"Optoelectronic measuring system for acquiring position and orientation measures, in an industrial machine"

DESCRIPTION [0001] The present invention relates to the technical field of position and orientation measuring systems of an object in space and relates in particular to an optoelectronic measuring system for acquiring position and orientation measurements of a working tool or of a workpiece in an industrial processing machine.

[0002] For the purposes of the present description, "industrial processing machine" or more simply "industrial machine" shall mean not only a mechanical machine tool (e.g. a lathe, a grinding machine, a milling machine or a drilling machine, a boring machine) but also an electronic machine tool (e.g. a laser processing machine, an electro-erosion machine) as well as a high pressure water-jet machine, a CMM (coordinate measuring machine) , a movement/handling machine and an assembling machine. Said industrial machine can be a machine where, indifferently, during processing:

- the working tool is mobile and the workpiece is fixed respect to the machine bedplate;

- the working tool is fixed and the workpiece is mobile respect to the machine bedplate;

- the working tool and the workpiece are both mobile. [0003] "Workpiece" shall mean not only a machinable workpiece of material such as, for example, wood, metal or plastic which can be fixed to an industrial machine for processing, but also a wall or large portion of solid material which cannot be mounted on an industrial machine but which, in any case, can be accessed and processed by an industrial machine or, in general, any workpiece whatsoever which can be transported and handled by an industrial machine.

[0004] "Processing" shall mean any of those operations which an industrial machine can perform on a workpiece such as, for example, not only removal of material, milling, bending, smoothing and similar, but also surface treatment of the material (for example, painting) as well as all other operations which can be carried out on a workpiece such as measuring, handling, moving or assembly. [0005] Furthermore, in general, "operation" of an industrial machine shall mean any function whatsoever which the machine can perform such as, for example, moving a tool within the operative space, maintaining the fool ^" in ^"" any ^{" ~} p ^~ os ^' i ^" t ^~ iόn whatsoeverT processing ^"" of ^™ a ^" workpiece, as well as adjusting, measuring and monitoring operations which can be performed not only on the

workpiece but also on other mechanical and structural parts belonging to the industrial machine. [0006] In the prior art, the position and orientation of a working tool or of a workpiece in an industrial machine are normally calculated by using measurements output from encoder and/or resolver transducers mounted on the fixed or mobile axes of the machine. Said measurements represent linear movement. Starting from said measurements, calculation of the position (and orientation) of the tool or workpiece is obtained by means of numerical processing which takes into account a kinematic model of the industrial machine. [0007] The kinematic model of the machine is a static model which does not take into account some important factors, such as: dynamic deformation that the structure undergoes during movement (e.g. bending of the axes) , thermal deformation, etc. For this reason, the real position and orientation of the working tool or the workpiece are different from those which can be calculated by numerical processing, by means of the machine model, of the signals output from the encoder/revolver transducers . [0008] This problem has a negative influence on the static ^" accuracy ^""" (mainTy depending on ^" theTiήar ^~ εeToTina1fi ^" on) and ^" the dynamic accuracy (mainly depending on bending deformation of the axes) of the industrial processing

machine. This is due to the fact that in the above- described prior-art industrial machines, the numerical control system of the machine cannot be based on knowledge of the true position and orientation of the tool or workpiece (or rather of the true reciprocal position between tool and workpiece) and, for this reason, it is unable to correct the deviation between the set path and the true path. For high-precision industrial machines, thermal compensation maps are used which, thanks to the use of temperature sensors on the machine, permit rough correction of the thermal errors. However, these corrections are not very effective in most cases. [0009] The document US 5,035,503 describes a hybrid system for measuring the coordinates of a Cartesian axis industrial machine, where the coordinate measurements are obtained from a processing system not only on the basis of output signals from optoelectronic devices installed along the machine axes but also on the basis of signals provided by position resolver/encoders . In particular, the signals provided by the position resolver/encoders are used to measure translation of the mobile parts of the axes along the direction of optical beam propagation.

^" [0010] ^~ I€ ^" Has ^" Eeen ^~ δb ^~ sefved ^~ tHat ^~ t ^" Ke ^~~ sysCem ^~ desc ^" ribe ^' d ^~ l ^" rr the above-mentioned document US 5,035,503 has a first drawback due to the presence of resolver/encoders which,

as explained, introduce inaccuracies in the measurements taken. It was further observed that said system has another drawback due to uncertainty in the measurement of coordinates because of the relative positioning between the optoelectronic elements arranged on consecutive axes of the machine .

[0011] The object of the present invention is to provide a system for measuring, in an industrial processing machine, the position and orientation of a working tool or of a workpiece without the above-described drawbacks of the known art .

[0012] Said object is reached by means of a measuring system as defined in the attached claim 1. Preferred embodiments of the measuring system according to the invention are defined in the dependent claims.

[0013] An industrial machine as defined and characterized in the attached claim 16 is also object of the present invention.

