JP2008182817A - Servo motor controller, method therefor, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the resolution in control of the rotational speed of a servo motor while suppressing increase of the frequency of a reference clock signal and addition of a constituent element to a conventional servo motor controller obviated as much as possible. <P>SOLUTION: Multiple frequency division ratios including different values are periodically set by a control unit 25. A pulse signal train after frequency division, is generated by successively dividing the reference clock signal, being a reference pulse signal train inputted in a predetermined cycle at a preset frequency division ratio with a frequency division clock generation unit α1. The generated pulse signal train after frequency division is supplied as a speed commanding signal to a servo amplifier 28 for driving a servo motor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a servo motor control apparatus and method for controlling a servo motor by a pulse signal sequence obtained by dividing a reference pulse signal input at a constant period, and an image forming apparatus having the control function. It is.

Conventionally, in an image forming apparatus such as a printer, a facsimile machine, and a copying machine, a servo motor or a stepping motor is often used as a drive source of a rotating device such as a photosensitive drum or an intermediate transfer member. In addition, servo motors are widely used as a drive source for rotating equipment that needs to control the rotational speed with high accuracy.
The servo motor is driven by a servo motor drive circuit (an example of servo motor drive means) that performs feedback control of rotation based on a speed command signal that is a pulse signal sequence representing a target rotation speed. A servo motor control device, which is a host control device, supplies the speed command signal (pulse signal train) to the servo motor drive circuit. The servo motor drive circuit is generally called a servo circuit or a servo amplifier.
In addition, the servo motor control device performs frequency division by sequentially dividing a reference clock signal composed of a series of reference pulse signals (hereinafter referred to as reference pulse signals) inputted at a constant cycle at a predetermined division ratio. The pulse signal train is generated and supplied to the servo motor drive circuit as the speed command signal. That is, when the servo motor control device wants to increase the rotation speed of the servo motor, it divides the speed command signal with a large number of pulses per time by dividing by a small division ratio (minimum is 1). Output to the servo motor drive circuit. Similarly, when the servo motor control device wants to reduce the rotation speed of the servo motor, it divides the speed command signal with a small number of pulses per time by dividing the servo motor drive circuit with the servo motor drive circuit. Supply against. At that time, the conventional servo motor control device does not change the setting of the division ratio unless the target rotational speed changes.

The frequency fy of the speed command signal obtained by dividing the reference clock signal is a frequency (fy = fx / N) obtained by dividing the frequency fx of the reference clock signal by a division ratio N (an integer equal to or greater than 1). It becomes.
Accordingly, the resolution of the rotational speed control of the servo motor is determined by the frequency of the reference clock signal (which may be referred to as the generation period of the reference pulse signal). For this reason, it is necessary to increase the frequency of the reference clock signal in order to increase the resolution of the servo motor rotation speed control.
On the other hand, in Patent Document 1, a drive pulse signal having a frequency twice that of the reference clock signal is generated by detecting both the rising and falling edges of the reference pulse signal in the reference clock signal, and the driving is performed. A technique for controlling a stepping motor by a pulse signal is shown. That is, the technique disclosed in Patent Document 1 is a technique that substantially doubles the frequency of the reference clock signal used for controlling the stepping motor.

By the way, in a color image forming apparatus provided with an intermediate transfer body (intermediate transfer belt, intermediate transfer roller, etc.), a plurality of colors (generally cyan, magenta, and yellow) of toner are sequentially transferred from the photosensitive drum to the intermediate transfer body. Then, the toner of multiple colors is further transferred from the intermediate transfer member to a recording material (typically a recording paper), thereby forming an image on the recording material. To an endless belt-shaped intermediate transfer belt (an example of an intermediate transfer member), toner is transferred from each of a plurality of photosensitive drums provided for each color, and a plurality of colors of toner (from the intermediate transfer belt to a recording material) A typical example is a so-called tandem color image forming apparatus for transferring a toner image. Hereinafter, such an image forming apparatus is referred to as an intermediate transfer type image forming apparatus.
In an intermediate transfer type image forming apparatus, it is very important to maintain the rotational speed of the intermediate transfer member at a predetermined speed with high accuracy. This is because if the rotational speed of the intermediate transfer member deviates even slightly from the set speed (target speed), color shift occurs in the formed image. For example, in an image forming apparatus with an image resolution of 600 dpi, when the pixel interval is about 42 microns and the photosensitive drum interval is 150 [mm], the servo motor rotation speed is only shifted by 0.0093%. A color shift of one pixel occurs.
JP 2000-261615 A

