JPH02211080A - Method of controlling speed - Google Patents

Abstract

PURPOSE:To prevent a vibration from generating by controlling to decelerate at a second stage after controlling to decelerate at a first stage. CONSTITUTION:An origin base 1 is reciprocated by the rotation of the shaft 3 of a motor 2. Its speed controller is composed of a PLL control loop having four transistors 4, a phase comparator 5, a filter 6, a PWM comparator 7, a triangular wave generator 8 and a pulse generator 9. A current detecting resistor 21 of the motor 2 is provided, a potential difference across the resistor is detected, and a current limit signal 23 is output from a current limiter 22. A deceleration is moderated at a first stage of deceleration control as compared with that at a second stage. After the speed is decelerated, it is so controlled as to move to a constant speed at a third stage and to again decelerate it.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the speed of a document table of a copying machine or a scanner at the time of return.

[Technical Background of the Invention] Many copying machines reciprocate a document table or a scanner (hereinafter simply referred to as document table) to form an electrostatic latent image of a document on a photoreceptor. In this type of copying machine, in order to increase the number of copies per unit time, it is necessary to move the document table back and forth at high speed.

In particular, it is preferable that the return speed, which is not related to image formation, be as fast as possible.

FIG. 1 shows an apparatus using a conventional document table speed control method. The document table 1 is configured to perform reciprocating motion by the rotation of the shaft 3 of the motor 2. The motor 2 turns on and off the four transistors 4'-1 to 4-4.
The rotation direction is controlled by the off control, and the phase comparator 5,
The rotation speed is controlled by a PLL control loop consisting of a filter circuit 6, a PWM comparator 7, a triangular wave generation circuit 8, and a pulse generator 9.

First, when the document table l moves forward, the second and third transistors 4-2, 4-3 are turned on by the operation of a control circuit (not shown). In this state, the phase comparator 5 is supplied with a clock signal 11 of a predetermined frequency. The phase comparator 5 receives a rotational speed signal 12 proportional to the rotational speed of the motor 20 from the pulse generator 9, and compares both signals 1112.

Then, an error signal 13 having a pulse width corresponding to these phase differences is output. The error signal 13 is input to the PWM comparator 7 via the filter circuit 6. The PWM comparator 7 receives a triangular wave signal supplied from the triangular wave generating circuit 8! 4, the output signal 15 of filter circuit #6 is pulse-width modulated. The motor drive pulse signal 16 thus obtained is supplied to the excitation coil of the motor 2, and the document table moves forward at a constant speed.

FIG. 2A shows the rotational speed of the motor in this copying machine for one reciprocating motion. Section T in the figure represents the forward movement section, and section 1 T represents the backward movement section. The area in which the speed is constant in section T1 is used for scanning the document.

When the document table l moves backward, the second and third transistors 4-2, 4-3 are turned off, and the first and fourth transistors 4-L 4-4 are turned on instead. Further, a higher frequency signal is supplied to the phase comparator 5 as a clock signal 11.

As a result, the motor 2 rotates at high speed in the opposite direction, and the document platen 1
begins to return rapidly. In section B, just before the end of the return, the second and third transistors 4-2, 4-3 are turned on again, and reverse braking is performed. 7
Thereafter, the motor 2 is driven at a constant speed at a low speed, and then the document table 1 is stopped at its starting position.

FIG. 2(B) shows changes in the current flowing through the motor during the above-mentioned reciprocating motion.

As can be understood from this figure, a large current flows at time C when reverse braking starts. This current is limited by the armature resistance of the motor 2 and the capacitance of the second and third transistors (power transistors 4-2.4-3), but it has a considerable value. C is subjected to rapid braking, which generates vibrations.This vibration may remain when the document table l moves forward, and may affect images. Shortening the return time has been difficult to achieve.

[Object of the Invention] In view of the above-mentioned circumstances, an object of the present invention is to provide a speed control method that can smoothly stop the document table of a copying machine at a fixed position in a short time.

[Means for Achieving the Object] The present invention provides a document reading method in which the document table or scanner, which reciprocates by driving a motor, performs deceleration control in the latter half of the backward motion to stop the document table or scanner at a desired position. In the speed control method of the apparatus, deceleration is performed more gently in the first stage of the deceleration control than in the second stage, and the speed of the document table or the scanner is decreased in the first stage and the second stage of the deceleration control. , in the third stage of deceleration control, the document table or scanner is moved at a nearly constant speed, and then in the fourth stage
At this stage, deceleration is performed again to stop the document table or scanner.

That is, in the present invention, by performing the second stage deceleration control after the first stage deceleration control, a sudden rise in deceleration is prevented and vibration of the document table is prevented. Also the second
By providing the third stage deceleration control after the first stage deceleration control, the document table is prevented from stopping abruptly, and the occurrence of vibration of the document table is also prevented. Moreover, by once shifting to the third deceleration control and then shifting to the fourth deceleration control near the desired stop position, an accurate stop position is ensured.

The present invention will be described in detail below with reference to Examples.

