The technology relates to linear actuators.
Linear actuators are employed in many and diverse environments. For many applications it is preferred that the linear actuator be unaffected by external shocks. A common method for limiting the effect of external mechanical shocks acting upon a linear actuator is to use a strong return spring that holds a plunger of the actuator in position up to a certain level of acceleration. Typically such strong return springs are either compression springs or conical springs. A major disadvantage of this strong return spring approach is that the strong return spring requires the actuator to have enough performance to overcome the return spring. The power necessary to achieve this spring-overcoming performance may be larger than necessary to move the actuator, and the larger power may in turn problematically increase heat in the actuator. An additional disadvantage is that these devices with higher return spring and actuation forces also have a significant increase in undesirable audible noise.
Some conventional actuators, represented by the actuator of
The technology disclosed herein concerns a linear actuator comprising a plunger receptacle; a magnetic plunger; a magnetic base; and a lock spring. The magnetic plunger is at least partially disposed within a cavity at least partially formed by an interior surface of the plunger receptacle for linear motion along a plunger axis. The magnetic base is radially disposed relative to the plunger. The lock spring is configured and oriented to lock the plunger in a plunger extended position but to be attracted to the magnetic base when the plunger moves to a retracted position.
In an example embodiment and mode a coil is wound about at least a portion of an exterior surface of the plunger receptacle. The lock spring is configured and oriented to lock the plunger in the plunger extended position when power is not applied to the coil but to be attracted to the magnetic base and thereby permit movement of the plunger to the plunger retracted position when the power is applied to the coil.
In an example embodiment and mode the linear actuator further comprises an actuator frame comprising a frame aperture through which a plunger distal portion extends when the plunger is in the plunger extended position. The magnetic base serves to retain the plunger receptacle in position on the frame. That is, in an example embodiment and mode a portion of the actuator frame is secured to the magnetic base.
In an example embodiment and mode the magnetic base is disposed radially outside of an inner circumference of the plunger receptacle by an amount to reduce residual magnetism between the magnetic base and the lock spring.
In an example embodiment and mode the lock spring comprises a lock spring first end connected to the plunger and a lock spring second end. The lock spring second end is oriented to lock the plunger in the plunger extended position when power is not applied to the coil but to be attracted to the magnetic base and thereby permit movement of the plunger to the plunger retracted position when the power is applied to the coil.
In an example embodiment and mode the plunger receptacle comprises a plunger receptacle end wall. A return spring is disposed to bias the plunger to a plunger extended position. A first end of the return spring contacts the plunger receptacle end wall and a second end of the return spring bears against the plunger. The plunger receptacle end wall comprises a catch feature which engages the lock spring second end when the power is not applied to the coil.
In an example embodiment and mode the catch feature comprises a beveled surface which engages the lock spring second end.
In an example embodiment and mode the plunger receptacle end wall comprises an aperture configured to accommodate the lock spring second end when the lock spring second end is attracted to the magnetic base when the power is applied to the coil.
In an example embodiment and mode the lock spring comprises a lock spring first end connected to the plunger receptacle and a lock spring second end. The lock spring second end is oriented to lock the plunger in the plunger extended position when power is not applied to the coil but to be attracted to the magnetic base and thereby permit movement of the plunger to the plunger retracted position when the power is applied to the coil.
In an example embodiment and mode the plunger receptacle comprises a plunger receptacle end wall, wherein the lock spring first end is connected to the plunger receptacle end wall and wherein the lock spring second end contacts a plunger lock spring catch which is connected to or comprises the plunger when power is not applied to the coil.
In an example embodiment and mode, the plunger receptacle comprises a plunger receptacle end wall, wherein a lock spring first end is connected to the plunger receptacle end wall and a lock spring second end contacts a plunger lock spring catch when power is not applied to the coil. The plunger lock spring catch is preferably formed on a non-magnetic portion of the plunger, e.g., a plunger non-magnetic collar. The lock spring second end and the plunger (including the plunger non-magnetic collar) are configured and positioned such that, after the second end of the lock spring has been attracted to the base and has released the plunger for motion, the second end of lock spring is again attracted to the plunger to reduce the hold power of the retracted position.
