JP2003186285A - Image forming apparatus and electrostatic charging potential correction system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and electrostatic charging potential correction system for obtaining an image free of ground staining due to insufficient electrostatic charging even when environment abruptly changes to low temperature. <P>SOLUTION: The image forming apparatus is equipped with a temperature sensor which detects temperature, an optical sensor 8 which detects the reflection density of the surface of an image carrier 1 having passed through a developing means 4, and a control means which varies the electrostatic charging potential of a non-image area on the image carrier 1 by varying a voltage applied from a voltage applying means to an electrostatic charging member 2 and controls the applied voltage in correspondence with the ratio of output signals of the optical sensor 8 to the non-image area on the image carrier 1 before and after the variation, and determines the control range of the applied voltage with the output signal of the temperature sensor. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile, and a charging potential correction method.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, an image forming unit is constructed by accommodating a photosensitive member, a developing device, a charging device, etc. in an integrated case, and the entire image forming apparatus is compact. It is becoming more and more popular to contribute to In this type of image forming unit, a contact charging device represented by a roller charging method is often used.
This contact charging device includes a charging roller, a charging brush,
In this method, a contact charging member such as a charging blade is pressed against the photoconductor and a voltage is applied from the power pad to the contact charging member to uniformly charge the photoconductor.

In a roller charging system using a charging roller,
A cleaning member such as a sponge is brought into contact with the charging roller, and the charging roller is bitten into the cleaning member by an appropriate amount. It is designed to remove toner and other foreign matter from the surface.

However, in actual use of the roller charging device, foreign matter such as toner adheres to the surface of the contact charging member to reduce the charging ability of the contact charging member, which causes background stain over time. . Therefore, many control methods for correcting the charging potential have been proposed. In the image forming apparatus IMAGIO 4550 released by the applicant, a method of controlling the voltage applied to the charging roller by using an optical sensor that detects the reflection density of the photoconductor is adopted as a cheap and stable charging potential correction method. is doing. In this method, the applied voltage of the charging roller is changed, and the dirt of the charging roller is detected by the fluctuation of the output signal of the photosensor at that time to control the applied voltage of the charging roller.

On the other hand, in view of environmental problems, ZESM (Zer
A plan called “Energy Stand by Mode” has also been proposed, and at room temperature, shortening the start-up time from turning on the power switch or from the sleep mode to the image-formable state has become a major issue.

Therefore, in the above charging potential correction method, when the temperature is below the set temperature by combining the temperature sensor and the optical sensor, the voltage applied to the charging roller is controlled as described above at the time of start-up to charge the power pack. A method has been proposed in which proper charging output to the roller is instructed, and when the temperature is above the set temperature, the power supplied from the commercial power source to the image forming apparatus is concentrated in the fixing device to enable startup in a short time. There is.

[0007]

In the above charging potential correction system, when the power switch is turned off and then the power switch is turned on, if the environment fluctuates sharply to a lower temperature than before, the development γ of the developing device is reduced. Change and process control becomes temporarily unavailable. As a result, there is a problem in that the charging ability of the charging roller is insufficient and scumming occurs.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus and a charging potential correction method capable of obtaining an image without background stains due to insufficient charging even when the environment suddenly changes to a low temperature.

[0008]

In order to achieve the above object, the invention according to claim 1 provides a charging member which is arranged in contact with or close to an image carrier to charge the image carrier, and the charging member. Voltage application means for applying a DC voltage, latent image forming means for forming an electrostatic latent image on the image carrier charged by a charging member, and developing means for developing the electrostatic latent image on the image carrier. In the image forming apparatus having: a temperature sensor for detecting a temperature; an optical sensor for detecting a reflection density of the surface of the image carrier after passing through the developing unit; and a voltage applied from the voltage applying unit to the charging member. Is changed to change the charging potential of the non-image area on the image carrier, and the applied voltage is changed corresponding to the output signal ratio of the photosensor to the non-image area on the image carrier before and after this change. Equipped with control means to control Is what determines the control range of the applied voltage by an output signal of the temperature sensor.

