Ink jet recording apparatus and method with modulatable driving pulse width

Abstract: An ink jet recording apparatus in which thermal energy is applied to ink in accordance with a driving signal applied to a heater to produce a bubble, by which ink is ejected onto a recording material includes a driver for applying a plurality of driving signals to the heater for one ejection of ink droplet, wherein the driving signals comprises a first driving signal not ejecting the ink and a second driving signal for ejecting the ink, the second driving signal is applied after a rest period after the first driving signal; a controller for changing an amount of ink ejected by changing a length of the rest period and changing the first driving signal; wherein the controller effects its changing operation in a first changing region in which the rest period is changed without changing the first driving signal and in a second changing region in which a length of the first drive signal is changed.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to an ink jet recording apparatus and method in which a driving pulse width is modulatable. Recently, various types of printers have been developed as output devices for personal computers, word processors, facsimile machines or the like in offices. Among such printers, ink jet type printers in which ink is ejected onto recording material, are advantageous in that the recording noise level is low, high quality recording is possible, downsizing is easy, or the like. Among ink jet recording type printers, a cartridge type is widely used in which an ink container for containing ink and a recording head for converting electric signals to thermal energy by electrothermal transducer element to produce film boiling of the ink so that the ink is ejected by pressure of a bubble created by the boiling. The ink jet cartridge is advantageous in that the cost can be reduced because the passage between the recording head and the ink container is shortened, and,in addition, the ink consumption for ink ejection recovery operation. If the quantity of the ink in the ink container corresponds to the service life of the recording head, the exchange of the cartridge by a user, in effect, performs the maintenance operation for the recording head and for ink replenishment. Corresponding to the intention of the user, color recording and monochromatic recording cartridge are exchangeable in some machines already on sale. In the recording apparatus using such a recording head, a driving pulse applied to the electrothermal transducer is determined in consideration of a quantity of heat per unit area of an ink contact surface of the electrothermal transducer element and durability against stress caused by the heat. On the other hand, as one of the conditions for accomplishing high quality of the image in an ink jet recording apparatus, there is information of ink ejection quantity to avoid non-uniformity in the image. In one example to achieve this, the temperature (ambient temperature) under which the recording head cartridge is placed, and the temperature of the recording head per se, are taken into account for the control of the driving pulse. This is because the viscosity and the surface tension or the like of the ink changes in accordance with the ambient temperature, with the result of change of the flow resistance in the ink supply system including ink container and ink supply path or the like, and because the change of temperature of the recording head namely the temperature of the ink in the ejecting portion results in a change in the ink ejection amount as the case may be. In such a case, if the driving pulses remain constant, the ejection amount changes, and therefore, uniformity is not achieved. Figure 2 is a diagram representing the ambient temperature dependence of the ejection amount when the driving pulse condition is fixed, in which Tenv is the ambient temperature and Vd is the ejection amount. As shown in the Figure, the ejection amount linearly increases with increase of the ambient temperature. The inclination of the line is defined as ambient temperature dependence coefficient, which is expressed as follows: Kenv = δVd/δTenv [pl/°C.drop] The coefficient Kenv is determined by the structure of the recording head cartridge, ink property and the like. Figure 3 is a diagram of the dependence of the ejection amount on the head temperature (the head temperature is equal to the ink temperature in the ejecting portion because the temperature property is static) when the driving pulse is fixed. As shown in this Figure, the ejection amount Vd substantially linearly increases in the temperature range shown therein with increase of the head temperature TH. The inclination is defined as a head temperature dependence coefficient KH, which is expressed: KH = δVd/δTH [pl/°C/drop] The coefficient KH is also determined by the ink property or the like. It has been proposed in an application having been assigned to the assignee of this application that the change of the ejection amount due to the ink temperature variation is removed by PWM (pulse width modulation) driving for the electrothermal transducer elements (ejection heaters) to accomplish a constant ejection amount. Figure 4 illustrates divided pulses relating to the PWM drive. In this Figure, the ordinate represents a driving voltage applied (v), and the abscissa represents the time period of the application of the pulse. In the Figure, P1 is a pulse width of the first one (pre-pulse) of the divided heat pulses; P3 is a pulse width of the second pulse (main pulse); P2 is an interval time (rest period) between the pulses P1 and P2; and T0, T1, T2, T3 are time periods for determining P1, P2 and P3. The PWM ejection amount controls are classified into two types. One of them is as disclosed in Japanese Laid-Open Patent Application No. 92565/1993 corresponding to EP496525A and EP686506A. This method is shown in Figure 5, wherein the time periods T2 and T3 are constant, and the period T1 is modulated. In other words, the width P1 of the prepulse is modulated. This will be called the prepulse width modulation driving method. With this driving method shown in Figure 5, the interval time P2 is also modulated in accordance with the modulation of the prepulse. Another method is as disclosed in Japanese Laid-Open Patent Application No. 169659/1993, corresponding to EP 526223A for example. This is shown in Figure 6 of this application, the time intervals (T1 - T0) and (T3 - T2) are constant, and the time interval (T2 - T1) is modulated. In other words, the interval time P2 between the prepulse P1 and the main pulse P3 is modulated without changing the pulse widths of the prepulse P1 and the main pulse P3. This is calledthe interval time modulation driving method. Referring to Figure 7, the change of the ejection amount in the prepulse width modulating method will be described. In Figure 7, the ordinate represents ejection amount Vd, and the abscissa represents a width of the prepulse P1, wherein arN designates a non-ejection area wherein the ink is not ejected, and arB is a bubble formation area wherein the ink is ejected by the prepulse P1. Figure 7 shows the change of the ejection amount when the main pulse P3 is constant. With the increase of T1 namely P1, the ejection amount increases. When a predetermined peak is exceeded, it is decreased, and falls in the region of bubble formation by the width P1. With this driving method, the setting of T1 may be optimized, so that the linearity in the change of the ejection amount relative to the modulation of T1 can be provided, in which case, the control is easy. Referring to Figure 8, the description will be made