Patent Description:
A printing apparatus, such as an inkjet printer, includes a liquid discharging head that discharges liquid, and prints an image using the discharged liquid. The liquid discharging head includes discharging openings from which the liquid is discharged, and heating elements that heat the liquid to discharge the liquid from the discharging openings to print the image on a printing medium. In such a liquid discharging head, for example, liquid inconveniently sticking near a discharging opening or air bubbles undesirably mixing inside the discharging opening may cause a difficulty in discharging liquid in the discharging opening. A discharging opening undergoing such a difficulty is hereinafter referred to as an 'inhibited discharging opening'. The difficulty in discharging the liquid may affect the printing quality, and thus this situation is handled by using a discharging opening near the inhibited discharging opening to make up for the printing that otherwise should have been carried out by the inhibited discharging opening in place thereof.

Under these circumstances, <CIT> discusses a method in which a temperature detecting element is provided to each of the heating elements, thus detecting temperature information for each discharging opening and identifying an inhibited discharging opening. The identifying of the inhibited discharging opening enables the liquid discharging head to correctly make up for the printing to be carried out originally by the inhibited discharging opening in place thereof.

In <CIT>, a period for inspecting a temperature waveform, which is the temperature information acquired by the temperature detecting element, is contained within a block time during which the heating element is driven. On the other hand, as the printing speed increases, the block time reduces according to the increase of the speed. However, even when the block time reduces, the period for inspecting the waveform, which is the temperature information obtained by the temperature detecting element, is not changed without reducing, and thus ends up extending across a plurality of block cycles. When the inspection period extends across the plurality of block cycles, due to simultaneous operations of logic circuits according to a rise of a latch signal that occurs per block cycle, an inrush current flows to a ground wiring and a voltage drop is caused by wiring resistance. Noise generated therefrom may be superimposed on the obtained temperature waveform and hinder accurate determination as to whether the discharging opening is the inhibited discharging opening, leading to an incorrect determination.

<CIT> discloses another example printing apparatus according to the preamble of claim <NUM>.

The present invention is directed to providing a liquid discharging head capable of making a correct determination as to whether a discharging opening is an inhibited discharging opening even in a case where the inspection period of the temperature detecting element extends across periods corresponding to a plurality of blocks.

One of the aspects of the present invention provides a printing apparatus, comprising a printing element substrate, including a heating element configured to heat liquid to discharge the liquid from a discharging opening, a substrate including the heating element, and a temperature detecting element configured to detect a temperature of the substrate, wherein a detection period, during which a result of detecting the temperature of the substrate by the temperature detecting element is obtainable, extends across a plurality of cycles of a latch signal periodically input to the printing element substrate, and wherein a data input circuit of the printing element substrate is configured to output a heating enabling signal, to be applied to the heating element, for discharging the liquid and the latch signal are output in such a manner that, in the detection period, an output value of a temperature waveform at a portion on which noise generated due to driving of a logic circuit of the printing element substrate based on the latch signal is superimposed does not exceed a preset threshold value, the temperature waveform being a temperature waveform of the substrate detected by the temperature detecting element, characterized in that the printing element substrate includes a mask signal generation unit configured to generate a mask signal, and wherein the one detection period is a period during which the mask signal is output at a high level.

Exemplary embodiments of the present invention will be described below with reference to the drawings.

In the present disclosure, "LT" represents a latch signal transmitted to a data input circuit <NUM> (<FIG>) disposed on a printing element substrate (<FIG>). A symbol "CLK" represents a clock signal transmitted to the data input circuit <NUM> disposed on the printing element substrate. A symbol "D" represents a data signal transmitted in a serial format to the data input circuit <NUM> disposed on the printing element substrate, and the data signal D includes information about which heating element and temperature detecting element are selected among pluralities of heating elements and temperature detecting elements. The data signal D further includes information regarding a heating duration when the heating element heats liquid. A symbol "l_lt" represents a latch signal that is generated by the data input circuit <NUM> based on "LT", and is transmitted to a heating element selection circuit <NUM> (<FIG>) and a temperature detecting element selection circuit <NUM> (<FIG>). A symbol "clk_h" represents a clock signal that is generated by the data input circuit <NUM> based on "CLK", and is transmitted to the heating element selection circuit <NUM>. A symbol "d_h" represents a data signal that is generated by the data input circuit <NUM> based on "D", and is transmitted to the heating element selection circuit <NUM>. A symbol "clk_s" represents a clock signal that is generated by the data input circuit <NUM> based on "CLK", and is transmitted to the temperature detecting element selection circuit <NUM> (<FIG>). A symbol "d_s" represents a data signal generated by the data input circuit <NUM> based on "D", and is transmitted to the temperature detecting element selection circuit <NUM>. A symbol "he" represents a heating enabling signal that is generated by the data input circuit <NUM> based on "D", and is input to a heating element <NUM> (<FIG>). A term "block" refers to a group of a plurality of heating elements targeted for driving simultaneously when a plurality of heating elements <NUM> is driven in a time-division manner.