However, when the technique disclosed in Patent Document 1 is adopted, it is necessary to add a circuit (double clock circuit) for doubling the frequency of the reference clock signal. There was a problem that increased. Even if the technology disclosed in Patent Document 1 is adopted, the control resolution of the servo motor is only doubled compared to the case where it is not adopted, and it cannot be handled when higher resolution is required. There was a problem.
In general, as the frequency of the clock signal is increased, the influence of noise in the clock signal becomes more prominent, and there has been a problem that the apparatus becomes complicated and the cost is increased for noise countermeasures.
Accordingly, the present invention has been made in view of the above circumstances, and its object is to increase the frequency of a reference clock signal (the reference clock signal) without increasing the frequency of the reference servo signal. It is an object of the present invention to provide a servo motor control device and method thereof that can increase the resolution of servo motor rotation speed control without adding components as much as possible, and an image forming apparatus having the control function.

In order to achieve the above object, a servo motor control device according to the present invention provides servo motor drive means for performing feedback control of servo motor rotation drive based on a speed command signal that is a pulse signal sequence representing a target rotation speed. The speed command signal is supplied, and includes the following components (1-1) and (1-2).
(1-1) Frequency division ratio setting means for periodically setting a plurality of frequency division ratios having different values.
(1-2) Generate a sequence of pulse signals after frequency division by sequentially dividing a sequence of reference pulse signals input at a constant period by a frequency division ratio set by the frequency division ratio setting means. Dividing signal generating means for supplying the pulse signal train after frequency division to the servo motor driving means as the speed command signal.
The component shown in (1-2) above also includes a conventional servo motor control device.

In the servo motor control device according to the present invention, the divided pulse signal generated by the divided signal generation means based on a plurality of different division ratios (that is, a plurality of types of pulse signals having different time intervals). The speed command signal (sequence of pulse signals) in which is mixed is generated. If the speed command signal is a unit of one cycle period for setting a plurality of division ratios, the reference clock signal has an intermediate division ratio that is an average value of the plurality of division ratio values. Can be regarded as a signal obtained by frequency division.
For example, when the frequency division ratio setting means alternately (periodically) sets the frequency division ratio “2” and the frequency division ratio “3” for the frequency division signal generation means, that is, combinations of the frequency division ratios. Consider the case where the ratio is 1: 1. In this case, if the speed command signal is averaged in the unit of the period of one cycle for setting the two frequency division ratios “2” and “3”, the reference clock signal has an intermediate frequency division ratio “2.5”. It can be regarded as a signal obtained by dividing the signal. Similarly, when the division ratio “2” and the division ratio “3” are set in the order of (2 → 3 → 2) or (3 → 2 → 3), that is, a mixing ratio of a plurality of division ratios. Is considered to be 2: 1 or 1: 2. In this case, if the speed command signal is averaged in the unit of one cycle period for setting the two frequency dividing ratios “2” and “3”, the intermediate frequency dividing ratio “2.33” or “2. 67 "can be regarded as a signal obtained by dividing the reference clock signal.
Therefore, according to the present invention, the frequency division ratio setting means adjusts and sets the value of each of the plurality of frequency division ratios and the mixing ratio (mixing ratio), thereby dividing the reference clock signal as it is. As compared with the conventional servo motor control device, the resolution of the rotational speed control of the servo motor can be substantially doubled. Further, the frequency division ratio setting means can be realized by, for example, changing the program executed by the arithmetic means (MPU) provided in the conventional servo motor control device. Requires little addition. In addition, since the frequency of the reference clock signal is not increased, the apparatus is not complicated and expensive for noise suppression.

By the way, the servo motor control device according to the present invention periodically changes the division ratio to be set even if the target rotational speed is constant, that is, the time interval of the pulse train in the speed command signal changes. Servo motor rotation unevenness may occur. However, if the moment of inertia around the rotation axis of the servo motor is sufficiently large compared to the rotation torque of the servo motor, even if the time interval of the pulse train in the speed command signal changes slightly, the rotation unevenness of the servo motor will hardly occur. Absent. Therefore, the present invention is effective when applied to a controlled object in which the ratio of the rotation torque of the servo motor to the moment of inertia around the rotation axis of the servo motor (hereinafter referred to as the rotation moment / torque ratio) is sufficiently large.
On the other hand, even if the rotational moment / torque ratio in the controlled object is relatively large, if the amount of change in the division ratio to be changed periodically (difference between the division ratios) is large, the servo motor A problem of uneven rotation occurs.
Therefore, it is desirable that the frequency division ratio setting means periodically sets a plurality of frequency division ratios whose value difference is within a predetermined range. For example, it is preferable that the frequency division ratio setting means periodically sets a plurality of frequency division ratios whose value difference is within one.
In this way, it is possible to avoid the occurrence of uneven rotation of the servo motor by limiting the amount of change in the division ratio that is periodically changed (difference between the division ratios) to be small.

