JP7463753B2 - MOTOR DRIVE DEVICE, IMAGE FORMING APPARATUS AND EXCITATION FREQUENCY CONTROL METHOD - Google Patents

Description

The present invention relates to a motor drive device, an image forming device, and an excitation frequency control method.

Conventionally, when a stepping motor is driven within a certain speed range, there is an issue that the stepping motor generates vibration.

For example, the configuration described in Patent Document 1 discloses a configuration in which the set value of the chopping frequency (excitation frequency) is changed according to the rotation speed of the stepping motor. Furthermore, the configuration described in Patent Document 2 discloses a configuration in which the drive frequency of the motor is diffused.

Japanese Patent Application Laid-Open No. 7-298691 JP 2010-224476 A

However, the configuration described in Patent Document 1 requires a device to detect motor vibration. In addition, if the excitation frequency during motor vibration shifts due to fluctuations in factors such as the load on the device, vibrations may occur at the changed excitation frequency.

In addition, in the configuration described in Patent Document 2, if the drive frequency of the motor is changed in a diffuse manner, the rotation speed of the motor may fluctuate, which may result in a deterioration in position accuracy.

The object of the present invention is to provide a motor drive device, an image forming device, and an excitation frequency control method that can suppress the occurrence of vibrations in a stepping motor without varying the rotation speed of the stepping motor.

The motor drive device according to the present invention comprises:
a stepping motor having a rotary shaft that rotates based on a drive frequency;
A drive control unit that controls an excitation frequency for constant current control of the stepping motor;
Equipped with
The drive control unit is
The excitation frequency is changed over time based on a ratio of the excitation frequency to a rotation frequency based on a rotation speed of the stepping motor;
If the ratio is less than a specified value, the amount of change in the excitation frequency over time is set to 0, and if the ratio is equal to or greater than the specified value, the amount of change in the excitation frequency over time is changed to a preset value .

The image forming apparatus according to the present invention comprises:
The motor drive device is provided.

The excitation frequency control method according to the present invention comprises the steps of:
A method for controlling an excitation frequency of a motor drive device including a stepping motor having a rotary shaft that rotates based on a drive frequency, comprising:
Controlling an excitation frequency for constant current control of the stepping motor;
Varying the excitation frequency over time based on a ratio of the excitation frequency to a rotation frequency based on a rotation speed of the stepping motor;
having
When changing the excitation frequency over time, if the ratio is less than a specified value, the amount of change in the excitation frequency over time is set to 0, and if the ratio is greater than or equal to the specified value, the amount of change in the excitation frequency over time is changed to a predetermined value .

According to the present invention, it is possible to suppress the occurrence of vibrations in a stepping motor without varying the rotation speed of the stepping motor.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram showing a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 4 is a diagram showing a change in excitation frequency over time. FIG. 4 is a diagram showing a pulse signal based on an excitation frequency. FIG. 13 is a diagram showing vibration of rotation speed. FIG. 13 is a diagram showing the results of frequency analysis of the rotation speed when the excitation frequency is set to a set value. FIG. 13 is a diagram showing the results of frequency analysis of the rotation speed when the excitation frequency is changed over time. FIG. 13 is a diagram showing how the time change in excitation frequency is repeated at regular intervals. 11 is a diagram for explaining a method of determining a change range of an excitation frequency. FIG. 11 is a diagram for explaining a method for determining a constant period of an excitation frequency. FIG. FIG. 11 is a diagram showing the relationship between the noise level and the rotation frequency of a stepping motor. 5 is a flowchart showing an example of an operation example when excitation frequency control is executed in the motor drive device. FIG. 13 is a diagram showing a modified example of the change in excitation frequency over time. FIG. 13 is a diagram showing a modified example of the change in excitation frequency over time. FIG. 13 is a diagram showing a modified example of the change in excitation frequency over time. FIG. 13 is a diagram showing a modified example of the change in excitation frequency over time.