<FIG> illustrates a connection diagram of signals between a control device <NUM> and a printing element substrate <NUM>. The control device generates printing control and printing information and information for controlling a discharge inspection. Signal lines are connected for a block signal LT, which measures a block time of time-division driving, a transfer clock signal CLK, a serial data signal D indicating control information, a serial data signal Do indicating determination data, and a transfer clock signal CLK2 of the serial data signal Do.

The configuration of the printing element substrate <NUM> will be described below with reference to <FIG> is a perspective view illustrating the printing element substrate <NUM>. <FIG> is a schematic view in cross section taken along a line a-a' illustrated in <FIG>.

Discharging openings <NUM> from which the liquid is discharged, terminals <NUM> electrically connected to the outside (for example, a control board of a printing apparatus), and a substrate <NUM> including the heating elements <NUM> for heating the liquid to discharge the liquid are formed on the printing element substrate <NUM>. The terminals <NUM> include reception terminals that individually receive, for example, the clock signal, the data signal, and the latch signal, which will be described below, a transmission terminal that outputs a signal such as a determination result signal to the outside, a plurality of power source terminals, a plurality of ground terminals, and the like. The terminals <NUM> supply energy, required to discharge the liquid, from the outside to the heating elements <NUM>. As illustrated in <FIG>, the printing element substrate <NUM> is configured in such a manner that the heating element <NUM> is formed immediately below the discharging opening <NUM>, and a temperature detecting element <NUM> is formed immediately below this heating element <NUM>.

An electric circuit disposed on the printing element substrate <NUM> will be described below with reference to <FIG> is a schematic view illustrating a circuit disposed on the printing element substrate <NUM>. In <FIG>, the plurality of heating elements <NUM> is arranged so as to be lined up in a predetermined direction. In the present example, <FIG> illustrates the heating elements <NUM> and the temperature detecting elements <NUM> corresponding to one column for simplification of the description.

As illustrated in <FIG>, the printing element substrate <NUM> mainly includes the data input circuit <NUM>, the heating element selection circuit <NUM>, the temperature detecting element selection circuit <NUM>, an inspection circuit <NUM>, the heating elements <NUM>, and the temperature detecting elements <NUM>. A broken line in <FIG> indicates a segment <NUM> (seg0). This segment indicates that the temperature detecting element <NUM> is arranged in correspondence with the heating element <NUM>. The state that the liquid is discharged due to the driving of the heating element <NUM> in the segment is detected by the temperature detecting element <NUM> in the same segment. The other segments (seg1,. segn) are similarly arranged.

The data input circuit <NUM> receives the latch signal LT, the clock signal CLK, and the data signal D transmitted from the outside. The data input circuit <NUM> then generates the latch signal l_lt, the clock signal clk_h for printing, the clock signal clk_s for the temperature detection, a clock signal clk_d for data processing, the data signal d_h for printing, the data signal d_s for the temperature detection, and the heating enabling signal he.

