JP4742552B2 - Toner density control device and image forming apparatus - Google Patents

Description

  The present invention relates to a toner density measuring device that measures toner density and an image forming apparatus that forms a toner image.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus using a two-component developer composed of a toner and a carrier is known. In such an image forming apparatus, a toner concentration sensor that detects toner concentration by measuring the magnetic force of the developer is provided, and a method of supplying toner to the developer based on the detection result by the toner concentration sensor is widely adopted. ing. In addition, in such an image forming apparatus, in order to prevent solidification and stagnation of the developer and to form a stable image, a stirring and conveying means that stirs and conveys the developer is widely adopted. The sensor detects the toner density of the developer that is being stirred and conveyed by the stirring and conveying means.

  Examples of such agitating / conveying means include a helical stirring blade type spirally arranged on a rotating shaft rotatably mounted in a developer container, and parallel to each other and each rotating shaft. There are parallel blade types in which a large number of inclined blades are arranged on the rotation shaft, and many of them periodically agitate the developer.

  When the object whose toner concentration sensor detects the toner concentration is a developer that is periodically stirred as described above, the developer can be periodically densely and densely developed by the agitating and conveying means. Since there are many agents and the magnetic force is strong, the sensor output representing the detection result of the toner density is high, and in the rough state, the sensor output is low because there is little developer and the magnetic force is weak. Accordingly, the sensor output of the toner concentration sensor has a periodic output waveform accompanying the rotation of the stirring and conveying means even if the toner concentration is constant.

  In order to obtain a stable detection value of toner density from such a periodic output waveform, for example, a representative value such as an average value of output, a maximum output value, or a minimum output value may be obtained as a detection value of toner density. It is done. In addition, as a simple method for improving the accuracy of such representative values, a first method in which a mechanism for detecting the phase of the agitating / conveying means is introduced and detection is always started from the same phase, or toner concentration is used. A second method of increasing the number of reading points by reducing the interval at which the sensor output is read from the sensor, a third method of calculating a representative value from an output waveform over multiple cycles, and the like can be considered.

  However, the first method causes a complicated device configuration and an increase in cost, the second method causes an increase in device size and cost due to an increase in memory capacity, and the third method is one representative. It takes a long time to calculate the value. When a small number of images are formed, the representative value cannot be calculated, and the toner density cannot be controlled.

  For this reason, there has been a need for a toner concentration measuring apparatus that can obtain a small number of measurement points in a short time and accurately calculate a representative value. There has been proposed a technique for obtaining a stable representative value regardless of the phase at which reading is started by making the reading interval coincide with half of the stirring cycle by the stirring and conveying means. This technique is based on the premise that a simple average value of a sine waveform is used as a representative value.

  However, the agitating / conveying means has a plate member attached to the rotating shaft for the purpose of avoiding toner sticking in the vicinity of the toner concentration sensor or forcibly feeding the developer in the vicinity of the toner concentration sensor. In many cases, the rotation of the plate member disturbs the output waveform from the sine wave. In this case, the technique of Patent Document 1 cannot be applied.

Further, it has been proposed that the upper average value is more suitable than the simple average value in consideration of the stability of the representative value with respect to fluctuations in the amount of developer to be stirred (for example, patents). In the case where such upper average value is a representative value, the technique of Patent Document 1 cannot be applied.
JP 2003-057938 A Japanese Patent Laid-Open No. 01-182750

  Even when a representative value other than the simple average is used or when an output waveform other than a sine wave is used, the toner that obtains a small number of measurement points in a short time measurement and accurately calculates the representative value as described above. A density measuring device is desired, but such a toner density measuring device has not been known in the past.

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a toner concentration measuring device capable of calculating a representative value with a small number of measurement points in a short time and a stable image formation by accurately detecting the toner concentration. An object of the present invention is to provide an image forming apparatus capable of performing the above.

The first toner concentration measuring apparatus of the present invention that achieves the above object provides:
A density sensor that measures the toner density of the developer when the developer including the toner and the carrier is stirred in the period A and outputs a measurement result;
The measurement result output from the concentration sensor is sampled over a time interval C longer than the period A at every time interval B that is not 1 / n of the period A for any integer n, and the sampled measurement result A toner concentration calculation unit for calculating a representative value biased to the upper side or lower side of the measurement result based on
(A ÷ B remainder)> B / 2, (B− (A ÷ B remainder)) × (C ÷ A quotient)> B / 2
Or the relationship
(A ÷ B remainder) <B / 2, (A ÷ B remainder) × (C ÷ A quotient)> B / 2
And a toner density calculation unit that satisfies the above relationship.

  According to the first toner concentration measuring apparatus of the present invention, the period A, the time interval B, and the measurement time section C satisfy the above-described relationship. Even with a small number of sampling points obtained in section C, the measurement results near the highest point and the lowest point of the periodic output waveform are reliably sampled, and the measurement results are biased toward the upper side or the lower side. The representative value is a stable value regardless of the sampling start phase, and the toner density can be accurately measured.