The following describes in detail an embodiment of the present invention with reference to the drawings. FIG. 1 is a diagram showing an outline of the overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a diagram showing the main parts of the control system of the image forming apparatus 1 according to this embodiment.

As shown in FIG. 1, the image forming apparatus 1 is an intermediate transfer type color image forming apparatus that utilizes electrophotographic process technology. That is, the image forming apparatus 1 primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 413 onto the intermediate transfer belt 421, superimposes the four color toner images on the intermediate transfer belt 421, and then performs a second transfer onto the paper S sent from the paper feed tray units 51a to 51c to form an image.

The image forming device 1 also employs a tandem system in which photoconductor drums 413 corresponding to the four colors YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and each color toner image is transferred sequentially to the intermediate transfer belt 421 in a single step.

As shown in FIG. 2, the image forming device 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, a control unit 101, and a motor driving device 200.

The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, etc. The CPU 102 reads out a program corresponding to the processing contents from the ROM 103, loads it into the RAM 104, and centrally controls the operation of each block of the image forming device 1 in cooperation with the loaded program. At this time, various data stored in the memory unit 72 is referenced. The memory unit 72 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.

The control unit 101 transmits and receives various data to and from an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. The control unit 101 receives, for example, image data (input image data) transmitted from an external device, and forms an image on paper S based on this image data. The communication unit 71 is composed of, for example, a communication control card such as a LAN card.

As shown in FIG. 1, the image reading unit 10 is configured with an automatic document feeder 11, also known as an ADF (Auto Document Feeder), and a document image scanning device 12 (scanner), etc.

The automatic document feeder 11 transports the document D placed on the document tray using a transport mechanism and sends it to the document image scanning device 12. The automatic document feeder 11 makes it possible to continuously read the images (including both sides) of multiple documents D placed on the document tray all at once.

The document image scanning device 12 optically scans the document transported from the automatic document feeder 11 onto the contact glass or the document placed on the contact glass, and forms an image of the reflected light from the document on the light receiving surface of a CCD (Charge Coupled Device) sensor 12a to read the document image. The image reading unit 10 generates input image data based on the results of the reading by the document image scanning device 12. This input image data is subjected to a predetermined image processing in the image processing unit 30.

As shown in FIG. 2, the operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, operation statuses of each function, etc. according to a display control signal input from the control unit 101. The operation unit 22 has various operation keys such as a numeric keypad and a start key, accepts various input operations by the user, and outputs operation signals to the control unit 101.

The image processing unit 30 includes a circuit that performs digital image processing on the input image data according to initial settings or user settings. For example, under the control of the control unit 101, the image processing unit 30 performs gradation correction based on gradation correction data (gradation correction table). In addition to gradation correction, the image processing unit 30 also performs various correction processes such as color correction and shading correction, as well as compression processing, on the input image data. The image forming unit 40 is controlled based on the image data that has been subjected to these processes.

As shown in FIG. 1, the image forming section 40 includes image forming units 41Y, 41M, 41C, and 41K, and an intermediate transfer unit 42 for forming images using color toners of the Y, M, C, and K components based on input image data.

Image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have the same configuration. For ease of illustration and explanation, common components are indicated with the same reference numerals, and when distinguishing between them, the reference numerals are followed by Y, M, C, or K. In FIG. 1, reference numerals are only assigned to the components of image forming unit 41Y for the Y component, and reference numerals are omitted for the components of the other image forming units 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, and a drum cleaning device 415.

The photoconductor drum 413 is, for example, an organic photoconductor in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal base.

The control unit 101 rotates the photoconductor drum 413 at a constant peripheral speed by controlling the drive current supplied to a drive motor (not shown) that rotates the photoconductor drum 413.

The charging device 414 is, for example, a charger, and generates a corona discharge to uniformly charge the surface of the photoconductive photoconductor drum 413 to a negative polarity.

The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photoconductor drum 413 with laser light corresponding to the image of each color component. As a result, an electrostatic latent image of each color component is formed in the image area on the surface of the photoconductor drum 413 irradiated with the laser light due to the potential difference with the background area.