The heating element selection circuit <NUM> selects a specific heating element <NUM> among the plurality of heating elements <NUM> based on the latch signal l_lt, the clock signal clk_h, the data signal d_h, and the heating enabling signal he transmitted from the data input circuit <NUM>. The heating element selection circuit <NUM> then drives the selected heating element <NUM>. This heating element selection circuit <NUM> switches the heating element <NUM> to be driven according to a block cycle (described below), thus driving the heating elements <NUM> in the time-division manner. This driving will be briefly described now. The heating elements <NUM> in seg0, seg8, and seg16 are assigned to a block <NUM>, and the heating elements <NUM> in seg1, seg9, and seg17 are assigned to a block <NUM>. The heating elements <NUM> in the other segments are also similarly assigned. The assigned heating elements <NUM> are driven periodically block by block. A block time is determined for this driving, and the block to be driven is switched each time the latch signal is received.

The temperature detecting element selection circuit <NUM> selects a specific temperature detecting element <NUM> among the plurality of temperature detecting elements <NUM> based on the latch signal l_lt, the clock signal clk_s, and the data signal d_s transmitted from the data input circuit <NUM>. The temperature detecting element selection circuit <NUM> then drives the selected temperature detecting element <NUM>. The inspection circuit <NUM> inspects the discharging opening for difficulty in discharging based on the information acquired by the temperature detecting element <NUM>. This temperature detecting element selection circuit <NUM> enables the temperature detecting elements <NUM> to detect the temperature in each two block cycle of a detection process.

The data signal D includes the not-illustrated externally generated printing control information, printing information, and information for controlling the discharge inspection, and is input to the data input circuit <NUM> according to the latch signal LT and the transfer clock signal CLK, which define the cycle of the data reception. Whether or not the information in the data signal D includes information indicating an instruction to drive the temperature detecting element <NUM> is determined based on whether predetermined identification information is included in the data signal D.

The data input circuit <NUM> expands the received latch signal LT, transfer clock signal CLK, and data signal D, and outputs l_lt, clk_s, and d_s to the temperature detecting element selection circuit <NUM>. The data input circuit <NUM> expands the received block signal LT, transfer clock signal CLK, and data signal D, and outputs l_lt, clk_h, d_h, and he to the heating element selection circuit <NUM>. The signal l_lt is the latch signal for the internal circuit that is generated with a predetermined pulse width at a timing of the rear edge of the latch signal LT. The signals clk_s and clk_h are the transfer clock signals. The signal d_s is the data signal for selecting the temperature detecting element <NUM> to be driven. The signal d_h is the data signal for selecting the heating element <NUM> to be driven. The signal he is an application signal for driving the heating element <NUM>.

The heating element selection circuit <NUM> mainly includes a shift resister and a decoder, and drives the plurality of heating elements <NUM> in the time-division manner in response to receiving the latch signal l_lt, the clock signal clk_h, the data signal d_h, and the heating enabling signal he from the data input circuit <NUM>. One terminal and the other terminal of the heating element <NUM> in seg0 are connected to a power source line VH and a driving switch <NUM>, respectively. The other terminal of the driving switch <NUM> is connected to a GNDH line, to which the power source line VH returns. The power source line VH and the GNDH line are each connected to the terminal <NUM>. The driving switch <NUM> connected to the heating element <NUM> in seg0 is connected to a selection signal h0 of the heating element selection circuit <NUM>, and is controlled to be switched on/off. The line connections of the other segments seg are also set up in a manner similar to seg0. Thus, a specific driving switch <NUM>, among the plurality of disposed driving switches <NUM>, is switched on by the heating element selection circuit <NUM> that has received the data signal d_h, and the selected heating element <NUM> connected to the specific driving switch <NUM> is driven. The liquid is discharged from the discharging opening corresponding to the driven heating element <NUM>. Further, the data input circuit <NUM> includes each of a shift register (not illustrated) and a latch circuit (not illustrated) that receive the signals from the outside. The latch circuit periodically receives the latch signal l_lt, and stores information imported into the shift register.

The temperature detecting element <NUM> is disposed in the electric circuit of the printing element substrate <NUM> in such a manner that one terminal thereof is connected to wiring of a constant current power source <NUM>, which supplies power to the temperature detecting element <NUM>, and the other terminal is connected to a selection switch <NUM>, which selects the temperature detecting element <NUM>. The other terminal of the selection switch <NUM> is connected to vss wiring (ground wiring) to which a constant current Is returns. Further, both terminals of the temperature detecting element <NUM> are each connected to a different one of one terminal of a reading switches <NUM> and one terminal of a reading switches <NUM>. The reading switches <NUM> and <NUM> are used for reading out terminal voltages. The other terminals of the reading switches <NUM> and <NUM> are connected to a pair of common wirings p and n. The selection switch <NUM> and the reading switches <NUM> and <NUM> are connected to a selection signal s0 of the temperature detecting element selection circuit <NUM>, and are controlled to be switched on/off. The line connections of the other segments seg are also set up in a manner similar to seg0.

