Belt drive control device, belt drive device and image forming apparatus

Abstract

To determine a state of a rotational speed of a belt within a range of an original difference from a predetermined target value.SOLUTION: A belt drive control device 30 includes: a control switching unit 39 that switches between and performs first feedback control of controlling a rotational speed of a driving unit based on the rotational speed of the driving unit and second feedback control of controlling the rotational speed of the driving unit based on the rotational speed of the driving unit and a rotational speed of a belt; a first determination unit 41 that determines whether or not the rotational speed of the driving unit falls within a predetermined range based on the rotational speed of the driving unit; a second determination unit 42 that determines whether or not the rotational speed of the belt falls within the predetermined range based on the rotational speed of the belt; and a determination switching unit 40 that performs switching to select a determination made by the first determination unit 41 in a case where the control switching unit 39 selects the first feedback control, and to select the second determination unit 42 in a case where the control switching unit 39 selects the second feedback control.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a belt drive control device, a belt drive device, and an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art Image forming apparatuses such as printers, fax machines, and copiers are known that include a belt drive control device that controls the drive of an endless belt such as an intermediate transfer belt or a conveyor belt.

[0003] For example, Patent Document 1 (Patent Publication No. 4351509) describes a belt drive control device to be installed in an image forming device that includes an encoder that detects the rotation angle of the motor that drives the belt, as well as a photosensor that detects scale marks provided on the surface of the belt at predetermined intervals in the direction of rotation.

[0004] In this belt drive control device, a photosensor detects scale marks on the rotating belt, and the resulting detection signal (pulse signal) is fed back to control the belt rotation speed to a target rotation speed. However, if there is a portion where the photosensor detection signal cannot be obtained due to a joint between the scale marks or the like from the start of belt rotation until the belt reaches a steady state, control may become unstable, making it difficult to reliably start up the drive. For this reason, in Patent Document 1, control is performed based on the detection signal from the encoder that detects the rotation angle of the motor from the start of belt rotation until the belt reaches a steady state, and then control is switched to the detection signal from the photosensor after the belt reaches a steady state. Summary of the Invention [Problem to be solved by the invention]

[0005] In some belt drive control devices, a determination is made as to whether the rotation speed of the motor is within a predetermined range (threshold) to detect abnormalities such as motor failure or excessive load. If the rotation speed of the motor is within the predetermined range, the rotation speed of the belt is also determined to be within a normal range.

[0006] However, if the drive roller that rotates the belt expands due to an increase in ambient temperature or the like, and the roller diameter changes, controlling the belt rotation speed based on the detection signal of a photosensor that detects scale marks on the belt will cause the motor rotation speed to stabilize at a speed that is deviated from the original target speed. Meanwhile, because the threshold value of the motor rotation speed used to determine an abnormality remains unchanged, the relative relationship (difference) between the motor rotation speed in a stable state and the threshold value (upper or lower limit) changes. Therefore, if abnormality determination is performed based on the motor rotation speed, it will no longer be possible to determine the abnormality within the original difference range from the predetermined target value, resulting in variations in the determination. [Means for solving the problem]

[0007] In order to solve the above problems, the belt drive control device according to the present invention includes: a rotation angle detection unit that detects a rotation angle of a drive unit that drives a belt to rotate; a first rotation speed calculation unit that calculates a rotation speed of the drive unit based on a detection result of the rotation angle detection unit; a position indication detection unit that detects a position indication unit provided on the belt; a second rotation speed calculation unit that calculates the rotation speed of the belt based on the detection result of the position indication detection unit; a control switching unit that switches between first feedback control to control the rotation speed of the drive unit based on a calculation result of the first rotation speed calculation unit and second feedback control to control the rotation speed of the drive unit based on the calculation results of the first rotation speed calculation unit and the second rotation speed calculation unit; a first determination unit that determines whether the rotation speed of the drive unit is within a predetermined range based on the calculation result of the first rotation speed calculation unit; a second determination unit that determines whether the rotation speed of the belt is within a predetermined range based on the calculation result of the second rotation speed calculation unit; and a determination switching unit that selects determination by the first determination unit when the control switching unit selects the first feedback control, and selects determination by the second determination unit when the control switching unit selects the second feedback control. The control switching unit switches from the first feedback control to the second feedback control when the position display detection unit becomes able to detect the position display unit, and the judgment switching unit switches from judgment by the first judgment unit to judgment by the second judgment unit when the first feedback control is switched to the second feedback control, and the second judgment unit judges whether the rotation speed of the belt calculated by the second rotation speed calculation unit is within a difference range set so that the ratio is the same as the difference between an upper limit value and a lower limit value with respect to a target value during the first feedback control, and judges that an abnormality has occurred when the rotation speed of the belt calculated by the second rotation speed calculation unit exceeds the difference range. A belt drive control device characterized by the above. [Effects of the Invention]

[0008] According to the present invention, it is possible to determine the state of the belt rotation speed within the original difference range with respect to a predetermined target value. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing an embodiment of an image forming apparatus equipped with a belt drive control device according to the present invention; [Figure 2] FIG. 2 is a diagram illustrating a configuration of a transfer device according to the present embodiment. [Figure 3] FIG. 2 is a block diagram of the belt drive control device according to the embodiment. [Figure 4] FIG. 4 is a diagram showing a flow of abnormality determination according to the present embodiment. [Figure 5]10A and 10B are diagrams illustrating the relationship between the rotation speeds of the drive roller and the intermediate transfer belt and the threshold value for determining an abnormality during first feedback control and second feedback control. [Figure 6] FIG. 10 is a diagram showing another flow of abnormality determination according to the present invention. [Figure 7] FIG. 10 is a diagram showing yet another flow of abnormality determination according to the present invention. [Figure 8] 10A and 10B are diagrams illustrating a configuration for moving a scale sensor toward and away from an intermediate transfer belt. [Figure 9] FIG. 10 is a diagram showing yet another flow of abnormality determination according to the present invention. [Figure 10] 10A and 10B are diagrams illustrating a configuration in which a primary transfer roller and a sensor holding member are brought into contact with and separated from an intermediate transfer belt. [Figure 11] FIG. 10 is a diagram illustrating a state in which the primary transfer roller and the sensor holding member are separated from the intermediate transfer belt. [Figure 12] FIG. 10 is a diagram showing yet another flow of abnormality determination according to the present invention. [Figure 13] 13 is a diagram for explaining the method of determining abnormality shown in FIG. 12. FIG. [Figure 14] 1 is a diagram illustrating an example of an ink-jet image forming apparatus to which the present invention is applied. [Figure 15] FIG. 2 is a diagram illustrating an example of the configuration of a line-type head unit. [Figure 16] FIG. 1 is a diagram for explaining a conventional problem. [Figure 17] FIG. 1 is a diagram for explaining a conventional problem. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and descriptions thereof will be omitted once they have been described.

