JPH0467762A - Linear dc motor - Google Patents

Abstract

PURPOSE:To relax the speed unevenness by motor thrust ripple so as to enable the driving excellent in constant velocity by attaching a dynamic vibration reducer, which has the torsional vibration system where torsional resonance frequency accords with the vibration frequency by motor thrust ripple, to a needle, and setting the resonance frequency of the torsional vibration system optionally. CONSTITUTION:A dynamic vibration reducer 19 is constructed by attaching a vibrator 20 having moment of inertial J in inertial moment to the A point of a needle 16 through a plate spring 21 of C in spring constant, and performs torsional vibration around the A point. However, since the shifting speed V of the needle 16 and the cycle a of thrust ripple are obvious at the time of design of a motor, the constants J and C of the dynamic vibration reducer 19 are so designed that the resonance frequency omega2 of the torsional vibration system may be omega2 =2pi v/a=(C/J)<1/2> =(k2/m2)<1/2>. Hereby, the speed unevenness caused by the thrust ripple of a linear DC motor 11 can be negated. Furthermore, it is possible to set the values of J and C so that the above formula may materialize by varying the position of the attachment of the vibrator 20, so constant velocity can be secured even at speed change control of a motor.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a linear DC motor.

2. Description of the Related Art In general, a linear DC motor is used as a drive source for linearly moving an optical head, an image scanner, or the like. As an example, there is a semiconductor DC near motor disclosed in Japanese Patent Laid-Open No. 59-86473.

Here, the outline of such a linear DC motor will be explained with reference to FIG. 5. This is an example of a three-phase, four-pole motor 1, which includes a stator 2 and a movable element 3 movably disposed above the stator 2 and facing each other. The stator 2 is constituted by a field magnet in which N-pole and S-pole magnetic poles 5 are arranged alternately in the longitudinal direction on a rail-shaped fixed base 4. The mover 3 has armature coils 6u, 6v for three phases of V+W,
The 6w group is composed of an armature attached to a movable base 7 so as to face the stator 2. At the center of each armature coil 6u, 6v, 6w group are Hall elements 8u, 8v,
8w is provided. These Hall elements 8u, 8v
, 8w is wider than the magnetization pitch of the north and south poles of the magnetic pole 5.

In such a configuration, each Hall element 8u.

When the excitation of the armature coils 6u, 6v, and 6w is switched and controlled according to the magnetic force detected by the magnets 8v and 8w, and magnetic forces of attraction and repulsion are applied between the magnetic poles 5 of the stator 2, thrust is generated. occurs, and the mover 3 moves linearly along the longitudinal direction.

Problems to be Solved by the Invention In such a linear DC motor, thrust ripples inevitably occur due to its structural characteristics. That is, in the case of the 3-phase 4-pole motor shown in Fig. 5, the magnetic flux density (not shown) has a sinusoidal distribution, so U, V, W
The thrust due to each phase also has a sinusoidal waveform as shown in FIG. Then, when the coil to be actually excited and its excitation direction are switched and adjusted based on the Hall element 8 at a certain point, the thrust obtained by the motor is a combination of the thrusts from each phase as shown in Fig. 6. This results in thrust ripple. In other words, since the magnetic flux density has a sinusoidal distribution, when a constant current is applied to drive the thrust, the resulting thrust has ripples. Such thrust ripples cause speed fluctuations and speed unevenness that impede the uniform motion of the movable element 3, reducing reliability. Furthermore, since the thrust ripple is a function of position, it can also be seen that the frequency of the thrust ripple changes depending on the speed of the mover.

Means for Solving the Problem A field magnet having magnetic poles of N and S poles alternately in the longitudinal direction, and an armature having one or more driving armature coil groups facing the field magnet are provided. , a dynamic vibration reducer with a torsional vibration system in which the torsional resonance frequency matches the vibration frequency due to motor thrust ripple in a linear DC motor in which one of the field magnets and armature is a mover and the other is a stator. is attached to the movable element, and a variable frequency setting means for arbitrarily setting the resonance frequency of the torsional vibration system is provided.

A dynamic vibration absorber with a torsional vibration system that matches the operating torsional resonance frequency to the vibration frequency caused by motor thrust ripple is attached to the mover, reducing speed unevenness caused by motor thrust ripple and enabling drive with good uniform velocity. becomes. Here, since the resonance frequency of the torsional vibration system can be arbitrarily varied by the variable frequency setting means, it is possible to cope with the case where the motor speed is controlled in variable speed, and it is possible to reduce speed unevenness due to motor thrust ripple.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 4. First, a linear DC motor 1 to which this embodiment is applied
1 will be outlined with reference to FIGS. 2 and 3. This embodiment also uses a field magnet as a stator 12, and this stator 12 has a rail-shaped fixed base 13 with a chevron-shaped cross section.
N-pole and S-pole magnetic poles 14 are arranged alternately in the longitudinal direction on the central convex portion of the magnetic pole. The stator 121- is provided with a movable element 16 having an armature structure and movable in the longitudinal direction by rolling bearings I5 that roll on both upper surfaces of the fixed base 130 as rails. This mover 16 has armature coil 18 groups (several groups in the longitudinal direction as in the case of FIG. 5) attached to the bottom surface of the movable element 16 via a back yoke 17 so as to face the magnetic pole 14. It is being

With such a basic configuration, the movable element 16 moves on the stator 12 on the same principle as in the case of FIG. 5.

Here, the period of vibration due to the thrust ripple generated in the linear DC motor 11 is as follows: moving speed of the mover 16 v Cm/sec], period of the thrust ripple a [ml(
(see FIG. 6), and f=v/a[Hzl. That is, the movable element 16 moves at a constant speed while f=v/
It is considered that the vibration is forced at a [Hzl].

