JP2010217730A - Speed control method, speed control device, and image forming device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speed control means which can control the conveyance speed of an intermediate transfer belt to a target value even when the interval between a plurality of detecting means for detecting the conveyance speed of the intermediate transfer belt changes. <P>SOLUTION: The speed control device includes sensors 22, 42 arranged with a predetermined interval and detecting the scale 14a of the intermediate transfer belt 14, and is provided with a means for repeatedly measuring at a predetermined time interval a pulse interval time T<SB>1</SB>and a phase difference time T<SB>p3</SB>which are cycles of pulse signals outputted from the sensors. The speed control device has: an extension/contraction determination means which determines the extension/contraction of the intermediate transfer belt and the extension/contraction of the predetermined interval based on the difference between a latest pulse interval time and a predefined reference pulse interval time and the difference between a latest phase difference time and a predefined reference phase difference time; and a conveyance speed target value determination means which determines a target value of conveyance speed control of the intermediate transfer belt based on the determination result of the extension/contraction determination means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a speed control method and a speed control apparatus for controlling the transport speed of an endless transport body, and an image forming apparatus having the speed control method.

  Some color electrophotographic image forming apparatuses use an intermediate transfer belt which is an endless carrier. Specifically, the images formed on the plurality of photosensitive drums are superposed on the intermediate transfer belt, and further transferred onto the transfer paper. In such an image forming apparatus, in order to improve the image quality, it is necessary to always convey the intermediate transfer belt at a constant conveyance speed. This is because, if the intermediate transfer belt is not always transported at a constant transport speed, color misregistration or the like may occur. In order to always convey the intermediate transfer belt at a constant conveyance speed, for example, a method is used in which a scale (scale) is provided on the intermediate transfer belt, which is directly read by a detection unit, and speed feedback is performed.

  By the way, since the intermediate transfer belt may expand and contract due to environmental changes such as temperature and humidity, the speed of the intermediate transfer belt cannot be made constant only by reading the scale with one detection means and feeding back the speed. Therefore, a technique is disclosed in which the scale on the intermediate transfer belt is read by a plurality of detection means and the change in the phase difference time is reflected in the speed feedback condition, thereby detecting the expansion and contraction of the intermediate transfer belt and correcting the speed. (For example, refer to Patent Document 1).

  However, in the conventional method of reading the scale on the intermediate transfer belt with a plurality of detection means, the control is performed on the premise that the interval between the plurality of detection means does not change even if there is an environmental change such as temperature or humidity. Specifically, the intervals between the plurality of detection means are always constant, and speed correction is performed on the basis of the intervals, assuming that all changes in the scale phase difference time are expansion and contraction of the intermediate transfer belt. In other words, the intermediate transfer belt is not expanded and contracted, and even when only the interval between the plurality of detection means fluctuates, speed correction is performed as the expansion and contraction of the intermediate transfer belt, so the conveyance speed of the intermediate transfer belt deviates from the target value. As a result, there is a problem that color misregistration or the like occurs and the image quality of the image forming apparatus deteriorates.

  In view of the above points, a speed control method and a speed control device capable of controlling the transport speed of the endless transport body to a target value even when the intervals of the plurality of detection means for detecting the transport speed of the endless transport body change, It is another object of the present invention to provide an image forming apparatus having the same.

  The speed control device includes an endless transport body that is transported in a first direction, and reflection units and non-reflections that are alternately arranged on the endless transport body along the first direction at a constant period. A scale having a portion, a first pulse signal output means for outputting a first pulse signal corresponding to the constant period of the scale, and a predetermined interval with respect to the first pulse signal output means Second pulse signal output means for outputting a second pulse signal corresponding to the fixed period of the scale, and a pulse interval time which is a period of the first pulse signal and the second pulse signal. Pulse interval time measuring means for repeatedly measuring at a predetermined time interval, phase difference time measuring means for repeatedly measuring a phase difference time between the first pulse signal and the second pulse signal at a predetermined time interval, and the pulse Measurement of interval time measurement means Based on the difference between the latest pulse interval time and the predetermined reference pulse interval time, and the difference between the latest phase difference time measured by the phase difference time measuring means and the predetermined reference phase difference time, Based on the determination result of the expansion / contraction determination means and the determination result of the expansion / contraction determination means, the target value for the conveyance speed control of the endless conveyance body is determined. And a conveyance speed target value determining means.

  In addition, the speed control apparatus method is alternately arranged on the endless carrier conveyed in the first direction at a constant cycle along the first direction using the first pulse signal output means. A first pulse signal output step for outputting a first pulse signal corresponding to the predetermined period of the scale having a reflecting portion and a non-reflecting portion, and a predetermined interval with respect to the first pulse signal output means A second pulse signal output step of outputting a second pulse signal corresponding to the fixed period of the scale using the second pulse signal output means arranged in the step, the first pulse signal, and the A pulse interval time measurement step of repeatedly measuring a pulse interval time, which is a cycle of the second pulse signal, at a predetermined time interval; and a phase difference time between the first pulse signal and the second pulse signal at a predetermined time interval. Repeat with A phase difference time measuring step, a difference between a latest pulse interval time measured in the pulse interval time measuring step and a predetermined reference pulse interval time, and a latest phase difference time measured by the phase difference time measuring means; Based on a difference between a predetermined reference phase difference time and an extension / contraction determination step for determining whether or not the endless carrier is expanded / contracted and expansion / contraction at the predetermined interval, and based on a determination result in the expansion / contraction determination step. And a transport speed target value determining step for determining a target value for transport speed control of the endless transport body.

  According to the disclosed technology, a speed control method and a speed control device capable of controlling the transport speed of the endless transport body to the target value even when the intervals of the plurality of detection means for detecting the transport speed of the endless transport body change, In addition, an image forming apparatus having the same can be provided.

1 is a diagram illustrating a schematic structure of an image forming apparatus according to a first embodiment. It is a functional block diagram which illustrates the function of a control part. FIG. 6 is a functional block diagram illustrating functions of an intermediate transfer FB control unit. It is a figure for demonstrating the general speed control using an intermediate transfer belt scale. FIG. 10 is a diagram for explaining a change in pulse output when the intermediate transfer belt is extended. FIG. 6 is a diagram for explaining extension correction of an intermediate transfer belt using two intermediate transfer scale detection sensors. FIG. 3 is a diagram illustrating a state where an intermediate transfer belt is extended. It is a figure which illustrates the state where the space | interval of two intermediate transfer scale detection sensors was extended. It is an example of the flowchart regarding the correction control which concerns on 1st Embodiment. FIG. 6 is a diagram illustrating a state in which an interval between an intermediate transfer belt and two intermediate transfer scale detection sensors is extended. It is an example of the flowchart regarding the correction control which concerns on 2nd Embodiment. FIG. 6 is a diagram illustrating a schematic structure of an image forming apparatus according to a third embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

<First Embodiment>
[Structure of Image Forming Apparatus According to First Embodiment]
FIG. 1 is a diagram illustrating a schematic structure of the image forming apparatus according to the first embodiment. Referring to FIG. 1, an image forming apparatus 10 is a color image forming apparatus using an intermediate transfer belt that is an endless conveyance body, and includes a scanner unit 11, a photosensitive drum 12a, a photosensitive drum 12b, and a photosensitive drum. A body drum 12c, a photosensitive drum 12d, a fixing unit 13, an intermediate transfer belt 14, a secondary transfer roller 15, a repulsive roller 16, a registration roller 17, a paper feed unit 18, and a paper feed roller 19. , Paper transport roller 20, paper discharge unit 21, intermediate transfer scale detection sensors 22 and 42, drive roller 23, driven roller 24, and control unit 30. Reference numeral 90 denotes a transfer sheet.

