Recording apparatus and method having a temperature overrise protection function

Abstract: Recording apparatus and method wherein when it is determined that an estimated temperature of an outer wall of a recording head is above a first predetermined temperature, a recording operation is stopped and waits until the temperature falls below a second predetermined safe temperature.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to recording apparatus and method, and more particularly to temperature control and accompanied process, particularly temperature overrise protection in the recording apparatus. Related Background Art A recording apparatus used in a printer, a copying machine and a facsimile machine is constructed to record an image comprising a dot pattern on a recording medium such as a paper or a plastic thin sheet, in accordance with recording information. Such recording apparatus may be classified by recording systems thereof into ink jet system, wire dot system, thermal transfer system and laser beam system. Of those, the ink jet system recording apparatus discharges ink droplets (recording liquid) from discharge ports (outlets or orifices) provided in a head and deposit them to a recording medium to record an image and it has been widely used because it satisfactorily meets general requirements of high speed recording, high resolution recording, high grade recording and low noise recording. As a general construction to meet the above requirements, a higher head drive frequency and a larger number of recording elements are used. In such a case, an energy applied to the recording head remarkably increases. Particularly, in the ink jet system in which air bubbles are generated in ink by using thermal energy to discharge ink droplets, this tendency is remarkable. For example, in the recording apparatus, a member for mounting a recording head, an ink tank, and a member for supplying ink serve to emit heat by the energy application, and when the drive frequency is doubled while a volume and a surface area of those members are kept fixed, a relatively double energy would be applied. When the number of discharge ports is doubled, a double energy would be applied, similarly. In actual, when the number of recording elements or discharge ports is increased, a volume near the discharge ports increases but a volume of other parts and a surface area thereof do not significantly increase. Thus, in the above case, approximately four times energy would be applied to the substantially constant volume and surface area. In this case, for the ink jet system using the thermal energy, several tens percent of the applied energy is emitted out of the recording head by a kinetic energy to discharge the ink and heat generation by the discharged ink. Thus, approximately two times temperature rise is generated in the recording head by the application of the four times energy. However, the temperature rise in such a recording head raises the following two problems. A first problem is due to the fact that the temperature of the recording head rises high by the approximately two times temperature rise. For example, when recording is made at a relatively high recording duty in an environment temperature of 30°C, a temperature in the apparatus rises approximately 10°C by the temperature rise of a power supply, a motor and a driver in the recording apparatus. In this case, if a recording head with a relatively low drive frequency and a relatively small number of discharge ports is used, the temperature rise will be approximately 25°C even for full painting or 100% duty recording, but when the drive frequency is doubled and the number of discharge ports of the recording head is doubled, the temperature rise will be double, that is, approximately 50°C. By summing the environment temperature and the temperature rises, the temperature of the recording head is approximately 65°C for the low drive frequency and the small number of discharge ports while it is approximately 90°C for the high drive frequency and the large number of discharge ports. When the temperature of the recording head reaches approximately 90°C, the failure of discharge is apt to occur. Further, in an apparatus in which the recording head is exchangeable or it may be touched by a user, it is necessary to pay attention to prevent the user from touching the recording head while the recording head is at a high temperature. A second problem relates to a break mode of the recording head. As explained above, the recording head temperature may reaches 90°C depending on the recording status. In this case, even if four times energy is applied to the recording head, the temperature rise thereof is approximately two times because several tens percent of energy is ejected out of the recording head as the thermal and kinetic energies when the ink is discharged. However, although the operation is that described above when the ink is normally discharge, the ink is not supplied to the recording head when an ink tank is empty and no ink to be discharged is present or when air bubbles stay in an ink supply path to block the supply of the ink, a so-called empty heat state in which the recording head is driven without ink takes place. In this case, since four times energy is supplied with no ink discharged in the above example, the energy for the discharge of the ink causes the abrupt rise of the temperature of the recording head so that the temperature of the recording head reaches one hundred and several tens °C. As a result, plastic parts of the recording head exceed a thermal deformation temperature and they may be deformed, adhered portions may be torn off by the abrupt thermal expansion or the ink stayed near the heater is burnt making the heater inoperable. The break mode which is inherent to the ink jet system is different from a break mode in the conventional thermal transfer system or wire dot system in which the temperature gently rises by the continuous recording to cause the break due to the temperature overrise determined by a heat capacity of the recording head unit. The existence of such a break mode makes difficult the solution by various countermeasures for the conventional