as to the interval time modulation method. In Figure 8, the ordinate represents the ejection amount Vd, the abscissa represents the interval time t. With the increase of the interval time P2, the ejection amount increases, and falls in an area arN in capable of bubble formation. With this driving method, it is preferable that the prepulse width is a maximum under the condition that the bubble is not formed. In this case, it is equal to the maximum of P1 in the prepulse width modulation driving method. In this driving method, the temperature increase of the recording head is a problem. When the temperature rise is suppressed by not using the divided pulses in the high temperature area and decreasing the pulse width (single pulse), (T2 - T1) is decreased with increase of the temperature, and (T1 - T0) is reduced from the point of time at which (T2 - T1) is zero. By doing so, the above-described control can be effected, and therefore, the modulation is possible with maintenance of the continuity of the pulse width. Figure 9 shows a pulse profile upon P2 = (T2 - T1) = 0. In either of the prepulse width modulating driving method and the interval time modulation driving method, the maximum width of the overall pulses (T3 - T0) is limited by driving frequency or the like from the standpoint of head driving. Therefore, (T3 - T0) is the same in both of the methods. When the main pulse P3 has the same width in one period, the waveforms of the driving pulses providing the maximum ejection amounts in both of the driving methods are the same in configurations. If the ejection properties of them are the same, the maximum ejection amounts are the same. It is assumed that the minimum unit determined by a logic circuit for the pulse controls 1st = 0.181 µsec, and the total length of the driving pulse T3 is 47st, and that the maximum width of the prepulse is 9st, and the pulse width of the main pulse 21st. Under these conditions, the number of modulation steps in the prepulse width modulation method is not more than 9 steps depending on the minimum unit of the logic circuit and the maximum width of the prepulse. On the other hand, in the case of the interval time modulation method, the maximum interval time is 17st (47 - 9 - 21), and therefore, the number of modulation steps is 17. However, the current actually flowing through the ejection heater is not sharp, that is, has a tail as indicated by ta in Figure 10, despite the configuration of the driving pulse. The length of the tail ta is different depending on the performance of the driver for driving the ejection heater or the like. Thus,a problem, that the number of usable steps for the modulation in the PWM driving method is limited, has been found. For example, if the width of the tail ta is approx. 4st, and if the interval time P2 is 0 - 4st in the interval time modulating method, the current pulse actually flowing through the ejection heater is a single pulse, in effect, by the resulting continuity between the prepulse P1 and the main pulse P2, as shown in Figure 11. With the single pulse, the ejection amount control is difficult, and therefore, the number of steps usable for the modulation reduces to 13 steps. EP-A-0-605207 describes a recording apparatus wherein ink ejection is effected using a plurality of drive pulses comprising a prepulse which is insufficient to cause ejection of ink followed after a rest period by a main heating pulse which causes ejection of ink with the driving pulse width being modulated in accordance with the temperature of the recording head. According to one aspect of the present invention, there is provided an ink jet recording apparatus for recording by ejecting ink from an ink jet recording head onto a recording medium by driving a recording element of the ink jet recording head, said apparatus comprising: driving means for causing ejection of one ink droplet by applying to the recording element of said ink jet recording head a plurality of pulses comprising a first voltage pulse which does not cause ejection of ink and, after a rest period after the first voltage pulse, a second voltage pulse for ejecting ink, the arrangemnet being such that the electrical current does not cease immediately at the end of a voltage pulse; modulating means for modulating the pulse width of the driving pulse supplied by the said driving means and said rest period; characterised in that; said modulating means is operable to set the minimum duration of said rest period to be no less than the delay between the moment at which the driving voltage is removed and the moment at which the current decays to a negligible value. In accordance with another aspect of the present invention, there is provided an ink jet recording head driving method for an ink jet recording apparatus wherein recording is effected by ejecting ink from an ink jet recording head onto a recording material by driving a recording element of the ink jet recording head, said method comprising the steps of: supplying a first voltage pulse to cause the recording element to generate insufficient energy to eject ink; after a rest period following said first voltage pulse supplying a second voltage pulse to cause the recording element to eject ink; and controlling the amount of ink ejected by modulating the first voltage pulse and the rest period, the electrical current not ceasing immediately at the end of a voltage pulse; characterised by: setting the minimum duration of said rest period to be no less than the delay between the moment at which the driving voltage is removed and the moment at which the current decays to a negligible value. An embodiment of the present invention provides an ink jet recording method and apparatus in which the problem of decrease of the modulating step number in the interval time modulation method is improved. An embodiment of the present invention provides an ink jet recording method and apparatus in which continuous ejection amount modulation is possible. In use of the apparatus embodying the invention, even if the current flowing through the recording element (ejection heater) has a tail due to the property of the head driver or the like, the interval period of the driving pulses for driving the heater is made larger than the time width (length), so that the continuity of the driving pulses can be prevented. In the PWM driving method in which the ejection amount is controlled by controlling the signal width of the driving signals, the interval time is modulated in the area where the interval time is longer than the trail , and the signal width of the driving signal (prepulse) supplied prior to the interval time is modulated, by which the ejection amount can be smoothly changed without decrease the number of steps for the effective pulse width modulation. These and other aspects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a waveform of a drive pulse for a recording head according to a first embodiment of the present invention. Figure 2 is a graph showing dependency of ejection amount on ambient temperature. Figure 3 is a graph showing a dependency of ejection amount on a heat temperature. Figure 4 shows a waveform of a general pulse wave in a PWM drive. Figure 5 shows a prepulse control in a PWM drive. Figure 6 illustrates an interval time control in a PWM drive. Figure 7 is a diagram indicating a prepulse dependency of the ejection amount. Figure 8 is a diagram indicating an interval time dependency of the ejection amount. Figure 9 shows a pulse waveform when the interval period is zero in an interval time control in a PWM driving method. Figure 10 shows a driving pulse of PWM drive and a current waveform flowing through the ejection heater. Figure 11 