JPH04372564A - Linear direct current motor and image scanner using this motor - Google Patents

Abstract

PURPOSE:To grasp the moved position of a moving element by making the constitution simple and cheap. CONSTITUTION:Field magnets having N- and S- magnetic poles alternately in the longitudinal direction, and an armature having more than one group of driving armature coils facing these field magnets are provided. Either the said field magnets or armature is made a moving element 1 and the remainder a stator 2 to produce a linear direct current motor. A displacement sensor 14 is fitted to the moving element 1 of the motor, and a sensor target 15 is fitted to the stator 2 being fitted so that the distance of the part facing this displacement sensor 14 may change continuously without an inflection point in proportion to the moved position of the moving element 1.

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, an image scanner, or the like. In other words, it is possible to use a rotary motor and convert it into linear motion using a transmission system, but with such a drive system, there is a limit to the high accuracy of feed due to play and backlash caused by the transmission system. .

[0003] Japanese Patent Laid-Open No. 122357/1983 discloses a linear DC motor equipped with an optical linear encoder for the purpose of highly accurate movement and stopping. This allows the position and propulsion speed of the movable element to be easily detected by reflecting the light from the optical wavelength generating element on an inclined reflecting surface provided on the side of the movable element and receiving it with the optical wavelength receiving element. It is something. According to this, the position and propulsion speed can be easily detected, making it possible to move or stop with high precision.At the same time, since there is no need to move the optical wavelength generating element and the optical wavelength receiving element together with the movable element, the power cord It has the advantage that it does not get in the way.

0004

[Problems to be Solved by the Invention] However, according to such a conventional method, it is necessary to use expensive optical components such as an optical wavelength generating element, an inclined reflection surface, an optical wavelength receiving element, etc. It also requires highly accurate assembly and adjustment, making it troublesome to handle.

[0005]

[Means for Solving the Problems] The invention according to claim 1 includes a field magnet having magnetic poles of N and S poles alternately in the longitudinal direction, and one or more driving electric machines facing the field magnet. A linear DC motor is provided with an armature having a group of child coils, and one of these field magnets and the armature is a mover and the other is a stator, and a displacement sensor is attached to the mover, and the displacement sensor is The stator is provided with a sensor target whose distance between opposing portions changes continuously without an inflection point according to the position of the movable element.

In this case, in the invention as claimed in claim 2, the sensor target is in the form of a tape, and the sensor target is stretched and supported by height-adjustable support means so that the inclination angle in the moving direction of the movable element can be adjusted.

In the third aspect of the invention, such a linear DC motor is used in an image scanner, and a reading optical system member is mounted thereon as a movable member for sub-scanning.

[0008]

According to the invention as set forth in claim 1, the position of the movable element as it moves is calculated by measuring the distance between the sensor target and the displacement sensor, which changes continuously according to the position in the moving direction using a displacement sensor. This ensures the functionality of the linear encoder and enables highly accurate operation control of the mover with an inexpensive and simple configuration.

At this time, the accuracy of measuring the distance between the displacement sensor and the sensor target becomes the accuracy of measuring the moving position of the movable element.According to the second aspect of the invention, the sensor target is tape-shaped, and its inclination angle is Since it is supported in a freely adjustable state, it is easy to adjust the inclination angle with strict precision.
More precise motion control can be maintained.

According to the third aspect of the invention, by using such a linear DC motor as a sub-scanning drive source in an image scanner, high-precision reading can be performed at low cost.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. First, the linear DC motor of this embodiment uses the armature as the mover and the field magnet as the stator 2.

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

The stator 2 also includes a long base plate 10 having a stepped or groove-shaped rail portion 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 consisting of magnetic poles 12 provided on the fixed back yoke 11 and magnetized alternately as north and south poles.

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

In this embodiment, a displacement sensor 14 is attached to a part of the movable element 1 in a manner that it projects laterally. This displacement sensor 14 uses a non-contact type, for example, an eddy current type displacement meter, but other types such as light, light, etc. are used.
It may also be one that uses sound or magnetism. A sensor target 15 is provided on the base plate 10 along the movement trajectory of the displacement sensor 14. This sensor target 15 has an opposing surface 15a facing the displacement sensor 14 that is sloped as shown in FIG. Has no points. Such a sensor target 15
In this case, only the facing surface 15a or the entire base plate 10 may be made of the target material for the displacement sensor 14, or the target material may be pasted in a band shape on the facing surface 15a. The detection output of this displacement sensor 14 is also
The signal is inputted to a control device, which will be described later, through the control device and used as a feedback control signal.