The second toner concentration measuring apparatus of the present invention that achieves the above object provides:
A density sensor that measures the toner density of the developer when the developer including the toner and the carrier is stirred in the period A and outputs a measurement result;
The measurement result output from the concentration sensor is sampled over a time interval C longer than the period A at every time interval B that is not 1 / n of the period A for any integer n, and the sampled measurement result Is a toner density calculation unit that calculates a representative value biased toward the upper side or the lower side of the measurement result, and at least one integer m is m × B / (the remainder of A ÷ B) = (C ÷ And a toner density calculation unit that satisfies the relationship of (quotient of A).

  According to the second toner concentration measuring apparatus of the present invention, the period A, the time interval B, and the measurement time interval C satisfy the above-described relationship. Even in the interval C, the vicinity of the highest point and the lowest point of the periodic output waveform are uniformly sampled with a small number of sampling points, and the representative value is a stable value regardless of the sampling start phase. The toner density can be accurately measured.

Here, the first and second toner concentration measuring apparatuses of the present invention are:
`` Equipped with a cycle acquisition unit that acquires the stirring cycle of the developer,
The toner concentration calculation unit determines a time interval for sampling the measurement result from the time interval B when the stirring cycle obtained by the cycle obtaining unit changes from the cycle A to another cycle A ′.
B ′ = A ′ × B / A
Is changed to a time interval B ′ that satisfies the relationship “
This form is preferable.

  The developer agitation cycle may be changed in accordance with a change in the productivity of the image forming apparatus. However, according to the toner concentration measuring apparatus of the above preferred embodiment, when the agitation cycle is changed as such. However, accurate measurement is realized.

The first image forming apparatus of the present invention that achieves the above object provides:
An image forming unit in which a developer containing toner and a carrier is contained, the developer is stirred at a period A, and a toner image is formed using the developer;
A density sensor that measures the toner density of the developer stirred in the image forming unit and outputs the measurement result;
The measurement result output from the concentration sensor is sampled over a time interval C longer than the period A at every time interval B that is not 1 / n of the period A for any integer n, and the sampled measurement result A toner concentration calculation unit for calculating a representative value biased to the upper side or lower side of the measurement result based on
(A ÷ B remainder)> B / 2, (B− (A ÷ B remainder)) × (C ÷ A quotient)> B / 2
Or the relationship
(A ÷ B remainder) <B / 2, (A ÷ B remainder) × (C ÷ A quotient)> B / 2
A toner concentration calculator that satisfies the relationship
And a control unit that controls the image forming unit based on a representative value of the toner density obtained by the toner density calculating unit.

  According to the first image forming apparatus of the present invention, the toner density is accurately measured according to the same principle as that of the first toner density measuring apparatus of the present invention, and a stable image is obtained based on the measured toner density. Formation is realized.

The second image forming apparatus of the present invention that achieves the above object provides:
An image forming unit in which a developer containing toner and a carrier is contained, the developer is stirred at a period A, and a toner image is formed using the developer;
A density sensor that measures the toner density of the developer stirred in the image forming unit and outputs the measurement result;
The measurement result output from the concentration sensor is sampled over a time interval C longer than the period A at every time interval B that is not 1 / n of the period A for any integer n, and the sampled measurement result Is a toner density calculation unit that calculates a representative value biased toward the upper side or the lower side of the measurement result, and at least one integer m is m × B / (the remainder of A ÷ B) = (C ÷ A toner density calculation unit that satisfies the relationship of
And a control unit that controls the image forming unit based on a representative value of the toner density obtained by the toner density calculating unit.

  According to the second image forming apparatus of the present invention, the toner density is accurately measured according to the same principle as that of the second toner density measuring apparatus of the present invention, and a stable image is obtained based on the measured toner density. Formation is realized.

Here, the first and second image forming apparatuses of the present invention are:
`` Equipped with a cycle acquisition unit that acquires the stirring cycle of the developer,
The toner concentration calculation unit determines a time interval for sampling the measurement result from the time interval B when the stirring cycle obtained by the cycle obtaining unit changes from the cycle A to another cycle A ′.
B ′ = A ′ × B / A
Is changed to a time interval B ′ that satisfies the relationship “
This form is preferable.

  In the image forming apparatus, there is a case where the developer agitation period is changed in accordance with a change in productivity, etc., but according to the image forming apparatus of the preferred embodiment, the agitation period is changed as such. In addition, accurate measurement of toner density is realized, and stable image formation is realized.

  As described above, according to the present invention, it is possible to obtain a small number of measurement points in a short time and obtain a representative value with high accuracy, and to stably detect the toner concentration with high accuracy. An image forming apparatus capable of performing the formed image is realized.

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

  FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

  The image forming apparatus of this embodiment is a full-color image forming apparatus having a tandem configuration using an intermediate transfer belt. The image forming apparatus according to the present embodiment includes an exposure unit 3 that emits exposure light modulated based on an input image signal, a yellow (Y) color, a magenta (M) color, a cyan (C) color, and a black color. (K) Four units 10Y, 10M, 10C, and 10K on which toner images of respective colors are formed, and an intermediate transfer belt 20 on which the toner images are primarily transferred while being in contact with these four units and circulatingly moved. I have. Note that the symbols Y, M, C, and K attached to the end of the reference numerals shown in FIG. 1 indicate elements corresponding to CMYK colors.