Therefore, when the movable element 16 is modeled, it can be expressed as shown in FIG. 4(b). ml is the mass of the mover 16. It is also assumed that the movable element 16 is held on the stator 12 by a support system having an arbitrary spring constant of 1. Here, mover 1
F cosω to 6 (ω=2πf=2πv/a
) is the state in which the movable element 16 is in the moving state.

On the other hand, consider a dynamic vibration absorber 19 with a mass m and a support system having a spring constant of 2 as shown in FIG. 4(a).

Then, simultaneous equations are established. Here, X, = a, cosω, and X7a,
Assuming CO3ωt, k,7m,=ω, ,7m,
When we set =tw,,m,/m+=μ,F/ as =ast, we get the following. In this case, when ω'/ω2=1, the numerator of the above equation becomes 0, so the movable element 16 with mass m1 does not vibrate. That is, by attaching the dynamic vibration absorber 19 with m, , which is set to ω2-2πv/a to the movable element 16, the thrust ripple is absorbed and the movable element 16 performs only uniform motion. It turns out.

Based on this idea, in this embodiment, first, as shown in FIG. 2, a dynamic vibration absorber 19 is mounted on the movable element 16. This dynamic vibration absorber 19 is constructed by attaching a vibrator 20 with a moment of inertia J to a point A of a movable element 16 via a plate spring 21 having a torsional spring constant C, and is configured as a vibration system that performs torsional vibration around point A. ing. This torsional vibration system can be considered equivalent to a translational vibration system when projected in the moving direction of the movable element 16 of the linear DC motor 11.

First, the moving speed (2) of the movable element 16 and the period (a) of the thrust ripple are made clear at the time of designing the motor.

Therefore, ω, = 2 πv/ a = (C/ J )”
By designing the constants J and C of the dynamic vibration absorber 19 so that ==(k, 7m,)'', the effect of the dynamic vibration absorber 19 reduces the vibration caused by the thrust ripple of the linear DC motor 11, that is, the speed. It is possible to cancel the unevenness, and mover 1
6 can be made to move only at a constant velocity.

By the way, in this embodiment, the dynamic vibration absorber 19 is installed so as to be able to cope with the case where the linear DC motor 11 is controlled to change speed.
is provided with a frequency variable setting means 22 that can vary the moment of inertia J and the torsional spring constant C that regulate the resonance frequency of the torsional vibration system. First, as shown in FIG. 1, a leaf spring 21 fixed to point A of the movable element 16 is constructed as a rotary elastic support system. The vibrator 20 is divided into two hemispherical parts 20a sandwiching the leaf spring 21,
20b, and one hemispherical part 20a has a fixing screw 2.
3, and a fixing screw hole 25 is formed in the other hemispherical portion 20b. Also, leaf spring 2
1 is formed with an elongated hole 26 for moving the fixing screw 23. Therefore, the fixing screw 2 installed in the screw hole 24
3 to the fixing screw hole 25,
The hemispherical portions 20a, 20b are fixed with the leaf spring 21 in between, and the fixed position can be arbitrarily set by loosening the fixing screw 24, adjusting the length 26, and moving it to an appropriate position. Such a fixed position of the vibrator 20 arbitrarily regulates the constants J and C of the vibration system. By varying the fixed position of the vibrator 20, the plate spring 21
This is because the effective length and moment of inertia of

Specifically, since the moving speed ■ and the period a of the thrust ripple are known before the mover 16 moves, the resonance frequency ω of the torsional vibration system is ω2−2π■/a=(c/J)” /
The vibrator 20 can be installed by changing its position and setting the values of J and C so that the speed is '-(k/m)''. can be reduced and uniform velocity can be ensured.

Although this embodiment has been described as an example in which only one dynamic vibration absorber 19 is provided, two torsional vibration systems, that is, two dynamic vibration absorbers are arranged line-symmetrically with respect to the moving direction of the movable element 16. They may be attached to the movable element 16, and each of them may be provided with variable frequency setting means.

Furthermore, although these embodiments are of a moving coil type in which the armature is a movable element, a movable magnet type in which the field magnet side is a movable element may be similarly applied.

Effects of the Invention In the present invention, as described above, a dynamic vibration absorber having a torsional vibration system that matches the torsional resonance frequency to the vibration frequency caused by motor thrust ripple is attached to the mover, thereby reducing speed unevenness caused by motor thrust ripple. However, since it is possible to drive with good uniformity of speed, and the resonance frequency of the torsional vibration system can be arbitrarily set variably using the variable frequency setting means, it is possible to perform variable speed control of the motor speed. However, it is possible to reduce speed unevenness due to motor thrust ripple.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention,
FIG. 1(a) is a plan view mainly showing the frequency variable setting means, FIG. 1(b) is a side view thereof, FIG. 2 is a plan view of the motor, FIG. 3 is a vertical side view thereof, and FIG. 4 5 is a front view showing a conventional example, and FIG. 6 is a characteristic diagram of each phase thrust and thrust ripple. 12... Stator, 14... Magnetic pole, 16... Mover, 18... Armature coil group, 19... Dynamic vibration reducer, 22
... Frequency variable setting means → N) Ayu

Claims (1)

[Claims] 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 are provided, and these field magnets and In a linear DC motor in which one side of the armature is a mover and the other side is a stator, a dynamic vibration absorber having a torsional vibration system in which the torsional resonance frequency matches the vibration frequency due to motor thrust ripple is attached to the mover, A linear DC motor characterized in that a variable frequency setting means is provided for arbitrarily setting the resonance frequency of the torsional vibration system.