MICRO-MECHANICAL DEVICE WITH LOCAL ELECTROMAGNETIC ACTUATION
A micromechanical device with electromagnetic actuation includes a base and a micro electro mechanical system (MEMS). The MEMS includes a mobile rotating element based on one or two axes of rotation. The base includes stators each forming a first internal pole, an external pole and an air gap. In order to increase the reliability and the mechanical stability of the device, the first internal poles are mounted in a connected manner to each other onto the base.
- 1-8. -8. (canceled)
- 9. A micromechanical device with electromagnetic actuation, comprising:
a base; a plate; a micro electro mechanical system (MEMS) mounted indirectly through the plate onto the base, the MEMS comprising a rotating element having a first axis of rotation and a first rotor comprising at least one first conductor line and two first segments detached from the rotating element so as to define two empty spaces internal and external to the first rotor, two first stators each made up of a first internal pole, a first external pole and a first air gap together defining a magnetic field B, each one of the two first segments arranged in one of the first air gaps perpendicularly to field B, so that the first internal poles and first external poles are placed in the two empty spaces internal to and external to the first rotor, the first internal poles are mounted in a connected manner to each other onto the base and the MEMS is mounted indirectly through the plate onto the base.
- View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
This application claims priority to Swiss Patent Application No. 01326/18 filed Oct. 31, 2018, the entirety of which is incorporated by this reference.
This invention is related to electromechanical microsystems, better known under the MEMS name, from the English Micro Electro Mechanical Systems. It concerns more specifically a micromechanical device including a mobile rotating element based on at least one rotation axis, and means of actuation of this electromagnetic type rotating element.
Such devices are generally optical devices in which the rotating element is comprised of a mirror connected to a fixed frame through two elastic beams in torsion defining the mirror'"'"'s axis of rotation. Alternately, the rotating element is mobile based on two axes of rotation. The mirror is then connected to a first mobile frame using two torsion beams, which is itself connected to the fixed frame through two other torsion beams. Whether it is mobile based on one axis or two axes of rotation, the mirror thus mounted allows redirecting a light beam between different fixed angular positions or scanning an angular space using a light beam. Such devices equip in particular optic spectrometers, printers, medical imagery devices, light sensors and numerous other devices including an optical control.
Among the aforementioned devices, we are interested in devices actuated electromagnetically using a rotor made up of at least one integrally-mounted arc runner of the rotating element, and a stator including two opposite magnetic poles separated by an air gap in which the rotor is placed. More specifically, we are interested here in devices equipped with a base on which an MEMS is mounted including a mobile rotating element based on at least one axis of rotation and at least a first rotor made up of a conductor line, which includes two segments detached from the rotating element so as to define two empty spaces interior and exterior to the rotor. Two stators, each made up of an internal pole, an external pole, and an air gap together defining a magnetic field
The device represented in FIG. 4 of patent EP 2 990 375 B1, although very efficient, is not exempt from defects, in particular regarding reliability. We understand well that with dimensions in the range of square centimeters, the type of device described in document EP 2 990 375 B1 requires great precision, in particular regarding the positioning of the stators in relation to the rotors. In fact, the conductor line segments placed inside the air gaps have little room to move under the effect of the magnetic field. A rigorous alignment of these segments with respect to the air gaps is therefore essential for the proper functioning of the device. The mounting of the MEMS and the stators on the base is thus done with the greatest care. But reliability tests taking the form of temperature cycles over the duration of one month show that the stators move on the base under the effect of thermal stress. The reason for this is the deterioration of the epoxy glue used to fix the stators onto their base, combined with the attraction and/or repulsion forces exercised together by neighboring stators. Repeated impacts or vibrations lead to the same result, which is explained also here by the pressures that the stators exert on each other and the breakdown of the glue. We observe that the breakdown of the glue is between the base and the stators, that is, at the point where the pressures are exerted in shear. The glue resists much better to simple traction forces. The movements observed, although small (in the range of one tenth of one millimeter), are enough to disturb the functioning of such devices, whose dimensions are themselves very small. We observe in particular that the conductor line segments are blocked or broken inside the air gaps, because of the change of position of the stators. The electromagnetic actuation is thus inoperative and the mobile mirror is blocked in a fixed position. It is important to observe, for the proper understanding of the invention, that the movement of the stators during reliability tests is caused by the combination of the deterioration of the glue and magnetic forces exerted between stators. These factors taken separately do not produce the movement of one or several elements on the base. The MEMS, for example, which is also glued to the base, but is not subjected to any force, remains fixed during reliability tests.
