The present invention relates generally to linear voice coil actuators, and in particular to a linear voice coil actuator with improved force characteristics and methods for achieving such improved force characteristics.
At least three prior art references describe improvements made to linear voice coil actuators by removing some material from one or more parts of the magnetic circuit. U.S. Pat. No. 5,808,379, issued to Zhao and assigned to Kulicke and Soffa Industries, Inc. shows such an improvement: at least one air gap 44 is provided in at least one of the pole pieces. See
Another prior art actuator is depicted in
Yet another prior art actuator, depicted in
All of the above three patents substantially describe rectangular voice coil actuators, although U.S. Pat. No. 5,677,963. mentions that the core could be cylindrical. However, the above mentioned patent describes field plates connected to end plates in a fashion which can be interpreted to mean that only two magnets or two sets of magnets are attached to the parallel plates and only two sides of the coil are involved in creating the force.
Despite improvements in actuator performance achieved by these earlier efforts, there continues to be a need for improvement in force imbalance as a function of the position of the coil and current direction in the coil.
The present invention addresses the need for an improved force balance characteristic and provides a method for achieving such improvements. In accordance with the present invention a linear actuator comprises a core having a longitudinal axis, a coil shaped for movement along the longitudinal axis of the core, and a magnet structure positioned along the longitudinal axis of the core, wherein the core includes first and second portions, each including an end face and a cavity formed in the end face and having an axis of symmetry along the longitudinal axis of the core, and further wherein the first and second portions are positioned so that the end faces oppose each other and are separated by a gap.
By forming a cavity in each of the first and second portions of the core in a direction along the longitudinal axis of the core, that is in the direction of motion of the coil, it has been found that a substantial improvement in force balance can be achieved. The cavity is preferably of substantially the same shape in each of the core portions. For example, a half-spherical cavity can be used, and when the first and second portions of the core are positioned so their end faces oppose each other to form the gap, the combination of half-spherical cavities form a substantially spherical chamber in the core subdivided by the gap.
Preferably, the cavity is widest at the end face of each portion of the core, and decreases in span in a direction away from the end face. The cavity is preferably curvilinear in cross section along the longitudinal axis.
In accordance with the method of the present invention, a linear actuator is formed by forming a core having a first portion and a second portion positioned along a longitudinal axis, defining an end face in each of the first and second portions, removing material symmetrically along the longitudinal axis of the core to form a cavity in each of the first and second portions; and positioning the first and second portions so that the end faces oppose each other and are separated by a gap, shaping a coil for movement along the longitudinal axis of the core, and positioning a magnet structure along the longitudinal axis of the core.
In accordance with the method of the present invention, the removal of material to form the cavity can be accomplished by forming in the end faces of the first and second portions of the core concentric bores of varying diameters having centers along the longitudinal axis. For example, the cavities can be formed by drilling out regions of material of selected depths and selected diameters which are coaxial with the longitudinal axis, and causing the selected diameters of the drilled out regions to increase in a direction toward the end face.
It is therefore an object of the present invention to provide a linear actuator, and a method for forming the same, which has improved force balance characteristics.
It is another object of the present invention to provide a linear actuator and method, in which a core is formed of a first portion and a second portion each with end faces that oppose one another to form a gap, and having a cavity formed in each end face which cavity extends symmetrically along a longitudinal axis of the core.
It is a further object of the present invention to provide a linear actuator and method therefore in which a core having a longitudinal axis is formed of two sections, each having a face transverse to the longitudinal axis and that opposes the other face to form a gap, and further in which each face has formed in it a curvilinear chamber having a span which decreases with distance from the face.
These and other objectives, features, and advantages of the present invention will be more readily understood upon considering the following detailed description and accompanying drawings.
The above referenced U.S. Pat. Nos. 5,808,379, 5,113,099. and 5,677,963. are hereby incorporated herein by reference.
In one embodiment of the actuator of the present invention, a cylindrical coil 50 is surrounded by the magnets 52 attached to the housing 54, as illustrated in
In the embodiments of
In the embodiments of
It is to be understood that actuators in accordance with the present invention can take various cross sections, including circular, rectangular and square cross sections transverse to the longitudinal axis 66.
In accordance with the present invention,
In order to improve Force vs. Stroke characteristic of the actuators of the present invention, some magnetic material should be removed from the magnetic circuit. But unlike the method described in U.S. Pat. No. 5,677,963. where a hole is drilled through the core perpendicular to its axis, in accordance with the present invention the magnetic material removal is done along the axis 66 of the core 64 to form a cavity 68. The particular shape of the cavity 68 in the core 64 is determined by the desired Force vs. Stroke characteristic.
