Ink jet recording apparatus having temperature control function

Abstract: An ink jet recording apparatus includes a recording head for ejecting an ink from an ejection unit to cause a change in temperature in a recording period, a temperature keeping unit for maintaining a temperature of the recording head at a predetermined keeping temperature higher than an upper limit of a surrounding temperature range in which recording is possible, a temperature prediction unit for predicting an ink temperature in the ejection unit in the recording period prior to recording, and an ejection stabilization unit for stabilizing ink ejection from the ejection unit according to the ink temperature in the ejection unit predicted by the temperature prediction unit.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink jet recording apparatus for stably performing recording by ejecting an ink from a recording head to a recording medium and also to a temperature calculation method for calculating a temperature drift of the recording head. Related Background Art In the recent industrial fields, various products for converting input energy into heat, and utilizing the converted heat energy have been developed. In most of such products utilizing the heat energy, the relationship between the time and the temperature of an object obtained based on the input energy is an important control item. A recording apparatus such as a printer, a copying machine, a facsimile machine, or the like records an image consisting of dot patterns on a recording medium such as a paper sheet, a plastic thin film, or the like on the basis of image information. The recording apparatuses can be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type, and the like. Of these types, the ink jet type apparatus (ink jet recording apparatus) ejects flying ink (recording liquid) droplets from ejection orifices of a recording head, and attaches the ink droplets to a recording medium, thus attaining recording. In recent years, a large number of recording apparatuses are used, and have requirements for high-speed recording, high resolution, high image quality, low noise, and the like. As a recording apparatus which can meet such requirements, the ink jet recording apparatus is known. In the ink jet recording apparatus for performing recording by ejecting an ink from a recording head, stabilization of ink ejection and stabilization of an ink ejection quantity required for meeting the requirements are considerably influenced by the temperature of the ink in an ejection unit. More specifically, when the temperature of the ink is too low, the viscosity of the ink is abnormally decreased, and the ink cannot be ejected with normal ejection energy. On the contrary, when the temperature is too high, the ejection quantity is increased, and the ink overflows on a recording sheet, resulting in degradation of image quality. For this reason, in the conventional ink jet recording apparatus, a temperature sensor is arranged on a recording head unit, and a method of controlling the temperature of the ink in the ejection unit on the basis of the detection temperature of the recording head to fall within a desired range, or a method of controlling ejection recovery processing is employed. As the temperature control heater, a heater member joined to the recording head unit, or ejection heaters themselves in an ink jet recording apparatus for performing recording by forming flying ink droplets by utilizing heat energy, i.e., in an apparatus for ejecting ink droplets by growing bubbles by film boiling of the ink, are often used. When the ejection heaters are used, they must be energized or powered on so as not to produce bubbles. In a recording apparatus for obtaining ejection ink droplets by forming bubbles in a solid state ink or liquid ink using heat energy, the ejection characteristics vary depending on the temperature of the recording head. Therefore, it is particularly important to control the temperature of the ink in the ejection unit and the temperature of the recording head, which considerably influences the temperature of the ink. However, it is very difficult to measure the ink temperature in the ejection unit, which considerably influences the ejection characteristics as the important factor upon temperature control of the recording head, since the detection temperature of the sensor drifts beyond the temperature drift of the ink necessary in control because the ejection unit is also a heat source, and since the ink itself moves. For this reason, even if the temperature sensor is merely arranged near the recording head to measure the temperature of the ink upon ejection with high precision, it is rather difficult to measure the temperature drift of the ink itself. As one means for controlling the temperature of the ink, an ink jet recording apparatus for indirectly realizing stabilization of the ink temperature by stabilizing the temperature of the recording head is proposed. U.S. Patent No. 4,910,528 discloses an ink jet printer, which has a means for stabilizing the temperature of the recording head upon recording according to the predicted successive driving amount of ejection heaters with reference to the detection temperature of the temperature sensor arranged very close to the ejection heaters. More specifically, a heating means of the recording head, an energization means to the ejection heaters, a carriage drive control means for maintaining the temperature of the recording head below a predetermined value, a carriage scan delay means, a carriage scan speed decreasing means, a change means for a recording sequence of ink droplet ejection from the recording head, and the like are controlled according to the predicted temperature, thereby stabilizing the temperature of the recording head. However, the ink jet printer disclosed in U.S. Patent No. 4,910,528 may pose a problem such as a decrease in recording speed since it