JPH08275496A - Signal detecting circuit for linear motor, linear motor, and image reader - Google Patents

Abstract

PURPOSE: To provide a signal detecting circuit for a linear motor which detects signals for controlling the motor operation with the reception of the output from a magnetic sensor for a linear encoder and which can eliminate, according to a specified driving velocity of a movable member, an offset caused by a field magnet for propulsion from the signal waves which are detected by the magnetic sensor and then are input into this detecting circuit. CONSTITUTION: A signal detecting circuit for a linear motor 6 receives the output of a magnetic sensor for a linear encoder S and detects signals for controlling the motor operation. In this detecting circuit 6, a high-pass filter circuit 61 is built in which eliminates, according to a specified driving velocity of a movable member, an offset which is caused by an influence of a field magnet for propulsion from signal waves of a fine-magnetized section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection circuit for controlling the operation of a linear motor, a linear motor provided with this circuit, and a linear motor for scanning an image in a scanning optical system of an original image. The present invention relates to an image reading device that drives a member.

[0002]

2. Description of the Related Art Today, various types of linear motors have been developed and applied to various devices. A linear motor usually includes a portion having a propulsion (driving) field magnet and a portion having an armature coil facing the field magnet, and one of these portions is movable as a stator and the other as a mover. Promote the child. Which one is the stator and which one is the mover can be decided in consideration of their respective merits. However, the armature coil movable by providing the stator with the propulsion field magnet and the mover with the armature coil Type linear motor has the advantage that the stator can be used as a guide means for the mover. For example, the stator is formed in a rod shape with a circular cross section, and the mover formed in a tubular shape is fitted into Those that drive the child along the stator are used.

The linear motor has a basic structure as described above, but in addition to this, normally, the position, the moving distance, the moving speed, etc. of the mover are detected for the control operation of the motor and the desired operation is performed. Therefore, an encoder is adopted. There are various types of encoders such as a magnetic type and an optical type. The magnetic type is provided on a magnetic sensor provided on a mover and a stator, and provides a magnetic signal to the sensor. And a fine magnetized portion (having magnetic poles arranged at a fine predetermined pitch).

In the magnetic encoder, the fine magnetized portion may be provided on the stator so as to be displaced from the field magnet. However, the field magnet is used for reasons such as the ease of manufacturing the stator including the fine magnetized portion. It may be formed on the magnet in an overlapping manner. On the other hand, the magnetic sensor normally detects a magnetic signal wave from the fine magnetizing section along with the movement of the mover, and the output of the sensor is a signal detection circuit for detecting a target signal for motor operation control. The signal obtained here is used for control operation of the motor.

[0005]

However, a stator having a field magnet for propulsion and a fine magnetizing portion for a linear encoder which is formed so as to overlap with the field magnet, an armature coil facing the field magnet, and In a linear motor provided with a mover having a magnetic sensor for detecting a magnetic signal wave from the fine magnetized portion, the signal wave from the fine magnetized portion detected by the magnetic sensor is affected by a field magnet. It includes the offset amount (deviation amount). Therefore, the target signal cannot be obtained accurately. This state is shown in FIG.
In FIG. 5A, a line a is a signal wave from the fine magnetized portion, and this signal wave is offset by the influence of the signal wave b from the field magnet, and an offset amount c is generated.

In a laser beam printer, the surface of an electrostatic latent image bearing member such as a photosensitive drum is scanned with laser light to reflect the laser light in order to form an electrostatic latent image corresponding to the original image. On the other hand, a so-called rotating polygon mirror is used which scans the surface of the electrostatic latent image carrier by shaking it at a constant cycle. In the rotary motor that drives this polygon mirror, a magnetized portion that serves as rotational position information is superposed on the rotor driving magnet as an element of an encoder that detects information about the rotation of the motor rotor for motor control. There is something. In the polygon mirror motor having the magnetized portion that provides the rotor position information in this way, the signal generated by the magnetized portion is offset (shifted) under the influence of the driving magnet.

Therefore, normally, a signal detection circuit which receives an output of the magnetic sensor and obtains a target signal, cuts this offset amount, and passes only the position signal from the magnetizing portion for providing position information. Incorporates a high-pass filter circuit. Therefore, it is conceivable to remove the noise signal from the signal detected by the magnetic sensor by using such a high-pass filter circuit even in the linear motor adopting the magnetic linear encoder described above.

