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This application is based on application Nos. 9-252480 Pat. and 10-223442 Pat. both filed in
Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear motor of a moving coil type provided with a stator having a field magnet as well as a movable piece which has an armature coil opposed to the field magnet and is movable along the stator. Also, the
present invention relates to an image reader using a linear motor of a moving coil type for optically scanning and reading an original image and, more specifically, for linearly driving a slider which carries optical parts including an illumination lamp.
2. Description of the Background Art
Linear motors have been utilized for linearly moving objects in a wide field including office automation equipments such as copying machines, printers and image scanners, factory automation equipments such as X-Y tables and object transporting
devices, and optical equipments such as cameras.
In one of known types of linear motors, a stator is provided with a field magnet having N-type magnetic poles and S-type magnetic poles, which are arranged alternately and linearly in a predetermined direction, and a movable piece, which is
movable along the stator, is provided with an armature coil opposed to the field magnet. This type of linear motor is called a moving coil type.
In the linear motor of the moving coil type, the armature coil of the movable piece is energized under control to move the movable piece along the stator. This energizing of (i.e., power supply to) the armature coil of the movable piece as well
as the control of energizing are performed based on information sent from various sensors which are arranged on the movable piece as will be described later. For these energizing and control, a harness (i.e., a bundle of electric cables) is extended
from the movable piece to connect a power supply circuit for the armature coil with the armature coil and the various sensors on the movable piece.
The sensor for controlling the power supply to the armature coil is provided, e.g., for the field magnet, and more specifically is provided, e.g., for detecting a polarity of magnetic pole of the field magnet to which the moving armature coil
opposes and/or for detecting an intensity of the magnetic field formed by the field magnet. As this sensor for the field magnet, a magnetoelectric conversion element such as a Hall element or a magnetic resistance element (MR element) is usually
employed. The magnetoelectric conversion element can issue an electric signal corresponding to the polarity of the magnetic pole and the intensity of the magnetic field.
In addition to the above, a sensor for an encoder is employed as the sensor which is arranged on the movable piece for controlling the power supply to the armature coil. The encoder is formed of the encoder sensor (i.e., sensor for the encoder)
arranged on the movable piece and an encoder scale which is arranged at a stationary position and extends in the lengthwise direction of the stator. The encoder may be of either an optical type or a magnetic type as is well known.
The encoder scale for the optical encoder is provided with two kinds of surfaces which have optically different properties and are arranged alternately in the lengthwise direction of the stator. For example, an encoder of a so-called reflection
type is completed by employing two kinds of (e.g., white and black) surfaces which have different reflectances to each other and are arranged alternately in the lengthwise direction of the stator. An encoder of a so-called transparent type is completed
by employing two kinds of surfaces which have different light transmittances to each other and are arranged alternately in the lengthwise direction of the stator. In either case, the sensor for the optical encoder includes a photoelectric conversion
element such as a photodiode or a phototransistor, which can issue electric signal corresponding to quantity of light. In some cases, the sensor for the optical encoder may be a photosensor (an optical sensor) which is one packaged combination of a
light emitting element such as a light emitting diode (LED), which emits light toward the encoder scale, and a photoelectric conversion element.
In the magnetic encoder, the encoder scale is provided with N- and S-type magnetic poles arranged alternately in the lengthwise direction of the stator. The sensor for the magnetic encoder usually may be a magnetoelectric conversion element such
as a magnetic resistance element (MR element) or a Hall element which issues an electric signal corresponding to the polarity of the magnetic pole of the magnetic encoder scale and/or the intensity of the magnetic field.
A power supply and drive circuit for supplying a current to the armature coil and thereby driving the movable piece along the stator usually operates to supply the current to the armature coil based on a field magnet signal sent from the
foregoing sensor for the field magnet and/or an encoder signal sent from the encoder sensor. For achieving a compact structure of the circuit, the power supply and drive circuit sometimes employs a motor drive IC. The power supply and drive circuit is
arranged at a fixed position outside the movable piece.
