JP7337554B2 - Motor control device, sheet conveying device and image forming device - Google Patents

Description

The present invention relates to a motor driving device and an image forming apparatus.

2. Description of the Related Art In electrophotographic image forming apparatuses such as copiers and printers, a stepping motor is widely used as a driving source of a transport system for transporting recording paper such as paper on which an image is formed. A stepping motor can easily perform speed control by controlling the pulse period given to the motor, even if it does not have a mechanism for detecting the rotational speed and position or the rotational phase of the motor. Moreover, the stepping motor has the advantage that position control can be easily performed by controlling the number of pulses applied to the motor. This control method is hereinafter referred to as synchronous control.

However, when the stepping motor is synchronously controlled, if the load torque required by the image forming apparatus exceeds the torque range that the stepping motor can output, stepping out may occur and the stepping motor may become uncontrollable. . When a step-out occurs, a paper jam occurs in the image forming apparatus, requiring the user to remove the jammed paper. In order to avoid this, a motor output torque capable of coping with changes in load torque required in the image forming apparatus is required. For this purpose, it is necessary to increase the drive current supplied to the motor so that the motor output torque having a predetermined margin with respect to the load torque required by the image forming apparatus can be obtained. As a result, in the stepping motor, power consumption increases, and motor vibration caused by excess torque may generate noise.

In order to avoid such a phenomenon, a motor control method called vector control (or FOC: Field Oriented Control) is known, as described in Patent Documents 1 and 2. Specifically, for example, the motor is controlled by performing phase feedback control for controlling the current value in the rotating coordinate system so that the deviation between the commanded phase of the rotor and the actual rotational phase is reduced. In the rotating coordinate system, the q-axis component (q-axis current) of the drive current flowing through the windings is the torque current component that generates torque, and the d-axis component (d-axis current) of the drive current is the strength of the magnetic flux that passes through the windings. is the excitation current component that affects the Typical vector control controls the amplitude and phase of the drive current to maintain a 90° rotor load angle for maximum efficiency operation.

In vector control in a stepping motor, ab-phase currents, which are currents flowing in motor windings in a fixed coordinate system, are coordinate-transformed into dq-axis currents in the above-described rotating coordinate system, and current control is performed in the rotating coordinate system. to generate the dq-axis voltage. The dq-axis voltages thus generated are converted into ab-phase voltages in a fixed coordinate system and applied to the motor windings. In general vector control, the torque is controlled by the q-axis current with the d-axis current set to "0". As a result, the minimum necessary drive current is generated according to the load amount of the rotor, and drive control with good power efficiency is realized. In addition, it is possible to suppress the vibration and noise of the motor caused by the surplus torque as described above.

Japanese Patent No. 3661864 JP-A-6-225595

Since the motor can be driven with maximum efficiency when the excitation current component is controlled to be 0, the torque current component is controlled with the excitation current component set to 0 in vector control. However, in a motor, when the rotor rotates at high speed, a back electromotive force is generated in the motor windings.
When the excitation voltage component is generated by the excitation current, the combined voltage of the torque voltage component and the excitation voltage component becomes a larger value than the combined voltage (that is, the torque voltage component) when the excitation voltage component is 0. As a result, ab The phase voltage may exceed the power supply voltage applied to the inverter circuit.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the voltage applied from an inverter circuit to the windings of a motor from exceeding a predetermined value.

A motor control device according to the present invention is a motor control device for controlling a motor. a phase determining means for determining a rotational phase; and a rotational phase determined by the phase determining means so as to reduce a deviation between the rotational phase determined by the phase determining means and a command phase representing a target phase of the rotor. generating a target value of a torque current component that is a current component expressed in a reference rotating coordinate system and that causes torque to be generated in the rotor; A first generation means for generating a target value of an excitation current component that affects the strength of the magnetic flux passing through and performing field weakening control by the excitation current component, wherein the temperature of the motor control device exceeds a predetermined temperature outputs the first predetermined value when the target value of the torque current component is larger than the first predetermined value , and outputs the torque current component when the target value of the torque current component is smaller than the first predetermined value and a torque current component output from the first generation means , which performs control to output a target value of and does not perform the control when the temperature of the motor control device is equal to or lower than the predetermined temperature; corresponding to the torque current component of the drive voltage to be applied to the winding so that the deviation between the target value or the first predetermined value of and the torque current component of the drive current detected by the detection means is small. a target value of an excitation current component, which is a current component expressed in the rotating coordinate system and affects the strength of the magnetic flux penetrating the winding, and is detected by the detection means second generation means for generating a value corresponding to the excitation current component of the drive voltage to be applied to the winding so that deviation from the excitation current component of the applied drive current is reduced; an inverter circuit for applying the drive voltage to the winding based on the value corresponding to the torque current component of the drive voltage and the value corresponding to the excitation current component of the drive voltage generated by a generating means; wherein the first predetermined value is a magnitude of a vector represented by a value corresponding to the torque current component of the drive voltage and a value corresponding to the excitation current component of the drive voltage is a second predetermined value and the first generating means increases the second predetermined value until the temperature of the motor control device exceeds the predetermined temperature to reduce the temperature of the motor control device exceeds the predetermined temperature, the second predetermined value is returned to the original value .

According to the present invention, it is possible to prevent the voltage applied from the inverter circuit to the windings of the motor from exceeding a predetermined value.

1 is an explanatory diagram of an image forming apparatus in which a motor driving device is mounted; FIG. FIG. 2 is a functional block diagram showing the configuration of the image forming apparatus; A functional block diagram showing vector control. Explanatory drawing of the relationship between α, β axes and d, q axes. Explanatory drawing of the relationship between Vq, Vd, and Vdq. 4 is a flowchart showing current limiting processing. 4 is a flowchart showing processing for increasing the value of V_LIM;

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated using drawing. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the solution of the invention.

