GB2087800A - Printing device - Google Patents

Abstract

A printing device, which may be hand held, having an ink-on-demand type ink jet head (1) and a clog- prevention cover (3) which is movable into and out of engagement with a nozzle of the ink jet head, a lever or push-button (4) being provided on the exterior of the device for manually moving the cover (3) at least out of engagement with the nozzle. <IMAGE>

Description

SPECIFICATION Printing device The present invention relates to printing devices having an ink-on-demand type ink jet head and a clog-preventing cover which is movable into and out of contact with a nozzle of the printing head.

Ink jet printers of the ink-on-demand type require a small amount of energy for printing and hence can be powered by a battery. It is therefore proposed to use this type of printer as a portable printer in an electronic desk calculator. However, the printer has a disadvantage in that the end of the nozzle of the printing head thereof, being only several tens of microns in diameter, tends to become clogged with dried ink, or highly viscous ink, thus rendering the printer incapable of printing. A conventional method of preventing the nozzle from becoming clogged has been to cover the front face of the nozzle automatically with the aid of a solenoid when the printer is not being used. However, for complete prevention of nozzle clogging, it is necessary to press the cover against the nozzle with a considerable force.A relatively large force is also required to press the cover against the nozzle to prevent ink from flowing out of the nozzle when the portable printer is accidentally dropped or is subjected to an impact. An increased amount of energy is thus required to cover the nozzle, offsetting the low energy consumption advantage of the ink jet head. A source of drive such as a solenoid or motor may be used to press the cover against the nozzle, but these are relatively large and are relatively expensive to manufacture. A complicated mechanism is also required for such a printer and this again increases manufacturing costs.

The present invention seeks to eliminate the problems discussed above. Thus, the present invention seeks to provide a cover for an ink jet head nozzle, the cover reliably preventing clogging and also preventing leakage when the head is subjected to an impact, whilst keeping the additional energy consumption due to the provision of the cover to a minimum.

According to the present invention there is provided a printing device having an ink-on-demand type ink jet head, and a clog-prevention cover movable into and out of engagement with a nozzle of the ink jet head, means being provided on the exterior of the device for manually moving the cover at least out of engagement with the nozzle.

The cover may be connected to or form part of a lever which projects out of a case in which the device is housed, or the cover may be connected to or form part of a lever which is engageable by a push-button which projects out of a case in which the device is housed when the cover is out of engagement with the nozzle.

A cover member may be provided to cover the device and to press against the said projecting lever or projecting push-button when the device is not to be used.

Preferably, spring means are provided for urging the cover into engagement with the nozzle.

The or further spring means may be arranged to hold the cover out of engagement with the nozzle when the device is to be used.

Preferably, detecting means are provided for detecting whether the cover is in or out of engagement with the nozzle.

Preferably the detecting means comprises two electrical contacts which are moved into and out of engagement with each other when the cover is moved.

The two electrical contacts may form part of a first circuit which is arranged to effect intermittent ink ejection out of the nozzle if the cover is out of engagement with the nozzle and the device has not been operated for a predetermined period of time.

An ink absorbing member may be provided adjacent to the nozzle for absorbing excess ink.

The two electrical contacts may form part of a second circuit which is arranged to generate an alarm if the cover is out of engagement with the nozzle and the device has not been operated for a predetermined period of time.

The detecting means may be arranged to govern the provision of electrical power to at least part of the printer.

The invention will now be described, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a first embodiment of a printing device according to the present invention, Figure 2 is a cross-sectional view of part of a second embodiment of a printing device according to the present invention, Figure 3 is a cross-sectional view of a third embodiment of a printing device according to the present invention, Figure 4 is a cross-sectional view of part of a fourth embodiment of a printing device according to the present invention, Figures 5 and 6 show case members in which the printing device as shown in Figures 4 and 3, respectively, may be housed, Figures 7 and 8 are cross-sectional views of part of a fifth embodiment of the printing device according to the present invention, Figure 9 shows a circuit diagram for incorporating into the printing device shown in Figures 7 and 8, Figure 10 shows the form of signals produced during the operation of the circuit shown in Figure 9, Figure 11 shows an alarm circuit which may be incorporated into printing devices such as those shown in Figures 2 and 4, Figure 12 shows the form of signals produced during the operation of the circuit shown in Figure 11, Figures 13 and 14 are cross-sectional views of parts of sixth and seventh embodiments of a printing device according to the present invention, Figures 15 and 16 are cross-sectional views of parts of eighth and ninth embodiments of a printing device according to the present invention, and Figures 17 and 18 show how printing devices such as those shown in Figures 15 and 16 may be used in practice.

