CONTROL DEVICE, IMAGE FORMING DEVICE, AND CONTROL METHOD

Abstract

To suppress occurrence of an undershoot and an overshoot while coping with variations in products.SOLUTION: A control device 100 includes: an actual speed detection unit 102 for detecting and outputting actual rotation speed of a control target (for example, a motor 120); a PID calculation unit 105 for performing PID calculation from target rotation speed and the actual rotation speed; a sudden deceleration control value calculation unit 107 for calculating and outputting a control value corresponding to the target rotation speed in advance; a PWM signal generation unit 106 for converting an input from the sudden deceleration control value calculation unit 107 or the PID calculation unit 105 into a control signal to output it; a brake control unit 104 for decelerating rotation of the control target; and a state control unit 103 for controlling the PID calculation unit 105 and the brake control unit 104. When it is determined that an input instruction related to the target rotation speed of the control target is a sudden deceleration instruction, the brake control unit 104 starts rotation reduction of the control target, and the sudden deceleration control value calculation unit 107 outputs a control value according to the target rotation speed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control device that controls a control target by PWM control, an image forming apparatus including the control device, and a method for controlling the control target. [Background technology]

[0002] When controlling the rotation of a motor such as a brushless motor with PWM control, a motor control method is known in which the output pulses of an encoder that detects the rotation of the motor are fed back to control the rotation speed and drive amount of the motor according to a desired set amount. As the feedback control, a proportional-integral-derivative controller (PID control) is used.

[0003] For example, Patent Document 1 discloses a sheet conveying device and an image forming device that can control (suppress) speed fluctuations during deceleration using a simple control method. This device employs a DC brushless motor, and is configured to perform power control and brake control for each PWM cycle during deceleration, and to use PID control for feedback of the duty value. The brake control is performed by short-circuiting the coil to form a closed loop circuit.

[0004] Generally, in PID control, the input value (control value) to a controlled object such as a motor is determined by three elements: the deviation between the output value indicating the state of the controlled object (for example, rotation speed) and a target value, the integral of the deviation, and the derivative of the deviation. When PID is used to PWM control a motor, the duty of the control pulse (PWM signal) is increased during acceleration and decreased during deceleration, causing the motor to follow the target rotation speed. In addition, the brake is used during deceleration. However, using the brake to suddenly decelerate the motor causes a very large undershoot and subsequent overshoot, resulting in problems such as poor speed following performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-12186 A [Patent Document 2] Patent No. 6512915 Summary of the Invention [Problem to be solved by the invention]

[0006] When decelerating the rotation of the motor, it is necessary to decelerate as quickly as possible, and it is also necessary to prevent undershooting of the rotation speed. Figures 10 and 11 are graphs showing the state when the motor is suddenly decelerated by braking (when the degree of deceleration is relatively large) under conventional PID control, and show the time change in the motor rotation speed (rpm) and the duty (%) of the PWM signal that controls the motor.

[0007] As shown in Figure 10, when the motor is decelerated from a constant speed to a target rotation speed, the brake is applied at time t1 and the duty value of the PWM signal is set to 0% at the same time. This causes the motor speed to decrease rapidly. At time t2, the brake is released and no longer applied as the motor has reached the target rotation speed.

[0008] The duty value of the PWM signal is basically 0% due to the PID calculation result during deceleration. Since the PID calculation is a calculation that multiplies the difference between the target value and the current value by a fixed gain value, if the difference is large, the calculation result becomes negative and the output duty value is fixed at 0%. In this way, when the brake is used, the motor cannot be driven normally immediately after the brake is released at time t2 because the duty value is 0%, and a large undershoot is likely to occur. Also, if the motor is accelerated after having been greatly decelerated once, an overshoot will occur. Since PID control performs cumulative calculations, if a negative limit is not set, it will take time for the calculation result to become positive even if the brake is turned off, further reducing responsiveness.

[0009] Also, as shown in Fig. 11, when the motor is decelerated from a state in which it is rotating at a constant speed to a target rotation speed, the duty value of the PWM signal is set to 0% at time t3 without operating the brake. This reduces the motor speed. At time t4, the target rotation speed is reached and the control is switched to PID control, but a normal duty value cannot be output immediately after the deceleration is completed, and undershoot and overshoot still occur. These problems cannot be solved by the configuration disclosed in Patent Document 1.

[0010] In order to solve the above problems, the present inventor has proposed a control device that enables smooth switching from deceleration to PID control by outputting a fixed duty even during deceleration (see Patent Document 2). During rapid deceleration, the duty value to be output is calculated by matching with the actual device, and in the case of a product that incorporates multiple motors, it is necessary to calculate the duty values ​​of the multiple motors. Therefore, the duty value of each motor must be checked every time the product is changed, the motor's performance is changed, or the motor manufacturer is changed, which requires evaluation man-hours and leaves room for improvement.

