JP2000236697A - Pulse motor drive method in image input/output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously set the delay and advance of a phase to a prescribed value or less by decreasing acceleration in an acceleration range, where acceleration torque can be used largely, and by increasing the acceleration with respect to a range where acceleration torque can be used largely, within the acceleration range with the small acceleration torque. SOLUTION: The torque characteristics of a motor include the maximum self-activation frequency fs 507 of a pulse motor, a drive target frequency f2 508 of the pulse motor, acceleration torque Ta1 509 where the pulse motor can be used at a self-activation frequency f1, and acceleration torque Ta2 510 where the pulse motor can be used at a drive target frequency f2. Pull-out torque 501 of the general pulse motor is decreased, as a motor drive frequency (f) decreases. As a result, torque that is obtained by subtracting friction torque T1 503 and a torque margin 504 from the pull-out torque 501 becomes torque Ta that can be used for accelerating the pulse motor, so that the acceleration torque also becomes smaller, as the drive speed of the motor increases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a pulse motor in an image input / output device.

[0002]

2. Description of the Related Art A stepping motor is capable of performing high-precision positioning in an open loop, and is preferably used in copying machines and printers. In an ideal system having no inertia of the drive system, a rotation angle of the motor shaft corresponding to the rotation control pulse of the stepping motor can be obtained. However, actually, since the stepping motor itself or the load has a moment of inertia, a phase delay or advance occurs between the rotation operation of the motor shaft and the actual operation of the load at the time of starting or stopping. If this phase difference causes the absolute value of the ideal motor shaft angle from the control pulse and the actual motor shaft angle to exceed τR / 2, which is half the pitch angle (τR) of the rotor tooth of the stepping motor, the stepping motor Becomes unable to follow the control pulse and loses synchronism.

The tooth pitch (.tau.R) of this rotor is .tau.R = 7.2 degrees in the case of a five-phase stepping motor as an example. Further, the phase difference is τ in a five-phase stepping motor.
Even if the stepping motor is driven at R / 2 or less and the step-out occurs, the maximum deviation amount is 3.6 degrees, which is a problem when the stepping motor is started or stopped by faithfully following the input pulse. Conventionally, as a start and stop control used when an inertial load is driven by a stepping motor, (1) a control method of starting up to a target speed with constant acceleration called trapezoidal drive or (2) motor frequency called exponential drive
A control method that starts according to the torque characteristic has been generally used.

[0004]

However, although the above-described control method can drive the stepping motor stably without step-out, it is necessary to start and stop the stepping motor in order to make the load ideally drive according to the input pulse. However, there is a disadvantage that the load also fluctuates in accordance with the deviation of the shaft of the stepping motor when the amount of deviation is less than the maximum deviation amount. The disadvantages are:
There is a case where the blur generated at the time of starting remains after the stepping motor is started up to the target speed. As a result, in a copying machine using a stepping motor, an image blur due to vibration occurs in an initial portion of an image read by an image reading unit, thereby deteriorating the quality of a read image, and an image blur in an initial image writing unit occurs in a printer unit. Has been an obstacle to high image quality.

Accordingly, the present invention provides a new control method in which the phase delay or advance, which occurs between the rotation of the motor shaft and the actual operation of the load when the stepping motor is started or stopped, is always below a predetermined value. provide. This makes it possible to reduce the vibration applied to the load during the start and stop control of the stepping motor as compared with the conventional control method. Image blurring and blurring during image printing are reduced.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an image reading apparatus for scanning an image on a document using a pulse motor, and an image input / output for driving a photosensitive drum using a pulse motor to form an image on the photosensitive drum. In a motor control method for sequentially controlling each of acceleration at start-up, constant speed, and deceleration at stop when driving an inertial drive load using a pulse motor in a device, the self-starting frequency of the pulse motor is set to The frequency range is set higher than its own resonance frequency and lower than the maximum self-starting frequency.