illustrates a problem arising in the current waveform. Figure 12 is a perspective view of an ink jet recording apparatus according to an embodiment of the present invention. Figure 13 is an exploded perspective view of a cartridge usable with the apparatus of Figure 12. Figure 14 is an outer perspective view of the cartridge. Figure 15 is a perspective view illustrating engagement between an ink container and a recording head constituting the cartridge. Figure 16 illustrates mounting and demounting of the cartridge relative to the carriage. Figure 17 is a schematic plan view of a substrate constituting the recording head. Figure 18 is a block diagram of a heat driver circuit in the Embodiment. Figure 19 is a PWM table for the head drive pulse control according to a first embodiment of the present invention. Figure 20 is a diagram showing a relationship between a PWM number and ejection amount in the PWM table. Figure 21 shows a PWM number selection table for the head drive pulse control according to the first embodiment. Figure 22 is a flow chart for the selection of the PWM number. Figure 23 shows a table of relationship between the prepulse and the main pulse in an interval control area in accordance with a rank of heat generation amount of the recording head according to a second embodiment of the present invention. Figure 24 shows a PWM table of the driving pulse in the case of the maximum prepulse 9st for the recording head according to the second embodiment. Figure 25 is a PWM table for the driving pulse control in the case of the maximum prepulse 8st of the recording head according to the second embodiment. Figure 26 shows a PWM table for a drive pulse control in the case of the maximum prepulse 7st for the recording head according to the second embodiment of the present invention. Figure 27 is a PWM table for the driving pulse in the case of the maximum prepulse 6st for the recording head according to the second embodiment of the present invention. Figure 28 is a timing chart for transfer of various signals in the head driving circuit shown in Figure 18. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, the embodiments of the present invention will be described in detail. Figures 12 - 17 illustrate an ink jet unit IJU, ink jet head IJH, ink container IT, ink jet cartridge IJC, ink jet recording apparatus main assembly IJRA, carriage HC, and the relationship among them, according to the embodiments of the present invention. (i) Main assembly of the apparatus Figure 12 shows an example of an ink jet recording apparatus IJRA to which the present invention is applicable. In this Figure, a carriage HC is engaged with a helical groove 50 of a lead screw 5005 rotated by drive transmission gears 5011 and 5009 by a reversible driving motor 5013. The carriage HC has a pin (not shown) engaged with the helical groove 5004. By this, it is reciprocable in the directions a and b. The carriage HC carries an ink jet cartridge IJC. Designated by 5002 is a sheet confining plate and confines the sheet on the platen 5000 along the movement direction of the carriage. Elements 5007 and 5000 constitute a photocoupler to detect the presence of a lever 5006 of the carriage in this area to switch the rotational direction of the motor 5013. The photocoupler functions as a home position detecting means. Designated by 5016 is a member for supporting a capping member 5022 for capping a front face of a recording head. Designated by 5015 is a sucking means for sucking the space in the cap to recover the recording head through an opening 5023 of the cap. A cleaning blade 5017 is movable to and fro by a member 5019. They are supported on a supporting plate 5018. The blade is not limited to this type, but known cleaning blade is usable. 5012 is used to start the sucking operation, and moves with the movement of the cam 5020 engaged with the carriage. The driving force from the driving motor is controlled by known transmitting means such as clutch or the like. The capping, cleaning and the sucking recovery operation, are carried out when the carriage comes to the home position. By the function of the lead screw 5005, these operations can be carried out. However, this is not limiting, and the desired operations are carried out at known predetermined timing. The ink jet cartridge IJC, as will be understood from Figure 13, the percentage of the ink containing portion is large, and the end of the ink jet unit IJU is slightly projected beyond a front face of the ink container IT. The ink jet cartridge IJC is securedly supported by known positioning means (which will be described hereinafter) for the carriage HC (Figure 12) in the main assembly IJRA and the electric contacts. It is detachable to the carriage HC. (ii) Ink jet unit IJU The ink jet unit IJU uses an electrothermal transducer for generating thermal energy for creating film boiling in the ink in response to an electric signal. Referring to Figure 13, a heater board 100 has an Si substrate, an array of electrothermal transducers (ejection heater), and electric wiring of Al or the like for supplying the electric energy thereto. A wiring board 200 for supplying the electric energy to the heater board 100 comprises wiring corresponding to the wiring of the heater board (they are connected by wire bonding or the like), and pads at the ends of the wiring to receive electric signals from the main assembly. A grooved top plate 1300 comprises grooves for forming partition walls for ink passages and a common liquid chamber or the like. It comprises an ink receiving port for receiving the ink from the ink container into the common liquid chamber, and an orifice plate 400 having a plurality of ejection outlets, which are integrally formed. The material for the integral formation or molding is preferably polysulfone resin material, but another molding resin material is usable. A support 300 is of metal and functions to support the backside of the wiring board 200 in a flat plain, and is a bottom plate of the ink jet unit. A confining spring 500 has M-shaped form, and the central portion thereof confines the common liquid chamber, and an apron portion 501 urges a part of the liquid passages along a line. The legs of the confining spring are penetrated through holes 3121 and are engaged with the backside of the support 300, by which the heater board 100 and the top plate 1300 are sandwiched, and they are pressed to each other by the urging force of the confining spring 500. The support 300 comprises positioning holes 312, 1900 and 2000 engageable with two positioning projections 1012 and positioning and fusing projections 1800 and 1801 of the ink container IT, and in addition, it comprises on the backside thereof positioning projections 2500 and 2600 for the carriage HC of the main assembly IJRA. Additionally, it comprises a hole 320 through which an ink supply tube 2200, which will be described hereinafter, penetrates to permit ink supply from the ink container. The mounting of the support 300 to the wiring board 200 is bonded by bonding material or the like. The recesses 2400 and 2400 of the support 300 are disposed adjacent to the positioning projections 2500 and 2600. In the ink jet cartridge IJC (Figure 14) after being assembled, the three sides are disposed in an extension of a head end constituted by a plurality of parallel grooves 3000 and 3001 to prevent foreign matter such as ink dust or the like from reaching to the projection 2500 and 2600. The cover member 800, as shown in Figure 13, constitutes an outer wall of the ink jet cartridge IJC, and also forms a space for accommodating the ink jet cartridge IJU. The ink supply member 600 in which the parallel groove 3001 is formed, has