  In the image forming apparatus of the present embodiment, primary transfer rolls 5Y, 5M, 5C, and 5K that primarily transfer toner images of respective colors formed on the four units 10Y, 10M, 10C, and 10K to the intermediate transfer belt 20, respectively. The secondary transfer roll 15 for secondary transfer of the toner image primarily transferred onto the intermediate transfer belt 20 onto the paper P transported by a transport roll (not shown), and the toner image transferred onto the paper P are heated and A fixing device (not shown) for fixing on the paper P by applying pressure is provided. The intermediate transfer belt 20 is stretched around a drive roll 21 that drives the belt, a driven roll 22, and a tension roll 23 that applies tension to the belt, and circulates and moves in the direction of arrow A in FIG. A belt cleaning device that does not appear in the drawing is provided on the upstream side of the unit 10Y in which is formed.

  The four units 10Y, 10M, 10C, and 10K include a photosensitive drum 1Y, 1M, 1C, and 1K on which a toner image is formed, and a charger 2Y that charges the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. 2M, 2C, and 2K, and the charged photosensitive drums 1Y, 1M, 1C, and 1K are exposed to the exposure light from the exposure unit 3, and toner of each color is applied to each of the electrostatic latent images formed by the respective electrostatic latent images. Developing units 4Y, 4M, 4C, and 4K that form toner images are provided.

  Each developing device 4Y, 4M, 4C, 4K contains a two-component developer composed of toner and carrier, and each developing device 4Y, 4M, 4C, 4K contains developer as photosensitive drums 1Y, 1M. Developer rolls 41Y, 41M, 41C, and 41K supplied to the surfaces of 1C and 1K, augers 42Y, 42M, 42C, and 42K that stir and convey the developer with rotating spiral blades, and the toner concentration of the developer Toner density sensors 8Y, 8M, 8C, and 8K are provided.

  Further, the image forming apparatus is provided with a temperature / humidity sensor 27 for measuring the temperature and humidity in the apparatus. In the image forming apparatus of the present embodiment, the detection results of the toner density sensors 8Y, 8M, 8C, and 8K and the temperature / humidity sensor 27 are sampled by the TC control unit 35, and the TC control unit 35 performs the toner density sensors 8Y, 8M. , 8C, and 8K, the toner density is calculated by a calculation method described later, and the calculated toner density is stored in the memory 37. The TC control unit 35 rotates the dispense motors 9Y, 9M, 9C, and 9K based on the toner density and the detection result of the temperature / humidity sensor 27, and via the developing devices 4Y, 4M, 4C, and 4K and a pipe. Toner is supplied from the toner boxes 7Y, 7M, 7C, and 7K connected to the developing devices 4Y, 4M, 4C, and 4K, respectively. The toner density sensors 8Y, 8M, 8C, and 8K correspond to an example of the density sensor according to the present invention, and the TC control unit 35 also serves as an example of the toner density calculation unit and an example of the control unit according to the present invention. is there. The toner concentration sensors 8Y, 8M, 8C, and 8K and the TC control unit 35 constitute an embodiment of the toner concentration measuring device of the present invention.

  The TC control unit 35 is instructed by a rotation number instruction unit 36 corresponding to an example of a period acquisition unit according to the present invention, and the rotation number according to the productivity of the image per unit time. The rotational speeds of the augers 42Y, 42M, 42C, and 42K are controlled so that the number is obtained. Further, the sampling interval of the detection result is also changed in accordance with the change in the rotation speed of the augers 42Y, 42M, 42C, and 42K. Of the image forming apparatus shown in this figure, an example of the image forming section referred to in the present invention is determined by a portion excluding the toner density sensors 8Y, 8M, 8C and 8K, the TC control section 35, the rotation speed instruction section 36 and the memory 37. It is configured.

  Image data output from an external device 50 such as a personal computer or image data read by the image reading unit (IIT) 30 and processed by the image processing unit 31 is separated into YMCK colors by the controller 32. Pulse width modulation is performed to convert the density of each color into the pulse width of the pulse signal. When this image data is sent to the exposure unit 3, exposure light is irradiated to the photosensitive drums 1Y, 1M, 1C, and 1K provided in the four units 10Y, 10M, 10C, and 10K, respectively. An electrostatic latent image is formed on each of the photosensitive drums 1Y, 1M, 1C, and 1K irradiated with the exposure light, and the electrostatic latent images are developed by the developing rollers 41Y and 41M of the developing devices 4Y, 4M, 4C, and 4K, respectively. , 41C, and 41K are developed on the photosensitive drums 1Y, 1M, 1C, and 1K to form toner images of respective colors. The respective color toner images are transferred onto the intermediate transfer belt 20 by the primary transfer rolls 5Y, 5M, 5C, and 5K. The toner image transferred onto the intermediate transfer belt 20 is transferred by the secondary transfer roll 15 onto the paper P transported by a transport roll (not shown), and further heated and pressurized by a fixing device (not shown) to be applied onto the paper P. It is fixed.