Image Forming Apparatus This embodiment shows an example in which a motor driving device is applied to an image forming apparatus. FIG. 1 is an explanatory diagram of an image forming apparatus in which a motor driving device is mounted. The image forming apparatus 100 includes an automatic document feeder 201 , a reading device 202 , and an image forming apparatus main body 301 .

Documents placed on the document placement unit 203 of the automatic document feeder 201 are fed one by one by the feed roller 204 and conveyed to the document glass platen 214 of the reading device 202 via the conveyance guide 206 . Further, the document is conveyed at a constant speed by the conveying belt 208 and discharged to the outside of the apparatus by the discharge rollers 205 . During this time, reflected light from the document image illuminated by the illumination system 209 at the reading position of the reading device 202 is guided to the image reading unit 101 by the optical system consisting of reflecting mirrors 210 , 211 , and 212 , and the image reading unit 101 scans the image. converted to a signal. The image reading unit 101 includes a lens, a CCD (Charge Coupled Device) that is a photoelectric conversion element, a drive circuit for the CCD, and the like. An image signal output from the image reading unit 101 is subjected to analog image processing and AD conversion by an image processing unit 112 configured by a hardware device such as an ASIC to generate digital image data. The image processing unit 112 performs various correction processes on the generated image data, and then outputs the data to the image forming apparatus main body 301 . This image data is data representing a document image.

As document reading modes in the reading device 202, there are a skimming mode and a fixed mode. The flow reading mode is a mode in which an image of a document is read while the document is conveyed at a constant speed with the illumination system 209 and the optical system stopped. In the fixed mode, a document is placed on the document glass table 214 of the reading device 202, and the image of the document placed on the document glass table 214 is read while the illumination system 209 and the optical system are moved at a constant speed. is. Generally, sheet-like documents are read in the skimming mode, and bound documents are read in the fixed mode.

The image forming apparatus 100 has a copy function of forming an image on a recording sheet (recording material) page by page in the image forming apparatus main body 301 based on an image signal output from the reading device 202 . The image forming apparatus 100 also has a printing function of forming an image on recording paper based on data received from an external device via a network.

An image signal output from the reading device 202 is input to the optical scanning device 311 . The optical scanning device 311 has a semiconductor laser and a polygon mirror, and outputs laser light (optical signal) modulated by an input image signal from the semiconductor laser. The surface of the photosensitive drum 309 is irradiated with a laser beam output from a semiconductor laser via a polygon mirror and mirrors 312 and 313, so that the photosensitive drum 309 is exposed. An electrostatic latent image is formed on the photosensitive drum 309 by exposing the photosensitive drum 309 whose surface is uniformly charged by the charger 310 to laser light. A toner image is formed on the photosensitive drum 309 by developing the electrostatic latent image formed on the photosensitive drum 309 with toner supplied from the developing device 314 . The toner image on the photosensitive drum 309 is transferred to the recording paper by the transfer separator 315 when it moves to a position (transfer position) facing the transfer separator 315 as the photosensitive drum 309 rotates.

Recording sheets are stored in paper cassettes 302 and 304, which can store different types of recording sheets. For example, the paper cassette 302 contains standard recording paper, and the paper cassette 304 contains tab paper. The recording paper stored in the paper cassette 302 is fed onto the transport path by the paper feed roller 303, transported to the position of the registration roller 308 by the transport roller 306, and temporarily stopped there. On the other hand, the recording paper stored in the paper cassette 304 is fed onto the transport path by the paper feed roller 305, transported to the position of the registration roller 308 by the transport rollers 307 and 306, and temporarily stopped there.

The recording paper conveyed to the position of the registration roller 308 is conveyed to the transfer position by the registration roller 308 in synchronization with the timing when the toner image on the photosensitive drum 309 reaches the transfer position. The recording paper on which the toner image has been transferred from the photosensitive drum 309 at the transfer position is conveyed to the fixing device 318 by the conveying belt 317 . A fixing device 318 fixes the toner image on the recording paper to the recording paper by heat and pressure.

When image formation is performed in the single-sided printing mode, the recording paper that has passed through the fixing device 318 is discharged to the outside of the apparatus by paper discharge rollers 319 and 324 . When image formation is performed in the double-sided printing mode, after passing through the fixing device 318 , the recording paper on which an image has been formed on the surface (first surface) is subjected to the following processes: It is conveyed to the reversing path 325 . Further, by reversing the rotation of the reversing roller 321 immediately after the trailing edge of the recording paper passes through the confluence point of the reversing path 325 and the double-sided path 326 , the recording paper begins to be conveyed in the opposite direction, to the double-sided path 326 . be transported. After that, the recording paper is conveyed through a double-sided path 326 by conveying rollers 322 and 323, conveyed again by the conveying rollers 306 to the position of the registration roller 308, and is temporarily stopped there. Further, in the same manner as the image formation on the front side (first side) of the recording paper, the toner image is transferred to the back side (second side) of the recording paper at the transfer position, and the fixing process is performed by the fixing device 318 . After that, the recording paper is ejected to the outside of the apparatus. In this manner, the reversing roller 321 functions as a reversing roller for reversing the conveying direction of the recording paper on the conveying path when forming images on both sides of the recording paper.

