JPH0258079A - Optical system driving method - Google Patents

Abstract

PURPOSE:To suppress a large current and reduce a mechanical shock when a driving motor for an optical system for exposure is scanning is inverted by adding a brake mode for the inversion. CONSTITUTION:When the driving motor M for the exposure optical system of an image reader which is normally rotated with transistors(TR) Q1 and Q2 on, and Q3 and Q4 off is inverted, only the TR Q2 is turned off with a short brake command. Consequently, a closed loop is formed of the TR Q2 and a diode D1 for the motor M, which enters a power generation brake state and is reduced in speed to a specific value. When an inversion command is generated at this point of time, the TRs Q1-Q4 are controlled and the motor M inverts. Inversion from backward rotation to forward rotation is the same and the addition of the brake mode suppresses a current flowing through the motor M to a small current to reduce the load on a switching element and also reduce the mechanical shock. Consequently, respective parts of the device are improved in stability and the life is prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a driving section of an optical system for exposure scanning of an image reading device.

[Background of the invention]

An image reading device is incorporated into, for example, a copying machine, and reads an image of a document and transmits the image information to an image forming section.

FIG. 3 is a diagram schematically showing the copying apparatus.

The original on the top surface of the platen glass 1 is exposed and scanned by a light source 2 moving in the direction of arrow a, and the optical image of the original obtained there passes through mirrors 3 to 6 and a lens system 7, and is exposed to high voltage by a charged electrode 8 in advance. incident on the charged photoreceptor drum 9,
An electrostatic latent image is formed there. The parts numbered 2 to 6 above constitute an optical system. Then, the latent image is transferred to the developing unit I.
The toner image is developed by O and converted into a toner image, and this toner image is transferred to a transfer paper fed from a registration roller 11 at a transfer pole 12, and the transfer paper is further transferred to a separation pole 13.
The sheet is separated from the photoreceptor drum 9 at 100, and is conveyed through the conveyance heald 14 to the thermal fixing roller 15, where it is fixed and ejected.

The toner remaining on the photoreceptor drum 9 is removed from the cleaning section 16.
It is cleaned by the charging electrode 8 and then charged again by the charging electrode 8 in preparation for the next latent image formation. The transfer paper is fed out from the cassette 17 by a feed roller 18, and is fed to a double feed prevention heald 19.
The images are fed one by one by the roller 20 to the registration roller 11 via the guide 21 and then put on standby, and then sent out as described above at the timing when the leading edge of the image on the photosensitive drum 9 coincides with the leading edge.

The light source 2 and the mirror 3 are integrated, and the mirror 4
and 5 are also integrally constructed, and the latter travels at yv in the same direction as the former with respect to the traveling speed of the former, and the optical system is driven so that the optical path length is always the same. This drive is performed in one reciprocating motion for each copy, and the DC motor of the drive portion is controlled as follows.

FIG. 4 is a diagram showing the control section, where M is a DC motor,
Q1 to Q4 are control transistors, and D1 to D4 are diodes.

During exposure scanning of the light source 2, that is, when moving in the direction of arrow a, the motor M rotates in the normal direction, and when moving in the opposite direction to the direction of the arrow a, it rotates in the reverse direction. transistors Q2 and Q3 are turned off, and current flows through the motor 22 in the direction indicated by the solid arrow. Further, when changing from normal rotation to reverse rotation, a command for reverse rotation is immediately given, transistors Q2 and Q3 are turned on, and transistors Q1 and Q4 are turned off in a few microseconds. FIG. 2 is a diagram showing the switching characteristics with respect to motor speed and induced voltage.

[Problem to be solved by the invention]

Therefore, in conventional optical system drive control, when switching the rotational direction of the motor M, rV+ is applied to both ends of the motor M.
An induced voltage of +V2 J is added, and an extremely large current determined by this voltage and the DC resistance inside the motor M flows, placing a large burden on the transistors Q1 to Q4, which are drive elements. The problem was that things were required. Furthermore, there is a risk that a large shock may occur during reversal from normal rotation to reverse rotation or from reverse rotation to normal rotation, which may adversely affect mechanical parts.

The present invention has been made in view of these points, and its purpose is to prevent the above-mentioned problems from occurring during reversal.

[Means to solve the problem]

For this reason, the present invention is configured such that when the motor that drives the optical system is reversed, a reversal command is given after the short brake mode is set.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing characteristics of motor control in one embodiment. In this example, when reversing from normal rotation to reverse rotation, a short brake is applied first, and a reversal command is issued when the motor speed has decreased to a predetermined value 1' or when time T has elapsed. Transistor switching is performed in the same way as in the past.

That is, during forward rotation, current is supplied to the motor M with transistors Q1 and Q4 turned on and transistors Q2 and Q3 turned off, and when a short brake command is issued, only transistor Q2 is turned on. As a result, motor M
, a closed loop is formed by the transistor Q2 and the diode D1, and a regenerative braking (generation braking) state is established, and the brake is applied. Therefore, since the motor M gradually decelerates, a reversal command is issued when its speed reaches 2,' or when time T has elapsed, and the mode is switched to the reversal mode. This causes a switch to reverse rotation after some reverse braking.

At this time of reversal, a voltage of 'VH' +VZ J is applied to the motor M, and a current determined by this voltage and the above-mentioned resistance value flows. This current is small compared to the current in the previous case,
Transistors Q1 to Q4 are not required to have large capacitance. Furthermore, the speed at the time of reversal is reduced to VI', and the shock is also significantly reduced. Furthermore, although not shown, when the speed of the motor M is controlled by a circuit such as a PLL, the damping characteristics are also improved and the time required to reach the target speed can be shortened.

The above is the case when reversing from normal rotation to reverse rotation, but for short braking when reversing from reverse rotation to normal rotation, only transistor Q3 is turned on, and a closed loop is formed by transistor Q4 and diode D3.

〔Effect of the invention〕

As described above, according to the present invention, a large current at the time of reversal can be suppressed, and the load on the switching element is reduced. Furthermore, since mechanical shock can be reduced, lamp life and wire life are extended, and reliability is improved.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of motor control according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of conventional motor control, FIG. 3 is a schematic configuration diagram of a copying machine, and FIG. 4 is a circuit diagram of a motor drive section. This is a diagram. Agent Patent Attorney Tsuneaki Nagao 1st 1me 2nd ime

Claims (1)

[Claims] (1) A method for driving an optical system for exposure scanning of an image reading device, characterized in that when reversing the motor for driving the optical system, a reversal command is given after setting the short brake mode. .