JPH0295198A - Driving device for document scanning - Google Patents

Abstract

PURPOSE:To enable picture reading having high accuracy in a low vibrations at the time of forwarding and optical system reading at high speed by large torque at the time of backing, and to eliminate the need for the improvement of the mechanical strength of an optical system and to reduce the cost of a device by changing over the drive control of a stepping motor used for driving the optical system of a copying machine in forwarding and backing. CONSTITUTION:A means 116 changing the sequence of a signal exciting a stepping motor 108 and a means 115 controlling currents or voltage flowing through the stepping motor 108 are provided. A driving method is changed over in response to the conditions of the drive of the stepping motor 108, and energy supplied is varied in response to the state of the drive of load and the alteration of torque required. To be concrete, the scanning rates of the scanning optical systems 101-103 of a copying machine are changed over at the time of the reading and scanning of a document and at the time of return scanning. Accordingly, vibrations peculiar to the stepping motor 108 are inhibited, thus largely increasing the speed of copying.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving device for a copying machine, and particularly to a driving device using a stepping motor.

[Conventional technology]

Conventionally, LBP (laser beam printer) and CCD
In a copying machine directly connected to an original reading device using a line sensor (charge coupled device) or the like, the continuous copying speed is determined by the return scanning time of the original scanning optical system. This is because printers are capable of continuous paper feeding, so the interval between each recording paper can theoretically be reduced to zero.

However, for example, in the case of continuous copying in a document reading device without page memory, between each document reading scan,
A return scan is required to return the optical system to the reading starting position. As a result, the distance between each recording sheet increases by the time required for this return scan, and the number of copies per unit time decreases.Therefore, attempts have been made to shorten the return time of the scanning optical system. However, there are increasing cases where the return scanning speed is required to be seven times or more the forward speed.

When a stepping motor is used as a driving device for a copying machine, a problem arises due to unique vibrations caused by driving pulses of the stepping motor. Therefore, this problem has been dealt with by using methods such as increasing the mechanical strength and mechanically shifting the natural frequency by one order of magnitude or more from the drive pulse frequency.

[Problem to be solved by the invention]

However, there is a problem in that an increase in mechanical strength leads to an increase in the size of the device or an increase in cost.

Further, for example, the scanning speed range of the scanning optical system of a copying machine can reach as much as 60 times the ratio of the minimum scanning speed to the maximum scanning speed, depending on the magnification ratio and scanning direction.

However, there is a problem in that it is often not possible to set a mechanical natural frequency outside the entire drive frequency band of the stepping motor that supports these wide range of scanning speeds.

SUMMARY OF THE INVENTION An object of the present invention is to provide a document scanning drive method that solves the above-mentioned problems and can significantly increase the copying speed of a copying apparatus.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a stepping motor as an original scanning drive source, a means for switching the sequence of signals for exciting each phase of the stepping motor, and a stepping motor as a document scanning drive source. A document reading device having means for controlling at least one of a current or a voltage flowing through a motor includes means for switching drive control of a stepping motor between document reading scanning and return scanning.

[For production]

According to the present invention, means for changing the sequence of signals that excite the stepping motor and means for controlling the current or voltage flowing through the stepping motor are provided, and the driving method is switched according to the driving conditions of the stepping motor to load the stepping motor. By changing the supplied energy in accordance with the driving state of the stepping motor and in response to changes in the required torque, vibrations peculiar to stepping motors can be suppressed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 shows the configuration of a copying apparatus according to an embodiment of the present invention. The main parts of this device include an operation section 109 for determining copy conditions;
A 5M driver 115 outputs an excitation signal 11.40 to a stepping motor (hereinafter abbreviated as SM), and a CPU (central processing unit) 116 sends a control signal to the SM driver 115 in accordance with instructions from the operation unit 109. The CPI 1116 is provided with a memory 116A, which stores a control program according to the flowchart shown in FIG. Before explaining the entire device, first, the 5M driver 115 will be described. Components other than those mentioned above will be described later.

FIG. 2 shows the Sl Kleiber path. One SM bipolar drive unit 301 is required for each phase of the 5M108, and therefore, four are required when the 5M108 has four phases.