The developing device 412 is a two-component reversible developing device that visualizes the electrostatic latent image by depositing the developer of each color component onto the surface of the photoconductor drum 413 to form a toner image.

The developing device 412 is applied with, for example, a DC developing bias having the same polarity as the charging polarity of the charging device 414, or a developing bias in which an AC voltage is superimposed with a DC voltage having the same polarity as the charging polarity of the charging device 414. As a result, reversal development is performed in which toner adheres to the electrostatic latent image formed by the exposure device 411.

The drum cleaning device 415 is in contact with the surface of the photosensitive drum 413 and has a flat drum cleaning blade made of an elastic material, and removes toner remaining on the surface of the photosensitive drum 413 that has not been transferred to the intermediate transfer belt 421.

The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a number of support rollers 423, a secondary transfer roller 424, and a belt cleaning device 426.

The intermediate transfer belt 421 is an endless belt that is stretched around a number of support rollers 423 in a loop shape. At least one of the support rollers 423 is a drive roller, and the others are driven rollers. For example, it is preferable that roller 423A, which is arranged downstream in the belt running direction from primary transfer roller 422 for K component, is the drive roller. This makes it easier to maintain a constant running speed of the belt in the primary transfer section. As drive roller 423A rotates, intermediate transfer belt 421 runs at a constant speed in the direction of arrow A.

The intermediate transfer belt 421 is a conductive and elastic belt having a high resistance layer on its surface. The intermediate transfer belt 421 is driven to rotate by a control signal from the control unit 101.

The primary transfer roller 422 is disposed on the inner peripheral side of the intermediate transfer belt 421, facing the photoconductor drum 413 of each color component. The primary transfer roller 422 is pressed against the photoconductor drum 413 with the intermediate transfer belt 421 sandwiched therebetween, forming a primary transfer nip for transferring the toner image from the photoconductor drum 413 to the intermediate transfer belt 421.

The secondary transfer roller 424 is disposed on the outer circumferential surface side of the intermediate transfer belt 421, facing the backup roller 423B, which is disposed downstream of the drive roller 423A in the belt running direction. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 sandwiched therebetween, thereby forming a secondary transfer nip for transferring a toner image from the intermediate transfer belt 421 to the paper S.

When the intermediate transfer belt 421 passes through the primary transfer nip, the toner image on the photoconductor drum 413 is sequentially superimposed and primarily transferred onto the intermediate transfer belt 421. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and a charge of the opposite polarity to the toner is applied to the back side of the intermediate transfer belt 421, i.e., the side that contacts the primary transfer roller 422, so that the toner image is electrostatically transferred to the intermediate transfer belt 421.

Then, when the paper S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the paper S. Specifically, a secondary transfer bias is applied to the secondary transfer roller 424, and a charge of the opposite polarity to the toner is applied to the back side of the paper S, that is, the side that contacts the secondary transfer roller 424, so that the toner image is electrostatically transferred to the paper S. The paper S with the transferred toner image is transported toward the fixing unit 60.

The belt cleaning device 426 removes residual toner remaining on the surface of the intermediate transfer belt 421 after secondary transfer.

The fixing section 60 includes an upper fixing section 60A having a fixing surface side member arranged on the fixing surface of the paper S, i.e., the surface on which the toner image is formed, a lower fixing section 60B having a back surface side support member arranged on the back surface of the paper S, i.e., the surface opposite the fixing surface, and a heating source. The back surface side support member is pressed against the fixing surface side member to form a fixing nip that clamps and transports the paper S.

The fixing unit 60 fixes the toner image onto the paper S by applying heat and pressure to the paper S, which has been transported and to which the toner image has been secondarily transferred, in the fixing nip. The fixing unit 60 is disposed as a unit within the fixing device F.

The upper fixing section 60A has an endless fixing belt 61, which is a fixing surface side member, a heating roller 62, and a fixing roller 63. The fixing belt 61 is stretched between the heating roller 62 and the fixing roller 63.