  The scanner unit 11 has a function of reading a document. The photosensitive drums 12a to 12d have a function of forming images of Y (yellow) color, C (cyan) color, M (magenta) color, and K (black) color, respectively, when irradiated with laser light. The fixing unit 13 has a function of fixing the transferred toner image on the transfer paper 90.

  The drive roller 23 is rotationally driven by an intermediate transfer belt drive motor (not shown), and the intermediate transfer belt 14 is conveyed accordingly. The driven roller 24 is driven by the driving roller 23. The intermediate transfer belt 14 has a function of superimposing images for each color formed by the photosensitive drums 12a to 12d. The secondary transfer roller 15 has a function of transferring the image on the intermediate transfer belt 14 to the transfer paper 90.

  The repulsive roller 16 is disposed at a portion facing the secondary transfer roller 15 and has a function of generating and maintaining a nip between the intermediate transfer belt 14 and the secondary transfer roller 15. The registration roller 17 has a function of performing skew correction of the transfer paper 90, transport of the transfer paper 90, and the like. The paper feed unit 18 has a function of loading the transfer paper 90. The paper feed roller 19 has a function of feeding the transfer paper 90 from the paper feed unit 18 to the paper transport roller 20. The paper transport roller 20 has a function of transporting the transfer paper 90 delivered from the paper feed roller 19 to the registration rollers 17. The paper discharge unit 21 has a function of discharging the transfer paper 90 on which an image has been transferred and fixed.

  An intermediate transfer belt scale 14 a is formed on the intermediate transfer belt 14. The intermediate transfer belt scale 14a is a scale having reflective portions and non-reflective portions that are alternately arranged at a constant cycle along the transport direction. Intermediate transfer scale detection sensors 22 and 42 are arranged at positions near the intermediate transfer belt 14 where the intermediate transfer belt scale 14a can be read. The intermediate transfer scale detection sensor 22 has a function as a first pulse signal output unit that outputs a first pulse signal corresponding to a certain period of the intermediate transfer belt scale 14 a formed on the intermediate transfer belt 14. The intermediate transfer scale detection sensor 42 is arranged at a predetermined interval with respect to the intermediate transfer scale detection sensor 22, and a second pulse signal corresponding to a certain period of the intermediate transfer belt scale 14 a formed on the intermediate transfer belt 14. As a second pulse signal output means.

  The control unit 30 has a function of performing various controls relating to the image forming apparatus 10. The control unit 30 includes, for example, a CPU, a ROM, a main memory, and the like, and various functions of the control unit 30 are realized by a control program recorded in the ROM or the like being read into the main memory and executed by the CPU. . However, a part or all of the control unit 30 may be realized only by hardware. The control unit 30 may be physically configured by a plurality of devices. The details of the function of the control unit 30 will be described later. The above is the schematic structure of the image forming apparatus according to the first embodiment.

[Operation of Image Forming Apparatus According to First Embodiment]
An image read by the scanner unit 11 of the image forming apparatus 10 illustrated in FIG. 1 is transferred to the control unit 30. FIG. 2 is a functional block diagram illustrating functions of the control unit. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof may be omitted. Referring to FIG. 2, the control unit 30 includes an image formation control unit 31, an intermediate transfer control unit 32, a secondary transfer control unit 33, a fixing control unit 34, and a paper feed conveyance control unit 35.

  The image forming control unit 31 is a part that mainly performs control related to driving of the photosensitive drums 12a to 12d. The image forming control unit 31 controls a photoconductor motor control unit 31a that controls a photoconductor motor (not shown) that drives the photoconductor drums 12a to 12d, and a part related to an electrophotographic process such as charging, exposure, and transfer. And an image forming process control unit 31b.

  The intermediate transfer control unit 32 is a part that performs control related to intermediate transfer. The intermediate transfer control unit 32 includes an intermediate transfer motor control unit 32a that controls an intermediate transfer motor (not shown) that drives the intermediate transfer belt 14, and an intermediate transfer FB control unit 32b that performs feedback control of the speed of the intermediate transfer belt 14. And a primary transfer control unit 32c that performs control and the like for transferring the toner images on the photosensitive drums 12a to 12d onto the intermediate transfer belt 14.

  The secondary transfer control unit 33 is a part that performs control related to secondary transfer. The secondary transfer control unit 33 has a secondary transfer motor control unit 33 a that controls a secondary transfer motor (not shown) that drives the secondary transfer roller 15, and a toner image on the intermediate transfer belt 14 on the transfer paper 90. And a transfer control unit 33b for performing transfer control and the like.

  The fixing control unit 34 is a part that performs control related to a fixing function for fixing the toner image transferred onto the transfer paper 90 onto the transfer paper 90. The paper feeding / conveying control unit 35 is a part that performs control including a series of operations from feeding, conveying, and discharging of the transfer paper 90.

  In the image forming apparatus 10, the image read from the scanner unit 11 is transferred to the control unit 30, and the control unit 30 generates image data (hereinafter referred to as image data) formed on the transfer paper 90. The generated image data is imaged on the photosensitive drums 12 a to 12 d by the image formation control unit 31. Subsequently, an image is formed on the intermediate transfer belt 14 by the intermediate transfer control unit 32. Further, the image formed on the intermediate transfer belt 14 is transferred onto the transfer paper 90 when the transfer paper 90 is conveyed from the paper supply unit 18 between the intermediate transfer belt 14 and the secondary transfer roller 15. The

  During this time, a photoreceptor motor (not shown) that drives the photoreceptor drums 12a to 12d is controlled by the photoreceptor motor controller 31a so that a normal image is formed on the transfer paper 90, and the intermediate transfer belt 14 is moved. The intermediate transfer motor (not shown) to be driven is controlled by the intermediate transfer motor controller 32a, and the secondary transfer motor (not shown) to drive the secondary transfer roller 15 is controlled by the secondary transfer motor controller 33a. .

  The image transferred onto the transfer paper 90 passes through the fixing unit 13. At this time, the fixing controller 34 performs control related to a fixing function for fixing the toner image transferred onto the transfer paper 90 onto the transfer paper 90, and the transfer paper 90 is fixed. Subsequently, the transfer paper 90 is discharged to the paper discharge unit 21 by the paper feed conveyance control unit 35.

FIG. 3 is a functional block diagram illustrating functions of the intermediate transfer FB control unit. 3, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description thereof may be omitted. Referring to FIG. 3, the intermediate transfer FB control unit 32b includes a pulse interval time measuring unit 32b ₁ , a phase difference time measuring unit 32b ₂ , an expansion / contraction determining unit 32b _3, and a conveyance speed target value determining unit 32b ₄ . Have.

