JPH09132340A - Sheet conveying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveying device for transferring a sheet in an image forming device, which can obtain a high torque at a high speed even in a condition such that the speed difference during conveyance of sheets is greater than twice, and which can restrain the heat generation of a motor running at a low speed. SOLUTION: A sheet feed sensor 55 delivers a signal indicating low or high speed conveyance in accordance of a position of a sheet to be conveyed in an image forming device. A control part 52 generates an input pulse signal for a low speed when a signal indicating low speed conveyance is delivered from the sensor 55, so that a two-speed control motor is energized in a single phase mode. Further, the control part 52 generates an input pulse signal for a high speed when a signal indicating high speed conveyance is delivered from the sensor 55, so that the two speed motor 52 is energized in a two phase mode or a 1-2 phase mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying device for conveying a sheet in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art In recent years, in image forming apparatuses such as copying machines and printers, increasing the printout speed has become an important factor for achieving high performance. The printout speed can be improved by increasing the paper speed at all positions in the apparatus. In this case, the image forming process of the exposure device, charging device, developing device, transfer device, cleaning device, fixing device, etc. Since the performance and reliability of all the devices related to the above must be improved, the device becomes large and expensive.

Therefore, there has been considered a method of increasing the print-out speed by increasing the paper-conveying speed in other portions without increasing the paper-conveying speed in the above-mentioned image forming process. In this case, the sheet conveying device needs to convey the sheet at two or more kinds of speeds by one driving source, and a stepping motor is used as a driving source satisfying this requirement. There are two general driving methods for the stepping motor: constant current driving and constant voltage driving. Among them, in the constant current drive, the current is limited by chopping, so that two or more kinds of speeds can be freely changed depending on how to select the winding, but the control circuit becomes complicated and expensive.

On the other hand, in the case of constant voltage drive, the current that flows depends on the number of windings and the rotational speed. Therefore, if the current is set so that a large torque is obtained at high speed, the current will flow too much at low speed and heat generation will increase. However, the burden on the power source will be increased and other adverse effects will occur. Therefore,
This is limited to the case where the two types of speed difference are small or the motor torque has a large margin. In addition, there is a method of adding a current limiting resistor by switching at a low speed in response to such a problem, but the merit of low price is lost due to the space of the control board and the addition of electronic parts.

On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 62-2895 proposes a conveying device which performs two-phase excitation when the sheet conveying speed is fast in constant voltage driving and 1-2 phase excitation when the sheet conveying speed is slow. There is.

[0006]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. Sho 62-62
According to the transport device of No. 2895, high torque can be obtained at high speed, stable transport can be performed, and heat generation at low speed can be suppressed. However, this method is limited to the case where the speed difference between the two types is small, and when the speed difference is twice or more, a large amount of current flows at low speed, resulting in large heat generation and a load on the motor. was there.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet conveying device which can obtain a high torque at a high speed and can suppress heat generation at a low speed even under the condition that the speed difference is twice or more.

[0008]

SUMMARY OF THE INVENTION A sheet conveying apparatus according to the present invention generates a roller for conveying a sheet, a stepping motor for driving the roller, and at least two kinds of input pulse signals for low speed and high speed. In a sheet conveying device having pulse signal generating means and exciting means for exciting the coils of the stepping motor in a predetermined order based on the input pulse signal, and for conveying the sheet at at least two kinds of conveying speeds. Instruction signal output means for outputting an instruction signal for low speed conveyance or high speed conveyance according to the position of the conveyed sheet is provided, and the pulse signal generating means is given an instruction signal for low speed conveyance from the instruction signal output means. In this case, a low speed input pulse signal is generated, and a high speed input pulse signal is generated when a high speed conveyance instruction signal is given. , The excitation means, when an instruction signal of the low speed conveyor from said instruction signal output unit is given to the one-phase excitation of the stepping motor, also the stepping motor when the instruction signal of high-speed conveyance is given 2
It is characterized in that the phase or 1-2 phase excitation is used.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As the above-mentioned image forming apparatus,
Copiers and printers are used.

As the above-mentioned roller, a carrying roller for carrying the paper supplied from the paper cassette in the image forming apparatus to the image forming means is used.

As the above-mentioned exciting means, a control unit for supplying current to the coils of the stepping motor in a predetermined order based on the input pulse signal, and a current supplied from the control unit for amplifying the currents are supplied to each coil. A drive circuit that sequentially excites is used.

The function of the pulse signal generating means described above is realized in the control section. The input pulse signal can also be generated by a separate pulse signal generator.