The lower fixing section 60B has a pressure roller 64, which is a back side support member. The pressure roller 64 forms a fixing nip between the fixing belt 61 and the pressure roller 64 to clamp and transport the paper S.

The paper transport section 50 includes a paper feed section 51, a paper discharge section 52, and a transport path section 53. The three paper feed tray units 51a to 51c that make up the paper feed section 51 store paper S (standard paper, special paper) identified based on basis weight, size, etc., by preset type. The transport path section 53 has multiple transport roller pairs including a registration roller pair 53a. The registration roller section in which the registration roller pair 53a is arranged corrects the inclination and deviation of the paper S.

The sheets S stored in the paper feed tray units 51a to 51c are sent out one by one from the top and transported to the image forming unit 40 by the transport path unit 53. In the image forming unit 40, the toner images on the intermediate transfer belt 421 are secondarily transferred all at once onto one side of the sheets S, and a fixing process is performed in the fixing unit 60. The sheets S with the image formed thereon are discharged outside the machine by the paper discharge unit 52 equipped with paper discharge rollers 52a.

The multiple transport roller pairs in the paper transport section 50 are driven by a motor drive device 200. The motor drive device 200 has a stepping motor 210 and a drive control section 220.

The stepping motor 210 has a rotating shaft that rotates based on a drive frequency commanded by the control unit 101, and drives the drive shaft of a predetermined conveying roller pair. The drive shaft has a gear that meshes with the gear of the rotating shaft, and is driven to rotate by the driving force of the stepping motor 210.

The drive control unit 220 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input/output circuit (not shown). The drive control unit 220 controls the drive and excitation frequency of the stepping motor 210 based on a preset program.

The drive control unit 220 inputs a signal of the drive frequency commanded by the control unit 101 to the stepping motor 210. The stepping motor 210 is driven to rotate by the input of this signal.

The drive control unit 220 controls the excitation frequency for constant current control of the stepping motor 210. The drive control unit 220 inputs a pulse signal based on the excitation frequency set to a predetermined setting value (e.g., 48 kHz) to a drive circuit (not shown) of the stepping motor 210. The pulse signal is input to turn the drive circuit on and off, thereby performing constant current control of the stepping motor 210.

The drive control unit 220 changes the excitation frequency over time. Specifically, as shown in FIG. 3, when the drive control unit 220 changes the excitation frequency over time, it changes the excitation frequency over time for a fixed period within a change range from a first frequency that is greater than the set value of the excitation frequency to a second frequency that is less than the set value.

The first frequency is, for example, a value that is greater than the set value by a predetermined value. The second frequency is, for example, a value that is less than the set value by a predetermined value. The predetermined value is, for example, a value that is about 2.4% of the set value, and is set appropriately according to the vibration amplitude of the rotation frequency based on the rotation speed of the stepping motor 210 described later.

As shown in Figure 4, if the excitation frequency remains at the set value, the pulse signal will have the same width, but if the excitation frequency is changed over time, the width of the pulse signal will gradually change.

During the time it takes for the stepping motor 210 to make one rotation, the above pulse signals are input to the drive circuit in a number that corresponds to the set value. However, due to some factor, the timing of the above pulse signals may differ from the time it takes for the stepping motor 210 to make one rotation, causing the number of pulse signals within that time to fluctuate.

Some of the factors may include fluctuations in the load on the motor drive device 200, variations in the voltage and current applied to the stepping motor 210, and changes in the environment around the motor drive device 200.

When the stepping motor 210 is driven at a medium speed, if the number of pulse signals based on the excitation frequency, which is the set value, varies within the time it takes for the stepping motor 210 to rotate once, vibration of the stepping motor 210 may occur.

The range in which the stepping motor 210 is driven at medium speed is the range in which a predetermined number (e.g., 5) of pulse signals based on the set excitation frequency are input to the drive circuit within the time it takes for the stepping motor 210 to rotate once.