The pulse interval time measuring means 32b ₁ has a function of measuring a pulse interval time which is a cycle of the first pulse signal and the second pulse signal detected from the intermediate transfer belt scale 14a by the intermediate transfer scale detection sensors 22 and 42. Have. The phase difference time measuring means 32b ₂ has a function of measuring the phase difference time between the first pulse signal and the second pulse signal detected from the intermediate transfer belt scale 14a by the intermediate transfer scale detection sensors 22 and 42.

The expansion / contraction determination unit 32b ₃ is configured to expand and contract the intermediate transfer belt 14 and two intermediate transfer scales based on the pulse interval time measured by the pulse interval time measurement unit 32b ₁ and the phase difference time measured by the phase difference time measurement unit 32b _2. It has a function of determining whether or not the distance between the detection sensors 22 and 42 is expanded or contracted. The conveyance speed target value determination unit 32b ₄ has a function of determining a target value for conveyance speed control of the intermediate transfer belt 14 based on the determination result of the expansion / contraction determination unit 32b ₃ , and the intermediate transfer belt scale 14a. When an intermediate transfer scale detecting sensor 22 and 42, the pulse interval time measuring means 32 b _1, the phase difference time measuring means 32 b _2, and expansion determination unit 32 b _3, the conveying speed target value determining means 32 b _4, first The speed control device according to the embodiment is configured. Details of the processing executed by the speed control device will be described later.
The above is the operation of the image forming apparatus according to the first embodiment.

[Control of intermediate transfer belt]
In the above-described operation, it is important that the intermediate transfer belt 14 is always conveyed at a constant speed in order to improve the image quality. Hereinafter, a control for always transporting the intermediate transfer belt 14 at a constant speed will be described.

FIG. 4 is a diagram for explaining general speed control using the intermediate transfer belt scale. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof may be omitted. Referring to FIG. 4A, an intermediate transfer belt scale 14 a is formed on the intermediate transfer belt 14, and an intermediate transfer scale detection sensor 22 is disposed in the vicinity of the intermediate transfer belt 14. The intermediate transfer belt scale 14a is intended a reflective portion 14b of the width L ₁ at a predetermined reflection factor, in which the non-reflective portion 14c having a width L ₂ less reflectivity than the reflection portion 14b are arranged alternately in a constant cycle It is. The width L ₁ and a width L _2, may be the same width.

  The intermediate transfer scale detection sensor 22 includes a light emitting element 22a, a light receiving element 22b, and a pulse generation unit 22c (not shown). The light emitting element 22a irradiates the intermediate transfer belt scale 14a with light, and the light receiving element 22b receives the reflected light from the intermediate transfer belt scale 14a and generates an electrical signal corresponding to the amount of received light. The pulse generator 22c generates a pulse signal from the electrical signal generated by the light receiving element 22b.

  For example, a light emitting diode or the like can be used as the light emitting element 22a. For example, a photodiode or the like can be used as the light receiving element 22b. For example, a comparator or the like can be used as the pulse generator 22c. The light emitting element 22a, the light receiving element 22b, and the pulse generating unit 22c may be separate components.

  At the time of image formation, the intermediate transfer belt drive motor is activated, and the intermediate transfer belt 14 on which the intermediate transfer belt scale 14a is formed is conveyed. When the intermediate transfer belt 14 is conveyed at a constant speed, the pulse output from the intermediate transfer scale detection sensor 22 has a constant cycle as shown in FIG. However, when the intermediate transfer belt 14 is not stably conveyed (when it is not moving at a constant speed), a pulse with an unstable period is output as shown in FIG.

  The intermediate transfer FB control unit 32b performs speed feedback control by performing control to adjust the rotation speed of the intermediate transfer belt drive motor so that the pulse output from the intermediate transfer scale detection sensor 22 has a constant cycle. In the speed feedback control, for example, the pulse interval time (current pulse interval time) of the pulse signal output from the intermediate transfer scale detection sensor 22 is compared with the target pulse interval time, and the current pulse interval time is shorter. In this case, it is determined that the conveyance speed of the intermediate transfer belt 14 is high, and the speed of the intermediate transfer motor is decreased. Conversely, if the current pulse interval time is longer, the conveyance of the intermediate transfer belt 14 is performed. In this control, it is determined that the speed is low, and the speed of the intermediate transfer motor is increased.

FIG. 5 is a diagram for explaining a change in pulse output when the intermediate transfer belt is extended. 5, the same components as those in FIG. 4 are denoted by the same reference numerals, and the description thereof may be omitted. For example, it is known that the intermediate transfer belt 14 expands and contracts due to environmental changes such as temperature and humidity. In FIG. 5A, the portion A shows a portion where the intermediate transfer belt 14 is extended, and the other portion shows a portion where the intermediate transfer belt 14 is not extended. When the intermediate transfer belt 14 is extended as in the A part, even if the intermediate transfer belt 14 is conveyed at a constant speed, the pulse interval of the intermediate transfer scale detection sensor 22 as in the B part of FIG. It does not match the time T _s is the target pulse interval time T _r, is longer than the target pulse interval time T _r. When the speed control of the intermediate transfer belt drive motor is performed based on the detected pulse interval time T _s , an erroneous transport speed is obtained although the actual transport of the intermediate transfer belt 14 is stable and constant. Will be controlled.

FIG. 6 is a diagram for explaining elongation correction of the intermediate transfer belt using two intermediate transfer scale detection sensors. 6, the same components as those in FIG. 4 are denoted by the same reference numerals, and the description thereof may be omitted. As shown in FIG. 6A, intermediate transfer scale detection sensors 22 and 42 are disposed in the vicinity of the intermediate transfer belt 14. The interval L ₃ between the intermediate transfer scale detection sensor 22 and the intermediate transfer scale detection sensor 42 is an integral multiple of the width L ₁ + the width L ₂ (three times in the example of FIG. 6).

  Similar to the intermediate transfer scale detection sensor 22, the intermediate transfer scale detection sensor 42 includes a light emitting element 42a, a light receiving element 42b, and a pulse generator 42c (not shown). The light emitting element 42a irradiates the intermediate transfer belt scale 14a with light, and the light receiving element 42b receives the reflected light from the intermediate transfer belt scale 14a and generates an electrical signal corresponding to the amount of received light. The pulse generator 42c generates a pulse signal from the electrical signal generated by the light receiving element 42b.

  As the light emitting element 42a, for example, a light emitting diode or the like can be used. For example, a photodiode or the like can be used as the light receiving element 42b. For example, a comparator or the like can be used as the pulse generator 42c. The light emitting element 42a, the light receiving element 42b, and the pulse generating unit 42c may be separate parts.

In FIG. 6B, output A indicates a pulse signal output from the intermediate transfer scale detection sensor 22, and output B indicates a pulse signal output from the intermediate transfer scale detection sensor 42. At the time of image formation, the intermediate transfer belt drive motor is activated, and the intermediate transfer belt 14 on which the intermediate transfer belt scale 14a is formed is conveyed. When the intermediate transfer belt 14 does not expand and contract and is conveyed at a constant speed, the output A and the output B have a constant pulse interval time (= period) T ₁ as shown in FIG. 6B. And the timing at which each pulse edge changes coincides. That is, the phase difference time between output A and output B is zero. FIG. 6 shows a state where neither the expansion / contraction of the intermediate transfer belt 14 nor the expansion / contraction of the interval between the intermediate transfer scale detection sensor 22 and the intermediate transfer scale detection sensor 42 has occurred.