More specifically, the frequency division ratio setting means selects a plurality of frequency division ratios having different values from a plurality of predetermined candidates according to the target set speed. It is conceivable to periodically set the selected division ratios for the divided signal generation means. In this case, it is simpler and easier to design if each of the plurality of sets of candidates is composed of the same number of division ratio sets.
In order to make the rotation of the servo motor as uniform as possible, the division ratio is switched as short as possible, that is, the division ratio is switched in one cycle period in which a plurality of division ratios are set periodically. It is desirable to distribute the timing uniformly. For example, when two or more types of division ratios with different values are mixed and set periodically, and the mixing ratio is 1: 1, the two types of division ratios are set alternately. It is desirable.

The present invention can also be understood as a servo motor control method for executing the output process of the speed command signal by the servo motor control device according to the present invention described above.
That is, the servo motor control method according to the present invention provides the speed command signal to the servo motor drive means for performing feedback control of the rotation drive of the servo motor based on the speed command signal which is a pulse signal sequence representing the target rotation speed. This is a control method to be supplied, and is a method for executing the following procedures (2-1) and (2-2).
(2-1) A frequency division ratio setting procedure in which a predetermined control means automatically executes a process of periodically setting a plurality of frequency division ratios having different values.
(2-2) A predetermined frequency dividing signal generating means sequentially divides a train of reference pulse signals inputted at a constant period by a frequency dividing ratio set by the frequency dividing ratio setting procedure, and then performs frequency division. A frequency division signal generation procedure for generating a pulse signal train and supplying the generated pulse signal train after the frequency division to the servo motor driving means as the speed command signal.

The present invention can also be understood as an image forming apparatus including the above-described servo motor control device according to the present invention.
That is, the image forming apparatus according to the present invention sequentially transfers each of a plurality of color developers (typically toner) from the image carrier to the intermediate transfer member, and then transfers the developer from the intermediate transfer member to the recording material. The image is formed on the recording material by transferring to the servomotor, and the servomotor for rotationally driving the intermediate transfer body and the servomotor based on a speed command signal that is a pulse signal string representing a target rotational speed. Servo motor driving means for performing feedback control of rotational driving is provided, and further, the constituent elements of the servo motor control device according to the present invention described above are also provided.
In general, in an intermediate transfer type image forming apparatus, the moment of inertia around the drive shaft (rotation shaft of the servo motor) of the intermediate transfer member is sufficiently larger than the rotation torque of the servo motor that drives the intermediate transfer member. In addition, as described above, the rotational speed of the intermediate transfer member is required to be controlled with very high accuracy in order to prevent color deviation of the formed image. Therefore, the servo motor for driving the intermediate transfer member in the intermediate transfer type image forming apparatus is very suitable as an application target of the present invention.
The present invention also relates to an image forming apparatus of the type in which the intermediate transfer member is rotationally driven by a stepping motor, and the stepping motor is controlled by the same control method as the servo motor control apparatus according to the present invention described above. It can also be understood as a device.
That is, the image forming apparatus according to the present invention controls a stepping motor that rotationally drives the intermediate transfer member and a rotational driving control of the stepping motor based on a speed command signal that is a pulse signal sequence representing a target rotational speed. Motor drive means, and further includes the constituent elements of the servo motor control device according to the present invention described above. However, the supply destination of the speed command signal by the frequency division signal control means is the stepping motor driving means.
Even when the present invention is applied to an image forming apparatus in which the intermediate transfer member is rotationally driven by a stepping motor, the same effects as those obtained when the intermediate transfer member is rotationally driven by a servo motor can be obtained.

