JPH0538124A - Linear dc motor and image scanner using same motor - Google Patents

Abstract

PURPOSE:To obtain the moving position of a movable element with high resolution by making the constitution of an apparatus into a low-cost and simple one, which can be further made longer. CONSTITUTION:In a linear DC motor which is provided with a field magnet alternately having the N-and S-poles of magnetic poles in the longitudinal direction and an armature having one or more driving armature coil groups facing this field magnet and in which one of these field magnet and armature is a movable element 1 and the other is a stator 2, a displacement sensor 14 is attached to the movable element 1 and a sensor target 15 formed into an irregular shape changing periodically in the direction of movement on the locus facing this displacement sensor 14 and also changing continuously without any point of inflection within a period is provided at the stator 2. Then, the position of the movable element 1 is calculated by an operating means on the basis of the irregular period of this sensor target 15 detected by the displacement sensor 14 and the distance between the displacement sensor 14 and sensor target 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear DC motor and an image scanner using this motor.

[0002]

2. Description of the Related Art Generally, a linear DC motor is used as a drive source for linearly moving an optical head or an image scanner. That is, it is possible to use a rotary motor to convert the motion into a linear motion, but such a drive system limits the accuracy of the feed due to backlash, backlash, and the like caused by the power transfer system. .

A linear DC motor provided with an optical linear encoder for the purpose of highly accurate movement and stop is disclosed in Japanese Patent Laid-Open No. 122322/1984. This is because the light from the light wavelength generating element is reflected by the tilted reflecting surface provided on the mover side and is received by the light wavelength receiving element so that the position and the propulsion speed of the mover can be easily detected. It is a thing. According to this, since the position and the propulsion speed can be easily detected, it can be moved or stopped with high accuracy, and at the same time, it is not necessary to move the optical wavelength generating element and the optical wavelength receiving element together with the mover. There is a merit that such things do not get in the way.

[0004]

However, according to such a conventional method, it is necessary to use expensive optical parts such as an optical wavelength generating element, a tilted reflecting surface, an optical wavelength receiving element, and these parts. It is also troublesome to handle because it requires highly accurate assembly adjustment.

Particularly in the case of an image scanner, when performing partial reading, it is necessary to start and stop the reading unit at an arbitrary position. For this reason, when a conventional linear DC motor is used as a drive source for an image scanner traveling system, this motor uses an expensive position sensor, which makes the image scanner expensive.
However, if it is constructed at low cost, the scanner position, and hence the reading position, cannot be measured with high resolution, so that the reading position accuracy will be poor when performing partial reading. Further, an image scanner generally requires a predetermined scanning length, and a linear DC motor for that purpose also needs to be elongated.

[0006]

A field magnet having N and S magnetic poles alternately arranged in the longitudinal direction, and an armature having one or more driving armature coil groups facing the field magnet. In a linear DC motor having one of the field magnet and the armature as a mover and the other as a stator, in the invention according to claim 1, a displacement sensor is attached to the mover and faces the displacement sensor. A sensor target formed in a concave and convex shape that is periodic in the movement direction on the locus and continuously changes within the cycle without an inflection point is provided on the stator, and the concave and convex cycle of the sensor target detected by the displacement sensor and Arithmetic means is provided for calculating the position of the mover based on the distance between the displacement sensor and the sensor target.

According to the second aspect of the present invention, a sensor whose output changes according to the target area is attached to the mover, and is periodically changed in the moving direction on a locus facing the sensor and increases or decreases within the period. The sensor target formed in the area change pattern indicating the above is provided on the stator, and the calculating means for calculating the position of the mover is provided based on the pattern period of the sensor target detected by the sensor and the sensor target area.

According to the third aspect of the present invention, such a linear DC motor is used in an image scanner, and a moving element for sub-scanning is provided by mounting a reading optical system member.

[0009]

According to the first aspect of the present invention, the displacement sensor attached to the mover and the periodical concave and convex shape provided on the stator side while being positioned on the movement locus of the displacement sensor,
In combination with a sensor target that has a shape that continuously changes within that cycle without an inflection point, the uneven cycle and displacement sensor
Since the position of the mover is calculated by measuring the distance between the sensor targets, the position of the mover can be detected with high sensitivity and high resolution with an inexpensive and simple structure, and the position control of the mover can be performed with high accuracy. In particular, the sensor target may have a long length, and there are few restrictions.