In addition, when the recording paper is turned upside down (the first side and the second side are turned over) and discharged to the outside of the apparatus, the recording paper that has passed through the fixing device 318 is directed toward the discharge roller 324. It is temporarily conveyed in the direction toward the conveying roller 320 instead of the direction. After that, by reversing the rotation of the transport roller 320 just before the trailing edge of the recording paper passes the position of the transport roller 320 , the recording paper starts to be transported in the opposite direction and is transported in the direction toward the paper discharge roller 324 . be. As a result, the recording paper is ejected to the outside of the apparatus by the paper ejection rollers 324 while being turned upside down. In this manner, the conveying roller 320 functions as a reversing roller for reversing the conveying direction of the recording paper on the conveying path when the recording paper on which an image has been formed is turned upside down and discharged.

As described above, the image forming apparatus main body 301 includes transport rollers 306 and 307, a paper discharge roller 319, a reversing roller 321, transport rollers 322 and 323, and a paper discharge roller as rollers for transporting recording paper on which an image is formed. 324 is provided. A motor control unit 157 controls a motor driving device for a motor that drives these rollers in accordance with an instruction from a system controller 151 as control means, as will be described later with reference to FIG.

Control Configuration of Image Forming Apparatus FIG. 2 is a block diagram showing an example of the control configuration of the image forming apparatus 100. As shown in FIG. A system controller 151 shown in FIG. 2 includes a CPU 151a, a ROM 151b, and a RAM 151c, and controls the image forming apparatus 100 as a whole. The system controller 151 is connected to the image processing section 112 , operation section 152 , analog/digital (A/D) converter 153 , high voltage control section 155 , motor control section 157 , sensors 159 and AC driver 160 . The system controller 151 can exchange data with each connected unit.

The CPU 151a reads and executes various programs stored in the ROM 151b to execute various sequences related to a predetermined image forming sequence. The RAM 151c is a volatile storage device, and the CPU 151a is used as a work area for executing various programs or as a temporary storage area for temporarily storing various data. The RAM 151c stores data such as set values for the high voltage control unit 155, command values for the motor control unit 157, and information received from the operation unit 152, for example.

The system controller 151 controls the operation unit 152 so that an operation screen for the user to make various settings is displayed on a display unit provided in the operation unit 152, so that the user can make settings via the operation unit 152. accept. The system controller 151 receives from the operation unit 152 information indicating the contents of settings (for example, a set value of copy magnification, a set value of density, etc.) made by the user via the operation unit 152 .

The system controller 151 also transmits data to the operation unit 152 to inform the user of the state of the image forming apparatus. Based on the data received from the system controller 151, the operation unit 152 receives information indicating the state of the image forming apparatus (for example, information indicating the number of images formed, information indicating whether or not image formation is in progress, information indicating the occurrence of a jam and the location of the occurrence). ) is displayed on the display.

The system controller 151 (CPU 151 a ) transmits setting value data of each device in the image forming apparatus 100 that is required for image processing in the image processing section 112 to the image processing section 112 . The system controller 151 also receives signals from each device (signals from the sensors 159) and controls the high voltage controller 155 based on the received signals. Based on the set values output from the system controller 151, the high voltage control unit 155 applies voltages required for the respective operations to the charging device 310, the developing device 314, and the transfer separator 315, which constitute the high voltage unit 156. supply.

The A/D converter 153 receives a detection signal from the thermistor 154 for detecting the temperature of the fixing heater 161 , converts the detection signal into a digital signal, and transmits the digital signal to the system controller 151 . The system controller 151 controls the temperature of the fixing heater 161 to a desired temperature for the fixing process by controlling the AC driver 160 based on the digital signal received from the A/D converter 153 . A fixing heater 161 is a heater included in the fixing device 318 and used for fixing processing.

Thus, the system controller 151 controls the operation sequence of the image forming apparatus 100. FIG. The system controller 151 also controls the drive sequence of each motor via the motor control unit 157 . The motor control unit 157 controls a motor (stepping motor 509 shown in FIG. 3) corresponding to a drive source for driving the rollers for conveying the recording paper according to instructions from the system controller 151 . Note that the image forming apparatus 100 includes a motor control unit 157 that controls each motor corresponding to each roller for conveying the recording paper. In this embodiment, the motor control unit 157 is an example of a motor control device that controls driving of the motor.

The system controller 151 (CPU 151 a ), which corresponds to an external controller of the motor control unit 157 , generates a command value (θ_ref) for the rotation phase of the rotor in the motor to be controlled (stepping motor 509 ), and outputs it to the motor control unit 157 . . For example, θ_ref is a pulsed rectangular wave signal, one pulse of which defines the minimum amount of change in the rotation angle of the stepping motor. Note that the command value for the rotation speed of the motor (speed command value ω_ref) is obtained as a frequency corresponding to θ_ref. When the motor drive sequence is started, the CPU 151a outputs the generated θ_ref to the motor control unit 157 at a predetermined time period (control period). The motor control unit 157 executes rotation phase (position) control and speed control of the rotor in the stepping motor 509 according to the phase command value given from the CPU 151a.

Vector Control Next, an outline of the vector control of the stepping motor 509 executed by the motor control unit 157 will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 is a block diagram showing a configuration example of the motor driving device 300. As shown in FIG. In FIG. 3, the basic configuration of the motor control unit 157 corresponds to inverter control using coordinate transformation from a stationary coordinate system to a rotating coordinate system, which is used in motors such as brushless DC motors and AC servomotors. Configuration.
Power supply voltage limiter section 524 receives power supply voltage V supplied from power supply 520 and limits the voltage so that voltage V_LIM, which is the limit value of the voltage in PWM inverter 506 , is supplied to motor control section 157 . In the motor control unit 157 , the stepping motor 509 is driven by the PWM inverter 506 supplying a driving current to the stepping motor 509 according to the driving voltages Vα and Vβ of the stepping motor 509 output from the vector control unit 515 . As shown in FIG. 3, the vector control section 515 is composed of a speed control section 502, an Iq_ref limiter section, current control sections 503 and 504, a Vdq overvoltage detection section, and coordinate converters 505 and 511. FIG.