Figure 1 shows a printer having an on-demand type ink jet head 1, an ink tank 2 for supplying ink to the ink jet head 1, a rubber cover 3 for covering a nozzle of the ink jet head 1, the rubber being of a composition which is not attacked or corroded by the ink, a lever 4 on which the cover 3 is mounted, a pin 5 about which the lever 4 is pivoted, a spring 6, recording paper 7, a platen 8, a roller 9 for pressing the paper 7 against the platen 8, a casing 10, a control circuit 11, a liquid crystal display 12, a push-button switch 13, a battery 14, a recess 15 in the casing 10, and a motor 16.

In such an arrangement, the lever 4 is in the solid-line position when the printer is not in operation, and in this position the cover 3 is pressed against the front face of the ink jet head 1 to prevent a nozzle of the latter from becoming clogged. During a printing operation, a portion of the lever 4 which projects out of the casing 10throughthe recess 15 is manually moved in the direction of the arrow A. The spring 6 is arranged with respect to the lever 4 and the pin 5 such that the lever 4 will have two stable positions.Thus, the lever 4 is caused to stay in the broken-line position, in which the cover 3 is spaced from a nozzle of the ink jet head 1, after the lever has been moved in the direction of the arrow A, and to stay in the solid line position when the lever 4 has been moved to press the cover 3 against the nozzle of the ink jet head 1. When the lever 4 is in the broken-line position, the push button switch 13is depressed to actuate the control circuit 11 in order to print an indication displayed by the liquid cyrstal display 12 on the printing paper 7, and also to energise the motor 16 to move the ink jet head 1 by means of a drive mechanism (not shown) in response to printing signals produced by the control circuit 11.

In the embodiment described above, the cover 3 may be moved into and out of contact with the front face of the nozzle of the printing head 1 in response to manual operation of the part of the lever 4 which extends to the exterior of the casing 10, and the cover can be pressed against the nozzle with a relatively large force without consuming energy from the battery. The nozzle can thus reliably be prevented from becoming clogged with ink, and the ink can be prevented from flowing out upon impact when the printer is dropped, a situation which frequently occurs with such portable devices.

Since there is no need for a complicated mechanism for automatically moving the cover into and out of engagement with the nozzle, the printer is less expensive to manufacture, and it can be made small-size. A liquid crystal display is used in the foregoing embodiment since it consumes only a small amount of energy and thus, together with the low energy consumption of the ink jets, it is possible to arrange for the battery powering the printer to have a long service life.

Figure 2 shows another embodiment of the present invention, in which the lever 4 can be moved by an opening push button 21 and a closing push button 22 to bring the cover 3 into and out of contact with the front face of the nozzle of the ink jet head 1 Contacts 23 connected to lead wires 24 are provided so that the wires 24 are in electrical contact with each other at a certain position of the lever 4.

The lead wires 24 may be connected in a circuit which includes a power supply for the printing device so that the mechanism for opening and closing the cover can serve also as an actuation switch for switching the printing device on and off. If the printing device is incorporated into an electric desk calculator, the calculator may be energized by a main power switch (not shown) for carrying out an arithmetic operation, and the nozzle may be closed by the cover 4 when recording is unnecessary, while the arithmetic operation is being carried out.When the nozzle is closed by the cover, the printing device is not actuated so there is no danger of it being accidentally switched on or damaged, or of the drive motor being continuously supplied with an excessive current, which would otherwise happen with such an arrangement if the ink jet head 1 was reciprocably movable across the guide shaft 25 to scan the recording paper 7 for printing. The lead wires 24 may also serve to give an alarm when the nozzle is not covered after a printing operation has been completed, orto detect whether or not the nozzle is closed in order to determine when intermittent ink ejections from the nozzle should be effected to prevent the nozzle from becoming clogged.