The speed command signal obtained by the present invention is a signal in which a plurality of pulse signals (pulse signals having different time intervals) obtained by dividing the reference clock signal by a plurality of different division ratios are mixed. For this reason, in the unit of one cycle period for setting a plurality of division ratios, the reference clock signal is divided by an intermediate division ratio that is an average value of the plurality of division ratio values. It can be regarded as a signal obtained in this way.
Therefore, according to the present invention, the frequency division ratio setting means adjusts and sets the value of each of a plurality of frequency division ratios and the ratio of the mixture, thereby dividing the reference clock signal as it is. Compared with a motor control device (or a conventional stepping motor control device), the resolution of motor rotational speed control can be substantially doubled or more. Further, the frequency division ratio setting means can be realized by, for example, changing the program executed by the arithmetic means (MPU) provided in the conventional servo motor control device (or the conventional stepping motor control device) Few components are added to the conventional control device. In addition, since the frequency of the reference clock signal is not increased, the apparatus is not complicated and expensive for noise suppression.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a servo motor system Y provided with a servo motor control device X according to an embodiment of the present invention. FIG. 2 is a reference clock signal and speed command signal in the conventional servo motor control device. FIG. 3 is a diagram illustrating a first example of the reference clock signal and the divided clock signal in the servo motor control device X. FIG. 4 is a diagram illustrating the reference clock signal and the divided clock signal in the servo motor control device X. FIG. 5 is a schematic diagram of a main part of a tandem type color image forming apparatus Z provided with a servo motor control device X. FIG.

First, the configuration of a servo motor control device X according to an embodiment of the present invention and a servo motor system Y including the same will be described with reference to the block diagram shown in FIG.
As shown in FIG. 1, the servo motor system Y includes an oscillator 21, a servo motor control device X, a servo amplifier 28, and a servo motor 27.
The servo motor control device X includes a divided clock generation unit α1, a control unit 25, and a signal control circuit 26. Further, the frequency-divided clock generation unit α1 includes a clock counter 22, a comparator 23, and a generation circuit 24.
The oscillator 21 generates a reference clock signal that is a sequence of reference pulse signals having a constant period. For example, the oscillator 21 generates the clock signal having a constant frequency of 20 MHz to 30 MHz.
The frequency-divided clock generator α1 receives a reference clock signal that is a sequence of reference pulse signals having a constant period from an oscillator 21 such as a crystal oscillator.
The frequency-divided clock generator α1 divides the reference clock signal, which is a series of reference pulse signals input at a constant cycle, by sequentially dividing the reference clock signal at a frequency-dividing ratio set by the control unit 25. A train of subsequent pulse signals (hereinafter referred to as a divided clock signal) is generated, and the generated divided clock signal is supplied to the servo amplifier 28 through the signal control circuit 26 (an example of the divided signal generating means). . The frequency-divided clock signal supplied to the servo amplifier 28 is a speed command signal described later.

More specifically, in the divided clock generation unit α1, the clock counter 22 detects the rising timing of the reference pulse signal that constitutes the reference pulse signal, so that the number of clocks of the reference clock signal (reference Count the number of pulse signals).
Further, the number of clocks of the reference clock signal counted by the clock counter 22 and two large and small integer values set by the control unit 25 are input to the comparator 23. Hereinafter, of the two large and small integer values, the larger integer is referred to as a first integer, and the smaller integer is referred to as a second integer.
Then, the comparator 23 first compares the number of clocks of the reference clock signal with the smaller second integer, and when they match, outputs a predetermined pulse rising signal to the generation circuit 24. Output. Thereafter, the comparator 23 compares the number of clocks of the reference clock signal with the larger first integer, and outputs a predetermined pulse falling signal to the generation circuit 24 when they match. .
In response to the pulse rise signal and the pulse fall signal from the comparator 23, the generation circuit 24 is a pulse signal in which the timing at which these signals are input becomes the rise and fall timings of the pulse signal, respectively. (Hereinafter referred to as a frequency-divided pulse signal).
On the other hand, the comparator 23 also outputs the pulse falling signal to the control unit 25 and the clock counter 22. Accordingly, the control unit 25 detects the falling timing of the pulse signal in the divided clock signal. Further, the clock counter 22 resets the number of clocks being counted (sets to 0) when detecting the pulse falling signal.
The clock counter 22, the comparator 23, and the generation circuit 24 sequentially repeat the processes described above.
As described above, the first integer set by the control unit 25 becomes a frequency division ratio when the frequency-divided clock signal is generated, and the frequency-divided clock generation unit α1 uses the frequency division ratio of the reference pulse signal. The frequency-divided clock signal is generated by performing frequency division by (the first integer).

The servo amplifier 28 is a circuit that performs feedback control of rotation drive of the servo motor 27 based on a speed command signal that is a pulse signal sequence representing a target rotation speed (an example of the servo motor drive means). The speed command signal is supplied from the servo motor control device X.
The servo amplifier 28 includes a deviation counter, a D / A converter and an amplifier (not shown). The deviation counter compares the speed command signal with a rotation speed detection signal of a servo motor detected by an encoder or the like connected to the rotation shaft of the servo motor 27 to thereby obtain a deviation of the actual rotation speed from the target rotation speed. Is detected. The deviation signal is converted into an analog signal by the D / A converter, and the amplifier adjusts a drive signal supplied to the servo motor 27 based on the analog signal. Thereby, feedback control of the rotational speed of the servo motor 27 is performed.