[0011] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a control device using PWM that can suppress the occurrence of undershoot and overshoot and has high speed tracking performance when a controlled device such as a motor is decelerated by PWM control, an image forming apparatus equipped with the same, and a control method. [Means for solving the problem]

[0012] The solution of the present invention for achieving the above object is a control device that controls the rotation speed of a controlled object by PWM control, and includes a detection means that detects and outputs an actual rotation speed of the controlled object, a PID calculation means that performs PID calculation from a target rotation speed of the controlled object and the actual rotation speed detected by the detection means, a control value calculation means that calculates in advance a control value according to the target rotation speed and outputs it, a signal generation means that converts an input from the control value calculation means or the PID calculation means into a control signal for the controlled object and outputs it, a deceleration means that decelerates the rotation of the controlled object, and a state control means that controls the PID calculation means and the deceleration means. When an instruction related to a target rotational speed of the controlled object is input, the state control means judges whether or not it is a rapid deceleration instruction such that the target rotational speed becomes equal to or lower than a predetermined value relative to the actual rotational speed, and if it is judged that it is a rapid deceleration instruction, the state control means causes the deceleration means to start decelerating the rotation of the controlled object, causes the control value calculation means to output a control value corresponding to the target rotational speed, and causes the signal generation means to generate a control signal of a duty corresponding to the control value, and when the actual rotational speed reaches close to the target rotational speed after the deceleration of the controlled object has started, the state control means causes the deceleration means to release the deceleration of the rotation of the controlled object.

[0013] Moreover, in the control device, it is preferable that the control value calculation means calculates a second duty, which is a duty value corresponding to the target rotation speed, as the control value based on a ratio between the actual rotation speed and a first duty, which is a duty value corresponding to the actual rotation speed.

[0014] In addition, the control device may further include a storage means for storing characteristic information indicating a relationship between a rotation speed and generated torque in the controlled object and a duty value, and the control value calculation means may calculate, as the control value, a second duty which is a duty value corresponding to the target rotation speed, in light of the actual rotation speed and a first duty which is a duty value corresponding to the actual rotation speed, in light of the characteristic information.

[0015] In this case, the generated torque may be approximated by a first approximation equation which is a linear function of the actual rotational speed, and a second duty which is a duty value according to the target rotational speed may be approximated by a second approximation equation which is a linear function of the target rotational speed, the memory means may have a first table including a plurality of the first approximation equations and a second table including a plurality of the second approximation equations, and the control value calculation means may be configured to select the first approximation equation and the second approximation equation from each table to calculate the control value.

[0016] The present invention also includes an image forming apparatus equipped with the control device, which is characterized in that the image forming apparatus of the present invention includes the control device and an image forming means for forming an image on a recording paper, and the controlled object is a motor used for transporting the recording paper.

[0017] Further, a solution of the present invention for achieving the above-mentioned object is a control method for controlling a rotation speed of a controlled object by PWM control, the method including: a detection step of detecting and outputting an actual rotation speed of the controlled object; a PID calculation step of performing a PID calculation from a target rotation speed of the controlled object and the actual rotation speed detected in the detection step; a control value calculation step of calculating and outputting a control value according to the target rotation speed; a signal generation step of converting the output value obtained by the control value calculation step or the PID calculation step into a control signal for the controlled object and outputting the control signal; a deceleration step of decelerating the rotation of the controlled object; and a determination step of determining, when an instruction related to the target rotation speed of the controlled object is input, whether or not the instruction is a rapid deceleration instruction in which the target rotation speed becomes equal to or lower than a predetermined value with respect to the actual rotation speed;

[0018] As a result, when the rotation of the controlled object is suddenly decelerated, it is possible to prevent the rotation speed from undershooting and then overshooting, thereby achieving good rotation speed tracking performance. Effect of the Invention

[0019] According to the present invention, when a controlled object is decelerated by PWM control, the occurrence of undershoot and overshoot can be suppressed, and speed following performance can be improved. [Brief description of the drawings]

[0020] [Figure 1] 1 is a block diagram showing a relationship between a control device and a motor according to an embodiment of the present invention. [Diagram 2] 5 is a graph showing a state in a rapid deceleration mode in the control device. [Diagram 3] 10 is a graph showing a state of a motor in a rapid deceleration mode in conventional PID control as a comparative example. [Figure 4] 5 is a flowchart showing a motor control configuration by the control device according to the first embodiment of the present invention. [Diagram 5] 10 is a flowchart showing a motor control configuration by a control device according to a second embodiment of the present invention. [Figure 6] 1 is a graph showing the relationship between the rotation speed, generated torque, and input current and the duty value, as an example of characteristic information of a motor to be controlled. [Figure 7] 4 is an explanatory diagram showing an example of a first approximate expression table of a linear function based on the characteristic information. FIG. [Figure 8] 10 is an explanatory diagram showing an example of a second approximate expression table of a linear function based on the characteristic information. FIG. [Figure 9] 1 is a schematic cross-sectional view illustrating an example of an image forming apparatus to which a control device according to an embodiment of the present invention is applied; [Figure 10] 1 is a graph showing a state during sudden deceleration of a motor in conventional PID control. [Figure 11]11 is a graph showing another example of a state during sudden deceleration of a motor in conventional PID control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A control device, a control method, and an image forming apparatus according to embodiments of the present invention will be described below with reference to the drawings.

[0022] The control device 100 and the control method according to the present embodiment can be applied to, for example, an image forming apparatus 1 that forms an image on a recording sheet. In particular, the control device 100 and the control method can use the motor 120 used for conveying the recording sheet in the image forming apparatus 1 as a control target.

[0023] In this embodiment, an example is described in which the control device and control method according to the present invention are applied to an image forming device 1, but the present invention is not limited to this, and the device can be suitably used in other devices as long as they control a motor.

