JP5127290B2 - Speed control device and image forming apparatus - Google Patents

Description

  The present invention relates to a speed control device and an image forming apparatus, and more particularly to a control technique for correcting a speed variation of a rotating body such as a photosensitive drum.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic process, it is known that speed fluctuations of a rotating body such as a photosensitive drum cause deterioration of an image.

  Here, an image forming apparatus using an electrophotographic process which is a premise of the present invention will be outlined.

  FIG. 17 is a schematic sectional view of the image forming apparatus.

  In FIG. 17, the image forming apparatus includes four sets of image forming units 1200Y, 1200M, 1200C, and 1200K that form images of each color of Y (yellow), M (magenta), C (cyan), and K (black). (Hereafter, Y, M, C, and K representing colors may be omitted). Each image forming unit 1200 includes a photosensitive drum 1201, a developing device 1206, a drum cleaner 1207, a charger 1208, a primary transfer roller 1209, and a laser optical system 1210, and forms images of different colors on the intermediate transfer belt 1202. .

The image forming operation is controlled by the system controller 1220, and color image data supplied from the image reading device 1221 and the image processing device 1222 is supplied to each image forming unit 1200. On the photosensitive drum 1201 of each image forming unit 1200, an optical semiconductor layer whose electrical characteristics are changed by light irradiation is formed, and while rotating at a constant speed during the image forming operation, the following (1) to (7) ).
(1) Charging: The photo semiconductor layer of the photosensitive drum 1201 is uniformly charged by the charger 1208.
(2) Laser exposure: An image pattern (electrostatic latent image) is irradiated by the laser optical system 1210 toward the photosensitive drum 1201 (on the photosensitive member) (broken line portion B).
(3) Development: A toner is attached to the electrostatic latent image by the developing device 1206.
(4) Primary transfer: The image is transferred onto the intermediate transfer belt 1202 by the primary transfer roller 1209.
The operations (1) to (4) are performed in each image forming unit 1200.
(5) Secondary transfer: The toner image on the intermediate transfer belt 1202 driven by the intermediate transfer roller 1204 is transferred to the recording paper P by the secondary transfer device 1211.
(6) Fixing: The recording paper P is heated and pressurized by the fixing device 1212 to fix the toner on the recording paper P and then discharged to the outside.
(7) Cleaning: The toner remaining on the photosensitive drum 1201 without being completely transferred onto the intermediate transfer belt 1202 is removed by the drum cleaner 1207. Further, the toner remaining on the intermediate transfer belt 1202 without being completely transferred onto the recording paper P is removed by the belt cleaner 1213.

  The secondary transfer device 1211 and the belt cleaner 1213 described above are separated from the intermediate transfer belt 1202 when the image forming apparatus is in a stopped state.

  The separation of the secondary transfer device 1211 is because when the “paper jam” or the like occurs in the image forming apparatus, it is necessary for the user to secure a space for removing the recording paper in the secondary transfer unit. . The belt cleaner 1213 is separated for the following reason. That is, in the case where the belt cleaner 1213 is a mechanism that performs cleaning by pressing a cleaning paper such as a web, for example, the intermediate transfer belt 1202 is prevented from being deteriorated due to contact with the intermediate transfer belt 1202 for a long time when stopped. .

  Then, the secondary transfer device 1211 and the belt cleaner 1213 are attached to the intermediate transfer belt 1202 at the start of the preparatory rotation (pre-rotation) drive for starting the image forming operation.

  Through the above series of operations, the toner images of the image forming units 1200Y, 1200M, 1200C, and 1200K are formed on the intermediate transfer belt 1202 so as to overlap each other.

  At this time, fluctuations in the rotational speed of the photosensitive drum 1201 and the intermediate transfer belt 1202 cause so-called “magnification fluctuation” in which the image size of the formed toner image changes. If the moving speed of the intermediate transfer belt 1202 when a toner image of a certain color is formed does not match the moving speed of the intermediate transfer belt 1202 when the next toner image is formed, the respective toner images A so-called “color shift” such as a shift occurs.

  The main speed fluctuation components of the rotating body such as the photosensitive drum 1201 and the intermediate transfer belt 1202 that generate such “magnification fluctuation” and “color shift” are components that exist constantly and have a relatively low frequency. . That is, “color misregistration” is caused by uneven rotation of the rotating body where the time integral value (displacement) in the speed fluctuation becomes large, or when the rotating body is driven via the driving gear, the uneven rotation of the gear ratio. doing.

  In addition, when the rotating body rotates, speed fluctuations of a relatively high frequency component due to gear pitch, natural vibration of the rotating body, load fluctuation applied to the rotating body, and the like occur simultaneously with the rotation unevenness of the low-frequency component described above. These speed fluctuation components mainly cause deterioration of the image called “pitch unevenness”.

Patent Document 1 discloses a technique for correcting the rotation unevenness. This is because the number of pulses of the encoder is determined from the number of teeth of the drive gear, the low frequency component is extracted by simple moving average processing, the low frequency component is corrected by feedforward control (fixing the drive pattern), and at the same time the high frequency component is corrected. Correction is performed by feedback control.
Japanese Patent Laid-Open No. 10-066373

  However, Patent Document 1 has the following problems. That is, the low frequency component that causes the rotation unevenness and the high frequency component that causes the pitch unevenness, that is, the frequency band for performing the feedforward control and the frequency band for performing the feedback control cannot be clearly separated, and therefore, they tend to diverge on the control.

  In addition, when the above correction control is applied to the rotation control of the photosensitive drum and intermediate transfer roller of the image forming apparatus, load fluctuation due to high voltage application, toner transfer, unit attachment / detachment, etc. is applied to the photosensitive drum and intermediate transfer roller in the image forming operation. Always occurs. For this reason, there is a high possibility that stable rotation drive cannot be performed due to the above-described problem.