[Embodiment] Fig. 3 shows an apparatus using the document table speed control method according to this embodiment. Components that are the same as those in FIG. 1 are designated by the same reference numerals, and their descriptions will be omitted as appropriate. This device is provided with a current detection resistor 21 for detecting the current flowing through the motor 2. The current limiting circuit 22 detects the potential difference generated across the current detection resistor 210, and outputs a current limiting signal 23 that becomes H (high) level when this potential difference is less than a predetermined value. The current limit signal 23 and motor drive pulse signal 16 are input to an AND circuit 24, and the output signal 25 controls the drive pulse width and current of the motor 2.

FIG. 4 corresponds to FIG. 3, with (A) showing changes in the rotational speed of the motor during reciprocating motion, and (B) showing changes in current. The speed control method of this embodiment will be specifically explained with reference to this figure.

First, when the document table 1 starts to move forward, the second and third transistors 4-2, 4-3 are turned on, and a large current begins to flow transiently into the excitation coil of the motor 2. The current limit circuit 22 uses this value as a predetermined limit value! (R), the current limit signal 23 is changed to L (low) level, and the second and third transistors 4-2, 4-3 are temporarily turned off. In this way, constant current control is temporarily performed at the start of scanning of the document table l. After this, the current limit signal 23 is held at H level, and the motor drive pulse signal 1
6 becomes the output signal 25 as it is, and constant speed drive control of the motor 2 to the area is performed.

In the reciprocating period T2, first and fourth transistors 4-1 and 4-4 are turned on in the first period. At this time, the clock signal 11 is set to a higher frequency, and the document table l
begins to return rapidly. Constant current control is performed during this first half acceleration period. When the document table 1 is driven at a constant speed of, for example, 800 mm for 7 seconds and reaches the vicinity of the home position, deceleration control is performed.

In this first section E, dynamic braking is performed (first stage deceleration control). In other words, only the first transistor 4-1 is turned on, and a closed circuit is formed between its emitter and collector, the amachinery resistor of the motor 2, and the diode connected in parallel to the fourth transistor 4-4. , the voltage induced by the rotation of the motor 2 is consumed.

In the next section F, reverse braking is performed (second stage deceleration control). At this time, constant current control is performed.

The document table 1 is smoothly decelerated by deceleration due to dynamic braking and current limitation during reverse braking. Furthermore, in the next section G, the first and fourth transistors 4-1, 4-4 are turned on again. At this time, the document table 1 moves back at a constant speed of about 200 mm for 7 seconds (third deceleration control) by the clock signal 11 set to a low frequency. And the last section H
Then, the second and third transistors 4-2, 4-3 are turned on, reverse braking is performed, and the document table l is stopped at the home position (fourth deceleration control).

Transistors 4-1 to 4-4 for each section explained above
The timing of the on/off operation is determined by time control from the start of scanning of the document table l. Of course, it is also possible to perform this by controlling the pulse count of the pulse generator 9. Further, in the device of the embodiment, the current of the motor 2 is limited inexpensively by the current limiting circuit 22, etc., but this may be done with high precision using a normal constant current circuit.

Further, in the embodiment, although dynamic braking and reverse braking are used to control the speed of the document table, similar speed control may be performed using other braking methods.

[Effects of the Invention] As explained above, according to the present invention, deceleration is performed more gently in the first stage of deceleration control than in the second stage, and the speed of the document table is sufficiently increased in the second stage of deceleration control. Once the original platen is lowered, the third stage of deceleration control moves the document table at a nearly constant speed, and the fourth stage
At this stage, the document table is decelerated again to stop it. Therefore, it is possible to prevent sudden rises and falls of deceleration, and even if the return time is reduced by a few seconds compared to conventional methods, it is possible to ensure a smooth stop of the document table and scanner, and it is possible to copy It also does not generate vibrations in the machine's casing. Therefore, the document can be scanned with high precision during the next forward movement of the document table or scanner, and it is possible to prevent image disturbances such as skipping or drifting of images, for example.

Furthermore, according to the present invention, it is possible to accurately stop the document table and scanner by one home position, and the deceleration control can be performed even when the motor load fluctuates, especially when a thick book is placed on the document table. At the stage , load fluctuations can be absorbed, the document table can be accurately stopped at a desired position, and the next document can be scanned with high precision.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a device using a conventional speed control method, Figure 2 (A) is a characteristic diagram showing the speed change of the document table due to this device, and Figure 2 (B) is the current flowing through the motor. FIG. 3 is a block diagram of a device using the speed control method according to an embodiment of the present invention.
FIG. 4(A) is a characteristic diagram showing changes in the speed of the stone document table in this embodiment, and FIG. 4(B) is a waveform chart showing changes in the current flowing through the motor. l...Original table, 2...Motor, 4...
...Transistor, 21...Resistor for current detection, 22...Current limiting circuit, 24...AND circuit. Applicant Fuji Xerox Co., Ltd.

Claims (1)

[Claims] In a speed control method for a document reading device, in which the document table or scanner, which is reciprocated by the drive of a motor, performs deceleration control in the latter half of the backward motion to stop the document table or scanner at a desired position, the first step of this deceleration control is The speed of the document table or scanner is reduced in the first and second stages of deceleration control, and the speed of the scanner is maintained at an almost constant speed in the third stage of deceleration control. A method for controlling the speed of a document reading device, which comprises moving the document table or the scanner, and then decelerating the document table or the scanner again in a fourth step to stop the document table or the scanner.