In FIG. 6B, assuming that the phase difference time has changed from zero to _Tp1 , the following equation (1) is established. In Expression (1), T ₀ is a reference pulse interval time, and N _p is a distance between two sensors (converted to the number of pulses).

(T _p1 ÷ N _p ) + T ₀ = T ₁ (1)
The distance between the two sensors (converted to the number of pulses) means how many pulses the interval between the intermediate transfer scale detection sensor 22 and the intermediate transfer scale detection sensor 42 corresponds to in an ideal state. In the case of FIG. 6A, since the interval L ₃ = (width L ₁ + width L ₂ ) × 3, “the distance between two sensors N _p = 3”. The reference pulse interval time is, for example, a value stored in advance in a nonvolatile memory or the like at the time of product shipment, and becomes a target value for the first speed control. That is, initially, the speed is controlled so that the current pulse interval time T ₁ matches the reference pulse interval time T ₀ . However, the target value for speed control may be updated thereafter.

FIG. 7 is a diagram illustrating a state where the intermediate transfer belt is extended (the interval between the two intermediate transfer scale detection sensors is not extended). 7, the same components as those in FIG. 6 are denoted by the same reference numerals, and the description thereof may be omitted. In FIG. 7 (a), when compared with FIG. 6 (a), the width _{L 1} of the reflective portion 14b of the intermediate transfer belt 14 is a width _{L 4,} the width _{L 2} of the non-reflective portion 14c is extended in the width _{L 5} . In FIG. 7B, an output C indicates a pulse signal output from the intermediate transfer scale detection sensor 22, and an output D indicates a pulse signal output from the intermediate transfer scale detection sensor. In a state where the intermediate transfer belt 14 is extended as shown in FIG. 7 (a), the output C and output D as shown in FIG. 7 (b) constant pulse interval time (= cycle) T ₂ and becomes the pulse The interval time (= period) T ₂ is longer than the pulse interval time (= period) T ₁ in the case of FIG. 6B (pulse interval time T ₂ > pulse interval time T ₁ ).

Further, since the intermediate transfer belt 14 is stretched, the timing for detecting the pulse edge is different. That is, the phase difference time between the output C and the output D changes from T _p1 to T _p2 (≠ 0) (phase difference time T _p2 > phase difference time T _p1 ). In the case of FIG.7 (b), the following formula | equation (2) is materialized.

{(T _p2 −T _p1 ) ÷ N _p } + T ₀ = T ₂ Equation (2)
In this case, the target value of the speed control is changed from the reference pulse interval time T ₀ to “{(current phase difference time T _p2 −1 phase difference time T _p1 measured _immediately before) / 2 sensor distance N _p } + By replacing with the “reference pulse interval time T ₀ ”, normal speed control can be performed.

FIG. 8 is a diagram illustrating a state in which the interval between the two intermediate transfer scale detection sensors is extended (the intermediate transfer belt is not extended). 8, the same components as those in FIG. 6 are denoted by the same reference numerals, and the description thereof may be omitted. In FIG. 8 (a), when compared with FIG. 6 (a), the distance _{L 3} of the two intermediate transfer scale detecting sensor 22 and 42 are extended to the distance _{L 6.} In FIG. 8B, an output E indicates a pulse signal output from the intermediate transfer scale detection sensor 22, and an output F indicates a pulse signal output from the intermediate transfer scale detection sensor 42. In elongation correction of the intermediate transfer belt 14 using an intermediate transfer scale detecting sensor 22 and 42 described with reference to FIG. 7, the distance L ₃ of the two intermediate transfer scale detecting sensor 22 and 42 are absolute, temperature Ya as there is no variation in the distance L ₃ due to an environmental change or aging, moisture was determined target value of the speed control.

However, the interval L ₃ may actually change for some reason, and the interval L ₃ may extend to the interval L ₆ as shown in FIG. 8A. In this case, as shown in FIG. 8 (b), the pulse interval time T ₁ is the same as FIG. 6 (b), when the elongation of the intermediate transfer belt 14 (FIG. 7 (a) and 7 ( As in (b), the phase difference time between the output E and the output F changes from T _p1 to T _p3 (≠ 0) (phase difference time T _p3 > phase difference time T _p1 ). As shown in FIG. 8, when the interval between the two intermediate transfer scale detection sensors 22 and 42 is extended, the above-described equation (2) is not established. That is, it becomes like Formula (3).

{(T _p3 −T _p1 ) ÷ N _p } + T ₀ ≠ T ₃ ... (3)
In this case, the target value of the speed control is simply changed from the reference pulse interval time T ₀ to “{(current phase difference time T _p3 −1 phase difference time T _p1 measured _immediately before) ÷ 2 sensor distance N _p. } + Reference pulse interval time T ₀ ], normal speed control cannot be performed. That is, it operates at a transport speed different from the target transport speed of the intermediate transfer belt 14. As a result, the movement time between the adjacent photosensitive drums (12a to 12c) changes, causing a shift between the colors, resulting in a deterioration in image quality.

In FIG. 7 and FIG. 8, when the case has been described where the distance L ₃ of the intermediate transfer case belt 14 is extended and two intermediate transfer scale detecting sensor 22 and 42 is extended, contracting the intermediate transfer belt 14 and If the two intervals L ₃ of the intermediate transfer scale detecting sensor 22 and 42 retracted is the same. In the first embodiment, control as shown in FIG. 9 is performed to prevent the occurrence of such a problem.

FIG. 9 is an example of a flowchart regarding correction control according to the first embodiment. Figure 9 is a process speed control apparatus according to the first embodiment is executed, in which also corresponds to the case where two intervals L ₃ of the intermediate transfer scale detecting sensor 22 and 42 extending. As shown in FIG. 7, when the intermediate transfer belt 14 does not extend the distance L ₃ and elongation, the phase difference time change (T _p1 → T _p2), also varies the pulse interval time (T ₁ → T ₂ ). On the other hand, as shown in FIG. 8, when extending the intermediate transfer belt 14 spacing L ₃ is not extended, although the phase difference time changes (T _p1 → T _p3), not the pulse interval time is changed (T ₁ ). Therefore, instead of determining the target value of the conveyance speed of the intermediate transfer belt 14 only by the phase difference time as in the prior art, the target value of the conveyance speed of the intermediate transfer belt 14 is determined in consideration of the phase difference time and the pulse interval time. decide.

Hereinafter, this will be specifically described with reference to FIG. Note that a reference pulse interval time T ₀ and a distance N _p between two sensors in a state where the interval L ₃ between the two intermediate transfer scale detection sensors 22 and 42 is not extended are set as initial values (known values).

In step 100 at the beginning, the pulse interval time measuring means 32 b ₁ measures the current pulse interval time _{T n} in the motor control period (S100). Then, in step 110, the phase difference time measurement means 32 b ₂ measures the current phase difference time _{T pn} (S110). Next, at step 120, the intermediate transfer FB control unit 32b determines whether or not the current phase difference time _Tpn measured at step 110 has changed with respect to the phase difference time _Tp0 measured _immediately before.