  The present invention has been made in view of the above-mentioned problems, and the problems are to realize the suppression of the speed fluctuation of the rotating body and the stable driving for a long time, and the “magnification fluctuation” and “color misregistration” which are image deterioration factors in the image forming apparatus. And a speed control device and an image forming apparatus that reduce “pitch unevenness”.

  In order to solve the above problems, a speed control device and an image forming apparatus of the present invention have the following configurations.

(1) Rotating body, driving means for driving the rotating body, detecting means for detecting the speed of the rotating body, and output to the driving means based on speed data of the rotating body detected by the detecting means And a control means for controlling the drive means by correcting the calculated drive signal, wherein the control means has a plurality of frequency components. One speed fluctuation component and a speed fluctuation component having a frequency component different from the first speed fluctuation component are extracted, and the extracted first speed fluctuation component converges within a predetermined range set in advance. A first correction table that stops updating correction values at a time and fixes all correction values, and the rotating body when the rotating body is driven by the driving means based on the fixed first correction table Is 1 A second correction table for correcting a difference between an average speed during rotation and a target speed set in advance for the driving unit, and the first correction table and the second correction table. Based on speed data detected at a predetermined timing by the detection means in a state where feedforward correction control is performed and the rotating body is driven by the feedforward correction control, and a preset target speed And a first correction value calculated by multiplying a difference between the first predetermined coefficient and a total sum of speed data detected in the predetermined time region by the detecting means. A second correction value calculated by multiplying the difference from the total of the target speeds by a second predetermined coefficient set in advance, and the feedforward correction The appropriate correction values of the first and second correction table in your, by adding the first correction value and the second correction value, the speed control device and performs feedback correction control .
(2) In the image forming apparatus for controlling the rotational speed so that the photosensitive member and the transfer member rub against each other and transferring the electrostatic latent image formed on the photosensitive member to the transfer member, The rotating body is the photosensitive body and the transfer body, and the control means is configured to calculate a speed data from the speed data during one rotation of the photosensitive body or the transfer body. In order to extract the speed fluctuation component due to the frequency of 1 and converge the speed fluctuation component due to the first frequency to the target value, the feedforward correction control is performed, and one of the photoconductor and the transfer body is 1 A speed fluctuation component due to a first frequency is extracted from speed data during rotation, and the feedforward correction control is performed to converge the speed fluctuation component due to the first frequency to a target value, and the photosensitive In addition, a speed fluctuation component due to a second frequency is extracted from speed data during one rotation of the transfer body, and the feedback correction control is performed in order to converge the speed fluctuation component due to the second frequency to a target value. An image forming apparatus.
(3) In the image forming apparatus for transferring the electrostatic latent image formed on the photosensitive member to the transfer member by controlling the rotation speed so that the photosensitive member and the transfer member rub against each other, (1) An image forming apparatus, wherein the rotating body is the photosensitive body and the transfer body, and the speed control apparatus controls the photosensitive body and the transfer body.

  According to the present invention, it is possible to suppress the speed fluctuation of the rotating body and to stably drive for a long time, and to reduce “magnification fluctuation”, “color shift” and “pitch unevenness” which are image deterioration factors in the image forming apparatus. it can.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  The embodiment described below is an example as means for realizing the present invention, and should be appropriately modified or changed according to the configuration and various conditions of the apparatus to which the present invention is applied. It is not limited to the embodiment.

  The present invention can also be realized by supplying a storage medium (or recording medium) storing software program codes for realizing speed fluctuation component correction control described later to a system or apparatus. In this case, it is achieved by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium.

[First Embodiment (Speed Control Device)]
FIG. 1 is a block diagram of a speed control apparatus according to an embodiment of the present invention.

  In FIG. 1, reference numeral 101 denotes a rotating body. A drive gear 102 is concentrically attached to the drive shaft of the rotating body 101, and has a predetermined number of teeth N_gear (N_gear is set to a reduction ratio designed in advance with respect to the output shaft of the motor 103 (drive means). Any positive integer). A motor 103 drives the rotating body 101 (denoted as STM in the drawing), and a gear having a predetermined number of teeth N_shaft (N_shaft is an arbitrary positive integer) meshed with the drive gear 102 is formed on the output shaft. In this embodiment, the motor 103 is a stepping motor (pulse motor) (hereinafter referred to as a stepping motor 103), but is not limited to this.

The stepping motor 103 is driven according to a frequency F_stm (Pulse Per Second: number of pulses per second: hereinafter referred to as pps) of a driving signal (hereinafter referred to as driving pulse) output to the motor. In the stepping motor 103, the rotation angle θ0 [rad] per pulse in the drive pulse is defined. The number of pulses M_stm (arbitrary positive integer) required for one rotation of the stepping motor 103 is given by the following equation (1).
M_stm = 2π / θ0 (1)

Therefore, the rotation speed V_stm of the stepping motor 103 (Revolution Per Minute: number of rotations per minute: hereinafter referred to as rpm) is given by the following equation (2).
V_stm = (F_stm / M_stm) × 60 [Second] (2)

  For example, in the case of a two-phase stepping motor, the rotation angle per pulse θ0 [rad] = 0.01π [rad]. Therefore, the number of pulses M_stm required per rotation is 200 pulses, and when the driving frequency F_stm = 3000 [pps], the rotational speed V_stm = 900 [rpm].