According to a second aspect of the present invention, a charging member which is disposed in contact with or close to the image carrier to charge the image carrier, a voltage applying means for applying a DC voltage to the charging member, and a charging member are used. An image forming apparatus comprising: a latent image forming unit that forms an electrostatic latent image on the charged image carrier; and a developing unit that develops the electrostatic latent image on the image carrier.
A temperature sensor for detecting the temperature, an optical sensor for detecting the reflection density of the surface of the image carrier after passing through the developing means, and the image carrier by changing the voltage applied from the voltage applying means to the charging member. Control means for changing the charging potential of the non-image area on the body and controlling the applied voltage in accordance with the output signal ratio of the photosensor to the non-image area on the image carrier before and after this change. The control range of the applied voltage is determined by the output signal of the temperature sensor when the device is started up.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the image forming apparatus described above, the lower limit value of the control range is raised when the temperature detected by the temperature sensor is lower than the set temperature.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the developing means is operated when the applied voltage is controlled.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, when the temperature detected by the temperature sensor is equal to or higher than a preset temperature when the apparatus is started up. The device is started up without controlling the applied voltage.

According to a sixth aspect of the present invention, there is provided a charging member which is arranged in contact with or close to the image carrier to charge the image carrier, a voltage applying means for applying a DC voltage to the charging member, and a charging member. In a charging potential correction method of an image forming apparatus having a latent image forming means for forming an electrostatic latent image on the charged image carrier and a developing means for developing the electrostatic latent image on the image carrier, Temperature sensor for detecting the temperature, an optical sensor for detecting the reflection density of the surface of the image carrier after passing through the developing means, and the image carrier by changing the voltage applied from the voltage applying means to the charging member. Changing the charging potential of the upper non-image area, the control means for controlling the applied voltage corresponding to the output signal ratio of the photosensor to the non-image area on the image carrier before and after this change, Output of the temperature sensor It is to determine the control range of the applied voltage by the signal.

[0014]

1 shows an embodiment of the present invention. The photoconductor as the image carrier is, for example, the photoconductor drum 1
Is used. Around the photosensitive drum 1, a charging roller 2 that is a contact charging member that is disposed close to or in contact with the photosensitive drum 1 and uniformly charges the photosensitive drum 1, and the photosensitive drum 1 are exposed. Then the photoconductor drum 1
An exposure device 3 which is a latent image forming means for forming an electrostatic latent image thereon.
A developing device 4 which is a developing means for developing the electrostatic latent image on the photoconductor drum 1 into a toner image, and a reversal developing method for transferring the toner image on the photoconductor drum 1 to a transfer sheet which is a transfer material. Belt 5 as a transfer means for the photosensitive drum 1
A cleaning device 6 for removing the upper residual toner, a charge eliminating lamp 7 for removing the residual electric charge on the photosensitive drum 1, an applied voltage of the charging roller 2 and a toner concentration of the two-component developer in the developing device 4 are controlled. The optical sensor 8 for is arranged.

To the developing device 4, toner is replenished from a toner replenishing device (not shown) through a toner replenishing port, and a DC voltage is applied to the charging roller 2 from a power pack which will be described later as a voltage applying means. A transfer bias is applied to the transfer belt 5 from a power pack (not shown) via a transfer bias roller 11 to give an electric charge.

The image forming operation of this embodiment is performed as follows. The photosensitive drum 1 is rotationally driven in the direction of the arrow by a driving unit (not shown). The photoconductor drum 1 is neutralized by the static elimination light 9 from the static elimination lamp 7 and has a surface potential of 0 to −.
Averaged to a reference potential of 150V. Next, the photosensitive drum 1 is uniformly charged by the charging roller 2 and the surface potential becomes a uniform potential of about -1000V.

Next, the photosensitive drum 1 is exposed by the exposure device 3 to form an electrostatic line image, and the surface potential of the portion (image portion) irradiated with light becomes 0 to -200V. The electrostatic latent image on the photoconductor drum 1 is developed into a toner image by the toner attached to the image portion by the developing device 4, and the toner image moves as the photoconductor drum 1 rotates.
On the other hand, the transfer paper as the transfer material is sent from the paper feeding unit 10 at a timing such that the front end of the transfer paper and the front end of the toner image on the photosensitive drum 1 are aligned at the transfer position by the transfer belt 5, The toner image on the photosensitive drum 1 is transferred at the transfer position by the transfer belt 5.