The same is true in the case of the invention according to claim 2, in which the sensor mounted on the mover and whose output changes according to the target area, and the sensor provided on the stator side while being located on the movement locus of this sensor Is a pattern that cyclically changes, and in combination with a sensor target of a pattern that shows only an increase change or a decrease change within the cycle, the pattern cycle and the sensor target area are measured to calculate the position of the mover. The low cost, simple structure and high sensitivity
The position can be detected with high resolution and the position of the mover can be controlled with high accuracy. In particular, the sensor target may have a long length, and there are few restrictions.

According to the third aspect of the present invention, by using such a linear DC motor as the sub-scanning drive source in the image scanner, it is possible to perform highly accurate position control, and it is possible to make inexpensive and highly accurate partial reading. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. First, the linear DC motor of this embodiment uses an armature as a mover and a field magnet as the stator 2.

The mover 1 includes a movable back yoke 3, a coil substrate 4 attached to the movable back yoke 3, shafts 5 fixed to the four corners on both sides of the movable back yoke 3, and rotatable shafts 5. It is composed of a mounted roller 6, an armature coil group including coils 7 fixed to the coil substrate 4 and continuously arranged along the substrate longitudinal direction, and a Hall element 8 for position detection. .

The stator 2 has a long base plate 10 having stepped or grooved rail portions 9 for guiding the rolling of the roller 6, and a fixed back yoke 11 fixed on the base plate 10. And a permanent magnet having magnetic poles 12 which are provided on the fixed back yoke 11 and are alternately magnetized such as N pole and S pole.

In such a basic structure, a constant gap is always present between the magnetic pole 12 and the coil 7, and the coil 7 and the Hall element 8 are connected via the connector 13 attached to the coil substrate 4. It is connected to a control device described later.

In this embodiment, however, the displacement sensor 14 is attached to a part of the mover 1 in a state of protruding laterally. The displacement sensor 14 is a non-contact type, for example, an eddy current type displacement sensor is used.
It may be one that utilizes light, sound or magnetism. A sensor target 15 is provided on the base plate 10 along the movement locus of the displacement sensor 14. The sensor target 15 has a sawtooth-like periodic concavo-convex pattern formed on the facing surface 15a facing the displacement sensor 14 along the moving direction of the mover 1. Therefore, the facing surface 15a has a pattern shape in which the distance to the displacement sensor 14 periodically and linearly decreases (or increases) within a cycle, and does not have an inflection point.
The concavo-convex pattern on the facing surface 15a of the sensor target 15 is not limited to the sawtooth shape, and the point is that the concavo-convex pattern in which the distance to the displacement sensor 14 changes periodically increases and decreases. It does not have to be linear as long as it has no shape. The detection output of the displacement sensor 14 is also input to the control device described later via the connector 13 and used as a feedback control signal.

Next, the structure of the control device will be described with reference to FIG. Basically, the microprocessor 16 and the RAM 17
It is controlled by a microcomputer 19 including a ROM 18 and a ROM 18. A command generation device 21 is connected to such a microcomputer 19 via a bus 20. The command generator 21 generates status command signals such as a position command signal and a speed command signal that command the status of the mover 1. In addition, the motor drive device 22 is responsive to the output signal of the hall element 8 and the output signal from the microcomputer 19 which is program-controlled.
General three-phase motor drive IC 23 for outputting signals to
Is provided. By such drive control, the mover 1 moves at the speed commanded by the command generator 21. The output of the displacement sensor 14 at this time is the waveform shaping circuit 2
4, taken into the microcomputer 19 via the detection interface device 25. The output of the waveform shaping circuit 24 is a counter 2 for counting the number of output pulses.
6 and the count value is also taken into the microcomputer 19. Furthermore, the output of the displacement sensor 14 is
It is converted into a digital value through the A / D conversion circuit 27 and taken into the microcomputer 19. These microcomputer 19, counter 26, A / D conversion circuit 2
7 constitutes a calculation means.

