JP6745666B2 - Image forming device - Google Patents

Description

The present invention relates to image quality in an image forming apparatus.

Fog is an index of image quality in an electrophotographic image forming apparatus. Fog is a phenomenon in which an image on a white paper should be "white" where no toner should be originally placed, but a little toner is placed on the image so that it appears "black".

The principle of fog generation in the image forming apparatus is described in Japanese Patent Application Laid-Open Nos. 2004-242242 and 2004-242242. In the electrophotographic method based on the reversal development method of Patent Document 1, the photosensitive drum is charged to the negative electrode, and the developing roller carrying the toner charged to the negative electrode is adjoined, and the potential is increased by being exposed on the photosensitive drum. The toner image is developed by moving the toner to a location by electrostatic force. Therefore, if the charge amount of the toner is lowered for some reason, the repulsive force is reduced and the toner is deposited on a place where it should not be deposited on the photosensitive drum. There are various causes of the decrease in the toner charge amount. For example, toner charging performance may deteriorate due to toner deterioration due to an increase in the number of printed sheets, and reversal toner may occur due to friction between the blade and the toner that regulates the thickness of the toner on the developing roller or between toner particles. There are things that can end up.

Further, in the system in which a potential difference is provided between the developing roller and the blade as described in Japanese Patent Laid-Open No. 2004-242, the electric charge charged to the toner is flowed by the current flowing between the developing roller and the blade. As a result, the amount of reversal toner is relatively large. Here, the reversal toner is a toner charged to the opposite polarity, and although the amount thereof is smaller than that of the toner charged to the negative polarity, it causes the fog because it develops in an unexposed area of the photoconductor drum. Becomes

Further, according to Patent Document 2, fog tends to worsen in a high temperature and high humidity environment, and in addition, the higher the potential difference between the developing roller and the blade (hereinafter, referred to as blade voltage), the further the fog tends to deteriorate. Is shown. Therefore, in high temperature and high humidity environment, the blade voltage should be small in order to suppress the deterioration of fog.

JP, 2001-337521, A JP, 2005-94895, A

However, in order to change the blade voltage depending on the environment, a means for detecting the environment and a means for changing the voltage are required. If the voltage has a constant difference regardless of the environment, it is sufficient to connect the voltage applied to the developing roller (hereinafter referred to as developing bias) and the blade with a Zener diode. However, in order to change the potential difference, it is necessary to add a switching element or the like, and in particular to handle a high voltage, a component having a high breakdown voltage or a large-scale circuit is required, and the required area of the circuit board and the cost increase remarkably.

The present invention for solving the above-mentioned problems is, for example, an image forming apparatus,
A developing member having a resistance layer having a negative temperature coefficient,
A regulating member which is in contact with the developing member and regulates the amount of toner adhering to the surface of the resistance layer of the developing member;
A power source for applying a voltage to the regulating member and the developing member,
A resistor provided in a path of a current flowing through the regulating member and the developing member by applying the voltage from the power source,
The resistance value of the resistor is a resistance value set so that the value of the current flowing through the resistance layer does not exceed the first value at the upper limit temperature in the temperature range in which the operation of the image forming apparatus is guaranteed, The first value is an upper limit value at which the fog phenomenon does not occur.

According to the present invention, the blade voltage of the image forming apparatus can be changed according to the environment by using the resistor, which is a simple circuit, and the image forming apparatus capable of reducing the fog phenomenon at low cost is provided.

Image showing an image forming apparatus Diagram showing temperature characteristics of blade current Diagram showing circuit for applying blade voltage Diagram showing circuit for applying blade voltage Diagram showing temperature characteristics of blade current Diagram showing circuit for applying blade voltage Diagram showing temperature characteristics of blade current

<Example 1>
[Configuration of image forming apparatus]
As a first embodiment of the present invention, a sectional view of a monochrome laser printer is shown in FIG. In FIG. 1A, reference numeral 101 denotes a paper feed unit that stores paper to be printed, and paper is stacked inside. A laser scanner 102 and a toner tank 103 contain magnetic toner. A developing roller (developing member) 104 is a roller in which a core made of aluminum is coated with rubber and urethane resin. Reference numeral 105 is a photosensitive drum, 106 is a transfer roller, 107 is a charging roller, 108 is a waste toner tank, 109 is a fixing roller, 110 is a pressure roller, 110 is a paper discharge unit, 112 is a paper conveyance path, and 113 is a laser optical path. is there. Reference numeral 114 is a blade that regulates the amount of toner that adheres to the developing roller 104, and is a blade whose surface is coated with urethane resin based on iron.