While in the foregoing embodiment the contacts 23 are held in contact with each other when the cover 4 is held away from the nozzle, they may be arranged so as to be out of contact with each other when the nozzle is not covered. Detection mechanisms other than such contacts may also be used.

While in the above embodiments the cover can be moved into and out of contact with the nozzle either directly or by manually operating push buttons projecting through the recess 15 in the casing 10, it is possible to dispense with the need for such a recess by constructing the casing 10 from a thin sheet of plastics material through which a force can be transmitted to move the cover into and out of contact with the nozzle.

Instead of moving the cover, it is possible instead to manually move the ink jet head so as to bring the nozzle into and out of contact with the cover.

While in the foregoing embodiments the lever and the cover are described as separate members, they may be integral with each other and may be formed of a plastics material.

Further embodiments of the present invention will now be described with reference to Figures 3 to 6.

These embodiments seek to provide an ink jet printer having means for ensuring that the cover is moved into engagement with the nozzle of the printing head once a printing operation has been completed should the operator forget the move a lever such as that described above to the closed position.

Figure 3 schematically shows a mechanism for bringing a cover into and out of contact with a nozzle in an ink jet printer.

The printer comprises a printing head 101, recording paper 102 which is in the form of a fanfold of paper in the illustrated embodiment, a cover 103, an ink tank 104, a spring 105, a paper feed roller 106, a display unit 107, a control circuit 108, input switches 109, a casing 110, an electrical cell 111, and a motor 112.

During a printing operation, the cover 103 is manually angularly moved in the direction of the arrow 1 B. With the spring 105 urging the cover 103 into one of two stable positions, the cover 103 is moved into and held in the dotted-line position. With the parts thus positioned, the control circuit 108 drives the printing head 101 to effect recording on the recording paper 102. The motor 112 is energized by the cell 111 to drive a carriage (not shown) of the printing head 101,the paper feed roller 106, and other parts. When the printing operation is completed, the cover 103 is manually pressed against the printing head 101 and held there by the spring 105 to thereby prevent the printing head 101 from becoming clogged with ink and the ink from flowing out of the printing head.If a relatively strong spring 105 is used, the cover 103 is reliably pressed against the printing head without the need to consume energy from the cell 111 and hence no large-size motor or solenoid is required for moving the cover 103. As shown in Figure 3, the cover 103 can project to a relatively large extent out of the casing 110. With such an arrangement, it is easily recognised when the cover 103 has not been closed as the device becomes awkward to carry and, therefore, the operator is likely to notice that he has forgotten to close the cover 103. Thus, there is less chance that someone will carry the device without closing the cover 103. This is obviously desirable as with the cover open ink is likely to leak out of the nozzle and stain articles, such as the operator's clothing, in the near vicinity.

Figure 4 illustrates another embodiment of the present invention. According to this embodiment, a cover 103 can be brought into and out of contact with a printing head by a cover-releasing button 120 and a cover-pressing button 121. Contacts 122 detect whether the cover 103 is in or out of contact with the printing head 101 and may also act as a switch for the printing device. The push buttons 120 and 121 are arranged to engage the cover 103 at distances from the pivot thereof such that the cover-pressing push button 121 projects out of the casing 110 to an appreciable extent when the cover 103 is not pressed against the printing head 101.

As shown in Figure 5, the printer shown in Figure 4 may be incorporated in a cover member 130 which is mounted on the casing 110 and is arranged to be closed when the device is carried. The coverpressing button 121 is depressed by the cover member 130 as the latter is closed, thereby pressing the cover 103 against the ink jet head 101.

Another way of ensuring that the cover 103 is closed is illustrated in Figure 6 which shows part of a cover 103 which is depressed when a cover member 140 is slid over the casing 110.

Further embodiments of the present invention will now be described with reference to Figures 7 to 10.

These embodiments seek to provide an ink jet printer with means for preventing the nozzle thereof from becoming blocked after a printing operation has been completed even if a manually operable cover for the nozzle has been left open.

Figures 7 and 8 schematically show a mechanism for bringing a cover into and out of contact with a nozzle in an ink jet printer.