an ink supply conduit 1600 in communication with the above-described ink supply tube 2200, and the ink supply tube 2000 side thereof is fixed, so that it is in the form of a cantilever A sealing pin 602 is inserted to assure the capillary force between the ink supply tube 2200 and the fixed side of the ink conduit. Designated by a reference numeral 601 is a gasket for sealing between the ink container IT and the supply tube 2200, and 700 is a filter provided in the container side end of the ink supply tube. The ink supply member 600 is produced by molding, and therefore, it is inexpensive and the positional accuracy is assured. Additionally, during the mass-production, the press-contact to the ink receiving port 1500 can be assured by the cantilever conduit 1600. In this embodiment, under this pressed state, the sealing bonding agent is supplied from the ink supply portion side, which is sufficient to assure the fluid communication. The ink supply member 600 is fixed to the support 300 by penetrating the backside pin (not shown) of the ink supply member 600 through the holes 1901 and 1902 of the support 300, and heat fusing the projected portions of the pins onto the backside of the support 300. The small projections provided by the heat fusing, are accommodated in a recess of a wall of the ink container IT, and therefore, the positioning of the unit IJU can be correctly accomplished. (iii) Ink container The ink container comprises a cartridge main assembly 1000 and an ink absorbing material 900. The ink container 900 is inserted into the main body of the cartridge 1000 from the side opposite from the side where it is mounted to the unit IJU, and thereafter, the main body 100 is capped with a covering member 1100. The ink absorbing material absorbs the ink and is within the main body of the cartridge 1000. Designated by 1200 is a supply port for supplying the ink to the unit IJU, and it also functions as an ink filling port for supplying the ink to the absorbing material 900 before the unit is mounted to the portion 1010 of the cartridge main body 100. In this example, the portions capable of supplying the ink, are only the air vent and the supply port. The air existing region of the container formed by ribs 2300 in the main body and ribs 2500 and 2400 of the cover 1100 to improve the ink supply property from the ink absorbing material, is extended from the air vent 1401 side to the corner remotest from the ink supply port 1200. Therefore, the ink supply to the ink absorbing material is preferably carried out through the supply port 1200 for the purpose of relatively uniform and sufficient ink supply thereto. Four of such ribs 1000 are provided in parallel with the carriage movement direction behind the main body 1000 of the ink container, thus preventing the close contact of the absorbing material to the rear surface. Partial ribs 2400 and 2500 are formed in the inside surface of the cover 1100 on an extension of the rib 1000. However, it is divided as contrasted to the rib 1000 to increase the air existing space. The partial ribs 2500 and 2400 are dispersed in a space smaller than one half of the total area of the cover member 1000. By these ribs, the ink in the corner region remotest from the supply port 1200 can be assuredly supplied to the supply port 1200 by the capillary force. An air vent 1401 is formed in the cover for communication between the ambience and the inside of the cartridge. Designated by 1400 is a water repelling material disposed in the air vent 1401, by which the ink leakage through the air vent 1401 is prevented. The ink containing space of the ink container IT is rectangular, and the long side may be at the side, and the positions of the ribs are particularly effective. When the long side is along the carriage movement direction, or when it is in the form of a cube, the rib may be provided in the entire of the cover member 1100, so that the ink supply from the ink absorbing material 900 is stabilized. The structure of the mounting surface of the ink container against the unit IJU is shown in Figure 15. Here, a line L1 is extended substantially through the center of the ejection outlet of the orifice plate 400 and parallel with a mounting reference surface of the carriage surface or the bottom surface of the container IT. Two positioning projections 1012 engageable with a hole 312 of the support 900 are on the line L1. The height of the projection 1012 is slightly smaller than the thickness of the support 300 to permit positioning of the support 300. On an extension of the line L1 on the Figure, a claw 2100 for engagement with an engaging surface 4002 of 90 degrees angle of positioning hook 4001 of the carriage, so that the positioning force relative to the cartridge acts in a surface region parallel with the reference surface including the line L1. As will be described hereinafter in conjunction with Figure 15, the relationships are advantageous since the positional accuracy of the ink container is equivalent with the positional accuracy of the head outlet. The projections 1800 and 1801 of the ink container corresponding to the fixing holes 1900 and 2000 for the fixing to the side surface of the ink container, are longer than the above-described projections 1012, and the projected portions are heat fused, thus fixing the support 300 to the side surface thereof. Designated by L3 is a line perpendicular to the line L1 and passing through the projection 1800, and L2 is a line passing through the projection 1801. On the line L3, substantial center of the supply port 1200 is disposed, and therefore, the connection between the supply port 1200 and the supply tube 2200 is stabilized. The shock due to falling or impact to the connecting portion can be released. The lines L2, L3 are not the same, and the projections 1800 and 1801 are adjacent the projection 1012 adjacent the ejection outlet side of the head IJH, and therefore, the reinforcing effect for the positioning of the head IJH to the container is enhanced. A curve designated by L4 is an outer wall position when the ink supply member 600 is mounted. Since the projections 1800 and 1801 are along the line L4, the sufficient strength and positional accuracy are provided against the weight of the leading portion structure of the head IJH. Designated by 2700 is a flange at an end of the ink container IT; it is inserted into a hole of a front plate 4000 of the carriage to be against the situation in which the position of the ink container is extremely wrong. Designated by 2101 is a further positioning and engaging portion relative to the carriage HC. The ink container IT encloses except for the bottom opening the unit IJU by covering with the cap 800 after the unit IJU is mounted. As for the ink jet cartridge IJC, the bottom opening for mounting on the carriage HC is close to the carriage HC, and therefore, it constitutes a four side closed space, substantially. Therefore, the heat generation from the head IJH in the enclosed space is effective to maintain the temperature in the space. However, for long term continuous use, a small temperature rise occurs. For this reason, in this embodiment, in order to assist the spontaneous heat radiation of the supporting member, the upper surface of the cartridge IJC is provided with a small width slit 1700 in communication with the space to prevent the temperature rise, while the temperature distribution in the entirety of the unit IJU is not influenced by the ambience. When the ink cartridge IJC is assembled, the ink is supplied to the ink container 600 from the inside of the cartridge through the supply port 1200, the hole 320 in the support 300 and an inlet in the inside back portion of