[0014] Further features and advantages of the present invention will become more apparent from the following detailed description of an exemplary but non-limiting embodiment thereof, as illustrated in the accompanying drawings ^" , ^~ whe ^~ rein ^" : - figure 1 shows a schematic view of a first example of a measuring system according to the present invention

applied to an industrial processing machine;

- figure 2 shows a schematic view of a second example of a measuring system according to the present invention applied to an industrial processing machine; - figure 3 shows a part of the machine in figure 1, together with an optoelectronic subsystem installed on an axis of the machine;

- figure 4 schematically shows a particular exemplary embodiment of an optoelectronic subsystem of a measuring system according to the present invention; figure 5 schematically shows a further exemplary embodiment of an optoelectronic subsystem of a measuring system according to the present invention; figure 6 schematically shows a further particular exemplary embodiment of an optoelectronic subsystem of a measuring system according to the present invention, and figure 7 schematically shows a variation in the embodiment of the subsystem in figure 3.

[0015] In the figures, similar or equal elements are indicated with the same reference numbers.

[0016] With reference to the schematic drawing in figure 1, a first exemplary embodiment of a measuring system ^" according ^"""" EoTHe ^~~ preseritr ^" invention ^" i ^" s ^~~ de ^~ scri"bed ^~ —-In- particular, the measuring system in the example in figure 1 identifies the six spatial coordinates (or degrees of

freedom), i.e. three translations and three rotations in space, of a working tool W__T in an industrial processing machine A_Z, A_X. Said working tool W_T is, for example, a tool for the machining of a workpiece W_P such as a mill connected to a mandrel. Other types of tools which can be used as processing instruments alternative to those described are, for example, a grinding wheel, a boring machine, a welding gun or laser head or painting head and they depend, more generally, on the type of industrial machine used.

[0017] In the example in figure 1, it has been supposed for simplicity that, during machining, the workpiece W_P occupies a fixed spatial position (respect to the industrial machine) and that the working tool W_T is mobile (respect to the industrial machine) . It should be observed however that in embodiments different from the one specifically represented in figure 1, a measuring system according to the present invention can also be used in an industrial machine where the workpiece W_P is mobile while the working tool W_T is fixed or in an industrial machine where both the working tool W_T and the workpiece W_P are mobile. In the latter case, just as

^~ aή ^™ example ^"" of ^~ a possible ^" variation cdmpare ^" d ^"~ wi ^" th ^~~ fl ^" gure ^~

1, the workpiece W_P can be held on a mobile support, such as a rotating platform (not illustrated in the

figure) . Since said alternative embodiments can easily be derived by the skilled in the art from the teachings of the present invention, they will not be further described herein. [0018] The industrial machine A_Z, A_X includes at least one first linear axis A_Z and at least one second linear axis A_X which are operatively connected to each other and slidingly coupled. In particular, the first axis A_Z includes a track 1, 2, 3 (which represents the stationary structural part of the machine axis A_Z) and a mobile structural part 4 operatively coupled to the track 1, 2,

3 and which can slide along the direction Z-Z of the track 1 , 2 , 3. In other words , the mobile structural part

4 is slidingly coupled to the track 1, 2, 3 to be moved, for example continuously, along the movement direction defined by the track and indicated with Z-Z in the figure .

[0019] In the example in figure 1, the track 1, 2, 3 comprises a bedplate 1, a head 2 and a pair of parallel bars 3 which extend between the bedplate 1 and the head 3 and are fixed to them. The two parallel bars 3 act as guiding means for the mobile structural part 4. [0020] ^~ The linear axis A_Z includes means for moving~the mobile structural part 4 , which in the particular example in figure 1 are represented by a rotating electric motor

5, fixed to the bedplate 1, and a screw shaft 6 operatively coupled to the shaft of the rotating motor 5 and which extends between the bedplate 1 and the head 2 of the axis A_Z. The screw shaft 6 is operatively coupled to the mobile structural part 4 in a known manner and not further described herein. The rotating motor 5 is controlled by output signals provided by a control unit

(not illustrated in the figure) of the industrial machine. The machine control 5 can be either of the totally automatic type or controlled at least partially by an operator. It should be noted that, instead of the above-mentioned rotating motor 5, for moving the mobile structural element 4, other motor means can be used, among which, for example, a linear electric motor, a pneumatic actuation system or a piezoelectric actuation system. It should be further noted that the rotating motor 5, or the other motor means mentioned above, instead of being fixed to the bedplate 1, in an embodiment alternative to the one represented in figure 1, can be provided in the mobile structural part 5 or fixed to the head 2 of the track 1 , 2 , 3.