[0011] FIG. 1 is a diagram showing an embodiment of an image forming apparatus equipped with a belt drive control device according to the present invention.

[0012] As shown in FIG. 1, the image forming apparatus 100 according to this embodiment includes an image reading unit 1 that reads an image on a document, an image forming unit 2 that forms an image on a recording medium, a fixing unit 3 that fixes the image on the recording medium, a recording medium supply unit 4 that supplies the recording medium, and a transport unit 5 that transports the recording medium to the fixing unit 3.

[0013] The image reading unit 1 scans an original document while irradiating it with light from a light source, and reads image data from the light reflected from the original document using, for example, a 3-line CCD (Charge Coupled Device) sensor. The read image data undergoes image processing such as scanner y correction, color conversion, image separation, and gradation correction by an image processing device, and is then sent to an image writing device 6 (described later) provided in the image forming unit 2.

[0014] The image forming section 2 includes four image creating units 10Y, 10M, 10C, and 10Bk, an image writing device 6 that writes an electrostatic latent image onto the photosensitive member 11 provided in each of the image creating units 10Y, 10M, 10C, and 10Bk, and a transfer device 7 that transfers the image onto a recording medium.

[0015] Each of the imaging units 10Y, 10M, 10C, and 10Bk has basically the same configuration, except that it contains toner (developer) of a different color, namely, yellow, magenta, cyan, and black, which correspond to the color separation components of a color image. Specifically, each of the imaging units 10Y, 10M, 10C, and 10Bk has a photoconductor 11 as an image carrier that carries an image on its surface, a charging member 12 that charges the surface of the photoconductor 11, a developing device 13 that supplies toner as developer to the surface of the photoconductor 11 to form a toner image, and a cleaning device 14 that cleans the surface of the photoconductor 11.

[0016] The image writing device 6 includes an LD (laser diode) that irradiates light (laser beam) onto the surface of the photoreceptor 11. The image writing device 6 modulates a drive signal for the LD in accordance with image data, and writes an electrostatic latent image onto the photoreceptor 11 with the light irradiated from the LD.

[0017] The transfer device 7 has an intermediate transfer belt 15, a primary transfer roller 16, and a secondary transfer roller 17. The intermediate transfer belt 15 is an endless belt and is stretched by a plurality of rollers. Four primary transfer rollers 16 are provided inside the intermediate transfer belt 15. Each primary transfer roller 16 contacts each photoconductor 11 via the intermediate transfer belt 15, thereby forming a primary transfer portion (primary transfer nip) between the intermediate transfer belt 15 and each photoconductor 11. The secondary transfer roller 17 contacts the outer peripheral surface of the intermediate transfer belt 15 and forms a secondary transfer portion (secondary transfer nip).

[0018] The fixing unit 3 includes a fixing rotor 21 that is heated by a heat source such as a heater, and a pressure rotor 22 that is in pressure contact with the fixing rotor 21 to form a fixing nip.

[0019] The recording medium supply unit 4 includes a paper feed cassette 18 that stores paper as a recording medium, and a paper feed roller 19 that feeds paper from the paper feed cassette 18. Hereinafter, the "recording medium" will be described as "paper," but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper (paper), but also transparencies, fabrics, metal sheets, plastic films, and prepreg sheets made of carbon fiber pre-impregnated with resin. Furthermore, "paper" includes not only plain paper, but also cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

[0020] The conveying section 5 is composed of a conveying rotating body such as a conveying belt.

[0021] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to FIG.

[0022] When an image formation command is issued in the image forming apparatus 100, the photosensitive elements 11 of the imaging units 10Y, 10M, 10C, and 10Bk and the intermediate transfer belt 15 of the transfer device 7 start to rotate. Also, the paper feed roller 19 starts to rotate, and paper is fed out from the paper feed cassette 18. The fed paper comes into contact with a pair of timing rollers 20 and stops, and the transport of the paper is temporarily halted until an image to be transferred onto the paper is formed.

[0023] In each of the imaging units 10Y, 10M, 10C, and 10Bk, the surface of the photoconductor 11 is first charged to a uniform high potential by the charging member 12. Next, the image writing device 6 irradiates the surface (charged surface) of each photoconductor 11 with light based on the image information of the original document read by the image reading unit 1 or the print image information instructed to be printed from a terminal. This reduces the potential of the irradiated area, forming an electrostatic latent image on the surface of each photoconductor 11. The developing device 13 then supplies toner to this electrostatic latent image, forming a toner image on each photoconductor 11. As each photoconductor 11 rotates, the toner image formed on each photoconductor 11 reaches a primary transfer unit (the position of the primary transfer roller 16), where it is transferred onto the rotating intermediate transfer belt 15 in a sequentially overlapping manner. In this way, a full-color toner image is formed on the intermediate transfer belt 15. It is also possible to form a monochrome image using any one of the imaging units 10Y, 10M, 10C, and 10Bk, or to form a two- or three-color image using any two or three of them. After the toner image is transferred from the photoreceptor 11 to the intermediate transfer belt 15, residual toner and the like on each photoreceptor 11 is removed by a cleaning device 14.

