JP3034280B2 - Driving method and driving device for stepping motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a driving method and a driving device for a stepping motor.

(Prior Art) As is well known, a stepping motor is driven by open loop control using digital signals. In a stepping motor, sufficient positioning accuracy can be obtained even with open loop control. For this reason, stepping motors are used in many fields including the field of OA equipment.

A typical stepping motor includes a rotatable rotor and a stator core disposed outside the rotor. A plurality of small teeth are provided at an equal pitch on the outer peripheral surface of the rotor. A number of stator salient poles corresponding to the number of phases are provided on the inner surface of the stator core. A plurality of small teeth are provided at the tip of these stator salient poles at an equal pitch. Excitation windings are respectively mounted on the outer periphery of each stator salient pole. The excitation windings are sequentially switched and excited in the order determined by the driving device. When the excitation is performed, an electromagnetic attractive force or a repulsive force acts between the small teeth on the stator side and the small teeth on the rotor side, and as a result, the step operation of the rotor is started.

By the way, when the stepping motor is rotated at a low speed, the step operation is emphasized, so that the rotation speed of the rotor fluctuates. The cycle of fluctuation of the rotation speed coincides with the cycle of the excitation switching frequency. On the other hand, when the motor is rotated at a high speed, the step operation is not emphasized due to a decrease in frequency response characteristics. However, the rotation speed of the rotor fluctuates due to variations in the output torque between the excitation phases. That is, it is difficult to make the conditions of each excitation phase equal at the stage of manufacturing the stepping motor. The rotation speed of the rotor fluctuates due to the irregularity. For example, when the hybrid 5-phase stepping motor is sequentially switched and excited at 1500 Hz (this is called a pulse rate of 1500 pps), the peak level of the speed fluctuation power spectrum appears at the position of 150 Hz. This frequency corresponds to 1/10 of the excitation switching frequency. Such a speed variation is caused by a variation in output torque between the respective excitation phases.

As described above, in the stepping motor, the speed changes at every step in the low-speed rotation region, and the speed changes in a cycle corresponding to several steps in the high-speed rotation region. Such a speed fluctuation is a major drawback of the stepping motor. In particular, when used as a drive source for precision equipment, the required performance is often not satisfied due to the above-described speed fluctuation. In addition, when incorporated in an actual system, if the load has a mass imbalance, the speed fluctuation caused by the imbalance is superimposed.

Therefore, in order to reduce the above-mentioned speed fluctuation, a method of mounting a dynamic damper on a rotor shaft or a load shaft, inserting a damping material in the middle of a torque transmission mechanism, or mounting a large flywheel is adopted. Have been. If the speed fluctuation cannot be reduced by such mechanical means, the pitch of the small teeth on the rotor side and the stator side is narrowed to reduce the amount of movement in one step, or to reduce the number of excitation phases. Attempts have been made to change the structure of the stepping motor itself, for example, to increase it. further,
Attempts have also been made to reduce the speed fluctuations by a so-called micro-step drive system in which the applied current (applied voltage) to the different excitation phases is increased or decreased stepwise to shift the rotor stop point stepwise. I have.

However, the method of reducing the speed fluctuation by providing a mechanical element not only increases the overall size but also cannot expect a large speed fluctuation reducing effect. Even if the micro-step driving method is adopted, if there is a variation in torque characteristics between different excitation phases, a large speed fluctuation reduction effect cannot be obtained.

(Problems to be Solved by the Invention) As described above, in the conventional driving method and the conventional driving device, there is a problem that a large speed fluctuation reduction effect cannot be obtained when torque characteristics vary between different excitation phases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a driving method and a driving device for a stepping motor which can make the speed fluctuation of the rotor extremely small by a simple electric method.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, according to an embodiment of the present invention, a drive device according to an embodiment of the present invention energizes a plurality of excitation windings provided in a stepping motor. A pulse generating means for generating a pulse train used as a timing pulse for sequentially switching the pulse train, a means for introducing the pulse train generated by the pulse generating means to excite a plurality of excitation windings in a predetermined order, and a stepping motor. Means for adjusting the current flowing through the plurality of excitation windings in order to reduce the periodic speed fluctuation provided by the stepping motor under the condition that the current flowing through the plurality of excitation windings is adjusted by the adjustment means Storage means for previously storing periodic speed fluctuation data, which is still provided, and reads the speed fluctuation data stored in the storage means, And means for varying the pulse rate of the timing pulses generated by said pulse generating means in correspondence with variation data.

(Operation) According to the present invention, the inherent speed fluctuation of the stepping motor is reduced by adjusting the current flowing through each excitation winding. The speed fluctuation of the stepping motor, which cannot be eliminated by adjusting the exciting current, is canceled by the speed fluctuation caused by the fluctuation of the pulse rate of the timing pulse. Therefore, the rotor can be smoothly rotated.

(Embodiment) FIG. 1 shows a block diagram of a driving apparatus to which the present invention is applied.

Reference numeral 1 indicates a stepping motor having a five-phase structure. This stepping motor 1 is driven by a driving device 2.

The stepping motor 1 includes a rotor 10 and a stator 20. The rotor 10 is connected to a rotating load (not shown) that is mass-balanced.

As shown in FIG. 2, the rotor 10 has a shaft 11 made of a non-magnetic material, a permanent magnet 12 mounted on the outer periphery of the shaft 11 and magnetized in the axial direction, and a permanent magnet. 12 are formed of magnetic material tooth cutting cups 13a, 13b mounted in caps from both ends. Gear cutting cup 13a, 1
In this example, 50 small teeth 14 are formed at equal pitches in the circumferential direction in 3b in this example. Note that the small teeth 14 on the gear cutting cup 13a side and the small teeth 14 on the gear cutting cup 13b side are
They are provided with a phase difference of pitch.