FIG. 4 is a diagram showing the relationship between a two-phase motor consisting of A and B phases and the dq axes of a rotating coordinate system. In the figure, the axes corresponding to the A-phase and B-phase windings in the static coordinate system are defined as the α-axis and the β-axis, respectively. The angle formed by the α-axis in the stationary coordinate system and the direction (d-axis) of the magnetic flux produced by the magnetic poles of the permanent magnet used as the rotor is defined as θ. In this case, the rotational phase of the output shaft of the rotor of the stepping motor 509 is represented by the angle θ. In vector control, as shown in FIG. 4, a stepping motor is represented by a d-axis along the rotor magnetic flux direction and a q-axis along a direction 90 degrees ahead of the d-axis (perpendicular to the d-axis). A rotating coordinate system based on the rotational phase θ of the rotor at 509 is used.

The motor control unit 157 performs vector control in which the drive current supplied to the stepping motor 509 is controlled by the current value of the rotating coordinate system based on the rotation phase θ of the rotor of the stepping motor 509 . In vector control, the current vectors corresponding to the driving currents flowing through the A-phase and B-phase windings of the stepping motor 509 are represented by the d-axis and q-axis from the static coordinate system represented by the α-axis and β-axis. Converted to a rotating coordinate system. As a result of such coordinate transformation, the driving current supplied to the stepping motor 509 is represented by a direct current d-axis component (d-axis current) and direct current q-axis component (q-axis current) in the rotating coordinate system. In this case, the q-axis current corresponds to the torque current component that causes the stepping motor 509 to generate torque, and the d-axis current corresponds to the exciting current component that affects the magnetic flux intensity of the rotor of the stepping motor 509 . The motor control unit 157 realizes vector control of the stepping motor 509 by independently controlling the q-axis current and the d-axis current in the rotating coordinate system.

Specifically, the motor control unit 157 estimates the rotational phase and rotational speed of the rotor in the stepping motor 509, and performs vector control based on the estimation results. Motor control 157 includes three control loops based on respective feedbacks to phase control 501, speed control 502, and current controls 503, 504, as shown in FIG. Realize control. In the motor control unit 157 shown in FIG. 3, estimation of the rotation phase θ of the rotor of the stepping motor 509 is performed by an induced voltage calculation unit 512 and a phase calculation unit (ATAN) 513 as phase determination means. Further, the estimation of the rotation speed ω(dθ/dt) of the stepping motor 509 is performed by the speed calculation unit 514 based on the estimated value of the rotation phase θ.

In the outermost control loop including the phase control unit 501 , phase control of the stepping motor 509 is performed based on the feedback of the estimated value of the rotation phase θ of the rotor of the stepping motor 509 . A phase command value θ_ref for the stepping motor 509 is provided to the motor control unit 157 from the CPU 151 a of the system controller 151 . The phase control unit 501 generates a speed command value ω_ref such that the deviation of the estimated value of the rotation phase θ of the rotor in the stepping motor 509 from the phase command value θ_ref (target value), which is fed back from the phase calculation unit 513, approaches zero. do. After that, the phase control unit 501 outputs the speed command value ω_ref to the ω_ref limiter unit 523 as speed limiting means. The ω_ref limiter unit 523 outputs ω_ref′ which is limited so that the speed command value ω_ref output from the phase control unit 501 is equal to or less than the limit value ω_LIM. Specifically, when the calculation result of ω_ref is equal to or greater than ω_LIM, ω_LIM is output as ω_ref'. Also, when the calculation result of ω_ref is less than ω_LIM, ω_ref is output as ω_ref'. ω_LIM is a value determined by the Vdq overvoltage detector 522 . The details of the calculation contents of the Vdq overvoltage detection unit 522 will be described later. In this manner, phase control of the stepping motor 509 by the phase control unit 501 is performed.

In the control loop including the speed controller 502, the speed of the stepping motor 509 is controlled based on the feedback of the estimated value of the rotational speed ω of the stepping motor 509. FIG. The speed control unit 502 generates the current command value Iq_ref so that the deviation of the estimated value of the rotation speed ω of the stepping motor 509 fed back from the speed calculation unit 514 from the speed command value ω_ref (target value) approaches zero. and output. Here, the Iq_ref limiter unit 521 outputs Iq_ref' that limits the current command value Iq_ref output from the speed control unit 502 to be equal to or less than Iq_LIM, which is the current limit value (limit value) of the stepping motor. Specifically, when the calculation result of Iq_ref is equal to or greater than Iq_LIM, Iq_LIM is output as Iq_ref'. Also, when the calculation result of Iq_ref is less than Iq_LIM, Iq_ref is output as Iq_ref'. Iq_LIM is a value determined by the Vdq overvoltage detection unit 522, and the details of calculation by the Vdq overvoltage detection unit 522 will be described later.