However, when such a linear motor is used to drive a member to be moved for image scanning of an original image scanning optical system of an image reading apparatus such as a copying machine or an image scanner, the member is connected to a mover. However, the member moves the linear motor mover while changing the speed from the stopped state to acceleration → constant speed (image scanning) → deceleration → return (normally faster than constant speed) → stop. It may be driven by changing the speed according to.

Further, in the image reading apparatus, the driving speed of the scanning optical system may be changed depending on the image reading magnification. When the mover is driven by changing the speed in this way, not only the frequency of the signal wave from the fine magnetized portion detected by the magnetic sensor mounted on the mover but also the noise signal from the field magnet. The frequency of the wave also changes according to the speed of the mover. Therefore, in order to remove the offset, it is necessary to remove a noise signal having a frequency corresponding to the moving speed of the mover.

In this respect, since the polygon mirror motor is always operated at a constant speed, removal of the offset of the fine magnetizing part signal caused by the rotation driving magnet of the motor eliminates the noise signal of a constant frequency. Just enough,
Therefore, the above high-pass filter circuit is also configured only to cut a noise signal having a constant frequency. Therefore, this high-pass filter circuit cannot be applied to a linear motor that drives a mover by changing its speed, such as a linear motor used to drive a scanning optical system of an image reading apparatus.

Therefore, in the present invention, firstly, a stator having a field magnet for propulsion and a fine magnetizing portion for a linear encoder formed on the field magnet, an armature coil facing the field magnet, and the above For a linear motor that receives an output of the magnetic sensor of a linear motor including a mover having a magnetic sensor that detects a magnetic signal wave from a fine magnetizing portion and detects a target signal for motor operation control A signal detection circuit, the offset amount resulting from the field magnet from a signal wave detected by the magnetic sensor and input to the linear motor signal detection circuit according to a predetermined driving speed of a linear motor mover. It is a first object of the present invention to provide a signal detection circuit that eliminates the above and can obtain a target signal with high accuracy.

Further, the present invention provides a stator having a propulsion field magnet and a fine magnetizing portion for a linear encoder which is superposed on the field magnet, an armature coil facing the field magnet, and the fine magnet. A linear motor provided with a mover having a magnetic sensor for detecting a magnetic signal wave from a magnetizing unit, wherein an offset component caused by the field magnet is removed from a signal wave detected by the magnetic sensor. A second object is to provide a linear motor that can perform control operation with such high accuracy.

Further, the present invention is an image reading apparatus in which at least one member of the scanning optical system for scanning an original image, which is to be driven for image scanning, is driven by a linear motor. A third object is to provide a linear motor that can be controlled and operated accurately according to the speed and that can perform image scanning as accurately and smoothly as that.

[0014]

A signal detecting circuit for a linear motor according to the present invention which solves the first problem is a field magnet for propulsion and a fine magnetizing for a linear encoder which is formed to be superposed on the field magnet. An output of the magnetic sensor of a linear motor including a stator having a portion, an armature coil facing the field magnet, and a mover having a magnetic sensor that detects a magnetic signal wave from the fine magnetized portion. A signal detection circuit for a linear motor that receives and detects a target signal for motor operation control, wherein the fine magnetization includes an offset amount detected by the magnetic sensor due to the influence of the propulsion field magnet. It is characterized in that a high-pass filter circuit that removes the offset component from the signal wave from the unit according to a predetermined mover driving speed is incorporated.

A linear motor of the present invention which solves the second problem is a stator having a propulsion field magnet and a fine magnetizing portion for a linear encoder which is superposed on the field magnet, and the field magnet. An armature coil facing the magnet and a mover having a magnetic sensor for detecting a magnetic signal wave from the fine magnetizing section, and a signal for controlling the intended motor operation by receiving the output of the magnetic sensor. A signal from the fine magnetizing section, which is a linear motor additionally provided with a signal detecting circuit for detecting, wherein the signal detecting circuit includes an offset detected by the magnetic sensor due to the influence of the propulsion field magnet. It is characterized by incorporating a high-pass filter circuit that removes the offset from the wave in accordance with a predetermined mover driving speed.

In the image reading apparatus of the present invention for solving the third problem, at least one member of the scanning optical system for scanning the original image which should be moved for image scanning solves the second problem. The linear motor is driven by being connected to a mover, and the high-pass filter circuit in the signal detection circuit is configured to be able to remove the offset amount according to a predetermined traveling speed of the member. .