[0024] (Schematic configuration of image forming apparatus) 9 is a schematic cross-sectional view showing an example of an image forming apparatus to which the control device 100 according to the present embodiment is applied. The image forming apparatus 1 according to the illustrated embodiment is a tandem color image forming apparatus having a configuration in which a plurality of image carriers (specifically, photoconductors 33) on which toner images are respectively formed are arranged in a predetermined direction.

[0025] This image forming device 1 includes a device main body 11 and a document reading device 20 arranged above it, and forms a color image or a monochrome image on a specified recording paper based on image data read by the document reading device 20 or image data transmitted from outside.

[0026] Note that the image forming apparatus 1 is not limited to this, and may be various image forming apparatuses including a color printer, a color multifunction machine, a monochrome printer, etc. As the recording paper, paper or an overhead projector sheet, etc., may be used.

[0027] The document reading device 20 of the image forming apparatus 1 is provided with a document reading section 21 including a light source, multiple mirrors, an imaging lens, a line sensor, etc. The document reading section 21 exposes the document surface to the light source, and guides the reflected light from the document surface to the imaging lens via multiple mirrors. The imaging lens then forms an image of the reflected light on the light receiving element of the line sensor. The line sensor detects the luminance or chromaticity of the reflected light that has formed an image on the light receiving element, and generates image data based on the image of the document surface.

[0028] An image forming section 30 as an image forming means and a control section (not shown) are provided in the apparatus main body 11. The image forming section 30 includes an exposure unit 31, a developing device 32, a photoconductor 33, a cleaner unit 34, a charger 35, an intermediate transfer belt unit 36, and a fixing unit 39, and forms an image on a recording paper conveyed from a recording paper stacking section such as a paper feed cassette 41, and discharges the recording paper with the image formed thereon to a paper discharge tray 46.

[0029] The control unit includes a CPU, a RAM, etc., and transmits control signals to each component of the image forming apparatus 1 to perform various operations in response to input operations to the operation unit, etc. The control unit also controls the operation of the control device 100 for the motor 120 as a host CPU 110, which will be described later.

[0030] Image data handled by the image forming apparatus 1 corresponds to color images of four colors: black (K), cyan (C), magenta (M) and yellow (Y). For this reason, four of each of the developing device 32, the photoconductor 33, the cleaner unit 34 and the charger 35 are provided so as to form four types of latent images corresponding to each color, and these constitute four image stations.

[0031] The photoconductor (photoconductor drum) 33 is an image carrier in which a photosensitive layer is formed on the surface of a cylindrical base body having electrical conductivity. The charger 35 charges the surface of the photoconductor 33 to a predetermined potential. The exposure unit 31 is configured as a laser scanning unit equipped with a laser emission section and a reflecting mirror, and exposes the charged surface of the photoconductor 33 to light, thereby forming an electrostatic latent image on the surface of the photoconductor 33 according to image data. The developer 32 visualizes the electrostatic latent image formed on the surface of the photoconductor 33 with four-color (YMCK) toners, forming a toner image. The cleaner unit 34 removes and collects toner remaining on the surface of the photoconductor 33 after development and image transfer.

[0032] The intermediate transfer belt unit 36 ​​includes an intermediate transfer belt 51, a belt drive roller (drive roller) 52, a belt driven roller 53, and four intermediate transfer rollers (primary transfer rollers), etc. The intermediate transfer belt 51 is provided so as to be able to come into contact with each photoconductor 33, and forms a multi-color toner image on the intermediate transfer belt 51 by transferring the toner images of each color formed on each photoconductor 33 to the intermediate transfer belt 51 in a superimposed manner.

[0033] A secondary transfer roller 54 is disposed in a region where the intermediate transfer belt 51 is sandwiched between the belt drive roller 52. The secondary transfer roller 54 performs a second transfer of the toner image formed on the intermediate transfer belt 51 onto a recording paper passing through a transfer nip region N1 between the intermediate transfer belt 51 and the secondary transfer roller 54.

[0034] The fixing unit 39 includes a fixing roller 391, a heating roller 392, and a pressure roller 393. The fixing roller 391 is pressed against the pressure roller 393 via a belt suspended between the fixing roller 391 and the heating roller 392. The recording paper is conveyed while being sandwiched in a fixing nip region N2 between the fixing roller 391 and the pressure roller 393 via the belt, and the toner image on the recording paper is heated and fixed.

[0035] During image formation, the recording paper stored in the paper feed cassette 41 is guided one by one to the recording paper transport path by the paper feed roller 42, and is transported to the registration roller 44 via the pre-registration roller 43. The registration roller 44 transports the recording paper to the secondary transfer roller 54 at the timing when the leading edge of the recording paper and the leading edge of the toner image on the intermediate transfer belt 51 are aligned, and the toner image is transferred onto the recording paper by passing through the transfer nip area N1 between the secondary transfer roller 54 and the intermediate transfer belt 51. Thereafter, the recording paper passes through the fixing unit 39, whereby the unfixed toner on the recording paper is melted and fixed by heat, and the recording paper is discharged onto the paper discharge tray 46 via the paper discharge roller 45. When double-sided printing is performed on the recording paper, the recording paper that has passed through the fixing unit 39 after the front side printing is completed is turned over so that the side on which the toner image has not been transferred faces the intermediate transfer belt 51, and is transported again to the image forming unit 30. Each of the rollers 42 to 45 of the conveying system provided in the recording paper conveying path is directly or indirectly driven to rotate by a motor 120, and the rotation speed and the like are controlled by a control device 100.