break mode. EP-A-0442705 describes a liquid ejection recording apparatus wherein recording is stopped and the recording apparatus becomes off-line if a predetermined temperature is exceeded. US-A-5166699 describes a recording apparatus wherein, below an abnormal temperature, the temperature is controlled by controlling the recording speed while above the abnormal temperature a suction recovery operation is carried out. It is an object of the present invention to provide recording apparatus and method which allows to prevent abrupt overrise of temperature which leads to the breaking of a recording head per se. In one aspect, the present invention provides a recording apparatus in accordance with claim 1. In another aspect, the present invention provides a method of recording in accordance with claim 10. An embodiment of the present invention provides a recording apparatus and method which enable a user to be prevented from touching a recording head which is at a high temperature. In an embodiment, when a temperature of an outer wall of a recording head reaches a high temperature such as a temperature which would be dangerous to a user if the user touched the recording head, the recording operation is suspended until it reaches a safe temperature. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a perspective view of an ink jet recording apparatus, Fig. 2 shows a developed perspective view of an internal structure of a recording head in the apparatus, Fig. 3 shows a block diagram of a control unit of the apparatus, Fig. 4 illustrates a relation between a temperature detected by a temperature sensor of the recording head and a temperature of an outer wall of the recording head, Fig. 5 shows a flow chart of a head temperature control process, and Fig. 6 shows a perspective view of the ink jet recording apparatus in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 shows an outer perspective view of a printer as an ink jet recording apparatus. In Fig. 1, numeral 111 denotes a record sheet on which a character image is to be printed. The record sheet 111 inserted from the substantially top of the apparatus is fed invertedly by a sheet feed roller 116. The record sheet has a record plane thereof regulated planar by a sheet retainer 117. A recording head 112 discharges liquid droplets from a plurality of discharge ports onto the record plane of the record sheet 111 to form an image. Numeral 113 denotes a carriage for supporting the recording head 112 to scan it horizontally to the record sheet 111 in forming the image. The movement thereof is done by a lead screw 119 and guided by a guide shaft 120. Numeral 114 denotes a cap for sealing the discharge ports at the tip end of the recording head in non-print state, and numeral 115 denotes a pump coupled to the cap 114 for sucking ink from the recording head 112. The lead screw and the suction pump are driven by a motor 118 as a motive force. Fig. 2 shows a developed perspective view of an internal structure of the recording head in the apparatus. In Fig. 2, numeral 221 denotes a top plate having a plurality of liquid paths, a plurality of grooves for forming the discharge ports and a groove for a common liquid chamber communication with the liquid paths, and numeral 222 denotes a heater board having discharge heaters 223 corresponding to the liquid paths and a temperature sensor 224 formed thereon. The top plate 221 and the heater board 222 are pressed onto a base plate 226 by a spring 225 so that they are fixedly joined together. Fig. 3 shows a block diagram of a control unit of the printer. Respective elements in Fig. 3 are first explained. Numeral 10 denotes an interface, numeral 11 denotes a gate array, numeral 12 denotes a ROM, numeral 13 denotes a dynamic RAM (hereinafter referred to as DRAM), numeral 14 denotes an MPU for controlling the entire apparatus and processing data, numeral 15 denotes a head driver for driving the recording head 112, numeral 16 denotes a sheet feed motor drive for driving a motor 120, and numeral 17 denotes a motor driver for driving a carrier motor 118. In the above arrangement, when record data is sent from a host unit, not shown, through the interface 10, it is temporarily stored in the DRAM 13 by the gate array 11. The stored data is then converted from a form of raster data to a form of print image data to be recorded by the recording head 112, by the gate array 111, and again stored in the DRAM 13. The data stored in this form is transferred to the head driver 15 by the DMA transfer through the gate array 11 by a start of record signal. Thus, the ink is selectively discharged from the discharge ports of the recording head 112 for recording. Fig. 4 shows a temperature rise in the continuous discharge from all of the discharge ports of the recording head 112. In Fig. 4, an upper curve shows an output, converted to temperature, from the temperature sensor 224 in the heater pump 222 when three size A4 cassette sheets are continuously printed, and a lower curve shows a surface temperature of the head outer wall, specifically the base plate 226. As seen from Fig. 4, the surface temperature of the outer wall of the recording head 112 is correlated to the head temperature based on the output from the temperature sensor 224 in the heater board 222. Thus, the surface temperature of the outer wall may be estimated based on the output of the temperature sensor 224, and when the estimated temperature is above a predetermined temperature, the recording operation is stopped for a predetermined time interval or until the temperature of the outer wall falls below a predetermined temperature to control the temperature of the outer wall within a predetermined range. Fig. 5 shows a flow chart of a process of the temperature control. In the illustrated process, it is started as 10 msec interruption process. In a step S51, the output of the temperature sensor 224 (see Fig. 2) is read. In a step S52, the estimated temperature of the outer wall is calculated based on the output. In a step S53, whether the estimated temperature of the outer wall is higher than a first predetermined temperature which is dangerous when a user touches it or not is