Light-emitting device, printer head, and printing device

Abstract

A light-emitting device (1) is positioned inside a printer head of a printing device. The light-emitting device (1) comprises: a self-luminous element (EL) having an anode (AN) and a cathode (CA); and a light emission control unit (10) that controls the light emission state of the self-luminous element (EL). In a first period, the light emission control unit (10) causes the self-luminous element (EL) to emit light by generating a first potential difference as the potential difference (ΔV) of the anode (AN) with respect to the cathode (CA). In a second period preceding the first period, the light emission control unit (10) generates a second potential difference, which is smaller than the first potential difference, as the potential difference (ΔV) of the anode (AN) with respect to the cathode (CA). In the first period and the second period, the potential (Va) of the anode (AN) is higher than the potential (Vc) of the cathode (CA).

Description

Light-emitting device, printer head, and printing device

[0001] One aspect of the present disclosure relates to a light-emitting device located inside a printer head in a printing device.

[0002] Patent Document 1 below discloses a configuration example of a printing device including a printer head having a self-emitting element.

[0003] Japanese Patent Application Laid-Open No. 2006-88344

[0004] It is desired to improve the print quality in a printing device.

[0005] A light-emitting device according to one aspect of the present disclosure is a light-emitting device located inside a printer head in a printing device, including a self-emitting element having an anode and a cathode, and a light-emitting control unit that controls the light-emitting state of the self-emitting element. The light-emitting control unit causes the self-emitting element to emit light by generating a first potential difference as the potential difference between the anode and the cathode in a first period, and generates a second potential difference smaller than the first potential difference as the potential difference between the anode and the cathode in a second period preceding the first period. In the first period and the second period, the potential of the anode is higher than the potential of the cathode.

[0006] According to one aspect of the present disclosure, the print quality in a printing device can be improved.

[0007] A schematic diagram of the configuration of the printing apparatus in Embodiment 1 is shown. A schematic diagram of the configuration of the light-emitting apparatus in Embodiment 1 is shown. An example of the relationship between the potential difference of the anode relative to the cathode and the light intensity in a self-luminous element is shown. An example of the light emission rise characteristics of a self-luminous element is shown. Another example of the light emission rise characteristics of a self-luminous element is shown. An example of the integrated light intensity of a self-luminous element is shown. An example of the relationship between the second potential difference and the light intensity ratio in a self-luminous element is shown. An example of the cathode signal in Embodiment 1 is shown. A schematic diagram of the configuration of the pixel circuit in Embodiment 2 is shown. An example of the waveforms of each signal in the pixel circuit of Figure 9 is shown. Another example of the configuration of the pixel circuit is shown. An example of the waveforms of each signal in the pixel circuit of Figure 11 is shown. An example of the relationship between the second anode potential and the light intensity ratio in Embodiment 2 is shown. An example of the light emission rise characteristics of a self-luminous element in Embodiment 2 is shown. A diagram for explaining the third period in Embodiment 2 is shown. A diagram for explaining the fourth period in Embodiment 2 is shown. A diagram for explaining the difference in anode potential in the first period, third period, and fourth period in Embodiment 2 is shown.

[0008] [Embodiment 1] Embodiment 1 will be described below. For the sake of explanation, components having the same function as those described in Embodiment 1 will be denoted by the same reference numerals in subsequent embodiments, and their descriptions will not be repeated. For the sake of simplification, explanations of known technical matters will be omitted as appropriate. Each component and each numerical value described herein is merely an example unless otherwise inconsistent. Therefore, for example, unless otherwise inconsistent, the positional and connection relationships of each component are not limited to the examples in the figures. Also, the figures are not necessarily drawn to scale.

[0009] In this specification, unless otherwise specified, the notation "A to B" for two numbers A and B means "greater than or equal to A and less than or equal to B". Also, in this specification, the term "connected" means "electrically connected" in the context of electrical circuits.

[0010] (Example of configuration of the printing device 151) Figure 1 schematically shows an example of the configuration of the printing device 151 in Embodiment 1. The printing device 151 comprises a plurality of printing units 100. For example, each of the plurality of printing units 100 may correspond to a different color.

[0011] The printing unit 100 includes a printer head 25, a photoreceptor 35, a charging unit 45, a toner supply unit 55, and a toner transfer unit 65. The charging unit 45 charges the photoreceptor 35. The toner supply unit 55 stores toner 75. The toner supply unit 55 supplies toner 75 to the photoreceptor 35 according to the latent image formed on the photoreceptor 35. The toner transfer unit 65 transfers the toner 75 supplied to the photoreceptor 35 to a recording medium (e.g., printing paper).

[0012] As shown in Figure 1, the printer head 25 has a light-emitting device 1. Thus, the light-emitting device according to one aspect of this disclosure only needs to be located inside the printer head of the printing device.

[0013] (Example of configuration of light-emitting device 1) Figure 2 schematically shows an example of the configuration of light-emitting device 1. Light-emitting device 1 is equipped with self-luminescent elements EL having an anode AN and a cathode CA. In the example of Figure 2, light-emitting device 1 has N self-luminescent elements EL, where N is an integer of 2 or more.

[0014] For example, the self-emitting element (EL) may be an OLED (Organic Light Emitting Diode). Alternatively, the self-emitting element (EL) may be a QLED (Quantum Dot LED). The self-emitting element (EL) only needs to be configured to produce electroluminescence.