The printer comprises a printing head 201, recording paper 202, a cover 203, an actuator lever 204 for actuating the cover 203, a pair of contacts 205, wires 206, a spring 207 for producing bistable conditions, a nozzle 208, a casing 210, a guide shaft 211 for guiding the printing head 201 in scanning relation to the recording paper 202, and a platen 212. The Figure also shows ink droplets 209 being projected from the printing head 201.

During a normal printing operation, the lever 204 is held in the position shown in Figure 7, i.e. out of engagement with the nozzle, by the spring 207, thereby closing the contacts 205. With the lever 204 thus positioned, the printing head 201 is caused by a drive mechanism (not shown) to move reciprocably along the guide shaft 211. In synchronism with this reciprocating movement, the printing head 201 is energized by signals from a control circuit (not shown) to print on the recording paper 202. After recording has been finished, the printing unit is rendered inoperative, if necessary, by manually moving the lever 204 angularly to the position shown in Figure 8, to hold the cover 203 against the nozzle 208, thereby preventing the nozzle from becoming clogged or preventing ink from flowing out of the nozzle.

By manually moving the cover 203 into and out of contact with the nozzle, the cover 203 can be pressed against the nozzle to reliably prevent clogging. The force with which the cover is pressed against the nozzle does not result in an increase in energy consumption, and does not render the device complicated, large in size, or expensive to manufacture.

However, the nozzle would tend to become clogged should the operator forget to close the cover 203 and leave the cover 203 open for a long period of time.

Figure 9 shows a circuit diagram of a circuit which may be incorporated into such a printing device to prevent nozzle clogging even if the cover 203 is left open. The contacts 205 shown in Figure 7 and Figure 8 are shown as contacts 220 in Figure 9. A main control circuit 221 effects information processing such as the processing of various inputs and operation processing. The circuit comprises a printing control circuit 222 for controlling the printing device, a timer switch 223, a printing head control circuit 224 for controlling the printing head 201, a driver 225, a piezo-electric element 226 serving as a source of drive for the printing head 201, a discharge resistor 227, an inverter 228, AND gates 229 and 230, and an OR gate 231.

In a normal printing operation, the main control circuit 221 produces a signal to energize the driver 225 via the printing device control circuit 222 and the printing head control circuit 224, whereupon the piezeo-electric element 226 is energised to cause the printing head 201 to eject ink 209 for recording.

When the cover 203 is closed, as shown in Figure 8, to leave the contacts 205 (the contacts 220 in Figure 9) open, the printing control circuit 222 is not energized even if commanded by the main control circuit 221 to effect printing. This prevents the printing device from being actuated while the cover 203 is being pressed againstthe nozzle, thus avoiding damage to the device by a continuous flow of an excessive current through a motor (not shown) for actuating the device.

The manner in which the device operates when the cover 203 remains open after a normal printing operation has been finished will now be described with referenceto Figure 10. Output signals from the circuit components shown in Figure 9 are indicated as signals S22, S23, S20, S24. A predetermined interval of time Ti after printing has been finished, the timer switch 223 produces a signal S23 for an interval of time T2. The signal energizes the printing head control circuit 224, which generates a signal S24 which is applied to the driver 225 to effect ink ejection. While the cover 203 remains open, the contacts 220 are closed to cause a signal S20 to be in the low state.Upon elapse of another interval of time Tithe timer switch 223 produces a signal for a time interval T2 so as to effect intermittent ink ejection.

Thus, when the operator forgets to close the cover 203, ink will be ejected at predetermined intervals of time, thereby preventing the nozzle from becoming clogged. When the cover 203 is manually closed after a certain interval of time, the signal from the contacts 220 goes high as indicated at S20 to prevent the signal from being applied to the driver 225 as shown at S24. No ink is therefore ejected at this time.

The magnitude of the intervals of time Ti, T2 are suitably selected in dependence upon the type of printing head, the ink used, and other parameters.

Generally, T1 should be as short as possible and T2 should be as long as possible in order to prevent clogging of the nozzle. Conversely, however, T1 should be as long as possible and T2 should be as short as possible to reduce the amount of ink and energy consumed during the intermittent ejection and for preventing the recording paper 202 and device from becoming stained with ink. In a typical embodiment T1 may be 12 hours and T2 may be 5ms.