[0024] The toner image transferred onto intermediate transfer belt 15 is transported to the secondary transfer unit (the position of secondary transfer roller 17) as intermediate transfer belt 15 rotates, and is transferred onto the transported paper by timing rollers 20. The paper is then transported to fixing unit 3 by transport unit 5, where the toner image on the paper is heated and pressurized by fixing rotor 21 and pressure rotor 22, and the toner image is fixed to the paper. The paper is then ejected outside the device. This completes the series of image forming operations.

[0025] FIG. 2 is a diagram showing the configuration of the transfer device according to this embodiment.

[0026] 2, the transfer device 7 according to this embodiment includes a motor 24 as a drive source and a drive roller 25 around which the intermediate transfer belt 15 is stretched, as a drive unit that drives and rotates the intermediate transfer belt 15. A speed reduction mechanism including gears or the like is provided between the motor 24 and the drive roller 25, and the rotation speed of the motor 24 is transmitted to the drive roller 25 at a speed reduced by the gear ratio of the speed reduction mechanism. When the drive roller 25 rotates, the intermediate transfer belt 15 is driven to rotate in the direction of arrow A in FIG. 2.

[0027] Furthermore, a plurality of scale marks M serving as a position indicator are provided on the inner peripheral edge of the intermediate transfer belt 15 according to this embodiment. The plurality of scale marks M are provided at predetermined intervals in the rotation direction A around the entire circumference of the intermediate transfer belt 15. Furthermore, a scale sensor 32 serving as a position indicator detector that detects the scale marks M is provided on the inner side of the intermediate transfer belt 15. The scale sensor 32 is disposed so as to face the scale marks M, and sequentially detects the scale marks M on the intermediate transfer belt 15, outputting a detection signal to a belt rotation speed calculation unit, which will be described later.

[0028] The drive roller 25 is provided with an encoder 31 as a rotation angle detector that detects the rotation angle of the drive roller 25. The rotation angle of the drive roller 25 detected by the encoder 31 is sent to a drive roller speed calculation unit, which will be described later. The encoder 31 may be provided on the rotation shaft of the motor 24 and detect the rotation angle of the motor 24.

[0029] FIG. 3 is a block diagram of a belt drive control device provided in the image forming apparatus according to this embodiment.

[0030] As shown in FIG. 3, the belt drive control device 30 according to this embodiment includes, in addition to the encoder 31 and the scale sensor 32, a drive roller speed calculation unit 33, a belt speed calculation unit 34, a drive roller target speed setting unit 35, a belt target speed setting unit 36, a drive roller speed compensator 37, a belt speed compensator 38, a control switching unit 39, a drive roller speed abnormality determination unit 41, a belt speed abnormality determination unit 42, a determination switching unit 40, a drive roller speed difference calculation unit 43, and a belt speed difference calculation unit 44.

[0031] The drive roller speed calculation unit 33 is a first rotation speed calculation unit that calculates the rotation speed of the drive roller 25 based on the detection result of the rotation angle by the encoder 31.

[0032] The belt speed calculation unit 34 is a second rotation speed calculation unit that calculates the rotation speed of the intermediate transfer belt 15 based on the detection result of the scale mark M by the scale sensor 32.

[0033] The drive roller target speed setting unit 35 sets the target rotation speed of the drive roller 25 (hereinafter referred to as the "drive roller target speed").

[0034] The belt target speed setting unit 36 ​​sets the target rotation speed of the intermediate transfer belt 15 (hereinafter referred to as the "belt target speed").

[0035] The belt speed difference calculation unit 44 calculates the difference between the target belt speed and the rotation speed of the intermediate transfer belt 15 calculated by the belt speed calculation unit 34 .

[0036] The belt speed compensator 38 calculates a correction value for the drive roller target speed based on the rotation speed of the intermediate transfer belt 15 calculated by the belt speed calculation unit 34. In this embodiment, the belt speed compensator 38 calculates the correction value based on the difference value calculated by the belt speed difference calculation unit 44. Here, the correction value is a correction value that suppresses fluctuations in the rotation speed of the intermediate transfer belt 15.

[0037] The drive roller speed difference calculation unit 43 calculates the difference between the drive roller target speed and the second rotation speed calculated by the drive roller speed calculation unit 33. In this embodiment, the drive roller speed difference calculation unit 43 adds the correction value calculated by the belt speed compensator 38 to the drive roller target speed, and then calculates the difference between the drive roller target speed and the rotation speed of the drive roller 25.

[0038] The drive roller speed compensator 37 is a drive unit speed compensation unit that performs feedback control of the drive roller 25 using the drive roller target speed, the correction value of the drive roller target speed, and the rotation speed calculated by the drive roller speed calculation unit 33. In this embodiment, the drive roller speed compensator 37 performs feedback control of the drive roller 25 based on the difference value input from the drive roller speed difference calculation unit 43.

[0039] Specifically, drive roller speed compensator 37 performs a preset control calculation based on the difference value input from drive roller speed difference calculation unit 43, and calculates a command value to be sent to motor driver 45, which controls the driving of motor 24. Then, drive roller speed compensator 37 outputs the calculated command value to motor driver 45. Motor driver 45 drives motor 24 in accordance with the command value input from drive roller speed compensator 37.

[0040] The control switching unit 39 switches between a first feedback control that controls the rotation speed of the motor 24 based on the calculation results of the drive roller speed calculation unit 33, and a second feedback control that controls the rotation speed of the motor 24 based on the calculation results of both the drive roller speed calculation unit 33 and the belt speed calculation unit 34.

[0041] Drive roller speed abnormality determination unit 41 is a first determination unit that determines whether the rotation speed of drive roller 25 is within a predetermined range based on the calculation result of drive roller speed calculation unit 33. If drive roller speed abnormality determination unit 41 determines that the rotation speed of drive roller 25 is not within the predetermined range, it issues a command to notification unit 46. Notification unit 46 is, for example, a display unit or alarm provided in the image forming apparatus, and upon receiving a command indicating an abnormality from drive roller speed abnormality determination unit 41, it notifies of the abnormality by displaying a message or sounding a sound.

