JPH09175687A - Belt conveyor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt conveyor capable of accurately measuring the surface speed of a belt in no contact with it. SOLUTION: Timing marks 4 having variable-density stripes with a constant pitch are printed on a belt 3 in advance, and two photoelectric sensors 5A, 5B reading the timing marks in sequence are provided. The time difference between two sensors 5A, 5B for detecting the same mark is calculated based on the outputs of two sensors 5A, 5B, and the average value is obtained over the prescribed period. The conveying speed of the belt 3 is detected for each mark thereafter, it is compared with the average value, and the rotation of a drive motor is controlled on the real-time basis. The drive motor is accurately controlled at a high speed without being affected by the drift in size of a device and the periodic speed fluctuation, and the conveying speed of the belt 3 can be kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt conveying device used in an image forming apparatus or the like, and more particularly to a belt conveying device for detecting a belt velocity and controlling the belt velocity.

[0002]

2. Description of the Related Art For example, in a color electrophotographic printer, Y (yellow) M (magenta) C (cyan) K
Each color image of (black) is sequentially formed on the photoconductor, and the color images of YMCK are superposed on the image carrier as an intermediate transfer member, for example, a belt rotated by a motor to obtain a color image. I have to. In an image forming apparatus that obtains a color image by superimposing each color image on such a belt, in order to realize a clear image without color misregistration or density unevenness, the speed fluctuation of the belt surface should be reduced as much as possible and the uniform surface should be used. It is necessary to realize the belt transportation.

However, in practice, as shown in FIG. 11 (a), the drive speed V of the motor for rotationally driving the belt.
_{Even if m} is maintained at a constant predetermined speed V _o , FIG.
As shown in (b), due to eccentricity of the driving roll of the belt and the decelerator, and other reasons, the belt surface speed V _b will have speed fluctuations of various frequencies. FIG. 11B shows
Relatively long period T due to eccentricity of the driving roll of the belt
The speed fluctuation of _{A and} the speed fluctuation of a relatively short period T _B due to a certain speed reducer among a plurality of speed reducers interposed between the motor and the drive roll are combined to show a state. Therefore, in order to reduce the fluctuation of the belt surface speed V _b and realize a clear image, it is necessary to perform speed control on the drive source in real time so as to detect the belt surface speed and make them uniform. Is coming.

[0004]

Conventionally, as a means for detecting the surface velocity of a belt, a method of calculating the belt velocity by attaching an encoder to the shaft of a roll that rotates with the belt and measuring the angular velocity ω of the roll. Are known (for example, JP-A-4-172376 and JP-A-4-23).
4064, etc.).

However, since this method indirectly calculates the surface velocity of the belt from the angular velocity of the encoder, it is accurate when slip occurs between the belt and the roll or when the roll is eccentric. The belt surface speed cannot be detected.

On the other hand, as a method of directly detecting the surface speed of the belt, the belt moves a distance L by detecting the passage of a mark printed on the belt at a constant pitch L by a sensor. Based on the time t required for
There is known a method of obtaining the belt speed v by a calculation such as = L / t (see Japanese Patent Laid-Open No. 6-130871).

Since this method directly detects the moving speed of the belt surface on which an image is formed, when the accuracy of the detecting method is high, a gap between the actual belt surface speed and the detection result hardly occurs. . However, in reality, since there is a random variation ΔL in the pitch of the marks on the belt, the measured belt speed V includes a detection error due to the variation. That is, V = (L + Δ
L) / t.

Further, in Japanese Unexamined Patent Publication No. 6-67480, a magnetic member is provided at the end of the belt, and a mark recorded on the belt by a recording head is read by a reproducing head. The belt surface speed v is obtained by calculating V = D / t by measuring the time t required for passing D.

With this method, a random detection error due to a mark pitch error does not occur. However, the distance D between the recording head and the reproducing head must be the tolerance Δ in manufacturing.
Since D is included, the detection result V eventually includes a certain measurement error. That is, V = (D + ΔD) / t. Further, since each head contacts the belt, it may affect the life of the belt and the meandering of the belt.

As described above, conventionally, there has been no means for accurately measuring the surface speed of a belt without contact.

[0011] Therefore, an object of the present invention is to provide a belt conveying device capable of accurately measuring the surface speed of a belt without contact.