The acceleration and deceleration control after the self-starting frequency
In the acceleration range in which the acceleration torque during acceleration and deceleration of the pulse motor can be used largely, the acceleration is reduced, and in the acceleration range in which the acceleration torque is small, the acceleration is increased with respect to the range in which the acceleration torque can be used largely.

The method of accelerating the motor in the image reading apparatus is performed by a stepping motor of the pulse motor such that a mechanical deviation of a rotor tooth pitch of the pulse motor always becomes equal to or less than a predetermined value with respect to an input pulse to the pulse motor. Determine the pulse speed for each.

First, the self-starting frequency f of the pulse motor is set so that the deviation of the pitch of the rotor teeth always becomes a predetermined value or less.
0 is set to be equal to or less than the resonance frequency fres of the motor itself, and the mechanical deviation of the rotor tooth pitch due to the inertia of the drive system including the motor is set so that the rotor pitch (τr) is at least τr / 2 or less.

Second, the self-starting frequency f0 determined in the first step
Next, the frequency f1 of the pulse input to the pulse motor is determined. For this, the mechanical deviation of the rotor tooth pitch is at least τr / 2 or less compared to the rotor pitch (τr) with respect to the acceleration torque (Ta0) obtained from the pull-out torque of the pulse motor at the self-starting frequency. Assuming that k is a predetermined constant, f1 = √ (k × Ta0) + f
0 is determined.

Third, the frequency f2 of the pulse input to the pulse motor after f1 determined in the second is determined. For this, the acceleration torque (Ta1) obtained from the pull-out torque of the pulse motor at the pulse frequency f1,
The mechanical deviation of the rotor tooth pitch is the rotor pitch (τ
r) so that it is at least τr / 2 or less,
Assuming that k is a predetermined constant, f2 = よ う (k × Ta1) + f1.

Then, the third determination method is repeated until a predetermined pulse speed fn for accelerating the pulse motor. In the relationship up to the predetermined speed fn, f0 is determined by the first determination method, and thereafter, k is a predetermined constant and fn = √ (k × T
a (n-1)) + f (n-1) to determine the motor acceleration method.

Further, the motor deceleration method at the time of deceleration in the image reading apparatus is such that the mechanical deviation of the rotor tooth pitch of the pulse motor with respect to the input pulse to the pulse motor is always less than a predetermined value. The deceleration is performed in the same manner as in the motor acceleration method.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. An embodiment in which the present invention is applied to an image reading unit of a copying machine will be described.

FIGS. 7 and 8 show views of the mechanism of the image reading apparatus. In brief, for example, a transparent platen 20 made of glass for loading a document, an illumination light source 22 for illuminating a document (not shown) loaded on the platen 20, a first mirror 24 for sequentially reflecting light reflected from the document, A lens 30 that transmits light from the second mirror 26 and the third mirror 28, a CCD 32 that receives light from the lens 30 and converts the light into a voltage,
And a CCD driver 34 for driving the CCD 32.

In order to scan the original, the illumination light source 22 and the first mirror 24 are moved at a certain speed, for example, as shown by arrows, and the second mirror and the third mirror are moved at half the speed. Must be moved at speed. Therefore, the rotation is transmitted from the motor 40 to the rotation shaft 44 via the belt 42, and further, the rotation of the rotation shaft 44 is transmitted to the belt 48 applied to the pulley 46, and the first mirror table 50 attached to the belt 48 And the second mirror base 52 are moved. The first mirror base 50 includes the illumination source 22
And the first mirror 24 are mounted, and are moved at a certain speed. The second mirror base 52 has the second mirror 26 and the third mirror 28 mounted thereon, and is moved at half the speed.