Therefore, when the rotating gear 101 is rotated by driving the drive gear 102 by the stepping motor 103, the rotational angular velocity (= rotational frequency) V_rot [rpm] of the rotating body 101 is given by the following equation (3).
V_rot = V_stm / (N_gear / N_shaft) = V_stm / R_gear (3)

  Here, R_gear (= N_gear / N_shaft) is a gear ratio (reduction ratio: arbitrary positive integer) between the drive gear 102 and the gear formed on the output shaft of the stepping motor 103. In the above example, when the gear ratio = 10, the rotational angular velocity Vrot of the rotating body 101 is 900/10 = 90 [rpm].

Reference numerals 105 and 106 denote encoders attached concentrically to the end of the drive shaft of the rotating body 101. The encoders 105 and 106 (detection means) output encoder signals synchronized with the slit pattern input interval of the code wheel 107 having a predetermined number N_wheel of slit patterns having a predetermined width L_wheel [m] designed in advance. In addition, 105 is an encoder A, 106 is an encoder B, and they are set to mutually opposite phases. The reason for this is to cancel the rotational speed of the rotating body 101 because it is affected by the speed fluctuation caused by the eccentric component of the rotating body itself and the eccentric component of the code wheel 107. In other words, the angular velocity of the rotating body 101 is often used as a reference, and the purpose of this embodiment is to detect the fluctuation of the angular velocity of the rotating body 101 based on the following formula (4) in the same manner. Here, the angular velocity ω_R of the rotating body 101 is given by the following equation (4), assuming that the velocity data V_encA is detected by a signal from the encoder A 105 and the velocity data V_encB is detected by a signal from the encoder B 106. .
ω_R = (V_encA + V_encB) / 2 (4)

  Reference numeral 108 denotes a home position sensor that detects the reference phase of the rotating body 101. Reference numeral 109 denotes a control unit (control means), which has a CPU 110 that performs a speed correction control calculation to be described later and controls the entire drive mechanism. 111 and 112 are counters that count the slit pattern input interval of the code wheel 107 using the output signals of the encoder A 105 and the encoder B 106 based on the reference clock C0 [Hz] (period of one clock = 1 / C0 [sec]). It is. Note that 111 is a counter A for the encoder A 105, and 112 is a counter B for the encoder B 106. A pulse generator 113 outputs a driving pulse for driving the stepping motor 103 to a motor driver 104 (simply referred to as a driver in the figure).

When the value set for the pulse generator 113 by the CPU 110 in the control unit 109 is S_pls (S_pls is an arbitrary integer), the frequency F_stm [pps] of the pulse signal output from the pulse generator 113 is expressed by the following equation ( 5).
F_stm = C0 / S_pls (5)

  FIG. 2 is a timing chart for explaining a method for detecting the angular velocity fluctuation of the rotating body 101 using the output signals of the encoder A 105 and the encoder B 106.

  First, FIG. 2A shows a reference clock of the counter A 111 (or counter B 112) (denoted as a counter reference clock in the figure). FIG. 2B shows a home position (HP) input signal of the rotating body 101, and HP is detected at the rising edge. FIG. 2C shows the input of encoder A 105 (or encoder B 106), and the encoder output signal after the home position input signal (hereinafter referred to as HP signal) is detected is the 0th input. The encoder output signal is based on either encoder A 105 or encoder B 106. In this embodiment, the signal input of the encoder A 105 is used as a reference. FIG. 2D shows the count number measured with reference to the rising edge of the encoder output signal. The counter A 111 measures the encoder input interval by the number of counter reference clocks. FIG. 2E shows speed data detected by the number of counts (for example, e1_data = 7 in the figure).

When the rising edge of an arbitrary n-th encoder output signal is measured, the CPU 110 acquires the (n-1) th encoder data e (n-1) _data. Here, the encoder data e (n−1) _data acquired by the CPU 110 is synonymous with “time: Second”, and the (n−1) th speed data V_e (n−1) is expressed by the following equation (5). Given.
V_e (n-1) = L_wheel [m] / e (n-1) _data [sec] (5)
Here, since L_wheel is a constant value, the angular velocity fluctuation of the rotating body 101 in an arbitrary phase can be detected from the acquired encoder data.

  Next, the angular velocity fluctuation correction control of the rotating body according to the present embodiment will be described.

  FIG. 3 is a flowchart showing the angular velocity fluctuation correction control (in the figure, simply referred to as speed fluctuation control) of the rotating body 101 according to the present embodiment.

  The flow in FIG. 3 is realized by the CPU 110 of the control unit 109 executing a control program stored in the internal memory.

  In FIG. 3, when the driving of the rotating body 101 is started, the angular velocity fluctuation of the rotating body 101 is detected using the encoder data described in FIG. 2 (step S201, the following steps are omitted). FIG. 4 shows an angular velocity variation data profile of the rotating body 101 obtained by experiments, where the horizontal axis represents the number of encoder inputs and the vertical axis represents encoder data e (n) _data, which is velocity data. FIG. 4 shows a data profile for two revolutions of the rotating body, that is, the number of encoder inputs = the number of slits N_wheel of one revolution of the code wheel 107 (N_wheel is an arbitrary positive integer). FIG. 5 is a diagram showing the result of FFT calculation (fast Fourier calculation) of the angular velocity fluctuation data profile of the rotator 101. In FIG. 5, in order to analyze the frequency component ratio of the angular velocity fluctuation | variation which the rotary body 101 has from the angular velocity fluctuation | variation data profile shown in FIG. 4, the result of having performed FFT calculation based on the following formula | equation (6) is shown.