[0042] The belt speed abnormality determination unit 42 is a second determination unit that determines whether the rotation speed of the intermediate transfer belt 15 is within a predetermined range based on the calculation result of the belt speed calculation unit 34. If the belt speed abnormality determination unit 42 determines that the rotation speed of the intermediate transfer belt 15 is not within the predetermined range, it issues a command to the notification unit 46. Upon receiving the command of the abnormality from the belt speed abnormality determination unit 42, the notification unit 46 notifies the abnormality by displaying a message or sounding a sound in the same manner as described above.

[0043] The determination switching unit 40 selects and executes either the abnormality determination by the drive roller speed abnormality determination unit 41 or the abnormality determination by the belt speed abnormality determination unit 42 .

[0044] Here, the problems with the conventional configuration will be explained.

[0045] For example, the belt drive control device described in Patent No. 50220868 is configured to be able to switch between a first feedback control that controls the rotation speed of the motor based on the detection signal of an encoder that detects the rotation angle of the drive roller, and a second feedback control that controls the rotation speed of the motor based on two signals: the detection signal of a sensor that detects scale marks on the belt and the detection signal of the encoder.

[0046] The reason for switching between first feedback control and second feedback control in this belt drive control device is that there are cases in which the sensor cannot accurately detect the scale marks. In the configuration described in Japanese Patent No. 50220868, a sensor holding member that holds the sensor is configured to be able to come into contact with and separate from the belt, and when image formation is not being performed, the sensor holding member is separated from the belt to suppress belt wear due to the sensor holding member coming into contact with the belt. However, when the sensor holding member is separated from the belt, the relative distance between the sensor and the belt increases, making it impossible for the sensor to accurately detect the scale marks on the belt. For this reason, when the sensor holding member is separated and the sensor cannot accurately detect the scale marks, first feedback control is performed using only the detection signal of the encoder. However, when the sensor holding member is in contact and the sensor can accurately detect the scale marks, second feedback control is performed using the detection signal of the sensor in addition to the detection signal of the encoder.

[0047] As described above, conventional belt drive control devices switch between first and second feedback control depending on whether the scale marks are detected by the sensor, but belt speed abnormalities are determined based on the rotational speed of the drive roller obtained from the detection results of the encoder in both first and second feedback control cases. That is, as shown in Figure 16, when the belt starts to be driven and the rotational speed of the drive roller increases, the rotational speed of the drive roller is controlled so that it approaches a target value between preset upper and lower limit values. At this time, if the motor fails or an excessive load is placed on the drive system, causing the rotational speed of the drive roller to exceed the upper limit or fall below the lower limit, an abnormality is determined.

[0048] The diameter of the drive roller varies depending on the ambient temperature. For example, as shown in FIG. 17, when the diameter of the drive roller 25 increases from d1 to d2 due to a rise in temperature, the circumferential length of the outer circumferential surface of the drive roller 25 increases, and the amount of belt surface movement per rotation of the drive roller 25 increases. In this case, if the belt is controlled by second feedback control based on the detection signals of the encoder and the sensor, the rotational speed of the drive roller is maintained at a value lower than the original target value (the value indicated by the dashed line in FIG. 16). Conversely, when the diameter of the drive roller decreases, the rotational speed of the drive roller is maintained at a value higher than the original target value.

[0049] In this way, when the diameter of the drive roller changes, the rotation speed of the drive roller is maintained at a speed that deviates from the original target value, while the thresholds (upper and lower limits) for determining whether the rotation speed is abnormal remain unchanged, so the difference between the maintained rotation speed and the thresholds changes. Specifically, as shown by the dashed dotted line in Figure 16, when the rotation speed of the drive roller is maintained at a value lower than the original target value, the range from the maintained rotation speed to the lower limit narrows, and conversely, the range to the upper limit widens.

[0050] For example, if the target output of the encoder is 1000 Hz when controlling the belt rotation speed to a target value of 100 mm / s, and fluctuations in the belt rotation speed exceeding ±2% are determined to be abnormal, then an abnormality is determined if the encoder output falls below the lower limit of 980 Hz or exceeds the upper limit of 1020 Hz. Here, during the second feedback control shown in FIG. 16, if the diameter of the drive roller increases due to expansion, the encoder output stabilizes at a value lower than the target value, for example, 995 Hz, but the upper and lower limits of the encoder output, which are the criteria for determining abnormality, do not change. Therefore, the relative relationship (difference) between the encoder output and the upper or lower limit when the rotation speed is stable changes. As a result, if the encoder output stabilizes at 995 Hz, which is lower than the original target value, and then fluctuates by approximately 1.5% from the lower limit of 980 Hz, an abnormality is determined. In other words, although a fluctuation range of ±2% should be allowed, an abnormality is detected within a smaller fluctuation range. For this reason, in the conventional belt drive control device, when second feedback control is performed, if the diameter of the drive roller changes, an abnormality in the rotation speed cannot be correctly detected within the allowable fluctuation range.

[0051] To address this issue, in the belt drive control device according to the present embodiment, the conditions for abnormality determination are changed in accordance with feedback control in order to prevent a decrease in the accuracy of abnormality determination due to changes in the diameter of the drive roller. The abnormality determination method according to this embodiment will be described below.

[0052] FIG. 4 is a diagram showing a flow of abnormality determination according to this embodiment.

[0053] As shown in FIG. 4, in this embodiment, first, the motor is driven by the first feedback control to start rotating the intermediate transfer belt. That is, the rotation speed of the motor is controlled based on the rotation angle of the drive roller detected by the encoder. Furthermore, abnormality determination in the first feedback control is performed based on the rotation speed of the drive roller. That is, in the first feedback control, the drive roller speed abnormality determination unit 41 is selected by the determination switching unit 40 shown in FIG. 3. Then, the drive roller speed abnormality determination unit 41 determines whether the rotation speed of the drive roller is within a predetermined range based on the calculation result of the drive roller speed calculation unit 33.