For example, when the stepping motor 210 is driven at a low rotation speed that is slower than a medium speed, the time for each rotation of the stepping motor 210 becomes longer, and more than a predetermined number of the above pulse signals (e.g., 20) are input to the drive circuit within that time.

Therefore, even if the number of pulse signals based on the set excitation frequency deviates, the fluctuation rate of the pulse signals is sufficiently small compared to the medium speed. In other words, at medium speed, the fluctuation rate of the pulse signals is sufficiently larger than at low speed, so the vibration of the stepping motor 210 becomes noticeable.

In addition, when the stepping motor 210 is driven at a high rotation speed that is faster than a medium speed, the time for each rotation of the stepping motor 210 becomes shorter, and therefore fewer than a predetermined number of the above pulse signals (e.g., one) are input to the drive circuit within that time.

As a result, the number of pulse signals based on the set excitation frequency is unlikely to deviate, and vibration of the stepping motor 210 does not occur.

In this way, when the stepping motor 210 is driven at a medium rotation speed between low and high speed, vibrations in the stepping motor 210 are likely to occur.

It has been experimentally confirmed that such vibrations increase over time, as shown in Figure 5. Figure 5 shows an example in which the vibrations gradually increase after time T1 when the stepping motor 210 reaches medium speed.

In addition, it has been experimentally confirmed that changing the excitation frequency of the stepping motor 210 causes the rotational speed at which vibration occurs in the stepping motor 210 to fluctuate.

For example, as shown in FIG. 6, when frequency analysis (FFT (Fast Fourier Transform) analysis) is performed on the fluctuations in the rotational speed of the stepping motor 210, it has been confirmed that the position of the peak indicating the occurrence of vibration changes by varying the excitation frequency.

In the example shown in Figure 6, when the excitation frequency is made smaller than the set value, a peak occurs on the side with a smaller rotation speed (rotation frequency), and when the excitation frequency is made larger than the set value, a peak occurs on the side with a larger rotation speed (rotation frequency). In other words, it has been experimentally confirmed that changing the excitation frequency causes the position where the peak occurs to shift.

Based on this phenomenon, in this embodiment, the excitation frequency of the stepping motor 210 is changed over time, so that the excitation frequency changes before the vibration (peak) becomes large when rotating at medium speed.

By doing this, as shown in FIG. 7, the excitation frequency changes before the vibration level of the stepping motor 210 increases, so that the vibration level can be prevented from increasing, and thus the occurrence of vibration in the stepping motor 210 can be prevented.

In addition, if the excitation frequency setting is changed, vibrations of the stepping motor 210 may occur at the changed excitation frequency due to some factor. For example, when the setting is changed to the excitation frequency corresponding to the peak of the dashed line shown in FIG. 6, the position of the peak may shift, resulting in the occurrence of the dashed peak.

However, in this embodiment, the excitation frequency is changed over time, so even if the position where the vibration occurs changes, the excitation frequency changes before the vibration (peak) becomes large at that position. This makes it possible to suppress the occurrence of vibration in the stepping motor 210.

Also, as shown in FIG. 8, the drive control unit 220 repeats the above-mentioned time change of the excitation frequency at regular intervals. Specifically, the drive control unit 220 controls the excitation frequency to form a sawtooth wave that changes so as to reduce the excitation frequency over time.

By doing this, the excitation frequency is no longer fixed at a specific frequency, so even if the position where the vibration occurs changes, the excitation frequency is no longer set to the frequency corresponding to that position. As a result, the occurrence of vibration in the stepping motor 210 can be suppressed.

The drive control unit 220 also determines the range of change in the excitation frequency based on the vibration amplitude of the rotation frequency, which is based on the rotation speed of the stepping motor 210. The vibration amplitude indicates the frequency width of the portion where the vibration level based on the FFT analysis is equal to or higher than a predetermined level, as shown in FIG. 9, for example.

The predetermined level is, for example, a vibration level at which the user can recognize the vibration of the stepping motor 210, and can be set appropriately. The vibration amplitude is, for example, a value determined in advance through experiments, etc.