Here, the FFT operation will be outlined (reference: introduction to digital signal processing).
X (k) = Σx (n) × exp (−2πknj / N) (6)
Here, x (n) is the acquired n pieces of sampling data, and corresponds to e (n) _data in this embodiment. j is an imaginary unit, and j = √ (−1). Further, k represents a frequency axis unit after frequency component conversion, and X (k) represents a power spectrum (intensity of the corresponding frequency component: arbitrary unit) calculated at the frequency k.

  As shown in FIG. 5, the rotating body 101 rotates with frequency components of various factors, and main frequency components and components calculated therefrom are one rotation unevenness F_r of the rotating body 101 and one of the stepping motor 103. Rotation unevenness F_g0 (single or plural frequency components). Further, the component calculated from the one rotation unevenness F_r is F_g0 = F_r × R_gear generated by the gear ratio multiplication of the rotating body 101, the frequency component F_g1 due to the meshing between the drive shaft of the stepping motor 103 and the drive gear 102, the rotation This is the natural vibration component F_p of the body itself.

  In each of the frequency components, the one rotation unevenness F_r having a relatively low frequency and the one rotation unevenness F_g0 caused by the gear ratio of the rotating body 101 have a time integration value with respect to the angular velocity fluctuation as described in the background art. For this reason, when the frequency components F_r and F_g0 are generated in the photosensitive drum 1201 and the intermediate transfer roller 1204 as the rotator in the image forming apparatus shown in FIG. 17, this becomes the main factor of “magnification fluctuation” and “color shift”. However, these frequency components F_r and F_g0 often show a steady and stable power spectrum when the rotating body 101 is driven. For this reason, in the present embodiment, the frequency components F_r and F_g0 are defined as low frequency speed fluctuation components (first speed fluctuation components). A correction drive table generation method and a correction drive method for correcting this low frequency velocity fluctuation component will be described below. The correction drive table is a low-frequency velocity fluctuation component correction table in which setting values to be set for the pulse generator 113 are stored for each phase during which the rotating body 101 makes one rotation. To do.

  In S202 of FIG. 3, in order to generate the correction table, a digital signal processing operation is performed on the detected encoder data e (n) _data using the low frequency component pass filter Filter0 shown in FIG. Here, FIG. 6 is a diagram showing the relationship between the FFT calculation result of the angular velocity fluctuation data profile of the rotating body 101 and the low-frequency component pass filter Filter0. Low-frequency component pass filter Filter 0 is a digital filter having a cutoff frequency F_c and an attenuation characteristic.

Here, it is assumed that the cutoff frequency F_c of the digital filter shown in FIG. 6 satisfies the following conditional expression (7).
F_r <F_g0 <F_c <F_g1, F_p (7)
The conditions shown in Formula (7) do not limit the present invention.

  The digital signal processing calculation (filter calculation) in S202 will be outlined below.

  As shown in the following equation (8), the digital signal processing operation is performed by detecting detected sampling data (corresponding to encoder data e (n) _data) and the coefficient profile of the low-frequency component pass filter Filter0 shown in FIG. It is defined as the product-sum operation of hM. FIG. 7 is a diagram showing a coefficient profile of the low-frequency component pass filter.

Here, FIG. 8 is a diagram showing a signal processing block of the digital filter. As shown in FIG. 8, “current” is recorded at the head address of the memory area Data_Original [n] (the same size as the number M + 1 of filter coefficients hM) for buffering the detected original encoder data (e (n) _data). Data is entered. Then, the product-sum operation according to the following equation (8) is executed, and the encoder data Data_FilterPass [n] after the operation using the filter coefficient table is output.

  The filter coefficient values h0 to hM are designed to be “1” in total. Further, as shown in FIG. 7, the filter coefficients are weighted so that the center value becomes the largest, and the weighting coefficients are changed with respect to data at an arbitrary point during signal processing. In other words, by changing the frequency characteristics of the digital filter, a data profile having only the necessary frequency components can be obtained.

  9 shows the result of performing the above filter operation on the detected encoder data shown in FIG. 4, and FIG. 10 shows the result of performing the FFT operation on the encoder data profile obtained by the filter operation shown in FIG. Is shown. That is, FIG. 10 is an encoder data profile when the low-frequency velocity fluctuation component correction control (feedforward correction control) according to the present invention is performed.

  From the filter calculation results shown in FIGS. 9 and 10, it can be seen that the extraction of the low frequency component and the removal of the high frequency component are performed accurately.

Then, a set value S1_pls corresponding to the frequency of the motor drive pulse obtained by multiplying the reference speed value for each rotation of the rotator 101 by a correction gain set in advance from the encoder data from which the low frequency component has been extracted. This is calculated and reflected in the next rotation of the rotating body 101. The calculation formula (9) is shown below.
S1_pls_New (n) = (e (n) _data−e_target) × Gain × S1_pls_Now (n) (9)
e (n) _data: n-th detected encoder data in “current” rotation e_target: target value of encoder data Gain: correction gain S1_pls_New (n): stepping motor 103 given n-th in “next” rotation Set value of drive pulse S1_pls_Now (n): set value (correction value) of drive pulse after correction of stepping motor 103 reflected in the next (n + 1) th

  Here, in the CPU 110, a correction table (first correction table) that can store the set value of the motor drive pulse calculated by the equation (9), which is the same number as the number of slits N_wheel for one turn of the code wheel 107. ). Then, the address for storing the set value of the drive pulse in the first correction table is updated as the encoder is input, that is, based on the phase of the rotator 101, based on the number of input HP signals or encoder signals. To do.

  By the above control, the encoder data of the low frequency component can be converged within a predetermined fluctuation range (predetermined range) as a preset target after several rotations.