The inspection circuit <NUM> outputs the determination result signal Do indicating whether the discharging opening is an inhibited discharging opening to the outside based on the temperature information input via the pair of common wirings p and n. Common ground wiring is used for ground wirings of logic circuits and the ground wiring connected to the temperature detecting element <NUM>. This configuration makes noise due to simultaneous operations of the logic circuits prone to be generated on the temperature waveform detected by the temperature detecting element <NUM>, as will be described in detail below. The logic circuits refer to, for example, the shift register (not illustrated) and the latch circuit (not illustrated) provided inside the heating element selection circuit <NUM>.

The inspection circuit <NUM> will be described with reference to <FIG>, which is a block diagram of the inspection circuit <NUM>.

A detection start signal generation unit <NUM> receives the latch signal l_lt and the clock signal clk_s from the data input circuit <NUM>, and generates a detection start signal lt_s. The detection start signal lt_s refers to a signal of a timing of starting measuring the temperature information of the substrate that the temperature detecting element <NUM> measures. The detection start signal generation unit <NUM> receives the clock signal CLK2 from the outside, but this is a clock signal for outputting the data indicating the determination about the result of the analysis.

A mask signal generation unit <NUM> receives the clock signal clk_s from the data input circuit <NUM> and receives the detection start signal lt_s from the detection start signal generation unit <NUM>, and generates a mask signal m having a predetermined duration.

A signal processing/determination unit <NUM> performs processing for determining whether the discharge opening currently being detected using the temperature detecting element <NUM> is an inhibited discharging opening based on the temperature information (the temperature waveform) that is measured by the temperature detecting element <NUM> and is input via the wirings p and n. If the discharging opening currently being detected is an inhibited discharging opening, the signal processing/determination unit <NUM> outputs a binarized signal cmp to a determination data holding unit <NUM>.

The determination data holding unit <NUM> converts the binarized signal cmp into the signal d based on the mask signal m from the mask signal generation unit <NUM>, the detection start signal lt_s from the detection start signal generation unit <NUM>, and the binarized signal cmp from the signal processing/determination unit <NUM>. The determination data holding unit <NUM> then outputs the signal d to an output unit <NUM>.

The output unit <NUM> converts the signal d into the output signal (the determination result signal) Do based on the clock signal CLK2 from the outside, and outputs it to the outside.

The signal processing/determination unit <NUM> will be described with reference to <FIG>, which is a block diagram of the signal processing/determination unit <NUM>.

As described above, the signal processing/determination unit <NUM> is a circuit that outputs the binarized signal cmp. First, a difference amplification circuit <NUM> amplifies voltages at both ends of the temperature detecting element <NUM> that are acquired via the wirings p and n as a difference output dif, and outputs the difference output dif to a filter circuit <NUM>. After that, the filter circuit <NUM> performs processing such as differentiation on the difference output dif, and outputs a result thereof to a binarization unit <NUM> as a filter output fo. The filter circuit <NUM> includes a bandpass filter configured to be sensitive to a feature point i (<FIG>) that appears on the temperature waveform of the substrate when the liquid can be discharged normally from the discharging opening.

The binarization unit <NUM> includes a comparator, and compares the filter output fo with a preset threshold value th fed from an adjustment unit <NUM> and generates the binarized signal cmp. As will be described in detail below, the threshold value th serves as, for example, a criterion for determining whether the liquid can be discharged normally from the discharging opening currently being detected.

The adjustment unit <NUM> includes a digital-analog (DA) converter that generates a reference current Iref to be input to the constant current power source <NUM>, and a DA converter that generates the threshold value th to be input to the binarization unit <NUM>. The value of each of the DA converters is set based on the latch signal l_lt, the clock signal clk_s, and the data signal d_s.

