PERMANENT-MAGNET LINEAR ACTUATOR Technical Field

The present invention relates to a permanent-magnet linear actuator. Background Art Permanent-magnet linear actuators are currently known which are constituted, as are in general most actuators, by a part that is fixed, i.e., to be jointly coupled to a first body that is designed to remain substantially stationaiy, and by a movable part, to be jointly connected to a second body that is adapted to be subjected to a translational motion or to be rotated or generally moved with respect to the first body.

One of the two parts, for example the fixed part, comprises guiding means, for example a rail, along which a series of permanent magnets is arranged, while the other part, for example the movable part, has one or more windings designed to be crossed by electrical current to generate a variable magnetic field, which by interacting with the magnetic field of the permanent magnets of the fixed part moves such movable part; the latter is understood to be provided with means for sliding with respect to the guiding means of the fixed part.

These known permanent-magnet linear actuators, despite being widespread and appreciated for their versatility, have drawbacks.

A first one of these drawbacks is the presence of the windings, which, being crossed by electric current, can overheat, with all the risks of breakage or malfunction that this event entails.

A second significant drawback is the high cost of production of such linear actuators, which restrains their diffusion and use in the domestic field as well as in the industrial field.

These high costs are due in particular to the provision of the complex electronic control unit, which is designed to drive such actuators and by means of which the magnetic field that determines its movement is managed.

Another important cost item is constituted by the presence of a braking device, which is necessary in order to stop the movable part with respect to the fixed part, since such braking generally cannot be obtained in an optimum manner merely by resorting to the electronic control unit and to the variation of the magnetic field generated by the windings.

Moreover, in particular cases, for the above cited risks of overheating of the actuator, such actuator can be provided with suitable cooling means, such as fans, or other heat exchange means, which are more or less costly also in terms of space occupation and consumption. Disclosure of the Invention

The aim of the present invention is to provide a permanent-magnet linear actuator that is capable of obviating the drawbacks of known types of permanent-magnet actuator.

Within this aim, an object of the present invention is to provide a permanent-magnet linear actuator that is not susceptible of overheating.

Another object of the present invention is to provide a permanent- magnet linear actuator that can be managed with an electronic control unit that is simpler and cheaper than that with which known types of actuator are equipped. Another object of the present invention is to provide a permanent- magnet linear actuator that can be stopped safely and precisely without the need for a specific dedicated braking device.

Another object of the present invention is to provide a permanent- magnet linear actuator that is simple to manufacture and is easy to apply. Another object of the present invention is to provide a permanent- magnet linear actuator that can be manufactured cheaply with known systems and technologies.

This aim and these and other objects, which will become better apparent hereinafter, are achieved by a permanent-magnet linear actuator, characterized in that it comprises a movable part, to be jointly connected to

a first body adapted to be moved with respect to a second fixed body, and a fixed part, to be jointly connected to said second body designed to remain substantially stationary, a first one of the two parts comprising guiding means for corresponding sliding means that are jointly connected to the second part, one of said parts having a series of first permanent magnets that are aligned in at least one row that lies along the direction of translational motion defined by the cooperation of said sliding means with said guiding means, the other one of said two parts having a rotor element which faces said row of first permanent magnets and comprises a series of second permanent, magnets, which are supported by a shaft associated with means for its rotation, said second magnets being arranged side by side in the direction of the axis of the shaft, with polarities that are offset by a preset angle. Brief description of the drawings Further characteristics and advantages of the invention will become better apparent from the following detailed description of seven preferred but not exclusive embodiments thereof, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a perspective view of an actuator according to the invention in a first embodiment;

Figure 2 is a partially exploded perspective view of the actuator of Figure 1;

Figure 3 is a schematic plan view of the actuator in its first embodiment; Figures 3a to 3d are examples of the operation of the actuator in its first embodiment;

Figure 4 is a schematic perspective view of the rotor element and of the means for rotating it;

Figure 5 is a schematic transverse sectional view of the invention in a second embodiment thereof;

Figure 6 is a schematic view of a third embodiment of a linear actuator according to the invention;

Figure 7 is a schematic transverse sectional view of an actuator according to the invention in a fourth embodiment thereof; Figure 8 is a schematic transverse sectional view of a linear actuator according to the invention in a fifth embodiment thereof;

Figures 9 and 10 are schematic views of an actuator according to the invention in a sixth embodiment thereof;

Figure 1 1 is a view of a seventh embodiment of a rotor element of an actuator according to the invention;

Figure 12 is a schematic view of an advantageous arrangement for the first permanent magnets in a row, for a device as shown in Figures 9 and 10. Ways of carrying out the Invention

With reference to the figures, a permanent-magnet linear actuator according to the invention is generally designated by the reference numeral 10 in its first embodiment, shown in Figures 1 to 4.