[0012]

As shown in FIG. 1, a belt 3 carrying a sheet or a toner image is wound around a pair of rolls 1 and 2. This belt 3 has
As shown in FIG. 5, the timing mark 4 having light and dark stripes having a substantially constant pitch is printed in advance over the entire periphery of the non-image area at the front end. Further, two photoelectric sensors 5A and 5B are provided at positions facing the timing mark 4 of the belt 3 so as to be shifted in the conveyance direction of the belt 3 (shown by an arrow). The passage of the timing mark 4 on the belt 3 is detected by these two sensors 5A and 5B. Two sensors 5
As shown in FIG. 3, the signals A and 5B output signals having the same waveform and having phases shifted by a time corresponding to the pitch D of the two sensors 5A and 5B. Two sensors 5A,
The output of 5B is supplied to the arithmetic unit 7 of the control circuit 6 as shown in FIG. 4, and the same mark is applied to each of the sensors 5A and 5B.
The time difference detected by is calculated. That is, the time required for a certain mark to pass the sensor pitch D which is a fixed section is calculated. Then, based on the time obtained by this calculation, the control unit 8 causes the belt 3
A drive motor (not shown) that rotationally drives the roll 1 or 2 is controlled.

In the above structure, the timing mark 4
The time taken for one of the marks to pass a predetermined section is measured.
No detection error due to the random variation in the pitch of the marks as seen in Japanese Patent No. 0871 is generated.

Further, since a photoelectric sensor is used instead of the magnetic head described in Japanese Patent Laid-Open No. 6-67480, the belt is not in contact with the belt. It can also be expected that it will not affect, low cost and space saving. However, if the speed detection is calculated as V = D / t based on the above result, that is, if the inter-sensor pitch D is used as a reference for the speed detection, when the error of D is large, it is necessary to consider the countermeasure. . Actually, it is considered that an error of about several percent always exists in the distance of the predetermined section D, and a difference in the detection characteristics of the sensors causes an error similar to the error caused in the manufacturing. Therefore, when speed detection is performed based on the inter-sensor distance D, the detection result has a value that includes an error of about several percent with respect to the actual belt speed.

Therefore, the present invention uses the following method without V = D / t for speed detection.

That is, the above-described measurement of the difference in time when the same mark is detected by each sensor is measured for a predetermined period.
Desirably, it is performed over a period that is an integral multiple of the rotation period of the drive roll, and the average value t _ave of the passage time Δt _n is calculated by the following formula.

T _ave = (Δt ₁ + Δt ₂ + Δt ₃ + ... + Δt _N )
/ N time Δt _n that each mark passes after the average value t _{ave is} determined
And the average value t _ave are compared with each other to detect the conveyance speed of the belt surface. Then, the control unit 8 controls a drive motor (not shown) that rotationally drives the roll 1 or 2 of the belt 3 so that the detected conveyance speed becomes constant.

As described above, in the present invention, the average value t _ave of the passage times Δt _n of the same mark is used as the reference for speed detection. That is, the predetermined speed used as a reference for speed detection is the average speed when the belt is conveyed over the time corresponding to the integral rotation of the drive roll. The recognition is that the average speed of the belt over the time of the integral rotation of the drive roll is almost equal to the rotation speed of the drive source, and the rotation speed of the drive source is suppressed within a certain number of commas of the predetermined speed. The average speed is from the predetermined speed to 0. It includes only a few percent error. Therefore, the average value t
_ave is an extremely accurate reference, and the conveyance speed of the belt 3 becomes a stable and constant value by controlling the rotation speed of the drive motor (not shown) based on this reference.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIG. 5 is a schematic sectional view of a color copying machine using a color image forming apparatus using an intermediate transfer belt, and shows an embodiment to which the present invention is applied for speed detection of the intermediate transfer belt.

The color copying machine 9 includes an image reading device 10 for reading an image of a document and converting it into an image signal, and an image output device 11 for forming an image on a sheet based on the image signal from the image reading device 10. I have it.

