Liquid ejection recording head

Abstract: A liquid injection recording apparatus comprises a recording head (1) having discharge ports for discharging recording liquid therethrough, a liquid path communicating with the discharge ports, a liquid chamber communicating with the liquid path and energy generating elements utilized for discharging the recording liquid, a temperature sensor (8) for detecting the temperature of the recording head and/or the recording liquid in the recording head, a storing tank (7) for storing the recording liquid to be supplied to the recording head, a communicating path for switchably communicating between a supply system (11) for supplying the recording liquid from the storing tank to the liquid chamber and a circulation system (11,12) for circulating the recording liquid between the storing tank and the liquid chamber, switch for switching the communicating path to either of the supply system or the circulation system in accordance with temperature information from the temperature sensor, and a control circuit for controlling the switch.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a liquid ejection recording head, and, more particularly, it relates to a liquid ejection recording head in which the recording is effected by flying liquid drops discharged from discharge ports. Related Background Art As prior art liquid ejection recording apparatus of this kind, a recording apparatus wherein minute liquid drops are discharged by creating pressure change in liquid passages due to the deformation of piezo-electric elements, and a recording apparatus wherein a pair of electrodes are further provided for deflecting liquid drops when discharged have been already known. Further, various recording systems, have been proposed such as a recording apparatus wherein exothermic elements are arranged in liquid passages and liquid drops are discharged from discharge ports by bubbles generated by suddenly heating such exothermic elements. Among these known recording apparatuses, the last mentioned recording system, i.e., the system that utilizes thermal energy to discharge the liquid drops is particularly effective in the point that it is easy to arrange the discharge ports with high density and it is possible to record at a high speed. Further, as recording heads applicable to such recording apparatus, a recording head of serial scanning type and a recording head of full-multi (full-line) type, in which the discharge ports are arranged in correspondence to a width of the record, are already known. Among them, the recording head of full-multi type is apparently effective in the point of the high speed recording operation. However, in the recording head used with the above-mentioned recording apparatus that utilizes the thermal energy, when a high density recording operation such a- a solid recording operation, particularly a high speed recording operation by high-frequency drive is carried out, there arise problems that the temperature of the recording head is excessively increased due to excessive heat which is not utilized to record (i.e., to form the liquid drops), thus changing viscosity of the recording liquid or generating dissolved bubbles in the recording liquid, and that the formation of desired bubbles cannot often be obtained when the temperature of the recording head is increased more than a certain value T1. The excessive temperature increase in the recording head often affects the formation of the proper or normal liquid drops and/or changes the diameter of a dot, thus deteriorating the quality of the record. Further, since the bubbles (dissolved bubbles) created by releasing dissolved gas in the recording liquid do not vanish immediately, they remain in the recording head for a long time. As a result, they absorb the sudden pressure change required for forming the liquid drops due to the formation of bubbles, thus often resulting to non-discharge of the liquid drops. For these reasons, in the known recording apparatus, in order to cope with the above problems and disadvantages, when the temperature of the recording head reached a predetermined value T2 set lower than the temperature T1, the recording operation was temporarily stopped until the recording head was cooled up to a certain temperature, and thereafter the recording operation was started again. Particularly, such temperature increase should cause a noticeable problem, since when the recording head is of full-multi type including the recording system for forming the liquid drops by utilizing the thermal energy, the number of the exothermic elements (heating elements) may be few thousands. However, if the recording operations are temporarily stopped, since the advantage of the high speed recording is lost even when the recording system for permitting the high speed recording operation is used, the ability of such recording system can not be effectively utilized. JP-A-56-86762 proposes an arrangement for an ink jet printer in which pressurised ink is fed to a heater, and the heated ink is then passed to an ink jet head for printing. Heated ink from the heater is also fed to a chamber which extends around a part of the ink jet head, so as to raise the temperature of the ink within the head to a reference temperature and retain it stably at the reference temperature. EP-A-0289347 proposes a substrate member for a thermal ink jet print head having a plurality of layers for circuit and ink supply interconnection. Additional layers can be provided in the form of cooling fluid channels, and cooling fluid can be circulated through the channels during operation of the print head to absorb heat from the substrate for disposal at some location external to the substrate. SUMMARY OF THE INVENTION According to the present invention there is provided a recording head as set out in claim 1. The remaining claims set out optional features. With the present invention, the temperature of the recording head can be quickly lowered to a desired range of temperature, when the temperature of the recording head increases above a predetermined value. Since the temperature of the recording head can easily be restored to the desired range of temperature quickly, the recording ability can also be restored in a very short time, thus fully utilizing the latent recording faculties of a recording system for performing the recording operation by means of drops of the recording liquid discharged by utilizing thermal energy, thereby realizing the more high speed recording operation with high quality. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a schematic partial sectional view of a main portion of a recording head according to an embodiment of the present invention; Fig. 1B is a schematic sectional view of the recording head taken along the line A - A of Fig. 1A; Fig. 1C is a block diagram showing a preferred example of a construction of a recording liquid supplying, cooling and circulating device used with the recording head of the embodiment; and Fig. 2 is a flow chart for explaining an example of control sequence of the liquid ejection recording head of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will now be explained in connection with the accompanying drawings. A liquid ejection recording apparatus using a recording head according to an embodiment of the present invention will be explained below with reference to Figs. 1A - 1C and Fig. 2. Figs. 1A - 1C show an embodiment of the present invention. In Figs. 1A and 1B, a recording head 31 of full-multi type can move relative to a recording medium (not shown) to record images on the recording medium by discharging recording liquid from discharge ports 32 facing the recording medium, in response to recording signals. The recording head 31 includes a common liquid chamber 33 formed therein, and a plurality of liquid passages 34 for directing the recording liquid from the common chamber 33 to the corresponding discharge openings 32. Heating elements 35 (e.g. electrothermal elements) are arranged in the corresponding liquid passages 34 arranged at predetermined intervals as shown in Fig. 1A. The common liquid chamber 33 includes a supply port 36A through which the recording liquid is supplied to the common chamber 33, and a second feed port 36B for feeding the recording liquid from a recording liquid storage tank 37 (Fig. 1C) (referred to as merely "tank" hereinafter) to the common chamber 33 when the recording liquid is circulated through the common liquid chamber 33. Further in the illustrated embodiment, as shown in Fig. 1B, a temperature sensor 38 is mounted on the back of a wall of the recording head 31 opposite to the liquid passages 34, and a secondary chamber 39 is formed to enclose the temperature sensor. The secondary chamber 39 is provided at its respective ends with a supply port 310A for supplying the recording liquid to the chamber 39 and a return port 310B for returning the recording liquid to the tank 37. Fig. 1C shows a recording liquid supplying, cooling and circulating system associated with the above described recording head 31. The reference numeral 311A designates a supply conduit for supplying the recording liquid from the tank 37 to the recording head 31, and the reference numeral 311B designates a return conduit for returning the recording liquid from the secondary chamber 39 to the tank 37. The reference numeral 312A designates a feed conduit for supplying the recording liquid to the secondary chamber 39 of the recording head 31 by means of a pump 313 when the head 31 is cooled, and the reference numeral 312B designates a second feed conduit for feeding the recording liquid to the common liquid chamber 33 of the head 31 when the recording liquid is circulated. The supply conduit 311A, the cooling feed conduit 312A and the circulating second feed conduit 312B are provided with valves such as solenoid valves 314, 315A and 315B, respectively. The tank 37 includes a vent valve 316. The pump 313 is driven by a driver 317, and the solenoid valves 314, 315A and 315B are controlled by corresponding switch elements 314A, 325A and 325B, respectively. A control unit 320 controls the energization and de-energization of the solenoid valves 314, 315A, 315B and pump 313 in response to a temperature detect signal from the temperature sensor 38, as will be described later. Next, the control sequence of the recording apparatus according to the embodiment will now be explained with reference to Fig. 2. When the recording operation is desired to start, the solenoid valve 314 and the vent valve 316 are opened in a step S31, and the solenoid valves 315A and 315B are closed in a next step S32. Then, the recording head 31 is driven to start the recording operation in a step S33, and then the temperature of the recording head 31 is detected by the temperature sensor 38 in a step S34. Thereafter, a step S35 determines whether the detected temperature T of the recording head 31 reaches a predetermined upper limit temperature T 0 on the basis of the temperature detect signal from the temperature sensor 38, and monitors the head until the detected temperature T reaches the upper limit temperature T 0 . And, if the step S35 judges that the temperature T has reached the upper limit temperature T 0 , the sequence goes to a step S36, where the solenoid valve 315A associated with the cooling feed conduit 312A is opened. Then, in a step S37 the pump 313 is driven to circulate the recording liquid between the tank 37 and the secondary chamber 39 of the recording head 31 in a direction shown by a chain and dot line in Fig. 1C, while detecting the temperature again in a step S38. A step S39 determines whether the detected temperature T reaches a predetermined lower limit temperature T 0 ' suitable for the recording operation. The circulation of the recording liquid is continued until the detected temperature T reaches the lower limit temperature T 0 '. When it is judged that the temperature T has reached the lower limit temperature T 0 ', the cooling solenoid valve 315A is closed in a step S40, and the