The permanent-magnet linear actuator 10 comprises a first movable part 1 1, to be jointly connected to a first body that is adapted to be moved with respect to a second fixed body, and a second fixed part 12, to be jointly connected to the second body designed to remain substantially stationary.

The first movable part 1 1 comprises guiding means 13 for corresponding sliding means 14 that are jointly connected to the other second part 12.

One of the parts 1 1 and 12, the first movable part 1 1 in the embodiment described here, is provided with a series of first permanent magnets 15, which are aligned in a row 16 that lies along the direction of translational motion, which is defined by the cooperation of the sliding means 14 with the guiding means 13.

The other one of the two parts 1 1 and 12, in this case the second fixed part 12, has a rotor element 17 that faces the row 16 of the first permanent

magnets 15.

The rotor element 17 comprises a series of second permanent magnets 18, which are supported by a shaft 19 that is associated with means 20 for its rotation. The second magnets 18 are arranged laterally adjacent in the direction of the axis of the shaft 19, with polarities that are offset by a preset angle.

In this first embodiment of the invention, which is a non-limiting example thereof, the rotor element 17 comprises four supports 21 for the second permanent magnets 18 which are keyed on the shaft 19, each support 21 carrying two magnets 18 arranged in diametrically opposite positions.

The second magnets 18 fixed to the first support 21 are offset by 90° with respect to magnets 18a carried by an axially adjacent support 21a, and the same applies for subsequent second magnets 18b and 18c.

In particular, Figure 3 illustrates a row 16 of first magnets 15, which are arranged alternately, one magnets having the outer face with positive polarity 15' and one magnet having the outer face with negative polarity

15"; the positive magnets 15' and the negative magnets 15" are further spaced.

The second magnets 18, as shown schematically by the symbols + (plus) and - (minus) are present on the same support 21 with outer faces having opposite polarity.

The permanent magnets 15, 18, 18a, 18b and 18c can be of the type made of neodymium or of other similar and equivalent rare earths, i.e., of the category of so-called "supermagnets". In the exemplary embodiment described here, the first part 11 is provided by a profile that is preferably made of materials with high magnetic permeability.

This profile has two opposite longitudinal grooves, which provide the guiding means 13. The associated sliding means 14, which are jointly connected to the

second part 12, are constituted by sliders which are contoured to enter the described longitudinal grooves of the movable part 1 1 ; such grooves, which constitute the guiding means 13, are designed to slide on such sliders.

The second part 12 is provided by a tubular container, which can be made of plastic material or aluminum.

The rotation means 20 for the shaft 19 are constituted by a direct- current electric motor 20a, with which a reduction unit 20b is associated.

The motor 20a can also be of the alternating-current type and can also be of the type that is supplied at low voltage or directly at 230-380 V. An electronic control unit 23 and a power supply 24, shown schematically in Figure 3, can be mounted jointly on the rotation means 20 or can be simply interconnected remotely with them.

The power supply 24 can be based on batteries.

The electronic unit 23 is designed to drive the motor 20a during starting in any direction and proximate to the stop positions and to the stroke limits.

The operation of the linear actuator 10 according to the invention entails that by operating the motor 20a in one direction, the second magnets 18, 18a et cetera of the rotor element 17 interact, by rotating, with the first fixed permanent magnets 15, producing the movement of the movable part 1 1 in the direction of translational motion set by the guiding means 13 and by the sliding means 14, in a certain direction, while by operating the motor 20a in the opposite direction a movement of the movable part 1 1 in the opposite direction is achieved. In particular, for the first embodiment of the linear actuator 10, from a stop position, shown schematically in Figure 3, in which the first positive magnets 15' face second negative magnets 18", the motor 20a, by rotating in a first direction, causes for example the second negative magnet 18" to move away from one first positive magnet 15', while a second positive magnet 18a' moves into the region without magnets between two first

magnets, a positive one 15' and a negative one 15"; the second positive magnet 18a' in an intermediate configuration between the two first magnets 15' and 15", repels the first magnet 15' having an equal charge and is attracted by the first negative magnet 15" having an opposite charge, determining the translational motion of the first movable part 1 1 in a first direction.

This is shown schematically in Figures 3a and 3b. Likewise, the rotation of the rotor element 17 in the same direction leads to translational motion in such first direction. Conversely, as shown schematically in Figures 3c and 3d, if, in the region without magnets between two first magnets, a positive one 15' and a negative one 15", a rotation in the opposite direction moves a second negative magnet 18a", the second negative magnet 18a" is repelled by the first magnet having an equal charge 15" and is attracted by the first magnet 15' having the opposite charge, determining the translational motion of the first part 1 1 , which can move in the second opposite direction.