In any of the above, the magnetic sensor for reading the magnetic signal wave from the fine magnetized portion on the linear motor stator is not limited to that, but is typically called an MR element or MR sensor. A magnetic sensor of the current magnetic effect type, which uses a magnetoresistive element, has a high sensitivity and includes a bias magnet. Also,
Examples of the high-pass filter circuit incorporated in the signal detection circuit according to the present invention include, for example, before an operational amplifier for amplifying a magnetic sensor output in a linear motor signal detection circuit (the operational amplifier and the magnetic sensor on the linear motor mover). Between) and removes the offset at that time according to the predetermined speed of the linear motor mover, and
An example thereof includes a frequency selection unit that can select a cutoff target frequency for passing a signal from the fine magnetized portion on the linear motor stator. As such a frequency selecting means, a resistance circuit including a plurality of resistors capable of switching and selecting for cutting a cutoff target frequency can be exemplified.

In the image reading apparatus of the present invention, a member to be driven for image scanning, which is driven by a linear motor, is usually an illumination lamp for illuminating a document and the same speed as the illumination lamp. A reflection mirror, a first carriage that supports them, a reflection mirror that should travel in the same sub-scanning direction as the first carriage at a speed half that of the first carriage during image scanning, and a second mirror that supports the reflection mirror. It can be considered as a carriage. In this case, the first,
Both of the second carriages may be driven by the linear motor of the present invention, but either one may be driven by the linear motor of the present invention and the other may be interlocked by an appropriate interlocking mechanism.

[0019]

In the signal detecting circuit for a linear motor according to the present invention, the high frequency signal from the fine magnetizing portion on the linear motor stator detected by the magnetic sensor on the linear motor mover is the field magnet on the stator. The noise is input from the magnet in a state including the offset due to the low-frequency signal (see FIG. 5A), but these signals pass through the high-pass filter circuit, so that the mover responds to a predetermined moving speed. The offset component at that time is removed, whereby the target high-frequency signal without offset from the fine magnetized portion at that time (see FIG. 5B) is accurately detected.

In the present specification, "high-frequency signal",
"Low-frequency signal" means that one is a high-frequency signal and the other is a low-frequency signal in the comparison of both signals. Further, according to the linear motor of the present invention, since the signal detection circuit is additionally provided, the fine magnetized portion for the linear encoder on the stator is formed on the field magnet in an overlapping manner. A high-frequency signal from the fine magnetized portion at that time corresponding to a predetermined moving speed of the mover is accurately detected, and this is used for motor operation control. Therefore, the motor can be precisely controlled and operated.

Further, according to the image reading apparatus of the present invention, at least one member to be driven for image scanning of the scanning optical system is driven by being connected to the mover of the linear motor of the present invention. The linear motor is controlled accurately according to a traveling speed such as acceleration / deceleration or a constant speed during scanning of the member, a predetermined traveling speed such as a traveling speed according to the magnification, in other words, a predetermined traveling speed of the mover. It is driven, and the image is scanned smoothly with high accuracy.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an example of an image reading apparatus that employs a linear motor according to the present invention. However, for the linear motor, only the position of the mover 2 is shown. FIG. 2 is a plan view of an example of a linear motor according to the present invention and components in the apparatus of FIG. 1 driven by the linear motor. FIG. 3 is a side view of the stator of the linear motor shown in FIG.
FIG. 4 is a diagram showing a signal detection circuit for the linear motor.

First, the image reading apparatus shown in FIG. 1 will be described. An illumination lamp 92 is provided below a document table glass 91 on which a document is placed, and the light from this lamp is reflected by the reflecting mirrors m1 and m2 to cause the glass 91 to be reflected. The reflected light of the document, which is condensed at the upper image reading position 93, is reflected by the mirror m3 and the pair of mirrors m4 and m5, and is imaged by the lens LN on the CCD image pickup unit 94 which is a linear image pickup device.

The lamp 92 and the mirrors m1, m2, m3 are mounted on the movable carriage C1, and the mirrors m4, m
5 is mounted on the movable carriage C2. At the time of image reading, the lamp 92 and the mirrors m1, m2, m3 are driven in the original image sub-scanning direction X by the movement of the carriage C1, and the mirrors m4, m5 are driven by the movement of the carriage C2. At this time, the lamp 92 and the mirror m
1, m2, m3 and mirrors m4, m5 are driven at a speed ratio of 2: 1. Therefore, the distance from the image reading position 93 to the lens LN does not change, and the image formation state is maintained.
The image formed on the CCD image pickup unit 94 is photoelectrically converted and sent to an image processing circuit (not shown) to complete the reading.