  The image quality of the toner image finally formed on the paper P in such a procedure depends on the accuracy of the toner density calculated by the TC control unit 35, and the toner density is accurately calculated by the TC control unit 35. As a result, a good quality toner image is formed.

  Here, the internal structure of the developing devices 4Y, 4M, 4C, and 4K will be described. However, in the following description, common matters will be described without particularly distinguishing each color of CMYK, and therefore, Y, M, C, and K at the end are described. In the following description, the symbols Y, M, C, and K are omitted from the description even if the symbols with the symbols are the elements attached in FIG.

  FIG. 2 is a diagram illustrating the internal structure of the developing device.

  A developer 60 is accommodated in the developing device 4, and an auger 42 for agitating and transporting the developer 60 is incorporated. The auger 42 is provided with a spiral blade 42a and a plate member 42b along the rotation axis. As the auger 42 rotates, the developer 60 is periodically stirred by the blade 42a. It will be transported to the right side of. Then, the developer 60 that has reached the rear end member 43 goes to the back side of the figure, and is conveyed to the left side of the figure by another auger that does not appear in this figure, and again toward the front side of the figure. Come back. Further, the developer 60 overflowing over the rear end member 43 is sent to the waste developer collection box 44.

  The toner density sensor 8 is provided on the side surface of the developing device 4 at a position facing the plate member 42b of the auger 42. The plate member 42b prevents toner from sticking near the toner density sensor 8. In addition, the developer 60 is constantly fed near the toner density sensor 8.

  When the developer 60 is stirred and conveyed by the spiral blade 42a, the output of the toner density sensor 8 has a periodic output waveform as described below.

  FIG. 3 is a diagram for explaining that the output of the toner density sensor has a periodic output waveform.

  In this figure, the plate member described above is omitted in order to explain the effect of stirring and conveying by the spiral blade 42a.

  As described above, the developer 60 in the developing device 4 is conveyed to the right side of the drawing while being agitated by the spiral blade 42a. As a result, the amount of developer present in the vicinity of the toner density sensor 8 changes. In front of the blade 42a, there is a large amount of developer 60 pushed on the blade 42a by the blade 42a. On the other hand, behind the blade 42a, the developer 60 is pushed away by the blade 42a, and a small amount of developer 60 is present. Only exists.

  Part (A) of FIG. 3 shows a state in which the amount of the developer present in the vicinity of the toner density sensor 8 is the minimum amount, immediately after the blade 42 a passes through the vicinity of the toner density sensor 8. This is the state. As described above, the toner density sensor 8 measures the magnetic force of the developer 60, and as shown in this part (A), the developer 60 magnetic force becomes minimum when the developer 60 is a minimum amount, and the toner density. The output of sensor 8 is also minimal.

  Further, part (B) of FIG. 3 shows a state in which the amount of developer existing in the vicinity of the toner density sensor 8 is the maximum amount, immediately before the blade 42 a passes through the vicinity of the toner density sensor 8. It will be in this state. As shown in Part (B), when the amount of the developer 60 is the maximum, the magnetic force of the developer 60 is maximized, and the output of the toner density sensor 8 is also maximized.

  Such a state where the amount of developer 60 is the maximum amount and a state where the amount of developer 60 is the minimum amount occurs alternately with the rotation of the spiral blade 42a, and the output of the toner density sensor 8 has a periodic waveform. .

  FIG. 4 is an example of a periodic output waveform of the toner concentration sensor.

  In this figure, the horizontal axis represents time, and the vertical axis represents the output of the toner density sensor. A thin solid line 71 in the graph is a periodic waveform caused by the rotation of the blade 42a of the auger 42 shown in FIGS. 2 and 3, and has a waveform close to a sine wave.

  On the other hand, rotation of the plate member 42b of the auger 42 shown in FIG. 2 also causes a periodic amount change of the developer 60 in the vicinity of the toner concentration sensor 8 and a periodic output change of the toner concentration sensor 8. It becomes. A wavy line 72 in the graph represents a periodic waveform resulting from such rotation of the plate member 42b, and has a waveform in which thin peaks are periodically generated.

  The actual output waveform in the toner density sensor 8 is a waveform in which these waveforms are superimposed, as shown by the thick solid line 73 of the graph, and is a waveform considerably deviated from the sine wave.

  As representative values calculated from such output waveforms, for example, the highest value, the lowest value, the simple average value, the upper average value, the lower average value, and the like can be considered. The influence of disturbance such as environmental changes is different.

  FIG. 5 is a graph showing the influence of disturbance on the maximum value and the minimum value of the output waveform.

  The graph of FIG. 5 shows the influence of the highest point and the lowest point among the various representative values described above when the toner density in the developer is constant. The horizontal axis of the figure indicates the disturbance. The vertical axis of the figure represents the maximum value and the minimum value.