If it is determined in step 120 that it has changed (in the case of Yes), in step 130, the intermediate transfer FB control unit 32b determines that “{(the phase difference measured before the current phase difference time T _pn −1). Time T _p0 ) ÷ 2 sensor distance N _p } + reference pulse interval time T ₀ ] is calculated (S 130).

Next, in step 140, the intermediate transfer FB control unit 32b calculates “{(current phase difference time T _pn −1 phase difference time T _p0 measured _immediately before) / 2 inter-sensor distance N _p } + Absolute value X = | [{(current phase difference time T _pn −1) measured before the reference pulse interval time T ₀ ”and“ current pulse interval time T _n ”measured in step 100 Phase difference time T _p0 ) ÷ 2 sensor distance N _p } + reference pulse interval time T ₀ ] −current pulse interval time T _n | is calculated (S 140).

Next, at step 150, the expansion / contraction determination means 32b ₃ determines whether or not the absolute value X of the difference is equal to or less than a predetermined threshold T _th1 (S150). The predetermined threshold value T _th1 is preferably controlled to a value close to zero, but can be set to an arbitrary value in consideration of a detection error or the like. If it is determined in step 150 that “it is equal to or less than a predetermined threshold” (in the case of Yes), the phase difference time T _pn measured _immediately before the current phase difference time T _pn due to the expansion / contraction of the intermediate transfer belt 14. It can be determined that it has changed with respect to _p0 . In this case, in step 160, the conveying speed target value determining means 32 b ₄ is the target value of conveying speed of the intermediate transfer belt 14, calculated in step 130 from the reference pulse interval time T ₀ "{(the current phase difference Time T _pn −1—previous phase difference time T _p0 ) ÷ 2 sensor distance N _p } + reference pulse interval time T ₀ ”(S160).

If it is not determined in step 150 that it is “below the predetermined threshold” (in the case of No),
It can be determined that the current phase difference time T _pn has changed with respect to the phase difference time T _p0 measured _immediately before because the interval between the two intermediate transfer scale detection sensors 22 and 42 is expanded or contracted. In this case, in step 170, the conveying speed target value determining means 32 b ₄ is the target value of conveying speed of the intermediate transfer belt 14, the reference pulse interval time T ₀ the current pulse interval time measured in step 100 from the T _n (S170).

  If it is not determined that the state has changed in step 120 (in the case of No), the process ends (the target value of the conveyance speed of the intermediate transfer belt 14 is not updated).

In the description of steps 100 to 170 above, “reference phase difference time” may be used instead of “phase difference time T _p0 measured _immediately before”. Here, the “reference phase difference time” is a reference phase difference time determined in advance at the time of factory shipment or adjustment by a serviceman, and is a value stored in a nonvolatile memory or the like. The above is the description of the flowchart relating to the correction control according to the first embodiment.

  The main factors of expansion / contraction of the intermediate transfer belt 14 and expansion / contraction of the interval between the two intermediate transfer scale detection sensors 22 and 42 are due to environmental changes such as temperature and humidity. Changes in pulse interval time and phase difference time due to environmental changes such as temperature and humidity are very slow in time compared to speed fluctuations that normally require feedback control. Therefore, the pulse interval time and phase difference time detection period used for correcting the elongation of the intermediate transfer belt 14 can be sufficiently handled by using values averaged over a period longer than the detection period for normal speed feedback control. Is possible.

  For example, using a value obtained by averaging a plurality of pulse interval times measured during continuous operation within a certain time and a value obtained by averaging a plurality of phase difference times within a certain time, intermediate transfer is performed according to the flowchart of FIG. The presence or absence of expansion / contraction of the belt 14 and the interval between the two intermediate transfer scale detection sensors 22 and 42 can be determined. Further, the expansion / contraction amount of the intermediate transfer belt 14 and the expansion / contraction amount of the interval between the two intermediate transfer scale detection sensors 22 and 42 can be predicted by the linear expansion coefficient of the material forming them, and are averaged. The time interval may be set as appropriate as long as the predicted fluctuation amount does not affect the image quality.

Further, temperature / humidity measuring means for measuring the ambient temperature and / or ambient humidity of the intermediate transfer belt 14 and the two intermediate transfer scale detection sensors 22 and 42, and the conveyance speed target value are determined based on the measurement results of the temperature / humidity measuring means. There may be provided a timing control means for controlling the timing at which the means 32b ₄ determines the target value for the conveyance speed control of the intermediate transfer belt 14. Thereby, conveyance speed control in consideration of ambient temperature and / or ambient humidity is possible. For example, the target value of the conveyance speed control is updated only when the temperature changes by a predetermined value or more.

Thus, according to the first embodiment, the current pulse interval time _Tn and the current phase difference time _Tpn are measured. Then, “{(current phase difference time T _pn −1 phase difference time T _p0 measured _immediately before) / 2 distance between sensors N _p } + reference pulse interval time T ₀ ” and “current pulse interval time T _n Is calculated, and it is determined whether or not the absolute value X of the difference is equal to or less than a predetermined threshold value T _th1 . Based on the determination result, it is determined whether the intermediate transfer belt 14 has expanded or contracted, or whether the interval between the two intermediate transfer scale detection sensors 22 and 42 has expanded or contracted. Based on the determination result, the target value of the conveyance speed of the intermediate transfer belt 14 is expressed as “{(current phase difference time T _pn −1 phase difference time T _p0 measured _immediately before) ÷ two-sensor distance N. _p } + reference pulse interval time T ₀ ”or“ current pulse interval time T _n ”. As a result, the conveyance speed of the intermediate transfer belt 14 can be controlled to a predetermined value not only when the intermediate transfer belt 14 expands and contracts but also when the interval between the two intermediate transfer scale detection sensors 22 and 42 expands and contracts. Therefore, it is possible to prevent a decrease in image quality.

<Second Embodiment>
In the first embodiment, the current pulse interval time T _n and the current phase difference time T _pn are measured, and the intermediate transfer belt 14 is expanded or contracted, or the interval between the two intermediate transfer scale detection sensors 22 and 42 is An example is shown in which it is determined whether or not it has been expanded and contracted, and the target value of the conveyance speed of the intermediate transfer belt 14 is updated based on the determination result. However, there may be a case where the expansion and contraction of the intermediate transfer belt 14 and the expansion and contraction of the interval between the two intermediate transfer scale detection sensors 22 and 42 occur simultaneously. In the second embodiment, a processing example in such a case will be described. The schematic structure and the like of the image forming apparatus are the same as those in the first embodiment. Hereinafter, the description of the parts common to the first embodiment will be omitted, and description will be made focusing on the parts different from the first embodiment.

FIG. 10 is a diagram illustrating a state in which the distance between the intermediate transfer belt and the two intermediate transfer scale detection sensors is extended. 10, the same components as those in FIGS. 7 and 8 are denoted by the same reference numerals, and the description thereof may be omitted. In FIG. 10 (a), the width _{L 1} is the width _{L 4} of the reflective portion 14b of the intermediate transfer belt 14, the width _{L 2} of the non-reflective portion 14c is extended in the width _{L 5.} Further, the interval _{L 3} of the two intermediate transfer scale detecting sensor 22 and 42 are extended to the distance _{L 6.} In FIG. 10B, the output G indicates a pulse signal output from the intermediate transfer scale detection sensor 22, and the output H indicates a pulse signal output from the intermediate transfer scale detection sensor 42.

