Linear actuator and its operating method

Abstract

Regarding linear actuator devices. [Solution] The linear actuator comprises a guide defining a linear path, a mass having one or more magnets and slidably mounted on the guide to move back and forth along the linear path, and a coil fixed to the guide and magnetically coupled to one or more magnets on the mass. Two or more individual bearings consist of magnetic fluids that converge in corresponding separate high magnetic flux density regions. Each is spread out around its linear path and operable to engage the mass and the guide during back and forth movement, and is spaced apart from one another along the linear path.

Description

TECHNICAL FIELD

[0001] The present specification relates to a linear actuator device.

BACKGROUND ART

[0002] A linear actuator typically includes a mass (weight body) that is movable back and forth along a linear path defined by a guide. Some linear actuators have a reaction force generator with one or more force elements, whereby the mass is held in a rest position. Depending on the type of actuator, the force element may comprise a magnet fixed to the guide, which magnet is magnetically coupled, for example, to a magnet integral with one or more springs and / or the mass. The linear actuator may also be provided with a driving force generator capable of exerting a force on the mass. This force typically acts to move the mass away from the rest position. If the mass comprises one or more magnetic elements, the driving force generator may be, for example, an electromagnetic coil, which is referred to as a linear magnetic ram configuration.

[0003] Once moved away from the rest position and released, the mass will oscillate back and forth on both sides of the rest position, and due to friction, the amplitude will gradually attenuate until eventually the mass comes to rest at the rest position. Such oscillations may occur at the natural resonant frequency of the system. The parameters of the system, that is, the detailed settings of the reaction force generating device, affect not only the resonant frequency but also the degree to which the mass resonates at frequencies different from the resonant frequency. Patent Document 1 presents a more detailed configuration example of a linear actuator. The driving force generator can be configured to exert a force on the mass in bursts whose timing is adjusted according to the resonant frequency, thereby amplifying the resonance and making it possible to obtain a larger vibration amplitude than that which a single burst can produce alone.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0329141 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Linear actuators have achieved a certain level of satisfactory performance and are gaining increasing attention as a means of providing haptic feedback in consumer electronics circuits, but there is still room for improvement. For example, there remain limitations related to how much friction and / or rattling can be reduced, and how much magnetic coupling can be achieved between one or more magnets integrated with the mass and the electromagnetic coil. Controlling production costs, widening the frequency response, reducing the volume (footprint), and providing high reliability are also major concerns in the design of linear actuators, and these often need to be balanced in relation to each other or to other concerns. [Means for solving the problem]

[0006] To make a mass movable relative to a guide, the mass should be smaller than the guide in the direction perpendicular to the direction of movement (hereinafter abbreviated as the transverse direction) (e.g., its cross-sectional shape should be consistent but smaller), thereby allowing for a transverse gap between the mass and the guide. In embodiments where the mass extends around the guide shaft, the internal flow path of the mass can be made larger than the shaft in the transverse direction. In fact, the gap between the mass and the guide can help prevent the desired longitudinal movement of the mass from being blocked or obstructed by the guide. Otherwise, excessive interference fit or interference fit may cause blockage or obstruction. On the other hand, it is sometimes desirable to reduce the gap; this is because the gap can be a source of undesirable effects, such as pivoting that leads to transverse displacement (lateral displacement) or axial displacement (skew) between the mass and the guide. Transverse displacement can cause rattle when the electronic device accompanying the linear actuator is in motion (e.g., translation, rotation, or pivot). Furthermore, axial displacement can cause unwanted dynamic effects such as increased friction, vibration, or noise, which can occur when the axially displaced mass is driven by a force generator. In addition, increasing the gap size may reduce the amount of magnetic coupling between the one or more magnets and electromagnetic coils forming part of the mass. Therefore, it is desirable to limit the gap size to a strictly minimum while maintaining suitable linear displacement capability. However, in practice, it is difficult to reliably achieve such a minimum gap for various reasons. For example, significant dimensional tolerances may occur in the mass and guide, especially when the size of the linear actuator is small. It becomes necessary to avoid interference fits and irritation fits, resulting in adjusting dimensional tolerances to prioritize safety, which can lead to increased gaps and associated problems. Also, in some cases, excessive interference fits can lead to increased friction.

[0007] Because friction can directly affect a system's ability to generate sustained motion with large amplitudes, sharp haptic effects, and / or provide a suitable response time, designers may intend to minimize it.

[0008] In some embodiments, adding lubricant between the mass and the guide proved to be an unsuitable method for minimizing friction. In fact, housing the mass within an airtight chamber can be an undesirable design constraint. Furthermore, in some embodiments, the lubricant may hinder the movement of the mass or otherwise prevent satisfactory results.

[0009] However, in at least some embodiments, it has been found that a magnetic fluid bearing can be maintained between the mass and the guide by utilizing annular high-flux-density regions formed to define discontinuous positions along the mass. Furthermore, magnetic fluid bearings spaced discontinuously along the mass may inhibit off-axis motion, potentially reduce rattling, and reduce friction between the mass and the guide, leading to an overall improvement in the performance of the linear actuator. More specifically, it may be preferable to provide a longitudinal air gap between two discontinuous magnetic fluid bearings, which is particularly useful in configurations having two or more annular high-flux-density regions, such as those particularly suitable for certain types of linear actuator embodiments. In fact, it has been found that the action of magnetic flux on magnetic fluid rings spaced along these discontinuous lines generates a force directed toward the mass. This force may, for example, counteract the effects of gravity between the mass and the guide when the linear actuator is moved in various orientations, thereby suppressing tilt, rattling, and / or skew. This is particularly useful when the mass is configured to have a relatively large amplitude of movement. Furthermore, when a magnetic fluid with lower magnetoresistance (reluctance) than air is used, it has been found that the presence of the magnetic fluid in the high magnetic flux density region provides an additional benefit: increased magnetic coupling between the magnets in the mass and the magnets in the guide.