[0015] In this specification, the potential of the anode AN in a self-emitting element (EL) is denoted as the anode potential Va, and the potential of the cathode CA is denoted as the cathode potential Vc. The potential difference of the anode relative to the cathode CA is denoted as the potential difference ΔV. In this specification, for example, the voltage signal supplied to the anode AN may also be denoted as Va.

[0016] The light-emitting device 1 has a light-emitting control unit 10 that controls the light-emitting state of the self-emitting element EL. The light-emitting control unit 10 may include any drive circuit. In the example in Figure 2, the light-emitting control unit 10 includes an anode line drive circuit 11 and a cathode line drive circuit 12.

[0017] As will be apparent to those skilled in the art, the method of driving the light-emitting device 1 is not particularly limited. In Embodiment 1, for the sake of clarity, a statically driven light-emitting device 1 is provided as an example. In static driving, the current flowing through each pixel of the light-emitting device 1 is constantly controlled by an independent signal line.

[0018] Figure 2 illustrates a case where the Va of each of the N self-luminous elements (ELs) is set to a constant value. Therefore, in the example in Figure 2, the anode AN of each of the N self-luminous elements (ELs) is connected to a single anode line AL. In the example in Figure 2, the anode line driving circuit 11 supplies a constant Va to each of the N self-luminous elements (ELs) via the single anode line AL. For the sake of clarity, in the example in Figure 2, we assume that Va = 0V.

[0019] In the static drive example in Figure 2, the same number of cathode lines CL as the number of pixels in the light-emitting device 1 are provided. In the example in Figure 2, the number of pixels in the light-emitting device 1 is equal to the number of self-emitting elements EL. Therefore, in the example in Figure 2, N cathode lines CL are provided. Accordingly, in the example in Figure 2, each cathode CA of the N self-emitting elements EL is connected to each of the N cathode lines CL. That is, in the example in Figure 2, the cathode CA of one self-emitting element EL is connected to one cathode line CL.

[0020] The light emission control unit 10 may supply a cathode signal Vc, which is a voltage signal having different signal values ​​in one period (e.g., the first period described below) and another period (e.g., the second period described below), to each of the N cathode wires CA. In the example in Figure 2, the cathode wire driving circuit 12 supplies the cathode signal Vc to each of the N cathode wires CA. This allows Vc having different signal values ​​depending on the time to be supplied to the cathode CA. In the example in Figure 2, Vc may be set for each of the N self-emitting element ELs. In this way, an individual ΔV can be set for each of the N self-emitting element ELs.

[0021] However, it should be noted that the connection relationship between the N self-emitting elements (EL), anode lines AL, and cathode lines CL is not limited to the example in Figure 2. As another example, N anode lines AL and a single cathode line CL may be provided. In this case, each cathode CA of the N self-emitting elements (EL) is connected to the single cathode line CL. And each anode AN of the N self-emitting elements (EL) is connected to each of the N anode lines AL.

[0022] In this example, the cathode wire drive circuit 12 supplies a constant Vc to each cathode CA of the N self-luminescent elements EL via a single cathode wire CL. The anode wire drive circuit 11 supplies a voltage signal Va, which has different signal values ​​in one period and another, to each of the N anode wires AL. This allows the anode AN to be supplied with Va that has different signal values ​​depending on the time. In this example, Va may be set for each of the N self-luminescent elements EL. In this example as well, an individual ΔV can be set for each of the N self-luminescent elements EL.

[0023] (Example of light emission control focusing on the light emission characteristics of self-luminescent elements (ELs)) Figures 3 to 7 show examples of the light emission characteristics of self-luminescent elements (ELs). Figure 3 shows an example of the relationship between ΔV in a self-luminescent element (EL) and the amount of light emitted from the EL. In the graph in Figure 3, the horizontal axis is ΔV and the vertical axis is the amount of light. In this specification, the amount of light is assumed to be a quantity normalized by a given reference value. As shown in Figure 3, a typical self-luminescent element (EL) tends to show an increase in the amount of light as ΔV increases.

[0024] As an example, the light emission control unit 10 generates a first potential difference ΔV1 as ΔV during the first period, thereby causing the self-emitting element EL to emit light. Therefore, during the first period, Va > Vc.

[0025] On the other hand, the light emission control unit 10 may generate a second potential difference ΔV2 as ΔV in the second period preceding the first period. ΔV2 should be smaller than ΔV1; that is, ΔV2 > ΔV1. As will be clear from the explanations below, the second period is also intended as a preliminary period to the first period. For this reason, Va > Vc is also true in the second period.

[0026] In this specification, the first period is intended to cause photosensitization in the photoreceptor 35. On the other hand, the second period is intended not to cause photosensitization in the photoreceptor 35. For this reason, the first period may be called the photosensitive period or the light period, and the second period may be called the non-photosensitive period or the dark period.

[0027] From the above, for example, during the first period, a relatively strong amount of light is emitted from the self-emitting element (EL), while during the second period, a considerably weaker amount of light is emitted from the self-emitting element (EL) compared to the first period. The light emitted from the self-emitting element (EL) during the second period may be of an intensity that is not visible to humans, or it may be of an intensity that is visible to humans. As an example, the amount of light emitted from the self-emitting element (EL) during the second period may be 1 / 10 or less of the amount of light emitted from the self-emitting element (EL) during the first period.

