JPH01308162A - Linear actuator - Google Patents

Abstract

PURPOSE:To make the ratio of thrust/weight of apparatus larger by providing a moving coil at the outer periphery of a permanent magnet with an annular external yoke. CONSTITUTION:In the central part of the top of a non-magnetic material yoke- supporting block 8, an axially N- and S-magnetized bar permanent magnet 9 as a center yoke is vertically held between internal yokes 10, 11. Also, a coil bobbin 4 is provided with two sets of coils 12-13 separated from each other axially and wound the same number of times in directions opposite to each other so that said coils correspond respectively to the sides of said upper and lower internal yokes 10-11. Then, an annular external yoke 14 is arranged at the outer periphery of said coil 12-13 via an air gap so as to face a center yoke, and the lower part of said external yoke is fixed to said supporting block 8. Thus, a leakage flux decreases and a magnetic flux generated by the permanent magnet can be used effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a linear actuator used in various mechanisms requiring linear motion.

(Problems to be Solved by the Invention) Generally, linear actuators used in the above-mentioned fields of application are required to be as small as possible and have high thrust characteristics, that is, high thrust/weight characteristics over a relatively long stroke. Conventionally, linear actuators called voice coil motors have been put into practical use, such as the magnetic pole type system shown in Figure 3 and the internal magnetic type system shown in Figure 4, but they have the following drawbacks. There is.

For example, in the case of the conventional example shown in FIG. 3, if the length of the cylindrical permanent magnet 1 provided along the central axis is increased, a uniform magnetic field can be obtained over a long stroke, and the permanent magnet 1 can be placed along the circumference. Although a relatively high amount of air gap magnetic flux can be obtained by arranging the permanent magnet 1, the volume of the permanent magnet 1 increases, resulting in an increase in the weight of the actuator body, which has the disadvantage of causing an increase in cost.

Note that 3 is a yoke, 4 is a coil bobbin, 5 is a coil, 6 is an operating shaft connected to the coil bobbin 4, and 7 is a center yoke.

In the conventional example shown in FIG. 4, by arranging the rod-shaped permanent magnet 2 as the center yoke 7, it is possible to eliminate the disadvantage of increasing weight and cost as in the conventional example described above, but it also has the disadvantage of large leakage of magnetic flux. ing. Figures 5 and 6 are respectively Figure 3 and Figure 6.
FIG. 4 shows the results of analysis and simulation of the magnetic flux path of the conventional example using the finite element method, and it can be seen that there is a large amount of leakage magnetic flux in the conventional example.

It is an object of the present invention to provide a linear actuator that improves these drawbacks, has a good thrust/weight ratio, and is inexpensive.

(Means for Solving the Problems) The linear actuator of the present invention includes a non-magnetic support, an axially magnetized permanent magnet provided as a center yoke on the support, and an outer periphery of the permanent magnet. It is characterized by comprising a moving coil arranged so as to surround it at a distance from the dirt, and an annular external yoke arranged to surround the outer periphery of the moving coil at a distance from the dirt.

(Example) The present invention will be explained in detail below with reference to the drawings.

In general, the thrust force F of a DC linear actuator follows Fleming's left-hand rule, where the magnetic flux density in the air gap is B, the current flowing to the coil placed in the air gap is I, and Eft.
When the effective length of the coil placed in the field is Il, and the number of turns of the coil is t, it is expressed as F=t-B-1-L (1). In order to obtain a good thrust/weight ratio (
1) It is necessary to consider the magnetic characteristics, shape, and arrangement of the magnet and magnetic field yoke while considering equation 1), and also consider the air gap length and coil specifications.

t, ■, and L in equation (1) are determined based on the results of studies under certain restrictive conditions, based on the temperature rise limit specifications related to the actuator body size restrictions and coil stacking ratio, and the main focus of improving thrust characteristics is on the coil. The important point is how to obtain an effective magnetic flux linkage, that is, it is important to efficiently make Equation (1) B a large value. The present invention is based on this idea.

In the present invention, as shown in FIG. 1, a rod-shaped permanent magnet 9 oriented NS in the axial direction is installed as a center yoke in the upper center of a yoke support block 8 made of a non-magnetic material.
Coil bobbin 4
is provided with two sets of coils 12.13 which are axially spaced apart and wound the same number of times in opposite directions, respectively, so as to correspond to the side surfaces of the upper and lower internal yokes 10.11, and these coils 12.13 An annular column-shaped external yoke 14 is disposed on the outer periphery of the center yoke with a gap therebetween, facing the center yoke, and its lower portion is fixed to the support block 8.

Since the device of the present invention has the above-described configuration, the coil 12.
When the coil 13 is energized, the magnetic flux flow shown by the arrow in Fig. 1 and the coil current act, and the thrust force F1 generated in the coil 12 is (
1) From the formula, Fl = t・B-1・■, however, the number of turns is 2, B: magnetic flux density of the air gap, ■: coil 12
energizing current value, L: the circumference length of the coil, and the spontaneous shear thrust F when the same value of current I is also applied to the coil 13.
2 becomes F2=t-B-1-L. The thrust generated in the operating shaft 6 is now in the direction of the arrow, and its value F is F=F1+r2=2t-B-I-L.

As is clear from the above equation, the problem with the thrust force F clarified in the above explanation is how to increase the magnetic flux interlinking with the coil placed in the air gap. As is clear from the magnetic flux flow diagram in Figure 2, the flow of magnetic flux in this embodiment has very little leakage magnetic flux, making it possible to effectively utilize the magnetic flux generated by the permanent magnets, resulting in a large (thrust/weight) The ratio is obtained.

(Effects of the Invention) As described in section 2, according to the present invention, the reduction in energy consumption is approximately 40% compared to the conventional example.
A large (thrust/weight) ratio is obtained.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the linear actuator of the present invention, Figure 2 is an explanatory diagram of its magnetic lines of force, Figures 3 and 4 are sectional views of a conventional linear actuator, and Figures 5 and 6 are its lines of magnetic force. FIG. 1.2.9...Permanent magnet, 3...Coke, 4...
Coil bobbin, 5... Coil, 6... Operating shaft, 7.
...Center yoke, 8...Yoke support block, 10
．． 11... Internal yoke, 11.1.3... Coil, 14... External yoke. Agent Patent Attorney Makoto Sawagi - Figure 5 Sukyo

Claims (2)

[Claims] (1) A non-magnetic support, an axially magnetized permanent magnet provided as a center yoke on the support, and a moving coil arranged to surround the outer periphery of the permanent magnet at a distance from the permanent magnet; A linear actuator characterized by comprising an annular external yoke arranged to surround the outer periphery of the moving coil at a distance from the outer yoke. (2) Both ends of the permanent magnet are held between internal yokes, and the movable coil is separated into two parts in the axial direction and arranged so as to face the upper and lower internal yokes, respectively. linear actuator.