In the control loop including the current control units 503 and 504, the drive current supplied to each phase winding of the stepping motor 509 is controlled based on the feedback of the detected value of the drive current flowing through each phase winding of the stepping motor 509. do. Here, it is assumed that the following currents flow through the A-phase and B-phase windings of the stepping motor 509, respectively.
iα=I×cos θ′
iβ=I×sin θ′ (1)

In this case, the current values Id and Iq of the d-axis current and the q-axis current (direct current) in the rotating coordinate system are represented by coordinate transformation shown in the following equations.
Id= cos θ×iα+sin θ×iβ
Iq=-sin θ×iα+cos θ×iβ (2)

By such coordinate conversion, the alternating current values iα and iβ respectively flowing in the A-phase and B-phase windings in the static coordinate system are converted into DC current values Iq and Id in the rotating coordinate system. Note that the q-axis current is a torque current component (first current component) that causes the stepping motor 509 to generate torque. The d-axis current is an exciting current component (second current component) that affects the magnetic flux intensity of the rotor of the stepping motor 509 and does not contribute to torque generation of the stepping motor 509 .

The drive currents flowing through the A-phase and B-phase windings of the stepping motor 509 are detected by current detectors 507 and 508 provided between the PWM inverter 506 and the stepping motor 509, respectively. The drive current values detected by the current detection units 507 and 508 are converted from analog values to digital values by the A/D conversion unit 510, so that they can be captured by a programming device such as a CPU or FPGA. The current values iα and iβ in the stationary coordinate system output from the A/D converter 510 are input to the coordinate converter 511 and the induced voltage calculator 512 .

The coordinate converter 511 converts the current values iα and iβ in the stationary coordinate system (αβ axes) into the current values Iq and Id in the rotating coordinate system (dq axes) according to Equation (2), and outputs the current values Iq and Id. Current controllers 503 and 504 receive difference values between detected current values Iq and Id in the rotating coordinate system and current command values Iq_ref′ and Id_ref output from coordinate converter 511 . The current command values Iq_ref' and Id_ref are current command values in the rotating coordinate system that are output from the Iq_ref limiter section 521 and the Id_REF limiter section 523, which will be described later.

The current control units 503 and 504 control the rotational coordinate system so that the input difference values (that is, the deviations of the detected current values Iq and Id from the target values of the current command values Iq_ref′ and Id_ref) approach zero. to generate and output voltage values Vq' and Vd' at . The phase control unit 501, the speed control unit 502, and the current control units 503 and 504 are each composed of, for example, a proportional compensator and an integral compensator, and realize feedback control by PI control.

Vdq overvoltage detection section 522 outputs Iq_LIM to Iq_ref limiter section 521 , ω_LIM to ω_ref limiter section 523 , and voltage values Vq′ and Vd′ to coordinate converter 505 . The details will be described later.

The coordinate converter 505 inversely transforms the voltage values Vq' and Vd' in the rotating coordinate system output from the current control units 503 and 504 to the current values Vα' and Vβ' in the stationary coordinate system according to the following equations.
Vα′=cos θ×Vd′−sin θ×Vq′
Vβ′=sin θ×Vd′+cos θ×Vq′ (3)

The coordinate converter 505 outputs the drive voltages Vα and Vβ after the coordinate conversion to the stationary coordinate system to the PWM inverter 506 configured by a full bridge circuit and the induced voltage calculator 512 .

In this way, the vector control unit 515 supplies the drive current to each phase winding of the stepping motor 509 according to the current value of the rotating coordinate system (dq axis) based on the rotation phase θ of the rotor of the stepping motor 509. Vector control is performed to control the The vector control unit 515 outputs drive voltages Vα and Vβ corresponding to the drive current supplied to the stepping motor 509 as a result of vector control based on feedback of the estimated value of the rotation phase θ of the rotor in the stepping motor 509 . Note that in vector control, the d-axis current is usually controlled so that its value becomes zero. However, in this embodiment, the CPU 151a outputs a predetermined negative Id command value id_ref based on the frequency of the phase command value θ_ref (that is, the target speed of the motor). This is a technique generally called field-weakening control, and by applying a predetermined d-axis current in the negative direction, it is possible to obtain the effect of improving the torque in the high-speed region.

In PWM inverter 506 , the full bridge circuit is driven by drive voltages Vα and Vβ input from coordinate converter 505 . As a result, PWM inverter 506 drives stepping motor 509 by supplying a driving current to each phase winding of stepping motor 509 according to driving voltages Vα and Vβ.

Sensorless Control As described above, vector control requires feedback of information indicating the phase and rotation speed of the motor in order to perform phase control and speed control of the motor. Specifically, in the configuration shown in FIG. Each needs feedback.

Normally, in order to detect (estimate) the phase and rotation speed of a motor, a rotary encoder is attached to the motor, the phase is detected based on the number of output pulses from the encoder, and the rotation speed is detected based on the output pulse period of the encoder. do. However, adding an encoder, which is essentially unnecessary for driving the stepping motor, raises the problem of cost increase and securing of arrangement space, as described above. Accordingly, sensorless control has been proposed in which the phase and rotation speed of a motor are estimated without using an encoder, and vector control is performed based on the estimation results. The sensorless control of the stepping motor 509 will be described below with reference to FIG. 3 again.

First, the induced voltage calculation unit 512 calculates the induced voltages (phase A and B phase counter-electromotive force). Specifically, the current values iα and iβ converted into digital values by the A/D conversion unit 510 and the drive voltages Vα and Vβ of the stepping motor 509 output from the vector control unit 515 are used to calculate the induced voltage. is input to section 512 . The induced voltage calculator 512 calculates the induced voltages Eα and Eβ of the stepping motor 509 from the drive voltages Vα and Vβ and the current values iα and iβ for the A-phase and B-phase, respectively, according to the following voltage equations.

Eα=Vα−R×iα−L×diα/dt
Eβ=Vβ−R×iβ−L×diβ/dt (4)

where R is the winding resistance and L is the winding inductance. The values of R and L are values unique to the stepping motor 509 being used, and are stored in advance in the ROM 151b or a memory (not shown) provided in the motor control section 157. FIG.