As shown in FIG. 10 (b), the output G and output H is constant pulse interval time (= cycle) _{T 2} and becomes a pulse when the pulse interval time (= cycle) _{T 2} FIG. 6 (b) It becomes longer than the interval time (= period) T ₁ (pulse interval time T ₂ > pulse interval time T ₁ ). Further, the phase difference time T _p4 ≠ 0 between the output G and the output H (phase difference time T _p4 > phase difference time T _p1 ). The phase difference time T _p4 is added to the phase difference time T _p3 generated by elongation of the phase difference caused by the elongation of the intermediate transfer belt 14 time T _p2 and two intermediate transfer scale detection interval L ₃ sensors 22 and 42 (T _p4 = T _p2 + T _p3 ).

Here, if only the intermediate transfer belt 14 is stretched, when the two intermediate transfer scale detection interval L ₃ sensors 22 and 42 do not extend Given (for T _{p3 = 0),} equation (4) is satisfied .

(T _p2 −T _p1 ) ÷ T _p1 = (T ₂ −T ₁ ) ÷ T ₁ Formula (4)
However, the intermediate transfer belt 14, if both elongation of the distance L ₃ of the two intermediate transfer scale detecting sensor 22 and 42, as shown in equation (5), one is a right-hand and left-hand sides of equation (4) I will not do it.

(T _p4 −T _p1 ) ÷ T _p1 ≠ (T ₂ −T ₁ ) ÷ T ₁ Formula (5)
That is, it can be seen that (T ₂ −T ₁ ) ÷ T ₁ is generated by the elongation of the intermediate transfer belt 14. Further, the rate of change in expansion and contraction of the intermediate transfer belt 14 is expressed as in Expression (6).

{(T _p4 −T _p1 ) ÷ T _p1 } − {(T ₂ −T ₁ ) ÷ T ₁ } (6)
An intermediate transfer belt 14, if both elongation of the distance L ₃ of the two intermediate transfer scale detecting sensor 22 and 42, taking into account the rate of change of expansion and contraction of the intermediate transfer belt 14 shown in equation (6), the target value of conveying speed of the intermediate transfer belt 14, from the reference pulse interval time T ₀ may be replaced with equation (7).

[{(T _p4 −T _p1 ) ÷ T _p1 } − {(T ₂ −T ₁ ) ÷ T ₁ }] × T _p1 + T ₀ Formula (7)
FIG. 11 is an example of a flowchart regarding correction control according to the second embodiment. 11, the same components as those in FIG. 9 are denoted by the same reference numerals, and the description thereof may be omitted. Figure 11 is a process speed control device according to the second embodiment is performed, it corresponds to the case where both the intermediate transfer belt 14 and the distance L ₃ of the two intermediate transfer scale detecting sensor 22 and 42 is extended To do. It is determined whether or not the absolute value of the calculation result of Expression (6) is equal to or less than a predetermined threshold value, and a target value for the conveyance speed of the intermediate transfer belt 14 is determined based on the determination result.

Hereinafter, this will be specifically described with reference to FIG. Note that a reference pulse interval time T ₀ and a distance N _p between two sensors in a state where the interval L ₃ between the two intermediate transfer scale detection sensors 22 and 42 is not extended are set as initial values (known values).

First, steps 100 to 120 of the first embodiment are executed (S100 to 120). Next, when it is determined that the state has changed in Step 120 (in the case of Yes), in Step 230, the intermediate transfer FB control unit 32b reads “(the phase difference measured before the current phase difference time T _pn −1). Time T _p0 ) ÷ Previously measured phase difference time T _p0 ”is calculated (S230). In Then step 240, the intermediate transfer FB control unit 32b calculates the "pulse interval time _{T n0} measured before (pulse interval time _{T n0} measured before one _T n -1 current pulse interval time) ÷ one" (S240).

Next, at step 250, the intermediate transfer FB control unit 32b calculates “(current phase difference time T _pn −1 phase difference time T _p0 ) measured before step _÷÷ phase difference time measured one time before. and T _p0 ", the absolute of the difference between the calculated in step 240" pulse interval time T _n0 measured before (pulse interval time T _n0 measured before one T _n -1 current pulse interval _time) ÷ one " the value Y = | {(current phase time _T pn -1 single retardation was measured before time _{T p0)} ÷ 1 single retardation was measured before time _T p0} - {(the current pulse interval time _{T n} - The pulse interval time T _n0 ) measured one time before / the pulse interval time T _n0 } | measured one time before is calculated (S250).

In Then step 260, expansion determination unit 32 b ₃ is the absolute value Y of the difference is equal to or a predetermined threshold value _{T th2} or less (S260). The predetermined threshold value T _th2 is preferably controlled to a value close to zero, but can be set to an arbitrary value in consideration of a detection error or the like. When it is determined in step 260 that “it is equal to or less than the predetermined threshold” (in the case of Yes), the phase difference time that the current phase difference time T _pn is measured _immediately before because the intermediate transfer belt 14 is expanded or contracted only. It can be determined that Tp ₀ has changed. In this case, in step 160, the conveyance speed target value determination unit 32b ₄ changes the target value of the conveyance speed of the intermediate transfer belt 14 from the reference pulse interval time T ₀ to “{(current phase difference time T _pn −1. The previous phase difference time T _p0 ) ÷ 2 sensor distance N _p } + reference pulse interval time T ₀ ”is replaced (S160).

If it is not determined in step 260 that “it is equal to or less than the predetermined threshold” (in the case of No), both the intermediate transfer belt 14 and the distance L ₃ between the two intermediate transfer scale detection sensors 22 and 42 are expanded and contracted. Thus, it can be determined that the current phase difference time T _pn has changed with respect to the phase difference time T _p0 measured _immediately before. In this case, in step 270, the conveyance speed target value determining unit 32b ₄ changes the target value of the conveyance speed of the intermediate transfer belt 14 from the reference pulse interval time T ₀ to “[{(current phase difference time T _pn − Previously measured phase difference time T _p0 ) ÷ Previously measured phase difference time T _p0 } − {(Current pulse interval time T _{n −1.Previous} pulse interval time T _n0 ) ÷ 1 The pulse interval time T _n0 }] measured _immediately before is replaced by the phase difference time T _p0 + reference pulse interval time T ₀ measured _immediately before (S270).

  If it is not determined that the state has changed in step 120 (in the case of No), the process ends (the target value of the conveyance speed of the intermediate transfer belt 14 is not updated).

In the description of steps 100 to 270 above, “reference phase difference time” may be used instead of “phase difference time T _p0 measured immediately before”. In addition, “reference pulse interval time T ₀ ” may be used instead of “pulse interval time T _n0 measured _immediately before”. Here, the “reference phase difference time” is a reference phase difference time determined in advance at the time of factory shipment or adjustment by a serviceman, and is a value stored in a nonvolatile memory or the like. The “reference pulse interval time T ₀ ” is a reference pulse interval time determined in advance at the time of factory shipment or adjustment by a service person, and is a value stored in a nonvolatile memory or the like. The above is the description of the flowchart regarding the correction control according to the second embodiment.

