Image reader for use in image forming apparatus

An image reader comprising:

• a CCD sensor for converting image information into image data composed of electrical signals,
• a mirror set for transmitting image data on an object of reading to the CCD sensor;
• a movement mechanism for moving the mirror set and/or the object of reading at a given speed;
• a drive unit for generating driving force;
• a driving force transmission mechanism for transmitting the driving force generated by the drive unit to the movement mechanism;
• and
• a transmission condition changing mechanism capable of changing a condition for the transmission of the driving force generated by the drive unit when a peak of a fluctuation frequency detected by means of a fluctuation detector is equal to a natural frequency of the drive unit, the fluctuation detector being externally connectable and capable of processing an output signal from the CCD sensor and detecting the fluctuation frequency attained as the movement mechanism is moved.

A method for detecting and restraining a fluctuation of an image of an image reader, comprising:

• transmitting image information on a straight-line image, extending in a first direction and having a length equal to the width of each pixel in a second direction perpendicular to the first direction, to a light receiving surface of a CCD sensor by means of a mirror set;
• moving the mirror set or the image in the first direction so that image data, continuous in the first direction and photoelectrically converted by means of the CCD sensor, is subjected to Fourier conversion;
• obtaining a frequency of a fluctuation of the image data obtained by the Fourier conversion and a maximum value of the amplitude thereof;
• comparing the frequency of the fluctuation with a natural frequency of a drive motor for generating driving force for moving the mirror set or the image in the case where the maximum value of the amplitude of the fluctuation is greater than a given value;
• increasing the level of current supplied to the drive motor in the case where the frequency of the fluctuation and the natural frequency are equal;
• and
• changing a condition for the transmission of the driving force from the drive motor to a mechanism for moving the mirror set or the image in the case where the frequency of the fluctuation and the natural frequency are not equal.

An image reader comprising:

• a transparent plate member for holding a test chart carrying thereon an image extending in a first direction and having a length equal to the width of each pixel in a second direction perpendicular to the first direction;
• an illuminating device capable of illuminating the test chart set on the plate member, thereby obtaining a reflected light containing image information on the test chart;
• a CCD sensor for photoelectrically converting the reflected light and outputting image data corresponding to the image information;
• a mirror member for transmitting the reflected light toward the CCD sensor;
• a carriage member for moving the illuminating device and the mirror member along the transparent plate member;
• a motor for generating driving force;
• a driving force transmission member for transmitting the driving force generated by the motor to the carriage member;
• and
• an image data input-output section connected with a fluctuation detector externally connectable and capable of processing the image data delivered from the CCD sensor and detecting the fluctuation frequency attained as the carriage member is moved.

A system capable of reducing fluctuation components of read image data attributable to oscillations of movable parts and movable components of an image reader having the movable parts and components and resonance of the whole image reader, comprising:

• a transparent plate member for holding an object of reading including a test chart;
• an illuminating device capable of illuminating the object of reading set on the plate member, thereby obtaining a reflected light containing image information on the object of reading;
• a CCD sensor for photoelectrically converting the reflected light and outputting image data corresponding to the image information;
• a mirror set for transmitting the reflected light toward the CCD sensor;
• a carriage member for moving the illuminating device and the mirror set along the transparent plate member;
• a motor for generating driving force;
• a driving force transmission member for transmitting the driving force generated by the motor to the carriage member;
• and
• an image data input-output section connected with a fluctuation detector externally connectable and capable of processing the image data delivered from the CCD sensor and detecting the fluctuation frequency attained as the carriage member is moved,
• wherein the image information on the test chart is transmitted to a light receiving surface of the CCD sensor by means of the mirror set,
• the image data continuous in a first direction, outputted as the image information on the test chart is photoelectrically converted by means of the CCD sensor when the mirror set or the test chart is moved in the first direction, is subjected to Fourier conversion by means of the fluctuation detector connected by means of the image data input-output section,
• the frequency of a fluctuation of the image data obtained by the Fourier conversion and a maximum value of the amplitude thereof are obtained,
• the frequency of the fluctuation is compared with a natural frequency of the drive motor for generating the driving force for moving the mirror set or the image when the maximum value of the amplitude of the fluctuation obtained by means of the fluctuation detector is greater than a given value,
• the value of current supplied to the drive motor is increased when the fluctuation frequency and the natural frequency are equal, and
• a condition for the transmission of the driving force from the drive motor to a mechanism for moving the mirror set or the image is changed when the fluctuation frequency and the natural frequency are not equal,
• in the case where the object of reading is the test chart containing the image information on a straight-line image having a length equal to the width of each pixel in a second direction perpendicular to the first direction.