While in the illustrated embodiment the main control circuit 221, the printing device control circuit 222, the printing head control device 224 and the other components are shown separately for ease of description, they may be arranged integrally. The polarity of currents for operation of the contacts 205 and drive 225 may be selected so as to be suitable for the situation in which the printer is to be used.

Besides the intermittent ink ejection described above, it is also possible to use a piezo-electric buzzer, a light-emitting diode, or similar devices which are intermittently actuated to provide a warning that the cover has been left open. A circuit for such an alarm system will be described below with reference to Figures 11 and 12. Such devices, although helping to prevent the nozzle from becoming clogged, may, of course, involve the consumption of more power and increase the manufacturing costs of the printer.

If the printer described in relation to Figures 7 to 10 is left with the cover open for a long period of time, energy will be consumed to intermittently eject ink, but the energy used is only in the order of a few FJ at the most, and hence this causes no energy consumption problem, particularly as it is not necessary to actuate the printing device each time the ink is ejected.

It is possible that the recording paper 202 or printing device might become stained with ejected ink if the cover 202 is left open for an exceedingly long period of time. To cope with such a problem, the printing device can be actuated simultaneously with the ejection of ink to intermittently feed the paper 202, thus preventing the paper 202 or device from becoming stained. If the platen 212 is made of a porous material capable of absorbing ink, the problem can be avoided without the need to intermittently feed the paper 202.

In the illustrated embodiment, the contacts 202 detect whether the cover 203 is open or closed, and the printing device is not actuated when the cover 203 is closed, i.e. the mechanism for bringing the cover 203 into and out of contact with the nozzle serves as a switch for operating the printing device.

However, as an alternative, the contacts may be disposed of and the printing head 201 may be actuated after a predetermined interval of time has elapsed irrespective of whether the cover 203 is open or closed after a printing operation has been completed. When the cover 203 is open, ink can be ejected, but when the cover 203 is closed, ink cannot be ejected. With such an arrangement, the contacts 205 can be dispensed of although energy consumption is increased.

A circuit for providing an intermittent alarm, rather than intermittent ejection, will now be described with reference to Figures 11 and 12. This circuit can, of course, be incorporated into any of the embodiments described above which have electrical contacts for detecting whether or not the cover is pressed against the nozzle of the ink jet head. For instance, the circuit can be incorporated into the printer shown in Figure 2 which has contacts 23, or into the printer shown in Figure 4 which has contacts 122.

Figure 11 is a block diagram of a circuit for providing an intermittent warning when a cover is left open.

The circuit comprises power supply switches 320 and 321, contacts 322 which may be the contacts 23 or 122 shown in Figures 2 and 4, a main control circuit 323, a first timer switch 324, an OR gate 325, a second timer switch 325, an AND gate 327, and signal generating means 328. During a normal printing operation, the power supply switch 320 is closed and the power supply switch 321 is open. The main control circuit 323 effects various information processings such as operation processing and control of the printing device. Each time a printing operation is effected, the timer switch 324 is reset.

When no printing is performed for a given interval of time, the first timer switch 324 produces as an output a signal S324 as shown in Figure 12.

The signal S324 energizes the second timer switch 326 which produces a signal S326 for a predetermined interval of time, for example, one minute. The signal S326 energizes the signal generating means 328 which may comprise a piezo-electric buzzer (not shown). The signal generating means 328 warns the operator that he has forgotten to close the cover until the cover is manually pushed against the nozzle causing the contacts 322 of Figure 11 to be opened whereupon the signal S322 goes high. The signal S328 is rendered low by the AND gate 327 to de-energize the piezo-electric buzzer (not shown).

The operation described above is started by the timer switch 324 when no printing has been effected for a predetermined interval of time. However, an alarm operation can be started when the power supply switch 320 is turned off. When the power supply switch 320 is turned off the control circuit 323 is de-actuated but the switch 320 is linked with the power switch 321 so that when the switch 320 is turned off the switch 321 is turned on. When the power supply switch 321 is turned on the second timer switch 326 produces a signal S326 for a predetermined interval of time to give an alarm to warn the operator that he has forgotten to close the cover in a manner similar to that described above.