Thereafter, the transfer paper is sent to the fixing device 12,
The toner is fused by heat and pressure in the fixing device 12 and is discharged as an image-formed product. The residual toner remaining on the photoconductor drum 1 is scraped off by the cleaning device 6, and then the photoconductor drum 1 is neutralized by the static elimination light 9 from the static elimination lamp 7 to be in the initial state in which there is no toner, and again the next state. Move to the image forming process.

In this embodiment, a contact charging device having a charging roller 2 is used. In this contact charging device, the charging roller 2 is formed by molding a conductive rubber having a small hygroscopicity and a stable resistance value on the outer circumference of a metal cored bar, and the surface of the conductive rubber is a photosensitive member. A high voltage is applied to the core metal from the power pack in a state of being in contact with the surface of the drum 1 to uniformly charge the surface of the photoconductor drum 1. A cleaning pad (foam) as a cleaning member for cleaning the surface of the charging roller 2 is attached to the cleaning pad holding member with an adhesive such as a double-sided tape.

The charging roller 2 is always in contact with the surface of the photosensitive drum 1, and the surface of the charging roller 2 is easily soiled by the minute toner adhering to the surface of the photosensitive drum 1 to cause uneven charging, as is well known. The cleaning pad is pressed against the surface, the surface is cleaned by the cleaning pad, and the toner adhering to the surface is removed, so that uneven charging caused when the surface is soiled is prevented. The optical sensor 8 is composed of a light emitting unit and a light receiving unit, and can change the amount of light emitted from the light emitting unit. The optical sensor 8 is used for controlling the voltage applied to the charging roller 2 and controlling the toner concentration of the two-component developer in the developing device 4.

Next, the control of the charging potential in this embodiment will be described. Since the charging roller is usually made of rubber or elastomer, the resistance changes depending on the environment, and as a result, the charging potential of the photoconductor changes depending on the environment. In the conventional charging potential correction method, a pattern having a white portion and a gray portion is formed on a photosensitive drum, and the amount of reflected light at the white portion and the gray portion of this pattern is detected by an optical sensor to detect the output difference. However, there is one that controls the voltage applied to the charging roller according to the result.

However, in this charging potential correction method, it is indispensable to move the photoconductor drum and the developing device in order to create the above pattern, and time and power are inevitably consumed. However, this factor conflicts with the reduction of power and the time required to turn on the power switch or to wake up from the sleep mode. Further, the density of the gray portion of the above pattern depends on the development γ of the developing device, and when the developing ability of the developing device is lowered due to environmental changes (for example, when the developing temperature is lowered from high temperature to low temperature), The density of the clay portion of the pattern formed on the image is reduced, and the charge potential of the photosensitive drum is within the correction range due to the output difference of the light sensor with respect to the white portion and the gray portion of the pattern on the photosensitive drum when controlling the voltage applied to the charging roller. Therefore, the voltage applied from the power pack to the charging roller may be controlled to fall to the lower limit of the correction range. On the other hand, since the temperature is actually low, the resistance of the charging roller is increased, and the charging potential of the photosensitive drum may be insufficient.

In view of the above problems, the present embodiment corrects the lower limit value of the control range (correction range) of the voltage applied from the power pack to the charging roller 2 by the output signal of the temperature sensor. As shown in FIG. 4, the control unit 13 as a control unit that controls each unit of the present embodiment uses the input signals from various sensors such as the optical sensor 8 and the temperature sensor 14 in the present embodiment to charge the charging roller 2. The power pack 15 as a voltage applying means for applying a DC voltage to the exposure device 3, the developing device 4, the fixing device 12, and the like are controlled. The temperature sensor 14 is attached to this embodiment and detects the outside air temperature.

FIG. 2 shows the control flow of this embodiment. In this embodiment, since the polarity of the voltage is different between the negative / positive method and the positive / positive method, all voltage values will be described as absolute values. In step 20, the power supply of this embodiment is turned on or returned from the sleep mode (the mode in which the power is on and no operation is performed). At this time, the fixing device 12 of the present embodiment is cold.