[0028] Therefore, for example, in the printing apparatus 151, during the first period, the photoreceptor 35 is exposed to light emitted from the self-emitting element EL, while during the second period, the photoreceptor 35 is not exposed to light.

[0029] The inventors of this application have found that the light emission rise characteristics of a self-luminescent element (EL) in the first period can be improved by applying ΔV2 in the second period. Figure 4 shows examples of light emission rise characteristics of a self-luminescent element (EL) for various ΔV2 values. In the graph in Figure 4, the horizontal axis represents time, and the vertical axis represents light intensity. In the example in Figure 4, the period from 0 to 5 μs is the second period, and the period from 5 μs onward is the first period.

[0030] Figure 4 shows the light emission rise characteristics for various ΔV2 values ​​in the range of 0V to 2.4V. The example of ΔV2 = 0V is a conventional example. As shown in Figure 4, the light intensity of the self-luminescent element EL increases more rapidly after the start of the first period as ΔV2 increases.

[0031] For example, in the conventional case where ΔV2 = 0V, the light intensity at time 10μs on the horizontal axis, which is 5μs after the start of the first period, has hardly increased from the light intensity at time 5μs on the horizontal axis. On the other hand, when ΔV2 > 0V, the light intensity at time 10μs on the horizontal axis has increased to some extent compared to the light intensity at time 5μs on the horizontal axis. The mechanism by which the light emission rise characteristics of the self-luminescent element EL are accelerated by supplying a positive ΔV2 will be described below.

[0032] In a self-luminescent element (EL), a parasitic capacitance exists between the anode (AN) and the cathode (CA). After the start of the first period, the current flowing through the self-luminescent element (EL) in conjunction with the supply of ΔV1 is first consumed to charge the parasitic capacitance. Therefore, the current flowing through the self-luminescent element (EL) only contributes to the electroluminescence of the self-luminescent element (EL) after the charging of the parasitic capacitance is complete.

[0033] In conventional designs, since ΔV2 = 0V, no pre-charging of the parasitic capacitance of the self-emitting element (EL) occurs during the second period preceding the first period. Consequently, a relatively long time after the start of the first period is spent charging the parasitic capacitance in conventional designs. Therefore, rapid light emission startup in the first period is not achieved in conventional designs.

[0034] On the other hand, when ΔV2 > 0V, pre-charging of the parasitic capacitance of the self-luminescent element (EL) is performed in the second period preceding the first period. Therefore, the time spent charging the parasitic capacitance after the start of the first period can be reduced compared to the conventional example. Consequently, a faster light emission rise time is achieved in the first period compared to the conventional example.

[0035] Incidentally, the response speed required for light-emitting devices for displays is at most on the order of milliseconds. Therefore, the aforementioned 5 μs time length for the light-emitting rise characteristic is a delay amount that does not pose a problem for light-emitting devices for displays, for example.

[0036] On the other hand, the aforementioned delay can be a problem for light-emitting devices used in printing presses. This is because light-emitting devices for printing presses require a fairly high response speed to maintain print quality (e.g., to keep up with high paper feeding speeds). For example, light-emitting devices for printing presses require a response speed on the order of microseconds.

[0037] From the above, the light emission control method according to one aspect of this disclosure is suitable for a light emission device for a printing apparatus. Specifically, this light emission control method makes it possible to increase the amount of light emitted from the light emission device compared to conventional methods. As a result, the printing speed can be improved in a printing apparatus having this light emission device. Furthermore, the printing resolution in the printing apparatus can also be improved compared to conventional methods. Therefore, the light emission device 1 makes it possible to realize a printing apparatus 151 with higher printing quality than conventional methods.

[0038] Figure 5 shows examples of the light emission rise characteristics of self-luminescent elements (ELs) for various lengths of the first period. In the examples labeled 510, 520, 530, and 540 in Figure 5, the lengths of the first period are 30 μs, 20 μs, 15 μs, and 10 μs, respectively. As can be seen from Figure 5, a faster light emission rise characteristic is desired as the length of the first period decreases. As mentioned above, a faster light emission rise characteristic can be achieved by setting ΔV2 to a larger value.

[0039] Figure 6 shows an example of the integrated light quantity of a self-luminescent element (EL). In this specification, the integrated light quantity is given as the time integral of the light quantity in the first period. Figure 6 shows the integrated light quantity when ΔV2 = 2.3V. For comparison with the case of ΔV2 = 2.3V, Figure 6 also shows the integrated light quantity when ΔV2 = 0V (conventional example). In the examples of reference numerals 610 and 620 in Figure 6, the length of the first period is 30 μs and 10 μs, respectively. Therefore, the example of reference numeral 610 corresponds to the example of reference numeral 510, and the example of reference numeral 620 corresponds to the example of reference numeral 540.

[0040] As described above, when ΔV2 > 0V, the light emission rise time in the first period can be accelerated compared to the conventional example. Therefore, as shown in Figure 6, when ΔV2 > 0V, the integrated light amount increases compared to the conventional example.

