries (not shown) connecting between the ink-jet nozzles 33 and the ink reservoir 31. Referring to Fig. 6, which shows a circuit constitution for energizing the resistors of the printing head cartridges shown in Figs. 2 and 3, the photosensor 50 (refer also to Figs. 4 and 5) has its output signal inputted to a flip-flop 61. Thus the flip-flop 61 outputs a high-level signal according to the type of the cartridge mounted on the cartridge holder 10. Namely, when the the thermal type printing head cartridge 20 is set on the cartridge holder 10, the photosensor 50 has its output depressed to zero level by being shaded by the L-shaped arm 27 (refer to Fig. 4) causing the output of the flip-flop 61 to turn low level (or high level), whereas, since the ink-jet type printing head cartridge is not provided with a photosensor shading means, the photosensor 50 outputs a positive signal, causing the fip-flop 61 to turn high level (or low level). According to the level of the flip-flop output, a one-shot multivibrator 62 has its time constant changed to either CR₁ or CR₂. The one-shot multivibrator 62, triggered by printing instruction signals, thus outputs pulse signals with their width changed in accordance with type of printing head cartridge mounted on the cartridge holder 10. The pulses outputted from the one-shot multivibrator 62 define the gate opening period of AND gates 63 to which print pattern data signals are inputted. In this manner, transistors 64 can supply to resistors R h (representing the resistors 22b of the thermal type printing head cartridge 20 or the built-in resistors of the ink-jet type printing head cartridge 30) resistor-heating pulse currents with their width varied in accordance with the type of the printing head cartridge mounted on the cartridge holder 10. In Fig. 6 the cartridge optionally selected is represented, with its contact termimals 22a or 34 excluded, by a reference symbol K. Needless to say, the above embodiment can be modified so as to function similarly with the photosensor shading arm (27) provided not to the thermal type printing head cartridge but to the ink-jet type printing head cartridge. The present invention is further embodied in another way, in which the type of the printing head cartridge mounted on the cartridge holder 10 is identified by making use of a difference in resistance of the resistors installed in the two types of printing head cartridges. In this embodiment, all the constituents other than the electronic circuit portion are substantially the same as those of the above described and mentioned embodiment and modification, excepting that there is no photosensor needed and that, therefore, neither of the two types of printing head cartridge is provided with a photosensor shading arm. Fig. 7 shows the microcomputerized electronic circuit for controlling, in this embodiment, current supply to the printing head cartridge mounted on the cartridg holder 10. In Fig. 7 the components common to those used in the circuit shown in Fig. 6 are indicated with the same reference numerals and signs used in Fig. 6. In this circuit the transistors 64 have their collector circuits (with the resistors R h included in series) current-supplied, through a switch 78, from either of two voltage sources supplying voltages V p and V t , respectively. The voltage V t is selected for judging which type of printing head cartridge is mounted on the cartridge holder 10, while the printing is carried out with the voltage V p selected. The line related to the voltage V t contains a resistor R in series. The voltage V t is kept low enough (5 volts for example) to avoid operating a printing head cartridge, if mounted, during the process of judging the type of the cartridge. On the other hand, the voltage V p for operating a printing head cartridge is typically 24 volts. Further, the AND gates 63 switching the transistors 64 have their gate signals are supplied from an AND gate 77. The switch 78 is operated by an instruction of a CPU 71, which not only controls, through a bus line 71a, also an A-D converter (analog-to-digital converter) 74, a print instruction pulse generator 75, two gating pulse generators 72, 73 and a selector 76, but also normally supplies print pattern data signals to the AND gates 63. In such a circuit constitution, with the switch 78 turned to the line supplying the voltage V t in the beginning, the print intruction pulse generator 75 and the gating pulse generator 72 output, respectively, a series of test pulses (which are not print instruction pulse signals) and another series of pulses covering said test pulses, with the selector 76 made to select the output from the gating pulse generator 72, and, at the same time, the CPU 71 directly supplies to the AND gates 63 pulses (which are not print pattern data signals) equal to those outputted from the gateing pulse generator 72. Thus, the transistors 64 are switched on for said test pulses. Under the circumstances, if no printing head cartridge is mounted on the cartridge holder 10, the resistor R outputs the voltage V t as it is, since no currents flows in the collector circuits of the transistors 64 owing to the omission of resistors R h . The A-D converter 74, instructed by the CPU 71, picks up and inputs the voltage V t to the CPU 71. Then the CPU 71 judges any one of the printing head cartridges not to be mounted on the cartridge holder 10, and indicates