[0021] Similarly, the second axis A_X includes a track 4,

^~ T ^~ 8 ^' (which rep>feseήEs-TEe ^" stationary structuraT ^~ part ^~ i5 ^" f ^" the axis A_X) and a mobile structural part 9 which is operatively coupled to said track 4, 7, 8 and which can

slide along the direction X-X of the track 4, 7, 8. In other words, the mobile structural part 9 is slidingly coupled to the track 4, 7, 8 to be moved, for example continuously, along the movement direction defined by the track and indicated with X-X in the figure. In the example in figure 1, the track 4, 7, 8 comprises a bedplate 4 fixed to the mobile structural part 4 of the axis A_Z,' a head 7 and a pair of parallel bars 8 which extend between the bedplate 4 and the head 7 and are fixed to them. It should be observed that in the particular example illustrated, the bedplate 4 of the axis A_X coincides with the mobile structural part 4 of the axis A_Z. The two parallel bars 8 act as guiding means for the mobile structural part 9. [0022] The linear axis A_X includes means for moving the mobile structural part 9 which, in the particular example in figure 1, are represented by a rotating electric motor 10, fixed to the bedplate 4, and a screw shaft 11 operatively coupled to the shaft of the rotating motor 10 and which extends between the bedplate 4 and the head 7 of the axis A_X. The screw shaft 11 is operatively coupled to the mobile structural part 9 in a known manner

^" and ^" not ^"" fϋrtEer ^~~ clescrϊbed ^~ Kereϊn ^~ . TKe ^" ^c^ta ^' tϊng ^{^} mot ^' or l ^" 0 ^~ is controlled by output signals provided by a control unit (not illustrated in the figure) of the industrial

machine. The machine control 10 can be either of the totally automatic type or controlled at least partially by an operator. It should be noted that, instead of the above-mentioned rotating motor 10, for moving the mobile structural element 9, other motor means can be used, among which, for example, a linear electric motor, a pneumatic actuation system or a piezoelectric actuation system. It should be further noted that the rotating motor 10, or the other motor means mentioned above, instead of being fixed to the bedplate 4, in an embodiment alternative to the one represented in figure 1, can be provided in the mobile structural part 9 or fixed to the head 7 of the track 4 , 7, 8. [0023] In the example in figure 1, the mobile structural part 9 of the axis A_X includes the working tool W_T. This can also be controlled by means of the control unit of the industrial machine.

[0024] It should be noted that the two above-described axes A_X and A_Z are, in practice, two consecutive, slidingly coupled linear axes of an industrial machine A_Z, A_Z with two or more axes. Furthermore, in the particular example described, said axes A_X and A_Z are at right

^"" angle ^' s ^~ t ^~ o ^~ eaϋh ^~" oeher, ^" for ^~ example ^"~ "f ^" oτ:mxng ^""" part ^~~ σf ^~~ a ^"~~ s'et ^~ of three axes of a three-axis Cartesian industrial machine. It must be remembered, however, that a measuring

system according to the present invention can generally be used in any industrial machine which includes at least one pair of consecutive, slidingly coupled linear axes A_X and AJZi ₁ independently of the angle of inclination defined between said axes and independently of the presence of other axes of a different type, for example rotating.

[0025] It should also be remembered that, only for exemplary purposes, a particular type of linear axis has been illustrated but that the teachings of the present invention can easily be applied by the skilled in the art to different types of axes of industrial machines where a linear and stationary structural part, defining a movement direction, and a mobile structural part, which can slide along said movement direction, can be identified.

[0026] With reference to figure 1, the optoelectronic measuring system includes a first ^' optoelectronic subsystem S2, R2 comprising a first unit S2 fixed to the track 1, 2, 3 (or more generally fixed to the stationary part of the axis A_Z) , in the example fixed to the bedplate 1 of said axes A_Z, and a second unit R2 fixed

^" to ^" the ^'"" mobile structural part ^" 4 ^" of the ^" axi ^" s ^~ K_Z and In ^" optical communication with the first unit S2. The first optoelectronic subsystem S2, R2 is such as to provide

output signals (for example electric) , assigning them for example to the control unit of the industrial machine A_Z, A_X, which carry information relating to the six spatial coordinates of the mobile' structural part 4 respect to the track 1, 2, 3 (or more generally respect to the stationary part of the axis A_Z) and, in particular, respect to its bedplate 1. Said signals are obtained by means of propagation of at least one optical frequency electromagnetic radiation, in brief of at least one optical beam B2, between the first S2 and the second R2 unit of the first optoelectronic system S2, R2. At least one of said first and second unit is such as to provide the output optical beam B2, therefore representing or including a source (active or passive) of said beam B2, in such a way as to direct said optical beam B2 towards the other of said units which, therefore, represents a target of said optical beam B2. For the purposes of the present invention, active source shall mean an optoelectronic device (for example a laser diode) such as to generate an optical beam in contrast with a passive source which, on the contrary, is an essentially passive optical component (for example, a reflecting or diE ^' fusing ^""" erement) ^~' which ^" is ^{~^} such ^""" as ^{" ~} to ^~" deviate ^"" an ^" incident optical beam. Embodiments of possible optoelectronic subsystems of the type mentioned above