In the image reading apparatus 10, the original 13 placed on the platen glass 12 is irradiated with light from the exposure lamp 14. The reflected light from the document 13 is reflected by the mirrors 15a, 15b, 15c, and is imaged on the image pickup surface of the image sensor 17 by the lens 16. Exposure lamp 1
4. The mirrors 15a, 15b, 15c move along the surface of the platen glass 12 to scan the image surface of the original document 13,
The image sensor 17 outputs an image signal corresponding to the image of the document 13.

In the image output device 11, a charging device 19, an image writing device 20 for exposing the photosensitive member 19 by a laser, a yellow (Y), a magenta (M), and a cyan (around the drum-shaped photosensitive member 18). C), black (K) 4
A rotary type developing device 21, a transfer device 22, a cleaner 23, and the like, which sequentially perform development with colors, are sequentially arranged.

Yellow, magenta, cyan, and black toner images corresponding to the original image are sequentially formed on the surface of the photosensitive member 18 by a well-known color electrophotographic process.

An intermediate transfer device 24 is arranged adjacent to the photosensitive member 19. The intermediate transfer device 24 includes three rolls 25, 26, 27 arranged in a triangular shape, an intermediate transfer belt 28 wound around these rolls 25, 26, 27, a cleaner 29, a speed detection sensor 30 and the like. ing. The roll 25 is a drive roll and is driven to rotate by a drive motor (not shown). The toner images of the respective colors sequentially formed on the surface of the photoconductor 18 are superimposed and transferred to the same position on the surface of the intermediate transfer belt 28 to form a full-color toner image.

The speed detection sensor 30 includes two sensors, which are arranged at a distance D in the belt conveyance direction, like the sensors 5A and 5B shown in FIG. In order to improve the frequency response of the measurement, if the mark pitch D'needs to be smaller than the distance in which the two sensors can be arranged on the same straight line in the conveyance direction of the belt, FIG. As shown, the two sensors 5A and 5B may be arranged in a direction perpendicular to the conveyance direction of the belt 28 and at a distance such that the mutual sensors do not interfere with each other. Also,
The marks on the belt are printed in advance on the non-image area at the end of the intermediate transfer belt 28 at a substantially constant pitch L ′ over the entire circumference.

The paper 32 in the paper feed tray 31 arranged below the image output device 11 is fed by the paper feed roll 33.
The full-color toner image on the surface of the intermediate transfer belt 28 is transferred by being sent out toward the intermediate transfer device 24, passing between the roll 26 and the transfer roll 34, and further fixed.
Is discharged to the outside of the device.

Next, a method for speed detection will be described with reference to the flowchart of FIG.

When a job start signal is input (step 101), the counter for counting the number of detected marks on the belt is reset (n = 0) (step 102). Note that this counter is included in the arithmetic unit 7 shown in FIG. Subsequently, the drive motor (not shown) for the belt 28 is activated (step 103), and the conveyance of the belt 28 is started, so that the sensors 5A and 5B start outputting the waveforms shown in FIG. Based on this waveform, the calculation unit 7 calculates the difference between the times when the two sensors 5A and 5B detect a certain same mark. That is, while incrementing the count value of the mark (step 104), the time Δt _n required for the nth mark to pass the distance D between the two sensors 5A and 5B is calculated (step 10).
5). In this embodiment, the rising edge of the signal is used, but of course the falling edge signal may be used.

Then, the marks are sequentially added until the number of marks reaches a predetermined number N (step 107), and at the same time when the Nth mark detection is completed (step 108), the average value t _ave thereof is obtained (step 109). Here, the time until the count number of the mark becomes N is almost equal to the time of an integral multiple (m times) of the rotation cycle of the drive roll. Therefore, by setting the reference value to t _ave , the predetermined speed of this system becomes the same speed as the average speed when the belt is conveyed for the time of m rotations of the driving roll.

After the detection of the Nth mark (after the mth cycle of the driving roll) (step 106), the passage time Δ of each mark until the job stop signal is input (step 111).
t _n is sequentially calculated, and the passing time Δt _n of each mark is
The conveyance speed of the belt is detected for each mark by comparing it with the previously calculated average value t _ave (step 11).
0). By giving this result to the belt drive unit 8 for each mark, the rotation speed of the drive motor can be controlled in real time to perform highly accurate speed control. When the job stop signal is input, the rotation of the drive motor is stopped (step 112).