Here, for example, the output of the displacement sensor 14 shown in FIG. 4 (a) is shaped into a rectangular wave by the waveform shaping circuit 24 as shown in FIG. 4 (b). That is, the waveform shaping circuit 24 has a function of converting a sine wave input into a rectangular wave output.

Next, a method of detecting the speed of the mover 1, that is, the function of the detecting interface device 25 will be described. The detection interface device 25 outputs the output of the displacement sensor 14 shaped into a rectangular wave by the waveform shaping circuit 24 to the interrupt terminal of the microprocessor 16 and includes a counter for counting the reference clock CLK.

Now, the state immediately before the edge E ₁ of the output OB of the waveform shaping circuit 24 in FIG. 5 is reached will be described.
The counter built in the detection interface device 25 decrements the pulse cycle of T _n-1 of the output OB from the count number (for example, 0FFFFH) given based on the reference clock CLK. When the edge E ₁ reaches the interrupt of the microprocessor 16, the interrupt routine shown in FIG. 6 is executed. Then, the decrement count value of the counter is latched in the storage register built in the detection interface circuit 25 (latch of the counter). Then, the latched decrement count value is stored in the RAM 17. Then, a count initial value (0FFFFH) for counting the pulse cycle of T _n is given, the decrement count is started again, and the interrupt processing is ended. Once again, when edge E ₂ reaches the interrupt,
The above process is repeated in the same manner.

At this time, the moving speed v of the mover 1 is obtained by the equation (1). However, T _CLK : CLK cycle, N _E :
The number of output pulses of the waveform shaping circuit 24 per unit length,
n: CLK count number (= OFFFFH-decrement count number).

[0022]

## EQU1 ## v = (1 / N _E ). {1 / (T _CLK.n )} (1) The speed information of the mover 1 thus obtained is used for feedback control. Used. For example, consider an example in which proportional control, which is commonly used, is applied to speed control. As described above, the moving speed of the mover 1 is calculated as a digital value and is taken into the microcomputer 19. Here, in proportional control, generally, the control voltage to the linear DC motor is expressed by the equation (2).

[0023]

## EQU2 ## V = R (Fr / K _F ) + K (Rv-v) (2) where V: control voltage, R: coil resistance, K: proportional gain, v: mover speed. , K _F : Thrust constant, Fr: Friction force.

In the equation (2), R, Fr, and K _F are numerical values peculiar to the motor, and K, K ′, and K ″ are design values of the control system, and are all known constants. Is a set value, and v is obtained as described above. Therefore, the equation (2) and the above-mentioned constant are set in advance in the RO in the microcomputer 19.
The voltage V necessary for control can be easily obtained by calculating the same equation by inputting it as a program or a list in M18. The control voltage V actually obtained is pulse-modulated in the microcomputer 19 and output to the three-phase motor drive IC 23.
WM control is executed.

On the other hand, the position measurement of the mover 1 will be described. As described above, the output signal of the waveform shaping circuit 24 is connected to the counter 26, and in the counter 26, the count number C of the output signal from the zero-cleared position is obtained.
n is sent to the microcomputer 19 as needed. At this time, the distance α traveled by the mover 1 with one pulse of the output signal of the waveform shaping circuit 24 is known in advance at the time of designing. Therefore, this distance α is stored in the ROM in the microcomputer 19.
By storing in advance in C18 and calculating Cn × α in the microcomputer 19, it is possible to obtain the position (concavo-convex period) of each periodical concavo-convex in the portion of the mover 1 facing the displacement sensor 14. it can.

As to the facing surface 15a, the facing surface 15a facing the displacement sensor 14 is a linear slant surface within one cycle of the periodic unevenness, as is clear from FIG. 1 (a). The position in the traveling direction of the mover 1 within one cycle of the unevenness and the distance between the displacement sensor 14 and the facing surface 15a have a proportional relationship as shown in FIG. Therefore, after measuring the distance to the facing surface 15a by the displacement sensor 14 and subtracting the initial value x ₀ thereof, the linear transformation by the constant coefficient K ′ is used to determine the distance within one cycle of the periodic unevenness of the mover 1. The position can be calculated.