As shown in FIG. 3, the stator 20 includes a stator core 21 disposed so as to surround the rotor 10, and ten stators projecting from the inner surface of the stator core 21. Salient poles 22, small teeth 23 provided at an equal pitch at the tip of the stator salient poles 22, and exciting windings 24A, 24 wound around the respective stator salient poles 22.
B, 24C, 24D, and 24E. Each exciting winding is divided into two and the stator salient poles facing each other
It is attached to 22. This results in five excitation phases A,
Stepping motor 1 with five-phase structure having B, C, D, and E
Is configured.

As shown in FIG. 1, the driving device 2 includes a switching circuit 30, a distribution circuit 40, a storage device 50, and a computing device 60.
, Speed setting device 75, amplitude setting device 80, phase setting device 85
And a DC power supply 90.

As shown in FIG. 4, the switching circuit 30 includes a bridge circuit 35A composed of power transistors 31a, 31b, 32a, and 32b in order to independently supply a positive or negative current to each of the excitation windings 24A to 24E. ~ 35E. Each bridge circuit 35
One input terminal of A to 35E is a power transistor
It is connected to one output line 33 of the DC power supply 90 via 36A to 36E. The other input terminals of the bridge circuits 35A to 35E are connected to the other output line 34 of the DC power supply 90 via shunt resistors 37A to 37E, respectively.

Current I _A ~I _E flowing through each exciting winding 24A~24E is converted into respective voltage V _CA ~V _CE by the corresponding shunt resistors 37A to 37E. The voltages V _{CA to} V _CE are determined by the corresponding comparator 38A.
3838E is introduced to one input terminal. Reference voltage V _{RA to} V _RE
Is introduced to the other input terminal of each of the comparators 38A to 38E. The difference voltages V _{EA to} V _EE are output from the respective comparators 38A to 38E. These difference voltages V _{EA to} V _EE correspond to the corresponding pulse width control circuits 39A to 39E.
Will be introduced. Each of the pulse width control circuits 39A to 39E outputs a signal corresponding to the input difference voltage. The corresponding power transistors 36A to 36E are turned on and off by the output signals of the pulse width control circuits 39A to 39E. In this example, the value of the reference voltage V _RA ~V _RE a variable resistor 42A~42E is finely adjusted. That is, the current flowing through each of the excitation windings 24A to 24E
I _{A to} I _E are held at values determined by the reference voltages V _{RA to} V _RE . By this current adjustment, variations in output torque caused by variations in winding resistance of each excitation winding and the like are corrected.

The distribution circuit 40 is configured similarly to a known circuit.
That is, the distribution circuit 40 responds to the timing pulse P given from the arithmetic unit 60 described later, and
The power transistors 31a, 31b and 32a, 32b incorporated in A to 35E are turned on and off. That is, the distribution circuit 4
0 indicates a typical operation sequence in FIG. 5,
In order to sequentially switch the excitation currents I _A , I _B , I _C , I _D , I _E in the order determined by the excitation windings 24A, 24B, 24C, 24D, 24E of each phase,
A base signal for controlling on / off of the power transistors 31a, 31b and 32a, 32b is output. In this example, 10 steps are repeated.

The storage device 50 stores a program for operating an arithmetic unit 60 to be described later, and a stepping motor 1 to be driven.
And the pulse rate data of the timing pulse P necessary for reducing the inherent speed fluctuation of.

In using the driving device 2, the following operation is adopted. That is, after the stepping motor 1 is manufactured, the range up to the maximum use speed is divided into a plurality of stages, and the speed fluctuation in a 10-step range in each stage is examined. Then, at each stage, the values of the reference voltages V _{RA to} V _{RE that} can minimize the speed fluctuation, in other words, the optimum current values of the excitation windings 24A to 24E are obtained. Normally, the speed fluctuation cannot be sufficiently reduced only by adjusting the exciting current. Thus, the optimal timing pulse P frequency, that is, pulse rate data that can sufficiently reduce the speed fluctuations at each stage in a state where the exciting windings 24A to 24E are excited with the obtained optimum current value, is obtained. Is stored in the storage device 50 in advance.

The arithmetic unit 60 reads the pulse rate data corresponding to the speed specified by the speed setting unit 75 from the storage device 50, and based on the read pulse rate data, the distribution circuit 40
The time interval (step interval) of the timing pulse P to be supplied to is controlled.

FIG. 6 shows a specific configuration of the storage device 50 and the arithmetic device 60. The storage device 50 includes a read-only memory (ROM) 51 storing a program for operating the arithmetic device 60, and a random access memory (RAM) 52 for storing pulse rate data.

On the other hand, the arithmetic unit 60 includes a central processing unit (CPU) 61, a counter / timer (CTC) 62, two peripheral interfaces (PIO) 63 and 64, and a reference clock generation circuit (CL
K) 65. In FIG. 6, thick arrow lines indicate data lines, solid arrow lines indicate address lines, and broken arrow lines indicate control lines.

The PIO 63 is used for controlling the CTC 62. Also, PIO64
It is used to take in the outputs of the speed setting device 75, the amplitude setting device 80, and the phase setting device 85. In addition, speed setting device 75, amplitude setting device
As shown in FIG. 7, the phase setting device 85 comprises 8-bit switches 76, 77 and 78, respectively.