has priority to stabilization of the temperature of the recording head. On the other hand, since a temperature detection member for the recording head, which is important upon temperature control of the recording head, normally suffers from variations, the detection temperatures often vary in units of recording heads. Thus, a method of calibrating or adjusting the temperature detection member of the recording head before delivery of the recording apparatus, or a method of providing a correction value of the temperature detection member to the recording head itself, and automatically correcting the detection temperature when the head is attached to the recording apparatus main body, is employed. However, in the method of calibrating or adjusting the temperature detection member before delivery of the recording apparatus, when the recording head must be exchanged, or contrarily, when an electrical circuit board of the main body must be exchanged, the temperature detection member must be re-calibrated or re-adjusted, and jigs for re-calibration or re-adjustment must be prepared. In order to provide the correction value to the recording head itself, the correction value must be measured in units of recording heads, and a special memory means must be provided to the recording head. In addition, the main body must have a detection means for reading the correction value, resulting in demerits in terms of cost and the arrangement of the apparatus. In the method of using the ejection heaters in temperature control, two major methods are proposed. One method is a method of simply using the ejection heaters in the same manner as a temperature keeping heater. In this method, short pulses, which do not cause production of bubbles, are continuously applied to the ejection heaters in a non-print state, e.g., in a standby state wherein no recording operation is performed, thereby keeping the temperature. The other method is a method based on multi-pulse PWM (pulse width modulation) control. In this method, in place of keeping the temperature in the non-print state such as the standby state, two pulses per ejection are applied to each heater, so that the temperature of the ink at a boundary portion with the heater is increased by the first pulse, and a bubble is produced by the next pulse, thus performing ejection. In order to change the ejection quantity in this method, the pulse width of the first pulse which is ON first is varied within a bubble non-production range to increase the energy quantity to be input to the heater, thereby increasing the temperature of the ink located at an interface portion with the heater. However, the above-mentioned method, which is executed for the purpose of stabilizing the ejection quantity, has the following problems to be solved. In the method using the temperature keeping heater, the entire head having a large heat capacity must be kept at a predetermined temperature by the temperature keeping heater, and extra energy therefor must be input. In addition, the temperature rise requires much time, and results in wait time in the first print operation. Furthermore, in a portable recording apparatus, since a battery must also be used for keeping the temperature, the maximum print count is undesirably decreased. When the temperature keeping heater and ejection heaters are simultaneously turned on, a large current must instantaneously flow through a power supply, a flexible cable, and the like, thus increasing cost and disturbing a compact structure. In the method using the multi-pulse PWM control, since the pulse width of the second pulse for bubble production is fixed, and that of the first pulse is varied to vary the energy quantity to be input to the head so as to vary the ejection quantity, energy larger than normal must be supplied to the head in order to obtain the maximum ejection quantity. Therefore, although real-time characteristics can be remarkably improved as compared to the method using the temperature keeping heater, a further improvement is required for instantaneous power and the load on the battery. It is also required to record a halftone image by controlling the ink ejection quantity according to a halftone signal. However, in the above-mentioned ejection quantity control, the ejection quantity variation range is not sufficient, and is required to be further widened. EP-A-0376314 describes a liquid jet recording apparatus wherein a non-recording period is measured and a procedure for determining a correction value for a temperature server of a recording head of the apparatus is executed when a predetermined period (a time period required for the recording head to reach an ambient temperature) passes without a recording operation. The present invention has been made to solve the above-mentioned problems, and has as its object to provide an ink jet recording apparatus, which predicts the ink temperature in an ejection unit with high precision, and stabilizes ejection so as to correspond to the ink temperature drift. According to one aspect of the present invention there is provided an ink jet recording apparatus comprising: a head temperature detection member provided on a recording head for ejecting ink; a reference temperature detection member provided on a main body of the apparatus; calibration means for calibrating a head temperature detected by said head temperature detection member at a predetermined timing on the basis of a reference temperature detected by said reference temperature detection member; said calibration means comprising timer means for measuring a non-recording period; and said calibration means being arranged to calibrate the head temperature detected by said head temperature detection member after the measured non-recording period exceeds a predetermined period of time, characterised by: said timer means being capable of measuring the non-recording period even when the apparatus is in a power OFF state; and