The reading magnification is changed by moving the position of the lens LN. The distance between the reading position 93 and the lens LN can be adjusted by moving the table 95 to which the lens LN is attached by the lens motor LM along the guide member 96 extending in the sub-scanning direction, and the distance between the lens LN and the CCD imaging unit 94 can be adjusted. The distance is the focus motor 97 attached to the base 95.
Thus, the adjustment can be performed by moving the CCD image pickup unit mounting base 98 that can move on the base 95 in the optical axis direction.

The carriage C1 is driven by the linear motor LDM according to the present invention. The carriage C2 is interlocked with the carriage C1 by an interlocking mechanism (not shown) which is already known and is driven at a speed half that of the carriage C1. As shown in FIG. 2, the carriage C1 is connected to the mover 2 of the motor LDM at one end c11 thereof, and the other end c12 of the carriage is guided in parallel with the stator 1 by a roller c13 provided therein. It can run on the member 99.

As shown in FIG. 2, the linear motor LDM
Is for driving the carriage C1, and has N pole and S on the surface.
Field magnet 11 having poles alternately arranged in the sub-scanning direction X
It is composed of a rod-shaped stator 1 having a cylindrical shape and a cylindrical mover 2 fitted on the stator 1 and having an armature coil 22 capable of reciprocating along the stator. The mover 2 is a cylindrical mover yoke 2 surrounding the armature coil 22.
1 and has bearings 23 at both ends thereof so that the bearings can move along the stator 1.

In addition to the field magnet 11 described above, the stator 1 is also provided with a fine magnetizing portion 12 for a linear encoder formed on the magnet 11 in an overlapping manner, as shown in FIG. The mover 2 includes a magnetic sensor S (see FIG. 2). The magnetic sensor S is a current magnetic effect type magnetic sensor called an MR element and has a bias magnet and high sensitivity.

The magnetic sensor S detects a magnetic high frequency signal from the fine magnetizing section 12 as the mover 2 on which the magnetic sensor S is mounted moves along the stator 1, and the signal detecting circuit 6 which will be described later. To enter. Here, the armature coil 22 in the mover 2 may be at a position shifted by 2π / 3 in electrical angle (a position in phase with a position shifted by 2π / 3) so that the armature coil 22 can be driven by the three-phase driving method. ) Are arranged in each phase coil, and each phase coil has a position detection element for detecting the magnitude and direction of the magnetic flux of the field magnet 11 for controlling energization to the coil, for example, a kind of magnetoelectric conversion element. Hall element (not shown) is attached. Then, a current having a magnitude and direction corresponding to the magnitude and direction of the magnetic flux sensed by these Hall elements is passed through the coil to generate a mover thrust, and the linear motor LDM is operated.

In addition to the three-phase drive method, here, in order to drive the carriage C1 and hence the mover 2 at a predetermined speed according to the magnification of image reading, a phase generally called PLL. A synchronous control method is also adopted. And a linear encoder is adopted to implement this phase synchronization control, and as the linear encoder,
Here, the fine magnetizing portion 12 on the stator 1, the magnetic sensor S on the mover 2, and the signal for the linear motor according to the present invention which receives the output from the magnetic sensor and detects the signal to be used for the phase synchronization control. A detection circuit is provided. FIG. 4 (A)
Shows an example of the signal detection circuit.

The signal detection circuit 6 shown in FIG. 4A is a high-pass filter circuit 61 to which the output of the magnetic sensor S is input.
And a signal amplification circuit 62 and a comparator circuit 63 that follow. The high pass filter circuit 61 is
As shown also in FIG. 4B, a circuit 611 including a resistor that controls the operation of the entire image reading apparatus and is switched based on an instruction from the computer CPU that outputs the reference clock signal used for the phase synchronization control is provided. Contains. In FIGS. (A) and (B), C ₁ and C ₂ are capacitors of the same capacity, R ₁ is a resistor, AP ₁ and AP ₂ are operational amplifiers, and CP is a comparator. In the resistance circuit 611, R _A , R _B , and R _C are resistors used for switching, and SW is an analog switch for switching.

The signal from the fine magnetizing section 12 detected by the magnetic sensor S on the mover 2 of the linear motor LDM is a high frequency signal according to the current moving speed of the mover, which is as described above and shown in FIG. As shown in FIG. 5 (A), the offset component due to the noise low frequency signal from the field magnet 11 is included. A signal wave including this offset amount is input from the sensor S to the high pass filter circuit 61.