determined. If the decision is negative, the process is terminated. In the step S53, if it is determined that the estimated temperature is above the first predetermined temperature, the process proceeds to a step S54 to stop the recording operation. Thereafter, the process waits until the estimated temperature of the outer wall falls below a second predetermined temperature which is lower than the first predetermined temperature (steps S55, S56 and S57), when the stop of the recording operation is released in a step S58 and the process is terminated. During the stop of the recording operation, the recording head 112 is returned to its home position and the pump is activate while the discharge plane is sealed by the cap 114 so that the ink in the recording head is sucked and the heat in the head is dissipated together with the ink discharged by the suction to shorten the cooling time of the head. Fig. 6 shows an outer perspective view of an ink jet recording apparatus embodying the invention. It differs from the apparatus of Fig. 1 in that a head cover 41 for preventing the removal of the recording head is provided at the home position. In the apparatus of Fig. 6, when the temperature of the head outer wall rises, the recording head is returned to the home position and the head stays under the head cover 41 until the temperature of the outer wall of the head falls below the predetermined temperature. Thus, the user is disabled to remove the recording head because the head cover 41 hinders it. Further, at the end of the recording operation, if the temperature of the outer wall of the recording head is above the first predetermined temperature explained in Figs. 4 and 5, the recording head 112 may be returned to the home position and causes the head to stay under the head cover 41 for the predetermined time interval or until the temperature of the head outer wall falls below the second predetermined temperature to inhibit the removal of the recording head. The present invention is particularly suitable for use in an ink jet recording head and a recording apparatus in which an elecro-thermal transducer, a laser beam or the like is used to cause a change of state of the ink to eject or discharge the ink, because the high density of pixels and high resolution of recording are attained. The typical construction and the operational principles are preferably the ones disclosed in USP 4,723,129 and USP 4,740,796. The principle and the structure are applicable to a so-called on-demand type recording system and a continuous type recording system. Particularly, however, it is suitable for the on-demand type because the principle is such that at least one driving signal is applied to an electro-thermal transducer disposed on a liquid (ink) retaining sheet or liquid passage, the driving signal being large enough to provide such a quick temperature rise beyond a departure from nucleation boiling point, by which the thermal energy is provided by the electro-thermal transducer to produce film boiling on the heating portion of the recording head, whereby a bubble can be formed in the liquid (ink) corresponding to each of the driving signals. By the generation, development and contraction of the bubbles, the liquid (ink) is ejected through a discharge port to produce at least one droplet. The driving signal is preferably in the form of pulse because the development and the contraction of the bubbles can be effected instantaneously, and therefore the liquid (ink) is ejected with fast response. The driving signal is preferably such as those disclosed in USP 4,463,359 and USP 4,345,262. In addition, the temperature rise rate of the heating surface is preferably such as those disclosed in USP 4,313,124. The structure of the recording head may be those shown in USP 4,558,333 and USP 4,459,600 in which the heating portion is disposed at a bent portion, as well as the structure of the combination of the ejection outlet, liquid passage and the electro-thermal transducer disclosed in the above-mentioned patents. In addition, the present invention is applicable to the structure disclosed in Japanese Laid-Open Patent Application No. 59-123670 in which a common slit is used as the discharge port for a plurality of electro-thermal transducers, and the structure disclosed in Japanese Laid-Open Patent Application No. 59-138461 in which an opening for absorbing a pressure wave of thermal energy is formed corresponding to the discharge port. This is because the present invention is effective to preform the recording with certainty and high efficiency irrespective of the type of the recording head. In addition, the present invention is applicable to a serial type recording head in which the recording head is fixed on a main assembly, to a replaceable chip type recording head which is connected electrically with the apparatus and can be supplied with the ink when it is mounted in the main assembly, or to a cartridge type recording head having an integral ink container. The provision of the recovery means and/or the auxiliary means for the preliminary operation are preferable because they further stabilize the effects of the present invention. As for such means, there are capping means for the recording head, cleaning means therefor, pressing or sucking means, preliminary heating means which may be an electro-thermal transducer, an additional heating element or a combination thereof. Also, means for effecting preliminary discharge (not for the recording) may stabilize the recording operation. As regards the variation of the recording head mountable, it may be a single for a single color or plural for a plurality of inks having different colors or densities. The present invention is effectively applicable to an apparatus having at least one of a monochromatic mode mainly with black, a multi-color mode with different color inks and/or full color mode using the mixture of colors, which may be an integrally formed recording unit or a combination of a plurality of recording heads. Furthermore, in the foregoing embodiment, the ink is liquid. Alternatively, ink which is solidified below a room temperature and liquefied at a room temperature may be used. Since