will be described more in detail hereunder. [0027] The optoelectronic measuring system further includes a second optoelectronic subsystem S3 , R3 comprising a first unit S3 fixed to the track of the axes A_X (or more generally fixed to the stationary part of said axis) , in the example fixed to the bedplate 4 of said axis A_X and, therefore, to the mobile structural part of the axis A_Z, and a second unit R3 fixed to the mobile structural part 9 of the axis A_X and in optical communication with the first unit S3. The second optoelectronic subsystem S3, R3 is such as to provide output signals (for example electric) , assigning them for example to the control unit of the industrial machine, which carry information relating to the six spatial coordinates of the mobile structural part 9 respect to the track of the axis A_X (or more generally respect to the stationary part of said axis) and, in particular, respect to its bedplate 4. Said signals are obtained by means of propagation of at least one optical frequency electromagnetic radiation, in brief of at least one optical beam B3 , between the first S3 and the second R3 unit of the first optoelectronic system S3, R3. At least one ^" of ^"" saϊd ^"" f ^' ifst ^~ and ^{~ "} second ^{" "} unit ^" is such as HEo ^" provide ^" the output optical beam B3, therefore representing a source (active or passive) of said beam B3, in such a way

as to direct said optical beam B3 towards the other of said units which, therefore, represents a target of said optical beam B3. Embodiments of possible optoelectronic subsystems of the type mentioned above will be described more in detail hereunder.

[0028] As schematically illustrated in figure 1, in the optoelectronic measuring system according to the present invention, the second unit R2 of the first optoelectronic subsystem S2, R2 and the first unit S3 of the second optoelectronic subsystem S3, R3 are spatially adjacent, for example in such a way that the two optical beams B2, B3 can be defined as substantially spatially consecutive to each other. Advantageously, this makes it possible, in measuring the six spatial coordinates of the mobile structural part 9 (and, therefore, of the working tool W_T) , in the example realizable starting from the output signals provided by the two optoelectronic subsystems, to eliminate or reduce an element of uncertainty due to the uncertainty of the relative position between the unit R2 of the first optoelectronic subsystem S2, R2 and the unit S3 of the second optoelectronic subsystem S3 , R3. In a particularly advantageous embodiment, the unit R2 and the UnTITiS2 ^~ axe ^~"" dxTe^tTy ^~' ]^cnanTcalTy ^~ coupled ^" to ^" eacH ^~ otller, ^"" i.e. without parts of the industrial machine arranged between them, and preferably integrated in the same

optoelectronic module. The reduced or eliminated element of uncertainty, compared with a measuring system where said units are not spatially adjacent, is due to the thermal and bending deformations of the part of the machine arranged between the two units of the two consecutive optoelectronic subsystems .

[0029] In the example in figure 1, in a first embodiment, the unit S2 includes, for example, an optical source (active or passive) such as to provide an output optical beam B2 while the unit R2 , in optical communication with the unit S2 , represents a target suitable to receive the optical beam B2. Similarly, the unit S3 includes, for example, an active optical source such as to generate the optical beam B3 while the unit R3 , in optical communication with the unit S3 , represents a target suitable to receive the optical beam B3. The group comprising the target R2 and the source S3 represent, for example, a single optoelectronic module, so as to form, between the bedplate 1 and the mobile structural part 9, a substantially continuous optical chain formed by at least two beams B2, B3, preferably substantially consecutive to each other. In a more specific example: - the ^{" "} unit S2 ^~" includes ^" a.tr ^~ Teast ^" one Tas ^t er ^" drode, for ^~ example such as to provide an output electromagnetic radiation B2 in the infrared spectrum;

- the unit S3 includes at least one laser diode, for example such as to provide an output electromagnetic radiation B3 in the infrared spectrum;

- the unit R2 includes a passive optical component, for example a reflecting element or a diffusing element, such as to reflect the received optical beam B2 back towards the unit S2 including, in addition or alternative to the passive optical component, ' an optoelectronic device suitable to convert the received optical beam B2 into one or more electric signals (such as a photodiode or an array of photo-electric transducers) ;

- the unit R3 includes a passive optical component, for example a reflecting element or a diffusing element, such as to reflect the optical beam B3 back towards the unit S3 including, in addition or alternative to the passive optoelectronic component, an optoelectronic device suitable to produce, from the received optical beam B3, one or more electric signals (such as a photodiode or an array of photo-electric transducers) . [0030] In an embodiment alternative to the one described above, in the first and second optoelectronic subsystems, it is possible to invert the source unit and the target ιini ^" t ^{~ ~} ih ^" ^ractϊc^r/ ^" with ^{" "} reference ^"' to ^{* "} figure ^~ ly ^~ the ^~ optoelectronic measuring system can be designed in such a way that: the unit R3 includes, for example, an optical