[0010] A linear actuator provided in one embodiment comprises a guide defining a linear path; a mass slidably mounted on the guide to move back and forth along the linear path, the mass having one or more magnets; a coil fixed relative to the guide, the coil magnetically coupled to one or more magnets of the mass; and two or more individual magnetic fluid bearings located in corresponding separate high magnetic flux density regions, each of which is spread around the aforementioned linear path and capable of operating to engage the mass-guide during back and forth movement, and two or more magnetic fluid bearings spaced apart from each other along the linear path.

[0011] A method provided in one alternative embodiment is a method for operating a linear actuator having a guide defining a linear path, a mass slidably mounted on the guide to move back and forth along the linear path, and two or more individual magnetic fluid bearings located in corresponding separate high magnetic flux density regions, wherein the orientation of the linear actuator is changed with respect to the direction of gravity, and after the change in orientation, the action of gravity on the mass pushes the mass to a position offset from the aforementioned linear path, and the action of the aforementioned high magnetic flux density regions on the two or more individual magnetic fluid bearings generates a force that at least partially cancels out the gravity acting on the mass.

[0012] A linear actuator provided according to one alternative embodiment comprises a guide having a shaft defining a linear path, a mass having one or more magnets having an internal channel defined parallel to the linear path and engaged with the shaft to move back and forth along the linear path, and a coil fixed to the guide, which is magnetically coupled to one or more magnets of the mass.

[0013] A reading of this disclosure will reveal many further features and combinations thereof to those skilled in the art. [Brief explanation of the drawing]

[0014] [Figure 1A] FIG. 2 is a schematic overview diagram of an example of a linear actuator. [Figure 1B] FIG. 3 is a diagram showing its force response curve. [Figure 1C] FIG. 4 is a diagram showing its frequency response curve. [Figure 2A] FIG. 5 is a block diagram of an example of an apparatus in which a controller and a linear actuator are incorporated. [Figure 2B] FIG. 6 is a block diagram of an example of an information processing apparatus. [Figure 3] FIG. 7 is a side view of an exemplary embodiment of a linear actuator. [Figure 3A] FIG. 8 is a diagram showing an individual part of FIG. 3, which is enlarged to show details. [Figure 3B] FIG. 9 is a diagram showing an individual part of FIG. 3, which is enlarged to show details. [Figure 3C] FIG. 10 is a diagram showing an individual part of FIG. 3, which is enlarged to show details. [Figure 4A] FIG. 11 is a longitudinal sectional view of an example of a linear actuator. [Figure 4B] FIG. 12 is a transverse sectional view of an example of a linear actuator. [Figure 5A] FIG. 13A is a longitudinal sectional view of an example of a linear actuator similar to that in FIG. 4A, and shows a state where a mass is arranged offset in the transverse direction with respect to a guide as illustrated. [Figure 5B] FIG. 13B is a transverse sectional view of an example of a linear actuator similar to that in FIG. 4B, and shows a state where a mass is arranged offset in the transverse direction with respect to a guide as illustrated. [Figure 6A] FIG. 14 is a diagram presenting an example of the motion caused by the control signal of FIG. 6B between the mass and the guide of the linear actuator of the foregoing example. [Figure 6B] FIG. 15 is a graph showing an example of a control signal. [Figure 7A] FIG. 16 is a diagram presenting an example of the motion caused by the control signal of FIG. 7B between the mass and the guide of the linear actuator of the foregoing example. [Figure 7B] It is a graph showing an example of a control signal. [Figure 8A] This is a diagram presenting an example of the motion caused by the control signal of Fig. 8B between the mass and the guide of the linear actuator in the aforementioned example. [Figure 8B] It is a graph showing an example of a control signal. [Figure 9A] It is a longitudinal cross-sectional view of another example of the linear actuator. [Figure 9B] It is a transverse cross-sectional view of another example of the linear actuator. [Figure 10A] It is a longitudinal cross-sectional view of still another example of the linear actuator. [Figure 10B] It is a transverse cross-sectional view of still another example of the linear actuator. [Modes for Carrying Out the Invention]

[0015] Shown in Figure 1A is a relatively simple example of a linear actuator 22, which can be used to provide haptic feedback. This example is used to introduce several terms that are helpful for the description of other linear actuators presented later. It can be said that the linear actuator 22 generally has a mass 12 that can move linearly back and forth along a linear path 24. The linear path 24 is defined by a linear guide, for example, by being enclosed by a housing 26 that defines the linear path 24 longer than the mass 12. And the mass 12 can be slidably fitted therein.

[0016] The linear actuator 22 may include a reaction force generator 32 that biases the mass 12 to a rest position 16. In the example shown in Figures 1A to 1C, the reaction force generator 32 has a single force element, namely a compression spring 14 with one end 28 fixed between the mass 12 and the housing 26. In this embodiment, since the compression spring 14 has a spring constant k that is kept constant over the entire range of displacement along a linear path 24, it is possible to generate the linear force response curve 18 shown in Figure 1B. As shown to the left of the rest position 16 in Figure 1B, the reaction force generator 32 generates a restoring force 30 that increases gradually (linearly). As the mass is moved away from the rest position 16 along the linear path to the left, the spring 14 is stretched considerably and follows the typical mass / spring behavior governed by the equation F = kx (where x is displacement). As shown to the right of the rest position 16 in Figure 1B, the reaction force generator 32 provides a gradually increasing restoring force 30, and as the mass is moved away from the rest position 16 to the right, the spring 14 is compressed. In this embodiment, the reaction force generator 32 does not generate a force on the mass at the rest position 16, and this position is, so to speak, the equilibrium position.