[0041] Furthermore, as shown in Figure 6, the integrated light amount decreases as the length of the first period decreases. If the integrated light amount is insufficient, a decrease in print quality may occur. Therefore, in the conventional example, if the length of the first period is set to be short, there is a risk that the predetermined print quality cannot be maintained. On the other hand, when ΔV2 = 0V, a certain amount of integrated light amount can be secured even when the length of the first period is set to be short. From this, it can be seen that the light-emitting device 1 makes it possible to realize a printing device 151 with higher print quality than conventional devices.

[0042] Figure 7 shows an example of the relationship between ΔV2 and the light intensity ratio in a self-luminescent element (EL). In the example in Figure 7, the light intensity ratio is given as a value obtained by normalizing the integrated light intensity at a given ΔV2 by the integrated light intensity at a reference ΔV2. In the example in Figure 7, the reference ΔV2 is set to 0V. Therefore, the light intensity ratio at ΔV2 = 0V is 1. Figure 7 shows the above relationship for first period lengths of 30 μs, 20 μs, 15 μs, and 10 μs, respectively.

[0043] As shown in Figure 7, in self-luminescent ELs, the light intensity ratio increases with increasing ΔV2. Also, as can be seen from the example in Figure 6 above, in self-luminescent ELs, the increase in the light intensity ratio with increasing ΔV2 becomes more pronounced as the length of the first period decreases.

[0044] Incidentally, if the value of ΔV2 is too small, the preliminary charging by ΔV2 in the second period may be insufficient. That is, if the value of ΔV2 is too small, the light emission rising characteristic of the self-emission element EL cannot be sufficiently accelerated. On the other hand, if the value of ΔV2 is too large, there is a possibility that light strong enough to cause photosensitivity in the photoreceptor 35 may be emitted from the self-emission element EL in the second period. That is, if the value of ΔV2 is too large, unnecessary photosensitivity may occur in the second period.

[0045] Therefore, as an example, as shown in FIG. 7, ΔV2 may be set to 0.5 V to 2.4 V. In this case, the light emission rising characteristic of the self-emission element EL can be sufficiently accelerated, and the possibility of unnecessary photosensitivity occurring in the second period can be reduced.

[0046] As shown in FIG. 7, for example, when a light quantity ratio that is not so large is required, ΔV2 may be set to 0.5 V to 2.0 V. On the other hand, when a relatively large light quantity ratio is required, ΔV2 may be set to be greater than 2.0 V and less than or equal to 2.4 V.

[0047] (Example of cathode signal) FIG. 8 shows an example of the cathode signal Vc supplied from the light emission control unit 10 to one self-emission element EL in the light emission device 1 of FIG. 2. In the example of FIG. 8, the light emission control unit 10 supplies a pulse signal in which a low level value and a high level value are alternately repeated as Vc. In the example of FIG. 8, the low level value of Vc is denoted as Vc1, and the high level value is denoted as Vc2.

[0048] Reference numeral 810 in FIG. 8 represents one low level period. The low level period is an example of the first period. Therefore, Vc1 corresponds to the first potential difference ΔV1 described above. On the other hand, reference numeral 820 in FIG. 8 represents the high level period immediately before the low level period indicated by reference numeral 810. The high level period is an example of the second period. Therefore, Vc2 corresponds to the second potential difference ΔV2 described above.

[0049] In the example in Figure 8, Vc1 = -3V and Vc2 = -2V. Therefore, in the example in Figure 8, ΔV1 = 3V and ΔV2 = 2V. Thus, in Embodiment 1, by supplying Vc1 and Vc2 that satisfy the relationship Vc1 < Vc2, it is possible to generate ΔV1 and ΔV2 that satisfy the relationship ΔV1 > ΔV2.

[0050] As described above, the light emission control unit 10 may generate ΔV1 in the first period and ΔV2 in the second period for each of the N cathode wires CL by supplying Vc having different signal values ​​(e.g., Vc1 and Vc2) in the first period and Vc2 in the second period.

[0051] [Embodiment 2] In Embodiment 2, unlike Embodiment 1, an active-drive type light-emitting device 1 is provided as an example. In active drive, the data writing period is selected by the scan line. During the data writing period, data is written to each of the multiple self-luminous elements (ELs) from a common data line. In active drive, the number of data lines is less than the number of pixels in the light-emitting device 1. In Embodiment 2 as well, the number of pixels in the light-emitting device 1 is equal to the number of self-luminous elements (ELs). Therefore, the number of data lines in the light-emitting device 1 of Embodiment 2 is less than the number of self-luminous elements (ELs).

[0052] (Example of Pixel Circuit GK Configuration) The light-emitting device 1 in Embodiment 2 may have a pixel circuit GK having a self-emitting element EL. Figure 9 shows an example of the configuration of the pixel circuit GK. The pixel circuit GK may have an initialization circuit for the self-emitting element EL. In the example in Figure 9, the pixel circuit GK is connected to the data-side drive circuit 910. The light-emitting control unit 10 may include the data-side drive circuit 910.

[0053] Figure 10 shows examples of the waveforms of each signal in the pixel circuit GK of Figure 9. In this specification, a signal line that supplies a certain signal may be referred to using the same symbol as the signal. For example, a signal line that supplies a data signal S(j) may be referred to as a data signal line S(j). The control signals S0 to S2 in Figure 10 are signals that switch the conduction state of an unillustrated switch in the data-side drive circuit 910. In the following description of Figures 9 and 10, explanations of matters shown in Figures 9 and 10 that are not related to the light emission control method of this invention will be omitted as appropriate. The same applies to Figure 11, which will be described later.