[0054] Thereafter, when the control switching unit 39 shown in Fig. 3 switches from the first feedback control to the second feedback control under conditions such as the scale sensor being able to detect the scale marks, the abnormality determination based on the rotational speed of the drive roller is switched to the abnormality determination based on the rotational speed of the intermediate transfer belt. That is, when the feedback control is switched from the first feedback control based on the rotational speed of the drive roller to the second feedback control based on the rotational speed of the intermediate transfer belt, the determination switching unit 40 shown in Fig. 3 switches the abnormality determination from the abnormality determination by the drive roller speed abnormality determination unit 41 to the abnormality determination by the belt speed abnormality determination unit 42. Note that if the control is not switched to the second feedback control even after a predetermined time has elapsed after the first feedback control, the process is terminated as a timeout. The same applies to the subsequent flows.

[0055] In this way, in this embodiment, when the first feedback control is performed, an abnormality determination is made based on the rotation speed of the drive roller, and then, when switching to the second feedback control, an abnormality determination is switched to one based on the rotation speed of the intermediate transfer belt.

[0056] FIG. 5 is a diagram showing the relationship between the rotation speeds of the drive roller and intermediate transfer belt and the threshold value for abnormality determination during the first feedback control and the second feedback control in this embodiment.

[0057] 5, in this embodiment, when the first feedback control is started, an abnormality is determined based on the rotation speed of the drive roller within the range (threshold) indicated by the shaded area in Fig. 5(a). At this time, if the target rotation speed of the intermediate transfer belt is 100 [mm / s] and the rotation speed of the intermediate transfer belt fluctuates by more than ±2%, an abnormality is determined when the output of the encoder detecting the rotation speed of the drive roller falls below a lower limit of 980 [Hz], which is 2% lower than the target value of 1000 [Hz], or exceeds an upper limit of 1020 [Hz], which is 2% higher than the target value.

[0058] Next, when the feedback control is switched from the first feedback control to the second feedback control, the abnormality determination is switched from based on the rotation speed of the drive roller to based on the rotation speed of the intermediate transfer belt. Therefore, the abnormality determination of the rotation speed is made within the range (threshold) indicated by the shaded area in FIG. 5B. The abnormality determination at this time is also made within the same allowable fluctuation range (within ±2%) as during the first feedback control. Therefore, an abnormality is determined when the rotation speed of the intermediate transfer belt based on the detection result of the scale sensor falls below the lower limit of 98 mm / s, which is 2% lower than the target value of 100 mm / s, or exceeds the upper limit of 102 mm / s, which is 2% higher than the target value.

[0059] As described above, in this embodiment, when switching from first feedback control to second feedback control, the abnormality determination is switched from determination based on the rotational speed of the drive roller to determination based on the rotational speed of the intermediate transfer belt, so that the presence or absence of an abnormality can be determined within the inherently tolerable fluctuation range (within a range of ±2% in the above example). In other words, by performing the abnormality determination during second feedback control based on the rotational speed of the intermediate transfer belt and its threshold value, rather than the rotational speed of the drive roller, it becomes possible to determine an abnormality without being affected by fluctuations in the roller diameter. This makes it possible to accurately determine the state of the rotational speed of the intermediate transfer belt within the inherent difference range from a predetermined target value, improving the reliability of control.

[0060] Another abnormality determination flow according to the present invention will now be described.

[0061] 6, the control is switched from the first feedback control to the second feedback control when it becomes possible for the scale sensor to detect the scale marks. Furthermore, with this switch to the second feedback control, the abnormality determination is switched from abnormality determination based on the rotation speed of the drive roller (drive roller speed abnormality determination unit 41) to abnormality determination based on the rotation speed of the intermediate transfer belt (belt speed abnormality determination unit 42). That is, once it becomes possible for the scale sensor to detect the scale marks, the second feedback control based on the rotation speed of the intermediate transfer belt becomes possible, so the control is switched to the second feedback control and the abnormality determination is also switched.

[0062] Specifically, the detection of the scale mark becomes possible when (i) the scale sensor is positioned at a predetermined distance from the intermediate transfer belt so that the scale mark can be detected, (ii) the vertical displacement of the intermediate transfer belt (displacement in a direction perpendicular to the image carrying surface) is below a predetermined value, or (iii) a predetermined time has elapsed since the intermediate transfer belt began to rotate.

[0063] Regarding (i) above, when the scale sensor is positioned at a predetermined distance from the intermediate transfer belt so that it can detect the scale marks, this means that in a configuration in which the scale sensor can move toward and away from the intermediate transfer belt, the scale sensor has approached the intermediate transfer belt and can detect the scale marks with high accuracy. If the scale sensor is spaced away from the intermediate transfer belt, it cannot detect the scale marks with high accuracy, so when the scale sensor has approached the intermediate transfer belt and is positioned at a predetermined distance, the control switches from the first feedback control to the second feedback control.

[0064] Furthermore, with regard to (ii) above, when the displacement of the intermediate transfer belt in the vertical direction becomes equal to or less than a predetermined value, this means that the behavior of the intermediate transfer belt as it rotates stabilizes, allowing the scale sensor to accurately detect the scale marks. Immediately after the intermediate transfer belt starts to rotate, the behavior of the intermediate transfer belt becomes unstable, making it difficult for the scale sensor to detect the scale marks. Therefore, when the behavior of the intermediate transfer belt stabilizes and the scale sensor can accurately detect the scale marks, the control is switched from first feedback control to second feedback control. The behavior of the intermediate transfer belt can be monitored by a sensor that measures the distance perpendicular to the intermediate transfer belt.

[0065] Regarding (iii) above, "when a predetermined time has elapsed since the rotational drive of the intermediate transfer belt started" means that the predetermined time has elapsed since the rotational drive of the intermediate transfer belt started and the behavior of the intermediate transfer belt has stabilized. In this case, the timing to switch to the second feedback control can be determined by counting the elapsed time from the start of the rotational drive of the intermediate transfer belt using a timer or the like.