The linear motor of such a moving coil type may be used in the image reader such as an image scanner for optically scanning and reading an original image. In the image reader, a slider carrying optical parts such as an illumination lamp is
linearly moved for optically scanning the original image, and the linear motor is used for driving the slider. A fluorescent lamp is used as the illumination lamp in many cases, and a turn-on circuit for the illumination lamp is arranged at a fixed
position outside the movable piece.
However, when the harness extended from the movable piece has many cables for energizing the armature coil on the movable piece, for transmitting the output signals from the sensors for the field magnet, for transmitting the output signals from
the sensors for the encoder and others, it is difficult to handle and rout the harness having such many cables. The armature coil is usually formed of two or more coils. For example, when three-phase energizing is performed, the armature coil is formed
of one or more coil group(s) each including three coils. In any of the structures, as the coils forming the armature coil increases in number, the cables extended from the movable piece increase in number so that smooth movement of the movable piece may
be impeded, and/or routing of the harness may be difficult. When the harness is bent excessively, and thereby the harness is broken, the movable piece cannot be driven.
As described above, the magnetoelectric conversion element for the field element, photoelectric conversion element for the encoder and/or the magnetoelectric conversion element for the encoder may be arranged on the movable piece for controlling
the power supply to the armature coil. In this case, each of electric signals issued from these elements are usually extremely weak analog signal so that the signal is liable to be affected
by noises during transmission through the harness extended from the movable piece. If the signals issued from these elements are affected by noises, the control of energizing the armature coil cannot be performed precisely, and therefore the
movable piece cannot be driven precisely.
Noise sources of such noises are, for example, as follows. The harness extended from the movable piece includes a cable for energizing the armature coil. This cable for energizing the armature coil transmits a current larger than signals or the
like issued from the foregoing sensing elements, and is routed in parallel with the cables for transmitting signals issued from the foregoing elements in many cases. Therefore, the cable for energizing the armature coil forms the noise source.
In the image reader for optically scanning and reading an original image, the linear motor can be used for linearly moving the slider carrying optical parts, as described above. If the image reader is provided with a liquid crystal display for
displaying various information, a display circuit of the liquid crystal display may form the noise source.
In the case where the linear motor is used, in the image reader, for driving the slider carrying optical parts including the illumination lamp such as a fluorescent lamp as described above, a cable for an illumination lamp turn-on circuit
arranged at a fixed position outside the movable piece is likewise extended from the movable piece or a slider portion near the same. This cable further increases the number of cables of the harnesses extended from the movable piece or a portion near
the same, which further makes the routing of the harness difficult. In the above image reader, if the movable piece is not driven precisely due to an influence by noises as described above, good image reading cannot be performed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a linear motor of a moving coil type which is provided with a stator having a field magnet and extending in a predetermined direction, and a movable piece having an armature coil opposed to
the field magnet and being movable along the stator, and more specifically, the followings are objects of the invention.
One of the objects of the invention is to provide a linear motor which can reduce the number of cables of a harness extended from the movable piece so that the harness can be routed easily.
Another object of the invention is to provide a linear motor, in which a sensor for the field magnet is arranged on the movable piece for controlling power supply to the armature coil, and an influence exerted by noises on an output electric
signal of this sensor can be suppressed so that the movable piece can be driven precisely.
Still another object of the invention is to provide a linear motor, in which a sensor for an encoder is arranged on the movable piece for controlling power supply to the armature coil, and an influence exerted by noises on an output electric
signal of this sensor can be suppressed so that the movable piece can be driven precisely.
Also, it is an object of the invention to provide an image reader, which uses the linear motor of the moving coil type for optically scanning and reading an original image and, more specifically, for linearly driving a slider carrying optical
parts such as an illumination lamp. Particularly, the followings are objects of the invention.