The foregoing and other objects, features, and advantages of the technology disclosed herein will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the technology disclosed herein.
In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the technology disclosed herein. However, it will be apparent to those skilled in the art that the technology disclosed herein may be practiced in other embodiments that depart from these specific details. That is, those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the technology disclosed herein and are included within its spirit and scope. In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the technology disclosed herein with unnecessary detail. All statements herein reciting principles, aspects, and embodiments of the technology disclosed herein, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
The plunger receptacle 22 comprises cylindrical wall 36 which is essentially centered about plunger axis 34. The cylindrical wall 36 has an exterior surface and an interior surface. The interior surface of cylindrical wall 36 defines a cavity in which a portion of plunger 26 is disposed. As shown in
The plunger receptacle 22 also comprises plunger receptacle end wall 42. An interior surface of plunger receptacle end wall 42 may also at least partially define the cavity which accommodates portions of plunger 26. A portion of plunger receptacle end wall 42 extends radially and parallel to lead wire-retaining flange 41, so that coil lead wire 44 is retained between plunger receptacle end wall 42 and lead wire-retaining flange 41. The coil lead wire 44 is connected to an unillustrated power source which is selectively operated, e.g. by a controller or the like, to supply power to coil 24
The plunger receptacle cylindrical wall 36, or a portion of plunger receptacle cylindrical wall 36, which has coil 24 wound about, may also be considered a bobbin. In some embodiments the plunger receptacle cylindrical wall 36 and the plunger receptacle end wall 42 may be integral and thus essentially form a one piece plunger receptacle 22. However, in other embodiments the plunger receptacle end wall 42 may be a different piece of same or similar material which is connected to plunger receptacle cylindrical wall 36. The plunger receptacle 22, comprising its plunger receptacle cylindrical wall 36, distal end wall 38, and proximal end wall section 39, together with coil 24 wound around plunger receptacle cylindrical wall 36, may also be considered a coil assembly,
Opposite its plunger receptacle end wall 42 the plunger receptacle end wall 22 is partially enclosed by plunger receptacle cap 45. The plunger receptacle cap 45 has a central aperture defined by plunger receptacle cap neck 46 centered on plunger axis 34. An O-ring 48 or other resilient cushion member is positioned between an inside surface of plunger receptacle cap 45 and plunger 26. The plunger receptacle cap neck 46 fits through an aperture in actuator frame 50. In the particular illustration of
As seen in
The plunger 26 comprises plunger main portion 52 and plunger distal portion 54. At least a portion of plunger 26 is ferromagnetic. For example, in an example embodiment at least a portion of plunger 26 is a natural magnet (e.g., a permanent magnet). In one example embodiment the entire plunger 26 may be magnetic. The plunger main portion 52 is essentially confined with the cavity defined by plunger receptacle cylindrical wall 36, and has a larger diameter than plunger distal portion 54. At least a portion of plunger distal portion 54 extends through the plunger receptacle cap neck 46 and through an aperture provided in actuator frame 50. The degree of protrusion of plunger distal portion 54 from the actuator frame 50 depends on whether the plunger 26 is in the plunger extended operational mode (as shown in
The magnetic base 28 is disposed radially with respect to outside of a circumference of plunger 26. In other words, magnetic base 28 is positioned outside of a circumference of plunger 26, and is not axially aligned with plunger 26. As such, no part of magnetic base 28 lies along plunger axis 34. Moreover, as shown in
The return spring 30 is disposed to bias the plunger 26 to its plunger extended position. Preferably the return spring 30 is a coiled compression spring. A first end of the return spring 30 contacts and is retained by (and may be connected to) an interior surface of plunger receptacle end wall 42. A second end of the return spring 30 bears against the plunger 26. In particular, the second end of return spring 30 bears against return spring support member 60. The return spring support member 60 is a washer-type structure which is captured under a head of plunger drive pin 62. The plunger drive pin 62 has a shaft which extends into a central aperture of plunger main portion 52. The plunger drive pin 62 thus secured by interference between the drive pin and the plunger aperture along plunger axis 34 of plunger 26. The return spring support member 60 also serves to secure, between itself and plunger main portion 52, a first or proximal end of lock spring 32, e.g., lock spring proximal end 64. The return spring 30 thus serves not only to bias the plunger 26 to its plunger extended position, but to exert a force on and move an entire plunger assembly (comprising plunger 26, lock spring 32, return spring support member 60, and drive pin 62) to the biased position. The return spring 30 thus serves to move the lock spring 32 leftward (as depicted in
The lock spring 32 is configured and oriented to lock the plunger 26 in a plunger extended position when power is not applied to the coil 24. But lock spring 32 is also configured and oriented to be attracted to the magnetic base 28 (e.g., into lock spring groove or trough 51) and thereby permit movement of the plunger 26 to a plunger retracted position when the power is applied to the coil 24. Different embodiments and configurations of lock spring 32 are described herein, with some embodiments differing by reason of, e.g., location at which a first end of the lock spring 32 is anchored or connected in a position and/or manner in which a second end of the lock spring permits movement of plunger 26 (when the coil 24 is activated) or alternatively limits movement or prevents full movement of the plunger.