As will be understood from the embodiment described above, an alarm is given for example by a buzzer unless the nozzle is covered when the power supply switch is turned off or when printing has not been effected for a predetermined interval of time, whereby the nozzle is prevented from becoming clogged even though the operator may have forgotten to cover the nozzle.

In the foregoing embodiment a piezo-electric buzzer is used to provide the alarm, however an electro-magnetic buzzer, an incandescent lamp, a light-emitting diode, or a liquid crystal display may be used either independently or in combination to give an alarm. Care should be taken, however, to ensure that the energy consumed by the alarm system is not unnecessarily high as besides reducing battery life this can impair the reliability with which the alarm is set off. If no timer switch 326 is used or the timer switch 326 is set to give an alarm for a relatively long interval of time until the nozzle is covered, signal generating means having a low energy consumption such as a liquid crystal display should preferably be used.

The time intervals involved in the alarm operation may be varied considerably but, as an example, an alarm lasting for 30 seconds may be given once every hour until the nozzle is covered as this consumes relatively little energy and the reliability with which the alarm is set off is not greatly affected by this level of energy consumption.

It is advantageous from the standpoint of manufacturing and running costs to construct the signal generating means such as the liquid crystal display mentioned above so that it not only provides the alarms, but is also arranged to indicate information.

As an alternative to the embodiments described above, the printer may be provided with means for automatically pressing the cover against the nozzle of the printing head when a printing operation is completed. Such a device will be described with reference to Figures 13 and 14.

Figure 13 shows a printer having an ink jet head 401, an ink tank 402 for supplying ink to the inkjet head 401, a rubber cover 403, a lever 404 on which the cover 403 is mounted and which has a pawl 404a, a pin 405 about which the lever 404 is pivotable, a first spring 406, recording paper 407, a platen 408, a roller 409 for pressing the paper 407 against the platen 408, a casing 410, a release lever 411, a roller 412 mounted on a distal end of the release lever 411, a second spring 413, a solenoid 414, a recess 415 in the casing 410, and a pin 416 about which the release lever 411 is angularly movable.

With such an arrangement, the lever 404 is in the solid-line position when the printer is not in operation, and the cover 403 is pressed against the front face of the ink jet head 401 to prevent a nozzle thereof from becoming clogged. During a printing operation, a portion of the lever 404 which projects out of the casing 410 through the recess 415 is manually angularly moved in the direction of the arrow 4A. As the lever 404 turns, the pawl 404a of the lever 404 pushes the roller 412 to move the release lever 411 angularly in the direction of the arrow 4B until the pawl 404a is able to pass around the roller 412. The release lever 411 then returns by means of the spring 413 to the position shown in Figure 13 to hold the lever 404 in the broken-line position even when the manual push on the lever 404 is released.

With the cover 403 spaced away from the inkjet head 401, a control circuit (not shown) generates a signal to actuate the ink jet head 401 to effect recording on the paper paper 407. After the recording is completed, either a printing stop switch (not shown) is actuated, or the control circuit generates a signal in the absence of a recording signal for a predetermined period of time, to energize the solenoid 414.The release lever 411 is magneticaiy attracted by the solenoid 414 and is anguiarly moved by the magnetic force thereof about the pin 416 in the direction of the arrow 4C until the roller 412 disengages from the pawl 404a of the lever 404, whereupon the lever 404 is caused by the first spring 406 to turn in the direction of the arrow 4D, thereby pressing the cover 403 against the front face of the ink jet head 401.If the first spring 406 is sufficiently strong and can overcome the second spring 413 which is acting to hold the lever 411 in the position shown in Figure 13, it may only be necessaryforthe lever 411 to be moved a small distance in the direction of the arrow 4B before the first spring 406 is able to cause the pawl 404a to disengage from the roller412. Thus, the solenoid 414 need only be designed so as to be able to move the lever 414 a small distance in the direction 4C. The solenoid 414 does not therefore need to be large and hence expensive to manufacture.