A further object of the invention is to provide an image reader which can reduce the number of cables of a harness extended from the movable piece so that the harness can be routed easily.
Further another object of the invention is to provide an image reader, in which a sensor for the field magnet is arranged on the movable piece for controlling power supply to the armature coil, and an influence exerted by noises on an output
electric signal of this sensor can be suppressed so that the movable piece can be driven precisely, and thereby, good image reading can be performed.
Still further another object of the invention is to provide an image reader, in which a sensor for an encoder is arranged on the movable piece for controlling power supply to the armature coil, and an influence exerted by noises on an output
electric signal of this sensor can be suppressed so that the movable piece can be driven precisely, and thereby, good image reading can be performed.
The invention provides a linear motor provided with a stator extending in a predetermined direction and a movable piece being movable along the stator, and comprising:
a field magnet arranged at the stator;
an armature coil arranged at the movable piece and opposed to the field magnet; and
a drive circuit for energizing the armature coil and thereby driving the movable piece, wherein
the drive circuit is formed at an electric circuit-board arranged on the movable piece.
Also, the invention provides an image reader for optically scanning and reading an original image, comprising:
a slider carrying an illumination light source for emitting light to the original image and being driven linearly in a predetermined direction;
a stator provided with a field magnet having N- and S-type magnetic poles arranged alternately in the predetermined direction;
a movable piece having an armature coil opposed to the field magnet, being movable along the stator, and coupled to the slider; and
a drive circuit for energizing the armature coil and thereby driving the movable piece, wherein
the drive circuit is formed at an electric circuit-board arranged on the movable piece.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF
THE DRAWINGS
FIG. 1 is a schematic plan showing an example of an image reader according to the invention;
FIG. 2 is a schematic cross section of the image reader taken along line X--X in FIG. 1;
FIG. 3 is a schematic cross section of the image reader taken along line Y--Y in FIG. 1;
FIG. 4 is a schematic perspective view showing an example of a linear motor according to the invention;
FIG. 5 is a fragmentary schematic cross section of the linear motor shown in FIG. 4;
FIG. 6 is a schematic cross section of the linear motor taken along line Z--Z in FIG. 5;
FIG. 7 shows an example of a distribution of magnetic fluxes formed in a lengthwise direction of the stator by a field magnet;
FIG. 8 shows a manner of mounting an electric circuit-board on a frame of the movable piece;
FIG. 9 is a schematic block diagram showing an example of a circuit on an electric circuit-board of the linear motor;
FIG. 10 shows an example of an encoder signal processing circuit;
FIG. 11 shows an example of a field magnet signal processing circuit;
FIG. 12 is a schematic block diagram showing an example of a motor drive circuit;
FIG. 13 shows a relationship between magnetic poles detected by respective Hall elements and timings for energizing respective coils in an operation of driving the movable piece of the linear motor in FIG. 5 leftward in FIG. 5;
FIG. 14 shows a relationship between magnetic poles detected by respective Hall elements and timings for energizing respective coils in an operation of driving the movable piece of the linear motor in FIG. 5 rightward in FIG. 5;
FIG. 15 shows more specifically an example of a motor drive circuit;
FIG. 16 is a schematic cross section of another example of a linear motor according to the invention; and
FIG. 17 shows another example of an encoder signal processing circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(1-1) Linear Motor
A linear motor of an embodiment of the invention is provided with a stator extending in a predetermined direction and a movable piece being movable along the stator, and comprises:
a field magnet arranged at the stator;
an armature coil arranged at the movable piece and opposed to the field magnet; and
a drive circuit for energizing the armature coil and thereby driving the movable piece, wherein
the drive circuit is formed at an electric circuit-board arranged on the movable piece.
This linear motor is of a so-called moving coil type, in which the field magnet forms the stator, and the armature coil forms the movable piece. The field magnet is provided with N- and S-type magnetic poles arranged alternately and linearly in
a predetermined direction.