[Explanation of operation of image forming apparatus]
Next, the operation of the image forming apparatus will be described. First, when a print job is received, each roller and the laser scanner 102 start operating. The charging roller 107 receives power from the circuit board and generates a negative high voltage to charge the surface of the photosensitive drum 105. When an image signal is sent from a personal computer or the like, the laser scanner 102 scans the surface of the photosensitive drum 105 in the longitudinal direction while causing the laser 113 to blink according to the pixel. On the photosensitive drum 105, the electric charge in the portion hit by the laser disappears and a latent image is formed. The developing roller 104 is supplied with a negative high voltage and at the same time has a magnet inside. The magnetic toner attracts the magnetic toner in the toner tank 103 by the magnetic force, and the electrostatic force attracts the toner to the photosensitive drum 105 according to the latent image. Move to. Further, the blade 114 is provided with a potential difference of −300 V with respect to the developing roller 104, and the toner on the developing roller 104 is evenly coated by the physical restriction of the blade body and the electrostatic force.

On the other hand, the paper fed from the paper feed unit 101 passes through the path 112 and is sandwiched between the transfer roller 106 and the photosensitive drum 105. At this time, a positive high voltage is applied to the transfer roller 106, and the toner on the photosensitive drum is transferred to the paper by being drawn by the transfer roller 106. Then, the paper on which the toner is placed moves toward the paper output unit 111 and is sandwiched between the fixing roller 109 and the pressure roller 110. Here, the fixing roller 109 is heated to several hundred degrees, and at the same time, it is pressed by the pressure roller 110, and the toner on the paper is fixed only by the electrostatic force. Then, the paper is discharged to the paper discharge unit 111 and stacked. On the other hand, some toner remains on the surface of the photosensitive drum 105 even after the transfer to the paper. Ideally, all the toner should be transferred to the paper, but in reality, there is toner that remains on the photosensitive drum 105 even after transfer because the charge amount of the toner is not uniform. The waste toner tank 108 is a place where the remaining toner is peeled off and collected by a blade that is in contact with the photosensitive drum 105. As a result, the toner is removed from the photosensitive drum 105, the toner is charged again by the charging roller 107, and the next latent image is drawn by the laser scanner 102. An image is formed by repeating the above operation. The image forming apparatus may be not only a laser printer, but also a copying machine, a multi-function peripheral, or a facsimile.

[Explanation of circuit between development and blade]
Subsequently, a circuit around the developing roller 104 of the printer of FIG. 1A will be described with reference to FIG. The same components as those in FIG. 1A are denoted by the same symbols. It should be noted that the values of voltage, current, resistance value, capacitance, etc. described below are merely examples for convenience of description. In FIG. 1B, reference numeral 115 denotes a negative voltage switching power supply circuit that generates development and blade bias, and is feedback-controlled so that the voltage of the development bias in the drawing is constant. Reference numeral 116 denotes a negative voltage power supply circuit that generates a charging bias, and performs feedback control so that the voltage of the charging roller 107 becomes constant. ZD1, ZD2, and ZD3 are 100V Zener diodes (constant voltage elements), and R1 and R2 are resistors. A voltage of -1500V is applied to the charging roller 107. The surface potential of the photosensitive drum 105 drops by about 500 V according to Paschen's law and becomes about −1000 V. On the other hand, the developing bias is applied to the developing roller 104, and the output voltage can be arbitrarily set, but in this embodiment, it is shown that the output voltage is set to -300V. Further, since the blade bias is connected to the developing bias by the Zener, it always follows with a potential difference of -300 V with respect to the developing bias. Therefore, the blade bias with respect to GND is -600V. The blade 114 to which the blade bias is applied is in contact with the developing roller 104, and there is a non-metal layer (resistive layer) 142 between the core portion 141 to which the development bias is applied and the surface, and the blade bias and the development bias are short-circuited. Instead, keep the voltage on the resistive layer. The resistance layer is hereinafter referred to as the developing roller resistance layer 142, and the voltage (=the potential difference between the blade 114 and the core of the developing roller 104) applied thereto is hereinafter referred to as the blade voltage.