[0066] FIG. 7 shows yet another flow.

[0067] 7, the control is switched from the first feedback control to the second feedback control when the sensor holding member comes into contact with the intermediate transfer belt. In addition, with this switch to the second feedback control, the abnormality determination is switched from abnormality determination based on the rotation speed of the drive roller (drive roller speed abnormality determination unit 41) to abnormality determination based on the rotation speed of the intermediate transfer belt (belt speed abnormality determination unit 42).

[0068] 8, the scale sensor 32 is held by a sensor holding member 29 serving as a detection unit holding member, and the sensor holding member 29 is configured to be switchable between a state in contact with the inner circumferential surface of the intermediate transfer belt 15 and a state in which it is separated (non-contact state) by a contact / separation mechanism described below. When the scale sensor 32 is not used, the sensor holding member 29 is separated from the intermediate transfer belt 15 as shown by the two-dot chain line in FIG. 8, thereby suppressing wear on the intermediate transfer belt 15 due to contact between the sensor holding member 29 and the intermediate transfer belt 15. On the other hand, when the scale sensor 32 is used, by bringing the sensor holding member 29 into contact with the intermediate transfer belt 15, the scale sensor 32 is positioned parallel to and at a predetermined distance from the scale mark arrangement surface on the intermediate transfer belt 15, thereby enabling the scale sensor 32 to detect the scale marks M with high accuracy.

[0069] Therefore, to perform the second feedback control using the scale sensor 32, the sensor holding member 29 must be brought into contact with the intermediate transfer belt 15 and placed in a position where the scale sensor 32 can accurately detect the scale marks M. For this reason, in the example shown in Figure 7, the control is switched to the second feedback control at the timing when the sensor holding member 29 is brought into contact with the intermediate transfer belt 15.

[0070] FIG. 9 shows yet another flow.

[0071] 9, the control is switched from the first feedback control to the second feedback control when the photosensitive member and the intermediate transfer belt come into contact with each other. With this switch to the second feedback control, the abnormality determination is switched from the abnormality determination based on the rotation speed of the drive roller (drive roller speed abnormality determination unit 41) to the abnormality determination based on the rotation speed of the intermediate transfer belt (belt speed abnormality determination unit 42).

[0072] In this case, as shown in FIGS. 10 and 11 , the transfer device 7 includes a contact / separation mechanism 50 that brings both the primary transfer roller 16 and the sensor holding member 29 into contact with and separates them from the intermediate transfer belt 15. When the primary transfer roller 16 comes into contact with and separates from the inner circumferential surface of the intermediate transfer belt 15, the sensor holding member 29 also comes into contact with and separates from the inner circumferential surface of the intermediate transfer belt 15 in conjunction with this contact / separation operation. Specifically, the contact / separation mechanism 50 includes multiple link members 51A-51D that hold the primary transfer roller 16 and the sensor holding member 29, and a cam member 52 that moves each of the link members 51A-51D. The cam member 52 is rotatably provided, and when the cam member 52 rotates, a receiving member (bearing) 53 provided on the link member 51A is pushed and moved. As a result, the link member 51A having the receiving member 53 is pushed and moved to the left in FIG. 11 against the tensile force of the spring 54. As link member 51A moves, the other link members 51B to 51D rotate about the fulcrum, and primary transfer roller 16 and sensor holding member 29 move away from intermediate transfer belt 15. At the same time, intermediate transfer belt 15 moves away from photoconductor 11. As a result, primary transfer roller 16, sensor holding member 29, and photoconductor 11 are no longer in contact with intermediate transfer belt 15, which reduces wear on intermediate transfer belt 15 caused by these members coming into contact with intermediate transfer belt 15. In this case, the contact and separation movement of primary transfer roller 16 and the contact and separation movement of sensor holding member 29 are performed in conjunction with each other, so the number of components that serve as drive sources for the contact and separation mechanisms can be reduced, resulting in cost and space savings.

[0073] However, in this configuration, when the sensor holding member 29 is separated from the intermediate transfer belt 15, the scale sensor 32 cannot accurately detect the scale marks on the intermediate transfer belt 15, as in the configuration shown in FIG. 8 above. Therefore, to perform the second feedback control, the sensor holding member 29 must be placed in contact with the intermediate transfer belt 15 so that the scale sensor 32 can accurately detect the scale marks. For this reason, in the example shown in FIG. 9, the control is switched to the second feedback control depending on the timing when the sensor holding member 29 comes into contact with the intermediate transfer belt 15, i.e., the timing when the photosensitive member 11 and the intermediate transfer belt 15 come into contact with each other. The timing when the photosensitive member 11, the primary transfer roller 16, or the sensor holding member 29 comes into contact with the intermediate transfer belt 15 can be determined from a detection signal of a sensor that detects the rotational phase of the cam member 52, or the like.

[0074] FIG. 12 shows yet another flow.

[0075] In the example shown in Fig. 12, when control is switched from first feedback control to second feedback control, the abnormality determination based on the rotational speed of the drive roller is stopped, and after a predetermined time has elapsed, the abnormality determination is switched from abnormality determination based on the rotational speed of the drive roller to abnormality determination based on the rotational speed of the intermediate transfer belt. Other than that, the flow is the same as that shown in Fig. 4. In the example shown in Fig. 12, the switch from first feedback control to second feedback control is performed when the scale sensor can accurately detect the scale marks (for example, when the sensor holding member 29 shown in Fig. 8 is in contact with the intermediate transfer belt 15, or when the photosensitive element 11 and the intermediate transfer belt 15 shown in Fig. 10 are in contact).

[0076] The reason why the abnormality determination is switched after a predetermined time has elapsed is that when the control is switched from the first feedback control to the second feedback control, the speeds of the drive roller and the intermediate transfer belt may temporarily fluctuate, as shown in Fig. 13. If the abnormality determination is made based on the speed fluctuations at this time, there is a risk that an abnormality will be determined even though no malfunction or the like has occurred.