A paper feed sensor is used as the above-mentioned instruction signal output means. This paper feed sensor is arranged, for example, before the image forming process in the image forming apparatus,
Monitor whether the paper has reached the area of the imaging process. Then, when the paper reaches the area of the image forming process, a low speed conveyance instruction signal is output, and when the paper passes through the area of the image forming process, a high speed conveyance instruction signal is output.

In the control section, whether the coil of the stepping motor is set to the two-phase excitation or the one-two-phase excitation at high speed is determined by the pulse speed when the motor is operated at high speed. That is, since the pulse speed at the time of high-speed operation of the motor varies depending on the specifications of the motor to be used, the operation pattern, etc., it is set according to various conditions whether 2-phase excitation or 1-2-phase excitation is used. .

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the sheet conveying apparatus according to the present invention will be described below. Before the explanation, the structure of a printer 1 to which the sheet conveying apparatus according to the present invention is applied will be explained.

FIG. 10 is a conceptual cross-sectional view of the printer 1 to which the sheet conveying apparatus according to the present invention is applied.

The printer 1 is roughly classified into an apparatus main body 2
And a paper discharge section 3 which is detachably mounted on the right side of the apparatus body 2, and a switchback which is detachably mounted on the bottom of the apparatus body 2 for reversing the traveling direction of the sheet and reversing the upper and lower sides thereof. It is composed of a section 4 and a second sheet cassette 5 which is detachably attached to the bottom surface of the switchback section 4 and accommodates a larger number (for example, about 500 sheets) of sheets than an ordinary sheet cassette.

The above-described paper discharge unit 3, switchback unit 4, and second paper cassette 5 are prepared as optional units that can be added to the outside of the apparatus main body 2, and among them, the paper discharge unit 3 and the switch. The back section 4 is an image forming process that is normally performed only by the apparatus main body 2,
That is, it is not used when an image is formed only on one side of a sheet-like recording sheet (hereinafter referred to as sheet).

On the other hand, in the apparatus main body 2, an optical unit 6 for outputting a laser beam containing image information and a photoconductor 7 are provided.
An electrostatic recording type image forming unit 8 composed of the above, a fixing unit 10 composed of a fixing roller 9 and the like, main constituent elements constituting the electrostatic recording system and the like are arranged, and a sheet is provided at the bottom thereof. A first paper cassette 12 accommodating and accommodating 11 is detachably mounted in the direction of arrow A.

In FIG. 10, reference numeral 13 is a foldable manual feed tray used in the manual feed mode, 14 is a manual feed tray storage cover that covers the manual feed tray 13 when the manual feed tray 13 is stored, and 15 Is a main tray cover that covers the main tray 16 formed on the upper surface of the apparatus main body 2, and 17 is a sub-tray that is arranged on the side of the paper discharge unit 3.

Next, the operation of the printer 1 described above will be briefly described.

First, the image forming process in the single-sided recording mode in which the image is formed on only one side of the paper will be described.

When one sheet 11 is fed by the feed roller 20 from the uppermost surface of the first sheet cassette 12, the sheet 11 is conveyed to the image forming means 8 along the first and second sheet guide chutes 21 and 22. Then, the image forming means 8 forms an image on one side surface of the sheet. In addition, the above-mentioned first and second sheet guide chutes 21,
In the middle of 22, there are conveying rollers 23 and 24, and a registration roller 25 for adjusting the conveying timing of the sheets separated from the manual feeding tray 13 in the manual feeding mode. The feed roller 20, the transport roller 23,
Reference numeral 24 designates a high speed and a low speed 2 by a 2 speed control motor (not shown).
It is driven at various speeds, and after the registration roller 25, it is driven at a constant speed by a constant speed control motor (not shown).

The paper 11 fed from the first paper cassette 12 by the feed roller 20 is conveyed by the conveying roller 2
It is conveyed at high speed to the speed switching position C by 3, 24 and is driven at low speed after the leading end thereof is taken in by the registration roller 25. That is, since the registration roller 25 and the subsequent rollers are driven at a constant speed by a constant speed control motor (not shown), when the paper 11 reaches the registration roller 25, it is conveyed at a low speed in accordance with the speed of the registration roller 25. Then, when the sheet 11 passes through the registration roller 25 while being transported at a low speed, the feed roller 20 and the transport rollers 23 and 24 are driven again at a high speed. A stepping motor is used as the second speed control motor and the constant speed control motor.