The temperature waveform of the substrate will be described with reference to <FIG> is a schematic view illustrating temperature waveforms of the substrate that the temperature detecting element <NUM> can measure. In <FIG>, a solid line <NUM> indicates a waveform obtained in a case where the liquid is not discharged normally and a broken line <NUM> indicates a waveform acquired in a case where the liquid is discharged normally. When the heating enabling signal he is applied to the heating element <NUM>, the heating element <NUM> is driven and a temperature waveform like a waveform sen can be obtained. When the driving of the heating element <NUM> is ended, the temperature of the substrate gradually reduces. If the discharging opening targeted for the detection is an inhibited discharging opening, the waveform of the temperature exhibits a continuous gradual reduction in the course of the temperature reduction of the temperature waveform. On the other hand, if the discharging opening targeted for the detection is not an inhibited discharging opening, i.e., a discharging opening from which the liquid is discharged normally, the temperature waveform exhibits a different behavior from the behavior of the temperature waveform at an inhibited discharging opening from a certain point i. This certain point i refers to the feature point. In a case where the liquid is discharged normally, the temperature waveform exhibits a greater reduction than the temperature reduction obtained at an inhibited discharging opening from the feature point i.

A cause for this phenomenon of great temperature reduction is considered to be that the rear edge of a liquid droplet discharged from the discharging opening contacts the surface of the printing element substrate <NUM> and the substrate is cooled down thereby. This phenomenon is employed as a criterion for determining whether the liquid is discharged normally from the discharging opening.

A waveform dif (the difference output dif) is obtained by inverting the waveform sen. A waveform fo (the filter output fo) is obtained by differentiating the difference output dif once. As indicated by the filter output fo, differentiating the difference output dif once can make a further noticeable difference between the behaviors of the two waveforms from the feature point i. The filter output fo is clipped at a vss voltage <NUM> and thus a lower limit voltage thereof is placed at the ground level.

Each point (f, g', and i') of the filter output fo appears on the waveform at a timing delayed from each point (f, g, and i) of the difference output dif. This is because a delay time td occurs due to the execution of the differential processing. The f point and the f point are points at which the measured temperature of the substrate is maximized, i.e., correspond to a timing of ending applying the voltage to the heating element <NUM>. In other words, the f point and the f point are a timing of ending the driving of the heating element <NUM>. The g point and the g' point are points at which the change speed is maximized in the course of the temperature reduction (hereinafter referred to as a temperature reduction fastest point). In other words, the temperature reduction fastest point g refers to a time at which the change speed is maximized while the waveform is being converging after transitioning from the temperature increase to the temperature reduction. The temperature reduction fastest point g is determined according to the thickness (the thermal time constant) of an insulation film between the heating element <NUM> serving as the heat source and the temperature detecting element <NUM>.

The discharging opening is determined to be a normal discharging opening if the filter output fo exceeds the threshold value th, and is determined to be an inhibited discharging opening if the filter output fo does not exceed the threshold value th. The threshold value th is set to a value between the maximum value g' of the filter output fo obtained in a case where the discharging opening currently being detected is an inhibited discharging opening, and a maximum value j' of the filter output fo obtained in a case where the liquid is discharged normally. Thus, the discharging opening currently being detected can be determined to be a discharging opening from which the liquid can be discharged normally in a case where the filter output fo exceeds the threshold value th, and can be determined to be an inhibited discharging opening in a case where the filter output fo does not exceed the threshold value th.

The above-described operation of inspecting the discharging opening of the circuit in the printing element substrate <NUM> will be described below with reference to <FIG> and <FIG>. <FIG> is a flowchart illustrating a series of operations from the start of the determination about whether the discharging opening is an inhibited discharging opening to the output of the determination result. <FIG> is a timing chart according to the flowchart illustrated in <FIG>. Each of <FIG> and <FIG> is presented in such a manner that block numbers illustrated in <FIG> and block numbers illustrated in <FIG> correspond to each other.

In a period <NUM>, the transmission of various signals from the outside is started. This means that the various signals do not reach the temperature detecting element selection circuit <NUM> yet, and thus the information for selecting the temperature detecting element <NUM> to be used in the inspection (the clock signal clk_s and the data signal d_s) is not generated either as illustrated in <FIG> (step S501 in <FIG>).