In step 21, the outside temperature is measured by the temperature sensor 14, and the control unit 13 judges from the input signal from the temperature sensor 14 whether the temperature detected by the temperature sensor 14 is the set temperature T1 or lower. If the detected temperature of the temperature sensor 14 is higher than the set temperature T1, the control unit 13 sets the lower limit value VL of the charging correction voltage (the control range of the voltage applied from the power pack 15 to the charging roller 2) to the default V0. The drive system of this embodiment is not operated, and each part of this embodiment is controlled so that 90% or more of the input power from the commercial power source is concentrated and supplied to the fixing device 12 immediately after this control flow is completed. Here, the drive system of the present embodiment is a drive system that drives each part of the present embodiment, and does not include a part that drives the fixing device 12 to start up.

In this way, 9% of the input power from the commercial power source is used.
By centrally supplying 0% or more to the fixing device 12,
In this embodiment, an image can be formed within 10 seconds after the power is turned on or the sleep mode is set. According to the research conducted by the applicant of the present invention, when the input power from the commercial power source is supplied to the main motor for driving the photosensitive drum 1 and the like, it is impossible to start the image forming state within 10 seconds from the power-on or the sleep mode. Met.

If the temperature detected by the temperature sensor 14 is less than or equal to the set temperature T1, the control unit 13 proceeds to step 22 and changes the lower limit value of the charge correction voltage (control range of the voltage applied from the power pack 15 to the charging roller 2). The lower limit value) V L from the default V 0 to V 0 + α (α is a value set arbitrarily). Next, the control unit 13 performs the power pack 1 in step 23.
5 determines whether or not the voltage (image portion applied voltage) actually applied to the charging roller 2 at present is equal to or lower than VL, and the voltage actually applied from the power pack 15 to the charging roller 2 at present is determined. If it is less than or equal to VL, the voltage actually applied from the power pack 15 to the charging roller 2 is replaced with VL.

Next, in step 25, the outside temperature is measured again by the temperature sensor 14, and the controller 13 causes the temperature sensor 14 to operate.
It is determined whether the temperature detected by the temperature sensor 14 is equal to or lower than the set temperature T2 according to the input signal from. Control unit 13
If the temperature detected by the temperature sensor 14 is higher than the set temperature T2, the drive system of this embodiment is not operated, and 90% or more of the input power from the commercial power source is immediately concentrated in the fixing device 12 after the control flow is terminated. The respective parts of the present embodiment are controlled so as to be supplied in such a manner that the image can be formed within 10 seconds.

If the temperature detected by the temperature sensor 14 is less than or equal to the set temperature T2, the control unit 13 proceeds to step 26 and causes the main motor drive unit to rotate the main motor to enter the pre-rotation mode. By controlling the exposure device 3 by operating the device 4 or the like, a control pattern including a dark pattern for charge correction is created on the photosensitive drum 1. Therefore, the charging roller 2 is the power pack 15
A DC voltage is applied to the surface of the photosensitive drum 1 to uniformly charge the same, and the exposure device 3 exposes the control pattern on the photosensitive drum 1 to form an electrostatic latent image of the control pattern. The image is developed by the developing device 4 and a control pattern is created on the photosensitive drum 1.

The optical sensor 8 detects the control density on the photosensitive drum 1 by detecting the reflection density of the photosensitive drum 1. The control patterns include a toner density detection pattern (P pattern), a background pattern, and a charge correction dark pattern. The output value of the optical sensor 8 for the P pattern is Vsp, and the output value of the optical sensor 8 for the background pattern is Vsp.
sg, the output value of the optical sensor 8 for the dark pattern for charge correction is Vsdp.

In steps 27 and 28, the control unit 13 determines whether to increase or decrease the output voltage of the power pack 15 based on the output value of the optical sensor 8. Here, power pack 15
The control unit 13 controls the timing of the voltage applied from the developing roller to the charging roller 2 (charging voltage), the application of the developing bias from the developing bias power source to the developing device 4, and the exposure (writing) of the exposure device 3.
3 is controlled by the power pack 15, the developing bias power source, and the exposure apparatus 3 by.