The CPU 61 operates according to a program stored in the ROM 51. When the speed is specified by the speed setting device 75, the CPU 61 outputs the pulse rate data corresponding to the specified speed to R.
Call from AM52. The read pulse rate data is used to determine the time interval of the timing pulse P.
It consists of 10 time data. The CPU 61 first reads the first time data, and reads this time data in CTC6.
Set to 2. The CTC 62 starts counting the reference clock pulses generated by the CLK 65 from the time when the first time data is set. Then, the CTC 62 supplies one timing pulse P to the distribution circuit 40 at the time when the number of clock pulses determined by the first time data is counted.
At the same time, CTC 62 provides an interrupt signal (INT) to CPU 61. The CPU 61 sets R when the interrupt signal is accessed.
The second time data is read from AM 52, and the second time data is set in CTC 62. Hereinafter, similar operations are sequentially performed. Accordingly, the arithmetic unit 60 outputs a timing pulse train in which one cycle is formed by ten timing pulses P and the pulse rate fluctuates as determined within this one cycle. This timing pulse train is supplied to the distribution circuit 40.

In order to drive and control the stepping motor 1 using the driving device 2, the pulse rate data must be stored in the RAM 52 before the actual operation. The storage of the pulse rate data in the RAM 52 is performed as follows.

Assuming that the pulse rate of the timing pulse is fluctuated in a pseudo sine wave form, the basic equation of the pulse rate Pr at that time is as shown in equation (1).

Here, Pr: pulse rate (pps) Pc: center pulse rate (pps) αi: fluctuation amplitude φi: fluctuation phase (0 ≦ φi ≦ 180) fi: target frequency n: number of target frequencies

In this embodiment, equation (1) is used. For example,
Take an example where n = 1 and fi = Pc / 10. First, when the driving speed is set by the speed setting device 75, the CPU 61 determines the center pulse rate Pc from the data. Next, to determine the target frequency f ₁ from the Pc. Next, the amplitude setting device 80 and the phase setting device
Determine α ₁ and φ ₁ from the data input via 85. Next, the CUP 61 calculates a pulse rate for one cycle of the target frequency f ₁ based on the equation (1), and temporarily stores time data for one cycle, which is the reciprocal thereof, as pulse rate data in the RAM 52.

The pulse rate data once stored in the RAM 52 is corrected to final pulse rate data as follows. That is, with the rotation detector attached to the rotating shaft 11 of the stepping motor 1, the driving device 2 is operated to rotate the stepping motor 1 for test rotation. The control at this time is RA
This is performed using the pulse rate data once stored in the M52. Then, the data of the amplitude setting device 80 and the phase setting device 85 are sequentially changed so that the speed fluctuation is minimized, and the pulse rate data having the minimum speed fluctuation is stored in the RAM 52 as final data. This final data is used during actual operation. That is, in this embodiment, the periodic speed fluctuation data of the stepping motor 1 is stored in the RAM 52.

With such a configuration, when a speed which is the speed setting device 75 is designated, pulse rate data corresponding to the designated speed is called from the RAM 52, and the time interval changes based on the pulse rate data. The timing pulse P is output from the arithmetic unit 60. The pulse rate of the timing pulse P fluctuates in a cycle, an amplitude, and a phase in which the speed fluctuation of the stepping motor 1 at the speed can be canceled. That is, the fluctuation phase of the pulse rate is opposite to the speed fluctuation. This timing pulse P is given to the distribution circuit 40. The distribution circuit 40 includes power transistors 31a and 31b of the switching circuit 30 and
As shown in FIG. 5, a base signal for turning on and off 32a and 32b in a predetermined sequence is output. Therefore, the rotor 10 of the stepping motor 1 starts smooth rotation at the designated speed. In this case, first, a current having a value that can reduce the speed fluctuation to a certain value is supplied to each of the excitation windings 24A to 2A.
4E, and the pulse rate of the timing pulse P is changed in the above-mentioned relationship in this state, so that the rotor 10 can be rotated sufficiently smoothly.

FIG. 8 (a) shows the time interval of the timing pulse P output from the arithmetic unit 60 when the stepping motor 1 is driven to rotate at a constant speed by the driving device 2 shown in FIG. I have. In synchronization with the timing pulse P, the excitation windings 24A to 24E are switched and excited as shown in FIG. In this example, the time interval of the excitation switching timing is
It fluctuates between Δt min and Δt max on the basis of Δt. The reciprocal of this time interval is the pulse rate, which fluctuates in a sinusoidal manner with a period T as shown in FIG. 8 (b).

If there is no inherent speed fluctuation in the stepping motor 1, the arithmetic unit 60 outputs the timing pulses P at the time intervals shown in FIG. 8A to drive the stepping motor 1. Rotates with the speed fluctuating in a cycle T shown in FIG. 8 (b). However, an ordinary stepping motor always has an inherent speed fluctuation. Accordingly, the pulse rate of the timing pulse P output from the arithmetic unit 60 is made to coincide with the speed fluctuation period unique to the stepping motor, and is changed almost in phase with a predetermined amplitude, thereby changing the speed fluctuation unique to the stepping motor. And the rotor 10 can be smoothly rotated.

FIG. 9 shows an example in which the speed fluctuation of the hybrid type five-phase stepping motor is reduced by using the driving device 2 shown in FIG. This sets the center pulse rate Pc to 15
This is a result when the target frequency fi is set to 150 Hz and the target frequency fi is set to 150 Hz. FIG. 10 shows the power spectrum at that time. 9 and 10 show the data obtained when the same stepping motor is driven by the conventional driving device by broken lines. As can be seen from these figures, the use of the driving device 2 shown in FIG. 1 makes it possible to sufficiently reduce speed fluctuations.

FIG. 11 shows a driving device 2b to which the present invention is applied to drive a two-phase stepping motor 1a. In FIG. 11, the same parts as those in FIG. 1 are indicated by the same reference numerals.

The above-described embodiment is directed to a stepping motor capable of changing the time interval of the excitation switching timing relatively smoothly. However, in a two-phase stepping motor, the output torque may fluctuate every four steps due to a variation in the excitation phase. In such a case, it is not possible to smoothly change the time interval of the excitation switching timing in a sinusoidal manner.