Thus, according to the second embodiment, the current pulse interval time _Tn and the current phase difference time _Tpn are measured. Then, “(current phase difference time T _pn −1 phase difference time T _p0 measured one time before) ÷ one phase previous time phase difference time T _p0 ” and “(current pulse interval time T _n −1 one. The absolute value Y of the difference from the previously measured pulse interval time T _n0 ) ÷ the previous measured pulse interval time T _n0 ”is calculated, and whether or not the absolute value Y of the difference is equal to or less than a predetermined threshold value T _th2 Determine whether. Based on the determination result, it is determined whether the intermediate transfer belt 14 has expanded or contracted, and whether both of the intervals between the intermediate transfer belt 14 and the two intermediate transfer scale detection sensors 22 and 42 have expanded or contracted. Based on the determination result, the target value of the conveyance speed of the intermediate transfer belt 14 is expressed as “{(current phase difference time T _pn −1 phase difference time T _p0 measured _immediately before) ÷ two-sensor distance N. _p} + reference pulse interval time _{T 0} "or" [{(the current phase difference time _T pn -1 single retardation was measured before time _{T p0)} ÷ 1 single retardation was measured before time _{T p0}} - {(Current pulse interval time T _n −1: pulse interval time T _n0 measured one time before) ÷ pulse interval time T _n0 measured one time before}] × phase difference time T _p0 measured one time before + reference Replace with any of the pulse interval times T ₀ ]. As a result, the conveyance speed of the intermediate transfer belt 14 is set to a predetermined value not only when the intermediate transfer belt 14 expands and contracts but also when both of the intervals between the intermediate transfer belt 14 and the two intermediate transfer scale detection sensors 22 and 42 expand and contract. Therefore, it is possible to prevent the image quality from being deteriorated.

<Third Embodiment>
FIG. 12 is a diagram illustrating a schematic structure of an image forming apparatus according to the third embodiment. 12, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof may be omitted. Referring to FIG. 12, the image forming apparatus 50 according to the third embodiment is different from the image forming apparatus 10 according to the first embodiment only in that an encoder 51 is provided. The configuration is the same as that of the image forming apparatus 10 according to the first embodiment. Hereinafter, the description of the parts common to the first embodiment will be omitted, and description will be made focusing on the parts different from the first embodiment.

  In the image forming apparatus 50, the encoder 51 has a function as a rotational speed detection unit that detects the rotational speed of the drive roller 23. That is, the encoder 51 outputs a pulse signal corresponding to the rotational speed of the drive roller 23.

  In the first embodiment, speed feedback control is realized by performing control to adjust the rotational speed of the intermediate transfer belt drive motor so that the pulse output from the intermediate transfer scale detection sensor 22 has a constant period. In the second embodiment, control for adjusting the rotational speed of the intermediate transfer belt drive motor is performed so that the pulse output from the encoder 51 has a constant period, thereby realizing speed feedback control. That is, the intermediate transfer scale detection sensor 22 is not used for speed feedback control.

  Speed feedback control is performed so that the pulse output from the encoder 51 has a constant period, and the intermediate transfer belt 14 is conveyed at a constant speed, and the pulse interval time and position are changed from the pulse output from the intermediate transfer scale detection sensors 22 and 42. By measuring the phase difference time, the expansion and contraction of the intermediate transfer belt 14 and the fluctuation of the distance between the two sensors can be detected. The detection of the expansion / contraction of the intermediate transfer belt 14 and the change in the distance between the two sensors is as shown in the flowchart of FIG. 9 or FIG.

  In this example, the feedback control is performed so that the pulse output from the encoder 51 that detects the rotational speed of the drive roller 23 has a constant period, and the intermediate transfer belt 14 is controlled to a constant speed. Thus, the conveyance speed of the intermediate transfer belt may be controlled to be constant. In that case, the same effect can be obtained.

  As described above, according to the third embodiment, similarly to the first embodiment and the second embodiment, the conveyance speed of the intermediate transfer belt can be controlled to a predetermined value, and the image quality can be controlled. Can be prevented. In addition, normal speed control of the intermediate transfer belt is performed using an encoder, and expansion / contraction correction is performed using an intermediate transfer scale detection sensor, so that normal speed control and expansion / contraction correction are not affected by each other. Therefore, it is possible to control the speed of the intermediate transfer belt with high accuracy and correct the expansion / contraction of the intermediate transfer belt with high accuracy.

  The preferred embodiment has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications and replacements are made to the above-described embodiment without departing from the scope described in the claims. Can be added.

DESCRIPTION OF SYMBOLS 10, 50 Image forming apparatus 11 Scanner unit 12a, 12b, 12c, 12d Photosensitive drum 13 Fixing unit 14 Intermediate transfer belt 14a Intermediate transfer belt scale 14b Reflecting part 14c Non-reflecting part 15 Secondary transfer roller 16 Repulsive roller 17 Registration roller 18 Paper feed unit 19 Paper feed roller 20 Paper transport roller 21 Paper discharge unit 22, 42 Intermediate transfer scale detection sensor 22a, 42a Light emitting element 22b, 42b Light receiving element 23 Drive roller 24 Followed roller 30 Control part 31 Image forming control part 31a Photoconductor Motor control unit 31b Image formation process control unit 32 Intermediate transfer control unit 32a Intermediate transfer motor control unit 32b Intermediate transfer FB control unit 32b ₁ pulse interval time measurement unit 32b ₂ phase difference time measurement unit 32b ₃ expansion / contraction determination unit 32b ₄ transport speed Target value determining means 32c primary transfer controller 33 the secondary transfer control unit 33a secondary transfer motor control unit 33b transfer controller 34 fixing control unit 35 sheet transportation control unit 51 encoder 90 transfer sheet _{L 1, L 2, L 3} , L ₄ , L ₅ , L ₆ width T ₁ , T ₂ , T _s pulse interval time T _r target pulse interval time T _p2 , T _p3 , T _p4 phase difference time

JP2006-085055

Claims (19)