Here, the coefficient K'can be expressed by the reciprocal of the slope of the graph shown in FIG. 7, that is, (a-a ₀ ) / (b-x ₀ ). The linear conversion coefficient K ′ and the initial value x _{0 of the} distance between the displacement sensor 14 and the facing surface 15a are known at the time of design and can be treated as constants. Therefore, by inputting the coefficient K ′ and the initial value x ₀ in the microcomputer 19 in advance, this linear conversion can be easily executed in the microcomputer 19.

In this way, the position of the movable element 1 within one cycle of the periodic unevenness and the position of each periodic unevenness are also obtained, so that the processing for adding the positional information is performed in the microcomputer 19 at any time. By doing so, the absolute position of the mover 1 can always be obtained with high resolution.

In this embodiment, the case where the facing surface 15a is a straight slope has been described. However, if the pattern shape does not have an inflection point within one cycle of periodic unevenness,
By approximating the relationship between the position of the mover 1 and the distance between the displacement sensor 14 and the facing surface 15a by a polynomial or the like, the absolute position of the mover 1 can be similarly obtained.

By the way, such a linear DC motor is used, for example, as a sub-scanning drive source of a reading optical system member of the image scanner 28, as shown in FIG. Figure 8
The image scanner 28 shown in FIG. 1 slit-exposes a document 30 placed on a contact glass 29 with an exposure lamp 31 such as a fluorescent lamp or a halogen lamp and a reflecting plate 32, and reflects the reflected light into an imaging element such as a SELFOC lens. 33
The reading optical system members 31 to 34 are fixedly mounted as the reading unit 35 on the movable element 1 so as to perform sub-scanning on the surface of the document 30. It is configured. The stator 2 is fixed to the housing 36 of the image scanner 28.

In such a structure, the reading unit 35 reads the image of the original 30 in the main scanning direction by self-scanning while being sub-scanned by the linear DC motor (movable element 1), and reads the original image two-dimensionally as a whole. . Here, since the reading unit 35 uses the above-described linear DC motor of the direct drive for driving in the sub-scanning direction, the driving control can be performed at a low cost without speed fluctuations caused by rattling or backlash of the transmission system, and thus the driving speed is high. Can read accurately. Further, position control such that the reading unit 35 is started at a desired position and stopped at a desired position in order to perform partial reading can be performed with high accuracy.

Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, first, instead of the displacement sensor 14, a sensor (probe) 37 whose output changes according to the target area is attached to the mover 1. A sensor target 38 is provided on the base plate 10 so as to face the movement trajectory of the sensor 37.
In this sensor target 38, the shaded portion in FIG. 10 serves as the sensor 37 sensing portion. As shown in the figure, the area periodically changes in the moving direction of the mover 1, and the area change is Decrease change (or increase change) within one cycle
It is formed as a triangular pattern that indicates only. However, the pattern shape of the sensor target 38 is not limited to the triangular shape, and the point is that the sensor target 38 only needs to have a shape in which the area changes periodically with a characteristic of an increase change or a decrease change within the cycle. In this way, the combination of the sensor 37 and the sensor target 38 is possible, for example, by shining light and measuring the level of the reflected light with a detector. Therefore, for example, the sensor 37 may be composed of a light source and a detector.

Even with such a configuration, the control system may be configured in the same manner as shown in FIG. 3 by replacing the displacement sensor 14 with the sensor 37. In this case, sensor 3
The output signal from 7 has a triangular saw-tooth shape as shown in FIG. 11A, and the waveform is shaped by the waveform shaping circuit 24 into a rectangular wave output as shown in FIG. Therefore, after that, it becomes possible to detect the moving speed and the absolute position of the mover 1 and to control them, as in the above embodiment.