FIG. 1 shows a structural diagram of a five-phase pulse motor used in the image reading apparatus. In FIG. 1, FIG. 1A is a diagram showing the relationship between a stator 101 and a rotor 102 of a five-phase pulse motor. As shown, the stator is 10
And two opposing main poles form one phase. FIG. 1B is an enlarged view of a stator and a rotor. Reference numeral 103 denotes a main pole of the stator, which rotates the rotor 104 in an arbitrary direction every time a pulse is input. FIG.
(C) is an enlarged view of the rotor, and the pitch of the rotor teeth 105 is τR106, where τR is represented by an angle with respect to the center of the rotor. In a general five-phase motor, τR = 7.2 degrees. As a structural phenomenon of the pulse motor, when the absolute value of the angle of the tooth of the rotor deviates by τR / 2 (degrees) or more from the ideal position due to external force or self-resonance during rotation according to the input pulse. Step out will occur.

Therefore, the driving of the motor at the resonance frequency is avoided as much as possible, and the displacement of the teeth of the rotor is at least τR / 2.
(Degree) The motor must be controlled so that: In particular, attention must be paid to the self-start frequency at the time of the initial pulse input for starting the inertial load from the state where the motor is stopped, since the pulse frequency becomes low.

First, the setting of the self-starting frequency will be described. The resonance frequency fres of the pulse motor itself can be generally expressed by the following equation, and the slope α (kgcm / s ² ) at the stable point of the angle-torque characteristics of the pulse motor, g = gravitational acceleration 980.7 (cm / fs (pps) = (1 / 2π) √ (α ・ (g / Jr))） (1) as s ² ).

FIG. 2 shows the pulse speed-motor shaft vibration characteristics of the pulse motor, and fres 201 substantially coincides with the value obtained from the above equation (1) at the resonance point of the motor. For example, a general five-phase pulse motor appears around fres = 160 (pps).

Next, the displacement of the tooth of the rotor of the pulse motor will be considered from the driving frequency and the inertia load to be driven. The acceleration torque required to drive an inertial body having a moment of inertia J (kgcm ² ) is Ta (kgcm)
Is the acceleration torque, ω (rad / s) angular velocity, g (cm / s)
² ) is the gravitational acceleration and can be expressed by the following equation. Ta = (J / g) · (ω / t) (2)

The pulse speed of the pulse motor is f (pp
s) and θs are the step angles of the pulse motor, the angular velocity ω can be expressed by the following equation. ω = f · θs · (π / 180) · · · (3)

When the maximum allowable displacement of the rotor is β, t
Is approximated by the following equation. t = (1 / (f · θ)) · β (4) From the above formulas (3) and (4), formula (2) is expressed as Ta = (J / g) · ((θs ² · π) / 180) · β · f ² (5), and the acceleration torque required to drive the inertial body is
It becomes a quadratic curve with respect to the frequency.

FIG. 3 is a characteristic diagram of the self-starting frequency of the pulse motor. 301 is a pull-out torque Tpout, 30
2 is the acceleration torque Ta obtained from the above equation 5, and 303 is the pull-in torque Tpin. Tpin is a value obtained by subtracting the acceleration torque Ta from the pull-out torque Tpout, and can be expressed by Tpin = Tpout−Ta (6).

Then, fs (30) where Tpin = 0 is satisfied.
4) is the maximum self-starting frequency, and the motor needs to start the inertial body at a frequency below this fs. The pull-in torque Tpin is set to a value that is at least equal to or greater than 0 and equal to or less than (τR / 2) by changing the maximum allowable deviation of Expression 5 with the value of β.

From the above, if the self-starting frequency f0 is set to be equal to or higher than the resonance frequency fres and equal to or lower than the maximum self-starting frequency Tpin, the motor can be self-started with a desired rotor tooth gap.