That is, at time t1, the power pack 1
5, the charging applied voltage from the charging roller 2 to the charging roller 2 and the developing bias voltage from the developing bias power source to the developing device 4 are turned off,
When writing is turned on, a P pattern is created on the photosensitive drum 1 and the output value of the optical sensor 8 becomes Vsp. At time t3, the voltage applied from the power pack 15 to the charging roller 2 and the developing bias power source are changed from the developing device 4 to the developing device 4.
By applying the developing bias to the normal state and turning off the writing, the background is formed on the photosensitive drum 1 and the output value of the optical sensor 8 becomes Vsg.

The control unit 13 controls the output value Vs of the optical sensor 8.
Vsp / Vsg is calculated from p and Vsg, and this Vsp / V
As is well known, the toner replenishing device is connected to the developing device 4 using sg.
The toner density of the two-component developer therein is controlled to a predetermined value. At time t2, the charging applied voltage from the power pack 15 to the charging roller 2 is turned off, the developing bias power supply from the developing bias power source to the developing device 4 is in the normal state, and the writing is turned off.
Thin background stain pattern (dark pattern for charge compensation)
Is created and the output value of the optical sensor 8 becomes Vsdp.

In step 27, the control unit 13 causes the optical sensor 8
From the output values Vsg and Vsdg of the ratio Vsdg / Vsg
It is determined whether or not the value of Vsdg / Vsg is 0.9 or less than the set value, and if the value of Vsdg / Vsg is larger than 0.9, the power pack 15 is controlled in step 31 to output the power pack 15. Drop the voltage by one predetermined step. If the value of Vsdg / Vsg is 0.9 or less, the control unit 13 determines whether the value of Vsdg / Vsg is 0.85 or more, which is the set value, in step 28.
If the value of g / Vsg is smaller than 0.85, the power pack 15 is controlled in step 32 to increase the output voltage of the power pack 15 by one predetermined step. In this case, the controller 13 corrects (controls) the value of Vsdg / Vsg by a predetermined value.
When the output voltage of the power pack 15 is within the range, control (correction) is performed to decrease or increase the output voltage as described above, and the lower limit value of the correction (control) range is VL.

As described above, in this embodiment, the temperature sensor 14 for detecting the temperature and the reflection density on the surface of the photosensitive drum 1 as the image carrier after passing through the developing device 4 as the developing means are detected. From the optical sensor 8 and the power pack 15 as the voltage applying means to the charging roller 2 as the charging member.
The voltage applied to the photosensitive drum 1 is changed to change the charging potential of the non-image area on the photosensitive drum 1, and the output signal ratio Vs of the photosensor to the non-image area on the photosensitive drum 1 before and after this change is changed.
Since the control range of the applied voltage is determined by the output signal of the temperature sensor 14, the control unit 13 as a control unit for controlling the applied voltage corresponding to dg / Vsg is provided, and thus the environment suddenly changes to a low temperature. Even if the process control cannot follow, the photoconductor drum 1 is limited by limiting the control range.
It is possible to guarantee the charging potential of and to obtain an image free from background stains due to insufficient charging.

Further, in the present embodiment, the control range of the applied voltage is determined by the output signal of the temperature sensor 14 at the time of starting the device, so that the temperature sensor is located at a place where the operating temperature of the device easily heats up. Can reliably detect that the environment has changed to a low temperature. Therefore, even when the environment suddenly changes to a low temperature and the process control cannot follow, the charge range of the photosensitive drum 1 can be guaranteed by limiting the above control range, and an image free from scumming due to insufficient charge can be obtained. it can.

Further, in this embodiment, the temperature sensor 14
When the detected temperature is lower than the set temperature, the lower limit value of the control range is raised. Therefore, even when the environment suddenly changes to low temperature and the process control cannot follow, the control range is limited to limit the photosensitive drum 1 Guarantees the electrostatic potential,
It is possible to obtain an image without background stains due to insufficient charging.