[0054] In Figure 10, during period t1, control signals S1 and S2 are at high levels, and control signal S0 is at a low level. During period t1, the data signal line S(j) and the internal data lines of the data-side drive circuit 910 (not shown) are connected in accordance with these control signal values. Also during period t1, the scan signal G(i) and the monitor control signal M(i) are maintained at high levels.

[0055] Therefore, during period t1, the write control transistor T91 and the monitor control transistor T93 in the pixel circuit GK are kept in the turn-on state. During period t1, in this state, the initialization potential Vpc is applied to the data signal line S(j). This initializes the state of the capacitor C91 and the anode potential Va in the self-luminescent element EL.

[0056] In the example shown in Figure 9, a constant cathode potential ELVSS is applied to the cathode CA of the self-luminescent element EL. That is, the cathode potential Vc is fixed at ELVSS. Therefore, the ΔV of the self-luminescent element EL during period t1 is determined according to Vpc.

[0057] Furthermore, as shown in Figure 10, in period t2 following period t1, a potential Vr_TFT higher than Vpc is applied to the data signal line S(j). Therefore, the ΔV of the self-emitting element EL in period t2 is determined according to Vr_TFT.

[0058] As described above, the light emission control unit 10 in Embodiment 2 may generate a first potential difference by applying a first anode potential to the anode AN during the first period. Furthermore, the light emission control unit 10 may generate a second potential difference by applying a second anode potential to the anode AN during the second period. In Figure 10, period t2 is an example of the first period, and period t1 is an example of the second period. Also, Vr_TFT corresponds to the first anode potential, and Vpc corresponds to the second anode potential.

[0059] In addition, as is clear from the above explanation, in the pixel circuit GK, pre-charging of the self-emitting element EL can be performed as initialization of the anode AN of the self-emitting element EL. Furthermore, the first anode potential can be determined by the potential applied to the pixel circuit GK via the data signal line S(j) (Vr_TFT in the example of Figure 10).

[0060] (Another example of pixel circuit GK) Figure 11 shows another example of the configuration of pixel circuit GK. In the example of Figure 11, the pixel circuit GK has a light emission control transistor T6, a power supply control transistor T5, and a discharge transistor T7. In the example of Figure 11 as well, the cathode potential Vc is fixed to ELVSS.

[0061] In the example shown in Figure 11, the anode AN of the self-emitting element EL is connected to the power line ELVDD via the light emission control transistor T6 and the power supply control transistor T5. In addition, node AN is connected to the anode potential initialization line VINI2 via the discharge transistor T7.

[0062] In the example shown in Figure 11, the light emission control unit 10 switches the conduction state of each transistor by applying a signal to the gate of each transistor. In the example shown in Figure 11, each transistor is a P-type transistor. Therefore, when a low-level signal is applied to the gate of a transistor, that transistor is turned on.

[0063] In the example shown in Figure 11, the gate of the light emission control transistor T6 is connected to the light emission control line em[n]. The gate of the power supply control transistor T5 is also connected to the light emission control line em[n]. The gate of the discharge transistor T7 is connected to the discharge control line dis[n]. The gate of the threshold compensation transistor T2 in Figure 11 is connected to the scan control line scan[n]. In Figure 11, n indicates the number of each control line.

[0064] Figure 12 shows examples of the waveforms of each signal in the pixel circuit GK of Figure 11. In Figure 12, examples of the light emission control signal em[n], the discharge signal dis[n], and the scan signal scan[n] are shown. In Figure 12, the reference numeral 1210 indicates the period during which the light emission control signal em[n] takes a low level value. The reference numeral 1220 indicates the period during which the discharge signal dis[n] takes a low level value. The period of reference numeral 1220 is also called the anode reset period. The period of reference numeral 1220 precedes the period of reference numeral 1210. The reference numeral 1230 indicates the period during which the scan signal scan[n] takes a low level value. The period of reference numeral 1230 is also called the data writing period. The period of reference numeral 1230 is after the period of reference numeral 1220 and before the period of reference numeral 1210.

[0065] During the period indicated by reference numeral 1210, the light emission control transistor T6 and the power supply control transistor T5 are turned on. As a result, a first anode potential is applied to the anode AN. Therefore, during the period indicated by reference numeral 1210, a first potential difference corresponding to the first anode potential is generated. In the example in Figure 11, the first anode potential is determined by the potential supplied to the pixel circuit GK via the data signal line DATA (i.e., the signal value of the data signal DATA).

[0066] During the period indicated by reference numeral 1220, the discharge transistor T7 is turned on. As a result, a second anode potential is applied to the anode AN. Therefore, during the period indicated by reference numeral 1220, a second potential difference corresponding to the second anode potential is generated. In the example in Figure 11, the second anode potential is equal to VINI2. Thus, if the second potential difference in the example in Figure 11 is denoted as ΔV2, then ΔV2 = VINI2 - ELVSS.

[0067] In the example in Figure 11, VINI2 is set to a value smaller than the first anode potential. Therefore, in the example in Figure 11, the second potential difference is also smaller than the first potential difference. For this reason, the period indicated by reference numeral 1210 in Figure 12 is an example of the first period, and the period indicated by reference numeral 1220 is an example of the second period.