the supply container 600. After passing through the ink container 600, it is supplied into the common liquid chamber through the supply tube, ink inlet 1500 of the top plate 400. In the connecting portion, gaskets of silicon rubber or butyl rubber are provided to effect the sealing to assure the ink supply path. In this embodiment, the top plate 1300 is of polysulfone, polyethersulfon, polyphenylene oxide, polypropylene or the like resin materials durable against ink. It is simultaneously and integrally molded in a metal mold together with the orifice plate 400. As described, the integral molded part contains ink supply member 600, top plate, orifice plate and the main body 1000 of the ink container, and therefore, the assembling accuracy is high, and is extremely effective to improve the quality in the mass-production. The number of parts is reduced as compared with the conventional structure, and the excellent properties can be assuredly provided. (iv) Mounting of the ink jet cartridge IJC to the carriage HC In Figure 16, a platen roller 5000 guides the recording material P from the bottom side. The carriage HC moves along the platen roller 3000. In front of the carriage, that is, adjacent the platen, there is provided a front plate 400 having thickness of approx. 2 mm at the front side of the ink jet cartridge IJC, a flexible sheet 4005 having a pad 2001 corresponding to the pad 201 of the wiring board 200 of the cartridge IJC, and an electric contact supporting plate 4003 for supporting the rubber pad 4006 for providing elastic force for urging it to the pad 2011 at the backside thereof, and a positioning hook 4001 for fixing the ink jet cartridge IJC to the recording position. The front plate 4000 has two projections 2500 and 2600, and after the mounting of the cartridge, the perpendicular force to the projected surface 4010 is provided. Therefore, a plurality of reinforcing ribs include unshown ribs extending along the perpendicular force direction adjacent the platen roller. The rib constitutes a head protection projection toward the platen roller beyond front position upon the mounting of the cartridge, by approx. 0.1 mm. The electric connection supporting plate 4003 has a plurality of reinforcing ribs 4004 in the direction perpendicular to that of the above-described ribs, so that the degree of lateral projection toward the hook 4001 from the platen side is decreased. This is effective to incline the position upon the mounting of the cartridge. The supporting plate 4003 has a platen side positioning surface 4008 and a hook side positioning surface 4007 to stabilize the electric connection to form a pad contact area. Additionally, the amount of deformation of the rubber sheet having projections corresponding to the pad 2011 is determined. When the cartridge IJC is fixed to a position capable of effecting recording operation, the positioning surface is contacted to the surface of the wiring substrate 300. In this embodiment, the pads 201 on the substrate 300 are distributed so as to be symmetrical relative to the line L1, and therefore, the deformation of the projections of the rubber sheet 4006 is made uniform to stabilize the contact pressure relative to the pads 2011 and 201. The distribution of the pads 201 are vertically and horizontally two lines. The hook 4001 has an elongated opening for engagement with a fixed shaft 4009. Utilizing the moving space of the elongated hole, the hook 4001 is rotated in the counterclockwise direction, and thereafter, it is moved to the left along the platen roller 5000, by which the ink jet cartridge IJC is correctly positioned relative to the carriage HC. The movement of the hook 4001 is not limited, but the use of a lever or the like is preferable. During the rotation of the hook 4001, the cartridge IJC moves toward the platen roller, and the positioning projections 2500 and 2600 are moved to a position contactable to the positioning surface 4010 of the front plate. By the leftward movement of the hook 4001, the 90 degrees hook surface 4002 is closely contacted to the 90 degrees surface of the claw 2100 of the cartridge IJC, and the cartridge IJC is rotated in a horizontal plane about the contact position between the positioning surface 2500 and 4010 to start the contact between the pads 201 and 2011. When the hook 4001 is secured at the predetermined fixed position, the pads 201 and 2011 are completely contacted, and the positioning surfaces 2500 and 4010 are completely contacted, and the contact between the 90 degrees surface 4002 and the 90 degrees surface of the claw are contacted, and in addition, the substrate 300 and the positioning surfaces 4007 and 4008 are contacted, simultaneously, thus completing the mounting of the cartridge IJC on the carriage. (v) Heater board Figure 17 schematically shows the heater board 100 of the head used in this embodiment. There are provided on the same substrate in the relationship shown in this Figure, a temperature control (subordinate) heater 8d for controlling the head temperature, a temperature sensor 8e for detecting the head temperature, ejection heater 8c for ejecting the ink constituting an array 8g, and a driving element 8h. In this manner, various elements are disposed on the same substrate so that the head temperature is detected and controlled efficiently. In addition, the head can be downsized, and the manufacturing steps can be simplified. In this Figure, an outer wall cross-section 8f of the top plate which is effective to divide the heater board into a region filled with the ink and the region not filled with the ink, is shown. The ejection heater 8c side of the wall 8f of the top plate functions as a common liquid chamber. By the groove formed on the array 8g of the wall 8f, liquid passages are formed. (Embodiment 1) In the following description, the total length of the driving pulse is expressed by "Tblock". The total length is mainly determined by the structure and the driving method for the recording head. Figure 18 shows a driving circuit for the recording head in this embodiment. The head driving circuit, as shown in this Figure, effects divided driving operations for 16 blocks each including 8 ejection outlets of 128 ejection heaters 1 - 128 of the recording head. For the thus divided 8 blocks, block selection signals are sequentially supplied by combination of three enabling signals BlockENBO, BlockENB1, and BlockENB2 additionally, selection signals OddENB, EvenENB for selecting odd number heaters and even number heaters, are supplied so that 16 block heaters are sequentially selected. An ejection heater is driven for a period in which an output is produced by an AND signal of a signal produced from latch for the block selected by BlockENB0 - 2 signals and OddENB signal, and EvenENB signal, and HENB signal indicative of the heating period of the ejection heater. The total length of the driving circuit TBlock is determined by a driving frequency, the number of elements to be driven and the number of simultaneously driven element. Figure 28 is a timing chart of various signal transfer in the driving circuit of Figure 13. In the Figure, CYL is a time period required for driving all the driving element, BLK is a time period required for driving one element. In the Figure, (a) shows the signal for data transfer for a shift register. The head of this embodiment is operated in HQ mode for high quality printing, and a smoothing mode in which smoothing processing is carried out for edge portions of images, and HS mode for high speed printing. In Figure 28, (b) shows the timing of transfer of the signal in the HQ mode, (c) is a timing chart for the signal transfer in the HS mode. In the HQ mode, the signals