The drive control unit 220 determines a range that is wider than the vibration amplitude and includes the vibration amplitude as the range of rotation speed that corresponds to the range of change in the excitation frequency. In this embodiment, as described above, the range of change is from a first frequency that is a predetermined value greater than the set value to a second frequency that is a predetermined value less than the set value.

The rotational speed corresponding to the first frequency is a rotational frequency greater than the upper limit of the vibration amplitude, and the rotational speed corresponding to the second frequency is a rotational frequency less than the lower limit of the vibration amplitude.

This ensures that there will be a period during which the rotation speed corresponding to the excitation frequency is outside the vibration width where vibration of the stepping motor 210 may occur. As a result, the rotation speed corresponding to the excitation frequency can be reliably moved outside the vibration width, and therefore the occurrence of vibration of the stepping motor 210 can be suppressed.

The drive control unit 220 also determines the constant period according to the vibration time of the stepping motor 210 when the excitation frequency is not changed over time. The drive control unit 220 determines the constant period so that it is shorter than the time equivalent to two vibrations of the stepping motor 210 in FIG. 10, for example. Note that the constant period is not limited to this and may be set as appropriate.

For example, if the constant period is set to the time from when the stepping motor 210 starts to vibrate until the vibration becomes sufficiently large, even if the excitation frequency is changed over time, the amount of change in the excitation frequency over time will be small. Therefore, the time during which the excitation frequency remains within the vibration width of the stepping motor 210 will also become longer, which may cause vibration of the stepping motor 210.

In contrast, in the present embodiment, the constant period is set to the time from when the stepping motor 210 starts to vibrate until the vibration does not become too large, so the amount of change over time when the excitation frequency is changed over time is large. As a result, the time during which the excitation frequency remains within the vibration amplitude of the stepping motor 210 is also shortened, making it easier to suppress the occurrence of vibration in the stepping motor 210.

In addition, the drive control unit 220 determines the constant period so that one period of pulse signals based on the time-varying excitation frequency contains a power of 2 (an integer number).

For example, if the excitation frequency is set to 48 kHz, the time equivalent to one period of the pulse signal is 1/48k = 0.02083 msec.

If the number of pulse signals is 64, which is 2 to the power of 6, then the constant period is 1.333 msec, which is the product of 0.02083 m and 64.

By determining the fixed period in this way, it is possible to prevent the fixed period from ending midway through one pulse signal period. In addition, by making the pulse signal a power of 2, it is possible to make it easier for a CPU or the like to process it.

However, when the excitation frequency is changed over time regardless of the rotation speed of the stepping motor 210, noticeable noise (excitation sound) may occur due to the change in the excitation frequency over time. Figure 11 shows the relationship between the noise value and the rotation frequency of the stepping motor 210.

For example, as shown in FIG. 11, it has been experimentally confirmed that when the rotational frequency (rotational speed) of the stepping motor 210 is varied, a change in noise level is observed when the excitation frequency is changed over time and when the excitation frequency is not changed over time. The set value of the excitation frequency shown in FIG. 11 is, for example, 48 kHz, and the excitation frequency is changed over time based on 48 kHz.

Specifically, it has been confirmed that in the region below L (e.g., 8000 Hz), where the excitation frequency is a relatively slow region, the noise level when the excitation frequency is changed over time is significantly higher than the noise level when the excitation frequency is not changed over time.

This is thought to be because the rotation speed of the stepping motor 210 slows down, which lengthens the time it takes for the stepping motor 210 to complete one rotation, making the excitation sound more noticeable.

Therefore, in this embodiment, the drive control unit 220 changes the excitation frequency over time based on the rotation speed of the stepping motor 210. Specifically, the drive control unit 220 determines the amount of change in the excitation frequency over time based on the ratio of the excitation frequency (the set value of the excitation frequency) to the rotation frequency of the stepping motor 210.

For example, if the ratio is less than a specified value (e.g., 6), that is, if the rotational frequency of the stepping motor 210 is less than L, the drive control unit 220 sets the amount of change in the excitation frequency over time to 0. In other words, in this case, the drive control unit 220 does not change the excitation frequency over time.