[0017] The linear actuator 22 includes a certain form of drive force generator (not shown) configured to selectively control whether or not to apply a driving force to the mass 12, thereby promoting the movement of the mass 12 along a linear path 24. The drive force generator can move the mass 12 away from the rest position 16. If the mass 12 has one or more magnetic segments, examples of which will be detailed later, the drive force generator may be an electromagnet which can be magnetically coupled, for example, to the permanent magnetic field of the mass 12; however, there are other embodiments in which other forms of drive force generators or mass motion driving mechanisms are preferred.

[0018] Therefore, when the mass 12 is moved away from the rest position 16, the force generated by the reaction force generator 32 can bias the mass 12 toward the rest position. This force accelerates the mass 12, allowing it to pass the rest position 16 at a non-zero velocity. After passing this point, the opposite force generated by the reaction force generator 32 can pull the mass 12 toward the rest position. As a result, the mass 12 can vibrate back and forth around the rest position 16. This vibration occurs at a resonant frequency W0 that depends on the variables of the system, as shown in Figure 1C. In reality, due to friction within the system, the intensity of the vibration gradually decreases (damping), and eventually the mass 12 comes to rest at the rest position when no external force is applied. The time it takes for this deceleration to complete also depends on the variables of the system, namely friction.

[0019] In this case, the force response curve 18 is linear in the sense that the gradient k is constant, and its force response is proportional to the distance from the rest position 16. Since the maximum spread 34 and maximum displacement amplitude 38 of the linear displacement path may differ from embodiment to embodiment, it would be practical to specify the value of the gradient k in relative units. In fact, regardless of the embodiment, the linear displacement path 24 may have a static rest position 16, also known as the equilibrium position, from which the mass 12 can be moved in two directions by a drive force generator towards the corresponding ends 28, 36 of the linear displacement path 24. The ends 28, 36 of the linear displacement path 24 can be defined by reaction force generators, and their range can even be limited by hard stops, etc., or they can be defined by the characteristics of the drive force generator, such as the maximum force, frequency, and friction that can translate it to the maximum amount of displacement in a perfect resonance state.

[0020] Therefore, the shape of the force response curve 18 is also one of the characteristics of the linear actuator, and can be influenced by the configuration of the force elements (groups) that constitute the reaction force generator. In the present embodiment shown in Figure 1A, a single force element, a compression spring 14, is provided, thereby defining the force response curve 18 throughout. However, it is understood that other embodiments (e.g., embodiments in which the force elements (groups) consist of one or more magnets, one or more springs, and / or combinations thereof) can be used as alternative embodiments. Various examples of such embodiments are described in Patent Document 1.

[0021] The shape of the force response curve 18 produces dynamic effects that can be visualized during operation. For example, in this example, the force response curve 18 includes a first region 40 on the first side of the rest position 16, extending from the rest position 16 to the first end 28 of the linear displacement path 24, where the restoring force 30 increases, and a second region 42 on the second side of the equilibrium position 16, extending from the equilibrium position 16 to the second end 36 of the linear displacement path 24, where the restoring force 30 increases. These two regions 40 and 42, where the restoring force 30 increases, define the entire force response curve 18. The restoring force 30 always acts in line with the direction of displacement due to the motion being constrained in its direction by the linear displacement path 24, and the direction in which it acts is reversed depending on which side it is on with respect to the rest position 16. It always acts to return the mass 12 to the rest position 16, hence the expression "restoring" force is used.

[0022] When the mass 12 is moved to one side against the restoring force of the spring 14 and then suddenly released from the external force, the spring 14 pulls the mass 12 back, causing it to move beyond the rest position 16 and oscillate back and forth around the rest position 16 for a certain amount of time; after that, the energy is dissipated by friction and the mass 12 stops at the "static" rest position 16 (this position may be a region rather than a point in a nonlinear system, but a point is usually preferable in haptics). The frequency at which the mass 12 oscillates back and forth is the natural frequency of the linear actuator, which is denoted as W0 in this application. In the simplified case where the force response curve has a constant slope as shown in Figure 1B, W0 depends on the slope of the force response curve 18, and in this embodiment, it is directly related to the spring constant k. If the drive force generator is configured to repeatedly supply drive energy into the system 10 at a frequency close to the natural frequency W0, for example by operating a coil with alternating current, then the repeatedly added energy accumulates to reach "resonance," and the moving mass 12 further increases the amplitude of displacement and acceleration until it reaches dynamic equilibrium oscillation. Under these dynamic equilibrium oscillation conditions, the energy loss due to friction becomes equal to the amount of energy introduced into the system in each cycle.

[0023] The expression "repeatedly supplying driving energy into the system at a frequency close to the natural frequency" is best understood by referring to Figure 1C. Figure 1C is a graph showing the force (acceleration) response spectrum 20 of the linear actuator 22 in Figure 1A as a function of the driving frequency at a predetermined driving energy amplitude. In fact, even if the same amount of energy is supplied to the mass 12 at a frequency other than W0, the mass 12 is driven, but because the motion of the spring 14 does not resonate with that drive, some of the energy is not efficiently converted into motion, and as a result the amplitude of the displacement and acceleration of the mass 12 driven by that driving force becomes smaller. In fact, the peak shown in this frequency response graph corresponds to that frequency W0. It can be seen that as the driving frequency moves away from the natural frequency W0, the generated force response gradually attenuates.