In a period <NUM>, the information for selecting the temperature detecting element <NUM> (the clock signal clk_s and the data signal d_s) is generated by the data input circuit <NUM> as illustrated in <FIG> (step S502 in <FIG>).

In a period <NUM>, the latch signal l_lt, the clock signal clk_s, and the data signal d_s are input to the temperature detecting element selection circuit <NUM>, and the detection start signal lt_s is also generated by the detection start signal generation unit <NUM> as illustrated in <FIG> (step S503 in <FIG>). Thus, the detection of the temperature by the temperature detecting element <NUM> is started by being triggered at the timing when the detection start signal lt_s rises (step S504 in <FIG>). In the period <NUM>, the heating enabling signal he is input to the heating element <NUM>, and the heating element <NUM> is driven. The temperature of the substrate of the printing element substrate <NUM> increases due to the driving of the heating element <NUM>. Then, the difference output dif, which is obtained by inverting the temperature waveform, and the filter output fo, which is obtained by differentiating the difference output dif once, can be obtained. Further, the mask signal m is generated by the mask signal generation unit <NUM> (step S505 in <FIG>). The determination data holding unit <NUM> does not obtain the temperature waveform in a case where the mask signal m is set to a low level and obtains the temperature waveform in a case where the mask signal m is set to a high level. Thus, in the detection period during which the temperature detecting element <NUM> can acquire the result of detecting the temperature of the substrate, the high-level mask signal m is output.

In a period <NUM>, the feature point i appears. A broken line <NUM> indicates the temperature waveform obtained in a case where the liquid is normally discharged and a solid line <NUM> indicates the temperature waveform obtained in a case where the discharging opening is an inhibited discharging opening. A binarized signal <NUM> having a duration corresponding to the duration during which the filter output fo exceeds the threshold value th is generated in a case where the filter output fo exceeds the threshold value th, and no binarized signal is generated in a case where the filter output fo does not exceed the threshold value th. Thus, the presence or absence of the binarized signal is a result of the detection by the temperature detecting element <NUM>. The threshold value th is set to a value between the peak voltage when the liquid is discharged normally and the peak voltage when the liquid is not discharged. The detection of the temperature is also ended along with the end of the period <NUM>. More specifically, the timing at which the next detection start signal lt_s rises serves as a detection end signal for ending the detection of the temperature and triggers the end of the detection of the temperature, and also serves as the detection start signal for starting the detection directed to the next discharging opening (switches the discharging opening). In other words, the next heating element <NUM> is driven, and the next temperature detection is carried out by the corresponding temperature detecting element <NUM>. In and after a period <NUM>, the above-described cycle from the period <NUM> to the period <NUM> is repeated.

In the above-described manner, the driving of the heating element <NUM> in this operation of detecting the temperature is different from the driving during the printing operation, and one heating element <NUM> is driven among the plurality of heating elements <NUM> belonging to the block. Further, the timing of driving the heating element <NUM> is also different from the driving during the printing operation. One block cycle is set as a downtime after the driving, and the next selected heating element <NUM> is driven in the block cycle subsequent to this downtime.

As illustrated in <FIG>, the detection period during which a result of detecting the temperature can be obtained extends across a plurality of cycles, each of which is the input cycle of the periodically input latch signal l_lt. More specifically, the detection period extends across two block cycles (two cycles), the period <NUM> and the period <NUM> in <FIG>. Thus, the noise due to the simultaneous operations of the logic circuits is superimposed on the filter output fo between the period <NUM> and the period <NUM>, erroneously leading to an output of a larger value than the value to be output normally. As a result, even for a case where the filter output fo is not to exceed the threshold value th, the superimposition of the noise may cause the filter output fo to erroneously exceed the threshold value th, thus causing the discharging opening that is an inhibited discharging opening to be undesirably incorrectly determined to be a normal discharging opening. In light of this, even when the noise due to the latch signal is undesirably superimposed on the filter output fo, the present exemplary embodiment can prevent the above-described incorrect determination from being made by performing control so as to prohibit this noise from being superimposed near the maximum value of the filter output fo. Data <NUM> of Di and Do in the blocks <NUM> and <NUM> indicates indefinite data.