[Explanation of the problem]
However, this configuration causes a problem. The resistance value of the developing roller resistance layer 142 has a temperature characteristic, and the resistance value decreases in a high temperature environment. Specifically, the developing roller resistance layer 142 has a resistance of 37 MΩ to 80 MΩ in a 15° C. environment, but decreases to 16 MΩ to 25 MΩ in a 32.5° C. environment. The reason why the resistance value has a range represents the dispersion when the roller is mass-produced.The reason why the range is wide is that the developing roller is not made as a resistance element, but it is an unintended resistance change due to the physical property value. is there. Further, the current that flows through the developing roller resistance layer 142 to the blade bias (hereinafter referred to as the blade current) has a great influence on the fog, and from the experiment, it is 2 uA or less in a 15° C. environment and 15 uA or more in a 32.5° C. environment. It is known that fog starts to occur when flowing. This is because if the blade current is too small, the amount of negative charge applied to the toner is insufficient and the repulsive force is reduced, causing fog. On the other hand, if the blade current is too large, negative charges on the developing roller will flow out this time, and the positive charges will relatively increase, causing fog. Therefore, when the blade voltage is 300 V as in this embodiment, the current value increases from the range of 3.75 uA to 8.11 uA to the range of 12.0 uA to 18.8 uA when the environment is 15° C. and 32.5° C. It will be. As a result, as shown in FIG. 2, fogging can be prevented in the 15° C. environment, but in the 32.5° C. environment, the blade current is too large and fogging occurs. In order to solve this problem on the assumption that the temperature characteristics of the developing roller resistance layer cannot be changed, there is no choice but to change the blade voltage according to the environment.

[Conventional method]
Before explaining the present invention, the simplest method will be described first. Two types of methods are introduced in FIG. In FIG. 3A, a switch is added in parallel to one of the Zener diodes included in the constant voltage circuit 117 of FIG. 1B. This switch is a conceptual one, and in reality, any device having a control function such as a semiconductor device or a mechanical switch may be used. The blade voltage can be reduced from 300V to 200V by forming a path that bypasses the Zener diodes connected in series in this manner. However, the added switch has a withstand voltage of 100 V or more, and considering that it is operated in a state floating from GND, photomos relays and mechanical relays are possible, but both are installed in mass-produced products. To be expensive. There is also a method in which the blade bias is not made to follow the developing bias in the first place and an independent power source is used as shown in FIG. 3B. With this method, the blade voltage can be obtained steplessly, so there is a high degree of freedom, but the number of power supply circuits is increased by one, which has a large impact on the circuit area and cost.

[Example 1]
Therefore, the present invention proposes to provide a resistor R3 in the blade current path as shown in FIG. 4 and set the resistance value r3 to a range determined by the following two conditions.

Condition 1: Vb/{r3+ra}<15uA
Condition 2: Vb/{r3+rb}>2uA
Here, Vb is a blade voltage. Ra is a lower limit value in the variation range of the resistance value of the developing roller resistance layer 142 in an environment of 32.5° C., and rb is an upper limit value in the variation range of the resistance value of the developing roller resistance layer 142 in an environment of 15° C. is there. In Condition 1, the left side shows the upper limit value of the blade current at which the fog phenomenon does not occur. In Condition 2, the left side shows the lower limit of the blade current at which the fog phenomenon does not occur. By adopting the resistor R3 having the resistance value r3 satisfying the conditions 1 and 2, the blade current is in a range where fogging is not generated in both the environment of 15° C. and 32.5° C. without having a special switching means. Can be set. If the resistance value r3 is too large, the condition 2 cannot be satisfied, and if the resistance value r3 is too small, the condition 1 cannot be satisfied. Therefore, as a guideline for the resistance value r3, a value close to the lower limit value in the variation range of the resistance value of the developing roller resistance layer 142 in the environment of 32.5° C. is preferable.

If the values are close to each other, even if the developing roller resistance layer 142 changes, the influence on the blade current can be reduced, and the value is sufficiently smaller than the internal resistance of the developing roller in the 15° C. environment. The drop can be minimized. As a specific example, when the resistance 401 of FIG. 4 is 10 MΩ, the blade current changes as shown in FIG.