Next, a description will be given of a method for controlling the acceleration of the motor with a desired rotor tooth shift after self-starting. First, the frequency f1 of the pulse input to the pulse motor after the self-starting frequency f0 is determined. In this case, since the pulse motor is rotating by performing a stepwise operation in a stepwise manner, it is considered that the process shifts from the self-starting frequency to the next step with a desired rotor tooth shift. One step before this is calculated from the acceleration torque that can be used by the pulse motor. The pull-in torque of the pulse motor at the rotor self-starting frequency is converted to Ta0, and Equation 5 is converted for the pulse frequency f (pps), and f1 = √ ((180 · g · Ta0 · β) / (π · J · θs ² ) ) + F0... (7).

The frequency f2 of the pulse input to the pulse motor next to f1 is f2 = √ ((180 · g · Ta1 · β) / (where Ta1 is the acceleration torque that can be used by the pulse motor at f1). π · J · θs ² )) + f1 (8).

By continuing this calculation n times up to the target frequency, acceleration and deceleration control that can start and stop the motor when the rotor displacement is less than the desired β up to the target frequency can be performed. Therefore, as the self-starting frequency f0, fres ≦ f0
By determining the value of ≤fs, setting the pull-in torque of the motor at the self-starting frequency f0 to Ta0, and creating an acceleration table based on the following equation 9, the inertial load can be driven stably. fn = √ ((180 · g · Ta (n−1) · β) / 8 (π · J · θs ² )) + f (n−1) (9)

FIG. 4 is an acceleration and deceleration control diagram created by the above equation (9). 405 is a self-starting frequency f1, 406 is a target frequency f2, t1 in the figure is acceleration and deceleration time, t0
Is the driving time of the pulse motor. Reference numerals 401 and 403 denote acceleration and deceleration curves during conventional trapezoidal driving. If the acceleration / deceleration method of Expression 9 is used, the acceleration / deceleration curves of 407 and 408 in FIG. 4 are obtained.

FIG. 5 shows the torque characteristics of the motor.
501 is a pulse motor pull-out torque, 502 is a pull-in torque, 503 is a driving load friction torque, 504
Is the torque margin for safely driving the motor, 50
5 is the resonance frequency fres of the motor, 506 is the self-start frequency f1 of the pulse motor, 507 is the maximum self-start frequency fs of the pulse motor, 508 is the drive target frequency f2 of the pulse motor, and 509 is the pulse motor with the self-start frequency f1. Usable acceleration torques Ta1, 510 are acceleration torques Ta2 usable by the pulse motor at the drive target frequency f2.

As shown in FIG. 5, there is a characteristic that the pull-out torque of a general pulse motor decreases as the motor driving frequency f (pps) increases. Therefore, the torque obtained by subtracting the friction torque T1 (503) and the torque margin 504 from the pullout torque becomes the torque Ta that can be used for accelerating the pulse motor, and the acceleration torque decreases as the driving speed of the motor increases. For this purpose, the acceleration table of the present invention is expressed by the above-mentioned equation 9 as 4 in FIG.
It looks like an acceleration table of 07 and 408.

FIG. 6 is a diagram showing the amount of vibration of the load and the speed displacement of the motor shaft when the inertial load is actually driven using a five-phase stepping motor. FIG. 6A shows a state during a conventional trapezoidal drive, and FIG. 6B shows a state during a drive according to the present invention. FIG.
In the case of the trapezoidal drive shown in (a), the displacement of the motor shaft is large and the vibration at the time of acceleration remains even after the end of acceleration. Further, it can be seen that the vibration of the driving load is considerably large. On the other hand, in FIG. 6B, which is the driving of the present invention, the displacement of the motor shaft is within a predetermined range during acceleration of the motor, and there is almost no displacement of the motor shaft after the end of acceleration. The vibration of the driving load is also significantly reduced as compared with the trapezoidal driving.

[0034]

As described above, by using the acceleration and deceleration control of the pulse motor according to the present invention, the vibration at the time of starting and stopping the inertial load can be greatly reduced. Conventionally, the vibration at the time of starting and stopping is reduced. The operation that has been performed since
This can be performed immediately after the end of acceleration and deceleration, and the sequence can be speeded up.