More specifically, the number of output pulses of the waveform shaping circuit 24 is counted by the counter 26, and the count value is set to 1
By multiplying the distance traveled by the mover 1 with a pulse, the position for each periodic change in the area of the portion facing the sensor 37 can be obtained. Then, the sensor 37 with respect to the position of the mover 1 within one cycle of the area change of the portion facing the sensor 37.
The areas of the facing portions are in a proportional relationship as shown in FIG. Therefore, as in the case of the above embodiment, the reciprocal of the slope
By using (c−c ₀ ) / (d−S ₀ ) and the initial value S ₀ of the area within one cycle, the position of the mover 1 within one cycle of the area change of the portion facing the sensor 37 is obtained. be able to. After that, as in the above-described embodiment, the absolute position of the mover 1 can be obtained with high resolution by adding these pieces of position information.

Also in this embodiment, as in the case of FIG. 8, it can be applied to the image scanner 28 as shown in FIG.

[0036]

Since the present invention is configured as described above, according to the invention of claim 1, the displacement sensor attached to the mover and the stator side by being positioned on the movement locus of the displacement sensor. In combination with the sensor target that is provided on the base and has a concavo-convex shape that changes cyclically and continuously within the cycle without an inflection point, measures the concavo-convex cycle and the distance between the displacement sensor and sensor target to determine the position of the mover. According to the invention as set forth in claim 2, the sensor is attached to the mover and the output of which changes depending on the target area, and the sensor is provided on the stator side while being positioned on the movement locus of the sensor. The position of the mover is calculated by measuring the pattern period and the sensor target area in combination with the sensor target whose pattern is periodic and changes so as to show an increasing change or a decreasing change within the period. The Rukoto, low price, and it is possible to secure the function of the precision of the linear encoder can be elongated into a simple construction, thus, it is capable of performing highly accurate position control of the movable element.

Further, according to the third aspect of the invention, since such a linear DC motor is position-controlled as a sub-scanning drive source in the image scanner, it is inexpensive and highly accurate reading is performed even in partial reading. It can be done.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, in which (a) is a front view and (b) is a side view.

FIG. 2 is a plan view.

FIG. 3 is a block diagram showing a control system.

FIG. 4 is a timing chart showing signal waveforms.

FIG. 5 is a timing chart showing signal waveforms.

FIG. 6 is a flowchart.

FIG. 7 is a graph showing the relationship between mover position and distance.

FIG. 8 shows an application example to an image scanner,
(a) is a front view and (b) is a side view.

FIG. 9 shows a second embodiment of the present invention, (a) is a front view and (b) is a side view.

FIG. 10 is a plan view.

FIG. 11 is a timing chart showing signal waveforms.

FIG. 12 is a graph showing the relationship between mover position and area change.

FIG. 13 shows an application example to an image scanner,
(a) is a front view and (b) is a side view.

[Explanation of symbols]

1 mover = armature 2 Stator = field magnet 14 Displacement sensor 15,38 sensor target 19, 26, 27 computing means 28 Image Scanner 37 sensors

Claims (3)

[Claims] 1. A field magnet having N-pole and S-pole magnetic poles alternately arranged in the longitudinal direction, and an armature having one or more drive armature coil groups facing the field magnet. In a linear DC motor having one of a field magnet and an armature as a mover and the other as a stator, a displacement sensor is attached to the mover, and the displacement sensor is periodically arranged on a locus facing the displacement sensor in a moving direction. Based on the unevenness cycle of the sensor target detected by the displacement sensor and the distance between the displacement sensor and the sensor target, the sensor target formed in the unevenness shape that continuously changes without an inflection point in the cycle is provided on the stator. A linear DC motor, comprising a calculation means for calculating the position of the mover. 2. A field magnet having N and S magnetic poles alternately arranged in the longitudinal direction, and an armature having one or more driving armature coil groups facing the field magnet. In a linear DC motor with one of the field magnet and armature as a mover and the other as a stator, a sensor whose output changes according to the target area is attached to the mover, and a sensor is installed on the path facing the sensor. Provided on the stator is a sensor target formed in an area change pattern that is periodic in the movement direction and shows an increase change or a decrease change within the period, and the pattern period and the sensor target area of this sensor target detected by the sensor A linear DC motor, characterized in that arithmetic means for calculating the position of the mover is provided based on the linear DC motor. 3. An image scanner using a linear DC motor according to claim 1 or 2, wherein a movable element for carrying out sub scanning is mounted with a reading optical system member.