DEVICE FOR CHECKING THE POSITION OF AN ACTUATOR

Abstract

A device for checking the position of a mechanical element in translational or rotational motion which performs a predetermined stroke, the device being provided with a magnetic component integral with the mechanical element whose position is to be determined and a stationary magnetic sensor, the magnetic component has at least one magnetic element arranged according to a helical pattern.

Claims

1. A device (10) for checking the position of a mechanical element in translational or rotational motion which performs a predetermined stroke, the device (10) comprising a magnetic component (4) integral with the mechanical element whose position is to be determined and a stationary magnetic sensor (3), wherein the magnetic component (4) comprises at least one magnetic element arranged according to a helical pattern wherein said magnetic component (4) comprises a bar (1) of non-magnetic material, provided with a plurality of holes (6) and in said plurality of holes (6) a plurality of magnetic cylinders (2) is fixed with interference, one cylinder (2) for each hole (6).

2. (canceled)

3. (canceled)

4. The device according to claim 1, wherein said at least one magnetic element ends, having, among them, an angular phase shift of the magnetic field comprised between 90° and 270°.

5. The device (10) according to claim 1, wherein said bar (1) has a length proportional to the predetermined stroke of the actuator.

6. (canceled)

7. (canceled)

8. The device (10) according to claim 1, wherein the magnetic sensor (3) is three-dimensional and comprises inside three different Hall effect sensors (5) arranged orthogonally between them to form a Cartesian reference triad.

9. The device (10) according to claim 8, wherein said magnetic sensor (3) returns three field components ({right arrow over (B)}.sub.x, {right arrow over (B)}.sub.y, {right arrow over (B)}.sub.z) on three axes of the triad.

10. The device (10) according to claim 1, wherein the magnetic sensor (3) is a magneto-resistive sensor.

11. A method for decoding a position signal by means of a device (10) as described by claim 1, comprising the following steps: a. detecting one or more quantities related to a generated magnetic field generated by the magnetic element arranged according to a helical pattern, and b. correlating a position of the mechanical element to one or more quantities related to the magnetic field.

12. The method according to claim 11, wherein step a. includes the following steps: a1. determining a mathematical function that expresses the trend of the flux lines slope of the magnetic field, a2. deriving the equation of the interpolating straight line of the mathematical function, and wherein step b. includes the phase of obtaining the position of the mechanical element using inverse formulas of the equation of the interpolating straight line.

13. The method according to claim 11, wherein step a. includes a phase defining a lock-up table or a mathematical function capable of determining the exact value of the components of the field at each point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of embodiment, in which:

[0027] FIG. 1 shows the schematic drawings of the individual components of the device for checking the position, according to one embodiment of the present invention,

[0028] FIG. 2 is an assembly diagram of the magnetic component of FIG. 1, and

[0029] FIG. 3 is a schematic representation of the final solution of the device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Referring now to the above figures, hereinafter a device 10 is described for checking the position of a mechanical element in a translational or rotational motion. The device comprises a magnetic component 4 integral with the mechanical element the position of which is to be determined and a stationary magnetic sensor 3.

[0031] The magnetic component 4 must be able to generate a particular field shape. In order to obtain such result one possible solution is that the magnetic component 4 comprises a bar 1 of non-magnetic material, for example aluminum, provided with a plurality of holes 6 and in said plurality of holes 6 a plurality of magnetic cylinders 2 is fixed with interference (glued or embedded), one cylinder 2 for each hole 6, wherein the cylinders 2 are polarized according to same direction, identified by the field vector {right arrow over (B)}.

[0032] The individual magnetic cylinders 2 are arranged along the non magnetic bar 1 following a helical pattern. The number and arrangement of the magnetic cylinders along the helix are determined so as to obtain an angular displacement of the magnetic field between the end magnetic cylinders 2′, 2″, equal to an angle sufficiently large to ensure an efficient interpretation of the values, for example an angle between 90° and 270° (in the figure, it must be noted, for example, that the referred angle is approximately flat). As the angular displacement and the distance between consecutive magnetic cylinders can be imposed at will, the length of the non-magnetic bar 1 is also imposed and, therefore, it can be proportional to the stroke of the actuator.

[0033] Therefore, it can be said that, with this technology, there is no measurable maximum stroke limit. For this reason, it is possible to develop different non-magnetic bars, always provided with a helix of magnetic cylinders and which have a different length, depending on the stroke to be actually measured.

[0034] As an alternative to this solution, the magnetic component can have a different design, as long as it is able to replicate the same shape of the magnetic field. An example could be to use a flexible material with high magnetic properties, with which to replicate the helical shape given by the arrangement of the magnetic cylinders in the case previously illustrated. Otherwise, according to a further example, the magnetic component can be devoid of the non-magnetic bar and comprise a plurality of small prismatic-shaped magnets, arranged with an angle of phase shift between them, in such a way as to reconstruct, also in this case, a helical profile.