  FIG. 11 shows a result of an experiment in which speed fluctuation correction is performed using low-frequency component encoder data. In the profile shown in FIG. 11, line C represents the center value (target value) of the target speed, line U represents the upper limit value of the target speed, and line L represents the lower limit value of the target speed. In FIG. 11, the speed of the rotating body 101 converges within the range of the upper limit value and the lower limit value after 5 turns of the rotating body 101. Here, the set values of all the motor drive pulses stored in the first correction table are fixed.

  At this time, when the rotating body 101 is driven based on the set value stored in the first correction table, ideally, the average speed of the stepping motor 103 and the rotating body 101 is not controlled as described above. Should be the same. However, in actuality, when calculating each correction value based on Equation (9), a quantization error occurs, and this error may cause a deviation in average speed. Such deviation of the average speed is obtained when the photosensitive drum 1201 or the intermediate transfer belt 1202 and the intermediate transfer roller 1204 in the image forming apparatus (see FIG. 15) are driven using the speed control device according to the present invention. It becomes a big "color shift" factor. In the experiment according to this embodiment, when the average speed of the intermediate transfer roller 1204 in the image forming apparatus shown in FIG. 15 has a deviation of about 0.01% with respect to a preset target speed, 100 μm or more. May cause “color shift”. In the case of an image forming apparatus with a resolution of 1200 dpi, 1 dot = about 21.2 μm, and a color misregistration value of 100 μm or more is a state in which the toner images of the respective colors do not overlap at all, resulting in a large image deterioration.

  Therefore, in this invention, the 2nd correction table for correct | amending the gap | deviation of the average speed of the stepping motor 103 mentioned above and the rotary body 101 is produced | generated. The second correction table has the same number (= N_wheel) of setting value storage areas as the first correction table.

  Hereinafter, a method for calculating the second correction table will be described.

When the first correction table is fixed, an average speed when the rotating body 101 is driven is calculated based on the first correction table. In order to calculate this average speed (average value), the difference Diff between the sum value Sum_S1_pls of the set values of the motor drive pulses stored in the first correction table and the reference value S_target of the motor drive pulses is calculated as calculate.
Diff = Sum_S1_pls− (S_target × N_wheel) (10)

Further, the difference Diff can be calculated as follows. That is, based on the first correction table, the total value Sum_e_data for one revolution of the encoder data when the rotating body 101 is driven one revolution (during one revolution) and the target value (e_target) (target speed) of the encoder data It is also possible to use a difference from the total value of.
Diff = Sum_e_data− (e_target × N_wheel) (11)
Note that the present invention is not limited to the difference calculation method.

  Since the calculated difference Diff corresponds to the deviation of the average speed, the difference Diff is distributed and stored in the second correction table.

Based on the generated first correction table and second correction table, the set value S_pls_T of the drive frequency that is actually supplied to the pulse generator 113 for driving the rotating body 101 is
S_pls_T (n) = S1_pls (n) + S2_pls (n) (12)
It becomes. By driving the rotating body 101 based on this set value (S203), it is possible to stably rotate the rotating body 101 while suppressing the speed fluctuation due to the low frequency component.

  Here, when the second correction table is generated, the difference Diff is stored in a distributed manner by avoiding bias of correction values in each phase of the rotating body 101 and steep driving frequency change in the rotational driving of the rotating body 101. Is to prevent. This is because a steep change in the drive frequency is likely to cause the stepping motor 103 or the drive system of the rotating body 101 to follow up, causing the step-out or the rotation control system to oscillate.

  As a specific method of dispersion, all initial values stored in the second correction table are first set to “0”. Then, the minimum unit of the correction value is stored at predetermined intervals set in advance from the start address of the second correction table for each minimum unit (for example, “1”) of the correction value stored in the second correction table. I will do it. Then, when the difference Diff value exceeds the number of stored correction tables, there is a method of adding to the already stored correction value.

  The speed control of the rotating body 101 using the first correction table and the second correction table described above is defined as low frequency speed fluctuation component correction control (feed forward control). Thus, this feedforward control is performed in S203 of the flowchart of FIG. In S206, the correction control using the first correction table and the second correction table described above is shown.

  Next, it is determined whether the encoder data detected at any time falls within a preset range in a state where the low-frequency velocity fluctuation component correction control is being executed on the rotating body 101 in S203 (S204). If the value is not within the preset range (including the case where the set range is “0”), high-speed velocity fluctuation component correction control (real-time feedback control) (feedback correction control) described later is executed together with feedforward control. (S205). On the other hand, when it is within the preset range (S204 YES), the feedforward control using the first and second correction tables of the low frequency velocity fluctuation component correction control is continued.

  Here, the high-frequency velocity fluctuation component correction control in S205 will be described.

  FIG. 12 shows the high-frequency speed fluctuation component correction control, and shows the state of the rotating body 101 in time series (sequentially from the n-th order).

  FIG. 12A shows the motor drive pulse set by the low frequency speed fluctuation component correction table (the feedforward control described above). FIG. 12B shows a motor operation clock supplied to the stepping motor 103. FIG. 12C shows an encoder input signal due to the rotation of the rotating body 101. FIG. 12D shows the calculation timing of the high-frequency speed fluctuation component correction value.

In synchronization with the input of the encoder signal, the correction value is calculated and the motor operation clock is supplied. When the n-th encoder signal is input (predetermined timing), the control unit 109 acquires the (n-1) th encoder data e (n-1) _data. Here, when the (n-1) th encoder data is not within the preset range (NO in S204), the high-frequency speed fluctuation component correction value Cf is calculated using the following equation (13).
Cf (n−1) = (e (n−1) _data−e_target) × Gain_f × CE (13)
Here, e_target is the reference encoder data calculated from the target speed. Gain_f is a reflection coefficient (first predetermined coefficient) when the correction value is calculated. CE is a coefficient for converting the correction value into a motor drive pulse.