The driving method of the circuit shown in FIG. 2 is called constant current chopper driving, and 302 is a chopper circuit. FIGS. 3(A) and 3(B) show the principle of constant current chopper driving of the chopper circuit 302. FIG. The reference voltage is the triangular wave shown by reference numeral 38 in FIG.
The current is kept constant by converting the current of 8 into a voltage and applying a motor voltage to the 5M 108 only in the section where this voltage is lower than the reference voltage, as shown in FIG. 3(B). 304 is a PWM (pulse width modulation) comparator, and 304B is an amplifier.

Due to this constant current chopper drive, the current flowing through the 5M108 becomes constant, and the current rises from off to on and falls from on to off become steep.
The responsiveness of M108 to high-speed rotation is improved.

Furthermore, by raising and lowering the voltage level of the triangular wave that is the reference voltage, it becomes possible to raise and lower the SM drive current level, which is kept constant. In other words, the voltage across the resistor 307 becomes an offset voltage with the output voltage of the oscillator 304 for determining the reference voltage (the voltage at point A in FIG. 2), so the voltage across the resistor 307 becomes By changing the current flowing through the 5M108 according to the C signal, the current flowing through the 5M108 can be changed according to the C signal.

When resistors 306 and 307 are respectively set to 1Ω, C
When the signal is +5■, the diode 308 is cut off, so the offset voltage is
It becomes 2.5V determined by the partial voltage ratio of 07. When the C signal is Ov, the diode 308 becomes conductive, and the resistor 307 has a forward voltage of 0.7
V is applied.

Therefore, by setting the C signal to Ov, the reference oscillation level in FIG.
08 is driven and controlled with a smaller electric combing value.

303 is a phase signal generation circuit, which generates phase excitation signals A and B to 5M108 in steps synchronized with the pulse signal CLK output from the CPU 116, as shown in FIG.

Output C, D, A, B, C and D. 4 phase 5M1
In the case of 08, the F/H signal is a signal for switching between full step drive in which the rotation angle in one pulse is 09 degrees and half step drive in which the rotation angle is 0.45 degrees.

Phase signal generation circuit 303 LL, F/H signal power 1
” At (f), in order to perform full step drive, a phase excitation sequence of four-phase excitation, that is, a phase excitation sequence of the forward drive dark region shown in the direction of arrow a in FIG. 4 is output. When the signal is "0°", a phase excitation sequence of 3-4 phase excitation to perform half-step drive, that is, a phase excitation sequence of backward drive dark region shown in the direction of the arrow in Fig. 4 is output. do.

Furthermore, control regarding the rotational direction of the 5M108 is performed by the F/■ signal. When the F/B signal is 1'', the phase signal generating circuit 303 controls the F/B so that it rotates in the opening direction, that is, in a copying machine, performs forward drive when reading an original.
When the signal is 0°, the pulse sequence is 5M10, as shown in Fig. 4, so as to perform counterclockwise or reverse drive.
Generates 8 phase excitation signals.

In FIG. 1, the rotation of 5M108 is transmitted to a pulley 107 attached coaxially with 5M108, and is transmitted to a pulley 10 having the same diameter as pulley 107 via a timing belt 117.
6. Pulleys 105 and 106 are coaxially attached, and wire 1 attached to pulley 105
18 drives the carriage 103.

The carriage 103 includes a light source 101 that illuminates the original and a contact sensor 102 that receives reflected light from the original. The ratio of the diameters of pulley 105 and 10ft is 3.1, so when 5M108 rotates 3 times, pulley 105 rotates 1
Rotate. Since the diameter of the pulley 105 is 48.9+nm, the process speed in this example is 84 mm.
/sec (original scanning speed at 100% copying magnification)
When half-step driving of deg is performed, 1312pps
It can be seen from the following equation that 5MIO3 is driven at a pulse frequency of .

= 1312 (pps) In other words, the carriage 103 has 0.64 (μ
m ) (84 (mm/5ec) ÷ 1312 (pul
se/5ec)) will be moved.

As described in the conventional example, in order to increase the copying speed in a continuous paper feeding copying machine, it is necessary to return the carriage 103 as quickly as possible after reading the document and shorten the interval until the next paper feeding.