An example of the linear motor of the moving coil type may be of a shaft type, in which the stator has a shaft-like form extending in the predetermined direction and has the field magnet provided with N- and S-type magnetic poles arranged
linearly and alternately in the predetermined direction, and the movable piece has an armature coil fitted around the field magnet and is movable along the stator. Another example of the moving coil type may be of a plain-type or plate type, in which
the stator has a field magnet provided with plate-like N-type magnetic poles and plate-like S-type magnetic poles arranged alternately and linearly in the predetermined direction, and the movable piece has an annular armature coil having an opening
opposed to the field magnet, and is movable along the stator.
When the armature coil is energized, the armature coil is subjected to an electromagnetic force produced by an interaction between a current flowing through the armature coil and a magnetic field formed by the field magnet so that the movable
piece can be driven in the lengthwise direction of the stator.
The energizing of the armature coil is performed by the drive circuit which is formed at the electric circuit-board arranged on the movable piece. The drive circuit may include a motor drive IC. The drive circuit may not include a circuit for
instructing start and stop of driving of the motor.
Owing to formation of the drive circuit on the electric circuit-board on the movable piece, a connection between the armature coil and the drive circuit can be formed on the movable piece. Therefore, it is not necessary to employ a conventional
structure in which a cable for connecting the armature coil and the drive circuit is included in a harness extended from the movable piece. Accordingly, cables in the harness extended from the movable piece can be reduced in number.
If the armature coil is formed of two or more single-coils, which are to be connected to achieve a predetermined connection, each coil may be electrically connected to the electric circuit-board carrying the drive circuit so that the
predetermined connection may be achieved by an interconnection pattern arranged on the electric circuit-board.
The predetermined connection may be, for example, such that the respective coils are star-connected if the armature coil is formed of one or more coil groups each including three coils. If the plurality of coil groups each including three coils
are star-connected, parallel connection may be employed for the start connection.
The respective coils may be electrically connected to the electric circuit-board provided with a connection pattern for achieving the predetermined connection, and thereby the respective coils are connected in the predetermined connection.
When the predetermined connection is achieved by the interconnection pattern formed on the electric circuit board, the predetermined connection can be achieved more easily than the case where the respective coils are connected in the
predetermined connection by soldering or the like without employing the electric circuit-board. Further, it is possible to suppress an error and a failure in connection of the respective coils.
When the drive circuit energizes the armature coil based on, e.g., the polarity of the magnetic pole of the field magnet to which the armature coil opposes, the linear motor may be further provided with a magnetoelectric conversion element for
the field magnet arranged at a position, on the movable piece, opposed to the field magnet, and a field magnet signal processing circuit for digitizing an electric signal issued from the magnetoelectric conversion element for the field magnet. In this
case, the field magnet signal processing circuit may be formed at the electric circuit-board carrying the drive circuit.
The magnetoelectric conversion element for the field magnet may be arranged to achieve a predetermined positional relationship in the lengthwise direction of the stator with respect to the armature coil. The magnetoelectric conversion element(s)
may be one or more, if necessary. The number of the field magnet signal processing circuit(s) may be equal to that of the magnetoelectric conversion element(s) for the field magnet.
The magnetoelectric conversion element for the field magnet may be a Hall element, a magnetic resistance element or the like. The Hall element can detect the polarity of the magnetic pole. The Hall element may be of a type containing InSb
(indium antimony), InAs (indium arsenic), GaAs (gallium arsenic) or the like. The InSb-contained Hall element can issue a large output signal (Hall voltage). The GaAs-contained Hall element exhibits good thermal characteristics. A Hall IC, in which
the magnetoelectric conversion element and the field magnet signal processing circuit are packaged in one chip, may be employed. The Hall IC usually includes a digitizing circuit, and may additionally include an amplifier circuit.