The A-phase and B-phase induced voltages Eα and Eβ calculated by the induced voltage calculator 512 are input to the phase calculator 513 . The phase calculator 513 calculates an estimated value of the rotation phase θ of the rotor of the stepping motor 509 from the ratio of the A-phase induced voltage Eα and the B-phase induced voltage Eβ by the following equation.
θ=tan ⁻¹ (−Eβ/Eα) (5)

Phase calculation section 513 outputs the estimated value of rotational phase θ obtained by such estimation calculation to phase control section 501 and speed calculation section 514 . Note that the estimated value of the rotational phase θ is also output from the phase calculator 513 to the coordinate converters 505 and 511 .

The speed calculator 514 calculates an estimated value of the rotational speed ω of the stepping motor 509 from the input rotational phase θ using the following equation.
ω=dθ/dt (6)

As shown in equation (6), the rotation speed ω is calculated based on the time change of the estimated value of the rotation phase θ. The speed calculator 514 outputs (feeds back) the obtained rotational speed ω to the speed controller 502 . A method for obtaining the Iq current limiter value (Iq_LIM) and the ω_ref limiter value by the Vdq overvoltage detection unit 522 described above will be described below.

As shown in FIG. 3 , the Vdq overvoltage detector 522 receives Vq′ and Vd′ output from the current controllers 503 and 504 . A method of calculating Iq_LIM by the Vdq overvoltage detection unit 522 in the first embodiment will be described with reference to FIG. FIG. 5 expresses the voltage vector V applied to the motor windings on the d/q coordinates, and the radius of the circle represents V_LIM.

V_LIM is generally the power supply voltage applied to PWM inverter 506 . As described above, the vector control performs coordinate conversion of the ab-phase currents flowing in the motor windings, which is a fixed coordinate system, into the dq-axis currents, which are a rotating coordinate system. are generated, converted into ab-phase voltages in a fixed coordinate system, and applied to the motor windings.

In general vector control, the d-axis current is controlled to be 0 and the q-axis current is used for torque control. In this case, since the d-axis current is 0, the d-axis voltage is also 0, and the motor is driven by applying the q-axis voltage. On the other hand, when the d-axis current is controlled to 0, it can be driven with maximum efficiency. There is a case where a current is dared to flow through the d-axis (weakening the field). In this case, the voltage is controlled so that Vd is non-zero, that is, the absolute value of Vd is greater than zero.

Since the ab-phase voltage applied to the motor windings is applied to the motor windings using the PWM inverter circuit, it is of course impossible to output the ab-phase voltage exceeding the power supply voltage applied to the inverter circuit. Therefore, in the vector control described below, the dq-axis voltages are controlled so that the ab-phase voltages do not exceed the power supply voltage applied to the inverter circuit.

With reference to FIGS. 5A and 5B, the behavior of the voltage on the rotating coordinate axis when the d-axis current is set to 0 and when the d-axis current is applied will be described.

FIG. 5(a) shows the voltage on the rotating coordinate axis when the d-axis voltage Vd is set to 0. FIG. At this time, the combined vector V of Vq and Vd matches Vq. Therefore, if Vq does not exceed V_LIM, there is no need to decrease Iq_LIM or ω_LIM.
In general, V_LIM is set so that the temperature of PWM inverter 506 and the like does not exceed a specified value in consideration of temperature rise. Also in this embodiment, the value is determined so as to prevent the temperature of the PWM inverter 506 from rising above the specified value.

FIG. 5(b) shows the case where Vd is controlled to be non-zero and Vd≠0. At this time, the synthesized vector V does not match Vq, and becomes a vector obtained by synthesizing Vq and Vd. Therefore, for example, when Vq has the same magnitude as V_LIM, the magnitude of the composite vector V exceeds V_LIM. In this case, if the magnitude of Iq_ref is limited, the current control output is limited, so Vd and Vq are also limited, and the combined vector can be limited to V_LIM or less.

As shown in FIG. 5B, the magnitude of the combined vector Vdq of Vd and Vq is √(Vq ² +Vd ² ). Iq_ref may be controlled so as to satisfy the following expression (8).
Vdq=√(Vq ² +Vd ² )≦V_LIM (8)

Specifically, using limit values V_LIM and Vdq, when an overvoltage is detected by Equation (8), Iq_LIM or ω_LIM is controlled to be smaller than the current value.

Next, an overview of current limiting processing in the first embodiment will be described with reference to the flowchart of FIG. In the following description, unless otherwise specified, Vd is controlled to be non-zero and Vd≠0. Each step is executed by the motor controller 157 under the CPU 151a in FIG. Also, to simplify the explanation, each step is assumed to be executed by the motor control unit 157 . Although FIG. 6 shows a flowchart for limiting Iq_ref by the motor control unit 157, instead of this, the motor control unit 157 may limit ω_ref.

When the motor drive starts (S100), the motor control unit 157 starts detecting the motor drive current by means of the current detection units 507 and 508 and the A/D conversion unit 510, as described in the above vector control. (S101). Then, the motor control unit 157 uses the detected current to calculate the rotation phase θ and speed ω of the motor (S102), and furthermore, the phase command value θ_ref representing the target rotation phase and the phase/speed control based on θ and ω is calculated (S103).

In S104, the Iq_ref limiter unit 521 determines whether Iq_ref calculated in S103 is greater than Iq_LIM. Iq_LIM is the Iq limit value determined by the Vdq overvoltage detector 522 . The Vdq overvoltage detection unit 522 determines the value of Iq_LIM so that √(Vq ² +Vd ² )≦V_LIM, that is, the combined voltage does not exceed V_LIM.