Further, since this resistance is a resistance for suppressing a change in blade current in μA unit, the resistance value r3 inevitably becomes a high resistance in MΩ unit, and also functions as a protective resistance in the event of an accidental grounding of the blade bias. In particular, IEC60950 stipulates that the current flowing when a 2 kΩ resistor is connected between the high voltage portion and GND is 2 mA or less for safety reasons. When 401 is 10 MΩ as in the present embodiment, the absolute value of the voltage of the blade bias with respect to GND is 600 V, so that the flowing current is 60 uA, which is sufficient for 2 mA.

Although 15° C. and 32.5° C. are used as examples this time, if the lowest temperature is X° C. and the highest temperature is Y° C. among the environmental conditions that should satisfy the image quality of the product, the above description is given. 15° C. can be read as X° C. and 32.5° C. as Y° C.

Further, since the element having the resistance value with the high absolute value is used as the resistor, it contributes to the overcurrent protection and the smoothing of the ripple when the output of the circuit is short-circuited.

<Example 2>
An explanatory view of the second embodiment is shown in FIG. In FIG. 6, the resistor R3 is replaced with R4 and the capacitor C1 is added in parallel with respect to FIG. The same components as those in FIG. 1 have the same symbols.

Example 2 introduces a method of minimizing the difference in blade current between the 15° C. environment and the 32.5° C. environment with a slight modification. First, the cause of this problem is that the resistance value of the developing roller resistance layer 142 has a negative temperature coefficient that the resistance value decreases as the temperature rises. Therefore, if a resistor having a positive temperature coefficient is used as the resistor R3 used in the first embodiment, the variation width of the blade current can be suppressed. The temperature coefficient of resistance is called TCR (Temperature Coefficient of Resistance), and it is generally said that it is better to have a smaller temperature coefficient. There are also vessels. In an extreme example, a PTC thermistor may be used. Therefore, a resistor R4 having a high TCR is placed instead of the resistor R3 in FIG.

Furthermore, the capacitance change of the ceramic capacitor is also used. The role of C1 in FIG. 6 is to transmit the AC component of the blade current. The power supply 115 is a switching power supply, and although it is a DC power supply, there is some switching ripple. The larger the capacity of C1, the more the ripple current is transmitted, and the average value of the blade current is increased. On the contrary, when the capacity is small, only the DC component is approached, and the average value of the blade current decreases.

Ceramic capacitors also have temperature characteristics, and the relationship between temperature and capacitance change is divided into several patterns. Each of them has a name such as B feature or F feature, and in this embodiment, the F feature, in which the capacity greatly decreases as the temperature rises, is suitable. Further, the ceramic capacitor also has a characteristic that the capacitance greatly decreases according to the voltage applied (voltage generated across R4) due to the DC bias characteristic. It is said that it is usually better not to change both the temperature characteristic and the DC bias characteristic like the TCR of the resistance, but in the present embodiment, the blade current is reduced by making the change to the contrary and greatly decreasing the capacity with temperature rise.

A specific numerical value is applied and exemplified. It is assumed that the resistance value R4 of R4 is 10 MΩ at 25° C., the TCR is 4500 ppm/K, the capacitance of C1 is 100 pF, and the capacitance decreases by 70% due to the change from the ambient temperature of 15° C. to 32.5° C. due to the temperature characteristic and the DC bias characteristic. The other conditions are the same as in Example 1. The results are shown in Fig. 7. As can be seen from FIG. 7, the distance between the resistance range at 15° C. and the resistance range at 32.5° C. is slightly close, and the difference is small. As described above, a capacitor having a temperature characteristic in which the capacity decreases in a temperature range where the temperature is higher than 25° C. may be adopted.

Note that the resistance values of the resistors R3 and R4 are ± with respect to the lower limit value (eg, 16 MΩ) of the resistance value tolerance of the resistance layer 142 at the upper limit temperature of the temperature range in which the operation of the image forming apparatus 100 is guaranteed. The resistance value may be within 50%. By setting the resistance values of the resistors R3 and R4 to such values, even if the resistance value of the resistance layer 142 changes, the influence on the blade current is reduced.