by said calibration means being arranged to calibrate the head temperature detected by said head temperature detection member on the basis of the reference temperature detected by said reference temperature detection member before the beginning of the next recording or on a power ON of said ink jet recording apparatus after the measured non-recording period exceeds a predetermined period of time. In another aspect the present invention provides a method of operating an ink jet recording apparatus having a head temperature detection member provided on a recording head for ejecting ink and a reference temperature detection member provided on a main body of the apparatus, the method comprising the steps of calibrating a head temperature detected by said head temperature detection member at a predetermined timing on the basis of a reference temperature detected by said reference temperature detection member, wherein the calibration step is carried out by measuring a non-recording period using timer means, and calibrating the head temperature detected by said head temperature detection member on the basis of the reference temperature detected by said reference temperature detection member when the measured non-recording period exceeds a predetermined period of time, characterised by measuring the non-recording period using as said timer means, timer means capable of measuring the non-recoding period even when the apparatus is in a power OFF state, and by calibrating the head temperature detected by said head temperature detection member on the basis of the reference temperature detected by said reference temperature detection member before the beginning of the next recording or on a power ON of said ink jet recording apparatus after the measured non-recording period exceeds a predetermined period of time. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing an arrangement of a preferable ink jet recording apparatus which can embody or adopt the present invention; Fig. 2 is a perspective view showing an exchangeable cartridge; Fig. 3 is a sectional view of a recording head; Fig. 4 is a perspective view of a carriage thermally coupled to the recording head; Fig. 5 is a block diagram showing a control arrangement for executing a recording control flow; Fig. 6 is a view showing the positional relationship among sub-heaters, ejection (main) heaters, and a temperature sensor of the head; Fig. 7 is a graph showing output characteristics of a temperature sensor of a recording head; Fig. 8 is a flow chart showing calibration of a temperature detection member of a recording head;. Fig. 9 is a flow chart showing calibration of a temperature detection member of a recording head; Fig. 10 is a flow chart showing calibration of a temperature detection member of a recording head. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 is a perspective view showing an arrangement of a preferable ink jet recording apparatus IJRA, which can embody or adopt the present invention. In Fig. 1, a recording head (IJH) 5012 is coupled to an ink tank (IT) 5001. As shown in Fig. 2, the ink tank 5001 and the recording head 5012 form an exchangeable integrated cartridge (IJC). A carriage (HC) 5014 is used for mounting the cartridge (IJC) to a printer main body. A guide 5003 scans the carriage in the sub-scan direction. A platen roller 5000 scans a print medium P in the main scan direction. A temperature sensor 5024 measures the surrounding temperature in the apparatus. The carriage 5014 is connected to a printed board (not shown) comprising an electrical circuit (the temperature sensor 5024, and the like) for controlling the printer through a flexible cable (not shown) for supplying a signal pulse current and a head temperature control current to the recording head 5012. Fig. 2 shows the exchangeable cartridge, which has nozzle portions 5029 for ejecting ink droplets. The details of the ink jet recording apparatus IJRA with the above arrangement will be described below. In the recording apparatus IJRA, the carriage HC has a pin (not shown) to be engaged with a spiral groove 5004 of a lead screw 5005, which is rotated through driving power transmission gears 5011 and 5009 in cooperation with the normal/reverse rotation of a driving motor 5013. The carriage HC can be reciprocally moved in directions of arrows a and b. A paper pressing plate 5002 presses a paper sheet against the platen roller 5000 across the carriage moving direction. Photocouplers 5007 and 5008 serve as home position detection means for detecting the presence of a lever 5006 of the carriage HC in a corresponding region, and switching the rotating direction of the motor 5013. A member 5016 supports a cap member 5022 for capping the front surface of the recording head. A suction means 5015 draws the interior of the cap member by vacuum suction, and performs a suction recovery process of the recording head 5012 through an opening 5023 in the cap member. A cleaning blade 5017 is supported by a member 5019 to be movable in the back-and-forth direction. The cleaning blade 5017 and the member 5019 are supported on a main body support plate 5018. The blade is not limited to this shape, and a known cleaning blade can be used, as a matter of course. A lever 5021 is used for starting the suction operation in the suction recovery process, and is moved upon movement of a cam 5020 to be engaged with the carriage HC. The movement control of the lever 5021 is made by a known transmission means such as a clutch switching means for transmitting the driving force from the driving motor. The capping, cleaning, and suction recovery processes can be performed at corresponding positions upon operation of the lead screw 5005 when the carriage HC reaches a home position region. The arrangement is not limited to this as long as desired operations are performed at known timings. Fig. 3 shows the details of the recording head 5012. A heater board 5100 formed by