In a first example embodiment shown in
As seen in
The configuration of lock spring proximal end 64 in an example embodiment is seen from a right end view of linear actuator 20 as illustrated in
In general, the spring rate of a cantilever (e.g., beam) is inversely proportional to the cube of the length of the cantilever. The configuration of the lock spring 32 as shown in
As shown in
A second example embodiment of a linear actuator 20′ is shown in
Lock spring proximal end 64′ extends in a plane orthogonal to axis 34. In that orthogonal plane the lock spring proximal end 64′ may have a circular shape with a central circular aperture. The central circular aperture of lock spring proximal end 64′ may fit over a central hub 80 formed on or mounted to an interior surface of plunger receptacle proximal side wall 24. The central hub 80 protrudes into the plunger cavity. Near its distal end central hub 80 comprises a spring mounting rim 81 against which an end of the return spring 30 bears. Intermediate the spring mounting rim 81 and the interior surface of plunger receptacle right side wall 24 the central hub 80 comprises hub circumferential groove 82. An interior surface of the central circular aperture of lock spring proximal end 64′ fits over central hub 80 and lodges in hub circumferential groove 82.
The plunger 26 of the second embodiment actuator 20′ comprises plunger non-magnetic collar 84. The plunger non-magnetic collar 84 has the shape of a hollow cylinder. A hollow center of the plunger non-magnetic collar 84 accommodates an end of the return spring 30 and thus forms the non-working end of plunger 26. As shown in the enlarged view of
As electrical power is applied to coil 24, the lock spring 32′ is attracted into lock spring groove 51 toward magnetic base 28, thereby enabling the plunger 26 to start to move from its fully extended position (shown in
With continued application of power to coil 24, the plunger 26 continues to retract so that a magnetic portion of plunger 26 (rather than plunger non-magnetic collar 84) is in radial proximity to the magnetic base 28. With such continued retraction the lock spring distal end 66′ is attracted to a peripheral surface of the magnetic portion of plunger 26. In the case where the lock spring 32′ is flat and the plunger 26 is a cylinder, there is only line contact between plunger 26 and lock spring 32′, which line contact imparts only a minimal amount of friction. However, since the magnetic force on the plunger 26 is increasing with position change, the friction only acts to slow the speed of plunger 26 as opposed to stopping motion. The advantage of this phenomena is exploited by realizing that this friction may be used to increase the holding force and thus reduce the overall power consumption and heating.
The plunger non-magnetic collar 84 serves not only to provide situs of plunger lock spring catch 86, but also to dampen flux at the innermost end of plunger 26 so that the magnetic force of plunger 26 does not overpower the attracting force of magnetic base 28 on lock spring 32′ when it is desired to unlock or move the plunger 26.