[0036] (Control device configuration) FIG. 1 is a block diagram showing the relationship between a control device 100 and a motor 120 according to an embodiment of the present invention.

[0037] The control device 100 includes an interface unit (IF unit) 101, an actual speed detection unit 102, a state control unit 103, a brake control unit 104, a PID calculation unit 105, a PWM signal generation unit 106, and a rapid deceleration control value calculation unit 107. The control device 100 controls a motor 120, which is an object to be controlled, under the control of a host CPU 110 provided in a device body 11 of the image forming device 1 in which the control device 100 is provided. The control device 100 also includes a ROM (Read Only Memory) and a RAM (Random Access Memory) as storage units (not shown). The host CPU 110 is started when the power is turned on, operates in synchronization with a clock signal input from a clock, reads a control program from the ROM, and executes the control program using the RAM as a working storage area.

[0038] In this example, the motor 120 is a DC brushless motor. However, the motor 120 is not limited to this, and may be, for example, a DC brushed motor. As shown in the figure, the motor 120 includes a control IC 121, a three-phase coil 122, an encoder 123, and the like.

[0039] The control IC 121 receives a control signal PWM from the control device 100 and controls a driver to turn on the brake. The encoder 123 detects the rotation of the rotor of the motor 120 and outputs a pulse signal according to the rotation state to the control device 100. The encoder 123 can be a known encoder (for example, an optical encoder or a magnetic encoder using a Hall element, etc.).

[0040] The PID control executed in the control device 100 is not a continuous time control (analog control) but a discrete time control (digital control) that operates on a predetermined clock. Each unit executes processing in synchronization with a common input clock.

[0041] Interface section An interface unit (IF unit) 101 receives a target rotation speed and a PID parameter value (gain value) from a host CPU 110, and outputs them to a state control unit 103 and a rapid deceleration control value calculation unit 107. The target rotation speed is input to the interface unit 101 at the timing of deceleration of a motor 120 to be controlled.

[0042] State control section The state control unit 103 generates an operation mode based on the input data, and outputs it to the brake control unit 104, the PID calculation unit, and / or the rapid deceleration control value calculation unit 107. When the target rotation speed of the motor 120 is set to a value smaller than the rotation speed input by the actual speed detection unit 102, the control data is set to the deceleration mode, and otherwise the normal mode. For example, the operation mode is set to "1" in the deceleration mode, and is set to "0" in the normal mode.

[0043] Actual speed detection section The actual speed detection unit 102 calculates the actual rotation speed of the motor 120 based on an ENCODE pulse signal indicating the current rotation state input from an encoder 123 of the motor 120 to be controlled, generates actual rotation speed data, and outputs it to the state control unit 103 and the rapid deceleration control value calculation unit 107. The rotation state of the motor 120 is represented by the actual rotation speed (or actual rotation number) which is the actual rotation speed of the rotating shaft of the motor 120. The actual speed detection unit 102 includes, for example, a known FV converter (FV conversion IC), generates a voltage according to the input pulse (frequency), and outputs corresponding digital data.

[0044] PID calculation section The PID calculation unit 105 executes a known PID calculation using the deviation between the input target value and the actual rotation speed of the motor 120 indicated by the data input from the actual speed detection unit 102. That is, the PID calculation unit 105 generates a P value, an I value, and a D value, and outputs the data obtained by adding them together.

[0045] ·PWM signal generation section The PWM signal generating unit 106 converts inputs from the PID calculation unit 105 and the rapid deceleration control value calculation unit 107 into a PWM signal that is a control signal for the motor 120, and outputs the PWM signal to the control IC 121 of the motor 120. The PWM signal generating unit 106 operates differently depending on the input control data (MODE). Specifically, if MODE=1 (deceleration mode), the PWM signal generating unit 106 generates and outputs a control signal PWM according to a target value. If MODE≠1 (MODE=0 (normal mode)), the PWM signal generating unit 106 changes the duty value of the current control signal according to the input data, and outputs a control signal of a new duty value to the control IC 121 of the motor 120. The control IC 121 controls a current control circuit for the coil 122 to rotate the rotor of the coil 122.

[0046] Brake control unit The brake control unit 104 outputs a signal BRAKE at a level according to the input control data to the control IC 121 of the motor 120. For example, the signal BRAKE is output at a high level if MODE=1 (deceleration mode), and is output at a low level if MODE≠1 (MODE=0 (normal mode)). If the control data is at a high level, the control IC 121 controls the brake to be turned ON, and the rotational speed of the coil 122 is decelerated.

[0047] Rapid deceleration control value calculation section The rapid deceleration control value calculation unit 107 calculates and outputs a control value according to the target rotation speed before the target rotation speed is reached, based on data relating to the target rotation speed input from the state control unit 103 and data corresponding to the rotation state of the motor 120 to be controlled input from the actual speed detection unit 102. A value according to the PWM signal generation method adopted by the PWM signal generation unit 106 is set as the control value.

[0048] There are multiple possible methods for calculating the control value, which will be described in the following embodiments 1 and 2. Note that the configuration of the control device 100 may be common to embodiments 1 and 2, and will be indicated and described with common reference symbols.