a semiconductor manufacturing process is arranged on the upper surface of a support member 5300. A temperature control heater (temperature rise heater) 5110, formed by the same semiconductor manufacturing process, for keeping and controlling the temperature of the recording head 5012, is arranged on the heater board 5100. A wiring board 5200 is arranged on the support member 5300, and is connected to the temperature control heater 5110 and ejection (main) heaters 5113 through, e.g., bonding wires (not shown). The temperature control heater 5110 may be realized by adhering a heater member formed in a process different from that of the heater board 5100 to, e.g., the support member 5300. A bubble 5114 is produced by heating an ink by the corresponding ejection heater 5113. An ink droplet 5115 is ejected from the corresponding nozzle portion 5029. The ink to be ejected flows from a common ink chamber 5112 into the recording head. Fig. 4 is a schematic view of an ink jet recording apparatus which can adopt the present invention. In Fig. 4, an ink cartridge 8a has an ink tank portion as its upper portion, and recording heads 8b (not shown) as its lower portion. The ink cartridge 8a is provided with a connector for receiving, e.g., signals for driving the recording heads 8b. A carriage 9 aligns and carries four cartridges (which store different color inks, e.g., black, cyan, magenta, and yellow inks). The carriage 9 is provided with a connector holder, electrically connected to the recording heads 23, for transmitting, e.g., signals for driving recording heads. The ink jet recording apparatus includes a scan rail 9a, extending in the main scan direction of the carriage 9, for slidably supporting the carriage 9, and a drive belt 9c for transmitting a driving force for reciprocally moving the carriage 9. The apparatus also includes pairs of convey rollers 10c and 10d, arranged before and after the recording positions of the recording heads, for clamping and conveying a recording medium, and a recording medium 11 such as a paper sheet, which is urged against a platen (not shown) for regulating a recording surface of the recording medium 11 to be flat. At this time, the recording head 8b of each ink jet cartridge 8a carried on the carriage 9 projects downward from the carriage 9, and is located between the convey rollers 10c and 10d for conveying the recording medium. The ejection orifice formation surface of each recording head faces parallel to the recording medium 11 urged against the guide surface of the platen (not shown). Note that the drive belt 9c is driven by a main scan motor 63, and the pairs of convey rollers 10c and 10d are driven by a sub-scan motor 64 (not shown). The ink jet recording apparatus incorporates a recovery system unit, arranged at the home position side (at the left side in Fig. 4). The recovery system unit includes cap units 300 arranged in correspondence with the plurality of ink jet cartridges 8a each having the recording head 8b. Upon movement of the carriage 9, the cap units 300 can be slid in the right-to-left direction and be also vertically movable. When the carriage 9 is located at the home position, the cap units 300 are coupled to the corresponding recording heads 8b to cap them, thereby preventing an ejection error of the ink in the ejection orifices of the recording heads 8b. Such an ejection error is caused by evaporation and hence an increased viscosity and solidification of the attached inks. The recovery system unit also includes a pump unit 500 communicating with the cap units 300. When the recording head 8b causes an ejection error, the pump unit 500 is used for generating a negative pressure in the suction recovery process executed by coupling the cap unit 300 and the corresponding recording head 8b. Furthermore, the recovery system unit includes a blade 401 as a wiping member formed of an elastic member such as rubber, and a blade holder 402 for holding the blade 401. The four ink jet cartridges carried on the carriage 9 respectively use a black (to be abbreviated to as K hereinafter) ink, a cyan (to be abbreviated to as C hereinafter) ink, a magenta (to be abbreviated to as M hereinafter) ink, and a yellow (to be abbreviated to as Y hereinafter) ink. The inks overlap each other in this order. Intermediate colors can be realized by properly overlapping C, M, and Y color ink dots. More specifically, red can be realized by overlapping M and Y; blue, C and M; and green, C and Y. Black can be realized by overlapping three colors C, M, and Y. However, since black realized by overlapping three colors C, M, and Y has poor color development and precise overlapping of three colors is difficult, a chromatic edge is formed, and the ink implantation density per unit time becomes too high. For these reasons, only black is implanted separately (using a black ink). (Control Arrangement) The control arrangement for executing recording control of the respective sections of the above-mentioned apparatus arrangement will be described below with reference to Fig. 5. In Fig. 5, a CPU 60 is connected to a program ROM 61 for storing a control program executed by the CPU 60, and a backup RAM 62 for storing various data. The CPU 60 is also connected to the main scan motor 63 for scanning the recording head, and the sub-scan motor 64 for feeding a recording sheet. The sub-scan motor 64 is also used in the suction operation by the pump. The CPU 60 is also connected to a wiping solenoid 65, a paper feed solenoid 66 used in paper feed control, a cooling fan 67, and a paper width detector LED 68 which is turned on in a paper width detection operation. The CPU 60 is also connected to a paper width sensor 69, a paper flit sensor 70, a paper feed sensor 71, a paper eject sensor 72, and a suction pump position sensor 73 for detecting the position of the suction pump. The CPU 60 is also connected to a carriage HP sensor 74 for detecting the home position of the