When it is determined that Iq_ref is not greater than Iq_LIM (S104: N), the Iq_ref limiter unit 521 outputs the value of Iq_ref calculated in S103 as it is as Iq_ref' (S105).

When it is determined that Iq_ref is greater than Iq_LIM (S104: Y), Iq_ref limiter section 521 outputs the value of Iq_LIM as Iq_ref' (S106). Using Iq_ref′ as the Iq current command value, the motor control unit 157 performs current control based on Id_ref, Id and Iq as described above, and calculates Vq and Vd (S107).

Next, the motor control unit 157 determines whether or not √(Vq ² +Vd ² )>V_LIM based on the detection result of the Vdq overvoltage detection unit 522 (S108). If √(Vq ² +Vd ² )>V_LIM (S108: Y), the motor control unit 157 decreases Iq_LIM so that √(Vq ² +Vd ² )≦V_LIM (S109), and proceeds to S110. . Otherwise (S108: N), the motor control unit 157 advances the process to S110. After that, the motor control unit 157 determines whether or not there is a drive stop command (S110). If there is no drive stop command (S110: N), S101 is executed again. In Y), the motor drive is terminated (S111).

In this way, motor control unit 157 limits Id_ref based on the detection result of Vdq overvoltage detection unit 522 , thereby controlling the voltage so that combined vector Vdq does not saturate at limit value V_LIM of PWM inverter 506 .
Although the torque current component is decreased in S104 to S107, at least one of the torque current component and the excitation current component may be decreased so that √(Vq ² +Vd ² )≤V_LIM.

Modification In the above-described embodiment, voltage control is performed when the Vdq overvoltage detection unit 522 detects √(Vq ² +Vd ² )>V_LIM shown in Equation (8). In this case, since the ab-phase voltage cannot exceed the power supply voltage, the ab-phase voltage is saturated at the power supply voltage.

However, when performing sensorless vector control without using a phase detection sensor such as a rotary encoder for detecting the rotor phase, the rotor phase is estimated from the ab-phase current and the ab-phase voltage. Estimation of the rotor phase is performed based on the back electromotive force generated in the motor windings, and it is premised that both the ab-phase current and the ab-phase voltage are sinusoidal waves.

When the ab phase voltage is saturated, its waveform does not become a sine wave. Therefore, an error occurs in estimating the rotor phase, and as a result, abnormal noise and step-out may occur. Therefore, in the voltage control in the modified example, the Iq_ref limiter unit 521 limits Iq_ref, or the ω_ref limiter unit 523 limits ω_ref, thereby avoiding saturation of the drive voltage Va/Vb to the limit value V_LIM of the PWM inverter 506. . As a result, the use of the drive voltages Va/Vb prevents errors in the estimated electrical angle.

However, if Iq_ref is limited, the speed will decrease due to the torque being limited, and if ω_ref is limited, the speed will also decrease. may not be possible.

Therefore, in the modified example, even if the Vdq overvoltage detector 522 detects √(Vq ² +Vd ² )>V_LIM, Iq_ref and ω_ref are not limited. Instead, power supply voltage limiter section 524 temporarily increases V_LIM, which is the limit value of PWM inverter 506 . The value of V_LIM after the increase is V′_LIM, and since this value is set to √(Vq ² +Vd ² ) or more, the upper limit value of the voltage is increased, and the restriction on the voltage value is relaxed.

In this case, the waveform of the drive voltages Va/Vb maintains a sine wave even in a region where the value exceeds V_LIM, so it is possible to correctly calculate the estimated electrical angle using the drive voltages Va/Vb.
As described above, the value of V_LIM is set so that the temperature of the PWM inverter 506 and the like does not exceed the specified value, taking into account the rise in temperature. Therefore, if V_LIM is changed to V'_LIM, which is a larger value than V_LIM, the temperature of PWM inverter 506 and the like may rise above the specified value.

Therefore, in the modified example, the time for changing V_LIM to V'_LIM is managed so that the temperature of PWM inverter 506 and the like does not exceed a specified value. For this purpose, the motor or the motor drive device is provided with at least one temperature detector, which measures the temperature at any given position in the motor. For example, the temperature of the PWM inverter 506 or the temperature of the motor drive device is detected. This variation senses the temperature of PWM inverter 506 and decreases V'_LIM back to V_LIM when the temperature exceeds a predetermined temperature limit. By doing so, the temperature of the PWM inverter 506 is lowered to a value equal to or lower than the predetermined value. This predetermined temperature limit value may be equal to the specified value of the temperature of PWM inverter 506 or the like, or may be set to a value greater than the specified value. When the predetermined temperature limit value is set to a value larger than the above specified value, the value of V'_LIM is set so that the PWM inverter 506 is not damaged by the temperature rise during the period from reaching V'_LIM to returning to V_LIM. is preferably set.

FIG. 7 shows a flowchart showing an overview of V_LIM restriction relaxation processing, which is processing for increasing the value of V_LIM in the modified example. As described in the explanation of the flowchart of FIG. 6, unless otherwise specified, Vd is controlled to be non-zero and Vd.noteq.0. Each step is executed by the motor controller 157 under the CPU 151a in FIG. Also, to simplify the explanation, each step is assumed to be executed by the motor control unit 157 .

When the motor starts to drive (S200), the motor control unit 157 starts detection of the motor current by the current detection units 507 and 508 and the A/D conversion unit 510 (S201), and uses the detected current to determine the rotation phase. θ and speed ω are calculated (S202). Thereafter, the motor control unit 157 further calculates Iq_ref by phase/speed control based on the phase command value θ_ref and θ and ω (S203). Here, since the contents of S101, S102 and S103 are the same as those of the vector control, the details thereof will be omitted.