  The maximum value graph 81 is a linear graph inclined slightly upward to the right, and it can be seen that the maximum value is less affected by changes in the developer amount. On the other hand, the minimum value graph 82 has a large upward-sloping and convex curve, and it can be seen that the minimum value is greatly affected by changes in the developer amount. In other words, the maximum value reflects only the toner density even when disturbances such as a decrease in the developer amount below a predetermined amount or a decrease in developer fluidity due to the environment occur. When it is desired to obtain an accurate toner density by eliminating disturbance, it is desirable to use the maximum value as a representative value. On the other hand, the minimum value is a value reflecting both the toner density and the disturbance, and is not suitable for accurate measurement of the toner density. However, as a representative value used for controlling the image forming apparatus, In some cases, it is useful for control because it also reflects disturbance.

  Such a maximum value or minimum value is data of only one point in the output waveform, and is naturally susceptible to noise and the like. Therefore, an upper average value and a lower average value obtained by sampling the output waveform and averaging some of the upper and lower points are considered useful. In the present embodiment, the upper average value is employed for the purpose of accurately measuring the toner density.

  Here, as a result of detailed consideration of the correspondence relationship between the sampling period and output waveform period when the upper average value and the lower average value are used as representative values, the measurement results are stable in the same measurement time and the same number of sampling points. It was found that it greatly affects sex.

  In the present embodiment, the correspondence in the sampling period for calculating the upper average value, the period of the output waveform, etc. is an appropriate correspondence as described below, and is stable in a short time with a small number of sampling points. A measurement result is obtained. Hereinafter, in describing this appropriate correspondence, first, a uniform symbol is assigned to the period or the like.

  FIG. 6 is a diagram for explaining the definition of symbols used in the following description.

  In this figure, the horizontal axis represents time, and the vertical axis represents the output of the toner density sensor. In this figure, a simple sine waveform is shown as the output waveform of the sensor. In the following, for convenience of illustration, a sine wave is used as the output waveform of the sensor. However, the contents described below are also applicable to a waveform collapsed from the sine wave as shown in FIG.

  The period of the output waveform shown in the graph of FIG. 6 coincides with the rotation period of the auger 42 shown in FIGS. 2 and 3, and is hereinafter referred to as “period A”.

  Triangles on the output waveform represent sampling points, and this sampling time interval is hereinafter referred to as “sampling interval B”.

  The total length in the horizontal axis direction of the graph represents the time required from the first sampling point to the last sampling point, and is hereinafter referred to as “measurement time C”.

  In the calculation of the upper average value and the lower average value, only some sampling points biased to the upper and lower levels are used among the sampling points indicated by the triangle, and the number of sampling points used for this calculation is referred to as D ".

  “Number of periods E” represents the number of the above-mentioned “period A” included in the above-mentioned “measurement time C” (less than one period is rounded down), and the number of periods E = measurement time C ÷ period. It is obtained by a calculation formula called A quotient.

Sampling points of “sampling point number F” are obtained by repeating sampling at “sampling interval B” over “measurement time C” described above. At this time,
Measurement time C = (number of sampling points F−1) × sampling interval B
This relationship holds.

  Among the sampling points of “sampling point number F”, the above-described sampling point of “usage point number D” is used to calculate the representative value, and the calculated representative value value is hereinafter referred to as “representative value G”.

  Here, a comparative example for the present embodiment will be described.

  FIG. 7 is a diagram illustrating a comparative example.

  Also in this figure, the horizontal axis represents time, and the vertical axis represents the output of the toner density sensor.

  In this comparative example, the sampling time B = sampling A = 4, and sampling time F = 9 is sampled. Therefore, the measurement time C = cycle A × 2, and the cycle number E = 2. is there. Further, in this comparative example, the number of used points D = the number of cycles E = 2, and the upper two points are used among the sampling points to obtain the upper average value.

  At the start of sampling in actual sampling, it is unknown where the position (phase) of the auger 42 shown in FIGS. 2 and 3 is. Therefore, the upper average value varies depending on the sampling start phase.

  FIG. 7 shows a sampling point represented by a circle symbol and a sampling point represented by a cross symbol. From the first pattern of sampling points represented by a circle symbol, the upper average is shown. The highest value is obtained, and the lowest value of the upper average value is obtained from the second pattern of sampling points represented by the cross symbol. The width ΔV between the maximum value and the minimum value becomes a measurement error in the toner density measurement, and the smaller the width, the more stable the measurement.

  In the comparative example shown in FIG. 7, since the sampling interval B = period A / 4 as described above, the upper two sampling points (sampling points with a circle in the figure) among the sampling points. Are always in the same phase, and when the highest point in the first cycle matches a sampling point, the highest point in the second cycle also matches the sampling point, and the highest point in the first cycle is the sampling interval B. If it is in the middle, the highest point in the second cycle and the highest point in the second cycle will come. For this reason, the width ΔV between the maximum value and the minimum value is large.

  In contrast to such a comparative example, in this embodiment, the sampling interval B and the period A satisfy the relationship that the sampling interval B is not equal to the period A ÷ n for any integer n.

  FIG. 8 is a diagram showing a sampling method in the present embodiment.

  Also in this figure, the horizontal axis represents time, and the vertical axis represents the output of the toner density sensor.