carriage, a door open sensor 75 for detecting an open/closed state of a door, and a temperature sensor 76 for detecting the surrounding temperature. The CPU 60 is also connected to a gate array 78 for performing supply control of recording data to the four color heads, a head driver 79 for driving the heads, the ink cartridges 8a for four colors, and the recording heads 8b for four colors. Fig. 5 representatively illustrates the Bk (black) ink cartridge 8a and the Bk recording head 8b. The head 8b has main heaters 8c for ejecting the ink, sub-heaters 8d for performing temperature control of the head, and temperature sensors 8e for detecting the head temperature. Fig. 6 is a view showing a heater board (H·B) 853 of the head used in this apparatus. Ejection unit arrays 8g on which the temperature control (sub) heaters 8d and the ejection (main) heaters 8c are arranged, the temperature sensors 8e, driving elements 8h are formed on a single substrate to have the positional relationship shown in Fig. 6. When the elements are arranged on the single substrate, detection and control of the head temperature can be efficiently performed, and a compact head and a simple manufacturing process can be realized. Fig. 6 also shows the positional relationship of outer wall sections 8f of a top plate for separating the H·B into a region filled with the ink, and the remaining region. (Embodiment of the invention) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In this embodiment, a temperature detection member capable of directly detecting the temperature of the recording head of the above-mentioned recording apparatus, and a temperature calculation circuit for this member are added. The control arrangement of this embodiment is the same as that shown in Fig. 5, and the arrangement of a recording head is the same as that shown in Fig. 6. In Fig. 6, head temperature sensors 8e are arranged on a heater board 853 of the recording head together with ejection heaters 8g and sub-heaters 8d, and are thermally coupled to the heat source of the recording head. In this embodiment, the output temperature characteristics of a temperature detection diode, which is formed simultaneously with a diode formed on the heater board as a portion of an ejection heater driver, are used as a temperature sensor (Di sensor). Fig.7 shows temperature characteristics of the temperature characteristics of the temperature detection member of the recording head of this embodiment. In this embodiment, the temperature detection member is driven at a constant current of 200 µA, and exhibits output characteristics, i.e., an output voltage V F of 575 ± 25 mV (25°C), and the temperature dependency of about -2.5 mV/°C. Although variations in temperature dependency are small in terms of the manufacturing process of the element, the output voltage deviates largely, and a variation of about 25°C may occur. The temperature detection precision required in this embodiment is ±2°C, and 12 ranks of identification information are required so as to measure a correction value and to provide information to the recording head upon delivery of the recording head. Variations of the temperature detection elements can be suppressed in the manufacturing process. For this purpose, however, the manufacturing cost of the recording head is undesirably increased, and it is very disadvantageous for an exchangeable recording head like in this embodiment. In this embodiment, the temperature sensor of the recording head is corrected using a reference sensor provided to the recording apparatus main body. When the detection temperature is corrected, the temperature of the ink in a common ink chamber surrounded by a top plate 8f, which temperature is important for stabilization of ejection, especially, the ink temperature in the ejection unit, can be detected with high precision, and ejection can be stabilized. (Temperature Calibration) Calibration of the temperature detection member of the recording head in this embodiment is performed using a chip thermistor 5024 arranged on an electrical circuit board of the main body in a non-record mode with the small ink temperature drift in the ejection unit. The chip thermistor 5024 is arranged on the electrical circuit board together with its detection circuit, and has already been calibrated as well as a variation of the detection circuit before delivery of the recording apparatus. Since the chip thermistor 5024 can detect the temperature in the recording apparatus main body, it is considered that the temperature of the recording head is equal to the detection value in a state wherein no energy for a temperature keeping operation and ejection is supplied to the recording head. When such energy is supplied to the recording head, the temperature in the recording apparatus main body becomes almost equal to the temperature of the recording head after an elapse of a predetermined period of time after the supply of energy. This embodiment comprises a non-record time measurement timer for measuring a non-record time. When a non-record state continues over a predetermined period of time, the temperature detection member of the recording head is calibrated to calculate a correction value for matching a value actually measured by the temperature detection member of the recording head with the detection temperature of the chip thermistor of the main body. The calculated correction value is stored in a RAM or an EEPROM 62. Thereafter, the temperature of the recording head is calculated by correcting the actually measured value using the correction value. The non-record time in this embodiment means a state wherein no energy is supplied to the recording head. Therefore, the non-record time does not include a time while the temperature of the recording head is maintained as a preliminary operation for recording. Even in a power OFF state, when a timer means backed up by a battery is available, the power OFF time may