The sheet on one side of which the image is formed by the image forming means 8 is then conveyed to the fixing means 10 through the third paper guide chute 26, and the unfixed image is fixed there. After the image is fixed, the sheet on which the image is formed on one side is then discharged via the discharge roller 27 to one of the fourth or fifth sheet guide chutes 28, 29.

At the base ends of the fourth or fifth paper guide chutes 28, 29, the recording paper discharged from the discharge roller 27 is attached to the fourth or fifth paper guide chutes 28, 29.
A first switching claw 30 that guides to either one of the two is disposed, and when the first switching claw 30 rotates counterclockwise and stops positioning at that position, the discharge roller 27
The recording paper discharged from is guided to the fourth paper guide chute 28. The recording paper guided to the fourth paper guide chute 28 is ejected onto the main tray 16 via the ejection roller 31.

On the other hand, when the above-mentioned first switching claw 30 rotates clockwise and is positioned at that position, the recording paper discharged from the discharge roller 27 is transferred to the fifth paper guide chute 2.
Guided to 9. The sheet guided to the fifth sheet guide chute 29 is then transferred to the sixth sheet through the second switching claw 30a.
Alternatively, the sheet is guided to the seventh sheet guide chutes 32 and 33, but in the case of the single-sided recording mode, the second switching claw 30a always rotates counterclockwise and is positioned at that position, so that the image is displayed on one side. The formed sheets are discharged onto the sub-tray 17 via the discharge rollers 34, and are stacked and stored therein.

Similarly, in the image forming process in the single-sided recording mode, when one sheet of paper 11 is fed from the uppermost surface of the second paper cassette 5 by the feed roller 35, the paper is next fed to the eighth paper guide chute 36, A ninth paper guide chute 37 connected to the eighth paper guide chute 36 and a first paper guide chute 37 connected to the ninth paper guide chute 37.
The sheet guide chute 38 of 0 and the first and second sheet guide chutes 21 and 22 connected to the tenth sheet guide chute 38 are conveyed to the image forming means 8, and the image forming means 8 conveys the paper. An image is formed on one side.

The paper with an image formed on one side is
After that, similarly to the recording paper in the above-mentioned single-sided recording mode, it is discharged to either the main tray 16 or the sub tray 17. Note that the paper transport roller 3 is also provided in the middle of each of the eighth and ninth paper guide chutes 36 and 37 described above.
9, 40 are interposed.

Also in the manual feed mode in the single-sided recording mode, the recording papers stacked and accommodated on the manual feed tray 13 are separated one by one by a separation roller (not shown) and guided to the eleventh paper guide chute 13a. afterwards,
The transfer timing is adjusted by the registration roller 25, and the second
The sheet is conveyed to the paper guide chute 22 of the main tray 1 and is then transferred to the main tray 1 similarly to the recording paper in the single-sided recording mode described above.
6 or the sub tray 17 is discharged.

Next, the image forming process in the double-sided recording mode for forming images on both sides of the paper will be described.

The paper that is fed from the first paper cassette 12 by the feed roller 20, the image is formed on one side by the image forming means 8, and the paper on which the image is fixed by the fixing means 10 is discharged through the discharge roller 27 to the paper discharge section 3 When it is guided inward, the second switching claw 30a rotates clockwise by a predetermined angle and stops at that position, so that the sheet on which the image is formed only on one side is guided to the seventh sheet guide. Guide to the shoot 33.

The sheet guided in the seventh sheet discharge chute 33 is guided to the switchback section 4 from the downstream end of the seventh sheet discharge chute 33.

On the other hand, the switchback unit 4 has a first holding chute 41 on which an image is formed on one side and which temporarily holds a sheet, and a switch capable of rotating in the forward and reverse directions to reverse the traveling direction of the temporarily held sheet. It is composed of the back roller 42, and the paper whose direction of travel is reversed and reversed is the first
The second holding chute 43 disposed on the lower surface side of the holding chute 41 is guided to the image forming means 8 of the apparatus main body 2 again.

On the other hand, a third switching claw 44 is arranged at the terminal end of the seventh paper discharge chute 33. When the third switching claw 44 rotates counterclockwise by a predetermined angle and stops at that position, it guides the sheet guided through the seventh sheet discharge chute 33 to the first holding chute 41, Further, when the sheet is guided by the first holding chute 41, the sheet is guided back to the second holding chute 43 through the twelfth sheet guiding chute 45 after the sheet is guided back to the first holding chute 41 by rotating back by a predetermined angle and stopping at that position. .