The process speed of the copying machine in this example is 84 mm/sec.
In order to copy 20 sheets of A4 size paper (paper length 210 mm) per minute, the paper spacing should be set to 4 as calculated from the following formula.
2mm (time interval 500m5ec = 42
(mm) ÷ 84 (mm/sec>).

Copying time for one sheet of 4 size paper (sec) x Process speed (mm/5ec) - (60 (sec)/2
0) x 84 (mm/sec) 210 (mm) =
4'2mm The actual copying procedure with the configuration above is explained by the CPU 11 in Figure 5.
The explanation will be based on the control sequence flow of No. 6. When copying is to be performed, first, in step 5501, copying conditions such as paper size and copying magnification are set.

The paper size is set using a paper selection key 113 provided on the operation panel 109, and the copy magnification is set using a copy magnification setting key 112. Now, assume that a magnification of 100% is set for 4-size paper.

The set copying conditions are sent to the CPU 116, and based on these, the scanning distance and scanning speed are calculated in step 5502. When the magnification is 100% for A4, the scanning distance is 210 mm (the length of A4 size paper) and the scanning speed is 1312 (pps) as described above.
)÷1). When it is confirmed in step 5503 that the copy key 110 has been pressed, step 5
The process moves to forward drive 504. During forward driving, the F/B signal is set to "i" and half-step driving is performed, so the F/H
The signal is set to '0°', and further the CD signal is set to '0°' in order to reduce the current without flowing to SMI 08. and 13
A pulse signal CLK is output at a frequency of 12 (pps).

However, when reading a manuscript at a constant speed, suddenly 131
2 (+11IS), the vibration immediately after startup becomes large, so as shown in Figure 6, 50n
(pps) , 1000 (pps) , +31
Increase the speed step by step to 2 (pps), and then increase the speed to 1
312 (pps), a vibration absorption time of 20 (msec) is set. Therefore, it takes 50 (msec) of time (the number of panels is 41 pulses) shown in the shaded area in Figure 6 to actually read the manuscript.To read an A4 size manuscript, it takes 3280 (pulses) (
= 210 (mm) ÷ 0.64 (p m / pu
lse) ) need.

Therefore, when you start reading a document at a constant speed +312 (pps), in step 5505, 3280 (pul
se) and the number of rising pulses 41 (pulse)
In total, 3321 (pulses) are counted and the forward drive is completed.

When the forward drive is finished, the process moves to step 5506, where the process moves to backward drive. During reverse drive, the F/B signal is set to 0°', and since it is a full-step drive, the F/H signal is set to 1°, and the CD signal is set to 1° because the rated current does not flow through SM.Then, the pulse signal CLK will be output, but 5M10
Since there is a limit to the acceleration that 8 can respond to, as shown in Figure 6, when driving backwards, every 10 m5 at the beginning and end, 10
The speed is accelerated and decelerated in steps of 00 (pps). 1000
0 (pps) is close to the limit frequency to which the 5M108 used in this example can respond.

Therefore, when going backwards, the home position (1
-IP) is difficult to return to.

Here, the time required for backward drive is 432 m5 ec, which is the time set to return within 550 m5 ec, which is the sum of the paper interval time of 500 m5 ec and the rising time of the shaded area during forward drive of 50 m5 ec.

3321 (puls
e) in step 5507, as shown in FIG.
The constant velocity drive section B is driven with 2321 pulses, and the deceleration drive section C is driven with 500 Hals pulses.

The reason why half-step drive is used when moving forward is that when 5M108 is used as a drive device as described in the conventional example, the unique vibration caused by the drive pulse becomes a problem, but half-step drive reduces the pulse frequency. This is because vibration can be suppressed by increasing the height. In other words, the vibration of 5M108 tends to increase at low frequencies,
Furthermore, it is the low frequency vibrations that are noticeable on the image. Furthermore, in half-step driving, since the rotation angle per pulse is small, the vibration per pulse becomes smaller. However, since vibrations during reversing do not affect image formation, full-step drive is used to achieve the highest speed when reversing.