The present invention is not limited to the above-described embodiment, and for example, the developing means can be applied even if the developing means is a normal developing type, and the voltage applied from the power pack 15 to the charging roller 2 can be changed. The voltage may be changed to a predetermined voltage without being turned on / off, and a contact charging member such as a charging belt may be used instead of the charging roller 2.

[0039]

As described above, according to the first to sixth aspects of the present invention, the control range of the voltage applied to the charging member is limited even when the environment suddenly changes to a low temperature and the process control cannot follow. Thus, the charged potential of the image carrier can be guaranteed, and an image free from background stain due to insufficient charging can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control flow of the same embodiment.

FIG. 3 is a timing chart showing the operation timing of the same embodiment.

FIG. 4 is a block diagram showing a part of a control system of the same embodiment.

[Explanation of symbols]

1 photoconductor drum 2 charging roller 3 exposure equipment 4 Developing device 8 optical sensor 13 Control unit 14 Temperature sensor 15 power packs

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H027 DA10 DA11 DE02 DE10 EA01                       EB01 EC03 EC06 EC07 EF01                 2H200 FA01 FA18 GA23 GA28 GA44                       GA59 GB02 HA02 HA29 HA30                       HB12 LB09 LB14 NA02 NA09                       PA03 PB18 PB27

Claims (6)

[Claims] 1. A charging member which is arranged in contact with or close to an image carrier to charge the image carrier, a voltage applying means for applying a DC voltage to the charging member, and the image carrier charged by the charging member. In an image forming apparatus having a latent image forming means for forming an electrostatic latent image on a body and a developing means for developing the electrostatic latent image on the image carrier, a temperature sensor for detecting temperature and the developing means are provided. An optical sensor for detecting the reflection density of the surface of the image carrier after passing through it, and changing the voltage applied from the voltage applying means to the charging member to change the charging potential of the non-image area on the image carrier. A control means for controlling the applied voltage corresponding to the output signal ratio of the photosensor with respect to the non-image area on the image carrier before and after the change, and the applied voltage of the applied voltage is controlled by the output signal of the temperature sensor. Determine control range An image forming apparatus comprising Rukoto. 2. A charging member which is arranged in contact with or close to an image carrier to charge the image carrier, a voltage applying means for applying a DC voltage to the charging member, and the image carrier charged by the charging member. In an image forming apparatus having a latent image forming means for forming an electrostatic latent image on a body and a developing means for developing the electrostatic latent image on the image carrier, a temperature sensor for detecting temperature and the developing means are provided. An optical sensor for detecting the reflection density of the surface of the image carrier after passing through it, and changing the voltage applied from the voltage applying means to the charging member to change the charging potential of the non-image area on the image carrier. , A control means for controlling the applied voltage corresponding to the output signal ratio of the photosensor with respect to the non-image area on the image carrier before and after this change, of the temperature sensor at the start-up of the apparatus. The above-mentioned mark according to the output signal Image forming apparatus and determines the control range of the voltage. 3. The image forming apparatus according to claim 1, wherein the lower limit value of the control range is increased when the temperature detected by the temperature sensor is lower than a set temperature. 4. The image forming apparatus according to claim 1, wherein the developing means is operated when the applied voltage is controlled. 5. The image forming apparatus according to claim 1, wherein the applied voltage is controlled when the temperature detected by the temperature sensor is equal to or higher than a preset temperature when the apparatus is started up. An image forming apparatus that starts up the apparatus without performing the operation. 6. A charging member which is arranged in contact with or close to an image carrier to charge the image carrier, voltage applying means for applying a DC voltage to the charging member, and the image carrier charged by the charging member. A temperature sensor for detecting a temperature in a charging potential correction system of an image forming apparatus having a latent image forming means for forming an electrostatic latent image on a body and a developing means for developing the electrostatic latent image on the image carrier. An optical sensor that detects the reflection density of the surface of the image carrier after passing through the developing unit, and a non-image area on the image carrier by changing the voltage applied from the voltage applying unit to the charging member. And a control means for changing the charging potential and controlling the applied voltage corresponding to the output signal ratio of the photosensor to the non-image area on the image carrier before and after the change, and the output signal of the temperature sensor. By the applied voltage Charge potential correction method characterized by determining the control range.