  In the sampling method shown here, a sampling interval B ′ slightly longer than the sampling interval B in the comparative example is used for sampling the waveform having the same period A as the period A in the comparative example, and the sampling interval is used for any integer n. B ′ ≠ cycle A ÷ n. In addition, sampling with the number of sampling points F ′ = 8 is performed, and measurement time C ′> period A × 2 and period number E = 2. The sampling point number F ′ in the present embodiment is smaller than the sampling point number F in the comparative example, and as shown in the figure, the measurement time C ′ in the present embodiment is shorter than the measurement time C (= period A × 2) in the comparative example. Slightly long. Further, the number of used points D = the number of cycles E = 2, and the upper two points are used among the sampling points to obtain the upper average value.

  FIG. 8 also shows sampling points represented by a circle symbol and sampling points represented by a cross symbol. From the first pattern of sampling points represented by a circle symbol, the upper average value is shown. Is obtained, and the lowest value of the upper average value is obtained from the second pattern of sampling points represented by the cross symbol.

  In the present embodiment, since the sampling interval B ′ and the period A are in a non-synchronized relationship, the upper two sampling points (sampling points circled in the figure) out of the eight sampling points are waveforms. They are in different phases above. For this reason, the highest value of the upper average value obtained by the first pattern of the present embodiment is lower than the highest value of the upper average value obtained by the first pattern in the comparative example, and is obtained by the second pattern of the present embodiment. The lowest value of the upper average value is higher than the lowest value of the upper average value obtained by the second pattern in the comparative example. For this reason, the width ΔV ′ between the highest value and the lowest value of the upper average value in the present embodiment is smaller than the width ΔV in the comparative example.

  Thus, since the sampling interval B and the period A are in a non-synchronized relationship, variation in the representative value G can be suppressed, and accurate measurement and accurate control based on the measurement can be performed. In general, the accuracy can be improved when the sampling interval B is small. However, in the case of this embodiment, the sampling interval B ′ is longer than the sampling interval B of the comparative example, and the accuracy is higher than that of the comparative example. High measurement is realized.

  Although FIG. 8 shows an example in which the number of periods E = 2, in the present embodiment, a larger number of periods E may be used in order to further improve the measurement accuracy. In this case, however, it is desirable to use the number of used points D equal to the number of periods E, whereby the highest sampling point is selected and averaged one by one from each period.

  By the way, there are cases where the effect of improving accuracy is insufficient if the sampling interval B and the period A are simply in a non-synchronized relationship. In this embodiment, the sampling interval B and the period A will be described below. Such additional correspondence is also satisfied.

  FIG. 9 is an explanatory diagram when the additional correspondence relationship is not satisfied, and FIG. 10 is an explanatory diagram when the additional correspondence relationship is satisfied.

  In these figures, the vicinity of the peak of the output waveform is shown enlarged, and the triangle symbol indicates the sampling point. However, in this figure, the positions of the sampling points at the peak of each cycle of the output waveform are shown to be overlapped, and when the peak comes in the middle of the sampling interval in the first cycle, sampling is performed at the subsequent cycle. It shows how the position of the points changes. In the example shown here, it is assumed that the number of periods E = 3.

  Even if the sampling interval B and the period A are non-synchronized, if they are almost synchronized, if the peak is in the middle of the sampling interval in the first period as shown in FIG. The positions of the sampling points with respect to are not moved so much and these sampling points are used for calculating the upper average value, so the representative value G represented by the line 91 is a low value. This means that if the peak coincides with the sampling point in the first period, the sampling point will be near the peak in the subsequent period. Therefore, in the case as shown in FIG. 9, the maximum value and the minimum value of the representative value G are substantially the same values as the maximum value and the minimum value in the comparative example described above, as described in FIG. It can be seen that the effect of non-synchronization is small.

Therefore, in this embodiment, paying attention to the remainder H of the period A ÷ sampling interval B,
Additional correspondence relationship of remainder H> sampling interval B ÷ 2, (sampling interval B−remainder H) × period E> sampling interval B ÷ 2, or
An additional correspondence relationship of remainder H <sampling interval B ÷ 2, remainder H × number of periods E> sampling interval B ÷ 2 is satisfied.

  In both cases shown in FIGS. 9 and 10, the remainder H> sampling interval B / 2. Further, in the case shown in FIG. 9, the remainder H≈sampling interval B, and the sampling interval B−residue H≈0, so the above additional correspondence relationship is not satisfied. On the other hand, in the case shown in FIG. 10, the remainder H is about 70% of the sampling interval B, and “sampling interval B-remainder H” is sufficiently large, satisfying the additional correspondence described above. . As shown in FIG. 10, when the above additional correspondence is satisfied, the phase of the sampling point is in the second period and the third period even if the peak is in the middle of the sampling interval in the first period. “Sampling interval B−remainder H” is moved by a large amount, and the peak is surely exceeded by the period number E. As a result, the representative value G represented by the line 92 is a high value. Conversely, even if the peak coincides with the sampling point in the first period, the sampling point is far away from the peak in the subsequent period, and the peak is surely set to the sampling interval before passing the number of periods E. It means to reach the middle. Thus, it can be seen that when the above additional correspondence is satisfied, the effect of non-synchronization as described in FIG. 8 is effectively exhibited.