[0077] Therefore, in this example, as shown in FIG. 13, when control is switched from first feedback control to second feedback control, abnormality determination based on the rotational speed of the drive roller is stopped. At this time, abnormality determination based on the rotational speed of the intermediate transfer belt is also not performed. After a predetermined time has elapsed and the conditions that could cause speed fluctuations in the drive roller and intermediate transfer belt are no longer met, abnormality determination based on the rotational speed of the drive roller is switched to abnormality determination based on the rotational speed of the intermediate transfer belt. This prevents unintended abnormality determination due to speed fluctuations when control is switched, thereby avoiding unnecessary downtime of the image forming apparatus (stop or interruption due to abnormality determination).

[0078] The above describes an embodiment of the present invention using the example of controlling the rotation speed of an intermediate transfer belt, but the present invention is not limited to intermediate transfer belts used in electrophotographic image forming apparatuses, and can also be applied to control of other belts.

[0079] For example, the present invention is also applicable to the control of a conveyor belt 62 that conveys paper (cut paper cut to a predetermined size) in an inkjet image forming apparatus 200 as shown in Fig. 14. That is, the present invention is applicable not only to a transfer device as a belt drive device equipped with an intermediate transfer belt as described above, but also to a belt drive device (belt conveying device) equipped with a conveyor belt 62 as shown in Fig. 14. The inkjet image forming apparatus 200 shown in Fig. 14 includes a paper feed unit 61 that supplies paper, an endless conveyor belt 62 that conveys the paper supplied from the paper feed unit 61, an image forming unit 63 that ejects ink onto the paper on the conveyor belt 62 to form an image, and a paper discharge unit 64 to which the paper on which the image has been formed is discharged.

[0080] A plurality of head units 65Bk, 65C, 65M, and 65Y are provided in the image forming section 63. These head units 65Bk, 65C, 65M, and 65Y are so-called line-type head units that eject ink without moving toward the transported paper.

[0081] FIG. 15 shows an example of the configuration of a line type head unit.

[0082] In the configuration shown in Fig. 15, four head units 65Bk, 65C, 65M, and 65Y that eject black (Bk), cyan (C), magenta (M), and yellow (Y) inks are arranged in this order from the upstream side in the paper transport direction (recording medium transport direction) X in which paper P is transported. Note that the order of the head units 65Bk, 65C, 65M, and 65Y may be other than that shown in Fig. 15. Furthermore, the ink colors used may be colors other than yellow, magenta, cyan, and black.

[0083] Each of the head units 65Bk, 65C, 65M, and 65Y has four liquid ejection heads 66. The liquid ejection heads 66 serving as liquid ejection sections have a plurality of nozzles 67, and ink (liquid) is ejected from each nozzle 67 onto the paper P. The liquid ejection heads 66 are arranged alternately across the entire width of the image formation area on the paper P.

[0084] The conveyor belt 62 conveys the paper P, and when the paper reaches a position facing each of the head units 65Bk, 65C, 65M, and 65Y, ink is ejected from each liquid ejection head 66 onto the paper P, forming an image. The conveyor belt 62 may be configured to electrostatically attract the paper P using a charging means, or may be configured to attract the paper P by sucking air through suction holes provided in the conveyor belt 62 using a suction fan.

[0085] As described above, in the inkjet image forming apparatus 200 equipped with the line-type image forming unit 63, an image is formed on the paper P while it is being transported by the transport belt 62, and therefore it is necessary to appropriately control the rotation speed (transport speed) of the transport belt 62. For this reason, as shown in Fig. 14, a scale sensor 68 is provided as a position indication detector that detects scale marks (position indication portions) on the transport belt 62, and an encoder 69 is provided as a rotation angle detector that detects the rotation angle of a drive roller 70 that drives and rotates the transport belt 62. The rotation speed of the transport belt 62 is controlled by controlling the rotation speed of a motor 71 that drives and rotates the drive roller 70 based on the detection results of at least one of the scale sensor 68 and the encoder 69.

[0086] Here, when controlling the rotation speed of the conveyor belt 62, the same problem as when controlling the rotation speed of the transfer belt occurs: If the diameter of the drive roller 70 that rotates the conveyor belt 62 changes due to temperature changes or the like, the rotation speed of the drive roller 70 stabilizes at a value different from the original target value, which changes the relative relationship between the stable rotation speed and the range (upper and lower limits) for abnormality determination, causing a problem that an abnormality in the rotation speed cannot be correctly determined.

[0087] Therefore, by applying the present invention to an inkjet image forming apparatus 200 equipped with such a conveyor belt 62, it becomes possible to accurately determine whether the conveyor belt 62 is abnormal without being affected by fluctuations in roller diameter.

[0088] In the inkjet image forming apparatus to which the present invention is applied, the term "liquid ejection head" refers to a functional component that ejects or sprays liquid from nozzles. The ejected liquid may have any viscosity or surface tension that allows it to be ejected from the head. While not particularly limited, it is preferable that the viscosity of the ejected liquid be 30 mPa·s or less at room temperature and pressure, or upon heating or cooling. More specifically, the liquid may be a solution, suspension, emulsion, or the like containing a solvent such as water or an organic solvent, a colorant such as a dye or pigment, a polymerizable compound, a resin, a surfactant, or another functional material, a biocompatible material such as DNA, amino acids, proteins, or calcium, or an edible material such as a natural dye. These liquids can be used, for example, as inkjet inks, surface treatment solutions, components of electronic or light-emitting elements, liquids for forming resist patterns for electronic circuits, and liquid materials for 3D modeling.

[0089] Energy sources for ejecting liquid include piezoelectric actuators (laminated piezoelectric elements and thin-film piezoelectric elements), thermal actuators that use electrothermal conversion elements such as heating resistors, and electrostatic actuators consisting of a vibration plate and an opposing electrode.