Thus, plunger receptacle 26 comprises a plunger receptacle end wall 42, wherein the lock spring first end 64′ is connected to the plunger receptacle end wall 42 and wherein the lock spring second end 66′ contacts a plunger lock spring catch 86 when power is not applied to the coil 24. The plunger lock spring catch 86 is preferably formed on a non-magnetic portion of the plunger, e.g., the plunger non-magnetic collar 84. The lock spring second end 66′ and the plunger 26 (including plunger non-magnetic collar 84) are configured and positioned such that, after lock spring second end 66′ has been attracted to the base and has released the plunger for motion (as shown in
Thus, in the second embodiment of
The lock spring 32 of the technology disclosed herein facilitates a lower spring rate for return spring 30, e.g., a spring rate of about 0.2 lb/in, which is lower than a spring rate of about 0.9 lb/in for the prior art example of
In some example embodiments the lock spring 32 is separated from magnetic base 28 by a nonmagnetic bobbin feature, e.g., catch feature 70, so any frictional drag is minimized. Since the magnetic lock spring 32 is attracted to the magnetic base 28, and since the magnetic force rises exponentially, without the lock spring 32 being separated from magnetic base 28 by plunger receptacle 22, the lock spring 32 would have a high normal force to the magnetic base 28 and ferromagnetic-to-ferromagnetic contact would result with a high friction as the lock spring 32 slides with the plunger 26.
The linear actuator 20 of the technology disclosed herein does not employ a closing air gap construction. Instead, the magnetic base 28 is radially disposed to the plunger 26. The plunger 26 is magnetically attracted to the radially disposed magnetic base 28 until the point where force is reduced and motion ceases. Consequently, among the advantages of the technology disclosed herein are noise reduction, e.g., there is no noise resulting from impact as the technology disclosed herein does not have impact between plunger 26 and magnetic base 28. Moreover, with no metal-to-metal contact, there is no concern for residual magnetism. Also, as the force reduces, due to the magnetic circuit, the plunger assembly is slowly brought to a stop minimizing shock that would otherwise be associated with impacting a bumper or cushion.
Since return spring 30 is only required to return the plunger 26, the impact of the returning plunger 26 is minimized. The low return spring force translates to low energization power and low heat dissipation. Thus, usage of the lock spring 32 allows for a vibration-resistant locking, and the radially disposed magnetic base 28 allows for, e.g., lower required force levels and substantial elimination of metal-on-metal impact noise.
The technology disclosed herein thus provides for a quiet, mechanically shock resistant, bidirectional, low-power utilizing linear motion actuator which is locked against movement without the application of power. Advantages are thus a linear actuator which is quiet, requires low power, generates little heat, is mechanically shock resistant, and which is fail safe in the sense that it returns to a known position upon power failure.
While the actuator frame 50 has been shown essentially as having an open, L-shaped configuration, other configurations of frame 50 are possible. For example, the frame may be essentially cylindrical and encapsulate the coil assembly (e.g., plunger receptacle 22) in a situation in which the actuator serves a tubular shaped solenoid. In another example embodiment the frame 50 may have essentially a “D” shape wherein the frame extends over the top and bottom of the coil assembly.
In at least some example embodiments magnetic base 28 is not only outside the circumference of plunger 26, but also axially spaced (along axis 34) away from coil 24, so that the plunger 26 can be attracted to magnetic base 28. Other configurations are also possible. For example, the coil assembly may be stepped such that there may be a pocket for the base to protrude through the back end, such that at least a part of the base would be inside the coil assembly.
In some embodiments the lock spring has been illustrated as having one end connected to a plunger receptacle. It should be understood that “connected to” does not require a direct mounting on the plunger receptacle, since the lock spring may be connected through other or intermediate structure to the plunger receptacle. Moreover, in yet other embodiments the lock spring may be connected to structure other than the plunger receptacle, e.g., to the frame or even to the magnetic base.
Although the description above contains many specificities, these should not be construed as limiting the scope of the technology disclosed herein but as merely providing illustrations of some of the presently preferred embodiments of the technology disclosed herein. Thus the scope of the technology disclosed herein should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the technology disclosed herein fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the technology disclosed herein is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the technology disclosed herein, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”
This application claims the priority and benefit of U.S. provisional Patent application 62/073,140 filed Oct. 30, 2014, which is incorporated herein by reference in its entirety, and is a divisional application of U.S. patent application Ser. No. 14/923,551 filed Oct. 27, 2015, entitled “Linear Actuators”, which is incorporated herein by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
62073140 | Oct 2014 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 14923551 | Oct 2015 | US |
Child | 15610135 | US |