On the other hand, if the ratio is equal to or greater than the specified value, that is, if the rotational frequency of the stepping motor 210 is equal to or greater than L, the drive control unit 220 changes the amount of change in the excitation frequency over time to a preset value. In other words, in this case, the drive control unit 220 changes the excitation frequency over time.

This makes it possible to suppress the vibration of the stepping motor 210 while suppressing the generation of noise caused by changes in the excitation frequency.

Next, an example of operation when the motor drive device 200 executes excitation frequency control will be described. FIG. 12 is a flowchart showing an example of operation when the motor drive device 200 executes excitation frequency control. The process in FIG. 12 is executed appropriately when the control unit 101 receives a command to execute a print job.

As shown in FIG. 12, the drive control unit 220 determines whether the ratio of the excitation frequency to the rotation frequency of the stepping motor 210 is less than a specified value (step S101).

If the result of the determination is that the ratio is equal to or greater than the specified value (step S101, NO), the drive control unit 220 sets the time change amount of the excitation frequency to 0 and does not change the excitation frequency over time (step S102).

On the other hand, if the ratio is less than the specified value (step S101, YES), the drive control unit 220 changes the excitation frequency over time, with the time change amount of the excitation frequency set to a preset value (step S103). After step S102 or step S103, this control ends.

According to the present embodiment configured as described above, by changing the excitation frequency over time, the excitation frequency can be changed based on the position where the peak of the vibration level occurs at the rotation frequency of the stepping motor 210.

In other words, the excitation frequency can be changed before the vibration level of the stepping motor 210 increases, so the occurrence of vibration in the stepping motor 210 can be suppressed.

In addition, because the excitation frequency is changed over time, it is no longer fixed at a specific excitation frequency. As a result, even if the position at which the vibration of the stepping motor 210 occurs changes due to some factor, the occurrence of vibration of the stepping motor 210 can be suppressed.

In this embodiment, the amount of change in excitation frequency over time is determined based on the rotation speed of the stepping motor 210, so that noise caused by changes in excitation frequency can be suppressed.

In the above embodiment, the excitation frequency is controlled to form a sawtooth wave that changes so as to decrease the excitation frequency over time, but the present invention is not limited to this. For example, as shown in FIG. 13, the excitation frequency may be controlled to form a sawtooth wave that changes so as to increase the excitation frequency over time.

In addition, in the above embodiment, the excitation frequency is controlled to form a sawtooth wave over time, but the present invention is not limited to this. For example, as shown in FIG. 14, the drive control unit 220 may control the excitation frequency to form a triangular wave that alternates between a first period and a second period. Also, as shown in FIG. 15, the drive control unit 220 may control the excitation frequency to form a sine wave that alternates between a first period and a second period.

In the first period, the drive control unit 220 changes the excitation frequency so that it increases over time. In the second period, the drive control unit 220 changes the excitation frequency so that it decreases over time.

In this way, the excitation frequency can be changed over time to suppress the generation of vibrations in the stepping motor 210.

Also, as shown in FIG. 16, the drive control unit 220 may control the excitation frequency so that it changes randomly over time.

In this way, the excitation frequency can be changed over time to suppress the generation of vibrations in the stepping motor 210.

In addition, in the above embodiment, the amount of change in the excitation frequency over time is set to 0 or a preset value, but the present invention is not limited to this, and the amount of change in the excitation frequency over time may be changed continuously according to the rotation speed of the stepping motor 210. Specifically, the range of change in the amount of change in the excitation frequency over time may be reduced as the rotation speed of the stepping motor 210 becomes slower.

In addition, as described above, considering that vibrations are less likely to occur when the rotation speed of the stepping motor 210 is high, the excitation frequency may be changed over time only when the rotation speed of the stepping motor 210 is medium.