The correction value calculation process is performed while the nth encoder signal is being input. When the n + 1-th encoder signal is input, a value that is offset with respect to the setting value S_pls_T (n + 1) (see equation (12)) of the motor drive pulse in the low frequency speed fluctuation component correction table is supplied as the motor drive pulse. Therefore, the set value S_pls_A of the drive frequency that is actually given to the pulse generator 113 for driving the rotating body 101 is given by the equation (14).
S_pls_A (n + 1) = S_pls_T (n + 1) + Cf (n−1) (14)

  The correction value Cf calculated by the equation (13) increases when the gain_f is set large, that is, the change in the drive pulse applied to the stepping motor 103 increases, and the rotation operation is increased. The possibility of instability arises.

Therefore, in the present invention, the correction value Cf calculated by the equation (13) is set as the first correction value. In addition to this correction value, a second correction value Cs is further defined. The second correction value Cs is calculated as follows. The difference between the sum of the speed data detected in an arbitrary time domain (predetermined time domain) (a total value for K encoder data e_data and K is a positive integer) and the preset sum of the target speed data On the other hand, it is calculated by multiplying a preset second predetermined coefficient. The control unit 109 performs high-frequency speed fluctuation component correction control based on both the first correction value Cf and the second correction value Cs. The set value of the drive pulse actually given to the pulse generator 113 is calculated again by the following equation (14) instead of the equation (14) shown above.
S_pls_A (n + 1) = S_pls_T (n + 1) + Cf (n−1) + Cs (14)

Here, a method for calculating the second correction value Cs will be described below. First, as shown in Expression (15), Cs is calculated as follows. That is, the difference Diff_s between the total value of K encoder data corresponding to a predetermined arbitrary time region and the total value of K encoder data set in advance is multiplied by Gain_s. It is calculated based on the obtained value. Here, Gain_s is a preset correction gain (second predetermined coefficient).
Cs (n) = [{e (n−K) _data + e (n−K + 1) _data + e (n−K + 2) _data +... + E (n−1) _data} − (e_target × K)] × Gain_s (15)
Here, Cs (n) is the nth correction value calculated for the encoder input, and the calculation source data is calculated based on the past K encoder data for the nth.

Further, as shown in the equation (16), the set value set for the actual stepping motor 103 reflects both the first correction value Cf and the second correction value Cs, so that two correction gains are used. Is set so as not to exceed “1” (less than 1). Thereby, the overshoot factor can be reduced with respect to the target speed.
Gain_f + Gain_s <= 1 Formula (16)

  Similarly to the reflection of the first correction value Cf, when the second correction value Cs is reflected in the motor drive pulse immediately after the correction value is calculated, the change in the drive pulse applied to the stepping motor 103 is large. Therefore, there is a possibility that the rotational operation becomes unstable.

  Therefore, as an actual reflection method, a value that is distributed in a preset time region M and multiplied by a preset predetermined weighting coefficient is reflected at any time (predetermined timing).

  Further, the preset time region M is set so that the value after dispersion does not exceed the preset value when the second correction value is dispersed (so as to be equal to or less than the preset predetermined value). By setting), the rotation operation can be stabilized.

  FIG. 13 is a schematic diagram showing calculation and reflection of values when M = 3 and M weighting coefficients (predetermined weighting coefficients) at the time of reflection are m1, m2, and m3.

  FIG. 13A shows the encoder input, and FIG. 13B shows the second correction value Cs calculated based on the equation (15). FIG. 13C shows a value obtained by dispersing the second correction value Cs in a preset reflection width M by weighting coefficients m1 to m3. FIG. 13D shows the pulse generator 113 when the motor is actually driven. Is a total value Cs_D of the past M correction variance values given as a set value.

  Here, the weighting coefficient mM (M = 3 in FIG. 13 and mM is m1 to m3) is designed to be “1” in total, and is changed according to the characteristics of the drive system that is actually controlled. It is possible.

  The speed control of the rotating body 101 using the first correction value Cf and the second correction value Cs_D described above is defined as high-frequency speed fluctuation component correction control (real-time feedback control).

  The first correction value Cf can theoretically correct a speed fluctuation component comparable to the frequency of the encoder input signal, that is, the sampling frequency Fs, and can secure the real-time response of the control system.

  In addition, when an encoder signal exceeding a preset range is continuously input m times (m is an arbitrary positive integer), by performing the high-frequency velocity fluctuation component correction control, the frequency component that this control follows is controlled. Fs / m can be set. For this reason, the type of load variation, that is, the followability to various high frequency components can be set relatively easily.

  Furthermore, verification of the response of the control can be performed by analyzing a speed fluctuation frequency component when a predetermined load fluctuation called a step response characteristic is applied, and verifying a time at which the speed fluctuation of this component converges. .

  The second correction value Cs is theoretically calculated so that the average speed in an arbitrary time region is always constant. Therefore, the positional deviation caused by the speed fluctuation of the rotating body 101 is always and limited. It becomes possible to approach “0”.

  FIG. 14 shows the correction effect of the real-time feedback control with respect to the positional deviation amount accompanying the speed fluctuation of the rotating body 101. FIG. 14A shows the speed of the rotating body 101, and FIG. 14B shows the frequency of the motor drive pulse given to the stepping motor 103 (denoted as motor drive frequency in the figure). In FIG. 14A, the vertical axis represents speed, in FIG. 14B, the vertical axis represents drive frequency (arbitrary unit), and in each case, the horizontal axis represents time. When the speed fluctuation as shown in FIG. 14A occurs in the rotating body 101, the above-described real-time feedback control corrects as follows. In other words, the positional deviation A caused by this fluctuation is corrected and driven mainly by the first correction value Cf, and the positional deviation B is mainly driven by the second correction value Cs.