[0049] (Embodiment 1) In the control device disclosed in the above-mentioned Patent Document 2, the fixed duty in the rapid deceleration mode is determined by measuring each motor in an actual machine. Fig. 3 is a graph showing, as a comparative example, the state of a motor in rapid deceleration mode in conventional PID control (see Patent Document 2), and shows the time change in the rotation speed (rpm) of the motor and the duty (%) of the PWM signal that controls the motor.

[0050] As shown in Figure 3, during deceleration, a fixed duty, which is a constant control value, is output while applying the brakes. This fixed duty is output to ensure stability when switching to PID control at time T10 and to suppress undershoot during deceleration. However, since the PID control formula uses the deviation value between the past target rotation speed and the current rotation speed and the past PID calculation results, it tends to take time for the PID control calculation results to become normal, and when multiple motors are used in one product, it is necessary to determine the fixed duty for each motor.

[0051] In contrast to this, in the control device 100 according to this embodiment, when an instruction related to a target rotational speed of the motor 120 is input, the state control unit 103 determines whether or not the target rotational speed is a predetermined value or less with respect to the actual rotational speed, in other words, whether or not the instruction is an instruction corresponding to a rapid deceleration mode, and then causes the rapid deceleration control value calculation unit 107 to output a control value corresponding to the target rotational speed.

[0052] FIG. 2 is a graph showing a state in the rapid deceleration mode in the control device 100 according to this embodiment, and shows the change in the rotation speed (rpm) of the motor 120 over time and the duty (%) of the PWM signal that controls the motor 120. In FIG.

[0053] The state control unit 103 judges whether the input target rotation speed is the rapid deceleration mode or not. If it is judged to be the rapid deceleration mode, the state control unit 103 causes the brake control unit 104 to start decelerating the rotation of the motor 120, and the brake is turned ON (time T1). At the same time, the state control unit 103 causes the rapid deceleration control value calculation unit 107 to start calculating a control value according to the target rotation speed, output the calculation result to the PWM signal generation unit 106, and generate a control signal of a duty according to the control value. Then, after the start of deceleration of the motor 120, when the actual rotation speed reaches close to the target rotation speed at time T2, the state control unit 103 causes the brake control unit 104 to cancel the deceleration of the rotation of the motor 120.

[0054] During this time, the rapid deceleration control value calculation unit 107 calculates a ratio from the target rotation speed (first target rotation speed) related to the previous input command, which is the actual rotation speed before the deceleration started, the duty value (first duty) corresponding to the first target rotation speed, and the target rotation speed (second target rotation speed) related to the current input command, and calculates a duty value (second duty) corresponding to the second target rotation speed as a control value based on these. The generated torque (load) is not related to the rotation speed of the motor 120, that is, Generated torque (N m) = tangential force (N) × radius of rotation (m) Therefore, the generated torque can be calculated as being constant. The control value is determined from the relationship between the first target rotation speed, the duty value corresponding to the first target rotation speed, and the second target rotation speed.

[0055] For example, the duty value when rotating at the first target rotation speed V1 is the first duty D1, and the duty value when rotating at the second target rotation speed V2 is the second duty D2. In this case, while the motor 120 is rotating at the first target rotation speed, the second duty D2 is unknown. At the timing when a deceleration command (second target rotation speed V2) is received from the upper CPU, the rapid deceleration control value calculation unit 107 starts calculating the second duty D2. Then, the second duty D2, which is a duty value corresponding to the second target rotation speed V2, can be obtained from the ratio of "V1:D1". That is, D2 = V2 ÷ V1 × D1 Thus, the second duty D2 is determined as a control value.

[0056] The state control unit 103 determines that the mode is the deceleration mode when the second target rotation speed V2 is smaller than the first target rotation speed V1 (V1>V2). When the mode is determined to be the deceleration mode, and the second target rotation speed V2 is equal to or smaller than a predetermined value with respect to the first target rotation speed V1, that is, when the difference between the first target rotation speed V1 and the second target rotation speed V2 is equal to or larger than a predetermined value, the mode is determined to be the rapid deceleration mode. Since the first target rotation speed V1 and the second target rotation speed V2 are not constant but are variable within the rotatable range of the motor 120, the rapid deceleration control value calculation unit 107 is configured to calculate and output the second duty D2 when the rapid deceleration mode is determined.

[0057] Fig. 4 is a flowchart showing a control configuration of the motor 120 by the control device 100 according to the embodiment 1. The operation of the control device 100 according to the operation mode will be described with reference to Fig. 4. The control program is stored in a non-volatile storage unit such as a ROM in the device main body 11 or the control device 100, and is read from the storage unit and executed when the device main body 11 is powered on.

[0058] In an initial state, the brake is ON and the motor 120 stops rotating. In step S201, the state control unit 103 determines whether or not a command related to a first target rotation speed has been received from the interface unit 101. If it is determined that a command has been received (YES in step S201), the control proceeds to step S202. If not, step S201 is repeated.

[0059] In step S202, the state control unit 103 generates an operation mode based on the input data, and outputs it to the brake control unit 104 and the PID calculation unit 105. The brake control unit 104 turns off the brake of the motor 120, and causes the motor 120 to start rotating.

[0060] In step S203, the PID calculation unit 105 executes a PID calculation, and the PWM signal generation unit 106 outputs a control signal with a duty corresponding to the first target rotation speed, and then the process shifts to PID control.