As will be understood from the above description, the cover 403 is releasable out of pressing engagement with the front face of the nozzle of the printing head 401 in response to manual operation of the part of the lever 411 on the exterior of the casing 410, and is automatically pressable back against the front face of the nozzle after a recording operation is finished.

Figure 14 shows another embodiment of a printer, the printer being somewhat similar to that shown in Figure 13. This embodiment differs from the embo diment of Figure 13 in that instead of the release lever 411 being angularly moved directly by the solenoid 414, the release lever 411 is normally held by a trigger lever 422, and the solenoid 414 is energized when the release lever 411 is spaced by a gap 424 from the release lever 422 by an eccentric cam 423. With this arrangement, there is no frictional force to overcome when solenoid 414 is actuated and the trigger 422 is moved out of engagement with the release lever 411, and hence the solenoid 421 can be made small-size and need consume only a small amount of energy.The eccentric cam 423 may be driven by a small electric motor having an efficiency better than that of the solenoid, and may be driven by the same motor which moves the printing head and feeds the recording paper.

Figure 14 shows the cover 403 when it is not engaged with the printing head 401. In this position the cover 403 is held in place by the release lever 411 which, in turn, is held in place by the eccentric cam 423. When the cover 403 is to be pressed against the printing head 401 the motor to which the eccentric cam is connected is de-actuated and the solenoid 414 is actuated so as to allow the release lever 411 to rotate and thus release its hold on a lever 404 on which the cover 403 is mounted. The cover 403 is then moved to press against the printing head 401 by the spring 406.

While in the foregoing embodiments the cover 403 is described as being angularly movable, the printing head 401 may instead be arranged so as to be movable into contact with the cover 403.

The lever 404 and the cover 403 are described as separate members, but they may be integrally formed from a plastics material.

Two further embodiments in which a cover is automatically closed after a printing operation has been completed will now be described with referenceto Figures 15to 18.

Figure 15 schematically shows a mechanism for bringing a cover into and out of contactwith a nozzle in an ink jet printer.

The ink jet printer comprises a printing head 501, recording paper 502, which is in the form of a fanfold of paper in the illustrated embodiment, a cover 503, an ink tank 504, a spring 505, a paper feed roller 506, a display unit 507, a control unit 508, input switches 509, a casing 510, an electrical cell 511, a motor 512, and a lever 513 for releasing the cover 503.

During a printing operation, the release lever 513 is depressed with a finger (not shown) for angular movement in the direction of the arrow 5E. With the parts thus positioned, the control circuit 508 drives the printing head 501 to effect a recording operation on the recording paper 502. The motor 512 is energized by the electrical cell 511 to drive a carriage (not shown) of the printing head 501, the paper feed roller 506, and other components. When the printing operation has been completed the release lever 513 is released of a finger push to allow the cover 503 to be pressed against the printing head 501 by the spring 505, thereby preventing the printing head 501 from becoming clogged with ink and inkfrom flowing out of the printing head 501.By releasing the finger after a printing operation has been completed, the cover 503 is automatically pressed against the nozzle so there is no risk of the operator forgetting to close the cover 403.

Figure 16 shows another embodiment of the present invention in which the cover is automatically closed a printing operation. In this embodiment, a cover 503 is brought into and out of contact with a printing head 501 by a cover-releasing button 520.

Contacts 522 detect whether the cover 503 is in or out of contact with the printing head 501 and also acts as a switch with a printing device. It will be apparent that when the button 520 is depressed the cover 503 is rotated out of engagement with the printing head 501, and that when the button 520 is released the cover is pressed against the printing head 501 by a spring 505a.

Figure 17 illustrates a way in which the printing device shown in Figure 16 may be used in practice. A printing operation can be carried out only when the cover-releasing button 520, shown in Figure 17(a), is depressed with a finger as illustrated in Figure 17(b).

Various systems of levers and buttons for releasing the cover may, of course, be used. In a further example, a release button 540 may be disposed on the side of the device as illustrated in Figure 18.

The cover, the release means, and the pressing means may be integrally made of a plastics material or some other material.

Although the above description has referred to the printing head of the printer as having a single nozzle which is to be prevented from becoming clogged by means of a cover, it should be understood that the printing head may have a plurality of nozzles and that each or all of these may be arranged to be covered by a cover or a plurality of covers.