<Summary>
As described in Embodiments 1 and 2, the developing roller 104 is an example of a developing member having the resistance layer 142 having a negative temperature coefficient. The developing blade 114 is an example of a regulating member that contacts the developing roller 104 and regulates the amount of toner that adheres to the surface of the resistance layer 142 of the developing roller 104. The power supply circuit 151 is an example of a power supply that applies a voltage to the developing blade 114 and the developing roller 104. The resistors R3 and R4 are an example of resistors provided in a path of a blade current flowing through the developing blade 114 and the developing roller 104 when a voltage is applied by the power supply circuit 151. As described in the first embodiment, the resistance value r3 of the resistor R3 can be set to satisfy a predetermined condition. In the case where the value of the current flowing through the resistance layer 142 exceeds the first value which is the upper limit value at which the fog phenomenon does not occur at the upper limit temperature (eg, 32.5° C.) as shown in FIG. Must be met. That is, as the condition 1 indicates, the resistance value r3 of the resistor R3 is set so that the value of the current flowing through the resistance layer 142 does not exceed the first value (eg, 15 uA) at the upper limit temperature in this temperature range. .. Since the blade current is controlled according to the environment by adopting the resistors R3 and R4 as described above, an image forming apparatus capable of reducing the fog phenomenon at a low cost is provided. On the other hand, when the value of the current flowing through the resistance layer 142 becomes less than the second value (example: 2 uA) at the lower limit temperature (example: 15° C.) of the above temperature range, the fog phenomenon occurs. In such a case, it is necessary to satisfy the condition 2. As Condition 2 indicates, the second value (eg, 2 uA) is the lower limit value at which the fog phenomenon does not occur at the lower limit temperature in the temperature range in which the operation of the image forming apparatus 100 is guaranteed. The resistance value r3 of the resistor R3 is set so as to exceed. If the resistance value r3 of the resistor R3 is set so that the value of the current flowing through the resistance layer 142 exceeds the second value and does not exceed the first value, the operation of the image forming apparatus 100 is guaranteed. The fog phenomenon is reduced in all the temperature ranges.

As shown in FIGS. 4 and 6, the resistance layer 142 and the resistors R3 and R4 are connected in series. Therefore, it is possible to compensate the change in the resistance value of the resistance layer 142 depending on the change in the environmental temperature by the resistors R3 and R4.

A constant voltage circuit 117 that is connected in parallel to the resistors R3 and R4 and the resistance layer 142 and limits the voltage applied to the developing blade 114 and the developing roller 104 to a constant voltage may be further provided. In particular, the constant voltage circuit 117 may be configured by connecting a plurality of constant voltage elements (Zener diodes ZD1, ZD2, ZD3) in series. By adopting such an inexpensive element, it becomes possible to easily and inexpensively maintain the blade voltage constant.

As described in the second embodiment, the temperature coefficient of the resistor R4 may be a positive temperature coefficient. Since the resistance layer 142 has a negative temperature coefficient, by adopting the resistor R4 having a positive temperature coefficient, the decrease of the resistance value of the resistance layer 142 is compensated by the increase of the resistance value of the resistor R4. It becomes possible to do. That is, when the environmental temperature rises, the resistance value of the resistor R4 increases, so that it is possible to compensate for the decrease in the resistance value of the resistance layer 142. Thereby, even if the environmental temperature changes, the change in the blade current is suppressed. The resistor R4 may be a thermistor. This makes it possible to reduce the fog phenomenon at low cost while suppressing changes in the blade current.

As described in the second embodiment, the capacitor C1 connected in parallel with the resistor R4 may be added. The capacitor C1 also allows the AC component superimposed on the DC component supplied from the power supply circuit 151 to pass therethrough, thereby increasing the blade current. Here, when the capacity of the capacitor C1 increases, the blade current increases, but when the capacity of the capacitor C1 decreases, the blade current decreases. Particularly, in order to reduce the fogging phenomenon that may occur when the temperature rises, the capacitor C1 having the characteristic that the capacitance decreases when the temperature rises is effective. For example, the capacitor C1 may be a capacitor having a temperature characteristic that the capacitance decreases in a temperature range where the temperature of the capacitor C1 is higher than 25°C. That is, the capacitor C1 may be a ceramic capacitor having F characteristics. Further, in order to reduce the fogging phenomenon that may occur when the temperature decreases, the capacitor C1 having the characteristic that the capacity increases when the temperature decreases is effective. Such a capacitor C1 helps reduce the change in the blade current even when the environmental temperature changes.