[0061] In step S204, the state control unit 103 determines whether or not a command related to the second target rotation speed has been received from the interface unit 101. If it is determined that the command has been received (YES in step S204), the control proceeds to step S205. If not, step S204 is repeated.

[0062] In step S205, the state control unit 103 determines whether the input command indicates the deceleration mode. That is, when the second target rotation speed is smaller than the first target rotation speed, the deceleration mode is set, and the state control unit 103 determines whether MODE=1 (deceleration mode). If MODE≠1 (MODE=0 (normal mode)), the PID control in step S213 is continued. If it is determined to be the deceleration mode (YES in step S205), the process proceeds to step S206.

[0063] In step S206, the state control unit 103 further judges whether the input command indicates a rapid deceleration mode. Specifically, when MODE=1 (deceleration mode) and the second target rotation speed is equal to or less than a predetermined value with respect to the first target rotation speed, the state control unit 103 judges the rapid deceleration mode (YES in step S206). If it is judged to be the rapid deceleration mode, the process proceeds to step S208. If it is judged not to be the rapid deceleration mode, the process proceeds to step S207, where deceleration of the motor 120 by PID control is started as a normal deceleration mode. Note that although the rapid deceleration mode is defined as the case where the second target rotation speed is equal to or less than a predetermined value with respect to the first target rotation speed, any type of deceleration can be determined as the rapid deceleration mode.

[0064] When it is determined in step S206 that the mode is the rapid deceleration mode, the state control unit 103 outputs MODE=1 (deceleration mode) as control data to the brake control unit 104, and the brake control unit 104 outputs the signal BRAKE at a high level to the control IC 121 of the motor 120. The control IC 121 of the motor 120 controls the brake to be ON, and the deceleration of the motor 120 starts (brake ON, step S208). At the same time, the rapid deceleration control value calculation unit 107 calculates the second duty of the rapid deceleration mode by ratio calculation based on the input from the state control unit 103 (step S209), and outputs the obtained second duty (step S210).

[0065] After the motor 120 starts to decelerate, when the actual rotation speed detected by the actual speed detection unit 102 approaches the second target rotation speed, the state control unit 103 cancels the deceleration of the rotation of the motor 120. In step S211, the state control unit 103 determines whether the actual rotation speed data from the actual speed detection unit 102 is close to reaching the second target rotation speed. If it is determined that the actual rotation speed is close to reaching the second target rotation speed (YES in step S211), the process proceeds to step S212, and if not, step S211 is repeated.

[0066] In step S212, the state control unit 103 generates an operation mode and outputs it to the brake control unit 104 and the PID calculation unit 105. The brake control unit 104 turns off the brake of the motor 120 and starts the rotation of the motor 120. The process proceeds to step S213, where PID control is started.

[0067] In this way, when the rapid deceleration mode is determined in step S206, the motor 120 starts to decelerate, and the second duty corresponding to the second target rotation speed is calculated and output. As shown in FIG. 2, a PWM signal generated from the second duty is input to the motor 120 during the deceleration period from time T1 to T2, and at time T2, the actual rotation speed approaches the second target rotation speed and the brake is released (brake OFF). When the control is switched to PID control at time T3, the motor 120 is driven by the second duty corresponding to the second target rotation speed, so that although the rotation speed slightly undershoots, it does not greatly undershoot as shown in FIG. 10 and FIG. 11. Therefore, the control device 100 can suppress undershoot and overshoot in the rapid deceleration mode, and the tracking performance of the rotation speed of the motor 120 can be improved.

[0068] The first target rotation speed and the second target rotation speed are variable, and by calculating the second duty by a ratio, it is not necessary to store the second duty for the combination of the first target rotation speed and the second target rotation speed. Therefore, after the second target rotation speed is reached and the control is switched to PID control, the information related to the second duty can be discarded. In addition, by using such a calculation method, it is possible to deal with product variations for each motor 120.

[0069] Also, depending on the motor 120, once the brake is turned ON, it may not be possible to immediately turn it OFF. Therefore, when the degree of deceleration is small, the brake is applied to the motor 120 more than necessary, and the rotation speed may decrease significantly below the target rotation speed (occurrence of undershoot). In contrast, in this embodiment, when the degree of deceleration is small, conventional deceleration control (normal deceleration mode, step S207) is performed, so that the rotation speed is prevented from decreasing significantly below the target rotation speed.

[0070] (Embodiment 2) In the control device 100 and the control method thereof according to the first embodiment, the rapid deceleration control value calculation unit 107 calculates the second duty in the rapid deceleration mode by ratio calculation based on an input from the state control unit 103. The present invention is not limited to this, and may be configured to calculate the second duty, which is a duty value according to a target rotation speed, as a control value based on characteristic information indicating the relationship between the rotation speed and generated torque of the motor 120 and the duty value.

[0071] FIG. 5 is a flowchart showing a control configuration of the motor 120 by the control device 100 according to the second embodiment.

[0072] In this embodiment, as shown in Fig. 5, steps S301 to S308 are common to steps S201 to S208 in the flowchart of Fig. 4, and are characterized by the method of calculating the second duty in steps S309 to S312. Also, steps S313 to S316 are common to steps S210 to S213 in Fig. 4. Therefore, in the following description of the second embodiment, the method of calculating the second duty will be described in detail, and overlapping descriptions will be omitted.