Using Iq_ref as the Iq current command value, the motor control unit 157 performs current control based on Id_ref, Id, and Iq as described above, and calculates Vq and Vd (S204). Next, the motor control unit 157 determines whether √(Vq ² +Vd ² )>V_LIM based on the detection result of the Vdq overvoltage detection unit 522 (S205). If √(Vq ² +Vd ² )>V_LIM (S205: Y), the motor control unit 157 increases V_LIM (S206) and executes S207, which will be described later. On the other hand, if √(Vq ² +Vd ² )≦V_LIM (S205: N), the motor control unit 157 executes S207 without changing the value of V_LIM.

Thereafter, the motor control unit 157 determines whether or not there is a drive stop command (S207). If there is no drive stop command (S207: N), S201 is executed again. :Y), the motor drive is terminated (S208).

Thus, the motor control unit 157 increases the value of V_LIM in the Vdq overvoltage detection unit 522, as shown in the flowchart of FIG. As a result, control can be performed so that the drive voltage Va/Vb does not saturate at the PWM inverter 506 limit value V_LIM.

As described above, according to the present invention, vector control in a motor such as a stepping motor can be improved. In one embodiment, the current command value Iq_ref output from the speed control unit 502 is set as the current limit value (limit value) of the stepping motor when the excitation voltage component is not zero. As a result, vector control is performed so that the combined voltage of the excitation voltage component and the torque voltage component does not exceed the value of V_LIM, and the temperature of PWM inverter 506 and the like is prevented from rising above a specified value.

Further, in the modified example, instead of controlling the value of Iq_ref, the value of V_LIM is raised when the excitation voltage component is not 0, so saturation of the ab phase voltage can be avoided. As still another modification, the motor control unit 157 may selectively control the current command value Iq_ref and increase the value of V_LIM. In this case, the motor control unit 157 increases the value of V_LIM until the temperature in the PWM inverter 506 or the motor driving device exceeds the predetermined temperature limit value, and increases it when the temperature exceeds the predetermined temperature limit value. Controls the value of Iq_ref. Controlling in this manner avoids saturation of the a-b phase voltages as much as possible and limits the undesirable effects of the temperature in the PWM inverter 506 or motor drive exceeding a predetermined temperature limit.

Claims (5)

In a motor control device that controls a motor,
detection means for detecting a drive current flowing through the windings of the motor;
phase determination means for determining a rotation phase of a rotor of the motor based on the drive current detected by the detection means;
It is expressed in a rotating coordinate system based on the rotational phase determined by the phase determining means so that the deviation between the rotational phase determined by the phase determining means and the command phase representing the target phase of the rotor is small. an excitation current that generates a target value of a torque current component that is a current component that generates torque on the rotor, and that is a current component expressed in the rotating coordinate system and that affects the strength of the magnetic flux passing through the windings; first generating means for generating a target value of the torque component and performing field-weakening control with the excitation current component, wherein when the temperature of the motor control device exceeds a predetermined temperature, the target value of the torque current component is the first performing control to output the first predetermined value when the target value of the torque current component is larger than the predetermined value of 1 and to output the target value of the torque current component when the target value of the torque current component is smaller than the first predetermined value; a first generating means that does not perform the control when the temperature of the motor control device is equal to or lower than the predetermined temperature ;
so that the deviation between the target value or the first predetermined value of the torque current component output from the first generation means and the torque current component of the drive current detected by the detection means is reduced. a second generating means for generating a value corresponding to the torque current component of the drive voltage to be applied to the second generating means, the current component expressed in the rotating coordinate system affecting the strength of the magnetic flux penetrating the winding A value corresponding to the excitation current component of the drive voltage to be applied to the winding is set so that the deviation between the target value of the excitation current component and the excitation current component of the drive current detected by the detection means is small. a second generating means for generating;
An inverter for applying the drive voltage to the winding based on the value corresponding to the torque current component of the drive voltage and the value corresponding to the excitation current component of the drive voltage generated by the second generating means. a circuit;
has
The first predetermined value is such that the magnitude of a vector represented by a value corresponding to the torque current component of the drive voltage and a value corresponding to the excitation current component of the drive voltage is smaller than a second predetermined value. is a value set as
The first generating means increases the second predetermined value until the temperature of the motor control device exceeds the predetermined temperature, and increases the second predetermined value when the temperature of the motor control device exceeds the predetermined temperature. characterized by returning the predetermined value of 2 to the original value ,
motor controller. The first generating means generates the first predetermined value so that the magnitude of the vector is equal to or less than the second predetermined value when the magnitude of the vector exceeds the second predetermined value. characterized by reducing
The motor control device according to claim 1. The first generating means sets Vq as a value corresponding to the torque current component of the drive voltage and Vd as a value corresponding to the excitation current component of the drive voltage, and the value of √(Vd ² +Vq ² ) is the above characterized by determining that the magnitude of the vector exceeds the second predetermined value when the second predetermined value is exceeded,
The motor control device according to claim 1 or 2. a motor control device according to any one of claims 1 to 3;
a conveying roller that conveys the sheet;
a motor that drives the conveying roller;
has
The motor control device controls the motor,
Sheet conveying device. a motor control device according to any one of claims 1 to 3;
a conveying roller that conveys the sheet;
a motor that drives the conveying roller;
an image forming unit that forms an image on the sheet conveyed by the conveying roller;
characterized by having
Image forming device.

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