The movement of the first movable part 1 1 occurs in the only allowed direction, i.e., the one defined by the coupling between the guiding means 13 and the sliding means 14. The braking operations, which in known types of actuator are entrusted to appropriately provided dedicated devices, are provided by the rotor element 17, which is associated with the second fixed part 12, whose second magnets 18, 18a and onward, when the motor 20a is switched off and the shaft 19 is stationary, interact by mutual attraction with the first magnets 15 of the first part 11, stopping the first movable part 1 1.

A second embodiment of the invention is shown schematically in Figure 5.

In this second embodiment of the actuator, designated by the reference numeral 1 10, the rotor element 117 comprises hexagonal supports 121 , which therefore carry six magnets 1 18, one for each face, so as to make

the movement of the first part 1 11 more continuous and less jerky.

Figure 6 shows schematically a sectional view of a third embodiment of the invention, whose particularity resides in that the first part 211 has three rows of first magnets 215, 215a and 215b, which are arranged on three contiguous sides of an imaginary hexagon, so as to define a trapezoidal cross-section.

In a fourth embodiment of the invention, whose cross-section is shown schematically in Figure 7, the first part 311 is tubular and has three rows 316, 316a and 316b of first magnets which are embedded therein along a circular arc.

In this embodiment, the rotor element 317 has octagonal supports 321, which therefore support eight magnets 318.

The first magnets 315 of the three rows 316, 316a and 316b are arranged, on the circular arc of the cross-section of the first part 31 1 , at a distance whose center angle is the same center angle that lies between the axes of two contiguous second magnets 318.

Figure 8 illustrates schematically a transverse cross-section of a fifth embodiment of a permanent-magnet linear actuator according to the invention. The first part 411 is tubular and has four rows 416, 416a, 416b and

416c of first magnets which are embedded symmetrically at a circumferential distance of 90°.

In this embodiment, the rotor element 417 is provided with octagonal supports 421, which therefore support eight magnets 418. Figure 9 illustrates schematically a front view of a rotor element 517 in a sixth embodiment of the invention.

In such sixth embodiment, the magnets 518 have a substantially circular arc-like symmetrical shape and are coupled in pairs so as to form a disc that is keyed centrally on the shaft 519. Figure 10 shows by way of example that the magnets 518, 518a and

onward are adjacent in an axial direction and with polarities that are offset by a preset angle.

In Figure 12, the second magnets 518 and 518a are shown facing first magnets 515 which are mutually contiguous and have alternating polarities, and in particular these last magnets are shaped so as to have a certain inclination in the direction of translational motion of the movable part.

The particular shape of the first magnets 515 defines assuredly the direction of advancement of the first movable part with respect to the second fixed part, and when the rotor element 517 rotates in one direction, the first movable part always moves in a preset direction of the preset orientation, while the rotation of the rotor element in the opposite direction determines the movement of the first movable part in the opposite direction.

In Figure 11, in a seventh embodiment of the invention, the rotor element 617 comprises two magnetic portions 618a and 618b, each of which is shaped like a diagonally cut cylinder; the two portions 618a and 618b have opposite polarities.

Of course, it is understood that all of the described embodiments, as well as the equivalent embodiments that have not been described, can have the first part 11 as the fixed part, while the second part 12, with the rotation means 20 and the rotor element 17, is the movable part.

In this case, if one battery power supply 24 is provided, the power supply 24, together with the electronic control unit 23, advantageously can be fixed to the rotation means 20 and can perform a translational motion with them and with the second part 12, which is movable. In practice it has been found that the invention thus conceived solves the drawbacks noted in known types of permanent-magnet linear actuator.

In particular, the present invention provides a permanent-magnet linear actuator that is not susceptible of overheating, since it has no winding designed to generate variable magnetic field and therefore lacks the component that typically generates heat.

Further, a permanent-magnet linear actuator has been devised which can be managed with a simpler and cheaper electronic control system than the one with which known types of actuator are provided.

Further, the present invention provides a permanent-magnet linear actuator that can be stopped safely and precisely without the need for a specifically provided dedicated braking device, since braking is entrusted to the spontaneous interaction between the first magnets of the fixed part and the second magnets of the movable part.

Moreover, the present invention provides a permanent-magnet linear actuator that is simple to manufacture and easy to apply; by way of its simple structure, it is in fact easy to assemble and disassemble and therefore also simple to repair.

Moreover, the present invention provides a permanent-magnet linear actuator that can be manufactured cheaply with known systems and technologies by way of the reduction of the number of mechanical components and of the simplicity of the electronic control unit.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. In practice, the materials employed, so long as they are compatible with the specific use, as well as the dimensions, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. PD2007A000380 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.