[0068] Figure 13 shows an example of the relationship between the second anode potential (e.g., VINI2) and the light intensity ratio in Embodiment 2. Figure 13 shows the above relationship when the length of the first period is 36 μs and 60 μs, respectively. In Figure 13 and the example in Figure 14 described below, ELVSS is set to -4V.

[0069] In the example in Figure 13, the light intensity ratio is given as a value obtained by normalizing the integrated light intensity at a given VINI2 by the integrated light intensity at a reference VINI2. In the example in Figure 13, the reference VINI2 is set to -7V. Therefore, the light intensity ratio at VINI2 = -7V is 1. As shown in Figure 13, the light intensity ratio increases with increasing VINI2 (in other words, with increasing ΔV2). Furthermore, as the length of the first period decreases, the increase in the light intensity ratio accompanying the increase in VINI2 becomes more pronounced.

[0070] Figure 14 shows an example of the light emission rise characteristics of a self-luminescent EL in Embodiment 2. The length of the first period in the examples of reference numerals 1410 and 1420 in Figure 14 is 36 μs and 60 μs, respectively. Figure 14 shows the light emission rise characteristics for various ΔV2 values ​​from -7 V to 1 V.

[0071] As shown in Figure 14, it was confirmed that in Embodiment 2 as well, the light emission rise time increases as the value of ΔV2 increases. In the example in Figure 14, the fastest rise time is achieved when ΔV2 = 1V. Therefore, ΔV2 may be set such that, for example, ΔV2 > 0V.

[0072] In active-drive pixel circuits for displays, VINI2 is generally set such that VINI2 ≤ ELVSS. Therefore, conventionally, ΔV2 ≤ 0V is common. In contrast, in Embodiment 2, as is clear from the above description, VINI2 may be set such that VINI2 > ELVSS.

[0073] (Supplement to Embodiment 2) (1) As an example, the light emission control unit 10 may generate a third potential difference as ΔV by applying a third anode potential to the anode AN during the third period. The third period may be a period during which the self-emitting element EL does not emit light.

[0074] Figure 15 is a diagram illustrating the third period in Embodiment 2. The upper part of Figure 15 shows examples of the waveforms of the light emission control signal em[n], the discharge signal dis[n], and the scan signal scan[n] described above. The lower part of Figure 15 shows an example of the anode potential (potential of anode AN) corresponding to the waveforms. In the example of Figure 15, the cathode potential Vc is assumed to be fixed at ELVSS.

[0075] In this specification, the third anode potential is represented as Va3. In the example in Figure 15, Va3 is a potential slightly higher than ELVSS and lower than Va4 (the fourth anode potential) in Figure 16, which will be described later.

[0076] The period indicated by reference numeral 1510 in Figure 15 is an example of the first period described above. During the first period, the light emission control signal em[n] takes a low level value. Therefore, as described above, during the first period, the light emission control transistor T6 and the power supply control transistor T5 are turned on. As a result, during the first period, a first anode potential is applied to the anode AN. Therefore, during the first period, a first potential difference corresponding to the first anode potential is generated. Consequently, during the first period, the photoreceptor 35 is exposed to light emitted from the self-emitting element EL.

[0077] In Figure 15, the symbols 1520A and 1520B represent periods when the discharge signal dis[n] takes a low level value (anode reset period), respectively. The period of symbol 1520A precedes the period of symbol 1510. On the other hand, the period of symbol 1520B follows the period of symbol 1510. Therefore, the period of symbol 1520A is an example of a second period that precedes the first period.

[0078] As described above, during the periods indicated by reference numeral 1520A and 1520B, the discharge transistor T7 is turned on. As a result, a second anode potential is applied to the anode AN. Therefore, during the periods indicated by reference numeral 1520A and 1520B, a second potential difference corresponding to the second anode potential is generated. In the example of Figure 15, the second anode potential is equal to VINI2. Thus, the second potential difference in the example of Figure 15 is "VINI2-ELVSS".

[0079] In the example shown in Figure 15, the second potential difference should be set such that the light emitted from the self-emitting element EL does not cause photosensitization of the photoreceptor 35 during the second period. Therefore, as one example, during the second period, a weak light is emitted that does not cause photosensitization of the photoreceptor 35. As another example, during the second period, the self-emitting element EL does not emit light. In this case as well, no photosensitization occurs in the photoreceptor 35.

[0080] In Figure 15, reference numerals 1530A and 1530B indicate periods when the scan signal scan[n] takes a low level value (data writing period), respectively. The period of reference numeral 1530A precedes the period of reference numeral 1510. On the other hand, the period of reference numeral 1530B follows the period of reference numeral 1510.

[0081] The period indicated by reference numeral 1513 in Figure 15 is an example of the third period described above. In the third period, the light emission control signal em[n] takes a low level value. Therefore, in the third period, as in the first period, the light emission control transistor T6 and the power supply control transistor T5 are turned on. However, unlike the first period, in the third period, Va3 is applied to the anode AN.

[0082] Therefore, during the third period, a third potential difference corresponding to the third anode potential is generated. The third potential difference is expressed as "Va3-ELVSS". In the example in Figure 15, the third potential difference is set so that the self-emitting element EL does not emit light during the third period. From this, in the example in Figure 15, the third anode potential is set to a potential approximately equal to ELVSS. Since the self-emitting element EL does not emit light during the third period, no photosensitivity occurs in the photoreceptor 35.