It will be appreciated that printing devices such as those described above can be made very small, may be incorporated into small electronic devices such as pocket-calculators, and may be designed to be powered by a small battery. Such printing devices may also be made to be very reliable in service, give a long battery life and be relatively inexpensive to manufacture.

Claims (23)

1. A printing device having an ink-on-demand type ink jet head, and a clog-prevention cover movable into and out of engagement with a nozzle of the ink jet head, means being provided on the exterior of the device for manually moving the cover at least out of engagement with the nozzle.

2. A printing device as claimed in claim 1 in which the cover is connected to or forms part of a lever which projects out of a case in which the device is housed.

3. A printing device as claimed in claim 1 in which the cover is connected to or forms part of a lever which is engageable by a push-button which projects out of a case in which the device is housed when the cover is out of engagement with the nozzle.

4. A printing device as claimed in claim 2 or 3 having a cover member which is arranged to cover the device and to press against the said projecting lever or projecting push-button when the device is not to be used.

5. A printing device as claimed in any preceding claims having spring means for urging the cover into engagement with the nozzle.

6. A printing device as claimed in claim 5 in which the or further spring means are arranged to hold the cover out of engagement with the nozzle when the device is to be used.

7. A printing device as claimed in any preceding claim having detecting means for detecting whether the cover is in or out of engagement with the nozzle.

8. A printing device as claimed in claim 7 in which the detecting means comprises two electrical contacts which are moved into and out of engagement with each other when the cover is moved.

9. A printing device as claimed in claim 8 in which the two electrical contacts form part of a first circuit which is arranged to effect intermittent ink ejection out of the nozzle if the cover is out of engagement with the nozzle and the device has not been operated for a predetermined period of time.

10. A printing device as claimed in claim 9 having an ink absorbing member adjacent to the nozzle for absorbing ink.

11. A printing device as claimed in claim 8,9 or 10 in which the two electrical contacts form part of a second circuit which is arranged to generate an alarm if the cover is out of engagement with the nozzle and the device has not been operated for a predetermined period of time.

12. A printing device as claimed in any of claims 7 to 11 in which the detecting means is arranged to govern the provision of electrical power to at least part of the printer.

13. A printing device substantially as herein described with reference to and as shown in any of the accompanying drawings.

14. A small-size printing device having an inkjet head of the ink-on-demand type, comprising a clog-prevention cover disposed so as to be manually actuable from the exterior of the printing device into and out of contact with the front face of a nozzle of the ink jet head.

15. A small-size printing device according to claim 14 in which a mechanism for opening and closing said clog-prevention cover has at least a portion thereof serving as an electrical switching mechanism.

16. A small-size printing device according to claim 14 said clog-prevention cover being containable substantially within a casing of said printing device when pressed against said nozzle of said front face of said ink jet head and being locatable out of said casing when spaced apart from said nozzle.

17. A small-size printing device according to claim 16 including a cover member for covering said printing device and for pressing said clog-prevention cover when the latter is being carried.

18. A small-size printing device according to claim 14 comprising said cover manually actuable from the exterior of said printing device out of pressing engagement with said front face of said nozzle of said ink jet head for recording operation, and automatically pressable against said front face of said nozzle after recording is completed.

19. A small-size printing device according to claim 14 including a timer for generating a signal a given interval of time after printing is completed, and a driver responsive to said signal from said timer for driving said ink jet head.

20. A small-size printing device according to claim 19 including means for detecting whether said cover is open or closed to produce a signal for controlling said ink jet head to be driven.

21. A small-size printing device according to claim 19 including an ink absorbing member disposed in confronting relation to said nozzle with recording paper positionable therebetween.

22. A small-size printing device according to claim 19 including means responsive to said signal from said timer for issuing a warning against opening of said cover.

23. A small-size printing device according to claim 14 comprising a cover release means for releasing said cover out of pressed contact with said nozzle in response to manual operation exterior of said printing device for effecting printing operation, and means for automatically pressing said cover against said nozzle when said cover release means is released of the manual force applied from the exterior of said printing device.