In the present embodiment, as described above, first, the average conveyance speed of the belt is obtained during a fixed period, for example, the period in which the belt makes one revolution, and thereafter, the conveyance speed of the belt is detected for each mark. Then, the rotation of the drive motor is controlled in real time. As a result, the drive motor can be controlled accurately and at high speed without being affected by the dimensional deviation of the apparatus and the periodical speed fluctuation, and the belt transport speed can be made constant.

In the above, the measurement time until the reference value (reference speed) is calculated is the time until the drive roll rotates m times (m is an integer). This is because the speed fluctuation on the belt surface is most affected by the eccentricity of the drive roll, and the cycle of occurrence of other fluctuation factors is smaller than the rotation cycle of the drive roll, that is, the average speed of the belt that should be the reference speed. This is because it is considered that the value calculated in the cycle of an integral multiple of the driving roll is the closest to the predetermined speed. However, although the cycle of occurrence of other fluctuation factors is smaller than the rotation cycle of the drive roll, if the cycle is not synchronized with the rotation cycle of the drive roll, naturally the average value will have an error due to the influence thereof. Therefore, in order to improve the accuracy of the average value, the time for measuring the average value is a time that is a common multiple of the rotation cycle of the drive roll and other factors, specifically, the rotation cycle of the speed reducer, and further It is desirable to make the time that is a common multiple as large as possible.

In the above, the measurement time until the reference value is calculated is not actually the time of m rotations of the drive roll but from the start of the belt conveyance until the Nth mark is detected. In order to make this time exactly equal to the time of m rotations of the drive roll, it is desirable that the peripheral length of the belt and the peripheral length of the drive roll be an integral multiple of the mark pitch.

[Embodiment 2] In Embodiment 1, the frequency of detectable speed fluctuations, that is, the frequency response of the system for detecting the speed is determined by the conveyance speed _Vb of the belt and the mark printed on the belt. It is dominated by the pitch L (see FIG. 2). That is, since the measurement frequency F _m is V _b / L, the frequency response F _r is substantially less than (V _b / L) / 2. Therefore, in order to maintain a sufficient frequency response even when the belt conveying speed is low, it is necessary that
As shown in, it becomes necessary to reduce the pitch L'of the marks on the belt. However, there is a limit to the printable pitch. In such a case, as shown in FIG.
If speed detection is performed not only for the rising signal of the output signal of the sensor but also for the falling signal, the number of samplings per unit time is doubled, so that double frequency response should be realized. You can In FIG.
The average time t _ave obtained based on the rising signal is t _ave = (Δt ₁ + Δt ₂ + Δt ₃ + ... + Δt _N ).
/ N, and the average time t ′ _ave obtained based on the falling signal is t ′ _ave = (Δt ′ ₁ + Δt ′ ₂ + Δt ′ ₃ + ... +
Δt ′ _N ) / N, the mark movement times Δt ₁ , Δt ₂ ,. . . And the average time t _ave are compared with each other to control the drive motor, and the mark moving times Δt ′ ₁ , Δt ′ ₂ ,. . . And the average time t ′ _ave are compared to control the drive motor.

Although the present invention is applied to the intermediate transfer belt 28 as shown in FIG. 5 in the above embodiment,
The present invention is not limited to this, and for example, as shown in FIG. 9, by the developing device 21a, yellow, magenta, cyan, and black toner images are sequentially formed at the same position on the surface of the photosensitive belt 18a. 10 to form a full-color toner image and transfer the full-color toner image onto the sheet 32.
A plurality of independent members corresponding to each color are provided along the paper transport belt 18b as shown in FIG. 1, each including a photoconductor 18, a charger 19, an image writing device 20, a developing device 21b, a transfer device 22, and a cleaner 29. Image forming units 36, 37, 3 of
8 and 39 are arranged, and the image forming units 36, 37, and 37 are arranged at the same position on the sheet conveyed by the sheet conveying belt 18b.
The present invention can also be applied to the paper transport belt 18b of a so-called tandem type image forming apparatus in which toner images of respective colors are sequentially transferred by 38 and 39 to form a full-color toner image directly on the paper. it can. That is, the present invention can be applied to all image carrier belts such as a paper transport belt, a photoconductor belt, and an intermediate transfer belt.