[0083] Furthermore, if the amount of light emitted from the self-emitting element (EL) during a certain period is 1 / 10 or less of the amount of light emitted from the self-emitting element (EL) during the first period, the self-emitting element (EL) can be considered not to have emitted light during that period.

[0084] (2) As another example, the light emission control unit 10 may generate a fourth potential difference as ΔV by applying a fourth anode potential to the anode AN during the fourth period. In this specification, the fourth anode potential is represented as Va4. In this case, for example, Va4 may be set such that VINI2 ≥ Va4 > ELVSS.

[0085] Figure 16 is a diagram illustrating the fourth period in Embodiment 2. Figure 16 is a counterpart to Figure 15. The period indicated by reference numeral 1614 in Figure 16 is an example of the fourth period. In the fourth period, the light emission control signal em[n] takes a low level value. Therefore, in the fourth period, as in the first period, the light emission control transistor T6 and the power supply control transistor T5 are turned on. However, unlike the first period, Va4 is applied to the anode AN in the fourth period.

[0086] Therefore, in the fourth period, a fourth potential difference corresponding to the fourth anode potential is generated. In the example in Figure 16, the fourth potential difference should be set such that the photoreceptor 35 is not exposed to light emitted from the self-luminescent element EL during the fourth period. The fourth potential difference is expressed as "Va4 - ELVSS". From this, as described above, Va4 is set such that VINI2 ≥ Va4 > ELVSS.

[0087] As an example, during the fourth period, a very weak light is emitted that is not strong enough to cause photosensitivity in the photoreceptor 35. As another example, during the fourth period, the self-emitting element EL does not emit light. In this case as well, no photosensitivity occurs in the photoreceptor 35. In the example of Figure 16, it is sufficient that Va4 is set so that the self-emitting element EL does not emit light during the fourth period.

[0088] As is clear from the above explanations, the luminescence of the self-light-emitting element (EL) in the first period is higher than the luminescence of the self-light-emitting element (EL) in the second period (see, for example, the anode potential in the period indicated by reference numeral 1510 and the anode potential in the period indicated by reference numeral 1520A in Figure 16). As described above, in the first period, the photoreceptor 35 is exposed to light emitted from the self-light-emitting element (EL). On the other hand, in the second period, the photoreceptor 35 is not exposed to light emitted from the self-light-emitting element (EL). Therefore, as an example, the luminescence of the self-light-emitting element (EL) in the first period is more than 10 times that of the self-light-emitting element (EL) in the second period.

[0089] Furthermore, as described above, if Va4 is set such that VINI2 ≥ Va4 > ELVSS, the luminescence of the self-emitting element EL in the second period may be higher than the luminescence of the self-emitting element EL in the fourth period (see, for example, the anode potential during the period indicated by reference numeral 1520A and the anode potential during the period indicated by reference numeral 1614 in Figure 16).

[0090] (3) Figure 17 is a diagram illustrating the differences in anode potential during the first, third, and fourth periods in Embodiment 2. The period indicated by reference numeral 1715 in Figure 17 collectively represents the first, third, and fourth periods. During the period indicated by reference numeral 1715, the light emission control signal em[n] takes a low level value.

[0091] The graph labeled 1781 in Figure 17 shows the time change of the anode potential during the first period. As described above, a first potential difference corresponding to the first anode potential is generated during the first period. Therefore, during the first period, the photoreceptor 35 is exposed to light emitted from the self-emitting element EL. For this reason, the first anode potential is higher than both the third anode potential and the fourth anode potential.

[0092] The graph labeled 1783 in Figure 17 shows the time variation of the anode potential during the third period. As described above, the third potential difference is set so that the self-emitting element EL does not emit light during the third period. Therefore, in the example in Figure 17, the third anode potential is lower than both the first and fourth anode potentials. As described above, the third anode potential may be set to a potential approximately equal to ELVSS.

[0093] The graph labeled 1784 in Figure 17 shows the time change of the anode potential during the fourth period. As described above, the fourth potential difference is set so that the photoreceptor 35 is not exposed to light emitted from the self-luminescent element EL during the fourth period. Therefore, during the fourth period, a weak light is emitted that does not cause the photoreceptor 35 to be exposed. From this, the fourth anode potential in the example in Figure 17 is lower than the first anode potential and higher than the third anode potential.

[0094] [Example of implementation by software] The functions of the printing apparatus 151 (hereinafter referred to as "apparatus") can be realized by a program that causes a computer to function as the apparatus, and by a program that causes a computer to function as each control block of the apparatus (particularly each part included in the light emission control unit 10).

[0095] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., memory) as hardware for executing the program. By executing the program using this control device and storage device, the functions described in each of the embodiments are realized.

[0096] The above program may be recorded on one or more computer-readable recording media, not temporary ones. These recording media may or may not be provided by the above device. In the latter case, the program may be supplied to the above device via any wired or wireless transmission medium.

[0097] Furthermore, some or all of the functions of each of the above control blocks can also be realized by logic circuits. For example, an integrated circuit in which logic circuits functioning as each of the above control blocks are formed is also included in the scope of the present invention. In addition, it is also possible to realize the functions of each of the above control blocks by, for example, a quantum computer.