OddENB and EvenENB are alternately produced, whereas in HS mode, the signals OddENB and EvenENB are produced at the same timing. Therefore, in the HS mode, all the driving elements are grouped into 8 blocks, so that the time period required for driving on the elements is shortened, thus permitting high speed printing. The pulse width modulation in the PWM driving method is carried out using HENB0, 1, 2, 3. Figure 1 illustrates the driving pulse modulating method in this embodiment. In the following explanation, P1LMT is a maximum pulse width not ejecting the ink by the prepulse in the ejection heater drive pulse, Pmain is the main pulse, Tlog is a minimum unit of the pulse width modulation by a logic circuit, and Ttail is a width of a tail of the current pulse waveform by the ejection heater driver. The driving pulse providing the maximum ejection amount is indicated by D. At this time, the prepulse width is P1LMT, the main pulse width is Pmain, and the interval time is (Tblock - P1LMT - Pmain). When the amount of ejection is larger than required because of the head temperature or the ambient temperature increase, the pulse wave is modulated sequentially to the pulse indicated by C. More particularly, the prepulse width P1LMT is not changed, but the interval time P2 is gradually decreased by Tlog from the initial width P2 to (Ttail + Tlog). When the head temperature or the ambient temperature is further increased, the waveform is modulated from C to A through B. The interval time P2 can not be made shorter than (Ttail + Tlog) in consideration of the width Ttail. For this reason, when the pulse waveform is modulated from C to A through B, the interval time P2 is fixed at (Ttail + Tlog), and the prepulse width P1 is decreased from P1LMT to 0 by Tlog gradually, so that in synchronism with the decrease of the width of the prepulse P1, the main pulse P3 is increased to (P1LMT + Pmain) by the width of Tlog. As described in the foregoing, when the interval time is reduced, the minimum time is the tail width Ttail plus minimum modulation width Tlog, so that the prepulse and the main pulse are prevented from combining with each other into a single pulse. As a result, the ejection amount or quantity control can be carried out with the advantage of the divided pulse drive. Figure 19 shows a driving pulse table used in the driving system. As described hereinbefore, the total width of the driving pulse is determined by the structure of the recording head and the driving method. The recording head of this embodiment, as described in conjunction with Figure 18, has 128 ejection outlets, which are divided into 18 blocks each having 8 ejection outlets. The maximum simultaneous driven ejection outlets are 8 ejection outlets, and the period of the ejections is 160 µsec. The total pulse width is Tblock (P0 + P1 + P2 + P3) is 48st (1st = 0.181 µsec) (P1 ≧ 1st). The total width of the optimum prepulse and the main pulse (P1 + P3) is determined by the structure of the heat generating element and the driving voltage or the like, and it is 30st in the case of the head of this embodiment. In the table shown in Figure 19, the modulations PWM No. 23 - PWM No. 10 correspond to the modulations from pulse D to pulse C, and the modulations PWM No. 10 - PWM No. 1 correspond to the modulation from pulse C to pulse A through pulse B. Figure 20 is a diagram showing ejection amount by each PWM drive pulse of Figure 19 when the ambient temperature is 23 °C and the head temperature is 23 °C. As shown in the Figure, the ejection amount is suppressed with the driving pulse having smaller PWM No., whereas the driving pulse having a larger PWM No. increases the ejection amount. On the basis of this, assuming that the target ejection amount of the ejection amount control in this embodiment is 85 ng/drop, the PWM number selected on the basis of the excessiveness or shortage of the ejection amount is determined, and the PWM selection table shown in Figure 21 is selected. The ambient temperature dependency coefficient in this embodiment Kenv is 1.4 (ng/°C.drop), and the head temperature dependency coefficient KH is 0.8 (ng/°C.drop). Referring to Figure 22, the description will be made as to the actual head driving method using the PWM table shown in Figures 19 and 21. At step S1001, the ambient temperature of the recording head is fetched. In step S1002, the increase or decrease dV1 of the ejection amount due to the ambient temperature obtained at step S1001 is determined by the following equation: dV1 = Kenv x (Tenv - 23 °C) At step S1003, the head temperature TH is fetched, and at step S1004, the increase or decrease dV2 of the ejection amount by the head temperature increase is determined by the following equation: dV2 = KH x (TH - Tenv) At step S1005, excessiveness or shortage dV from reference ejection amount, of the ejection amount varied due to the ambient temperature Tenv, head temperature TH or the like, is determined using the following equation: dV = dV1 + dV2 At step S1006, the PWM number is determined referring to the table show in Figure 21 on the basis of the difference dV of the ejection amount determined by the equation (3). From the PWM No. fetched at step S1006, the pulse waveform for the head drive is determined, referring to the table of Figure 19. In this embodiment, the tail of the current width of the head driving pulse Ttail is deemed as 3st, and on the basis of this, the waveform of the PWM drive is modulated. When the PWM drive using the conventional interval time control is carried out on the assumption that the Ttail is 3st, the number of control steps for the modulation is 14 steps. According to this embodiment, the consideration is paid to the lack of sharpness Ttail of the pulse current. In the range in which the advantage of the divided pulse in the PWM driving method is provided by the interval time P2, the interval time P2 is controlled, and outside the range, the width of the prepulse P1 is controlled to effect the modulation. Therefore, smoother pulse width modulation than the conventional is accomplished. On the basis of the ambient temperature and the head temperature, the difference of the ejection amount from the reference amount is obtained, on the basis of the difference, the driving pulse waveform is determined, so that correct ejection amount control and high quality print are accomplished. (Embodiment 2) As another embodiment, the description will be made as to the PWM driving method in which the method is switched depending on the range of the head temperature. The structure and function of the recording apparatus and recording head are the same as with Embodiment 1, and the detailed description thereof are omitted for simplicity. The recording head of this embodiment has ejection heaters through film forming process, and therefore, the configuration in the direction of the surface of the heater board, that is, the area can be relatively accurately controlled, but there is a higher liability that the thicknesses vary. For this reason, when the thicknesses of the ejection heater are not constant, the amount of heat generation is different if the driving voltages and the driving pulses are the same, respectively. Therefore, in this embodiment, the width or the voltage of the driving pulse is properly set in accordance with the heat generation amount. However, when the pulse width is selected to the proper level, there arises a problem, although the problem does not arise when the voltage is set properly in the structure as in Embodiment 1. The recording heads are classified into 13 ranks (head ranks) depending on the heat generating amount of the ejection heaters thereof. If the attempt is made to set