[0035] The sensor 3 sensitive to the magnetic field, suitably constrained, must be chosen so that it can detect the field simultaneously on several conventionally defined directions. Advantageously, a solution is represented by a three-dimensional magnetic sensor 3, which contains inside it three distinct Hall effect sensors 5, arranged orthogonally to each other to form a reference Cartesian triad and compacted in a single electronic board. This allows to obtain the intensity of the magnetic field on the three axes defined by the reference triad, given by the orientation of the individual Hall effect sensors 5, strictly connected to the spatial orientation of the sensor itself. Therefore, the sensor 3 does not directly return a position value, but the three field components {right arrow over (B)}.sub.x, {right arrow over (B)}.sub.y, {right arrow over (B)}.sub.z on the three axes of the triad. Therefore, the same results can also be obtained with sensors of different types capable of returning the intensity of the field in several directions. A schematic drawing of the device as a whole is shown in FIG. 3.

[0036] The extrapolation of the value of the instantaneous position of the mechanical element is obtained thanks to a specific method based on a decoding algorithm. The aim of the method is to associate the quantities related to the magnetic field with the relative position between the sensor and the magnetic component. Ultimately the method includes the following steps of: [0037] detecting one or more quantities linked to the generated magnetic field; [0038] correlating the position of the mechanical element to the quantities linked to the magnetic field.

[0039] In order to do this, two different approaches have been developed. The first one is based on the analysis of the trend of the lines of force of the magnetic field. This is equivalent to quantifying the slope of the lines of force, an operation which coincides with the calculation of the angle of inclination, point by point, of the individual field vectors {right arrow over (B)} tangentially to the lines of force themselves. In order to avoid complex considerations with solid angles, it is necessary to determine the trend of the lines of force projected on a Cartesian reference plane, chosen on the basis of the geometry of the field and the relative orientation between sensor and magnetic component. This means that, by selecting two components of the field corresponding to the Cartesian reference plane still previously chosen, it is theoretically possible, by exploiting the arctangent and modifying its trend with a scale factor k set by the user, to determine a mathematical function which expresses the trend of the slope of the lines of force in relation to the position. Supposing, for example, to choose the XY plane as the Cartesian reference plane, then using the components {right arrow over (B)}.sub.x and {right arrow over (B)}.sub.y, extrapolated from the sensor, it is possible to calculate:

[00001]${\vartheta }_{XY}=\arctan \left(\frac{B_x}{k.Math.B_y}\right)\underset{\_}{\mathrm{or}}{\vartheta }_{YX}=\arctan \left(\frac{B_Y}{k.Math.B_x}\right)$

[0040] The advantage is that, considering the magnetic field generated by the helix bar, the mathematical function in question is monotonous and easily interpolated with a straight line. Therefore, once the equation of the interpolating straight line has been obtained, a linear relationship will be available between the position of the mechanical system and the slope of the lines of force. Therefore, by exploiting the inverse formulas, it is possible to return to the target variable (position of the mechanical element) from the Cartesian components of the magnetic field. In this way, the problem of the non-linearity is drastically reduced, as linear curves are considered. Furthermore, thanks to the optimum repeatability of the measurement, it can be sure that the same position value will always correspond to each slope value.

[0041] By using a magneto-resistive sensor, which measures the total intensity of the magnetic field and its angle of inclination, it is possible to reach the same conclusions, without resorting to the calculation of the angle with the arctangent function,

[0042] The second approach of the decoding algorithm instead exploits all three Cartesian components {right arrow over (B)}.sub.x, {right arrow over (B)}.sub.y, {right arrow over (B)}.sub.z In fact, it can be observed how, in no point of the space, {right arrow over (B)}.sub.x, {right arrow over (B)}.sub.y, {right arrow over (B)}.sub.z be repeated, by assuming the same values. In other words, by moving the sensor 3 in any direction with respect to the magnetic component 4, although remaining in any case at a distance such as to obtain suitable values from the measurement, ternary values {right arrow over (B)}.sub.x, {right arrow over (B)}.sub.y, {right arrow over (B)}.sub.z are always obtained, which are different from each other. This constitutes a considerable advantage, as thanks to an appropriately defined lock-up table or by referring to a mathematical function capable of determining the exact value of the components of the field at each point, it is possible to define the correct relative position between sensor and magnetic bar. Furthermore, by exploiting this algorithm, as the exact value of the field is known in any point of the space, it is possible to discriminate the presence of small displacements or vibrations, the presence of which is inevitable in a real case, by extrapolating only the exact position of the mechanical system, only in the direction of the motion to be detected. This is particularly useful when the system is able to act and control only one axis, but small movements occur outside the control, even in the other directions.

[0043] In addition to the embodiments of the invention, as described above, it is to be understood that numerous further variants exist. It must also be understood that said embodiments are only exemplary and do not limit neither the aim of the invention, nor its applications, nor its possible configurations. On the contrary, although the above description makes it possible for the skilled person to implement the present invention at least according to an exemplary configuration thereof, it must be understood that numerous variations of the components described are conceivable, without thereby departing from the object of the invention, as defined in the attached claims.