In addition, in the above embodiment, the excitation frequency is changed over time based on the ratio of the excitation frequency to the rotation frequency of the stepping motor 210, but the present invention is not limited to this. For example, the excitation frequency may be changed over time based on the set rotation speed of the stepping motor 210.

In addition, in the above embodiment, the drive control unit 220 drives the stepping motor 210, but the present invention is not limited to this, and the control unit 101 may drive the stepping motor 210.

In addition, in the above embodiment, the motor drive device 200 drives the paper transport unit 50, but the present invention is not limited to this, and other parts may also be driven.

In addition, in the above embodiment, the motor drive device 200 is provided in the image forming device 1, but the present invention is not limited to this, and the motor drive device 200 may be provided in a device other than an image forming device.

In addition, the above embodiments are merely examples of how the present invention can be implemented, and the technical scope of the present invention should not be interpreted in a limiting manner based on these. In other words, the present invention can be implemented in various forms without departing from its gist or main features.

1 Image forming apparatus 101 Control unit 200 Motor driving device 210 Stepping motor 220 Drive control unit

Claims (14)

a stepping motor having a rotary shaft that rotates based on a drive frequency;
A drive control unit that controls an excitation frequency for constant current control of the stepping motor;
Equipped with
The drive control unit is
The excitation frequency is changed over time based on a ratio of the excitation frequency to a rotation frequency based on a rotation speed of the stepping motor;
When the ratio is less than a specified value, the time change amount of the excitation frequency is set to 0, and when the ratio is equal to or greater than the specified value, the time change amount of the excitation frequency is changed to a preset value.
Motor drive unit. The drive control unit determines a time change amount of the excitation frequency based on a rotation speed of the stepping motor.
The motor drive device according to claim 1 . When the drive control unit changes the excitation frequency over time, the change range of the excitation frequency is set to a range between a first frequency that is greater than a set value of the excitation frequency and a second frequency that is smaller than the set value.
The motor drive device according to claim 1 or 2 . The drive control unit determines the change range based on a fluctuation range of a rotation frequency based on the rotation speed of the stepping motor.
The motor drive device according to claim 3 . The drive control unit repeats the time change of the excitation frequency at a constant cycle.
The motor drive device according to any one of claims 1 to 4 . the drive control unit determines the constant period in accordance with a vibration time of the stepping motor when the excitation frequency is not changed over time.
6. The motor drive device according to claim 5 . The drive control unit determines the constant period so that the constant period is within an integer number of excitation periods based on the excitation frequency that is changed over time.
The motor drive device according to claim 5 or 6 . the integer is a power of 2,
8. The motor drive device according to claim 7 . The drive control unit controls the excitation frequency to form a triangular wave that alternately repeats a first period in which the excitation frequency is changed so as to increase over time and a second period in which the excitation frequency is changed so as to decrease over time.
The motor drive device according to any one of claims 5 to 8 . The drive control unit controls the excitation frequency to form a sawtooth wave that changes so as to increase or decrease the excitation frequency over time.
The motor drive device according to any one of claims 5 to 8 . The drive control unit controls the excitation frequency to form a sine wave that alternately repeats a first period in which the excitation frequency is changed so as to increase over time and a second period in which the excitation frequency is changed so as to decrease over time.
The motor drive device according to any one of claims 5 to 8 . The drive control unit controls the excitation frequency so that the excitation frequency changes randomly over time.
The motor drive device according to any one of claims 5 to 8 . The motor drive device according to any one of claims 1 to 12 is provided.
Image forming device. A method for controlling an excitation frequency of a motor drive device including a stepping motor having a rotary shaft that rotates based on a drive frequency, comprising:
Controlling an excitation frequency for constant current control of the stepping motor;
Varying the excitation frequency over time based on a ratio of the excitation frequency to a rotation frequency based on a rotation speed of the stepping motor;
having
In varying the excitation frequency over time, if the ratio is less than a specified value, the amount of change in the excitation frequency over time is set to 0, and if the ratio is equal to or greater than the specified value, the amount of change in the excitation frequency over time is changed to a preset value.
Excitation frequency control method.

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