[0073] Referring to FIG. 5, when the operation of the control device 100 according to the operation mode is determined to be a rapid deceleration mode in step S306, the state control unit 103 outputs MODE=1 (deceleration mode) as control data to the brake control unit 104, and the brake control unit 104 outputs the signal BRAKE at a high level to the control IC 121 of the motor 120.

[0074] The control IC 121 of the motor 120 controls the brake to be turned ON, and the deceleration of the motor 120 is started (brake ON, step S308). At the same time, the rapid deceleration control value calculation unit 107 starts calculation for the second duty in the rapid deceleration mode based on the characteristic information of the motor 120 in response to an input from the state control unit 103.

[0075] 6 is a graph showing the relationship between the rotation speed, generated torque, and input current and the duty value as an example of characteristic information of the motor 120. The percentages given to the TN curve and the TI curve in the graph indicate the respective duty values.

[0076] As shown in the figure, when a constant voltage is applied to a representative motor (motor 120), for example, the relationship between the rotation characteristics, generated torque, and input current (motor current) is as shown in Figure 6. As shown in the torque-rotation characteristics (TN curve) of motor 120, as the load torque is gradually applied, the rotation speed of motor 120 decreases. Also, as shown in the torque-current characteristics (TI curve) of motor 120, as the load torque increases, the input current increases gradually in proportion. The characteristic information of motor 120 is prepared by the manufacturer of motor 120, etc., and can be obtained as needed.

[0077] In this embodiment, the rapid deceleration control value calculation unit 107 calculates a second duty corresponding to the second target rotation speed based on the characteristic information of the motor 120 shown in such a TN curve and TI curve. This is based on the fact that the product variation of the motor 120 is considered to be small, and the characteristic information of the representative motor can be used as the characteristic information of the motor 120 to be controlled. As shown in the figure, the TI curve is almost linear in the used torque region, and can be approximated and expressed as a linear function. Similarly, the second duty can be found by approximating the TN curve as a linear function.

[0078] FIG. 7 is an explanatory diagram showing an example of a first approximate expression table of a linear function based on the characteristic information of motor 120, and FIG. 8 is an explanatory diagram showing an example of a second approximate expression table of a linear function based on the characteristic information of motor 120.

[0079] 7, the generated torque of the motor 120 is approximated by a first approximation formula, which is a linear function of the actual rotation speed (revolutions per minute), and a plurality of first approximation formulas (torque conversion approximation formulas) are included in a first approximation formula table (first table). For example, for a duty of 50%, the generated torque can be expressed by a first approximation formula, which is a linear function obtained by multiplying the rotation speed by a first constant for a duty of 50% and adding a second constant for a duty of 50%.

[0080] 8, the second duty (duty), which is a duty value according to the second target rotation speed, is approximated by a second approximation formula, which is a linear function of the second target rotation speed (revolutions per minute), and a plurality of second approximation formulas (duty conversion approximation formulas) are included in a second approximation formula table (second table). For example, for a torque of 20 mN·m, the duty can be expressed by a second approximation formula, which is a linear function of the rotation speed multiplied by a first constant of the torque of 20 mN·m and the second constant of the torque of 20 mN·m. The first approximation formula table and the second approximation formula table are stored in advance in a non-volatile storage unit such as a ROM in the control device 100, and can be read out from the storage unit for reference.

[0081] Specifically, in response to the determination that the mode is the rapid deceleration mode in step S306, the rapid deceleration control value calculation unit 107 refers to the first approximate expression table and selects a corresponding first approximate expression (torque conversion approximate expression) from the first target rotation speed and the first duty according to the first target rotation speed (step S309). Then, the torque value is calculated from the selected first approximate expression (step S310).

[0082] Next, by referring to the second approximate expression table, a corresponding second approximate expression (duty conversion approximate expression) is selected from the torque value corresponding to each duty value and the second target rotation speed (rotation speed) (step S311). Then, the second duty is calculated from the selected second approximate expression (step S312). The second duty thus obtained is output by the rapid deceleration control value calculation unit 107 during the deceleration period from time T1 to T2 in the rapid deceleration mode (step S313).

[0083] After the motor 120 starts to decelerate, when the actual rotation speed detected by the actual speed detection unit 102 approaches the second target rotation speed, the state control unit 103 cancels the deceleration of the rotation of the motor 120. If it is determined in step S314 that the actual rotation speed data from the actual speed detection unit 102 has approached the second target rotation speed (YES in step S314), the process proceeds to step S315; otherwise, step S314 is repeated.

[0084] In this embodiment, the second duty corresponding to the second target rotation speed is calculated from the characteristic information of the representative motor, and there is no need to specify the motor 120 to be controlled from among the multiple motors attached to the actual machine and calculate the control value. This is based on the idea that the product variation of a single motor is smaller than the product variation of the device main body (image forming device 1). In addition, the first approximation formula corresponding to each duty value and the second approximation formula corresponding to each torque value can be included in each table as a more detailed approximation formula, thereby improving the calculation accuracy. Note that the approximation formula based on the characteristic information of the motor 120 is not limited to the approximation formula of the linear function, and may be an approximation formula of a quadratic function, etc.