The control unit 25 includes a calculation unit such as a CPU and a storage unit such as a RAM and a ROM, and performs various calculations and controls in the servo motor control device X.
Specifically, the control unit 25 sets a division ratio for the divided clock generation unit α1.
Further, the signal control circuit 26 supplies (outputs) the frequency-divided clock signal (that is, the speed command signal) to the servo amplifier 28 based on the control signal from the control unit 25 to cause the servo motor 27 to operate. This is a circuit for switching between a driving state and a state in which the servo motor 27 is stopped without supplying the divided clock signal.
The hardware configuration of the servo motor control device X described above is the same as that of the conventional servo motor control device.
However, the servo motor control device X and the conventional servo motor control device differ in the content of the frequency division ratio setting process by the control unit 25. That is, the contents of the frequency division ratio setting program (software) executed by the control unit 25 are different.

The control unit 25 in the servo motor control device X provides a plurality of frequency division ratios with different values to the frequency division clock generation unit α1 when one target speed of the servo motor 27 is determined. Periodically set (an example of the frequency division ratio setting means). Of course, depending on the target rotational speed, the control unit 25 may set a constant frequency division ratio to the frequency-divided clock generation unit α1, as long as the target rotational speed is not changed, as in the prior art.
More specifically, the control unit 25 selects a plurality of division ratios having different values in accordance with the target rotational speed of the servomotor 27 from a plurality of predetermined candidates, The plurality of selected division ratios are periodically set for the divided signal generation means. The plurality of sets of candidates are each composed of the same number of division ratio sets.
For example, the plurality of sets of candidates are (2000, 2000), (2000, 2001), (2001, 2001), (2001, 2002), (2002, 2002), (2002, 2003), (2003, 2003). , (2003, 2004). When the frequency division ratio candidate (2000, 2001) is selected, the control unit 25 alternately sets the frequency division ratios “2000” and “2001” every time one pulse signal after frequency division is generated. Set to (periodic). In this case, the obtained divided clock signal (that is, the speed command signal) is divided into two division ratios “2000” and “2001” in terms of a unit of one cycle setting two division ratios. ”Can be regarded as a signal obtained by dividing the reference clock signal by an intermediate value (= 2000.5) which is an average value of the values of“ ”.

FIG. 2 is a diagram illustrating an example of the reference clock signal and the divided clock signal in a conventional servo motor control apparatus. FIGS. 3 and 4 are diagrams showing a first example and a second example of the reference clock signal and the divided clock signal in the servo motor control device X. FIG.
In the following description, an example in which the frequency division ratio is a small value such as 5 or 6 will be described for the sake of simplification. However, the frequency division ratio actually set is, for example, 2000 to 3000 or the like. A large division ratio is preferred.
The conventional servo motor controller does not change the division ratio setting unless the target rotational speed changes. Therefore, as long as the target rotational speed does not change, as shown in FIG. 2, the frequency t2 (time interval) of the frequency-divided pulse signal is constant in the frequency-divided clock signal, and the frequency division ratio N to be set is changed by 1. Then, the period t2 changes by t1. Therefore, in the conventional servo motor control apparatus, when the division ratio is N, the resolution of the divided clock signal (the speed command signal) is 1 / N. FIG. 2 shows an example in which the frequency division ratio N = 6.

On the other hand, the servo motor control device X can periodically change the setting of the division ratio even if the target rotational speed does not change, and even if the target rotational speed does not change, as shown in FIG. The time interval of the divided pulse signal in the divided clock signal changes periodically.
For example, the example shown in FIG. 3 is an example in which the division ratios “5” and “6” are alternately (periodically) set every time one of the divided pulse signals is generated. In this case, the obtained frequency-divided clock signal (that is, the speed command signal) is obtained in units of one cycle period (period in which eleven reference pulse signals are generated) for setting two frequency division ratios. It can be regarded as a signal obtained by dividing the reference clock signal by a division ratio of an intermediate value (= 5.5) which is an average value of the two division ratios “5” and “6”. . Therefore, when the state in which the constant frequency division ratio “6” is set (the state in FIG. 2) is changed to the state in which the two frequency division ratios “5” and “6” are alternately set (the state in FIG. 3). , The average time interval of the frequency-divided clock signal changes by (t1 / 2) in terms of a unit of one cycle period (a period in which eleven reference pulse signals are generated) for setting two frequency division ratios. To do. Therefore, in the servo motor control device X that generates the divided clock signal as shown in FIG. 3, when the dividing ratio is N, the resolution of the divided clock signal (the speed command signal) is (1 / 2N). This is twice the conventional level.
In the servo motor control device X that generates the frequency-divided clock signal as shown in FIG. 3, the plurality of sets of frequency division ratios to be selected by the control unit 25 are, for example, (5, 5), (6,5), (6,6), (7,6), (7,7), (8,7), (8,8), (9,8), etc. As a result, the reference clock signal is divided into the division ratios “5.0”, “5.5”, “6.0”, “6.5”, “7.0”, “7.5”, “8”. 0.0 ”,“ 8.5 ”... The frequency-divided clock signal that can be regarded as frequency-divided can be generated by each setting.