source (active or passive) such as to provide an output optical beam B3 while the unit S3, in optical communication with the unit R3, includes a target suitable to receive said optical beam B3. Similarly, the unit R2 includes, for example, an optical source (active or passive) such as to generate the optical beam B2 while the unit S2 , in optical communication with the unit R2 , includes a target suitable to receive said optical beam B2. [0031] It should be further noted that in the case, not illustrated in the figure for simplicity, where the industrial machine includes a further axis consecutive to the first A_Z or to the second axis A_X, it is possible to provide a third optoelectronic subsystem, for example by providing the measuring system with a further source unit and a further target unit, at least one of which is spatially adjacent to the unit S2 or to the unit R3 and providing for the propagation of at least one further optical beam between said further units. For example, the bedplate 1 of the first axis A_Z could represent the mobile structural part of a further axis of the machine which can be moved along the direction indicated in the figure with Y-Y (in the example, lout not limited to this, at right angles to directions X-X and Z-Z) . In this case, the measuring system should include a third

optoelectronic subsystem (not illustrated in the figure) including a unit spatially adjacent to the unit S2 (for example, integrated with this in the same optoelectronic module) , and a further unit fixed to the stationary part of the further axis of the machine. In this case, the measuring system provides a continuous optical chain, formed by at least three substantially consecutive optical beams, which extends from a fixed part of the further axis to the mobile structural part 9 of the axis A_X. In practice, said optical chain makes it possible to measure the six spatial coordinates of the working tool W_T (i.e. three translations and three rotations) respect to a fixed part of the further axis of the machine. It should be noted that the industrial machine described above represents, in practice, the so-called three-axis Cartesian industrial machine.

[0032] Figure 2 represents a second example of a measuring system applied to the same industrial machine in figure 1. unlike the measuring system illustrated in figure 1, the measuring system in figure 2 and, in particular, the second optoelectronic subsystem includes, besides the units S3 and R3, a further unit S2_3 fixed to the

^" b ^' edplate ^{" ~} ϊ ^"~ of ^~ εhe ^" first ^~ axϊs ^" α ^~ Z and ^~ spaϊfIaIIy-ITdj ^' aceήtT to the unit S2. In this case, the unit S3, spatially adjacent to the unit R2, represents a deviating element

(for example it includes a reflecting mirror) , and the optical beam B3, propagating between the unit S3 and the unit R3, represents a segment of an optical beam B2_3 , B3 propagating between the further unit S2_3 and the unit R3 and deviating in an intermediary point from the unit S3. [0033] One of the two units S2_3 and R3 represents a source of the optical beam B2_3, B3, while the other unit represents the target, in optical communication with the source . [0034] Still referring to figure 2 , in a particularly advantageous embodiment, the units S2 and S2_3 represent sources of the optical beams B2 and B2_3 respectively, the unit S3 is a deviating element and the units R2 and R3 represent targets. This makes it possible to concentrate the "optically active" elements of the measuring system on only one fixed part of the industrial machine (in the example, on the bedplate 1) , so reducing the overall dimensions and the wiring of the measuring system on the industrial machine. It should be observed that, in this case, installation of the measuring system on the machine is also simplified since the units of the measuring system installed on the mobile parts of the itϊacKine ^" are generalXy ^~ nό ^~ f ^~ sό ^~ complex, bϋlKy ^" and ^~ Heavy ^~~ as ^~ the units installed on the fixed part of the industrial machine .

[0035] The extension of the embodiment illustrated in figure 2 to a three-axis industrial machine can easily be derived by the skilled in the art from the above description with reference to figures 1 and 2. [0036] Figure 3 shows a schematic view of a possible example of an optoelectronic subsystem S2, R2 in figure 1 applied to the axis A_Z of the industrial machine. [0037] In said example, the unit S2 of the optoelectronic subsystem S2, R2 includes an optical source 30 such as to provide an output optical beam B2 while the unit R2 includes a target 31, 32, 33. More in detail, the optical source 30 includes a laser source, for example infrared, while the target includes a reflecting element 31 (for example, a mirror) , a beam-splitter 32 and a CCD (Charge- Coupled Device) 33. As an alternative to the CCD, any other optoelectronic device, made up of a two-dimensional matrix of photosensitive elements (or image sensor for acquiring a digital image) , can be used. The reflecting element 31 makes it possible to reflect the incident optical beam B2 so as to redirect it towards the optical source 30, while the beam-splitter 32 makes it possible to tap a portion of the optical beam B2 and direct said

[0038] By propagating the optical beam B2, preferably substantially parallel to the movement direction Z-Z of

the mobile structural part 4, the optoelectronic subsystem S2, R2 makes it possible to provide output signals sgl, sg2 (for example, electrical and transmitted to the control unit C_U of the industrial machine by means of the control bus C_BUS) bearing information relating to the six spatial coordinates of the mobile structural part 4 respect to the bedplate 1. In the embodiment in figure 3, the laser source 30 is an interferometric laser, for example with self-mixing, further including an integrated photodiode suitable to receive the optical beam B2 reflected by the reflecting element 31 and such as to generate in reply, through interferometric effect (preferably based on the so-called self-mixing phenomenon) , the electrical signal sgl bearing information relating to the translation of the mobile structural part 4 along the propagation axis tl of the optical beam B2. Said signal sgl, processed if necessary by means of local processing means Pm_33, is sent to the control unit C_ϋ of the industrial machine by the control bus C_BUS.