Next, the configuration of the control device will be explained with reference to FIG. Basically, microprocessor 16, RAM 17
A command generating device 21 is connected to such a microcomputer 19 via a bus 20. This command generation device 21 generates state command signals such as a position command signal and a speed command signal for commanding the state of the movable element 1. The motor drive device 22 also responds to the output signal of the Hall element 8 and the output signal from the program-controlled microcomputer 19.
General 3-phase motor drive IC23 that outputs signals to
is provided. Through such drive control, the movable element 1 moves at a speed commanded by the command generating device 21. The moving position of the movable element 1 at this time is measured by the displacement sensor 14, and is taken into the microcomputer 19 as the velocity of the movable element 1 via the differentiator 24 and the A/D converter 25. However, if only the position of the movable element 1 is controlled, the output of the displacement sensor 14 may be directly A/D converted by the A/D converter 25.

Here, the measurement of the moving position of the movable element 1 by the displacement sensor 14 will be explained. First, since the facing surface 15a of the sensor target 15 is a linearly inclined surface, the movement position of the movable element 1 and the displacement sensor 14/the facing surface 15a
As shown in FIG. 4, there is a proportional relationship with the distance. Therefore, basically, the displacement sensor 14
By measuring the distance from 4 to the opposing surface 15a,
It can be seen that the position of the movable element 1 in the traveling direction can be determined using linear transformation using a constant coefficient K'. Here, the coefficient K' can be expressed as the reciprocal of the slope of the graph shown in FIG. 4, that is, a/b. In fact, this linear transformation can be easily executed within the microcomputer 19 by inputting the coefficient K' into the microcomputer 19 in advance.

The position information of the movable element 1 obtained in this manner is used for feedback control. For example, consider an example in which proportional control, which is commonly used, is applied to speed control. As mentioned above, the output of the displacement sensor 14 is differentiated by the differentiator 24 to become a velocity signal, which is converted into a digital value by the A/D converter 25 and input to the microcomputer 19. In proportional control, the control voltage to the linear DC motor is generally expressed by equation (1).

[0019]

[Formula 1] V=R(Fr/KF)+K(Rv-v)
……………(1) Here, V: control voltage, R: coil resistance, K: proportional gain, v: mover speed, KF: thrust constant, Fr: friction force.

Furthermore, the speed v of the movable element 1 is actually determined by the linear conversion coefficient K' of the displacement sensor 14, which is determined by the distance x between the measured displacement sensor 14 and the facing surface 15a facing the displacement sensor 14. By multiplying by the sensitivity coefficient K'' of the differentiator 24, it is obtained as shown in equation (2).

[0021]

[Math 2] v=K′・K″・x ……
………………………(2) In equations (1) and (2), R, Fr, and KF are values specific to the motor, and K, K', and K'' are design values for the control system, so all This is a known constant. Also, Rv is a set value and v is obtained as described above, so (1
)(2) and the above-mentioned constants on the microcomputer 1.
The voltage V required for control can be easily obtained by inputting the program or list into the ROM 18 in the ROM 9 and calculating the same equation. Furthermore, the actually obtained control voltage V is pulse-modulated within the microcomputer 19 and output to the three-phase motor drive IC 23 to perform so-called PWM control.

By the way, in FIG. 1, the facing surface 15a facing the displacement sensor 14 is sloped in a straight line, but this does not necessarily have to be a straight line, and it is sufficient if there is no inflection point. That is,
When there is no inflection point on the opposing surface 15a, the relationship between the position of the mover 1 and the distance between the displacement sensor 14 and the opposing surface 15a is as shown in FIG. 5 when the opposing surface 15a is upwardly convex. In the case of a downwardly convex shape, it becomes as shown in FIG. 6, and both can be expressed by polynomials. That is, as a result, the speed V of the mover 1
can be expressed by equation (3).

[0023]

[Math 3]

Here, an+1, an, an-1,...,
a1 is an arbitrary coefficient uniquely determined by the shape of the facing surface 15a facing the displacement sensor 14, and the other coefficients have the same meaning as in the above-mentioned formula.

In this way, when the shape of the opposing surface 15a has no inflection point in the moving direction of the mover 1, (
1) Using equation (3), the displacement sensor 14 and the opposing surface 15a
By measuring the distance between them, the voltage required for control can be easily obtained.

By the way, as shown in FIG. 7, such a linear DC motor is used, for example, as a sub-scanning drive source for a reading optical system member of an image scanner 26. Figure 7
An image scanner 26 shown in FIG. 2 exposes a document 28 placed on a contact glass 27 to a slit using an exposure lamp 29 such as a fluorescent lamp or a halogen lamp and a reflector 30, and directs the reflected light to an imaging element such as a SELFOC lens. 31
These reading optical system members 29 to 32 are fixedly mounted on the movable member 1 as a reading unit 33 to sub-scan the surface of the document 28. It is configured. The stator 2 is fixed to a housing 34 of the image scanner 26.

In such a configuration, the reading unit 33 reads the image of the original 28 in the main scanning direction by self-scanning while being sub-scanned by the linear DC motor (mover 1), and reads the original image two-dimensionally as a whole. . Here, since the reading unit 33 uses the above-mentioned direct drive linear DC motor for driving in the sub-scanning direction, it is possible to drive at low cost and without speed fluctuations caused by play or backlash in the transmission system, and to achieve high precision. can be read.