Further, in the example shown in FIG. 4, every time one of the divided pulse signals is generated, three division ratios in which the division ratios “5” and “6” are mixed are set (periodically). It is an example. That is, the example shown in FIG. 4 is an example in which three frequency division ratios “6”, “5”, and “5” are sequentially set every time one frequency division pulse signal is generated. In this case, the obtained frequency-divided clock signal (that is, the speed command signal) can be obtained in units of one cycle period (a period in which 16 reference pulse signals are generated) for setting three frequency division ratios. It is obtained by dividing the reference clock signal by an intermediate value (= 5.33) which is an average value of the three frequency dividing ratios “6”, “5” and “5”. It can be regarded as a signal. Therefore, when the state of setting the constant frequency division ratio “5” is changed to the state shown in FIG. 3, the period of one cycle in which the three frequency division ratios are set (the period in which 16 reference pulse signals are generated). In terms of units, the average time interval of the divided clock signal changes by (t1 / 3). Therefore, in the servo motor control device that generates the divided clock signal as shown in FIG. 4, when the dividing ratio is N, the resolution of the divided clock signal (the speed command signal) is (1 / 3N). Yes, it is three times as much as before.
In the servo motor control device X that generates the divided clock signal as shown in FIG. 4, the plurality of sets of division ratio candidates to be selected by the control unit 25 are, for example, (5, 5, 5 ), (6, 5, 5), (6, 5, 6), (6, 6, 6), (7, 6, 6), (7, 6, 7), (7, 7, 7), (8, 7, 7)... Thus, the reference clock signal is divided into frequency division ratios “5.00”, “5.33”, “5.67”, “6.00”, “6.33”, “6.67”, “7”. .00 ”,“ 7.33 ”... The frequency-divided clock signal that can be regarded as frequency-divided can be generated by each setting.

As described above, according to the servo motor control device X, the speed command signal (the divided clock signal) supplied to the servo amplifier 28 is divided by a plurality of different division ratios (that is, The divided pulse signals having different time intervals can be mixed signals.
Therefore, according to the servo motor control device X, the control unit 25 divides the reference clock signal as it is by adjusting and setting the value of each of a plurality of frequency division ratios and the ratio of the mixture thereof. Compared with the servo motor control device, the resolution of the motor rotation speed control can be substantially doubled or more. Further, the control unit 25 can be realized by, for example, changing a program executed by the control unit provided in the conventional servo motor control device, so that almost no addition of components to the conventional control device is required. In addition, since the frequency of the reference clock signal is not increased, the apparatus is not complicated and expensive for noise suppression.

By the way, as described above, the present invention is effective when applied to a controlled object in which the rotational moment / torque ratio (ratio of the rotational torque of the servo motor to the inertia moment around the rotational axis of the servo motor) is sufficiently large. is there.
On the other hand, even if the rotational moment / torque ratio is relatively large, if the amount of change in the division ratio that is periodically changed (difference between the division ratios) is large, the rotation unevenness of the servo motor will still be reduced. Problems arise. For example, in the servo motor control device X, the frequency division corresponding to the frequency division ratio “5.5” by setting the two frequency division ratios is 1: 1 for the frequency division ratio “4” and the frequency division ratio “7”. Even if the ratio is set in a mixed ratio, the frequency division ratio “5” and the frequency division ratio “6” can be set in a ratio of 1: 1. However, in order to prevent rotation unevenness of the servo motor, it is preferable to perform the latter setting (setting of the frequency division ratios “5” and “6”).
That is, it is desirable that the control unit 25 periodically sets a plurality of frequency division ratios in which the difference in values is within a relatively narrow range set in advance. For example, it is preferable that the control unit 25 periodically sets a plurality of frequency division ratios whose value difference is within one. The above-described specific examples of the plurality of sets are all examples in which a plurality of division ratios whose value difference is within 1 are periodically set.
In this way, it is possible to avoid the occurrence of uneven rotation of the servo motor by limiting the amount of change in the division ratio that is periodically changed (difference between the division ratios) to be small.