Therefore, as shown in S206 + S207 of FIG. 3 and Expression (17), the speed control apparatus according to the present invention is based on a combination (addition) of feedforward control with two correction tables and real-time feedback control with two correction values. Function. And by these controls, it becomes possible to suppress the speed fluctuation of the rotating body 101 and realize stable driving for a long time.
S_Pls_A (n) = [S1_pls (n) + S2_pls (n)] + [Cf (n) + Cs (n) _D] (17)

[Second Embodiment]
Next, the second embodiment in which the speed fluctuation control according to the present invention described in the first embodiment is applied to the control of the rotating body (photosensitive drum (photosensitive body) and intermediate transfer roller (intermediate transfer body)) of the image forming apparatus. Embodiments will be described.

  FIG. 15 shows a configuration in which the speed control apparatus of the first embodiment is applied to an image forming apparatus. In FIG. 15, the same components as those in FIG.

  15, reference numeral 1223 denotes a speed including the encoder A 105, the encoder B 106, the code wheel 107, the HP sensor 108, the stepping motor 103, and the motor driver 104 (simply referred to as a driver in the figure) of the speed control device shown in FIG. It is a fluctuation control unit. The control unit 109 rotates the photosensitive drum 1201 and the intermediate transfer roller 1204 (corresponding to the rotating body 101 of the first embodiment) of each of the image forming units 1200Y, 1200M, 1200C, and 1200K according to a command from the system controller 1220. Control.

  FIG. 16 is a timing chart showing a control sequence of the photosensitive drum 1201 and the intermediate transfer roller 1204 during the image forming operation by the image forming apparatus (FIG. 15) according to the present invention.

  In FIG. 16, when the control unit 109 receives an image forming operation start (ON command) from the system controller 1220 (S1301), the control unit 109 starts accelerating the output shaft of the stepping motor 103 and reaches a preset target speed. Drive at a constant speed (S1302).

  Next, the low frequency speed fluctuation component correction control (feed forward control) for the speed fluctuation component due to the low frequency (first frequency) described in the first embodiment is executed on the photosensitive drum 1201 and the intermediate transfer roller 1204. . Here, the photosensitive drum 1201 and the intermediate transfer roller 1204 are not controlled simultaneously. This is because, in the low-frequency speed fluctuation component correction control, there is a state in which the average speeds of the photosensitive drum 1201 and the intermediate transfer roller 1204 as the rotating bodies rotate differently with respect to the target values in the control transition period. If the photosensitive drum 1201 and the intermediate transfer belt 1202 rotate while being rubbed against each other, an unexpected load fluctuation is caused by the fluctuation of the friction coefficient in the rubbing portion, and the correction table is generated (converged). This is because it takes a long time.

  The control unit 109 first performs correction control on the photosensitive drum 1201 (any one) (S1303). When the correction table of the photosensitive drum 1201 is fixed (S1304), the same correction control is performed on the intermediate transfer roller 1204 (whichever is the other) (S1305).

  When the speed fluctuations of the photosensitive drum 1201 and the intermediate transfer roller 1204 are stabilized (when each correction table is fixed) (S1306), the control unit 109 starts an image forming operation in accordance with a command from the system controller 1220 ( S1307). For example, a high voltage necessary for the electrophotographic process is applied to the charger 1208, the developing device 1206, and the primary transfer roller 1209. On the other hand, the attaching operation of the belt cleaner 1213 and the secondary transfer device 1211 is performed (S1308).

  At this time, as an example of an operation that causes a large load fluctuation to the photosensitive drum 1201 and the intermediate transfer belt 1202, there is an “attaching” operation of the secondary transfer device 1211 and the belt cleaner 1213. However, since the load fluctuation converges after a predetermined time after the wearing operation, it is often unnecessary to follow the high-frequency speed fluctuation component correction control (real-time feedback control) according to the present embodiment.

  Therefore, the control unit 109 executes high frequency (second frequency) speed fluctuation component correction control for the photosensitive drum 1201 and the intermediate transfer roller 1204 in the time zone between S1308 and S1310 in FIG. 16 (S1309). In other words, after convergence of load fluctuations (after S1308) during the “wearing” operation of the secondary transfer device 1211 and the belt cleaner 1213, a toner image is formed in the image forming operation (toner image transfer) a predetermined time (before S1310). The high-frequency speed fluctuation component correction control is executed in the time zone.

  As described above, the low-frequency speed fluctuation component correction control and the high-frequency speed fluctuation component correction control are executed on the photosensitive drum 1201 and the intermediate transfer roller 1204, so that the magnification fluctuation of the toner image formed by the image forming unit 1200 can be reduced. Color shift and pitch unevenness can be reduced. In addition, image quality can be stabilized over a long period of time.