As the movable piece moves, the magnetoelectric conversion element is successively and alternately opposed to the N- and S-type magnetic poles of the field magnet, and issues electric signals corresponding to the intensity and/or direction
(polarity of the magnetic pole) of the magnetic field formed by the magnetic poles of the field magnet.
The electric signal issued from the magnetoelectric conversion element is usually an analog signal, which is extremely weak in many cases. The output signal of the magnetoelectric conversion element is converted into a digital form by the field
magnet signal processing circuit.
The digitization produces an electric signal of either a large or small value based on, typically, a voltage value of the input electric signal. The digitization can be performed, for example, by comparing between the value of the input electric
signal and a predetermined threshold value. This comparison can be performed, for example, by a circuit including a comparator. Alternatively, when the magnetoelectric conversion element issues two kinds of electric signals which are inverted from each
other with respect to a predetermined reference value, the digitization can be performed by comparing between these two output signals. These comparison can be performed, e.g., by a differential amplifier. This can suppress an influence by noises which
may be superposed on the two output signals of the magnetoelectric conversion element. In any one of the above cases, the comparison may be performed under a hysteresis characteristic. Amplification or the like may be effected on the output signal of
the magnetoelectric conversion element before digitization, if necessary.
The foregoing drive circuit utilizes the electric signal, which is issued from the magnetoelectric conversion element for the field magnet and is digitized by the field magnet signal processing circuit, for supplying to the armature coil the
current corresponding to, typically, the direction and/or intensity of the magnetic field, which is formed by the field magnet and acts on the armature coil.
The magnetoelectric conversion element for the field magnet or the Hall IC may be arranged on and carried by the electric circuit-board on which the
drive circuit is formed.
In the structure wherein the drive circuit, the magnetoelectric conversion element for the field magnet and the field magnet signal processing circuit are arranged on the same electric circuit-board, interconnection distances between these
circuits and element can be reduced, which can suppress an influence by noises. Thereby, the drive circuit can precisely control the power supply to the armature coil based on the field magnet signal, and thereby can precisely drive the movable piece.
In the prior art, the drive circuit is arranged outside the movable piece and therefore is spaced by a long distance from the magnetoelectric conversion element for the field magnet arranged on the movable piece so that signals are liable to be affected
by noises.
Owing to provision of the drive circuit at the electric circuit-board on the movable piece, field magnet information obtained by the magnetoelectric conversion element for the field magnet can be sent on the movable piece to the drive circuit.
Accordingly, it is not necessary to employ such a structure that the harness extended from the movable piece contains a cable for transmitting field magnet information obtained by the magnetoelectric conversion element for the field magnet to the drive
circuit, as is done in the prior art. Thereby, it is possible to reduce the number of cables in the harness extended from the movable piece.
When the magnetoelectric conversion element for the field magnet is arranged on and carried by the electric circuit-board on which the drive circuit is formed, the electric circuit-board may be arranged on the movable piece such that the position
thereof can be adjusted in the lengthwise direction of the stator. This allows easy adjustment of the position, in the lengthwise direction of the stator, of the magnetoelectric conversion element for the field magnet with respect to the armature coil
so that a predetermined relationship between the magnetoelectric conversion element and the armature coil may be established easily.
If the magnetoelectric conversion element for the field magnet is the foregoing Hall element and, particularly, the InSb-contained Hall element which can issue a larger output signal than the GaAs-contained Hall element but has inferior thermal
characteristics, it is preferable that the Hall element is arranged at a position less affected by a heat. If the stator extends horizontally, the Hall element or the electric circuit-board carrying the Hall element may be arranged at a position
vertically under the movable piece or at a lower portion of the movable piece and, particularly, vertically under the armature coil, whereby it is possible to suppress an influence by a heat generated by the energized armature coil.