Further, according to the present invention, by changing the pulse output method of the motor at the time of acceleration and deceleration, it becomes possible to drive the inertial load optimally.
The desired effect can be obtained without any.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a five-phase pulse motor used in an image reading device.

FIG. 2 is a diagram showing a pulse speed-motor shaft vibration characteristic of a pulse motor.

FIG. 3 is a characteristic diagram of a self-starting frequency of a pulse motor.

FIG. 4 is an acceleration and deceleration control diagram created by Expression 9.

FIG. 5 is a diagram showing torque characteristics of a motor.

FIG. 6 is a diagram illustrating a vibration amount of a load and a speed displacement of a motor shaft when an inertial load is actually driven using a five-phase stepping motor.

FIG. 7 is a diagram of a mechanism portion of the image reading apparatus.

FIG. 8 is a view of a mechanism portion of the image reading apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Stator 102 Rotor 103 Stator 104 Rotor 105 Rotor tooth 106 Rotor tooth pitch 20 Transparent platen 22 Illumination light source 24 First mirror 26 Second mirror 28 Third mirror 30 Lens 32 CCD 34 CCD driver

Claims (3)

[Claims] An inertial driving load is applied to an image reading apparatus that scans an image of a document using a pulse motor or an image input / output apparatus that drives a photosensitive drum using a pulse motor to form an image on the photosensitive drum. In a pulse motor control method that sequentially performs each control of acceleration, constant speed, and deceleration at stop when driving using a motor, the self-starting frequency of the pulse motor is higher than the resonance frequency of the pulse motor itself and the maximum. Acceleration and deceleration control after the self-starting frequency is set in the frequency range below the self-starting frequency. According to the pulse mode of the image input / output device, the acceleration is increased with respect to a range in which the acceleration torque is large. Control method. 2. The pulse motor control method according to claim 1, wherein in the motor acceleration method during acceleration, a mechanical deviation of a rotor tooth pitch of the pulse motor with respect to an input palace to the pulse motor is always less than a predetermined value. First, the pulse motor's self-starting frequency f0 is set to the resonance frequency of the motor itself so that the deviation of the pitch of the rotor teeth is always equal to or less than a predetermined value. Fres or less, and the mechanical deviation of the rotor tooth pitch due to the inertia of the drive system including the motor is set so that the rotor pitch (τr) is at least τr / 2 or less. The frequency f1 of the pulse input to the pulse motor after the self-starting frequency f0 is determined, which is determined from the pull-out torque of the pulse motor at the self-starting frequency. F = √ (k ×) where k is a predetermined constant so that the mechanical deviation of the rotor tooth pitch is at least Tr / 2 or less compared to the rotor pitch (τr) with respect to the acceleration torque (Ta0) to be applied. Ta0) + f0
Third, the frequency f2 of the pulse input to the pulse motor after f1 determined in the second is determined, and this includes pull-out of the pulse motor at the pulse frequency f1. With k as a predetermined constant, f2 = √ so that the mechanical deviation of the rotor tooth pitch is at least Tr / 2 or less compared to the rotor pitch (τr) with respect to the acceleration torque (Ta1) obtained from the torque. (K × Ta1) + f1 and a predetermined pulse speed fn for accelerating the pulse motor
The third determination method is repeated until the predetermined speed fn is reached. F0 is determined by the first determination method, and thereafter, k is a predetermined constant and fn = (k × √Ta (n−
1)) A pulse motor control method characterized in that a method of accelerating a motor is determined based on a relationship of + f (n-1). 3. The pulse motor control method according to claim 2, wherein in the motor deceleration method at the time of deceleration, a mechanical deviation of a rotor tooth of the pulse motor with respect to an input pulse to the pulse motor always becomes a predetermined value or less. A pulse motor control method characterized in that deceleration is performed in the same manner as the motor acceleration method determined as described above.