In order to accomplish the formation of the cavity in accordance with the present invention, a core preferably comprises two halves 64A, 64B, separated by a gap 69. The optimal size of this gap 69 is also calculated as part of the magnetic circuit. For example,
In the preferred embodiment of the present invention, the magnets can be radially magnetized ring magnets or a plurality of segmented magnets of the same polarity facing the coil and shaped to be positioned inside or outside of the coil. As can be seen from
The advantage of having a cavity formed in the manner of the present invention is demonstrated by
In contrast, the solid lines illustrate the Force vs. Stroke characteristics of an actuator with a core having a spherical cavity in accordance with the present invention. The solid line with square markers illustrates the Force vs. Stroke characteristics for a left-to-right motion, while the solid line with “X” markers illustrates the right-to-left Force vs. Stroke characteristics. A variation of only approximately 5N is present, indicating that the force imbalance has been cut in half over the entire stroke in the illustrated example of an actuator in accordance with the present invention. Further, it can be seen that in the region extending from 11.4 mm to 26.6 mm of the stroke the force variation in either direction is less than approximately 1N.
Preferably, the volume of the cavity should be optimized so that the armature reaction effect is minimized, the force characteristic is as flat as possible, and the force created by the actuator is not reduced. If the volume is smaller than optimal, the armature reaction effect will not be minimized, and the force characteristic will not be as flat as it could be. On the other hand, if the volume of the material removed from the core is greater than optimal, it would reduce the primary magnetic flux created by the permanent magnets and, consequently, reduce the force generated by the actuator.
Among the cavity shapes which can be employed in accordance with the present invention are half-spherical, hemispherical, curvilinear, stepped bore of increasing diameter towards the face, concentric circular regions of progressively increasing diameter, or a shape which is symmetrical about the longitudinal axis of the core and which decreases in span with distance along the longitudinal axis from the face of the core sections.
It is to be understood that the housing and/or the core could also be of a rectangular, preferably square, configuration in the direction perpendicular to the plane of the figures. If a cross-section of the core is rectangular or square, the cavity in both halves of the core can be obtained by milling. An actuator with a housing having a square configuration in the direction perpendicular to its axis is presented in
Two examples of square cross-section actuators in accordance with the present invention are represented in
Disclosed is a linear actuator comprising a core, a coil assembly, a magnet assembly, and a housing. The core has a longitudinal axis and the coil assembly includes a coil that is shaped to be positioned about the core for movement along the longitudinal axis. The housing is supported by the core flanges and positioned about the coil assembly and the core. The magnet assembly comprises a radially magnetized ring magnet or a plurality of segmented magnets of the same polarity facing the coil and shaped to be positioned inside or outside of the coil, and supported by the housing or by the core. The core comprises first and second portions, each having an end face, wherein the first and second portions are positioned along the longitudinal axis so that the end faces oppose each other and are separated by a gap. A cavity is formed in each of the end faces along the longitudinal axis. The core, coil, housing and magnets of the above actuator of the present invention can be cylindrical in shape in a direction perpendicular to the longitudinal axis, and the cavity formed in each face of the first and second portions of the core can be half-spherical.
The cavities of the above embodiments, can be formed from concentric holes of varying diameters formed in the end faces of the first and second portions of the core with centers spaced along the longitudinal axis.
The core, coil, housing and magnets of the above actuator of the present invention can be rectangular, for example square, in shape in a direction perpendicular to the longitudinal axis, and the cavity formed in each face of the first and second portions of the core can be a plurality of the rectangular or square cavities of the increasing cross-section, similar to a plurality of cylindrical holes shown in
The terms and expressions employed herein are terms of description and not of limitation, and there is no intent in the use of such terms and expressions of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.
The present application claims priority under 35 U.S.C. §119(e) from provisional application No. 60/421,929, filed Oct. 28, 2002.
Number | Name | Date | Kind |
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3743870 | Hunt | Jul 1973 | A |
4652779 | Wilcox | Mar 1987 | A |
4808955 | Godkin et al. | Feb 1989 | A |
5539262 | Strugach | Jul 1996 | A |
5731642 | Ogawa | Mar 1998 | A |
5808379 | Zhao | Sep 1998 | A |
7499555 | Isvan | Mar 2009 | B1 |
Number | Date | Country |
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0 397 322 | Nov 1990 | EP |
59-193700 | Nov 1984 | JP |
61177897 | Aug 1986 | JP |
11-027920 | Jan 1999 | JP |
Entry |
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English Translation: JP 61177897A. “Oscillating Device for Pump Speaker or the Like.” Feb. 1, 1986. Inventor: Nakamatsu, Yoshiro. |
International Search Report mailed Mar. 16, 2004. |
Number | Date | Country | |
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20040156526 A1 | Aug 2004 | US |
Number | Date | Country | |
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60421929 | Oct 2002 | US |