[0039] It should also be noted that, to improve conveying of the optical beam B2 directed towards the target 31 and

^"" of ^~ the δpFi ^' cal ^" beam ^'~ B2 ^""' refIecEecTT5y ^~~ the ^" target ^~ 3 ^" ϊ ^~ fr3wa ^" r ^~ d ^" s ^~ the interferometric laser 30, therefore improving quality of the measurement obtained by the self-mixing

interferometric laser, the optoelectronic subsystem S2, R2 can advantageously include one or more optoelectronic components, such as optical lenses, attenuators or amplifiers (not shown in the figure) to be placed, for example, between the unit S2 and the unit R2.

[0040] From an operative point of view, a self-mixing interferometric laser is based on a self-mixing effect, already known, which takes place when the electromagnetic radiation reflected by a mobile target, if representative of a fraction of the direct electromagnetic radiation, falling within the interference cavity and therein interacting with the direct electromagnetic radiation, causes a change in some parameters of the direct electromagnetic radiation, such as laser emission threshold, laser emission power, wavelength, spectral width. Advantageously, the laser emission power can be monitored so as to extract information relating to the distance, for example relative, between the interferometer and the mobile target. [0041] By means of the CCD 33 and, if necessary, by means of local processing means associated to it and not illustrated in the figure, it is possible to obtain a signal sg2 (for example digital) bearing information on: - translation of the mobile structural part 4 respect to the bedplate 1 along the axis t2 perpendicular to the

propagation axis tl of the optical beam B2;

- translation of the mobile structural part 4 respect to the bedplate 1 along the axis t3 perpendicular to the propagation axis tl of the optical beam B2 ; - rotation rl of the mobile structural part 4 respect to the bedplate 1 around the propagation axis tl of the optical beam B2;

- rotation r2 of the mobile structural part 4 respect to the bedplate 1 around the axis t2; - rotation r3 of the mobile structural part 4 respect to the bedplate 1 around the axis t3.

[0042] For example, said information can be obtained on the basis of image processing techniques, analyzing the digital image produced by the CCD and representative of the cross-section of the optical beam B2 (substantially elliptical-shaped) at the point of incidence of said optical beam B2 with the photosensitive surface of the CCD 33, and in particular analyzing: size, inclination, shape and translation of said elliptical trace. [0043] It should be noted that figure 2 also illustrates unit S3 of the optoelectronic subsystem S3, R3 suitable to provide output signals bearing information on the six spatial coordinates of the mobi ^' le structural ^" part 9 of ^" the other axis A_X (visible in figure 1) of the industrial machine respect to the mobile structural part

4 of the axis A_Z . In the example in figure 3, said unit S3 is absolutely identical to unit S2, in practice including: an optical source 34 (in the example an interferometric laser diode similar to the laser diode 30 described above with reference to unit S2) , suitable to provide an output optical beam B3 (not visible in figure 3 but visible in figure 1) and further including, if necessary, local processing means Pm_34 communicating with the control bus C_BUS of the industrial machine by means of the signal sg3. As illustrated in figure 3, the unit S3 is spatially adjacent to the unit R2 and, preferably, together with this, it is integrated into the same optoelectronic module R2 , S3. The remaining part of the optoelectronic subsystem S3, R4 can be made in exactly the same way as that already described for the optoelectronic subsystem S2 , R2.

[0044] Figure 4 schematically shows a further example of an optoelectronic subsystem S2, R2 for measuring, by means of propagation of at least one optical beam B2, the six spatial coordinates of the unit R2 compared with the unit S2 (therefore, with reference to figure 3, of the mobile structural part 4 respect to the bedplate 1) . For ^" simpTicl ^" ty, ^" tEe ^~~ ilTTusTraEion ^{" ~} ϊn fi ^' gure ^~~ 4 ITS muchr ^~ more ^~ schematic than the illustration in figure 3. [0045] In the particular example in figure 4, the at least

one optical beam B2 comprises six optical beams of which three are unidirectional B2_a, B2_b and B2_c and three are bi-directional B2_ar, B2br and B2_cr.