The filter circuit 61 can determine the signal frequency fc to be cut off in order to remove the offset component by the combination of the capacitor and the resistor. The cutoff frequency fc is determined by which of the resistors R _A , R _B , and R _C is used, and fc = 1 / 2πC ₁ √ (R ₁ · R
_X ) (where R _X is one of R _A , R _B , and R _C )
Becomes The resistors R _A , R _B , and R _C are selectively used according to the signal input from the sensor S at the scanning speed (scan speed) corresponding to the image reading magnification (0.5 ×, 1 ×, 2 ×). The cut-off target frequency component is cut off so as to remove the offset component at that time, and only the target high-frequency signal resulting from the fine magnetizing portion is passed. This is performed based on an instruction from the computer CPU in conjunction with magnification setting buttons or keys on the operation panel (not shown) in the image reading apparatus.

Thus, the high-frequency signal in the state shown in FIG. 5B, in which the noise is removed by passing through the high-pass filter circuit 61 and the offset component is removed, is the amplifier circuit 62.
The signal is amplified by, and further converted into a rectangular wave by the comparator circuit 63, adjusted to 5 V by the clamp diode, set to the TTL level, and output. This output signal is used for speed control by the phase synchronization method, and as a result, the carriages C1 and C2 are driven at a predetermined speed at that time in association with the image reading magnification, and image scanning is performed accurately. -Reading is performed. The output from the signal detection circuit 6 can be used as position information of the carriages C1 and C2 by counting with a counter or the like.

Next, a specific example of signal detection by the signal detection circuit 6 will be described. Field magnet 11 on the stator 1
The magnetic pole pitch is set to 30 mm, and the magnetic pole pitch of the fine magnetized portion 12 is set to 200 μm. Scanning operation is 600m for 0.5x, 1x and 2x image reading magnification.
m / sec, 300 mm / sec, 150 mm / sec
And In this case, the respective frequencies of the low frequency signal that causes the offset from the field magnet 11, the desired high frequency signal from the fine magnetizing unit 12, and the cutoff frequency signal set by the resistance circuit 611 are as follows. Field magnet signal Fine magnetizing part signal Cut-off signal 0.5 times (600 mm / sec) 10 Hz 1500 Hz 1000 Hz 1 × (300 mm / sec) 5 Hz 750 Hz 500 Hz 2 times (150 mm / sec) 2.5 Hz 375 Hz 250 Hz For example, at the same magnification, since the fine magnetizing signal of 750 Hz is superimposed on the field magnet signal of 5 Hz, the cutoff frequency is set to, for example, 500.
It is sufficient to set the frequency to Hz and pass the signal of 750 Hz to cut off the offset amount due to the signal of 5 Hz. Then, the resistance of the resistance circuit 611 used to set the cutoff frequency at each magnification as described above is as follows.

Assuming that the capacitor C ₁ = C ₂ = 0.01 μF and the resistance R ₁ = 22 KΩ, the following is calculated from the fc calculation formula. fc Rx 0.5 times 1000 Hz 11 KΩ equal size 500 Hz 46 KΩ 2 times 250 Hz 180 KΩ Switching of the resistance in the resistance circuit 611 will be further described.

Each of the resistors R _A , R _B and R _C is a computer C.
Based on an instruction from the PU, the analog switch SW is used to switch in accordance with the magnification. In that case, the computer CPU
The signals A, B, and C from are set to high “Hi” or low “Lo”, respectively, and the resistors are turned on and off by the combination. The resistance to which the Hi signal is input is turned on, and the resistance to which the Lo signal is input is turned off. It is also possible to set three types of resistance values by predetermining resistance values assuming that resistors are connected in parallel as described below. In this case, the switching signal may be one action. In the example of the control input signal is selected resistor _{R A R A + R B R} A + R B + R C A Hi Hi Hi B Lo Hi Hi C Lo Lo Hi above, 0.5 times, magnification, resistance at the time of 2-fold magnification change Although a specific example in which R _A , R _B , and R _C are used by switching has been shown, in an image reading device with a zoom mechanism in which the scan speed changes steplessly, the speed range is divided into several areas, and the speed range is divided into several areas. You can change it.

Further, in the above-mentioned specific example, when the magnification is changed, the cutoff target frequency is changed in accordance with the scan speed at the magnification, however, for example, other operation,
For example, the cutoff frequency may be set for the return operation of the carriages C1 and C2. Set the other conditions as above and set the return speed to 12
When set to 00 mm / sec, the field magnet signal at the time of return operation is 20 Hz and the fine magnetizing signal is 3000 H.
z, and the cutoff signal is set to 2000 Hz, for example. The resistance Rx at this time is 2.8 KΩ. In this case, the resistance of this value is added to the resistance circuit 611.