[0098] Furthermore, each process described in the above embodiments may be performed by AI (Artificial Intelligence). In this case, the AI ​​may operate on the control device described above, or it may operate on another device (for example, an edge computer or a cloud server).

[0099] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0100] 1 Light-emitting device 10 Light-emitting control unit 25 Printer head 35 Photoreceptor 151 Printing device EL Self-emitting element AN Anode CA Cathode GK Pixel circuit T5 Power control transistor T6 Light-emitting control transistor T7 Discharge transistor Va Anode potential (potential of the anode) Vc Cathode potential (potential of the cathode) ΔV Potential difference of the anode relative to the cathode ΔV1 First potential difference ΔV2 Second potential difference

Claims

1. A light-emitting device located inside the printer head of a printing device, comprising: a self-luminous element having an anode and a cathode; and a light-emitting control unit that controls the light-emitting state of the self-luminous element, wherein the light-emitting control unit causes the self-luminous element to emit light by generating a first potential difference as the potential difference of the anode with respect to the cathode during a first period; generates a second potential difference smaller than the first potential difference as the potential difference of the anode with respect to the cathode during a second period preceding the first period; and the potential of the anode is higher than the potential of the cathode during both the first and second periods.

2. The light-emitting device according to claim 1, wherein the second potential difference is 0.5V or more and 2.4V or less.

3. The light-emitting device according to claim 2, wherein the second potential difference is 0.5V or more and 2.0V or less.

4. The light-emitting device according to claim 2, wherein the second potential difference is greater than 2.0 V and less than or equal to 2.4 V.

5. The light-emitting device according to any one of claims 1 to 4, wherein light is emitted from the self-luminous element during the second period described above.

6. The light-emitting device according to claim 5, wherein the amount of light emitted from the self-emitting element during the second period is 1 / 10 or less of the amount of light emitted from the self-emitting element during the first period.

7. The light-emitting device according to any one of claims 1 to 6, wherein, during the first period, light emitted from the self-luminous element causes photosensitivity in a photoreceptor located inside the printing device, and during the second period, no photosensitivity occurs in the photoreceptor.

8. A light-emitting device according to any one of claims 1 to 7, comprising a pixel circuit having the above-mentioned self-luminous element and an initialization circuit for the self-luminous element, wherein a constant cathode potential is applied to the cathode, and the light-emitting control unit generates the above-mentioned first potential difference by applying a first anode potential to the anode during the first period, and generates the above-mentioned second potential difference by applying a second anode potential to the anode during the second period.

9. A light-emitting device according to any one of claims 1 to 8, comprising a pixel circuit having the above-mentioned self-luminous element, a light-emitting control transistor, a power supply control transistor, and a discharge transistor, wherein the anode is connected to a power line via the light-emitting control transistor and the power supply control transistor, and is also connected to an anode potential initialization line via the discharge transistor, a constant cathode potential is applied to the cathode, and the light-emitting control unit generates the first potential difference by turning on the light-emitting control transistor and the power supply control transistor during the first period and applying a first anode potential to the anode, and generates the second potential difference by turning on the discharge transistor and applying a second anode potential to the anode during the second period.

10. The light-emitting device according to claim 8 or 9, wherein the first anode potential is determined by a potential applied to the pixel circuit via a data signal line.

11. The light-emitting device according to any one of claims 8 to 10, wherein when the cathode potential is expressed as ELVSS, the second anode potential is expressed as VINI2, and the second potential difference is expressed as ΔV2, then ΔV2 = VINI2 - ELVSS.

12. The light-emitting device according to claim 11, wherein ΔV2 > 0V.

13. The light-emitting device according to any one of claims 8 to 12, wherein the light-emitting control unit generates a third potential difference as the potential difference of the anode with respect to the cathode by applying a third anode potential to the anode during the third period, and the self-emitting element does not emit light during the third period.

14. The light-emitting device according to any one of claims 8 to 12, wherein the light-emitting control unit generates a fourth potential difference as the potential difference of the anode with respect to the cathode by applying a fourth anode potential to the anode during the fourth period, and when the cathode potential is represented as ELVSS, the second anode potential is represented as VINI2, and the fourth anode potential is represented as Va4, then VINI2 ≥ Va4 > ELVSS.

15. The light-emitting device according to claim 14, wherein the luminescence brightness of the self-luminous element during the first period is higher than the luminescence brightness of the self-luminous element during the second period, and the luminescence brightness of the self-luminous element during the second period is higher than the luminescence brightness of the self-luminous element during the fourth period.

16. The light-emitting device according to any one of claims 8 to 15, wherein pre-charging of the self-luminous element is performed as initialization of the anode.

17. The light-emitting device according to any one of claims 1 to 7, wherein the cathode of each of the N (where N is an integer of 2 or more) of the above-mentioned self-luminous elements is connected to each of the N cathode wires, a constant anode potential is applied to the anode of each of the N above-mentioned self-luminous elements, and the light-emitting control unit supplies a cathode signal which is a voltage signal having different signal values ​​in the first period and the second period to each of the N cathode wires, thereby generating the first potential difference in the first period and the second potential difference in the second period for each of the N above-mentioned self-luminous elements.

18. A printer head comprising a light-emitting device according to any one of claims 1 to 17.

19. A printing apparatus comprising a printer head according to claim 18 and a photoreceptor.

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