When the drive circuit energizes the armature coil based on, e.g., the position, in the lengthwise direction of the stator, of the movable piece and/or the moving speed of the movable piece, the linear motor may further include a linear encoder
scale extending in the lengthwise direction of the stator and arranged at a fixed position, an encoder sensor arranged on the movable piece and opposed to the encoder scale, and an encoder signal processing circuit for effecting processing (e.g.,
digitization) on an electric signal issued from the encoder sensor, the encoder signal processing circuit may be formed on the electric circuit-board on which the drive circuit is formed.
In the structure wherein a photosensor including a light emitting element and a photoelectric conversion element is employed as the encoder sensor, the encoder scale may be of an optical type, whereby the optical encoder can be formed. The light
emitting element may be a light emitting diode (LED). The photoelectric conversion element may be a photodiode or a phototransistor.
The optical encoder scale may be provided with surfaces having different light reflectances, i.e., high and low reflectances and arranged alternately in the lengthwise direction of the stator. In this case, the light emitting element and the
photoelectric conversion element are arranged on the movable piece, and are opposed to the surface of the encoder scale provided with these high and low reflectance surfaces. As the movable piece moves, the light emitting element and the photoelectric
conversion element are successively and alternately opposed to the high and low light reflectance surfaces, and the photoelectric conversion element issues an electric signal corresponding to the intensity of the light which is emitted from the light
emitting element and is reflected by the high or low reflectance surface.
Alternatively, the optical encoder scale may be provided with surfaces having different properties, i.e., high and low light transmittances arranged alternately in the lengthwise direction of the stator. In this case, the light emitting element
and the photoelectric conversion element are arranged on the movable piece, and are opposed to the above surfaces with the encoder scale therebetween. As the movable piece moves, the light emitting element and the photoelectric conversion element are
successively and alternately opposed to the high and low light transmittance surfaces, and the photoelectric conversion element issues an electric signal corresponding to the intensity of light which is emitted from the light emitting element and
transmitted through the high or low light transmittance surfaces.
In either case, the electric signal issued from the photoelectric conversion element is usually an extremely weak analog signal. This output signal of the photoelectric conversion element is digitized, and thereby is converted into a digital
form by the encoder signal processing circuit.
A magnetoelectric conversion element may be employed, instead of the photosensor, as the encoder sensor, in which case the encoder scale of the magnetic type is employed. The magnetoelectric conversion element may be a magnetic resistance
element (a so-called MR element) or a Hall element.
The magnetic encoder scale is provided with N- and S-type magnetic poles arranged alternately in the lengthwise direction of the stator. As the movable piece moves, the magnetoelectric conversion element for the encoder is successively and
alternately opposed to the N- and S-type magnetic poles, and issues electric signals corresponding to the intensity and/or direction (polarity of the magnetic pole) of the magnetic field formed by the magnetic poles of the magnetic encoder scale.
The electric signal issued from the magnetoelectric conversion element is usually an extremely weak analog signal. The output signal of the magnetoelectric conversion element for the encoder is digitized by the encoder signal processing circuit.
In any one of the above cases, the drive circuit utilizes the encoder signal, which is issued from the encoder signal processing circuit, for drive control (e.g., position control, speed control and PLL control) when the movable piece is driven
by energizing the armature coil. The encoder signal can also be utilized for detecting the position and speed of the linearly moving movable piece.
The photosensor including the light emitting element and the photoelectric conversion element for the encoder may be arranged on the electric circuit-board on which the drive circuit is formed. Likewise, the magnetoelectric conversion element
for the encoder may be arranged on the electric circuit-board on which the drive circuit is formed.
In the structure wherein the drive circuit, the photosensor or the magnetoelectric conversion element for the encoder, and the encoder signal processing circuit are arranged on the same electric circuit-board, interconnection distances between
these circuits, sensor and element can be reduced, which can suppress an influence by noises. Thereby, the drive circuit can precisely control the power supply to the armature coil based on the encoder signal, and thereby can precisely drive the movable
piece. In the prior art, the drive circuit is arranged outside the movable piece and therefore is spaced by a long distance from the photosensor or the magnetoelectric conversion element for the encoder arranged on the movable piece so that encoder
signal is liable to be affected by noises.