The resistance used for switching in the resistance circuit 611 may be adjusted as necessary.

[0040]

As described above, according to the present invention, a stator having a field magnet for propulsion and a fine magnetized portion for a linear encoder formed on the field magnet and a stator are provided. An output of the magnetic sensor of a linear motor including an armature coil and a mover having a magnetic sensor for detecting a magnetic signal wave from the fine magnetized portion is received to output a target signal for motor operation control. A signal detection circuit for a linear motor for detecting,
According to a predetermined driving speed of the linear motor mover, an offset component caused by the field magnet is removed from a signal wave detected by the magnetic sensor and input to the signal detection circuit for the linear motor, thereby accurately aiming. It is possible to provide a signal detection circuit capable of obtaining the signal

Further, according to the present invention, a stator having a field magnet for propulsion and a fine magnetized portion for a linear encoder formed on the field magnet, an armature coil facing the field magnet, and the above A linear motor having a mover having a magnetic sensor for detecting a magnetic signal wave from a fine magnetizing section, wherein an offset component caused by the field magnet is removed from a signal wave detected by the magnetic sensor. Therefore, it is possible to provide a linear motor that can be controlled and controlled with such accuracy.

Further, according to the present invention, there is provided an image reading device in which at least one member of the scanning optical system for scanning an original image, which is to be moved for image scanning, is driven by a linear motor, and the predetermined member of the member is used. It is possible to provide the one that can control and operate the linear motor with high accuracy in accordance with the traveling speed, and can perform image scanning with high accuracy as much as that.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an example of an image reading apparatus according to the present invention.

FIG. 2 is a plan view of an example of a linear motor according to the present invention and components driven by the linear motor in the apparatus of FIG.

FIG. 3 is a side view of a stator of the linear motor shown in FIG.

4A is a diagram showing a signal detection circuit attached to the linear motor shown in FIG. 2, and FIG. 4B is a diagram showing a switchable resistance circuit in the circuit.

FIG. 5A is a diagram showing a signal wave from the fine magnetized portion including an offset due to the influence of a field magnet, and FIG. 5B is a signal wave of the fine magnetized portion from which noise is removed. It is a figure.

[Explanation of symbols]

LDM linear motor 1 stator 11 field magnets 12 Fine magnetized portion 2 moving element 21 movable piece yoke 22 the armature coils 23 bearing S magnetic sensor 6 signal detecting circuit 61 high-pass filter circuit 611 resistor circuit R _1, R _A, R _B , R _C resistor C ₁ and C ₂ capacitor CPU computer 92 document illumination lamp in image reading device m1, m2, m3 mirror that moves with lamp C1 carriage c11 one end of carriage C1 c12 other end of carriage C1 c13 roller 99 guide member m4, m5 Mirror C2 Carriage X Sub-scanning direction

Claims (3)

[Claims] 1. A stator having a propulsion field magnet and a fine magnetized portion for a linear encoder formed on the field magnet, an armature coil facing the field magnet, and the fine magnetized portion. A linear motor signal detection circuit for detecting a target signal for motor operation control by receiving an output of the magnetic sensor of a linear motor including a mover having a magnetic sensor for detecting a magnetic signal wave of A high-pass filter circuit that removes the offset component from the signal wave from the fine magnetizing unit that includes the offset component due to the influence of the propulsion field magnet detected by the magnetic sensor according to a predetermined mover driving speed. A signal detection circuit for a linear motor, which is characterized by incorporating. 2. A stator having a propulsion field magnet and a fine magnetizing portion for a linear encoder formed to overlap the field magnet, an armature coil facing the field magnet, and the fine magnetizing portion. A linear motor equipped with a mover having a magnetic sensor for detecting a magnetic signal wave, and a signal detection circuit for detecting a signal for target motor operation control by receiving an output of the magnetic sensor, The signal detection circuit detects the offset from the signal wave from the fine magnetizing section, which includes the offset due to the influence of the propulsion field magnet, detected by the magnetic sensor, and adjusts the offset according to a predetermined mover driving speed. A linear motor characterized by incorporating a high-pass filter circuit that removes it. 3. A signal detecting means for driving at least one member of a scanning optical system for scanning an original image, which is to be driven for image scanning, by being connected to a mover of a linear motor according to claim 2. An image reading apparatus characterized in that the high-pass filter circuit in the circuit is configured to be able to remove the offset amount in accordance with a predetermined traveling speed of the member.