In such a case, it is preferable to use the micro-step driving method together. In the micro step drive method, usually,
The voltage applied to the different exciting windings that are simultaneously excited is increased or decreased stepwise, thereby finely changing the rotor stop position stepwise.

The driving device 2b shown in FIG. 11 uses a micro step driving method.

The stepping motor 1a includes a rotor 10a and a stator 20a. The rotor 10a and the stator 20a have substantially the same configuration as the five-phase stepping motor. However, 2
Only one excitation winding 24X, 24Y is provided.

The driving device 2b includes a switching circuit 30b and a distribution circuit 40a.
, Storage device 50, arithmetic device 60a, speed setting device 75,
It comprises an amplitude setting device 80, a phase setting device 85, and a DC power supply 90.

The switching circuit 30b, as shown in FIG.
Basically, the configuration is the same as that shown in FIG. That is, also in this example, the comparators 38X and 38Y
In addition, a chopping drive four system that controls on / off of the power transistors 36X and 36Y by using the pulse width control circuits 39X and 39Y is adopted. However, in this example, the reference voltages V _RX and V _RY are supplied from the arithmetic unit 60a described later via the terminals 43X.43Y, respectively.

The distribution circuit 40a outputs a base signal for controlling ON / OFF of the power transistors 31a, 31b and 32a, 32b constituting the bridge circuits 35X, 35Y. These base signals make the phases of the currents flowing through the excitation windings 24X and 24Y differ by 90 degrees, and the timing pulse P
Each time the current is input, it is output in such a manner that the direction of the current flowing through the excitation windings 24X and 24Y is switched.

As shown in FIG. 13, the arithmetic unit 60a reads pulse rate data corresponding to the speed specified by the speed setting device 75 from the storage device 50, and distributes the pulse rate data based on the read pulse rate data. The time interval (step interval) of the timing pulse P supplied to the circuit 40a is controlled. However, in this embodiment, the digital signals D _X and D _Y having a phase difference of 90 degrees between the digital signals D _X and D _Y while increasing and decreasing in a stepwise manner in synchronization with the timing pulse P, respectively, are respectively determined. Output from This digital signal D
_X and _DY are obtained by the CPU 61 based on the data obtained during the test operation and stored in the storage device 50. Then, the digital signal D _X is converted into an analog signal by a D / A converter 66a, the analog signal is supplied to the comparator 38X as a reference voltage V _RX. Similarly, the digital signal D _Y
Is converted into an analog signal by the D / A converter 66b, and this analog signal is provided to the comparator _38Y as the reference signal VRY.

FIG. 14 shows the currents I _X and I _Y flowing through the excitation windings 24X and 24Y when the stepping motor 1a is driven by the driving device 2b according to this embodiment, and the timing pulse P output from the arithmetic unit 60a. It is shown. The figure also shows a change in the pulse rate at this time.

In this embodiment, microstep driving is realized by increasing and decreasing the reference voltages V _RX and V _RY in synchronization with the timing pulse P. In addition, the current flowing through each of the excitation windings 24X and 24Y is adjusted by adjusting the amount of change in each of the reference voltages V _RX and V _RY , thereby correcting the output torque fluctuation due to the irregular winding resistance. In addition to these, the pulse rate of the timing pulse P is changed in an 8-step cycle and in a phase opposite to the periodic speed fluctuation of the stepping motor 1a, thereby canceling the above-mentioned speed fluctuation. Therefore, even in the case of a two-phase stepping motor, the speed fluctuation can be sufficiently reduced.

FIG. 15 shows a driving device 2c to which the present invention is applied to drive the five-phase stepping motor 1.
In FIG. 15, the same parts as those in FIG. 1 are indicated by the same reference numerals.

In the driving device 2c, the five-phase stepping motor 1 is driven by the same method as the driving method employed by the driving device 2b shown in FIG.

The driving device 2c includes a switching circuit 30c and a distribution circuit 40b.
, Storage device 50, arithmetic device 60b, speed setting device 75,
It comprises an amplitude setting device 80, a phase setting device 85, and a DC power supply 90.

The switching circuit 30c, as shown in FIG.
Basically, it has the same configuration as the switching circuit shown in FIG. That is, also in this example, a chopping drive system in which the comparators 38A to 38E and the pulse width control circuits 39A to 39E are used to turn on and off the power transistors 36A to 36E is employed. In addition, each comparator 38
The reference voltages V _{RA to} V _RE of A to 38E are supplied from an arithmetic unit 60b to be described later via terminals 43A to 43E, respectively.

From the distribution circuit 40b, the power transistors 31a, 31b and 32a, 32b constituting each of the bridge circuits 35A to 35E are turned on,
A base signal for turning off is output. These base signals are applied to each excitation winding 24A as shown in FIG.
24E are output in such a manner that a phase difference corresponding to four timing pulses P output from the arithmetic unit 60b is formed in the current flowing through .about.24E.

As shown in FIG. 17, the arithmetic unit 60b is basically configured in the same manner as that shown in FIG. That is, the arithmetic unit 60b reads the pulse rate data corresponding to the speed specified by the speed setting device 75 from the storage device 50, and based on the read pulse rate data, outputs the timing pulse P to be supplied to the distribution circuit 40b. Control the time interval (step interval). However, in this embodiment, another PIO 67 is provided. Then, the output digital signal D _A to D _E to increase and decrease the stepwise by a change amount that is set in advance, respectively in synchronism from PIO63 and PIO67 the timing pulse P. These digital signals D _A to D _E is obtained during the test operation, a storage device
It is formed by the CPU 61 based on the data stored in 50. Each digital signal D _A to D _E is D / A converter 66a
It is converted to an analog signal at ~ 66e. These analog signals are provided to comparators 38A to 38E as reference voltages V _{RA to} V _RE .