Owing to provision of the drive circuit at the electric circuit-board on the movable piece, encoder information obtained by the photosensor or the magnetoelectric conversion element for the encoder can be sent on the movable piece to the drive
circuit. Accordingly, it is not necessary to employ such a structure that the harness extended from the movable piece contains a cable for transmitting encoder information obtained by the photosensor or the magnetoelectric conversion element for the
encoder to the drive circuit, as is done in the prior art. Thereby, it is possible to reduce the number of cables in the harness extended from the movable piece.
The input/output harness for the electric circuit-board may be extended in the lengthwise direction of the stator from an end, in the lengthwise direction of the stator, of the electric circuit-board. This facilitates routing of the harness.
The input/output harness is employed, e.g., for supplying a power source voltage to circuits formed on the electric circuit-board.
The electric circuit-board may be a single-side board, which reduces a cost compared with a double-side board. The electric circuit-board may be the double-side board, in which case an effective mount area is substantially twice as large as that
of the single-side board so that the board can be reduced in size.
(1-2) Image Reader
According to an embodiment of the invention, an image reader for optically scanning and reading an original image, comprises:
a slider carrying an illumination light source for emitting light to the original image and being driven linearly in a predetermined direction;
a stator provided with a field magnet having N- and S-type magnetic poles arranged alternately in the predetermined direction;
a movable piece having an armature coil opposed to the field magnet, being movable along the stator, and coupled to the slider; and
a drive circuit for energizing the armature coil and thereby driving the movable piece, wherein
the drive circuit is formed at an electric circuit-board arranged on the movable piece.
This image reader can be utilized, e.g., as an image scanner. The image reader can be arranged, e.g., in a copying machine.
In this image reader, the slider carrying optical parts such as the illumination light source is driven linearly in the predetermined direction for optically scanning and reading the original image arranged at the predetermined position. The
illumination light source may be an illumination lamp such as a fluorescent lamp.
For driving the slider carrying the optical parts in the predetermined direction, the image reader has the stator having the field magnet, the movable piece having the armature coil, and the drive circuit for energizing the armature coil and
thereby driving the movable piece. The drive circuit is formed on the electric circuit-board arranged on the movable piece. This linear motor is of the shaft type already described in the item (1-1).
The movable piece is coupled to the slider carrying the optical parts including the illumination lamp. The linear motor can operate to drive the slider in the predetermined direction.
In the image reader of the invention, the linear motor according to the invention drives the slider so that cables in a harness extended from the movable piece can be reduced in number compared with the prior art, as already described in the
foregoing item (1-1). This facilitates routing of the harness extended from the movable piece in the image reader. The contents discussed in connection with the foregoing item (1-1) can be true also with respect to the linear motor employed in the
image reader of the invention. The same effects can be achieved.
In the structure employing the illumination lamp as the illumination light source, a lamp turn-on circuit for turning on the illumination lamp may be formed at the electric circuit-board, on which the drive circuit is formed, arranged on the
movable piece.
(2) Examples of the linear motor and image reader according to the invention will be described below with reference to the drawings.
FIGS. 1 to 3 show an example of an image reader according to the invention. FIG. 1 is a schematic plan of the image reader. FIG. 2 is a schematic cross section of the image reader taken along line X--X in FIG. 1. FIG. 3 is a schematic cross
section of the image reader taken along line Y--Y in FIG. 1.
The image reader shown in FIGS. 1 to 3 employs linear motors of the invention for driving two sliders carrying optical parts, respectively, as described later.
This image reader is provided at its upper portion with a transparent platen glass GL on which an original is laid. An openable cover CV, which is not shown in FIG. 1, is arranged over the platen glass GL. Two sliders SL1 and SL2, which are
movable | | |