An endless transport body transported in a first direction;
A scale having reflection parts and non-reflection parts arranged alternately on the endless transport body at a constant cycle along the first direction;
First pulse signal output means for outputting a first pulse signal corresponding to the fixed period of the scale;
Second pulse signal output means that outputs a second pulse signal that is arranged at a predetermined interval with respect to the first pulse signal output means and that corresponds to the constant period of the scale;
Pulse interval time measuring means for repeatedly measuring a pulse interval time which is a cycle of the first pulse signal and the second pulse signal at a predetermined time interval;
Phase difference time measuring means for repeatedly measuring a phase difference time between the first pulse signal and the second pulse signal at a predetermined time interval;
The difference between the latest pulse interval time measured by the pulse interval time measuring means and a predetermined reference pulse interval time, and the latest phase difference time measured by the phase difference time measuring means and the predetermined reference phase difference. Expansion / contraction determination means for determining whether or not the endless transport body is expanded and contracted and expanded / contracted at a predetermined interval based on a difference with time;
A speed control device comprising: a transport speed target value determining means for determining a target value for transport speed control of the endless transport body based on a determination result of the expansion / contraction determination means.   The expansion / contraction determining means has the latest pulse interval time measured by the pulse interval time measuring means changed with respect to the predetermined reference pulse interval time, and has been measured by the phase difference time measuring means When the latest phase difference time has changed with respect to the predetermined reference phase difference time, the endless transport body is expanded and contracted, and the predetermined interval is not expanded or contracted. The speed control device according to claim 1, wherein it is determined that there is expansion and contraction of the cylindrical transport body and expansion and contraction of the predetermined interval.   The expansion / contraction determining means has the latest pulse interval time measured by the pulse interval time measuring means not changed with respect to the predetermined reference pulse interval time, and is measured by the phase difference time measuring means. When the latest phase difference time changes with respect to the predetermined reference phase difference time, it is determined that there is no expansion / contraction of the endless transport body and expansion / contraction of the predetermined interval. The speed control device according to 1.   The expansion / contraction determining means has the latest pulse interval time measured by the pulse interval time measuring means changed with respect to the predetermined reference pulse interval time, and has been measured by the phase difference time measuring means 2. The speed according to claim 1, wherein when the latest phase difference time has not changed with respect to the predetermined reference phase difference time, it is determined that there is no expansion and contraction of the endless carrier and the predetermined interval. Control device. When the expansion / contraction determination means determines that the endless carrier has expansion / contraction,
The transport speed target value determining means determines a target value of the transport speed control as a difference between the latest phase difference time measured by the phase difference time measuring means and the predetermined reference phase difference time. The speed control device according to claim 1 or 2, wherein the speed control device determines a value obtained by adding a value divided by the number of pulses corresponding to the interval and a predetermined reference pulse interval time. When the expansion / contraction determination means determines that there is expansion / contraction at the predetermined interval,
The speed control according to any one of claims 1 to 3, wherein the transport speed target value determining means determines the target value of the transport speed control as the latest pulse interval time measured by the pulse interval time measuring means. apparatus. When the expansion / contraction determination means determines that there is expansion / contraction at the predetermined interval,
The transport speed target value determining means determines the target value of the transport speed control as a product of a rate of change of expansion / contraction of the endless transport body and the predetermined reference phase difference time, and a predetermined reference pulse interval. The speed control apparatus according to claim 1, wherein the speed control apparatus determines a value obtained by adding time.   The expansion / contraction determining means averages a plurality of pulse interval times measured by the pulse interval time measuring means within a certain time and a plurality of phase difference times measured by the phase difference time measuring means within a certain time. The speed control device according to any one of claims 1 to 7, wherein the presence or absence of expansion and contraction of the endless transport body and expansion and contraction at the predetermined interval is determined based on the converted value. Furthermore, temperature and humidity measuring means for measuring the ambient temperature and / or ambient humidity of the endless carrier, the first pulse signal output means, and the second pulse signal output means,
9. A timing control unit that controls a timing at which the conveyance speed target value determination unit determines a target value for the conveyance speed control based on a measurement result of the temperature and humidity measurement unit. The speed control device according to item. Reflecting portions and non-reflecting portions that are alternately arranged at a constant cycle along the first direction on the endless carrier that is conveyed in the first direction by using the first pulse signal output means. A first pulse signal output step of outputting a first pulse signal corresponding to the constant period of the scale having;
The second pulse signal output means arranged at a predetermined interval with respect to the first pulse signal output means is used to output a second pulse signal corresponding to the constant period of the scale. A pulse signal output step;
A pulse interval time measuring step of repeatedly measuring a pulse interval time which is a cycle of the first pulse signal and the second pulse signal at a predetermined time interval;
A phase difference time measurement step of repeatedly measuring a phase difference time between the first pulse signal and the second pulse signal at a predetermined time interval;
The difference between the latest pulse interval time measured in the pulse interval time measuring step and a predetermined reference pulse interval time, and the latest phase difference time measured by the phase difference time measuring means and the predetermined reference phase difference. Expansion / contraction determination step for determining whether or not the endless carrier is expanded and contracted based on a difference with time, and expansion / contraction at the predetermined interval;
A speed control method comprising: a transport speed target value determining step for determining a target value for transport speed control of the endless transport body based on a determination result in the expansion / contraction determination step.   In the expansion / contraction determination step, the latest pulse interval time measured in the pulse interval time measurement step is changed with respect to the predetermined reference pulse interval time, and is measured in the phase difference time measurement step. When the latest phase difference time has changed with respect to the predetermined reference phase difference time, the endless transport body is expanded and contracted, and the predetermined interval is not expanded or contracted. The speed control method according to claim 10, wherein it is determined that there is expansion and contraction of the cylindrical transport body and expansion and contraction of the predetermined interval.   In the expansion / contraction determination step, the latest pulse interval time measured in the pulse interval time measurement step does not change with respect to the predetermined reference pulse interval time, and is measured in the phase difference time measurement step. When the latest phase difference time changes with respect to the predetermined reference phase difference time, it is determined that there is no expansion / contraction of the endless transport body and expansion / contraction of the predetermined interval. 10. The speed control method according to 10.   In the expansion / contraction determination step, the latest pulse interval time measured in the pulse interval time measurement step is changed with respect to the predetermined reference pulse interval time, and is measured in the phase difference time measurement step. The speed according to claim 10, wherein when the latest phase difference time has not changed with respect to the predetermined reference phase difference time, it is determined that there is no expansion and contraction of the endless carrier and the predetermined interval. Control method. When it is determined in the expansion / contraction determination step that the endless transport body has expansion / contraction,
In the transport speed target value determining step, the target value of the transport speed control is set to a difference between the latest phase difference time measured in the phase difference time measuring step and the predetermined reference phase difference time. The speed control method according to claim 10 or 11, wherein a value obtained by adding a value divided by the number of pulses corresponding to the interval and a predetermined reference pulse interval time is determined. When it is determined in the expansion / contraction determination step that there is expansion / contraction at the predetermined interval,
The speed control according to any one of claims 10 to 12, wherein in the transport speed target value determining step, a target value of the transport speed control is determined to be the latest pulse interval time measured in the pulse interval time measuring step. Method. When it is determined in the expansion / contraction determination step that there is expansion / contraction at the predetermined interval,
In the transport speed target value determining step, the transport speed control target value is determined by multiplying a product of a rate of change of expansion and contraction of the endless transport body and the predetermined reference phase difference time, and a predetermined reference pulse interval. The speed control method according to any one of claims 10 to 12, wherein the speed is determined to be a value obtained by adding time.   In the expansion / contraction determination step, a value obtained by averaging a plurality of pulse interval times measured in the pulse interval time measurement step within a certain time and a plurality of phase difference times measured in the phase difference time measuring step are averaged within a certain time. The speed control method according to any one of claims 10 to 16, wherein the presence / absence of expansion / contraction of the endless transport body and expansion / contraction of the predetermined interval is determined based on the converted value. Furthermore, a temperature and humidity measuring step for measuring the ambient temperature and / or ambient humidity of the endless carrier, the first pulse signal output means, and the second pulse signal output means;
The timing control step of controlling the timing for determining the target value of the transport speed control in the transport speed target value determining step based on the measurement result in the temperature and humidity measuring step. The speed control method according to one item.   An image forming apparatus comprising the speed control device according to claim 1.

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