[0024] In a situation where a drive force generator has a maximum drive force value (maximum amount of drive energy), in the case of electromagnet (coil) drive, for example, it can correspond to the highest voltage, but the maximum acceleration response value Gmax will be produced by that maximum drive force value only if the highest voltage input is precisely timed to oscillate between positive and negative at the natural frequency W0, and the further the frequency at which it operates is from the natural frequency W0, the smaller the acceleration response produced at the maximum drive force value becomes; in the example in Figure 1C, precisely when the frequency is shifted by 1 / 5 from W0, only a negligible acceleration response is produced, which is less than 5% of the maximum acceleration response value. In some embodiments described in this specification, the frequency response characteristics (e.g., natural frequency W0) of the linear actuator 22 can be selected and / or changed by moving the force element from one location to another. In some embodiments described in this specification, the frequency response characteristics may have multiple peak frequencies.

[0025] To reiterate, the frequency response spectrum 20 is defined by the force response curve 18, and consequently by the force elements (group) that form the reaction force generator. Therefore, the frequency response spectrum 20 of the linear actuator 22 can be said to be a characteristic of the linear actuator 22, just as the force response curve 18 can be a characteristic of the linear actuator 22, or just as the details of the force elements (group) can be a characteristic of the linear actuator 22.

[0026] Linear actuators have applications across a wide variety of technologies and industrial fields. Figure 2A is a schematic diagram of an example of an electronic device 200, which incorporates an information processing device 202 and a linear actuator 204. In certain embodiments, the information processing device 202 can be used as a controller and can be used to control the operation of the linear actuator 204. In some embodiments, the information processing device 202 will be the controller. In some embodiments, the linear actuator will be controlled by a controller other than the information processing device. In this embodiment, the electronic device 200 is a mobile phone 206 with a screen 208. As can be seen, the device 200 may be any other type of electronic device, and the screen 208 may or may not be present.

[0027] Figure 2B is a block diagram showing the components of an example information processing device 202. As shown in the figure, the information processing device 202 has a processor 252, a memory 254, and an input / output interface 256.

[0028] The processor 252 can be embodied in the form of a general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field-programmable gate array (FPGA), a reconfigurable processor, a programmable read-on rememory (PROM), and many other designs.

[0029] Memory 254 can be any preferred type of computer-readable memory, located inside or outside the processor, and accessible by the processor via a network, such as the Internet, or directly, either wired or wirelessly, in any preferred combination. Computer-readable memory can be embodied in the form of, for example, random access memory (RAM), read-only memory (ROM), compact disk read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), electro-erasable programmable read-only memory (EEPROM), and ferroelectric RAM (FRAM: registered trademark).

[0030] The information processing device 202 may have one or more input / output (I / O) interfaces 256 that enable communication with another computer and / or a human user via cooperating input, output, or input / output devices such as a keyboard, mouse, touchscreen, antenna, port, etc. Each I / O interface enables the computer to communicate with other components and / or exchange data, access and connect to network resources, provide applications, and / or execute other information processing applications by connecting to a data-carrying network (or multiple networks), such as the Internet, Ethernet, Conventional Telephone Service (POTS) lines, Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN; registered trademark), Digital Subscriber Line (DSL), coaxial cable, optical fiber, satellite, mobile, wireless (e.g., Wi-Fi, Bluetooth®, WiMAX®), SS7 signaling network, fixed line, local area network, and wide area network.

[0031] As you can understand, in the information processing device 202, functions or processes may be executed by hardware, or by a combination of both hardware and software. For example, hardware may include a group of logic gates incorporated as part of a silicon chip that constitutes a processor. Software (e.g., applications, processes) may be in data form, and an example of this is computer-readable instructions 258 stored in non-temporary computer-readable memory accessible from one or more processing units. With respect to a computer or processing unit, "configured to" refers to the existence of hardware, or a combination of hardware and software, that can be made to operate in order to perform the relevant functions.

[0032] In certain embodiments, the information processing device 202 may be configured to selectively operate and / or deactivate the linear actuator 204. For example, the information processing device 202 may be configured to transmit a control signal to receive a voltage input to the electromagnet at an appropriate timing so as to oscillate between positive and negative at or near the natural frequency or peak response frequency W0, for example, to achieve efficient use of the driving energy when applying acceleration to a mass.

[0033] Figure 3 is a partially schematic diagram of an example of a linear actuator that can be used to provide haptic feedback. As shown, a mass 120 is housed in a housing 110, and a linear path is defined by a guide provided in the housing 110. The mass 120 is slidably mounted relative to the guide so as to move back and forth along the linear path. Although the linear path in this embodiment is linear, it will be understood that in some embodiments, it may be desirable to have some form of curvature in the linear path. In any case, the term displacement axis can be used to refer to the linear displacement along the longitudinal direction of the linear path. Embodiments of a linear actuator may have a relatively large span of linear displacement, which may involve challenges such as off-axis displacement. In this specification, an embodiment may be considered to have a large displacement span if the ratio of the dimension of the maximum displacement span during normal operation to the width of the mass is, for example, greater than 0.1, greater than 0.25, or around 0.5 or greater. Normally, such large displacement spans cannot be achieved when the mass is connected to the guide by a flexure mechanism or spring, but they can be achieved when the only connection point between the guide and the mass, i.e., the only force-responding element, is composed solely of magnets, as in the illustrated embodiment.