  When the remainder H <sampling interval B ÷ 2, the above description is the same when it is assumed that the moving direction of the sampling points is reversed and the remainder moves by H as compared with the case where remainder H> sampling interval B ÷ 2. It turns out that it is true.

  As described above, in the present embodiment, since the correspondence as described above is satisfied, a stable representative value can be calculated by obtaining a small number of sampling points in a short time. Then, the toner density can be obtained with high accuracy by such a stable representative value, and stable image formation is performed by the control based on the toner density with high accuracy.

  In the following, another embodiment in which another desirable correspondence different from the above-described correspondence is used will be described. This another embodiment is substantially the same as the above-described embodiment except that the correspondence relationship between the sampling interval B and the period A in the sampling method is different from the above-described correspondence relationship. In the following, another embodiment will be described by focusing only on the points different from the above-described embodiment, and FIG. 1 and FIG. 2 showing the configuration common to the above-described embodiment are the other embodiment. Will be used as is.

  FIG. 11 is a diagram illustrating a sampling method in another embodiment.

  Also in this figure, the horizontal axis represents time, and the vertical axis represents the output of the toner density sensor.

  In this alternative embodiment, the sampling interval B and the period A satisfy the relationship that the sampling interval B ≠ period A ÷ n for any integer n. Further, in this alternative embodiment, at least one integer is used. For m, the correspondence relationship m × sampling interval B / remainder H = period number E is satisfied. An example satisfying such a correspondence is shown in FIG.

  In the example shown in FIG. 11, for a predetermined time unit t, the period A = 10 t, the sampling interval B = 3 t, the measurement time C = 33 t, the number of used points D = the number of periods E = 3, and the number of sampling points F = 12. It has become. Therefore, when the remainder H of the period A ÷ sampling interval B = 1t and the integer m is “1”, the above-described correspondence relationship of m × sampling interval B / remainder H = period number E is satisfied.

  Further, in FIG. 11, sampling points represented by triangular symbols and sampling points represented by square symbols are shown. From the first pattern of sampling points represented by triangular symbols, The highest value of the upper average value is obtained, and the lowest value of the upper average value is obtained from the second pattern of sampling points represented by square symbols.

  Of the twelve sampling points, the upper three sampling points (sampling points circled in the figure) have a phase difference corresponding to the time interval 1t, and during the measurement time C, The vicinity of the vertex of the output waveform is sampled once at a time interval that divides the sampling interval B into three equal parts, and the representative value G is calculated from each sampled sampling point. The representative value G calculated in this way is exactly the same value as when the representative value G is obtained from a large number of sampling points, such as the sampling interval B = 1t, the sampling point number F = 36, and the use point number D = 9. The width ΔV ″ between the highest value and the lowest value is also exactly the same as the width of the representative value G at such a large number of sampling points. That is, when the above-described correspondence relationship in this another embodiment is satisfied, A measurement equivalent to a measurement in which the number of sampling points is increased by N times is realized with a small number of sampling points, and a variation reduction similar to a variation in representative values due to an increase in the number of sampling points is also realized. Since each sampling point corresponding to the time interval that divides the sampling interval B into three is obtained, the representative value G is not the upper average value, for example, If the maximum value and the minimum value of the ring points are used, there is an advantage that it is possible to obtain a value close to the peak value of the really captured want waveform.

  According to such another embodiment, as described above, a measurement equivalent to the measurement in which the sampling points are increased N times is realized, and a highly accurate measurement is realized. Further, stable image formation is realized by controlling the image forming apparatus by control based on such high-precision measurement.

In the image forming apparatus shown in FIG. 1, the rotational speeds of the augers 42Y, 42M, 42C, and 42K are controlled by the TC control unit 35, and the image productivity per unit time, etc., from the rotational speed instruction unit 36. The rotation speed is such that the rotation speed corresponding to the rotation speed is instructed and the specified rotation speed is obtained. Therefore, if sampling is continued at a constant sampling interval B without considering the rotational speeds of the augers 42Y, 42M, 42C, and 42K, when the rotational speeds of the augers 42Y, 42M, 42C, and 42K are changed, The correspondence as described above is broken. Therefore, when the rotation speed of the augers 42Y, 42M, 42C, and 42K is changed and the period A becomes the period A ′, the TC control unit 35 sets the sampling interval B to
Sampling interval B ′ = cycle A ′ ÷ cycle A × sampling interval B
The above correspondence is maintained by changing to a new sampling interval B ′ that satisfies the above relationship.

  In the above description, as an example of calculating the representative value G, a calculation method using all the upper values to calculate the upper average value is shown. However, the calculation of the representative value in the present invention is, for example, noise. In order to remove the influence, a calculation method that does not use the true most significant value may be used in which the average value excluding the most significant 2 points among the top 8 points is used as the representative value G.