pump 313 is stopped in a step S41. Then, it is determined whether the recording operation is further continued or not in a step S42; and if YES, the sequence returns to the step S34 again, thus continuing the detection of the temperature. On the other hand, if No (not continued), the liquid supplying solenoid valve 314 and the vent valve 316 of the tank 37 is closed in a step S43. Further, although not shown in Fig. 2, when a restoring operation is desired, for positively discharging the recording liquid from the discharge port 32 under pressure, the solenoid valve 314 is closed and the circulating solenoid valve 315B is opened, and the pump 313 is driven to discharge the recording liquid from the discharge openings 32. Furthermore, if the recording operation may be temporarily stopped when the temperature of the recording head 31 is increased, it is possible to control for quickly cooling the head by circulating the recording liquid through both of the secondary chamber 39 and the common liquid chamber 33 by opening the solenoid valve 315B as well as the solenoid valve 315A. Incidentally, in the illustrated embodiment, an example is described when the recording head 31 is cooled through the recording liquid only by the circulation of the recording liquid by means of the pump 313, but it is possible to further provide a fan (not shown) to cool the recording head 31 directly while circulating the recording liquid or to cool the recording liquid being circulated, thus shortening the cooling time and accordingly shut-down time of the apparatus, thereby improving the efficiency of the recording operation. As mentioned above, according to the embodiment of the present invention, even if the temperature of the recording head is increased, since the recording head can be quickly cooled through the recording liquid by circulating the recording liquid between the secondary chamber in the recording head and the tank by means of the pump, even when the recording operation is not stopped, the temperature of the recording head can be decreased, thus carrying out the high speed recording operation effectively with high quality while maintaining stable discharging operation of the liquid. Of course, the temperature when the circulation of the recording liquid is stopped is not limited to the above-mentioned lower limit temperature T 0 ' suitable for the recording operation. That is to say, such temperature can be set to any temperature T 0 '' between the lower limit temperature T 0 ' suitable for the recording operation and the upper limit temperature T 0 . In other words, the temperature T 0 '' may meet the relation T 0 ' ≦ T 0 '' ≦ T 0 . However, if the temperature T 0 '' is near the temperature T 0 , the liquid circulation cooling mode will start again shortly after the recording operation is re-started so the temperature T 0 '' should preferably be set to a value near the temperature T 0 ', and more preferably set to the relation T 0 '' = T 0 ' . However, since there may be the case that the temperature of the recording head cannot be lowered to the temperature T 0 ' by the circulation of the recording liquid, it is desirable to set temperature T 0 '' appropriately. Further, the amount of the recording liquid to be circulated can be suitably selected experimentally on the basis of the cooling ability of the liquid; however, when the recording liquid in the common liquid chamber as well as the recording liquid in the secondary chamber is circulated, it is desirable to set the circulating amount of the liquid to the extent that the recording liquid does not leak from the discharge ports while being circulated, thus shortening the shut-down time of the apparatus and preventing contamination of the recording medium.

Claims: A liquid ejection recording head (31) of the kind comprising: a plurality of discharge ports (32); a plurality of heat generating members (35) for recording by discharging recording liquid from the discharge ports by utilizing thermal energy generated by the heat generating members (35); a first liquid chamber (33) for receiving a flow of recording liquid through it in a first direction, for supply of said recording liquid to said heat generating members (35); characterised in that there is: a temperature sensor (38) for detecting the temperature of the recording head (31) and/or the recording liquid in the recording head; and a second liquid chamber (39) for receiving a cooling flow of said recording liquid. A head according to claim 1 in which the first and second liquid chambers (33, 39) are bounded by respective first and second opposed sides of a wall which separates the chambers. A head according to claim 1 or claim 2 in which said cooling flow of said recording liquid through the second liquid chamber (39) is in a second direction opposed to the first direction. A head according to any one of the preceding claims in which the temperature sensor (38) is mounted in the second liquid chamber. A head according to claim 4 in which a plurality of passages (34) for the recording liquid extend from the first liquid chamber (33) to the discharge ports (32), a wall bounds the passages (34) and the second liquid chamber (39) on opposite sides of the wall, and the temperature sensor (38) is mounted on the wall opposite the passages (34). A head according to claim 4 or claim 5 in which a control circuit initiates the cooling flow when said temperature sensor detects that the temperature (T) of said recording head exceeds a predetermined temperature (To). A head according to any one of the preceding claims further comprising a fan for cooling the recording head or the recording liquid during the said cooling flow. A head according to any one of the preceding claims further comprising a pump (313) for pumping the recording liquid in the said cooling flow.

Inventors: KOIZUMI YUTAKA, MORI TOSHIHIRO, NOZAWA MINORU, SAITO ATSUSHI, KOIZUMI, YUTAKA, MORI, TOSHIHIRO, NOZAWA, MINORU, SAITO, ATSUSHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J29
IPC codes: B41J2