Next, a tandem type color image forming apparatus Z to which the servo motor control apparatus X is applied will be described.
FIG. 5 is a schematic configuration diagram of a main part of a tandem color image forming apparatus Z provided with a servo motor control device X.
The color image forming apparatus Z includes four image forming portions Y, M, C, B and transfer devices 6 corresponding to toners of four colors (yellow, magenta, cyan, black), and an endless belt-shaped intermediate transfer. The apparatus includes a belt 1, the servo motor system Y including the servo motor 27 that rotationally drives the intermediate transfer belt 1, a camera 31, and an image processing unit 32. Each of the image forming units Y, M, C, and B includes a photosensitive drum 5 (an example of an image carrier), a charging device 7, a developing device 9, a transfer device 6, and a cleaning device 10. Note that the components of the image forming units Y, M, C, and B are well known and will not be described here.
When the color image forming apparatus Z forms a color image on the recording paper 2, first, toners of a plurality of colors (cyan, magenta and yellow) are transferred from the photosensitive drum 5 provided for each color to an intermediate transfer. Intermediate transfer type image formation in which a plurality of color toners on the intermediate transfer belt 1 are transferred from the intermediate transfer belt 1 to a recording sheet by the transfer device 6 provided for each color in order. Device.

The camera 31 is a camera that captures moving images. The image processing unit 32 is an arithmetic unit that performs image processing on an image captured by the camera 31.
The camera 31 and the image processing unit 32 detect the rotational speed of the intermediate transfer belt 1.
On the surface of the intermediate transfer belt 1, equidistant marks are written along the rotation direction (recording paper conveyance direction).
The camera 31 continuously captures the marks on the intermediate transfer belt 1 and transmits the captured images to the image processing unit 32.
The image processing unit 32 detects the movement speed of the mark, that is, the rotational speed of the intermediate transfer belt 1 by observing the movement of the mark in the image captured by the camera 31 by image processing. The detection result is transmitted to the control unit 25 in the servo motor control device X.
The control unit 25 sets the frequency division ratio setting contents for the frequency division clock generation unit α1 according to the difference between the rotation speed of the intermediate transfer belt 1 and a predetermined set speed (a plurality of periodically set values). The value of the frequency division ratio and the mixture ratio are adjusted.
Thereby, the servo motor control device X can control the rotational speed of the servo motor 27 that rotationally drives the intermediate transfer belt 1 with high accuracy (high resolution).
In the intermediate transfer type color image forming apparatus Z, the moment of inertia around the drive shaft of the intermediate transfer belt 1 (the rotation shaft of the servo motor 27) is sufficiently larger than the rotation torque of the servo motor 27 that drives the intermediate transfer belt 1. large. In addition, as described above, the rotational speed of the intermediate transfer belt 1 is required to be controlled with very high accuracy in order to prevent color deviation of the formed image. Therefore, the servo motor 27 for driving the intermediate transfer belt 1 in the color image forming apparatus Z is very suitable as an application target by the servo motor control apparatus X.

In the color image forming apparatus Z shown in FIG. 5, the driving source of the intermediate transfer belt 1 is a servo motor. However, an embodiment in which this is driven by a stepping motor is also conceivable.
In general, the stepping motor is controlled in the same manner as the servo motor. That is, in the servo motor system Y shown in FIG. 1, if the servo motor 27 is replaced with a stepping motor and the servo amplifier 28 is replaced with an amplifier for driving a stepping motor, a stepping motor drive system is obtained.
However, the stepping motor driving amplifier (an example of the stepping motor driving means) counts the number of pulse signals (number of rising edges) in the speed command signal and rotates the stepping motor by the number of steps corresponding to the counted number. This circuit does not perform feedback control.
Further, the servo motor control device X is diverted as a stepping motor control device, and the stepping motor control device supplies the speed command signal to the amplifier for driving the stepping motor.
As described above, there is also a system in which the servo motor control device X is diverted as a stepping motor control device, and the rotation speed of the stepping motor that rotationally drives the intermediate transfer belt 1 in the color image forming apparatus Z is controlled by the stepping motor control device. , The same operational effects as the image forming apparatus Z provided with the servo motor control device X are obtained.
In the above-described embodiment, the control unit 25 generates the divided clock signal by setting the division ratio with respect to the divided clock generation unit α1, but the present invention is not limited to this. Another computer having a storage unit such as a RAM and a ROM that assists the operation of the CPU sets a division ratio for the divided clock generator α1 by executing a predetermined program. It is also possible.