  In the above description, the upper average value is shown as an example of the representative value G. However, the representative value referred to in the present invention is not limited to the upper average value, and may be the lower average value, the upper average value, It may be a representative value calculated by extracting a part of the waveform, such as a lower average value.

  In the above description, for convenience of explanation, a sine wave is shown as an example of an output waveform, but the present invention can also be applied to a non-sine wave as shown in FIG.

  In the above description, the obtained representative value G is used for controlling the dispense motor. However, the control unit according to the present invention controls elements other than the dispense motor in the image forming apparatus based on the representative value. It may be a thing.

  The present invention can also be applied to a system that detects the position of an auger in a developing device by judging the phase of a feature point such as an inflection point of the output of a toner density sensor. As an example of such a system, the position of the auger is adjusted to prevent the toner from sticking when the plate member provided on the auger stops the auger at a position where a large amount of developer is fed before the toner concentration sensor. A system that controls the stop timing of the auger so that it does not stop at a position that is well detected and toner sticks easily can be considered.

  In the above description, an image forming apparatus having a tandem configuration using the intermediate transfer belt 20 is illustrated as an embodiment of the image forming apparatus of the present invention. However, the image forming apparatus of the present invention is limited to a tandem configuration. The system may be a multi-cycle configuration. The image forming apparatus of the present invention is not limited to the one using the intermediate transfer belt 20, and may use an intermediate transfer member. Further, the image forming apparatus of the present invention is not limited to the intermediate transfer type, but is a direct type that directly transfers to a recording medium carried on a paper conveying belt or a recording medium conveyed by a roll. Also good.

It is a whole lineblock diagram showing one embodiment of the present invention. It is a figure showing the internal structure of a developing device. It is a figure explaining that the output of a toner concentration sensor becomes a periodic output waveform. 3 is an example of a periodic output waveform of a toner concentration sensor. It is a graph showing the influence which the maximum value and the minimum value of an output waveform receive from a disturbance. It is a figure explaining the definition of the symbol used by description of this specification. It is a figure showing a comparative example. It is a figure which shows the system of sampling in this embodiment. It is explanatory drawing when the additional correspondence is not satisfied. It is explanatory drawing in the case of satisfy | filling additional correspondence. It is a figure which shows the system of sampling in another embodiment.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 2Y, 2M, 2C, 2K Charger 3 Exposure unit 4Y, 4M, 4C, 4K Developer 5Y, 5M, 5C, 5K Primary transfer roll 7Y, 7M, 7C, 7K Toner Box 8Y, 8M, 8C, 8K Toner density sensor 9Y, 9M, 9C, 9K Dispense motor 10Y, 10M, 10C, 10K Unit 15 Secondary transfer roll 20 Intermediate transfer belt 21 Drive roll 22 Driven roll 23 Tension roll 30 Image reading unit 31 Image processing unit 32 Controller 35 TC control unit 41Y, 41M, 41C, 41K Developing roll 42Y, 42M, 42C, 42K Developing roll 42a Blade 42b Plate member 43 Rear end member 44 Waste developer collection box 50 External device 60 Developer

Claims (4)

A density sensor that measures the toner density of the developer when the developer including the toner and the carrier is stirred in the period A and outputs a measurement result;
The measurement result output from the concentration sensor is sampled over a time interval C longer than the period A at every time interval B that is not 1 / n of the period A for any integer n, and the sampled measurement A toner density calculation unit that calculates a representative value biased toward the upper side or lower side of the measurement result based on the result, and at least one integer m is m × B / (A ÷ B remainder) = (C A toner concentration measuring device comprising a toner concentration calculating unit satisfying a relationship of ÷ (quotient of A). Provided with a cycle obtaining unit for obtaining the developer agitation cycle,
The toner concentration calculating unit determines a time interval for sampling the measurement result from the time interval B when the stirring cycle obtained by the cycle obtaining unit changes from the cycle A to another cycle A ′.
B ′ = A ′ × B / A
2. The toner density measuring apparatus according to claim 1, wherein the time interval is changed to a time interval B ′ satisfying the following relationship. An image forming unit in which a developer containing toner and a carrier is contained, the developer is stirred at a period A, and a toner image is formed using the developer;
A density sensor that measures the toner density of the developer stirred in the image forming unit and outputs a measurement result;
The measurement result output from the concentration sensor is sampled over a time interval C longer than the period A at every time interval B that is not 1 / n of the period A for any integer n, and the sampled measurement A toner density calculation unit that calculates a representative value biased toward the upper side or lower side of the measurement result based on the result, and at least one integer m is m × B / (A ÷ B remainder) = (C A toner density calculation unit that satisfies the relationship of ÷ quotient of A),
An image forming apparatus comprising: a control unit that controls the image forming unit based on a representative value of toner density obtained by the toner density calculating unit. A period obtaining unit for obtaining a stirring period of the developer in the image forming unit;
The toner concentration calculating unit determines a time interval for sampling the measurement result from the time interval B when the stirring cycle obtained by the cycle obtaining unit changes from the cycle A to another cycle A ′.
B ′ = A ′ × B / A
The image forming apparatus according to claim 3, wherein the time interval B ′ satisfies the following relationship.

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