Next, a second embodiment of the present invention will be explained with reference to FIGS. 8 and 9. In this embodiment, a tape-shaped sensor target 35 is placed opposite the movement locus of the displacement sensor 14.
It has been established. One end of the sensor target 35 in the longitudinal direction is fixed between a high support post 36, and the other end is supported on a low support post 37 by an appropriate spacer 38 and a presser plate 39, which serve as supporting means. The whole structure is supported in a tilted state. Here, an elastic support means 40 such as a coil spring whose tension can be adjusted is attached to the other lower end side of the sensor target 35 to maintain the tensioned state.

According to such a configuration, the sensor target 35 can be easily attached, and its inclination angle can also be easily adjusted. Therefore, a method for attaching the sensor target 35 and a method for adjusting the inclination angle will be explained. First, one end of the tape-shaped sensor target 35 is fixed to the support column 36. Next, the spacer 3 with the design value given in advance
8 is installed on the support 37. Thereafter, an elastic support means 40 is attached to the other end of the sensor target 35, the other end of the elastic support means 40 is fixed to the support column 37, and a presser plate 39 is temporarily fixed so as to sandwich the sensor target 35 therebetween. The elasticity of the elastic support means 40 makes this work extremely easy.

After temporary fixing, the movable member 1 is moved to the left in FIG. 8 so that the displacement sensor 14 is at point A, and the output β of the displacement sensor 14 at this position is recorded. Next, move the mover 1 to the right by exactly the dimension α,
The output γ of the displacement sensor 14 at the position of point B is recorded. Therefore, by calculating (γ-β)/α, the spacer 3 is adjusted so that this value matches the slope b/a shown in FIG.
Adjust by changing the thickness of step 8. At this time, the presser plate 39 is temporarily fixed, and the sensor target 35 is attached to the elastic support means 4.
0, the spacer 38 can be easily removed by slightly pulling the sensor target 35.
can be attached and detached. In this way, sensor target 3
Once the inclination adjustment in step 5 is completed, the holding plate 39 is firmly fixed to complete the installation. Therefore, according to this embodiment, the inclination angle of the sensor target 35, which requires high precision, can be easily adjusted.

Furthermore, according to this embodiment, the displacement sensor 14
Since the movement from point A to point B is used as a reference, that is, the movement of the actual displacement sensor 14 is used as a reference, the inclination angle can be adjusted without depending on the accuracy of the rail portion 9 of the roller 6 of the linear DC motor. It also has the advantage of

This embodiment can also be applied to the image scanner 26 as shown in FIG. 9, as in the case of FIG.

[0033]

Effects of the Invention Since the present invention is constructed as described above, according to the first aspect of the invention, the position of the movable element as it moves is determined by a displacement sensor attached to the movable element.
By measuring and determining the distance between the sensor targets, the function of the linear encoder can be ensured, and the movable element can be controlled with high precision with an inexpensive and simple configuration.

At this time, the accuracy of measuring the distance between the displacement sensor and the sensor target becomes the accuracy of measuring the moving position of the movable element.According to the second aspect of the invention, the sensor target is tape-shaped, and its inclination angle is Since the movable member is supported in an adjustable state, the inclination angle can be easily adjusted with strict precision, and the operation of the movable member can be controlled more accurately.

Further, in the invention as set forth in claim 3, since such a linear DC motor is used as a sub-scanning drive source in an image scanner, highly accurate reading can be performed at low cost.

[Brief explanation 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 graph showing the relationship between mover position and distance.

FIG. 5 is a graph showing characteristics when the opposing surface is upwardly convex.

FIG. 6 is a graph showing characteristics when the facing surface is downwardly convex.

[Figure 7] This shows an example of application to an image scanner.
A) is a front view, and (b) is a side view.

FIG. 8 is a front view showing a second embodiment of the present invention.

FIG. 9 is a front view showing an example of application to an image scanner.

[Explanation of symbols]

1 Mover = armature 2 Stator = field magnet 14 Displacement sensor 15, 35 Sensor target 26 Image scanner 36, 37, 38 Support means

Claims (3)

[Claims] 1. A field magnet having magnetic poles of N and S poles alternately in the longitudinal direction, and an armature having one or more drive armature coil groups facing this field magnet, and these In a linear DC motor in which one of the field magnet and armature is a mover and the other is a stator,
A displacement sensor is attached to the movable element, and the stator is provided with a sensor target whose distance of a portion facing the displacement sensor changes continuously without an inflection point according to the position of the movable element. Linear DC motor. 2. The sensor target according to claim 1, wherein the sensor target is in the form of a tape, and the sensor target is stretched and supported by height-adjustable support means such that the inclination angle in the moving direction of the movable element can be freely adjusted. Linear DC motor. 3. An image scanner using a linear DC motor according to claim 1, wherein the movable element is mounted with a reading optical system member and performs sub-scanning.