The timing chart of the temperature waveform obtained in the present exemplary embodiment will be described with reference to <FIG> is a schematic view illustrating the timing chart of each waveform obtained in the present exemplary embodiment, and indicates the waveform in a case where the discharging opening on which the temperature detection is being performed is an inhibited discharging opening.

Due to the simultaneous operations of the logic circuits based on a rise <NUM> of the latch signal LT, an inrush current flows to the vss wiring and a voltage drop is caused by wiring resistance. As a result, a voltage fluctuation (noise) <NUM> occurs on vss. Due to the superimposition of the noise <NUM> on vss, the temperature detecting element <NUM> and the inspection circuit <NUM> sharing the vss wiring are affected by the noise <NUM>, and noise <NUM> also generates on the difference output dif (the inverted waveform) obtained by inverting the temperature waveform. Due to the generation of the noise <NUM> on the difference output dif, noise <NUM> is also generated on the filter output fo (the differential waveform) obtained by differentiating the difference output dif once.

The present exemplary embodiment adjusts the timing at which the latch signal LT rises and the timing of the heating enabling signal he, thus allowing the noise to be superimposed before the timing at which the maximum value of the filter output fo can be obtained as illustrated in <FIG>. With this adjustment, even in a case where the noise is superimposed on the filter output fo, the output value does not exceed the threshold value th at the portion of the filter output fo on which the noise is superimposed within the period during which the temperature of the substrate is detected, so that the incorrect determination for the temperature detection can be prevented from being made. More specifically, the present exemplary embodiment makes the adjustment in such a manner that the rise of the latch signal LT is located between the minimum point f of the difference output di and the point f that corresponds to the minimum point f of the filter output fo. Thus, the noise also generates between the point f and the point f, which can further ensure that the incorrect determination is prevented from being made with respect to the temperature detection in a case where the noise is superimposed on the filter output fo.

A binarized signal <NUM> is generated due to the superimposition of the noise on the filter output fo so as to cause the filter output fo to exceed the threshold value th at the beginning of the next block, but this does not lead to the incorrect determination because this period is set to the period during which the binarized signal is not sensed using the mask signal m.

A second exemplary embodiment will be described with reference to <FIG>. The second exemplary embodiment will be described, assigning similar reference numerals to portions similar to the first exemplary embodiment and omitting the descriptions thereof. <FIG> is a schematic view illustrating various waveforms obtained in the present exemplary embodiment. A broken line and a solid line in <FIG> indicate the waveform acquired when the liquid is discharged normally and the waveform acquired when the discharging opening is an inhibited discharging opening, respectively. Further, the threshold value th indicated by a broken line corresponds to the value of the threshold value th according to the first exemplary embodiment. In the present exemplary embodiment a method will be described in which the discharge state is inspected by applying an application pulse for emphasizing the temperature change to the heating element <NUM>, to make a further difference in behavior between the waveform obtained when the liquid is normally discharged and the waveform obtained when it is difficult to discharge the liquid.

The heating enabling signal he is applied in such a manner that, after first application <NUM> for causing the discharge is conducted, second application <NUM> adjusted so as not to cause foaming is conducted at a timing immediately before the feature point appears in the course of the temperature reduction of the temperature waveform. Thus, the substrate is cooled down by the liquid droplet after the temperature of the liquid first increases before the feature point appears, and therefore the waveform obtained when the liquid is normally discharged exhibits a further noticeable temperature change after the feature point appears. Accordingly, a larger value is output as the maximum value of the filter output fo obtained by differentiating this temperature waveform than the maximum value of the filter output fo according to the first exemplary embodiment. This allows the threshold value th to be set to a higher value, thus contributing to preventing the noise from exceeding the threshold value th even when the noise generates on the temperature waveform.