Also, in order to move the 5M108 at high speed when going backwards, the 5
M108 requires large torque. However, when moving forward, the speed is low and a large torque is not originally required, so if a large torque is used to rotate at a low speed when moving forward, large vibrations will occur. For this purpose, on the path 115 to the SM try-out shown in FIG.
It becomes necessary to control the current flowing through 108. In other words, when driving forward at low speeds and when large torque is not required, 5M1
The torque of 5M108 is reduced by reducing the current flowing through 08, and the rated current is passed through 5M108 when driving in reverse, which requires large torque at high speed rotation.

Embodiment 2 There are two ways to drive a stepping motor: constant voltage drive and constant current drive. As explained in Embodiment 1, constant current drive requires turning on the voltage, This is a drive in which the current is kept constant by repeatedly turning off, and the current rises steeply. Therefore, although the high-speed response is improved, the sudden change in the value of the current flowing through the SM often makes the vibration of the SM jerky. Therefore, when the 5M108 is used in the driving device of the scanning optical system of a copying machine as shown in Fig. 1, the vibration becomes a problem, and the 5M108 moves only at a relatively low speed when reading documents, that is, when driving forward. It is conceivable to use constant voltage drive with relatively little vibration.

Constant voltage driving is a method of driving using a constant voltage source,
The rise time of the current is determined by the time constant L/R due to the resistance R and inductance of the motor windings. The current rise due to this time constant is slower than in constant current driving, so high-speed response is poor, but the vibration of 5M108 is reduced.

However, during reverse driving, high-speed rotation is required as described in the first embodiment, so it is necessary to perform constant current driving. Therefore, by switching between surface drive during forward drive and reverse drive, optimal drive becomes possible.

FIG. 7 shows a circuit for this purpose. In Figure 7, the second
The same parts as in the figure are given the same reference numerals.

The signal V/C that changes constant current drive to constant voltage drive is "1"
” (+sv), the output of the chopper circuit 302 described in Example 1 becomes Ov, and the current detection resistor 305 is also short-circuited, changing from constant current chip drive to constant voltage drive. Signal When V/C is o'' (+ov), constant current liquid drive is performed.

This signal V/C is used in the same manner as the current down signal CD of the first embodiment in the actual copy sequence, and is used at a level of 1° to 1° for constant voltage drive control of SMI 0B when the optical system moves forward. Sometimes CPI111 is set as °0“ level for constant current drive control of 5MIO3.
6.

〔Effect of the invention〕

As explained above, in the present invention, a means is provided for switching the drive control of the stepping motor used to drive the optical system of the copying machine between forward and backward movement of the optical system, so that when the optical system is moving forward, it can be operated with low vibration and high precision. During image reading and when moving backward, high-speed optical system reading is possible due to large torque, and there is no need to improve the strength of the mechanical optical system, which has the effect of reducing device costs.

In addition, the simple switching means described above makes it possible to shorten the time for the optical system to move backward without deteriorating the read image quality when the optical system moves forward. It is possible to significantly speed up high-quality copying devices.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a circuit diagram of a 5M driver for driving a constant current chopper in an embodiment of the invention, and Fig. 3 is the chopper circuit shown in Fig. 2. Fig. 4 is a time chart of an embodiment of the present invention, Fig. 5 is a 5M drive flowchart of a copier according to an embodiment of the invention, and Fig. 6 is an embodiment of the invention. FIG. 7 is an SM driver circuit diagram of another embodiment of the present invention. 101...Light source, +02...Contact type sensor, 103...Carriage, 104...Document stand, 105.106,107...Pulley, 108...
Stepping motor (SM), 109...Operation unit, 110...Copy key 111...Copy magnification display section, 112...Copy magnification setting key 113...Paper selection key 115...Stepping motor try Ba, 116...
・CPU (central processing unit), 117... Timing belt, 118... Wire, 301... SM bipolar drive unit equivalent to 1, 302
... constant current chopper drive unit, 303 ... phase signal generation circuit, 304 ... triangular wave oscillation circuit, 306.307 ... resistor, ... diode.

Claims (1)

[Claims] 1) A stepping motor as a document scanning drive source;
A document reading device comprising means for switching the sequence of signals for exciting each phase of the stepping motor, and means for controlling at least one of a current or a voltage flowing through the stepping motor, wherein drive control of the stepping motor is performed during document reading. A document scanning drive device characterized by comprising means for switching between scanning and return scanning.