be measured for the purpose of simplifying timer control. Furthermore, as a calibration execution timing, every time the non-record time exceeds a predetermined period of time, calibration may be executed. When the non-record time exceeds the predetermined period of time, only a calibration request signal is generated, and the calibration is not executed actually at that time. Thereafter, the calibration may be executed before new energy is supplied to the recording head, e.g., before the beginning of the next recording or immediately after the power switch is turned on. The heat source in the recording apparatus includes a power supply unit of the recording apparatus, and a control element itself on the electrical circuit board in addition to the recording head. In some cases, the detection temperature of the chip thermistor 5024 as the reference temperature sensor in the main body may exceed the temperature of the remaining portion in the recording apparatus including the recording head. For this reason, in this embodiment, the detection temperature of the chip thermistor 5024 is corrected on the basis of the power-ON time of the recording apparatus. As a correction table for this operation, Table 5 presented below is used, and the same timer as that for measuring the non-record time is used for measuring the power-ON time. Internal Temperature Increase Correction Timer (min) Correction Value (°C) 0 to 2 0 2 to 5 -2 5 to 15 -4 15 to 30 -6 more than 30 -7 In this embodiment, the power-ON timer simply measures a time elapsed from when the power switch is turned on until the temperature sensor of the recording head is corrected. When the influences of the heat generation amount of the power supply and the heat generation amount of the driver for the recording head are large, a temperature rise calculated based on energy supplied to the recording head may be corrected in addition to the power-ON time. Furthermore, correction may be made on the basis of all the past factors such as the power-ON time or energy supplied to the recording head that influence the local temperature rise of the chip thermistor 5024 of the main body. Fig. 8 shows a processing flow for calibrating the temperature detection member of the recording head in this embodiment. Calibration processing will be described in detail below with reference to Fig. 8 and the block diagram of Fig. 5. When the power switch is turned on in step S400, a CPU 60 reads a Di sensor correction value (a) stored in the EEPROM 62 into its internal RAM so as to set a state wherein the Di sensor is corrected and used (S410). Then, the power-ON timer is reset/started to prepare for temperature rise correction of the chip thermistor sensor 5024 in the main body (S420). Then, the non-record timer for determining the correction timing of the Di sensor is reset/started (S440). In this state, the control stands by while checking if the non-record timer reaches a time-out state (S450) or if a print signal is input (S460). When the print signal is input first, a head heating operation is started to prepare for the print operation (S470). In this case, temperature detection for the head heating operation is performed by correcting the temperature detected by the Di sensor using the correction value stored in the EEPROM 62. After the head heating operation, the recording (print) operation is performed (S480). Thereafter, the head heating operation is stopped (S490). During the print operation, as described above, ejection stabilization control can be performed by a PWM ejection quantity control method based on the detection temperature of the recording head. In the head heating operation and the recording operation, since energy is supplied to the recording head, the temperature of the recording head is different from (normally higher than) the temperature of the chip thermistor 5024 on the main body electrical circuit board. For this reason, after the recording operation is completed, the non-record timer is reset/started (S440), thus re-waiting for the correction timing of the Di sensor. When the non-record timer has reached the time-out state in the standby state, i.e., when it is considered that the temperature in the recording apparatus main body (the temperature of the chip thermistor 5024) becomes almost equal to the temperature of the recording head, the Di sensor correction is performed. In the Di sensor correction, the temperature (Tt) of the reference thermistor (chip thermistor 5024) is read (S500), and the temperature rise correction of the temperature of the reference thermistor is performed with reference to the data from the power-ON timer for temperature rise correction (S510). The temperature rise correction is performed using a correction value b in a table (Table 5) stored in a program ROM 61 (Tt + b). Then, the Di sensor temperature (Td) is read (S530), and the Di sensor correction value (a) is calculated (S540). The Di sensor correction value is calculated as a difference (Tt + b - Td) between the temperature (Tt + b) of the reference thermistor 5024 after the temperature rise correction, and the Di sensor temperature (Td). The correction value (a) obtained as described above of the Di sensor as the temperature sensor of the recording head is stored in the backup EEPROM, and is left in the internal RAM of the CPU 60 for the next temperature control (S550). In this manner, the correction of the Di sensor is completed, and the flow returns to step S440 to prepare for the next correction timing or the print operation. As described above, since the temperature detection member of the recording head can be easily calibrated, even when an exchangeable recording head is used like in this embodiment, the temperature control of the recording head can be stably performed. When control is made using the temperature detection member of the recording head, which member is corrected easily as described above, an actual ejection