FIG. 18 shows the excitation windings 24A to 24E when the stepping motor 1 is driven by the driving device 2c according to this embodiment.
Timing pulse P which is output from the current I _A ~I _E and arithmetic unit 60b flows in is shown. Also, in the figure,
The change of the pulse rate at this time is also shown.

Also in this embodiment, the micro-step driving is realized by using the reference voltages V _{RA to} V _RE which increase and decrease in synchronization with the timing pulse P. Further, the current flowing through each of the excitation windings 24A to 24E is adjusted by adjusting the amount of change of each of the reference voltages V _{RA to} V _RE , thereby correcting the fluctuation of the output torque due to the irregular winding resistance. In addition to these, the pulse rate of the timing pulse P is changed in a cycle of eight pulses and in a phase opposite to the speed fluctuation of the stepping motor 1, thereby canceling the above-mentioned speed fluctuation.

FIG. 19 shows a mechatronics applied device in which a stepping motor drive device according to the present invention is actually incorporated, here a laser page printer.

First, the printing process of the laser page printer will be briefly described with reference to FIG.

In the figure, reference numeral 101 denotes a photosensitive drum. On the surface portion of the photosensitive drum 101, a photoconductor layer such as an organic photoconductor whose specific resistance changes when irradiated with light is formed. The photosensitive drum 101 is driven to rotate at a constant speed. In this state, the surface of the photosensitive drum 101 is uniformly charged by the charger 102. A laser beam deflected by the polygon mirror 103 is irradiated onto the charged surface of the photosensitive drum 101 while blinking according to image information. The specific resistance of the portion of the surface of the photosensitive drum 101 irradiated with the laser light is reduced, and the charges charged on that portion are eliminated through the ground line connected to the photosensitive drum 101. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 101.

Toner on the surface of the photosensitive drum 101 on which the electrostatic latent image has been formed is supplied with toner having the same polarity as the charged charge by the developing device 104. As a result, the toner adheres to the electrostatic latent image portion to form a toner image. On the other hand, a sheet (not shown) stored in the sheet cassette 105 is taken out, and the sheet is conveyed by rollers 106 and sent to a lower portion of the photosensitive drum 101. At the same time, the transfer charger 107 is driven to transfer the toner image to the sheet. The sheet is further conveyed and sent to a fixing device 108 including a heat roller. As a result, the toner adhering to the paper is melted and pressed, and the image is fixed.
The sheet on which fixing has been completed is discharged to the sheet stacker 109.
Further, the surface of the photosensitive drum 101 after the transfer is finished is a cleaner 110.
Cleaning. This cleaning removes the remaining toner, and enters a standby state for the next image forming process.

In a laser page printer that undergoes such a printing process, if the rotation speed of the photosensitive drum 101 fluctuates, a formed image is disturbed. Therefore, in order to improve the image quality, it is necessary to minimize fluctuations in the rotation speed of the photosensitive drum 101.

Therefore, in this embodiment, the photosensitive drum 10 is
Drive 1 is performed. That is, as shown in FIG. 20, the rotation output of the
12, a timing belt 113, and a large-diameter pulley 114 are transmitted to the shaft 115 of the photosensitive drum 101.

The stepping motor 111 is driven by the driving device 2d.
The driving device 2d has the same configuration as that shown in FIG. That is, in the driving device 2d, the pulse rate of the timing pulse for determining the excitation switching timing of the stepping motor 111 is made to coincide with the inherent speed fluctuation period of the system including the stepping motor 111 and the photosensitive drum 101 driven by the stepping motor 111. , And in a relationship of substantially opposite phases. Then, the fluctuation amplitude of the pulse rate is also set optimally. Therefore, the storage device 50 (see FIG. 1) built in the driving device 2d has pulse rate data capable of canceling the inherent speed fluctuation of the system including the stepping motor 111 and the photosensitive drum 101 driven by the stepping motor 111. Is stored. Further, in the case of this embodiment, in order to cope with the change of the inherent speed fluctuation caused by the exchange of the photosensitive drum 101, the speed fluctuation of the photosensitive drum 101 measured with the pulse rate of the timing pulse constant at the place of use is measured. The data is recorded on the card 116, and the data in the storage device 50 can be rewritten using the card 116. In FIG. 20, 117 indicates a semiconductor laser device that converts image information into a blinking signal of light, 118 indicates a reflection mirror, and S indicates a drive start and stop signal given to the drive device 2d. .

With such a configuration, the inherent rotation fluctuation of the photosensitive drum vibration system can be canceled by the rotation fluctuation caused by the fluctuation of the pulse rate of the timing pulse, so that the photosensitive drum 101 can be rotated at a substantially constant speed. . Therefore, an extremely good image can be formed.
In particular, when the image to be formed is a pictorial image including a halftone, a slight rotation fluctuation of the photosensitive drum 101 causes unevenness in the halftone image portion, but such a problem can be surely solved. .

In the above example, the driving device according to the present invention is incorporated in a laser page printer. However, similar effects can be obtained by incorporating the driving device in a printer using a LED array head in which a large number of LEDs are arranged as a light source. Further, the driving device according to the present invention can be incorporated in a printer of an electrostatic recording system using an ion current or a magnetic head recording system, for example.

FIG. 21 shows a main part of an image scanner incorporating a stepping motor driving device according to the present invention. FIG. 22 and FIG. 23 show the optical system.

First, the principle of reading an image by an image scanner will be described with reference to the drawings.

As shown in FIG. 21, an image original 201 to be read is placed on an original placing plate 203 made of transparent glass placed above a scanner unit 202. Scanner unit 202
Includes a light source lamp 204. Light emitted from the light source lamp 204 illuminates the image document 201 on the document placing plate 203.
The illuminated original image passes through mirrors 205, 206, 207 and a lens 208 in order, and is read by an image reading element, in this example, a CCD line sensor 2.
Image on 09.