[0036]

EFFECTS OF THE INVENTION By setting the reference for detecting the surface speed of the belt to the average speed shown by the belt in the time corresponding to the number of rotations of the driving rolls, the error originally possessed by the set reference is canceled out to obtain an accurate speed. Detection can be realized.
Therefore, by controlling the driving speed based on this, the belt is conveyed at a uniform speed, and a clear image without color misregistration or density unevenness can be obtained.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a belt conveyance device for explaining the present invention.

FIG. 2 is a schematic diagram showing a timing mark formed on a belt.

FIG. 3 is a waveform diagram showing an output of a sensor for speed detection.

FIG. 4 is a block diagram showing a control system of a belt conveyance speed.

FIG. 5 is a schematic sectional view of a color copying machine using a color image forming apparatus using an intermediate transfer belt.

FIG. 6 is a schematic diagram showing another example of a timing mark.

FIG. 7 is a flowchart showing a method for speed detection.

FIG. 8 is a waveform diagram in the case of detecting both the rising edge and the falling edge of the output of the sensor.

FIG. 9 is a schematic sectional view showing another example of a color image forming apparatus.

FIG. 10 is a schematic cross-sectional view showing still another example of the color image forming apparatus.

FIG. 11 is a graph showing a relationship between a motor driving speed and a belt surface speed.

[Explanation of symbols]

1, 2 ... roll, 3 ... belt, 4 ... timing mark,
5A, 5B ... Sensor, 6 ... Control circuit, 7 ... Arithmetic unit, 8
... control unit, 9 ... color copying machine, 10 ... image reading device, 1
DESCRIPTION OF SYMBOLS 1 ... Image output device, 12 ... Platen glass, 13 ... Original document, 14 ... Exposure lamp, 15a, 15b, 15c ... Mirror, 16 ... Lens, 17 ... Image sensor, 18 ... Photoconductor, 19 ... Charger, 20 ... Image Writing device, 21 ... Developing device, 22 ... Transfer device, 23 ... Cleaner, 24 ... Intermediate transfer device, 25, 26, 27 ... Roll, 28 ... Intermediate transfer belt, 29 ... Cleaner, 30 ... Speed detection sensor, 31 ... Paper feed tray, 32 ... Paper, 33 ... Paper feed roll, 34 ... Transfer roll, 35 ... Fixing device, 36-39 ... Image forming unit

Claims (6)

[Claims] 1. A carrier comprising an endless belt for carrying a sheet or a toner image, wherein a plurality of marks are repeatedly provided at a predetermined pitch with respect to the carrying direction, and the carrier is provided so as to be offset from each other in the carrying direction of the carrying body. , Two photoelectric sensors that sequentially read a plurality of marks provided on the carrier, driving means for driving the carrier, and the two sensors when the carrier is driven by the driving means. And a control unit for controlling a drive speed of the drive unit based on a calculation result of the calculation unit, and a calculation unit for calculating a time difference in which the two sensors detect the same mark based on the output of one sensor. Belt transport device characterized by. 2. An average value calculation means for calculating an average value of a plurality of calculation results by the calculation means, wherein the control means determines a calculation result of the average value calculation means and each mark by the calculation means. 2. The belt conveying apparatus according to claim 1, wherein the driving speed of the driving means is controlled based on the calculation result. 3. The driving means presses a rotating body that is rotationally driven against the supporting body to drive the supporting body, and the average value calculating means is for the rotating body that is rotationally driven. 3. The belt conveying device according to claim 2, wherein an average value of the calculation results by the calculation means corresponding to the integral rotation amount is obtained. 4. The average value calculating means obtains an average value of the calculation results of the calculating means of the time corresponding to a common multiple of the rotation cycle of the rotationally driven rotating body and the rotation cycle of the driving means. The belt conveyance device according to claim 3, which is characterized in that. 5. The time for averaging the calculation results by the calculating means by the average value calculating means is managed based on the number of marks on the carrier read by the sensor. Belt conveyor described. 6. The time for averaging the calculation results by the calculating means by the average value calculating means is such that the peripheral length of the rotating body and the peripheral length of the carrier are integral multiples of the pitch of the marks. The belt conveyance device according to claim 5.