quantity can be stably controlled independently of the ink temperature, and a high-quality recorded image having a uniform density can be obtained. In this embodiment, when 30 minutes have elapsed as the non-record time, the correction is performed. However, this time period may be properly set according to the required precision of calibration (correction). In this embodiment, as an example of using the calibrated temperature detection member of the recording head, double-pulse PWM control for controlling the ejection quantity is used. However, single-pulse PWM control or PWM control using three or more pulses may be used. In this embodiment, control is made to perform optimal ejection according to the temperature of the recording head. For example, this embodiment may be used in control for changing a recording speed or delaying (standing by) recording so that the temperature of the recording head falls within a predetermined range. The detection temperature of the calibrated temperature detection member may be used not only in driving control of the recording head but also in control of a known recovery system as ejection stabilization means, for example, a means for forcibly discharging the ink from the recording head, wiping means, and pre-ejection means. (1st Example pertinent to the above embodiment) In this example, the calibration timing of a temperature detection member (Di sensor) of a recording head is determined by measuring the change rate of the detection temperature of the temperature detection member. The arrangement of the temperature detection member of the recording head, and the like, the same arrangements as those in the embodiment described above are used, and only a calibration timing determination method will be described below with reference to Fig. 9. The same reference numerals in Fig. 9 denote the same steps as in Fig. 8. In this example, the change rate of the detection sensor of the Di sensor is measured from a timing immediately after the power switch is turned on (S600). The change rate of the detection temperature is measured by calculating a difference between temperatures at predetermined time intervals. In this example, the detection temperature is read every minute, and a difference between the current detection temperature stored in the internal RAM of the CPU 60 and the detection temperature one minute before is calculated as the detection temperature change rate (α). If it is determined in step S610 that the change rate is smaller than 0.2 deg/min, i.e., if it is considered that the temperature in the recording apparatus main body (the temperature of the chip thermistor 5024) becomes almost equal to the temperature of the recording head, the Di sensor of the recording head is calibrated (S610). In this example, in order to avoid frequent calibration, the presence/absence of execution of correction is checked so that correction is performed once per power ON operation (S620). If it is determined that the Di sensor is corrected for the first time, calibration is performed in the same manner as in the above embodiment, and finally, a signal indicating the end of calibration, i.e., the end of Di sensor correction is recorded (S630). In this example, since the sensor need only be corrected once when, e.g., the head is exchanged, it is sufficient that the correction is performed at least once after the power ON operation. For this reason, the temperature rise correction of the reference temperature sensor of the main body as a temperature correction method after a relatively long period of time elapses after the power ON operation described in the above embodiment may be omitted. In this example, since it is considered that the recording head is calibrated at a relatively early timing after the power switch is turned on, when the power switch is not so frequently turned on/off, the print operation for several pages after the power ON operation may be performed using an average value of temperature correction pre-stored in the ROM without using a rewritable storage element such as the EEPROM 62. When the exchange operation of the recording head can be detected by, e.g., detecting attachment/detachment of the recording head using a mechanical switch, if it is determined that the change rate is smaller than a predetermined value after an exchange signal of the recording head is input, calibration may be performed only once. In this example, when the change rate is smaller than 0.2 deg/min, the Di sensor of the recording head is calibrated. However, the reference change rate may be set according to the required precision of calibration (correction). (2nd Example pertinent to the above embodiment) This example exemplifies a method of preventing erroneous correction of a temperature detection member of a recording head. The normal temperature often cannot be detected due to a trouble such as disconnection of the temperature detection member of the recording head or an abnormality of a detection circuit of the main body. In particular, in the case of an exchangeable head, the electrical connection of the temperature detection member may be temporarily disabled. Also, the detection circuit may temporarily cause an abnormality due to electrostatic noise. As shown in Fig. 10 , when the temporary abnormality occurs, calibration of the temperature detection member is delayed or stopped. The same reference symbols in Fig.10 denote the same steps as in Fig.9. In step S640 in Fig. 10, if the correction value becomes equal to or larger than 10, it is determined that the above-mentioned abnormality occurs, and the correction value is neither stored nor updated. When the correction value is smaller than 10, the correction value is updated (S550). When an abnormal correction value is calculated, the control waits for the next correction timing. However, an abnormal temperature alarm may be generated to urge a user to re-attach the recording head.