[0034] The mass 120 may have one or more magnets 130B (indicated by regions tagged with arrow lines indicating the direction of the magnetic field), and may also have one or more non-magnetic but permeable segments 130A, etc. In this specific embodiment, the mass 120 has two magnetic segments formed of magnets, and the direction of the magnetic fields exhibited by both of them is parallel to the linear path / displacement axis but in opposite directions. These two magnetic segments 130B are separated from each other by another segment 130C that is permeable but does not exhibit a permanent magnetic field, such as a ferromagnetic core. When an electromagnet (210, Figure 6A) is used as a driving force generator, by using this inverted magnet configuration within the mass 120, the magnetic flux density in the area between the two magnets can be increased, and as a result, the degree of magnetic coupling between the electromagnet and the mass can be increased. However, as you can see, this is only one type of embodiment that can be adopted, and many variations can be adopted as alternative forms.

[0035] In these embodiments, the mass 120 has three high magnetic flux density regions extending in the transverse direction, some of which are shown enlarged in Figures 3A to 3C. These high magnetic flux density regions correspond to the regions with high density of magnetic field lines shown in Figure 3. These high magnetic flux density regions include regions that surround (i.e., extend around) the ferromagnetic core. This corresponds to the region where magnetic field lines emanate from the opposite pole of the magnet (where the magnetic field is directed, as indicated by the arrows in Figure 3), and also includes regions surrounding the other ends of the magnet.

[0036] As will be described later, these high magnetic flux density regions can be used to form and maintain individual bearings 160a, 160b, and 160c made of magnetic fluid 140. Each of these bearings extends around the mass and surrounds a linear path, and can be operated to engage between the mass and the guide when the mass moves back and forth along that linear path. These liquid bearings 160a, 160b, and 160c can be said to be individual (discrete) in the sense that they are linearly separated from each other by regions without magnetic fluid 140 (e.g., regions of air).

[0037] In reality, magnetic fluids are liquids that are attracted to high magnetic flux density regions, such as the poles of magnets. Magnetic fluids are usually provided in the form of colloidal liquids in which nanoscale ferromagnetic or ferrimagnetic particles are suspended in a carrier fluid such as an organic solvent or water. Clamping can be suppressed by thoroughly coating these magnetic particles with a surfactant. Larger ferromagnetic particles may be stripped from the homogeneous colloidal mixture by exposure to a strong magnetic field, forming separate magnetic dust clumps. This is one way to ensure that the magnetic fluid contains only smaller ferromagnetic or ferrimagnetic particles. The particles in the magnetic fluid are suspended by Brownian motion, which prevents them from settling (at least under normal conditions). Because the magnetic attraction of such small particles is extremely weak, the van der Waals forces of the surfactant alone are sufficient to prevent magnetic clumping or aggregation. In magnetic fluids, magnetization is usually not maintained when no external magnetic field is applied.

[0038] One of the challenges in introducing magnetic fluid into the linear path of a linear actuator is to avoid loss of magnetic fluid over time while ensuring that the magnetic fluid accumulates in a configuration useful for the intended use of the linear actuator. To achieve this objective, it is sometimes desirable to confine the magnetic fluid to a specific region. It has been found that this objective can be satisfactorily achieved by designing a linear actuator that has a region with high magnetic flux density and is specifically configured to meet this objective.

[0039] For example, in the embodiment shown in Figure 3, it was found that the achievement of the objective can be facilitated by attaching additional segments (shown in white without hatching) to the linearly opposing ends of the mass 120. In fact, the presence of such additional segments prevents the magnetic fluid from moving to the linearly opposing ends of the magnet without compromising the intended magnetic field configuration of the linear actuator. The presence of these additional segments makes it easier for bearings 160a and 160c to remain trapped in the transverse peripheral area of ​​the mass in the corresponding high magnetic flux density region, which helps to achieve smooth and low-friction engagement between the mass and the guide.

[0040] In certain embodiments, it is considered useful to provide the mass 120 with one or more transverse grooves (grooves extending in the transverse direction) corresponding to one or more of the high magnetic flux density regions. Three examples of such groove configurations are shown in Figures 3A, 3B, and 3C. Figure 3A shows the narrowest groove example among these three, and consists only of an annular depression that extends around the mass in a linear path. In this specific example, the annular depression may be formed at the interface between the magnetic segment 130B and the additional segment 130A.

[0041] The example of such grooves shown in Figure 3B represents the widest of the three grooves, in which the ferromagnetic core 130C is narrower in the transverse direction than the magnet along its entire length, forming a constriction. The example of such grooves shown in Figure 3C has a length intermediate between the grooves in Figure 3A and Figure 3B, and this also represents another preferred example. These grooves have been found to function as passages that help accumulate magnetic fluid and prevent the leakage of magnetic fluid from such areas. However, these grooves are optional and may be omitted in other embodiments. Depending on the embodiment, it may be desirable to make the surface area of ​​these grooves sufficiently smaller than the surface area of ​​the remaining portion of the outward-facing surface of the mass, for example, less than 25%, less than 10%, or less than 5%.

[0042] The terms "annular" or "ring" used herein do not necessarily imply a circular cross-section; for example, as shown in Figures 4B and 5B, they also include oval cross-sectional shapes and other closed-loop shapes defined around a linear path.

[0043] Furthermore, while the grooves shown in Figures 3A, 3B, and 3C are external lateral grooves defined within the outward-facing surface of the mass, in some embodiments, it may be beneficial to form internal lateral grooves defined within the inward-facing surface of the guide.