the situation on a not shown display means or through any suitable alarm means. If any one of the two types of printing head cartridges has been mounted or is mounted according to the indication by the CPU 71, a series of pulse current reflecting the above mentioned test pulses flow the collector circuits of the transistors 64, causing a potential drop on the resistor R. Since the potential drop depends on the resistance of the resistors R h , namely on the type of the printing head cartridge mounted on the cartridge holder 10, the CPU 71 judges, from a voltage outputted from the A-D converter 74, which type printing head cartridge is mounted. According to the type of the printing head cartridge mounted on the cartridge holder, the CPU 71 instructs, with the switch turned to the line of the voltage V p , the print instruction pulse generator 75 to output predetermined print instruction pulse signals, and either of the two gating pulse signal generators 72 and 73 to output gating pulses covering the print instruction pulse signals. In this case the CPU 71 instructs, of course, the selector 76 to select the output of the gating pulse generator 72 or 73 outputting the gating pulses. Under the circumstances, with the AND gates 63 supplied with print pattern data signals, the printer functions either as a thermal type printer or as an ink-jet type printer. Of course, the print pattern data signals are not directly inputted to the AND gates 63 externally, but they are coded-signalized by the CPU 71 and then inputted to the AND gates 63. The process of coding the print pattern data signals is well-known, and has its description is omitted here. Incidentally, although the traveling of the cartridge holder 10 is also controlled by the CPU 71, the details of the cartridge holder control function of the CPU 71 is also omitted in the present specification together with the mechanism of making the holder travel, since they are conventional and out of the subject matter of the invention.

Claims: A printer comprising an ink-jet type printing head cartridge (30), a thermal type printing head cartridge (20), cartridge holder (10) devised so as to accept any optionally selected one of the above two types of printing head cartridges, a sensor (50) for detecting which type of cartridge is mounted on the cartridge holder, and an electronic circuit for supplying pulse currents to the respective printing head cartridges in accordance with the output from the sensor, the cartridge holder (10) comprising a main frame (11) to receive either type of cartridge, a terminal plate (12) mounted in the frame and a latch member (13) pivotable on the frame to press against the cartridge and bring contacts on the cartridge into engagement with the terminal plate. A printer for printing characters, symbols and the like on a sheet of paper placed on a platen roller by means of a travelling printing head made to travel in parallel with the platen roller, wherein either of a thermal type printing head cartridge (20) and an ink-jet type printing head cartridge (30) can optionally be selected and mounted, to constitute said travelling printing head, on a main frame (11) of a cartridge holder (10) made to travel in parallel with said platen roller, said cartridge holder (10) being provided with first electrical contact terminals (12a) on a terminal plate (12) mounted in the frame, said thermal type printing head cartridge (20) being provided with second electrical contact terminals (23a), said printing head cartridge (30) being provided with third electrical contact terminals (34) and said first electrical contact terminals (12a) being engageable with said second electrical contact terminals (23a) or said third electrical contact terminals (34), said cartridge holder (10) having a latch member (13) pivotable on the frame to press against the cartridge and bring the contact terminals (23a or 34) on the cartridge into engagement with the terminal plate (12); and a sensing means (50, 27) is provided for judging which one of said thermal type printing head cartridge (20) and said ink-jet type printing head cartridge (30) is mounted on said cartridge holder (10), and said thermal type printing head cartridge (20) and said ink-jet type printing head cartridge (30) have their respective dot resistors (22a) and ink-jet making resistors energized through an electronic circuit devised so as to generate, in accordance with an output from said sensing means (50, 27) one of two kinds of pulse currents, said two kinds of pulse currents complying with requirements of said thermal type printing head cartridge (20) and said ink-jet type printing head cartridge (30). A printer as claimed in claim 1 or 2 in which the frame of the cartridge holder has a pair of holes (18) to receive positioning tenons (28, 36) on the cartridge. A printer as claimed in any of the preceding claims in which the sensing means comprises a photosensor (50), one type of printing head cartridge (20) having an arm (27) which shades the photosensor when the cartridge is mounted in the holder and the other type of printing head cartridge (30) leaving the photosensor exposed to ambient light.

Inventors: KOHSAKA ITARU, NAKAMURA MITSUAKI, TAKIMOTO SHINGO, KOHSAKA, ITARU, NAKAMURA, MITSUAKI, TAKIMOTO, SHINGO
Applicants: SHIMADZU CORP, SHIMADZU CORPORATION
Application year: 1990
Main classification: B41J25
IPC codes: B41J25, B41J2, B41J3