Block diagram of a speed control device according to an embodiment of the present invention FIG. 3 is a timing chart for explaining a method for detecting angular velocity fluctuations of a rotating body using an output signal of an encoder; (a) a timing chart showing a counter reference clock; (b) a timing chart showing a home position input signal of the rotating body; c) Timing chart showing encoder input, (d) Timing chart showing count number measured with reference to rising edge of encoder output signal, (e) Diagram showing speed data detected by count number The flowchart which shows the angular velocity fluctuation correction control of the rotary body which concerns on embodiment of this invention. The figure which shows the angular velocity fluctuation data profile of the rotary body obtained by the experiment which concerns on embodiment of this invention. The figure which shows the FFT calculation result of the angular velocity fluctuation data profile of a rotary body The figure which shows the relationship between the FFT calculation result of the angular velocity fluctuation data profile of a rotary body, and a low frequency component passage type filter The figure which shows the coefficient profile of the low frequency component passage type filter The figure which shows the signal processing block of the digital filter The figure which shows the result of having performed the filter operation for the detection encoder data The figure which shows the encoder data profile at the time of low frequency speed fluctuation component correction control (feedforward control) implementation based on this invention The figure which shows the experimental result which corrected the speed fluctuation with the encoder data of the low frequency component (A) The figure showing the motor drive pulse set by the low frequency speed fluctuation component correction table, (b) The figure showing the motor operation clock supplied to the stepping motor, (c) The encoder input signal by the rotation of the rotating body FIG. 4D is a diagram showing the calculation timing of the high-frequency speed fluctuation component correction value. FIG. 5 is a schematic diagram showing a second correction value calculation and reflection method in real-time feedback control according to the present invention, (a) a diagram showing an encoder input, (b) a diagram showing a second correction value, and (c) a second. The figure which shows the dispersion value of the correction value of (a), and the figure which shows the correction value actually set (d) FIG. 4 is a schematic diagram showing the correction effect of real-time feedback control on the amount of positional deviation caused by the speed fluctuation of the rotating body, (a) a diagram showing the speed of the rotating body, and (b) a diagram showing the motor drive frequency. 1 is a diagram illustrating a configuration in which a speed control apparatus according to a first embodiment is applied to an image forming apparatus. 6 is a timing chart showing a control sequence of the photosensitive drum and the intermediate transfer roller during an image forming operation by the image forming apparatus according to the present invention. Schematic configuration cross-sectional view of a conventional image forming apparatus

Explanation of symbols

101 Rotating body 102 Drive gear 103 Stepping motor (drive means)
104 Motor driver 105 Encoder A (detection means)
106 Encoder B (detection means)
107 Code wheel 108 Home position sensor 109 Control unit (control means)
110 CPU
111 Counter A
112 Counter B
113 Pulse Generator 1201 Photosensitive drum (photosensitive member) (rotating member)
1202 Intermediate transfer belt (intermediate transfer member) (rotating member)
1220 System controller 1223 Speed fluctuation control unit

Claims (7)

Rotating body, driving means for driving the rotating body, detecting means for detecting the speed of the rotating body, and a driving signal output to the driving means based on speed data of the rotating body detected by the detecting means And a control means for controlling the drive means by correcting the calculated drive signal, and a speed control device comprising:
The control means extracts a first speed fluctuation component having a plurality of frequency components and a speed fluctuation component having a frequency component different from the first speed fluctuation component, and the extracted first speed fluctuation When the component converges within a predetermined range set in advance, the updating of the correction value is stopped, and the driving means is based on the first correction table for fixing all the correction values and the fixed first correction table. And a second correction table that corrects a difference between a target speed set in advance for the driving unit and an average speed during one rotation of the rotating body when the rotating body is driven by
Perform feedforward correction control based on the first correction table and the second correction table, and
In a state in which the rotating body is driven by the feedforward correction control, a preset first speed is set with respect to a difference between the speed data detected at a predetermined timing by the detection means and a preset target speed. For the difference between the first correction value calculated by multiplying by one predetermined coefficient, the sum of speed data detected in a predetermined time region by the detecting means, and the preset sum of target speeds, A second correction value calculated by multiplying a preset second predetermined coefficient,
Feedback correction control is performed by adding the first correction value and the second correction value to the corresponding correction values in the first and second correction tables in the feedforward correction control. Speed control device. The speed control device according to claim 1 ,
An average speed during one rotation of the rotating body serving as a reference for calculating the second correction table is an average value calculated based on speed data detected by the detection means, or the first speed A speed control device calculated from an average value calculated based on a correction value in the correction table. The speed control device according to claim 1 ,
A speed control apparatus, wherein a sum of the first predetermined coefficient and the second predetermined coefficient is 1 or less. The speed control device according to claim 1 ,
The control means disperses the calculated second correction value in a preset time region and multiplies a preset predetermined weighting coefficient as a new second correction value. A speed control device. The speed control device according to claim 4 ,
The speed control device, wherein the preset time region is set such that a value obtained by dispersing the second correction value is equal to or less than a preset predetermined value. In the image forming apparatus for controlling the rotational speed so that the photosensitive member and the transfer member rub against each other, and transferring the electrostatic latent image formed on the photosensitive member to the transfer member,
A speed control device according to claim 1 is provided,
The rotating body is the photosensitive body and the transfer body,
The control means extracts a speed fluctuation component due to a first frequency from speed data during one rotation of either the photoconductor or the transfer body, and sets the speed fluctuation component due to the first frequency as a target value. In order to converge to the above, the feedforward correction control is performed,
In order to extract a speed fluctuation component due to the first frequency from speed data during one rotation of the other of the photoconductor and the transfer body, and to converge the speed fluctuation component due to the first frequency to a target value , Performing the feedforward correction control,
In order to extract a speed fluctuation component due to the second frequency from speed data during one rotation of the photoconductor and the transfer body, and to converge the speed fluctuation component due to the second frequency to a target value, the feedback correction An image forming apparatus that performs control. In the image forming apparatus for controlling the rotational speed so that the photosensitive member and the transfer member rub against each other, and transferring the electrostatic latent image formed on the photosensitive member to the transfer member,
Comprising a speed controller according to any one of claims 1 through 5,
The rotating body is the photosensitive body and the transfer body,
The image forming apparatus, wherein the speed control device controls the photosensitive member and the transfer member.