the ink is controlled within a temperature range of not lower than 30°C and not higher than 70°C to stabilize the viscosity of the ink to provide the stable discharge in a conventional recording apparatus of this type, the ink may be such that it is liquid within the temperature range when the recording signal is applied. The present invention is applicable to other type of ink. In one of them, the temperature rise due to the thermal energy is positively prevented by consuming it for the state change of the ink from the solid state to the liquid state. Other ink is solidified when it is left, to prevent the evaporation of the ink. In any case, the application of the recording signal producing thermal energy, the ink is liquefied, and the liquefied ink may be discharged. Other ink may start to be solidified at the time when it reaches the recording sheet. The present invention is also applicable to the ink which is liquefied by the application of the thermal energy. Such ink may be retained in liquid state or solid state in holes or recesses formed in a porous sheet as disclosed in Japanese Laid-Open Patent Application No. 54-56847 and Japanese Laid-Open Patent Application No. 60-71260. The sheet is faced to the electro-thermal transducers. The most effective one of the inks described above is the film boiling system. The ink jet recording apparatus may be used as an output terminal of an information processing apparatus such as a computer or the like, as a copying machine combined with an image reader or the like, or as a facsimile machine having information sending and receiving functions. In accordance with the present invention, the danger to the user is prevented and the abnormal temperature rise which causes the break of the recording head is also prevented. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and the present invention is intended to cover such modifications or changes as may come within the scope of the claims.

Claims: A recording apparatus for recording on a recording medium by using a recording head (112), said recording apparatus comprising: acquiring means (224,14) for acquiring information regarding a temperature of the recording head; means (14) for determining if the temperature of the recording head is equal to or higher than a predetermined temperature from the information acquired by said acquiring means regarding the temperature of the recording head; and control means (14) for suspending a recording operation when the determination means (14) determines that the temperature of the recording head is equal to or higher than the predetermined temperature characterised by said control means (14) being arranged to move the recording head to a predetermined waiting position at which it is difficult for a user to touch the recording head when a recording operation is suspended and to cause a recording operation to be resumed after a predetermined period following suspension of that recording operation or when the temperature of an outer wall of the recording head falls below a second, lower predetermined temperature after suspension of that recording operation. A recording apparatus according to claim 1 further comprising suction means (114,115) for sucking ink from an ink discharge port of the recording head (112) said control means (14) being arranged to cause said suction means to suck ink from said discharge port during suspension of a recording operation. A recording apparatus according to claim 1 or 2 wherein said control means (14) is arranged to cause said recording head to be covered by a cover member (41) during suspension of a recording operation. A recording apparatus according to claim 1, 2 or 3 further comprising a mechanism for enabling exchange of said recording head, said control means (14) being arranged to inhibit operation of said exchange enabling mechanism while a recording operation is suspended. A recording apparatus according to any one of the preceding claims, further comprising a carriage (113) for receiving said recording head (112). A recording apparatus according to any one of the preceding claims, comprising a recording head arranged to discharge ink by using thermal energy to generate bubbles in the ink. A facsimile apparatus comprising a recording apparatus according to any one of the preceding claims. A copying machine comprising a recording apparatus according to any one of the preceding claims. A word processor comprising a recording apparatus according to any one of the preceding claims. A method of recording on a recording medium by using a recording head in a recording apparatus, said method comprising the steps of: acquiring information regarding a temperature of the recording head; determining from the information acquired by the acquiring means if the temperature of the recording head is equal to or higher than a predetermined temperature, and suspending a recording operation of the recording apparatus when it is determined that the temperature of the recording head is equal to or higher than the predetermined temperature characterised by moving the recording head to a predetermined waiting position at which it is difficult for a user to touch the recording head when a recording operation is suspended and causing a recording operation to be resumed after a predetermined period following suspension of that recording operation or when the temperature of an outer wall of the recording head falls below a second, lower predetermined temperature after suspension of that recording operation. A method according to claim 10 further comprising sucking ink from a discharge port of said recording head during suspension of a recording operation. A method according to claim 10 or 11 further comprising causing said recording head (112) to be covered by a cover member (41) during suspension of a recording operation. A method according to any one of claims 10 to 12, further comprising inhibiting operation of a mechanism for exchanging said recording head during suspension of a recording operation.

Inventors: SHIMODA JUNJI, SHIMODA, JUNJI, SHIMODA, JUNJI, C/O CANON K.K.
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: B41J2
IPC codes: B41J2, B41J29, B41J19