The resistance values of the resistors R3 and R4 are, for example, ±50% with respect to the lower limit value (for example, 16 MΩ) of the resistance tolerance of the resistance layer 142 at the upper limit temperature of the temperature range in which the operation of the image forming apparatus 100 is guaranteed. The resistance value may be within the range. By setting the resistance values of the resistors R3 and R4 to such values, even if the resistance value of the resistance layer 142 changes, the influence on the blade current is reduced.

104... Developing roller, 114... Blade, 115... Power supply, R3, R4... Resistor, 100... Image forming apparatus

Claims (15)

An image forming apparatus,
A developing member having a resistance layer having a negative temperature coefficient,
A regulating member which is in contact with the developing member and regulates the amount of toner adhering to the surface of the resistance layer of the developing member;
A power source for applying a voltage to the regulating member and the developing member,
A resistor provided in a path of a current flowing through the regulating member and the developing member by applying the voltage from the power source,
The resistance value of the resistor is a resistance value set so that the value of the current flowing through the resistance layer does not exceed the first value at the upper limit temperature in the temperature range in which the operation of the image forming apparatus is guaranteed, The image forming apparatus is characterized in that the first value is an upper limit value at which a fog phenomenon does not occur. The resistance value of the resistor is a resistance value that is set so that the value of the current flowing through the resistance layer exceeds the second value at the lower limit temperature in the temperature range in which the operation of the image forming apparatus is guaranteed. The image forming apparatus according to claim 1, wherein the second value is smaller than the first value and is a lower limit value at which a fog phenomenon does not occur. The image forming apparatus according to claim 1, wherein the resistance layer and the resistor are connected in series. 4. A constant voltage circuit, which is connected in parallel to the resistor and the resistance layer and limits the voltage applied to the regulating member and the developing member to a constant voltage. The image forming apparatus according to item 1. The image forming apparatus according to claim 4, wherein the constant voltage circuit is configured by connecting a plurality of constant voltage elements in series. The image forming apparatus according to claim 5, wherein each of the plurality of constant voltage elements is a Zener diode. 7. The image forming apparatus according to claim 1, wherein the temperature coefficient of the resistor is a positive temperature coefficient. The image forming apparatus according to claim 7, wherein the resistor is a PTC thermistor. 9. The image forming apparatus according to claim 1, further comprising a capacitor connected in parallel to the resistor. 10. The image forming apparatus according to claim 9, wherein the capacitor is a capacitor having a temperature characteristic that the capacity decreases in a temperature range where the temperature of the capacitor is higher than 25° C. The image forming apparatus according to claim 9, wherein the capacitor is a ceramic capacitor having an F characteristic. 12. The resistance value of the resistor is a resistance value within ±50% with respect to a lower limit value of the tolerance of the resistance value of the resistance layer at the upper limit temperature. The image forming apparatus according to item 1. An image forming apparatus,
A developing member having a resistance layer having a negative temperature coefficient,
A regulating member which is in contact with the developing member and regulates the amount of toner adhering to the surface of the resistance layer of the developing member;
A power source for applying a voltage to the regulating member and the developing member,
A resistor provided in a path of a current flowing through the regulating member and the developing member by applying the voltage from the power source,
The resistance value of the resistor is within ±50% of the lower limit of the tolerance of the resistance value of the resistance layer at the upper limit temperature in the temperature range in which the operation of the image forming apparatus is guaranteed. Image forming apparatus. A developing member having a resistance layer having a negative temperature coefficient,
A regulating member which is in contact with the developing member and regulates the amount of toner adhering to the surface of the resistance layer of the developing member;
A power source for applying a voltage to the regulating member and the developing member,
An image forming apparatus, comprising: a resistor having a positive temperature coefficient, which is provided in a path of a current flowing through the regulating member and the developing member when the voltage is applied by the power source. A developing member having a resistance layer whose resistance value decreases when the temperature rises;
A regulating member which is in contact with the developing member and regulates the amount of toner adhering to the surface of the resistance layer of the developing member;
A power source for applying a voltage to the regulating member and the developing member,
A resistor that is provided in a path of a current flowing through the regulating member and the developing member by applying the voltage from the power source and compensates for a decrease in the resistance value of the resistance layer by increasing the resistance value as the temperature rises. And an image forming apparatus.

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