[0090] In the present invention, the term "liquid ejection unit" refers to a liquid ejection head integrated with functional parts and mechanisms, and includes an assembly of parts related to ejecting liquid. For example, the term "liquid ejection unit" includes a combination of a liquid ejection head and at least one of a head tank, a supply mechanism, a maintenance and recovery mechanism, and a liquid circulation device.

[0091] Here, "integrated" includes, for example, a liquid ejection head and a functional part or mechanism fixed to each other by fastening, bonding, engaging, etc., or one held movably relative to the other. The liquid ejection head, functional part, or mechanism may also be configured to be detachable from each other.

[0092] Furthermore, the head unit may include a single liquid ejection head in addition to the head unit including the liquid ejection heads in the above-described embodiments.

[0093] Furthermore, the inkjet image forming apparatus to which the present invention is applied is not limited to those that visualize meaningful images such as letters and figures by ejecting liquid, but also includes those that form patterns that have no meaning in themselves and those that form three-dimensional images.

[0094] The term "image forming apparatus" may also include means for feeding, transporting, and discharging materials onto which liquid can be attached, as well as pre-processing devices and post-processing devices.

[0095] The above-mentioned "object onto which a liquid can adhere" refers to an object to be transported onto which a liquid can adhere at least temporarily, such as an object onto which the liquid adheres and sticks, or an object onto which the liquid adheres and penetrates, etc. Specific examples include media such as paper, recording paper, film, cloth, electronic circuit boards, electronic components such as piezoelectric elements, powder layers, organ models, and test cells, and unless otherwise specified, includes all objects onto which a liquid can adhere.

[0096] Furthermore, the material of "something to which a liquid can adhere" may be anything to which a liquid can adhere, even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, or ceramics.

[0097] Furthermore, the "object onto which liquid can be attached" may be a sheet (such as cut paper) that has been cut to a predetermined size in advance, or a continuous sheet (such as roll paper) that has been formed into a long length. [Explanation of symbols]

[0098] 15 Intermediate transfer belt (belt) 24 Motor (drive unit) 25 Drive roller (drive unit) 29 Sensor holding member (detection unit holding member) 30 Belt drive control device 31 Encoder (rotation angle detection unit) 32 Scale sensor (position display detection section) 33 Drive roller speed calculation unit (first rotation speed calculation unit) 34 Belt speed calculation unit (second rotation speed calculation unit) 39 Control switching unit 40 Judgment switching unit 41 Drive roller speed abnormality determination unit (first determination unit) 42 Belt speed abnormality determination unit (second determination unit) 62 Conveyor belt (belt) 68 Scale sensor (position display detection part) 69 Encoder (rotation angle detection unit) 70 Drive roller (drive unit) 71 Motor (drive unit) 100 Image forming device 200 Image forming device M Scale mark (position display) P Paper (recording medium) [Prior art documents] [Patent documents]

[0099] [Patent Document 1] Patent No. 4351509

Claims

1. a rotation angle detection unit that detects the rotation angle of a drive unit that drives and rotates the belt; a first rotation speed calculation unit that calculates the rotation speed of the drive unit based on the detection result of the rotation angle detection unit; a position indication detection unit that detects a position indication unit provided on the belt; a second rotation speed calculation unit that calculates the rotation speed of the belt based on the detection result of the position display detection unit; a control switching unit that switches between a first feedback control that controls the rotation speed of the drive unit based on a calculation result of the first rotation speed calculation unit and a second feedback control that controls the rotation speed of the drive unit based on each of the calculation results of the first rotation speed calculation unit and the second rotation speed calculation unit; a first determination unit that determines whether the rotation speed of the drive unit is within a predetermined range based on a calculation result of the first rotation speed calculation unit; a second determination unit that determines whether the rotation speed of the belt is within a predetermined range based on a calculation result of the second rotation speed calculation unit; a determination switching unit that selects the determination by the first determination unit when the control switching unit selects the first feedback control, and selects the determination by the second determination unit when the control switching unit selects the second feedback control, the control switching unit switches from the first feedback control to the second feedback control when the position display detection unit is able to detect the position display unit; the determination switching unit, when switching from the first feedback control to the second feedback control, switches from determination by the first determination unit to determination by the second determination unit; the second determination unit determines whether the rotation speed of the belt calculated by the second rotation speed calculation unit is within a difference range set so that the difference between an upper limit value and a lower limit value with respect to a target value during the first feedback control is the same ratio as that of the difference between an upper limit value and a lower limit value with respect to the target value during the first feedback control, and determines that an abnormality has occurred when the rotation speed of the belt calculated by the second rotation speed calculation unit exceeds the difference range.

2. A belt drive control device as described in claim 1, wherein when a detection unit holding member that holds the position display detection unit and the belt are switched from a state in which they are spaced apart to a state in which they are in contact with each other, the control switching unit switches from the first feedback control to the second feedback control, and the judgment switching unit switches from judgment by the first judgment unit to judgment by the second judgment unit.

3. A belt drive control device as described in claim 2, wherein when the image carrier and the belt are switched from a state where they are spaced apart to a state where they are in contact with each other in conjunction with the operation of switching the detection unit holding member and the belt from a state where they are spaced apart to a state where they are in contact with each other, the control switching unit switches from the first feedback control to the second feedback control, and the judgment switching unit switches from judgment by the first judgment unit to judgment by the second judgment unit.

4. A belt drive control device as described in any one of claims 1 to 3, wherein the control switching unit stops judgment by the first judgment unit for a predetermined time after switching from the first feedback control to the second feedback control, and then the judgment switching unit switches from judgment by the first judgment unit to judgment by the second judgment unit.

5. A belt drive control device described in any one of claims 1 to 4, wherein the belt is an intermediate transfer belt onto which images on multiple image carriers are superimposed and transferred.

6. A drive unit that rotates and drives the belt; A belt drive device comprising the belt drive control device according to any one of claims 1 to 5, which controls the rotation speed of the drive unit.

7. An image forming unit that forms an image on a recording medium; An image forming apparatus comprising the belt driving device according to claim 6.

Images