[0085] As a result, as shown in FIG. 2, a PWM signal generated from the second duty is input to motor 120 during the deceleration period from time T1 to T2, and when control is switched to PID control at time T3, motor 120 is driven at the second duty corresponding to the second target rotation speed, so that although the rotation speed slightly undershoots, it does not significantly undershoot as shown in FIGS. 10 and 11.

[0086] As described above, in the control device 100 and the control method according to either of the first and second embodiments, the instability (undershoot) of the rotation speed after deceleration in the rapid deceleration mode can be improved, and the tracking performance of the rotation speed of the motor 120 can be improved. Furthermore, since the second duty is automatically calculated by the rapid deceleration control value calculation unit 107 upon determination of the rapid deceleration mode, it is possible to significantly reduce the evaluation man-hours required to check each motor on an actual machine. In addition, since checking on an actual machine is not required, the versatility of the control device 100 for other models and other devices can be improved.

[0087] The present invention is not limited to the above-described embodiment, but can be embodied in various other forms. Therefore, the above-described embodiment is merely illustrative in all respects and should not be interpreted as being restrictive. The scope of the present invention is defined by the claims, and is not limited in any way by the text of the specification. Furthermore, all modifications and changes within the scope of the claims are within the scope of the present invention. [Explanation of symbols]

[0088] 1. Image forming device 30 Image forming section 33 Photoreceptor 36 Intermediate transfer belt unit 51 Intermediate transfer belt 52 Belt drive roller 53 Belt driven roller 54 Secondary transfer roller 100 Control device 101 Interface section (IF section) 102 Actual speed detection unit 103 State control section 104 Brake control unit 105 PID calculation unit 106 PWM signal generation section 107 Rapid deceleration control value calculation unit 110 Top CPU 120 Motor (Control object) 121 Control IC 122 Coil 123 Encoder

Claims

1. A control device that controls the rotation speed of a controlled object by PWM control, A detection means for detecting and outputting an actual rotation speed of the controlled object; a PID calculation means for performing a PID calculation based on the target rotation speed of the controlled object and the actual rotation speed detected by the detection means; a control value calculation means for calculating in advance a control value corresponding to the target rotation speed and outputting the control value; a signal generating means for converting an input from the control value calculating means or the PID calculating means into a control signal for the controlled object and outputting the control signal; a deceleration means for decelerating the rotation of the controlled object; a state control means for controlling the PID calculation means and the deceleration means; a storage means for storing characteristic information indicating a relationship between a rotation speed and a generated torque of the controlled object and a duty value; When an instruction related to a target rotation speed of the controlled object is input, the state control means determines whether or not the instruction is a rapid deceleration instruction for making the target rotation speed a predetermined value or less with respect to the actual rotation speed, When it is determined that the sudden deceleration instruction is given, the state control means causes the deceleration means to start deceleration of the rotation of the controlled object, causes the control value calculation means to output a control value corresponding to the target rotation speed, and causes the signal generation means to generate a duty control signal corresponding to the control value, the control value calculation means calculates, as the control value, a second duty, which is a duty value corresponding to the target rotation speed, in light of the actual rotation speed and a first duty, which is a duty value corresponding to the actual rotation speed, in light of the characteristic information; a state control means for causing the deceleration means to cancel deceleration of the rotation of the controlled object when the actual rotation speed reaches close to the target rotation speed after deceleration of the controlled object has started, the state control means causing the deceleration means to cancel deceleration of the rotation of the controlled object.

2. 2. The control device according to claim 1, The generated torque is approximated by a first approximation equation that is a linear function of the actual rotational speed, a second duty, which is a duty value according to the target rotation speed, is approximated by a second approximation formula, which is a linear function of the target rotation speed; the storage means has a first table including a plurality of the first approximation expressions and a second table including a plurality of the second approximation expressions; The control device according to claim 1, wherein the control value calculation means selects the first approximation formula and the second approximation formula from each of the tables to calculate the control value.

3. A control device according to claim 1 or 2; an image forming means for forming an image on a recording paper, The image forming apparatus according to claim 1, wherein the object to be controlled is a motor used for transporting the recording paper.

4. A control method for controlling a rotation speed of a controlled object by PWM control, comprising: a detection step of detecting and outputting an actual rotation speed of the controlled object; a PID calculation step of performing a PID calculation based on the target rotation speed of the controlled object and the actual rotation speed detected in the detection step; a control value calculation step of calculating and outputting a control value corresponding to the target rotation speed; a signal generating step of converting an output value obtained by the control value calculation step or the PID calculation step into a control signal for the controlled object and outputting the control signal; a deceleration step of decelerating the rotation of the controlled object; a determination step of determining, when an instruction related to a target rotation speed of the controlled object is input, whether or not the instruction is a rapid deceleration instruction in which the target rotation speed is a predetermined value or less with respect to the actual rotation speed; a storage step of storing characteristic information indicating a relationship between a rotation speed and a generated torque of the controlled object and a duty value, When it is determined in the determination step that the rapid deceleration instruction is given, the deceleration step is started and the control value calculation step is started. In the control value calculation step, a second duty, which is a duty value corresponding to the target rotation speed, is output as the control value in light of the actual rotation speed and a first duty, which is a duty value corresponding to the actual rotation speed, in light of the characteristic information; generating the control signal in the signal generating step in response to the control value output in the control value calculating step; A control method comprising the steps of: canceling deceleration of rotation of the controlled object when the actual rotation speed reaches near the target rotation speed after deceleration of the controlled object has started.

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