the pulse widths to the proper levels for the respective ranks, P1LMT and Pmain are as shown in Figure 23. Thus, the P1LMT changes depending on the rank of the head, and therefore, the usable range for the ejection amount by the change of P1 (the range indicated by the PWM number as in Figure 19) is different. This means that the head temperature range for the switching of the PWM drive is different. Therefore, in this embodiment, a proper PWM table is provided corresponding to the head rank, so that the temperature range for the PWM drive switching is made constant. Figure 24 is a PWM table when P1LMT is 9st, Figure 25 is a PWM table when P1LMT is 8st, Figure 26 is a PWM table when P1LMT is 7st, and Figure 27 is a PWM table when P1LMT is 6st. That is, when the head rank is 12 or 13 shown in Figure 24, the table of Figure 24 is used to determine the waveform for the PWM drive. Similarly, referring to a table corresponding to P1LMT for the head rank, the waveform of the PWM control is determined, by which the temperature range for the control switching is constant, and therefore, the ejection amount can be made constant despite the difference in the ejection performance of the individual recording heads. As shown in Tables 24 - 27, if the total of the pulse widths of the driving pulse namely the total of P1LMT and Pmain is decreased, the maximum width of the interval time can be increased, correspondingly. Then, the decrease of the control step due to P1 can be compensated for by the increase of the control steps by P2. (Another Embodiment) When the driving period for the recording head is decreased by switching, the total length (P0 + P1 + P2 + P3) of the driving pulse width is limited. Therefore, the PWM tables used in the foregoing embodiments, are unable to be used, as they are. Therefore, the decrease of the total length of the pulse due to the switching of the driving condition on the basis of the total length (P0 + P1 + P2 + P3) of the pulse in each of the embodiments, is determined. The difference of P0 in the PWM table in each of the embodiments from the decrease is used as a new P0. Here, the PWM No. which is smaller than 1 may be produced. Therefore, the upper limit is set corresponding to the PWM number for P0 - 1 upon the PWM selection, thus limiting the PWM selection table, so that the table having the PWM number larger than the PWM number corresponding to P0 = 1. By doing so, even if the change of the driving condition which limits the total length of the pulse (P0 + P1 + P2 + P3), occurs, the PWM table in the foregoing embodiments are usable. As described in the foregoing, according to this invention, even if the current flowing through the recording element or electrothermal transducer element has a waveform including a tail relative to the driving pulse, because of the property of the head driving means, the minimum of the driving pulse rest period can be made longer than the tail period, so that the effective number of steps usable for the pulse width modulation can be maintained, thus accomplishing smooth ejection amount control. The present invention is particularly suitably usable in an ink jet recording head and recording apparatus wherein thermal energy by an electrothermal transducer, laser beam or the like is used to cause a change of state of the ink to eject or discharge the ink. This is because the high density of the picture elements and the high resolution of the recording are possible. The typical structure and the operational principle are preferably the ones disclosed in U.S. Patent Nos. 4,723,129 and 4,740,796. The principle and 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 electrothermal transducer disposed on a liquid (ink) retaining sheet or liquid passage, the driving signal being enough to provide such a quick temperature rise beyond a departure from nucleation boiling point, by which the thermal energy is provided by the electrothermal 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 production, development and contraction of the the bubble, the liquid (ink) is ejected through an ejection outlet to produce at least one droplet. The driving signal is preferably in the form of a pulse, because the development and contraction of the bubble can be effected instantaneously, and therefore, the liquid (ink) is ejected with quick response. The driving signal in the form of the pulse is preferably such as disclosed in U.S. Patents Nos. 4,463,359 and 4,345,262. In addition, the temperature increasing rate of the heating surface is preferably such as disclosed in U.S. Patent No. 4,313,124. The structure of the recording head may be as shown in U.S. Patent Nos. 4,558,333 and 4,459,600 wherein 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 electrothermal transducer as disclosed in the above-mentioned patents. In addition, the present invention is applicable to the structure disclosed in Japanese Laid-Open Patent Application No. 123670/1984 wherein a common slit is used as the ejection outlet for plural electrothermal transducers, and to the structure disclosed in Japanese Laid-Open Patent Application No. 138461/1984 wherein an opening for absorbing pressure wave of the thermal energy is formed corresponding to the ejecting portion. This is because the present invention is effective to perform the recording operation with certainty and at high efficiency irrespective of the type of the recording head. The present invention is effectively applicable to a so-called full-line type recording head having a length corresponding to the maximum recording width. Such a recording head may comprise a single recording head and plural recording head combined to cover the maximum width. In addition, the present invention is applicable to a serial type recording head wherein the recording head is fixed on the main assembly, to a replaceable chip type recording head which is connected electrically with the main 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 provisions of the recovery means and/or the auxiliary means for the preliminary operation are preferable, because they can 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 the electrothermal transducer, an additional heating element or a combination thereof. Also, means for effecting preliminary ejection (not for the recording operation) can stabilize the recording operation. As regards the variation of the recording head mountable, it may be a single corresponding to a single color ink, or may be plural corresponding to the plurality of ink materials having different recording color or density. 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 ink materials and/or a full-color mode using the-mixture of the colors, which may be an integrally formed recording unit or a combination of plural recording heads. Furthermore, in the foregoing embodiment, the ink has been liquid. It may be, however, an ink material which is solidified below the room temperature but liquefied at the room temperature. Since the ink is controlled within the temperature not lower than 30 °C and not higher than 70 °C to stabilize the viscosity of the ink to provide the stabilized ejection in usual recording apparatus of this type, the ink may be such that it is liquid within the temperature range when the recording signal is the present invention is applicable to other types 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. Another ink material is solidified when it is left, to prevent the evaporation of the ink. In either of the cases, the application of the recording signal producing thermal energy, the ink is liquefied, and the liquefied ink may be ejected. Another ink material may start to be solidified at the time when it reaches the recording material. The present invention is also applicable to such an ink material as is liquefied by the application of the thermal energy. Such an ink material may be retained as a liquid or solid material in through holes or recesses formed in a porous sheet as disclosed in Japanese Laid-Open Patent Application No. 56847/1979 and Japanese Laid-Open Patent Application No. 71260/1985. The sheet is faced to the electrothermal transducers. The most effective one for the ink materials 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 computer or the like, as a copying apparatus combined with an image reader or the like, or as a facsimile machine having information sending and receiving functions. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