[0044] Furthermore, as shown in Figures 4A to 5B, interestingly, the magnetic force that attracts the magnetic fluid, causing it to accumulate and form individual bearings spaced apart from one another along the longitudinal direction of the linear path, simultaneously produces an automatic centering effect between the mass 120 and the guide 110. This not only prevents bias, misalignment, and rattle, but also reduces losses due to noise and dynamic friction sources during operation. In fact, if the mass 120 is smaller than the guide 110, a gap 150 remains between them, and gravity acting on the guide 110 may pull the mass towards one side of the guide, along the direction in which gravity acts (which depends on the orientation of the linear actuator relative to the ground). Changing the orientation of the linear actuator changes the relative direction of gravity's action on the mass 120, which can result in misalignment between the mass 120 and the guide 110, as exaggeratedly shown in Figures 5A and 5B for illustrative purposes. It has been found that the magnetic force within the individual bearings made of magnetic fluid 140 helps to counteract this misalignment. In fact, the magnetic forces within the individual bearings 160a, 160b, and 160c, each composed of the magnetic fluid 140, tend to uniformly distribute the magnetic fluid around the mass 120. These forces, in response to gravity pushing the mass 120 to one side, resist its movement and push it back to the opposite side, thereby at least partially counteracting the gravitational force acting on the mass 120. This automatic centering effect is particularly useful in the case of the linear actuator 100. This automatic centering effect is especially effective when the individual magnetic fluid bearings are separated from each other by a relatively large distance, or when there are three or more individual bearings 160a, 160b, and 160c composed of the magnetic fluid 140 arranged along a linear path. The gap 150 between the mass 120 and the guide 110 can be formed to appropriate dimensions and shapes to accommodate the movement of the mass 120 while ensuring sufficient clearance for lubrication of the magnetic fluid base.

[0045] In some embodiments described above, a reaction force generator can be provided to generate a reaction force path. In the specific examples shown in Figures 3 to 8B, as more clearly shown in Figure 4A, the reaction force generator may have one or more magnets that are fixed in place relative to the guide 110. In the specific examples shown, one such magnet 132 is used. This magnet 132 is provided around the guide, i.e., along a linear path, and is mainly magnetically coupled to one of the two magnets 130B provided in the mass 120. Figure 4A shows the rest position obtained in this way, with the polarity of the magnet 132 provided in the guide 110 being parallel to the polarity of the magnet 130B provided in the mass to which it is coupled. The coupling between these two permanent magnets 130B and 132 can increase the magnetic flux density in the annular region arranged transversely between them. Other embodiments may adopt different configurations, and examples of these are presented in Patent Document 1.

[0046] In this example, a drive force generator can be provided to move the mass away from the rest position shown in Figure 4A in order to impart motion to the mass.

[0047] Examples of operating modes are shown in Figures 6A to 8B. Specifically, in this example, the drive force generator may be configured to have an integrated electromagnet that remains fixed to the guide and extends around a linear path. This electromagnet may be provided in the form of a coil 210 capable of selectively circulating current along any angular direction, and when operating, it can generate an "operating" magnetic field coupled to the mass 120 (more specifically, the magnet 130B attached thereto), thereby acting a force on the mass 120 in the corresponding direction along the orientation of the linear path. A controller 220 can be used to control the current circulation in the electromagnet. Depending on the embodiment, one or more feedback sensors 230 may or may not be provided, for example, to supply information about the position or velocity of the moving mass to the controller 220. If one or more feedback sensors 230 are provided, the controller 220 can be operated to adapt the control of the coil 210 based on the closed feedback loops related to the feedback sensors.

[0048] Figures 6B and 7B show control signals representing drive impulses with the same amplitude but different durations. Figures 6A and 7A show the configuration of the linear actuator at the end of the drive impulse, i.e., the position of the mass 120 along a linear path. As shown in these figures, the electromagnetic magnetic field generated by the coil 210 when the impulse is generated affects the magnetic field lines, and this effect is indirectly demonstrated in these figures through the change in the shape of the magnetofluid bearing. The maximum amount of movement can vary depending on the embodiment. In the control signal example shown in Figure 8B, the current flow in the coil is reversed, and a force is applied to the mass in the opposite direction to the example shown in Figures 6A and 6B.

[0049] As shown in these figures, the individual bearings 160a, 160b, and 160c, each made of magnetic fluid 140, may dynamically change shape based on the relative motion and / or changes in the magnetic field between the mass 120 and the guide 110, but the individual bearings 160a, 160b, and 160c can remain substantially trapped / attracted to their corresponding high magnetic flux density regions throughout the operation of the linear actuator 100. In some cases, at various stages of operation of the linear actuator, some of the magnetic fluid may be exchanged between one high magnetic flux density region and another, but overall, the magnetic fluid remains confined to those high magnetic flux density regions.

[0050] It will be understood that, in some cases, some magnetic fluids tend to leak out from high magnetic flux density regions or simply evaporate over time. Specific structures can be provided to mitigate or inhibit these phenomena.

[0051] As shown in Figures 4A and 4B, in some cases, one or more additional magnetic flux density regions 190 may be provided in positions where the mass 120 does not come into contact with any adjacent mass 120 when the mass 120 is in a rest position, or outside the maximum displacement span of the mass 120 along the linear guide 110. Thus, one or more additional magnetic flux density regions 190 may be capable of accumulating magnetic fluid but not function as bearings, intrinsically and / or by design. Such one or more additional magnetic flux density regions 190 may be configured solely for the purpose of capturing magnetic fluid that might otherwise leak out from high magnetic flux density regions intended to form two or more individual bearings 160a, 160b, 160c made of magnetic fluid 140. An example of such a region 190 is shown in Figures 6A, 7A, and 8A, which is provided at the linear end of a magnet 132 integrated with a guide 110 positioned away from the position of the mass 120.