The block diagram showing the schematic structure of the servomotor system Y provided with the servomotor control apparatus X which concerns on embodiment of this invention. The figure showing an example of a standard clock signal and a speed command signal in the conventional servo motor control device. The figure showing the 1st example of the reference clock signal and the frequency-divided clock signal in the servo motor control device X. The figure showing the 2nd example of the reference clock signal in the servomotor control apparatus X, and a frequency-divided clock signal. 1 is a schematic configuration diagram of a main part of a tandem color image forming apparatus Z including a servo motor control device X. FIG.

Explanation of symbols

X: Servo motor control device Y according to the embodiment of the present invention ... Servo motor system Z ... Color image forming device 1: Intermediate transfer belt 2: Recording paper 5: Photoconductor drum 6: Transfer device 7: Charging device 9: Developing device 10: Cleaning device α1: Divided clock generation unit 21: Oscillator 22: Clock counter 23: Comparator 24: Generation circuit 25: Control unit 26: Signal control circuit 27: Servo motor 28: Servo amplifier

Claims (8)

A servo motor control device for supplying the speed command signal to a servo motor drive means for performing feedback control of the rotation drive of the servo motor based on a speed command signal which is a pulse signal sequence representing a target rotation speed,
A frequency division ratio setting means for periodically setting a plurality of frequency division ratios having different values mixed together;
A series of divided pulse signals is generated by sequentially dividing a series of reference pulse signals input at a constant period by a division ratio set by the division ratio setting means. A frequency dividing signal generating means for supplying the train of pulse signals to the servo motor driving means as the speed command signal;
A servo motor control device comprising:   2. The servo motor control device according to claim 1, wherein the frequency division ratio setting means periodically sets a plurality of frequency division ratios having a value difference within a predetermined range.   The servo motor control device according to claim 2, wherein the frequency division ratio setting means periodically sets a plurality of frequency division ratios having a value difference of 1 or less.   The frequency division ratio setting means selects a plurality of frequency division ratios in which different values are mixed according to the target set speed from a plurality of predetermined candidates, and the plurality of frequency divisions selected 4. The servo motor control device according to claim 1, wherein a ratio is periodically set with respect to the divided signal generation means.   The servo motor control device according to claim 4, wherein each of the plurality of sets of candidates includes the same number of sets of division ratios. A servo motor control method for supplying the speed command signal to a servo motor drive means for performing feedback control of the rotation drive of the servo motor based on a speed command signal which is a pulse signal sequence representing a target rotation speed,
A frequency division ratio setting procedure for automatically executing a process for periodically setting a plurality of frequency division ratios having different values mixed by a predetermined control means;
By dividing a series of reference pulse signals input at a constant cycle by a predetermined division ratio by the predetermined division signal generation means at a division ratio set by the division ratio setting procedure, the divided pulse signal series is obtained. A frequency division signal generation procedure for generating and supplying the generated pulse signal train after frequency division to the servo motor driving means as the speed command signal;
A servo motor control method characterized by comprising: Each of a plurality of color developers is sequentially transferred from the image carrier to the intermediate transfer member, and then the developer is transferred from the intermediate transfer member to the recording material to form an image on the recording material. Image forming comprising: a servomotor that rotationally drives the intermediate transfer member; and a servomotor drive unit that performs feedback control of the rotational drive of the servomotor based on a speed command signal that is a pulse signal sequence representing a target rotational speed A device,
A frequency division ratio setting means for periodically setting a plurality of frequency division ratios having different values mixed together;
A series of divided pulse signals is generated by sequentially dividing a series of reference pulse signals input at a constant period by a division ratio set by the division ratio setting means. A frequency dividing signal generating means for supplying the train of pulse signals to the servo motor driving means as the speed command signal;
An image forming apparatus comprising: Each of a plurality of color developers is sequentially transferred from the image carrier to the intermediate transfer member, and then the developer is transferred from the intermediate transfer member to the recording material to form an image on the recording material. A stepping motor that rotationally drives the intermediate transfer member, and a stepping motor drive unit that controls the rotational drive of the stepping motor based on a speed command signal that is a pulse signal sequence representing a target rotational speed of the stepping motor. An image forming apparatus that
A frequency division ratio setting means for periodically setting a plurality of frequency division ratios having different values mixed together;
A series of divided pulse signals is generated by sequentially dividing a series of reference pulse signals input at a constant period by a division ratio set by the division ratio setting means. A frequency dividing signal generating means for supplying the pulse signal train to the stepping motor driving means as the speed command signal;
An image forming apparatus comprising:

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