[0046] The unit R2 includes a first target 33 which is, for example, a CCD (or more generally an image sensor) and a second target 31 which is a reflecting element. The unit S2 includes a group of three optical sources 30a, 30b, 30c (which, for example, are optical sources of the interferometric type and, therefore, include a respective integrated photodiode) , arranged according to a triangular scheme for generating the optical beams B2_a, B2_b and B2_c respectively. Said beams are split by three beam-splitters 32a, 32b and 32c into two beams with right-angled directions. In practice, the three beam- splitters are such as to provide, besides the beams B2_a, B2_b and B2_c directed towards the CCD 33, also the output optical beams B2_ar, B2_be and B2_cr which, striking a reflecting element 35 provided in the unit S2, are directed towards the reflecting element 31 of the unit R2 which, in its turn, is such as to reflect them back (passing through the reflecting element 35 and the beam-splitters 32a, 32b, 32c) towards the respective ^~~ inteiffefometrϊc sources ^" 3Da7 ^~ 3D ^" &, ^" 3 ^" Oc, according ^~ to ^~ - ^~ th ^" e ^~ working principles of laser interferometry. [0047] By means of propagation (bidirectional) of the

optical beams B2_ar, B2_br and B2_cr, exploiting the interferometric technique preferably of the self-mixing type, the unit S2 makes it possible to provide an output signal sgl bearing information relating to the translation along the axis tl and of the two rotations r2 and r3 of the mobile structural part 4 (visible in figure 2) respect to the stationary structural part 1 (visible in figure 2) . [0048] By means of propagation of the optical beams B2_a, B2_b and B2_c which, striking the CCD 33, identify the three vertexes of a triangle, the unit R2 makes it possible to provide an output signal sg2 bearing information relating to the translations along the axes t2 and t3 and of the three rotations rl, r2 and r3 of the unit R2 respect to the unit S2. In particular, said information can be obtained starting from the positions of the three vertexes of the triangle identified on the CCD 33. Obviously, in this example the information on the rotations r2 and r3 is redundant. [0049] Figure 5 schematically shows a further example of an optoelectronic subsystem S2, R2 for measuring, by means of propagation of at least one optical beam B2, the six spaεϊaϊ ^"" coordinates ^" of ^"" the unit R2 respect to ^~~ th ^~ e unit ^" S2. For simplicity, the illustration in figure 5 is much more schematic than the illustration in figure 3.

[0050] In the particular example, the optical beam B2 comprises four optical beams of which three are unidirectional B2_a, B2_b, B2_c and one bidirectional B2_d. [0051] The unit R2 includes a first target 33 which is, for example, a CCD and a second target 31 which is a reflecting element . The unit T2 includes a group of three optical sources 30a, 30b, 30c (for example three laser diodes) arranged according to a triangular scheme for generating the three optical beams B2_a, B2_b- and B2_c respectively. Said optical beams are directed towards the CCD 33 of the unit R2.

[0052] The unit R2 further includes an interferometric optical source 3d such as to generate the optical beam B2_d and direct said beam towards the reflecting element 31 of the unit R2. The reflecting element 31, in its turn, is such as to reflect the incident optical beam B2_d back towards the source 32d, according to the working principles of laser interferometry. [0053] By means of propagation (bidirectional) of the optical beam B2_d, by exploiting the interferometric technique preferably of the self-mixing type, unit S2 makes it possible to provide an output signal sgl bearing information relating to the translation along the axis tl of the mobile structural part 4 (visible in figure 2)

respect to the fixed structural part 1 (visible in figure 2) .

[0054] By means of propagation (unidirectional) of the optical beams B2_a, B2_b and B2_c which, striking the CCD 33, identify the three vertexes of a triangle, unit R2 makes it possible to provide an output signal sg2 bearing information relating to the translations along the axes t2 and t3 and of the three rotations rl, r2 and r3 of the unit R2 respect to the unit S2. In particular, said information can be obtained starting from the positions of the three vertexes of the triangle identified on the CCD 33.

[0055] The optical subsystem S2 , R2 in figure 5 compared with the subsystem S2, R2 in figure 4 has a simpler architecture (and, therefore, less sensitive to tolerance errors) , but lacks of redundant information on the rotations r2 and r3.

[0056] Figure 6 schematically shows a further example of an optoelectronic subsystem S2, R2 for measuring, by means of propagation of at least one optical beam B2, the six spatial coordinates of the unit R2 compared with the unit S2. For simplicity, the illustration in figure 6 is much more schematic than the illustration ^" in TT

[0057] In the particular example, the optical beams B2 comprises four optical beams of which three B2_a, B2_b,

B2_c are bidirectional and one is unidirectional B2_d. [0058] The unit R2 includes a first target 33 which is, for example, a CCD and a second target 31 which is a reflecting element. In the particular example schematically illustrated in figure 6, the reflecting element 31 surrounds the CCD 33.

[0059] The unit S2 includes a group of three optical sources 30a, 30b, 30c (which for example are interferometric type optical sources and, therefore, include a respective photodiode) arranged according to a triangular scheme for generating the optical beams B2_a, B2_b and B2_c respectively and direct them towards the reflecting element 31 of the unit R2 which, in its turn, is such as to reflect them back towards the respective interferometric sources 30a, 30b, 30c, according to the working principles of laser interferometry. [0060] By means of propagation (bidirectional) of the optical beams B2_a, B2_b and B2_c, by exploiting the interferometric technique preferably of the self-mixing type, the unit S2 makes it possible to provide an output signal sgl bearing information relating to the translation along the axis tl and of the two rotations r2

^~ axrd-^3 ^~ σf ^~ ^^ ^~ mωh±Te ^~ stra^txϊr&Tηf&F£r ^~ 4 ^" (vi ^' sible ^" ±n—f±gure— ^■

2) respect to the stationary structural part 1 (visible in figure 2) .