Claims: An ink jet recording apparatus for recording by ejecting ink from an ink jet recording head (IJC) onto a recording medium by driving a recording element (H1,...H128) of the ink jet recording head, said apparatus comprising: driving means for causing ejection of one ink droplet by applying to the recording element of said ink jet recording head (IJC) a plurality of pulses comprising a first voltage pulse (P1) which does not cause ejection of ink and, after a rest period (P2) after the first voltage pulse, a second voltage pulse (P3) for ejecting ink, the arrangement being such that the electrical current does not cease immediately at the end of a voltage pulse; modulating means for modulating the pulse width of the driving pulse supplied by the said driving means and said rest period; characterised in that ; said modulating means is operable to set the minimum duration of said rest period to be no less than the delay between the moment at which the driving voltage is removed and the moment at which the current decays to a negligible value. An apparatus according to claim 1, further comprising ambient temperature detecting means for detecting a temperature of the ambience of said ink jet recording head, wherein said modulating means is arranged to modulate the first voltage pulse and the rest period in accordance with the output of the ambient temperature detecting means. An apparatus according to claim 1 or 2, further comprising head temperature detecting means (8e) for detecting a temperature of the ink jet recording head, wherein said modulating means is arranged to modulate the duration of the first voltage pulse and the rest period in accordance with the output of the head temperature detecting means. An apparatus according to claim 1, further comprising ambient temperature detecting means for detecting a temperature of the ambience of said ink jet recording head, and head temperature detecting means for detecting temperature of the ink jet recording head, wherein said modulating means is arranged to modulate the first voltage pulse and the rest period in accordance with the outputs of the ambient temperature detecting means and the head temperature detecting means. An apparatus according to any one of the preceding claims wherein said modulating means is operable either in a first modulating region in which the rest period is modulated without modulating the first voltage pulse or in a second modulating region in which the first voltage pulse is modulated. An apparatus according to claim 5 when dependent on claim 4, wherein said modulating means is arranged to operate in the first modulating region when outputs of said ambient temperature and head temperature detecting means are relatively low. An apparatus according to claim 1 or 2, further comprising head temperature detecting means (8e) for detecting a temperature of the ink jet recording head, wherein said modulating means is arranged to modulate the driving pulses in accordance with the output of said head temperature detecting means. An apparatus according to claim 7, wherein said modulating means is operable either in a first modulating region or in second modulating region according to the range of outputs of the said temperature detecting means, wherein the first modulating region the modulating means is arranged to modulate the said rest period (P2) with fixed width of the said first voltage pulse (P1) and with fixed width of the said second voltage pulse (P3), whereas in the second modulating region the modulating means is arranged to modulate the said first voltage pulse with fixed duration of the rest period. An apparatus according to any one of the preceding claims, wherein heating means is operable to generate thermal energy resulting in the formation of a bubble causing ink ejection. An ink jet recording head driving method for an ink jet recording apparatus wherein recording is effected by ejecting ink from an ink jet recording head (IJC) onto a recording material by driving a recording element of the ink jet recording head, said method comprising the steps of: supplying a first voltage pulse (P1) to cause the recording element to generate insufficient energy to eject ink; after a rest period (P2) following said first voltage pulse supplying a second voltage pulse (P3) to cause the recording element to eject ink; and controlling the amount of ink ejected by modulating the first voltage pulse and the rest period, the electrical current not ceasing immediately at the end of a voltage pulse; characterised by : setting the minimum duration of said rest period to be no less than the delay between the moment at which the driving voltage is removed and the moment at which the current decays to a negligible value. A method according to claim 10, wherein said controlling step effects the modulation either in a first modulating region in which the rest period is modulated without modulating the first voltage pulse or in a second modulating region in which the first voltage pulse is modulated. A method according to claim 11, further comprising the steps of detecting a temperature of the ambience of said ink jet recording head, detecting the temperature of the ink jet recording head and determining the duration of the first voltage pulse and the rest period in the controlling step using the detected temperatures. A method according to claim 12, wherein said controlling step effects its modulating operation in the first modulating region when a recording head temperatures region based on the ambient and head temperatures is relative low. A method according to claim 10 or 11, further comprising a head temperature detecting step of detecting a temperature of the ink jet recording head, wherein the driving pulses are modulated in accordance with the results of said temperature detecting step. A method according to claim 10, wherein said modulating step effects modulation either in a first modulating region or in a second modulating region according to the range of results of the temperature detecting step, where in the first modulating region the said rest period (P2) is modulated with fixed width of said first voltage pulse (P1) and with fixed width of the second voltage pulse (P3), whereas in the second modulating region the said first voltage pulse is modulated with fixed duration of the rest period. A method according to any one of claims 10 to 15, wherein heating means generates thermal energy resulting in the formation of a bubble which causes ink ejection.

Inventors: IWASAKI OSAMU, KANEMATSU DAIGORO, OTSUKA NAOJI, TAKAHASHI KIICHIRO, YANO KENTARO, IWASAKI, OSAMU, KANEMATSU, DAIGORO, OTSUKA, NAOJI, TAKAHASHI, KIICHIRO, YANO, KENTARO, IWASAKI, OSAMU, C/O CANON K.K., KANEMATSU, DAIGORO, C/O CANON K.K., OTSUKA, NAOJI, C/O CANON K.K., TAKAHASHI, KIICHIRO, C/O CANON K.K., YANO, KENTARO, C/O CANON K.K.
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: B41J2
IPC codes: B41J2