Claims: An ink jet recording apparatus comprising: a head temperature detection member (8e) provided on a recording head for ejecting ink; a reference temperature detection member (5024) provided on a main body of the apparatus; calibration means for calibrating a head temperature detected by said head temperature detection member at a predetermined timing on the basis of a reference temperature detected by said reference temperature detection member; said calibration means comprising timer means (S440, S450) for measuring a non-recording period; and said calibration means being arranged to calibrate the head temperature detected by said head temperature detection member (8e) after the measured non-recording period exceeds a predetermined period of time, characterised by : said timer means being capable of measuring the non-recording period even when the apparatus is in a power OFF state; and by said calibration means being arranged to calibrate the head temperature detected by said head temperature detection member (8e) on the basis of the reference temperature detected by said reference temperature detection member (5024) before the beginning of the next recording or on a power ON of said ink jet recording apparatus after the measured non-recording period exceeds a predetermined period of time. An apparatus according to claim 1, further comprising correction means for correcting a reference temperature detected by said reference temperature detection member based on the rise in temperature during a time from power-on counted by said timer means. An apparatus according to claim 1 or 2, further comprising ejection amount control means for controlling an amount of ink to be ejected from the recording head, wherein said ejection amount control means is arranged to control the amount of ink to be ejected based on the head temperature calibrated by said calibration means. An apparatus according to any one of the preceding claims, further comprising recovery means for recovering the ejection capability of the recording head in accordance with the head temperature calibrated by said calibration means. An apparatus according to any one of the preceding claims, further comprising a recording head which is arranged to eject ink by causing a change in state in the ink using heat energy. A method of operating an ink jet recording apparatus having a head temperature detection member (8e) provided on a recording head for ejecting ink and a reference temperature detection member (5024) provided on a main body of the apparatus, the method comprising the step of calibrating a head temperature detected by said head temperature detection member at a predetermined timing on the basis of a reference temperature detected by said reference temperature detection member, wherein the calibration step is carried out by measuring (S440, S450) a non-recording period using timer means, and calibrating the head temperature detected by said head temperature detection member (8e) on the basis of the reference temperature detected by said reference temperature detection member (5024) when the measured non-recording period exceeds a predetermined period of time, characterised by measuring the non-recording period using as said timer means, timer means capable of measuring the non-recoding period even when the apparatus is in a power OFF state, and by calibrating the head temperature detected by said head temperature detection member (8e) on the basis of the reference temperature detected by said reference temperature detection member (5024) before the beginning of the next recording or on a power ON of said ink jet recording apparatus after the measured non-recording period exceeds a predetermined period of time. A method according to claim 6, which further comprises correcting a reference temperature detected by the reference temperature detection member based on an amount of a rise in temperature according to an elapsed time from power-on measured by said timer means. A method according to claim 6 or 7, further comprising the step of controlling the amount of ink to be ejected from the recording head based on the head temperature calibrated in said calibrating step. A method according to any one of claims 6 to 8, further comprising the step of recovering ejection capability of the recording head based on a head temperature calibrated in said calibrating step. A method according to any one of claims 6 to 9, wherein the recording head causes a change in state in the ink by heat energy, and ejects the ink based on the change in state.

Inventors: FUJITA MIYUKI, HIRABAYASHI HIROMITSU, SUGIMOTO HITOSHI, TAKAHASHI KIICHIRO, FUJITA, MIYUKI, HIRABAYASHI, HIROMITSU, SUGIMOTO, HITOSHI, TAKAHASHI, KIICHIRO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: B41J2
IPC codes: B41J2