[0052] Furthermore, in some cases, linear grooves or slots 170 may be formed in the guide 110 (e.g., shown in Figure 4B) and / or in the mass 120 (not shown), extending in a generally linear direction. Such linear grooves or slots 170 extend across one or more high magnetic flux density regions and are specifically intended to form magnetic fluid reservoirs designed to accumulate magnetic fluid that has leaked or evaporated undesirably from one or more bearings. These linear grooves or slots 170 may be configured to redistribute / return magnetic fluid to predetermined high magnetic flux density regions.

[0053] Needless to say, the examples described and illustrated above are merely examples. In fact, various embodiments are possible, and in each embodiment, it may be necessary to adjust the concepts presented in this specification to some extent so that they can be more appropriately applied to specific situations.

[0054] For example, in the embodiments shown in Figures 9A and 9B, channels are formed in the mass 120 and the guide has a shaft. Both the channel and the shaft are centered on a linear path and parallel to that linear path, with the shaft extending through the channel. That is, in this example, the mass is extended around the shaft / guide rather than the guide extending around the mass. The magnetic fluid ring can still be located between the inward-facing surface of the channel and the outward-facing surface of the shaft (inside and outside here are relative to the straight or curved axis of the linear path). In another embodiment, the magnetic fluid ring can be located both inside and outside the mass 120. For example, it can be located both between the mass 120 and the shaft, and between the mass 120 and the guide 110. Some of the concepts described above can optionally be applied to these embodiments without inferiority, for example, by extending a groove 170 around the linear path to promote the localization of the magnetic fluid bearing accumulation. In fact, such grooves 170 can be provided, for example, within the inward-facing surface of the channel and / or within the outward-facing surface of the shaft, and in some embodiments, they may not be provided at all.

[0055] For example, a seal (not shown), such as a labyrinth seal, can be optionally provided between the mass 120 and the end of the shaft, for example, by being integrally formed with the mass 120. In such an example, a straight groove can be provided to balance the magnetic fluid between two or more individual bearings in order to retain the reserve of magnetic fluid, and this groove may be integrally formed, for example, on the inward surface of the channel or the outward surface of the shaft.

[0056] In yet another embodiment shown in Figures 10A and 10B, individual magnetic fluid bearings are disposed both between the inward-facing surface of the channel and the outward-facing surface of the shaft, and between the outward-facing surface of the mass and the inward-facing surface of the channel.

[0057] Furthermore, a variety of applications are possible. Among the examples, linear actuators for smartphones and other small consumer electronic devices can be based on a miniaturized design in which two or three magnetic fluid bearings are spaced apart along a relatively short stroke to provide nearly silent operation and clear haptic pulses. Another example is a gaming or virtual reality (VR) controller with an extended stroke using a magnetic flux guide in the stator. This utilizes the magnetic flux guide within the stator to form four or more bearing zones, providing robust off-axis control and improved user immersion. Moreover, by using a robust version with a labyrinth seal and heat-resistant magnetic fluid, linear actuators for automotive haptic feedback applications that can withstand vibration, shock, and fluctuating environmental conditions can also be conceivable. Depending on the embodiment, a wide range of tactile sensations can be generated by adjusting the waveform of the coil current.

[0058] The technical scope is defined in the claims in a separate section.

Claims

1. A linear actuator, A guide that defines a straight path, A mass having one or more magnets is slidably mounted on the guide to move back and forth along the aforementioned linear path, A coil fixed to the guide and magnetically coupled to one or more magnets in the mass, Two or more individual bearings, each consisting of magnetic fluids that converge in corresponding separate high magnetic flux density regions, each extending around the linear path and capable of operating to engage the mass and the guide during the forward and backward motion, the two or more bearings being spaced apart from each other along the linear path, A linear actuator equipped with the following features.

2. A linear actuator according to claim 1, The guide has an inward-facing surface that extends around the linear path, A linear actuator in which two or more individual magnetic fluid bearings are arranged outside the mass with respect to the linear path between the inward-facing surface of the guide and the mass.

3. A linear actuator according to claim 1 or 2, The mass has an internal channel defined inside so as to be parallel to the linear path, The guide extends through the internal channel and has a shaft parallel to the linear path, The two or more individual magnetic fluid bearings are arranged between the mass and the shaft, on the inside of the mass as seen from the linear path, and spaced apart from each other along the linear path. A linear actuator in which the inward-facing surface of the guide extends around the linear path.

4. A linear actuator according to any one of claims 1 to 3, The mass has a transverse groove that extends around the linear path and is located in one of the high magnetic flux density regions. The aforementioned lateral grooves guide the convergence of corresponding bearings among the two or more individual bearings in a linear actuator.

5. A linear actuator according to any one of claims 1 to 4, The guide has one or more straight grooves arranged parallel to the straight path, The aforementioned one or more straight grooves are provided in a state that they are in fluid communication with one or more of the two or more individual bearings. A linear actuator in which the one or more straight grooves function as a reservoir and hold a portion of the magnetic fluid inside.

6. A linear actuator according to any one of claims 1 to 5, A linear actuator further comprising one or more magnets that are magnetically connected to one or more magnets of the mass and bias the mass to at least one rest position along the linear path.

7. A linear actuator according to any one of claims 1 to 6, The aforementioned mass has a first magnet that is spaced apart from the second magnet, A linear actuator in which the first magnet and the second magnet exhibit magnetic fields with opposite polarity in a direction parallel to the linear path.