The movement of the scanner unit 202 and the mirror unit 210 including the mirrors 206 and 207 are controlled by the stepping motor 211 and the timing belts 212 and 213 in the directions indicated by arrows H and H 'in the figure, as shown in FIG. The direction indicated by H indicates the direction when reading the image document, and the direction indicated by H 'indicates the direction when returning. The scanner unit 202 and the mirror unit 210 are controlled to move at a speed ratio of 2: 1 by a timing belt and a timing pulley. During this by being scanning a document surface, as shown in FIG. 23, the distance f ₁ between the lens 208 and the document surface is always kept constant, even the size of the image on the CCD line sensor 209 Be kept constant.

In the image scanner having the above configuration, the scanner unit
While the 202 and the mirror unit 210 are moving in the H direction at a constant speed, image data is read from the CCD line sensor 209 at a constant reading frequency.

The reading resolution in the moving direction of this image scanner is
It is determined by the amount of movement of the scanner unit 202 within the reading cycle of the CCD line sensor 209. The resolution in the direction perpendicular to the moving direction is determined by the number of bits of the CCD line sensor 209. In this example, the CCD line sensor 209
, The reading frequency is always constant, so that if the speed of the scanner unit 202 is not constant, a portion shifted from the original document position to be read is read. As a result, when the image data read by the CCD line sensor 209 is displayed on a printer or a display, the image becomes uneven and reproduced.

Therefore, in this example, the stepping motor 211 that drives the scanner unit 202 and the mirror unit 210 is driven by the driving device 2e. This driving device 2e is basically configured in the same manner as that shown in FIG.
That is, in the driving device 2e, the stepping motor 21
The pulse rate of the timing pulse that determines the timing of the excitation switching in step 1 is made to coincide with the period of the inherent speed fluctuation of the system including the stepping motor 211 and the element driven by the stepping motor 211, and to be almost in phase. Let me. Then, the fluctuation amplitude of the pulse rate is also set optimally. In FIG. 21, S ₁ indicates a forward rotation control command,
S ₂ represents a reverse rotation control command, S ₃ are enlarged, shows the speed switching control command for selecting a reduction. Therefore, the storage device 50 (see FIG. 1) in the driving device 2e stores pulse rate data that can cancel the speed fluctuation of the stepping motor 211 at various speeds.

With such a configuration, the inherent speed fluctuation of the scanner unit vibration system can be canceled by the speed fluctuation due to the fluctuation of the pulse rate of the timing pulse, and as a result, the speed fluctuation of the stepping motor 211 can be sufficiently reduced. . Therefore, the reproducibility of the read image data can be improved. Further, in this example, while the reading frequency of the CCD line sensor 209 is kept constant, the image can be read while being enlarged or reduced by changing the moving speed of the scanner unit 202. The effect is great. That is, when reading the image while enlarging the image, the moving speed of the scanner unit 202 is lower than at the time of equal magnification. At low speed, the speed fluctuation of the stepping motor 211 tends to be large. Further, the reading pitch in the moving direction of the scanner unit 202 becomes smaller, so that the influence of the speed fluctuation is more likely to appear on the read image.
However, in this embodiment, the speed fluctuation of the scanner unit 202 can be suppressed regardless of the magnification set, so that the above-described problem can be solved.

FIG. 24 shows a main part of a wire dot serial printer incorporating a stepping motor driving device according to the present invention.

The image forming principle of this printer is as follows. That is, a print wire (not shown) provided in the print head 301 is controlled by a magnetic force so as to protrude from the tip of the print head for a predetermined time. Print head 301 and paper 302
And an ink ribbon (not shown) in which the fiber is impregnated with ink. The printing wire presses the ink ribbon against the paper 302 to print dots on the paper 302. In this example, 24 print wires are provided in the print head 301. Each wire is selectively controlled to protrude, and an image such as a character is formed by combining dots printed by the protrusion.

The print head 301 is fixed to the carriage 303. The carriage 303 is mounted on the guide shaft 305 via the oil-impregnated bearing 304.
a, 305b. The carriage 303 is reciprocated by a stepping motor 306 and a timing belt 307 in a direction indicated by an arrow K in the drawing. At this time, the print wire of the print head 301 is driven and one of the carriages 303 is moved.
The image of the round trip is printed. When the printing for one reciprocation is completed, the rotation of the platen roller 308 holding the sheet 302 is controlled by a fixed amount, and then the image printing for the next one reciprocation is started.

The platen roller 308 is driven by a stepping motor 309 as shown in FIG. That is, the rotation output of the stepping motor 309 is transmitted to the platen roller 308 via the gears 310, 311 and 312. The sheet 302 is held in close contact with the platen roller 308 by the pressure roller 313.

In this example, the drive frequency of the print head 301 is kept constant. Therefore, when the moving speed of the carriage 303 on which the print head 301 is mounted fluctuates, the print position shifts and the image is disturbed. Therefore, the carriage 303
Is desired to be always constant.

Therefore, in this example, the stepping motor 306 for driving the carriage 303 is driven by the driving device 2f. The driving device 2f has basically the same configuration as that shown in FIG. That is, this drive
In step 2f, the pulse rate of the timing pulse for determining the excitation switching timing of the stepping motor 306 is made to coincide with the inherent speed fluctuation period of the system including the stepping motor 306 and the elements driven by the stepping motor 306, and the phases are almost opposite. As follows. Then, the fluctuation amplitude of the pulse rate is also set optimally. In FIG. 24,
S ₁ denotes a normal rotation control command, S ₂ represents the reverse rotation control command. In this example, since the carriage 303 reciprocates and prints once, the storage device 50 (see FIG. 1) in the driving device 2f stores the pulse rate data at the time of forward movement and the pulse rate at the time of backward movement. Rate data is stored.