[0061] The unit R2 further includes an optical source 32d such as to generate the optical beam B2_d and to direct said beam towards the CCD 33 of the unit R2. The latter further includes a polarizing filter 35 placed before the CCD 33 ^' and, therefore, such that the optical beam B2_d incident upon the CCD 33 can pass through it. [0062] By means of propagation of the optical beam B2_d, the unit R2 makes it possible to provide an output signal sg2 bearing information relating to the translations along the axis t2 and t3 and of the rotation rl of the mobile structural part 4 (visible in figure 2) respect to the fixed structural part 1 (visible in figure 2) . In particular, the two translations can be measured on the basis of the point of incidence of the optical beam B2_d upon the CCD 33 while the rotation can be measured by- identifying the intensity of the optical beam B2_d incident upon the CCD. In fact, said attenuation depends on the angle between the polarizing direction of the optical beam and the polarizing direction of the filter 35.

[0063] The optical subsystem S2 , R2 in figure 6 , compared with the subsystem S2, R2 in figure 5, has a more complex

^" arcnTtectύre ^"~ (and ^" Oϊerefore, more sensxirrve ^~ tω ^~ tOϊerancB- errors) , in the case of a reduction in size of the CCD (which is equivalent to lower cost of the subsystem and

greater frequency bandwidth) .

[0064] With. reference to the examples of measuring optoelectronic subsystems described above, it should be noted that in a measuring system according to the present invention, it is not necessary for the two subsystems, associated to two consecutive linear axes A_Z, A_X of the machine, to be of the same type. In fact, it is also possible to associate different types of subsystems to said axes. Just by way of example, with reference to figure 1, an optoelectronic subsystem S2, R2 according to the example in figure 4 could be associated to the axis A_Z, while an optoelectronic subsystem S2, R2 according to the example in figure 6 could be associated to the axis A_X of the machine . [0065] In embodiments alternative to those described above, in particular with reference to subsystems described in the figures from 3 to 6, it is possible to use different types of interferometers instead of self-mixing laser interferometers, for example Michelson interferometers or Doppler effect interferometers .

[0066] Finally, figure 7 illustrates a particularly advantageous variation of the embodiment of an optical ^" subsystem in ^" figure ^{" '} 3. ^" For ^"" sϊmpriclty, ^" in ^' figure l ^~ compared with figure 3, the unit S3 has been omitted. [0067] In the embodiment in figure 7, means for protecting

the optical beam B2 are provided between the unit S2 and the unit R2, in the form of a variable-length protection structure 40 which extends from the unit S2 to the unit R2 and has an internal cavity from which the optical beam B2 can be propagated. In the particular example in figure 7 said structure is, in particular, a telescopic structure, i.e. formed by a plurality of telescopically- coupled tubular elements . Said structure can increase or decrease in length along the movement axis Z-Z, as the position of the mobile structural element 4 varies respect to the bedplate 1.

[0068] In alternative, said protection structure 40 could be a folding structure. It should be noted that it is possible to provide one or more variable-length protection structures identical or similar to the one described above also for the embodiments of subsystems illustrated schematically in the figures from 4 to 6. Each of said protection structures can indifferently be intended for protecting one or more optical beams propagating between the unit S2 and the unit R2. In the particular case where several optical beams are to be propagated inside a protection structure, it is possible to conveniently further provide one or more separators inside said structures which are such as to avoid the risk of interference between distinct optical beams.

[0069] Advantageously, inside the protection structure 40, a plurality of sensors can be provided, distributed in a chain-like arrangement, such as to detect, for example, the physical parameters detectable inside the propagation region of the optical beam such as temperature, pressure, humidity. Monitoring of these parameters is particularly advantageous since it makes it possible to observe, continuously and/or discretely, the environmental conditions in which the electromagnetic radiation is propagated so that it is possible to correct, if necessary, the measurements of fluctuations produced by any gradients .

[0070] In alternative to the external protection structure, it is possible for the stationary parts of the machine axes, i.e. the tracks, to have a longitudinally hollow structure and for the laser beams, used for measuring, to propagate inside the hollow structure of said axes. In this case, protection of the optical beams is guaranteed by the structure of the axes themselves, without the need of any external protection system whatsoever.

[0071] As is evident from the above description, a measuring system as described above makes it possible to fuIYy reach ^~~~ the obj ^" e ^' cts ^~" ϊd ^' entifled above ^{' "} wϊEti ^"" Feference ^" to the drawbacks of the measuring systems of the prior art .

[0072] Naturally, in order to satisfy contingent and specific requirements, a person skilled in the art may apply to the above-described measuring system according to the invention many modifications and variations, all of which, however, are included within the scope of protection of the invention as defined by the following claims .