Paper transport rollers 46, 47, 48 for transporting the paper are also interposed in the twelfth paper guide chute 45 and the second holding chute 43.

Therefore, the seventh paper guide chute 33
The sheet guided to the switchback unit 4 by the third switching claw 44 is temporarily guided to the first holding chute 41 side, and the whole of the sheet is temporarily held in the first holding chute 41 by the switchback roller 42 which rotates forward. Housed in.
The switchback roller 42 maintains the posture of gripping the trailing edge of the sheet guided in the first holding chute 41 even when the sheet is temporarily held.

Next, when it is detected that the paper is temporarily held in the first holding chute 41, the third switching claw 44 is formed.
Is rotated clockwise by a predetermined rotation angle and stopped, and the upstream side of the twelfth paper guide chute 45 is expanded. Then, the switchback roller 42 is reversely rotated and is temporarily held in the first holding chute 41. The trailing edge of the sheet is conveyed, and the sheet is guided to the second holding chute 43 through the twelfth sheet guiding chute 45.

The sheet guided in the second holding chute 43 is conveyed to the ninth sheet guide chute 37 via the curved thirteenth sheet guide chute 49, and further passes through the tenth sheet guide chute 38. It is guided again to the first paper guide chute 21 in the main body 2 of the apparatus.

As described above, since the sheet conveyed again to the image forming means 8 through the second holding chute 43 of the switchback section 4 is turned upside down, this time the image forming means 8 outputs other sheets. An image is formed on the side surface, and further conveyed to the fixing unit 10, where the image on the other side surface is fixed. After that, the paper on which images are formed on both sides is discharged to one of the main tray 16 and the sub-tray 17 via the discharge roller 27 and the first switching claw 30.

In the double-sided recording mode, even the sheets separated one by one from the manual feed tray 13 in the manual feed mode,
Also, for the sheets that are separated and conveyed one by one from the second sheet tray 5, images are formed on both sides of the sheet through the same steps as those described above.

In the printer 1 described above, as already described, the feed roller 20, the transport rollers 23, 2
4 is driven by a second speed control motor (not shown). Next, the sheet conveying device according to the present invention will be described by taking the case of driving the second speed drive motor as an example.

FIG. 1 is a block diagram showing the functional structure of the sheet conveying device provided in the printer 1 described above.

The sheet conveying device 50 is roughly classified into a second speed control motor 51 for driving each roller, a control unit 52 and a drive circuit 53 functioning as an exciting means, and a second speed control motor 51 for operating. It is composed of a power supply unit 54 and a paper feed sensor 55 that detects a paper conveyance position.

The paper feed sensor 55 is arranged near the speed switching position C in FIG. 10, and when the leading edge of the paper 11 reaches a predetermined position before the registration roller 25, that is, the paper 11
When the sheet 11 is conveyed to the position where it is taken in by the registration roller 25, a low speed conveyance instruction signal is output to the control unit 52, and when the paper 11 passes through the registration roller 25, a high speed conveyance instruction signal is output to the control unit 52. As the paper feed sensor 55, for example, a transmissive photo sensor can be used.

The power supply unit 54 is a DC power supply for applying a rated voltage to a coil (not shown) of the second speed control motor 51, and in this embodiment, a DC stabilized power supply is used.

The control unit 52 and the drive circuit 53 use the second-speed control motor 51 based on an input pulse signal described later.
A current is supplied to the coils (not shown) in a predetermined order to excite each coil. The control unit 52 and the drive circuit 53
Can be configured by a control circuit having a CPU (central processing unit), a ROM, a RAM, and the like as constituent elements. The functions such as switching of the excitation method and generation of the input pulse signal, which will be described later, can be executed according to the control program.

In the controller 52, the paper feed sensor 55 is used.
The excitation system is switched to the coil (not shown) of the second speed control motor 51 in accordance with an instruction signal (low speed conveyance, high speed conveyance) given from the. In this embodiment, the second speed control motor 51 is driven by one-phase excitation when the paper feed sensor 55 gives a low speed conveyance instruction signal, and the second speed control is given when the paper feed sensor 55 gives a high speed transportation instruction signal. The motor 51 is driven by 1-2 phase excitation.