With such a configuration, the speed fluctuation due to the fluctuation of the pulse rate and the speed fluctuation inherent to the carriage vibration system can be reversed, so that the speed fluctuation of the stepping motor 306 can be sufficiently reduced, and the carriage 303 can be moved at a substantially constant speed. Can be moved. Therefore, the quality of the printed image can be improved.

Although the above example controls the carriage driving stepping motor of the wire dot serial printer with the driving device according to the present invention, the same applies when the print head is applied to another serial printer such as an ink jet head or a thermal head. The effect is obtained.

FIG. 26 shows a main part of a sublimation type thermal transfer line printer incorporating a stepping motor driving device according to the present invention.

First, the principle of the printer will be described. In FIG. 26, reference numeral 401 denotes a thermal head, and 402 denotes a thermal head.
Reference numeral 401 denotes a platen roller disposed opposite to the reference numeral 401. Reference numeral 403 denotes a sheet guided by the platen roller 402 and moving on the front surface of the thermal head 401. A number of resistance elements 404 are arranged in the thermal head 401 in a direction orthogonal to the paper 403 feeding direction. The length of the area where the resistance element 404 is provided is set to be substantially the same as the width of the paper 403 on which an image is recorded. A sheet 40 is provided between the sheet 403 guided by the platen roller 402 and the resistance element 404.
Ink film 405 guided in the same direction at the same speed as 3
Is arranged. This ink film 405 is composed of a base film 406 and a color material layer 407 made of a sublimable ink.

When the resistance element 404 of the thermal head 401 is energized, the resistance element 404 generates heat. This heat causes the ink of the color material layer 407 in the ink film 405 to sublime, and the receiving layer 408 of the paper 403
, And a dot is printed on the paper 403 by this adhesion. An image is formed on the paper 403 by a combination of these dots.

The paper 403 is held in close contact with the platen roller 402 by a pressure roller 409, as shown in FIG. The platen roller 402 is driven by a stepping motor 411 via a timing belt 410. In this example, a thermal head was used to reduce the image formation time.
The platen roller 402 is driven even while the 401 is being driven.

In the sublimation type thermal transfer line printer configured as described above, since the driving frequency of the thermal head 401 is constant, if the rotation speed of the platen roller 402 fluctuates, the printing position shifts and the image quality deteriorates. Will be lost.

Therefore, in this embodiment, the stepping motor 411 is driven by the driving device 2g. The driving device 2g is
Basically, the configuration is the same as that shown in FIG. That is, this driving device 2g is a stepping motor
The pulse rate of the timing pulse for determining the excitation switching timing of the step 411 is made to coincide with the inherent speed fluctuation period of the system including the stepping motor 411 and the elements driven by the stepping motor 411, and is changed so as to have almost the opposite phase. . Then, the fluctuation amplitude of the pulse rate is also set optimally.

With such a configuration, the inherent speed fluctuation of the platen roller vibration system and the speed fluctuation due to the pulse rate fluctuation can be made in opposite phases, and both fluctuations can be canceled each other. Can be reduced sufficiently, and the platen roller 402 can be rotated at a substantially constant speed. Therefore, the image quality of the printed image can be improved.

Although the above example is applied to a sublimation type line printer, the same effect can be obtained by applying the present invention to another type of thermal transfer line printer such as a heat melting type line printer or an energizing type line printer.

Further, the present invention provides a stepping motor,
The shape and the number of phases are not limited. Further, in the above-described embodiment, the application to the case where the speed fluctuation inherent to the stepping motor has a single frequency component is described.
Even if there are a plurality of frequency components, the present invention can be applied as long as the frequencies are in a range smaller than the stepping motor driving frequency. The present invention also relates to a stepping mode.
It can be applied to all mechatronics-applied devices that incorporate a stepping motor, including when driving a CT scanner bed with a computer.

[Effects of the Invention] As described above, according to the present invention, speed fluctuations can be sufficiently mitigated only by an electric method without causing a complicated or large-sized configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a stepping motor driving device according to the present invention, and FIG. 2 is a longitudinal section showing a rotor of the stepping motor driven by the driving device shown in FIG. FIG. 3 is a cross-sectional view of FIG.
FIG. 4 is a plan view of a switching circuit incorporated in the driving device shown in FIG. 1, and FIG. 5 is a distribution diagram incorporated in the driving device shown in FIG. FIG. 6 is a diagram showing an operation sequence of the circuit, FIG. 6 is a block diagram of an arithmetic unit incorporated in the driving device shown in FIG. 1, and FIG. 7 is a speed incorporated in the driving device shown in FIG. Configuration diagram of setting device, amplitude setting device and phase setting device,
FIG. 8 (a) is a diagram showing an example of a pulse train output from an arithmetic unit incorporated in the driving device shown in FIG. 1, and FIG. 8 (b) is a pulse train shown in FIG. 8 (a). FIG. 9 is a diagram showing the results of speed fluctuations when the high-speed rotation range is controlled by the driving device shown in FIG. 1, and FIG. 10 is a diagram showing the speed under the conditions shown in FIG. FIG. 11 shows a fluctuation power spectrum, FIG. 11 is a block diagram showing another embodiment of a driving device for a stepping motor according to the present invention, and FIG. 12 is a diagram showing a switching circuit incorporated in the driving device shown in FIG. FIG. 13 is a block diagram incorporated in the driving device shown in FIG. 11, and FIG. 14 is a current level flowing through each excitation winding of the stepping motor driven by the driving device shown in FIG. And the pulse rate under these conditions FIG. 15 is a block diagram showing still another embodiment of the driving device of the stepping motor according to the present invention, and FIG. 16 is a switching circuit incorporated in the driving device shown in FIG. FIG. 17 is a block diagram of an arithmetic unit incorporated in the driving device shown in FIG. 15, and FIG. 18 is each excitation winding of a stepping motor driven by the driving device shown in FIG. FIG. 19 is a diagram showing an example of a current waveform flowing through the laser device and a change in pulse rate under the conditions, FIG. 19 is a schematic configuration diagram of a laser page printer incorporating the driving device according to the present invention, and FIG. 20 is shown in FIG. FIG. 21 is a perspective view showing only a photosensitive drum drive system of a printer taken out, FIG. 21 is a main part configuration diagram of an image scanner incorporating a drive device according to the present invention, and FIG. 22 is a view of the image scanner shown in FIG. FIG. 23 is an equivalent view of the optical system shown in FIG. 22, FIG. 24 is a perspective view of a main part of a wire dot serial printer incorporating a driving device according to the present invention, and FIG. A diagram showing a platen roller drive system of the printer shown in FIG. 24,
FIG. 26 is a side view of a main part of a thermal transfer line printer incorporating the driving device according to the present invention, and FIG. 27 is a diagram showing a platen roller driving system of the printer shown in FIG. 1,1a, 111,211,306,309,411 …… Stepping motor, 2,
2b, 2c, 2d, 2e, 2f, 2g …… Drive device, 24A to 24D, 24X, 24Y…
… Exciting winding, 30,30b, 30c …… Switching circuit, 40,40
a, 40b ... distribution circuit, 50 ... storage device, 60, 60a, 60b ...
Arithmetic unit, 75 Speed setting device, 80 Amplitude setting device, 85
… Phase setting device, 90 …… DC power supply.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 8/00-8/38