This invention has the goal of remedying this disadvantage, by offering a micromechanical device in which the stators are mounted on the base in a fixed manner relative to each other.
More specifically, the invention concerns a micromechanical device with electromagnetic actuation including a base and an MEMS mounted on this base, the MEMS including a mobile rotating element based on a first axis of rotation and a first rotor made up of a conductor line, which includes two first segments detached from the rotating element so as to define two empty spaces internal and external to the first rotor. The base even includes two first stators each made up of a first internal pole, a first external pole, and a first air gap together defining a magnetic field
By virtue of the fact that the internal poles of the stators are mounted connected to each other, and in particular are presented as a single part, the magnetic forces that exercise pressure in shear between the stators and the base cannot produce any movement relative to each other. Only the complete unit made up of all the poles internal to the rotors can move theoretically, but it does not undergo any specific pressures that, added to the deterioration of the epoxy glue, could generate accidental movement. The characteristics and advantages of this invention will appear more clearly upon reading the following description, given only as an example, and made in reference to the appended drawings.
The micromechanical device with local electromagnetic actuation represented in
Fixed frame 11 is mounted glued onto a metallic base 20 made up of a parallelipiped rectangle including a recess 21 of dimensions chosen to receive rotating element 10, rotor 13, and all parts of device 1. Two stators 22 each including two poles 23, 24 separated from each other by an air gap 25, are mounted on metallic base 20, in recess 21, so as to receive in air gaps 25 segments 15 of rotor 13. Poles 23 located in empty spaces 16 internal to rotor 13 are called internal poles 23, whereas poles 24 being placed in empty spaces 17 external to rotor 13 are called external poles 24. In this configuration, rotating element 10 is actuated in rotation by stators 22 that work together with segments 15 of rotor 13, without loss of magnetic power and with an efficiency that is greater than that of legacy devices.
We refer now to
As per the invention, internal poles 23 are mounted connected to each other on base 20. More precisely, poles 23 are made up of a U-shaped part 27, with a single strip, mounted on base 20 so as to become inserted into internal empty spaces 16. This way, internal poles 23 do not exert any mutual pressures likely to produce movement of one or the other under the effect of the aging of the glue and the forces present. External poles 24 are themselves connected to internal poles 23 through magnets 26, which are glued on one side to internal poles 23 and on the other side to external poles 24. Thus, the two stators 22 make up a unit of parts assembled by gluing, and the pressures experienced by the unit are internal but not external. The unit made up of the two stators 22 therefore does not move as a whole, but it experiences internal magnetic pressures of three types: From internal pole 23 towards internal pole 23, from internal pole 23 towards external pole 24, and from external pole 24 towards external pole 24. The first ones do not produce any movement because of the fact that internal poles 23 only make up one part 27. The second and third types of pressures, of attraction and repulsion, may induce shear forces, but only in the case of repulsion between an opposite internal pole 23 and an external pole 24, or between the two external poles 24. In these two cases, the gluing of external poles 24 to U-shaped part 24, through magnets 26, ensures the stability of external poles 24. Thus mounted, micromechanical device 1 successfully undergoes the thermal stress tests, without movement of stators 22 and therefore without blockage of rotor 13.
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In the same way, the iteration illustrated in
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Finally, we refer to
A device with local electromagnetic actuation has thus been described. Certainly, this invention is not limited to the iterations described above, but extends to all variants within the scope of skilled persons, becoming part of the framework of the claims below.