In this manner, the present exemplary embodiment can further reduce the possibility of undesirably making the incorrect determination due to the influence of the noise by applying the second application pulse <NUM>. In the exemplary embodiments, the example has been described in which the period of the detection by the temperature detecting element <NUM> extends across the two blocks, but the present invention is not limited thereto. More specifically, the present invention can be effectively employed even in a case where the detection period extends across any plurality of blocks. The timings of outputting the heating enabling signal he and the latch signal l_lt are adjusted in such a manner that the noise is generated before the timing at which the maximum value of the filter output fo can be acquired, but the present invention is not limited thereto. More specifically, the timings may be adjusted in such a manner that the noise due to the latch signal is generated after the timing at which the maximum value of the filter output fo can be acquired, as long as the temperature waveform affected by the noise does not exceed the threshold value th.

A comparative example of the exemplary embodiments of the present invention will be described with reference to <FIG> and <FIG>. <FIG> is a schematic view illustrating a timing chart of each waveform in the comparative example of the exemplary embodiments of the present invention, and indicates the waveform in a case where the discharging opening on which the temperature detection is being performed is an inhibited discharging opening. <FIG> illustrates a timing chart when the inspection is conducted within one block time. As illustrated in <FIG>, the information for selecting a temperature detecting element seg1 is input in the block <NUM>. The inspection of seg1 is conducted and the information for selecting a next temperature detecting element seg2 is also input in the block <NUM>. The data indicating the determination for seg1 is output and the inspection of seg2 is also conducted in the block <NUM>. After that, the inspection procedure is repeated in a similar manner.

Due to the simultaneous operations of the logic circuits according to a rise <NUM> of the latch signal LT, an inrush current flows to the vss wiring and a voltage drop is caused by the wiring resistance. As a result, a voltage fluctuation (noise) <NUM> occurs on vss. Due to the superimposition of the noise <NUM> on vss, the temperature detecting element <NUM> and the inspection circuit <NUM> sharing the vss wiring are affected by the noise <NUM>, and noise <NUM> also generates on the difference output dif obtained by inverting the temperature waveform. Due to the generation of the noise <NUM> on the difference output dif, noise <NUM> also generates on the filter output fo.

In <FIG>, the noise <NUM> generates in the state that the value of the filter output fo does not fully reduce yet. As a result, the filter output fo exceeds the threshold value th, which erroneously leads to generation of a binarized signal <NUM> and thus undesirably causes an inhibited discharging opening to be incorrectly determined to be a normal discharging opening. The filter output fo when the liquid is normally discharged does not yield the incorrect determination because the filter output fo exceeds the threshold value th regardless of whether the noise is superimposed or not. However, the threshold value th should be set to an appropriate voltage between the peak voltage when the liquid is normally discharged and the peak voltage when the liquid cannot be discharged. Thus, if the peak voltage when the liquid is normally discharged is emphasized in response to the noise, this makes it difficult to set the appropriate determination threshold value th. The influence of the noise also becomes an issue from this viewpoint.

Therefore, in the exemplary embodiments of the present invention, the timing of outputting the heating enabling signal he and the timing of outputting the latch signal LT are adjusted in such a manner that the output generating on the waveform due to the latch signal of the latch circuit does not exceed the threshold value th, as described above. Due to this adjustment, the exemplary embodiments of the present invention can reduce the influence of the noise due to the latch signal when the inspection period extends across the plurality of blocks, thereby preventing the incorrect determination from being made.

Claim 1:
A printing apparatus comprising:
a printing element substrate (<NUM>) including
a heating element (<NUM>) configured to heat liquid to discharge the liquid from a discharging opening (<NUM>),
a substrate (<NUM>) including the heating element, and
a temperature detecting element (<NUM>) configured to detect a temperature of the substrate,
wherein a detection period, during which a result of detecting the temperature of the substrate by the temperature detecting element is obtainable, extends across a plurality of cycles of a latch signal (LT) periodically input to the printing element substrate, and
wherein a data input circuit (<NUM>) of the printing element substrate is configured to output a heating enabling signal (he), to be applied to the heating element, for discharging the liquid and the latch signal are output, in such a manner that, in the detection period, an output value of a temperature waveform at a portion on which noise generated due to driving of a logic circuit of the printing element substrate based on the latch signal is superimposed does not exceed a preset threshold value (th), the temperature waveform being a temperature waveform of the substrate detected by the temperature detecting element, characterized in that
the printing element substrate includes a mask signal generation unit (<NUM>) configured to generate a mask signal (m), and
wherein the detection period is a period during which the mask signal is output at a high level.