Since the pulse speed during high-speed conveyance differs depending on the type and specifications of the motor used and the operation pattern, it depends on various conditions whether 2-phase excitation or 1-2-phase excitation is used during high-speed conveyance. Is set. For example, in the case of a PM type stepping motor that is widely used in office automation equipment such as copiers and printers, it is 2 in 1-phase or 2-phase excitation.
It has a resonance frequency of 50 to 300 pps (pulse speed). The resonance frequency is the frequency of the input pulse signal that matches the natural frequency of the rotor inside the motor.In the range of this resonance frequency, vibrations become large and step out easily occurs. Will select frequencies outside this range of resonance frequencies. However, at 250 pps or less, the vibration at each step is large even if the resonance does not occur, and the rotation unevenness and the vibrating noise become large. On the other hand, assuming that the speed difference is twice or more at high speed, it is sufficient to drive at a frequency of 600 pps or more, but in order to obtain higher torque, the frequency is 6
If it is in the range of 00 to 750 pps, it is driven by two-phase excitation,
If it is 750 pps or more, it is desirable to drive by 1-2 phase excitation.

Further, the control unit 52 generates an input pulse signal according to the instruction signal (low speed conveyance, high speed conveyance) after switching the above-mentioned excitation method. In this embodiment, the pulse speed varies depending on the paper transport speed.
Generating different types of input pulse signals. That is, a low-speed input pulse signal is generated when the paper feed sensor 55 gives a low-speed conveyance instruction signal, and a high-speed input pulse signal is generated when the paper feed sensor 55 gives a high-speed conveyance instruction signal. I am trying.
By the way, since the rotation speed of the stepping motor is determined by the pulse speed (frequency) of the input pulse signal and the step angle, an input pulse signal with a high pulse speed (a large number of pulses) is generated at high speed, and the pulse speed is low at low speed. Generate a low (low pulse count) input pulse signal (same step angle).

The actual input pulse signal is not composed of the same pulse at both low speed and high speed, but is composed of a series of pulse trains having different pulse speeds (start-up / fall-down control is performed). For).
However, in this embodiment, in order to simplify the explanation,
It is assumed that each of the high speeds is composed of pulses having a single pulse speed.

The drive circuit 53 amplifies the pulse train of the input pulse signal supplied from the control section 52, and
Current is supplied to the coils of the second speed control motor 51 in a predetermined order to excite each coil.

In the above-described sheet conveying device 50, FIG.
0 to the feed roller 2 from the first paper cassette 12
The paper 11 fed by 0 is conveyed by the conveyance roller 23,
It is conveyed at high speed to the speed switching position C by 24.
Then, the sheet feed sensor 55 outputs a low speed conveyance instruction signal to the control unit 52 shown in FIG. The control unit 52 sets the coil of the second speed control motor 51 to one-phase excitation according to the instruction signal for low speed conveyance, generates an input pulse signal for low speed, and outputs it to the drive circuit 53. In the drive circuit 53, the second speed control motor 5 is driven based on the input low speed input pulse signal.
1 is driven by one-phase excitation. In the case of driving by the one-phase excitation method, each phase is excited at the timing shown in FIG. 2 with respect to the input pulse signal. 3 shows the relationship between the input pulse signal and the waveform of the current flowing in each phase of the motor at this time. The current waveform of each phase is a simplified waveform of the waveform that appears when the coil is excited, and is not necessarily an actual current waveform.

Here, as a comparative example, the excitation timing with respect to the input pulse signal when the 1-2 phase excitation is performed at low speed (the method of Japanese Patent Laid-Open No. 62-2895) is shown in FIG. The current waveforms are shown in FIG. 5, respectively.
As shown in FIG. 5, when the 1-2 phase excitation is performed at a low speed, a current equivalent to the total of the saw-shaped portions flows, which imposes a heavy burden on the motor and the power supply. However, when one-phase excitation is performed at low speed, the amount of current can be reduced as shown in FIG.

When the sheet 11 passes the sheet feed sensor 55, the sheet feed sensor 55 outputs a high-speed conveyance instruction signal to the control section 52. The controller 52 turns on the coil of the second speed control motor 51 in accordance with the high speed conveyance instruction signal.
The −2 phase excitation is performed, and then a high-speed input pulse signal is generated and output to the drive circuit 53. The drive circuit 53 drives the second speed control motor 51 by 1-2 phase excitation based on the input high speed input pulse signal.

When the second speed control motor 51 is driven by the 1-2 phase excitation method, each phase is excited at the timing shown in FIG. 6 with respect to the input pulse signal. FIG. 7 shows the relationship between the input pulse signal and the waveform of the current flowing in each phase of the motor at this time. On the other hand, when driving by the two-phase excitation method during high-speed conveyance, each phase is excited at the timing shown in FIG. 8 with respect to the input pulse signal. 9 shows the relationship between the input pulse signal and the waveform of the current flowing through each phase of the motor at this time.