8. A linear actuator according to claim 7, A linear actuator in which the first magnet is positioned at a distance from the second magnet via a ferromagnetic segment, the region defined around the linear path and surrounding the ferromagnetic segment coincides with one of the high magnetic flux density regions, and one of the two or more bearings is concentrated in the high magnetic flux density region.

9. A linear actuator according to claim 7 or 8, The mass further includes a first end segment connected to one end of the first magnet, and a second end segment connected to one end of the second magnet on the opposite side from the first end segment. A linear actuator in which the interface between the first end segment and the first magnet, and the interface between the second end segment and the second magnet, coincide with corresponding high magnetic flux density regions, and corresponding bearings from the two or more bearings are clustered around the periphery along the linear path.

10. A linear actuator according to any one of claims 1 to 9, The system further comprises at least one magnet fixed to the guide, which contributes to defining the force response curves for various positions of the mass along the linear path, A linear actuator in which the mass is biased to a rest position along the linear path according to the force response curve, and when the mass is in the rest position, the coil is magnetically coupled to one or more magnets of the mass, and one of the high magnetic flux density regions extends between at least one magnet fixed to the guide and one or more magnets of the mass.

11. A linear actuator according to any one of claims 1 to 10, The system further includes a controller capable of driving the coil and operating it to selectively radiate a magnetic field that brings about the magnetic coupling to one or more magnets of the mass, A linear actuator in which the direction of the magnetic field is parallel to the linear path, and a force is applied to the mass along the direction parallel to the linear path by the action of the magnetic field.

12. A linear actuator according to any one of claims 1 to 11, A linear actuator comprising at least three individual bearings, wherein the two or more individual bearings described above include at least three individual bearings.

13. A linear actuator according to any one of claims 1 to 12, The system further comprises one or more additional and individual magnetic fluid rings located in corresponding separate high-flux regions. A linear actuator in which one or more individual magnetic fluid rings are arranged outside the maximum displacement span of the mass along the linear path.

14. A method for operating a linear actuator having a guide for defining a linear path, a mass slidably mounted on the guide to move back and forth along the linear path, and two or more individual magnetic fluid bearings arranged in corresponding separate high magnetic flux density regions, A step of changing the orientation of the linear actuator with respect to the direction of gravity, Following the change in orientation, the mass is moved to a position deviated from the linear path by the action of gravity on the mass, The steps include generating a force that at least partially cancels out the gravitational force acting on the mass by the action of the high magnetic flux density region on the two or more individual magnetic fluid bearings, A method that includes this.

15. A linear actuator, A guide having a shaft that defines a straight path, A mass having an internal channel defined parallel to the linear path and engaged with the shaft to move back and forth along the linear path, the mass having one or more magnets, A coil fixed to the guide, which is magnetically coupled to one or more magnets in the mass, A linear actuator equipped with the following features.

16. A linear actuator according to claim 15, It further comprises two or more individual bearings, each consisting of magnetic fluids that converge in corresponding separate high magnetic flux density regions. The two or more individual bearings are positioned between the mass and the shaft, on the inside of the mass as seen from the linear path, and spaced apart from each other along the linear path. A linear actuator in which each of the two or more bearings extends around the linear path and is capable of engaging the mass and the guide during the forward and backward movement, and two or more of the two or more bearings are spaced apart from each other along the linear path.

17. A linear actuator according to claim 15 or 16, The guide further comprises an inward-facing surface extending around the linear path and two or more individual magnetic fluid bearings. A linear actuator in which two or more individual magnetic fluid bearings are positioned outside the mass with respect to the linear path between the inward-facing surface of the guide and the mass, and are spaced apart from each other along the linear path.

18. A linear actuator according to any one of claims 15 to 17, The mass has one or more transverse grooves extending around the linear path and located in one of the high magnetic flux density regions, A linear actuator in which the transverse grooves guide the convergence of corresponding bearings among the two or more individual bearings, and the one or more transverse grooves are formed on one or more of the inward-facing surfaces of the channel and the outward-facing surfaces of the shaft.

19. A linear actuator according to any one of claims 15 to 18, At least one of the guide and the mass has one or more straight grooves arranged parallel to the straight path, A linear actuator in which the one or more straight grooves are arranged in fluid communication with one or more of the two or more individual bearings, and the one or more straight grooves function as a reservoir and hold a portion of the magnetic fluid inside.

20. A linear actuator according to any one of claims 15 to 19, The guide further comprises one or more magnets that are magnetically connected to the one or more magnets of the mass, A linear actuator that biases the mass to at least one rest position along the linear path using one or more of the aforementioned magnets.

21. A linear actuator according to any one of claims 15 to 20, The aforementioned mass has a first magnet that is spaced apart from the second magnet, A linear actuator in which the first magnet and the second magnet exhibit a magnetic field parallel to the linear path and have opposite polarities.

22. A linear actuator according to any one of claims 15 to 21, The system further comprises at least one magnet fixed to the guide and contributing to defining force response curves for various positions of the mass along the linear path, A linear actuator in which the mass is biased to a rest position along the linear path according to the force response curve, and when the mass is in the rest position, the coil is magnetically coupled to one or more magnets of the mass, and one of the high magnetic flux density regions expands between at least one magnet fixed relative to the guide and one or more magnets of the mass.

23. A linear actuator according to any one of claims 15 to 22, The system further includes a controller capable of driving the coil and operating it to selectively radiate a magnetic field that brings about the magnetic coupling with the one or more magnets of the mass, A linear actuator in which the direction of the magnetic field is parallel to the linear path, and a force can be applied to the mass along the direction parallel to the linear path by the action of the magnetic field.

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