Claims (9)

(57) [Claims] In order to rotate a rotor of a stepping motor, a plurality of excitation windings of the stepping motor are sequentially switched and excited in a predetermined order.
A first step of obtaining at least a periodic speed fluctuation characteristic provided in the stepping motor; and a second step of obtaining a current value of each of the exciting windings for relaxing the periodic speed fluctuation obtained in the first step. And a third step of obtaining a periodic speed fluctuation characteristic still provided in the stepping motor under the condition that the respective exciting windings are sequentially switched and excited with the current value obtained in the second step.
And changing the time interval for sequentially switching and exciting each of the excitation windings in accordance with the periodic speed fluctuation characteristic obtained in the third step, using the current value obtained in the second step. And a fourth step of exciting each of the exciting windings. 2. In the fourth step, the excitation switching timing of each of the excitation windings is determined by a pulse train.
2. The stepping motor driving method according to claim 1, wherein the pulse rate of the pulse train is changed in a phase opposite to the periodic speed change obtained in the third step. 3. The method according to claim 1, wherein in the fourth step, the fluctuation amplitude of the pulse rate is determined in accordance with the fluctuation amplitude of the periodic speed fluctuation obtained in the third stepping. 3. The method for driving a stepping motor according to item 2. 4. The driving of the stepping motor according to claim 1, wherein in the fourth step, a micro-step excitation method for increasing or decreasing a voltage applied to each of the excitation windings in a stepwise manner is used together. Method. 5. A drive device for switching and exciting a plurality of excitation windings provided in a stepping motor in a predetermined order, wherein the DC power supply supplies an excitation current to the plurality of excitation windings. And switching means provided between the plurality of exciting windings and comprising a plurality of switching elements; and a pulse generator for generating a pulse train used as a timing pulse for switching the excitation of the plurality of exciting windings. Means, means for introducing a pulse train generated by the pulse generating means to control the switching elements of the switching means to be turned on and off in a predetermined order, and at least a periodic speed fluctuation provided in the stepping motor. Means for adjusting the current flowing through the plurality of excitation windings to relax the current; and Storage means for storing in advance at least the periodic speed fluctuation data provided in the stepping motor under the condition that the current to be adjusted is adjusted; and reading out the speed fluctuation data stored in the storage means. Means for changing the pulse rate of the timing pulse generated by the pulse generating means in accordance with the speed fluctuation data. 6. A driving device for switching and exciting a plurality of exciting windings provided in a stepping motor in a predetermined order, wherein the DC power supply supplies an exciting current to the plurality of exciting windings. And a switching means provided between the plurality of exciting windings and comprising a plurality of switching elements, and for switching excitation to the plurality of exciting windings and exciting currents of the plurality of exciting windings in a stepwise manner. Pulse generating means for generating a pulse train used as a timing pulse for increasing and decreasing the pulse, and introducing a pulse train generated by the pulse generating means to control on / off of the switching elements of the switching means in a predetermined order. Means for switching and exciting the plurality of exciting windings, and introducing the pulse train generated by the pulse generating means to the plurality of exciting windings. Means for increasing and decreasing the exciting current flowing in a stepwise manner, and means for adjusting the current increasing and decreasing in a stepwise manner flowing through the plurality of exciting windings in order to reduce at least periodic speed fluctuations provided in the stepping motor. Under the condition that the current is adjusted by the current adjusting unit, a storage unit for storing in advance at least the periodic speed fluctuation data provided in the stepping motor, and a storage unit that is stored in the storage unit. Means for reading the speed fluctuation data, and changing the pulse rate of the timing pulse generated by the pulse generation means in accordance with the speed fluctuation data. 7. The storage device according to claim 5, wherein said storage means stores periodic speed fluctuation data provided in a system including said stepping motor and a load connected to said stepping motor. 3. The driving device for a stepping motor according to claim 1. 8. The apparatus according to claim 1, wherein said means for varying the pulse rate varies the pulse rate of said timing pulse in a phase opposite to a velocity variation obtained from velocity variation data stored in said storage means. 7. The driving device for a stepping motor according to claim 5, wherein 9. The method according to claim 1, wherein the means for varying the pulse rate varies the pulse rate of the timing pulse in accordance with the amplitude of the speed variation obtained from the speed variation data stored in the storage means. The driving device for a stepping motor according to claim 8, wherein