According to the above-described sheet conveying device 50, even when the speed difference between the low speed and the high speed is twice or more, as is apparent from FIGS. 7 and 9, the amount of current flowing at the low speed is reduced. Therefore, heat generation at low speed can be suppressed, and the load on the motor and the power supply can be reduced. Moreover, even under the condition that the speed difference between the low speed and the high speed is twice or more, the difference in the current value between the low speed and the high speed can be reduced, so that the motor can be downsized. Moreover, since it is not necessary to consider the amount of current at low speed, the current can be set so that a large torque can be obtained at high speed.

In the above embodiment, the feed roller 20 and the conveying rollers 23 and 24 are driven by the second speed control motor 51. However, it is needless to say that the present invention can be applied to all rollers controlled at the second speed. Yes.

Further, in this embodiment, the paper transporting device for transporting the paper in the printer has been described, but the present invention is not limited to this, and is housed inside such as a copying machine or a facsimile machine. Recorded media 1
The present invention can be applied to all apparatuses that record information on the surface of these recording media while conveying them one by one.

[0060]

As described above, in the sheet conveying apparatus according to the present invention, the instruction signal for low speed conveyance or the high speed conveyance is output according to the position of the conveyed sheet, and the instruction signal for low speed conveyance is given. At this time, the stepping motor is driven by one-phase excitation, and when the high-speed conveyance instruction signal is given, the stepping motor is driven by two-phase or 1-2-phase excitation, so that the amount of current flowing at low speed is reduced. be able to. Therefore, even when the speed difference between the low speed and the high speed is twice or more, high torque can be obtained at the high speed and heat generation at the low speed can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a functional configuration of a sheet conveying device.

FIG. 2 is an explanatory diagram showing an input pulse signal and an excitation timing at a low speed (one-phase excitation).

FIG. 3 is an explanatory diagram showing a relationship between an input pulse signal and a current waveform at a low speed (one-phase excitation).

FIG. 4 is an explanatory diagram showing an input pulse signal and an excitation timing at a low speed (comparative example of 1-2 phase excitation).

FIG. 5 is an explanatory diagram showing a relationship between an input pulse signal and a current waveform at a low speed (comparative example of 1-2 phase excitation).

FIG. 6 is an explanatory diagram showing an input pulse signal and excitation timing at high speed (1-2 phase excitation).

FIG. 7 is an explanatory diagram showing a relationship between an input pulse signal and a current waveform at a high speed (1-2 phase excitation).

FIG. 8 is an explanatory diagram showing an input pulse signal and excitation timing at high speed (two-phase excitation).

FIG. 9 is an explanatory diagram showing a relationship between an input pulse signal and a current waveform at high speed (two-phase excitation).

FIG. 10 is a conceptual cross-sectional view of a printer to which the sheet conveying device according to the invention is applied.

[Explanation of symbols]

1 ... Printer, 8 ... Image forming means, 11 ... Paper, 12 ...
First paper cassette, 20 ... Feed rollers, 21, 2
2 ... Second paper guide chute, 23, 24 ... Conveying rollers, 25 ... Registration roller, 50 ... Paper conveying device, 51 ... 2
Speed control motor, 52 ... Control unit, 53 ... Drive circuit, 54 ...
Power supply, 55 ... Paper feed sensor

Claims (2)

[Claims] 1. A roller for conveying a sheet, a stepping motor for driving the roller, pulse signal generating means for generating at least two kinds of input pulse signals for low speed and high speed, and based on the input pulse signal. And a magnetizing means for exciting the coils of the stepping motor in a predetermined order, and transporting a sheet at at least two types of transport speeds, a low-speed transport or a low-speed transport depending on the position of the transported paper. An instruction signal output means for outputting an instruction signal for high-speed conveyance is provided, and the pulse signal generation means receives an input pulse signal for low speed when the instruction signal for low-speed conveyance is given from the instruction signal output means, and also for high-speed conveyance. Input pulse signals for high speed are respectively generated, and the exciting means is configured to output the low speed conveyance finger from the instruction signal output means. The coil of the stepping motor is set to one-phase excitation when a signal is given, and the coil of the stepping motor is set to two-phase or 1-2-phase excitation when a high-speed conveyance instruction signal is given. Paper transport device. 2. The sheet conveying apparatus according to claim 1, wherein the roller is a conveying roller that conveys the sheet accommodated in the sheet cassette in the image forming apparatus to the image forming unit.